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Factors influencing the recovery of molybdenum during the hypochlorite leaching of low grade molybdenite-copper.. Mounsey, Diana Mary 1979

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FACTORS INFLUENCING THE RECOVERY OF MOLYBDENUM DURING THE HYPOCHLORITE LEACHING OF LOW GRADE MOLYBDENITE-COPPER CONCENTRATES by  DIANA MARY MOUNSEY .Sc.(Eng.), A . R . S . M . , Imperial College of and Technology  ( U n i v e r s i t y o f London),  Science 1977  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department o f M e t a l l u r g i c a l  We a c c e p t t h i s t h e s i s as t o the r e q u i r e d  Engineering)  conforming  standard  THE UNIVERSITY OF BRITISH COLUMBIA September 1979 Ccj  Diana Mary Mounsey,  1979  In p r e s e n t i n g  this  thesis  an a d v a n c e d d e g r e e a t the L i b r a r y I  further  for  agree  scholarly  by h i s of  shall  this  written  in p a r t i a l  the U n i v e r s i t y  make  it  freely  that permission  thesis  for  It  financial  of of  British  gain  Columbia  2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date  »**  QcUeT  Columbia,  British  '777  for  the  requirements  reference copying of  I agree and this  shall  that  not  copying or  for  that  study. thesis  by t h e Head o f my D e p a r t m e n t  is understood  M  The U n i v e r s i t y  of  for extensive  permission.  Department  of  available  p u r p o s e s may be g r a n t e d  representatives.  fulfilment  or  publication  be a l l o w e d w i t h o u t  my  (ii)  ABSTRACT  An i n v e s t i g a t i o n i n t o the f a c t o r s  i n f l u e n c i n g the e x t r a c t i o n o f  molybdenum from copper s u l p h i d e m o l y b d e n i t e c o n c e n t r a t e s i n a l k a l i n e h y p o c h l o r i t e s o l u t i o n s has been c a r r i e d  out.  Sodium c a r b o n a t e b u f f e r components were found t o a c t as c o m p l e x i n g agents f o r the c o p p e r , e n a b l i n g i t t o e x i s t i n s o l u t i o n as a c u p r i carbonate species  s e v e r a l o r d e r s o f magnitude more s o l u b l e than  t h e r m o d y n a m i c a l l y s t a b l e copper phase a t pH 9 . 0 . molybdenum e x t r a c t i o n i s t h e r e f o r e i n g no  the  Completely s e l e c t i v e  o n l y p o s s i b l e from s o l u t i o n s  contain-  carbonate. The removal o f the c a r b o n a t e produced adverse s i d e e f f e c t s  for  the sodium h y p o c h l o r i t e l i x i v i a n t as a r e s u l t o f copper h y d r o x i d e f o r m a t i o n on the m i n e r a l s u r f a c e w h i c h l e d t o r a p i d d e c o m p o s i t i o n o f the h y p o c h l o r i t e by heterogeneous c a t a l y s i s . T h i s h y d r o x i d e s a l t was found to c o n s i s t a t l e a s t p a r t i a l l y o f t r i - v a l e n t copper and i t was c o n f i r m e d t h a t sodium h y p o c h l o r i t e has a s u f f i c i e n t l y h i g h redox p o t e n t i a l a t pH 9.0 t o enable the o x i d a t i o n o f copper  1 1  > copper " " t o t a k e p l a c e . 11  1  Experiment a l s o showed t h a t a t r i -  v a l e n t copper c a r b o n a t e compound p r e c i p i t a t e d c o n t a i n i n g copper a f t e r  from l e a c h i n g  a suitable nucleation period.  solutions  I t was thus e s t a -  b l i s h e d t h a t the copper p r e s e n t i n c a r b o n a t e c o n t a i n i n g h y p o c h l o r i t e s o l u 3-  t i o n s e x i s t s as the t r i - v a l e n t complex CuCCO^)^  ; t h a t the i n d u c t i o n time  t o p r e c i p i t a t i o n i s a f u n c t i o n o f the t o t a l c a r b o n a t e c o n t e n t o f  the  (iii)  system, and t h a t the s o l i d p r e c i p i t a t e hypochlorite  i s a l s o an a c t i v e c a t a l y s t  for  decomposition.  The l e a c h i n g o f m o l y b d e n i t e - copper c o n c e n t r a t e s i n a c i d s o l u t i o n s was s t u d i e d ,  and r e s u l t s showed t h a t such a p r o c e s s would not be  f e a s i b l e due t o the f o r m a t i o n and p r e c i p i t a t i o n o f copper CuMoO^.  T h i s compound i s v e r y i n s o l u b l e , b u t i t s  molybdate,  f o r m a t i o n was found t o  be suppressed by the p r e s e n c e o f sodium b i c a r b o n a t e  a t pH v a l u e s  greater  than 6 . 0 . S e v e r a l o t h e r i n s o l u b l e molybdate compounds were found t o be c a p a b l e o f forming i n b o t h a c i d and a l k a l i n e s o l u t i o n s as a r e s u l t h y p o c h l o r i t e d i s s o l u t i o n o f i m p u r i t y elements c o n t a i n e d i n the sulphide ores.  P o t e n t i a l - p H diagrams c o n s t r u c t e d  s t a b i l i t y o f the molybdate s a l t s o f c o p p e r , cadmium are  t o show the  of  copper thermodynamic  i r o n , c a l c i u m , z i n c , l e a d and  included.  C a l c i u m was i s o l a t e d as b e i n g the most d e t r i m e n t a l ment i n t h i s r e s p e c t , due t o i t s common o c c u r r e n c e  impurity ele-  i n copper p o r p h y r y  o r e s as w e l l as i t s s o l u b i l i t y i n c h l o r i d e c o n t a i n i n g s o l u t i o n s . l i m i t e d study was c a r r i e d o u t t o show t h a t t h i s  s o l u b i l i t y increased  p r o p o r t i o n t o the c h l o r i d e c o n t e n t and hence the h y p o c h l o r i t e t i o n of leaching solutions.  A  C a l c i u m c a r b o n a t e was found t o  in  concentraprecipitate  i n p r e f e r e n c e t o c a l c i u m m o l y b d a t e , b u t the use o f s i l i c a t e s and p h o s p h a t e s as c a l c i u m s u p p r e s s a n t s was a l s o c o n s i d e r e d as a means o f a v o i d i n g copper - c a r b o n a t e c o m p l e x i n g w h i l e m a i n t a i n i n g good molybdenum  extraction.  Xiv)  TABLE OF CONTENTS Page CHAPTER ONE : G e n e r a l  1  1.1  Introduction  1  1.2  C u r r e n t Molybdenum P r o d u c t i o n  3  1.3  Hydrometallurgical Production o f Molybdenum  6  L i t e r a t u r e Review  9  1.4  1.4.1 1.4.2  The e x t r a c t i o n o f m o l y b d e n i t e w i t h sodium h y p o c h l o r i t e s o l u t i o n s  9  The b e h a v i o u r o f copper i n a l k a l i n e carbonate s o l u t i o n s  17  1.4.3  D e c o m p o s i t i o n o f sodium h y p o c h l o r i t e in alkaline solution  27  1.4.4  Copper  39  1 1 1  compounds  CHAPTER TWO : E x p e r i m e n t a l  i  47  2.1  Scope o f the P r e s e n t I n v e s t i g a t i o n  47  2.2  Materials  49  2.2.1  Natural minerals  49•  2.2.2  Synthetic minerals  54  2.2.3  Sodium h y p o c h l o r i t e  54  2.2.4  Chemical reagents  55  2.3  Apparatus  55  2.4  Experimental procedure  57  2.4.1  Leaching experiments  57  2.4.2  Copper  58  2.5  1 1 1  preparation  Analysis  58  2.5.1  5;8  Chemical a n a l y s i s i)  Copper  5'8  (v)  TABLE OF CONTENTS  (Cont'd) Page  ii) iii) iv) v) vi) 2.5.2  Molybdenum  59  Calcium  59  Sodium h y p o c h l o r i t e  59  Sodium c h l o r a t e  59  Total chloride  60  Instrumental i) ii)  analysis  60  Minerals III Copper  60 61  CHAPTER THREE : R e s u l t s and O b s e r v a t i o n s 3.1  Sodium H y p o c h l o r i t e L e a c h i n g o f Copper Sulphide Minerals 3.1.1  62  L e a c h i n g o f ground c o n c e n t r a t e s i n the p r e s e n c e o f c a r b o n a t e  62  3.1.2  E f f e c t o f c a r b o n a t e removal  64  3.1.3  L e a c h i n g o f s y n t h e t i c copper sulphides Determination of decomposition products  3.1.4 3.1.5  3.1.6  3.1.7  3.2  62  67 69  Sodium h y p o c h l o r i t e l e a c h i n g o f massive samples o f copper sulphide minerals  72  V a r i a t i o n o f t o t a l carbonate c o n t e n t d u r i n g the l e a c h i n g o f ground copper s u l p h i d e m i n e r a l s  75  E f f e c t o f v a r y i n g the concentration  79  hypochlorite  3.1.8  E f f e c t o f h y p o c h l o r i t e removal  84  Copper  1 1 1  87  3.2.1  Analysis of c o p p e r  1 1 1  90  3.2.1.1  Effect of a c i d i f i c a t i o n  90  3.2.1.2  Evaluation of oxidation state by i d o m e t r i c t i t r a t i o n  90  Measurement o f oxygen e v o l u t i o n u s i n g a mercury column  92  3.2.1.3  (vi)  TABLE OF CONTENTS (Cont'd) Page 3.2.1.4  Gas chromatography  94  3.2.1.4  Instrumental  94  i) ii) iii) 3.2.2  3.3  analysis  Magnetic s u s c e p t i b i l i t y  94  Infra-red  spectra  95  X-ray d i f f r a c t i o n  96  P r e c i p i t a t i o n o f copper - - i n the 11  1  presence o f carbonate  97  3.2.2.1  E f f e c t o f seeding  97  3.2.2.2  Effect of a c i d i f i c a t i o n  98  3.2.2.3  I.R. spectra  98  3.2.2.4  X-ray analysis  99  3.2.3  Hypochlorite decomposition studies  100  3.2.4  Analysis of leaching solutions  100  Sodium H y p o c h l o r i t e O x i d a t i o n o f Molybdenite 3.3.1  3.3.2  3.3.3  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 9.0  104  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 5.5  114  Copper molybdate  120  3.3.3.1  S o l u b i l i t y o f copper molybdate  127  3.3.3.2  Catalyzed decomposition of h y p o c h l o r i t e i n the p r e s e n c e o f copper molybdate  130  X-ray analysis  132  3.3.3.3 3.3.4  102  S o l u b i l i t y of calcium i n hypochlorite solutions 3.3.4.1  3.3.4.2 3.3.4.3  133  Sodium h y p o c h l o r i t e l e a c h i n g o f c a l c i u m s u l p h a t e and c a l c i u m carbonate minerals  137.  Effect of chloride concentration on c a l c i u m s o l u b i l i t y  140  Removal o f c a l c i u m from s o l u t i o n  14 0  (vii)  TABLE OF CONTENTS  (Cont'd) Page  CHAPTER FOUR : D i s c u s s i o n 4.1.1  Sodium h y p o c h l o r i t e l e a c h i n g o f copper s u l p h i d e m i n e r a l s i n the presence of carbonate  154  Removal o f c a r b o n a t e from the system  156  4.1.4  Hypochlorite decomposition products  158  4.1.5  Sodium h y p o c h l o r i t e l e a c h i n g o f massive samples o f copper s u l p h i d e minerals  160  V a r i a t i o n o f the t o t a l c a r b o n a t e content during leaching  161  E f f e c t of v a r y i n g the concentration  165  4.1.2  4.1.6 4.1.7  4.3  154  hypochlorite  4.1.8  E f f e c t o f h y p o c h l o r i t e removal  166  4.2.1  Analysis of c o p p e r  170  4.2.2  P r e c i p i t a t i o n of c o p p e r presence o f carbonate  1 1 1  1 1 1  in  the 172  Sodium H y p o c h l o r i t e L e a c h i n g o f M o l y b d e n i t e 4.3.1  173  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 9.0  174  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 5.5  174  4.3.3  Copper molybdate  179  4.3.4  S o l u b i l i t y of calcium i n hypochlorite solutions  183  4.3.2  4.3.4.1 4.3.4.2 4.3.4.3  Sodium h y p o c h l o r i t e of calcium minerals  leaching 196  Effect of chloride concentrat i o n on c a l c i u m s o l u b i l i t y  196  Removal o f c a l c i u m from leaching solutions  200  (viii)  TABLE OF CONTENTS ( C o n t ' d ) Page  CHAPTER FIVE  202  5.1  Conclusions  202  5.2  S u g g e s t i o n s f o r F u t u r e Work  204  REFERENCES  206  APPENDICES  211  Appendix A  Tables o f experimental r e s u l t s  Appendix B B.l B.2  B. 3 Appendix C  211 268  C a l c u l a t i o n of surface areas f o r ground m i n e r a l samples  268  C a l c u l a t i o n o f a v a i l a b l e copper f o r p r e c i p i t a t i o n on m i n e r a l surface a f t e r c o p p e r H I formation  269  H y p o c h l o r i t e redox e q u i l i b r i a a t pH 9.0  269  E q u i l i b r i a f o r metal-molybdate Eh-pH diagrams  271  C. l  Cu-H 0-Mo0  4  271  C.2  Ca-H 0-Mo0  4  277  C.3  Pb-H 0-Mo0  4  280  C.4  Zn-H 0-Mo0  4  285  C.5  Fe-H 0-Mo0  4  288  C.6  Cd-H 0-Mo0  4  293  2  2  2  2  2  2  (ix)  LIST OF TABLES  X-ray d i f f r a c t i o n pattern for c o v e l l i t e X-ray d i f f r a c t i o n pattern for X-ray d i f f r a c t i o n pattern  chalcocite  for chalcopyrite  D e t e r m i n a t i o n o f copper"'""'""'" by i d o m e t r i c titration X-ray d i f f r a c t i o n pattern copper oxides  for  X-ray d i f f r a c t i o n pattern carbonate  for  1 1  1 1 1  copper copper  and III  E f f e c t o f m i x i n g and a g e i n g e q u i - m o l e c u l a r volumes o f Na„MoO. and CuSO„ a t pH 5.3 and pH 9.0 X-ray d i f f r a c t i o n pattern for molybdate  copper  2" 3Effect of S i 0 , C 0 , and P 0 (sodium s a l t s ) on c a l c i u m p r e c i p i t a t i o n from OC1 s o l u t i o n s a t pH 9.0 2  3  3  4  S t r o n g e s t X - r a y peaks f o r v a r i o u s molybdate s p e c i e s  copper  Comparison o f e x p e r i m e n t a l and l i t e r a t u r e v a l u e s f o r s o l u b i l i t y o f i ) CaS04 and i i ) CaCO^ i n c h l o r i d e s o l u t i o n s o f v a r y i n g strengths  NaOCl l e a c h i n g o f c o v e l l i t e w i t h c a r b o n a t e buffers NaOCl l e a c h i n g o f c h a l c o c i t e w i t h c a r b o n a t e buffers NaOCl l e a c h i n g o f c h a l c o p y r i t e w i t h c a r b o n a t e buffers  (x)  LIST OF TABLES  IV  (Cont'd)  E f f e c t o f s e p a r a t i n g l e a c h i n g s o l u t i o n from m i n e r a l s l u r r y d u r i n g a g i t a t i o n o f CuFeS i n NaOCl 2  V  E f f e c t o f s e p a r a t i n g l e a c h i n g s o l u t i o n from mineral s l u r r y during a g i t a t i o n o f Cu S i n NaOCl 2  VI  VII VIII IX X XI XII XIII  NaOCl l e a c h i n g o f c o v e l l i t e i n the absence of carbonate buffers NaOCl l e a c h i n g o f c h a l c o c i t e i n the absence of carbonate buffers NaOCl l e a c h i n g o f c h a l c o p y r i t e i n the of carbonate buffers  absence  M i c r o p r o b e e x a m i n a t i o n o f massive c h a l c o c i t e , b e f o r e and a f t e r l e a c h i n g i n NaOCl M i c r o p r o b e e x a m i n a t i o n o f massive c o v e l l i t e , b e f o r e and a f t e r l e a c h i n g i n NaOCl NaOCl l e a c h i n g o f c u p r i c s u l p h i d e i n the absence o f c a r b o n a t e b u f f e r s NaOCl l e a c h i n g o f cuprous s u l p h i d e i n absence o f c a r b o n a t e b u f f e r s  the  NaOCl l e a c h i n g o f c o v e l l i t e w i t h v a r i a b l e [ C 0 ~ ] a t pH 9 . 0 , 35°C 2  3  XIV  T  NaOCl l e a c h i n g o f c h a l c o c i t e w i t h v a r i a b l e [ C 0 ] a t pH 9 . 0 , 35°C 2 -  3  XV  T  NaOCl l e a c h i n g o f s y n t h e t i c w i t h 5 g/1 [ C 0 - ]  sopper  sulphides  2  3  XVI  T  NaOCl l e a c h i n g o f c o v e l l i t e i n the p r e s e n c e o f 5 g/1 [ C 0 ] and 20 g/1 [NaOCl] 2 -  3  XVII  T  A g i t a t i o n o f c o v e l l i t e i n the p r e s e n c e o f c a r b o n a t e ± NaCl  (xi)  LIST OF TABLES  (Cont'd) Page  XVIII  NaOCl l e a c h i n g o f c o v e l l i t e i n the p r e s e n c e o f 10 g/1 [ C 0 ~ ] and N a M o 0  228  Sodium h y p o c h l o r i t e d e c o m p o s i t i o n i n the p r e s e n c e o f t r i - v a l e n t copper s a l t s  229  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 9 . 0  230  NaOCl o x i d a t i o n o f ' r e a g e n t molybdenum d i s u l p h i d e  231  2  3  XIX  XX XXI  XXII  T  2  4  grade'  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e ± carbonate buffers  232  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o c i t e ± carbonate buffers  233  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e ± carbonate buffers  234  NaOCl o x i d a t i o n o f molybdenum d i s u l p h i d e and c h a l c o p y r i t e ± c a r b o n a t e b u f f e r s  235  NaOCl o x i d a t i o n o f m o l y b d e n i t e i n the p r e s e n c e o f copper s u l p h a t e s o l u t i o n  236  NaOCl o x i d a t i o n o f c o v e l l i t e i n the p r e s e n c e o f sodium molybdate s o l u t i o n  237  XXVIII  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 5.5  238  XXIX  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 5.5 i n the absence o f carbonate  239  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 5.5 i n the absence o f c a r b o n a t e  240  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 5.5 i n the p r e s e n c e o f NaHCO  241  NaOCl l e a c h i n g o f c h a l c o p y r i t e a t pH 5.5 ± NaHCO„  242  XXIII XXIV XXV XXVI XXVII  XXX XXXI  XXXII  (xii)  LIST OF TABLES  XXXIII XXXIV  XXXV  XXXVI  (Cont'd)  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o c i t e a t pH 6 . 5 , w i t h NaHCO^ NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o c i t e a t pH 6 . 5 , w i t h o u t NaHC0  3  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c u p r i c s u l p h i d e a t pH 6 . 0 , w i t h NaHCO^ NaOCl l e a c h i n g o f m o l y b d e n i t e and c u p r i c s u l p h i d e a t pH 6 . 0 , w i t h o u t NaHC0 3  XXXVII XXXVIII IXL  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 7 . 0 , w i t h NaHC0  3  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 7 . 0 , w i t h o u t NaHC0  3  NaOCl d e c o m p o s i t i o n i n t h e p r e s e n c e o f copper molybdate a t pH 5.5  XL  D e t e r m i n a t i o n o f t h e s o l u b i l i t y o f copper molybdate a t pH 5 . 0 -  XLI  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 10.0  XLII  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 10.0 i n t h e absence o f c a r b o n a t e buffers  XLIII  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and cuprous s u l p h i d e i n the absence o f c a r b o n a t e buffers  XLIV  XLV  XLVI  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and cuprous s u l p h i d e a t pH 9 . 0 , i n t h e p r e s e n c e of carbonate buffers NaOCl o x i d a t i o n o f C u F e S ; C u S and CuS a t pH 9 . 0 i n the absence o f c a r b o n a t e b u f f e r s 2  2  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and c h a l c o c i t e i n the p r e s e n c e o f 0.1 g/1 c a l c i u m as C a C l s o l u t i o n 2  (xiii)  LIST OF TABLES  (Cont'd) Page  XLVII  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o c i t e i n the p r e s e n c e o f C a C l  XLVIII IL L LI LII  2  and N a C 0 / N a H C 0 2  3  3  NaOCl l e a c h i n g o f m o l y b d e n i t e and c a l c i t e  258  NaOCl l e a c h i n g o f powdered c a l c i t e a t pH 9.0  259  NaOCl l e a c h i n g o f P l a s t e r o f P a r i s a t 9.0  260  Effect of increasing chloride concentration on c a l c i u m d i s s o l u t i o n from CaSO^-^H-jO Effect of increasing chloride concentration on c a l c i u m d i s s o l u t i o n from CaC0  261  E f f e c t o f c a r b o n a t e on c a l c i u m c o n t e n t i n hypochlorite solutions  262  NaOCl l e a c h i n g o f c o v e l l i t e and m o l y b d e n i t e w i t h 5 g/1 c a r b o n a t e  263  NaOCl l e a c h i n g o f m o l y b d e n i t e and c o v e l l i t e w i t h 10 g/1 c a r b o n a t e  264  NaOCl l e a c h i n g o f c o v e l l i t e i n the p r e s e n c e o f sodium molybdate and 5 g/1 c a r b o n a t e  265  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and c h a l c o c i t e w i t h 10 g/1 c a r b o n a t e  266  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 9.0 i n the p r e s e n c e o f 1 g / 1 N a S i 0  267  3  LIII LIV LV LVI LVII LVIII  257  2  3  261  (xiv)  LIST OF FIGURES  Conventional flowsheet for production o f molybdenum t r i o x i d e S t a b i l i t y r e l a t i o n s f o r copper i n the system C u - H 0 - 0 ~ S - C o 2  2  P o t e n t i a l - p H diagrams f o r the C u - C 0 - H 0 , a) and b) 2  compounds  2  system  2  A c t i v i t y r a t i o diagram and s o l u b i l i t y diagram f o r the C u - C 0 ~ H 0 system 2  2  Experimental l e a c h i n g apparatus O x i d a t i o n o f copper s u l p h i d e by NaOCl Effect of separating from m i n e r a l s l u r r y  minerals  leaching solution  NaOCl consumption d u r i n g l e a c h i n g o f copper s u l p h i d e s E f f e c t o f c a r b o n a t e removal on NaOCl decomposition NaOCl d e c o m p o s i t i o n d u r i n g l e a c h i n g o f s y n t h e t i c copper s u l p h i d e s Sodium c h l o r a t e p r o d u c t i o n d u r i n g NaOCl decomposition a) ' b)  E f f e c t of v a r i e d carbonate content on Cu d i s s o l u t i o n from c o v e l l i t e Cu d i s s o l u t i o n and NaOCl d e c o m p o s i t i o n f o r c o v e l l i t e l e a c h i n g w i t h 10 g/1  [co "] 2  3  T  E f f e c t o f v a r i e d c a r b o n a t e c o n t e n t on NaOCl d e c o m p o s i t i o n ( c o v e l l i t e ) E f f e c t o f v a r i e d c a r b o n a t e c o n t e n t on Cu d i s s o l u t i o n from c h a l c o c i t e  (xv)  LIST OF FIGURES  (Cont'd) Page  15  16  E f f e c t o f v a r i e d c a r b o n a t e c o n t e n t on NaOCl d e c o m p o s i t i o n ( c h a l c o c i t e )  81  Cu d i s s o l u t i o n and NaOCl d e c o m p o s i t i o n f o r c u p r i c s u l p h i d e l e a c h i n g (5 g/1 fC0 -] )  82  2  3  17  T  Cu d i s s o l u t i o n and NaOCl d e c o m p o s i t i o n f o r cuprous s u l p h i d e l e a c h i n g (5 g/1  tco -] ) 2  3  18  19  Cu d i s s o l u t i o n and NaOCl d e c o m p o s i t i o n f o r c o v e l l i t e l e a c h i n g (20 g/1 [NaOCl])  85  Agitation of c o v e l l i t e i n solutions of N a C 0 / N a H C 0 ± NaCl  86  Cu d i s s o l u t i o n and NaOCl d e c o m p o s i t i o n f o r c o v e l l i t e w i t h 10 g/1 [ C 0 ] o v e r a p e r i o d o f 6 hours  89  NaOCl d e c o m p o s i t i o n i n the p r e s e n c e o f o x i d e and c a r b o n a t e s a l t s o f c o p p e r  101  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 9.0  103  NaOCl o x i d a t i o n o f r e a g e n t grade m o l y b denum d i s u l p h i d e a t pH 9.0  105  NaOCl o x i d a t i o n o f '98%+' molybdenum d i s u l p h i d e a t pH 9.0  106  NaOCl o x i d a t i o n o f m o l y b d e n i t e and covellite a) i n the p r e s e n c e o f c a r b o n a t e b u f f e r s b) i n t h e absence o f c a r b o n a t e b u f f e r s  108 109  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l cocite a) i n the p r e s e n c e o f c a r b o n a t e b u f f e r s b) i n the absence o f c a r b o n a t e b u f f e r s  110 111  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l copyrite a) i n the p r e s e n c e o f c a r b o n a t e b u f f e r s b) i n the absence o f c a r b o n a t e b u f f e r s  112 113  2  20  8 3  T  3  3  2 -  3  21  1 1 1  22 23 24 25  26  27  (xyi)  LIST OF FIGURES  (Cont'd) Page  28  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 5.5  116  29  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 5.5  117  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 5.5 a) i n the absence of b i c a r b o n a t e b) i n the presence o f b i c a r b o n a t e  118 119  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o c i t e a t pH 6.5 a) i n the p r e s e n c e o f b i c a r b o n a t e b) i n the absence o f b i c a r b o n a t e  121 122  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c u p r i c s u l p h i d e a t pH 6.0 a) i n the presence o f b i c a r b o n a t e b) i n the absence o f b i c a r b o n a t e  123 124  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 7.0 a) i n the presence o f b i c a r b o n a t e b) i n the absence o f b i c a r b o n a t e  125 126  D e t e r m i n a t i o n o f the s o l u b i l i t y o f copper molybdate a t pH 5.0  128  NaOCl d e c o m p o s i t i o n i n the p r e s e n c e o f copper molybdate a t pH 5.5  131  NaOCl o x i d a t i o n o f molybdenum d i s u l p h i d e and cuprous s u l p h i d e a t pH 9 . 0  134  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 10.0 a) i n the presence o f carbonate b u f f e r s b) i n the absence o f carbonate b u f f e r s  135 136  NaOCl l e a c h i n g o f c h a l c o p y r i t e , c h a l c o c i t e and c o v e l l i t e a t pH 9.0  138  NaOCl l e a c h i n g o f powdered P l a s t e r o f P a r i s a t pH 9.0  139-  30  31  32  33  34 35 36 37  38 39  40  c a l c i t e and  NaOCl l e a c h i n g o f m o l y b d e n i t e and c a l c i t e i n the absence o f c a r b o n a t e  141  (xvii)  LIST OF FIGURES  (Cont'd) Page  41  Effect of chloride concentration Ca d i s s o l u t i o n from C a S 0 - % H 0 4  42 43  44 45  46  on 1  4  1  4  2  2  C a l c i u m s u l p h a t e s o l u b i l i t y as a function of c h l o r i d e content Effect of chloride concentration Ca d i s s o l u t i o n from CaCO^  3  on ^44  C a l c i u m c a r b o n a t e s o l u b i l i t y as a function of c h l o r i d e content  145  E f f e c t o f c a r b o n a t e on c a l c i u m i n hypochlorite solutions  147  NaOCl l e a c h i n g o f c o v e l l i t e and m o l y b d e n i t e a t pH 9.0 w i t h 5 g/1 [CO ~] and 10 g/1 [ C 0 " ]  148  NaOCl l e a c h i n g o f c h a l c o c i t e and m o l y b denum d i s u l p h i d e w i t h 10 g/1 [ C 0 ]  14 9  NaOCl l e a c h i n g o f c o v e l l i t e i n the p r e s e n c e o f NaMoO^ and 5 g/1 c a r b o n a t e  151  NaOCl o x i d a t i o n o f molybdenum d i s u l p h i d e and c h a l c o p y r i t e i n the p r e s e n c e o f Na Si0  15 2  2  2  3  47  T  2 -  3  48 49  2  50  T  3  Mercury column f o r measurement o f e v o l u t i o n from C u  gas 92  1 1 1  51  P o t e n t i a l - p H diagram f o r the system Cu-CO - H 0 w i t h 1 0 M [C0 ~]  17 5  52  Eh-pH diagram f o r the system Cu--H 0--MoO. 4 (oxide s p e c i e s )  181  53  Eh-pH diagram f o r the system Cu--H 0--MoO,, 4 (hydroxide s p e c i e s )  18 2  54  Eh-pH diagram  f o r the system Ca--H 0--Mo0„ 4  18-5  55  Eh-pH diagram  f o r the system Pb--H 0--Mo0„ 4  18 7  56  Eh-pH diagram  f o r the system Zn--H 0--Mo0„ 4  18 8  - 1  2  3  2  2  2  2  2  (xviii)  LIST OF FIGURES ( C o n t ' d ) Page 57  Eh-pH diagram f o r the system Fe-H 0-MoO  189  58  Eh-pH diagram f o r t h e system C d - H ^ - M o O ^  191  2  (xix)  LIST OF PLATES F a c i n g Page I II  Effect of hypochlorite solutions on massive c h a l c o c i t e samples  73  Effect of hypochlorite solutions on massive c o v e l l i t e samples  74  (xx)  Acknowledgement  The a u t h o r generous a d v i c e ,  i s g r e a t l y indebted constant  out t h e p e r i o d o f t h i s  i n t e r e s t and i n v a l u a b l e encouragement  b y members o f F a c u l t y a n d t e c h n i c a l s t a f f  o f t h e Department o f M e t a l l u r g y ,  and t h e h e l p and c o m p a n i o n s h i p o f f e l l o w  h a v e b e e n much a p p r e c i a t e d .  t o D r . F. W e i n b e r g f o r t h e many m u s i c a l from, i f n o t i n s p i r a t i o n F i n a n c i a l support acknowledged.  through-  study.  The a s s i s t a n c e p r o v i d e d  graduate students  t o D r . I.H. Warren f o r h i s  Thanks a r e a l s o e x t e n d e d  i n t e r l u d e s which provided  respite  f o r , the rigours of research. i n the form o f a CIL f e l l o w s h i p i s g r a t e f u l l y  - 1 -  CHAPTER ONE  1.1  Introduction  M o l y b d e n i t e , M c ^ / i s the p r i n c i p a l source o f the molybdenum m e t a l used c o m m e r c i a l l y .  I t o c c u r s b o t h i n p r i m a r y molybdenum d e p o s i t s  and i n  more complex ore b o d i e s a s s o c i a t e d w i t h o t h e r s u l p h i d e m i n e r a l s . P o w e l l i t e , CaMoO^; W u l f e n i t e , PbMoO^ and h y d r a t e d f e r r i c m o l y b d a t e , FeMo^O^ *  8 H  2°  a  r  e  t  '  i e  m  o  s  t  common secondary molybdenum m i n e r a l s b u t  they  are n o t c o n s i d e r e d t o be o f economic importance a t the p r e s e n t t i m e . Molybdenum i s one o f the l e s s common elements w i t h an average c o n c e n t r a t i o n i n the e a r t h ' s c r u s t o f 0.001%."'" an a l l o y i n g element i n i r o n ,  I t s p r i n c i p a l use i s  s t e e l and c e r t a i n non f e r r o u s m e t a l s .  a l o n e o r i n the p r e s e n c e o f o t h e r elements such as n i c k e l , manganese and chromium, molybdenum enhances the s t r e n g t h ,  as Either  vanadium, toughness and  h a r d e n a b i l i t y o f t h e s e m a t e r i a l s and can a l s o improve c o r r o s i o n  resistance.  Molybdenum compounds have wide a p p l i c a t i o n as l u b r i c a n t s , c h e m i c a l r e a g e n t s and as c a t a l y s t s .  They a r e a l s o used e x t e n s i v e l y i n p a i n t and pigment  manufacture. Consumption o f molybdenum has i n c r e a s e d on a w o r l d wide b a s i s an average r a t e o f about 5% p e r annum f o r the p a s t decade,  at  and demand i s  expected t o grow a t l e a s t a t t h i s l e v e l t o the y e a r 2000 and beyond. Western w o r l d p r o d u c t i o n f o r 1977 amounted t o 89,500 m e t r i c t o n s ,  of  2 w h i c h the U n i t e d S t a t e s produced 68% and Canada 17%.  Current estimates  o f molybdenum r e s e r v e s i n d i c a t e t h a t s u p p l i e s s h o u l d be adequate i n the foreseeable  future.  molybdenum as MoS  0  A few h i g h grade d e p o s i t s  c o n t a i n i n g up t o 20%  i n r i c h q u a r t z v e i n s e x i s t , but over 95% o f  current  - 2 -  and p r e v i o u s p r o d u c t i o n has been from low grade p o r p h y r y type  deposits  and i t seems l i k e l y t h a t t h i s f i g u r e w i l l i n c r e a s e as more o f the o r e s a r e worked o u t . 1)  richer  P o r p h y r y o r e s can be c h a r a c t e r i z e d i n t o two t y p e s :  Molybdenum p o r p h y r i e s ; where m o l y b d e n i t e i s the o n l y c o n t a i n e d  m i n e r a l o f economic importance and averages 0.15 - 0.8% 2)  Copper-molybdenum p o r p h y r i e s ;  M  o  S 2  .  from w h i c h copper i s  extracted  as the p r i m a r y m e t a l v a l u e and molybdenum i s r e c o v e r e d as a b y - p r o d u c t . The m o l y b d e n i t e c o n t e n t o f t h e s e o r e s i s much lower and ranges from 0.005 - 0.01% M o S . 2  Copper m i n e r a l i z a t i o n c o n s i s t s o f p r i m a r y and s e c o n -  dary s u l p h i d e o r e s i n c l u d i n g c h a l c o p y r i t e , CuFeS,,; c o v e l l i t e , CuS; c h a l cocite, Cu S; bornite, 2  Cu^FeS^; and e n a r g i t e ,  Cu^sS^.  There i s o f t e n a  l e a c h e d cap a s s o c i a t e d w i t h the o r e body c o n t a i n i n g secondary and o x i d e s such as c u p r i t e , C u 0 ; m a l a c h i t e C u ( O H ) C 0 ; t e n o r i t e , 2  2  2  3  tertiary  CuO, and 2  c h r y s o c o l l a , Cu^H^Si^O^Q(OH)g.  The o v e r a l l copper c o n t e n t  averages 0.8%.  B y - p r o d u c t molybdenum r e c o v e r y from p o r p h y r y copper o r e s  '  accounts  f o r a l m o s t 50% o f t o t a l w o r l d p r o d u c t i o n , b u t the f a c t t h a t o r e grades i n v o l v e d are so low means h i g h r e c o v e r i e s a r e d i f f i c u l t cases.  t o o b t a i n i n many  S e p a r a t i o n o f m o l y b d e n i t e from copper o r e s i s a c h i e v e d by s e l e c t i v e  f l o t a t i o n i n almost a l l cases.  The p r i n c i p a l aim o f p r o d u c t i o n  plants  t r e a t i n g t h e s e o r e s i s t o o p t i m i z e copper r e c o v e r y and v a l u e s o f about 80% a r e t y p i c a l l y o b t a i n e d .  The o v e r a l l molybdenum y i e l d i s u s u a l l y  much l o w e r and averages 50 - 60%.  The r e c e n t depressed  copper market f o l l o w e d by r a p i d i n c r e a s e s  state of  i n the p r i c e o f molybdenum t o  a c u r r e n t v a l u e o f $ 9 / l b , has g i v e n b y - p r o d u c t r e c o v e r y a more perspective.  the  important  I n c a s e s where copper o r e s are r e l a t i v e l y l e a n the two  m e t a l s are almost e q u a l i n terms o f end p r o d u c t v a l u e .  The molybdenum  - 3 -  not r e c o v e r e d i s t h e r e f o r e  o f economic s i g n i f i c a n c e and r e p r e s e n t s a  substantial  resources.  1.2  l o s s of metal  C u r r e n t Molybdenum P r o d u c t i o n  A m o l y b d e n i t e c o n c e n t r a t e a v e r a g i n g 90% MoS^ i s the u s u a l o f b e n e f i c i a t i o n o f r u n o f mine o r e .  T h i s i s then c o n v e r t e d t o  grade molybdenum t r i - o x i d e , MoO^, f o r f u r t h e r p r o c e s s i n g i n t o molybdenum and o t h e r compounds.  product technical  ferro-  The c o n v e n t i o n a l method o f o b t a i n i n g  molybdenum t r i - o x i d e f o l l o w s a f l o t a t i o n - r o a s t i n g method as o u t l i n e d i n F i g u r e 1. Molybdenum-bearing copper o r e s are most o f t e n mined by open p i t methods,  after  w h i c h the r u n - o f - m i n e o r e i s s u b j e c t e d  t o c r u s h i n g and wet  g r i n d i n g t o g i v e a p r o d u c t y i e l d i n g 50 - 70% minus 200 mesh m a t e r i a l . B e n e f i c i a t i o n by f l o t a t i o n i s used i n a l l c a s e s , l a r g e l y due t o the good n a t u r a l f l o t a b i l i t y o f m o l y b d e n i t e , making i t the e a s i e s t method by which separation  from copper can be a c h i e v e d .  o r e s are s u b j e c t e d  Complex copper-molybdenum  t o a c o l l e c t i v e rougher f l o t a t i o n t o g i v e a rougher  c o n c e n t r a t e a v e r a g i n g 0.3% Mo and 12.5% Cu w i t h some i r o n , s u l p h u r and calcium oxide.  T h i s c o n c e n t r a t e i s r e - g r o u n d and c l e a n e d to g i v e an up-  graded copper f l o t a t i o n c o n c e n t r a t e a v e r a g i n g 25 - 35% C u . denite  The m o l y b -  i s then s e p a r a t e d by a s e l e c t i v e f l o t a t i o n s t a g e , c a r r i e d out  e i t h e r by d e p r e s s i n g the copper and a l l o w i n g the m o l y b d e n i t e t o  float,  o r by the o p p o s i t e t e c h n i q u e o f d e p r e s s i n g the m o l y b d e n i t e and f l o a t i n g off  the o t h e r c o n s t i t u e n t s  i s generally preferred,  o f the copper c o n c e n t r a t e .  The former method  g i v i n g an i n i t i a l molybdenum rougher  concentrate  -  Run  4  -  of mine ore  CRUSHING  L_  8 GRINDING  COLLECTIVE ROUGHER FLOTATION j  Rougher concentrate (!2-4%Cu,0-3% MoS ) 2  • REGRINDING, CLEANING  i  Copper flotation concentrate (25-35%Cu) <Q-2% Mo  >D-2%Mol THICKENING  THICKENING  Cu SELECTIVE ROUGHER FLOTATION Mo I  FILTRATION  I DRYING T  Mo rough e c onc• (35% Mo S ) I 2 r  C u . concentrate  CLEANING, REGRINDING  Mo flotation c one. ( 8 0 % M o SJ*°' THICKENING  Mo  50/o(  f  u  Cu  LEACH  FILTRATION DRYING  Mo concentrate ( Mo0  Figure 1:  I  3  90%MoS )  PRODUCTION  Conventional flowsheet f o r the production of molybdenum trioxide.  2  - 5 -  which i s p u r i f i e d f u r t h e r MoS p r o d u c t , 2  i n a counter-current  c i r c u i t u n t i l a 90%  c o n t a i n i n g l e s s than 0.5% C u , i s o b t a i n e d .  A low tempera-  t u r e r o a s t i s sometimes i n c o r p o r a t e d i n t o the c l e a n i n g c i r c u i t t o p a r t i a l o x i d a t i o n o f copper s u l p h i d e m i n e r a l s , thereby r e t a r d i n g  effect their  flotability. W i t h c a r e f u l use o f the c o r r e c t f l o t a t i o n r e a g e n t s f o r the m i n e r a l i z a t i o n p r e s e n t i n a s p e c i f i c o r e , as w e l l as o p t i m i z a t i o n o f pH by the use o f m o d i f i e r s , and s u i t a b l e c h o i c e o f t e m p e r a t u r e , up t o 85% o f c o n t a i n e d molybdenum can be r e c o v e r e d .  the  However, as noted above, c o n d i -  t i o n s are u s u a l l y s e l e c t e d t o g i v e maximum copper r e c o v e r y , and t h i s results  i n a much l o w e r average l e v e l o f molybdenum r e c o v e r y .  molybdenum can o c c u r on account o f the f o l l o w i n g i)  Loss o f  factors:"''^  The ore i s ground t o a s i z e s u i t a b l e f o r optimum copper  r e c o v e r y and t h i s i s u s u a l l y c o a r s e r than the i d e a l s i z e f o r m o l y b d e n i t e . T h i s problem i s o f t e n a c c e n t u a t e d  d u r i n g p e r i o d s o f depressed  p r i c e s when an even c o a r s e r g r i n d i s used t o i n c r e a s e ii)  copper  throughput.  M o l y b d e n i t e can be l o s t from the copper rougher  flotation  t a i l i n g s because i t o f t e n e x i s t s as l a r g e f l a k e s w h i c h are t r a p p e d by quartz  particles. iii)  F i n e r p a r t i c l e s are l o s t from the o v e r f l o w o f m i d d l i n g  thickeners after  p r o d u c t i o n o f the molybdenum rougher c o n c e n t r a t e ,  and  t h i s l o s s i s i n c r e a s e d by the p r e s e n c e o f f l o c c u l a n t s . iv)  The p r e s e n c e o f v a r y i n g copper s u l p h i d e m i n e r a l i z a t i o n i n  an ore can n e c e s s i t a t e the use o f d i f f e r e n t ences i n s u r f a c e p r o p e r t i e s , covellite.  d e p r e s s a n t s due to  differ-  f o r example between c h a l c o p y r i t e and  C e r t a i n r e a g e n t s can a l s o i n h i b i t m o l y b d e n i t e  flotation.  - 6 -  Naturally floating materials be e q u a l l y d e t r i m e n t a l denum o x i d e s i s a l s o v)  such as s u l p h u r ,  t a l c , graphite  and c o a l can  t o molybdenum recovery,, and the p r e s e n c e o f m o l y b undesirable.  P o r p h y r y o r e s o f t e n have a n o n - u n i f o r m d i s t r i b u t i o n o f  molybdenum, r e s u l t i n g i n l a r g e v a r i a t i o n s o f head v a l u e s i n the  feed  m a t e r i a l t o the f l o t a t i o n c i r c u i t , which p r e s e n t a d d i t i o n a l d i f f i c u l t i e s i n m a i n t a i n i n g c o n t i n u o u s h i g h molybdenum  recoveries.  I n many cases the f i n a l m o l y b d e n i t e c o n c e n t r a t e i s s u b j e c t e d s u l p h u r i c a c i d o r sodium c y a n i d e l e a c h a f t e r r e - c l e a n i n g and p r i o r t h i c k e n i n g and f i l t r a t i o n . i n the  T h i s s e r v e s t o remove any copper  to a to  remaining  concentrate. C o n v e r s i o n t o molybdenum t r i - o x i d e i s by means o f an o x i d i z i n g  r o a s t , u s u a l l y c a r r i e d o u t i n " N i c h o l s - H e r r e s h o f f " type r o a s t e r s w h i c h e n a b l e the temperature t o be c l o s e l y m o n i t o r e d and k e p t between 600 - 7 0 0 ° C . The f i n a l MoO^ p r o d u c t c o n t a i n s  56 - 62% Mo and has maximum a l l o w a b l e 7  s u l p h u r and copper c o n t e n t s o f 0.25% and 0.75%  respectively.  •* 1.3  H y d r o m e t a l l u r g i c a l P r o d u c t i o n o f Molybdenum W h i l e e x i s t i n g r e s e r v e s o f m o l y b d e n i t e are expected to be adequate  t o s u p p l y an i n c r e a s e d demand o f up t o 5% p e r annum f o r some time t o come, p r o d u c t i o n o f molybdenum on a d a y - t o - d a y b a s i s i s not always adequate. I n 1977 t h e r e was a p r o d u c t i o n d e f i c i t o f some 9 m i l l i o n pounds o f m o l y b 2 denum, w h i c h had t o be s u p p l i e d from e x i s t i n g s t o c k p i l e s . seem d e s i r a b l e t o r e s e a r c h recovery.  i n t o ways o f i n c r e a s i n g c u r r e n t  As more o f the w o r l d ' s h i g h e r grade d e p o s i t s  I t would thus molybdenum  are worked o u t ,  molybdenum b e a r i n g copper o r e s t y p i c a l o f t h o s e found i n B r i t i s h  - 7 -  Columbia w i l l assume an even more i m p o r t a n t r o l e as a source o f the For these types o f o r e s ,  metal.  a h y d r o m e t a l l u r g i c a l method f o r molybdenum  r e c o v e r y has the p o t e n t i a l o f g i v i n g h i g h e r m e t a l e x t r a c t i o n and b e t t e r u t i l i z a t i o n o f raw m a t e r i a l s than can be o b t a i n e d by c o n v e n t i o n a l  methods.  A h y d r o m e t a l l u r g i c a l route could a l s o e l i m i n a t e e i t h e r or both of  the  p r e l i m i n a r y and f i n a l r o a s t i n g s t a g e s .  T h i s would be p r e f e r a b l e  from an  e n v i r o n m e n t a l p o i n t o f view by p r e v e n t i n g the e v o l u t i o n o f SO^ i n t o  the  atmosphere. M o l y b d e n i t e i s g e n e r a l l y u n r e a c t i v e c h e m i c a l l y and i t s d i s s o l u t i o n i n aqueous media e n t a i l s o x i d a t i o n t o the M o  V I  state.  Molybdenum  w i l l e x i s t i n water i n o x i d a t i o n s t a t e s o f +3 t o +6, but o n l y the +6 s t a t e i s s t a b l e o v e r a wide range o f p o t e n t i a l - p H v a l u e s .  The o t h e r  v a l e n c e s t a t e s can be s t a b i l i z e d by c e r t a i n c o m p l e x i n g a g e n t s . o f m o l y b d e n i t e from Mo"  tV  n i t r i c a c i d , concentrated  to M o  V I  can be e f f e c t e d  Oxidation  by d i s s o l u t i o n i n hot  s u l p h u r i c a c i d , aqua r e g i a and by oxygen under  p r e s s u r e i n aqueous s o l u t i o n ; as w e l l as by v a r i o u s o x i d i z i n g agents such as a c i d sodium c h l o r a t e and sodium h y p o c h l o r i t e .  On the a l k a l i n e s i d e o f  2VI n e u t r a l i t y the monomer MoO^ i s the u s u a l form o f Mo , b u t a t pH v a l u e s below 7 . 0 , and w i t h a molybdenum c o n t e n t Q is usually polymerized. metal c a t i o n s ,  i n excess o f 10  -4  The molybdate i o n r e a d i l y combines w i t h most  and w i t h the e x c e p t i o n o f the a l k a l i m e t a l s ,  salt is precipitated.  M, t h i s i o n  an i n s o l u b l e  The a n i o n i s a b l e t o a t t a i n r a p i d e q u i l i b r i u m i n  aqueous s o l u t i o n w h i c h i s o f c o n s i d e r a b l e advantage when c o n s i d e r i n g a wet method f o r molybdenum e x t r a c t i o n . S e v e r a l s t u d i e s have been c a r r i e d out i n the l a s t two decades t o i n v e s t i g a t e p o s s i b l e methods o f e x t r a c t i n g molybdenum by l e a c h i n g  - 8 -  molybdenite.  The m a j o r i t y o f t h e s e suggested  the use o f n i t r i c a c i d o r  a s t r o n g o x i d a n t i n a l k a l i n e s o l u t i o n as a l i x i v i a n t , w i t h subsequent r e c o v e r y o f molybdenum by means o f an ion-exchange o r s o l v e n t technique,  extraction  o r by r e d u c t i v e p r e c i p i t a t i o n i n a c i d s o l u t i o n s u s i n g m e t a l  (mercury, z i n c , cadmium o r molybdenum) o r gaseous (hydrogen, sulphide, sulphur dioxide) reductants.  Investigations  hydrogen  i n t o the use o f  o t h e r r e d u c i n g agents such as h y d r a z i n e and sodium s u l p h i t e have  recently  9  been c a r r i e d o u t i n t h i s department. The b i g g e s t l o s s o f molybdenum i n c u r r e n t p r o c e s s e s o c c u r s d u r i n g the c o l l e c t i v e rougher f l o t a t i o n stage and amounts t o some 36%. l o s s e s o f about 10% o c c u r between t h i s p o i n t and the f i n a l product.  Further  molybdenite  The most l o g i c a l h y d r o m e t a l l u r g i c a l t r e a t m e n t s h o u l d  therefore  use r u n o f mine o r e as the s t a r t i n g m a t e r i a l f o r a l e a c h i n g c i r c u i t , but t h i s would n o t be e c o n o m i c a l l y p r a c t i c a l f o r many p o r p h y r y o r e s w h i c h c o n t a i n l e s s than 0.02% Mo.  Most o f the p r o c e s s e s e n v i s a g e d  to  date have thus worked on the b a s i s o f a l e a c h i n g c i r c u i t i n c o n j u n c t i o n w i t h e x i s t i n g f l o t a t i o n methods, c o n c e n t r a t e s as feed m a t e r i a l .  u s i n g e i t h e r molybdenum o r copper  rougher  B o t h methods appear t o be f e a s i b l e p r o v i d -  ed the l e a c h i s s u f f i c i e n t l y s e l e c t i v e f o r molybdenum o v e r copper and other sulphide minerals. W h i l e the t r e a t m e n t o f u n - b e n e f i c i a t e d o r e s i s n o t acceptable,  generally  the p o s s i b i l i t y o f e x t r a c t i n g molybdenum by i n - s i t u l e a c h i n g  o r s o l u t i o n m i n i n g methods,  c o u l d have c o n s i d e r a b l e p o t e n t i a l v a l u e .  The  advantages o f s o l u t i o n m i n i n g i n terms o f reduced c a p i t a l and o p e r a t i n g c o s t s and a r e d u c t i o n i n m a t e r i a l s h a n d l i n g , a more e f f i c i e n t u t i l i z a t i o n of resources  and l e s s e n v i r o n m e n t a l d i s t u r b a n c e s ,  as w e l l as  the  - 9 -  disadvantages  a s s o c i a t e d w i t h h a n d l i n g and s t o r i n g l a r g e volumes o f  l e a c h i n g s o l u t i o n s and c a r e f u l p r e d i c t i o n and c o n t r o l o f t h e i r ground movements,  have been w e l l documented i n the l i t e r a t u r e .  underLow  1 0  grade copper-molybdenum o r e s c o u l d be v e r y amenable t o t h i s type o f l e a c h i n g p r o v i d e d the l i x i v i a n t used gave a s u f f i c i e n t l y r a p i d and s e l e c t i v e l e a c h o f the c o n t a i n e d molybdenum v a l u e s , and c o u l d be e c o n o m i c a l l y produced.  1.4  L i t e r a t u r e Review  1.4.1  The e x t r a c t i o n o f m o l y b d e n i t e w i t h sodium h y p o c h l o r i t e s o l u t i o n s Cox and S c h e l l i n g e r c a r r i e d o u t l a b o r a t o r y s c a l e t e s t s i n an  i n v e s t i g a t i o n t o determine the f e a s i b i l i t y o f a l e a c h - i o n exchange process  type  f o r p r o d u c i n g m o l y b d i c o x i d e , i n w h i c h they used sodium h y p o c h l o r -  i t e as a l i x i v i a n t f o r t h r e e d i f f e r e n t 0.015%, 1,05% and 63% MoS  2  grades o f m a t e r i a l  respectively.  1 1  containing  D r e s h e r , Wadsworth and F a s s e l  had p r e v i o u s l y s t u d i e d the k i n e t i c s o f d i s s o l u t i o n o f m o l y b d e n i t e i n a l k a l i n e s o l u t i o n s w i t h p o t a s s i u m h y d r o x i d e a t t e m p e r a t u r e s i n excess o f 100°C and p r e s s u r e s up t o 700 p s i , and had found t h a t s u i t a b l e r a t e s o f 12 l e a c h i n g c o u l d be o b t a i n e d w i t h t h e s e c o n d i t i o n s .  Cox e t a l . c o n c l u d e d  t h a t use o f h y p o c h l o r i t e r e a g e n t s c o u l d g i v e a much more e c o n o m i c a l p r o c e s s than one n e c e s s i t a t i n g  a high pressure-high  temperature l e a c h ,  and optimum c o n d i t i o n s f o r molybdenum r e c o v e r y were o b t a i n e d w i t h a 3% s o l u t i o n o f sodium h y p o c h l o r i t e a t room t e m p e r a t u r e .  They put  forward  the f o l l o w i n g s t o i c h i o m e t r i c r e l a t i o n s h i p as b e i n g o p e r a t i v e d u r i n g leach:  the  - 10 -  7NaOCl  +  MoS  +  +  7NaCl  The r a t e o f l e a c h i n g was found t o d e c r e a s e t o z e r o a f t e r  about  2  4e  >- MoC> ~  +  4  S 0 2  2 3  (1) thirty  m i n u t e s , a t which p o i n t molybdenum e x t r a c t i o n s r a n g i n g from 91 - 99% had been a c h i e v e d . that thiosulphate  Both Cox and S c h e l l i n g e r , and Dresher e t a l . o b s e r v e d i o n s were p r e s e n t i n the l e a c h i n g s o l u t i o n s , but  the  2l a t t e r workers c o n c l u d e d t h a t p r o d u c t and t h a t a f t e r  S 2  C>  was o n l y an i n t e r m e d i a t e  3  reaction  complete o x i d a t i o n , o n l y molybdate and  sulphate  i o n s would e x i s t i n s o l u t i o n : MoS  2  +  9 - °  +  6  0  H  -  y  M o 0  2  4  2  +  -  2 S 0  4  2  -  +  3 H  2°  ( 2 )  A k i n e t i c study o f the o x i d a t i o n o f m o l y b d e n i t e u s i n g sodium h y p o c h l o r 13 i t e s o l u t i o n s was r e p o r t e d by I o r d i n o v and Z e l i k m a n i n 1961. used a r e a g e n t c o n c e n t r a t i o n v a r y i n g from 15 t o 60 g/1 OC1  They at  t u r e s o f 20 - 80°C and t h e i r s t a r t i n g m a t e r i a l was pure MoS 2  d e s c r i p t i o n as t o the t h e o r y o f the d i f f e r e n t  temperaA detailed  stages i n v o l v e d i n molyb-  d e n i t e o x i d a t i o n from a p h y s i c o - c h e m i c a l s t a n d p o i n t i s g i v e n , and the o v e r a l l r e a c t i o n was found t o b e : MoS  2  +  9NaOCl  +  6NaOH  > Na MoO 2  +  2Na S0 2  4  +  9NaCl  +  H 0 2  (3)  T h i s i s i n good agreement w i t h the f i n d i n g s o f Dresher e t a l . , w i t h 9 moles o f o x i d a n t r e q u i r e d p e r mole o f m o l y b d e n i t e .  Zelikman a l s o found  t h a t t h i o s u l p h a t e was p r e s e n t i n i t i a l l y but t h a t i t s c o n c e n t r a t i o n went t h r o u g h a maximum v a l u e and had reached z e r o by the end o f the The o x i d a t i o n o f m o l y b d e n i t e t o molybdate was found t o be f i r s t  reaction. order,  w i t h an a c t i v a t i o n energy o f about 5.25 k c a l / m o l e o v e r the temperature range under s t u d y .  The r a t e c o n s t a n t  increased both w i t h  increased  - 11 -  h y p o c h l o r i t e c o n t e n t and w i t h i n c r e a s e d  temperature.  S h a p i r o and K u l e n k e v a c a r r i e d o u t t e s t s u s i n g a sodium h y p o c h l o r i t e l i x i v i a n t t o t r y and o b t a i n e f f i c i e n t molybdenum r e c o v e r y from  intermediate  c o n c e n t r a t e s c o n t a i n i n g 2 - 6% Mo produced d u r i n g the p r o c e s s i n g o f 14 d i s s e m i n a t e d m o l y b d e n i t e or p o l y s u l p h i d e o r e s .  L e a c h i n g experiments  were done i n the p r e s e n c e o f sodium c a r b o n a t e and i t was found t h a t a 30 g/1 s o l u t i o n o f h y p o c h l o r i t e gave a maximum r a t e o f m o l y b d e n i t e decomp o s i t i o n at MoS  2  +  50°C:  9NaOCl  +  3Na C0 2  3  HNa MoC>  +  4  2Na S0 2  +  4  9NaCl  +  3CC>  (4)  2  The l e a c h was s t a t e d as b e i n g s e l e c t i v e f o r molybdenum because any o t h e r m e t a l s u l p h i d e s p r e s e n t would be c o n v e r t e d t o i n s o l u b l e c a r b o n a t e s , r e p r e s e n t e d by the f o l l o w i n g  . MeS. +  4NaOCl .+  as  equation:  Na C0 2  3  v  N a  2 °4 S  +  4  N  a  C  1  +  MeC0  (5)  3  Bhappu, Reynolds and Stahman made a s t u d y o f the sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e from t h r e e d i f f e r e n t  sources:  a h i g h grade c o n -  c e n t r a t e c o n t a i n i n g 96 - 98% M o S , low grade o r e s t y p i c a l o f those found 2  i n a waste dump (0.2 - 0.8% MoS ) and medium grade lumps o f m o l y b d e n i t e 2  a v e r a g i n g 60%.  They c a l c u l a t e d the s t o i c h i o m e t r i c r e l a t i o n s h i p  h y p o c h l o r i t e consumption t o be the same f o r each t e s t sample, n e g l i g i b l e consumption by gangue m a t e r i a l ,  for  indicating  and i n agreement w i t h the  f i n d i n g s o f I o r d i n o v and Z e l i k m a n , t h a t n i n e moles o f OC1 were  required  t o o x i d i z e each mole o f MoS . 2 They a l s o c o n f i r m e d r e p o r t s by Choppin and F a u l k e r b e r r y ^ w h i c h 1  showed t h a t p r o v i d e d an excess o f h y p o c h l o r i t e i s p r e s e n t i n s o l u t i o n ,  the  - 12  end  product of  sulphide  -  oxidation i s entirely  sulphate.  e x p r e s s e d c o n c e r n i n g Cox's c l a i m t h a t t h i o s u l p h a t e product of hypochlorite thiosulphate  or other  their opinion, oxidized to  o x i d a t i o n , and  intermediate  e x i s t only  p r e s e n t as  Bhappu e t a l . s t r e s s e d  o x i d a t i o n state of sulphur  for very  short periods  thus a  final  that  any  would, i n  of time before  being  sulphate.  These a u t h o r s c o n c l u d e d t h a t considerable ment o f low r e a g e n t by  was  D o u b t was  such a h y p o c h l o r i t e  process  offered  p o t e n t i a l f o r molybdenite l e a c h i n g , e s p e c i a l l y f o r the grade ores,  on  account of the  s e e m i n g l y low  treat-  consumption  of  gangue m a t e r i a l .  17 I n a l a t e r p a p e r however, Bhappu e t a l . o x i d i z i n g agents f o r the h y d r o m e t a l l u r g i c a l and  concluded that while  r e v i e w e d a number  treatment of molybdenite  alkaline hypochlorite  s o l u t i o n s gave r a p i d  s e l e c t i v e molybdenum e x t r a c t i o n , t h e  r e a g e n t was  unstable  economically  and  generation  c o r r o s i v e ; and  i n t h i s type of  re-generation  circuit  oxidation reaction.  the  only  leaching  from the  of  expensive to  and  manufacture,  f e a s i b l e method f o r i t s  s y s t e m w o u l d be  i n an  electrolytic  s o d i u m c h l o r i d e s o l u t i o n p r o d u c e d by  the  included  sodium  chlorate  i n a c i d s o l u t i o n s , m a n g a n e s e d i o x i d e - s u l p h u r i c a c i d and  nitric  acid.  The  Other reagents considered  ores  p o s s i b i l i t i e s o f b a c t e r i a l l e a c h i n g as w e l l a s  in-situ  leaching  were  a l s o reviewed, e s p e c i a l l y i n the presence of non-sulphide ores such ferrimolybdate mixed oxides  and  and  limonite.  sulphides  carbonate l i x i v i a n t  For  t h e s e o r e s and  e i t h e r an  containing  a c i d - c h l o r a t e or a basic  seemed f e a s i b l e , w i t h  the  f e r r e d because of p o t e n t i a l problems w i t h the compounds i n a c i d s o l u t i o n s .  f o r those  l a t t e r being  as  hypochlorite-  generally  p r e c i p i t a t i o n of  pre-  molybdate  - 13 -  Z e l i k m a n r e v i e w e d the p o s s i b i l i t y o f l e a c h i n g m o l y b d e n i t e w i t h 18 h y p o c h l o r i t e a g a i n i n 1970,  p a r t i c u l a r l y from low grade c o n c e n t r a t e s  which would p r o b a b l y a l s o c o n t a i n copper and i r o n s u l p h i d e s .  Although  such s u l p h i d e s would be o x i d i z e d by h y p o c h l o r i t e i n a l k a l i n e s o l u t i o n , o x i d a t i o n p r o d u c t s would be i n s o l u b l e h y d r o x i d e s w h i c h i n h i b i t the t i o n and p r e v e n t subsequent d i s s o l u t i o n , thus g i v i n g a s e l e c t i v e num l e a c h .  reac-  molybde-  I t was p o i n t e d o u t i n t h i s a r t i c l e t h a t the h y d r o x i d e s o f  c e r t a i n t r a n s i t i o n m e t a l e l e m e n t s , i n c l u d i n g copper and i r o n , are active catalysts media.  the  also  f o r the d e c o m p o s i t i o n o f sodium h y p o c h l o r i t e i n a l k a l i n e  C a t a l y s i s can e i t h e r be homogeneous o r h e t e r o g e n e o u s , and i t was  suggested the l a t t e r i n v o l v e s the f o r m a t i o n o f u n s t a b l e h y d r o x i d e s o f higher valence s t a t e s , e s p e c i a l l y for copper.  Optimum c o n d i t i o n s  for  c o n c e n t r a t e s c o n t a i n i n g 23% Mo and 9% Cu were found t o e x i s t w i t h a hypoc h l o r i t e c o n t e n t o f 30 g/1 and 20 - 30 g/1 f r e e a l k a l i . t u r e s were found t o i n c r e a s e  H i g h e r tempera-  the r a t e o f molybdenum e x t r a c t i o n ,  t h i s a l s o gave an i n c r e a s e d r a t e o f c a t a l y z e d h y p o c h l o r i t e l e a c h i n g a t room temperature was  but  as  decomposition,  recommended.  I n a l l the above s t u d i e s m o l y b d e n i t e l e a c h i n g has been c a r r i e d o u t on the a l k a l i n e s i d e o f n e u t r a l i t y , optimum i n s e v e r a l c a s e s .  w i t h pH 10.0 b e i n g s t a t e d as  Sodium h y p o c h l o r i t e i s much more s t a b l e i n  a l k a l i n e s o l u t i o n s than i t i s i n a c i d media. was used i n an e l e c t r o o x i d a t i o n t e c h n i q u e  A pH range o f 5.0 -  7.0  i n v e s t i g a t e d by the U n i t e d  S t a t e s Bureau o f Mines f o r e x t r a c t i n g molybdenum and rhenium from low grade 19 ores,  d e s p i t e t h i s b e i n g the r e g i o n i n w h i c h d e c o m p o s i t i o n o f h y p o c h l o r -  i t e to c h l o r a t e t a k e s p l a c e most r a p i d l y . hypochlorite generation  The method was based on i n - s i t u  by e l e c t r o l y s i s i n b r i n e o r e p u l p .  Extractions  - 14 -  o f 90 - 99% molybdenum were r e p o r t e d and a s t o i c h i o m e t r i c r a t i o o f MoS^: 90C1  was a g a i n found t o be o p e r a t i v e  (equation 3 ) .  The r e q u i r e d pH  v a l u e was m a i n t a i n e d by s e m i - c o n t i n u o u s a d d i t i o n o f sodium carbonate and a temperature o f 30 - 40°C was u s e d . was r e p o r t e d as 9.7 k w h / l b Mo e x t r a c t e d ,  The o v e r a l l power consumption w i t h a c u r r e n t d e n s i t y o f 0.5  amp/in . 2  The s t u d y was extended t o determine t h e e x t r a c t a b i l i t y o f m o l y b denum from copper-molybdenum f l o t a t i o n c o n c e n t r a t e s ,  a v e r a g i n g 3 - 28% Mo  20 and 2 - 15% C u . f i n a l pH o f 7 . 0 : pH l e v e l s .  A maximum e x t r a c t i o n o f 97% Mo was a c h i e v e d w i t h a t h i s v a l u e a p p a r e n t l y d e c r e a s e d a t b o t h lower and h i g h e r  I t was s t a t e d t h a t a minimum copper s o l u b i l i t y o f 1 - 3 ppm  o c c u r r e d a t pH 7 . 0 , and i n a l k a l i n e s o l u t i o n s copper was d i s s o l v e d to the e x t e n t o f 25 ppm due t o f o r m a t i o n o f the s o l u b l e compound ( C u X ^ C O ^ where X = CI  o r OH .  S c h e i n e r e t a l . suggested copper molybdate com-  pounds c o u l d a d v e r s e l y a f f e c t molybdenum r e c o v e r y , but o x i d a t i o n o f copper s u l p h i d e s by h y p o c h l o r i t e c o u l d be p r e v e n t e d by a d d i n g s u f f i c i e n t sodium carbonate  t o the  system. 21 22  I n two l a t e r p a p e r s  '  p r o c e s s s o l u t i o n s were t r e a t e d , and the  t e c h n i q u e was demonstrated w i t h a p r o t o t y p e c e l l . e x t r a c t i o n was o b t a i n e d from c o n c e n t r a t e s and about 36% Mo.  89 - 98% molybdenum  c o n t a i n i n g l e s s than 1% Cu  No copper was d i s s o l v e d i n the pH range 5.5 - 7 . 0 ,  but l a r g e amounts o f c h l o r a t e were produced i n t h i s r e g i o n and an SO2 r e d u c t i o n s t e p was t h e r e f o r e  i n c o r p o r a t e d i n t o the p r o c e s s .  This pro-  cedure a l s o s e r v e d t o reduce t h e pH o f molybdate s o l u t i o n s f o r subsequent molybdenum r e c o v e r y by s o l v e n t e x t r a c t i o n .  Power consumption f o r  f l o t a t i o n c o n c e n t r a t e s was 13.7 kwh which i s 4% h i g h e r t h a n the  treating  corresponding  - 15 -  v a l u e f o r h i g h e r grade m o l y b d e n i t e c o n c e n t r a t e s . c e l l demonstration  ' o f f grade'  I n the  prototype  f l o t a t i o n c o n c e n t r a t e s c o n t a i n i n g 16 - 35%  Mo and 6 ~ 15% Cu as c h a l c o p y r i t e a n d / o r c h a l c o c i t e were t r e a t e d . r e p o r t e d t h a t the molybdenum e x t r a c t i o n decreased presence o f h i g h e r i n i t i a l copper c o n t e n t s , were r e p o r t e d l y found i n l e a c h i n g t a i l s .  I t was  to o n l y 75% i n the  and copper molybdate  compounds  I t was c l a i m e d t h a t any c h a l c o -  p y r i t e p r e s e n t i n the feed m a t e r i a l was u n a f f e c t e d  by e l e c t r o l y s i s ,  but  t h a t c h a l c o c i t e was o x i d i z e d by sodium h y p o c h l o r i t e w i t h subsequent f o r m a t i o n o f s o l u b l e copper compounds.  These then r e a c t e d w i t h m o l y b -  date i o n s i n s o l u t i o n t o g i v e i n s o l u b l e copper A l l subsequent t r i a l s were t h e r e f o r e h i g h molybdenum c o n c e n t r a t e s ' a n d  molybdates.  performed w i t h low c o p p e r /  no i n f o r m a t i o n was g i v e n as to how, i f  a t a l l , the copper molybdate problem c o u l d be r e c t i f i e d . w i t h these s t u d i e s ,  In conjunction  B a r r and c o - w o r k e r s i n v e s t i g a t e d the e f f e c t s  of  c h l o r a t e p r o d u c t i o n on molybdenum r e c o v e r y d u r i n g e l e c t r o o x i d a t i o n ,  and  c o n c l u d e d t h a t b y - p r o d u c t sodium c h l o r a t e was d e t r i m e n t a l t o molybdenum r e c o v e r y as w e l l as r e p r e s e n t i n g these factors  are u n f a v o u r a b l e  a power l o s s from the system.  economically.  To m i n i m i z e c h l o r a t e  t i o n the a u t h o r s recommended a low t e m p e r a t u r e - l o w i n w h i c h the pH was a l s o reduced t o 4 . 0 - 5 . 0 . c e l l s was shown t o be p r e f e r a b l e  Both  current density  The use o f ' f l o w  producleach  through'  t o l e a d d i o x i d e anode b a t c h c e l l s .  23 24 '  By measuring r e s p e c t i v e o x i d a t i o n r a t e s o f m o l y b d e n i t e and c h a l c o p y r i t e i n a l k a l i n e s o l u t i o n s , Stumpf and Berube  concluded that  the  s e l e c t i v e l e a c h i n g o f molybdenum from t y p i c a l f l o t a t i o n c o n c e n t r a t e s 25 was u n l i k e l y .  The u n i t consumption o f oxygen f o r the two m i n e r a l s  a p p a r e n t l y v e r y s i m i l a r , and t h i s was taken t o mean t h a t b o t h  species  is  - 16 -  would be s i m u l t a n e o u s l y a t t a c k e d ,  t h e r e b y p r e v e n t i n g s e l e c t i v e molybdenum  dissolution. These p r e d i c t i o n s are i n d i r e c t c o n t r a s t  t o the f i n d i n g s o f  26 Warren, Ismay and K i n g ,  who showed t h a t m o l y b d e n i t e c o u l d be r a p i d l y  and s e l e c t i v e l y l e a c h e d i n a l k a l i n e h y p o c h l o r i t e s o l u t i o n s .  The feed  m a t e r i a l i n t h i s case was a copper rougher c o n c e n t r a t e c o n t a i n i n g 12.4% Cu and 0.3% Mo.  The use o f e x t e r n a l l y g e n e r a t e d h y p o c h l o r i t e was p r o p o s e d .  By c o n s i d e r a t i o n o f power r e q u i r e m e n t s , other factors  sodium c h l o r i d e consumption and  f o r t h e p r o d u c t i o n o f sodium h y p o c h l o r i t e by t h i s  method;  and a l s o t a k i n g i n t o account the p o t e n t i a l r e d u c t i o n i n molybdenum l o s s e s by the use o f a p r o c e s s w h i c h e l i m i n a t e d c l e a n e r f l o t a t i o n s t e p s , Warren e t a l . suggested  t h a t d i s m i s s a l o f t h i s type o f h y p o c h l o r i t e l e a c h i n g  system on economic grounds was no l o n g e r v a l i d ;  and t h a t i t would compare  f a v o u r a b l y w i t h the e l e c t r o o x i d a t i o n t e c h n i q u e s o u t l i n e d above. was t h e r e f o r e  A study  c a r r i e d o u t t o determine optimum c o n d i t i o n s f o r molybdenum  e x t r a c t i o n and these were found t o e x i s t a t pH 9 . 0 , w i t h an excess o f h y p o c h l o r i t e and a temperature range o f 30 - 4 0 ° C .  S e l e c t i v i t y of molyb-  denum o v e r copper was o b t a i n e d w i t h a r a t i o o f about 1 0 0 : 1 , but presence o f even s m a l l amounts o f copper i n s o l u t i o n a t pH 9.0 to c o n t r a d i c t s o l u b i l i t y d a t a .  I t was p o s t u l a t e d  the appeared  that p a r t i a l l y oxidized  s u l p h u r s p e c i e s c o u l d be c o m p l e x i n g the copper and h o l d i n g i t i n s o l u t i o n . E x c e s s i v e h y p o c h l o r i t e consumption o v e r t h a t p r e d i c t e d by the of equation 3  was observed i n c e r t a i n c a s e s , and t h i s was  stoichiometry  attributed  t o the f o r m a t i o n o f s u r f a c e o x i d e s d u r i n g the o v e n - d r y i n g o f copper p h i d e m i n e r a l s , w h i c h s u b s e q u e n t l y a c t as c a t a l y s t s composition. cess .  sul-  for h y p o c h l o r i t e de-  The s t u d y i n c l u d e s a proposed f l o w s h e e t  f o r the o v e r a l l p r o -  - 17 -  1.4.2  The b e h a v i o u r o f copper i n a l k a l i n e carbonate s o l u t i o n s A d d i t i o n o f a number o f a n i o n i c l i g a n d s t o s o l u t i o n s c o n t a i n i n g  d i s s o l v e d copper i n the form o f the a q u o - i o n f o r m a t i o n o f complexes. distant  [Cu(H 0) ] 2 6  2+  leads to  the  Because the s i x water m o l e c u l e s are not e q u i -  from the c e n t r a l copper atom, s u c c e s s i v e d i s p l a c m e n t by o t h e r  l i g a n d s can r e a d i l y o c c u r .  Ammonia, N H ^ , i s one such c o m p l e x i n g agent i n  a l k a l i n e s o l u t i o n and the f a c t t h a t c u p r i c h y d r o x i d e i s r e a d i l y s o l u b l e i n ammonia s o l u t i o n s has been used t o advantage i n a number o f f o r copper e x t r a c t i o n .  Ammonium c a r b o n a t e s  are used i n t h i s  processes  respect,  b u t due t o the s t r o n g complexing a c t i o n o f the ammonia i t s e l f , the t h a t carbonate overlooked.  fact  a l s o a c t s as a c o m p l e x i n g l i g a n d f o r copper i s g e n e r a l l y 2-  The [CO^  ] a n i o n forms a s t r o n g e r complex than do any o f  the  h a l i d e i o n s , f o r example, i n a l k a l i n e s o l u t i o n s , but the l a t t e r are more often considered to s t a b i l i z e cupric s a l t s i n s o l u t i o n . I t was o b s e r v e d i n the m i d d l e o f t h e l a s t c e n t u r y t h a t the a d d i t i o n o f c e r t a i n copper s a l t s t o sodium carbonate  s o l u t i o n s produced i n t e n s e l y  blue s o l u t i o n s which subsequently p r e c i p i t a t e d l i g h t blue c r y s t a l s of some b a s i c copper carbonate  salt. P i c k e r i n g p u b l i s h e d the most d e t a i l e d 28 e a r l y study on t h i s s u b j e c t and he c o n f i r m e d t h a t s a l t s o b t a i n e d by the 27 29 above methods r e p o r t e d by D e v i l l e  and Reynolds  w i t h the t y p i c a l f o r m u l a N a ^ C u ( C O ^ ) ^ •  3 H  0 2  '  were ' d o u b l e  P i c k e r i n g noted t h a t  carbonates' the  l i q u i d r e t a i n e d n e g l i g i b l e amounts o f copper a f t e r p r e c i p i t a t i o n and assumed t h a t as the l i q u i d and s o l i d were q u i t e d i f f e r e n t different  s u b s t a n c e s were i n v o l v e d .  c o l o u r s , two  He a l s o o b s e r v e d t h a t the s o l u t i o n  was much d a r k e r than a copper s u l p h a t e  s o l u t i o n c o n t a i n i n g an e q u i v a l e n t  - 18 -  amount o f c o p p e r .  He p o s t u l a t e d t h a t i t c o n t a i n e d a ' c u p r i  s p e c i e s i n w h i c h copper formed p a r t o f the a n i o n .  carbonate'  Cuprammmonium com-  pounds w i t h copper d i s p l a c i n g the hydrogen atoms o f ammonium s a l t s g i v e a deep p u r p l e - b l u e s o l u t i o n were c i t e d as an analogous Reynolds  29  and Wood and Jones  30  had p r e v i o u s l y shown i n  s t u d i e s t h a t e l e c t r o l y s i s o f t h e s e b l u e carbonate copper a t b o t h the anode and the  3  2  , and m a l a c h i t e , C u C 0 ( 0 H ) .  3  2  several other s a l t s  carbonate.  3  2  3  2  and 8 C u O , 3 C 0 ,  6 H  2  0 2  '  t o be i n s o l u b l e i n water  He a l s o o b s e r v e d t h a t i n t r o d u c i n g copper  phate s o l u t i o n s i n t o a l k a l i n e carbonates 2  azurite,  s o l u t i o n s , but s l i g h t l y s o l u b l e i n c a r b o n i c a c i d  and sodium b i c a r b o n a t e .  3  liberated  s o l u t i o n s w i t h e i t h e r sodium carbonate o r sodium b i -  He found a l l t h e s e b a s i c c a r b o n a t e s  of NaHC0 :Na C0  solutions  Pickering reported i s o l a t i n g  2  and sodium carbonate  independent  are the m i n e r a l s  i n c l u d i n g 5Cu0,2C0 ; 5Cu0,3C0  by m i x i n g copper s u l p h a t e  case.  cathode.  The two most common copper c a r b o n a t e s Cu (OH) (C0 )  to  containing various  sul-  proportions  produced a v e r y b l u e s o l u t i o n w i t h a copper  content  2dependent on the C 0  : 3  H  C  0 3  ratio  (and thus o f p H ) , but which f o r any  m i x t u r e was d i r e c t l y p r o p o r t i o n a l t o the t o t a l carbonate  content.  It  was o b s e r v e d t h a t on a l l o w i n g t h e s e s o l u t i o n s t o stand f o r a c o u p l e o f days p r e c i p i t a t i o n o f e i t h e r m a l a c h i t e o r a ' d o u b l e s a l t , ' Cu(C0 ) 3  2  Na  2  o c c u r r e d , l e a v i n g an a l m o s t c o l o u r l e s s s o l u t i o n c o n t a i n i n g  very l i t t l e copper. occur a f t e r  No c l e a r e x p l a n a t i o n as t o why d e c o m p o s i t i o n s h o u l d  a c e r t a i n time was g i v e n , but P i c k e r i n g does suggest t h a t  the degree o f e l e c t r o p o s i t i v e and e l e c t r o n e g a t i v e  copper p r e s e n t i n  a g i v e n case d e t e r m i n e d whether m a l a c h i t e o r the double s a l t and t h a t i n f a c t the double carbonate  had two i s o m e r i d e s ; one  formed, (the  - 19 -  cupri-carbonate)  c o n t a i n i n g a n i o n i c copper and the o t h e r c a t i o n i c c o p p e r .  A proposed m o l e c u l a r s t r u c t u r e  f o r each substance i s g i v e n .  Other o b s e r v a t i o n s made by P i c k e r i n g i n c l u d e d : i)  A s l i g h t i n c r e a s e i n temperature  produced a s m a l l  increase  i n the amount o f copper d i s s o l v e d i n a g i v e n amount o f c a r b o n a t e ,  but  strong  h e a t i n g o f the s o l u t i o n gave b l a c k c o l o u r a t i o n and d e p o s i t i o n o f a b l a c k p r e c i p i t a t e , p r o b a b l y copper o x i d e . ii)  A d d i t i o n o f excess sodium h y d r o x i d e t o a carbonate  containing  copper s o l u t i o n removes carbon d i o x i d e c a u s i n g d e c o m p o s i t i o n o f the s o l u t i o n and f o r m a t i o n o f a b l u e b a s i c c a r b o n a t e  salt.  D i l u t i o n w t i h excess water  a l s o decomposed the s o l u t i o n , w i t h a b l a c k p r e c i p i t a t e a p p e a r i n g i n some cases. 31 Appleby and Lane  a l s o c a r r i e d out a s t u d y o f the double  carbonates  o f sodium and p o t a s s i u m w i t h v a r i o u s t r a n s i t i o n m e t a l s i n c l u d i n g c o p p e r . They p r e p a r e d samples o f the s a l t N a C u ( C 0 ) , 3 H 0 by a l l o w i n g i t to p r e c i p i 2  t a t e from copper carbonate  solutions:  added t o a sodium c a r b o n a t e / b i c a r b o n a t e  3  2  2  c o n c e n t r a t e d c u p r i c a c e t a t e was m i x t u r e (100 g N a C O : 4 0 g NaHCO^) 2  3  a t 50°C and a c l e a r deep b l u e s o l u t i o n f r e e o f any p r e c i p i t a t e was i m m e d i a t e l y formed.  On s t a n d i n g o v e r n i g h t , c r y s t a l s o f the double  salt  were o b t a i n e d from t h i s s o l u t i o n and i t was o b s e r v e d t h a t the mother l i q u o r c o u l d be r e u s e d a f t e r  s e p a r a t i o n o f the c r y s t a l s , i n which case  a s l i g h t l y b e t t e r y i e l d was o b t a i n e d . These a u t h o r s a l s o o b s e r v e d t h a t b o t h c r y s t a l s and s o l u t i o n s d e composed a t h i g h e r temperatures  g i v i n g c u p r i c o x i d e and sodium c a r b o n a t e ,  as a r e s u l t o f l o o s i n g w a t e r and carbon d i o x i d e . decomposed by a d d i t i o n o f e x c e s s w a t e r .  The s o l u t i o n was  Appleby and Lane c o n c l u d e d t h a t  - 20 -  c r y s t a l d e p o s i t i o n w a s . not due t o the s o l u t i o n b e i n g i n t h e normal sense because, and o n l y a f t e r  super-saturated  although p r e c i p i t a t i o n occurred slowly  s e v e r a l hours o f s t a n d i n g , a d d i t i o n o f p r e v i o u s l y formed  c r y s t a l s d i d not speed up the n u c l e a t i o n p r o c e d u r e .  I t was a l s o shown  t h a t c r y s t a l l i z a t i o n time was u n a f f e c t e d by a t m o s p h e r i c carbon d i o x i d e and was c o n s t a n t f o r s o l u t i o n s i n e i t h e r open o r s e a l e d f l a s k s as w e l l as those i n a d e s i c c a t o r connected t o a K i p p ' s apparatus f o r carbon dioxide.  The f o l l o w i n g reasons were t h u s p u t f o r w a r d t o e x p l a i n the  p r e c i p i t a t i o n behaviour: i)  A v e r y slow r a t e o f c r y s t a l l i z a t i o n i s o p e r a t i v e and no  stable super-saturated ii)  solutions exist.  The c r y s t a l s are p r e c i p i t a t e d v i a f o r m a t i o n o f an  compound which undergoes slow t r a n s f o r m a t i o n i n t o the f i n a l  intermediate  produce.  I n agreement w i t h the o b s e r v a t i o n s o f P i c k e r i n g t h i s s t u d y showed t h a t the e q u i l i b r i u m copper c o n t e n t i n s o l u t i o n i n c r e a s e d as a f u n c t i o n of t o t a l carbonate  concentration.  I t was a l s o noted t h a t c l e a r s o l u t i o n s  c o u l d o n l y be o b t a i n e d i n the presence o f b o t h sodium b i c a r b o n a t e and sodium c a r b o n a t e .  O m i s s i o n o f the b i c a r b o n a t e l e d t o a l m o s t  p r e c i p i t a t i o n o f a b a s i c carbonate  salt.  d i s s o l v e d by the c a r b o n a t e / b i c a r b o n a t e  instantaneous  The f a c t t h a t more copper was  m i x t u r e than would be o b t a i n e d by  d i s s o l v i n g CuCO^ i n w a t e r was a t t r i b u t e d t o the f o r m a t i o n o f the complex 26i o n CuCCO^)^ , o r even CuCCO^)^ i n the case o f a double s a l t .  The  p o s s i b i l i t y o f copper b e i n g p r e s e n t as a c o l l o i d a l substance as w e l l  as  (or i n s t e a d of) a complex i o n , was a l s o d i s c u s s e d . A number o f o t h e r s t u d i e s o f t h e s e c h a r a c t e r i s t i c a l l y b l u e copper carbonate  s o l u t i o n s and o f t h e b a s i c s a l t s d e r i v e d from them have been  - 21 -  made, i n c l u d i n g a p o l a r o g r a p h i c study by M e i t e s , the e f f e c t s Hsu,  33  32  an i n v e s t i g a t i o n i n t o  o f a l t e r i n g the N a ^ O ^ C u S O ^ on subsequent p r e c i p i t a t i o n by  and a d e t e r m i n a t i o n o f the s o l u b i l i t y o f m a l a c h i t e by S c a i f e .  34  I n t h i s l a s t s t u d y S c a i f e observed t h a t m a l a c h i t e s o l u b i l i t y i n sodium b i c a r b o n a t e s o l u t i o n s was f a r g r e a t e r l a t i o n s f o r the c u p r i c i o n .  than would be expected form c a l c u -  I t was t h e r e f o r e  suggested t h a t  ionic  a s s o c i a t i o n o r complex f o r m a t i o n o c c u r s between c u p r i c and b i c a r b o n a t e ions.  An a n a l o g y was drawn between t h i s case and t h a t o f c u p r i c /  a c e t a t e i o n complexes.  The t o t a l c o n c e n t r a t i o n o f copper i n s o l u t i o n  was suggested as b e i n g g i v e n by the e x p r e s s i o n  [Cu ] T  =  [CuC0 ] 3  +  [CuHC0 ] +  3  +  [Cu ]  (6)  2 +  which seemed t o g i v e good agreement w i t h e x p e r i m e n t a l l y determined v a l u e s f o r copper d i s s o l u t i o n . G a r r e l s and C h r i s t , ^ g i v e an Eh-pH diagram f o r the  system  Cu-0 -S-CO - H 0 a t 25°C w h i c h shows t h a t a t a t m o s p h e r i c p r e s s u r e Z  Z  Z  (P_„_ = C^2  -3.5 10  ) m a l a c h i t e has a l a r g e zone o f s t a b i l i t y i n a pH range from 7.0 -  13.0 and p o t e n t i a l s h i g h e r than 0 - 0.2 V .  An i n c r e a s e i n the d i s s o l v e d  carbon d i o x i d e c o n t e n t would e x t e n d t h i s r e g i o n o f s t a b i l i t y ( F i g u r e 2 ) . The s o l u b i l i t y c o n s t a n t ,  K , f o r the r e a c t i o n s  Cu (OH) C0 2  i s g i v e n as K = 10 s  2  3  =  2Cu  2 +  +  C0 ~ 2  3  +  20H~  (7)  -31.90  De Zoubov e t a l . .  36 i n v e s t i g a t e d the b e h a v i o u r o f copper i n sodium  bicarbonate solutions of varying strengths,  and found t h a t the c o r r o s i o n  o f copper m e t a l was s i g n i f i c a n t l y a f f e c t e d by the c a r b o n a t e  content.  - 22 -  Figure 2:  S t a b i l i t y r e l a t i o n s for copper compounds in the system Cu-H„0-0„-S-C0„.  - 23 -  Experiment showed t h a t s o l u t i o n s c o n t a i n i n g l e s s t h a n 0.0032 M b i c a r b o n a t e were m i l d l y c o r r o s i v e towards copper w i r e ; t h o s e w i t h 0.01 - 0.032 M were p r a c t i c a l l y n o n - c o r r o s i v e and a f u r t h e r i n c r e a s e o f b i c a r b o n a t e above 0.1 M produced s t r o n g l y c o r r o s i v e s o l u t i o n s .  Electrochemical equil-  i b r i u m (Eh-pH) diagrams were drawn t o e x p l a i n t h e s e o b s e r v a t i o n s .  I t was  found t h a t c o n d i t i o n s of. s t a b i l i t y o f the b a s i c copper c a r b o n a t e m a l a c h i t e c o r r e s p o n d e d t o the p a s s i v a t i o n e f f e c t o b s e r v e d i n the r e g i o n o f 0.01 = 0.032 M b i c a r b o n a t e , b u t t h a t d i s s o l u t i o n o f m a l a c h i t e t o g i v e s t a b l e , complex c u p r i - c a r b o n a t e i o n s c o u l d o c c u r i n s o l u t i o n s w i t h a v e r y low b i c a r b o n a t e c o n t e n t , o r i n those c o n t a i n i n g more t h a n 0.1 M. A s e r i e s o f f o u r diagrams a r e g i v e n i n w h i c h the t o t a l d i s s o l v e d CO^ c o n t e n t , d e f i n e d as [H C0 ] 2  +  3  [HC0 ~]  +  3  [C0 ~] 2  3  -3 i n c r e a s e s from 10  M to 1 M i n concentration (Figure 3 ) .  As t h i s v a l u e  o f d i s s o l v e d CO^ i n c r e a s e s , t h e r e g i o n o f m a l a c h i t e s t a b i l i t y grows t o h i g h e r pH v a l u e s c a u s i n g c u p r i t e and t e n o r i t e zones t o c o r r e s p o n d i n g l y diminish. at  Azurite,  2 C u C 0 C u ( O H ) , becomes s t a b l e i n a pH range o f ^3 - 7 3  2  [C0 ] v a l u e s g r e a t e r t h a n 10  1  2  M.  The d i s s o l v e d s p e c i e s which are  s t a b i l i z e d by the presence o f carbonate i n c l u d e the CuC0 2-  3  (aq.) m o l e c u l e ,  the c u p r i d i h y d r o x o c a r b o n a t e i o n , C u C 0 ( O H ) , and t h e c u p r i 3  2  carbonate  2ion, Cu(C0 ) 3  2  .  The CuC0  3  (aq.)  s p e c i e s e x i s t s a t the l o w e r end o f the  pH s c a l e , b e i n g s t a b l e from 6.5 - 10.0 a t low c a r b o n a t e  concentrations,  and b e i n g pushed downwards to 5.0 - 7.0 a t h i g h e r l e v e l s o f  [C0 ]. 2  The  c u p r i - c a r b o n a t e i o n appears i n a narrow band o f pH (9.0 - 10.5) a t -2 C 0 l e v e l s i n excess o f 10 M and expands t o a much w i d e r band (7.0 2  - 24 -  Figure 3 (a): Potential - pH diagram . f o r the system Cu-CC^-H^O with 10 M [CO = ] . _3  T  - 25 -  Figure 3 (b):  Potential - pH diagram with 10 ° M [C0 =] . 3  T  for the system Cu-CCL-H-O 2  2  - 26 >  11.5) a t the 1 M CO^ l e v e l .  These s o l u b l e c a r b o n a t e  s p e c i e s a l s o become  s t a b l e a t i n c r e a s i n g l y h i g h e r p o t e n t i a l v a l u e s f o r a g i v e n pH as d i s s o l v e d CO^ c o n t e n t goes u p . i s shown as the s t a b l e  the  A t E v a l u e s above t h i s , Cu^O^ (hydrated)  species.  Diagrams showing t h e o r e t i c a l c i r c u m s t a n c e s o f c o r r o s i o n , p a s s i v a t i o n and immunity f o r copper as a f u n c t i o n o f pH and c a r b o n a t e  content,  t o g e t h e r w i t h s o l u b i l i t y diagrams f o r a z u r i t e , t e n o r i t e and m a l a c h i t e , are a l s o g i v e n . 37 S c h i n d l e r and c o - w o r k e r s  a l s o s t u d i e d the s o l u b i l i t i e s o f a z u r i t e  and m a l a c h i t e , and w i t h the h e l p o f thermodynamic d a t a produced by S i l m a n f o r the Cu-H 0-CO^ system, s t a b i l i t y diagrams showing the 2  zones  o f predominance f o r the v a r i o u s components o f t h i s system are g i v e n . The o c c u r r e n c e o f the u n i q u e l y s t a b l e c a r b o n a t e  complexes CuCO^Caq.) and  2Cu(C0 ) 3  2  i s a g a i n r e c o g n i z e d as c a u s i n g d i s s o l u t i o n o f the  basic  copper carbonate m i n e r a l s : %Cu (0H) C0 2  JjCu (OH) C0 2  2  3  +  JsC0  =  +  2HC0 ~  2  3  CuC0 =  3  (aq.)  Cu(C0 ) 3  2 2  + "  IjH 0  +  %C0  (8)  2  +  |  ^0  (9)  f o r w h i c h the f o l l o w i n g e q u i l i b r i a a p p l y : Cu  2+  +  C0  23  c=^  CuC0  3  (aq.)  l o g k - - 6.73 Cu  2+  +  2C0  23  .  Cu(C0 ) 3  22  l o g k = 9.83  I t was noted t h a t i n a i r - s a t u r a t e d  s o l u t i o n s the m a j o r i t y o f the  copper  - 27 -  2+ 2i s p r e s e n t as Cu a t pH v a l u e s below 7 . 0 , and as C u ( C 0 ) i n more 3  alkaline  2  solutions. 38  Stumm and Morgan  g i v e b o t h an a c t i v i t y r a t i o diagram and a  s o l u b i l i t y diagram f o r the predominant  s o l i d phases and s o l u b l e  species  o f the Cu-J^O-CO^ system. They have been c o n s t r u c t e d f o r a t o t a l -2 II c a r b o n a t e c o n t e n t o f 10 M f o r the r e l e v a n t Cu e q u i l i b r i a , and show 2+ t h a t the i m p o r t a n t s o l u b l e s p e c i e s w i t h i n c r e a s i n g pH are Cu , CuCO^ ( a q . ) , 2II Cu(C0 ) and h y d r o x o - c o p p e r anions (Figure 4 ) . 3  2  I n a paper w h i c h c o n s i d e r s the c o r r o s i o n o f m e t a l l i c copper i n 39 t y p i c a l sea water s o l u t i o n s , B i a n c h i and L o n g h i  g i v e a s t a b i l i t y diagram  showing predominance a r e a s o f the s p e c i e s w h i c h can e x i s t as c u p r i c comp l e x e s i n s o l u t i o n s c o n t a i n i n g b o t h c h l o r i d e and c a r b o n a t e i o n s . These 0 224i n c l u d e CuCl , C u C l , C u C l , C u C l , Cu(C0 ) , Cu(C0 ) and 32Cu(HC0 ) . I t i s a g a i n a p p a r e n t t h a t the C u ( C 0 ) i o n i s predominant 3 5 5 2 2  3  4  3  2  3  3  o  a t pH 9 . 0 ,  i n d i c a t i n g t h a t the c a r b o n a t e complexes copper more  strongly  than c h l o r i d e i n a l k a l i n e s o l u t i o n s . The f a c t t h a t c o p p e r - c h l o r i d e complexes are weak i n a l k a l i n e s o l u t i o n s , even i n the p r e s e n c e o f l a r g e q u a n t i t i e s  of C l , i s  also  40 noted by Van Muylder e t a l .  and i t i s s t a t e d t h a t copper would be  p r e c i p i t a t e d from such s o l u t i o n s as CuO (or C u ( 0 H ) ) . 2  1.4.3  D e c o m p o s i t i o n o f sodium h y p o c h l o r i t e in alkaline solution Sodium h y p o c h l o r i t e , NaOCl,  i s a strong oxidant i n a l k a l i n e  s o l u t i o n s and has been shown t o be an e f f e c t i v e  l i x i v i a n t f o r the  t i o n o f molybdenum from m o l y b d e n i t e o r e s and c o n c e n t r a t e s ,  extrac-  as o u t l i n e d  - 28 -  Figure 4:  S o l u b i l i t y of Cu (II) i n the system 10 M. a) a c t i v i t y r a t i o diagram. b) s o l u b i l i t y diagram. _2  Cu-H 0-CO • [ C O - ] = 2 2 2 =  T  - 29 -  above.  There are two p o t e n t i a l problems a s s o c i a t e d w i t h the use o f  r e a g e n t from a commercial s t a n d p o i n t i)  this  however:  I t i s expensive to generate,  ii)  I t i s unstable  and undergoes spontaneous d e c o m p o s i t i o n  under c e r t a i n c o n d i t i o n s o f pH and i o n i c s t r e n g t h .  This decomposition  r e a c t i o n can be c a t a l y z e d , e s p e c i a l l y by t h e s a l t s o f c e r t a i n  transition  metals. Most e a r l y i n v e s t i g a t o r s  c o n c l u d e d t h a t the c o s t s i n c u r r e d i n  h y p o c h l o r i t e g e n e r a t i o n would be t o o g r e a t t o g i v e an e c o n o m i c a l l y f e a s i b l e process  f o r molybdenum e x t r a c t i o n .  I n v i e w o f the c u r r e n t  strong  demand and h i g h p r i c e o f molybdenum, t o g e t h e r w i t h the c a p a b i l i t i e s o f modern e l e c t r o l y t i c g e n e r a t o r s f o r m a n u f a c t u r i n g h y p o c h l o r i t e , t h i s  type  o f h y d r o m e t a l l u r g i c a l p r o c e s s would now seem t o compare f a v o u r a b l y w i t h existing  technology.  In a process using e x t e r n a l l y generated h y p o c h l o r i t e ,  however,  any d e c o m p o s i t i o n o f t h e r e a g e n t d u r i n g l e a c h i n g i s d e t r i m e n t a l  and  would n e c e s s i t a t e g e n e r a t i o n o f more t h a n t h e s t o i c h i o m e t r i c hypoc h l o r i t e r e q u i r e d f o r the o x i d a t i o n o f m o l y b d e n i t e t o m o l y b d a t e . therefore  important to appreciate  It  is  the c o n d i t i o n s under w h i c h decomposi-  t i o n t a k e s p l a c e , and the e x t e n t t o w h i c h i t  occurs.  S e v e r a l i n v e s t i g a t i o n s have r e p o r t e d the r e s u l t s o f  studies  c a r r i e d o u t t o determine the e x a c t n a t u r e o f h y p o c h l o r i t e d e c o m p o s i t i o n under v a r y i n g c o n d i t i o n s o f p H , t e m p e r a t u r e , i o n i c s t r e n g t h  etc.  It  i s g e n e r a l l y agreed t h a t the p r o d u c t s o f d e c o m p o s i t i o n are oxygen, c h l o r i d e and c h l o r a t e i n v a r y i n g p r o p o r t i o n s . can be r e p r e s e n t e d as  follows:  The u n c a t a l y z e d  reaction  - 30 -  HC10  +  20C1~  >  2HC10  +  OCl"  HCIO  +  O C l ~ — - y 2C1~  c  l  ~  0 3  >• C 1 0 ~ 3  +  2 C 1  +  +  ~  2C1~  0  +  2  +  H  + . 2H  H  ( )  +  1 0  (11)  +  (12)  2  E q u a t i o n s 10 and 11 b o t h r e p r e s e n t d e c o m p o s i t i o n to c h l o r a t e . former i s g e n e r a l l y a p p l i c a b l e i n a l k a l i n e s o l u t i o n s w h i l e the  The  latter  41 more o f t e n o c c u r s i n a c i d i c m e d i a .  D'ans and Fruend  suggested  that  i n v e r y p u r e h y p o c h l o r i t e s o l u t i o n s c h l o r a t e can be the s o l e d e c o m p o s i t i o n product,  b u t t h i s i s more g e n e r a l l y accompanied by s i m u l t a n e o u s 42  decomposi-  t i o n t o oxygen, as shown by L i s t e r . I t i s t h i s oxygen forming r e a c t i o n w h i c h i s u s u a l l y thought o f as b e i n g c a t a l y s e d by c e r t a i n t r a n s i t i o n m e t a l h y d r o x i d e s and o x i d e s . W h i l e d e t a i l e d c o n s i d e r a t i o n o f the many mechanisms w h i c h have been p u t forward t o e x p l a i n t h i s b e h a v i o u r has hot been u n d e r t a k e n ,  a review of  some o f the r e l e v a n t work i s i n c l u d e d as i t i n t r o d u c e s concepts w h i c h are a p p l i c a b l e t o the p r e s e n t  study:  43 Bell  measured the v e l o c i t y o f oxygen e v o l u t i o n from s o l u t i o n s  o f c a l c i u m h y p o c h l o r i t e , C a ( 0 C l ) , i n the p r e s e n c e o f a number o f 2  i n b o t h a c i d and a l k a l i n e s o l u t i o n . solutions containing Co(N0 ) 3  2  This v e l o c i t y increased r a p i d l y i n  and NiSO^ and was s l i g h t l y i n c r e a s e d by  t h e p r e s e n c e o f B a C l , CaSO , AgNO , HgCl , F e C l , K Cr O *i  4tC  L i C l , N a C 0 , KCN, N a S and KN0 2  3  2  salts  O 2  -C-  were r e p o r t e d  £  and FeSO . I  4  to r e t a r d oxygen e v o l u t i o n .  44 Hofman and R i t t e r  i n a s t u d y o f the s t a b i l i t y and redox  poten-  t i a l s o f h y p o c h l o r i t e s , c o n c l u d e d t h a t d e c o m p o s i t i o n was c a t a l y z e d t o a p p r o x i m a t e l y t h e same degree by CoO, NiO and I r O , w h i l e the o x i d e s o f manganese, u r a n i u m , b i s m u t h , p a l l a d i u m , t e l l u r i u m and vanadium had no  - 31 -  effect. A d e t a i l e d s t u d y o f the r a t e o f d e c o m p o s i t i o n o f sodium h y p o c h l o r i t e s o l u t i o n s i n the p r e s e n c e o f c o b a l t and n i c k e l p e r o x i d e s , CoO^ and N i O ^ , and o x i d e s o f c o p p e r ,  i r o n and c o b a l t , was made by C h i r n o a g a i n  45 1923.  He r e p o r t e d t h a t oxygen e v o l u t i o n d u r i n g d e c o m p o s i t i o n was l e s s  than f i r s t o r d e r and c o u l d be r e p r e s e n t e d = dt  v  1  /  by the g e n e r a l  equation  n  (  1  3  1  where c = c o n c e n t r a t i o n o f h y p o c h l o r i t e a t time t , C h i r n o a g a p o s t u l a t e d t h a t OCl  and k ^ , n are  constants.  i o n s were adsorbed onto the  of c a t a l y s t p a r t i c l e s .  D e c o m p o s i t i o n o f t h e s e i o n s would then  the r e a c t i o n v e l o c i t y .  The a d s o r p t i o n s t e p would be f a s t e r  sequent d e c o m p o s i t i o n , and thus the s u r f a c e  surface  determine  t h a n the  sub-  l a y e r would be k e p t i n a d -  s o r p t i o n e q u i l i b r i u m w i t h the b u l k o f the s o l u t i o n . Experiment showed t h a t oxygen e v o l u t i o n i n c r e a s e d w i t h time and with concentration  (and hence s u r f a c e area) o f the c a t a l y s t .  The o x i d e s  under study were found t o d e c r e a s e i n o r d e r o f c a t a l y t i c a c t i v i t y : Co > Cu > F e , and e q u a t i o n 13 was found t o be more a p p l i c a b l e f o r c a t a l y s t s with higher a c t i v i t i e s .  Ni > the  C h i r n o a g a n o t e d t h a t a mixed CoO/NiO  c a t a l y s t was more a c t i v e t h a n e i t h e r o x i d e a l o n e . T h i s i n c r e a s e d c a t a l y t i c a c t i v i t y o f mixed o x i d e s was a l s o ' r e p o r t e d 46 by L e w i s .  He suggested l e s s a c t i v e c a t a l y s t s c o u l d have a p r o m o t i n g  i n f l u e n c e when combined w i t h a more a c t i v e one.  Fe^O^ i n the presence o f  CuO f o r example, gave a more e f f e c t i v e c a t a l y t i c a c t i o n than t h a t produced by e i t h e r c a t a l y s t  )  alone.  Lewis suggested a more s i m p l e e q u a t i o n t o d e s c r i b e the r a t e o f  - 32 -  decomposition:  dc dt representing  k  (14)  a l i n e a r r e l a t i o n s h i p between e v o l v e d oxygen and t i m e .  found the r a t e t o be c o n s t a n t f o r a wide range o f i n i t i a l concentrations, tration.  He  hypochlorite  and t h a t i t was d i r e c t l y p r o p o r t i o n a l t o c a t a l y s t  concen-  The mechanism was c o n s i d e r e d t o be one t h a t i n v o l v e d the  forma-  t i o n and subsequent d e c o m p o s i t i o n o f a h y p o c h l o r i t e - c a t a l y s t complex i n a continuous c y c l e .  Such a p r o c e s s would o c c u r a t a c o n s t a n t r a t e p r o -  v i d e d the a c t i v e c e n t r e s on the c a t a l y t i c s u r f a c e were e n t i r e l y c o v e r e d by r e a c t a n t .  Any l o s s o f t h e s e due t o c o a g u l a t i o n , d e h y d r a t i o n  would l e a d t o d e c r e a s e d t h a t the  'promoter'  catalytic action.  effect  Lewis t h e r e f o r e  suggested  o c c u r r e d as a r e s u l t o f the second substance  p r e s e r v i n g t h e a c t i v e c e n t r e s on the c a t a l y s t i t s e l f , more e f f i c i e n t  etc.  (and prolonged)  thus producing a  reaction.  The f i r s t r e p o r t e d s t u d y t h a t h y p o c h l o r i t e c o u l d be c a t a l y t i c a l l y decomposed t o c h l o r a t e as w e l l as t o oxygen was g i v e n i n a R u s s i a n paper 47 o f Glikman and D a i n i n 1941. accelerated  the  They showed t h a t c o b a l t h y d r o x i d e  reaction (15)  but gave no d e t a i l s o f the pH r e g i o n i n w h i c h t h i s e f f e c t was o b s e r v e d . 48 A y r e s and Booth as d e c o m p o s i t i o n p r o d u c t s  showed t h a t b o t h oxygen and c h l o r a t e are i n a"catalysed  reaction.  formed  Oxidative decomposition  was more predominant i n l e s s s t r o n g l y a l k a l i n e s o l u t i o n s and o v e r a l l d e c o m p o s i t i o n reached a maximum around pH = 9 . 0 .  I t was a l s o  observed  - 33 -  t h a t where the i n i t i a l pH had a v a l u e below 10, d e c o m p o s i t i o n was accomp a n i e d by a c i d i f i c a t i o n o f t h e s o l u t i o n s , g i v i n g a f i n a l v a l u e o f 3 - 4 . C h l o r i n e e v o l u t i o n was a l s o o b s e r v e d i n such c a s e s . i n g t h i s o b s e r v a t i o n were c i t e d  2HC10  v0  3HC10  y  HC10  +  c  l  Equations represent-  as:  +  2  0 3  2C1~  ~  Cl~ +  +  H  2  C  +  +  1  y  ~  2H  +  CI  (16)  +  3  +  H  +  H 0  (18)  2  The c a t a l y s t used i n t h i s s t u d y was i x i ' d i u m o x i d e and A y r e s and Booth proposed an o v e r a l l mechanism i n v o l v i n g the f o r m a t i o n o f an  intermediate  a c t i v e complex a l l o w i n g t h e p r o d u c t i o n o f m o l e c u l a r oxygen w h i c h can then recombine w i t h more h y p o c h l o r i t e t o g i v e C10~  +  chlorate:  c~ ==  x~  +  Cl~  (19)  x~ =  c~  +  0  (20)  where c = c a t a l y s t and x = a c t i v e complex C10~  +  O  y  C10 ~ 2  (21)  CIO"  +  O  y  C10  3  (22)  L i s t e r , on the o t h e r hand, c o n c l u d e d a f t e r s t u d y o f b o t h u n c a t a l y s e d and c a t a l y s e d r e a c t i o n s  c a r r y i n g o u t an  extensive  o f sodium h y p o c h l o r i t e  d e c o m p o s i t i o n , t h a t c h l o r a t i v e d e c o m p o s i t i o n was not c a t a l y s e d .  42 49 '  I n the former study he c o n f i r m e d the f i n d i n g s o f F o e r s t e r e t a l . ^ ° t h a t the u n c a t a l y s e d r e a c t i o n produces m a i n l y c h l o r a t e , and o c c u r s i n a two stage p r o c e s s :  i s second  order  - 34 -  2NaOCl NaOCl The f i r s t ,  +  y NaC10 NaC10  2  +  2  NaCl  >• NaC10  3  (23) +  NaCl  (24)  c h l o r i t e f o r m i n g s t e p i s the s l o w e r o f the two.  Lister  found t h a t a s m a l l p a r t o f the d e c o m p o s i t i o n r e a c t i o n produced oxygen:  NaOCl  • NaCl  +  ^0  and t h a t t h i s was a f i r s t o r d e r r e a c t i o n .  (25)  2  He noted t h a t i t c o u l d n o t be  c o n c l u d e d w i t h c e r t a i n t y t h a t a b s o l u t e l y no c a t a l y s t s his  were p r e s e n t d u r i n g  experiments. 49 I n h i s s t u d y o f the c a t a l y s e d d e c o m p o s i t i o n r e a c t i o n  used manganese, i r o n , c o b a l t , n i c k e l and copper o x i d e s and  Lister determined  t h a t none o f t h e s e i n c r e a s e d the r a t e o f f o r m a t i o n o f c h l o r a t e h y p o c h l o r i t e , but t h a t the oxygen r e a c t i o n was c a t a l y s e d t o a e x t e n t by each m e t a l o x i d e .  from different  F o r c o b a l t and n i c k e l t h i s was found t o be  a z e r o o r d e r r e a c t i o n and f o r copper i t was almost f i r s t o r d e r .  The  p r e v i o u s l y made p r o p o s a l t h a t t h i s heterogeneous c a t a l y s i s i n v o l v e s o x i d a t i o n o f the m e t a l t o a h i g h e r o x i d e w i t h subsequent l o s s o f oxygen, f o l l o w e d by r e o x i d a t i o n , was c o n s i d e r e d by L i s t e r t o be q u i t e  feasible.  The f a c t t h a t i r o n and manganese showed o n l y v e r y weak c a t a l y t i c a c t i v i t y c o u l d then be e x p l a i n e d by the s t a b i l i t y o f the h i g h e r o x i d a t i o n s t a t e s of these metals, o f w h i c h e x i s t as  i n contrast  t o the cases o f c o b a l t , n i c k e l and copper a l l  'higher oxides' i n r e l a t i v e l y unstable  conditions.  This  mechanism would n o t r e s u l t i n i n c r e a s e d c h l o r a t e p r o d u c t i o n and t h i s was a l s o i n agreement w i t h e x p e r i m e n t a l o b s e r v a t i o n s .  However, more oxygen  was e v o l v e d than c o u l d be accounted f o r by t h i s type o f o x i d a t i o n - r e d u c t i o n  - 35 -  c y c l e so an a l t e r n a t i v e mechanism was s u g g e s t e d .  This s t i l l involved  t h e f o r m a t i o n o f h i g h e r v a l e n c e o x i d e s , but i t was proposed t h a t o x i d e formed an adsorbed m e t a l - h y p o c h l o r i t e complex on the surface,  and s u b s e q u e n t l y  2M0  M 0 2  +  1  +  3  • 2M0  +  3  Cl~ +  Cl~  (26)  (ads.)  (27)  0  (28)  2  d i s m i s s e d t h i s mechanism o f L i s t e r as b e i n g e x p e r i -  m e n t a l l y unfounded.  He c o n c l u d e d from h i s own work t h a t h i g h e r o x i d e s  were formed as i n t e r m e d i a t e catalysts  2  2  3  Prokopchik^  • M 0  C10~ — M 0 C 1 0 ~  M 0 C10~ 2  catalytic  decomposed:  C10~  +  3  this  compounds and t h a t t h e s e were a c t u a l l y  for hypochlorite decomposition.  the  I t was found t h a t b o t h o x i d a -  t i v e and c h l o r a t i v e d e c o m p o s i t i o n were c a t a l y s e d , w i t h the l a t t e r  occurring  as a r e s u l t o f p a r t i a l h y p o c h l o r i t e o x i d a t i o n t o c h l o r a t e d u r i n g the d e c o m p o s i t i o n o f the h i g h e r v a l e n c e o x i d e . homogeneous  Thus i n h i s study o f b o t h  and heterogeneous h y p o c h l o r i t e d e c o m p o s i t i o n i n the p r e s e n c e  o f c o p p e r , P r o k o p c h i k determined t h a t an i m p o r t a n t r o l e was p l a y e d by copper"'""'" compounds.  When i n s o l u t i o n t h e s e e x i s t e d as a n i o n i c  1  f o r example, N a C u ( O H ) , w h i l e s o l i d compounds such as Cu C> 4  2  3  cuprates,  produced  heterogeneous c a t a l y s i s . The t r i - v a l e n t c u p r a t e was found t o be u n s t a b l e  i n s o l u t i o n and  i t s f o r m a t i o n i n t h e p r e s e n c e o f h y p o c h l o r i t e was f o l l o w e d by r a p i d decomp o s i t i o n to b i - v a l e n t  4Cu(OH)  4  +  cuprite: 40H  > 4Cu(OH)  24  +  °2  +  H  2°  ^  2 9 )  - 36 -  w i t h a r e a c t i o n r a t e g i v e n by  -d  (Cu(OH) ~)  =  4  k  2  k  2  (Cu(OH) ~)•(OH )  (30)  _  4  dt (Cu(OH) "), 4  s i n c e h y d r o x y l i o n c o n c e n t r a t i o n i s always g r e a t e r than t h a t o f c u p r a t e anions. The d e c o m p o s i t i o n o f h y p o c h l o r i t e o c c u r r e d  simultaneously:  2Cu(OH) ~  +  2  4  2Cu(OH)  4  +  +  Clef  +  H 0 2  20H  > 2Cu(OH) ~ 4  > 2Cu(OH)  C10~ v = =  a  Cl~ +  24  Cl~ +  +  +  OH~  (31)  JjO  (32)  ( 33)  J5O  The r a t e o f r e a c t i o n was found t o be f i r s t o r d e r f o r h y p o c h l o r i t e c o n c e n t r a t i o n s up t o 0.1 M, above w h i c h i t d e v i a t e d towards z e r o  order.  I n the case o f heterogeneous d e c o m p o s i t i o n i t was o b s e r v e d  that  the a c t i o n o f sodium and c a l c i u m h y p o c h l o r i t e s on b l u e c u p r i c h y d r o x i d e caused r a p i d t r a n s f o r m a t i o n  to a b r o w n i s h - b l a c k compound accompanied by  c a t a l y s e d d e c o m p o s i t i o n o f the h y p o c h l o r i t e s o l u t i o n . c a t a l y s t was c o n s i d e r e d ,  The n a t u r e o f  the  and P r o k o p c h i k c o n c l u d e d t h a t w h i l e a copper  p e r o x i d e compound c o u l d be produced by t h i s method, the observed decompos i t i o n d a t a suggested  f o r m a t i o n o f c u p r a t e s a t h i g h pH v a l u e s , and  t r i - v a l e n t h y d r o x i d e a t lower l e v e l s o f a l k a l i n i t y , as b e i n g more  the likely.  F o r m a t i o n o f a r e d compound was n o t e d a t the end o f some e x p e r i m e n t s ,  and  t h i s was t a k e n t o be a d e a c t i v a t e d c u p r a t e w h i c h no l o n g e r had c a t a l y t i c properties.  - 37 -  A c e r t a i n amount o f c o n f u s i o n appears t o e x i s t c o n c e r n i n g compound r e s p o n s i b l e 11.0.  the  f o r h y p o c h l o r i t e d e c o m p o s i t i o n a t pH l e v e l s below  Prokopchik states f i r s t l y ,  as noted above, t h a t c u p r a t e s cannot  e x i s t a t low a l k a l i n i t y and t h a t o x i d a t i o n o f b i - v a l e n t t o hydroxide thus occurs.  He l a t e r  s t a t e s , however,  tri-valent  that i t i s  impossible  t o o b t a i n a t r i - v a l e n t h y d r o x i d e , and t h a t i n f a c t no o x i d a t i o n o f b i v a l e n t copper w i l l o c c u r below pH 1 1 . 5 , so t h a t dehydrated ide i s responsible  f o r c a t a l y t i c a c t i o n a t lower pHs.  cupric hydrox-  Since i t  is  emphasized t h a t no h y p o c h l o r i t e d e c o m p o s i t i o n can o c c u r i n the absence o f copper "'""'", 1  t h e s e s t a t e m e n t s appear t o be  self-contradictory.  I n the proposed mechanism f o r heterogeneous d e c o m p o s i t i o n , b o t h the h y d r o x i d e and c u p r a t e are i)  however,  considered:  a t lower a l k a l i n i t i e s :  Cu(0H)„ CIO  +  2Cu(0H)  + OH  2  +  -> Cu(OH)  H 0 2  •>• CI  + +  e  (34)  2Cu(0H)  (35)  4Cu(0H)  (36) (37)  ii)  higher a l k a l i n i t y  (pH > 1 2 . 0 ) : +Cu(0H)  +  4 *C1  (38)  e +  2Cu(0H)  (39) (40) (41)  - 38 -  34-41  -  C o n s i d e r a t i o n o f the redox p o t e n t i a l f o r r e a c t i o n s  ^.confirmed:  t h a t o x i d a t i o n t o the t r i - v a l e n t s t a t e by h y p o c h l o r i t e s o l u t i o n s was thermodynamically p o s s i b l e . A further  a m b i g u i t y e x i s t s r e g a r d i n g the c h l o r a t e f o r m i n g r e a c t i o n :  the above e q u a t i o n s  suggest t h i s o c c u r s o n l y a t h i g h e r pH v a l u e s ,  and  P r o k o p c h i k i n f a c t s t a t e s t h a t c h l o r a t i v e d e c o m p o s i t i o n becomes more p r o nounced as a l k a l i n i t y i n c r e a s e s ,  and may even p r e d o m i n a t e .  Considerable  d i s c u s s i o n p r e v i o u s l y however had l e d t o the c o n c l u s i o n t h a t i n s t r o n g a l k a l i n e s o l u t i o n s h y p o c h l o r i t e decomposes t o oxygen, w h i l e a t pH 11.0 and below copper h y d r o x i d e s i g n i f i c a n t l y a c c e l e r a t e d to chlorate.  decomposition  A t pH 9.0 the mole r a t i o o f C l O ^ O , , a t t a i n e d  Graphical representation this  the  a v a l u e o f 3.  based on e x p e r i m e n t a l d a t a i s g i v e n t o  illustrate  point. By c o n s i d e r a t i o n o f the c a t a l y t i c a c t i o n o f c o b a l t ,  n i c k e l under s i m i l a r c o n d i t i o n s , P r o k o p c h i k c o n c l u d e d t h a t a c t i v i t y decreased  i n the o r d e r Co > N i > Cu > F e .  iron,  and  catalytic  The g e n e r a l i z e d  mechanism f o r any m e t a l Me was g i v e n a s : CIO  4  Me (OH)  -> CI  +  Me (OH)  n Me (OH) Me (OH)  . n+1  . n+1 +  y  Me (OH)  +  (42)  ho^  n CIO  . n+1  (43)  2  »• C 1 0 3 o  +  Me (OH)  n  (44)  - 39 -  1.4.4  Copper  compounds  Copper e x i s t s i n the t r i - v a l e n t s t a t e as a r e s u l t o f 4s and 3d e l e c t r o n s b e i n g removed from the copper atom t o g i v e a I s ,  2s  3s  nickel " "  2  2  3p^ 3d^ c o n f i g u r a t i o n .  structure,  T h i s i s i s o - e l e c t r o n i c w i t h the  2  2p , 6  1  1  and t r i - v a l e n t copper compounds are g e n e r a l l y d i a m a g n e t i c  a r e s u l t of a l l electrons being p a i r e d . r a r e o x i d a t i o n s t a t e f o r copper,  as  Although t h i s i s a r e l a t i v e l y  i t s e x i s t e n c e has been acknowledged  s i n c e the m i d d l e o f the l a s t c e n t u r y ,  and s e v e r a l workers have  studied  t h e . f o r m a t i o n and s t a b i l i t y o f copper "'"''" compounds: 1  Crum, i n 1845, o b t a i n e d what he d e s c r i b e d as a c u p r a t e by the a c t i o n o f an a c i d i c s o l u t i o n o f " b l e a c h i n g powder" on copper  nitrate.  T h i s o c c u r r e d as a r e d powder and was a s s i g n e d the f o r m u l a H^Cu^O^ c o r r e s 55 p o n d i n g t o the h y d r a t e d form o f the s e s q u i o x i d e , C ^ O ^ . . Moser used hydrogen p e r o x i d e t o o x i d i z e copper h y d r o x i d e and o b t a i n e d a compound a p p r o a c h i n g the f o r m u l a C u C ^ - f ^ O . Tests w i t h c h l o r i n e 56 and bromine produced no o x i d a t i o n . 57 S c a g l i a r n i and T o r e l l i produced an amaranth r e d compound by the a c t i o n of potassium persulphate, K S 0 , on copper h y d r o x i d e s o l u t i o n s . Z Z 8 The compound e v o l v e d oxygen when t r e a t e d w i t h d i l u t e H^SO^, d e c o l o u r i s e d KMnO^, and d i d n o t c o n t a i n a p e r o x i d e g r o u p .  I t was thus t a k e n t o be t r i -  v a l e n t copper o x i d e , Cu^O^. The e a r l i e s t r e p o r t o f o x i d a t i o n o f copper "'" by h y p o c h l o r i t e s o l u 1  t i o n s i s one by M u l l e r and S p i t z e r  6 0  i n w h i c h i t was shown t h a t  copper c o u l d be produced i n s t r o n g l y b a s i c s o l u t i o n s h y d r o x i d e by o x i d a t i o n w i t h h y p o c h l o r i t e . bromine produced s i m i l a r e f f e c t s .  tri-valent  (>3N) o f copper  Hypobromite, c h l o r i n e and  The c o l o u r o f the r e s u l t a n t  solution  - 40 -  a p p a r e n t l y v a r i e d from r e d and v i o l e t t o brown and b l a c k , dependent on the degree o f a l k a l i n i t y . The same a u t h o r s c a r r i e d o u t e l e c t r o c h e m i c a l t e s t s t o t r i - v a l e n t copper o x i d e , and suggested i)  produce  i t s f o r m a t i o n t o be caused by  o x i d a t i o n o f m e t a l i o n s c o n t a i n e d w i t h i n the copper anode,  ii)  o x i d a t i o n o f m e t a l i o n s c o n t a i n e d i n the e l e c t r o l y t e  or  solution,  ^ w i t h subsequent o x i d e p r e c i p i t a t i o n . 59 A l d r i d g e and Appleby i n 1922 investigate  d i d a number o f experiments  the p e r o x i d i c compounds o f c o p p e r .  to  Hydrogen p e r o x i d e was  added t o copper c o n t a i n i n g c a r b o n a t e s o l u t i o n s and a y e l l o w - b r o w n compound was r a p i d l y p r e c i p i t a t e d .  A n a l y s i s showed t h i s p r e c i p i t a t e  to  c o n t a i n more oxygen than would c o r r e s p o n d t o C ^ O ^ , b u t i n s u f f i c i e n t g i v e CuO^.  to  I t was assumed, however, t h a t a p e r o x i d e had been p r o d u c e d ,  but t h a t i t s s e p a r a t i o n i n a pure s t a t e was not p o s s i b l e . Lepore r e p o r t e d o b t a i n i n g the compound Cu^0„ (or C u ' C u . O . ) by t r e a t fa 4 5 4 i n g F e h l i n g ' s s o l u t i o n w i t h hydrogen p e r o x i d e . the a d d i t i o n o f copper n i t r a t e  6 0  He a l s o c l a i m e d t h a t  s o l u t i o n s t o b a r i u m h y d r o x i d e gave  the  compound Cu.O -3H O o r Cu (OH) . 2 3 2 2 6 More r e c e n t s t u d i e s  r e g a r d i n g the e x i s t e n c e o f a l k a l i n e and  a l k a l i n e e a r t h m e t a l c u p r a t e s have been made by S c h o l d e r and V o e l s k o w , Prokopchik,  6 2  Ba(CuO^) * 2° H  and Magee and W o o d . w  a  s  2  6 3  C r y s t a l l i n e barium  o b t a i n e d by the a d d i t i o n o f p o t a s s i u m  cuprate, hypobromite  s o l u t i o n s to c u p r i c h y d r o x i d e i n the p r e s e n c e o f b a r i u m s a l t s such as BaCl2 o r BaCO^ i n a l k a l i n e s o l u t i o n , i n experiments S c h o l d e r i n 1951.  The sodium s a l t ,  c a r r i e d o u t by  NaCu02, was produced i n a s i m i l a r  manner by t h e a c t i o n o f h y p o b r o m i t e , NaOBr, and sodium bromate,  NaBrO^.  6 1  - 41 -  C a l c i u m and s t r o n t i u m c u p r a t e s c o u l d not be o b t a i n e d by t h i s method. C a l c i u m c u p r a t e was produced by P r o k o p c h i k who used c a l c i u m h y p o c h l o r i t e t o o x i d i z e c u p r i c c h l o r i d e , C u C l ^ , a t a pH v a l u e o f 1 2 . 2 .  A  r e d - p u r p l e p r e c i p i t a t e was o b s e r v e d , h a v i n g a C u : 0 r a t i o o f 1 : 0 . 5 . S i m i l a r o x i d a t i o n was e f f e c t e d by the use o f an e q u i v a l e n t amount o f sodium h y p o c h l o r i t e (0.2 M ) . Magee and Wood c a r r i e d o u t an i n v e s t i g a t i o n o f sodium cuprate " "" " 1  s t a b i l i t y i n a l k a l i n e solutions of varying strength. t h a t the s a l t was v e r y u n s t a b l e CuO^  i o n had a h a l f  t o e x i s t i n s o l u t i o n o n l y when complexed.  Copper  1  They c o n c l u d e d  i n a l l cases and e s t i m a t e d t h a t  l i f e o f o n l y 25 s e c o n d s .  1  1 1 1  the  was t h u s assumed  The f a c t t h a t S c h o l d e r and  Voelskow found t r i - v a l e n t copper s o l u t i o n s t o be s t a b l e i n the  presence  o f e x c e s s base and hypobromite was suggested t o be caused by a hypobromite-copper"'""'""'" complex. copper " " 1  1  1  A number o f workers have, i n f a c t ,  shown t h a t  can be complexed and hence s t a b i l i z e d e i t h e r i n s o l u t i o n o r  as a s o l i d compound, by t h e p r e s e n c e o f c e r t a i n c o m p l e x i n g i o n s . d a t e s and t e l l u r a t e s  Perio-  are t h e commonest such g r o u p s :  M a l a t e s t a , i n 1941  64  o b t a i n e d a s t a b l e p e r i o d a t e copper  III  complex  w i t h both chemical o x i d a t i o n of c u p r i c hydroxide using persulphate, e l e c t r o l y t i c o x i d a t i o n of copper, resultant  and  f o l l o w e d by a d d i t i o n o f p e r i o d i t e .  The  compound was d i a m a g n e t i c and was a n a l y s e d c h e m i c a l l y t o be t r i 65  valent.  Malaprade  a l s o s t a b i l i z e d the t r i - v a l e n t s t a t e by the  of potassium periodate,  K I O ^ . He produced f i r s t l y a c u p r a t e ,  o x i d i z i n g copper h y d r o x i d e w i t h a KOH/K S 0  presence  KCuCOH)^ by  m i x t u r e , and then added  2 2 o periodate  t o g i v e a s t a b l e complex compound. 66  Lister  made e s s e n t i a l l y the same compound, Na_Cu (10,.) . • 16H„0, 7 6 2 2  as  - 42 -  w e l l as the c o r r e s p o n d i n g t e l l u r a t e , c h l o r i t e as o x i d a n t .  Na^CuCTeOg), u s i n g sodium hypo-  A c u p r i c c h l o r i d e / s o d i u m h y d r o x i d e m i x t u r e was  added t o a 1.5 M NaOCl s o l u t i o n and the b l u e p r e c i p i t a t e w h i c h formed initially,  t u r n e d r a p i d l y b l a c k , g i v i n g what L i s t e r presumed t o be  e i t h e r a t r i - v a l e n t o x i d e , Cu^O^, o r h y d r o x i d e , CuCOH)^. an a c i d i f i e d sodium p e r i o d a t e after  Addition of  s o l u t i o n , NaH 10^, gave a brown compound 3 6  standing for a short time.  Both t h i s p r e c i p i t a t e  and the complex  t e l l u r a t e were found t o c o n t a i n t r i - v a l e n t copper by i o d i d e and by use o f t h e i r o x i d a t i o n e q u i v a l e n t w e i g h t s .  I t was observed  oxygen was e v o l v e d on a c i d i f i c a t i o n o f each p r e c i p i t a t e a scarlet  c o l o u r was b r i e f l y v i s i b l e .  be t h e c o l o u r o'f t h e C u  3 +  titration that  and i n some cases  T h i s was t h e r e f o r e  suggested  to  ion.  To determine the amount o f copper p r e s e n t i n these compounds i n an uncomplexed s t a t e , L i s t e r measured oxygen e v o l u t i o n as a r e s u l t o f NaOCl d e c o m p o s i t i o n b o t h b e f o r e and a f t e r agent.  a d d i t i o n o f the c o m p l e x i n g  I n the former case he found the r e a c t i o n t o be c a t a l y z e d by  c o p p e r , presumably as the C u ( 0 H ) order w i t h respect to copper. tellurate  4  ion.  The r a t e o f r e a c t i o n was  After addition of either periodate  a n i o n s the r a t e o f oxygen e v o l u t i o n was found t o drop  a b l y , and t o c o r r e s p o n d to a r a t e r e p r e s e n t i n g decomposition.  I t was t h e r e f o r e  or consider-  uncatalyzed hypochlorite  assumed t h a t when v i r t u a l l y a l l the  copper e x i s t e d i n a complex s t a t e i t was no l o n g e r an a c t i v e f o r the  first  catalyst  reaction. J e n s o v s k y p r e p a r e d complex c u p r a t e s by a n o d i c o x i d a t i o n o f copper  i n a l k a l i n e solutions containing periodate  and t e l l u r a t e  ions.  The  maximum y i e l d was o b t a i n e d a t pH 1 0 . 2 , and i n c r e a s e d w i t h t e m p e r a t u r e .  - 43 -  The compounds were found to be d i a m a g n e t i c , and t h e r m a l d e c o m p o s i t i o n c u r v e s showed l o s s o f water caused d e c o m p o s i t i o n o f the copper " "" " complex. 1  1  1  On account o f t h e i r r e l a t i v e s t a b i l i t y and s t r o n g o x i d a t i v e powers, complexes o f t r i - v a l e n t copper w i t h p e r i o d a t e s and t e l l u r a t e s can be used f o r t h e o x i d i m e t r i c d e t e r m i n a t i o n o f a number o f i n o r g a n i c and o r g a n i c compounds. ^  T i t r a t i o n s u s i n g s t a n d a r d s o l u t i o n s o f copper " "" "  6  1  are c a r r i e d o u t i n a l k a l i n e media and a p p l i c a t i o n s i n c l u d e the t i o n o f antimony, c a l c i u m , t h a l l i u m , c y a n i d e and t h i o s u l p h a t e  1  1  determinasalts.  Most o t h e r copper " "'" " complexes w h i c h have been i s o l a t e d are o r g a n i c i n 1  nature.  1  1  These i n c l u d e s a l t s made from carborane i o n s , C u ( B ^ Q H ^ C H ) ^ , Q  a potassium b i s oxidation of  (birueto)  cuprate " "' ' p r e p a r e d by p e r o x o d i s u l p h a t e 1  1  1  [Cu(-NHC0N-)], and a number o f p e p t i d e c o m p l e x e s . ^  2 , 6 9  M e y e r s t e i n ^ ° c a r r i e d out a study o f the c h e m i c a l p r o p e r t i e s o f a t r i - v a l e n t copper that C u  1 1 1  1  aquo  complex by r a d i o l y t i c means.  1  e x i s t s i n n e u t r a l s o l u t i o n as a C u O H  (aq.)  2+  He r e p o r t e d or Cu(OH)  + 2  (aq.)  i o n and decomposes by the mechanism 2+  2+  2CuOH  v 2Cu  +  H 0 2  (45)  2  Such i o n s were made by the r e a c t i o n Cu + OH ——+ C u i n r a d i o l y z e d s o l u t i o n s , f o l l o w e d by a t r i - v a l e n t copper o x i d a t i o n o f 2 +  1 1 1  (46)  water:  Cu  3 +  I t was s t a t e d t h a t C u  1 1 1  +  H 0 2  >- C u O H  2+  +  H  +  w i l l be formed by any o x i d a n t which can lower  (47)  - 44 -  t h e redox p o t e n t i a l o f the c o u p l e C u  1 1 1  - C u ^ i n the presence o f v a r i o u s +  ligands. The p o t e n t i a l f o r the  Cu  reaction  2+  3+ > Cu  +  e  (48)  i s quoted by L a t i m e r t o be 1.8 V i n a l k a l i n e medium a t 71 Shams E l D i n and c o - w o r k e r s  25°C.  75  r e p o r t e d the f o r m a t i o n o f  the  s e q u i o x i d e Cu^O^ by a l t e r n a t e a n o d i c / c a t h o d i c p o l a r i z a t i o n o f a copper electrode tials,  i n 0.1 N sodium h y d r o x i d e s o l u t i o n s , a t oxygen e v o l u t i o n p o t e n -  i . e . a t 0.76 V . 2Cu(OH)  2  The r e a c t i o n i n v o l v e d was thought +  20H  • Cu 0  I n an e x t e n s i v e study t o i n v e s t i g a t e  +  3H 0  +  2  to be:  2e  (49)  the f o r m a t i o n o f the s e s q u i o x i d e by 72  v a r i o u s wet and d r y c h e m i c a l methods and e l e c t r o c h e m i c a l l y , Delhez c a l c u l a t e d the redox p o t e n t i a l f o r C u d e r i v e d from the  3 +  f o r m a t i o n as 2.3 V .  T h i s was  equation:  Cu(0H)  3  +  e~  +  H  +  Cu(OH)  2  +  H 0  (50)  2  f o r w h i c h E = 1.57 - 0.054 pH (pH < 1 3 . 9 ) . 2+ 3+ Approximate Eh-pH diagrams f o r the Cu / C u oxidation-reduction  system  are g i v e n , and t h i s s t u d y was l a t e r used as a b a s i s f o r the e x t e n s i o n o f e x i s t i n g diagrams o f the Cu~H 0 system g i v e n by P o u r b a i x and c o - w o r k e r s 74  73  2  t o t a k e account o f t r i - v a l e n t copper and i t s  derivatives.  D e l h e z c o n c l u d e d from h i s work t h a t the o n l y f e a s i b l e method o f p r e p a r i n g Cu  was by o x i d a t i o n o f c u p r i c h y d r o x i d e i n a l k a l i n e s o l u t i o n  using either hypochlorite or peroxodisulphate  i o n s as o x i d a n t .  While  - 45 -  e l e c t r o c h e m i c a l methods may produce Cu^O^ i n some c a s e s , u s u a l l y i n s u f f i c i e n t to c a r r y out meaningful a n a l y s i s .  the y i e l d He t h u s  is  suggested  t h a t a l l p r e v i o u s workers who had used o x i d a n t s i n c l u d i n g hydrogen p e r o x i d e , p e r o x o m o n o s u l p h u r i c a c i d , c h l o r i n e o r bromine, had a c t u a l l y produced e i t h e r copper p e r o x i d e , CuC> o r cuprous o x i d e , Cu-jO, w h i c h i n many cases 2  had been confused w i t h the  sesquioxide.  U s i n g a method o f p o t a s s i u m p e r s u l p h a t e phate i n a l k a l i n e s o l u t i o n s  (pH 12.0 - 13.0)  oxidation of cupric s u l -  s i m i l a r t o t h a t o u t l i n e d by  57 S c a g l i a r n i and T o r e l l i  Delhez produced a r e d amaranth  precipitate  which c o n t a i n e d , b u t was n o t e x c l u s i v e l y , t r i - v a i e n t copper o x i d e . was t h e r e f o r e  presumed t o be a m i x t u r e o f Cu(OH)  a r a t i o of C u * : C u 1  2Cu(OH)„  1 1 1  +  and O^O^/Cu(OH)  2  dependent on the r a t e s o f the r e l e v a n t 20H~  +  S_0 Z o  2 _  o  Z  The r e a c t i o n f o r m i n g c o p p e r  1 1 1  ^2Cu(OH)_  3  >• 4Cu(OH)  2  , with  reactions:  +  2S0 " 4  +  0  6  4Cu(OH)  It  (51)  2  2  +  H 0  (52)  2  was c a t a l y z e d by the presence o f B a  2 +  ions,  i n agreement w i t h the p r e v i o u s f i n d i n g s o f S c h o l d e r and V o e l s k o w . ^ I t was a l s o found t h a t the compound e x i s t e d i n an u n i d e n t i f i e d s t a t e o f h y d r a t i o n , f l u c t u a t i n g between Cu F o r the case o f C u  1 1  and C u ( O H ) , a p p a r e n t l y a t random. 3  o x i d a t i o n w i t h hypohalogen s o l u t i o n s , Delhez  found the r e s u l t s o f p r e v i o u s s t u d i e s t o be c o n f u s i n g . gave s t r o n g e v i d e n c e t o show C u difficult  1 1 1  S e v e r a l workers  had been p r o d u c e d , but i t was o f t e n  t o a s c e r t a i n whether i t was C u , ^ ^ , o r a t r i - v a l e n t  cuprate.  S c h o l d e r and Voelskow, f o r example, had found t h a t o x i d a t i o n o f a b i v a l e n t c u p r a t e w i t h hypobromite produced a copper " " compound w h i c h they 11  assumed t o be a c u p r a t e .  1  Delhez c o n c l u d e d i t was p r o b a b l y C u , ^ ^ .  In  - 46 -  l e s s a l k a l i n e s o l u t i o n s , u s i n g c u p r i c h y d r o x i d e as a s t a r t i n g they obtained a d i f f e r e n t product,  material  h a v i n g a maximum C u : a v a i l a b l e  r a t i o o f 1 : 0 . 3 , b u t i n h i s own work Delhez never produced more t h a n 35% C u  1 1 1  by any method.  C o n s i d e r a t i o n o f the p o t e n t i a l s o f 01 , OBr  and 0C1  ions  showed t h a t o n l y the l a t t e r has a s u f f i c i e n t l y h i g h v a l u e t o g i v e a good y i e l d o f C u  1 1 1  .  Barium i o n s a l s o c a t a l y z e d t h i s  hypochlorite  r e a c t i o n and a mechanism s i m i l a r t o t h a t g i v e n by P r o k o p c h i k  (equations 2+  34 - 37) was thought t o be o p e r a t i v e . i o n s was due t o an i n c r e a s e  The c a t a l y t i c a c t i o n o f Ba  i n the redox p o t e n t i a l o f the  s o l u t i o n i n w h i c h t h e y were p r e s e n t .  oxidizing  CHAPTER TWO Experimental  2.1  Scope o f the P r e s e n t  Investigation  A number o f s t u d i e s have been made t o i n v e s t i g a t e the l e a c h i n g c h a r a c t e r i s t i c s o f m o l y b d e n i t e i n a l k a l i n e s o l u t i o n s o f sodium hypochlorite,  as o u t l i n e d above; b u t v e r y l i t t l e work has been done t o d e t e r -  mine the o x i d a t i o n b e h a v i o u r o f copper s u l p h i d e m i n e r a l s when exposed to s i m i l a r s o l u t i o n s .  As one o f the p r i n c i p a l o b j e c t i v e s o f f i n d i n g a  h y d r o m e t a l l u r g i c a l process s u i t a b l e for t r e a t i n g molybdenite  concentrates  i s t o enhance b y - p r o d u c t molybdenum r e c o v e r y from p o r p h y r y o r e s ,  it  would seem t o be o f prime importance t o g a i n an u n d e r s t a n d i n g o f any r e a c t i o n s o c c u r r i n g between copper and the l i x i v i a n t , and hence t o del i n e a t e any s t e p s n e c e s s a r y t o p r e v e n t copper d i s s o l u t i o n .  T h i s would  ensure optimum c o n d i t i o n s f o r a s e l e c t i v e molybdenum l e a c h , and a t same time p r e v e n t copper l o s s e s , b o t h o f w h i c h are fundamental economically feasible  the  t o an  process. 76  P r e v i o u s work i n t h i s department  was c a r r i e d out by Ismay,  to  r e s e a r c h the p o s s i b i l i t i e s o f e x t r a c t i n g molybdenum from c o p p e r molybdenum s u l p h i d e rougher c o n c e n t r a t e s , ite leach.  by means o f a sodium h y p o c h l o r -  A proposed p r o c e s s f l o w s h e e t was drawn up on the b a s i s o f  s u c c e s s f u l m o l y b d e n i t e l e a c h i n g ; and a l t h o u g h molybdenum r e c o v e r i e s were h i g h , i t was found t h a t some copper was a l s o e x t r a c t e d by the h y p o c h l o r i t e . The o b j e c t o f the p r e s e n t work a t i t s i n c e p t i o n was thus to d e t e r mine the e x t e n t o f the r e a c t i o n between v a r i o u s copper s u l p h i d e m i n e r a l s  - 48 -  and sodium h y p o c h l o r i t e under s i m i l a r c o n d i t i o n s t o those found by Ismay t o be optimum f o r molybdenum e x t r a c t i o n , w i t h a v i e w e i t h e r t o  preventing  copper from e n t e r i n g s o l u t i o n , o r t o f i n d i n g a s u i t a b l e method f o r  its  removal: 1)  I n i t i a l experiments r e v e a l e d t h a t the d i s s o l u t i o n o f copper  i n h y p o c h l o r i t e s o l u t i o n s a t pH 9.0 o n l y o c c u r r e d i n the p r e s e n c e o f c a r b o n a t e b u f f e r r e a g e n t s but t h a t removal o f the carbonate had undesirable side 2)  effects.  T h i s l e d t o an i n v e s t i g a t i o n o f the k i n e t i c s o f copper  catalysed h y p o c h l o r i t e decomposition r e a c t i o n s . t i o n p r o d u c t s was a l s o 3)  The n a t u r e o f decomposi-  considered.  The mechanism o f r e a c t i o n between sodium h y p o c h l o r i t e and  copper was s t u d i e d on a g e n e r a l b a s i s , w i t h and w i t h o u t the presence of carbonate,  t o i n c r e a s e an u n d e r s t a n d i n g o f the e f f e c t s  observed  during leaching. 4)  As the study p r o g r e s s e d  i t became apparent t h a t the p r e s e n c e  o f copper s u l p h i d e m i n e r a l s a d v e r s e l y a f f e c t e d molybdenum e x t r a c t i o n a t pH 9 . 0 .  A number o f experiments were t h u s c a r r i e d o u t a t pH l e v e l s  o f 5.5 - 6 . 0 , w h i c h had p r e v i o u s l y been suggested  t o be optimum f o r  molybdenum r e c o v e r y i n an i n v e s t i g a t i o n by the U . S . Bureau o f M i n e s . 5)  F u r t h e r work i n a l k a l i n e s o l u t i o n s was done u s i n g  synthetic  m i n e r a l s and t h i s h i g h l i g h t e d the f a c t t h a t c e r t a i n elements n o r m a l l y p r e s e n t as i m p u r i t i e s were d e t r i m e n t a l t o h i g h l e v e l s o f molybdenum extraction.  A thermodynamic s t u d y o f the s t a b i l i t y o f v a r i o u s molybdate  compounds i n aqueous s o l u t i o n was t h u s c a r r i e d out and s e v e r a l Eh-pH diagrams were  constructed.  - 49 -  6)  I t was then n e c e s s a r y  t o determine the l e a c h i n g  t i c s o f c e r t a i n c a l c i u m m i n e r a l s i n h y p o c h l o r i t e and o t h e r  characterischloride-  containing solutions. 7)  C o n s i d e r a t i o n o f a l l t h e above f a c t o r s  e s t a b l i s h i n g the n e c e s s a r y  led finally  to  c o n d i t i o n s f o r maximum molybdenum e x t r a c t i o n  w h i l e m i n i m i z i n g h y p o c h l o r i t e d e c o m p o s i t i o n and copper d i s s o l u t i o n .  2.2 2.2.1  Materials Natural minerals  C h a l c o c i t e , Cu^S, and c o v e l l i t e , CuS, were o b t a i n e d as massive samples from B u t t e , Montana.  C h a l c o p y r i t e , C u F e S , was purchased 2  massive form from Ward's N a t u r a l S c i e n c e E s t a b l i s h e m n t ,  in  and o b t a i n e d  a ground c o n c e n t r a t e from the P h o e n i x mine, B r i t i s h C o l u m b i a .  as  Large  p i e c e s o f o r e were c r u s h e d i n r o d and b a l l m i l l s and wet ground t o pass a-200 mesh s i e v e i n p r e p a r a t i o n  f o r l e a c h i n g as powdered samples.  p i e c e s o f broken o r e were p o l i s h e d on a 'Texamat' wheel f o r s u r f a c e  e x a m i n a t i o n b e f o r e and a f t e r  samples were mounted i n epoxy r e s i n  5tf  Small  diamond p o l i s h i n g  leaching.  I n some cases  (Epon 828/DETA) p r i o r t o p o l i s h i n g .  M o l y b d e n i t e , M o S , was o b t a i n e d as a h i g h grade c o n c e n t r a t e from 2  A l i c e Arm, B r i t i s h C o l u m b i a , ground t o p a s s a -325 mesh s i e v e . C a l c i t e , CaCO^  was o b t a i n e d i n powdered form from the  company (Texas) L t d . Mineral Analysis Wet c h e m i c a l a n a l y s i s gave the f o l l o w i n g  results:  Micro-ionized  - 50 -  i)  Covellite: Element  Weight %  Cu  58.80  Fe  3.00  Ca  0.16  Zn,Ni  Trace  (<0.05%)  T h i s i n d i c a t e s a CuS c o n t e n t o f 88.3%. ii)  Chalcocite: Element  Weight %  Cu  64.50  Fe  4.80  Ca  0.12  Pb  0.06  Zn  Trace  T h i s g i v e s a C u S c o n t e n t o f 81.0%. 2  iii)  Chalcopyrite: Weight %  Element Cu  31.6  Fe  29.20  Ca  1.51 Trace  Zn,Ni T h i s g i v e s a CuFeS^ c o n t e n t o f 93.3%.  Q u a l i t a t i v e X - r a y a n a l y s i s u s i n g the Scanning E l e c t r o n M i c r o s c o p e showed t h a t the c o v e l l i t e and c h a l c o c i t e samples a l s o c o n t a i n e d amounts o f s i l i c o n ,  and t r a c e s o f sodium and p o t a s s i u m .  s t u d i e s gave good agreement w i t h l i t e r a t u r e  values.  significant  X-ray d i f f r a c t i o n  Silica,  Si0  2  and  - 51 -  p y r i t e , FeS  2  were the o n l y o t h e r major peaks o b t a i n e d  (All diffraction  s t u d i e s r e p o r t e d f o r copper k  I/I o  dA 8.11  0  CuS  - species FeS  2  2  7.  4.26  36  3.33  100  1-3).  radiation)  1  identified  sio  (Tables  dA  I/I  0  - CuS  (Reported)  8.18  7  3.28  9  3.29  14  3.21  27  3.22  28  3.04  64  3.05 .  67  2.80  83  2.81  100  2.72  100  2.72  56  2.70  84  2.31  10  2.32  10  2.04  13  2.04  7  1.90  28  1.90  25  1.89  68  1.89  75  • 1.73  33  1.74  34  1.63  3  1.63  100  1.55  31  1.55  37  1.46  6  1.46  6  1.35  8  1.35  7  1.27  6  1.28  9  1.09  10  Tabl=e 1:  X-ray D i f f r a c t i o n  P a t t e r n f o r C o v e l l i t e Sample  - 52 -  I/I o  dA  0  - species  Cu S 2  4. 25 3.35  identified  sio  I/I O  2  dA  0  - Cu S 2  (Reported)  35  3.77  10  100  3.60  10  3.39  30  3.31  10  3.26  20  3.05  20  2.86  30  2.88  20  2.74  15  2.73  10  2.63  12  2.67  10  2.54  10  2.47  20  2.39  60  2.40  70  2.28  21  2.20  20  1.96  79  1.97  80  1.87  100  1.87  100  1.69  40  1.64  20  1.82  17  1.70  36  T a b l e 2:  X-ray D i f f r a c t i o n  Pattern for  Chalcocite:Sample  - 53 -  ::i/I o  0  -  CuFeS  dA  o  species i d e n t i f i e d SiC)  2  3.35  dA I / I  0  CuFeS  2  (Reported)  2  100  3.03  100  3.03  100  1.90  50  1.87  40  1.87  78  1.86  80  1.59  49  1.59  60  1.57  19  1.57  20  1.32  10  1.23  26  1.20  30  1.10  43  1.08  60  T a b l e 3:  X - r a y D i f f r a c t i o n P a t t e r n f o r C h a l c o p y r i t e Sample iv)  r  Q u a l i t a t i v e spectrographic  showed i t t o have the f o l l o w i n g  Element  Weight %  a n a l y s i s of the  molybdenite  analysis:  Element  Weight %  Al  0.10  Mg  0.01  Bi  0.05  Mn  0.001  Ca  0.50  Mo  58.52  Cr  0.01  S  39.02  Cu  0.05  Si  1.00  Fe  0.50  Sn  0.20  Pb  0.01  Ti  0.03  - 54 -  Traces  (<0.001%)of g o l d , s i l v e r and s t r o n t i u m were a l s o  2.2.2  Synthetic minerals i)  detected.  C u p r i c s u l p h i d e a n a l y z i n g 99.9% CuS was purchased from the  Rocky Mountain Research C o . , Denver, C o l o r a d o . ii)  Cuprous s u l p h i d e , a n a l y z i n g 99% + Cu S was o b t a i n e d 2  Matheson, Coleman & B e l l ,  East Rutherford, N . J .  m a t e r i a l s were c r u s h e d i n a p e s t l e and m o r t a r ,  from  S m a l l amounts o f t h e s e  and screened t o g i v e 100%  -200 mesh m a t e r i a l . iii)  Reagent grade molybdenum d i s u l p h i d e from BDH C h e m i c a l s , P o o l e  England was u s e d .  This analyzed as: Element  iv)  Weight %  Mo  53.4  S  35.6  Si  =10  Molybdenum d i s u l p h i d e a n a l y z i n g >98% MoS was purchased 2  from  the Venton Company, Danvers, Mass.  2.2.3  Sodium h y p o c h l o r i t e The source o f h y p o c h l o r i t e used i n a l l experiments was a household  b l e a c h s o l d under the t r a d e name ' J A V E X , ' and c o n t a i n i n g 50 - 60 g/1 i n the a s - p u r c h a s e d  condition.  S u i t a b l e d i l u t i o n s w i t h water were made  to t h i s s t o c k s o l u t i o n t o o b t a i n the d e s i r e d c o n c e n t r a t i o n f o r l e a c h i n g experiments.  - 55 -  2.2.4  Chemical r e a g e n t s A l l o t h e r c h e m i c a l s used were r e a g e n t  2.3  grade.  Apparatus  The m a j o r i t y o f l e a c h i n g experiments were c a r r i e d out i n a 1 l i t r e glass vessel f i t t e d with 4 Teflon baffles at equi-distant points i t s inner surface. titanium s t i r r e r  S o l u t i o n a g i t a t i o n was e f f e c t e d  using a turbine  c o a t e d w i t h a t h i n l a y e r o f 'MICROSTOP' p a i n t .  and v e s s e l dimensions t o g e t h e r conformed to a ' s t a n d a r d tion.  around  tank'  type  Agitator  configura-  The s t i r r e r was m e c h a n i c a l l y powered w i t h a F i s h e r - D y n a mix motor,  and the a g i t a t i o n r a t e was measured f o r each experiment u s i n g a T e c k l o c k c h r o n o m e t r i c hand t a c h o m e t e r . The l e a c h i n g v e s s e l was p l a c e d i n an open water b a t h w h i c h c o n t a i n e d a Micro-set thermo-regulator Company.  manufactured  by the P r e c i s i o n S c i e n t i f i c  A f t e r s e t t i n g a d e s i r e d t e m p e r a t u r e , t h i s u n i t was c a p a b l e o f  maintaining i t to ±0.1°C. The pH o f l e a c h i n g s o l u t i o n s was m o n i t o r e d d u r i n g each r u n by p l a c ing electrodes  i n s i d e the g l a s s v e s s e l .  I n i n i t i a l experiments  a  Beckman Expandomatic pH meter was used; t h i s was l a t e r r e p l a c e d w i t h a C h e m t r i x pH c o n t r o l l e r  ( H o r i z o n E c o l o g y C o . , C h i c a g o , 111.)  I n combina-  t i o n w i t h an ASCO 2-way t e f l o n c o a t e d s o l e n o i d v a l v e , t h i s c o n t r o l l e d the pH a u t o m a t i c a l l y -to w i t h i n ± 0 . 2 pH u n i t s . The e x p e r i m e n t a l a p p a r a t u s i s o u t l i n e d s c h e m a t i c a l l y i n F i g u r e 5.  - 56 -  JO  PH  CONTROLLER  A Water bath  •F Thermometer  B  Glass leaching vessel  G pH electrodes  C  T i mechanical s t i r r e r  H  2 way solenoid valve c o n t r o l l i n g addition of buffering solution from  D  Fisher Dyna Mix  I  E  burette, to leaching vessel via  Thermo-regulator  Figure 5:  J  c a p i l l a r y tube  Experimental leaching apparatus  - 57 -  2.4 2.4.1  Experimental Procedure L e a c h i n g experiments Experiments l e a c h i n g copper m i n e r a l s , and copper s u l p h i d e s and  molybdenite together,  were c a r r i e d o u t i n the f o l l o w i n g way:  A r e q u i r e d amount o f JAVEX r e a g e n t was added t o 700-800 ml d i s t i l l e d water and the r e s u l t a n t pH (=12.5) was lowered to the r e q u i r e d v a l u e by a d d i t i o n o f 1 N HC1. employed, N a C 0 2  3  In cases where carbonate b u f f e r i n g was  and NaHC0 were added i n r a t i o s c a l c u l a t e d from pka 3  v a l u e s t o b u f f e r the s o l u t i o n a t the n e c e s s a r y pH l e v e l . was made up t o 1 l i t r e , i n the water b a t h .  The s o l u t i o n  t r a n s f e r r e d t o the l e a c h i n g v e s s e l and p l a c e d  Slow a g i t a t i o n was i m p a r t e d u n t i l the s o l u t i o n had  a t t a i n e d the temperature o f the s u r r o u n d i n g w a t e r , then were t a k e n f o r h y p o c h l o r i t e and m e t a l a n a l y s e s . w h i l e m i n e r a l samples were i n t r o d u c e d :  'blank'  samples  A g i t a t i o n was stopped  where copper s u l p h i d e s and  m o l y b d e n i t e were l e a c h e d s i m u l t a n e o u s l y they were added as two s e p a r a t e powders, and i n some cases a d d i t i o n o f one sample was not made u n t i l r e a c t i o n w i t h the o t h e r had proceeded f o r s e v e r a l m i n u t e s . was t h e n i n c r e a s e d .  the  The a g i t a t i o n  Samples were t a k e n a t t i m e d i n t e r v a l s by s o l u t i o n w i t h -  drawal through a p i p e t t e ,  and f i l t e r e d u s i n g e i t h e r f i l t e r paper o r  Gooch f i l t e r c r u c i b l e s . In experiments where no carbonate b u f f e r i n g was used the r e q u i r e d pH was m a i n t a i n e d by d r o p w i s e a d d i t i o n o f 2 N NaOH from a b u r e t t e , i n l a t e r e x p e r i m e n t s by u s i n g the pH c o n t r o l l e r .  or,  - 58 -  2.4.2  Copper  preparation  Samples o f copper"'""'""'" were made by the a c t i o n o f sodium h y p o c h l o r i t e on c u p r i c c h l o r i d e u s i n g two methods: i)  A sodium h y p o c h l o r i t e s o l u t i o n o f the r e q u i r e d  was made up as o u t l i n e d above, the pH a d j u s t e d 35°C.  concentration  t o 9 . 0 , and heated  8 g o f C u C l - 2 H 0 ( e q u i v a l e n t t o 3 g/1 Cu) were then added, 2  2  to and  the pH m a i n t a i n e d by NaOH a d d i t i o n . ii)  8 g o f C u C l 2 H 0 were d i s s o l v e d i n water and the pH r a i s e d -  2  2  to 9 . 0 w i t h NaOH, t o g i v e a b l u e p r e c i p i t a t e o f c u p r i c h y d r o x i d e . measured volume o f s t o c k h y p o c h l o r i t e s o l u t i o n was then added.  A  After  an  i n i t i a l r a p i d r i s e i n pH t h i s dropped, and had t o be m a i n t a i n e d a t a v a l u e o f 9 . 0 as  before.  A f t e r about 5 minutes a g i t a t i o n the s o l u t i o n was c o m p l e t e l y b l a c k , and a f t e r  a period of brief  s t a n d i n g t o a l l o w some s e t t l i n g o f the c o n -  t a i n e d p r e c i p i t a t e t h i s was f i l t e r e d , c o l l e c t e d and d r i e d i n a d e s i c c a t o r . Samples made i n the presence o f sodium carbonate  required a longer  p e r i o d o f a g i t a t i o n t o g i v e complete p r e c i p i t a t i o n o f the c o p p e r , but method used was e s s e n t i a l l y the same (method  the  ( i ) was found t o be  preferable).  2.5 2.5.1  Analysis Chemical a n a l y s i s i)  Copper:  The amount o f copper c o n t a i n e d i n l e a c h i n g s o l u t i o n s  was d e t e r m i n e d u s i n g a P e r k i n Elmer 306 spectrophotometer a c e t y l e n e flame and a wavelength o f 324.7 ran, a f t e r  w i t h an a i r -  suitable dilutions with  - 59 -  d i s t i l l e d water, standards.  and by comparison w i t h a c a l i b r a t i o n c u r v e from known  To determine any e f f e c t caused by the presence o f l a r g e  amounts o f c h l o r i d e i n t h e s e s o l u t i o n s , t e s t a n a l y s e s were done u s i n g s t a n d a r d s o l u t i o n s swamped w i t h excess N a C l , but no d i f f e r e n c e s  were  detected. Copper i n o r e samples was d e t e r m i n e d by atomic a b s o r p t i o n a n a l y s i s after  d i s s o l u t i o n i n a warm m i x t u r e o f c o n c e n t r a t e d h y d r o c h l o r i c and  n i t r i c a c i d s , and subsequent d i g e s t i o n w i t h bromine, Br^. ii)  Molybdenum:  molybdenum i n l e a c h i n g s o l u t i o n s was d e t e r -  mined by atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y w i t h a n i t r o u s o x i d e - a c e t y l e n e flame a t a w a v e l e n g t h o f 313.3 nm.  D i l u t i o n s p r i o r t o a n a l y s i s were  made w i t h a s o l u t i o n c o n t a i n i n g 10% aluminum c h l o r i d e and 5% ammonium chloride. 2+ iii)  Calcium:  [Ca  ] i n s o l u t i o n was s i m i l a r l y determined a t a  w a v e l e n g t h o f 422.7 nm u s i n g an a i r - a c e t y l e n e iv)  Sodium H y p o c h l o r i t e :  flame.  the h y p o c h l o r i t e c o n c e n t r a t i o n o f each  b a t c h o f ' J A V E X ' used was a c c u r a t e l y d e t e r m i n e d by p o t a s s i u m i o d i d e 77 sodium t h i o s u l p h a t e t i t r a t i o n as o u t l i n e d i n ASTM D2022-64. s m a l l sample was d i l u t e d w i t h w a t e r ,  A  then added t o an a c i d i f i e d p o t a s s i u m  i o d i d e s o l u t i o n and t i t r a t e d a g a i n s t s t a n d a r d i z e d t h i o s u l p h a t e . i n d i c a t o r s o l u t i o n was added and the d i s a p p e a r a n c e o f i t s  Starch  characteristic  b l u e c o l o u r marked the end p o i n t . Sodium h y p o c h l o r i t e c o n c e n t r a t i o n s o f samples taken d u r i n g l e a c h ing  runs were d e t e r m i n e d by the same method, u s u a l l y u n d i l u t e d .  77 v)i n e dSodium : the [ClO^ o f ASTM l e a c D2022-64. hing solutions was d e t e r m by a rc ehllaotreadt e method, a l s o o] uct ol innt e nd t i n  - 60 -  The c h l o r a t e was reduced by a d d i t i o n o f sodium bromide, NaBr, and c o n c e n trated hydrochloric acid.  A f t e r d i l u t i o n and a d d i t i o n o f p o t a s s i u m  i o d i d e , the r e l e a s e d i o d i n e was t i t r a t e d as b e f o r e .  against  standard  T h i s g i v e s the t o t a l c o n c e n t r a t i o n o f  (OC1  thiosulphate  + ClO^) so  the  a c t u a l c h l o r a t e c o n t e n t was determined from the d i f f e r e n c e between  this  v a l u e and t h a t f o r h y p o c h l o r i t e i n the same sample. vi)  Chloride:  the t o t a l c h l o r i d e c o n t e n t  s o l u t i o n s b o t h b e f o r e and a f t e r a)  of hypochlorite  l e a c h i n g was f o u n d :  by s i l v e r n i t r a t e / p o t a s s i u m  thiocyanate t i t r a t i o n ,  as  77 o u t l i n e d i n ASTM D2022-64.  A l l the h y p o c h l o r i t e and any  p r e s e n t are reduced t o c h l o r i d e by sodium b i s u l p h a t e d i l u t e HNO^. The t o t a l c h l o r i d e c o n t e n t standard Volhard b)  chlorate  i n the presence o f  i s then determined u s i n g a  titration. potentiometrically:  t h i s method i s e s s e n t i a l l y  same as a) above, but the e n d p o i n t o f the s i l v e r n i t r a t e  t i t r a t i o n was  more a c c u r a t e l y determined by immersion o f a p l a t i n u m e l e c t r o d e the s o l u t i o n , and making a g r a p h i c a l p l o t o f p o t e n t i a l v s . 2.5.2  Instrumental i)  the  into  [AgNO^]-  analysis  Minerals.  Q u a l i t a t i v e a n a l y s i s f o r powdered samples and  massive m i n e r a l p i e c e s was c a r r i e d o u t u s i n g the X - r a y energy a n a l y z i n g f a c i l i t y o f the scanning e l e c t r o n microscope.  Quantitative X-ray analy-  s i s f o r the ground c o n c e n t r a t e s was o b t a i n e d w i t h a P h i l i p s X - r a y d i f f r a c t o m e t e r , and f o r s u r f a c e a n a l y s i s o f massive samples the e l e c t r o n m i c r o - a n a l y z e r was u s e d .  probe  - 61 -  ii)  Copper a)  Infra-red spectrophotometry:  samples o f the b l a c k  compound were p r e p a r e d i n m u l l form w i t h f l u o r o l u b e o i l , and r u n t h r o u g h a P e r k i n Elmer 621 g r a t i n g i n f r a - r e d b)  spectrophotometer.  Magnetic s u s c e p t i b i l i t y :  a s m a l l sample was weighed on  a 'Gouy' magnetic b a l a n c e , b o t h i n and o u t o f a magnetic f i e l d .  More  d e t a i l e d measurements o f the gram magnetic s u s c e p t i b i l i t y were a l s o made. c)  U l t r a - v i o l e t v i s i b l e spectrophotometry:  leaching solu-  t i o n s were examined i n the U V / v i s i b l e r e g i o n s u s i n g a P e r k i n Elmer u l t r a v i o l e t s p e c t r o p h o t o m e t e r w i t h a p a t h l e n g t h o f 2 - 10 nm. d) diffractometer.  X - r a y d i f f r a c t i o n p a t t e r n s were o b t a i n e d u s i n g the  - 62 -  CHAPTER THREE R e s u l t s and O b s e r v a t i o n s  3.1  Sodium H y p o c h l o r i t e L e a c h i n g o f Copper S u l p h i d e M i n e r a l s  Experiments were c a r r i e d o u t t o determine the o x i d a t i o n b e h a v i o u r o f c e r t a i n copper s u l p h i d e m i n e r a l s i n s o l u t i o n s o f a l k a l i n e sodium hypochlorite. Cu^S,  The s e l e c t e d m i n e r a l s were c o v e l l i t e , CuS, c h a l c o c i t e ,  and c h a l c o p y r i t e , CuFeS^.  These are t h r e e o f the most commonly  o c c u r r i n g copper o r e s a s s o c i a t e d w i t h molybdenum b e a r i n g  3.1.1  porphyries.  L e a c h i n g o f ground c o n c e n t r a t e s i n the p r e s e n c e o f c a r b o n a t e 10 g samples o f each m i n e r a l , p r e v i o u s l y ground to pass a -200  mesh s i e v e were a g i t a t e d  i n solutions containing 7 - 8  g/1 h y p o c h l o r i t e  a t a t e m p e r a t u r e o f 35°C and a pH v a l u e o f 9 . 0 , b u f f e r e d w i t h a sodium 2carbonate/bicarbonate  mixture.  The r a t i o o f HCO^ :CO^  10.7 g/1 t o t a l c a r b o n a t e were used  was 14:1 and  initially.  A s m a l l amount o f copper was found t o be r a p i d l y d i s s o l v e d i n each c a s e .  S m a l l v a r i a t i o n s were observed between the t h r e e m i n e r a l s ,  b u t the copper c o n t e n t o f s o l u t i o n averaged 100 - 130 ppm and r e p r e s e n t e d 2 - 3% o f t h e copper i n t r o d u c e d i n t o t h e system  ( F i g u r e 6, T a b l e s I -  Copper c o n c e n t r a t i o n d i d not m a i n t a i n a c o n s t a n t v a l u e w i t h r e s p e c t t i m e , and a f t e r  III).  to  a t t a i n i n g a maximum i n i t i a l v a l u e i t f l u c t u a t e d i n an  a p p a r e n t l y random manner.  L e a c h i n g s o l u t i o n s e p a r a t e d from the m i n e r a l  Time (minutes) Figure 6:  Oxidation.of copper sulphide minerals by NaOCl.  - 64 -  s l u r r y i n the e a r l y s t a g e s o f a g i t a t i o n m a i n t a i n e d an almost copper c o n t e n t colouration:  ( F i g u r e 7, T a b l e s I V , V ) .  constant  A l l s o l u t i o n s showed deep b l u e  s i g n i f i c a n t l y more so than s t a n d a r d copper s u l p h a t e  c o n t a i n i n g an e q u i v a l e n t amount o f c o p p e r .  S o l u t i o n s l e f t to stand o v e r -  n i g h t were o b s e r v e d t o d e p o s i t a b l a c k p r e c i p i t a t e w h i c h , a f t e r time p e r i o d o f 1 - 3 d a y s , was accompanied by l o s s o f the b l u e c o l o u r a t i o n o f the s o l u t i o n .  solutions  a  further  characteristic  Subsequent a n a l y s i s r e v e a l e d t h e s e  c l e a r s o l u t i o n s t o c o n t a i n n e g l i g i b l e amounts o f c o p p e r .  Heating to  50 - 60°C a l s o produced a b l a c k p r e c i p i t a t e and t h i s was found t o be copper o x i d e by a n a l y s i s u s i n g the Debye S c h e r r e r powder method f o r X - r a y diffraction.  I n s u f f i c i e n t o f the m a t e r i a l p u t down from f i l t e r e d l e a c h -  i n g samples c o u l d be c o l l e c t e d t o c a r r y out m e a n i n g f u l a n a l y s i s . o f samples w i t h water a l s o produced a b l a c k p r e c i p i t a t e  i n some  Dilution cases.  Sodium h y p o c h l o r i t e consumption was found t o v a r y s l i g h t l y f o r each o f the t h r e e m i n e r a l s :  e q u a l samples o f CuFeS^, CuS and Cu^S c o n -  sumed 10%, 27% and 18% o f the i n i t i a l h y p o c h l o r i t e p r e s e n t r e s p e c t i v e l y . One mole o f copper thus consumed 0.28 M, 0.4 M and"0.22 M OC1 respective minerals  3.1.2  ( F i g u r e 8, T a b l e s I -  E f f e c t o f carbonate  i n the  III).  removal  E x p e r i m e n t s were c a r r i e d out i n which no  carbonate/bicarbonate  r e a g e n t s were added t o the l e a c h i n g s o l u t i o n , t o determine the e f f e c t , any, on copper s o l u b i l i t y . hydroxide buffer,  The pH was m a i n t a i n e d i n s t e a d w i t h a sodium  added dropwise from a b u r e t t e , t o c o u n t e r a c t  o b s e r v e d drop i n p H .  the  A l l o t h e r c o n d i t i o n s were i d e n t i c a l t o those o f  if  Time Figure 7:  (minutes)  Effect of separating leaching solution from mineral slurry.  - 66 -  i - -  6.0J  4-OJ  •  chalcocite  •  covellite  .A  chalcopyrite  (pH 9.0,35°C)  2.0J  1  r~  30  90 Time  Figure 8:  150  (minutes)  NaOCl Consumption-during copper sulphide leaching.  - 67 -  previous  runs.  The a n a l y t i c a l r e s u l t s  showed t h i s c a r b o n a t e removal from the  system t o have a v e r y s i g n i f i c a n t i)  effect:  Less than 1 ppm copper was d i s s o l v e d from a 10 g sample o f  each m i n e r a l . ii)  The s o l u t i o n pH was found t o drop r a p i d l y as  agitation  commenced, and t h i s was accompanied by sodium h y p o c h l o r i t e d e c o m p o s i t i o n . The a c t u a l r a t e o f d e c o m p o s i t i o n was a f u n c t i o n o f the p a r t i c u l a r  copper  mineral being leached:  CuS produced 50% d e c o m p o s i t i o n i n 9 minutes CuFeS^ produced 50% d e c o m p o s i t i o n i n 12.5  minutes  Cu^S produced 50% d e c o m p o s i t i o n i n 82 m i n u t e s .  T o t a l d e c o m p o s i t i o n o c c u r r e d i n a l l t h r e e c a s e s , b u t the r a t e o f decomposit i o n was n o t l i n e a r  3.1.3  ( F i g u r e 9, T a b l e s V I - V I I I ) .  L e a c h i n g o f s y n t h e t i c copper  sulphides  D e c o m p o s i t i o n was presumed t o be caused by c a t a l y t i c a c t i o n o f copper a t the m i n e r a l s u r f a c e .  To determine whether the o b s e r v e d  ences i n the r a t e o f r e a c t i o n were a t t r i b u t a b l e  t o copper a l o n e ,  differsamples  o f cuprous and c u p r i c s u l p h i d e powder were l e a c h e d under i d e n t i c a l c o n d i t i o n s to those used f o r the n a t u r a l m i n e r a l s .  I n the presence o f  c a r b o n a t e r e s u l t s were almost i d e n t i c a l t o t h o s e o f c o v e l l i t e and c h a l c o c i t e w i t h r e s p e c t t o b o t h copper d i s s o l u t i o n and h y p o c h l o r i t e consumption. I n the absence o f c a r b o n a t e no copper was d e t e c t e d  i n s o l u t i o n and  the  - 68  -  Time (minutes) Figure 9:  Effect of carbonate removal on NaOCl decomposition.  - 69 -  r a t e o f h y p o c h l o r i t e d e c o m p o s i t i o n was c o n s t a n t i n each case (Tables X I , XII; Figure 10). remaining after  3.1.4  T h i s was l i n e a r and gave 50% o f the i n i t i a l 0C1  content  52 and 54 minutes f o r C ^ S and CuS r e s p e c t i v e l y .  Determination of decomposition products  L e a c h i n g s o l u t i o n s were a n a l y s e d f o r sodium c h l o r a t e c o n t e n t determine whether t h i s was a d e c o m p o s i t i o n p r o d u c t ,  to  as g i v e n by the  equation:  30C1~  * C10 ~ 3  +  2C1~  (53)  o r whether oxygen was the o n l y p r o d u c t : 20C1~  v 0  2  +  2C1~  (54)  I t was found t h a t some c h l o r a t e was produced i n a l l t h r e e c a s e s , t h a t the r e s u l t s  but  f o r t h e d i f f e r e n t m i n e r a l s were v e r y v a r i a b l e :  c o v e l l i t e and c h a l c o p y r i t e b o t h showed a d e c r e a s e i n the p e r c e n t a g e c h l o r a t e p r e s e n t i n s o l u t i o n as h y p o c h l o r i t e d e c o m p o s i t i o n b e i n g 13.7% and 36.15% r e s p e c t i v e l y a f t e r 9.57% a f t e r  5 minutes,  45 minutes f o r c o v e l l i t e and 20.22% a f t e r  chalcopyrite  (Figure 11, Tables VI - V I I I ) .  progressed,  and d e c r e a s i n g 90 minutes  C h a l c o c i t e on the  to  for  other  hand, which produced a much s l o w e r r a t e o f c a t a l y z e d d e c o m p o s i t i o n , showed the r e v e r s e t r e n d i n t h a t 8.7% o f the d e c o m p o s i t i o n p r o d u c t was chlorate after leaching.  5 minutes,  and t h i s i n c r e a s e d t o o v e r 23% a f t e r  150 minutes  These g e n e r a l p a t t e r n s were o b s e r v e d i n s e v e r a l d i f f e r e n t  a l t h o u g h t h e a b s o l u t e v a l u e s v a r i e d s l i g h t l y i n each  experiment.  runs,  -  70  -  8.0  150 . Time Figure 10:  (minutes)  NaOCl decomposition during leaching of synthetic copper Sulphides.  - 71  -  Time Figure 11:  (minutes)  NaC10 production during NaOCl decomposition. 3  - 72 -  3.1.5  Sodium h y p o c h l o r i t e l e a c h i n g o f massive samples o f copper s u l p h i d e minerals S m a l l p i e c e s o f c h a l c o c i t e , c o v e l l i t e and c h a l c o p y r i t e were  p o l i s h e d on one face and immersed i n s o l u t i o n s o f sodium h y p o c h l o r i t e a t pH 9.0 f o r v a r y i n g amounts o f t i m e .  Slow a g i t a t i o n was m a i n t a i n e d i n  most cases and the experiments were c a r r i e d o u t w i t h and w i t h o u t the presence o f c a r b o n a t e .  M i n e r a l s u r f a c e s were examined b e f o r e and  after  l e a c h i n g u s i n g the s c a n n i n g e l e c t r o n m i c r o s c o p e , the e l e c t r o n m i c r o p r o b e and o p t i c a l m i c r o s c o p y ; and t o t h i s end s p e c i f i c areas were marked so t h a t q u a n t i t a t i v e a n a l y s i s c o u l d be c a r r i e d o u t : i)  Chalcocite.  Immersion i n carbonate  s o l u t i o n s a t pH 9 . 0  f o r p e r i o d s o f up t o 3 hours produced l i t t l e d i f f e r e n c e to the p o l i s h e d surface,  a l t h o u g h some t a r n i s h i n g was o b s e r v e d .  copper were d e t e c t e d  A p p r o x i m a t e l y 0.003  g/1  i n s o l u t i o n (3 ppm) from a t o t a l s u r f a c e a r e a o f  2 about 6 cm .  E l e c t r o n m i c r o p r o b e e x a m i n a t i o n o f marked a r e a s r e v e a l e d  t h a t i n most cases b o t h the copper and s u l p h u r c o n t e n t a t the had d e c r e a s e d ,  w i t h an o v e r a l l i n c r e a s e i n the Cu:S r a t i o .  surface  In a few  s m a l l a r e a s an i n c r e a s e d s u l p h u r c o n t e n t was o b s e r v e d g i v i n g a decreased Cu:S r a t i o  (Table I X ) .  Samples immersed i n t o carbonate for longer periods,  containing hypochlorite solutions  i n excess o f f i f t e e n h o u r s , began to form dark green  a r e a s on the s u r f a c e .  These a r e a s grew i n magnitude w i t h time and  one week the m i n e r a l was e n t i r e l y c o v e r e d w i t h a green d e p o s i t ,  after  which  a n a l y s i s showed t o have a s i g n i f i c a n t l y i n c r e a s e d copper c o n t e n t .  The  d e p o s i t was n o t water s o l u b l e , and resembled m a l a c h i t e , Cu (OH) CO .'  - 72(b) -  PLATE  1  1)  Cu^S, unleached  2)  after 3 hours i n hypochlorite/carbonate  3)  after 24 hours i n hypochlorite/carbonate  4)  a f t e r 3 weeks i n hypochlorite/carbonate  5)  after 12 hours i n hypochlorite solution (no carbonate)  6)  a f t e r 3 days i n hypochlorite solution (no carbonate)  7)  a f t e r 1 week i n hypochlorite solution (no carbonate)  solution solution solution  Effect of NaOCl ± Na„ C0„/NaHC0_ on massive chalcocite samples at pH 9.0, 35°C.  - 73 -  (Plate I ) .  After  3 weeks immersion i n h y p o c h l o r i t e s o l u t i o n , s m a l l b l a c k  p a t c h e s were o b s e r v e d on the green c o a t i n g c o v e r i n g the c h a l c o c i t e  sur-  face . A g i t a t i o n of solutions containing 7 - 8 carbonate, after  g/1 h y p o c h l o r i t e , b u t no  produced s i m i l a r t a r n i s h i n g o f the c h a l c o c i t e s u r f a c e ,  and  about 12 hours a powdery green d e p o s i t formed i n c e r t a i n a r e a s .  W i t h i n 3 days t h e e n t i r e s u r f a c e was g r e e n , and a f t e r d e p o s i t c o v e r e d most o f the ii)  Covellite.  sample.  CuS was o b s e r v e d t o have a more r a p i d r e a c t i o n  t h a n Cu^S when exposed t o b o t h c a r b o n a t e - c o n t a i n i n g c h l o r i t e alone.  1 week a b l a c k  s o l u t i o n s and h y p o -  I n the former case the p o l i s h e d s u r f a c e l o s t i t s  shine  w i t h i n 10 minutes and w h i t e p a t c h y a r e a s were v i s i b l e .  A f t e r 4 hours  a g i t a t i o n the s u r f a c e was c o v e r e d by a w h i t e d e p o s i t .  Probe a n a l y s i s  showed a r e a s w i t h d i f f e r e n t a)  leaching characteristics  to be p r e s e n t :  a r e a s w i t h an i n c r e a s e d Cu:S r a t i o caused by a l a r g e  decrease i n s u l p h u r c o n t e n t and a r e l a t i v e l y s m a l l d e c r e a s e i n c o p p e r , b)  areas w i t h a s i g n i f i c a n t l y increased sulphur  and hence a decreased Cu:S r a t i o . c h l o r i d e , C C l ^ , removed t h i s elemental sulphur deposit  1  content  Subsequent washing i n carbon  excess'sulphur  tetra-  and suggested i t was an  (Table X ) .  A f t e r exposure t o carbonate  solutions for longer periods,  the  e n t i r e c o v e l l i t e s u r f a c e was c o v e r e d by a dark green d e p o s i t s i m i l a r t h a t formed on t h e c h a l c o c i t e .  to  G r a d u a l d i s s o l u t i o n o f copper o c c u r r e d  t o g i v e a deep b l u e s o l u t i o n c o n t a i n i n g up t o 100 ppm C u .  After  2 - 3  weeks s t a n d i n g t h i s s o l u t i o n l o s t i t s c h a r a c t e r i s t i c b l u e c o l o u r w i t h i n a 24 hour p e r i o d and the m i n e r a l s u r f a c e was s i m u l t a n e o u s l y c o a t e d w i t h  - 73(a)  -  - 73(b) -  PLATE II  CuS, unleached. after 10 minutes i n hypochlorite/carbonate solution, after 15 hours i n hypochlorite/carbonate solution, after 1 week i n hypochlorite/carbonate solution, after 3 weeks i n hypochlorite/carbonate solution, after 5 minutes i n hypochlorite solution after 15 hours i n hypochlorite solution  (no carbonate), (no carbonate).  after 1 week i n hypochlorite solution (no carbonate).  ect of NaOCl ± Na„C0_/NaHC0„ on massive c o v e l l i t e samples pH 9.0, 35°C.  - 74 -  a very black deposit (Plate I I ) .  T h i s phenomenon was found t o be q u i t e  r e p r o d u c i b l e , a l t h o u g h the time t o p r e c i p i t a t i o n v a r i e d s l i g h t l y different  for  samples.  C o v e l l i t e samples were r a p i d l y t a r n i s h e d by sodium h y p o c h l o r i t e s o l u t i o n s c o n t a i n i n g no c a r b o n a t e , w i t h the appearance o f brown p a t c h e s w i t h i n 10 m i n u t e s .  A powdery green d e p o s i t d e v e l o p e d w i t h i n 12 hours  and c o v e r e d the e n t i r e s u r f a c e a f t e r  about 15 h o u r s , e x p o s u r e .  This  substance was found to have a s i g n i f i c a n t l y i n c r e a s e d copper count (Table X) and was s i m i l a r i n appearance t o c u p r i c h y d r o x i d e . A f t e r 1 week a dark b r o w n / b l a c k d e p o s i t had d e v e l o p e d on top o f the g r e e n .  I t was ' f l a k y , '  and e a s i l y removable, u n l i k e the  produced by c a r b o n a t e s o l u t i o n s .  precipitate  The copper c o n t e n t s o f b o t h b l a c k  d e p o s i t s were s i m i l a r t o those o f the green l a y e r s which t h e y s u p e r c e d e d . iii)  Chalcopyrite.  Immersion i n t o ' u n b u f f e r e d ' h y p o c h l o r i t e  s o l u t i o n s produced a t a r n i s h i n g o f the CuFeS,, s u r f a c e , and s e v e r a l brown p a t c h e s were o b s e r v e d t o form. coating after  The e n t i r e sample was c o v e r e d by a brown  2 weeks s t a n d i n g .  Samples exposed t o carbonate s o l u t i o n s underwent l i t t l e  change:  some t a r n i s h i n g o f the p o l i s h e d s u r f a c e was o b s e r v e d and s e v e r a l dark brown p a t c h e s appeared a f t e r  long standing.  SEM e x a m i n a t i o n showed t h a t b o t h t r e a t m e n t s produced a s i m i l a r surface c o a t i n g .  Probe a n a l y s i s i n d i c a t e d a s l i g h t i n c r e a s e i n copper  and a c o r r e s p o n d i n g d e c r e a s e i n s u l p h u r a t the s u r f a c e .  No green  m a t e r i a l appeared on samples l e f t i n e i t h e r s o l u t i o n f o r p e r i o d s o f up t o 4 weeks.  - 75 -  3.1.6  V a r i a t i o n o f t o t a l carbonate content d u r i n g the l e a c h i n g o f ground copper sulphide minerals The s u r f a c e s t u d i e s r e p o r t e d above, t o g e t h e r w i t h the o b s e r v e d  dependence o f copper d i s s o l u t i o n and h y p o c h l o r i t e d e c o m p o s i t i o n on the presence o f N a C 0 / N a H C 0 2  3  3  i n the l e a c h i n g system, i n d i c a t e d t h a t these  r e a g e n t s p l a y e d a s i g n i f i c a n t l y more i m p o r t a n t r o l e t h a n had been  initially  supposed when a c a r b o n a t e m i x t u r e was added as a b u f f e r component.  Several  experiments were t h u s c a r r i e d o u t i n w h i c h the t o t a l carbonate c o n t e n t o f the system was v a r i e d from 0.55 g/1 leaching of  2[CO^ ] t o 10.0 g/1  2[CO^ ] d u r i n g the  covellite.  T h i s was found t o have a r a t h e r remarkable e f f e c t on the b e h a v i o u r o f b o t h copper and h y p o c h l o r i t e .  2As [CO^ ]  i n c r e a s e d , the amount o f  copper i n i t i a l l y t a k e n i n t o s o l u t i o n i n c r e a s e d i n an a l m o s t l i n e a r manner 2and v a r i e d from 6 ppm w i t h 0.55 g/1  [CO^  ] t o 125 ppm w i t h 10 g/1  2[CO^  ] as shown i n F i g u r e 12 a , b and T a b l e X I I I .  copper r e p r e s e n t e d  This value of d i s s o l v e d  a peak c o n c e n t r a t i o n w h i c h o c c u r r e d w i t h i n the  first  f i v e minutes o f l e a c h i n g and t h e n dropped t o a s l i g h t l y l o w e r l e v e l . The second v a l u e was m a i n t a i n e d f o r a f i n i t e p e r i o d o f t i m e and was a p p a r e n t l y a f u n c t i o n o f the amount o f added c a r b o n a t e .  I t was f o l l o w e d  by a f u r t h e r r a p i d drop i n the copper c o n c e n t r a t i o n , accompanied by e q u a l l y r a p i d d e c o m p o s i t i o n o f the h y p o c h l o r i t e , w h i c h had p r e v i o u s l y m a i n t a i n e d a c o n s t a n t v a l u e ( F i g u r e 13, T a b l e X I I I ) .  I n experiments  2u s i n g 5 g/1 [CO^ ]. and above, the copper c o n t e n t remained a t a second ' p l a t e a u ' l e v e l a f t e r h y p o c h l o r i t e d e c o m p o s i t i o n , b u t those c a s e s c o n 2t a i n i n g 0 . 5 , 1.0 and 2.0 g/1 this point.  [CO^  ] showed z e r o copper i n s o l u t i o n a f t e r  2.0 120J  80J  A 10.7  g/1  -  g/1 g/1 g/1 g/1 g/1  • o  E cl ol  7.5 5.0 2.0 1.0 0.55  (pH 9.0,  [co ]  35°C)  3  L1.5 _ o E  T  CO  O  .1.0 CD  a a o  a a o  404 U0.5  Time (minutes) Figure 12(a):  Effect of varied carbonate content on Cu d i s s o l u t i o n from C o v e l l i t e .  o  1  !  40  1  1  120  1  200 TIME  Figure 12(b):  I  •  1  280  I  360  minutes  Cu dissolution and NaOCl decomposition  for C o v e l l i t e leaching with 10 g/1  [00^ ]T  -  QL  -  - 79 -  I t was observed t h a t the r a t e o f sodium h y p o c h l o r i t e d e c o m p o s i t i o n was c o n s t a n t , and not t h e r e f o r e carbonate c o n c e n t r a t i o n .  a f u n c t i o n o f d i s s o l v e d copper o r  initial  I n a l l cases the r a t e was almost i d e n t i c a l t o  t h a t produced d u r i n g the l e a c h i n g o f c o v e l l i t e i n the absence o f To determine whether or not s i m i l a r e f f e c t s  carbonate.  o c c u r r e d w i t h the  other  copper s u l p h i d e m i n e r a l s , i d e n t i c a l runs were c a r r i e d out u s i n g c h a l c o c i t e and s y n t h e t i c c u p r i c and cuprous s u l p h i d e powders. showed the d i s s o l v e d copper c o n t e n t  A l l three  t o pass t h r o u g h a r a p i d l y  samples attained  maximum v a l u e and then t o m a i n t a i n a c o n s t a n t v a l u e f o r an amount o f time dependent on the c a r b o n a t e c o n t e n t o f the system.  T h i s was a g a i n  f o l l o w e d by r a p i d l o s s o f copper and s i m u l t a n e o u s h y p o c h l o r i t e decomposition  ( F i g u r e s 14 - 17, T a b l e s X I V , X V ) . The n e c e s s a r y  induction period  t o copper p r e c i p i t a t i o n was almost i d e n t i c a l t o t h e analogous case f o r c o v e l l i t e b e i n g 10, 25 and 65 minutes f o r 1.0, respectively.  2.0 and 5.0 g/1 c a r b o n a t e  The amounts o f copper d i s s o l v e d from each sample were  a l s o v e r y s i m i l a r , b u t the observed r a t e s o f h y p o c h l o r i t e d e c o m p o s i t i o n were n o t c o n s t a n t .  They were however c o n s i s t e n t w i t h t h e r a t e s  i n each case d u r i n g l e a c h i n g w i t h o u t  3.1.7  E f f e c t o f v a r y i n g the concentration  obtained  carbonate.  hypochlorite  To d e t e r m i n e whether an i n c r e a s e o f h y p o c h l o r i t e s t r e n g t h effect  had any  on copper d i s s o l u t i o n , a c o v e l l i t e sample was l e a c h e d i n a  s o l u t i o n c o n t a i n i n g 20 g/1  [OC1 ] , r a t h e r than 7 - 8  used p r e v i o u s l y , and i n the p r e s e n c e o f 5 g/1  g/1  concentration  carbonate.  R e s u l t s showed t h a t the copper e x t r a c t e d had i n c r e a s e d from  60  cL  •  5 g/1  A  2 g/1  O  1 g/i  (pH 9.0,  .0.75  [C0 "]T 3  CO  _ o E  35°C)  CO  Q.  -0.50 <x> o. CL o  O X  (-—1 CP Q. Q. O  O.  .O.  20-  -0.25 A-A  -1—  40 Figure 14:  —I  80 TIME  120  Q  160  minutes  Effect of varied carbonate content on Cu d i s s o l u t i o n from Chalcocite.  CO o  -  83  -  - 84 -  0.045 g/1 t o 0.1 g / 1 , and t h a t t h i s copper was h e l d i n s o l u t i o n f o r a l o n g e r p e r i o d b e f o r e b o t h i t and the h y p o c h l o r i t e c o n c e n t r a t i o n decreased.  The r a t e o f 0C1  rapidly  d e c o m p o s i t i o n was c o n s i s t e n t w i t h t h a t o b -  t a i n e d i n a l l p r e v i o u s runs u s i n g c o v e l l i t e , and the copper r e m a i n i n g in solution after 5 g/1 c a r b o n a t e  3.1.8  d e c o m p o s i t i o n was the same as i n a l l o t h e r runs u s i n g ( F i g u r e 18, Table X V I ) .  E f f e c t o f h y p o c h l o r i t e removal  Samples o f c o v e l l i t e were a g i t a t e d  i n sodium c a r b o n a t e  solutions  i n t h e absence o f h y p o c h l o r i t e t o g a i n a b e t t e r i n s i g h t i n t o the r o l e p l a y e d by the  precise  oxidant.  Copper was d i s s o l v e d t o a l e v e l o f 0.06 g/1 i n the p r e s e n c e o f 10 g / 1 t o t a l c a r b o n a t e .  T h i s g r a d u a l l y decreased  to zero a f t e r  70  minutes a g i t a t i o n i n cases where sodium c h l o r i d e was a l s o p r e s e n t , after  30 minutes i n ' c a r b o n a t e o n l y ' s o l u t i o n s  or  ( F i g u r e 19, T a b l e X V I I ) .  F i l t e r e d samples t a k e n f o r a n a l y s i s were observed t o p r e c i p i t a t e  a green  powder a f t e r  blue  standing overnight.  These s o l u t i o n s had l o s t t h e i r  c o l o u r a t i o n and c o n t a i n e d n e g l i g i b l e amounts o f As noted e a r l i e r , c a r r i e d out by Ismay  copper.  b o t h i n the p r e s e n t s t u d y and i n p r e v i o u s work  f i l t e r e d s o l u t i o n s from experiments  copper s u l p h i d e m i n e r a l s i n h y p o c h l o r i t e d e p o s i t e d a b l a c k after  standing for a short time.  Ismay p o s t u l a t e d  leaching precipitate  t h a t complexing  between copper and a p a r t i a l l y o x i d i z e d s u l p h u r s p e c i e s c o u l d o c c u r , w i t h slow t r a n s f o r m a t i o n  i n t o sulphate  i n the p r e s e n c e o f h y p o c h l o r i t e ,  p r e c i p i t a t i o n o f copper from s o l u t i o n as copper o x i d e , CuO.  causing  - 85  TIME Figure 18:  -  minutes  Cu dissolution and NaOCl decomposition from C o v e l l i t e leaching with 20 g/1 [NaOclJ and 5 g/1 [ C 0 v = ] T  - 86 -  1  I  I  I  40  TIME Figure 19:  Agitation  I  80  1 120  minutes  of C o v e l l i t e i n Na C0 /NaHC03 solution 2  3  ± NaCl.  - 87 -  To t e s t t h i s h y p o t h e s i s , copper s u l p h a t e was a g i t a t e d i n a s o l u t i o n c o n t a i n i n g 7 g/1 sufficient  [0C1 ] and 10 g/1 Na CO /NaHCO  a t pH 9 . 0 , i n  amounts t o g i v e 0.1 g/1 copper i n s o l u t i o n .  I f less  t h i s d i s s o l v e d i t c o u l d be t a k e n as an i n d i c a t i o n t h a t the  than  carbonate  c o u l d n o t h o l d t h i s much copper i n s o l u t i o n i n the presence o f  fully  2o x i d i z e d s u l p h u r , i . e . as SO^ I t was found however t h a t a l l the copper was taken i n t o s o l u t i o n , g i v i n g the same deep b l u e c o l o u r o b s e r v e d i n l e a c h i n g s o l u t i o n s . F u r t h e r e x p e r i m e n t showed a maximum o f under t h e s e c o n d i t i o n s . only  0 . 1 2 7 g/1 Cu t o be d i s s o l v e d  Removal o f h y p o c h l o r i t e from t h i s system e n a b l e d  0 .065 g/1 o f the copper t o be d i s s o l v e d g i v i n g a l e s s i n t e n s e l y b l u e  solution.  Samples l e f t t o s t a n d a g a i n produced a s o l i d  precipitate:  b l a c k i n the former c a s e , and green i n the l a t t e r where no h y p o c h l o r i t e was p r e s e n t .  I t was a l s o o b s e r v e d t h a t t h i s p r e c i p i t a t i o n e f f e c t  be " s e e d e d , " and a d d i t i o n o f a s m a l l amount o f t h i s green t o f r e s h l y made copper - c a r b o n a t e  could  precipitate  s o l u t i o n s produced complete p r e c i p i t a -  t i o n o f t h e d i s s o l v e d c o p p e r , as more green powder, w i t h i n one h o u r . 3.2^  Copper H I From the above o b s e r v a t i o n s i t i s e v i d e n t t h a t h y p o c h l o r i t e has a  d i r e c t e f f e c t on the s o l u b i l i t y o f copper i n sodium c a r b o n a t e  solutions,  and on t h e n a t u r e and c o l o u r o f s u b s t a n c e s p r e c i p i t a t e d from them.  The  resemblances between copper s u l p h i d e l e a c h i n g and copper s u l p h a t e d i s s o l u t i o n and the subsequent b e h a v i o u r o f s o l u t i o n s w i t h and w i t h o u t hypoc h l o r i t e were found t o be s i g n i f i c a n t :  - 88 -  i)  The copper d i s s o l v e d by a g i v e n 0C1 / [ C O  ] solution is  c o n s t a n t whether the s t a r t i n g m a t e r i a l i s a copper s u l p h i d e m i n e r a l , o r copper s u l p h a t e ii)  reagent.  A l e s s e r amount o f copper i s h e l d i n carbonate  c o n t a i n i n g no h y p o c h l o r i t e .  T h i s amount i s  d u r i n g copper s u l p h i d e l e a c h i n g a f t e r  i d e n t i c a l t o t h a t found  h y p o c h l o r i t e d e c o m p o s i t i o n and l o s s  o f some o f t h e i n i t i a l l y d i s s o l v e d copper iii)  ( F i g u r e s 12b,  19).  The copper c a r b o n a t e complex decomposes a f t e r  time p e r i o d .  solutions  a certain  Copper i s thus p r e c i p i t a t e d as a s o l i d compound w h i c h i s  b l a c k i n h y p o c h l o r i t e c o n t a i n i n g s o l u t i o n s and green These f a c t o r s  otherwise.  l e d t o the c o n c l u s i o n t h a t o x i d a t i o n o f copper  p h i d e s i n t h e system under study o c c u r s i n a "two s t a g e " p r o c e s s . due c o n s i d e r a t i o n o f the redox p o t e n t i a l s tation of relevant  literature,  and D e l h e z ^ ' ^ ' ^  i t was p o s t u l a t e d  2  2  sulAfter  i n v o l v e d , together with consul-  p a r t i c u l a r l y studies of L i s t e r , Prokopchik t h a t the o b s e r v e d l e a c h i n g b e h a v i o u r  i n v o l v e s o x i d a t i o n o f copper t o a t r i - v a l e n t s t a t e .  Thus the  initial,  h i g h e r copper c o n t e n t o f the l e a c h i n g s o l u t i o n i s caused by a copper***c a r b o n a t e complex w h i c h s u b s e q u e n t l y decomposes p r e c i p i t a t i n g a b l a c k copper*"*"" " s o l i d and causes s i m u l t a n e o u s 1  hypochlorite. complex.  c a t a l y t i c decomposition of  The same c y c l e i s then r e p e a t e d f o r a  T h i s a l s o decomposes a f t e r  Cu (OH) C0 2  2  3  ( F i g u r e 20, T a b l e X V I I ) .  copper**-carbonate  a certain time, p r e c i p i t a t i n g  r e m a i n i n g copper as a green powder w h i c h i s presumably  the  malachite,  the  - 90 -  3.2.1  Analysis of  copper  A b l a c k compound s i m i l a r i n appearance t o t h a t p r e c i p i t a t e d  from  f i l t e r e d l e a c h i n g s o l u t i o n s was produced by the a c t i o n o f sodium h y p o c h l o r i t e on copper h y d r o x i d e , as o u t l i n e d i n S e c t i o n 2 . 4 . 2 . t e s t s were t h e n c a r r i e d out  The f o l l o w i n g  ( i n i t i a l l y on samples made i n the absence o f  carbonate).  3.2.1.1  Effect of a c i d i f i c a t i o n A s m a l l amount o f the substance was added t o a s o l u t i o n o f 5 N  hydrochloric acid.  T h i s produced r a p i d d i s s o l u t i o n o f the powder g i v i n g  a p a l e b l u e s o l u t i o n , accompanied by v i g o r o u s gas e v o l u t i o n . of t h i s gas t h r o u g h a c a l c i u m h y d r o x i d e s o l u t i o n  ("limewater  Passage test")  showed no c l o u d i n e s s w h a t s o e v e r , i n d i c a t i n g t h a t no carbon d i o x i d e was present.  3.2.1.2  Evaluation of oxidation state by i d o m e t r i c t i t r a t i o n The amount o f excess oxygen c o n t a i n e d i n the sample was  from t h e  formula  2Cu = >  u s i n g the  determined  5  l  =  2  1 mlN. Na„S 0_ 2  2  2Na S 0 2  5  2  3  0.0635 g Cu  3  f o l l o w i n g method:  I o d i d e w i l l reduce b o t h Cu  3+  and Cu  2+  t o the +1 o x i d a t i o n s t a t e  - 91 -  with formation of a Cul p r e c i p i t a t e .  Thus a d i f f e r e n c e i n the  quantity  o f t h i o s u l p h a t e t i t r a n t r e q u i r e d i n cases a) and b) below a l l o w s the 3+ amount o f Cu a)  t o be c a l c u l a t e d :  A weighed sample o f the compound was added t o an  p o t a s s i u m i o d i d e s o l u t i o n and the l i b e r a t e d i o d i n e t i t r a t e d  acidified against  s t a n d a r d i z e d sodium t h i o s u l p h a t e . b)  An i d e n t i c a l sample was added t o d i l u t e s u l p h u r i c a c i d ,  o f c r y s t a l l i n e K I were d i s s o l v e d and the s o l u t i o n was then against N a S 0 2  2  3  as  (g)  a)  1 1 1  by I d o m e t r i c T i t r a t i o n  Cu (g)  Na S „ 0 , (0.1 N) 2 (ml) 2  3  Cu o, "o  i)  0.5  47.5  0 .302  60.3  2)  0.5  47.5  0 .303  60.6  3)  0.5  47.5  0 .302  60.3  Excess S  b)  titrated  before.  T a b l e 4: D e t e r m i n a t i o n o f C o p p e r  Sample  2 g  2°3 " 2  Cu (g)  °2 (g)  °2 Moles  1)  0.5  90.47  42.97  0.302  0 .034  0.0021  2)  0.5  91.53  44.03  0.302  0 .035  0.0022  3)  0.5  89.50  42.00  0.302  0 .034  0.0021 Av.=0.00214 M  - 92 -  T h e r e f o r e , 0.0021 M o f oxygen a r e p r e s e n t as Cu C U  2°3"  C  u  a  s  s  o  c  i  a  t  e  w i t h t h i s i s 0.002 x 2/3 M  d  =  , presumably  0.00143 M o r  0.091 g. Therefore C u ^  =  0.034 g 0 + 0.091 g Cu  =  0.125 g t o t a l ,  e q u i v a l e n t t o 25% o f t h e sample. For and  no d i f f e r e n c e was o b s e r v e d between c a s e s a) and b ) .  3.2.1.3 0  comparison, t h e same t e s t was done u s i n g a s t a n d a r d CuO sample  Measurement —  1  '  1  '"  o f oxygen e v o l u t i o n "  u s i n g a mercury column  F i g u r e 50:  Apparatus f o r Measuring Gas E v o l u t i o n  - 93 -  The gas e v o l v e d on a c i d i f i c a t i o n o f a weighed sample o f the b l a c k s u b s t a n c e was measured u s i n g a mercury column connected t o a mercury r e s e r v o i r i n a d e v i c e r e s e m b l i n g a Lunge a p p a r a t u s o u t l i n e d above (Figure 50).  The mercury column was a t t a c h e d  d i l u t e n i t r i c a c i d and the specimen sample.  to a f l a s k  containing  E v o l u t i o n o f gas on d i s s o l u -  t i o n o f each sample caused a d e p r e s s i o n o f the mercury l e v e l .  T h i s was  assumed t o be oxygen and i t s volume determined by r e d u c t i o n t o STP. Sample  :  2 g  D e p r e s s i o n of. Hg column  :  23.4 cm  Barometric pressure  : 755 mm Hg  Temperature  :  18°C  Reducing t o STP: V  G  =  234 x  755  273 x —-  =  21.56 cm Oxygen  1 mole gas a t STP o c c u p i e s 22.4 1 Therefore,  215.6 mm  215.6 22400  _  g_QQgg  M  oxygen  Copper a s s o c i a t e d w i t h t h i s as C u ^ O : 2/3 x 0.0096 Therefore,  =  0.064 M Cu o r 0.4064 g  p e r c e n t a g e o f sample w h i c h i s Cu^O^ = 0.406 g Cu  This i s i n reasonable  =  0.154 g 0 +  0.56 g o r 28% o f sample.  agreement w i t h the r e s u l t o b t a i n e d  titrametrically.  Atomic a b s o r p t i o n a n a l y s i s showed the amount o f copper  contained  i n a s o l u t i o n o b t a i n e d by a c i d d i s s o l u t i o n o f the b l a c k compound t o v a r y between 60 - 64% c o p p e r .  T h i s i s i n s u f f i c i e n t t o account f o r 70 - 75%  o f t h e sample b e i n g p r e s e n t as pure c u p r i c o x i d e , CuO, and i t i s  likely  - 94 -  t h a t some water i s a l s o p r e s e n t ,  e i t h e r as adsorbed H^O o r as a hydroxy  group.  3.2.1.4  Gas chromatography  F u r t h e r c o n f i r m a t i o n o f the presence o f a v a i l a b l e oxygen i n the sample was o b t a i n e d u s i n g t h e gas chromatograph.  A sample o f gas e v o l v e d  by a c i d d i s s o l u t i o n o f the b l a c k compound was p a s s e d t h r o u g h the chromat o g r a p h and peaks o b t a i n e d had a  N  2 °2 :  r a t  compares t o a r a t i o o f 7 8 : 4 0 , o r 1 . 9 5 : 1 ,  ^ ° ° ^ 71:46 o r 1 . 5 4 : 1 .  This  f o r a s t a n d a r d a i r sample.  The  former case t h u s showed an oxygen enrichment o f about 22%. R e p l i c a t i o n s o f the above a n a l y s e s produced v a r i a t i o n s i n the amount o f excess oxygen p r e s e n t , 30%.  b u t the v a l u e was always between 20 -  The v a r i a t i o n s appeared t o be f a i r l y random, b u t two d i s t i n c t  t r e n d s were o b s e r v e d : i)  An i n c r e a s e i n pH d u r i n g the p r e p a r a t i o n o f the sample gave  s l i g h t l y more copper " ".. No change i n the n a t u r e o f the substance was 11  1  o b s e r v e d however, and even a t pH v a l u e s o f 12 - 14 no more t h a n 30% a v a i l a b l e oxygen was o b t a i n e d . ii)  An i n c r e a s e i n the t i m e p e r i o d between p r e c i p i t a t i o n o f the  b l a c k s o l i d t o the end o f f i l t r a t i o n  seemed t o d e c r e a s e the  percentage  y x e l d o f copper  3.2.1.5  Instrumental a n a l y s i s i)  Magnetic s u s c e p t i b i l i t y  The above r e s u l t s i n d i c a t e the presence o f copper  III . i n the  - 95 -  substance produced by h y p o c h l o r i t e o x i d a t i o n o f c u p r i c s a l t s , but  it  was e v i d e n t t h a t the compound d i d not c o n s i s t e n t i r e l y o f a t r i - v a l e n t copper o x i d e .  T e s t s t o determine i t s magnetic s u s c e p t i b i l i t y were 3  therefore  carried out:  as noted p r e v i o u s l y the d  copper " "" " s a l t s produces d i a m a g n e t i c 1  1  1  c o n f i g u r a t i o n of  substances.  I n i t i a l w e i g h i n g o f samples on a magnetic b a l a n c e b o t h i n and o u t o f a f i e l d however, i n d i c a t e d t h a t the compound was p a r a m a g n e t i c . More d e t a i l e d measurements o f the gram magnetic s u s c e p t i b i l i t y were t h e n made, and a v a l u e f o r lO^Xg e q u a l t o 6 . 9 3 ± 0 . 0 3 cgs u n i t s was o b t a i n e d . U s i n g s u i t a b l e c o r r e c t i o n s f o r the diamagnetism o f copper and oxygen and a v a l u e f o r t o t a l copper c o n t e n t o f t h e sample from atomic a b s o r p t i o n a n a l y s i s gave: 10 o r magnetic moment, y e f f '  6  X Cu =  Considering that C u 3 -1 o v e r 1500 cm mol and a  1 1  =  3 •— 1 753 cm mol  1.33 B . M . compounds n o r m a l l y have 10^ x Cu v a l u e s o f  o f =1.98 M, i t can be assumed t h a t XXX 11 7 8 compound c o n t a i n s 30 - 40% copper and 60 - 70% copper ii)  Infra-red  ueff.  this  spectra  To t r y and determine the n a t u r e o f the compound more p r e c i s e l y , and e s p e c i a l l y whether the copper was p r e s e n t as an o x i d e o r a h y d r o x i d e , a sample p r e p a r e d i n m u l l form w i t h F l u o r o l u b e o i l was r u n i n the red  infra-  spectrophotometer. The r e s u l t s o b t a i n e d were f a r from b e i n g c o n s i s t e n t :  i n some cases  a d i s t i n c t absorbance peak was o b t a i n e d i n the 2700 - 3000 cm  1  wavenumber  - 96 -  band, i n d i c a t i n g the presence o f a h y d r o x y , OH g r o u p , w h i l e o t h e r gave no peaks a t a l l .  samples  D r y i n g t h e compound a t 110°C o v e r n i g h t and r e -  r u n n i n g through the I . R . spectrum caused the d i s a p p e a r a n c e o f a p r e v i o u s l y o b t a i n e d h y d r o x i d e peak i n about 80% o f a l l samples.  iii)  X-ray d i f f r a c t i o n  S m a l l samples were a n a l y z e d i n the X - r a y d i f f r a c t o m e t e r , resultant  and the  d i f f r a c t i o n p a t t e r n was compared w i t h one o b t a i n e d from a  s t a n d a r d CuO sample:  CuO Cu 0  dA  <Sample  CuO Sample  I/I  x  (Reported) o  dA  I/I*  dA  V i i  2.77  9  2.75  12  2.75  12  2.54  100  2.52  100  2.52  100  2. 34  96  2.32  96  2.32  96  1.87  28  1.87  25  1.87  25  1.71  9  1.71  9  1.71  8  1.59  14  1.58  14  1.58  14  1.51  19  1.51  21  1.51  20  1.41  21  1.42  14  1.42  12  1.38  17  1.41  16  1.41  15  1.38  18  1.38  19  1.30  6  Table 5:  X-ray D i f f r a c t i o n Patterns  f o r Copper  •  1.304  7  1.27  6  1.19  2  and Copper  Oxides  - 97 -  These r e s u l t s are s t r o n g l y i n d i c a t i v e t h a t the substance c o n s i s t s  pri-  m a r i l y o f CuO.  3.2.2  P r e c i p i t a t i o n o f copper " "" " i n presence of carbonate 1  1  1  the  Samples made by t h e a c t i o n o f sodium h y p o c h l o r i t e on c u p r i c h y d r o x i d e a t pH 9.0 i n s o l u t i o n s w h i c h a l s o c o n t a i n e d sodium c a r b o n a t e and b i c a r b o n a t e  s a l t s were v e r y s i m i l a r t o t h o s e made i n the absence o f  c a r b o n a t e , b u t t h e r e was a ' n u c l e a t i o n p e r i o d ' b e f o r e occurred.  T h i s was a s i m i l a r e f f e c t  phide l e a c h i n g , before h y p o c h l o r i t e  [co  3.2.2.1  Effect of  2 3  -]  T  any p r e c i p i t a t i o n  t o t h a t observed d u r i n g copper decomposition: Time t o p r e c i p i t a t i o n  0.5  g/1  30 seconds  2.0  g/1  5 minutes  5.0  g/1  165 minutes  10.0  g/1  12 hours  seeding  A d d i t i o n o f a s m a l l amount o f the f i l t e r e d p r e c i p i t a t e bonate-hypochlorite  sul-  to a c a r -  s o l u t i o n c o n t a i n i n g d i s s o l v e d copper caused  instan-  taneous b l a c k e n i n g o f the b l u e s o l u t i o n w i t h subsequent p r e c i p i t a t i o n o f more b l a c k m a t e r i a l . i n i t i a l carbonate  This occurred i n a l l cases, regardless of  concentration.  the  - 98 -  3.2.2.2  Effect of  acidification  A d d i t i o n o f d i l u t e n i t r i c a c i d t o the sample produced a c l e a r blue s o l u t i o n .  R a p i d gas e v o l u t i o n was o b s e r v e d and a l i m e w a t e r t e s t  i n d i c a t e d a c e r t a i n amount o f carbon d i o x i d e , CO^, was p r e s e n t .  Some  excess oxygen was a l s o d e t e c t e d by passage o f a gas sample t h r o u g h  the  chromatograph and comparison o f the o b s e r v e d r e t e n t i o n t i m e s w i t h those o f a s t a n d a r d a i r sample.  3.2.2.3  I.R.  spectra  A n a l y s i s o f the i n f r a - r e d s p e c t r a produced by samples o f t h i s b l a c k p r e c i p i t a t e gave a c o n s i s t e n t peak i n the 950 - 1000 cm * wave2number band.  T h i s i n d i c a t e s the p r e s e n c e o f an HCO^ o r CO^  Peaks i n t h e 2500 - 3000 cm  1  group.  band, c o r r e s p o n d i n g t o a hydroxy g r o u p ,  were a g a i n found t o be r a t h e r random i n  appearance.  - 99 -  3.2.2.4  X-ray analysis X-ray d i f f r a c t i o n  o  dA  I / I l - species i d e n t i f i e d  dA  16  I/I  D  - malachite  7.41  11  5.99  55  5.02  64  5.06  75  3.68  80  4.07  13  3.25  uniden : i f i e d  3.69  85  -  3.02 2.98 2.86 2.81 2.52 2.51  100  2.52  96  2.47  45  41  2.32  1.99  100  2.81  100  10  pattern:  (Reported)  CuO  Malachite 7.43  s t u d i e s gave the f o l l o w i n g d i f f r a c t i o n  2.46  35  2.43  20  2.32  17  1.99  11  1.87  25  Table 6:  X - r a y D i f f r a c t i o n P a t t e r n f o r Copper  Carbonate  - 100 -  I t i s t h u s apparent t h a t the substance made by the o x i d a t i o n o f c u p r i c h y d r o x i d e i n the p r e s e n c e o f c a r b o n a t e i s a m i x t u r e o f copper*"'""'" carbonate  ( e s s e n t i a l l y an o x i d i z e d form o f m a l a c h i t e )  and c o p p e r *  and t h a t i t i s t h i s compound w h i c h i s p r e c i p i t a t e d from l e a c h i n g  oxide,  1  solutions  on l o n g s t a n d i n g . A s i m i l a r b l a c k compound was produced by the a c t i o n o f u n d i l u t e d 'JAVEX' 7 - 8  3.2.3  (50 - 60 g/1 0C1 ) on m a l a c h i t e , b u t s o l u t i o n s c o n t a i n i n g o n l y  g/1 gave no v i s i b l e change t o the green powder.  Hypochlorite decomposition  studies  2 g samples o f each p r e c i p i t a t e , carbonate,  were a g i t a t e d  t o determine the r e s u l t s  i.e.  the o x i d e / h y d r o x i d e and  i n h y p o c h l o r i t e s o l u t i o n s a t pH 9 . 0 and 35°C,  the r a t e o f h y p o c h l o r i t e d e c o m p o s i t i o n . suggested  Graphical p l o t s of  t h i s r a t e t o be v e r y s i m i l a r t o t h a t  observed  d u r i n g c o v e l l i t e l e a c h i n g , and c o n s i d e r a b l y more r a p i d than t h a t produced by t h e analogous case o f c u p r i c o x i d e a g i t a t i o n i n h y p o c h l o r i t e  (Figure  21, Table X I X ) .  3.2.4  Analysis of leaching I t was p o s t u l a t e d  solutions  t h a t i f copper*** e x i s t s i n h y p o c h l o r i t e s o l u -  t i o n s as a r e l a t i v e l y s t a b l e c a r b o n a t e complex, then the spectrum from an u l t r a - v i o l e t - v i s i b l e s p e c t r o p h o t o m e t r i c  scan s h o u l d be  obtained  different  from t h a t produced by a copper** c a r b o n a t e complex, the c o l o u r o f w h i c h i s much l e s s i n t e n s e l y  blue.  However, the o n l y d e t e c t a b l e d i f f e r e n c e between the two s o l u t i o n s  - 101 -  - 102 -  was a s t r o n g h y p o c h l o r i t e peak i n the UV r e g i o n o f the d a r k e r sample. s e n s i b l e peaks were o b t a i n e d i n the v i s i b l e r e g i o n w h a t s o e v e r , the b l u e c o l o u r a t i o n o f the samples.  A c u p r i c c h o r i d e sample  No  despite significantly  more c o n c e n t r a t e d i n copper t h a n the carbonate s o l u t i o n s was then r u n as a s t a n d a r d , and a v e r y b r o a d peak appeared i n the 440 - 650 ym r e g i o n . I t was thus assumed t h a t the c a r b o n a t e complexes were t o o d i l u t e t o g i v e any m e a n i n g f u l peaks  3.3  ( [Cu] - 1.6 x 10  -3  M).  Sodium H y p o c h l o r i t e O x i d a t i o n of Molybdenite  0.3 g samples o f n a t u r a l m o l y b d e n i t e , M o S , were l e a c h e d i n 2  s o l u t i o n s c o n t a i n i n g 7 — 8 g/1 0C1  ± c a r b o n a t e a t pH 9.0 and 35°C. :  A  v a l u e o f 0.3 g/1 was chosen because i t r e p r e s e n t s the t y p i c a l  concentra-  t i o n o f molybdenum found i n copper rougher c o n c e n t r a t e s  flotation.  after  E x t r a c t i o n s o f the o r d e r o f 93 - 94% Mo were o b t a i n e d w i t h i n 5 m i n u t e s o f the commencement o f l e a c h i n g .  H y p o c h l o r i t e consumption  amounted t o about 12% o f the i n i t i a l v a l u e ( F i g u r e 22, T a b l e X X ) , c o r r e s -2 p o n d i n g t o the use o f 1.69 x 10 (1.77 x 10  3  moles) from MoS  2  These r e s u l t s t h e r e f o r e  moles 0C1  t o o x i d i z e 0.17 g/1 Mo  > NaMo0 . 4  c o n f i r m e d the f i n d i n g s o f Ismay,  that  h y p o c h l o r i t e i s a r a p i d and e f f i c i e n t l i x i v i a n t f o r m o l y b d e n i t e o x i d a t i o n ; b u t the f a c t t h a t g r e a t e r  than 94% molybdenum e x t r a c t i o n was not o b t a i n e d  was n o t e n t i r e l y s a t i s f a c t o r y .  The amount o f m o l y b d e n i t e sample used was  t h u s i n c r e a s e d t o produce s u f f i c i e n t r e s i d u e a f t e r X - r a y a n a l y s i s t o be c a r r i e d o u t :  leaching to  enable  Figure 22:  NaOCl oxidation of molybdenite at pH  9.0.  - 104 -  i)  X-ray fluorescence  i n d i c a t e d the f o l l o w i n g elements t o be  present i n decreasing order of  magnitude:  Fe > Pb •> Cu,Mo > Zn  ii) species,  X-ray d i f f r a c t i o n studies  i d e n t i f i e d two l e a d molybdate  Pb_MoO and Pb MoO. as b e i n g p r e s e n t . 2. b 4 r  Both o f t h e s e were  assumed t o be i n s o l u b l e , s i n c e r e - l e a c h i n g o f about 0.2 g o f  residue  produced no d e t e c t a b l e molybdenum i n s o l u t i o n . S p e c t r o s c o p i c a n a l y s i s c o n f i r m e d t h a t the c o n c e n t r a t e d i d not c o n t a i n 100% MoS^ ( S e c t i o n 2 . 2 . 1 . 1 ( i v ) ) , and t h a t a t l e a s t t i e s were p r e s e n t .  3% o f i m p u r i -  The l e v e l o f e x t r a c t i o n o b t a i n e d t h e r e f o r e  represented  more than the apparent 94%. Samples o f r e a g e n t grade molybdenum d i s u l p h i d e were u s e d , but gave no b e t t e r r e s u l t s by X - r a y a n a l y s i s  (Figure 23).  subsequently  T h i s m a t e r i a l was shown  (SEM) t o c o n t a i n s i g n i f i c a n t amounts o f  silicon.  L e a c h i n g t e s t s were f i n a l l y c a r r i e d out w i t h m a t e r i a l g u a r a n t e e d t o c o n t a i n o v e r 98% MoS^. 24).  E x t r a c t i o n s o f n e a r l y 98% were then o b t a i n e d  (Figure  H y p o c h l o r i t e consumption was s l i g h t l y h i g h e r than f o r the o x i d a t i o n  o f an e q u i v a l e n t amount o f the n a t u r a l m i n e r a l (Table X X I ) . The p r e s e n c e o r o t h e r w i s e o f c a r b o n a t e b u f f e r r e a g e n t s was found t o have no e f f e c t  3.3.1  on molybdenum e x t r a c t i o n .  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 9.0  In o r d e r t o determine the s e l e c t i v i t y o f molybdenum e x t r a c t i o n molybdenite-copper  s u l p h i d e m i x t u r e s , samples o f b o t h m i n e r a l s were  from  Figure 23:  NaOCl oxidation of reagent grade molybdenum disulphide. -  - 106 -  1  0.0  Figure 24:  1 12.0  1  1  1  36.0  48.0  TIME WINS! 24.0  NaOCl oxidation of 98% molybdenum disulphide.  To 60.0  - 107 -  leached simultaneously. was o b t a i n e d , g/1).  I n the p r e s e n c e o f c a r b o n a t e ,  89% Mo e x t r a c t i o n  accompanied by d i s s o l u t i o n o f 2 - 3% o f the copper  (-0.12  H y p o c h l o r i t e consumption i n the p r e s e n c e o f a l l t h r e e copper  m i n e r a l s was v i r t u a l l y the same as f o r o x i d a t i o n o f m o l y b d e n i t e ( F i g u r e s 25a, 26a, 27a, T a b l e s XXII -  alone  XXIV).  Removal o f c a r b o n a t e from the system r e s u l t e d i n n e g l i g i b l e amounts of  copper b e i n g d i s s o l v e d , but a l s o produced a s i g n i f i c a n t decrease i n the  l e v e l o f molybdenum e x t r a c t i o n :  74% Mo d i s s o l u t i o n was o b t a i n e d i n the  p r e s e n c e o f c o v e l l i t e , 77% i n the p r e s e n c e o f c h a l c o c i t e and 79% w i t h chalcopyrite  ( F i g u r e s 25b, 26b, 27b, T a b l e s XXII -  To c o n f i r m t h a t t h i s was a r e a l e f f e c t ,  XXIV).  and not caused by the  s m a l l amount o f M0S2 sample used g i v i n g u n r e p r e s e n t a t i v e r e s u l t s , of  c h a l c o p y r i t e were l e a c h e d w i t h 5 g ' r e a g e n t g r a d e '  wise i d e n t i c a l c o n d i t i o n s .  M0S2 under  10 g other-  A 2% l o s s o f molybdenum o c c u r r e d i n the  p r e s e n c e o f c a r b o n a t e and a 4 - 5% l o s s i n the absence o f c a r b o n a t e (Table X X V ) . S c h e i n e r e t a l . s t a t e d t h a t copper molybdate compounds were t o be d e t r i m e n t a l  found  t o good molybdenum r e c o v e r y i n the U . S . Bureau o f  20/22 Mines p r o c e s s .  E x p e r i m e n t s were t h e r e f o r e c a r r i e d o u t to see i f  copper molybdate f o r m a t i o n c o u l d be i n d u c e d , a l t h o u g h i n the  present  s t u d y i t appeared t h a t the g r e a t e r molybdenum l o s s was o c c u r r i n g from s o l u t i o n s c o n t a i n i n g no d i s s o l v e d c o p p e r : i)  Copper s u l p h a t e  during molybdenite ii)  s o l u t i o n was added dropwise from a b u r e t t e  leaching.  Sodium molybdate s o l u t i o n was added t o a c o v e l l i t e l e a c h  under s i m i l a r c o n d i t i o n s .  - 108 -  Figure 25 (a) : NaOCl oxidation of molybdenite and c o v e l l i t e i n the presence of carbonate buffer.  - 109  Figure 25 (b):  -  NaOCl oxidation of molybdenite and c o v e l l i t e i n the absence of carbonate buffer.  - 110 a  .Q.O  12.0  24.0  36.0  48.0  60.<&  TIMECMINSJ Figure 26 ( a ) : NaOCl oxidation of molybdenite and chalcocite i n the presence of carbonate buffer.  - Ill-  o  O.O-  12.0  24.0  36.0  48.0  60  in  in  pi-I CO  in. r-  + MO EXTRACTION  in  OJ  x  a en  NAOCL CONCENTRATION  in  in  CO Figure 26 (b):  12.0  24.0  36.0  TIME(MINS)  48.0  60.0  NaOCl oxidation of molybdenite.and chalcocite i n the absence.of carbonate buffer.  - 112 -  o 0.0  a.  12.0 _1  24.0  36.0  48.0 _l  60  .na  in .a  in £-1  in.  in to  a_ ID  in  x  LU  o  -z.  UJ  63  *<  O  6D in  "1—I  o  00  CE  z.  + M0 EXTRACTION  C3  in  x  NflOCL CONCENTRATION  in  in  OJ"  C3  0.0  Figure 27 (a)  12.0  TIME(MINS) 24.0  36.  48.0  NaOCl oxidation of molybdenite and chalcopyrite in the presence of carbonate buffer.  60.0  - 113 -  Figure 27 (b):  NaOCl oxidation of molybdenite and chalcopyrite in the absence of carbonate buffer.  - 114 -  I n b o t h runs copper and molybdenum c o n t e n t s were m o n i t o r e d w i t h respect to time.  I n t h e former case no copper was d e t e c t e d  b u t s i g n i f i c a n t amounts o f molybdenum were removed.  in solution,  The p r e s e n c e o f  copper was a l s o d e t e c t e d on the m o l y b d e n i t e s u r f a c e a f t e r  leaching.  I n t h e second case w i t h no c a r b o n a t e p r e s e n t and hence no copper d i s s o l u t i o n , n e a r l y 20% o f the molybdenum added t o the system was l o s t from solution after  3.3.2  60 minutes a g i t a t i o n  (Tables X X V I ,  XXVII).  L e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e s a t pH 5.5  A pH v a l u e o f 9.0 had been m a i n t a i n e d i n a l l experiments  reported  t o d a t e , l a r g e l y because t h i s was p r e v i o u s l y found t o be b e n e f i c i a l by Ismay f o r two r e a s o n s : i)  pH 9.0 i s the p o i n t a t w h i c h a maximum r a t e o f m o l y b d e n i t e  o x i d a t i o n o c c u r s i n sodium h y p o c h l o r i t e ii)  solutions.  I t i s c o i n c i d e n t l y t h e pH v a l u e a t w h i c h c h l o r a t e  production  i s minimized during hypochlorite decomposition. I n v i e w o f the adverse e f f e c t s  apparently  caused by i n t r o d u c t i o n  o f copper m i n e r a l s i n t o the system however, the l e a c h i n g o f m o l y b d e n i t e on the a c i d s i d e o f n e u t r a l i t y was i n v e s t i g a t e d .  A pH v a l u e o f  was chosen because t h i s i s below the r e g i o n i n w h i c h c h l o r a t e  5.5  production  i s most r a p i d (6.0 - 7.0) . I n most cases m o l y b d e n i t e was l e a c h e d f o r 5 - 1 0 any copper samples were added t o the Sodium  bicarbonate  minutes  before  system.  was added one gram a t a t i m e , a f t e r  s u l p h i d e a d d i t i o n , and t h i s m a i n t a i n e d the d e s i r e d pH v a l u e  copper  initially.  - 115 -  A f t e r 10 g o f r e a g e n t had been added, and i n cases where no c a r b o n a t e was used,  sodium h y d r o x i d e was used as a b u f f e r r e a g e n t , as b e f o r e .  results  The  c l e a r l y showed t h a t an even g r e a t e r l o s s o f molybdenum o c c u r r e d  under t h e s e c o n d i t i o n s .  L e a c h i n g o f m o l y b d e n i t e a l o n e gave o v e r 90%  r e c o v e r y , b u t the i n t r o d u c t i o n o f c o v e l l i t e , c h a l c o c i t e o r c h a l c o p y r i t e reduced the l e v e l o f molybdenum i n s o l u t i o n t o about 10% ( F i g u r e s 28 30a, T a b l e s X V I I I - X X X ) .  The amount o f copper d i s s o l v e d was a l s o much  lower than t h a t found l e a c h i n g CuFeS^ o r CuS a l o n e a t pH 5 . 5 . A d d i t i o n o f sodium b i c a r b o n a t e slightly  t o the system i n c r e a s e d t h i s  value  (Table X X X I I ) , but d i d n o t h i n g t o p r e v e n t the p r e c i p i t a t i o n o f  molybdenum ( F i g u r e s 28 - 3 0 b ) .  I t was thus presumed t h a t copper m o l y b -  date r e a d i l y formed a t t h i s pH l e v e l . as a c a t a l y s t l o s s o f OC1  Furthermore t h i s substance a c t e d  f o r h y p o c h l o r i t e d e c o m p o s i t i o n as shown by the v e r y r a p i d accompanying molybdenum p r e c i p i t a t i o n .  t h e l i x i v i a n t was h i g h e r i n experiments  The consumption o f  l e a c h i n g only molybdenite  at  -2 pH 5.5 t h a n f o r t h e c o r r e s p o n d i n g case a t pH 9.0  (8.3 x 10  M 0C1  for  -3 5.72 x 10  M Mo w h i c h i s h i g h e r than the s t o i c h i o m e t r i c requirement  of  9 moles OC1 per mole M o S ) . 2  A number o f runs were c a r r i e d out a t s l i g h t l y h i g h e r pH v a l u e s : 6.0,  6.5 and 7 . 0 , t o determine the e f f e c t  on molybdenum r e c o v e r y .  Con-  s i d e r a b l e l o s s e s o f b o t h molybdenum and [OC1 ] a g a i n o c c u r r e d i n the p r e s e n c e o f copper m i n e r a l s w i t h no c a r b o n a t e i n the system, b u t was s i g n i f i c a n t l y i n c r e a s e d on a d d i t i o n o f NaHCO^.' m o l y b d e n i t e l e a c h a t pH 6.5 w i t h b i c a r b o n a t e  recovery  A chalcocite/  i n the system gave 89%  Mo e x t r a c t i o n and t h e copper and h y p o c h l o r i t e c o n c e n t r a t i o n s  i n solution  m a i n t a i n e d a c o n s t a n t v a l u e f o r the d u r a t i o n o f the e x p e r i m e n t .  I n an  -116-  Figure 28:  NaOCl oxidation of molybdenite at pH.5.5.  - 117  TIME Figure 29:  -  minutes  NaOCl leaching of Chalcopyrite/Mplybdenite  at pH  5.5.  - 118 °0.0  0.0  12.0  12.0  24.0  24.0  35.0  36.0  48.0  48.0  TIME(MINS) Figure 30 (a): NaOCl oxidation of molybdenite and c o v e l l i t e at pH 5.5 i n the absence of NaHC0_.  60.&  60.0  - 119 -  -0.0  12.0  24.0  36.0  48.0  TIME TMINS1 Figure 30 (b): NaOCl oxidation of molybdenite'and c o v e l l i t e at pH 5.5 i n the presence NaHCO-.  B0.&  - 120 -  i d e n t i c a l r u n c a r r i e d o u t i n the absence o f b i c a r b o n a t e , i n t r o d u c t i o n o f the c h a l c o c i t e sample reduced the molybdenum i n s o l u t i o n from 80% t o 15% w i t h i n 30 minutes  (Figure 31a,b, Tables XXXIII,  XXXIV).  The copper  d i s s o l v e d i n i t i a l l y a l s o d e c r e a s e d w i t h r e s p e c t t o t i m e , and t h e r e was a rapid loss of hypochlorite. The  f a c t t h a t copper was e n t i r e l y r e s p o n s i b l e f o r molybdenum  p r e c i p i t a t i o n was c o n f i r m e d by a s i m i l a r experiment u s i n g s y n t h e t i c CuS a t pH 6 . 0 .  R e s u l t s showed the same molybdenum l o s s e s o c c u r r e d w i t h o u t  b i c a r b o n a t e i n the system, and t h a t t h i s was p r e v e n t e d by l e a c h i n g w i t h NaHC0 p r e s e n t 3  ( F i g u r e 3 2 a , b , T a b l e s XXXV,  XXXVI).  Molybdenum d e p r e s s i o n l e s s e n e d s l i g h t l y as the pH was increased: extraction.  a CuFeS^/MoS^ l e a c h a t pH 7.0 w i t h no c a r b o n a t e gave 30% Mo Subsequent a d d i t i o n o f sodium b i c a r b o n a t e i n a s i m i l a r r u n  i n c r e a s e d t h i s t o o v e r 95%.  The h y p o c h l o r i t e decomposed more r a p i d l y i n  the l a t t e r case ( F i g u r e 3 3 a , b , T a b l e X X X V I I ,  3.3.3  further  XXXVIII).  Copper molybdate To d e t e r m i n e more about the c o n d i t i o n s o f f o r m a t i o n o f t h i s  sub-  s t a n c e , e s p e c i a l l y w i t h r e s p e c t t o p H , experiments were c a r r i e d out i n b o t h a c i d and a l k a l i n e s o l u t i o n s i n w h i c h e q u i - m o l e c u l a r s o l u t i o n s o f sodium m o l y b d a t e , Na^MoO^ and copper s u l p h a t e , CuSO^ were m i x e d .  A t pH  9.0 a f i n e b l u e - g r e e n p r e c i p i t a t e was o b s e r v e d w h i l e a t pH 5.3 a d a r k e r green g e l a t i n o u s p r e c i p i t a t e was v i s i b l e .  A n a l y s i s o f each s o l u t i o n  b o t h b e f o r e and a f t e r m i x i n g r e v e a l e d t h a t : i)  a t pH 5.3 copper and molybdenum were l o s t from s o l u t i o n i n a  s t o i c h i o m e t r i c r a t i o o f 1:1.  - 121 -  Figure 31 (a):  NaOCl oxidation of molybdenite and chalcocite at pH 6.5 i n the presence of NaHCO-..  - 122 °-0.0  12.0  24.0  36.0  48.0  .  TIMF(MINS) Figure 31 (b): NaOCl oxidation of molybdenite-and chalcocite at pH 6.5 i n the absence of NaHCO-.  60.$  - 123 °-0.0  § J  0.0  12.0 1  12.0  24.0 1  24.0  36.0 1  36.0  48.0 1  48.0  60.&  UCN  60.0  TIME(MINS) Figure 32 (a):  NaOCl oxidation of molybdenite and cupric sulphide at pH 6.0 i n the presence of bicarbonate.  - 124  Figure 32 (b): NaOCl oxidation of molybdenite and cupric sulphide at pH 6.0 i n the absence of bicarbonate.  -125  -  Figure 33 (a): NaOCl oxidation of molybdenite and chalcopyrite at pH 7.0 i n the presence of NaHC0„.  - 126 -  o  0.0  12.0  24.0  48.0  36.0  60  _l  .a  in a  in  a en  in _ r-  in  ID  z.  O  i—i  h-  a:  •I—  ID 2 1 LU CJ  O O  CE  a  MO EXTRRCTION v NAOCL CONCENTRATION * X  in  r 24.0  Figure 33 (b):  36.  a  o  48.0  TIME(MINS)  NaOCl oxidation of molybdenite and chalcopyrite at pH 7.0 i n the absence of NaHC0 . 3  60,0  - 127 -  ii)  a t pH 9.0 a l l the copper p r e c i p i t a t e d and a s m a l l f r a c t i o n  o f the molybdenum was a l s o l o s t from s o l u t i o n . Each p r e c i p i t a t e was l e f t to s t a n d o v e r n i g h t and then heated o v e r a steam b a t h a t 60°C f o r 1 h o u r . i)  A t pH 5 . 3 :  The s o l u t i o n s were then r e a n a l y z e d .  On s t a n d i n g , s l i g h t l y more copper and molybdenum  had dropped o u t o f s o l u t i o n , a g a i n i n an approximate Cu:Mo r a t i o o f ii)  pH 9 . 0 :  C o n v e r s e l y a t the h i g h e r p H , a g i n g had a n e g l i g i b l e  e f f e c t on the copper c o n t e n t o f s o l u t i o n (which remained v i r t u a l l y b u t t h e molybdenum c o n t e n t i n c r e a s e d a f t e r on h e a t i n g  3.3.3.1  1:1.  zero)  s t a n d i n g o v e r n i g h t , and a g a i n  (Table 7 ) .  S o l u b i l i t y o f copper molybdate A d d i t i o n o f NajyioO„ s o l u t i o n t o CuSO. o f an e q u a l c o n c e n t r a t i o n 2 4 4  -2 (10  M) was made dropwise from a b u r e t t e a t pH 5 . 4 .  I t was o b s e r v e d  t h a t about 0.8 g/1 molybdenum c o u l d be added b e f o r e any p r e c i p i t a t i o n occurred.  Copper was a l s o removed from s o l u t i o n a t t h i s p o i n t ,  after  w h i c h t h e molybdenum c o n t e n t , remained c o n s t a n t even w i t h the a d d i t i o n o f -  more molybdate s o l u t i o n : 840 ppm Mo 0.00875 M CuMo0  4  =  0.00875 M  =  1.4 g/1  (Table X L , F i g u r e 34)  A f u r t h e r t e s t o f s o l u b i l i t y was c a r r i e d out by a d d i n g some o f the filtered,  green CuMoO^ p r e c i p i t a t e t o 100 ml water and l e a v i n g i t  to  s t a n d f o r s e v e r a l weeks, d u r i n g w h i c h time the Cu and Mo c o n t e n t s o f the s o l u t i o n were p e r i o d i c a l l y m o n i t o r e d . 0.49 g/1 Cu were d e t e c t e d .  Maximum v a l u e s o f 0.75 g/1 Mo and  T h i s c o r r e s p o n d s t o a copper molybdate  128  Molybdenum Figure 34:  -  added  (moles x 10 ) 2  S o l u b i l i t y of Copper Molybdate at pH 5.0, 35°C.  - 129 -  PH  Condition  [Mo] M  [Cu] M  Before Mixing  0.00979  0.00913  —  —  After Mixing  0.00875  0.00813  0.00104  0.00100  24 Hours Stand  0.00792  0.00740  0.00188  0.00173  30 M i n a t 60°C  0.00396  0.00252  0.00583  0.00661  Before Mixing  0.00979  0.00913  —  —  After Mixing  0.007192  1.57xl0~  5  0.00260  0.00911  24 Hours Stand  0.00792  5.12xl0~  5  0.00187  0.00908  30 M i n a t 60°C  0.00849  7.08xl0~  5  0.00130  0.00906  Mo p p t M  Cu p p t M  5.3  9.0  T a b l e 7:  E f f e c t o f M i x i n g and A g e i n g E q u i - m o l e c u l a r Volumes o f Na^MoO and CuSO,, a t pH 5.3 and pH 9.0  - 130 -  s o l u b i l i t y o f 1.24 g / 1 , o r 7.83 x 10 w i t h t h e above v a l u e . sodium b i c a r b o n a t e  M which i s i n r e a s o n a b l e agreement  To c o n f i r m the e f f e c t s  observed d u r i n g l e a c h i n g ,  was added t o one o r o t h e r s o l u t i o n p r i o r t o m i x i n g .  At pH 5.3 t h i s had no e f f e c t  on e i t h e r  copper o r molybdenum p r e c i p i t a t i o n .  -3 At pH 9.0 1.57 x 10  moles Cu (100 ppm) were h e l d i n s o l u t i o n and o n l y  s l i g h t l o w e r i n g o f the i n i t i a l Mo c o n t e n t was 3.3.3.2  observed.  Catalyzed decomposition o f h y p o c h l o r i t e i n the p r e s e n c e o f copper molybdate A 2 g sample o f copper molybdate was a g i t a t e d  c o n t a i n i n g 7.0 g/1 h y p o c h l o r i t e a t pH 5.0 and 3 5 ° C .  in a solution Samples were  a t timed i n t e r v a l s and a n a l y s i s showed t h a t 50% o f the i n i t i a l  taken  hypo-  c h l o r i t e decomposed w i t h i n 35 minutes and t h a t the r a t e was almost linear.  About 4% o f t h i s d e c o m p o s i t i o n was t o sodium c h l o r a t e ,  presumably b e i n g t o oxygen and c h l o r i d e d e t a i l e d i n v e s t i g a t i o n o f the e f f e c t s temperature e t c .  the  ( F i g u r e 35, T a b l e I X L ) . No  of v a r y i n g surface  d u r i n g copper molybdate c a t a l y s i s was  area, pH, undertaken.  rest  - 131 -  (pH 5.0, 35°C)  ~ l —  I  10  30 TIME  gure 35:  minutes  Effect of Copper Molybdate on NaOCl decomposition at pH 5.0, 35°C.  50  - 132 -  3.3.3.3  X-ray a n a l y s i s  X-ray d i f f r a c t i o n following diffraction  s t u d i e s o f a copper molybdate sample gave the  pattern:  . T h i s Study  Reported o dA  0  dA  I/I  0  - 2CuMo0 'Cu(OH) 4  7.155  10  7.01  20  4.392  20  4.34  35  4.207  50  4.15  55  3.517  100  3.50  100  2.979  10  2.96  20  2.794  18  2.76  20  2.699  8  2.72  20  2.531  36  2 .67  40  2.416  22  2.50  25  2 . 313  12  2.40  20  1.728  10  2.29  25  T a b l e 8:  x - r a y D i f f r a c t i o n P a t t e r n f o r Copper Molybdate  2  - 133 -  3.3.4  S o l u b i l i t y of calcium i n hypochlorite solutions The f a c t t h a t copper and molybdenum a p p a r e n t l y  do not combine  pH 9.0 t o form a s t o i c h i o m e t r i c CuMoO^ compound, t o g e t h e r w i t h the  at  obser-  v a t i o n s made d u r i n g l e a c h i n g t h a t s o l u t i o n s c o n t a i n i n g copper as a s o l u b l e c a r b o n a t e s p e c i e s were n o t t h o s e i n w h i c h molybdenum e x t r a c t i o n was a d versely affected,  r a i s e d the q u e s t i o n t h a t o t h e r elements c o n t a i n e d  in  t h e copper s u l p h i d e m i n e r a l s as i m p u r i t i e s c o u l d be p r e c i p i t a t i n g i n s o l u b l e molybdate  salts.  An Eh-pH diagram f o r the C u - ^ O - M o O ^ was c o n s t r u c t e d  ( F i g u r e 51)  and t h i s c o n f i r m e d t h a t copper molybdate e x i s t s as a s t a b l e compound a t pH l e v e l s below about 9 . 2 . responsible i)  F u r t h e r e v i d e n c e t h a t copper was not p r i m a r i l y  f o r the molybdenum l o s s e s a t pH 9.0 was then o b t a i n e d by l e a c h i n g r e a g e n t grade molybdenum d i s u l p h i d e and  synthetic  cuprous o r c u p r i c s u l p h i d e s t o g e t h e r and o b t a i n i n g >95% molybdenum e x t r a c t i o n whether o r n o t c a r b o n a t e solution ii)  (Figure 36);  (and hence copper)  was p r e s e n t i n  and  l e a c h i n g c o v e l l i t e and m o l y b d e n i t e a t pH 1 0 . 0 , w h i c h s h o u l d  be w e l l o u t s i d e the zone o f s t a b i l i t y o f CuMoO^. c a r b o n a t e -91% o f the molybdenum was r e c o v e r e d ,  I n the p r e s e n c e o f but t h i s dropped t o o n l y  78% i n a l e a c h w i t h no c a r b o n a t e ( F i g u r e 37, T a b l e s X L I , X L I I ) . X - r a y and c h e m i c a l a n a l y s i s o f the o r e s i n d i c a t e d t h a t i r o n , c a l c i u m and l e a d were the major m e t a l l i c i m p u r i t i e s .  zinc,  L e a c h i n g i n hypo-  c h l o r i t e s o l u t i o n s produced no d i s s o l u t i o n o f l e a d o r i r o n , and o n l y n e g l i g i b l e amounts o f z i n c .  However, 0.067 g / 1 , 0.058 g/1 and 0 . 0 0 4 ' g / 1  c a l c i u m were d e t e c t e d i n s o l u t i o n d u r i n g t h e l e a c h i n g o f 10 g samples o f  Figure 36:  NaOCl oxidation of molybdenum disulphide and sulphide at pH 9.0 ± carbonate.  cuprous  Figure 37 (a): NaOCl oxidation of molybdenite and c o v e l l i t e at pH 10.0 i n the presence of carbonate buffers.  Figure 37 (b):  NaOCl oxidation of molybdenite and c o v e l l i t e at pH 10.0 i n the absence of carbonate buffers.  - 137 -  o f c h a l c o p y r i t e , c o v e l l i t e and c h a l c o c i t e r e s p e c t i v e l y Table XLV).  ( F i g u r e 38,  I t i s w e l l known t h a t c a l c i u m molybdate and c a l c i u m c a r -  bonate are b o t h i n s o l u b l e  salts.  The f a c t t h a t c a l c i u m w i l l remove molybdenum from h y p o c h l o r i t e s o l u t i o n s a t pH 9 . 0 , e x c e p t i n the p r e s e n c e o f c a r b o n a t e r e a g e n t s , was i l l u s t r a t e d by a d d i n g a c a l c i u m c h l o r i d e s o l u t i o n t o a m o l y b d e n i t e -4 leach.  L o s s o f 1.25 x 10  moles o f b o t h c a l c i u m and molybdenum was  o b s e r v e d when no c a r b o n a t e was added, b u t v i r t u a l l y a l l the c a l c i u m was removed and 98% molybdenum m a i n t a i n e d i n s o l u t i o n s w h i c h a l s o sodium c a r b o n a t e / b i c a r b o n a t e 3.3.4.1  buffers  (Tables X L V I ,  contained  XLVII).  Sodium h y p o c h l o r i t e l e a c h i n g o f calcium sulphate/calcium carbonate minerals The most commonly o c c u r r i n g c a l c i u m m i n e r a l s are c a l c i t e , CaCO^,  and gypsum, C a S o - 2 H 0 . 4  2  W i t h the assumption t h a t e i t h e r o r b o t h o f  t h e s e form the p r i n c i p a l source o f c a l c i u m i m p u r i t y i n t h e copper p h i d e m i n e r a l s under s t u d y ,  samples o f each m i n e r a l were l e a c h e d  i d e n t i c a l c o n d i t i o n s t o t h o s e used f o r  sulunder  copper/molybdenum: 2+  10 g o f CaCO^ c o n t a i n i n g 4 g c a l c i u m y i e l d e d =0.016 g Ca  in  s o l u t i o n , amounting t o 0.4% e x t r a c t i o n . 10 g o f CaSO -IjH 0 ( " P l a s t e r  o f P a r i s " ) gave 2 g/1 d i s s o l v e d  c a l c i u m w h i c h i s e q u i v a l e n t t o 64.5% e x t r a c t i o n  ( F i g u r e 39, T a b l e s I L , L ) .  That the s m a l l amount o f c a l c i u m d i s s o l v e d by the a c t i o n o f a 7 g/1 s o l u t i o n o f sodium h y p o c h l o r i t e on c a l c i t e was s u f f i c i e n t t o a d v e r s e l y a f f e c t molybdenum r e c o v e r y was c o n f i r m e d by a combined c a l c i t e / molybdenite l e a c h .  T h i s gave o n l y 80% molybdenum e x t r a c t i o n .  The same  - 138 -  J •  1  10 Figure 38:  r  1  r  r  30 50 minutes d i s s o l u t i o nTIME during NaOCl leaching of  Calcium Copper Sulphide Minerals.  - 140 -  experiment i n the presence o f carbonate produced o v e r 95% e x t r a c t i o n ( F i g u r e 40, T a b l e X L V I I I ) . 3.3.4.2  Effect of chloride concentration on c a l c i u m s o l u b i l i t y  Calcium s o l u b i l i t y increases  i n the presence o f c h l o r i d e s o l u t i o n s .  A number o f experiments were c a r r i e d o u t t o determine whether the s o l u b i l i t y o b s e r v e d d u r i n g the l e a c h i n g o f c a l c i u m m i n e r a l s i n h y p o c h l o r i t e s o l u t i o n s p r e p a r e d from a commercial b l e a c h , was i n l i n e w i t h t h a t e x p e c t e d from sodium c h l o r i d e s o l u t i o n s o f e q u i v a l e n t s t r e n g t h .  The  t o t a l c h l o r i d e c o n t e n t was v a r i e d from z e r o t o 2 M and i t was f o u n d : i)  The amount o f c a l c i u m d i s s o l v e d from 10 g samples o f b o t h  c a l c i t e and gypsum i n c r e a s e d as a f u n c t i o n o f the t o t a l c h l o r i d e c o n t e n t . (Figures 41, 43, Tables L I , L I I ) . latter  The a b s o l u t e amounts were h i g h e r i n the  case. ii)  I d e n t i c a l r e s u l t s were o b t a i n e d whether the c h l o r i d e was  p r e s e n t as NaCl o n l y , NaOCl made from ' J A V E X ' , o r as a m i x t u r e o f b o t h . iii)  The r e s u l t s were i n good agreement w i t h v a l u e s r e p o r t e d i n  the l i t e r a t u r e  for calcium s o l u b i l i t y i n chloride solutions  ( F i g u r e s 42,  44) . iv)  The r a t e o f e x t r a c t i o n was f a s t  i n a l l c a s e s and t h e r e was  a s l i g h t i n c r e a s e as the c h l o r i d e c o n t e n t was i n c r e a s e d . 3.3.4.3  Removal o f c a l c i u m from s o l u t i o n I t i s e v i d e n t t h a t l e a c h i n g m o l y b d e n i t e i n the presence o f s o l u b l e  calcium s a l t s i s undesirable.  I t was t h e r e f o r e  n e c e s s a r y t o f i n d a method  - 141 -  Figure 40:  NaOCl oxidation of molybdenite and c a l c i t e at pH in the absence of carbonate.  9.0,  - 142  -  40 TIME Figure 41:  80 minutes  E f f e c t of Chloride Concentration on Ca from CaS0 - 1/2 H 0. 4  2  dissolution  - 143  moles  Sodium  -  Chloride  1.5  0.5  _i  L5.0  1.64 CD CO jD  O  CO  •  E CO  •  E  Experimental  •2.5 o  Literature  (pH 9.0,  x  35°C)  0.84  E  E  O CO .O.  O co .O.  40 [Sodium Figure 42:  —i— 80  Chloride]  120 9  r a m s  /litre  Calcium Sulphate S o l u b i l i t y as a Function of Chloride Content.  - 144  TIME Figure 43:  -  minutes  Effect of Chloride Concentration on Ca from CaC0„.  dissolution  - 14 5 -  Figure  44:  Calcium Carbonate S o l u b i l i t y as a Function of Chloride Concentration.  - 146 -  o f removing Ca molybdenum.  2+  from t h e l e a c h i n g s o l u t i o n , w i t h o u t d e t r i m e n t  to  the  D e s p i t e the f a c t t h a t c a l c i t e i s s l i g h t l y s o l u b l e i n hypo-  c h l o r i t e s o l u t i o n s , experiment showed t h a t the p r e s e n c e o f c a r b o n a t e i n the system suppressed  f o r m a t i o n o f CaMoO^.  excess  Further  tests  2i n d i c a t e d t h a t a minimum o f 3.19 M CO^  p e r mole Ca were r e q u i r e d  to  ensure complete p r e c i p i t a t i o n as CaCO^ ( F i g u r e 4 5 , T a b l e L I I I ) . I n p r a c t i c e however, i t appeared  t h a t the q u a n t i t y o f c a r b o n a t e  r e q u i r e d by the system may be d i c t a t e d by f a c t o r s o t h e r than f o r c a l c i u m suppression. trations  I t was noted i n S e c t i o n 3 . 1 . 6 t h a t low carbonate c o n c e n -  produced a l o s s o f h y p o c h l o r i t e more q u i c k l y than h i g h e r c o n -  centrations  d u r i n g the l e a c h i n g o f Cu^S, CuS and C u F e S . 2  Experiments  i n w h i c h m o l y b d e n i t e and copper s u l p h i d e s were l e a c h e d t o g e t h e r showed 2t h i s n u c l e a t i o n time decreased  further  f o r a g i v e n [CO^  T h i s was a p p a r e n t l y due t o the p r e s e n c e o f m o l y b d e n i t e .  ]^  concentration.  CuS/MoS  2  runs  a t the 5 g/1 and 10 g/1 c a r b o n a t e l e v e l showed h y p o c h l o r i t e d e c o m p o s i t i o n to occur a f t e r  45 and 110 minutes r e s p e c t i v e l y , r e p r e s e n t i n g  o f 30 - 50% o v e r the n u c l e a t i o n t i m e f o r CuS a l o n e .  a decrease  Copper d i s s o l u t i o n  was a l s o s l i g h t l y l o w e r ( F i g u r e 46, T a b l e s L I V , L V ) . A s i m i l a r was observed w i t h C u S / M o S 22  A t the 5 g/1  [CO^  2  ]  effect  and 10 g/1 c a r b o n a t e ( F i g u r e 47, T a b l e L V I I ) . l e v e l i t was a l s o found t h a t a g r a d u a l  loss  o f h y p o c h l o r i t e o c c u r r e d c o n t i n u o u s l y from the b e g i n n i n g o f a g i t a t i o n and b e f o r e t h e r a p i d l o s s caused by c o p p e r  1 1 1  catalysis.  L e a c h i n g CuS i n the  p r e s e n c e o f sodium molybdate c o n f i r m e d t h i s t r e n d and showed l o s s o f b o t h copper and molybdenum from s o l u t i o n i n a 1:1 r a t i o s u g g e s t i n g t h a t some CuMoO. forms even i n the p r e s e n c e o f c a r b o n a t e . T h i s then causes 4 c a t a l y z e d h y p o c h l o r i t e decomposition before C u precipitation 1 1 1  moles Figure 4 5 :  of  Carbonate  added  Effect of Carbonate Addition on Calcium P r e c i p i t a t i o n from Solution.  120.  8  A  -6 -  A>.:  NaOCl  CD  N  --: • . C u  E  Q.  cL  •  10 g/1 [co ]  A  5 g/1  CO  =  3  14 ^  [C0 =] 3  CO  O)  (pH .9.0, 35°C) O O  CD  a  V2  CL  o  .o.  80 TIME Figure 46:  E  120  160  minutes  Copper dissolution and NaOCl Decomposition during Covellite/Molybdenite leaching at pH 9.0, with varied [C03~JT>  CO  Z  4^ 03  8  160  T  1—  1  40  1  80 TIME  Figure 47:  1  3  120  1  I  160  minutes  Copper Dissolution and NaOCl Decomposition at pH 9.0 (10 g/1 [ C 0 ] ). =  '  during Chalcocite/Molybdenite Leaching  - 150 -  ( F i g u r e 48, T a b l e L V I ) . A s i m i l a r run w i t h double t h e amount o f c a r b o n ate produced no l o s s o f copper o r molybdenum and no h y p o c h l o r i t e decomp o s i t i o n f o r o v e r 4 hours  ( F i g u r e 12b, T a b l e X V I I I ) .  L e a c h i n g i n t h e p r e s e n c e o f l a r g e r amounts o f c a r b o n a t e would thus extend the p e r i o d o f maximum molybdenum e x t r a c t i o n p r i o r t o p r e c i p i t a t i o n and 0C1  copper  1 1 1  d e c o m p o s i t i o n , as w e l l as p r e v e n t i n g CuMoO^ and  CaMoO^ f o r m a t i o n . S i l i c a t e s and phosphates a l s o have i n s o l u b l e c a l c i u m s a l t s . V a r i o u s beaker experiments were done t o i n v e s t i g a t e t h e  effectiveness  o f t h e s e r e a g e n t s i n p r e c i p i t a t i n g c a l c i u m , as an a l t e r n a t i v e t h e r e b y p r e v e n t i n g copper d i s s o l u t i o n .  to  carbonate,  Sodium meta s i l i c a t e , N a ^ i O ^ - S H ^ O  was found t o be most e f f i c i e n t i n t h i s r e s p e c t  (Table 9 ) .  A m o l y b d e n i t e / c h a l c o p y r i t e l e a c h was s u b s e q u e n t l y  c a r r i e d out i n  2the p r e s e n c e o f 1 g/1 S i O ^ (Figure 49, Table L V I I ) .  •  Almost 99% Mo r e c o v e r y was o b t a i n e d  No copper was d e t e c t e d  i n s o l u t i o n and the  h y p o c h l o r i t e m a i n t a i n e d a c o n s t a n t v a l u e f o r the d u r a t i o n o f l e a c h i n g .  - 151 -  - 152  Figure 49:  -  NaOCl oxidation of molybdenite and chalcopyrite i n the presence of Na„SiO„.  - 153 -  Additive  [Ca] i n s o l n .  (g/D  (ppm) 94.12  —  Additive  [Ca] p p t  (Moles)  (Moles) 2.35xl0~  —  Ratio 2  [C0 -]:  CO^  2  3  [Si0  2 3  0.25  90.31  4.166xl0~  0.50  53.17  8.33xl0~  1.00  18.8  0.25  2-  2+ :Ca^  9.50xl0~  4  4.39:1  3  1.02xl0~  3  8.17:1  1.66xl0~  2  1.88xl0~  3  8.83:1  20.03  3.28xl0~  3  1.85xl0~  3  1.77:1  1.00  3.45  1.31xl0~  2  2.26xl0~  3  5.04:1  0.25  53.17  3.16xl0~  3  1.02xl0~  3  3.09:1  1.00  25.20  1.27xl0~  2  1.70xl0~  3  7.47:1  3  -]:  [P0 -]: 3  4  T a b l e 9:  E f f e c t o f SiO , CO and P 0 (sodium s a l t s ) on C a l c i u m P r e c i p i t a t i o n a t pH 9 . 0 , i n H y p o c h l o r i t e S o l u t i o n s . 4  - 154 -  CHAPTER 4 Discussion  4.1.1  Sodium H y p o c h l o r i t e L e a c h i n g o f Copper S u l p h i d e M i n e r a l s i n the Presence o f Carbonate  I n i t i a l t e s t s to i n v e s t i g a t e  the l e a c h i n g b e h a v i o u r o f c o v e l l i t e ,  c h a l c o c i t e and c h a l c o p y r i t e i n sodium h y p o c h l o r i t e s o l u t i o n s a t pH 9.0 r e a f f i r m e d I s m a y s o b s e r v a t i o n made d u r i n g l e a c h i n g experiments w i t h 1  copper rougher c o n c e n t r a t e s ,  t h a t a c e r t a i n amount o f copper was r a p i d l y  e x t r a c t e d by t h e h y p o c h l o r i t e and h e l d i n s o l u t i o n . The thermodynamic s o l u b i l i t y o f copper h y d r o x i d e w h i c h i s stable  specxes a t pH 9 . 0 , as g i v e n by P o u r b a i x  73  i s 8.0 x 10  -9  the  which i s  s e v e r a l o r d e r s o f magnitude l e s s than t h e observed e x p e r i m e n t a l  value  -3 o f 10  M.  occurring. series,  I t t h u s seemed l i k e l y t h a t c o m p l e x i n g o f some k i n d was Copper, i n common w i t h o t h e r elements o f the f i r s t  transition  i s capable o f forming aqueous complexes w i t h a l a r g e number o f  a n i o n s , but t h e s e are more l i m i t e d on the a l k a l i n e s i d e o f than i n a c i d s o l u t i o n s .  neutrality  The most common a t h i g h e r pH l e v e l s are ammonia  and c y a n i d e , but t h e o n l y components p r e s e n t i n t h e system under were c h l o r i d e (as CI  and as 0C1 ) and c a r b o n a t e ,  study  as w e l l as s u l p h i d e c o n -  t a i n e d i n the copper o r e s w h i c h would be expected t o o x i d i z e t o  sulphate,  2SO^  , i n hypochlorite solution.  To determine  i f one o r more o f t h e s e  s p e c i e s c o u l d complex copper under the p r e s c r i b e d c o n d i t i o n s , literature i)  relevant  was r e v i e w e d and i t was f o u n d : C e r t a i n c u p r i c c h l o r i d e complexes are known t o e x i s t ,  but  - 155 -  39,40 are found p r e d o m i n a n t l y i n a c i d s o l u t i o n . ii)  Copper h y p o c h l o r i t e can e x i s t i n aqueous s o l u t i o n b u t  the  o n l y known method o f p r e p a r a t i o n i s w i t h a c i d i c h y p o c h l o r i t e , and the 79 species i s r e l a t i v e l y unstable.  Various references  t o Cu - 0C1  complexes were found but none c o n t a i n e d d e f i n i t e p r o o f t h a t such a complex c o u l d be made. iii)  B i v a l e n t copper can combine w i t h v a r i o u s i n t e r m e d i a t e  sul-  phur o x i d a t i o n s p e c i e s t o form a number o f s a l t s ,  such as CuS„0 ' 4 H „ 0 , z 6 2 79 CuS^Og, some o f w h i c h are s o l u b l e i n aqueous s o l u t i o n . iv)  C u p r i c carbonate  complexes e x i s t , and are r e l a t i v e l y s t a b l e  27-40 in alkaline solution. Thus carbonate  seemed t o be the most l i k e l y c o m p l e x i n g agent a t  a pH v a l u e o f 9 . 0 , and the f a c t t h a t the l e a c h i n g s o l u t i o n s showed such s t r o n g b l u e c o l o u r a t i o n f o r the amounts o f copper t h e y c o n t a i n e d was 27 30 31 i n l i n e w i t h o b s e r v a t i o n s made by D e v i l l e , P i c k e r i n g and Appleby t h a t the a l k a l i n e ' c u p r i c a r b o n a t e s '  '  '  have a c h a r a c t e r i s t i c deep b l u e  colour. A l t h o u g h s l i g h t v a r i a t i o n s i n t h e amount o f copper d i s s o l v e d o c c u r r e d between the t h r e e m i n e r a l s , they were a l l o f the same magnitude -3 (0.12 - 0.13 g/1 e q u i v a l e n t t o 2.0 x 10  M copper).  The f a c t t h a t the same amount o f sample was used i n each c a s e , i m p l y i n g t h a t d i f f e r e n t amounts o f copper were i n i t i a l l y p r e s e n t , that t h i s value represented  the maximum amount o f copper w h i c h i s s o l u b l e  under the g i v e n c o n d i t i o n s o f pH, temperature F o r a t o t a l carbonate s o l u b i l i t y of copper  1 1  suggests  and c a r b o n a t e  concentration.  c o n t e n t o f 10 ^ M, De Zoubov e t a l . show the  t o be 4 . 0 x 10 ^ M a t pH 9 . 0 , where i t e x i s t s  as  - 15'6 -  the c u p r i c a r b o n a t e i o n CuCCO^)^  (Figure 51).  This i s  slightly  lower than the v a l u e o b t a i n e d i n t h i s study and s u g g e s t s t h a t  carbonate 2-  may n o t be the o n l y c o m p l e x i n g agent f o r c o p p e r .  Assuming t h a t  forms the major complex s p e c i e s , however, and t h a t a l l the a s s o c i a t e d w i t h e x t r a c t e d copper i s o x i d i z e d t o s u l p h a t e , can be d e s c r i b e d by the CuS  +  Cu(C0 ) 3  2  sulphide the r e a c t i o n  equation:  4NaOCl  +  2NaOH  Cu(C0 ) 3  2-  + +  2  2HCC> ~  >-  3  4NaCl  +  Na S0 2  4  +  2H 0  The r e a s o n s why such a p p a r e n t l y random v a r i a t i o n s i n the copper  (55)  2  content  o c c u r r e d t h r o u g h o u t a l e a c h i n g r u n , o r why a b l a c k p r e c i p i t a t e was d e p o s i t e d from f i l t e r e d s o l u t i o n s on s t a n d i n g o v e r n i g h t , were n o t immediately  4.1.2  apparent.  Removal o f Carbonate from the System Experiment c o n f i r m e d t h a t the carbonate b u f f e r components were  p r i m a r i l y r e s p o n s i b l e f o r h o l d i n g copper i n s o l u t i o n :  n e g l i g i b l e amounts  were d i s s o l v e d when the NaHC0 /Na CC> m i x t u r e was r e p l a c e d by sodium 3  2  3  hydroxide s o l u t i o n . T h i s would seem t o be an i m p o r t a n t f a c t o r when c o n s i d e r i n g a l e a c h i n g p r o c e s s w h i c h r e q u i r e s the s e l e c t i v e e x t r a c t i o n o f molybdenum from p o r p h y r y copper o r e s .  The s o l u b i l i t y o f copper i n c a r b o n a t e  solu-  t i o n s has been o v e r l o o k e d by a number o f o t h e r workers i n c l u d i n g S h a p i r o 14 and K u l e n k e v a  who c l a i m e d t h a t i n a c a r b o n a t e  system, any m e t a l  p h i d e s o t h e r than molybdenum would be p r e c i p i t a t e d as i n s o l u b l e  sul-  carbonates;  - 15-7 -  and Bhappu  and S c h e i n e r e t a l .  '  '  b o t h o f whom suggested  hypo-  c h l o r i t e l e a c h i n g i n the p r e s e n c e o f c a r b o n a t e would g i v e a s e l e c t i v e molybdenum l e a c h . However, the p o t e n t i a l advantage o f removing the c a r b o n a t e , hence any s o l u b l e c o p p e r , effects  from the system i s o f f s e t by the  on t h e h y p o c h l o r i t e .  and  observed  The s m a l l amounts o f copper d i s s o l v e d i n  the c a r b o n a t e b u f f e r e d case consumed v e r y l i t t l e h y p o c h l o r i t e and no further  l o s s o f s t r e n g t h was o b s e r v e d f o r up t o f o u r hours l e a c h i n g .  On  the o t h e r hand, l e a c h i n g w i t h no c a r b o n a t e caused r a p i d d e c o m p o s i t i o n o f t h e h y p o c h l o r i t e , accompanied by a drop i n t h e pH o f the necessitating  solution,  the a d d i t i o n o f sodium h y d r o x i d e as an e x t e r n a l  buffer  component. Sodium h y p o c h l o r i t e i s a s t r o n g o x i d a n t and i t i s l i k e l y the s u r f a c e s it.  that  o f t h e copper m i n e r a l s are r a p i d l y o x i d i z e d on c o n t a c t w i t h  A t pH 9 . 0 and w i t h no c o m p l e x i n g agent p r e s e n t , the copper  as a h y d r o x i d e on the m i n e r a l s u r f a c e ,  precipitates  t h e r e b y p r e v e n t i n g any copper  dissolution: CuS  +  4NaOCl  +  2Na0H  >- Cu(OH)  2  +  NaS0  4  +  The f a c t t h a t m o l y b d e n i t e and c h a l c o p y r i t e have  4NaCl  (56)  approximately  25 e q u a l o x i d a t i o n r a t e s suggested  t o Stumpf and Berube  that a selective  molybdenum l e a c h was n o t p o s s i b l e , but t h e s e a u t h o r s seem t o have o v e r l o o k e d the r e l a t i v e s o l u b i l i t i e s o f the two s p e c i e s i n a l k a l i n e s o l u t i o n . The f o r m a t i o n o f a s u r f a c e h y d r o x i d e i s presumably the cause o f observed h y p o c h l o r i t e decomposition: t r a n s i t i o n metals,  i n c l u d i n g copper,  o x i d e s and h y d r o x i d e s o f v a r i o u s are known t o be a c t i v e  catalysts  the  - 158 -  /  43-51 f o r the heterogeneous d e c o m p o s i t i o n o f h y p o c h l o r i t e s o l u t i o n s . Decomposition can o c c u r e i t h e r and c h l o r a t e .  t o oxygen and c h l o r i d e o r t o c h l o r i d e  The former r e a c t i o n i s g e n e r a l l y thought t o be the more  common i n a l k a l i n e s o l u t i o n s .  I t was r e p o r t e d by P r o k o p c h i k ,  however,^  t h a t some c h l o r a t e i s produced a t h i g h pH v a l u e s , and t h a t i n the p r e s e n c e o f copper h y d r o x i d e c a t a l y s t s t h e pH i s l o w e r e d . was o b t a i n e d .  t h i s r e a c t i o n becomes more predominant  Thus a t pH 9.0 a r a t i o o f C1C> :0 o f about 3  Sodium c h l o r a t e i s u n d e s i r a b l e  3:1  2  i n a hypochlorite  u t i l i z i n g complete s a l t r e c y c l e f o r r e g e n e r a t i o n  system  o f the l i x i v i a n t .  p r o d u c t i o n o f NaClO^ i n l a r g e amounts would t h e r e f o r e  as  The  necessitate solu-  t i o n t r e a t m e n t t o remove i t ; f o r example, u s i n g S 0 r e d u c t i o n , as 20 r e p o r t e d i n t h e U . S . Bureau o f Mines p r o c e s s . C h l o r a t e has a l s o been shown t o i n t e r f e r e w i t h the subsequent r e c o v e r y o f molybdenum from l e a c h 23 24 ing solutions. ' 2  4.1.4  D e c o m p o s i t i o n P r o d u c t s D u r i n g the L e a c h i n g o f Copper S u l p h i d e M i n e r a l s The p r o d u c t i o n o f NaClO^ as a r e s u l t o f NaOCl d e c o m p o s i t i o n i n the  p r e s e n t study was found t o v a r y from m i n e r a l t o m i n e r a l .  The f a c t  that  c h l o r a t i v e d e c o m p o s i t i o n i n c r e a s e d w i t h r e s p e c t t o time d u r i n g c h a l c o c i t e l e a c h i n g , b u t decreased  i n the cases o f c o v e l l i t e and c h a l c o p y r i t e may be  associated with t h e i r r e l a t i v e c a t a l y t i c rates, considering that chalcoc i t e produced a much s l o w e r r a t e o f d e c o m p o s i t i o n than the o t h e r I n no case was a C 1 0 : 0  2  r a t i o o f a n y t h i n g a p p r o a c h i n g the 3:1  by P r o k o p c h i k a t pH 9.0 found t o  two.  reported  exist.  The most o b v i o u s r e a s o n f o r the o b s e r v e d d i f f e r e n c e s  in catalytic  - 159 -  d e c o m p o s i t i o n r a t e between c h a l c o c i t e , c h a l c o p y r i t e and c o v e l l i t e would be a d i f f e r e n c e i n the a c t i v e s u r f a c e a r e a , heterogeneous.  s i n c e the r e a c t i o n i s  C a l c u l a t i o n s f o r the o v e r a l l s u r f a c e a r e a o f -200 mesh 2  samples o f c o v e l l i t e and c h a l c o c i t e , g i v e v a l u e s o f 33,300 cm  and  2 27,000 cm  r e s p e c t i v e l y (Appendix B ) .  sufficient  t o a c c o u n t f o r the 6:1 r a t i o o b s e r v e d between the r a t e s o f  d e c o m p o s i t i o n g i v e n by CuS and C ^ S .  The d i f f e r e n c e i s t h e r e f o r e  in-  F u r t h e r m o r e , the use o f s y n t h e t i c  copper s u l p h i d e s i n d i c a t e d a c o n s t a n t r a t e o f NaOCl d e c o m p o s i t i o n f o r b o t h c u p r i c and cuprous s a l t s .  T h i s c o u l d be the a c t u a l r a t e o f c a t a l y -  s i s o f copper h y d r o x i d e , w i t h t h a t o b s e r v e d d u r i n g c o v e l l i t e and c h a l c o p y r i t e l e a c h i n g b e i n g caused by some s o r t o f "promoted c a t a l y s i s . " Both t h e s e m i n e r a l s were found t o c o n t a i n t r a c e s o f n i c k e l and c o b a l t as i m p u r i t i e s .  N i c k e l s a l t s have been shown by s e v e r a l workers to be  more a c t i v e c a t a l y s t s t h a n t h e c o r r e s p o n d i n g copper s a l t s ,  and i t  is  known t h a t n e g l i g i b l e amounts o f b o t h n i c k e l and c o b a l t can cause s i g 45 49 51 n i f i c a n t hypochlorite decomposition.  '  '  Chirnoaga a l s o  reported  t h a t the a c t i o n o f ' m i x e d ' c a t a l y s t s produced a more r a p i d r e a c t i o n than e i t h e r one a l o n e .  T h i s was c o n f i r m e d by Lewis who proposed a mechanism 45 46  f o r t h i s type o f r e a c t i o n .  '  I t i s therefore  suggested t h a t  enhanced r a t e s o f d e c o m p o s i t i o n o b s e r v e d i n the p r e s e n t  study are  by the combined a c t i o n o f copper and n i c k e l h y d r o x i d e c a t a l y s t s , a faster  the caused giving  r a t e t h a n would be produced by copper a l o n e .  The p r e s e n c e o f c a r b o n a t e i n the system o b v i o u s l y d e a c t i v a t e s the m i n e r a l s u r f a c e :  c o m p l e x i n g a s m a l l amount o f o x i d i z e d copper as 2-  the c u p r i - c a r b o n a t e i o n , C u ( C 0 ) 2  3  , prevents  formation of a hydroxide  c a t a l y s t , and the s o l u b l e copper s p e c i e s does n o t i n i t s e l f  a c t as a  - 160 -  catalyst,  4.1.5  so t h a t no h y p o c h l o r i t e d e c o m p o s i t i o n  occurs.  Sodium H y p o c h l o r i t e L e a c h i n g o f M a s s i v e Samples o f Copper S u l p h i d e M i n e r a l s E x p e r i m e n t s u s i n g massive samples were c a r r i e d out t o o b t a i n more  i n f o r m a t i o n , b o t h q u a l i t a t i v e l y and q u a n t i t a t i v e l y , of surface  reactions  occurring during leaching.  about the  nature  C o v e l l i t e was found  t o have a more r a p i d r e a c t i o n w i t h the h y p o c h l o r i t e t h a n whether o r n o t c a r b o n a t e was p r e s e n t i n the system.  C u  2  chalcocite, S  n  a  s  been  shown t o l e a c h i n a two stage p r o c e s s i n a c i d s o l u t i o n , w i t h the  second  80,81 stage r e s e m b l i n g the l e a c h i n g o f CuS o r s i m i l a r m i n e r a l .  It  is  p o s s i b l e t h a t even i n the l i m i t e d r e a c t i o n w h i c h o c c u r s on exposure hypochlorite solutions,  there i s a difference  b e h a v i o u r o f c h a l c o c i t e and c o v e l l i t e . fundamental noted  cause f o r the d i f f e r e n c e s  to  between the o x i d a t i o n  T h i s would r e p r e s e n t a more i n the r a t e s o f NaOCl d e c o m p o s i t i o n  above. The p a t c h y w h i t e a r e a s p r e s e n t on the c o v e l l i t e s u r f a c e  after  immersion i n t o h y p o c h l o r i t e c o n t a i n i n g c a r b o n a t e s o l u t i o n s f o r  short  p e r i o d s p r o b a b l y i n d i c a t e s u l p h a t e f o r m a t i o n a l t h o u g h why e l e m e n t a l  sul-  phur s h o u l d be p r e s e n t i n c e r t a i n areas as w e l l i s a l i t t l e p u z z l i n g . 16 Choppm and F a u l k e n b e r r y  reported  t h a t e l e m e n t a l s u l p h u r c o u l d be  produced d u r i n g the o x i d a t i o n o f aqueous s u l p h i d e s o l u t i o n s by h y p o c h l o r i t e whenever the r a t i o o f S:0C1  was l e s s than 1:4.  I n a l l o t h e r cases  2sulphate,  SO^  , was the o n l y end p r o d u c t .  I t i s thus p o s s i b l e  that  h y p o c h l o r i t e d e p l e t i o n o c c u r r e d i n l o c a l i z e d a r e a s o f the m i n e r a l e n a b l i n g s m a l l amounts o f s u l p h u r t o be  formed.  surface,  - 161 -  Green d e p o s i t s produced on b o t h c o v e l l i t e and c h a l c o c i t e after  surfaces  l o n g e r p e r i o d s o f exposure t o h y p o c h l o r i t e s o l u t i o n s are almost  c e r t a i n l y m a l a c h i t e , (^^(OH^CO^.  T h i s substance  forms the s t a b l e phase  (Figure 2 ) .  F u r t h e r o x i d a t i o n o f the  i n the Cu-CO^-I^O system a t pH 9 . 0 mineral surface after  the s a t u r a t i o n p o i n t f o r the c u p r i - c a r b o n a t e  species  i n s o l u t i o n has been reached w i l l r e s u l t i n p r e c i p i t a t i o n o f a b a s i c copper  carbonate. In the absence o f c a r b o n a t e ,  copper h y d r o x i d e forms on the m i n e r a l  s u r f a c e as a l i g h t g r e e n , powdery d e p o s i t .  Micro-probe a n a l y s i s confirmed  t h a t b o t h d e p o s i t s had a s i g n i f i c a n t l y i n c r e a s e d Cu:S s u r f a c e r a t i o , t o a l a r g e i n c r e a s e i n the copper c o n t e n t a t the  surface.  The appearance o f a b l a c k d e p o s i t on top o f b o t h green c o a t i n g the o r i g i n a l c o v e l l i t e s u r f a c e ,  due  substances  accompanied by a l o s s o f b l u e  c o l o u r a t i o n from the carbonate c o n t a i n i n g s o l u t i o n s was t a k e n t o be a n a l o gous t o t h e d e p o s i t i o n o f a b l a c k p r e c i p i t a t e from f i l t e r e d s o l u t i o n s o b t a i n e d d u r i n g the l e a c h i n g o f CuS and C u S powders. 2  Subsequent  i n g o f ground m a t e r i a l w i t h v a r i a b l e amounts o f c a r b o n a t e i n the  leachsystem,  51 c o n s i d e r a t i o n o f the f i n d i n g s o f P r o k o p c h i k  and o t h e r s on the mechanism  o f h y p o c h l o r i t e d e c o m p o s i t i o n i n the presence o f copper h y d r o x i d e c a t a lysts,  t o g e t h e r w i t h e x t e n s i v e a n a l y s i s o f the compounds made by the  a c t i o n o f NaOCl on copper s a l t s a t pH 9.0 c o n c l u s i o n t h a t these b l a c k substances 4.1.6  (Section 3.2.1)  l e d to  the  are t r i - v a l e n t copper compounds.  V a r i a t i o n o f t h e T o t a l Carbonate Content During Leaching  A l o w e r amount o f c a r b o n a t e  i n the l e a c h i n g system caused  less  - 162 -  copper t o be d i s s o l v e d , and i t was h e l d i n s o l u t i o n f o r o n l y a f i n i t e period of time.  T h i s time p e r i o d , and the copper c o n c e n t r a t i o n  in  s o l u t i o n were found t o be p r o p o r t i o n a l t o t h e c o n t a i n e d c a r b o n a t e . r a p i d drop i n copper c o n c e n t r a t i o n w h i c h s u b s e q u e n t l y o c c u r r e d , by s i m u l t a n e o u s  The  accompanied  h y p o c h l o r i t e d e c o m p o s i t i o n can be e x p l a i n e d by assuming  sodium h y p o c h l o r i t e i s c a p a b l e o f o x i d i z i n g copper t o the  tri-valent  s t a t e , and t h a t i t i s h e l d i n s o l u t i o n i n t h i s o x i d a t i o n s t a t e by the c o m p l e x i n g a c t i o n o f c a r b o n a t e u n t i l such time as a s o l i d  copper "'"' ' 1  compound i s a b l e t o n u c l e a t e and p r e c i p i t a t e on the m i n e r a l  1  surface.  T h i s then becomes an a c t i v e c a t a l y s t f o r h y p o c h l o r i t e d e c o m p o s i t i o n . the absence o f any c a r b o n a t e , i s therefore  the h y d r o x i d e formed on the m i n e r a l  In  surface  a copper* " " compound r a t h e r than normal c u p r i c h y d r o x i d e , 1  1  C u ( O H ) , and h y p o c h l o r i t e d e c o m p o s i t i o n presumably o c c u r s by the mechanism 2  o u t l i n e d by P r o k o p c h i k ( a p p l i c a b l e t o pH v a l u e s below 1 2 . 0 ) : C10~  +  2Cu(OH)  4Cu(OH) (4Cu(OH)  3  +  3  CIO"  2  +  H <3  > Cl~ +  2  >• 4Cu(OH)  +  2  >• 4Cu(OH)  2  °  2Cu(OH)  +  H  2  +  2  C10 ~ 3  ° +  The o b s e r v a t i o n t h a t exposure o f a s m a l l s u r f a c e a hypochlorite s o l u t i o n w i t h minimal a g i t a t i o n , copper  1 1  results  (  2H 0) 2  5  8  )  (59)  a r e a o f copper  to  i n formation of  h y d r o x i d e b e f o r e d e p o s i t i o n o f the b l a c k c o p p e r *  illustrates  (57)  3  1 1  hydroxide  s t e p ( i ) o f t h i s mechanism and subsequent h y p o c h l o r i t e decom-  p o s i t i o n would presumably f o l l o w a +2/+3 o x i d a t i o n - r e d u c t i o n c y c l e . The l o s s o f copper from s o l u t i o n c o n t a i n i n g 10 g/1 c a r b o n a t e accompanying h y p o c h l o r i t e d e c o m p o s i t i o n amounted t o about 0.06 g/1 C u .  - 163 -  I f the t o t a l s u r f a c e a r e a o f m i n e r a l p r e s e n t i s t a k e n t o be 33,000 cm 2 f o r c o v e l l i t e and 27,000 cm  f o r c h a l c o c i t e , t h e n i t can be shown t h a t  t h i s 60 ppm copper i s s u f f i c i e n t t o form a mono-molecular l a y e r c o v e r i n g the e n t i r e  surface  (Appendix B ) .  A n a l y s i s showed t h a t the compound made  i n the p r e s e n c e o f c a r b o n a t e was a c t u a l l y a t r i - v a l e n t c o p p e r  carbonate,  1 1 1  r a t h e r t h a n the t r i - v a l e n t o x i d e / h y d r o x i d e made w i t h no c a r b o n a t e p r e s e n t . The b l a c k p r e c i p i t a t e observed t o be d e p o s i t e d from f i l t e r e d l e a c h s o l u tions i s therefore  a copper " " c a r b o n a t e and i s presumably the same 11  1  substance which c o a t s the m i n e r a l s u r f a c e when p r e c i p i t a t e d from s o l u t i o n s s t i l l i n c o n t a c t w i t h m i n e r a l samples. the t r i - v a l e n t hydroxide apparently  The f a c t t h a t t h i s compound and  c a t a l y z e the d e c o m p o s i t i o n o f hypo-  c h l o r i t e a t the same r a t e i s n o t too s u r p r i s i n g ; b u t the reason why chalcocite,  c o v e l l i t e and s y n t h e t i c copper s u l p h i d e s t i l l produce  ent r a t e s o f d e c o m p o s i t i o n a f t e r  l o s s o f copper from a c a r b o n a t e system,  when i t i s assumed t h a t the e n t i r e a t e l a y e r i n each c a s e ,  differ-  surface  i s less obvious.  i s c o v e r e d by a C u  1 1 1  I t c o u l d w e l l be t h a t  carboncatalysis  i s enhanced a t c e r t a i n a c t i v e s i t e s on the m i n e r a l s u r f a c e and a l t h o u g h the e n t i r e sis.  s u r f a c e i s c o v e r e d by Cu "'""'", o n l y c e r t a i n a r e a s produce 1  cataly-  Any a r e a i n w h i c h a d s o r p t i o n can o c c u r more r e a d i l y than i n o t h e r  s u r r o u n d i n g a r e a s w i l l a c t as a p r e f e r e n t i a l  s i t e for  catalysis.  The redox p o t e n t i a l o f a sodium h y p o c h l o r i t e s o l u t i o n a t pH 9.0 has a v a l u e o f 1.2 V (Appendix B ) .  T h i s i s w i t h i n the r e g i o n shown by.  Delhez and coworkers t o c o n t a i n t r i - v a l e n t copper as a s t a b l e 74 d e s c r i b e d as h y d r a t e d  C u  0 2  3-  compound,  V a r i o u s o t h e r s t u d i e s have shown t h a t  copper " " s a l t s can be o x i d i z e d t o the +3 o x i d a t i o n s t a t e i n the p r e s e n c e 1  1  o f h y p o c h l o r i t e s o l u t i o n s , a l t h o u g h most o f t h i s work was c a r r i e d o u t  at  - 16 4  pH l e v e l s g r e a t e r t h a n 9 . 0 . ^ ' ^ ' ^ 2  -  i n fact Prokopchik s p e c i f i c a l l y  2  s t a t e s t h a t t r i - v a l e n t copper compounds cannot be made a t pH l e s s 1 1 . 5 , and the b l a c k p r o d u c t so o b t a i n e d i s m e r e l y d e h y d r a t e d hydroxide.  The p r e s e n t  than  copper  1 1  s t u d y would seem t o d i s p u t e t h i s v i e w .  I n t h e i r paper acknowledging the e x i s t e n c e o f  cupri-carbonate  i o n s and the r o l e t h e y p l a y i n the s o l u b i l i t y o f m a l a c h i t e , De Zoubov 36 et a l .  do n o t c o n s i d e r the p o s s i b i l i t y t h a t a t s u f f i c i e n t l y h i g h  redox p o t e n t i a l s a t r i - v a l e n t copper - c a r b o n a t e complex s p e c i e s e x i s t , r a t h e r t h a n the diagrams  (Figure 3 ) .  C u 2  ° 3 s o l i d substance  could  shown i n the r e l e v a n t Eh-pH  I t i s u n l i k e l y t h a t t h e s e workers used  sufficiently  s t r o n g o x i d i z i n g s o l u t i o n s t o produce such a s p e c i e s , b u t i t seems p e r f e c t l y r e a s o n a b l e t o assume t h a t a c o m p l e x i n g agent f o r c o p p e r e q u a l l y c a p a b l e o f h o l d i n g c o p p e r ^ ^ ^ i n s o l u t i o n , g i v e n t h a t the  is  1 1  aqueous  medium has a s u f f i c i e n t l y h i g h p o t e n t i a l w h i c h the h y p o c h l o r i t e s o l u t i o n does.  E q u a t i o n 55 c o u l d then be m o d i f i e d : CuS  +  4NaOCl  + 3NaOH 3 - + 3HC0 ~ Cu(C0 ) + Na S0 3  The C u tion:  3 +  i t s half  3  2  >+ 4NaCl  4  +  3H 0 2  (60)  i o n i s n o t g e n e r a l l y thought o f as b e i n g s t a b l e i n s o l u l i f e has been suggested by Magee and Wood^  o r d e r o f 25 seconds.  However, L i s t e r ,  B e r k a e t a l . ^ and o t h e r s ,  66  Malatesta,  64  3  t o be o f the  Malaprode,  65  have a l l shown t h a t c o m p l e x i n g agents such as  t e l l u r a t e s and p e r i o d a t e s w i l l s t a b i l i z e copper " "" " i n s o l u t i o n . 1  1  1  Tri-  v a l e n t c u p r a t e s are a l s o known t o be s o l u b l e and r e l a t i v e l y s t a b l e  '  b u t t h e s e substances o c c u r o n l y a t h i g h e r pH v a l u e s . Due t o i t s r e l e v a n c e t o the p r e s e n t  study, i t i s i n t e r e s t i n g  note L i s t e r ' s o b s e r v a t i o n t h a t any copper p r e s e n t  i n s o l u t i o n i n an  to  - 165 -  uncomplexed s t a t e , as Cu(OH)^ towards  f o r example, showed c a t a l y t i c a c t i v i t y  sodium h y p o c h l o r i t e ; but a d d i t i o n o f complexing i o n s t o the  prevented  any such d e c o m p o s i t i o n .  T h i s i s i n l i n e w i t h the  noted above t h a t copper e x i s t i n g i n s o l u t i o n as a C u  1 1 1  system  observation  - c a r b o n a t e com-  p l e x d i d n o t produce any h y p o c h l o r i t e d e c o m p o s i t i o n , b u t as soon as any solid material precipitated  the d e c o m p o s i t i o n r e a c t i o n was c a t a l y z e d  heterogeneously.  4.1.7  E f f e c t o f V a r y i n g the H y p o c h l o r i t e Concentration The f a c t t h a t more copper c o u l d e x i s t i n l e a c h i n g s o l u t i o n s  taining 7 - 8  g/1 h y p o c h l o r i t e i n the p r e s e n c e o f c a r b o n a t e , than  conthat  t h e r m o d y n a m i c a l l y c a l c u l a t e d by De Zoubov e t a l . f o r an e q u i v a l e n t amount o f c a r b o n a t e and no o x i d a n t , Cu  1 1 1  s u g g e s t s t h a t more copper can e x i s t as a  complex than f o r the c o r r e s p o n d i n g C u  i l l u s t r a t e d i n experiments below).  The i n c r e a s e  1 1  complex.  T h i s was a l s o  done i n the absence o f h y p o c h l o r i t e  i n s o l u b l e copper caused by an i n c r e a s e  hypochlorite concentration  i s thus a r e l a t e d phenomenon:  c h l o r i d e i s known t o i n c r e a s e  (see i n the  the p r e s e n c e o f  the s o l u b i l i t y o f c e r t a i n m e t a l s a l t s and  i n the p r e s e n t study t h i s was found t o a p p l y t o c a l c i u m i n r e l a t i o n a n o t h e r p a r t o f the work ( S e c t i o n 4 . 3 . 4 . 2 ) . t h a t copper i s an analogous  I t seems l i k e l y  to  therefore  c a s e , and t h a t w h i l e c a r b o n a t e i s the  princi-  p a l complexing a g e n t , c h l o r i d e i n c r e a s e s b o t h the s o l u b i l i t y and s t a b i l i t y o f the complex, g i v i n g a l o n g e r n u c l e a t i o n time t o C u  1 1 1  precipitation.  - 166 -  4.1.8  E f f e c t o f H y p o c h l o r i t e Removal Removal o f h y p o c h l o r i t e from a copper s u l p h i d e c a r b o n a t e l e a c h 2-  i n g system showed q u i t e c l e a r l y t h a t l e s s copper e x i s t e d as the CutCO^)^ s p e c i e s than as CuCCO^)^  3  .  I t was a l i t t l e s u r p r i s i n g t h a t any copper  a t a l l was d i s s o l v e d by a g i t a t i n g c o v e l l i t e i n a s o l u t i o n o f sodium carbonate/bicarbonate, o f t h e copper d u r i n g  but t h i s i s probably a t t r i b u t a b l e  to a i r - o x i d a t i o n  agitation.  I t i s s i g n i f i c a n t t h a t the d i s s o l v e d copper c o n t e n t o f t h e s e s o l u t i o n s c o n t a i n i n g no h y p o c h l o r i t e , was i d e n t i c a l t o t h a t c o n t a i n e d by the l e a c h i n g s o l u t i o n s a f t e r d e c o m p o s i t i o n o f the h y p o c h l o r i t e . was a s c e r t a i n e d  t h a t a t the h i g h e r v a l u e s o f t o t a l c a r b o n a t e (5.0 g / 1 ;  7.5 g/1 and 10.0 g/1) Cu  1 1  It  a second  'plateau'  c a r b o n a t e complex e x i s t e d b e f o r e  copper i n s o l u t i o n .  l e v e l corresponding to  t h i s a l s o decomposed,  the  l e a v i n g no  A t lower v a l u e s o f c o n t a i n e d c a r b o n a t e t h e amounts  o f copper and time p e r i o d s i n v o l v e d are too low t o observe a d i s t i n c t "3-stage" curve.  The r e a s o n why a s m a l l drop i n the copper c o n t e n t o f  the s o l u t i o n was so c o n s i s t e n t l y o b s e r v e d i n a l l experiments  carried  o u t i n the p r e s e n c e o f c a r b o n a t e w i t h i n the f i r s t f i v e minutes o f l e a c h i n g i s s t i l l n o t known p r e c i s e l y . saturation  I t c o u l d be a r e s u l t o f s u p e r -  by the v e r y r a p i d o x i d a t i v e a c t i o n o f h y p o c h l o r i t e on the  mineral surface,  necessitating  p r e c i p i t a t i o n o f a s m a l l amount o f  copper t o r e t a i n e q u i l i b r i u m s o l u b i l i t y . W h i l e i t i s c l e a r t h a t the b l a c k p r e c i p i t a t e p u t down from hypoc h l o r i t e c o n t a i n i n g s o l u t i o n s i s an o x i d i z e d form o f the m a l a c h i t e  precip-  itated  substance,  from copper*" " c a r b o n a t e s o l u t i o n s , 1  the appearance o f e i t h e r  and the r e l a t e d p r e c i p i t a t i o n o f copper d u r i n g l e a c h i n g i s most p e c u l i a r .  - 167 -  I s m a y ' s h y p o t h e s i s t h a t the substance c o u l d be a p a r t i a l l y o x i d i z e d s u l p h u r s p e c i e s was d i s m i s s e d by showing t h a t the same amount o f copper was d i s s o l v e d i n the p r e s e n c e o f c a r b o n a t e and h y p o c h l o r i t e whether the s t a r t i n g m a t e r i a l was a copper s u l p h i d e o r copper s u l p h a t e .  It  i s now c l e a r , however, t h a t copper*' *"'" was a l s o produced i n t h i s  study  1  d u r i n g the l e a c h i n g o f c h a l c o p y r i t e w i t h an u n s p e c i f i e d , b u t presumably s m a l l , amount o f c a r b o n a t e b u f f e r a t pH 9 . 0 , because the c u r v e s o b t a i n e d were v e r y s i m i l a r t o those shown i n F i g u r e s 11 and 13 f o r c o v e l l i t e and chalcocite leaching. i n carbonate  O b s e r v a t i o n s made d u r i n g copper s u l p h a t e  agitation  s o l u t i o n s b a r e a s t r o n g resemblance t o those i n s i m i l a r  e x p e r i m e n t s c a r r i e d out by P i c k e r i n g  28  and Appleby and L a n e .  31  These  workers found t h a t m i x i n g Na^CO^/NaHCO^ s o l u t i o n s w i t h copper s u l p h a t e o r copper a c e t a t e produced a deep b l u e s o l u t i o n which s u b s e q u e n t l y  precipi-  t a t e d e i t h e r a greeen powder, CuCOH^CO^, o r w e l l d e f i n e d b l u e c r y s t a l s assumed t o be a s o d i o - c u p r i c double s a l t , N a ^ C u ^ O ^ ) ^ .  The green powder  o b s e r v e d i n t h e p r e s e n t work i s a l m o s t c e r t a i n l y m a l a c h i t e .  Appleby  noted t h a t p r e c i p i t a t i o n o f the double s a l t c o u l d n o t be a c c e l e r a t e d by " s e e d i n g , " but i n t h i s case i t was found t h a t a d d i t i o n o f p r e v i o u s l y p r e c i p i t a t e d powder, e i t h e r as copper*"''"'" t o h y p o c h l o r i t e s o l u t i o n s , o r as m a l a c h i t e t o copper** c a r b o n a t e , p r e c i p i t a t i o n w i t h i n a very short  gave l o s s o f copper and  further  time.  T h i s would seem t o c o n f i r m t h a t the o b s e r v e d p r e c i p i t a t i o n can . o n l y o c c u r a f t e r n u c l e a t i o n o f a s m a l l amount o f s o l i d has t a k e n p l a c e , and t h a t t h i s i s the slow s t e p o f the p r o c e s s .  Filtered solutions  take  l o n g e r t o p u t down a p r e c i p i t a t e than the c o r r e s p o n d i n g l e a c h i n g s o l u t i o n s i n c o n t a c t w i t h a m i n e r a l because the m i n e r a l s u r f a c e can p r o v i d e  - 168 -  f a v o u r a b l e s i t e s on w h i c h n u c l e i can form.  Nucleation generally occurs  when the s u p e r - s a t u r a t i o n o f t h e separating phase has reached a c e r t a i n v a l u e such t h a t the a c t i v a t i o n b a r r i e r has been surmounted.  The f r e e  energy o f f o r m a t i o n o f a n u c l e u s c o n s i s t s o f two t e r m s : 3 AG.  :  =  ~  V°  M  3V  where a / a  I n -  o  a  +  4T7r  Z  0  i s the c o n c e n t r a t i o n r a t i o o r of  degree  supersaturation  V  = m o l e c u l a r volume  3  = i h t e r f a c i a l energy  r  = radius  The second term r e p r e s e n t s the work n e c e s s a r y t o c r e a t e a new s u r f a c e , i.e.  f o r the f o r m a t i o n o f a new phase, w h i l e t h e f i r s t t a k e s account o f  the energy i n v o l v e d i n making new bonds.  T h i s assumes the n u c l e i t o be  spherical. As the degree o f s u p e r s a t u r a t i o n  increases,  then AG_. w i l l  and t h i s u s u a l l y r e s u l t s i n s m a l l e r n u c l e i f o r m i n g by a decrease radius,  decrease, in  r. The term d e s c r i b i n g the r a t e o f f o r m a t i o n o f c r y s t a l n u c l e i ,  J,  can be e x p r e s s e d : J  =  A exp  -  A G_ — kT a  where A r e p r e s e n t s the e f f i c i e n c y o f i o n i c or molecular c o l l i s i o n s . Homogeneous n u c l e a t i o n i s a v e r y slow p r o c e s s w h i c h r a r e l y o c c u r s i n p r a c t i c e ; v a r i o u s f o r e i g n p a r t i c l e s can a c t as  'catalysts'  for nucleation  - 169 -  by r e d u c i n g t h e energy b a r r i e r p r e s e n t e d by AG, thus i n d u c i n g h e t e r o g e n eous n u c l e a t i o n . The i n d u c t i o n p e r i o d f o r n u c l e a t i o n may be d e f i n e d by the  k  =  expression  tc*"- * 1  where n = number o f i o n s  required  t o form a c l u s t e r o f  critical  size c = concentration  of solution  k = constant n i s e f f e c t i v e l y reduced d u r i n g heterogeneous n u c l e a t i o n by the ation of foreign p a r t i c l e s  into a nucleation  incorpor-  site.  The i n d u c t i o n p e r i o d i n v o l v e d i n the p r e c i p i t a t i o n o f copper*"'""'" from l e a c h i n g s o l u t i o n s i n the p r e s e n c e o f v a r y i n g amounts o f c a r b o n a t e under o t h e r w i s e  identical conditions,  ship w i t h carbonate  f o l l o w s an almost l i n e a r  relation-  concentration.  A f t e r n u c l e a t i o n and p r e c i p i t a t i o n o f c o p p e r leaving a s o l u t i o n containing a copper*  1  1 1 1  has  occurred  - c a r b o n a t e complex, the same  c y c l e i s repeated w i t h p r e c i p i t a t i o n of malachite a f t e r another i n d u c t i o n p e r i o d f o r t h e n u c l e a t i o n o f copper** c r y s t a l s .  Appleby's  suggestion  t h a t d e l a y e d p r e c i p i t a t i o n o c c u r s due t o a v e r y slow r a t e o f c r y s t a l l i z a 31 tion,  t h u s appears t o be r e a s o n a b l e .  His observation t h a t seeding d i d  not enhance p r e c i p i t a t i o n o f the double s a l t ,  N a 2 C u ( C 0 ) , may be an 3  i n d i c a t i o n t h a t s o l u t i o n s decomposing t o g i v e m a l a c h i t e ,  2  Cu(OH)  (CO^) ,  a r e more s u p e r - s a t u r a t e d . The r e a s o n f o r t h e observed v a r i a t i o n s  i n copper c o n c e n t r a t i o n o f  - 170 -  some l e a c h i n g s o l u t i o n s some copper  XXX  (Section 3.1.1),  p r i o r to a n a l y s i s .  i s probably p r e c i p i t a t i o n of  Pickering  28  noted t h a t excess  c o u l d i n d u c e p r e c i p i t a t i o n o f the s o l i d compound.  water  I t was found i n t h i s  study t h a t f i l t e r e d s o l u t i o n s sometimes t u r n e d b l a c k on d i l u t i o n w i t h water.  Subsequent  a n a l y s i s would t h e r e f o r e  i n d i c a t e a lower copper c o n -  t e n t than was a c t u a l l y p r e s e n t on i n i t i a l removal o f the  4.2.1  Analysis of Copper  sample.  1 1 1  Because i n s u f f i c i e n t o f the p r e c i p i t a t e d m a t e r i a l c o u l d be c o l l e c t e d t o c a r r y o u t any m e a n i n g f u l a n a l y s i s , s i m i l a r m a t e r i a l was manufactured  i n much l a r g e r q u a n t i t i e s  c h l o r i t e on copper " " s a l t s a t pH 9 . 0 . 1  1  by the a c t i o n o f sodium hypoThe b l a c k compound so formed was  assumed t o be the same as t h a t produced by L i s t e r ^ under almost i d e n t i c a l c o n d i t i o n s , w h i c h he s u b s e q u e n t l y t o g i v e a t r i - v a l e n t copper s a l t . a copper"'""'"" " h y d r o x i d e .  complexed w i t h p e r i o d a t e  or  tellurate  He presumedthe i n i t i a l m a t e r i a l was  S i m i l a r l y i n the p r e s e n t s t u d y the gas e v o l v e d  1  on a c i d i f i c a t i o n o f the b l a c k p r e c i p i t a t e was t a k e n t o be oxygen, p r o duced as a r e s u l t o f the r e d u c t i o n o f Cu ""''""  v Cu* :  1  2Cu(OH)  +  3  Cu  3+  4HC1 +  e  -  y 2CuCl  2  1  +  5^0  + ho^  2+ > Cu  (61)  The p r e s e n c e o f oxygen was proven by iodometric t i t r a t i o n and gas chromatography,  arid i t s volume measured by the use o f a mercury column.  Compounds made i n the absence o f c a r b o n a t e d i d n o t c o n t a i n carbon dioxide.  - 171 -  The r e s u l t s  c o n s i s t e n t l y showed, however, t h a t i n s u f f i c i e n t  oxygen was p r e s e n t f o r the b l a c k powder t o be 100% c o p p e r  1 1 1  ,  and  the  v a r i o u s a n a l y t i c a l methods i n d i c a t e d t h a t 25 - 30% a v a i l a b l e oxygen existed.  W h i l e t h e p e r c e n t a g e o f copper "'""'" d i d i n c r e a s e 1  s l i g h t l y with  pH, t h e r e was no s i g n i f i c a n t change i n appearance o f the compound when p r e p a r e d i n more s t r o n g l y a l k a l i n e s o l u t i o n s .  A number o f o t h e r  workers  have s t a t e d t h a t the s e s q u i o x i d e , Cu^O^, o c c u r s as a r e d compound, and t h a t i t s f o r m a t i o n i s c a t a l y z e d by the p r e s e n c e o f b a r i u m and c a l c i u m ions.  I n the p r e s e n t s t u d y , a d d i t i o n o f t h e s e i o n s t o s o l u t i o n s c o n -  t a i n i n g 0.1 M h y p o c h l o r i t e made l i t t l e d i f f e r e n c e and no r e d m a t e r i a l was e v e r I t i s therefore  to the f i n a l  product,  detected.  proposed t h a t the b l a c k compound produced i s a  mixed copper o x i d e o r h y d r o x i d e , c o n s i s t i n g p a r t i a l l y o f copper i n the +3 s t a t e , and p a r t i a l l y i n the +2 s t a t e , w i t h the l a t t e r s e n t i n g the m a j o r i t y .  actually  The f a c t t h a t i t i s b l a c k would s u p p o r t  repre-  this  72 view:  this is a characteristic  o f mixed o x i d e s .  Delhez  also  reported  o b t a i n i n g a m i x t u r e o f copper"""" "" " and copper "'", w i t h the t r i - v a l e n t 1  1  1  state  a g a i n amounting t o no more than 30% o f the t o t a l , b u t h i s compound was exclusively red.  I t s h o u l d be noted however t h a t he was u s i n g  s i g n i f i c a n t l y more c o n c e n t r a t e d  i n h y p o c h l o r i t e t h a n 0.1 M, a t a h i g h e r  pH l e v e l and w i t h a g r e a t e r i o n i c s t r e n g t h  than i n t h i s case.  i s q u i t e l i k e l y t h a t he o b t a i n e d a m i x t u r e o f the two d i f f e r e n t 30% C  u 2  °3  +  solutions  It oxides:  70% CuO w h i c h appeared r e d , w h i l e the b l a c k compound d e s -  c r i b e d here i s a c t u a l l y a mixed v a l e n c e s t a t e compound c o n s i s t i n g o f Cu^O^ and CuO t o g e t h e r . Assuming a m i x t u r e o f 75% copper"'""'" and 25% III 2+ 3+ copper the r a t i o Cu :Cu would be 3 : 1 .  - 172 -  Cu-O,  +  3CuO  "-Cu^Cv 3 6  2 3  (62)  T h i s g i v e s a compound h a v i n g an o x i d a t i o n s t a t e o f 2 . 4 . further  analogy w i t h D e l h e z ' s work, and from the r e s u l t s o b t a i n e d by  i n f r a - r e d spectrophotometry,  i t appears t h a t the compound  between an o x i d e and a h y d r o x i d e . Cu(OH) 2.5.  By  2  fluctuates  Thus i t c o u l d c o n s i s t o f Cu(OH)  g i v i n g a compound such as Cu^(OH)  3  and  w i t h an o x i d a t i o n s t a t e o f  T h i s would have a copper c o n t e n t o f about 60% w h i c h f i t s  the  e x p e r i m e n t a l a n a l y s i s more c l o s e l y . Magnetic s u s c e p t i b i l i t y t e s t s f u r t h e r is only p a r t i a l l y C u cupric oxide. was found.  1 1 1  ,  w h i l e X - r a y d i f f r a c t i o n suggested  i t t o be  No r e p o r t e d X - r a y d i f f r a c t i o n d a t a f o r copper "'""'" compounds 1  It i s possible that  d i f f r a c t i o n peaks would be  4.2.2  c o n f i r m e d t h a t the compound  C u  2°3  1  S  amorphous,  i n w h i c h case no  detected.  P r e c i p i t a t i o n o f copper " " i n the presence o f carbonate 11  1  X - r a y t e s t s c a r r i e d o u t on compounds made i n h y p o c h l o r i t e c o n t a i n i n g c a r b o n a t e s o l u t i o n s showed peaks c o r r e s p o n d i n g t o b o t h m a l a c h i t e and c u p r i c o x i d e , c o n f i r m i n g i t t o be a m i x t u r e o f a c a r b o n a t e and an oxide.  There were a l s o some u n i d e n t i f i e d peaks w h i c h c o u l d r e p r e s e n t  the  d i f f e r e n c e between Cu """ c a r b o n a t e and the Cu""*"'"'"" s a l t . 1  Infra-red  s t u d i e s and l i m e w a t e r t e s t s suggested  compound was a t l e a s t p a r t i a l l y a c a r b o n a t e . involved i n i t s preparation concentrations.  further  The n u c l e a t i o n  that  this  times  are n o t l i n e a r w i t h r e s p e c t t o c a r b o n a t e  The c o n d i t i o n s o f t e m p e r a t u r e , a g i t a i t o n e t c . were not  m a i n t a i n e d p e r f e c t l y c o n s t a n t d u r i n g p r e p a r a t i o n o f each sample however, as t h e y were i n the l e a c h i n g e x p e r i m e n t s .  I t was a g a i n shown t h a t  ' s e e d i n g ' would i n d u c e p r e c i p i t a t i o n o f the compound. B o t h o x i d e / h y d r o x i d e and c a r b o n a t e samples were found t o  catalyze  t h e h y p o c h l o r i t e d e c o m p o s i t i o n r e a c t i o n a t a p p r o x i m a t e l y the same r a t e , when added i n e q u a l amounts t o a 0.1 M s o l u t i o n .  T h i s i s t o be  because b o t h compounds c o n t a i n a p p r o x i m a t e l y the same amount o f and i t has been shown by L i s t e r , ^ P r o k o p c h i k ^ and D e l h e z ^ - 3  4  i s the a c t i v e c a t a l y s t f o r decomposition.  2  1  2+ s e t t i n g up a Cu  copper " ", 11  1  t h a t Cu"""""" 1  When none i s p r e s e n t  o x i d a t i o n o f Cu""""" must t a k e p l a c e b e f o r e the r e a c t i o n o c c u r s ,  expected,  initially  thereby  3+ /Cu  oxidation-reduction cycle.  T h i s i s presumably  why c u p r i c o x i d e showed a s l o w e r r a t e o f d e c o m p o s i t i o n under i d e n t i c a l conditions. 4.3  Sodium H y p o c h l o r i t e L e a c h i n g o f M o l y b d e n i t e , MoS,, L e a c h i n g m o l y b d e n i t e m i n e r a l i n sodium h y p o c h l o r i t e s o l u t i o n s  at  2- . pH 9.0 d i d n o t i n i t i a l l y y i e l d 100% molybdenum as MoO^ Examination of leach residues and s i l i c a ,  in solution.  r e v e a l e d the p r e s e n c e o f i r o n , c o p p e r ,  as w e l l as l e a d molybdate w h i c h i s i n s o l u b l e .  zinc  Thus t h e  assumption o f 100% MoS^ was a f a l s e one, and s p e c t r o s c o p i c a n a l y s i s o f u n l e a c h e d samples r e v e a l e d a t l e a s t a 3% i m p u r i t y c o n t e n t .  Subsequent  l e a c h i n g w i t h "98% +" molybdenum d i s u l p h i d e produced e x t r a c t i o n s excess o f 97%, c o n f i r m i n g I s m a y ' s f i n d i n g s t h a t m o l y b d e n i t e r a p i d l y and c o m p l e t e l y a t pH 9 . 0 , 0.1 M OC1 .  in  leaches  35°C and i n s o l u t i o n s c o n t a i n i n g about  H y p o c h l o r i t e consumption was found t o c o r r e s p o n d t o  the  - 174 -  previously reported MoS  2  stoichiometric +  9NaOCl  +  6NaOH  Na Mo0 2  4.3.1  4  +  :  —*  9NaCl  +  2Na S0 2  +  4  3H 0  (63)  2  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e m i n e r a l s a t pH 9.0 I t has a l r e a d y been r e p o r t e d i n c o n j u n c t i o n w i t h the  leaching  b e h a v i o u r o f copper s u l p h i d e m i n e r a l s , t h a t c a r b o n a t e p l a y s a s i g n i f i c a n t r o l e i n t h i s system b e s i d e s  that of a buffering reagent.  In a d d i t i o n  t o a c t i n g as a c o m p l e x i n g agent f o r copper and hence a s t a b i l i z e r o f  the  h y p o c h l o r i t e however, i t was a l s o found t o a f f e c t molybdenum e x t r a c t i o n . When e x c l u d e d from the system, the l e v e l o f molybdenum e x t r a c t i o n from 98% t o o n l y 76 - 84%.  dropped  The a c t u a l d e p r e s s i o n was a f u n c t i o n o f  the  p a r t i c u l a r mineral being leached. I t was p o s t u l a t e d  t h a t copper molybdate compounds were  interfering  w i t h molybdenum e x t r a c t i o n , b u t i t was r a t h e r s u r p r i s i n g t h a t the case i n which no copper was p r e s e n t i n s o l u t i o n showed the g r e a t e s t molybdenum loss.  O x i d a t i o n o f m o l y b d e n i t e i n the p r e s e n c e o f C u S 0  ed f u r t h e r  4  s o l u t i o n suggest-  t h a t p r e c i p i t a t i o n o f copper molybdate was o c c u r r i n g .  This  d i d n o t e x p l a i n why molybdenum was a l s o p r e c i p i t a t e d from a c o v e l l i t e / sodium molybdate l e a c h , i n w h i c h no copper had been d i s s o l v e d .  4.3.2  L e a c h i n g o f m o l y b d e n i t e and copper s u l p h i d e s a t pH 5.5  E x p e r i m e n t s were c a r r i e d o u t i n a c i d i c s o l u t i o n s t o see i f an  - 175 -  - 176 -  improved molybdenum y i e l d c o u l d be o b t a i n e d , even i f t h i s i n c u r r e d p r o d u c t i o n o f more sodium c h l o r a t e than a t pH 9 . 0 . Copper e x i s t s i n s o l u t i o n t o a maximum c o n c e n t r a t i o n o f 10 2+ as the Cu i o n a t pH 5 . 5 . 2+ denum e x t r a c t i o n .  Cu  -2  M  This f a c t proved very d e t r i m e n t a l to molyb-  i o n s can combine w i t h the molybdate  species  2MoO^  g i v i n g i n s o l u b l e CuMoO^.  The r a p i d l o s s o f 90% o f the molybdenum  i n s l u t i o n on i n t r o d u c t i o n o f a copper s u l p h i d e m i n e r a l can be as p r e c i p i t a t i o n o f t h i s molybdate  interpreted  salt.  The presence o r o t h e r w i s e o f c a r b o n a t e s  i n the system d i d not have  the e f f e c t o f p r e v e n t i n g molybdenum l o s s e s t h a t had been o b s e r v e d i n alkaline solutions. and non-carbonate  The o n l y d e t e c t a b l e  d i f f e r e n c e between a  carbonate  l e a c h i n the e x p e r i m e n t s a t pH 5.5 was a s l i g h t l y  h i g h e r copper c o n t e n t i n the former c a s e .  The f a c t t h a t such a s m a l l  i n c r e a s e i n p H , a v a l u e o f 6 . 0 , r e s u l t e d i n the c a r b o n a t e b e i n g a b l e t o suppress  f o r m a t i o n o f copper m o l y b d a t e , can be e x p l a i n e d by c a r e f u l 36  c o n s i d e r a t i o n o f the Eh-pH diagrams g i v e n by De Zoubov e t a l .  showing  the e x i s t e n c e o f the s t a b l e copper c a r b o n a t e compounds and complex i o n s f o r the Cu-H^O-CO^ system ( F i g u r e 3 ) .  The C u ( C 0 ) a q . m o l e c u l e e x i s t s 3  as a s o l u b l e s p e c i e s a t pH l e v e l s between 5.0 and 7.0 dependent on the t o t a l c a r b o n a t e c o n t e n t o f the s o l u t i o n . HCO^  E 1.6 x 10  i t i s s t a b l e a t pH v a l u e s above 5 . 4 ; below 2+ t h i s the copper e x i s t s e x c l u s i v e l y as the Cu i o n ( F i g u r e 5 1 ) . Thus 2+ 1  M t  A t the l e v e l used here (10 g/1  c 0  3  ] ) T  l e a c h i n g a t pH 5.5 p u t s copper a t the s t a b i l i t y boundary between Cu CujCO^) a q .  /  The e x p e r i m e n t a l r e s u l t s i n d i c a t e d t h a t copper i s o n l y com-  p l e x e d by carbonate t o a v e r y s m a l l d e g r e e ,  shown by the s m a l l  increase  i n d i s s o l v e d c o p p e r , and t h a t t h i s a s s o c i a t i o n i s i n s u f f i c i e n t t o p r e v e n t  - 177 -  copper molybdate f o r m a t i o n .  An i n c r e a s e i n pH t o 6 . 0 p u t s copper i n t o  the r e g i o n where Cu(CC> ) a q . i s s t a b l e i n s o l u t i o n , t h e r e b y p r e v e n t i n g 3  a r e a c t i o n w i t h the molybdate. 2+ however, e n a b l e s Cu  L e a c h i n g i n t h e absence o f  carbonate,  2and MoO^  t o combine as b e f o r e .  The o b s e r v e d  r a p i d d e c o m p o s i t i o n o f the h y p o c h l o r i t e was presumed t o be caused by copper molybdate c a t a l y s i s , s u g g e s t i n g a g a i n t h a t t h i s cannot form i n carbonate  s o l u t i o n s above pH 5.5 - 6 . 0 where no e x c e s s h y p o c h l o r i t e  d e c o m p o s i t i o n was o b s e r v e d . As the pH o f the l e a c h i n g system i s f u r t h e r i n c r e a s e d , the 2+ -5 s o l u b i l i t y o f the Cu i o n d e c r e a s e s t o 1.6 x 10 M. T h i s i s s t i l l s u f f i c i e n t t o g i v e a 60% l o s s o f the molybdenum, c o u p l e d w i t h an even g r e a t e r l o s s o f h y p o c h l o r i t e i ) due t o CuMoO^ c a t a l y s i s and i i ) because t h i s i s the r e g i o n i n w h i c h h y p o c h l o r i t e most r e a d i l y decomposes  to  chlorate. These f i n d i n g s would seem t o q u e s t i o n the f e a s i b i l i t y o f the U . S . Bureau o f Mines e l e c t r o o x i d a t i o n p r o c e s s a t the suggested pH l e v e l s o f 20 21 23 5.0-7.0.  '  '  The statement made i n c o n j u n c t i o n w i t h t h i s  investi-  g a t i o n t h a t a minimum o f copper s o l u b i l i t y o c c u r s a t pH 7.0 i s i n i t s e l f a l i t t l e dubious s i n c e t h i s i s shown to o c c u r f o r CuO and C u ( 0 H )  2  at a  73 value of 9.0,  and i s not g r e a t l y m o d i f i e d by the p r e s e n c e o f c h l o r i d e s .  S e c o n d l y , no mention i n the l i t e r a t u r e o f the s o l u b l e compounds C u ( O H ) C 0 2  3  o r C u C ^ C O ^ which S c h e i n e r e t a l . c l a i m as b e i n g r e s p o n s i b l e f o r copper s o l u b i l i t y i n a l k a l i n e s o l u t i o n s , has been found; and the  cupri-carbonate  2ion, Cu(C0 ) 3  2  appears t o be the o n l y s p e c i e s w h i c h can i m p a r t s i g n i f i c a n t  s o l u b i l i t y t o copper a t pH v a l u e s above 9 . 0 .  S c h e i n e r mentions  the  compound copper molybdate as b e i n g d e t r i m e n t a l t o molybdenum e x t r a c t i o n  - 178 -  and r e p o r t s d e t e c t i n g i t i n l e a c h i n g t a i l s , b u t does not appear to have s t u d i e d the c o n d i t i o n s f o r i t s f o r m a t i o n .  In t h i s  electrooxidation  p r o c e s s the pH i s a l l o w e d t o r i s e d u r i n g l e a c h i n g by t h e a d d i t i o n o f sodium c a r b o n a t e on a s e m i - c o n t i n u o u s b a s i s .  In the l i g h t o f present  findings  any copper molybdate w h i c h d i d form, would be i n the i n i t i a l s t a g e s o f a r u n when the pH i s s t i l l below 6 . 0 .  The most s u r p r i s i n g c o n c l u s i o n  o f t h e U . S . Bureau o f Mines s t u d y , however, i s the f a c t t h a t c h a l c o p y r i t e i s unaffected  by h y p o c h l o r i t e , b u t t h a t c h a l c o c i t e i s o x i d i z e d t o a  c e r t a i n e x t e n t g i v i n g s o l u b l e copper compounds w h i c h are c a p a b l e o f combining w i t h the molybdate i o n s t o form i n s o l u b l e copper m o l y b d a t e . I n the p r e s e n t study no d i f f e r e n c e ferent  i n the l e a c h i n g b e h a v i o u r o f the  dif-  copper s u l p h i d e m i n e r a l s exposed t o h y p o c h l o r i t e s o l u t i o n s has been  detected,  e x c e p t i n the c a t a l y z e d r a t e o f h y p o c h l o r i t e d e c o m p o s i t i o n .  Furthermore,  and i n c o n t r a s t  t o S c h e i n e r ' s s t a t e m e n t , i t i s i n the p r e s e n c e  o f the s o l u b l e copper compound C u ( C 0 ) 3  2  a q . t h a t copper molybdate  formation 2+  i s suppressed.  Only when copper e x i s t s i n s o l u t i o n as the c u p r i c i o n Cu  ,  i n the absence o f c a r b o n a t e o r a t pH <6.0 can a r e a c t i o n w i t h molybdate ions occur. the  T h i s s h o u l d h o l d t r u e f o r any copper m i n e r a l i n t r o d u c e d  into  system. T h i s i m p l i e s t h a t l e a c h i n g copper - molybdenum c o n c e n t r a t e s on the  a c i d s i d e o f n e u t r a l i t y i s o n l y f e a s i b l e i n the p r e s e n c e o f and i n a l i m i t e d pH r e g i o n o f =6.0 - 7 . 5 .  carbonate,  T h i s would not g i v e any i m p r o v e -  ment i n molybdenum s e l e c t i v i t y o v e r t h a t a t pH 9.0 i n t h e p r e s e n c e o f carbonate,  and would have the added d i s a d v a n t a g e  amounts o f sodium c h l o r a t e .  of producing large  B a r r and coworkers have shown t h a t  this  r e p r e s e n t s a source o f power l o s s i n the e l e c t r o o x i d a t i o n p r o c e s s and t h a t  - 179 -  i t a l s o i n t e r f e r e s w i t h subsequent molybdenum r e c o v e r y .  '  Their  s u g g e s t i o n o f l e a c h i n g a t pH v a l u e s o f 4 . 0 - 5.0 t o overcome the  chlorate  p r o b l e m , i s h a r d l y p r a c t i c a l on a c c o u n t o f the s t a b i l i t y o f copper m o l y b date i n . t h i s r e g i o n .  4.3.3  Copper molybdate  The s i m p l e m o l y b d a t e , CuMoO^, i s not w e l l documented i n the literature.  I t i s known t o be i n s o l u b l e , i n common w i t h most o t h e r 82  t r a n s i t i o n m e t a l molybdate s a l t s .  Zelikman  quotes t h i s  solubility  as 0.017 M w h i c h i s s l i g h t l y h i g h e r than t h a t found i n the p r e s e n t work o f 0.00783 M . X - r a y d a t a f o r a number o f copper molybdate s p e c i e s has been published.  The one c o r r e s p o n d i n g c l o s e l y t o d i f f r a c t i o n p a t t e r n s o b t a i n e d i n  t h i s s t u d y (Table 8 ) , i s the h y d r a t e d s p e c i e s C u ( M o O ^ ) ( O H ) 3  i n n a t u r e as the m i n e r a l L i n d g r e n i t e .  2  2  which o c c u r s  Data f o r o t h e r :copper molybdates  are shown i n T a b l e 10: Species CuMoO,, 4 CuMoO. 4 Cu Mo0 2  C u  M o 3  5  2°9  C U  4-x  C U  4-x °3°12  M O  3 12 0  M  6 °4°15 ( T h i s study C U  M  ( Cu (Mo0 ) (OH) 3  Table 10:  4  2  2  dA (1)  dA (2)  dA (3)  3.72  3.36  2.71  3.05  3.30  3.53  3.54  3.45  3.32  3.44  2.63  3.39  3.42  3.31  2.65  3.42  2.64  2.76  3.38  2.89  2.63  3.52  4.20  2.53 )  3.50  4.15  2.67 )  S t r o n g e s t X - r a y Peaks f o r V a r i o u s Copper Molybdate S p e c i e s  - 18 0 -  The c a t a l y t i c e f f e c t s  on h y p o c h l o r i t e d e c o m p o s i t i o n observed  d u r i n g l e a c h i n g i n a c i d s o l u t i o n s were c o n f i r m e d by a g i t a t i n g molybdate i n sodium h y p o c h l o r i t e s o l u t i o n s . preventing  This i s a further  copper reason  for  ' i n - s i t u ' f o r m a t i o n o f the compound even i n s m a l l amounts  during molybdenite l e a c h i n g . An Eh-pH diagram f o r the Cu-H^O-MoO^ system was c o n s t r u c t e d  to  c o n f i r m t h e thermodynamic s t a b i l i t y o f copper molybdate i n a c i d h y p o c h l o r ite solutions. CuO, CuMo0 Cu 0 . 2  3  2+ Cu  4  I n F i g u r e 52 the s o l i d s p e c i e s c o n s i d e r e d are C u , C ^ O ,  and C u 0 , and i n F i g u r e 5 3 , 2  3  C u , C u 0 , C u ( O H ) , CuMo0 2  2  4  and  I n b o t h diagrams t h e d i s s o l v e d s p e c i e s have been t a k e n as C u , +  3+ , Cu  —  2—  , Cu0 H , C u 0 2  2  2— and Mo0  4  —  , HMo0  4  .  The diagrams show the  e q u i l i b r i a between s t a b l e s u b s t a n c e s when the a c t i v i t i e s o f copper c o n t a i n i n g i o n s i n s o l u t i o n are 10 ^ M, and o f molybdenum s p e c i e s are 10  1  M.  C o n s i d e r i n g the s o l i d s p e c i e s t o be o x i d e s , F i g u r e 52 shows t h a t copper molybdate has a r e g i o n o f s t a b i l i t y from pH - 0 . 3 t o 8 . 6 5 , w i t h an o x i d a t i o n p o t e n t i a l v a r y i n g from =:0.03 t o 2.4 V . s h o u l d be no i n t e r f e r e n c e tion.  An i n c r e a s e  f o r CuMo0 it  4  Thus a t pH 9.0 t h e r e  w i t h molybdenum e x t r a c t i o n from CuMo0  4  forma-  i n copper c o n c e n t r a t i o n would d e c r e a s e the pH l i m i t  s t a b i l i t y , w h i l e d e c r e a s i n g molybdenum a c t i v i t y would i n c r e a s e  (and v i c e v e r s a ) . I n F i g u r e 53, i n w h i c h the h y d r o x i d e s are shown as the  stable  phase, the zone o f copper molybdate s t a b i l i t y i s extended s l i g h t l y t o a pH v a l u e o f 9 . 1 8 .  As t h e h y d r o x i d e i s the m e t a - s t a b l e phase and would  form p r i o r t o the o x i d e , i t i s apparent from t h i s diagram t h a t CuMo0 f o r m a t i o n c o u l d pose a problem t o a l e a c h a t pH 9 . 0 .  4  I t a l s o shows  c l e a r l y why a m o l y b d e n i t e - copper s u l p h i d e l e a c h would not be  feasible  - 181 -  Figure 52:  Eh-pH diagram f o r the system Cu-H 0 - M 0 (oxide species). ( A c t i v i t i e s of copper ions 10 M and a c t i v i t i e s of molybdenum ions 10 M). 2  o  4  _6  _1  \  - 182 -  Figure 53:. Eh-pH diagram f o r the system Cu-H 0 - M Q O ^ (hydroxide system). ( A c t i v i t i e s of copper ions 1 0 ~ M and a c t i v i t i e s of molybdenum ions 1 0 M ) . 2  6  _ 1  - 18.3 -  i n the pH r e g i o n from 5.0 - 7 . 0 , and i l l u s t r a t e s t h a t copper  formation  would n o t be encountered i n a c i d s o l u t i o n s due t o the h i g h e r redox p o t e n t i a l o f the +3 s t a t e . A l t h o u g h copper molybdate c o u l d t h e r e f o r e  e x i s t a t pH 9.0 from a  thermodynamic p o i n t o f v i e w , t h e f a c t t h a t no copper was d i s s o l v e d i n the absence o f c a r b o n a t e ,  t o g e t h e r w i t h r e s u l t s o b t a i n e d from l e a c h i n g  w i t h s y n t h e t i c copper s u l p h i d e s and a t pH 1 0 . 0 ( S e c t i o n 3 . 3 . 4 ) , c o n f i r m e d t h a t copper i t s e l f was n o t the p r i n c i p a l cause o f poor molybdenum r e c o v e r y a t t h i s pH v a l u e . I n a d d i t i o n t o t h i s , a g i n g o f copper c o n t a i n i n g molybdate s o l u t i o n s showed t h a t a t pH 5.5 CuMoO^ r e a d i l y formed as a s t o i c h i o m e t r i c compound w h i l e a t pH 9.5 a c o - p r e c i p i t a t i o n phenomenon o c c u r r e d .  Any copper added  t o a s o l u t i o n a t t h i s pH w i l l p r e c i p i t a t e as C u ( 0 H ) , and the f a c t 2  that  some molybdenum dropped o u t o f s o l u t i o n i n i t i a l l y b u t reappeared on s t a n d i n g o r h e a t i n g , i s s t r o n g l y i n d i c a t i v e o f the molybdenum c o - p r e c i p i t a t i n g w i t h the  copper.  A s i m i l a r e f f e c t would e x p l a i n why molybdenum was l o s t from a l e a c h i n g s o l u t i o n t o w h i c h copper s u l p h a t e was added a t pH 9 . 0 ,  i.e.  due t o c o - p r e c i p i t a t i o n w i t h the copper as C u ( O H ) . 2  4.3.4  S o l u b i l i t y of calcium i n hypochlorite solutions A c o m b i n a t i o n o f t h e s e v a r i o u s f a c t o r s b r o u g h t t o l i g h t the  t h a t other elements,  fact  c o n t a i n e d i n the copper s u l p h i d e m i n e r a l s under  s t u d y as i m p u r i t i e s , c o u l d be c a p a b l e o f f o r m i n g i n s o l u b l e molybdates and t h u s be d e t r i m e n t a l t o good molybdenum r e c o v e r y .  In order  to  - 18 4 -  e l u c i d a t e w h i c h one o r more elements were r e s p o n s i b l e i n the p r e s e n t  case,  as w e l l as t o d e t e r m i n e i f any o t h e r l i k e l y gangue elements c o u l d cause s i m i l a r problems w i t h o t h e r o r e samples, the f o l l o w i n g f a c t o r s were t a k e n into consideration: i)  whether an element can combine w i t h the molybdate i o n and  form an i n s o l u b l e s p e c i e s w h i c h i s t h e r m o d y n a m i c a l l y s t a b l e a t pH 9 . 0 . ii)  whether h y p o c h l o r i t e o x i d a t i o n l e a d s t o t h e element e x i s t i n g  as a s t a b l e c a t i o n i n s o l u t i o n s a t pH 9 . 0 . iii)  whether the element i s l i k e l y t o be found as an i m p u r i t y i n  copper - molybdenum p o r p h y r i e s , and a s s o c i a t e d m i n e r a l s . To determine t h e r e g i o n s o f s t a b i l i t y o f the s i m p l e molybdates o f elements known t o be c o n t a i n e d i n the copper s u l p h i d e m i n e r a l s under s t u d y , Eh-pH diagrams were c o n s t r u c t e d f o r the f o l l o w i n g  Ca-H 0-Mo0 2  4  Fe-H 0-Mo0 2  "Pb-H 0-Mo0 2  systems:  4  4  Cd-H 0-MoO„ 2 4 Zn-H 0-Mo0 2  4  shown as F i g u r e s 54-58 r e s p e c t i v e l y .  The a c t i v i t y o f the molybdate i o n  has been t a k e n as 10 ^ M i n a l l c a s e s , and t h a t o f the m e t a l c o n t a i n i n g s p e c i e s i s {10  -6  } e x c e p t f o r l e a d , where {10  -4  } was found t o more a p p r o -  priate. F i g u r e 54:  calcium molybdate:  The diagram drawn up f o r c a l c i u m  2+ s p e c i e s and t h e i r i n t e r a c t i o n w i t h m o l y b d a t e , shows t h a t the Ca ion has a much l a r g e r zone o f s t a b i l i t y than the c o r r e s p o n d i n g r e g i o n f o r Cu  2+  r e s u l t i n g i n a c a l c i u m molybdate compound w i t h a wide range o f s t a b i l i t y .  - 18 6 -  When c o n s i d e r i n g the s o l i d s p e c i e s CaO, c a l c i u m molybdate i s s t a b l e up t o a pH o f 19.14, w h i l e f o r t h e h y d r o x i d e system the molybdate would extend t o a pH .of. 14..0. F i g u r e 55:  l e a d molybdate:  PbMoO^ i s s t a b l e up t o a pH v a l u e 2-  o f 14.2 b e f o r e d i s s o l u t i o n i n t o p l u m b i t e i o n s , HPbO^  , occurs.  The  redox p o t e n t i a l v a r i e s between 0.3 V a t t h i s p H , t o 2.0 V a t pH 0.  Thus  a t a v a l u e o f 9 . 0 , the p o t e n t i a l a t w h i c h PbMoO^ decomposes t o g i v e PbO^ i s 0.92 V and t h i s molybdate s h o u l d n o t be s t a b l e i n h y p o c h l o r i t e  solutions  w i t h a p r e d i c t e d v a l u e o f 1.2 V below pH v a l u e s o f 1 3 . 5 . F i g u r e 56:  z i n c molybdate:  I t i s seen t h a t z i n c molybdate  has  a l a r g e zone o f s t a b i l i t y w h i c h e x i s t s a t a l l p o t e n t i a l s more p o s i t i v e t h a n 0.4 V and up t o a pH v a l u e o f 1 8 . 6 .  The w h i t e , amorphous  zinc  h y d r o x i d e was c o n s i d e r e d as the s t a b l e o x i d e phase i n s e t t i n g up the d i a g r a m , and i t i s a p p a r e n t t h a t t h e molybdate i s more s t a b l e 2+ 2d y n a m i c a l l y than Zn final  , Z n ( O H ) , HZnC> 2  2  and ZnC>  thermo-  u n t i l d i s s o l u t i o n of  2  this  s p e c i e s o c c u r s a t pH 1 8 . 0 . F i g u r e 57:  i r o n molybdate:  I r o n i s o f major i n t e r e s t  with respect  t o i t s i n t e r a c t i o n w i t h m o l y b d a t e , b e i n g p r e s e n t i n l a r g e amounts i n c h a l c o p y r i t e , CuFeS  2  and b o r n i t e ,  i n c h a l c o c i t e and c o v e l l i t e .  Cu^FeS^, as w e l l as a common i m p u r i t y  I t i s u n l i k e l y however t h a t f e r r o u s  iron  c o u l d e x i s t i n h y p o c h l o r i t e s o l u t i o n s , t h u s FeMoO^ s h o u l d n o t pose a problem.  T h i s i s c o n f i r m e d i n the Eh-pH d i a g r a m ; FeMoO^ i s s t a b l e up t o  a pH o f 1 0 . 8 , b u t the maximum p o t e n t i a l i t can w i t h s t a n d i s 1.2 V , a t pH 2 . 4 , and a t pH 9.0 d e c o m p o s i t i o n t o F e ( 0 H ) would o c c u r a t 3  less  than 0.5 V . Zelikman  92  mentions t h e e x i s t e n c e  o f a f e r r i c molybdate compound,  Figure 55:  Eh-pH diagram for the system Pb-H„0-MoO^ ( A c t i v i t i e s of lead ions 10~^M, a c t i v i t i e s of molybdenum ions 10 ^M). _  PH Figure 56: Eh-pH diagram f o r the system Zn-H^O-MoO^. a c t i v i t i e s of molybdenum ions ^ Q - I J M ) •  ( A c t i v i t i e s of zinc ions 10~^M, and '  Figure 57:  Eh-pH diagram for the system Fe-H„0 MoO^ ( A c t i v i t i e s of f e r r i c and ferrous ions 10"%, ana a c t i v i t i e s of molybdenum ions 10 M). _1  - 19 0 -  Fe^(MoO^)  and n o t e s t h a t i t w i l l p r e c i p i t a t e from aqueous s o l u t i o n under  certain conditions.  The m i n e r a l f e r r i m o l y b d i t e , Fe^(MoO^)  -SH^O, i s  commonly found i n n a t u r e b u t i s n o t a source o f molybdenum m e t a l .  quite  No  thermodynamic d a t a f o r such an i r o n " ' " molybdate compound c o u l d be found 11  and i t has not been i n c l u d e d i n t h e Eh-pH diagram shown. F i g u r e 58:  cadmium m o l y b d a t e :  Cadmium and z i n c have s e v e r a l  c h e m i c a l s i m i l a r i t i e s and a r e found i n c l o s e a s s o c i a t i o n i n many o r e bodies.  The p r e s e n t study a l s o shows t h a t t h e i r r e s p e c t i v e  form under s i m i l a r c o n d i t i o n s :  molybdates  CdMoO^ i s s t a b l e up t o pH 12.5 and  above a p o t e n t i a l o f 0.4 V (pH 0 . 0 ) - - 0 . 9 V (pH 1 4 . 0 ) .  The presence o f  2+ Cd  i o n s i n s o l u t i o n i s thus u n d e s i r a b l e d u r i n g m o l y b d e n i t e l e a c h i n g . 2The s t a b i l i t y boundary between the s i m p l e molybdate i o n MoO^  and p o l y m o l y b d a t e s p e c i e s , d e s c r i b e d as HMoO^ , o c c u r s a t pH 6 . 0 .  Above  t h i s v a l u e , combination w i t h metal cations w i l l r e s u l t i n p r e c i p i t a t i o n o f a s i m p l e molybdate s a l t such as CuMoO^.  In more a c i d i c s o l u t i o n s  i s p o s s i b l e t h a t a complex molybdate s p e c i e s w i l l  form the s t a b l e  species. 2-  On the o t h e r hand, w i t h a s u f f i c i e n t l y l a r g e c o n c e n t r a t i o n o f MoO^ e q u i l i b r i u m w i t h HMoO^ , a s i m p l e molybdate may s t i l l  it  in  precipitate.  E x p e r i m e n t a l r e s u l t s f o r m o l y b d e n i t e - copper s u l p h i d e l e a c h i n g c a r r i e d o u t a t pH 5.5 s u g g e s t s a s t o i c h i o m e t r i c Cu:Mo r a t i o o f 1 : 1 , i n d i c a t i n g f o r m a t i o n o f the s i m p l e molybdate CuMoO^.  The e x a c t n a t u r e o f m o l y b -  denum s p e c i e s a t low pH v a l u e s i s n o t known. a t h i g h e r p o t e n t i a l s below pH 3 . 0 .  MoO^ i s the s t a b l e  MoC> p r e c i p i t a t e s 2  species  at a p o t e n t i a l of  0.4 V (pH 0 . 0 ) , d e c r e a s i n g t o - 0 . 1 V a t pH 6.0 and - 0 . 5 5 a t pH 1 0 . 0 . Between t h e s e two s p e c i e s molybdenum p r o b a b l y e x i s t s i n the +5 o x i d a t i o n 9 state.  - 191 -  Figure 58: Eh-pH diagram f o r the system Cd-H^O-MoO^. (Activities of cadmium ions 10~^M and a c t i v i t i e s of molybdenum ions 10 M) _1  - 19 2 -  I n c o n j u n c t i o n .with t h e s e thermodynamic c o n s i d e r a t i o n s f o r  the  s t a b i l i t y o f v a r i o u s m o l y b d a t e s , the f o l l o w i n g d a t a was accumulated  for  the s o l u b i l i t y o f a number o f molybdate compounds:  Compound  PbMo0  Solubility  (g M o 0 / 1 )  1.2 x l o "  4  Source  4  6  83  4  83  SrMoCK 4  3.0 x l o "  CaMoO„ 4  a) 5.0 x 1 0 ~ ; b) 1.3 x 1 0 ~  BaMo0  5.5 x l o "  4  83  CdMoO„ 4  6.7 x i o "  4  83  FeMoO„ 4  7.6 x l o "  4  82  CuMoO. 4  3.8 x i o "  3  82  4  4  Ag Mo0 2  ZnMoO. 4  4  3.86 x 10 a) 3.70 x 10  a) 83;  3  83  3  ; b) 5.0 x 10  b) 82  2  a) 82;  b) 83  Of the above elements b a r i u m , s t r o n t i u m and s i l v e r were not c o n s i d e r e d because i t was not f e l t they would be p r e s e n t i n s u f f i c i e n t l y l a r g e q u a n t i t i e s t o cause molybdenum l o s s e s . From the remainder i t appears from the Eh-pH diagrams t h a t l e a d and i r o n are b o t h i n s o l u b l e i n h y p o c h l o r i t e s o l u t i o n s as d i s c u s s e d above. T h i s was borne o u t e x p e r i m e n t a l l y : FeS  2  samples o f g a l e n a , PbS and p y r i t e ,  were l e a c h e d under i d e n t i c a l c o n d i t i o n s t o t h o s e used f o r  molybdenum m i n e r a l s and no l e a d o r i r o n whatsoever was d e t e c t e d  copper/ in  solution. Copper molybdate can be d e s c r i b e d as a b o r d e r l i n e case w i t h  respect  - 193 -  t o l e a c h i n g a t pH 9 . 0 s i n c e the thermodynamic boundary o c c u r s a t pH 8.65 f o r the o x i d e and 9.2 f o r the h y d r o x i d e ' ; b u t the f a c t t h a t b o t h these s a l t s are i n s o l u b l e s h o u l d p r e v e n t any molybdate f o r m a t i o n . As n o t e d p r e v i o u s l y , the presence o f carbonate  imparts a c e r t a i n  o f s o l u b i l i t y t o copper i n a l k a l i n e s o l u t i o n , and e x p e r i m e n t a l  degree  results  suggested t h a t a copper - carbonate a s s o c i a t i o n o c c u r r e d i n p r e f e r e n c e CuMoO^ f o r m a t i o n .  Cu  2 +  The r e l e v a n t e q u i l i b r i a  +  2C0 ~ 2  3  2+ Cu  are:  v==^  Cu(C0 ) ~  l o g k = 9.83  v=^  CuMo0  l o g k = -2.027  2  3  to  2  2+  Mo0  4  4  I t was o b s e r v e d , however, t h a t l e a c h i n g i n the presence o f s m a l l amounts o f c a r b o n a t e d i d r e s u l t i n some copper molybdate f o r m a t i o n (Section 3 . 3 . 4 . 3 ) , Cu-C0  3  s u g g e s t i n g t h a t l e s s carbonate produced a weaker  bond. Z i n c , cadmium and c a l c i u m are a l l u n d e s i r a b l e elements i n t h i s  system on account o f t h e i r a b i l i t y t o e x i s t as s o l u b l e s p e c i e s a t pH 9.0 and hence t o combine w i t h Mo0  24  and p r e c i p i t a t e .  I t has been shown  t h a t sodium h y p o c h l o r i t e i s a f e a s i b l e l i x i v i a n t f o r the e x t r a c t i o n o f 84 z i n c from s p h a l e r i t e o r e s . o r cadmium would be p r e s e n t  However, i t i s not l i k e l y t h a t e i t h e r  zinc  i n more t h a n t r a c e amounts i n most copper -  molybdenum ore b o d i e s , and a n a l y s i s c e r t a i n l y showed t h a t i n s u f f i c i e n t amounts were p r e s e n t t o a c c o u n t f o r the l a r g e l o s s e s o f molybdenum observed d u r i n g l e a c h i n g experiments. By a p r o c e s s o f e l i m i n a t i o n i n c o n s i d e r a t i o n o f a l l the f a c t o r s i t was c o n c l u d e d t h a t c a l c i u m was the element p r i m a r i l y i b l e f o r the o b s e r v e d p o o r molybdenum r e c o v e r i e s .  above respons-  T h i s would r e a d i l y  - 19.4 -  e x p l a i n t h e l o s s o f molybdenum from combined copper s u l p h i d e m o l y b d e n i t e experiments  i n the absence o f c a r b o n a t e .  C a l c i u m was p r e s e n t as an i m p u r i -  t y i n a l l t h r e e m i n e r a l samples u s e d ; i t can e x i s t as a s o l u b l e a t pH 9 . 0 , and has a v e r y i n s o l u b l e molybdate s a l t . carbonate,  species  I n the p r e s e n c e o f  however, the c a l c i u m w i l l p r e c i p i t a t e p r e f e r e n t i a l l y as CaCO^  so t h a t n e g l i g i b l e i n t e r f e r e n c e  w i t h molybdate o c c u r s .  copper i s a l s o d i s s o l v e d i n t h e l a t t e r  Ca Ca  2+  2+  +  2MoO. 4  +  2— CO., 3  The f a c t  that  case i s c o i n c i d e n t a l . ^  log k log k  S  S  =  -7.38  =  -8.55  S t o i c h i o m e t r i c amounts o f c a l c i u m and molybdenum t o g i v e a  1:1  r a t i o f o r CaMoO^ were p r e c i p i t a t e d from a s o l u t i o n c o n t a i n i n g m o l y b d e n i t e and c a l c i u m c h l o r i d e , e x c e p t i n the p r e s e n c e o f c a r b o n a t e b u f f e r s when a l l the c a l c i u m was p r e c i p i t a t e d w i t h no e f f e c t  on the molybdenum.  The f a c t t h a t e x t r a c t i o n i n the p r e s e n c e o f c a r b o n a t e and copper s u l p h i d e m i n e r a l s was s l i g h t l y below the l e v e l s o b t a i n e d f o r l e a c h i n g m o l y b d e n i t e a l o n e , c o u l d be a t t r i b u t e d  t o one o r more o f the  following  factors: i)  f o r m a t i o n o f s m a l l amounts o f copper m o l y b d a t e , even i n 2-  the p r e s e n c e o f s o l u b l e C u ( C 0 . j ) ii) iii)  2  ,  c o - p r e c i p i t a t i o n o f the molybdenum w i t h c a l c i u m c a r b o n a t e , s l i g h t s o l u b i l i t y o f CaCO^ due t o the p r e s e n c e o f c h l o r i d e ,  e n a b l i n g CaMoO^ t o form i n s m a l l amounts. The i m p l i c a t i o n s o f c a l c i u m molybdate p r e c i p i t a t i o n are a b l e f o r an a l k a l i n e l e a c h i n g p r o c e s s i s a copper - rougher c o n c e n t r a t e ,  unfavour-  i n w h i c h the p o t e n t i a l feed m a t e r i a l  w h i c h would u n a v o i d a b l y c o n t a i n a  c e r t a i n amount o f gangue m a t e r i a l as w e l l as t h e copper - molybdenum  - 195 -  metal values.  The problems o f such gangue m a t e r i a l s b e i n g s o l u b l e i n hypo-  c h l o r i t e s o l u t i o n and c a p a b l e o f f o r m i n g i n s o l u b l e molybdates would pose an even g r e a t e r t h r e a t t o an ' i n - s i t u ' l e a c h i n g p r o c e s s where good s e l e c t i v i t y of metal values i s a n e c e s s i t y . comments i n t h i s r e s p e c t :  I t i s i n t e r e s t i n g t o note Bhappu's  he s t a t e s t h a t e i t h e r a b a s i c c a r b o n a t e -  h y p o c h l o r i t e o r an a c i d c h l o r a t e l e a c h would be c a p a b l e o f d i s s o l v i n g molybdenum from mixed s u l p h i d e - o x i d e o r e s , would be p r e f e r a b l e  b u t t h a t an a l k a l i  leach  on account o f the tendency o f f e r r i c i r o n , c a l c i u m  and aluminum t o p r e c i p i t a t e  as i n s o l u b l e molybdates i n a c i d s o l u t i o n .  Presumably he was a l s o r e l y i n g on the p r e s e n c e o f c a r b o n a t e t o suppress molybdate f o r m a t i o n i n a l k a l i s o l u t i o n . The major c a l c i u m m i n e r a l s l i k e l y t o be a s s o c i a t e d w i t h copper  -  molybdenum p o r p h y r y o r e s were c o n s i d e r e d t o be c a l c i t e and gypsum, and a b r i e f r e v i e w o f the geology o f p o r p h y r y type d e p o s i t s  confirmed t h i s :  C h a l c o p y r i t e , m o l y b d e n i t e and p y r i t e are the most commonly o c c u r r i n g m i n e r a l s i n such o r e b o d i e s . these three i n c l u d e b o r n i t e ,  Other s u l p h i d e s found i n a s s o c i a t i o n w i t h c h a l c o c i t e , galena,  p y r r h o t i t e , b i s m u t h i n i t e and e n a r g i t e . is  quartz but magnetite,  common.  sphalerite,  covellite,  The most abundant gangue m a t e r i a l  t o u r m a l i n e , h e m a t i t e and f l u o r i t e are  also  C a l c i t e , CaCO^, and gypsum, CaSO^'211^0, are found i n a s s o c i a t i o n  w i t h e i t h e r quartz or tourmaline d i s t r i b u t i o n s .  I n most o r e  deposits  they o c c u r i n the youngest r o c k s p r e s e n t , and r e p r e s e n t l a t e stage v e i n i n g which i s t h e r e f o r e  usually post-ore.  C a l c i t e , t o g e t h e r w i t h z e o l i t e can  i n t e r g r o w w i t h the s u l p h i d e m i n e r a l s and i s a l s o f o u n d , w i t h gypsum i n v e i n s and f r a c t u r e  fillings  i n the q u a r t z .  F i b r o u s gypsum can a l s o be  p r e s e n t as vugs i n the main l a t e stage q u a r t z - s u l p h i d e v e i n s . The d i s t r i b u t i o n o f the copper and molybdenum m i n e r a l i z a t i o n can  - 19 6 -  v a r y c o n s i d e r a b l y between d i f f e r e n t o r e b o d i e s .  I n some cases b o t h  are c o n t a i n e d w i t h i n the c e n t r a l c o r e o f a d e p o s i t , w h i l e i n o t h e r s copper e s p e c i a l l y i s found i n the o u t e r z o n e s , and t h e r e f o r e tion with quartz,  s e r i c i t e , pyrite etc.  metals the  i n associa-  The m o l y b d e n i t e i s o f t e n  unsystem-  a t i c a l l y d i s t r i b u t e d throughout  the o r e body and can c r o s s c u t the a r e a s  i n w h i c h c a l c i t e and gypsum are  found.  Of the molybdenum-bearing p o r p h y r y copper o r e s mined i n B r i t i s h C o l u m b i a , d e p o s i t s a t Bethlehem Copper, L o r n e x , V a l l e y Copper, Ox L a k e , Brenda and the  'J.A.'  o r e body are a l l known t o c o n t a i n c a l c i t e  gypsum i n c l o s e p r o x i m i t y t o the m e t a l s u l p h i d e s .  I n the  and/or  so-called  molybdenum p o r p h y r i e s , c a l c i u m c o n t a i n i n g m i n e r a l s are l e s s common, b u t i n the Boss M o u n t a i n d e p o s i t and a t Endako, s i g n i f i c a n t amounts o f c a l c i t e are found i n a s s o c i a t i o n w i t h q u a r t z and c l a y m i n e r a l s c o n t a i n e d i n the ore  bodies.  4.3.4.1  4  Sodium h y p o c h l o r i t e l e a c h i n g o f calcium minerals Having e s t a b l i s h e d t h a t c a l c i t e and gypsum are l i k e l y gangue m a t e r -  i a l s i n low grade copper-molybdenum o r e s ,  experiments were c a r r i e d o u t i n  which samples o f t h e s e m i n e r a l s were l e a c h e d i n h y p o c h l o r i t e  solutions  under i d e n t i c a l c o n d i t i o n s t o t h o s e used f o r m o l y b d e n i t e . 2+ I t was c o n f i r m e d t h a t b o t h m i n e r a l s y i e l d Ca  i n s o l u t i o n i n the  p r e s e n c e o f h y p o c h l o r i t e , and t h a t the amounts e x t r a c t e d were  sufficient  t o a c c o u n t f o r t h e observed molybdenum l o s s e s d u r i n g copper s u l p h i d e molybdenite l e a c h i n g . 4.3.4.2  Effect of chloride concentration on c a l c i u m s o l u b i l i t y Samples o f c a l c i t e and gypsum l e a c h e d i n the p r e s e n c e o f v a r y i n g  - 197 -  amounts o f t o t a l c h l o r i d e showed t h a t c a l c i u m s o l u b i l i t y i n c r e a s e s as a function of  [CI ] and t h a t the r e s u l t s were i n good agreement  l i t e r a t u r e values  (Table 1 1 ) .  S t r o n g e r h y p o c h l o r i t e s o l u t i o n s can thus  be e x p e c t e d to e x t r a c t more c a l c i u m . whether 0C1  with  I d e n t i c a l r e s u l t s were o b t a i n e d  o r an e q u i v a l e n t amount o f NaCl a l o n e were u s e d .  This d i d  not s u p p o r t the s u g g e s t i o n made i n c o n j u n c t i o n w i t h the e x p e r i m e n t a l observation that calcium sulphate i s soluble i n h y p o c h l o r i t e s o l u t i o n s , namely t h a t t h i s was due t o c a l c i u m c o m p l e x i n g agents c o n t a i n e d i n a commercial b l e a c h .  F u r t h e r m o r e , an assurance was o b t a i n e d from the manu-  f a c t u r e r s o f JAVEX t h a t the p r o d u c t , when s o l d , c o n s i s t s e x c l u s i v e l y o f 89 sodium h y p o c h l o r i t e and w a t e r . The r e a s o n f o r the i n c r e a s e d s o l u b i l i t y o f c a l c i u m i n c h l o r i d e s o l u t i o n s i s a change i n a c t i v i t y c o e f f i c i e n t due t o an i n c r e a s e d i o n i c strength.  The thermodynamic s o l u b i l i t y p r o d u c t f o r c a l c i u m s u l p h a t e  d e r i v e d from the  equation: C a S 0 * x H 0 ===== Ca 4  2  2+  +  S0  24  +  xH^O .  is  - 198  i)  Calcium sulphate C h l o r i d e Content (Moles C l ~ )  [Ca] D i s s o l v e d (Experiment) g/1  [Ca] D i s s o l v e d (Reported) g/1  Source  0.0  0.712  0.666  85  0.825  86  1.068  85  1.224  87  1.532  87  1.442  88  0.2  0.5  ii)  -  1.326  1.528  0.7  1.688  1.496  88  1.0  1.860  1.833  88  1.800  87  1.5  2.012  1.959  88  2.0  2.024  2.116  88  2.180  87  Calcium carbonate C h l o r i d e Content (Moles CI )  [Ca] D i s s o l v e d (Experiment) g/1  [Ca] D i s s o l v e d (Reported) g/1  Source  0.0  0.016  0.022  85  0.014  86  Table 1 1 :  0.25  0.016  0.048  85  0.60  0.049  0.056  85  0.70  0.060  0.056  85  1.37  0.055  0.055  85  Comparison o f E x p e r i m e n t a l and L i t e r a t u r e V a l u e s S o l u b i l i t y o f i ) CaSC~> and i i ) CaCCy i n C h l o r i d e of Varying Strengths 4  for Solutions  - 199 -  f o r which  sp  k  =  t m  Ca  2 + ]  [ m  S0  2 4  "  ]  [ 6  Ca  2 + ]  ^ S O ^  [ a  H 0  ] X  2  where m„ , m„ „ a r e i h o l a l c o n c e n t r a t i o n s Ca S0„ 4 &n ' &cr\ activity coefficients 4 x = number o f moles o f water a  a  =  r  e  water a c t i v i t y i n t h e s o l u t i o n .  2+ 2S u b s t i t u t i n g f o r a c t i v i t y c o e f f i c i e n t s o f Ca and S 0 from the Debye 4  Huckel e x p r e s s i o n : -A z log 6 1 +B/l  1  where i o n i c s t r e n g t h I  =  4 m CaSo  z  =  charge on i o n i  A,B then l o g k  = S  log k  P  + 2 S  Assuming t h a t m 2+ Ca.  =  -  constants  x log a  B/F  1+  P  are  = m NaCl  4  TT  H  „  2°  m 2bu 4 I * 3  then, l o g S  =  l o g S°  +  4A  j1+B1 2  where S  =  -  —log a 2  n  2  H  m o l a l s o l u b i l i t y fo CaSC> a t any i o n i c strength, I 4  and S° i s the t h e o r e t i c a l s o l u b i l i t y when  1=0.  I t i s apparent t h e r e f o r e t h a t S i n c r e a s e s w i t h an i n c r e a s e i n m , NaCl and hence o f i o n i c s t r e n g t h , I . n  l  l  - 200 -  4.3.4.3  Removal o f c a l c i u m from leaching solutions The minimum c a r b o n a t e : c a l c i u m r a t i o f o r e f f e c t i v e  precipitation  o f CaCo^ and p r e v e n t i o n o f c a l c i u m molybdate f o r m a t i o n was found t o be 23.19 M [CO^  2+ ] : 1 M [Ca  ]•  F o r t h e amount o f c a l c i u m c o n t a i n e d i n the  c o v e l l i t e m i n e r a l under s t u d y ,  0.058 g / 1 , t h i s gave a minimum c a r b o n a t e  r e q u i r e m e n t o f 0.55 g / 1 . However, l e a c h i n g w i t h t h i s v a l u e o f t o t a l 2III [CO^ ] a t pH 9.0 gave almost i n s t a n t a n e o u s p r e c i p i t a t i o n o f copper and r a p i d d e c o m p o s i t i o n o f the sodium h y p o c h l o r i t e , as noted  earlier.  I n c r e a s i n g the c a r b o n a t e above the s t o i c h i o m e t r i c r e q u i r e m e n t  lengthened  the i n d u c t i o n p e r i o d t o p r e c i p i t a t i o n o f copper " "''', but gave more  copper  in solution i n i t i a l l y .  seeming-  1  1  The f a c t t h a t the p r e s e n c e o f m o l y b d e n i t e  l y d e c r e a s e d t h i s i n d u c t i o n p e r i o d i s p r o b a b l y due t o the l o w e r hypoc h l o r i t e c o n t e n t o f s o l u t i o n as a r e s u l t o f the o x i d a t i o n o f MoS N a ^ o O ^ , r a t h e r than any e f f e c t  o f the molybdenum i t s e l f .  to  2  The s m a l l  degree o f copper molybdate f o r m a t i o n w h i c h o c c u r r e d a t l o w e r c a r b o n a t e l e v e l s has been p o i n t e d o u t p r e v i o u s l y t o be d e t r i m e n t a l t o molybdenum r e c o v e r y and an u n d e s i r a b l e  catalyst  for hypochlorite  There would seem t o be two a l t e r n a t i v e s  t h e r e f o r e f o r the  o f molybdenum from m o l y b d e n i t e - copper s u l p h i d e i)  extraction  concentrates:  t o l e a c h i n the p r e s e n c e o f l a r g e amounts o f c a r b o n a t e  r e a g e n t s and hence t o p r e c i p i t a t e purities  decomposition.  buffer  c a l c i u m , as w e l l as o t h e r s o l u b l e i m -  such as z i n c and cadmium, as i n s o l u b l e c a r b o n a t e s a l t s and to  p r e v e n t any copper molybdate p r e c i p i t a t i o n . p e r c e n t a g e o f the copper would be d i s s o l v e d . molybdenum t o be e x t r a c t e d b e f o r e  A t the same time a s m a l l T h i s would enable a l l  the  n u c l e a t i o n o f copper "'"''" and d e c o m p o s i t i o n 1  - 201 -  o f the h y p o c h l o r i t e l i x i v i a n t c o u l d o c c u r , but would p r o b a b l y n e c e s s i t a t e a copper - molybdenum s e p a r a t i o n the  s t e p p r i o r t o molybdenum r e c o v e r y  from  solution. ii)  t o l e a c h w i t h no c a r b o n a t e i n the system, and t h e r e b y t o o b -  t a i n complete s e l e c t i v i t y o f molybdenum o v e r c o p p e r ,  but t o decompose  the h y p o c h l o r i t e r e a g e n t as a r e s u l t o f heterogeneous copper T h i s would n e c e s s i t a t e c o n s t a n t r e g e n e r a t i o n I n case ( i i ) an a l t e r n a t i v e  all  catalysis.  o f the l e a c h i n g s o l u t i o n .  s u p p r e s s a n t f o r c a l c i u m would have t o  be found, and experiment suggested e i t h e r phosphates o r s i l i c a t e s may be feasible.  L e a c h i n g c h a l c o p y r i t e and m o l y b d e n i t e t o g e t h e r i n the presence  of s i l i c a t e i n fact obtained,  showed t h a t v e r y good molybdenum r e c o v e r i e s  c o u p l e d w i t h no copper d i s s o l u t i o n and an apparent s t a b i l i z a -  t i o n o f the h y p o c h l o r i t e . exist,  Copper m e t a - s i l i c a t e ,  CuSiO^, i s known t o  and such a compound c o u l d form a t the m i n e r a l s u r f a c e  t o C u ( 0 H ) a n d / o r C u ( 0 H ) and t h u s p r e v e n t r a p i d c a t a l y t i c 2  o f the  were  3  i n preference decomposition  hypochlorite. W h i l e t h e use o f s i l i c a t e appears t o be a v e r y v i a b l e  f o r l e a c h i n g a t pH 9 . 0 , i)  i t s h o u l d be  alternative  noted:  S i l i c a t e s and polymolybdates can combine i n a c i d  solutions  and problems c o u l d be i n c u r r e d d u r i n g subsequent molybdenum r e c o v e r y i f s i l i c a t e was p r e s e n t i n the l e a c h i n g ii)  solutions.  S i l i c a t e r e a g e n t s a r e l i k e l y t o be more e x p e n s i v e  than  carbonates. The most f a v o u r a b l e p r o c e s s t h u s seems t o be one  incorporating  l e a c h i n g i n t h e p r e s e n c e o f sodium c a r b o n a t e / b i c a r b o n a t e a t pH 9 . 0 , v i d e d a s u i t a b l e method f o r copper - molybdenum s e p a r a t i o n can be f o u n d .  after  pro-  leaching  - 202 -  CHAPTER 5  5.1  Conclusions  1)  The s e l e c t i v e e x t r a c t i o n o f molybdenum from copper s u l p h i d e  -  m o l y b d e n i t e c o n c e n t r a t e s can be r a p i d l y and c o m p l e t e l y o b t a i n e d by l e a c h i n g w i t h sodium h y p o c h l o r i t e s o l u t i o n s a t pH 9.0 and a temperature o f 35°C, i n the absence o f c a r b o n a t e b u f f e r  2)  reagents.  Under t h e s e c o n d i t i o n s the s u r f a c e s  a c t as c a t a l y s t s  o f the copper m i n e r a l s  f o r the heterogeneous d e c o m p o s i t i o n o f sodium h y p o c h l o r -  i t e due t o the f o r m a t i o n o f an o x i d e o r h y d r o x i d e s a l t o f copper on the m i n e r a l 3)  tri-valent  surface.  A l k a l i n e c a r b o n a t e s o l u t i o n s are c a p a b l e o f d i s s o l v i n g s m a l l  amounts o f copper as copper - c a r b o n a t e complexes w h i c h are  considerably  2+ more s o l u b l e than the Cu suggested  i o n a l o n e a t pH v a l u e s above 7 . 0 .  t h a t the p r e s e n c e o f h y p o c h l o r i t e i n such s o l u t i o n s  t h e copper t o e x i s t as a t r i - v a l e n t c u p r i - c a r b o n a t e  species,  It  is  enables and t h a t  p r e c i p i t a t i o n o f a s o l i d c a r b o n a t e compound c o n t a i n i n g up t o 30% o f copper i n the +3 o x i d a t i o n s t a t e o c c u r s a f t e r p e r i o d has p a s s e d .  a suitable  the  nucleation  T h i s time p e r i o d and t h e o r i g i n a l copper c o n t e n t o f  the s o l u t i o n are a f u n c t i o n o f the t o t a l c a r b o n a t e c o n c e n t r a t i o n  i n the  system. 4)  S o l u b l e i m p u r i t y elements w h i c h have i n s o l u b l e molybdate  s a l t s are d e t r i m e n t a l t o good molybdenum e x t r a c t i o n .  Calcium i s  suggested  as b e i n g the p r i n c i p a l source o f p o t e n t i a l molybdenum l o s s e s i n the  - 20 3 -  proposed copper s u l p h i d e - m o l y b d e n i t e l e a c h i n g p r o c e s s .  The p r e s e n c e  of c a r b o n a t e i n the system would p r e v e n t c a l c i u m molybdate f o r m a t i o n by the a l t e r n a t i v e p r e c i p i t a t i o n o f c a l c i u m c a r b o n a t e ,  and a s i m i l a r  mechanism would a p p l y t o z i n c and cadmium i m p u r i t i e s .  The use o f  sili-  c a t e s would p r o v i d e an a l t e r n a t i v e means o f c a l c i u m p r e c i p i t a t i o n w i t h o u t the c o i n c i d e n t a l s i d e e f f e c t s  o f copper c o m p l e x i n g , but may prove  d e t r i m e n t a l t o subsequent molybdenum r e c o v e r y .  6)  Lead and i r o n do n o t e x i s t as s o l u b l e s p e c i e s i n h y p o c h l o r i t e  s o l u t i o n s a t pH 9.0 and w i l l n o t i n t e r f e r e  w i t h molybdenum e x t r a c t i o n .  Copper molybdate i s o f m i n o r importance a t pH 9.0 due t o the low 2+ s o l u b i l i t y o f the Cu  i o n i n a l k a l i n e s o l u t i o n , but i n a c i d s o l u t i o n  p r e c i p i t a t i o n o f 90% o f the d i s s o l v e d molybdenum can be a t t r i b u t e d copper molybdate f o r m a t i o n .  T h i s compound i s a c a t a l y s t  to  for hypochlorite  d e c o m p o s i t i o n and has a s o l u b i l i t y o f about 1.25 g/1 as CuMoO^. 7)  L e a c h i n g i n a c i d s o l u t i o n s would be f e a s i b l e o n l y i n the  p r e s e n c e o f c a r b o n a t e and above a pH v a l u e o f 6 . 0 , because t h i s i s  the  2+ r e g i o n i n w h i c h the c u p r i c i o n , Cu  , i s complexed by c a r b o n a t e a n i o n s ,  and copper molybdate f o r m a t i o n i s t h e r e f o r e  prevented.  The pH r e g i o n  6 . 0 - 7.0 has p r e v i o u s l y been shown t o be the most f a v o u r a b l e f o r sodium chlorate 8)  formation. L e a c h i n g i n a l k a l i n e h y p o c h l o r i t e s o l u t i o n s i n the p r e s e n c e 2-  of  s u f f i c i e n t l y l a r g e amounts o f c a r b o n a t e  (25 g/1  [CO^  would g i v e good molybdenum e x t r a c t i o n w i t h approximate  ]  example)  stoichiometric  consumption o f t h e l i x i v i a n t ; b u t would e n t a i l s i m u l t a n e o u s o f a c e r t a i n amount o f c o p p e r .  for  dissolution  T h i s copper would p r o b a b l y r e q u i r e  separation  - 204 -  from the molybdenum b e f o r e the r e c o v e r y s t a g e . h y p o c h l o r i t e d e c o m p o s i t i o n such a s e p a r a t i o n copper  5.2  III  To m i n i m i z e sodium  s t e p s h o u l d be made b e f o r e  . • . p r e c i p i t a t i o n can o c c u r .  Suggestions  f o r F u t u r e Work  F u r t h e r work c o u l d be u s e f u l l y done i n the f o l l o w i n g a r e a s t o the p r e s e n t i)  relating  study:  A more d e t a i l e d study o f the s u r f a c e  between h y p o c h l o r i t e and d i f f e r e n t  reactions  occurring  copper s u l p h i d e m i n e r a l s would d e t e r -  mine more p r e c i s e l y why such v a r i a t i o n s were o b s e r v e d i n the r a t e s o f catalyzed  decomposition.  ii) solutions,  F u r t h e r a n a l y s i s o f the c a r b o n a t e c o n t a i n i n g  t o p r o v i d e a more c o n c l u s i v e i n d i c a t i o n o f the s o l u b l e  species present.  P o l a r o g r a p h i c t e c h n i q u e s would p r o b a b l y g i v e  h a l f wave p o t e n t i a l s dation  copper  different  f o r copper c a r b o n a t e complexes i n the +2 and +3 o x i -  states. iii)  copper  hypochlorite  A n a l y s i s o f s o l i d compounds t h o u g h t t o c o n t a i n  p r o v e d t o be somewhat d i f f i c u l t  f o r s t a n d a r d compounds. manufactured,  iv)  due t o a l a c k o f p u b l i s h e d d a t a  I f pure samples o f Cu^O^ o r (""^(CO^)^ c o u l d be  X - r a y d i f f r a c t i o n p a t t e r n s , gram magnetic  s o l u b i l i t y data e t c .  tri-valent  c o u l d be u s e f u l l y  susceptibilities,  obtained.  L e a c h i n g was found t o be most s u c c e s s f u l  I t would t h e r e f o r e be l o g i c a l t o r e s e a r c h  in alkaline  solutions.  i n t o ways o f r e c o v e r i n g m o l y b -  denum from l e a c h s o l u t i o n s w i t h o u t l o w e r i n g p H .  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Chem., 1_, No. 12, 1956, p .  2778.  -  211  APPENDIX A Tables o f Experimental  Table I :  Results  NaOCl l e a c h i n g o f c o v e l l i t e i n the p r e s e n c e o f c a r b o n a t e b u f f e r s ( F i g u r e s 6,8)  Temp. 35°C,CuS 10 g ,  pH 9 . 0 , A g i t a t i o n 748 rpm, NaHC0 14.15 g , °3 N a  3  Time (mins)  C  2  [Cu] ppm  5  133  10  133  15  125  20  127  30  127  45  127  60  121  90  126  120  128  150  130  1  [NaOCl] 7.68 0  1  9-  [NaOCl] g/1  5.64  5.60  5.62  5.64  g/1,  - 212 -  Table I I :  NaOCl l e a c h i n g o f c h a l c o c i t e i n the presence o f c a r b o n a t e b u f f e r s ( F i g u r e s 6,8)  Temp 35°C, A g i t a t i o n 720 rpm, NaHC0 14.15 g , N a C 0 1.01 g 3  2  [NaOCl] 7.8 g / 1 ,  pH 9 . 0 ,  [Cu] ppm  [NaOCl] g/1  3  Time (mins)  5  122.5  10  122  15  115  30  116  45  118  60  118  90  113  120  118  150  115  ) /  7.08  6.07  6.10  6.05  6.07  C u S 10 g , 2  - 213 -  Table I I I :  NaOCl l e a c h i n g o f c h a l c o p y r i t e i n the p r e s e n c e o f c a r b o n a t e b u f f e r s ( F i g u r e s 6,8)  Temp 35°C, A g i t a t i o n 803 rpm, NaHC0  3  14.15 g , N a C 0 2  Time '(mins)  3  1.01  [NaOCl] 8.13 g ' / l , pH 9 . 0 , C u F e S  g.  [Cu] ppm  [NaOCl] g/1  2  105  5  104  7.56  10  96  7.44  20  99  7.36  30  96  7.29  50  101  7.24  60  106  7.24  80  106  100  99  120  95  150  101  180  104  210  106  7.22  7.20  2  10 g ,  - 214 -  Table I V :  Temp 35°C, NaHC0  3  E f f e c t o f s e p a r a t i n g l e a c h i n g s o l u t i o n from m i n e r a l s l u r r y d u r i n g a g i t a t i o n o f CuFeS^ i n NaOCl ( F i g u r e 7)  A g i t a t i o n 760 rpm,  14.15 g ,  Time (mins)  Na C0 2  3  1.01  [NaOCl] 8.0 g / 1 ,  pH 9 . 0 ,  C u F e S 10 g , 2  g.  [Cu] s l u r r y ppm  [Cu] f i l t e r e d ppm  5  118  129  10  111  129  15  108  129  20  105  130  30  103  128  45  109  130  65  105  129  100  104  130  140  110  130  180  117  131  soln  - 215 -  Table V :  Temp 35°C, NaHC0  3  E f f e c t o f s e p a r a t i n g l e a c h i n g s o l u t i o n from m i n e r a l d u r i n g a g i t a t i o n o f Cu^S i n NaOCl ( F i g u r e 7 ) .  A g i t a t i o n 782 rpm,  14.15 g ,  Na C0 2  Time (mins)  3  1.01  NaOCl 7.45 g / 1 ,  pH 9 . 0 ,  slurry  C u S 10 g , 2  g.  [Cu] s l u r r y ppm  [Cu] f i l t e r e d ppm  5  112  123  10  115  123  15  106  123  20  110  122  30  108  122  45  113  123  70  109  123  90  110  123  145  106  123  soln  -216 -  Table V I :  Temp 35°C,  Time (mins)  NaOCl l e a c h i n g o f c o v e l l i t e i n the absence o f carbonate b u f f e r s ( F i g u r e s 9,11) A g i t a t i o n 784 rpm,  pH 9 . 0 ,  [NaOCl] 7.61 g / 1 ,  CuS 10 g .  [Cu] ppm  [NaOCl] g/1  [NaC10 ] g/1  0  0.05  7.61  0.179  5  0.29  5.93  0.304  10  0.22  2.70  0.429  20  0.40  0.39  0.490  9.40  30  0.30  0.08  0.537  9.57  45  0.20  —  0.540  3  NaC10 %  3  13.70  - 217 -  Table V I I :  NaOCl l e a c h i n g o f c h a l c o c i t e i n the absence o f c a r b o n a t e b u f f e r s ( F i g u r e s 9,11)  Temp 35°C,  A g i t a t i o n 780 rpm,  Time (mins)  [Cu] ppm  pH 9 . 0 ,  [NaOCl] g/i  [NaOCl] 7.69 g / 1 ,  [NaCIO ] g/i  C u S 10 g . 2  NaCIO %  0  0.13  7 .69  0.304  5  0.19  6.98  0.340  8.73  6.60  0.358  9.21  6.30  0.429  17.70  5.63  0.501  21.22  5.03  0.633  22.81  4.53  0.716  20.20  3.30  0.859  23.42  2.78  0.913  23.03  2.18  0.922  23.31  10 20  0.20  30 45  0.25  60 80  0.21  100 120  0.19  150 180  0.23  3.91  1.56  - 218 -  Table V I I I :  Temp 35°C,  Time (mins)  NaOCl l e a c h i n g o f c h a l c o p y r i t e i n t h e absence o f c a r b o n a t e b u f f e r s ( F i g u r e s 9.11)  A g i t a t i o n 785 rpm,  [Cu] ppm  pH 9 . 0 ,  [NaOCl] g/1  [NaOCl] 7.73 g / 1 ,  [NaC10 ] g/1 3  CuFeS  NaCIO %  0  0.03  7.73  0.358  5  0.09  5.70  0.751  35.0  10  0.08  4.54  0.805  25.9  20  0.11  2.78  0.966  22.8  30  0.10  1.73  1.048  21.4  45  0.09  0.64  1.199  20.7  60  0.05  0.23  1.180  80  0.11  0.11  1.191  100  0.10  20.2  10 g .  - 219 -  Table I X :  Microprobe examination o f m a s s i v e c h a l c o c i t e before and a f t e r l e a c h i n g i n NaOCl.  Temp 35°C,  A g i t a t i o n 729 rpm, 2 P o l i s h e d Cu„S s u r f a c e 3.2 cm  Area  1  2  pH 9 . 0 ,  [NaOCl] 7.06  Cu Count Before  Cu/S Ratio  S Count After  Cu Count After  Cu/S Ratio  7287  81631  11.18  4873  71025  14.58  7963  74964  9.41  4429  70794  15.98  5699  71766  12.59  4463  70688  15.84  4698  73564  15.66  4555  71092  15.61  5136  75063  14.19  4517  71194  15.76  5449  75061  13.33  4496  71196  15.84  5528  75144  13.59  4508  70874  15.72  7283  82548  11.33  7867  79133  10.06  7094  82268  11.60  8000  77862  9.73  7232  82722  11.44  8072  78918  9.78  7243  82370  11.37  8030  79544  9.91  7220  82314  10.95  8459.  76290  8.88  S Count Before  g/1  - 220 -  Table X :  M i c r o p r o b e e x a m i n a t i o n o f massive c o v e l l i t e , b e f o r e and a f t e r l e a c h i n g i n NaOCl  Temp 3 4 . 9 ° C ,  A g i t a t i o n 730 rpm, 2 CuS s u r f a c e 4 . 5 cm .  Area  1  2  S Count Before  Cu Count Before  pH 9 . 0 ,  Cu/S Ratio  [NaOCl] 8.1 g / 1 ,  S Count After  Cu Count After  Polished  Cu/S Ratio  14161  67660  4.78  10338  67705  6.55  14132  67131  4.75  10434  67189  6.44  14408  66725  5.63  10264  66974  6.53  14356  66850  4.66  9733  66380  6.82  14516  66570  4.59  9593  66683  6.95  14191  66695  4.70  29880  32991  1.10  14020  66912  4.77  28731  33094  1.15  13932  66553  4.78  28605  52541  1.84  14111  66321  4.69  29641  50942  1.72  13400  64360  4.80  13352  64230  4.81  12751  64821  4.71  13748  64491  4.69  A f t e r CuCl„ Wash A  13704 3 (Green D e p o s i t ) 13826  66909  4.88  00541  79590  147.11  66894  4.84  00670  83579  124.74  - 221 -  Table X I :  NaOCl l e a c h i n g o f c u p r i c s u l p h i d e , o f c a r b o n a t e ( F i g u r e 10)  Temp 35°C,  Time (mins)  A g i t a t i o n 821 rpm,  pH 9 . 0 ,  [Cu] ppm  CuS i n t h e absence  [NaOCl] 7.67 g/1  [NaOCl] g/1  3  0.15  7.52  10  0.17  7.48  20  0.19  6.17  35  0.20  5.04  80  0.20  3.01  100  0.20  1.65  CuS 1 0 . 0 g .  - 222 -  Table X I I :  NaOCl l e a c h i n g o f cuprous s u l p h i d e , o f c a r b o n a t e ( F i g u r e 10)  Temp 35°C,  A g i t a t i o n 806 rpm,  pH 9 . 0 ,  C u  2  S >  -*-  n  t  n  e  [NaOCl] 7.14 g / 1 ,  [Cu] ppm  [NaOCl] g/i  0  0.02  7.14  5  0.10  6.84  25  0.10  5.49  45  0.10  4.04  55  0.08  2.73  85  0.10  1.63  100  0.10  0.45  Time (mins)  absence  C u S 10.0 g . 2  Time (mins)  0.55 g/1 [Cu] ppm  0  [CO ]  1.0 g/1  [C0 ] 3  NaOCl g/i  [Cu] ppm  NaOCl g/i  7.82  0.19  7.67  2 . 0 g/1 [Cu] ppm  [C0 ] 3  5.0 g/1  [C0 ] 3  NaOCl g/i  [Cu] ppm  NaOCl g/i  7.66  0.2  7.44 6.43  5  5.6  6.94  14.5  6.84  21.5  7.05  46.4  10  5.0  5.48  3.0  6.24  12.0  6.69  44.1  20  1.3  3.38  3.9  4.29  12.0  6.59  40.3  30  3.8  1.13  3.3  1.32  13.0  6.39  38.0  45  2.5  —  3.5  0.38  7.5  4.96  37.6  60  2.5  —  3.4  --  4.5  0.52  1.5  0.09  7.5 g/1 [Cu] ppm  84.0  [C0 ] 3  77.4  NaOCl g/i  7.45  0.9  7.85  6.69  119.2  7.07  119.3  6.31  6.64  114.3 105.8  6.47  80.0  113.7  29.0  5.53  77.2  6.62  117.2  20.2  0.25  75.0  6.69  116.5  67.2  6.65  116.2  140  41.8  4.71  107. 3  180  42.1  120  17.3  —  3  [Cu] ppm  77.8  90  [C0 ]  NaOCl g/i  76.8 6.43  10.7 g / 1  —  6.32 6.31  110.1  200  110.8  240  116.1  6.30  255  91.0  5.00  280  64.0  2.00  320  64.0  Table X I I I :  NaOCl l e a c h i n g o f c o v e l l i t e w i t h v a r i a b l e  [C0  3  ]  T  a t pH 9 . 0 ,  35°C ( F i g u r e s  —  12,13)  - 224 -  1.0 g/1 l c o - ]  2.0 g/1 [ c o - ]  5.0 g/1 [ c o - ]  [Cu] ppm  [Cu] ppm  [Cu] ppm  2  Time (mins)  3  0  [NaOCl] g/i  2  3  8.12  [NaOCl] g/i  2.93  7.67  8.5  7.52  10  1.00  7.52  8.0  7.52  20  1.55  7.14  8.0  30  0.85  6.92  6.3  45  0.33  6.39  [NaOCl] g/i 8.06  7.89  5  60  2  3  40.8  7.59  7.52  7.52 38.3  6.00  6.3  6.47  35.2  7.52  90  0.33  5.45  4.8  5.65  23.5  7.00  120  0.28  4.49  2.8  4.86  22.5  5.94  160  0.25  3.81  22.5  4.90  190  0.30  3.08  22.0  4.35  2.3  3.30  240  2.2  0.45  300  3.0  Table XIV:  —  NaOCl l e a c h i n g o f c h a l c o c i t e w i t h v a r i a b l e [CO., a t pH 9.0 , 35°C ( F i g u r e s 14,15)  I  - 225 -  T a b l e XV: NaOCl l e a c h i n g o f s y n t h e t i c copper s u l p h i d e s w i t h 5 g/1 [CO.,""* ] ( F i g u r e s 16,17) >  pH i) . 0 ,  Temp 35 °C,  A g i t a t i o n 821 rpm  Cu S  CuS Time (mins)  [Cu] ppm  0  2  [NaOCl] g/i  [Cu] ppm  7.14  7.67 7.52  [NaOCl] g/i  5  46.6  44.8  15  44.8  30  44.0  7.52  43.8  45  40.0  7.48  43.7  6.84  60  27.5  6.17  30.0  5.49  80  27.5  5.04  23.8  4.04  100  24.6  3.01  10.0  2.73  120  11.0  1.65  7.1  1.63  140  6.7  5.4  0.45  43.8  7.07  - 226  Table X V I :  -  NaOCl l e a c h o f c o v e l l i t e i n the presence o f 5 g/1 and 20 g/1 [NaOCl] ( F i g u r e 18)  Temp 35°C, 6.5165 g ,  Time (mins)  pH 9 . 0 , Na C0 2  3  Agitation  800 rpm,  CuS 10 g ,  [CO  NaHCO  0.4720 g .  [Cu] ppm  0  [NaOCl] g/1  19.17 18.04  2  106  10  117  25  109  40  103  60  97  155  94  13.53  195  49  5.86  205  28  3.35  225  22  0.75  265  22  16.54  ]  - 227  Table X V I I :  Agitation of c o v e l l i t e NaCl ( F i g u r e 19)  Temp 3 5 ° C , NaHC0  3  -  i n the p r e s e n c e o f NaHCO^/Na^CO^ ±  A g i t a t i o n 817 rpm,  14.15 g ,  Na CC> 1.01 2  3  pH 9 . 0 ,  CuS l O g ,  g.  Time  Carbonate o n l y  (mins)  [Cu] ppm  Carbonate and 14.0 g/1 NaCl [Cu] ppm  10  62.5  64.5  20  62.3  64.5  35  60.0  64.0  60  28.5  53.0  75  11.9  41.5  90  9.5  25.0  120  16.0  - 228 -  Table XVIII:  NaOCl l e a c h i n g o f c o v e l l i t e i n t h e presence o f 10 g/1 [ C 0 ~ ] , and Na MoQ (Figure 20) 2  3  Temp 35°C, NaHC0  3  2  [NaOCl] 7.82 g/1,  14.15 g,  Na C0 2  3  4  A g i t a t i o n 803 rpm,  1.01 g,  CuS 10 g,  pH 9.0,  Na^MoO„ 1.538 g = 2 4  0.6 g/1 Mo.  Time (mins)  [Cu] ppm  0  [NaOCl]  [Mo]  g/i  g/i  Mo %  100  7.82  0.66  6.76  0.63  95.5  0.63  95.5  0.65  98.5  0.65  98.5  0.61  92.0  0.65  98.5  5  136  20  133  60  133  6.54  120  131  6.54  180  133  6.52  255  132  6.50  270  118  4.96  290  85  1.65  305  66  0.60  360  64  —  410  20  —  440  9  - 229 -  T a b l e X I X : Sodium h y p o c h l o r i t e d e c o m p o s i t i o n i n the p r e s e n c e o f t r i -v a l e n t copper s a l t s ( F i g u r e 21)  Temp 35 °C,  A g i t a t i o n 700 -• 760 rpm,  copper samples:  Time (mins)  pH 9 . 0 ,  2 g.  Ill copper oxide [NaOCl] g/1  III copper carbonate [NaOCl] g/1  cupric o x i d e , CuO [NaOCl]  0  7.74  7.67  7.82  5  5.94  6.75  7.80  10  3.99  5.40  7.37  20  1.80  3.50  7.22  30  0.38  2.05  6.58  0.20  6.35  45 60 90  —  —  6.00 5.45  g/1  - 230 -  T a b l e XX: NaOCl o x i d a t i o n o f m o l y b d e n i t e  Temp 35°C, MoS  2  pH 9 . 0 ,  ( F i g u r e 22)  A g i t a t i o n 780 rpm,  [NaOCl] 7.7 g / 1 ,  0.3 g .  Time (mins)  [Mo] ppm  0  —  5  Mo e x t r a c t e d %  [NaOCl] g/1  —  7.70  168  93.3  6.83  10  168  93.3  15  169  93.8  20  170  94.4  30  170  94.4  45  170  94.4  60  169  93.8  6.82  6.82  - 231 -  Table X X I :  NaOCl o x i d a t i o n o f ' r e a g e n t g r a d e ' molybdenum d i s u l p h i d e (Figures23,24)  Temp 35°C,  A g i t a t i o n 803 rpm,  pH 9 . 0 ,  98%  Reagent grade MoS^ Time (mins)  [Mo] g/i  Mo e x t r n . "O  MoS  [NaOCl] g/i  [Mo] g/i  2  1.0 g  +  Mo e x t r n . %  5  0 .535  89.3  10  0 .535  89.3  20  0 .535  89.3  30  0 .536  89.3  45  0 .536  89.3  60  0 .536  89.3  [NaOCl] g/i  8.72  8.54  0  MoS„ 2  0.375  62.5  6.91  0.531  88.5  6.05  0.587  97.9  5.68  0.587  97.9  5.59  0.584  97.9  5.00  5.59  0.587  97.9  4.65  5.62  5.60  - 232 -  Table XXII:  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e , w i t h and w i t h o u t c a r b o n a t e b u f f e r s ( F i g u r e 25)  Temp 35°C,  A g i t a t i o n 800 rpm,  CuS 1 0 . 0 g  (10 g/1 t o t a l  MoS , 2  Time (mins)  [Mo] ppm  CuS + NaHCO^/Na  Mo e x t r %  [Cu] ppm  0  —  5  160  88.9  110  10  160  88.9  108  20  160  88.9  106  30  160  88.9  104  45  160  88.9  107  60  160  88.9  103  —  —  pH 9 . 0 ,  [NaOCl] g/i  4.66  4.04  0.3 g  M o S , CuS + NaOH 2  C  4.89  2  carbonate)  2 °3  7.37  MoS  [Mo] ppm  —  Mo e x t r . %  —  [Cu] ppm  —  [NaOCl] g/i 7.43  132  73.3  0.25  4.44  132  73.3  0.30  3.01  133  73.8  0.27  1.13  133  73.8  0.23  0.38  133  73.8  0.32  —  133  73.8  0.27  —  - 233 -  Table X X I I I :  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o c i t e , and w i t h o u t c a r b o n a t e b u f f e r s ( F i g u r e 26)  Temp 35°C,  A g i t a t i o n 785 rpm  C u S 10.0 g (10 g/1 t o t a l 2  M o S , C u S + NaHC0 /Na 2  Time (mins)  [Mo] ppm  2  Mo e x t r . %  3  [Cu] ppm  0  —  5  159  88.5  96.0  10  169  89.2  93.0  20  160  89.0  94.0  30  162  89.9  93.0  45  162  89.9  90.0  60  162  90.0  89.0  —  pH 9 . 0 ,  MoS  with  0. 3 g ,  2  carbonate)  MoS ,  2 °3  2  C  [NaOCl] g/i 7.89  4.61  4.53  4.44  [Mo] ppm  —  C u S + NaOH 2  Mo e x t r . %  —  [Cu] ppm  —  [NaOCl] g/i 7.35  139  77.2  0.13  6.50  139  77.2  0.13  6.35  139  77.2  0.25  6.02  139  77.2  0.25  5.57  139  77.2  0.25  4.95  139  77.2  0.23  3.60  - 234 -  Table XXIV:  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e w i t h and w i t h o u t carbonate b u f f e r s ( F i g u r e 27)  Temp 3 4 . 9 ° C , CuFeS  A g i t a t i o n 792 rpm,  10.0 g (10 g/1 t o t a l  M o S , CuFeS + NaHC0 /Na Time (mins)  [Mo] ppm  0  3  2  2  Mo e x t r . %  —  [Cu] ppm  pH 9 . 0 ,  MoS  0.3 g ,  2  carbonate).  MoS  2 °3 C  [NaOCl] g/i  [Mo] ppm  CuFeS + NaOH  2  2  Mo e x t r . Q. "6  [Cu] ppm  [NaOCl] g/i  7.13  —  7.50  —  5.32  143  79.4  0.53  4.51  144  80.0  0.41  4.17  142  78.8  0.32  2.82  144  80.0  0.32  1.97 0.94  —  —  5  154  86.1  106  10  156  86.6  100  20  156  86.6  98  30  158  87.8  98  45  158  87.8  94  5.25  144  80.0  0.27  60  158  87.8  99  5.20  144  80.0  0.11  5.30  —  - 235 -  Table XXV:  NaOCl o x i d a t i o n o f molybdenum d i s u l p h i d e and c h a l c o p y r i t e w i t h and w i t h o u t c a r b o n a t e b u f f e r s  Temp 35°C, MoS  A g i t a t i o n 780 rpm,  [Mo] g/i  2  10 g ,  5 g (reagent grade)  0  MoS , CuFeS  MoS^ o n l y Time (mins)  pH 9 . 0 , CuFeS  Mo e x t r . 0.  ~o  2  [NaOCl] g/i  24.55  0 5  2.67  89.0  10  2.66  88.7  20  2.68  89.3  30  2.67  89.0  45  2.67  89.0  60  2.67  89.0  [Mo] g/i  —  2  Mo e x t r .  + NaOH  %  [NaOCl] g/i  —  20.32  M o S , CuFeS 2  [Mo] g/i  —  Mo e x t r . %  —  2.54  84.7  8.32  2.64  87.5  2.54  84.7  4.62  2.64  87.5  2.54  84.7  2.83  2.62  87.5  2.54  84.7  1.56  2.62  87.3  11.27  2.54  84.7  0.34  2.62  87.3  11.25  2.54  84.7  —  2.64  87.5  11.32  11.30  + [co -] 2  2  3  [NaOCl] g/i  20.21 7.37  7.28  7.26  - 236 -  Table X X V I :  NaOCl o x i d a t i o n o f m o l y b d e n i t e i n the presence o f copper s u l p h a t e s o l u t i o n  Temp 3 5 . 1 ° C , MoS  2  Time (mins)  0.3 g ,  NaOCl 7.5 g / 1 , CuS0  4  A g i t a t i o n 792 rpm, pH 9 . 0 ,  0.4 g/1 = 0.1 g/1 Cu  Cu added ppm  [Cu] i n s o l n ppm  —  —  168  93.3  10  12.8  0.05  142  79.1  20  25.6  0.10  136  75.3  30  38.4  0.08  135  75.2  45  67.5  0.08  134  74.8  0.11  132  73.5  5  60  100  [Mo] ppm  Mo e x t r d . %  - 237 -  Table XXVII:  NaOCl o x i d a t i o n o f c o v e l l i t e i n the presence o f sodium molybdate s o l u t i o n  Temp 3 5 . 1 ° C , Na Mo0 2  Time (mins)  4  Mo added ppm  A g i t a t i o n 821 rpm,  2.15g= 0.1 g Mo,  [Mo] i n s o l n ppm  pH 9 . 1 ,  [NaOCl] 7.63  CuS 10.0 g ,  g/1  Mo i n s o l n %  [Cu] ppm  10  11.04  9.79  89.0  0.23  20  25.55  22.48  88.0  0.31  30  39.23  33.38  85.1  0.31  45  51.80  44.55  86.0  0.32  60  75.45  62.62  83.0  0.33  90  100.00  81.00  81.0  0.33  - 238 -  Table X X V I I I :  NaOCl o x i d a t i o n o f m o l y b d e n i t e a t pH 5.5 ( F i g u r e 28)  Temp 35°C,  A g i t a t i o n 880 rpm, pH 5 . 4 ,  [NaOCl] 6.92 g / 1 ,  Time (mins) 0  [Mo] g/1 —  Mo S  2  1.0 g  Mo e x t r a c t e d % —  5  0.550  91.6  10  0.563  93.8  20  0.548  91.3  30  0.563  93.8  45  0.564  94.0  60  0.563  93.8  [NaOCl] g/1 6.92  2.71  2.53  2.21  - 239 -  T a b l e XXIX:  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 5.5 ( F i g u r e 29)  A g i t a t i o n 803 rpm,  Temp 3 5 ° C , CuFeS  2  10 g ,  MoS  2  [NaOCl]  6.54 g / i  0. 3 g .  2  MoS , C u F e S  pH 5 . 5 5 ,  2  [Mo] ppm  Mo e x t r .  142  78.8  10  4.1  2.27  20  4.5  30  + NaOH  M o S , CuFeS 2  2  + 10 g NaHC0  3  [Mo] ppm  Mo e x t r .  146  82.2  12.9  0.2  0.10  37.5  2.50  8.7  0.3  0.16  33.7  4.6  2.56  8.1  1.7  0.94  27.2  45  4.5  2.50  8.1  1.6  0.88  25.0  60  4.6  2.56  8.4  1.2  0.66  25.0  Time  5 (CuFeS  2  %  [Cu] ppm  —  %  [Cu] ppm  —  added)  - 240 -  Table  XXX:  NaOCl o x i d a t i o n o f molybdenite and c o v e l l i t e a t pH 5.5 (no c a r b o n a t e ) ( F i g u r e 30 a)  Temp 35°C, CuS 10.0 g,  A g i t a t i o n 802 rpm, MoS  2  pH 5.45,  [NaOCl] 6.17 g/1  0.3 g.  Time (mins)  [Mo] ppm  Mo e x t r a c t e d %  [Cu] ppm  5  141  78.3  10  5.8  3.2  18.0  1.54  20  6.2  3.4  15.2  0.03  30  6.6  3.6  13.5  45  6.6  3.6  12.9  60  6.7  3.7  12.8  90  6.2  3.4  12.4  —  [NaOCl] g/1  5.55  (CuS added)  - 241 -  Table XXXI:  NaOCl o x i d a t i o n o f m o l y b d e n i t e and c o v e l l i t e a t pH 5 . 5 , w i t h sodium b i c a r b o n a t e ( F i g u r e 30 b)  Temp 3 4 . 9 ° C , CuS 10 g ,  Time (mins) 5  [Mo] ppm  A g i t a t i o n 800 rpm,  Mo S  0.3 g ,  NaHCO  Mo e x t r a c t e d %  pH 5 . 5 0 ,  [NaOCl] 6.92  g/1  10.0 g .  [Cu] ppm  [NaOCl] g/1  153  85.0  —  6.92  10  2.4  1.33  36.0  0.15  20  2.4  1.33  35.0  30  2.5  1.38  32.0  45  3.0  1.66  30.0  60  2.4  1.33  30.0  (CuS added)  - 242 -  T a b l e XXXII:  NaOCl l e a c h i n g o f c h a l c o p y r i t e a t pH 5.5 w i t h and without b i c a r b o n a t e i n the system  Temp 35°C,  A g i t a t i o n 805 rpm,  [NaOCl] 7.2 g/1,  CuFeS  2  CuFeS  2  10 g,  pH 5.40, NaHC0  3  9.28 g.  CuFeS  only  2  + HCO3-  [Cu] ppm  [NaOCl] g/i  [Cu] ppm  5  36.5  5.7  48.8  5.64  10  34.2  4.6  46.2  4.52  20  30.6  3.4  45.3  3.30  30  28.5  1.7  44.8  3.30  45  25.0  0.5  43.6  3.28  60  24.1  —  42.5  3.25  90  24.3  —  Time (mins)  [NaOCl] g/i  - 243 -  T a b l e XXXIII:  NaOCl l e a c h i n g o f molybdenite and c h a l c o c i t e a t pH 6.5, w i t h b i c a r b o n a t e i n t h e system ( F i g u r e 31 a)  Temp 35°C,  A g i t a t i o n 880 rpm,  Cu S 10 g, MoS 2  Time (mins)  0  [Mo] g/1  —  2  1.0 g, NaHC0  Mo e x t r a c t e d %  3  pH 6.5,  [NaOCl] 6.92 g/1  10 g.  [Cu] ppm  [NaOCl] g/1  6.92  —  10  0.531  88.3  34.7  2.71  20  0.531  88.3  29.5  2.11  30  0.529  88.1  25.0  2.11  45  0.529  88.1  25.0  2.10  60  0.529  88.1  25.0  2.06  - 244 -  T a b l e XXXIV:  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o c i t e a t pH 6 . 5 , w i t h no c a r b o n a t e p r e s e n t ( F i g u r e 31 b)  Temp 35°C,  A g i t a t i o n 880 rpm,  [NaOCl]7.52 g / 1 ,  Mo S  2  l.Og,  pH 6 . 5 , C u S 10 g 2  Time (mins)  [Mo] g/1  Mo e x t r a c t e d %  [Cu] ppm  [NaOCl] g/1  10  0.515  85.8  32.6  2.65  20  0.472  78.6  30.0  2.34  30  0.465  77.5  29.5  1.97  45  0.387  64.5  24.3  1.03  60  0.280  46.6  18.7  0.20  90  0.253  42.2  16.2  - 245 -  T a b l e XXXV:  NaOCl l e a c h i n g o f molybdenite and c u p r i c s u l p h i d e a t pH 6.0 i n t h e presence o f carbonate (Figure 32)  Temp 35°C,  A g i t a t i o n 803 rpm,  [NaOCl] 7.04 g/1,  Time (mins)  [Mo] g/1  CuS 10.0 g,  Mo e x t r a c t e d %  pH 6.5, MoS  2  1.0 g,  [Cu] ppm  NaHC0  3  10.0 g  [NaOCl] g/1  10  0.539  89.8  39.5  5.04  20  0.531  88.5  24.5  2.86  30  0.549  91.5  25.5  45  0.560  93.3  25.5  60  0.560  93.3  24.9  100  0.560  93.3  25.0  2.63  2.56  - 246 -  T a b l e XXXVI:  NaOCl l e a c h i n g o f molybdenite and c u p r i c s u l p h i d e a t pH 6.0, w i t h no carbonate p r e s e n t  Temp 35°C, 6.39 g/1,  Time (mins)  [Mo] g/1  A g i t a t i o n 857 rpm, CuS 10.0 g,  MoS  2  pH 6.5,  [NaOCl]  1.0 g.  Mo e x t r a c t e d %  [Cu] ppm  [NaOCl] g/1  10  0.473  78.8  32.7  3.39  20  0.455  75.8  37.2  2.63  30  0.441  73.5  17.2  2.18  45  0.288  48.0  11.8  2.03  60  0.093  15.5  4.5  1.28  90  0.061  10.2  0.3  0.38  - 247 -  T a b l e XXXVII:  NaOCl l e a c h i n g o f molybdenite and c h a l c o p y r i t e a t pH 7.0 w i t h b i c a r b o n a t e p r e s e n t ( F i g u r e 33 a)  Temp 35°C, 6.5 g/1,  Time (mins)  [Mo] g/1  A g i t a t i o n 785 rpm, CuFeS  2  10 g,  MoS  Mo e x t r a c t e d %  2  pH 7.0,  1.1 g,  [Cu] ppm  [NaOCl]  NaHC0  3  10 g  [NaOCl] g/1  5  0.62  93.9  56.6  2.63  10  0.64  96.9  58.2  0.23  20  0.65  98.5  52.5  —  30  0.64  96.9  48.5  —  50  0.65  98.5  42.5  —  70  0.65  98.5  41.3  - 248 -  Table X X X V I I I :  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o p y r i t e a t pH 7 . 0 , no c a r b o n a t e ( F i g u r e 33 b)  Temp 35°C,  Time (mins)  A g i t a t i o n 785 rpm,  6.54 g / 1 ,  CuFeS  [Mo] g'/l  Mo e x t r a c t e d %  2  10 g ,  MoS  2  pH 7 . 0 , 1.0  [NaOCl]  g.  [Cu] ppm  [NaOCl] g/1  5  0.173  28.75  12.5  10  0.180  30.00  8.2  3.01  20  0.185  30.83  3.0  2.11  30  0.190  31.66  1.9  60  0.195  32.50  1.3  120  0.195  32.50  0.7  205  0.203  33.75  0.5  1.96  1.94  - 249 -  T a b l e IXL: NaOCl d e c o m p o s i t i o n i n t h e p r e s e n c e o f copper molybdate a t pH 5.5 ( F i g u r e 35)  Temp 35°C, 6.84 g/1,  Time (mins)  0  A g i t a t i o n 792 rpm, Cu Mo0  4  pH 5.40,  [NaOCl]  2 g.  [NaOCl] g/1  [NaCIO ] g/1  6.84  —  10  6.39  0.109  20  5.30  0.785  30  4.14  1.430  45  2.31  1.480  - 250 -  T a b l e X L : D e t e r m i n a t i o n o f the s o l u b i l i t y o f copper molybdate a t pH 5.0 ( F i g u r e 34)  pH 5.0  Na Mo0 -2H 0  4.13 g = 0.096 g/1 Mo  CuSO -5H 0  6.22 g 5 0.064 g / 1 Cu  2  4  4  Mo added (Moles)xlO  2  Mo i n s o l n (Moles)xlO  2  2  2  Cu i n s o l n (Moles)xlO  2  Mo p p t d (Moles)xlO  Cu p p t d (Moles)xlO  0.2  0.188  0.889  0.12  0.24  0.4  0.350  0.884  0.50  0.29  0.6  0.604  0.883  --  0.30  0.8  0.792  0.860  0.08  0.53  1.0  0.881  0.795  1.20  1.18  1.2  0.880  0.595  3.20  3.18  1.4  0.881  0.385  5.20  5.28  - 251 -  Table X L I :  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e and c o v e l l i t e pH 1 0 . 0 , w i t h c a r b o n a t e ( F i g u r e 37 a)  Temp 3 5 . 1 ° C , 7.54 g / 1 , NaHC0  Time (mins)  3  A g i t a t i o n 789 rpm,  MoS  2  0.3 g ,  pH 1 0 . 0 ,  CuS 1 0 . 0 g,  Na C0 2  [NaOCl] 3  5.37 g ,  7.24 g .  [Mo] ppm  Mo e x t r n . %  [NaOCl] g/1  5  148  82.2  6.63  10  150  83.3  20  154  85.5  30  158  87.8  45  160  88.9  6.25  60  164  91.1  6.23  6.43  - 252 -  Table X L I I :  Sodium h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e . and c o v e l l i t e a t pH 1 0 . 0 w i t h no c a r b o n a t e ( F i g u r e 37 b)  Temp 35°C, 7.61 g / 1 ,  A g i t a t i o n 790 rpm, CuS 10 g ,  MoS  [Mo] ppm  Mo e x t r n .  5  142  10  pH 1 0 . 0 ,  [NaOCl]  0.3 g .  [Cu] ppm  [NaOCl] g/i  78.9  0.5  6.01  142  78.9  0.7  3.10  20  142  78.9  0.5  0.60  30  141  78.3  0.5  0.05  45  143  79.4  0.4  60  143  79.4  0.3  Time (mins)  %  —  - 253 -  Table X L I I I :  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and cuprous s u l p h i d e a t pH 9 . 0 , w i t h no carbonate ( F i g u r e 36)  Temp 35°C,  A g i t a t i o n 808 rpm,  33.32 g / 1 ,  MoS  Time (mins)  2  5 g,  pH 9 . 0 ,  [NaOCl]  C u S 10 g . 2  [Mo] g/1  Mo e x t r n . %  5  2.66  88.67  10  2.65  88.30  20  2.66  88.67  30  2.66  89.0  45  2.68  89.0  70  2.68  89.0  [NaOCl] g/1  19.36  10.53  4.14  - 254 -  Table XLIV:  NaOCl l e a c h i n g o f molybdenum d i s u l p h i d e and cuprous s u l p h i d e a t pH 9 . 0 , w i t h 10 g/1 c a r b o n a t e ( F i g u r e 36)  Temp 35°C,  A g i t a t i o n 803 rpm,  33.08 g / 1 ,  MoS  Time (mins)  2  5 g,  pH 9 . 0 ,  [NaOCl]  C u S 10 g . 2  [Mo] g/1  Mo e x t r n . %  [NaOCl] g/1  5  2.68  89.01  10  2.68  89.01  20  2.70  90.00  30  2.72  90.67  45  2.72  90.67  16.16  60  2.72  90.67  13.90  20.14  19.36  - 255 -  T a b l e XLV:  NaOCl l e a c h i n g o f c h a l c o p y r i t e , c h a l c o c i t e and c o v e l l i t e a t pH 9.0 w i t h no c a r b o n a t e ( F i g u r e 38)  Temp 35°C, 7.74 g / 1 ,  CuFeS  A g i t a t i o n 799 rpm,  pH 9 . 0 ,  [NaOCl]  Cu samples 10 g-  2  C U  2  CuS  S  [Ca] ppm  [Cu] ppm  [Ca] ppm  [Cu] ppm  [Ca] ppm  [Cu] ppm  5  65.0  0.68  3.48  0.07  8.0  0.13  10  65.3  0.75  3.55  0.12  9.2  0.15  20  66.2  0.52  5.35  0.15  9.5  0.09  30  66.8  0.33  4.03  0.08  8.1  0.05  40  66.8  0.32  4.10  0.04  8.5  0.12  50  66.6  0.30  4.18  0.07  8.8  0.17  60  66.8  0.52  4.20  0.13  9.8  0.13  Time (mins)  - 256 -  Table X L V I :  NaOCl l e a c h i n g o f MoS^ and Cu^S i n the p r e s e n c e o f 0.1 c a l c i u m as C a C l ^ s o l u t i o n Temp 35°C, 8.0 g / 1 , CaCl  Time (mins)  2  A g i t a t i o n 821 rpm, M o S  2  1  g  pH 9 . 0 ,  (reagent g r a d e ) ,  g/1  [NaOCl]  C u S 10 g , 2  0.3703 g = 0.1 g C a .  [Ca] ppm  [Mo] g/1  Mo e x t r . %  Mo p p t d . (x 10 M)  Ca p p t d . (x 10 M) 4  0  97.25  10  92.50  0.522  87.2  1.56  1.24  20  91.25  0.522  87.2  1.56  1.50  30  92.50  0.525  87.5  1.25  1.24  45  92.50  0.525  87.5  1.25  1.24  60  92.50  0.525  87.5  1.25  1.24  —  —  —  —  - 257 -  Table X L V I I :  NaOCl l e a c h i n g o f m o l y b d e n i t e and c h a l c o c i t e i n the p r e s e n c e o f CaCl^, and Na^CO^/NaHCO^ Temp 3 4 . 9 ° C , 7.89 g / 1 ,  Agitation  MoS  2  NaHCt> 14 .15 g , 3  820 rpm,  1.0 g , Na C0 2  pH 9 . 0 ,  CU S 10 g ,  CaCl  2  3  [NaOCl] 2  0.3703 g,  1.01 g-  [Mo] g/i  Mo e x t r .  5  0.487  81.5  2.15  10  0.538  89.2  1.90  30  0.537  89.0  1.90  60  0.538  89.2  1.90  100  0.540  89.9  1.90  135  0.542  90.0  1.90  Time [mins)  %  [Ca] ppm  - 258 -  Table X L V I I I :  NaOCl l e a c h i n g o f m o l y b d e n i t e and c a l c i t e w i t h no c a r b o n a t e ( F i g u r e 40)  Temp 3 4 . 9 ° C , 9.5 g / 1 ,  Time (mins)  MoS  A g i t a t i o n 805 rpm, 2  1 g,  [Mo] g/1  CaC0  3  pH 9 . 0 ,  [NaOCl]  10 g .  Mo e x t r n . %  [Ca] ppm  10  0.495  82.5  9.00  20  0.495  82.5  10.12  30  0.495  82.5  10.13  60  0.500  83.3  10.25  120  0.505  83.4  10.36  - 259 -  Table I L :  NaOCl l e a c h i n g o f powdered c a l c i t e , CaCO^, a t pH 9.0 ( F i g u r e 39)  Temp 35°C, A g i t a t i o n 780 rpm, CaCO., 10 g = 4 g Ca  Time (mins)  [Ca] ppm  pH 9 . 0 ,  [NaOCl] 6.69  Ca e x t r . %  0  0.25  5  13.35  0.33  10  13.40  0.34  20  14.50  0.36  30  15.25  0.38  50  15.50  0.39  70  16.00  0.40  g/1  - 260 -  .:  NaOCl l e a c h i n g o f ( F i g u r e 39)  Time (mins)  p l a s t e r of p a r i s ,  [Ca] g/i  CaSO^*%H 0 a t pH 9.0 4 2 n  Ca e x t r n .  5  1.81  60.2  10  1.87  62.1  20  1.89  63.0  30  1.89  63.0  50  1.90  64.5  70  1.90  64.5  Temp 3 5 ° C ,  Agitation  C a S O ^ H ^ O 10 g  [NaOCl]  Q, "O  805 rpm,  pH 9 . 0 ,  7.89  7.89  7.94  [NaOCl] 8.01 g / 1 ,  LI:  i)  CaSo -J5H 0 4  Time (mins)  2  0 g/1 NaCl [Ca]  g/1  0.435  10  12 g/1 NaCl [Ca]  g/1  0.960  20  28 g/1 NaCl [Ca]  g/1  0.659  g/1  0.712  1.326  90  0.712  1.326  ii)  [Ca]  g/1  1.860 1.684  1.864  CaC0  2.06 2.012  2.08  2.012  2.10 2.10  1.686 1.528  1.690  1.860  2.012  3  0 g/1 NaCl  13 g/1 NaCl  20 g/1 NaCl  35 g/1 NaCl  40 g/1 NaCl  80 g/1 NaCl  [Ca] ppm  [Ca] ppm  [Ca] ppm  [Ca] ppm  [Ca] ppm  [Ca] ppm  6.5  20  12.25  16.80  21.50  14.50  18.30  33.50  34.75  48.75  56.80  49.00  58.60  49.00  60.30  30  15.5  15.25  45  16.0  15.50  60  16.5  16.00  Tables L I , L I I :  [Ca]  1.868  1.528  60  10  [Ca]  1.688  50  Time (mins)  g/1  58.5 g/1 NaCl 86.8 g/1 NaCl 117 g/1 NaCl  1.314  40  LII:  [Ca]  1.394 1.548  30  40 g/1 NaCl  35.0  43.20  35.75 55.05  55.00  E f f e c t o f i n c r e a s i n g c h l o r i d e c o n c e n t r a t i o n on c a l c i u m d i s s o l u t i o n from i ) c a l c i u m s u l p h a t e i i ) c a l c i u m carbonate ( F i g u r e 41-44) pH 9 . 0 ,  Temp 35°C,  A g i t a t i o n 780 - 860 rpm  g/1  - 262 -  Table L I I I :  E f f e c t o f carbonate on c a l c i u m c o n t e n t i n h y p o c h l o r i t e s o l u t i o n s ( F i g u r e 45) pH 9 . 0 ,  [C0  2 3  ] added g/1 T  0  Temp 35°C,  [CO^ ] (moles) -  —  NaOCl 8.0  [Ca] ppm  g/1  [Ca] (moles)  1.750  0.0438  [Ca] p p t d . (moles)  2.838  0.047  0.330  0.0082  0.0356  5.00  0.083  0.110  0.0027  0.0411  10.00  0.167  0.020  3.8xl0~  4  0.0434  25.00  0.417  0.005  9.3xl0~  5  0.0437  - 263 -  Table L I V :  NaOCl l e a c h i n g o f c o v e l l i t e and m o l y b d e n i t e w i t h 5 g/1 c a r b o n a t e ( F i g u r e 46) Temp 3 5 ° C , 8.77 g / 1 ,  A g i t a t i o n 821 rpm, CuS 10 g ,  MoS  2  1 g,  pH 9 . 0 , [C0 "]  [NaOCl]  2  3  T  5 g/1  Time (mins)  [NaOCl] g/1  [Cu] ppm  [Mo] g/1  10  2.71  14.3  0.510  85.0  30  2.71  14.0  0.510  85.0  45  2.11  10.0  0.516  86.0  65  0.75  6.5  0.510  85.0  85  0.23  4.0  0.546  91.0  —  5.0  0.540  90.0  120  Mo e x t r n . %' -  - 264 -  T a b l e L V : NaOCl l e a c h i n g o f m o l y b d e n i t e and c o v e l l i t e i n the p r e s e n c e o f 10 g/1 carbonate ( F i g u r e 46)  Temp 35°C, MoS  Time (mins)  2  A g i t a t i o n 803 rpm, pH 9 . 0 , [NaOCl] 7.5 21.0 g , CuS 10 g , [C0 ] 10.7 g / 1 .  g/1  3  [Cu] ppm  [Mo] g/1  Mo e x t r n . %  [NaOCl] g/1  5  109  0.485  80.8  2.33  10  89  0.490  81.7  2.20  40  99  0.535  89.1  2.18  60  98  0.542  90.3  2.18  120  98  0.542  90.3  2.02  150  79  0.543  90.5  0.25  180  63  0.542  90.5  - 265 -  Table L V I :  NaOCl l e a c h i n g o f c o v e l l i t e and sodium molybdate w i t h 5 g/1 c a r b o n a t e ( F i g u r e 48)  Temp 35°C, Na Mo0 2  4  6.52 g ,  A g i t a t i o n 785 rpm,  0.5 g = 0.35 g [Mo], [NaOCl] 7.5  pH 9 . 0 , NaHC0  3  CuS 10 g ,  0.46 g ,  Na C0 2  3  g/1.  Time (mins)  [Cu] ppm  [Mo] g/1  Mo i n s o l n %  [NaOCl] g/1  10  39.0  0.341  97.4  6.32  30  37.0  0.323  92.3  5.68  60  27.5  0.315  90.0  1.95  70  19.5  0.305  87.1  1.65  85  8.4  0.295  84.3  0.60  - 266 -  Table L V I I :  NaOCl l e a c h o f molybdenum d i s u l p h i d e and c h a l c o c i t e w i t h 10 g / 1 carbonate ( F i g u r e 47)  Temp 35°C, C u S 10 g , 2  Time (mins) 0  A g i t a t i o n 803 rpm, pH 9 . 0 , 2[C0 ] 10.68 g / 1 . 3  MoS  1.0  g,  T  [Cu] ppm  [Mo] g/1  —  —  Mo e x t r n . % —  [NaOCl] g/1 7.06  10  96.0  0.403  67.16  3.61  30  93.0  0.555  92.50  2.71  60  90.0  0.570  95.00  2.48  120  89.0  0.570  95.00  2.36  150  66.0  0.570  95.00  1.55  180  64.0  0.570  95.00  0.60  240  16.0  0.570  95.00  - 267 -  Table L V I I I :  NaOCl o x i d a t i o n o f molybdenum d i s u l p h i d e and c h a l c o p y r i t e w i t h 1 g/1 S i 0 ~ added t o the system, pH 9.0 ( F i g u r e 49T 2  o  Temp 35°C, MoS  2  1 g,  A g i t a t i o n 803 rpm, CuFeS  2  10 g ,  Na Si0 2  [NaOCl] 8.4 3  g/1,  3.29 g , pH 9 . 0 .  Time (mins)  [Cu] ppm  [Mo] g/1  Mo e x t r n . %  10  0.25  0.579  96.5  20  0.13  0.579  96.5  30  0.17  0.583  97.2  60  0.22  0.590  98.4  90  0.15  0.593  98.9  [NaOCl] g/1  5.04  5.04  5.04  - 268 -  APPENDIX B B.l  C a l c u l a t i o n o f s u r f a c e areas f o r ground m i n e r a l samples The s p e c i f i c s u r f a c e ( s u r f a c e p e r u n i t w e i g h t ) o f a screened m a t e r i a l i s g i v e n by the e x p r e s s i o n : x *l *2 xx  k-l  2  S  n = A V  =  6hk . A (k-l)  *2  k-l "  X  I  k X  2  k "  l  X  where x^ = u n i t c r y s t a l s i z e x^ = s i z e o f -mesh p a r t i c l e h  = shape f a c t o r  k  = constant  A  = specific gravity  F o r copper s u l p h i d e m i n e r a l s ground t o pass a -200 mesh s c r e e n : x^ = 5 x 10 x  cm  = 0.0074 cm  2  h  = 1 . 7 5 ( i . e . assume i r r e g u l a r l y shaped p a r t i c l e s have 1.75 x the s u r f a c e a r e a o f a cube f o r same screen size)  k  = 1.02  A  = 5.6 - 5.8 (Cu S) 2  = 4.5 - 4 . 6 (CuS) 6 x 1.75 x 1.02 Cu^S 2  -  0.0074 -° ( 0  2 )  UT021 0.0074 '  5.65 x 0.02  v  =  94.779 x 28.632 c m g  =  2 -1 2713.71 cm g  2  - 1  -  (5 x 1 0 ~ ) "  -  ~ , -8,1.02 (5 x 10 )  8  0  2 -1  0 2  c m  g  - 269 -  6 x 1.75 x 1.02 C U S  ~  •  0.0074 °(  4 . 6 0 x 0.02  0.0074  116.41 x 28.632 c m g 2  =  3333.05  cmV  ( 1  0 2 )  -°  2 )  -  (5 x 10  -  (5 x I O " ) '  8  )°8  1  -1  0 2 2 0 2  "  ?  - 1  1  10 g o f c h a l c o c i t e w i l l have a t o t a l s u r f a c e a r e a o f 27,137 cm and 10 g o f c o v e l l i t e w i l l have a t o t a l s u r f a c e a r e a o f 33,330 2 cm . 90 ( E r r o r o f c a l c u l a t i o n can be 30 - 50%) B.2  2  C a l c u l a t i o n o f a v a i l a b l e copper f o r p r e c i p i t a t i o n on m i n e r a l s u r f a c e a f t e r c o p p e r formation 1 1 1  o  Radius o f copper m o l e c u l e = 1A = 10  -a  cm  copper p r e c i p i t a t e d = 60 ppm = 0 . 0 6 g/1 23 A v a g a d r o ' s number = 6 x 10 0.06 , 23 Number o f Cu m o l e c u l e s = ,- x 6 x 10 63. D l n  T o t a l a r e a o f Cu  =  5.660 x 1 0  =  5.669 x 1 0  2 1  2 1  x 10~  8  =  5.669 x 1 0  1 5  T h i s compares w i t h a s u r f a c e a r e a o f 2.71 x 1 0 ' cm" f o r a 10 g 4 2 sample o f c h a l c o c i t e , and 3.33 x 10 covellite.  cm  f o r a 10 g sample o f  The s m a l l amount o f copper p r e c i p i t a t e d as C u  1 1 1  is  t h u s s u f f i c i e n t t o form a mono-molecular l a y e r on the m i n e r a l surface. B.3  H y p o c h l o r i t e redox e q u i l i b r i a a t pH 9.0  1) HC10 +  H  + E  e  = =  1.59  JgCl^aq) +  0.0591  +  H 0 2  { l o g (HC10) - Jglog ( C l ) - pH} 2  cm . 2  - 270 -  2)  *SCl (aq)  +  2  e  Cl"  E  =  +  2e  E  =  1.40  +  0.0591  {%log ( C l ) 2  -  l o g ( C l )}  -  log (Cl )  (1) + (2) 3)  4)  HC10 +  HC10  H  =  +  5)  CIO  Cl~ +  1.49  HCIO  +  H  E° (2) -  =  =  +  0  ,  °^  9  H 0 2  { l o g (HC10)  1  - pH}  + CIO"  1.49  (4) + (1) : +  2H  +  +  2e  =  Cl" +  E  =  1.738  +  °' ^  E  =  1.738  +  { 0  =  1.738  -  =  1.206 V  0  H 0 2  9 1  ( l o g (CIO )  a t pH 9.0  E  -  0 5  9 1 ) 2  0.532  •  (-18)  -  log (Cl ) -  2pH>  - 271 -  APPENDIX C R e a c t i o n s and e q u i l i b r i a p e r t a i n i n g t o p o t e n t i a l pH diagrams f o r v a r i o u s m e t a l molybdate systems shown i n F i g u r e s 52-58  C.1 C.l.l  Cu-H^O-MoO^ system Substances  considered.  Oxidation Number  0  AG°  Species  (kcal)  Cu°  Source o f Data  —  +1  Cu 0  -34.98  73  +1  Cu  +12.00  73  +2  CuO  -30.40  73  +2  Cu(OH)  -85.30  73  +2  -202.70  91  +15.53  73  -43.50  73  +2  CuMo0 ^ + Cu 2Cu0 Cu0 H  -61.42  73  +3  C U  -41.50  74  -26.87  74  +72.50  74  -120.00)  73  -161.95)  73  -213.60)  73  -205.42  35  2  +  4  2  +2 +2  2  2  +3 +3 (+4 (+6 (+6 +6  2  2°3 CuO r,  3  Cu Mo0  +  3  HMoO„~ 4 MoO ~ 4 CuMoO. 4 2  A c t i v i t y o f copper c o n t a i n i n g s p e c i e s i n s o l u t i o n s has been t a k e n as 10 ^ M, and t h a t o f molybdenum c o n t a i n i n g s p e c i e s as 10  1  M.  272  C.1.2 1)  Two d i s s o l v e d + Cu  substances  2+ ->Cu  +  e  E  =  0.153  2+ 0.0591 l o g ^ (Cu )  +  +  E 2)  Cu  +  +  =  0.153  2H 0  >-HCu0  2  +  2  E  = 1.733  3H  +  +  e"  0.1773 pH  -  +  0.0591 l o g  ( H C u  ° -i2  (Cu ) E  3)  + Cu  +  =  1.733  2H 0  >Cu  2  E  =  0.1773 pH  -  2-  °2  „ + +  2.510  +  e  0.2364 pH  -  +  0.0591 l o g  -^^-2—-  (Cu ) E  4)  Cu  +  2 +  =  2.510  2H 0  >flCu0  2  log  0.2364 pH  -  +  3H  =  -2.72  +  3pH; pH = 8.91  -39.88  +  4 pH; pH = 13.15  2  °2-^(Cu )  ( H C U  +  +  5)  HCu0  2-  > °2 Cu  2  +  H  2log - ^ ^ 2 (HCu0 ~) ]  +  =  2  ^ , 2 + 6) Cu  3+ • Cu  +  e 3+  E  7)  Cu0  2-  =  Cu0  2  E  =  2.475  2  + 0.721  +  0.0591  log  ; E = 2.475  U  (Cu  )  (CuO log (Cii0  )  e +  0.0591  2  ; E = 0.721 )  - 273 -  8)  HCu0  > C u 0 2  2  +  6  (Cu0 E  =  1.498  -  0.0591 pH  +  2  )  0.0591 l o g (HCu0 ~) 2  E 9)  Cu  2 +  +  =  2H 0  1.498  -  =*CuO  2  0.0591 pH +  4H  +  +  e" (CuO  E  =  3.078  -  0.2364 pH  +  )  0.0591 l o g (Cu ) 2+  E 10)  3+ Cu  +  =  2H.0  3.078 >-Cu0  -  0.2364 pH + + 4H  o  (Cu0 ) log * — = (Cu ) 2  -10.28  +  4 pH; pH  =  2.57  3+  C.1.3  11)  12)  13)  One s o l i d substance and one substance Cu 0 2  Cu 0 2  Cu  +  +  + 2H  2+ >-2Cu  +  H 0  +  0.0591 pH  E  =  0.203  E  =  -0.152  3H 0  +  2  dissolved  4H  +  +  + 2e  2  +  2e 2+ 0.0591 l o g (Cu )  +  0.0591 pH »- 2HCu0 ~ + 2  E  =  1.783  -  0.1182 pH  E  =  1.428  -  0.118 pH  +  2+ 0.0295 l o g (Cu ) ; E  2+ ->Cu  + E  =  +  4H  +  +  2e~  0.0591 l o g (HCu0 ~) 2  2e 0.337  =  0.337  274  . 14)  2 a)  + Cu  +  H 0  b)  2+ Cu  +  =  7.89  -  2 pH; pH  > Cu(OH)  +  + 2H  2+ (Cu )  log +  2H 0 2  + 2H  CuO  2  2  =  6.93  2+ log 15)  a)  CuO +  b)  Cu(OH)  (Cu  H 0  (HCu0 ~)  18)  2+ Cu  a)  b)  +  C  2  +  (CuO  3H 0  )  2  2  +  + 2H  =  -31.98 + 6H  +  +  -  0.1182 pH  E  =  1.428  -  0.118 pH  C u 0  2  _  +  2  H  +  =  2.609  -  0.1182 pH  E  =  2.254  -  0.118 pH  >  C u 0  2~  +  2  H  12.83  +  +  2  e  E  =  1,267  -  0.118 pH  E  =  1.149  -  0.118 pH  =  =  12.4  12.99  -  +  +  E  2  pH; pH 2e  1.783  •  =  2 pH; pH  +  =  2  pH; pH  +  E  H 0  7.54  +  -30.80  3  =  +  +  2  >• C u 0  2  H  =  2-  H  2 pH; pH  -18.83 2  )  2  Cu0  2  Cu(0H)  0  (Cu0  H 0  CuO +  u  -  +  =  2  >  2  log 17)  9.071  2  log CuO +  =  y HCu0 ~  2  log  16)  )  0.0591 l o g (HCu0  2  e  +  2  _  0.0591 l o g (Cu0 ~) 2  " -  0  '°  9 2  1  l o g (Cu0 ~) 2  )  - 275 -  19)  ' 3 + Cu  +  3H 0  y Cu 0  2  2  3+ (Cu )  log 20)  C u 2  °3  +  2°  H  21)  2-  Cu0  2  +  =  2 C u 0 2  log Mo0  +  2  =  2  2-  -6.09  ~  (Cu0 ~)  H  + 3  pH; pH  =  -0.3  +  -16.31  + 4H  +  4  + + 6H  3  +  y CuMo0  p H ; pH +  4  =  10.31  2H 0 2  24 pH  =  67.18  -  222)  Cu0 H  +  2  Mo0  3 pH  23)  24)  C.1.4 25)  CuMo0  =  CuMoO„ 4  +  +  -  Mo0  E  =  3.026  E  =  2.671  a)  Cu  +  4  +  0.0591 l o g  +  MoO„ 4  3.626  -  0.236 pH  E  =  3.271  -  0.236 pH  y Cu 0 2  y  2  E  =  2  +  2H -  CuO +  0.570  -  +  + +  +  2e~  0.0591 pH 2H  24  ) ) ; pH = 9.99  3 +  substances  H 0  2H 0  ((Cu )•(MoC^ ))  2-  =  2  )'); pH = 10.815  4  e  E  H 0  +  +  4  y CuO„ 2  0.471 26)  y CuMo0  ) • (Mo0  2  0.0591 l o g ((CuC^H ) • ( M o 0 2-  +  2H O 2  Two s o l i d 2Cu  49.06 3+ y Cu  4  + 3H  +  4  0.0591 l o g ( ( C u 0  2-  +  +  2e~  0.0591 pH  + 4H  2 -  +  e  -  0.0591 l o g ( ( C u 0  2  )•(MoO  2-  )  - 276 -  b)  Cu  +  2H 0  y Cu(OH)  2  E 27)  a)  Cu 0  +  2  =  H 0  Cu 0  +  2  =  0.669  3H 0 = 2-  28)  Cu 0 2  +  2Mo0  E  =  0.35  E  =  0.379  -  a)  CuO +  Mo0  +  4  =  17.23  pH  =  8.62  2 pH  30)  a)  b)  +  2  =  +  +  +  +  2  2H  0.0591 pH  +  2H -  Mo0 18.46  > CuMo0  H 0 2  +  2e  0.029 l o g (MoO ~ ) 2  +  4  H 0 2  2  + +  4  -  2H  CuMo0  4  +  0.0591 l o g ( M o O ^ ) 2-  y Cu 0 2  =  2e~  0.0591 l o g (MoO ~ )  C u  E  +  4  -  +  2  H  +  +  2  2  +  +  0.0591 pH  pH = 9.25 CuO + H Q > 2°3 E = 1.648 2Cu(OH)  2e~  +  2 pH  Cu(OH)  2e~  0.0591 pH  2b)  2H  • 2CuMo0  229)  +  +  0.0591 pH  + 2H  +  4  +  -  0.741  2H  0.0591 pH  y 2Cu(OH)  2  E  -  y 2CuO  2  E b)  0.609  +  2  1.572  +  3  -  2  e  "  0.0591 pH H 0 2  +  0.0591 pH  2H* +  2e~  2H 0 2  - 277 -  31)  2CuMo0  4  +  3H 0 E  32)  C. 2  C.2.1  Cu  + MoO  Ca-H 0-Mo0 2  4  Substances  0 +2 +2 +2  =  2-  22MO0,,  +  4  2.658  -  0.0197 pH  2.677  -  0.0197 pH  4 * CuMoO„ 4 E  =  0.0589  E  =  0.118  + -  -  + 6H  +  +  2e  0.0197 l o g (MoC>  2e 0.0591 l o g (Mo0  4  )  considered  Species  CaH  AG (kcal)  Source o f Data  -35.80  73  -144.40  73  -157.64  73  -345.80  91  -132.18  73  2 Ca CaO Ca(OH)  +2  CaMoO„ n Ca  +4  Ca0  2  -143.00  73  ( +4  Mo0  2  -120.00 )  73  ( +6  MoO„ 3 HMoO ~ 4 MoO. ~  -161.95 )  73  -213.60 )  73  -205.42  35  ( +6 +6  )  4  system  Oxidation Number  -2  Cu„0^ 2 3  2  2  +  2  A c t i v i t y o f c a l c i u m c o n t a i n i n g s p e c i e s i n s o l u t i o n has been  taken  as 10 ^ M and the a c t i v i t y o f molybdenum c o n t a i n i n g s p e c i e s  as  IO  - 1  M.  278  C.2.2  1)  One s o l i d substance and one d i s s o l v e d substance 2+ Ca  a)  +  H 0  b)  Ca  +  2 +  (Ca )  H 0  3)  C.2.3 4)  5)  Ca  y  2+ (Ca )  a)  2  CaH  CaH  a)  Ca  +  +  -  2 pH;  pH = 14.45  4e~ 0.0295 pH  E  =.  -1.134  -  0.0295 pH  2+ Ca  +  2e  E  =  -2.866  -  2+ 0.0295 l o g (Ca ) ; E = - 3 . 0 4 3  -  0.0148 l o g ( C a ) 2 +  substances y Ca  +  2H  E  =  0.776  H 0  +  +  =  -0.563  2H 0  -  0.0591 pH  H 0  y  2  =  -  4H  -  CaO +  -1.902  -  +  +  4e~  0.0591 pH  y Ca(OH)  2  E  2e"  y CaO +  2  -0.706 6)  22.91  +  -  +  2  +  2H  -1.045  E b)  2H  +  2  2pH; pH = 19.315  =  +  2  +  2 +  =  -  E  Two s o l i d CaH  32.63  • Ca(OH)  2  > Ca  =  2 +  log CaH„ 2  + CaO + 2H  y  2  log  2)  -  +  2  4H  +  0.0591 pH 2H  +  +  2e  0.0591 pH  +  4e  - 279 -  b)  r  Ca  +  2H 0  >-Ca(OH)  2  E 7)  Ca  =  -2.189  2MoO. 4  +  =  -3.044  2a)  b)  9)  10)  CaO +  Mo0 =  38.36  pH  =  19.15 +  2  =  28.99  pH  =  14.00  CaMoO. 4  +  +  2e~  2e 0.0591 2l o g (Mo0 );  -  4  >• CaMo0  log  24  +  4  l o g (Mo0  24  2  + 2H  +  +  -  0.0295 pH  E  =  -1.192  -  0.0295 pH  y CaO„ 2  +  +  4  MoO„ 4  11)  a)  b)  pH  =  20.52  CaO  +  Ca(OH)  H 0  y  2  2  E  =  +  H 0  E  =  l o g (Mo0  - 0.0148 l o g (Mo0  2-  + + 4H  C  a  1.260  2  1.547  ° 2  +  -  2  +  +  2  e  _  0.0591 pH  y Ca0 -  H  )  4  2  +  2  4e  2-  2H 0  )  -1.134  2H_0 2  H 0  • CaMo0  =  81.09  -3.0.14  2  E  =  =  4  y CaMoO„ 4  4 pH  E  (Mo0 ~)  + 2H  +  +  2MoO. 4  +  +  +  0.0591 pH  2H +  Mo0  2 pH  CaH„ 2  2H  + +  4  2 pH  Ca(OH)  -.  > CaMoO„ 4 E  8)  +  2  2H  0.0591 pH  +  +  2e~  2-. 4  - 280 -  C.3 C.3.1  Pb-H^O-MoO^ system Substances  considered  Oxidation Number  0  „ . Species  Pb PbO  +2  PbMo0  +2  Pb  +2  HPb0 ~  +2.67  Pb,0„ 3 4 2°3  4  2 +  2  P b  +4  Pb0  +4  Pb  +4  PbO ~ 2PbO, 4  +4  2  4 +  2  ( +4  Mo0  ( +6 ( +6 +6  Source o f Data  73  —  +2  +3  AG° , (kcal)  -45.25  91  -205.42  73  -5.81  73  -81.00  73  -147.6  73  -98.42  73  -52.34  73  +72.30  73  -66.34  73  -67.42  73  -120.00 )  73  Mo0 HMo0 -  -161.95 ) -213.60 )  73 73  MoO.  -205.42  35  2  3  4  2 -  -4 A c t i v i t y o f l e a d c o n t a i n i n g s p e c i e s i n s o l u t i o n t a k e n as 10 and o f molybdenum c o n t a i n i n g s p e c i e s as 10  M,  M.  S t a b l e b i - v a l e n t o x i d e c o n s i d e r e d t o be anhydrous plumbous o x i d e , PbO.  281  C.3.2 1)  Two d i s s o l v e d substances Pb  2+  +  2H 0  -  y HPb0  2  log  ( H P b  °2  =  )  + 3H  +  2  -28.02  +  3 pH;  pH  =  9.34  (Pb ) 2 +  2)  Pb  4+  +  3H 0  y Pb0  2  2-  + 6H  +  3  (PbO "~) 2  —  log  =  -23.06  +  6 pH;  pH V=  3.84  +  2 pH;  pH  20.44  (Pb ) 4 +  3)  Pb0  2-  +  3  H 0  (PbO log  4  Pb  2+  y  Pb  4  4+  +  +  2H  +  ")  r-j-  (PbO 4)  4-  y Pb0  2  =  -40.87  =  ) 2e 4+  E  =  1.694  +  0.0295- l o g  (  }  (Pb ) 2 +  E° = 5)  Pb  2+  +  3H O  1.694  y  PbO  2-  + 6H  +  +  2e  2(PbO  E  =  2.375  -  0.177 pH  =  0.0295 l o g  )  (Pb ) 2 +  6)  HPbO  Z  +  HO  y PbO  Z  2-  j>  +  + 3H  +  2e  (Pb0  E  =  1.547  -  0.0886 pH  +  0.0295 l o g  ")' _ (HPb0 ) 3  2  E  =  1.547  -  0.0886 pH  - 282  C.3.3 7)  Two s o l i d Pb  +  substances  H 0  y  2  E 8)  3PbO  +  =  H 0  3°4  2 p b  +  H 2  =  °  Pk 0 3  +  4  2H 0 E  11)  p  b 0 2  +  3  =  H 0 — E  12)  Pb  =  2MoO, 4  +  +  =  -0.613  +  +  + 2H  -  0.0591 pH +  -  2H  +  +  +  +  ~  2 e  2e~  2e~  0.0591 pH  y PbMoO, 4  E  H  2  1.093  -0.672  2  0.0591 pH  2  =  2e"  -  1.127  E  +  +  0.0591 pH  2°3  -> 2Pb0  2  2H  -  1.228  2e"  0.0591 pH +  4  > 3Pb0  2  +  +  -  0.972 3 P b  =  2H  0.248  3  E 10)  +  y Pb 0  2  E 9)  PbO  + +  2e l o g (Mo0 ~) 2  4  213)  PbMo0  +  4  2H 0  y Pb0  2  E  =  1.99  E  =  1.931  +  2  -  Mo0  + +  4  0.1182 pH -  +  4H  3PbMo0  4  +  4H 0  y Pb 0  2  3  +  2e  0.0591 l o g (MoO^")  0.1182 pH 2-  14)  -  4  +  3Mo0  E  =  3.724  -  0.236 pH  E  =  3.547  -  0.236 pH  + +  4  +  8H  +  2e  3(0.0591) l o g (MoO^"  - 283  C.3.4  15)  One s o l i d substance and one d i s s o l v e d substance Pb  2+  +  H 0  y  2  log 16)  PbO  +  PbO  (Pb  H 0  2+  )  Pb  4+  +  2H 0  2  > Pb0  2  +  2  H 0  -> P b 0  2  log 19)  20)  21)  22)  Pb  Pb  3Pb  • Pb  +  )  =  -15.36  2  +  + 4H  3HPb0 ~ 2  +  pH;  4 pH;  -  pH  pH  +  2e  E  =  -0.126  +  0.0295 l o g ( P b )  E  =  -0.244 +  3H  y HPb0  2  +  +  +  0.702  -  0.0886 pH  E  =  0.584  -  0.0886 pH  4  +  3  + 8H  +  E  =  2.094  -  0.2364 pH  E  =  2.448  -  0.2364 pH  H —~-y P b ^ +  E  =  +  - 0 . 3 9 0 ••+  =  11.36  -1.065  2 pH;  pH  =  13.66  2e"  =  y Pb 0  =  2 +  E  2  8.325  + 2H  +  -31.22  4H 0  +  2-  =  +  -8.26  3  pH  =  2  +  2 pH;  H  =  2-  -  )  2+  (PbO.  2H 0  2+  12.65 +  4 +  Pb0  = 2  log (Pb ) 18)  + 2H  y HPb0 ~  2  l o g (HPb0 17)  +  2H 0 2  +  0.295 pH  +  2e -  0.0295 l o g (HPb0  2  0.0886 l o g ( P b ) 2 +  2e~ -  0.0886 l o g (HPbO^)  )  - 284 -  E 23)  24)  Pb  +  2 +  HPb0 ~ 2  =  -0.0356  2 H 0 — -> P b 0 2  +  +  +  2  0.0295 pH  4H  +  +  2e~  E  =  1.449  -  0.1182 pH  E  =  1.567  -  0.1182 pH  Mo0 ~  +  2  4  log  3H  • PbMo0  +  (HPb0 ~)  =  2  -46.33  -  0.0295 l o g ( P b ) 2 +  +  4  +  2H <3 2  3pH;  pH  =  14.11  4+ 25)  PbMo0  y Pb  4  +  4e  E  =  3.347  E  =  3.288  -  0.0147 l o g ( P b ) 4 +  226)  PbMo0  4  +  3H 0  >- P b 0  2  3  2+  Mo0  E  =  2.915  -  0.177 pH  E  =  2.797  -  0.177 pH  + +  4  +  6H • +  2e  0.0295 l o g (PbO ~ ) 2  - 285 -  C. 4 C.4.1  Zn-H^O-MoO^ system Substances c o n s i d e r e d  Oxidation Number  AG° (kcal)  Species  0  Source o f Data  73  Zn  +2  Zn(OH)„  -76.94  91  +2  ZnMoO„ * Zn  -294.40  73  -35.18  73  +2  HZn0 ~  -110.90  73  +2  ZnO  -93.03  73  ZnOH  -78.70  73  ( +4  Mo0  2  -120.00 )  73  ( +6  Mo0  3  -161.95 )  73  ( +6  HMoO.~ ' 4 MoO ~  -213.60 )  73  -205.42  35  2  +2  +  2  ~  2 2  +2  +  +6  2  A c t i v i t y o f z i n c c o n t a i n i n g s p e c i e s t a k e n t o be 10 ^ M, and o f molybdenum c o n t a i n i n g s p e c i e s as 10 -1 M. S t a b l e o x i d e c o n s i d e r e d t o be z i n c h y d r o x i d e Z n ( O H )  C.4.2 1)  (orthorhombic)  2  Two d i s s o l v e d s u b s t a n c e s Zn  +  2 +  H 0  • ZnOH  2  +  +  H  +  (7nOH~'~ ^  log  =  -9.67  +  pH;  pH  =  9.67  (Zn ) +  2)  ZnOH  +  +  H 0 2  > HZn0 (HZn0 ~) log — (ZnOH )  2  +  2H  +  2  =  -17.97  +  2 pH;  pH  =  8.98  - 286 -  3)  2+ Zn  +  2H 0  y HZnC>  2  (HZn0 ~) — (Zn )  + 3H  +  2  2  log  =  -27.63  +  3 pH;  pH  =  9.21  pH;  pH  = 13.11  +  24)  HZnO  + + H 2(Zn0 )  y ZnO  2  log  C.4.3  5)  Two s o l i d  Zn  +  (HZn0  2H 0  >- Zn (OH)  2  =  -0.439  2Zn(OH)  2  -13.11  +  +  2H  2e  species  E  6)  = 2  +  Mo0  0.0591 pH  + 2H  +  4  -  +  +  • ZnMo0  +  4  2H 0 2  22 pH  =  91.84  pH  =  45.42  +  l o g (Mo0  4  )  27)  C.4.4  8)  Zn  +  Mo0  +  4  2e  >- Z n M o 0  E  =  -1.929  E  =  -1.899  -  4  2-  0.0295 l o g ( M o 0  4  )  One s o l i d substance and one d i s s o l v e d substance Zn(OH)  2  +  H 0 2  log  *• H Z n 0 ~ 2  (HZn0  2  )  =  +  H  -16.68  +  +  pH;  pH  =  10.68  - 287 -  9)  10)  HZnC-  ZnO„ 2  2MoO. 4  +  2  2-  +  +  + 3H  3 pH  =  66.94  pH  =  20.31  2MoO, 4  +  + 4H  y ZnMoO„ 4 -  +  l o g ((HZn0  y ZnMoO, 4  +  2H„0 2 2  )•(Mo0  2-  ))  4  2H~0 2 2-  11)  Zn  4 pH  =  80.04  pH  =  18.51  2+ Zn E  y  + =  2e -0.763  -  +  13)  Zn  +  2+ Zn  H 0  y Zn0  2  +  Zn  +  2  +  4H  +  0.1182 pH  E  =  0.264  -  0.1182 pH + + 2H  (Zn  2H 0  )  10.96  y HZn0 ~  2  2  =  +  2  E  =  0.054  E  =  -0.123  -  3H  +  - 2 pH; +  +  =  -0.94  0.0295 l o g ( Z n 0 ~ ) 2  2  pH  =  8.48  2e~  0.0886 pH -  E  2e  -  y Zn(OH) 2+  ))  -  0.441  log 14)  +  =  2  )•(MoO  2 +  E  2H 0  2  0.0295 l o g ( Z n ) ;  212)  l o g ((Zn0  0.0886 pH  +  0.0295 l o g  (HZn0 ~) 2  - 288 -  C. 5 C.5.1  Fe-H^O-MoO^ system Substances  considered  Oxidation Number  „ . Species  0  AG° (kcal)  Source o f Data  Fe  +2  Fe(OH) 2+  -58.88  73  +2  Fe  -20.30  73  +2  HFe0 ~  -90.63  73  +2  FeMoO, 4 Fe(OH). 3+ Fe Fe(OH) 2+  -235.30  91  -161.93  73  -2.53 -106.20  73 73  -55.91  73  2  +3 +3 +3 +3  +  FeOH  ( +4  Mo0  2  -120.00 )  .73  ( +6  Mo0  3  -161.95 )  73  ( +6  HMoO  -213.60 )  73  MoO„ ~ FeO„ 4  -205.42 -111.69  35 73  +6 +6  V  A c t i v i t y o f i r o n c o n t a i n i n g s p e c i e s i n s o l u t i o n t a k e n as 10 ^ M, and o f molybdenum s p e c i e s as 10 f e r r i c hydroxides, Fe(OH)  2  and Fe(OH)  M.  F e r r o u s and  have been used as  the s t a b l e o x i d e s .  C.5.2  1)  Two d i s s o l v e d s p e c i e s  Fe  2+  +  2H 0 ——* HFe0 2  <  -  (HFeO  log  + 3H  +  2  ) =  (Fe ) 2 +  -31.58  +  3 pH;  pH  =  10.53  - 289 -  2)  Fe  3+  +  H 0  FeOH  2  log  (  2+  + + H  2+ ° " (Fe )  F  e  -2.43  =•-  )  +  pH;  pH  =  2.43  J  3)  FeOH  +  2+  H 0 —>• F e ( O H ) 2  log  ( F e (  °  2  H )  +  + 2  H  =  }  +  -4.69  +  pH;  pH  =  4.69  (Fe(OH) ) 2+  . , 2 +  4)  Fe  Fe  3+  +  e (Fe ) 3 +  5)  Fe  +  2 +  E  =  0.771  E  =  0.771  H 0  >: F e ( O H )  2  E  =  +  0.0591 l o g  +  2 +  0.914  -  H  +  +  (Fe^ )  e"  0.0591 pH  +  0.0591 l o g  (Fe (OH)  2+.  (Fe ) 2 +  E 6)  Fe  +  2 +  2H 0  =  0.914  -  ^-r* Fe (OH)  9  0.059 pH +  +  2H  +  +  e~ + )  2  7)  HFeO  +  H  E  =  1.91  -  0.1182 pH  E  =  1.91  -  0.1182 pH  — F e (OH)  +  +  +  +  0.0591 l o g  (Fe(OH) (Fe ) 2 +  e~ (Fe(OH)  E  =  -0.675  +  0.0591  pH  +  0.0591 l o g  2  + )  :  (Fe0 H~) 2  E 8)  HFe0  2  +  2H 0 2  =  -0.675  — F e 0  + 2-  4  0.0591 pH +  + 5H  +  e  (Fe0 ~) 2  4  E  =  1.001  -  0.0738 pH  +  0.0148 l o g (HFe0  E  =  1.001  -  0.0738 pH  2  - 290 -  9)'  Fe  3+  +  4H 0 — F e 0 2  E  =  2-  + 8H  +  4  1.700  -  +  -  3e  0.1580 pH  (FeO ") 0.0197 l o g (Fe )  +  3 +  E 10)  Fe(OH)  +  2 +  =  1.700  -  0.1580 pH  3H 0 ——> F e 0 ~  +  2  2  4  7H  +  +  3e~ (FeO ~ ) 2  E  =  1.652  -  0.1379 pH  +  0.0197 l o g (Fe(OH) ) 2+  E 11)  Fe(OH)  +  +  2  =  1.652  -  2H 0  —y F e 0  4  E  1.559  -  2  =  0.1379 pH 2-  + 6H  +  +  0.1182 pH  3e  +  -  0.0197 l o g  ( F e  °4  )  (Fe(OH) ) +  2  1.559  C.5.3 12)  Two s o l i d Fe  +  Fe  2H 0  y Fe(OH)  2  +  =  3H 0  Fe(OH)  2  +  =  Fe  = +  0.271 2e  Fe(OH)  2  +  E  =  -0.648  E  =  -0.6185  Mo0  4  2e~  2H  +  +  2e~  0.0591 pH  -  3  +  2H  +  +  2e~  0.0591 pH >• FeMoO, 4  216)  + -  +  +  0.0591 pH  >-Fe(OH)  2  2MoO, 4  +  0.059  2H  -  Fe (OH)  H 0 E  15)  +  2  -0.047 y  2  E 14)  0.1182 pH  substances  E 13)  -  +  + 2H  -  0.0295 l o g (Mo0  >- FeMo0  4  +  24  )  2H 0 2  291 -  17)  C.5.4  18)  FeMo0  +  4  2 pH  =  61.804  pH  =  30.402  3H 0  y Fe (OH)  2  +  3  -  0.1773 pH  E  =  1.578  -  0.1773 pH  2-  )  +  MoO ~  +  0.0591 l o g (MoO ~ )  2  One s o l i d substance and one d i s s o l v e d substance Fe  2 +  +  2H 0  y Fe(OH)  2  Fe(OH)  +  2  Fe  3 +  Fe (OH)  =  13.29  pH  =  9.645  2 +  y HFe0 ~ (HFe0  )  2  =  3H 0  y Fe (OH)  2+  +  (Fe  2H O log  3+  +  +  H 0 2  •  3H  pH  =  3.613  H  +  + pH  +  -  3 pH  + + 2H  Fe (OH)  pH  2  + 4.84  2+  2pH  12.30  =  (Fe(OH) )  -  -18.30  )  y  +  +  2  +  Fe(OH)  2H  (Fe )  2  log  22)  +  1.637  pH • =  21)  3H  =  log  20)  l o g (MoO 4  E  log  19)  +  =  2.41  =  4.205  >-Fe(OH)  3  +  -  H  +  2 pH  +  e~ 2  - 292  log  23)  24)  25)  Fe  Fe  Fe  y  +  2+  27)  Fe  2+  HFe0  +  pH  =  4.28  E  =  -0.440  E  =  -0.617  ^ HFe0  Fe  2  0.0295 l o g ( F e )  +  3H  29)  FeMo0  4  FeMoO. 4  +  +  2e~  0.493  -  0.0886pH  E  =  0.316  -  0.0886 pH  +  3e  =  -0.037  +  E  =  1.057  E  =  1.4116  H 0  -  -  y HFe0  2H 0 2  3 pH  =  38.46  pH  =  10.82  4- Fe E  3+  =  +  +  =  +  e -  2+  )  -0.1552  0.0591 l o g ( F e ) 2 +  0.1773 pH +  3  e  0.0591 l o g (HFe0 +  2  2MoO, 4  1.186  + 3H  0.1773 pH  -y 2Fe(OH)  2  0.0295 l o g (Fe  3 +  +  -  +  0.0197 l o g ( F e ) ; E  • Fe(OH)  2  +  2 +  =  3+  pH  +  -0.810 28)  -  E  3H 0  +  2  -2.28  2e  E 26)  =  +  2  Bj  2  +  2H 0  Fe  (Fe(OH) )  +  Mo0  24  +  );  2  E  =  -0.4356  + 3H  l o g ((HFe0 ~)-(Mo0 ~)) 2  2  +  4  e  0.0591 l o g (Mo0  24  );  E  =  1.127  - 293 -  r  30.)  FeMoO  +  HO  y Fe (OH)  E  =  1.326  2-H  -  +  MoO  0.0591 pH  2 —•  +  "I  +  H  -  +  e  0.0591 l o g ( ( F e O H ) 2+  (Mo0 *)) 2  4  E 31)  FeMo0  4  +  =  2H 0  0.971  -  y Fe(OH)  2  E  =  1.599  -  (Mo0 E  C.6 C.6.1  Cd-H Q-MoQ 2  4  0.0591 pH  =  1.244  + 2  +  + 2H  0.1182 pH 2 4  + +  e  -  +  Mo0  24  0.0591 l o g ((FeOH )• +  ))  -  0.1182 pH  system  Substances c o n s i d e r e d Oxidation Number  „ . Species  0  Cd  2  Cd(OH)  2  CdMoO„ 2+ Cd HCdO ~  2  AG° ,, (kcal)  Source _ „ , o f Data  —  73  -56.44  73  ' -283.30  91  -18.58 -86.50  73 73  -205.42  35  4  2 2 6  MoO„ 4  2-  A c t i v i t y o f cadmium c o n t a i n i n g s p e c i e s i n s o l u t i o n t a k e n as 10  6  M, and t h a t o f molybdenum s p e c i e s as 10  1  M.  ' I n a c t i v e ' cadmium h y d r o x i d e , C d ( O H ) , has been used as 2  the o x i d e s p e c i e s .  - 294  C.6.2 1)  Two d i s s o l v e d Cd  +  2 +  species  2H 0  HCd0  2  +  2  (HCdO ) —  log  3H  +  =  -33.34  -  3 pH;  +  2H  2e~  pH  =  11.11  E  =  (CcT )  C.6.3 2)  Two s o l i d Cd  +  species  H 0  >- Cd(OH)  2  E  =  0.05  23)  Cd(OH)  +  2  Mo0  2  +  0.0591 pH  + 2H  +  4  -  +  • CdMo0  +  4  2H 0 2  2-  4)  Cd  2 pH  =  65.73  pH  =  32.365  2MoO, 4  +  + E  C.6.4  5)  2e  =  Cd  2 +  +  4  )  > CdMoO, 4  -0.713  2H 0  -  >-Cd(OH)  2  Cd(OH)  (Cd )  0.0295 l o g (Mo0  > HCd0  2  Cd  y Cd  2 +  E  +  2  (HCd0  +  2  =  2+  log 7)  l o g (MoC>  24  );  -0.684  One s o l i d substance and one d i s s o l v e d substance  log 6)  +  13.81  H  2H  +  -  2 pH;  pH  9.905  +  )  =  -19.54  +  2e~  =  -0.403  +  0.0295 l o g ( C d ) ;  2  =  +  pH;  pH  2 +  =  13.54  E  =  -0.508  - 295 -  8)  9)  Cd  +  CdMo0  y HCd0 ~  2H 0 2  4  +  C.8.1  +  +  2e~  =  0.583  -  0.0886 pH  E  =  0.406  -  0.0886 pH  2H 0 • 2  y HCd0  +  2  MoC>  +  2-  4  (HCd0 ~)  -  3 pH  pH  =  12.564  2  Molybdenum s p e c i e s Substances  3H  E  log  C.8  +  2  =  0.0295 l o g (HCd0  +  3H  +  -43.69  ( a l l systems)  considered  Oxidation Number  „ . Species  AG° „ ,\ (kcal)  Source _ „ ^ o f Data  0  Mo  +3  Mo  -13.80  73  +4  Mo0  2  -120.00  73  +6  Mo0  3  -161.95  73  +6  MoO, " 4 HMoO ~ 4  -205.42  73  -213.60  73  3 +  2  +6  A c t i v i t y o f d i s s o l v e d s p e c i e s taken as 10 "*" M.  Hexa-  v a l e n t o x i d e c o n s i d e r e d t o be m o l y b d i c t r i o x i d e ,  C.8.2  1)  Two d i s s o l v e d  HMoO. 4  substances  2+ y MoO. + H 4 2-, (MoO ) log — = (HMoO )  -6.00  +  pH;  pH  =  6.0  MoO^  2  296  C.8.3  2)  One s o l i d substance and one d i s s o l v e d substance Mo0  3  +  K HMo0 ~  H 0 2  log 3)  4)  5)  6)  7)  Mo  y  Mo +  3+ Mo  3+ Mo  Mo0  2  +  Mo0  2  +  -3.70  +  0.0197 l o g ( M o ) ;  E  =  -0.200 Mo0  +  =  3e  y  H  )  +  2  +  4  3+ Mo  2-  pH;  + 8H  +  0.154  -  0.0788 pH  E  =  0.144  -  0.0788 pH  y Mo0  2  +  2  + 4H  +  e  E  =  0.311  -  0.2364 pH  E  =  0.370  -  0.2364 pH  3H 0  y Mo0  2  +  3  + 6H  +  =  0.317  -  0.1182 pH  E  =  0.337  -  0.1182 pH  y HMo0  2  =  2H 0  3H  +  +  0.429  -  0.0886 pH  0.399  -  0.0886 pH  y Mo0  2  +  4  24  +  + 4H  E  2.70  =  -0.2197  +  E  =  0.606  -  0.1182 pH  E  =  0.577  -  0.1182 pH  2-  +  0.0098 l o g (Mo0  -  0.0591 l o g  (Mo )  0.0197 l o g  (Mo )  4  -  3e  E  2H 0  =  6e  =  2H 0  pH  3 +  +  4  +  E  E 8)  (HMo0  4H 0  +  +  4  3+  -  3+  2e~ +  0.0295 l o g (HMo0 ) 4  2e +  0.0295 l o g (Mo0  24  )  - 297 -  C.8.4 9)  Two s o l i d Mo +  substances  2H 0  > Mo0  2  E 10)  Mo0  2  +  H 0 =  4H  -0.072 y Mo0  2  E  C  =  +  2  3  0.320  -  +  +  4e~  0.0591 pH  +  2H  -  0.0591 pH  +  +  2e  

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