Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

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

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1979_A7 M68_6.pdf [ 11.21MB ]
Metadata
JSON: 1.0078702.json
JSON-LD: 1.0078702+ld.json
RDF/XML (Pretty): 1.0078702.xml
RDF/JSON: 1.0078702+rdf.json
Turtle: 1.0078702+rdf-turtle.txt
N-Triples: 1.0078702+rdf-ntriples.txt
Citation
1.0078702.ris

Full Text

FACTORS INFLUENCING THE RECOVERY OF MOLYBDENUM DURING THE HYPOCHLORITE LEACHING OF LOW GRADE MOLYBDENITE-COPPER CONCENTRATES by DIANA MARY MOUNSEY . S c . ( E n g . ) , A . R . S . M . , I m p e r i a l C o l l e g e o f Science and Technology ( U n i v e r s i t y o f London), 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of M e t a l l u r g i c a l Engineer ing) We accept t h i s t h e s i s as conforming to the r e q u i r e d s tandard THE UNIVERSITY OF BRITISH COLUMBIA September 1979 Ccj Diana Mary Mounsey, 1979 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag ree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rposes may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l no t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f M The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date » * * Q c U e T '777 ( i i ) 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 su lph ide molybdeni te concent ra tes 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 ou t . Sodium carbonate b u f f e r components were found to ac t as complexing agents f o r the copper , enab l i ng i t to e x i s t i n s o l u t i o n as a c u p r i - carbonate spec ies s e v e r a l orders o f magnitude more s o l u b l e than the thermodynamical ly s t a b l e copper phase a t pH 9 . 0 . Completely s e l e c t i v e molybdenum e x t r a c t i o n i s the re fo re o n l y p o s s i b l e from s o l u t i o n s c o n t a i n - i n g no carbonate . The removal o f the carbonate produced adverse s ide e f f e c t s fo r 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 hydroxide format ion on the m i n e r a l sur face which l e d to r a p i d decomposi t ion o f the hypoch lo r - i t e by heterogeneous c a t a l y s i s . Th i s hydroxide 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 confirmed t ha 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 igh 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 c o p p e r 1 1 > copper 1 1" 1" to take p l a c e . Experiment a l s o showed tha t a t r i - v a l e n t copper carbonate compound p r e c i p i t a t e d from l e a c h i n g s o l u t i o n s c o n t a i n i n g copper a f t e r a s u i t a b l e n u c l e a t i o n p e r i o d . I t was thus e s t a - b l i s h e d t h a t the copper present i n carbonate 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 ha t the i n d u c t i o n time to 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 carbonate content o f the ( i i i ) system, and t ha t the s o l i d p r e c i p i t a t e i s a l s o 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 decompos i t ion . The l e a c h i n g o f molybdeni te - copper concent ra tes 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 tha t such a process would not be f e a s i b l e due t o the format ion and p r e c i p i t a t i o n o f copper molybdate, CuMoO^. Th i s compound i s ve ry i n s o l u b l e , but i t s format ion was found to be suppressed by the presence o f sodium b icarbona te a t pH va lues g rea te r than 6 . 0 . S e v e r a l o ther i n s o l u b l e molybdate compounds were found to be capable o f forming i n both 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 o f 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 con ta ined i n the copper su lph ide o r e s . P o t e n t i a l - p H diagrams cons t ruc t ed to show the thermodynamic s t a b i l i t y of the molybdate s a l t s o f copper , i r o n , c a l c i u m , z i n c , l e a d and cadmium are i n c l u d e d . Calc ium was i s o l a t e d as be ing the most d e t r i m e n t a l i m p u r i t y e l e - ment i n t h i s r e s p e c t , due t o i t s common occurrence i n copper porphyry ores 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 . A l i m i t e d study was c a r r i e d out to show t h a t t h i s s o l u b i l i t y i nc reased i n p r o p o r t i o n to the c h l o r i d e content and hence the h y p o c h l o r i t e concen t r a - t i o n o f l e a c h i n g s o l u t i o n s . Ca lc ium carbonate was found to p r e c i p i t a t e i n preference t o c a l c i u m molybdate, but the use o f s i l i c a t e s and phos- phates as c a l c i u m suppressants was a l s o cons idered as a means o f a v o i d i n g copper - carbonate complexing w h i l e m a i n t a i n i n g good molybdenum e x t r a c t i o n . X i v ) TABLE OF CONTENTS Page CHAPTER ONE : General 1 1.1 I n t r o d u c t i o n 1 1.2 Curren t Molybdenum P r o d u c t i o n 3 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 6 1.4 L i t e r a t u r e Review 9 1.4.1 The e x t r a c t i o n o f molybdeni te 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 1.4.2 The behaviour o f copper i n i a l k a l i n e carbonate s o l u t i o n s 17 1.4.3 Decomposit ion 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 s o l u t i o n 2 7 1.4.4 C o p p e r 1 1 1 compounds 3 9 CHAPTER TWO : Exper imen ta l 4 7 2.1 Scope o f the Presen t I n v e s t i g a t i o n 4 7 2.2 M a t e r i a l s 49 2 .2 .1 N a t u r a l m i n e r a l s 49• 2 .2 .2 S y n t h e t i c m ine ra l s 5 4 2 .2 .3 Sodium h y p o c h l o r i t e 5 4 2 .2 .4 Chemical reagents 5 5 2.3 Apparatus 5 5 2.4 Exper imen ta l procedure 5 7 2 .4 .1 Leaching experiments 5 7 2 .4 .2 C o p p e r 1 1 1 p r e p a r a t i o n 5 8 2.5 A n a l y s i s 5 8 2 .5 .1 Chemical a n a l y s i s 5;8 i ) Copper 5'8 (v) TABLE OF CONTENTS (Cont 'd) Page i i ) Molybdenum 59 i i i ) Ca lc ium 59 i v ) Sodium h y p o c h l o r i t e 59 v) Sodium c h l o r a t e 59 v i ) T o t a l c h l o r i d e 60 2 .5 .2 Ins t rumenta l a n a l y s i s 60 i ) M i n e r a l s 60 I I I i i ) Copper 61 CHAPTER THREE : Resu l t s and Observat ions 62 3.1 Sodium H y p o c h l o r i t e Leaching of Copper Su lph ide M i n e r a l s 62 3 .1 .1 Leaching of ground concent ra tes i n the presence o f carbonate 62 3 .1 .2 E f f e c t o f carbonate removal 64 3 .1 .3 Leaching o f s y n t h e t i c copper su lph ides 67 3 .1 .4 Dete rmina t ion o f decomposi t ion products 69 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 of copper su lph ide mine ra l s 72 3 .1 .6 V a r i a t i o n o f t o t a l carbonate content du r ing the l e a c h i n g o f ground copper su lph ide mine ra l s 75 3 .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 c o n c e n t r a t i o n 79 3 .1 .8 E f f e c t of h y p o c h l o r i t e removal 84 3.2 C o p p e r 1 1 1 87 3 .2 .1 A n a l y s i s o f c o p p e r 1 1 1 90 3 . 2 . 1 . 1 E f f e c t o f a c i d i f i c a t i o n 90 3 . 2 . 1 . 2 E v a l u a t i o n o f o x i d a t i o n s t a t e by i d o m e t r i c t i t r a t i o n 90 3 . 2 . 1 . 3 Measurement o f oxygen e v o l u - t i o n u s ing a mercury column 92 ( v i ) TABLE OF CONTENTS (Cont 'd) Page 3 . 2 . 1 . 4 Gas chromatography 94 3 . 2 . 1 . 4 Ins t rumenta l a n a l y s i s 94 i ) Magnetic s u s c e p t i b i l i t y 94 i i ) I n f r a - r e d s p e c t r a 95 i i i ) X - r a y d i f f r a c t i o n 96 3 .2 .2 P r e c i p i t a t i o n o f copper 1 1 - 1 - i n the presence o f carbonate 97 3 . 2 . 2 . 1 E f f e c t o f seeding 97 3 . 2 . 2 . 2 E f f e c t o f a c i d i f i c a t i o n 98 3 . 2 . 2 . 3 I . R . spec t r a 98 3 . 2 . 2 . 4 X - r a y a n a l y s i s 99 3 .2 .3 H y p o c h l o r i t e decomposi t ion s t u d i e s 100 3 .2 .4 A n a l y s i s o f l e a c h i n g s o l u t i o n s 100 3.3 Sodium H y p o c h l o r i t e O x i d a t i o n o f Molybdeni te 102 3 .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 molybdeni te and copper su lph ide mine ra l s a t pH 9.0 104 3 .3 .2 Sodium h y p o c h l o r i t e l e a c h i n g o f molybdeni te and copper su lph ide mine ra l s a t pH 5.5 114 3 .3 .3 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 C a t a l y z e d decomposi t ion o f h y p o c h l o r i t e i n the presence o f copper molybdate 130 3 . 3 . 3 . 3 X - r a y a n a l y s i s 132 3 .3 .4 S o l u b i l i t y of c a l c i u m i n h y p o c h l o r i t e s o l u t i o n s 133 3 . 3 . 4 . 1 Sodium h y p o c h l o r i t e l e a c h i n g o f ca l c ium sulphate and c a l c i u m carbonate mine ra l s 137. 3 . 3 . 4 . 2 E f f e c t o f 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 s o l u b i l i t y 140 3 . 3 . 4 . 3 Removal of c a l c i u m from s o l u t i o n 14 0 ( v i i ) TABLE OF CONTENTS (Cont 'd) Page CHAPTER FOUR : D i s c u s s i o n 154 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 su lph ide mine ra l s i n the presence o f carbonate 154 4 . 1 . 2 Removal o f carbonate from the system 156 4 .1 .4 H y p o c h l o r i t e decomposi t ion 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 su lph ide mine ra l s 160 4 . 1 . 6 V a r i a t i o n o f the t o t a l carbonate content d u r i n g l e a c h i n g 161 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 c o n c e n t r a t i o n 165 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 A n a l y s i s o f c o p p e r 1 1 1 170 4 . 2 . 2 P r e c i p i t a t i o n o f c o p p e r 1 1 1 i n the presence o f carbonate 172 4.3 Sodium H y p o c h l o r i t e Leaching o f Molybdeni te 173 4 . 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 molybdeni te and copper su lph ide mine ra l s a t pH 9.0 174 4 . 3 . 2 Sodium h y p o c h l o r i t e l e a c h i n g o f molybdeni te and copper su lph ide mine ra 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 o f c a l c i u m i n h y p o c h l o r i t e s o l u t i o n s 183 4 . 3 . 4 . 1 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 mine ra l s 196 4 . 3 . 4 . 2 E f f e c t o f c h l o r i d e concen t r a - t i o n on c a l c i u m s o l u b i l i t y 196 4 . 3 . 4 . 3 Removal o f c a l c i u m from l e a c h i n g s o l u t i o n s 200 ( v i i i ) TABLE OF CONTENTS (Cont 'd) Page CHAPTER FIVE 202 5.1 Conc lus ions 202 5.2 Suggest ions f o r Future Work 204 REFERENCES 206 APPENDICES 211 Appendix A Tables o f exper imenta l r e s u l t s 211 Appendix B 268 B . l C a l c u l a t i o n o f sur face areas f o r ground m i n e r a l samples 268 B . 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 surface a f t e r c o p p e r H I format ion 269 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 9.0 269 Appendix C E q u i l i b r i a f o r metal-molybdate Eh-pH diagrams 271 C. l Cu-H 2 0-Mo0 4 271 C.2 Ca -H 2 0-Mo0 4 277 C.3 Pb -H 2 0-Mo0 4 280 C.4 Zn-H 2 0-Mo0 4 285 C.5 F e - H 2 0 - M o 0 4 288 C.6 Cd-H 2 0-Mo0 4 293 ( ix ) LIST OF TABLES 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 o v e l l i t e 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 c i t e 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 Dete rmina t ion o f copper"'""'""'" by t i t r a t i o n 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 o p p e r 1 1 ox ides 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 carbonate E f f e c t o f mix ing and ageing equ i -mo lecu l a r volumes o f Na„MoO. and CuSO„ a t pH 5.3 and pH 9.0 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- 2 " 3-E f f e c t o f S i 0 3 , C 0 3 , and P 0 4 (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 S t ronges t X - r a y peaks fo r v a r i o u s copper molybdate spec ies Comparison o f exper imenta l and l i t e r a t u r e va lues 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 s t reng ths c h a l c o p y r i t e i d o m e t r i c 1 1 1 copper and I I I copper NaOCl l e a c h i n g o f c o v e l l i t e w i t h carbonate bu f f e r s NaOCl l e a c h i n g of c h a l c o c i t e w i t h carbonate bu f f e r s 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 carbonate bu f fe r s (x) LIST OF TABLES (Cont 'd) IV E f f e c t o f s epa ra t i ng 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 du r ing a g i t a t i o n o f CuFeS 2 i n NaOCl V E f f e c t o f s epa ra t ing 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 Cu 2 S i n NaOCl VI 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 bu f fe r s 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 carbonate bu f f e r s V 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 absence o f carbonate bu f fe r s IX Microprobe examinat ion o f massive 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 X Microprobe examinat ion o f massive c o v e l l i t e , before and a f t e r l e a c h i n g i n NaOCl XI NaOCl l e a c h i n g o f c u p r i c su lph ide i n the absence o f carbonate bu f fe r s X I I NaOCl l e a c h i n g o f cuprous su lph ide i n the absence o f carbonate bu f fe r s 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 [ C 0 3 2 ~ ] T a t pH 9 .0 , 35°C 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 [ C 0 3 2 - ] T a t pH 9 .0 , 35°C XV NaOCl l e a c h i n g o f s y n t h e t i c sopper su lph ides w i t h 5 g/1 [ C 0 3 2 - ] T XVI NaOCl l e a c h i n g o f c o v e l l i t e i n the presence o f 5 g/1 [ C 0 3 2 - ] T and 20 g/1 [NaOCl] XVI I A g i t a t i o n o f c o v e l l i t e i n the presence o f carbonate ± NaCl (x i ) LIST OF TABLES (Cont 'd) Page X V I I I NaOCl l e a c h i n g o f c o v e l l i t e i n the presence o f 10 g/1 [ C 0 3 2 ~ ] T and Na 2 Mo0 4 XIX Sodium h y p o c h l o r i t e decomposi t ion i n the presence o f t r i - v a l e n t copper s a l t s XX NaOCl o x i d a t i o n o f molybdeni te a t pH 9.0 XXI NaOCl o x i d a t i o n o f ' reagent grade ' molybdenum d i s u l p h i d e 228 229 230 231 XXII NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e ± carbonate bu f fe r s 232 X X I I I NaOCl o x i d a t i o n o f molybdeni te and c h a l c o c i t e ± carbonate bu f fe r s 233 XXIV NaOCl o x i d a t i o n o f molybdeni te and c h a l c o p y r i t e ± carbonate bu f fe r s 234 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 ± carbonate bu f f e r s 235 XXVI NaOCl o x i d a t i o n o f molybdeni te i n the presence o f copper su lphate s o l u t i o n 236 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 XXVII I NaOCl o x i d a t i o n o f molybdeni te a t pH 5.5 XXIX NaOCl o x i d a t i o n o f molybdeni te 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 237 238 239 XXX NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 5.5 i n the absence o f carbonate 240 XXXI NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 5.5 i n the presence o f NaHCO 241 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 ± NaHCO„ 242 ( x i i ) LIST OF TABLES (Cont 'd) XXXII I NaOCl o x i d a t i o n o f molybdeni te and c h a l c o c i t e a t pH 6 . 5 , w i t h NaHCO^ XXXIV NaOCl o x i d a t i o n o f molybdeni te and c h a l c o c i t e a t pH 6 . 5 , w i thou t NaHC0 3 XXXV NaOCl o x i d a t i o n o f molybdeni te and c u p r i c su lph ide a t pH 6 . 0 , w i t h NaHCO^ XXXVI NaOCl l e a c h i n g o f molybdeni te and c u p r i c su lph ide a t pH 6 . 0 , w i thou t NaHC0 3 XXXVII NaOCl l e a c h i n g of molybdeni te and c h a l c o p y r i t e a t pH 7 . 0 , w i t h NaHC0 3 XXXVIII NaOCl l e a c h i n g o f molybdeni te and c h a l c o p y r i t e a t pH 7 . 0 , w i thou t NaHC0 3 IXL NaOCl decomposi t ion i n the presence o f copper molybdate a t pH 5.5 XL Dete rmina t ion o f the 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 molybdeni te a t pH 10.0 X L I I NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 10.0 i n the absence o f carbonate bu f fe r s 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 su lph ide i n the absence o f carbonate bu f f e r s 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 su lph ide a t pH 9 .0 , i n the presence o f carbonate bu f fe r s XLV NaOCl o x i d a t i o n o f CuFeS 2 ; Cu 2 S and CuS at pH 9.0 i n the absence o f carbonate buf fe r s XLVI 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 presence o f 0.1 g/1 c a l c i u m as C a C l 2 s o l u t i o n ( x i i i ) LIST OF TABLES (Cont 'd) Page XLVII NaOCl l e a c h i n g o f molybdeni te and c h a l c o c i t e i n the presence o f C a C l 2 and N a 2 C 0 3 / N a H C 0 3 257 X L V I I I NaOCl l e a c h i n g of molybdeni te and c a l c i t e 258 IL 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 L 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 L I 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 CaSO^-^H-jO 261 L I I 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 CaC0 3 261 L I I I E f f e c t o f carbonate on c a l c i u m content i n h y p o c h l o r i t e s o l u t i o n s 262 LIV NaOCl l e a c h i n g o f c o v e l l i t e and molybdeni te w i t h 5 g/1 carbonate 263 LV NaOCl l e a c h i n g o f molybdeni te and c o v e l l i t e w i t h 10 g/1 carbonate 264 LVI NaOCl l e a c h i n g o f c o v e l l i t e i n the presence o f sodium molybdate and 5 g/1 carbonate 265 L V 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 c h a l c o c i t e w i t h 10 g/1 carbonate 266 L V I I I NaOCl l e a c h i n g o f molybdeni te and c h a l c o p y r i t e a t pH 9.0 i n the presence o f 1 g/1 N a 2 S i 0 3 267 (x iv) LIST OF FIGURES Conven t iona l f lowsheet f o r p r o d u c t i o n 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 compounds i n the system C u - H 2 0 - 0 2 ~ S - C o 2 P o t e n t i a l - p H diagrams f o r the system C u - C 0 2 - H 2 0 , a) and b) 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 2 ~ H 2 0 system Exper imen ta l l e a c h i n g apparatus O x i d a t i o n o f copper su lph ide mine ra l s by NaOCl E f f e c t o f s epa ra t ing 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 NaOCl consumption du r ing l e a c h i n g o f copper su lph ides E f f e c t o f carbonate removal on NaOCl decomposi t ion NaOCl decomposi t ion 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 su lph ides Sodium c h l o r a t e p r o d u c t i o n du r ing NaOCl decomposi t ion a) E f f e c t o f 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 ' b) Cu d i s s o l u t i o n and NaOCl decomposi t ion 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 3 2"] T E f f e c t o f v a r i e d carbonate content on NaOCl decomposi t ion ( c o v e l l i t e ) E f f e c t o f v a r i e d carbonate content 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 E f f e c t o f v a r i e d carbonate content on NaOCl decomposi t ion ( c h a l c o c i t e ) 81 16 Cu d i s s o l u t i o n and NaOCl decomposi t ion f o r c u p r i c su lph ide l e a c h i n g (5 g/1 f C 0 3 2 - ] T ) 82 17 Cu d i s s o l u t i o n and NaOCl decomposi t ion f o r cuprous su lph ide l e a c h i n g (5 g/1 tco 3 2-] T) 8 3 18 Cu d i s s o l u t i o n and NaOCl decomposi t ion fo r c o v e l l i t e l e a c h i n g (20 g/1 [NaOCl]) 85 19 A g i t a t i o n o f c o v e l l i t e i n s o l u t i o n s o f N a 2 C 0 3 / N a H C 0 3 ± NaCl 86 20 Cu d i s s o l u t i o n and NaOCl decomposi t ion fo r c o v e l l i t e w i t h 10 g/1 [ C 0 3 2 - ] over a p e r i o d o f 6 hours 89 21 NaOCl decomposi t ion i n the presence o f ox ide and carbonate s a l t s o f c o p p e r 1 1 1 101 22 NaOCl o x i d a t i o n o f molybdeni te a t pH 9.0 103 23 NaOCl o x i d a t i o n o f reagent grade molyb- denum d i s u l p h i d e a t pH 9.0 105 24 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 25 NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a) i n the presence o f carbonate bu f fe r s 108 b) i n the absence o f carbonate bu f fe r s 109 26 NaOCl o x i d a t i o n o f molybdeni te and c h a l - c o c i t e a) i n the presence o f carbonate bu f f e r s 110 b) i n the absence of carbonate bu f fe r s 111 27 NaOCl o x i d a t i o n o f molybdeni te and c h a l - c o p y r i t e a) i n the presence o f carbonate bu f fe r s 112 b) i n the absence o f carbonate bu f fe r s 113 (xyi ) LIST OF FIGURES (Cont 'd) Page 28 NaOCl o x i d a t i o n o f molybdeni te a t pH 5.5 116 29 NaOCl o x i d a t i o n o f molybdeni te and c h a l c o p y r i t e a t pH 5.5 117 30 NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 5.5 a) i n the absence of b ica rbona te 118 b) i n the presence o f b ica rbona te 119 31 NaOCl o x i d a t i o n o f molybdeni te and c h a l c o c i t e a t pH 6.5 a) i n the presence o f b ica rbona te 121 b) i n the absence o f b ica rbona te 122 32 NaOCl o x i d a t i o n o f molybdeni te and c u p r i c su lph ide a t pH 6.0 a) i n the presence o f b ica rbona te 123 b) i n the absence o f b ica rbona te 124 33 NaOCl o x i d a t i o n o f molybdeni te 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 ica rbona te 125 b) i n the absence o f b ica rbona te 126 34 Dete rmina t ion o f the s o l u b i l i t y o f copper molybdate a t pH 5.0 128 35 NaOCl decomposi t ion i n the presence o f copper molybdate a t pH 5.5 131 36 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 su lph ide a t pH 9.0 134 37 NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 10.0 a) i n the presence o f carbonate bu f fe r s 135 b) i n the absence o f carbonate bu f f e r s 136 38 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 39 NaOCl l e a c h i n g o f powdered c a l c i t e and P l a s t e r o f P a r i s a t pH 9.0 139- 40 NaOCl l e a c h i n g o f molybdeni te and c a l c i t e i n the absence o f carbonate 141 ( x v i i ) LIST OF FIGURES (Cont 'd) Page 41 E f f e c t o f c h l o r i d e c o n c e n t r a t i o n on Ca d i s s o l u t i o n from CaS0 4 -%H 2 0 1 4 2 42 Calc ium sulphate s o l u b i l i t y as a f u n c t i o n of c h l o r i d e content 1 4 3 43 E f f e c t o f c h l o r i d e c o n c e n t r a t i o n on Ca d i s s o l u t i o n from CaCO^ ^44 44 Calc ium carbonate s o l u b i l i t y as a f u n c t i o n o f c h l o r i d e content 145 45 E f f e c t o f carbonate on c a l c i u m i n h y p o c h l o r i t e s o l u t i o n s 147 46 NaOCl l e a c h i n g o f c o v e l l i t e and molyb- den i t e a t pH 9.0 w i t h 5 g/1 [CO 2 ~] and 10 g/1 [ C 0 3 2 " ] T 148 47 NaOCl l e a c h i n g o f c h a l c o c i t e and molyb- denum d i s u l p h i d e w i t h 10 g/1 [ C 0 3 2 - ] T 14 9 48 NaOCl l e a c h i n g o f c o v e l l i t e i n the presence o f NaMoO^ and 5 g/1 carbonate 151 49 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 presence o f N a 2 S i 0 3 15 2 50 Mercury column fo r measurement o f gas e v o l u t i o n from C u 1 1 1 9 2 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 - 1 M [ C 0 3 2 ~ ] 17 5 52 Eh-pH diagram f o r (oxide species) the system Cu--H 2 0--MoO. 4 181 53 Eh-pH diagram f o r the (hydroxide species) system Cu--H 2 0--MoO,, 4 18 2 54 Eh-pH diagram f o r the system Ca--H 2 0--Mo0„ 4 18-5 55 Eh-pH diagram f o r the system Pb--H 2 0--Mo0„ 4 18 7 56 Eh-pH diagram f o r the system Zn--H 2 0--Mo0„ 4 18 8 ( x v i i i ) LIST OF FIGURES (Cont 'd) Page 57 Eh-pH diagram f o r the system Fe-H 2 0-MoO 189 58 Eh-pH diagram f o r the system Cd-H^-MoO^ 191 (x ix) LIST OF PLATES Fac ing Page I E f f e c t o f h y p o c h l o r i t e s o l u t i o n s on massive c h a l c o c i t e samples 7 3 I I E f f e c t o f h y p o c h l o r i t e s o l u t i o n s on massive c o v e l l i t e samples 7 4 (xx) Acknowledgement The a u t h o r i s g r e a t l y i n d e b t e d t o Dr. I.H. Warren f o r h i s generous a d v i c e , c o n s t a n t i n t e r e s t and i n v a l u a b l e encouragement t h r o u g h - o u t t h e p e r i o d o f t h i s s t u d y . The a s s i s t a n c e p r o v i d e d by members o f F a c u l t y and 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 the h e l p and com p a n i o n s h i p o f f e l l o w g r a d u a t e s t u d e n t s have been much a p p r e c i a t e d . Thanks a r e a l s o e x t e n d e d t o Dr. F. Weinberg f o r t h e many m u s i c a l i n t e r l u d e s w h i c h p r o v i d e d r e s p i t e from, i f n o t i n s p i r a t i o n f o r , t h e r i g o u r s o f r e s e a r c h . F i n a n c i a l s u p p o r t i n t h e form o f a C I L f e l l o w s h i p i s g r a t e f u l l y acknowledged. - 1 - CHAPTER ONE 1.1 I n t r o d u c t i o n Molybden i t e , M c ^ / i s the p r i n c i p a l source o f the molybdenum metal used commerc ia l ly . I t occurs both i n p r imary molybdenum d e p o s i t s and i n more complex ore bodies a s s o c i a t e d w i t h o ther su lph ide 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 hydrated f e r r i c molybdate, FeMo^O^ * 8 H 2 ° a r e t ' i e m o s t common secondary molybdenum mine ra l s but they are not cons idered t o be of economic importance a t the present t ime . 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%."'" I t s p r i n c i p a l use i s as an a l l o y i n g element i n i r o n , s t e e l and c e r t a i n non fe r rous me ta l s . E i t h e r a lone or i n the presence o f o the r elements such as n i c k e l , vanadium, manganese and chromium, molybdenum enhances the s t r e n g t h , toughness and h a r d e n a b i l i t y o f these 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 r e s i s t a n c e . 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 , chemica l reagents and as c a t a l y s t s . They are 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 of molybdenum has inc reased on a w o r l d wide b a s i s at an average r a t e of about 5% per annum f o r the pas t decade, 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 to the year 2000 and beyond. Western w o r l d p r o d u c t i o n f o r 1977 amounted to 89,500 me t r i c tons , o f 2 which the Un i t ed S ta tes produced 68% and Canada 17%. Curren t es t imates of molybdenum rese rves i n d i c a t e tha t s u p p l i e s should be adequate i n the foreseeable f u t u r e . A few h igh grade depos i t s c o n t a i n i n g up to 20% molybdenum as MoS 0 i n r i c h quar tz ve ins e x i s t , but over 95% o f cu r r en t - 2 - and p rev ious p roduc t ion has been from low grade porphyry type depos i t s and i t seems l i k e l y t ha t t h i s f i g u r e w i l l i nc r ea se as more o f the r i c h e r ores are worked ou t . Porphyry ores can be c h a r a c t e r i z e d i n t o two types : 1) Molybdenum p o r p h y r i e s ; where molybdeni te i s the o n l y con ta ined m i n e r a l o f economic importance and averages 0.15 - 0.8% M o S 2 . 2) Copper-molybdenum p o r p h y r i e s ; from which copper i s e x t r a c t e d as the pr imary meta l va lue and molybdenum i s recovered as a by -p roduc t . The molybdeni te content o f these ores 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 imary and secon- dary su lph ide ores 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 - c o c i t e , C u 2 S ; b o r n i t e , Cu^FeS^; and e n a r g i t e , C u ^ s S ^ . There i s o f ten a leached cap a s s o c i a t e d w i t h the ore body c o n t a i n i n g secondary and t e r t i a r y ox ides such as c u p r i t e , C u 2 0 ; ma lach i t e C u 2 ( O H ) 2 C 0 3 ; t e n o r i t e , 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 content averages 0.8%. ' By-produc t molybdenum recovery from porphyry copper ores accounts f o r a lmost 50% o f t o t a l w o r l d p r o d u c t i o n , but the f a c t t ha t ore grades i n v o l v e d are so low means h igh r e c o v e r i e s are d i f f i c u l t to o b t a i n i n many cases . Sepa ra t ion o f molybdeni te from copper ores i s ach ieved 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 p l a n t s t r e a t i n g these ores i s to op t im ize copper recovery and va lues of about 80% are 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 lower and averages 50 - 60%. The recen t depressed s t a t e o f the copper market f o l l o w e d by r a p i d i nc reases i n the p r i c e o f molybdenum to a cu r r en t va lue o f $ 9 / l b , has g i v e n by-product recovery a more important p e r s p e c t i v e . In cases where copper ores are r e l a t i v e l y l e an the two meta ls are almost equal i n terms o f end product v a l u e . The molybdenum - 3 - not recovered i s the re fo re o f economic s i g n i f i c a n c e and represents a s u b s t a n t i a l l o s s o f meta l r e sou rces . 1.2 Curren t Molybdenum P r o d u c t i o n A molybdeni te concent ra te averaging 90% MoS^ i s the u s u a l product o f b e n e f i c i a t i o n o f run o f mine o r e . Th i s i s then conver ted to t e c h n i c a l grade molybdenum t r i - o x i d e , MoO^, f o r f u r t h e r p roces s ing i n t o f e r r o - molybdenum and o ther compounds. The conven t iona l method of 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 igu re 1. Molybdenum-bearing copper ores are most o f ten mined by open p i t methods, a f t e r which the run-of-mine ore i s subjec ted to c rush ing and wet g r i n d i n g to g ive a product 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 cases , l a r g e l y due to the good n a t u r a l f l o t a b i l i t y o f molybdeni te , making i t the e a s i e s t method by which sepa ra t ion from copper can be ach ieved . Complex copper-molybdenum ores are subjec ted t o a c o l l e c t i v e rougher f l o t a t i o n to g ive a rougher concent ra te averag ing 0.3% Mo and 12.5% Cu w i t h some i r o n , su lphur and c a l c i u m o x i d e . Th i s concent ra te i s re-ground and c leaned to g ive an up- graded copper f l o t a t i o n concent ra te averaging 25 - 35% Cu. The molyb- den i t e i s then separated by a s e l e c t i v e f l o t a t i o n s tage , c a r r i e d out e i t h e r by depress ing the copper and a l l o w i n g the molybdeni te to f l o a t , or by the oppos i t e technique o f depress ing the molybdeni te and f l o a t i n g o f f the o ther c o n s t i t u e n t s o f the copper concen t ra t e . The former method i s g e n e r a l l y p r e f e r r e d , g i v i n g an i n i t i a l molybdenum rougher concent ra te - 4 - Run of mine ore L _ CRUSHING 8 GRINDING COLLECTIVE ROUGHER FLOTATION j Rougher concentrate (!2-4%Cu,0-3% MoS2) • REGRINDING, CLEANING i Copper flotation concentrate (25-35%Cu) >D-2%Mol <Q-2% Mo THICKENING Cu THICKENING SELECTIVE ROUGHER FLOTATION FILTRATION Mo I I Mo rough e r c onc• (35% Mo S ) I 2 Cu . concentrate DRYING T CLEANING, REGRINDING Mo flotation c one. ( 8 0 % M o SJ*°' 5 0 / o (f u THICKENING Mo LEACH Cu FILTRATION DRYING Mo concentrate ( 9 0 % M o S 2 ) I M o 0 3 PRODUCTION Figure 1: Conventional flowsheet for the production of molybdenum trioxide. - 5 - which i s p u r i f i e d f u r t h e r i n a coun te r - cu r r en t c i r c u i t u n t i l a 90% MoS 2 p roduc t , c o n t a i n i n g l e s s than 0.5% Cu, i s o b t a i n e d . A low tempera- tu re 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 to e f f e c t p a r t i a l o x i d a t i o n o f copper su lph ide m i n e r a l s , thereby r e t a r d i n g t h e i r f l o t a b i l i t y . With c a r e f u l use of the c o r r e c t f l o t a t i o n reagents fo r the m i n e r a l - i z a t i o n present 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 cho ice o f temperature, up to 85% of the conta ined molybdenum can be r ecovered . 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 to g ive maximum copper r ecove ry , and t h i s r e s u l t s i n a much lower average l e v e l o f molybdenum recove ry . Loss o f molybdenum can occur on account o f the f o l l o w i n g f a c t o r s : " ' ' ^ i ) The ore i s ground to a s i z e s u i t a b l e f o r optimum copper recovery and t h i s i s u s u a l l y coa r se r than the i d e a l s i z e f o r molybdeni te . Th i s problem i s o f ten accentuated du r ing pe r iods o f depressed copper p r i c e s when an even coa r se r g r i n d i s used to i nc rease throughput . i i ) Molybdeni te can be l o s t from the copper rougher f l o t a t i o n t a i l i n g s because i t o f t en e x i s t s as l a r g e f l a k e s which are t rapped by quar tz p a r t i c l e s . i i i ) F i n e r p a r t i c l e s are l o s t from the ove r f low o f m i d d l i n g t h i c k e n e r s a f t e r p r o d u c t i o n o f the molybdenum rougher concen t ra te , and t h i s l o s s i s i nc reased by the presence o f f l o c c u l a n t s . i v ) The presence of v a r y i n g copper su lph ide 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 depressants due to d i f f e r - ences i n sur face p r o p e r t i e s , fo r example between c h a l c o p y r i t e and c o v e l l i t e . C e r t a i n reagents can a l s o i n h i b i t molybdeni te f l o t a t i o n . - 6 - N a t u r a l l y f l o a t i n g m a t e r i a l s such as su lphu r , t a l c , g r aph i t e and c o a l can be e q u a l l y d e t r i m e n t a l t o molybdenum recovery,, and the presence o f molyb- denum oxides i s a l s o u n d e s i r a b l e . v) Porphyry ores o f t en have a non-uniform 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 va lues 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 present 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 cont inuous h igh molybdenum r e c o v e r i e s . In many cases the f i n a l molybdeni te concent ra te i s subjec ted to a s u l p h u r i c a c i d o r sodium cyanide l each a f t e r r e - c l e a n i n g and p r i o r to t h i c k e n i n g and f i l t r a t i o n . Th i s serves to remove any copper remaining i n the concen t ra t e . Convers ion to 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 out i n "Nicho l s -Her reshof f " type r o a s t e r s which enable the temperature to be c l o s e l y moni tored and kept between 600 - 700°C. The f i n a l MoO^ product con ta ins 56 - 62% Mo and has maximum a l l o w a b l e 7 su lphur and copper contents o f 0.25% and 0.75% r e s p e c t i v e l y . •* 1.3 H y d r o m e t a l l u r g i c a l P roduc t ion o f Molybdenum While e x i s t i n g reserves o f molybdeni te are expected to be adequate to supply an inc reased demand o f up to 5% per annum f o r some time to come, p r o d u c t i o n o f molybdenum on a day- to-day b a s i s i s not always adequate. In 1977 there 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 molyb- 2 denum, which had to be s u p p l i e d from e x i s t i n g s tock p i l e s . I t would thus seem d e s i r a b l e to resea rch i n t o ways o f i n c r e a s i n g cu r r en t molybdenum r e c o v e r y . As more o f the w o r l d ' s h igher grade depos i t s are worked ou t , molybdenum bea r ing copper ores t y p i c a l o f those found i n B r i t i s h - 7 - Columbia w i l l assume an even more impor tant r o l e as a source o f the m e t a l . For these types o f o r e s , a h y d r o m e t a l l u r g i c a l method fo r molybdenum recovery has the p o t e n t i a l of g i v i n g h ighe r metal 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 ob ta ined by conven t iona l methods. A h y d r o m e t a l l u r g i c a l route c o u l d a l s o e l i m i n a t e e i t h e r or both o f 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 tages . Th i s would be p r e f e r a b l e from an envi ronmenta l p o i n t o f view by p reven t ing the e v o l u t i o n o f SO^ i n t o the atmosphere. Molybdeni te i s g e n e r a l l y un reac t i ve 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 to the M o V I s t a t e . 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 of +3 to +6, but o n l y the +6 s t a t e i s s t a b l e over a wide range o f p o t e n t i a l - p H v a l u e s . The other va lence 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 complexing agents . O x i d a t i o n o f molybdeni te from Mo" t V to M o V I can be e f f e c t e d by d i s s o l u t i o n i n hot n i t r i c a c i d , concent ra ted s u l p h u r i c a c i d , aqua r e g i a and by oxygen under p ressure 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 ide o f 2- VI n e u t r a l i t y the monomer MoO^ i s the usua l form o f Mo , but a t pH va lues -4 below 7 .0 , and w i t h a molybdenum content i n excess o f 10 M, t h i s i o n Q i s u s u a l l y p o l y m e r i z e d . The molybdate i o n r e a d i l y combines w i t h most meta l c a t i o n s , and w i t h the excep t ion o f the a l k a l i me ta l s , an i n s o l u b l e s a l t i s p r e c i p i t a t e d . The an ion i s able to 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 which 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 to 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 - molybdeni te . The m a j o r i t y o f these suggested the use o f n i t r i c a c i d or a s t rong 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 recovery o f molybdenum by means o f an ion-exchange or so lven t e x t r a c t i o n technique , or 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 ing meta l (mercury, z i n c , cadmium or molybdenum) or gaseous (hydrogen, hydrogen s u l p h i d e , sulphur d i o x i d e ) r educ t an t s . I n v e s t i g a t i o n s i n t o the use of o ther r educ ing agents such as hydraz ine and sodium s u l p h i t e have r e c e n t l y 9 been c a r r i e d out i n t h i s department. The b i g g e s t l o s s o f molybdenum i n cu r r en t processes occurs du r ing the c o l l e c t i v e rougher f l o t a t i o n stage and amounts to some 36%. Fur the r l o s s e s o f about 10% occur between t h i s p o i n t and the f i n a l molybdeni te p roduc t . 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 reatment should the re fore use run o f mine ore as the s t a r t i n g m a t e r i a l fo r a l e a c h i n g c i r c u i t , but t h i s would not be economica l ly p r a c t i c a l fo r many porphyry ores which c o n t a i n l e s s than 0.02% Mo. Most o f the processes envisaged 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 con junc t ion w i t h e x i s t i n g f l o t a t i o n methods, us ing e i t h e r molybdenum or copper rougher concent ra tes as feed m a t e r i a l . Both methods appear to be f e a s i b l e p r o v i d - ed the l each 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 over copper and o the r su lph ide m i n e r a l s . Whi le the t reatment o f u n - b e n e f i c i a t e d ores i s not g e n e r a l l y accep t ab l e , 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 mining methods, c o u l d have cons ide rab 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 mining i n terms o f reduced c a p i t a l and o p e r a t i n g cos 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 environmenta 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 hand l ing and s t o r i n g l a rge 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 under- ground movements, have been w e l l documented i n the l i t e r a t u r e . 1 0 Low grade copper-molybdenum ores c o u l d be ve ry amenable to t h i s type o f l e a c h - i n g p rov ided 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 conta ined molybdenum v a l u e s , and cou ld be economica l ly 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 of molybdeni te 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 out 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 to 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 type process f o r producing molybdic o x i d e , i n which they used sodium hypoch lo r - i t e as a l i x i v i a n t f o r three d i f f e r e n t grades o f m a t e r i a l c o n t a i n i n g 0.015%, 1,05% and 63% MoS 2 r e s p e c t i v e l y . 1 1 Dresher , Wadsworth and F a s s e l had p r e v i o u s l y s t ud i ed the k i n e t i c s o f d i s s o l u t i o n o f molybdeni te i n a l k a l i n e s o l u t i o n s w i t h potass ium hydroxide a t temperatures i n excess o f 100°C and pressures up to 700 p s i , and had found tha 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 cou ld be ob ta ined w i t h these c o n d i t i o n s . Cox e t a l . concluded tha t use o f h y p o c h l o r i t e reagents cou ld g ive a much more economical process than one n e c e s s i t a t i n g a h igh p r e s s u r e - h i g h temperature l e a c h , and optimum c o n d i t i o n s fo r molybdenum recovery were ob ta ined 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 temperature. 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 be ing o p e r a t i v e du r ing the l e a c h : - 10 - 7NaOCl + MoS 2 + 4e >- MoC>4~ + S 2 0 3 2 + 7NaCl (1) The r a t e of l e a c h i n g was found to decrease to zero a f t e r about t h i r t y minutes , at which p o i n t molybdenum e x t r a c t i o n s rang ing from 91 - 99% had been ach ieved . Both Cox and S c h e l l i n g e r , and Dresher e t a l . observed t ha t t h i o s u l p h a t e i ons were present i n the l e a c h i n g s o l u t i o n s , but the 2- l a t t e r workers concluded t ha t S 2 C> 3 was on ly an in te rmed ia te r e a c t i o n product and t ha t a f t e r complete o x i d a t i o n , o n l y molybdate and sulphate ions would e x i s t i n s o l u t i o n : 9 - 2 - 2 - MoS 2 + - ° 2 + 6 0 H y M o 0 4 + 2 S 0 4 + 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 molybdeni te u s i n g sodium hypoch lo r - 13 i t e s o l u t i o n s was r epor t ed by Io rd inov and Zel ikman i n 1961. They used a reagent c o n c e n t r a t i o n v a r y i n g from 15 to 60 g/1 OC1 a t tempera- tu res 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 - A d e t a i l e d d e s c r i p t i o n as to the theory o f the d i f f e r e n t stages i n v o l v e d i n molyb- den 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 andpoin 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 to be: MoS 2 + 9NaOCl + 6NaOH > Na2MoO + 2Na 2 S0 4 + 9NaCl + H 2 0 (3) Th 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 of ox idan t r e q u i r e d per mole o f molybden i te . Zelikman a l s o found t ha t t h i o s u l p h a t e was p resen t i n i t i a l l y but t ha t i t s c o n c e n t r a t i o n went through a maximum va lue and had reached zero by the end o f the r e a c t i o n . The o x i d a t i o n o f molybdeni te to molybdate was found to be f i r s t o rde r , 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 over the temperature range under s tudy . The r a t e constant i nc reased both w i t h i nc reased - 11 - h y p o c h l o r i t e content and w i t h inc reased temperature. Shapi ro and Kulenkeva c a r r i e d out 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 to t r y and o b t a i n e f f i c i e n t molybdenum recovery from in te rmedia te concent ra tes 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 dissemina ted molybdeni te or p o l y s u l p h i d e o r e s . Leaching experiments were done i n the presence o f sodium carbonate and i t was found tha 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 ra t e o f molybdenite decom- p o s i t i o n a t 50°C: MoS 2 + 9NaOCl + 3Na 2 C0 3 HNa MoC>4 + 2 N a 2 S 0 4 + 9NaCl + 3CC>2 (4) The l e a c h was s t a t e d as be ing s e l e c t i v e f o r molybdenum because any o ther metal su lph ides present would be conver ted to i n s o l u b l e carbonates , as represented by the f o l l o w i n g equa t ion : . MeS. + 4NaOCl .+ N a 2 C 0 3 v N a 2 S ° 4 + 4 N a C 1 + MeC0 3 (5) Bhappu, Reynolds and Stahman made a s tudy 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 molybdeni te from three d i f f e r e n t sources : a h igh grade con- cen t ra te c o n t a i n i n g 96 - 98% M o S 2 , low grade ores t y p i c a l o f those found i n a waste dump (0.2 - 0.8% MoS 2) and medium grade lumps o f molybdeni te averaging 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 fo r h y p o c h l o r i t e consumption to be the same f o r each t e s t sample, i n d i c a t i n g n e g l i g i b l e consumption by gangue m a t e r i a l , 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 Ze l ikman, t ha t n ine moles o f OC1 were r e q u i r e d to o x i d i z e each mole o f MoS . 2 They a l s o confirmed r e p o r t s by Choppin and F a u l k e r b e r r y 1 ^ which showed t h a t p rov ided an excess o f h y p o c h l o r i t e i s p resent i n s o l u t i o n , the - 12 - end p r o d u c t o f s u l p h i d e o x i d a t i o n i s e n t i r e l y s u l p h a t e . Doubt was t h u s 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 was p r e s e n t as a f i n a l p r o d u c t o f h y p o c h l o r i t e o x i d a t i o n , and Bhappu e t a l . s t r e s s e d t h a t any t h i o s u l p h a t e o r o t h e r i n t e r m e d i a t e o x i d a t i o n s t a t e o f s u l p h u r w o u l d , i n t h e i r o p i n i o n , e x i s t o n l y f o r v e r y s h o r t p e r i o d s o f t i m e b e f o r e b e i n g o x i d i z e d t o s u l p h a t e . These a u t h o r s c o n c l u d e d t h a t such a h y p o c h l o r i t e p r o c e s s o f f e r e d c o n s i d e r a b l e p o t e n t i a l f o r m o l y b d e n i t e l e a c h i n g , e s p e c i a l l y f o r t h e t r e a t - ment o f low g r ade o r e s , on a c c o u n t o f t h e s e e m i n g l y low c o n s u m p t i o n o f r e a g e n t by 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 . r e v i e w e d a number o f o x i d i z i n g a g e n t s f o r t h e 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 o f m o l y b d e n i t e o r e s and c o n c l u d e d t h a t w h i l e 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 gave r a p i d and 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 e x p e n s i v e t o m a n u f a c t u r e , u n s t a b l e and c o r r o s i v e ; and t h e o n l y e c o n o m i c a l l y f e a s i b l e method f o r i t s g e n e r a t i o n i n t h i s t y p e o f l e a c h i n g s y s t e m would be i n an e l e c t r o l y t i c r e - g e n e r a t i o n c i r c u i t f r o m t h e sodium 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 t h e o x i d a t i o n r e a c t i o n . O t h e r r e a g e n t s c o n s i d e r e d i n c l u d e d sodium c h l o r a t e i n a c i d s o l u t i o n s , manganese d i o x i d e - s u l p h u r i c a c i d and n i t r i c a c i d . The 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 as i n - s i t u l e a c h i n g were a l s o r e v i e w e d , e s p e c i a l l y i n t h e p r e s e n c e o f n o n - s u l p h i d e o r e s s u c h as f e r r i m o l y b d a t e and l i m o n i t e . F o r t h e s e o r e s and f o r t h o s e c o n t a i n i n g m ixed o x i d e s and s u l p h i d e s e i t h e r an a c i d - c h l o r a t e o r a b a s i c h y p o c h l o r i t e - c a r b o n a t e l i x i v i a n t seemed f e a s i b l e , w i t h t h e l a t t e r b e i n g g e n e r a l l y p r e - f e r r e d b ecause o f p o t e n t i a l p roblems w i t h t h e p r e c i p i t a t i o n o f m olybdate compounds i n a c i d s o l u t i o n s . - 13 - Zel ikman reviewed the p o s s i b i l i t y o f l e a c h i n g molybdenite w i t h 18 h y p o c h l o r i t e aga in i n 1970, p a r t i c u l a r l y from low grade concentra tes which would probably 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 . Al though such su lph ides 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 , the o x i d a t i o n products would be i n s o l u b l e hydroxides which i n h i b i t the r e a c - t i o n and prevent 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 molybde- num l e a c h . I t was p o i n t e d out i n t h i s a r t i c l e t ha t the hydroxides o f c e r t a i n t r a n s i t i o n meta l elements , i n c l u d i n g copper and i r o n , are a l s o a c t i v e c a t a l y s t s fo r the decomposi t ion 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 media. C a t a l y s i s can e i t h e r be homogeneous or heterogeneous, and i t was suggested the l a t t e r i n v o l v e s the format ion o f uns tab le hydroxides o f h ighe r va lence s t a t e s , e s p e c i a l l y fo r copper . Optimum c o n d i t i o n s f o r concent ra tes c o n t a i n i n g 23% Mo and 9% Cu were found to e x i s t w i t h a hypo- c h l o r i t e content o f 30 g/1 and 20 - 30 g/1 f ree a l k a l i . Higher tempera- tu re s were found to i nc rease the r a t e o f molybdenum e x t r a c t i o n , but as t h i s a l s o gave an inc reased 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 decomposi t ion , l e a c h i n g a t room temperature was recommended. In a l l the above s t u d i e s molybdeni te l e a c h i n g has been c a r r i e d out on the a l k a l i n e s ide o f n e u t r a l i t y , w i t h pH 10.0 be ing s t a t e d as optimum i n s e v e r a l cases . 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. A pH range o f 5.0 - 7.0 was used i n an e l e c t r o o x i d a t i o n technique i n v e s t i g a t e d by the Un i t ed S ta tes Bureau o f Mines f o r e x t r a c t i n g molybdenum and rhenium from low grade 19 o r e s , de sp i t e t h i s be ing the r e g i o n i n which decomposi t ion o f hypoch lo r - i t e to c h l o r a t e takes p l a c e most r a p i d l y . The method was based on i n - s i t u h y p o c h l o r i t e genera t ion by e l e c t r o l y s i s i n b r i n e ore p u l p . E x t r a c t i o n s - 14 - o f 90 - 99% molybdenum were r epor ted 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 aga in found to be ope ra t i ve (equat ion 3 ) . The r e q u i r e d pH va lue was mainta ined by semi-cont inuous a d d i t i o n o f sodium carbonate and a temperature o f 30 - 40°C was used. The o v e r a l l power consumption was r epor t ed as 9.7 kwh/ lb Mo e x t r a c t e d , w i t h a cu r r en t d e n s i t y o f 0.5 a m p / i n 2 . The study was extended to determine the e x t r a c t a b i l i t y o f molyb- denum from copper-molybdenum f l o t a t i o n concen t ra t e s , averag ing 3 - 28% Mo 20 and 2 - 15% Cu. A maximum e x t r a c t i o n o f 97% Mo was achieved w i t h a f i n a l pH o f 7 .0 : t h i s va lue apparen t ly decreased a t both lower and h igher pH l e v e l s . I t was s t a t e d t ha t a minimum copper s o l u b i l i t y o f 1 - 3 ppm occur red at 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 extent of 25 ppm due to format ion o f the s o l u b l e compound (CuX^CO^ where X = CI or OH . Sche iner e t a l . suggested copper molybdate com- pounds cou ld adve r se ly a f f e c t molybdenum recove ry , but o x i d a t i o n o f copper su lph ides by h y p o c h l o r i t e cou ld be prevented by adding s u f f i c i e n t sodium carbonate to the system. 21 22 In two l a t e r papers ' p rocess s o l u t i o n s were t r e a t e d , and the technique was demonstrated w i t h a pro to type c e l l . 89 - 98% molybdenum e x t r a c t i o n was ob ta ined from concent ra tes c o n t a i n i n g l e s s than 1% Cu and about 36% Mo. 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 tep was the re fo re i n c o r p o r a t e d i n t o the p roces s . Th i s p r o - cedure a l s o served to reduce the pH o f molybdate s o l u t i o n s for subsequent molybdenum recovery by s o l v e n t e x t r a c t i o n . Power consumption fo r t r e a t i n g f l o t a t i o n concentrates was 13.7 kwh which i s 4% h igher than the cor responding - 15 - va lue f o r h ighe r grade molybdeni te concen t ra t e s . In the p ro to type c e l l demonstra t ion ' o f f grade ' f l o t a t i o n concentra tes 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 and/or c h a l c o c i t e were t r e a t e d . I t was r epor ted tha t the molybdenum e x t r a c t i o n decreased to on ly 75% i n the presence of h igher i n i t i a l copper con ten t s , and copper molybdate compounds 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 c la imed tha t any c h a l c o - p y r i t e p resen t i n the feed m a t e r i a l was unaf fec ted by e l e c t r o l y s i s , but t ha 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 format ion o f s o l u b l e copper compounds. These then reac ted w i t h molyb- date ions i n s o l u t i o n to g ive i n s o l u b l e copper molybdates . A l l subsequent t r i a l s were the re fo re performed w i t h low copper/ h i g h molybdenum concen t ra t e s ' and no i n f o r m a t i o n was g iven 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 . In con junc t ion w i t h these s t u d i e s , B a r r and co-workers 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 recovery d u r i n g e l e c t r o o x i d a t i o n , and concluded t h a t by-product sodium c h l o r a t e was d e t r i m e n t a l to molybdenum recovery as w e l l as r e p r e s e n t i n g a power l o s s from the system. Both these f a c t o r s are unfavourable e c o n o m i c a l l y . To minimize c h l o r a t e produc- t i o n the authors recommended a low temperature- low cu r r en t d e n s i t y l each i n which the pH was a l s o reduced to 4 .0 - 5 .0 . The use o f ' f l o w through ' 23 24 c e l l s was shown to be p r e f e r a b l e t o l e a d d i o x i d e anode batch c e l l s . ' 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 molybdeni te 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 tha t 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 concent ra tes 25 was u n l i k e l y . The u n i t consumption of oxygen fo r the two minera l s i s appa ren t ly ve ry s i m i l a r , and t h i s was taken to mean tha t both spec ies - 16 - would be s imul taneous ly a t t a c k e d , thereby p reven t ing s e l e c t i v e molybdenum d i s s o l u t i o n . 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 to the f i n d i n g s o f 26 Warren, Ismay and K i n g , who showed tha t molybdeni te cou ld be r a p i d l y and s e l e c t i v e l y leached 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 concent ra te 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 generated h y p o c h l o r i t e was proposed. By c o n s i d e r a t i o n o f power requi rements , sodium c h l o r i d e consumption and o ther f a c t o r s for the 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 los se s by the use o f a process which e l i m i n a t e d c l eane r f l o t a t i o n s t eps , Warren e t a l . suggested tha 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 longer v a l i d ; and tha t i t would compare favourab ly w i t h the e l e c t r o o x i d a t i o n techniques o u t l i n e d above. A study was the re fo re c a r r i e d out to determine optimum c o n d i t i o n s fo r molybdenum e x t r a c t i o n and these were found to 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 - 40°C. S e l e c t i v i t y o f molyb- denum over copper was ob ta ined w i t h a r a t i o o f about 100:1 , but the presence o f even sma l l amounts o f copper i n s o l u t i o n a t pH 9.0 appeared 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 tha t p a r t i a l l y o x i d i z e d su lphur spec ies c o u l d be complexing 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 over t ha t p r e d i c t e d by the s t o i c h i o m e t r y of equa t ion 3 was observed i n c e r t a i n cases , and t h i s was a t t r i b u t e d to the format ion o f sur face ox ides d u r i n g the oven-d ry ing o f copper s u l - phide m i n e r a l s , which subsequent ly ac t as c a t a l y s t s fo r h y p o c h l o r i t e de- compos i t i on . The study i n c l u d e s a proposed f lowsheet f o r the o v e r a l l p r o - cess . - 17 - 1.4.2 The behaviour 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 to s o l u t i o n s c o n t a i n i n g 2+ d i s s o l v e d copper i n the form o f the aquo- ion [Cu(H 0) ] leads to the 2 6 format ion o f complexes. Because the s i x water molecules are not e q u i - d i s t a n t from the c e n t r a l copper atom, success ive d isplacment by o ther l i g a n d s can r e a d i l y o c c u r . Ammonia, NH^, i s one such complexing 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 ha t c u p r i c hydroxide 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 to advantage i n a number o f processes for copper e x t r a c t i o n . Ammonium carbonates are used i n t h i s r e spec t , but due t o the s t rong complexing a c t i o n o f the ammonia i t s e l f , the f a c t t ha t carbonate a l s o ac t s as a complexing l i g a n d f o r copper i s g e n e r a l l y 2- o v e r l o o k e d . The [CO^ ] anion forms a s t ronger complex than do any o f the h a l i d e i o n s , for 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 o f t en cons idered to s t a b i l i z e c u p r i c s a l t s i n s o l u t i o n . I t was observed i n the middle o f the l a s t century tha 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 to sodium carbonate s o l u t i o n s produced i n t e n s e l y b lue s o l u t i o n s which subsequent ly p r e c i p i t a t e d l i g h t b lue c r y s t a l s of some b a s i c copper carbonate s a l t . 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 sub jec t and he confirmed tha t s a l t s ob ta ined by the 27 29 above methods r epor t ed by D e v i l l e and Reynolds were 'double carbonates ' w i t h the t y p i c a l formula N a ^ C u ( C O ^ ) ^ • 3 H 2 0 ' P i c k e r i n g noted tha t 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 c o l o u r s , two d i f f e r e n t substances were i n v o l v e d . He a l s o observed tha t the s o l u t i o n was much darker than a copper su lphate 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 copper . He p o s t u l a t e d t h a t i t conta ined a ' c u p r i carbonate ' spec ies i n which copper formed p a r t o f the a n i o n . 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 to g ive 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 case . 29 30 Reynolds and Wood and Jones had p r e v i o u s l y shown i n independent s tud i e s tha t e l e c t r o l y s i s of these b lue carbonate s o l u t i o n s l i b e r a t e d copper a t bo th the anode and the cathode. The two most common copper carbonates are the mine ra l s a z u r i t e , C u 3 ( O H ) 2 ( C 0 3 ) , and m a l a c h i t e , C u 2 C 0 3 ( 0 H ) 2 . P i c k e r i n g r epor ted i s o l a t i n g s e v e r a l o ther s a l t s i n c l u d i n g 5Cu0,2C0 2 ; 5Cu0,3C0 2 and 8 C u O , 3 C 0 2 , 6 H 2 0 ' by mix ing copper su lphate s o l u t i o n s w i t h e i t h e r sodium carbonate or sodium b i - carbonate . He found a l l these b a s i c carbonates to be i n s o l u b l e i n water and sodium carbonate 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 ca rbon ic a c i d and sodium b i c a r b o n a t e . He a l s o observed t ha t i n t r o d u c i n g copper s u l - phate s o l u t i o n s i n t o a l k a l i n e carbonates c o n t a i n i n g v a r i o u s p r o p o r t i o n s o f N a H C 0 3 : N a 2 C 0 3 produced a ve ry b lue s o l u t i o n w i t h a copper content 2- dependent on the C 0 3 : H C 0 3 r a t i o (and thus o f pH) , but which fo r any mixture 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 con ten t . I t was observed t ha t on a l l o w i n g these s o l u t i o n s to stand fo r a couple o f days p r e c i p i t a t i o n o f e i t h e r ma lach i t e o r a 'double s a l t , ' N a 2 C u ( C 0 3 ) 2 o c c u r r e d , l e a v i n g an almost 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 ve ry l i t t l e copper. No c l e a r e x p l a n a t i o n as to why decomposi t ion should occur a f t e r 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 ha 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 present i n a g i v e n case determined whether ma lach i t e or the double s a l t formed, and t ha t i n f a c t the double carbonate had two i somer ides ; one (the - 19 - cupr i -ca rbona te ) c o n t a i n i n g a n i o n i c copper and the o ther c a t i o n i c copper. A proposed molecu la r s t r u c t u r e fo r each substance i s g i v e n . Other obse rva t ions 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 nc rease i n temperature produced a s m a l l i nc rease 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 carbonate , but s t rong hea t ing of 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 robably copper o x i d e . i i ) A d d i t i o n o f excess sodium hydroxide to a carbonate c o n t a i n i n g copper s o l u t i o n removes carbon d i o x i d e caus ing decomposi t ion of the s o l u t i o n and format ion o f a b lue b a s i c carbonate s a l t . 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 appear ing i n some cases . 31 Appleby and Lane a l s o c a r r i e d out a s tudy o f the double carbonates of sodium and potass ium w i t h v a r i o u s t r a n s i t i o n metals i n c l u d i n g copper . They prepared samples o f the s a l t N a 2 C u ( C 0 3 ) 2 , 3 H 2 0 by a l l o w i n g i t to p r e c i p i - t a t e from copper carbonate s o l u t i o n s : concent ra ted c u p r i c ace ta te was added to a sodium carbona te /b ica rbona te mix ture (100 g Na 2 CO 3 : 40 g NaHCO^) a t 50°C and a c l e a r deep b lue s o l u t i o n free o f any p r e c i p i t a t e was immediately formed. On s tand ing o v e r n i g h t , c r y s t a l s o f the double s a l t were ob ta ined from t h i s s o l u t i o n and i t was observed tha t the mother l i q u o r c o u l d be reused a f t e r s epa ra t i on 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 authors a l s o observed tha t both c r y s t a l s and s o l u t i o n s de- composed a t h ighe r temperatures g i v i n g cupr i c ox ide and sodium carbonate , as a r e s u l t o f l o o s i n g water and carbon d i o x i d e . The s o l u t i o n was decomposed by a d d i t i o n o f excess wate r . Appleby and Lane concluded tha t - 20 - c r y s t a l d e p o s i t i o n was. not due to the s o l u t i o n be ing super - sa tu ra ted i n the normal sense because, a l though p r e c i p i t a t i o n occur red s l o w l y and o n l y a f t e r 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 of 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 procedure . I t was a l s o shown t ha t c r y s t a l l i z a t i o n time was unaffec ted by atmospheric carbon d i o x i d e and was cons tant fo r s o l u t i o n s i n e i t h e r open or sea led 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 to a K i p p ' s apparatus fo r carbon d i o x i d e . The f o l l o w i n g reasons were thus put forward to e x p l a i n the p r e c i p i t a t i o n behav iour : i ) A ve ry 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 s t a b l e super - sa tu ra ted s o l u t i o n s e x i s t . i i ) 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 format ion o f an in te rmed ia te compound which undergoes slow t r ans fo rma t ion i n t o the f i n a l produce. In agreement w i t h the obse rva t ions o f P i c k e r i n g t h i s study showed t ha t the e q u i l i b r i u m copper content i n s o l u t i o n inc reased as a f u n c t i o n of t o t a l carbonate c o n c e n t r a t i o n . I t was a l s o noted tha 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 ob ta ined i n the presence o f both sodium b ica rbona te and sodium carbonate . Omission of the b ica rbona te l e d to almost ins tantaneous p r e c i p i t a t i o n o f a b a s i c carbonate s a l t . The f a c t t ha t more copper was d i s s o l v e d by the carbona te /b icarbona te mix ture than would be ob ta ined by d i s s o l v i n g CuCO^ i n water was a t t r i b u t e d to the format ion o f the complex 2- 6- i 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 be ing presen 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 ther s t u d i e s o f these c h a r a c t e r i s t i c a l l y b lue copper carbonate s o l u t i o n s and o f the b a s i c s a l t s d e r i v e d from them have been - 21 - 32 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 , an i n v e s t i g a t i o n i n t o the e f f e c t s 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 33 34 Hsu, and a de t e rmina t ion o f the s o l u b i l i t y o f ma lach i t e by S c a i f e . In t h i s l a s t s tudy S c a i f e observed tha t ma lach i t e s o l u b i l i t y i n sodium b icarbona te s o l u t i o n s was f a r g rea te r than would be expected form c a l c u - l a t i o n s fo r the c u p r i c i o n . I t was the re fo re suggested tha t i o n i c a s s o c i a t i o n or complex format ion occurs between c u p r i c and b ica rbona te i o n s . An analogy was drawn between t h i s case and tha t o f c u p r i c / ace ta te 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 be ing g iven by the express ion [ C u T ] = [CuC0 3] + [CuHC0 3 + ] + [ C u 2 + ] (6) which seemed to 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 va lues fo 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 ive an Eh-pH diagram fo r the system Cu-0 -S-CO - H 0 a t 25°C which shows t ha t a t atmospheric pressure (P_„_ = Z Z Z C^2 - 3 . 5 10 ) ma lach 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 igher than 0 - 0.2 V . An inc rease i n the d i s s o l v e d carbon d i o x i d e content would extend t h i s r e g i o n o f s t a b i l i t y (Figure 2 ) . The s o l u b i l i t y cons tan t , K , fo r the r e a c t i o n s C u 2 ( O H ) 2 C 0 3 = 2 C u 2 + + C 0 3 2 ~ + 20H~ (7) -31 .90 i s g i v e n as K = 10 s 36 De Zoubov e t a l . . i n v e s t i g a t e d the behaviour o f copper i n sodium b ica rbona te s o l u t i o n s o f v a r y i n g s t r e n g t h s , and found tha t the c o r r o s i o n o f copper metal was s i g n i f i c a n t l y a f f e c t e d by the carbonate con ten t . - 22 - Figure 2: Stability relations for copper compounds in the system Cu-H„0-0„-S-C0„. - 23 - Experiment showed t ha t s o l u t i o n s c o n t a i n i n g l e s s than 0.0032 M b icarbona te were m i l d l y c o r r o s i v e towards copper w i r e ; those 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 fu r t he r i nc rease o f b ica rbona te 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 . E l e c t r o c h e m i c a l e q u i l - i b r i u m (Eh-pH) diagrams were drawn to e x p l a i n these o b s e r v a t i o n s . I t was found tha 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 carbonate mala- c h i t e corresponded to the p a s s i v a t i o n e f f e c t observed i n the r e g i o n o f 0.01 = 0.032 M b i ca rbona t e , but t ha t d i s s o l u t i o n o f ma lach i t e to g ive s t a b l e , complex cupr i - ca rbona te i ons cou ld occur i n s o l u t i o n s w i t h a very low b ica rbona te con ten t , o r i n those c o n t a i n i n g more than 0.1 M. A s e r i e s o f four diagrams are g iven i n which the t o t a l d i s s o l v e d CO^ con ten t , de f ined as [H 2 C0 3 ] + [HC0 3~] + [C0 3 2 ~] -3 inc reases from 10 M to 1 M i n c o n c e n t r a t i o n (Figure 3 ) . As t h i s va lue o f d i s s o l v e d CO^ i n c r e a s e s , the r e g i o n o f ma lach i t e s t a b i l i t y grows to h ighe r pH va lues caus ing c u p r i t e and t e n o r i t e zones to co r r e spond ing ly d i m i n i s h . A z u r i t e , 2CuC0 3 Cu(OH) 2 , becomes s t a b l e i n a pH range o f ^3 - 7 a t [C0 2] va lues g rea te r than 10 1 M. The d i s s o l v e d spec ies 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 3 (aq.) molecu le , 2- the c u p r i d ihydroxo carbonate i o n , CuC0 3 (OH) 2 , and the c u p r i carbonate 2- i o n , C u ( C 0 3 ) 2 . The CuC0 3 (aq.) spec ies e x i s t s a t the lower end of the pH s c a l e , be ing s t a b l e from 6.5 - 10.0 a t low carbonate c o n c e n t r a t i o n s , and be ing pushed downwards to 5.0 - 7.0 a t h igher l e v e l s o f [ C 0 2 ] . The cupr i - ca rbona te i o n appears i n a narrow band o f pH (9.0 - 10.5) a t -2 C 0 2 l e v e l s i n excess o f 10 M and expands to a much wider band (7.0 - - 24 - Figure 3 (a): Potential - pH diagram . for the system Cu-CC^-H^O with 10 _ 3M [CO =] T. - 25 - Figure 3 (b): Potential - pH diagram for the system Cu-CCL-H-O with 10 ° M [C0 3=] T. 2 2 - 26 - > 11.5) a t the 1 M CO^ l e v e l . These s o l u b l e carbonate spec ies a l s o become s t a b l e at i n c r e a s i n g l y h ighe r p o t e n t i a l va lues fo r a g iven pH as the d i s s o l v e d CO^ content goes up. At E va lues above t h i s , Cu^O^ (hydrated) i s shown as the s t a b l e s p e c i e s . Diagrams showing t h e o r e t i c a l c i rcumstances 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 carbonate con ten t , toge ther w i t h s o l u b i l i t y diagrams fo 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 co-workers 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 he lp o f thermodynamic data produced by Si lman fo r the Cu-H 2 0-CO^ system, s t a b i l i t y diagrams showing the zones of 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 occurrence o f the u n i q u e l y s t a b l e carbonate complexes CuCO^Caq.) and 2- C u ( C 0 3 ) 2 i s again recogn ized as caus ing d i s s o l u t i o n o f the b a s i c copper carbonate m i n e r a l s : %Cu (0H) 2 C0 + JsC0 2 = CuC0 3 (aq.) + IjH 0 (8) J jCu 2 (OH) 2 C0 3 + 2HC0 3~ = Cu(C0 3 ) 2 2 " + %C0 2 + | ^ 0 (9) f o r which 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 : 2+ 2-Cu + C 0 3 c=^ CuC0 3 (aq.) l o g k - - 6.73 2+ 2- . 2- Cu + 2C0 3 C u ( C 0 3 ) 2 l o g k = 9.83 I t was noted tha 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+ 2-i s p resent as Cu a t pH va lues below 7 .0 , and as C u ( C 0 3 ) 2 i n more a l k a l i n e s o l u t i o n s . 38 Stumm and Morgan g ive both 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 spec ies o f the Cu-J^O-CO^ system. They have been cons t ruc t ed fo r a t o t a l -2 I I carbonate content o f 10 M for the r e l e v a n t Cu e q u i l i b r i a , and show 2+ tha t the impor tant s o l u b l e spec ies w i t h i n c r e a s i n g pH are Cu , CuCO^ ( a q . ) , 2- I I C u ( C 0 3 ) 2 and hydroxo-copper anions (Figure 4 ) . In a paper which cons ide 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 Longhi g ive a s t a b i l i t y diagram showing predominance areas o f the spec ies which can e x i s t as c u p r i c com- p lexes i n s o l u t i o n s c o n t a i n i n g both c h l o r i d e and carbonate i o n s . These - 0 - 2- 2- 4-i n c l u d e CuCl , C u C l 2 , C u C l 3 , C u C l 4 , C u ( C 0 3 ) 2 , C u ( C 0 3 ) 3 and 3- 2-Cu(HC0 ) . I t i s aga in apparent t ha t the Cu(C0 o ) i o n i s predominant 3 5 5 2 at pH 9 .0 , i n d i c a t i n g tha t the carbonate complexes copper more s t r o n g l y 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 ha 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 presence o f l a r g e q u a n t i t i e s o f C l , i s a l s o 40 noted by Van Muylder e t a l . and i t i s s t a t e d tha 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 Decomposi t ion 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 s o l u t i o n Sodium h y p o c h l o r i t e , NaOCl, i s a s t rong ox idan t i n a l k a l i n e s o l u t i o n s and has been shown to be an e f f e c t i v e l i x i v i a n t fo r the e x t r a c - t i o n o f molybdenum from molybdeni te ores and concen t ra t e s , as o u t l i n e d - 28 - Figure 4: Solubility of Cu (II) in the system Cu-H 0-CO •[CO- =] T = 10_2M. 2 2 2 a) activity ratio diagram. b) solubility diagram. - 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 t h i s reagent from a commercial s t andpoin t however: i ) I t i s expensive to generate , i i ) I t i s uns tab le and undergoes spontaneous decomposi t ion 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 . Th i s decomposi t ion 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 the s a l t s o f c e r t a i n t r a n s i t i o n me ta l s . Most e a r l y i n v e s t i g a t o r s concluded t ha t the cos t s i n c u r r e d i n h y p o c h l o r i t e gene ra t ion would be too grea t t o g ive an economica l ly f e a s i - b l e process f o r molybdenum e x t r a c t i o n . In view o f the cu r r en t s t rong demand and h i g h p r i c e o f molybdenum, together 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 genera tors f o r manufactur ing 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 process would now seem to compare favourab ly w i t h e x i s t i n g t echnology . In a process u s ing 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 decomposi t ion o f the reagent 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 gene ra t ion o f more than the s t o i c h i o m e t r i c hypo- c h l o r i t e r e q u i r e d fo r the o x i d a t i o n o f molybdeni te t o molybdate. I t i s t he re fo re important t o app rec i a t e the c o n d i t i o n s under which decomposi- t i o n takes p l a c e , and the ex ten t t o which i t o c c u r s . S e v e r a l i n v e s t i g a t i o n s have repor ted the r e s u l t s o f s t ud i e s c a r r i e d out t o determine the exact nature o f h y p o c h l o r i t e decomposi t ion under v a r y i n g c o n d i t i o n s o f pH, temperature, i o n i c s t r eng th e t c . I t i s g e n e r a l l y agreed t ha t the products of decomposi t ion 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 . The unca ta lyzed r e a c t i o n can be represented as f o l l o w s : - 30 - HC10 + 20C1~ > c l 0 3 ~ + 2 C 1 ~ + H + ( 1 0 ) 2HC10 + O C l " >• C10 3 ~ + 2C1~ + . 2H + (11) HCIO + OCl~ — - y 2C1~ + 0 2 + H 2 (12) Equat ions 10 and 11 both represent decomposi t ion to c h l o r a t e . The 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 l a t t e r 41 more o f ten occurs i n a c i d i c media. D'ans and Fruend suggested tha t i n ve ry pure 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 so l e decomposi t ion p roduc t , but t h i s i s more g e n e r a l l y accompanied by simultaneous decomposi- 42 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 which i s u s u a l l y thought o f as be ing 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 meta l hydroxides and o x i d e s . Whi le 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 which have been put forward t o e x p l a i n t h i s behaviour has hot been undertaken, a review o f 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 roduces concepts which are a p p l i c a b l e to the present s tudy: 43 B e l l 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 ) 2 , i n the presence o f a number o f s a l t s i n both a c i d and a l k a l i n e s o l u t i o n . Th i s v e l o c i t y i nc reased r a p i d l y i n s o l u t i o n s c o n t a i n i n g C o ( N 0 3 ) 2 and NiSO^ and was s l i g h t l y i nc reased by the presence o f BaCl , CaSO , AgNO , HgCl , F e C l , K Cr O and FeSO . 4tC * i O -C- £ I 4 L i C l , N a 2 C 0 3 , KCN, Na 2 S and KN0 2 were r epor ted 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 study o f the s t a b i l i t y and redox po ten- t i a l s o f h y p o c h l o r i t e s , concluded tha t decomposi t ion was c a t a l y z e d to approximate ly the same degree by CoO, NiO and I rO , w h i l e the ox ides of manganese, uranium, b ismuth , p a l l a d i u m , t e l l u r i u m and vanadium had no - 31 - e f f e c t . A d e t a i l e d study o f the r a t e o f decomposi t ion o f sodium hypoch lo r - i t e s o l u t i o n s i n the presence 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 ox ides o f copper, i r o n and c o b a l t , was made by Chirnoaga i n 45 1923. He repor ted t ha t oxygen e v o l u t i o n du r ing decomposi t ion was l e s s than f i r s t o rde r and cou ld be represented by the genera l equa t ion = v 1 / n ( 1 3 ) dt 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 t ime t , and k^ , n are cons t an t s . Chirnoaga p o s t u l a t e d t ha t OCl i o n s were adsorbed onto the surface of c a t a l y s t p a r t i c l e s . Decomposi t ion o f these ions would then determine the r e a c t i o n v e l o c i t y . The adso rp t ion s tep would be f a s t e r than the sub- sequent decompos i t ion , and thus the sur face l a y e r would be kept i n ad - s o r p t i o n e q u i l i b r i u m w i t h the bu lk o f the s o l u t i o n . Experiment showed tha t oxygen e v o l u t i o n inc reased w i t h time and w i t h c o n c e n t r a t i o n (and hence sur face area) o f the c a t a l y s t . The ox ides under study were found to decrease i n order o f c a t a l y t i c a c t i v i t y : N i > Co > Cu > Fe , and equat ion 13 was found to be more a p p l i c a b l e f o r the c a t a l y s t s w i t h h igher a c t i v i t i e s . Chirnoaga noted tha t a mixed CoO/NiO c a t a l y s t was more a c t i v e than e i t h e r ox ide a l o n e . This i nc r ea sed c a t a l y t i c a c t i v i t y o f mixed ox ides was a l s o ' r epor ted 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 promoting 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 tha t produced by e i t h e r c a t a l y s t a l one . Lewis suggested a more s imple equat ion to desc r ibe the r a t e of - 32 - decompos i t ion : dc d t k (14) r e p r e s e n t i n g a l i n e a r r e l a t i o n s h i p between evolved oxygen and t ime . He found the r a t e t o be cons tant f o r a wide range o f i n i t i a l 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 , and t ha t i t was d i r e c t l y p r o p o r t i o n a l to c a t a l y s t concen- t r a t i o n . The mechanism was cons idered to be one tha t i n v o l v e d the forma- t i o n and subsequent decomposi t ion 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 cont inuous c y c l e . Such a process would occur a t a constant r a t e p r o - v i d e d the a c t i v e cen t res on the c a t a l y t i c surface were e n t i r e l y covered by r e a c t a n t . Any l o s s of these due to c o a g u l a t i o n , dehydra t ion e t c . would l ead to decreased c a t a l y t i c a c t i o n . Lewis the re fo re suggested t ha t the 'promoter ' e f f e c t occur red as a r e s u l t o f the second substance p r e s e r v i n g the a c t i v e cen t res on the c a t a l y s t i t s e l f , thus produc ing a more e f f i c i e n t (and prolonged) r e a c t i o n . The f i r s t r epor t ed study t ha 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 to c h l o r a t e as w e l l as to oxygen was g iven i n a Russ ian paper 47 o f Glikman and Dain i n 1941. They showed tha t c o b a l t hydroxide a c c e l e r a t e d the r e a c t i o n but gave no d e t a i l s o f the pH r e g i o n i n which t h i s e f f e c t was observed . 48 Ayres and Booth showed tha t both oxygen and c h l o r a t e are formed as decomposi t ion products i n a " c a t a l y s e d r e a c t i o n . O x i d a t i v e decomposi t ion 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 decomposi t ion reached a maximum around pH = 9 . 0 . I t was a l s o observed (15) - 33 - t ha t where the i n i t i a l pH had a va lue below 10, decomposi t ion was accom- panied by a c i d i f i c a t i o n o f the s o l u t i o n s , g i v i n g a f i n a l va lue 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 observed i n such cases . Equat ions r ep resen t - i n g t h i s o b s e r v a t i o n were c i t e d a s : 2HC10 v 0 2 + 2C1~ + 2 H + (16) 3HC10 y c l 0 3 ~ + 2 C 1 ~ + 3 H + HC10 + C l ~ + H + y CI + H 2 0 (18) The c a t a l y s t used i n t h i s study was i x i ' d i u m oxide and Ayres and Booth proposed an o v e r a l l mechanism i n v o l v i n g the format ion o f an in te rmed ia te a c t i v e complex a l l o w i n g the p r o d u c t i o n o f molecu la r oxygen which can then recombine w i t h more h y p o c h l o r i t e to g ive c h l o r a t e : C10~ + c~ == x~ + C l ~ (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 ther hand, concluded a f t e r c a r r y i n g out an ex tens ive study o f bo th unca ta lysed and c a t a l y s e d r e a c t i o n s o f sodium h y p o c h l o r i t e 42 49 decompos i t ion , t h a t c h l o r a t i v e decomposi t ion was not c a t a l y s e d . ' In the former study he confirmed the f i n d i n g s of F o e r s t e r e t a l . ^ ° t h a t the unca ta lysed r e a c t i o n produces main ly c h l o r a t e , i s second order and occurs i n a two stage p roces s : - 34 - 2NaOCl y NaC10 2 + NaCl (23) NaOCl + NaC10 2 >• NaC10 3 + NaCl (24) The f i r s t , c h l o r i t e forming step i s the s lower o f the two. L i s t e r found t ha t a s m a l l p a r t o f the decomposi t ion r e a c t i o n produced oxygen: NaOCl • NaCl + ^ 0 2 (25) and t ha t t h i s was a f i r s t order r e a c t i o n . He noted tha t i t c o u l d not be concluded w i t h c e r t a i n t y t ha t a b s o l u t e l y no c a t a l y s t s were present d u r i n g h i s exper iments . 49 In h i s study o f the c a t a l y s e d decomposi t ion r e a c t i o n L i s t e r used manganese, i r o n , c o b a l t , n i c k e l and copper ox ides and determined t ha t none o f these i nc rea sed the r a t e o f format ion o f c h l o r a t e from h y p o c h l o r i t e , but t ha t the oxygen r e a c t i o n was c a t a l y s e d to a d i f f e r e n t ex tent by each meta l o x i d e . For c o b a l t and n i c k e l t h i s was found to be a zero order r e a c t i o n and fo 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 roposa l t ha 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 meta l to a h ighe r ox ide 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 cons ide red by L i s t e r to be q u i t e f e a s i b l e . The f a c t t ha t i r o n and manganese showed o n l y very 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 igher o x i d a t i o n s t a t e s o f these me ta l s , i n c o n t r a s t t o the cases o f c o b a l t , n i c k e l and copper a l l o f which e x i s t as ' h ighe r o x i d e s ' i n r e l a t i v e l y uns tab le c o n d i t i o n s . Th i s mechanism would not r e s u l t i n i nc r ea sed 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 exper imenta l o b s e r v a t i o n s . However, more oxygen was evolved 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 suggested. Th i s s t i l l i n v o l v e d the format ion o f h ighe r va lence o x i d e s , but i t was proposed tha t t h i s ox ide formed an adsorbed m e t a l - h y p o c h l o r i t e complex on the c a t a l y t i c su r face , and subsequently decomposed: 2M0 + C10~ • M 2 0 3 + C l ~ (26) M 2 0 3 + C10~ — M 2 0 3 C 1 0 ~ (ads.) (27) M 2 0 3 C10~ • 2M0 + C l ~ + 0 2 (28) P r o k o p c h i k ^ 1 d i smi s sed t h i s mechanism o f L i s t e r as be ing e x p e r i - men ta l l y unfounded. He concluded from h i s own work tha t h ighe r ox ides were formed as in t e rmed ia te compounds and tha t these were a c t u a l l y the c a t a l y s t s f o r h y p o c h l o r i t e decompos i t ion . I t was found tha t both o x i d a - t i v e and c h l o r a t i v e decomposi t ion were c a t a l y s e d , w i t h the l a t t e r o c c u r r i n g as a r e s u l t of 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 to c h l o r a t e du r ing the decomposi t ion o f the h ighe r va lence o x i d e . Thus i n h i s study o f both homogeneous and heterogeneous h y p o c h l o r i t e decomposi t ion i n the presence o f copper , Prokopchik determined tha t an impor tant r o l e was p l ayed by copper"'""'"1 compounds. When i n s o l u t i o n these e x i s t e d as a n i o n i c cupra tes , fo r example, NaCu(OH) 4 , w h i l e s o l i d compounds such as Cu2C>3 produced heterogeneous c a t a l y s i s . The t r i - v a l e n t cuprate was found to be uns tab le i n s o l u t i o n and i t s format ion i n the presence 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 decom- p o s i t i o n t o b i - v a l e n t c u p r i t e : - - 2- 4Cu(OH) 4 + 40H > 4Cu(OH) 4 + °2 + H 2 ° ^ 2 9 ) - 36 - w i t h a r e a c t i o n r a t e g iven by - d (Cu(OH) 4~) = k 2 (Cu(OH) 4 ~)•(OH _ ) (30) d t k 2 (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 rea t e r than tha t o f cuprate an ions . The decomposi t ion o f h y p o c h l o r i t e occur red s imu l t aneous ly : 2Cu(OH) 4 2 ~ + Clef + H 2 0 > 2Cu(OH) 4~ + C l ~ + OH~ (31) - - 2- 2Cu(OH) 4 + 20H > 2Cu(OH) 4 + + JjO (32) C10~ v== a C l ~ + J5O ( 33) The r a t e o f r e a c t i o n was found to be f i r s t o rder f o r h y p o c h l o r i t e concen- t r a t i o n s up to 0.1 M, above which i t dev i a t ed towards zero o r d e r . In the case o f heterogeneous decomposi t ion i t was observed tha t 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 lue c u p r i c hydroxide caused r a p i d t r ans fo rma t ion to a b rownish -b lack compound accompanied by c a t a l y s e d decomposi t ion of the h y p o c h l o r i t e s o l u t i o n . The nature o f the c a t a l y s t was cons ide red , and Prokopchik concluded tha t w h i l e a copper pe rox ide compound cou ld be produced by t h i s method, the observed decompo- s i t i o n data suggested format ion o f cupra tes a t h igh pH v a l u e s , and the t r i - v a l e n t hydroxide a t lower l e v e l s o f a l k a l i n i t y , as be ing more l i k e l y . Format ion o f a red compound was noted a t the end o f some exper iments , and t h i s was taken to be a d e a c t i v a t e d cuprate which no longer had c a t a l y t i c p r o p e r t i e s . - 37 - A c e r t a i n amount o f confus ion appears to e x i s t concerning the compound r e s p o n s i b l e f o r h y p o c h l o r i t e decomposi t ion a t pH l e v e l s below 1 1 . 0 . Prokopchik s t a t e s f i r s t l y , as noted above, t ha t cuprates cannot e x i s t a t low a l k a l i n i t y and tha t o x i d a t i o n of b i - v a l e n t to t r i - v a l e n t hydroxide thus o c c u r s . He l a t e r s t a t e s , however, t ha t i t i s imposs ib l e to o b t a i n a t r i - v a l e n t hydrox ide , and t ha 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 occur below pH 11 .5 , so tha t dehydrated c u p r i c hydrox- ide i s r e s p o n s i b l e f o r c a t a l y t i c a c t i o n a t lower pHs. S ince i t i s emphasized t ha t no h y p o c h l o r i t e decomposi t ion can occur i n the absence o f copper1"'""'", these statements appear t o be s e l f - c o n t r a d i c t o r y . In the proposed mechanism f o r heterogeneous decompos i t ion , however, both the hydroxide and cuprate are cons ide red : i ) a t lower a l k a l i n i t i e s : Cu(0H)„ + OH -> Cu(OH) + e (34) CIO + 2Cu(0H) 2 + H 2 0 •>• CI + 2Cu(0H) (35) 4Cu(0H) (36) (37) i i ) h ighe r a l k a l i n i t y (pH > 1 2 . 0 ) : +Cu(0H) 4 + e (38) *C1 + 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 ha 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 thermodynamical ly p o s s i b l e . A f u r t h e r ambigui ty e x i s t s r ega rd ing the c h l o r a t e forming r e a c t i o n : the above equat ions suggest t h i s occurs o n l y a t h ighe r pH v a l u e s , and Prokopchik i n f a c t s t a t e s tha t c h l o r a t i v e decomposi t ion 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 predominate. Cons iderab le 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 to the c o n c l u s i o n t ha t i n s t rong 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 to oxygen, w h i l e a t pH 11.0 and below copper hydroxide s i g n i f i c a n t l y a c c e l e r a t e d the decomposi t ion t o c h l o r a t e . At pH 9.0 the mole r a t i o o f C l O ^ O , , a t t a i n e d a va lue o f 3. G r a p h i c a l r e p r e s e n t a t i o n based on exper imenta l data i s g iven to i l l u s t r a t e t h i s p o i n t . 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 , i r o n , and n i c k e l under s i m i l a r c o n d i t i o n s , Prokopchik concluded tha t c a t a l y t i c a c t i v i t y decreased i n the o rder Co > N i > Cu > Fe . The g e n e r a l i z e d mechanism fo r any meta l Me was g i v e n as : CIO 4 Me (OH) -> CI + Me (OH) . (42) n n+1 Me (OH) . y Me (OH) + ho^ (43) n+1 n 2 Me (OH) . + CIO »• C10 o + Me (OH) (44) n+1 3 n - 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 be ing removed from the copper atom to g ive a I s 2 , 2 s 2 2 p 6 , 3 s 2 3p^ 3d^ c o n f i g u r a t i o n . Th i s i s i s o - e l e c t r o n i c w i t h the n icke l 1 " 1 " s t r u c t u r e , and t r i - v a l e n t copper compounds are g e n e r a l l y diamagnet ic as a r e s u l t o f a l l e l e c t r o n s be ing p a i r e d . Al though t h i s i s a r e l a t i v e l y r a re o x i d a t i o n s t a t e f o r copper, i t s ex i s t ence has been acknowledged s i n c e the middle o f the l a s t cen tu ry , and s e v e r a l workers have s t u d i e d the. format ion and s t a b i l i t y o f copper1"'"''" compounds: Crum, i n 1845, ob ta ined what he de sc r i bed as a cuprate 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 each ing powder" on copper n i t r a t e . Th i s occur red as a red powder and was ass igned the formula H^Cu^O^ c o r r e s - 55 ponding to the hydrated 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 to o x i d i z e copper hydroxide and ob ta ined a compound approaching the formula CuC^-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 red compound by the a c t i o n o f potass ium pe r su lpha t e , K S 0 , on copper hydroxide s o l u t i o n s . Z Z 8 The compound evo lved 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 not c o n t a i n a pe rox ide group. I t was thus taken to 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 copper1"'" by h y p o c h l o r i t e s o l u - 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 which i t was shown tha t t r i - v a l e n t copper cou ld 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 (>3N) o f copper hydroxide 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 . Hypobromite, c h l o r i n e and bromine produced s i m i l a r e f f e c t s . The c o l o u r o f the r e s u l t a n t s o l u t i o n - 40 - apparen t ly v a r i e d from red and v i o l e t to 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 authors c a r r i e d out e l e c t r o c h e m i c a l t e s t s to produce t r i - v a l e n t copper o x i d e , and suggested i t s format ion to be caused by i ) o x i d a t i o n o f metal ions con ta ined w i t h i n the copper anode, or i i ) o x i d a t i o n o f meta l ions conta ined i n the e l e c t r o l y t e s o l u t i o n , ^ w i t h subsequent ox ide 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 d i d a number o f experiments to i n v e s t i g a t e the p e r o x i d i c compounds o f copper . Hydrogen perox ide was added to copper c o n t a i n i n g carbonate s o l u t i o n s and a ye l low-brown com- pound 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 correspond to C ^ O ^ , but i n s u f f i c i e n t to g ive CuO^. I t was assumed, however, t h a t a pe rox ide had been produced, but t ha 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 epor ted o b t a i n i n g the compound Cu^0„ (or Cu 'Cu .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 . 6 0 He a l s o c la imed t ha t the a d d i t i o n o f copper n i t r a t e s o l u t i o n s to barium hydroxide gave the compound Cu.O -3H O o r Cu (OH) . 2 3 2 2 6 More recen t s tud i e s r ega rd ing the ex i s t ence o f a l k a l i n e and a l k a l i n e ea r th meta l cuprates have been made by Scholder and V o e l s k o w , 6 1 P r o k o p c h i k , 6 2 and Magee and W o o d . 6 3 C r y s t a l l i n e barium cupra te , B a ( C u O ^ ) 2 * H 2 ° w a s ob ta ined by the a d d i t i o n of potass ium hypobromite s o l u t i o n s to c u p r i c hydroxide i n the presence o f barium 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 c a r r i e d out by Scholder i n 1951. The sodium s a l t , NaCu02, was produced i n a s i m i l a r manner by the a c t i o n o f hypobromite , NaOBr, and sodium bromate, NaBrO^. - 41 - Ca lc ium and s t ron t ium cuprates cou ld not be ob ta ined by t h i s method. Ca lc ium cuprate was produced by Prokopchik who used c a l c i u m hypo- c h l o r i t e to 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 va lue o f 12 .2 . A r ed -pu rp le p r e c i p i t a t e was observed, having a Cu: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 out an i n v e s t i g a t i o n of sodium cuprate1"1""1" s t a 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 o f v a r y i n g s t r e n g t h . They concluded t ha t the s a l t was ve ry uns tab le i n a l l cases and es t imated tha t the CuO^ i o n had a h a l f l i f e o f on ly 25 seconds. C o p p e r 1 1 1 was thus assumed to e x i s t i n s o l u t i o n on ly when complexed. The f a c t t ha t Scholder and Voelskow found t r i - v a l e n t copper s o l u t i o n s to be s t a b l e i n the presence o f excess base and hypobromite was suggested to be caused by a hypo- bromite-copper"'""'""'" complex. A number o f workers have, i n f a c t , shown tha t copper 1" 1" 1 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 or as a s o l i d compound, by the presence o f c e r t a i n complexing i o n s . P e r i o - dates and t e l l u r a t e s are the commonest such groups: 64 I I I M a l a t e s t a , i n 1941 ob ta ined a s t a b l e pe r i oda t e copper complex w i t h both chemica l o x i d a t i o n o f c u p r i c hydroxide u s ing pe r su lpha t e , and e l e c t r o l y t i c o x i d a t i o n o f copper, 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 r e s u l t a n t compound was diamagnet ic and was analysed c h e m i c a l l y t o be t r i - 65 v a l e n t . 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 presence o f potass ium p e r i o d a t e , KIO^ . He produced f i r s t l y a cupra te , KCuCOH)^ by o x i d i z i n g copper hydroxide w i t h a KOH/K S 0 m i x t u r e , and then added 2 2 o pe r i oda t e to g ive a s t a b l e complex compound. 66 L i s t e r made e s s e n t i a l l y the same compound, Na_Cu (10,.) . • 16H„0, as 7 6 2 2 - 42 - w e l l as the cor responding t e l l u r a t e , Na^CuCTeOg), u s ing sodium hypo- c h l o r i t e as o x i d a n t . A c u p r i c c h l o r i d e / s o d i u m hydroxide mix ture was added to a 1.5 M NaOCl s o l u t i o n and the b lue p r e c i p i t a t e which formed i n i t i a l l y , turned 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 to be e i t h e r a t r i - v a l e n t o x i d e , Cu^O^, or hyd rox ide , CuCOH)^. A d d i t i o n o f an a c i d i f i e d sodium pe r ioda t e s o l u t i o n , NaH 10^, gave a brown compound 3 6 a f t e r s tanding f o r a shor t t ime . 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 to c o n t a i n t r i - v a l e n t copper by i o d i d e t i t r a t i o n 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 we igh t s . I t was observed tha t oxygen was evo lved 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 and i n some cases a s c a r l e t c o l o u r was b r i e f l y v i s i b l e . Th i s was there fore suggested to be the c o l o u r o'f the C u 3 + i o n . To determine the amount o f copper p resen 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 decomposi t ion both before and a f t e r a d d i t i o n of the complexing agent . In the former case he found the r e a c t i o n to be c a t a l y z e d by copper, presumably as the Cu(0H) 4 i o n . The r a t e o f r e a c t i o n was f i r s t o rder w i t h r e spec t to copper . A f t e r a d d i t i o n o f e i t h e r pe r ioda t e or t e l l u r a t e anions the r a t e o f oxygen e v o l u t i o n was found to drop c o n s i d e r - a b l y , and to correspond to a r a te r e p r e s e n t i n g unca ta lyzed h y p o c h l o r i t e decompos i t ion . I t was the re fo re assumed tha 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 longer an a c t i v e c a t a l y s t fo r the r e a c t i o n . Jensovsky prepared complex cuprates by anodic o x i d a t i o n of copper i n a l k a l i n e s o l u t i o n s c o n t a i n i n g pe r ioda t e and t e l l u r a t e i o n s . The maximum y i e l d was ob ta ined a t pH 1 0 . 2 , and inc reased w i t h temperature. - 43 - The compounds were found to be d iamagnet ic , and thermal decomposi t ion curves showed l o s s o f water caused decomposi t ion o f the copper1"1""1" complex. 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 rong 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 pe r ioda t e s and t e l l u r a t e s can be used f o r the o x i d i m e t r i c de t e rmina t ion o f a number o f i n o r g a n i c and o rgan ic compounds. 6 ^ T i t r a t i o n s u s ing s tandard s o l u t i o n s of copper1"1""1" are c a r r i e d out 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 de termina- t i o n o f antimony, c a l c i u m , t h a l l i u m , cyanide and t h i o s u l p h a t e s a l t s . Most o ther copper1"1"'"1" complexes which have been i s o l a t e d are o rgan ic i n na tu re . These i n c l u d e s a l t s made from carborane i o n s , C u (B^QH^ QCH)^ , a potass ium b i s (b i rue to) cuprate1"1"'1' prepared by pe roxod i su lpha te o x i d a t i o n o f [Cu(-NHC0N-)] , and a number o f pep t ide 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 chemica l p r o p e r t i e s o f a t r i - v a l e n t copper 1 aquo 1 complex by r a d i o l y t i c means. He repor ted t ha t C u 1 1 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 CuOH 2 + (aq.) or C u ( O H ) 2 + (aq.) i o n and decomposes by the mechanism 2+ 2+ 2CuOH v 2Cu + H 2 0 2 (45) Such ions were made by the r e a c t i o n C u 2 + + OH ——+ C u 1 1 1 (46) 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 wate r : C u 3 + + H 2 0 >- C u O H 2 + + H + (47) I t was s t a t ed tha t C u 1 1 1 w i l l be formed by any ox idan t which can lower - 44 - the redox p o t e n t i a l o f the couple C u 1 1 1 - C u ^ + i n the presence o f v a r i o u s l i g a n d s . The p o t e n t i a l f o r the r e a c t i o n 2+ 3+ Cu > Cu + e (48) 75 i s quoted by La t imer t o be 1.8 V i n a l k a l i n e medium at 25°C. 71 Shams E l Din and co-workers r epor ted the format ion o f the sequ iox ide 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 of a copper e l e c t rode i n 0.1 N sodium hydroxide s o l u t i o n s , a t oxygen e v o l u t i o n po ten- t i a l s , i . e . a t 0.76 V . The r e a c t i o n i n v o l v e d was thought to be: 2Cu(OH) 2 + 20H • Cu 0 + 3H 2 0 + 2e (49) In an ex tens ive study to i n v e s t i g a t e the format ion o f the sesqu iox ide by 72 v a r i o u s wet and dry chemica 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 3 + format ion as 2.3 V . Th i s was d e r i v e d from the equa t ion : C u ( 0 H ) 3 + e~ + H + Cu(OH) 2 + H 2 0 (50) fo r which E = 1.57 - 0.054 pH (pH < 1 3 . 9 ) . 2+ 3+ Approximate Eh-pH diagrams f o r the Cu / C u o x i d a t i o n - r e d u c t i o n system are g i v e n , and t h i s study was l a t e r used as a b a s i s f o r the ex tens ion o f 73 e x i s t i n g diagrams o f the Cu~H 20 system g i v e n by Pourba ix and co-workers 74 to take account o f t r i - v a l e n t copper and i t s d e r i v a t i v e s . Delhez concluded from h i s work t ha t the o n l y f e a s i b l e method of 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 hydroxide i n a l k a l i n e s o l u t i o n u s i n g e i t h e r h y p o c h l o r i t e o r pe roxod i su lpha te i ons 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 cases , the y i e l d i 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 . He thus suggested t h a t a l l p rev ious workers who had used ox idan t s i n c l u d i n g hydrogen pe rox- i d e , peroxomonosulphuric a c i d , c h l o r i n e or 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>2 o r cuprous o x i d e , Cu-jO, which i n many cases had been confused w i t h the s e s q u i o x i d e . Us ing a method o f potass ium persu lpha te o x i d a t i o n o f c u p r i c s u l - 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) s i m i l a r to t ha 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 red amaranth p r e c i p i t a t e which con ta ined , but was not 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 . I t was the re fo re presumed to be a mix ture o f Cu(OH) 2 and O^O^/Cu(OH) , w i t h a r a t i o of C u * 1 : C u 1 1 1 dependent on the r a t e s o f the r e l e v a n t r e a c t i o n s : 2Cu(OH)„ + 20H~ + S _ 0 o 2 _ ^2Cu(OH)_ + 2 S 0 2 " (51) Z Z o 6 4 4Cu(OH) 3 >• 4Cu(OH) 2 + 0 2 + H 2 0 (52) The r e a c t i o n forming c o p p e r 1 1 1 was c a t a l y z e d by the presence o f B a 2 + i o n s , i n agreement w i t h the p rev ious f i n d i n g s o f Scholder and V o e l s k o w . ^ I t was a l s o found tha 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 and Cu(OH) 3 , apparen t ly at random. For the case o f C u 1 1 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 of p r ev ious s t u d i e s to be con fus ing . S e v e r a l workers gave s t rong evidence to show C u 1 1 1 had been produced, but i t was o f t en d i f f i c u l t to a s c e r t a i n whether i t was C u , ^ ^ , or a t r i - v a l e n t cupra te . Scho lde r and Voelskow, fo r example, had found tha t o x i d a t i o n o f a b i - v a l e n t cuprate w i t h hypobromite produced a copper 1 1" 1" compound which they assumed to be a cupra te . Delhez concluded i t was probably 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 hydroxide as a s t a r t i n g m a t e r i a l they ob ta ined a d i f f e r e n t p roduc t , having a maximum C u : a v a i l a b l e r a t i o o f 1 :0 .3 , but i n h i s own work Delhez never produced more than 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 igh va lue t o g i v e a good y i e l d o f C u 1 1 1 . Barium ions a l s o c a t a l y z e d t h i s h y p o c h l o r i t e r e a c t i o n and a mechanism s i m i l a r to t ha t g iven by Prokopchik (equations 2+ 34 - 37) was thought to be o p e r a t i v e . The c a t a l y t i c a c t i o n o f Ba ions was due t o an inc rease i n the redox p o t e n t i a l o f the o x i d i z i n g s o l u t i o n i n which they were p r e sen t . CHAPTER TWO Exper imen ta l 2.1 Scope o f the Present I n v e s t i g a t i o n A number o f s t u d i e s have been made to 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 molybdenite i n a l k a l i n e s o l u t i o n s o f sodium hypo- c h l o r i t e , as o u t l i n e d above; but very l i t t l e work has been done to de t e r - mine the o x i d a t i o n behaviour o f copper su lph ide mine ra 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 f o r t r e a t i n g molybdeni te concent ra tes i s to enhance by-product molybdenum recovery from porphyry o re s , i t would seem to be o f prime importance to g a i n an unders tanding 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 to de- l i n e a t e any s teps necessary t o prevent copper d i s s o l u t i o n . Th 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 at the same time prevent copper l o s s e s , both o f which are fundamental to an economica l ly f e a s i b l e p roces s . 7 6 P rev ious work i n t h i s department was c a r r i e d out by Ismay, to r e sea rch 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 copper- molybdenum su lph ide rougher concen t ra t e s , by means o f a sodium hypoch lo r - i t e l e a c h . A proposed process f lowsheet was drawn up on the b a s i s o f s u c c e s s f u l molybdeni te l e a c h i n g ; and a l though molybdenum r e c o v e r i e s were h i g h , i t was found t ha 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 ob jec t of the present 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 extent o f the r e a c t i o n between v a r i o u s copper su lph ide minera 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 to those found by Ismay to be optimum for molybdenum e x t r a c t i o n , w i t h a view e i t h e r to p r even t ing copper from e n t e r i n g s o l u t i o n , o r to f i n d i n g a s u i t a b l e method fo r i t s removal : 1) I n i t i a l experiments r evea l ed tha 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 occur red i n the presence o f carbonate bu f f e r reagents but t ha t removal o f the carbonate had unde- s i r a b l e s i d e e f f e c t s . 2) T h i s l e d to 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 c a t a l y s e d h y p o c h l o r i t e decomposi t ion r e a c t i o n s . The nature of decomposi- t i o n products was a l s o cons ide red . 3) 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 genera l b a s i s , w i t h and wi thou t the presence o f carbonate , to i n c r e a s e an unders tanding o f the e f f e c t s observed du r ing l e a c h i n g . 4) As the study progressed i t became apparent tha t the presence of copper su lph ide mine ra l s adve r se ly 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 thus c a r r i e d out a t pH l e v e l s o f 5.5 - 6 .0 , which had p r e v i o u s l y been suggested to be optimum fo r molybdenum recovery i n an i n v e s t i g a t i o n by the U . S . Bureau of Mines . 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 ing s y n t h e t i c mine ra l s and t h i s h i g h l i g h t e d the f a c t t ha t c e r t a i n elements normal ly p resen t as i m p u r i t i e s were d e t r i m e n t a l to h igh l e v e l s o f molybdenum e x t r a c t i o n . A thermodynamic study o f the s t a b i l i t y of v a r i o u s molybdate compounds i n aqueous s o l u t i o n was thus c a r r i e d out and s e v e r a l Eh-pH diagrams were c o n s t r u c t e d . - 49 - 6) I t was then necessary to determine 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 c e r t a i n c a l c i u m mine ra l s i n h y p o c h l o r i t e and o ther 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 . 7) C o n s i d e r a t i o n o f a l l the above f a c t o r s l e d f i n a l l y to e s t a b l i s h i n g the necessary 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 decomposi t ion and copper d i s s o l u t i o n . 2.2 M a t e r i a l s 2 .2 .1 N a t u r a l mine ra l s C h a l c o c i t e , Cu^S, and c o v e l l i t e , CuS, were ob ta ined as massive samples from B u t t e , Montana. C h a l c o p y r i t e , CuFeS 2 , was purchased i n massive form from Ward's N a t u r a l Science Es t ab l i shemnt , and ob ta ined as a ground concent ra te from the Phoenix mine, B r i t i s h Columbia . Large p i eces o f ore were crushed i n rod and b a l l m i l l s and wet ground to 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. Smal l p i e c e s o f broken ore were p o l i s h e d on a 'Texamat' 5tf diamond p o l i s h i n g wheel fo r sur face examinat ion before and a f t e r l e a c h i n g . In some cases samples were mounted i n epoxy r e s i n (Epon 828/DETA) p r i o r to p o l i s h i n g . Molybden i t e , MoS 2 , was ob ta ined as a h i g h grade concent ra te from A l i c e Arm, B r i t i s h Columbia , ground to pass a -325 mesh s i e v e . C a l c i t e , CaCO^ was ob ta ined i n powdered form from the M i c r o - i o n i z e d company (Texas) L t d . M i n e r a l A n a l y s i s Wet chemica l a n a l y s i s gave the f o l l o w i n g r e s u l t s : - 50 - i ) C o v e l l i t e : Element Cu Fe Ca Z n , N i Th i s i n d i c a t e s a CuS content o f 88.3%. i i ) C h a l c o c i t e : Element Cu Fe Ca Pb Zn Th i s g ive s a Cu 2 S content o f 81.0%. i i i ) C h a l c o p y r i t e : Element Cu Fe Ca Z n , N i Weight % 58.80 3.00 0.16 Trace (<0.05%) Weight % 64.50 4.80 0.12 0.06 Trace Weight % 3 1 . 6 29.20 1.51 Trace T h i s g ives a CuFeS^ content 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 Microscope showed t ha 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 conta ined s i g n i f i c a n t amounts o f s i l i c o n , and t r aces o f sodium and potass ium. X - r a y d i f f r a c t i o n s t u d i e s gave good agreement w i t h l i t e r a t u r e v a l u e s . S i l i c a , S i 0 2 and - 51 - p y r i t e , F e S 2 were the o n l y o ther major peaks ob ta ined (Tables 1-3). ( A l l d i f f r a c t i o n s t u d i e s repor ted f o r copper k r a d i a t i o n ) I / I 0 - spec ies i d e n t i f i e d 1 I / I 0 - CuS o d A CuS F e S 2 sio 2 dA (Reported) 8.11 7. 8.18 7 4.26 36 3.33 100 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 1.63 100 1.63 3 1.55 31 1.55 37 1.46 6 1.46 6 1.35 8 1.35 7 1.27 6 1.28 1.09 9 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 0 - spec ies i d e n t i f i e d I / I 0 - Cu 2 S o dA Cu 2 S sio 2 O dA (Reported) 4. 25 35 3.77 10 3.35 100 3.60 3.39 3.31 3.26 3.05 10 30 10 20 20 2.86 30 2.88 20 2.74 15 2.73 10 2.63 12 2.67 2.54 2.47 10 10 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 1.82 17 1.69 40 1.70 36 1.64 20 Table 2: X- ray D i f f r a c t i o n P a t t e r n fo r Cha lcoc i t e :Sample - 53 - o o dA : : i / I 0 - spec ies i d e n t i f i e d dA I / I 0 CuFeS 2 CuFeS 2 SiC) 2 (Reported) 3.35 100 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 Table 3: X- ray 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 spec t rograph ic a n a l y s i s of the molybdeni te showed i t to have the f o l l o w i n g a n a l y s i s : Element Weight % Element Weight % A l 0.10 Mg 0.01 B i 0.05 Mn 0.001 Ca 0.50 Mo 58.52 Cr 0.01 S 39.02 Cu 0.05 S i 1.00 Fe 0.50 Sn 0.20 Pb 0.01 T i 0.03 - 54 - Traces (<0.001%)of g o l d , s i l v e r and s t ron t ium were a l s o de t ec t ed . 2 .2 .2 S y n t h e t i c mine ra l s i ) Cupr i c su lph ide a n a l y z i n g 99.9% CuS was purchased from the Rocky Mountain Research C o . , Denver, Co lo rado . i i ) Cuprous s u l p h i d e , a n a l y z i n g 99% + Cu 2 S was ob ta ined from Matheson, Coleman & B e l l , Eas t Ru the r fo rd , N . J . Smal l amounts o f these m a t e r i a l s were crushed i n a p e s t l e and mor tar , and screened to g ive 100% -200 mesh m a t e r i a l . i i i ) Reagent grade molybdenum d i s u l p h i d e from BDH Chemica ls , Poole England was used. Th i s analyzed as : Element Weight % Mo 53.4 S 35.6 S i =10 i v ) Molybdenum d i s u l p h i d e a n a l y z i n g >98% MoS 2 was purchased 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 rade name ' J A V E X , ' and c o n t a i n i n g 50 - 60 g/1 i n the as-purchased c o n d i t i o n . 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 tock s o l u t i o n to 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 fo r l e a c h i n g exper iments . - 55 - 2 .2 .4 Chemical reagents A l l o ther chemicals used were reagent grade. 2.3 Apparatus The ma jo 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 g l a s s v e s s e l f i t t e d w i t h 4 T e f l o n b a f f l e s a t e q u i - d i s t a n t p o i n t s around i t s i nne r su r f ace . S o l u t i o n a g i t a t i o n was e f f ec t ed u s ing a t u r b i n e type t i t a n i u m s t i r r e r coated w i t h a t h i n l a y e r o f 'MICROSTOP' p a i n t . A g i t a t o r and v e s s e l dimensions together conformed to a ' s t andard tank ' c o n f i g u r a - t i o n . The s t i r r e r was mechan ica l ly powered w i t h a F i she r -Dyna mix motor, and the a g i t a t i o n r a t e was measured fo r each experiment u s ing a Tecklock chronometr ic hand tachometer. 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 bath which conta ined a M i c r o - s e t the rmo-regu la to r manufactured by the P r e c i s i o n S c i e n t i f i c Company. A f t e r s e t t i n g a d e s i r e d temperature, t h i s u n i t was capable o f m a i n t a i n i n g 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 moni tored d u r i n g each run by p l a c - i n g e l e c t r o d e s i n s i d e the g l a s s v e s s e l . In 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 ep l aced w i t h a Chemtrix pH c o n t r o l l e r (Hor izon Ecology C o . , Chicago , 111.) In combina- t i o n w i t h an ASCO 2-way t e f l o n coated 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 exper imenta l apparatus 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 B Glass leaching vessel •F Thermometer G pH electrodes C T i mechanical st i r r e r D Fisher Dyna Mix E Thermo-regulator Figure 5: Experimental leaching apparatus H 2 way solenoid valve controlling addition of buffering solution from I burette, to leaching vessel via J capillary tube - 57 - 2.4 Exper imenta l Procedure 2 .4 .1 Leaching experiments Experiments l e a c h i n g copper m i n e r a l s , and copper su lph ides and molybdeni te toge ther , were c a r r i e d out 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 reagent was added to 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 va lue by a d d i t i o n o f 1 N HC1. In cases where carbonate b u f f e r i n g was employed, N a 2 C 0 3 and NaHC0 3 were added i n r a t i o s c a l c u l a t e d from pka va lues to b u f f e r the s o l u t i o n a t the necessary pH l e v e l . The s o l u t i o n was made up to 1 l i t r e , t r a n s f e r r e d to the l e a c h i n g v e s s e l and p l aced i n the water b a t h . Slow a g i t a t i o n was imparted 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 surrounding water , then ' b l a n k ' samples were taken f o r h y p o c h l o r i t e and meta l ana ly se s . A g i t a t i o n was stopped w h i l e m i n e r a l samples were i n t r o d u c e d : where copper su lph ides and molybdenite were leached s imul t aneous ly they were added as two separate 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 the r e a c t i o n w i t h the o the r had proceeded f o r s e v e r a l minutes . The a g i t a t i o n was then i n c r e a s e d . Samples were taken a t t imed 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 or 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 main ta ined by dropwise a d d i t i o n o f 2 N NaOH from a b u r e t t e , o r , i n l a t e r experiments by u s i n g the pH c o n t r o l l e r . - 58 - 2 .4 .2 Copper p r e p a r a t i o n Samples o f copper"'""'""'" were made by the a c t i o n of 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 ing 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 c o n c e n t r a t i o n was made up as o u t l i n e d above, the pH adjus ted to 9 . 0 , and heated to 35°C. 8 g o f C u C l 2 - 2 H 2 0 (equ iva len t to 3 g/1 Cu) were then added, and the pH mainta ined by NaOH a d d i t i o n . i i ) 8 g o f C u C l 2 - 2 H 2 0 were d i s s o l v e d i n water and the pH r a i s e d to 9.0 w i t h NaOH, to g ive a b lue p r e c i p i t a t e o f c u p r i c hydrox ide . A measured volume o f s tock h y p o c h l o r i t e s o l u t i o n was then added. A f t e r 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 to be mainta ined a t a va lue o f 9.0 as be fo re . 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 comple te ly b l a c k , and a f t e r a p e r i o d o f b r i e f s tand ing to a l l o w some s e t t l i n g of the con- 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 r e q u i r e d a longer p e r i o d o f a g i t a t i o n to g ive complete p r e c i p i t a t i o n o f the copper, but the method used was e s s e n t i a l l y the same (method ( i ) was found to be p r e f e r a b l e ) . 2.5 A n a l y s i s 2 .5 .1 Chemical a n a l y s i s i ) Copper: The amount o f copper conta ined i n l e a c h i n g s o l u t i o n s was determined us ing a P e r k i n Elmer 306 spectrophotometer w i t h an a i r - ace ty lene flame and a wavelength o f 324.7 ran, a f t e r s u i t a b l e d i l u t i o n s w i t h - 59 - d i s t i l l e d water , and by comparison w i t h a c a l i b r a t i o n curve from known s tandards . 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 these s o l u t i o n s , t e s t analyses were done us ing s tandard 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 de t ec t ed . Copper i n ore samples was determined by atomic a b s o r p t i o n a n a l y s i s a f t e r d i s s o l u t i o n i n a warm mixture o f concent ra ted 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^. i i ) 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 spectrophotometry w i t h a n i t r o u s o x i d e - a c e t y - lene flame a t a wavelength o f 313.3 nm. D i l u t i o n s p r i o r to 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 c h l o r i d e . 2+ i i i ) Ca l c ium: [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 wavelength o f 422.7 nm us ing an a i r - a c e t y l e n e f lame. i v ) Sodium H y p o c h l o r i t e : 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 of each ba tch o f ' JAVEX' used was a c c u r a t e l y determined by potass ium 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. A s m a l l sample was d i l u t e d w i t h water , then added to an a c i d i f i e d potass ium i o d i d e s o l u t i o n and t i t r a t e d aga ins t s t andard ized t h i o s u l p h a t e . S t a r ch i n d i c a t o r s o l u t i o n was added and the disappearance o f i t s c h a r a c t e r i s t i c b lue 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 concen t r a t ions o f samples taken du r ing l e a c h - i n g runs were determined by the same method, u s u a l l y u n d i l u t e d . v) Sodium c h l o r a t e : the [ClO^ ] content o f l e a c h i n g s o l u t i o n s 77 was determined by a r e l a t e d method, a l s o o u t l i n d i n ASTM D2022-64. - 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 concen- t r a t e d h y d r o c h l o r i c a c i d . A f t e r d i l u t i o n and a d d i t i o n of potass ium i o d i d e , the r e l ea sed i o d i n e was t i t r a t e d aga ins t s tandard t h i o s u l p h a t e as be fo re . Th i s g ives the t o t a l c o n c e n t r a t i o n of (OC1 + ClO^) so the a c t u a l c h l o r a t e content was determined from the d i f f e r e n c e between t h i s va lue and tha t fo r h y p o c h l o r i t e i n the same sample. v i ) C h l o r i d e : the t o t a l c h l o r i d e content o f h y p o c h l o r i t e s o l u t i o n s both before and a f t e r l e a c h i n g was found: a) by s i l v e r n i t r a t e / p o t a s s i u m th iocyana te 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 c h l o r a t e p resen t are reduced to c h l o r i d e by sodium b i s u l p h a t e i n the presence o f d i l u t e HNO^. The t o t a l c h l o r i d e content i s then determined us ing a s tandard Vo lha rd t i t r a t i o n . b) p o t e n t i o m e t r i c a l l y : t h i s method i s e s s e n t i a l l y the same as a) above, but the endpoint 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 of a p l a t i num e l ec t rode i n t o 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 . [AgNO^]- 2 .5 .2 Ins t rumenta l a n a l y s i s i ) M i n e r a l s . 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 out u s i n g the X- ray 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 . Q u a n t i t a t i v e X- ray a n a l y - s i s f o r the ground concentra tes was ob ta ined w i t h a P h i l i p s X - r a y d i f f r a c - tometer , and for surface a n a l y s i s o f massive samples the e l e c t r o n probe m i c r o - a n a l y z e r was used. - 61 - i i ) Copper a) I n f r a - r e d spectrophotometry: samples of the b l ack compound were prepared 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 run through a P e r k i n Elmer 621 g r a t i n g i n f r a - r e d spectrophotometer . b) Magnetic s u s c e p t i b i l i t y : a sma l l sample was weighed on a 'Gouy' magnetic ba lance , both i n and out 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: l e a c h i n g s o l u - t i o n s were examined i n the U V / v i s i b l e r eg ions u s ing a P e r k i n Elmer u l t r a - v i o l e t spectrophotometer w i t h a path l eng th o f 2 - 10 nm. d) X- ray d i f f r a c t i o n pa t t e rn s were ob ta ined us ing the d i f f r a c t o m e t e r . - 62 - CHAPTER THREE Resu l t s and Observat ions 3.1 Sodium H y p o c h l o r i t e Leaching o f Copper Sulphide M i n e r a l s Experiments were c a r r i e d out to determine the o x i d a t i o n behaviour o f c e r t a i n copper su lph ide mine ra l s i n s o l u t i o n s of a l k a l i n e sodium h y p o c h l o r i t e . The s e l e c t e d mine ra l s were c o v e l l i t e , CuS, c h a l c o c i t e , Cu^S, and c h a l c o p y r i t e , CuFeS^. These are three o f the most commonly o c c u r r i n g copper ores a s s o c i a t e d w i t h molybdenum bea r ing p o r p h y r i e s . 3 .1 .1 Leaching o f ground concent ra tes i n the presence o f carbonate 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 eve were a g i t a t e d i n s o l u t i o n s c o n t a i n i n g 7 - 8 g/1 h y p o c h l o r i t e a t a temperature of 35°C and a pH va lue o f 9 . 0 , buf fe red w i t h a sodium 2- ca rbona te /b ica rbona te m i x t u r e . The r a t i o o f HCO^ :CO^ was 14:1 and 10.7 g/1 t o t a l carbonate were used i n i t i a l l y . A sma l l amount o f copper was found to be r a p i d l y d i s s o l v e d i n each case . Smal l v a r i a t i o n s were observed between the three m i n e r a l s , but the copper content o f s o l u t i o n averaged 100 - 130 ppm and represented 2 - 3% o f the copper in t roduced i n t o the system (Figure 6, Tables I - I I I ) . Copper c o n c e n t r a t i o n d i d not ma in t a in a constant va lue w i t h r e spec t to t ime , and a f t e r a t t a i n i n g a maximum i n i t i a l va lue i t f l u c t u a t e d i n an appa ren t ly random manner. Leaching s o l u t i o n separated 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 stages o f a g i t a t i o n main ta ined an almost constant copper content (Figure 7, Tables I V , V ) . A l l s o l u t i o n s showed deep b lue c o l o u r a t i o n : s i g n i f i c a n t l y more so than s tandard copper su lphate s o l u t i o n s c o n t a i n i n g an e q u i v a l e n t amount o f copper . S o l u t i o n s l e f t to stand ove r - n i g h t were observed to d e p o s i t a b l a c k p r e c i p i t a t e wh ich , a f t e r a fu r the r t ime p e r i o d of 1 - 3 days, was accompanied by l o s s o f the c h a r a c t e r i s t i c b lue c o l o u r a t i o n o f the s o l u t i o n . Subsequent a n a l y s i s r evea l ed these 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 copper . Heat ing 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 to be copper ox ide by a n a l y s i s u s i n g the Debye Scher re r powder method f o r X- ray d i f f r a c t i o n . I n s u f f i c i e n t o f the m a t e r i a l put 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 to c a r r y out meaningful a n a l y s i s . D i l u t i o n 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 cases . Sodium h y p o c h l o r i t e consumption was found to vary s l i g h t l y fo r each o f the three m i n e r a l s : equal samples o f CuFeS^, CuS and Cu^S con- sumed 10%, 27% and 18% of the i n i t i a l h y p o c h l o r i t e present 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 i n the r e s p e c t i v e mine ra l s (Figure 8, Tables I - I I I ) . 3 .1 .2 E f f e c t o f carbonate removal Experiments were c a r r i e d out i n which no ca rbona te /b ica rbona te reagents were added to the l e a c h i n g s o l u t i o n , to determine the e f f e c t , i f any, on copper s o l u b i l i t y . The pH was main ta ined i n s t e a d w i t h a sodium hydroxide b u f f e r , added dropwise from a b u r e t t e , to counterac t the observed drop i n pH. A l l o ther c o n d i t i o n s were i d e n t i c a l to those o f Time (minutes) Figure 7: 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 30 r~ 90 150 Figure 8: Time (minutes) NaOCl Consumption-during copper sulphide leaching. - 67 - p rev ious runs . The a n a l y t i c a l r e s u l t s showed t h i s carbonate removal from the system to have a very s i g n i f i c a n t e f f e c t : i ) 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 . i i ) The s o l u t i o n pH was found to drop r a p i d l y as a g i t a t i o n commenced, and t h i s was accompanied by sodium h y p o c h l o r i t e decompos i t ion . The a c t u a l r a t e o f decomposi t ion was a f u n c t i o n o f the p a r t i c u l a r copper m i n e r a l be ing l eached : CuS produced 50% decomposi t ion i n 9 minutes CuFeS^ produced 50% decomposi t ion i n 12.5 minutes Cu^S produced 50% decomposi t ion i n 82 minutes . T o t a l decomposi t ion occur red i n a l l th ree cases , but the r a t e o f decomposi- t i o n was not l i n e a r (Figure 9, Tables VI - V I I I ) . 3 .1 .3 Leaching o f s y n t h e t i c copper su lph ides Decomposit ion was presumed to be caused by c a t a l y t i c a c t i o n o f copper at the m i n e r a l su r f ace . To determine whether the observed d i f f e r - 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 to copper a lone , samples o f cuprous and c u p r i c su lph ide powder were leached under i d e n t i c a l con- 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 . In the presence o f carbonate r e s u l t s were almost i d e n t i c a l to those 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 spec t to both 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. In the absence o f carbonate no copper was de tec ted 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 decomposi t ion was cons tant i n each case (Tables X I , X I I ; F i g u r e 10 ) . Th i s was l i n e a r and gave 50% o f the i n i t i a l 0C1 content remaining a f t e r 52 and 54 minutes f o r C ^ S and CuS r e s p e c t i v e l y . 3 .1 .4 De te rmina t ion o f decomposi t ion products Leaching s o l u t i o n s were analysed fo r sodium c h l o r a t e content to determine whether t h i s was a decomposi t ion p roduc t , as g i v e n by the equa t ion : 30C1~ * C10 3 ~ + 2C1~ (53) or whether oxygen was the o n l y p roduc t : 20C1~ v 0 2 + 2C1~ (54) I t was found t ha t some c h l o r a t e was produced i n a l l three cases , but t h a t the r e s u l t s f o r the d i f f e r e n t mine ra l s were very 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 both showed a decrease i n the percentage c h l o r a t e present i n s o l u t i o n as h y p o c h l o r i t e decomposi t ion progressed , be ing 13.7% and 36.15% r e s p e c t i v e l y a f t e r 5 minutes , and dec reas ing to 9.57% a f t e r 45 minutes f o r c o v e l l i t e and 20.22% a f t e r 90 minutes f o r c h a l c o p y r i t e (F igure 11, Tables VI - V I I I ) . C h a l c o c i t e on the o ther hand, which produced a much slower r a t e o f c a t a l y z e d decompos i t ion , showed the reverse t r end i n tha t 8.7% o f the decomposi t ion product was c h l o r a t e a f t e r 5 minutes , and t h i s i nc r ea sed to over 23% a f t e r 150 minutes l e a c h i n g . These genera l pa t t e rns were observed i n s e v e r a l d i f f e r e n t runs , a l though the abso lu te va lues v a r i e d s l i g h t l y i n each experiment . - 70 - 8.0 150 . Time (minutes) Figure 10: NaOCl decomposition during leaching of synthetic copper Sulphides. - 71 - Figure 11: Time (minutes) NaC103 production during NaOCl decomposition. - 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 su lph ide m i n e r a l s Smal l p i eces 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 fo r v a r y i n g amounts o f t ime . Slow a g i t a t i o n was mainta ined i n most cases and the experiments were c a r r i e d out w i t h and wi thou t the presence o f carbonate . M i n e r a l sur faces were examined before and a f t e r l e a c h i n g u s ing the scanning e l e c t r o n microscope, the e l e c t r o n microprobe and o p t i c a l microscopy; and to 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 ou t : i ) C h a l c o c i t e . Immersion i n carbonate s o l u t i o n s a t pH 9.0 fo r p e r i o d s o f up to 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 su r face , a l though some t a r n i s h i n g was observed . Approximate ly 0.003 g/1 copper were de tec ted i n s o l u t i o n (3 ppm) from a t o t a l surface area o f 2 about 6 cm . E l e c t r o n microprobe examinat ion o f marked areas r evea l ed t h a t i n most cases both the copper and su lphur content at the surface had decreased, w i t h an o v e r a l l i nc rease i n the Cu:S r a t i o . In a few sma l l areas an inc reased su lphur content was observed 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 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 t i o n s f o r longer p e r i o d s , i n excess o f f i f t e e n hours , began to form dark green areas on the s u r f a c e . These areas grew i n magnitude w i t h time and a f t e r one week the m i n e r a l was e n t i r e l y covered w i t h a green d e p o s i t , which a n a l y s i s showed to have a s i g n i f i c a n t l y i nc reased copper con ten t . The d e p o s i t was not 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 in hypochlorite/carbonate solution 3) after 24 hours in hypochlorite/carbonate solution 4) after 3 weeks in hypochlorite/carbonate solution 5) after 12 hours in hypochlorite solution (no carbonate) 6) after 3 days in hypochlorite solution (no carbonate) 7) after 1 week in hypochlorite solution (no carbonate) Effect of NaOCl ± Na„ C0„/NaHC0_ on massive chalcocite samples at pH 9.0, 35°C. - 73 - (P la te I ) . A f t e r 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 patches were observed on the green c o a t i n g cove r ing the c h a l c o c i t e s u r - face . A g i t a t i o n o f s o l u t i o n s c o n t a i n i n g 7 - 8 g/1 h y p o c h l o r i t e , but no carbonate , 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 su r f ace , and a f t e r about 12 hours a powdery green d e p o s i t formed i n c e r t a i n a reas . W i t h i n 3 days the e n t i r e surface was green, and a f t e r 1 week a b l a c k d e p o s i t covered most o f the sample. i i ) C o v e l l i t e . CuS was observed to have a more r a p i d r e a c t i o n than Cu^S when exposed to both ca rbona t e - con ta in ing s o l u t i o n s and hypo- c h l o r i t e a l one . In the former case the p o l i s h e d sur face l o s t i t s shine w i t h i n 10 minutes and whi te patchy areas 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 surface was covered by a whi te d e p o s i t . Probe a n a l y s i s showed areas w i t h d i f f e r e n t l e a c h i n g c h a r a c t e r i s t i c s to be p re sen t : a) areas w i t h an i nc rea sed Cu:S r a t i o caused by a l a r g e decrease i n su lphur content and a r e l a t i v e l y sma l l decrease i n copper , b) areas w i t h a s i g n i f i c a n t l y i nc reased su lphur content and hence a decreased Cu:S r a t i o . Subsequent washing i n carbon t e t r a - c h l o r i d e , C C l ^ , removed t h i s 1 e x c e s s ' s u l p h u r and suggested i t was an e lementa l su lphur d e p o s i t (Table X ) . A f t e r exposure to carbonate s o l u t i o n s fo r longer p e r i o d s , the e n t i r e c o v e l l i t e surface was covered by a dark green d e p o s i t s i m i l a r t o t h a t formed on the c h a l c o c i t e . Gradual d i s s o l u t i o n o f copper occur red to g ive a deep b lue s o l u t i o n c o n t a i n i n g up to 100 ppm Cu. A f t e r 2 - 3 weeks s tand ing 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 lue 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 surface was s imul t aneous ly coated w i t h - 73(a) - - 73(b) - PLATE II CuS, unleached. after 10 minutes in hypochlorite/carbonate solution, after 15 hours in hypochlorite/carbonate solution, after 1 week in hypochlorite/carbonate solution, after 3 weeks in hypochlorite/carbonate solution, after 5 minutes in hypochlorite solution (no carbonate), after 15 hours in hypochlorite solution (no carbonate). after 1 week in hypochlorite solution (no carbonate). ect of NaOCl ± Na„C0_/NaHC0„ on massive covellite samples pH 9.0, 35°C. - 74 - a very b l ack d e p o s i t (P la te I I ) . Th i s phenomenon was found to be q u i t e r e p r o d u c i b l e , a l though the time to 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 for d i f f e r e n t 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 carbonate , w i t h the appearance o f brown patches w i t h i n 10 minutes . A powdery green depos i t developed w i t h i n 12 hours and covered the e n t i r e surface a f t e r about 15 hours ,exposure . This substance was found to have a s i g n i f i c a n t l y i nc reased copper count (Table X) and was s i m i l a r i n appearance to c u p r i c hyd rox ide . A f t e r 1 week a dark brown/black d e p o s i t had developed on top o f the green. I t was ' f l a k y , ' and e a s i l y removable, u n l i k e the p r e c i p i t a t e produced by carbonate s o l u t i o n s . The copper contents o f both b l a c k depos i t s were s i m i l a r to those o f the green l a y e r s which they superceded. i i i ) C h a l c o p y r i t e . Immersion i n t o ' unbuf fe red ' 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,, su r f ace , and s e v e r a l brown patches were observed to form. The e n t i r e sample was covered by a brown c o a t i n g a f t e r 2 weeks s t a n d i n g . Samples exposed to 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 sur face was observed and s e v e r a l dark brown patches appeared a f t e r long s t a n d i n g . SEM examinat ion showed tha t both t reatments produced a s i m i l a r sur face 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 nc rease i n copper and a cor responding decrease i n su lphur a t the su r f ace . 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 fo r pe r iods o f up to 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 su lph ide mine ra l s The sur face s t u d i e s r epor ted above, toge ther w i t h the observed 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 decomposi t ion on the presence o f N a 2 C 0 3 / N a H C 0 3 i n the l e a c h i n g system, i n d i c a t e d tha t these reagents p l ayed a s i g n i f i c a n t l y more important r o l e than had been i n i t i a l l y supposed when a carbonate mixture was added as a bu f f e r component. S e v e r a l experiments were thus c a r r i e d out i n which the t o t a l carbonate content of 2- 2-the system was v a r i e d from 0.55 g/1 [CO^ ] to 10.0 g/1 [CO^ ] 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 . Th i s was found to have a r a t h e r remarkable e f f e c t on the behaviour 2- o f both copper and h y p o c h l o r i t e . As [CO^ ] i n c r e a s e d , the amount o f copper i n i t i a l l y taken i n t o s o l u t i o n inc reased i n an almost l i n e a r manner 2- and v a r i e d from 6 ppm w i t h 0.55 g/1 [CO^ ] to 125 ppm w i t h 10 g/1 2- [CO^ ] as shown i n F igu re 12 a,b and Table X I I I . Th i s va lue o f d i s s o l v e d copper represented a peak c o n c e n t r a t i o n which occur red w i t h i n the f i r s t f i v e minutes of l e a c h i n g and then dropped to a s l i g h t l y lower l e v e l . The second va lue was main ta ined f o r a f i n i t e p e r i o d o f t ime and was appa ren t ly a f u n c t i o n o f the amount o f added carbonate . I t was f o l l o w e d by a fu r t he 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 decomposi t ion o f the h y p o c h l o r i t e , which had p r e v i o u s l y main ta ined a cons tant va lue (Figure 13, Table X I I I ) . In experiments 2- us ing 5 g/1 [CO^ ]. and above, the copper content 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 decompos i t ion , but those cases con- 2- t a i n i n g 0 . 5 , 1.0 and 2.0 g/1 [CO^ ] showed zero copper i n s o l u t i o n a f t e r t h i s p o i n t . 2.0 120J 8 0 J E cl ol a a o A 10.7 g/1 - 7.5 g/1 [co3 ]T L1.5 • o (pH 5.0 g/1 2.0 g/1 1.0 g/1 0.55 g/1 9.0, 35°C) 404 .1.0 _ o E CO O CD a a o U0.5 Time (minutes) Figure 12(a): Effect of varied carbonate content on Cu dissolution from Covellite. o 1 ! 1 1 I 1 • 1 I 40 120 200 280 360 TIME minutes Figure 12(b): Cu dissolution and NaOCl decomposition for Covellite leaching with 10 g/1 [00^ ]T - QL - - 79 - I t was observed t ha t the r a t e o f sodium h y p o c h l o r i t e decomposi t ion was cons tan t , and not the re fo re a f u n c t i o n o f d i s s o l v e d copper or i n i t i a l carbonate c o n c e n t r a t i o n . In a l l cases the r a t e was almost i d e n t i c a l to t h a t produced du r ing 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 carbonate . To determine whether or not s i m i l a r e f f e c t s occur red w i t h the o ther copper su lph ide 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 ing 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 su lph ide powders. A l l three samples showed the d i s s o l v e d copper content to pass through a r a p i d l y a t t a i n e d maximum va lue and then to ma in t a in a cons tant va lue fo r an amount o f time dependent on the carbonate content o f the system. Th i s was aga in fo l lowed by r a p i d l o s s o f copper and simultaneous h y p o c h l o r i t e decomposi- t i o n (Figures 14 - 17, Tables XIV, X V ) . The necessary i n d u c t i o n p e r i o d to 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 to the analogous case fo r c o v e l l i t e be ing 10, 25 and 65 minutes f o r 1.0, 2.0 and 5.0 g/1 carbonate r e s p e c t i v e l y . The amounts o f copper d i s s o l v e d from each sample were a l s o very s i m i l a r , but the observed r a t e s o f h y p o c h l o r i t e decomposi t ion were not cons tan t . They were however c o n s i s t e n t w i t h the r a t e s ob ta ined i n each case du r ing l e a c h i n g wi thou t carbonate . 3 .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 c o n c e n t r a t i o n To determine whether an i nc r ea se o f h y p o c h l o r i t e s t r eng th had any e f f e c t 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 leached 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 g/1 c o n c e n t r a t i o n used p r e v i o u s l y , and i n the presence o f 5 g/1 carbonate . Resu l t s showed tha t the copper e x t r a c t e d had inc reased from 60 cL Q. <x> o. CL o O . 20- A - A -1— 40 80 • 5 g/1 [C0 3"]T A 2 g/1 O 1 g/i (pH 9.0, 35°C) —I 120 Q 160 Figure 14: TIME minutes Effect of varied carbonate content on Cu dissolution from Chalcocite. .0.75 -0.50 CO _ o E CO O X (-—1 CP Q. Q. O . O . -0.25 CO o   - 83 - - 84 - 0.045 g/1 to 0.1 g / 1 , and tha 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 longer p e r i o d before both i t and the h y p o c h l o r i t e concen t r a t i on r a p i d l y decreased. The r a t e of 0C1 decomposi t ion was c o n s i s t e n t w i t h t ha t ob- t a i n e d i n a l l p r ev ious runs u s i n g c o v e l l i t e , and the copper remaining i n s o l u t i o n a f t e r decomposi t ion was the same as i n a l l o ther runs u s i n g 5 g/1 carbonate (Figure 18, Table X V I ) . 3 .1 .8 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 carbonate s o l u t i o n s i n the absence o f h y p o c h l o r i t e to g a i n a b e t t e r i n s i g h t i n t o the p r e c i s e r o l e p l ayed by the o x i d a n t . Copper was d i s s o l v e d to a l e v e l o f 0.06 g/1 i n the presence o f 10 g/1 t o t a l carbonate . Th 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 re sen t , or a f t e r 30 minutes i n 'carbonate o n l y ' s o l u t i o n s (Figure 19, Table X V I I ) . F i l t e r e d samples taken f o r a n a l y s i s were observed to p r e c i p i t a t e a green powder a f t e r s t and ing o v e r n i g h t . These s o l u t i o n s had l o s t t h e i r b lue c o l o u r a t i o n and con ta ined n e g l i g i b l e amounts o f copper . As noted e a r l i e r , both i n the p resen t study and i n p rev ious work c a r r i e d out by Ismay f i l t e r e d s o l u t i o n s from experiments l e a c h i n g copper su lph ide mine ra l s i n h y p o c h l o r i t e depos i t ed a b l a c k p r e c i p i t a t e a f t e r s tand ing f o r a shor t t ime . Ismay p o s t u l a t e d tha t complexing between copper and a p a r t i a l l y o x i d i z e d sulphur spec ies c o u l d o c c u r , w i t h slow t r ans fo rma t ion i n t o su lphate i n the presence o f h y p o c h l o r i t e , caus ing 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. - 85 - TIME minutes Figure 18: Cu dissolution and NaOCl decomposition from Covellite leaching with 20 g/1 [NaOclJ and 5 g/1 [ C 0 v = ] T - 86 - 1 I I I I 1 40 80 120 TIME minutes Figure 19: Agitation of Covellite in Na2C03/NaHC03 solution ± NaCl. - 87 - To t e s t t h i s hypo thes i s , copper su lphate 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 [0C1 ] and 10 g/1 Na CO /NaHCO at pH 9 .0 , i n s u f f i c i e n t amounts to g i v e 0.1 g/1 copper i n s o l u t i o n . I f l e s s than t h i s d i s s o l v e d i t c o u l d be taken as an i n d i c a t i o n tha t the carbonate c o u l d not 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 f u l l y 2- o x i d i z e d su lphur , i . e . as SO^ I t was found however tha 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 blue c o l o u r observed 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 experiment showed a maximum of 0 .127 g/1 Cu to be d i s s o l v e d under these c o n d i t i o n s . Removal o f h y p o c h l o r i t e from t h i s system enabled o n l y 0 .065 g/1 o f the copper to 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 lue s o l u t i o n . Samples l e f t to s tand aga in produced a s o l i d p r e c i p i t a t e : b l a c k i n the former case , 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 re sen t . I t was a l s o observed tha t t h i s p r e c i p i t a t i o n e f f e c t c o u l d be "seeded," 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 p r e c i p i t a t e to f r e s h l y made copper - carbonate 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 the d i s s o l v e d copper, as more green powder, w i t h i n one hour . ^ H I 3.2 Copper From the above obse rva t ions i t i s ev iden t t ha 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 carbonate s o l u t i o n s , and on the nature and c o l o u r o f substances p r e c i p i t a t e d from them. The resemblances between copper su lph ide l e a c h i n g and copper su lphate d i s s o l u - t i o n and the subsequent behaviour o f s o l u t i o n s w i t h and wi thou t hypo- c h l o r i t e were found to 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 / [CO ] s o l u t i o n i s cons tant whether the s t a r t i n g m a t e r i a l i s a copper su lph ide m i n e r a l , or copper su lphate reagent . i i ) A l e s s e r amount o f copper i s h e l d i n carbonate 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 . Th i s amount i s i d e n t i c a l to t ha t found dur ing copper su lph ide l e a c h i n g a f t e r h y p o c h l o r i t e decomposi t ion and l o s s o f some o f the i n i t i a l l y d i s s o l v e d copper (Figures 12b, 19) . i i i ) The copper carbonate complex decomposes a f t e r a c e r t a i n time p e r i o d . Copper i s thus p r e c i p i t a t e d as a s o l i d compound which i s b l ack 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 o t h e r w i s e . These f a c t o r s l e d to 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 s u l - phides i n the system under study occurs i n a "two stage" p roces s . A f t e r 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 i n v o l v e d , together w i t h c o n s u l - t a t i o n o f r e l e v a n t l i t e r a t u r e , p a r t i c u l a r l y s t u d i e s o f L i s t e r , Prokopchik and D e l h e z ^ ' ^ 2 ' ^ 2 i t was p o s t u l a t e d tha t the observed l e a c h i n g behaviour i n v o l v e s o x i d a t i o n o f copper to a t r i - v a l e n t s t a t e . Thus the i n i t i a l , h ighe r copper content of the l e a c h i n g s o l u t i o n i s caused by a copper***- carbonate complex which subsequent ly decomposes p r e c i p i t a t i n g a b l ack copper*"*""1" s o l i d and causes s imultaneous c a t a l y t i c decomposi t ion o f the h y p o c h l o r i t e . The same c y c l e i s then repeated f o r a copper**-carbonate complex. Th i s a l s o decomposes a f t e r a c e r t a i n t ime , p r e c i p i t a t i n g the remaining copper as a green powder which i s presumably m a l a c h i t e , C u 2 ( O H ) 2 C 0 3 (F igure 20, Table X V I I ) .  - 90 - 3 .2 .1 A n a l y s i s o f copper A b l a c k compound s i m i l a r i n appearance to t ha 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 hypoch lo 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 . The f o l l o w i n g t e s t s were then c a r r i e d out ( i n i t i a l l y on samples made i n the absence of ca rbona te ) . 3 . 2 . 1 . 1 E f f e c t o f 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 to a s o l u t i o n o f 5 N h y d r o c h l o r i c a c i d . Th 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 pa l e b lue s o l u t i o n , accompanied by v igorous gas e v o l u t i o n . Passage of t h i s gas through a c a l c i u m hydroxide s o l u t i o n ("l imewater t e s t " ) showed no c l o u d i n e s s whatsoever, i n d i c a t i n g t ha t no carbon d i o x i d e was p r e sen t . 3 . 2 . 1 . 2 E v a l u a t i o n o f o x i d a t i o n s t a t e 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 con ta ined i n the sample was determined from the formula 2Cu 5 l 2 = 2 N a 2 S 2 0 3 = > 1 mlN. Na„S 0_ 5 0.0635 g Cu 2 2 3 u s i n g the f o l l o w i n g method: 3+ 2+ Iodide w i l l reduce both Cu and Cu to the +1 o x i d a t i o n s t a t e - 91 - w i t h format ion o f a C u l 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 q u a n t i t y 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 lows the 3+ amount o f Cu to be c a l c u l a t e d : a) A weighed sample o f the compound was added to an a c i d i f i e d potass ium 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 aga ins t s t anda rd ized 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 to d i l u t e s u l p h u r i c a c i d , 2 g o f c r y s t a l l i n e KI were d i s s o l v e d and the s o l u t i o n was then t i t r a t e d a g a i n s t N a 2 S 2 0 3 as be fo re . Table 4: Dete rmina t ion o f C o p p e r 1 1 1 by Idometr ic T i t r a t i o n Sample (g) Na S „ 0 , (0.1 N) 2 2 3 (ml) Cu (g) Cu o, "o a) 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 2 ° 3 2 " Cu (g) °2 (g) °2 Moles b) 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 - Therefore, 0.0021 M of oxygen are present as Cu , presumably C U 2 ° 3 " C u a s s o c i a t e d with t h i s i s 0.002 x 2/3 M = 0.00143 M or 0.091 g. Therefore C u ^ = 0.034 g 0 + 0.091 g Cu = 0.125 g t o t a l , equivalent to 25% of the sample. For comparison, the same t e s t was done using a standard CuO sample and no d i f f e r e n c e was observed between cases a) and b). 3.2.1.3 Measurement of oxygen evolution 0 — 1 ' 1 ' " " using a mercury column Figure 50: Apparatus f o r Measuring Gas Evolution - 93 - The gas evolved on a c i d i f i c a t i o n o f a weighed sample o f the b l ack substance was measured u s ing a mercury column connected to a mercury r e s e r v o i r i n a dev ice resembl ing a Lunge apparatus o u t l i n e d above (Figure 50) . The mercury column was a t tached to a f l a s k c o n t a i n i n g d i l u t e n i t r i c a c i d and the specimen sample. 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 depress ion o f the mercury l e v e l . Th i s was assumed to be oxygen and i t s volume determined by r e d u c t i o n to STP. Sample : 2 g Depress ion of. Hg column : 23.4 cm Baromet r ic p ressure : 755 mm Hg Temperature : 18°C Reducing to STP: 755 273 V G = 234 x x — - = 21.56 cm Oxygen 1 mole gas a t STP occupies 22.4 1 Therefore , 215.6 mm 215.6 _ g_QQgg M oxygen 22400 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 = 0.064 M Cu or 0.4064 g There fore , percentage o f sample which i s Cu^O^ = 0.154 g 0 + 0.406 g Cu = 0.56 g or 28% o f sample. Th i s i s i n reasonable agreement w i t h the r e s u l t ob ta ined t i t r a m e t r i c a l l y . 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 con ta ined i n a s o l u t i o n ob ta ined 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 to vary between 60 - 64% copper . Th i s i s i n s u f f i c i e n t to account f o r 70 - 75% of the sample be ing present as pure c u p r i c o x i d e , CuO, and i t i s l i k e l y - 94 - t h a t some water i s a l s o p resen t , e i t h e r as adsorbed H^O or 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 ob ta ined u s i n g the gas chromatograph. A sample o f gas evolved by a c i d d i s s o l u t i o n o f the b l ack compound was passed through the chroma- tograph and peaks ob ta ined had a N 2 : ° 2 r a t ^ ° ° ^ 71:46 or 1 .54 :1 . Th i s compares to a r a t i o o f 78:40, or 1 .95 :1 , fo r a s tandard a i r sample. The former case thus showed an oxygen enrichment o f about 22%. R e p l i c a t i o n s o f the above ana lyses produced v a r i a t i o n s i n the amount o f excess oxygen p re sen t , but the va lue was always between 20 - 30%. The v a r i a t i o n s appeared to be f a i r l y random, but two d i s t i n c t t rends were observed: i ) An inc rease i n pH du r ing 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 1 1" 1".. No change i n the nature o f the substance was observed however, and even a t pH va lues o f 12 - 14 no more than 30% a v a i l a b l e oxygen was o b t a i n e d . i i ) An inc r ea se i n the t ime p e r i o d between p r e c i p i t a t i o n of the b l a c k s o l i d to the end o f f i l t r a t i o n seemed to decrease the percentage y x e l d o f copper 3 . 2 . 1 . 5 Ins t rumenta l a n a l y s i s i ) Magnetic s u s c e p t i b i l i t y I I I . The above r e s u l t s i n d i c a t e the presence o f copper 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 i t was ev iden t t ha 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 . Tes ts t o determine i t s magnetic s u s c e p t i b i l i t y were 3 t he re fo re c a r r i e d ou t : as noted p r e v i o u s l y the d c o n f i g u r a t i o n of copper1"1""1" s a l t s produces diamagnet ic substances . I n i t i a l weighing of samples on a magnetic balance both i n and out of a f i e l d however, i n d i c a t e d t ha t the compound was paramagnet ic . 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 then made, and a v a l u e f o r lO^Xg equal to 6 . 9 3 ± 0 . 0 3 cgs u n i t s was o b t a i n e d . Us ing s u i t a b l e c o r r e c t i o n s fo r the diamagnetism o f copper and oxygen and a va lue f o r t o t a l copper content o f the sample from atomic a b s o r p t i o n a n a l y s i s gave: 6 3 •— 1 10 X Cu = 753 cm mol o r magnetic moment, y e f f ' = 1.33 B . M . C o n s i d e r i n g t ha t C u 1 1 compounds normal ly have 10^ x Cu va lues o f 3 -1 over 1500 cm mol and a u e f f . o f =1.98 M, i t can be assumed tha t t h i s XXX 11 7 8 compound con ta ins 30 - 40% copper and 60 - 70% copper i i ) I n f r a - r e d spec t r a To t r y and determine the nature 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 present as an ox ide or a hydrox ide , a sample prepared 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 run i n the i n f r a - red spectrophotometer . The r e s u l t s ob ta ined were f a r from be ing 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 ob ta ined 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 hydroxy, OH group, w h i l e o ther samples gave no peaks a t a l l . Dry ing the compound a t 110°C ove rn igh t and r e - running through the I . R . spectrum caused the disappearance o f a p r e v i o u s - l y ob ta ined hydroxide peak i n about 80% o f a l l samples. i i i ) X - r a y d i f f r a c t i o n Smal l samples were ana lyzed i n the X- ray d i f f r a c t o m e t e r , and the r e s u l t a n t 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 ob ta ined from a s tandard CuO sample: Cu < CuO Sample CuO Sample (Reported) 0 dA I / I x dA I / I * o 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 1.304 7 1.27 6 1.19 2 Table 5: X - r a y D i f f r a c t i o n Pa t t e rns f o r Copper 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 p r i - 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 copper1"1""1" i n the presence o f carbonate Samples 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 hydroxide a t pH 9.0 i n s o l u t i o n s which a l s o con ta ined sodium carbonate and b icarbona te s a l t s were very s i m i l a r to those made i n the absence o f carbonate , but there was a ' n u c l e a t i o n p e r i o d ' before any p r e c i p i t a t i o n o c c u r r e d . Th i s was a s i m i l a r e f f e c t to t ha t observed du r ing copper s u l - phide l e a c h i n g , before h y p o c h l o r i t e decompos i t ion : [ c o 3 2 - ] T Time to 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 3 . 2 . 2 . 1 E f f e c t o f 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 to a c a r - b o n a t e - h y p o c h l o r i t e 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 i n s t a n - taneous b l a c k e n i n g o f the b lue 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 . Th i s occur red i n a l l cases , r ega rd l e s s o f the i n i t i a l carbonate c o n c e n t r a t i o n . - 98 - 3 . 2 . 2 . 2 E f f e c t o f a c i d i f i c a t i o n A d d i t i o n of d i l u t e n i t r i c a c i d to the sample produced a c l e a r b lue s o l u t i o n . Rapid gas e v o l u t i o n was observed and a l imewater 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 re sen t . Some excess oxygen was a l s o de tec ted by passage o f a gas sample through the chromatograph and comparison o f the observed r e t e n t i o n t imes w i t h those o f a s tandard a i r sample. 3 . 2 . 2 . 3 I . R . spec t r a A n a l y s i s o f the i n f r a - r e d spec t r a produced by samples of 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 * wave- 2- number band. Th i s i n d i c a t e s the presence o f an HCO^ o r CO^ group. Peaks i n the 2500 - 3000 cm 1 band, cor responding to a hydroxy group, were again found to be r a t h e r random i n appearance. - 99 - 3 .2 .2 .4 X- ray a n a l y s i s X - r a y d i f f r a c t i o n 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 p a t t e r n : o dA I / I l - spec ies M a l a c h i t e i d e n t i f i e d CuO dA I / I D - ma lach i t e (Reported) 7.43 16 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 2.86 100 2.81 100 2.81 2.52 100 2.52 45 2.51 41 2.32 96 2.47 2.46 35 2.43 20 2.32 17 1.99 10 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 fo r Copper Carbonate - 100 - I t i s thus 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 hydroxide i n the presence o f carbonate i s a mixture 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 malachi te ) and copper* 1 o x i d e , and t ha t i t i s t h i s compound which i s p r e c i p i t a t e d from l e a c h i n g s o l u t i o n s on long 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' (50 - 60 g/1 0C1 ) on m a l a c h i t e , but s o l u t i o n s c o n t a i n i n g on ly 7 - 8 g/1 gave no v i s i b l e change to the green powder. 3 .2 .3 H y p o c h l o r i t e decomposi t ion s t u d i e s 2 g samples o f each p r e c i p i t a t e , i . e . the o x i d e / h y d r o x i d e and carbonate , were a g i t a t e d 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, to determine the r a t e o f h y p o c h l o r i t e decompos i t ion . G r a p h i c a l p l o t s o f the r e s u l t s suggested t h i s r a t e to be very s i m i l a r to tha 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 tha t produced by the analogous case o f c u p r i c ox ide 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 A n a l y s i s o f l e a c h i n g s o l u t i o n s I t was p o s t u l a t e d t ha 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 carbonate complex, then the spectrum ob ta ined from an u l t r a - v i o l e t - v i s i b l e spec t rophotomet r ic scan should be d i f f e r e n t from t h a t produced by a copper** carbonate complex, the c o l o u r o f which i s much l e s s i n t e n s e l y b l u e . However, the o n l y de t ec t ab le 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 rong 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 darker sample. No s e n s i b l e peaks were ob ta ined i n the v i s i b l e r e g i o n whatsoever, de sp i t e the b lue c o l o u r a t i o n o f the samples. A c u p r i c chor ide sample s i g n i f i c a n t l y more concent ra ted i n copper than the carbonate s o l u t i o n s was then run as a s tandard , and a ve ry broad peak appeared i n the 440 - 650 ym r e g i o n . I t was thus assumed t ha t the carbonate complexes were too d i l u t e to g ive -3 any meaningful peaks ( [Cu] - 1.6 x 10 M) . 3.3 Sodium H y p o c h l o r i t e O x i d a t i o n o f Molybdeni te 0.3 g samples o f n a t u r a l molybden i te , MoS 2 , were leached i n s o l u t i o n s c o n t a i n i n g 7 — 8 g/1 0C1 ±: carbonate a t pH 9.0 and 35°C. A va lue o f 0.3 g/1 was chosen because i t r epresen ts the t y p i c a l concen t r a - t i o n o f molybdenum found i n copper rougher concent ra tes a f t e r f l o t a t i o n . E x t r a c t i o n s o f the order o f 93 - 94% Mo were ob ta ined w i t h i n 5 minutes 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 to about 12% o f the i n i t i a l va lue (Figure 22, Table X X ) , c o r r e s - -2 ponding t o the use o f 1.69 x 10 moles 0C1 to o x i d i z e 0.17 g/1 Mo (1.77 x 10 3 moles) from MoS 2 > NaMo0 4 . These r e s u l t s the re fo re confirmed the f i n d i n g s o f Ismay, tha t 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 fo r molybdeni te o x i d a t i o n ; but the f a c t t ha t g rea te r than 94% molybdenum e x t r a c t i o n was not ob ta ined was not e n t i r e l y s a t i s f a c t o r y . The amount o f molybdeni te sample used was thus i nc rea sed to produce s u f f i c i e n t r e s idue a f t e r l e a c h i n g to enable X - r a y a n a l y s i s to be c a r r i e d ou t : Figure 22: NaOCl oxidation of molybdenite at pH 9.0. - 104 - i ) X - r a y f luorescence i n d i c a t e d the f o l l o w i n g elements to be present i n dec reas ing order o f magnitude: Fe > Pb •> Cu,Mo > Zn i i ) X- ray d i f f r a c t i o n s t u d i e s i d e n t i f i e d two l e a d molybdate s p e c i e s , Pb_MoO r and Pb MoO. as be ing p re sen t . Both o f these were 2. b 4 assumed to 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 of about 0.2 g o f r e s idue produced no de t ec t ab l e molybdenum i n s o l u t i o n . Spec t ro scop ic a n a l y s i s confirmed tha t the concent ra te d i d not c o n t a i n 100% MoS^ (Sec t ion 2 . 2 . 1 . 1 ( i v ) ) , and tha t a t l e a s t 3% o f i m p u r i - t i e s were p r e sen t . The l e v e l o f e x t r a c t i o n ob ta ined the re fo re represented more than the apparent 94%. Samples o f reagent grade molybdenum d i s u l p h i d e were subsequently used, but gave no b e t t e r r e s u l t s (Figure 23) . Th i s m a t e r i a l was shown by X - r a y a n a l y s i s (SEM) to c o n t a i n s i g n i f i c a n t amounts of s i l i c o n . Leaching 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 guaranteed to con- t a i n over 98% MoS^. E x t r a c t i o n s o f n e a r l y 98% were then ob ta ined (Figure 24) . H y p o c h l o r i t e consumption was s l i g h t l y h ighe r than fo 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 presence or o therwise o f carbonate bu f f e r reagents was found to have no e f f e c t on molybdenum e x t r a c t i o n . 3 .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 molybdeni te and copper su lph ide mine ra l s a t pH 9.0 In order to 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 from molybdeni te-copper su lph ide m i x t u r e s , samples o f both mine ra l s were Figure 23: NaOCl oxidation of reagent grade-molybdenum disulphide. - 106 - 1 1 1 1 1 T o 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 6 0 . 0 TIME WINS! Figure 24: NaOCl oxidation of 98% molybdenum disulphide. - 107 - leached s i m u l t a n e o u s l y . In the presence o f carbonate , 89% Mo e x t r a c t i o n was ob ta ined , accompanied by d i s s o l u t i o n of 2 - 3% of the copper (-0.12 g / 1 ) . H y p o c h l o r i t e consumption i n the presence o f a l l th ree copper m ine ra l s was v i r t u a l l y the same as fo r o x i d a t i o n o f molybdenite a lone (Figures 25a, 26a, 27a, Tables XXII - X X I V ) . Removal o f carbonate from the system r e s u l t e d i n n e g l i g i b l e amounts o f copper be ing 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 of 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 ob ta ined i n the presence o f c o v e l l i t e , 77% i n the presence o f c h a l c o c i t e and 79% w i t h c h a l c o p y r i t e (Figures 25b, 26b, 27b, Tables XXII - X X I V ) . To conf i rm tha t t h i s was a r e a l e f f e c t , and not caused by the s m a l l amount o f M0S2 sample used g i v i n g un rep resen ta t ive r e s u l t s , 10 g o f c h a l c o p y r i t e were leached w i t h 5 g ' reagent grade ' M0S2 under o t h e r - wise i d e n t i c a l c o n d i t i o n s . A 2% l o s s o f molybdenum occur red i n the presence o f carbonate and a 4 - 5% l o s s i n the absence o f carbonate (Table XXV) . Scheiner e t a l . s t a t e d tha t copper molybdate compounds were found to be d e t r i m e n t a l to good molybdenum recovery i n the U . S . Bureau o f 20/22 Mines p roces s . Experiments were the re fo re c a r r i e d out to see i f copper molybdate format ion cou ld be induced , a l though i n the present study i t appeared t ha t the g rea 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 copper: i ) Copper su lphate s o l u t i o n was added dropwise from a bu re t t e d u r i n g molybdeni te l e a c h i n g . i i ) Sodium molybdate s o l u t i o n was added to 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 covellite in the presence of carbonate buffer. - 109 - Figure 25 (b): NaOCl oxidation of molybdenite and covellite in the absence of carbonate buffer. - 110 - a . Q . O 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 60.<& TIMECMINSJ Figure 26 (a): NaOCl oxidation of molybdenite and chalcocite in the presence of carbonate buffer. - I l l - o O.O- i n pi-I CO in. r- i n OJ i n CO 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 + MO EXTRACTION x NAOCL CONCENTRATION 1 2 . 0 2 4 . 0 3 6 . 0 TIME(MINS) 4 8 . 0 60 i n a en i n 6 0 . 0 Figure 26 (b): NaOCl oxidation of molybdenite.and chalcocite in the absence.of carbonate buffer. - 112 - o a. 0.0 in £ - 1 in. in to x UJ *< 6D in in 00 C3 in in OJ" 12.0 _1 24.0 36.0 48.0 _ l + M0 EXTRACTION x NflOCL CONCENTRATION 60 .na in . a a_ ID LU o -z. 63 O "1—I o C E z. in C3 0.0 Figure 27 (a) 12.0 24.0 36. TIME(MINS) 48.0 60.0 NaOCl oxidation of molybdenite and chalcopyrite in the presence of carbonate buffer. - 113 - Figure 27 (b): NaOCl oxidation of molybdenite and chalcopyrite in the absence of carbonate buffer. - 114 - In both runs copper and molybdenum contents were moni tored w i t h r e spec t to t ime . In the former case no copper was de tec ted i n s o l u t i o n , but s i g n i f i c a n t amounts o f molybdenum were removed. The presence o f copper was a l s o de tec ted on the molybdeni te surface a f t e r l e a c h i n g . In the second case w i t h no carbonate present and hence no copper d i s s o l u - t i o n , n e a r l y 20% of the molybdenum added to the system was l o s t from s o l u t i o n a f t e r 60 minutes a g i t a t i o n (Tables XXVI , X X V I I ) . 3 .3 .2 Leaching o f molybdeni te and copper su lph ides a t pH 5.5 A pH va lue o f 9.0 had been main ta ined i n a l l experiments r epor ted to da te , l a r g e l y because t h i s was p r e v i o u s l y found to be b e n e f i c i a l by Ismay f o r two reasons : i ) pH 9.0 i s the p o i n t a t which a maximum ra t e o f molybdeni te o x i d a t i o n occurs i n sodium h y p o c h l o r i t e s o l u t i o n s . i i ) I t i s c o i n c i d e n t l y the pH va lue a t which c h l o r a t e p r o d u c t i o n i s min imized du r ing h y p o c h l o r i t e decompos i t ion . In view o f the adverse e f f e c t s apparen t ly caused by i n t r o d u c t i o n o f copper mine ra l s i n t o the system however, the l e a c h i n g o f molybdeni te on the a c i d s ide 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 va lue o f 5.5 was chosen because t h i s i s below the r e g i o n i n which c h l o r a t e p r o d u c t i o n i s most r a p i d (6.0 - 7.0) . In most cases molybdeni te was leached f o r 5 - 1 0 minutes before any copper samples were added to the system. Sodium b i c a r b o n a t e was added one gram a t a t ime , a f t e r copper su lph ide a d d i t i o n , and t h i s main ta ined the d e s i r e d pH va lue i n i t i a l l y . - 115 - A f t e r 10 g o f reagent had been added, and i n cases where no carbonate was used, sodium hydroxide was used as a bu f f e r reagent , as b e f o r e . The r e s u l t s c l e a r l y showed tha t an even g rea te r l o s s o f molybdenum occur red under these c o n d i t i o n s . Leaching o f molybdeni te alone gave over 90% recove ry , but 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 or 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 to about 10% (Figures 28 - 30a, Tables 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 tha t found l e a c h i n g CuFeS^ or CuS alone a t pH 5 . 5 . A d d i t i o n o f sodium b ica rbona te to the system inc reased t h i s va lue s l i g h t l y (Table X X X I I ) , but d i d no th ing to prevent the p r e c i p i t a t i o n o f molybdenum (Figures 28 - 30b) . I t was thus presumed tha t copper molyb- date r e a d i l y formed a t t h i s pH l e v e l . Furthermore t h i s substance ac ted as a c a t a l y s t f o r h y p o c h l o r i t e decomposi t ion as shown by the ve ry r a p i d l o s s o f OC1 accompanying molybdenum p r e c i p i t a t i o n . The consumption o f the l i x i v i a n t was h ighe r i n experiments l e a c h i n g o n l y molybdeni te a t -2 pH 5.5 than f o r the cor responding case a t pH 9.0 (8.3 x 10 M 0C1 f o r -3 5.72 x 10 M Mo which i s h ighe r than the s t o i c h i o m e t r i c requirement o f 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 ighe r pH v a l u e s : 6 . 0 , 6.5 and 7 . 0 , to 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 both molybdenum and [OC1 ] aga in occur red i n the presence o f copper mine ra l s w i t h no carbonate i n the system, but recovery was s i g n i f i c a n t l y i nc reased on a d d i t i o n o f NaHCO^.' A c h a l c o c i t e / molybdeni te l each a t pH 6.5 w i t h b ica rbona te i n the system gave 89% Mo e x t r a c t i o n and the copper and h y p o c h l o r i t e concen t ra t ions i n s o l u t i o n main ta ined a cons tant va lue f o r the d u r a t i o n o f the experiment . In an -116- Figure 28: NaOCl oxidation of molybdenite at pH.5.5. - 117 - TIME minutes Figure 29: NaOCl leaching of Chalcopyrite/Mplybdenite at pH 5.5. - 118 - ° 0 . 0 1 2 . 0 2 4 . 0 3 5 . 0 4 8 . 0 6 0 . & 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 6 0 . 0 TIME(MINS) Figure 30 (a): NaOCl oxidation of molybdenite and covellite at pH 5.5 in the absence of NaHC0_. - 119 - -0.0 12.0 24.0 36.0 48.0 B0.& TIME TMINS1 Figure 30 (b): NaOCl oxidation of molybdenite'and covellite at pH 5.5 in the presence NaHCO-. - 120 - i d e n t i c a l run c a r r i e d out i n the absence o f b i ca rbona te , i n t r o d u c t i o n of 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% to 15% w i t h i n 30 minutes (Figure 31a,b , Tables X X X I I I , 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 decreased w i t h r e spec t to t ime , and there was a r a p i d l o s s o f h y p o c h l o r i t e . The f a c t t ha 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 confirmed by a s i m i l a r experiment u s ing s y n t h e t i c CuS a t pH 6 . 0 . Resu l t s showed the same molybdenum l o s s e s occur red wi thou t b ica rbona te i n the system, and tha t t h i s was prevented by l e a c h i n g w i t h NaHC0 3 p resent (F igure 32a,b , Tables XXXV, X X X V I ) . Molybdenum depress ion lessened s l i g h t l y as the pH was fu r the r i n c r e a s e d : a CuFeS^/MoS^ l e a c h a t pH 7.0 w i t h no carbonate gave 30% Mo e x t r a c t i o n . Subsequent a d d i t i o n o f sodium b ica rbona te i n a s i m i l a r run inc reased t h i s t o over 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 (Figure 33a,b, Table XXXVII , X X X V I I I ) . 3 .3 .3 Copper molybdate To determine more about the c o n d i t i o n s o f format ion o f t h i s sub- s tance , e s p e c i a l l y w i t h r e spec t to pH, experiments were c a r r i e d out i n both a c i d and a l k a l i n e s o l u t i o n s i n which equ i -molecu la r s o l u t i o n s o f sodium molybdate, Na^MoO^ and copper su lpha te , CuSO^ were mixed. At pH 9.0 a f i n e b lue -g reen p r e c i p i t a t e was observed w h i l e a t pH 5.3 a darker 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 both before and a f t e r m i x i n g r evea l ed 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 in the presence of NaHCO-.. - 122 - °-0.0 12.0 24.0 36.0 48.0 . 60.$ TIMF(MINS) Figure 31 (b): NaOCl oxidation of molybdenite-and chalcocite at pH 6.5 in the absence of NaHCO-. - 123 - ° - 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 6 0 . & § J 1 1 1 1 UCN 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 4 8 . 0 6 0 . 0 TIME(MINS) Figure 32 (a): NaOCl oxidation of molybdenite and cupric sulphide at pH 6.0 in the presence of bicarbonate. - 124 Figure 32 (b): NaOCl oxidation of molybdenite and cupric sulphide at pH 6.0 in the absence of bicarbonate. -125 - Figure 33 (a): NaOCl oxidation of molybdenite and chalcopyrite at pH 7.0 in the presence of NaHC0„. - 126 - o 0 . 0 1 2 . 0 2 4 . 0 i n i n _ r - i n ID 3 6 . 0 _ l 4 8 . 0 MO EXTRRCTION v NAOCL CONCENTRATION * X r 2 4 . 0 3 6 . TIME(MINS) o 4 8 . 0 60 .a in a a en z. O i—i h - a: • I— ID 2 1 LU CJ O O CE a i n a 6 0 , 0 Figure 33 (b): NaOCl oxidation of molybdenite and chalcopyrite at pH 7.0 in the absence of NaHC03. - 127 - i i ) 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 tand ove rn igh t and then heated over a steam bath a t 60°C fo r 1 hour . The s o l u t i o n s were then r e a n a l y z e d . i ) At pH 5 .3 : On s t and ing , s l i g h t l y more copper and molybdenum had dropped out of s o l u t i o n , aga in i n an approximate Cu:Mo r a t i o o f 1 :1 . i i ) pH 9 . 0 : Converse ly a t the h ighe r pH, aging had a n e g l i g i b l e e f f e c t on the copper content o f s o l u t i o n (which remained v i r t u a l l y zero) but the molybdenum content i nc reased a f t e r s tand ing o v e r n i g h t , and aga in on hea t ing (Table 7 ) . 3 . 3 . 3 . 1 S o l u b i l i t y o f copper molybdate A d d i t i o n of NajyioO„ s o l u t i o n to CuSO. o f an equal c o n c e n t r a t i o n 2 4 4 -2 (10 M) was made dropwise from a bu re t t e a t pH 5 .4 . I t was observed t h a t about 0.8 g/1 molybdenum cou ld be added before any p r e c i p i t a t i o n o c c u r r e d . 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 , a f t e r which the molybdenum content - , remained cons tant 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 0.00875 M CuMo0 4 = 1.4 g/1 (Table XL, F igu re 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 adding some of the f i l t e r e d , green CuMoO^ p r e c i p i t a t e to 100 ml water and l e a v i n g i t to s tand f o r s e v e r a l weeks, du r ing which time the Cu and Mo contents o f the s o l u t i o n were p e r i o d i c a l l y moni to red . Maximum va lues o f 0.75 g/1 Mo and 0.49 g/1 Cu were de t ec t ed . Th i s corresponds to a copper molybdate 128 - Molybdenum added (moles x 102) Figure 34: Solubility of Copper Molybdate at pH 5.0, 35°C. - 129 - PH C o n d i t i o n [Mo] M [Cu] M Mo ppt M Cu ppt M 5.3 Before M i x i n g 0.00979 0.00913 — — A f t e r M i x i n g 0.00875 0.00813 0.00104 0.00100 24 Hours Stand 0.00792 0.00740 0.00188 0.00173 30 Min a t 60°C 0.00396 0.00252 0.00583 0.00661 9.0 Before M i x i n g 0.00979 0.00913 — — A f t e r M i x i n g 0.007192 1 . 5 7 x l 0 ~ 5 0.00260 0.00911 24 Hours Stand 0.00792 5 . 1 2 x l 0 ~ 5 0.00187 0.00908 30 Min a t 60°C 0.00849 7 . 0 8 x l 0 ~ 5 0.00130 0.00906 Table 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 M which i s i n reasonable agreement w i t h the above v a l u e . To conf i rm the e f f e c t s observed du r ing l e a c h i n g , sodium b ica rbona te was added to one o r o ther s o l u t i o n p r i o r to 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 ower ing o f the i n i t i a l Mo content was observed. 3 . 3 . 3 . 2 C a t a l y z e d decomposi t ion o f h y p o c h l o r i t e i n the presence o f copper molybdate A 2 g sample o f copper molybdate 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 7.0 g/1 h y p o c h l o r i t e a t pH 5.0 and 35°C. Samples were taken a t t imed i n t e r v a l s and a n a l y s i s showed t ha t 50% o f the i n i t i a l hypo- c h l o r i t e decomposed w i t h i n 35 minutes and t ha t the r a t e was almost l i n e a r . About 4% o f t h i s decomposi t ion was t o sodium c h l o r a t e , the r e s t presumably be ing to oxygen and c h l o r i d e (Figure 35, Table I X L ) . No d e t a i l e d i n v e s t i g a t i o n of the e f f e c t s o f v a r y i n g surface a r ea , pH, temperature e t c . du r ing copper molybdate c a t a l y s i s was under taken. - 131 - (pH 5.0, 35°C) I 10 ~ l — 30 50 TIME minutes gure 35: Effect of Copper Molybdate on NaOCl decomposition at pH 5.0, 35°C. - 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 s tud i e s o f a copper molybdate sample gave the f o l l o w i n g d i f f r a c t i o n p a t t e r n : . Th i s Study Reported 0 dA o dA I / I 0 - 2CuMo0 4 'Cu(OH) 2 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 Table 8: x - ray D i f f r a c t i o n P a t t e r n f o r Copper Molybdate - 133 - 3 .3 .4 S o l u b i l i t y o f c a l c ium i n h y p o c h l o r i t e s o l u t i o n s The f a c t t ha t copper and molybdenum apparen t ly do not combine a t pH 9.0 to form a s t o i c h i o m e t r i c CuMoO^ compound, together w i t h the obse r - v a t i o n s made d u r i n g l e a c h i n g t ha 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 carbonate spec ies were not those i n which molybdenum e x t r a c t i o n was ad- v e r s e l y a f f e c t e d , r a i s e d the ques t ion tha t o ther elements con ta ined i n the copper s u l p h i d e mine ra 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 s a l t s . An Eh-pH diagram fo r the Cu-^O-MoO^ was cons t ruc t ed (Figure 51) and t h i s confirmed t ha 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 . Fu r the r evidence t ha t copper was not p r i m a r i l y r e s p o n s i b l e fo r the molybdenum l o s s e s a t pH 9.0 was then ob ta ined by i ) l e a c h i n g reagent grade molybdenum d i s u l p h i d e and s y n t h e t i c cuprous o r c u p r i c su lph ides toge ther and o b t a i n i n g >95% molybdenum e x t r a c t i o n whether or not carbonate (and hence copper) was present i n s o l u t i o n (F igure 36) ; and i i ) l e a c h i n g c o v e l l i t e and molybdeni te a t pH 10 .0 , which should be w e l l ou t s i de the zone o f s t a b i l i t y o f CuMoO^. In the presence o f carbonate -91% of the molybdenum was recovered , but t h i s dropped to o n l y 78% i n a l e a c h w i t h no carbonate (Figure 37, Tables X L I , X L I I ) . X - r a y and chemica l a n a l y s i s o f the ores i n d i c a t e d tha t i r o n , z i n c , 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 . Leaching 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 or 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 .004 'g /1 c a l c i u m were de tec ted i n s o l u t i o n d u r i n g the l e a c h i n g o f 10 g samples o f Figure 36: NaOCl oxidation of molybdenum disulphide and cuprous sulphide at pH 9.0 ± carbonate. Figure 37 (a): NaOCl oxidation of molybdenite and covellite at pH 10.0 in the presence of carbonate buffers. Figure 37 (b): NaOCl oxidation of molybdenite and covellite at pH 10.0 in 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 (Figure 38, Table X L V ) . I t i s w e l l known t h a t c a l c i u m molybdate and ca l c ium c a r - bonate are both i n s o l u b l e s a l t s . The f a c t t ha 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 , except i n the presence o f carbonate reagents , was i l l u s t r a t e d by adding a ca l c ium c h l o r i d e s o l u t i o n to a molybdeni te -4 l e a c h . Loss o f 1.25 x 10 moles o f both c a l c i u m and molybdenum was observed when no carbonate was added, but 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 main ta ined i n s o l u t i o n s which a l s o con ta ined sodium carbona te /b icarbona te buf fe r s (Tables X L V I , X L V I I ) . 3 . 3 . 4 . 1 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 / c a l c i u m carbonate mine ra l s The most commonly o c c u r r i n g c a l c i u m mine ra l s are c a l c i t e , CaCO^, and gypsum, C a S o 4 - 2 H 2 0 . With the assumption t ha t e i t h e r or both o f these 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 the copper s u l - phide mine ra l s under s tudy , samples of each m i n e r a l were leached 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 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 i n s o l u t i o n , amounting to 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 ca l c ium which i s e q u i v a l e n t to 64.5% e x t r a c t i o n (Figure 39, Tables 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 of 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 to ad- v e r s e l y a f f e c t molybdenum recovery was confirmed by a combined c a l c i t e / molybdeni te l e a c h . Th i s gave on ly 80% molybdenum e x t r a c t i o n . The same - 138 - J • 1 r 1 r r 10 30 50 TIME minutes Figure 38: Calcium dissolution during NaOCl leaching of Copper Sulphide Minerals.  - 140 - experiment i n the presence o f carbonate produced over 95% e x t r a c t i o n (Figure 40, Table X L V I I I ) . 3 . 3 . 4 . 2 E f f e c t o f 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 s o l u b i l i t y Calc ium s o l u b i l i t y inc reases 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 out to determine whether the s o l u - b i l i t y observed d u r i n g the l e a c h i n g o f c a l c i u m mine ra 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 prepared from a commercial b l e a c h , was i n l i n e w i t h tha t expected 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 content was v a r i e d from zero to 2 M and i t was found: 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 both c a l c i t e and gypsum inc reased 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 content . (F igures 41 , 43, Tables L I , L I I ) . The abso lu te amounts were h igher i n the l a t t e r case . i i ) I d e n t i c a l r e s u l t s were ob ta ined whether the c h l o r i d e was p resen t as NaCl o n l y , NaOCl made from ' J A V E X ' , o r as a mix ture o f b o t h . i i i ) The r e s u l t s were i n good agreement w i t h va lues r epor t ed i n the l i t e r a t u r e f o r c a l c i u m s o l u b i l i t y i n c h l o r i d e s o l u t i o n s (F igures 42, 44) . i v ) 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 cases and there was a s l i g h t i nc r ea se as the c h l o r i d e content 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 ev iden t t ha t l e a c h i n g molybdeni te i n the presence o f s o l u b l e c a l c i u m s a l t s i s u n d e s i r a b l e . I t was the re fore necessary to f i n d a method - 141 - Figure 40: NaOCl oxidation of molybdenite and calcite at pH 9.0, in the absence of carbonate. - 142 - 40 80 TIME minutes Figure 41: Effect of Chloride Concentration on Ca dissolution from CaS04- 1/2 H20. - 143 - moles Sodium Chloride 0.5 CD CO E CO E O CO .O. 1.64 0.84 1.5 _ i • Experimental • Literature (pH 9.0, 35°C) 40 —i— 80 120 Figure 42: [Sodium Chloride] 9 r a m s / l i t r e Calcium Sulphate Solubility as a Function of Chloride Content. L5.0 CO j D O E •2.5 o x E O co .O. - 144 - TIME minutes Figure 43: Effect of Chloride Concentration on Ca dissolution from CaC0„. - 14 5 - Figure 44: Calcium Carbonate Solubility as a Function of Chloride Concentration. - 146 - 2+ o f removing Ca from the l e a c h i n g s o l u t i o n , wi thou t de t r iment to the molybdenum. Despi te the f a c t t ha 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 ha t the presence o f excess carbonate i n the system suppressed format ion o f CaMoO^. Fu r the r t e s t s 2- i n d i c a t e d t h a t a minimum o f 3.19 M CO^ per 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^ (Figure 45, Table L I I I ) . In p r a c t i c e however, i t appeared t ha t the q u a n t i t y o f carbonate 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 ther than for c a l c i u m suppres s ion . I t was noted i n S e c t i o n 3 .1 .6 t ha t low carbonate concen- t r a t i o n s 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 igher con- c e n t r a t i o n s d u r i n g the l e a c h i n g of Cu^S, CuS and CuFeS 2 . Experiments i n which molybdeni te and copper su lph ides were leached together showed 2- t h i s n u c l e a t i o n time decreased f u r t h e r f o r a g i v e n [CO^ ] ^ c o n c e n t r a t i o n . Th i s was appa ren t ly due t o the presence o f molybden i te . CuS/MoS 2 runs a t the 5 g/1 and 10 g/1 carbonate l e v e l showed h y p o c h l o r i t e decomposi t ion 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 a decrease o f 30 - 50% over the n u c l e a t i o n t ime f o r CuS a l o n e . 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 lower (Figure 46, Tables L I V , L V ) . A s i m i l a r e f f e c t was observed w i t h C u 2 S / M o S 2 and 10 g/1 carbonate (Figure 47, Table L V I I ) . 2 - At the 5 g/1 [CO^ ] l e v e l i t was a l s o found tha t a g radua l l o s s o f h y p o c h l o r i t e occur red c o n t i n u o u s l y from the beg inn ing o f a g i t a t i o n and before the r a p i d l o s s caused by c o p p e r 1 1 1 c a t a l y s i s . Leaching CuS i n the presence o f sodium molybdate confirmed t h i s t r end and showed l o s s of both copper and molybdenum from s o l u t i o n i n a 1:1 r a t i o sugges t ing t ha t some CuMoO. forms even i n the presence o f carbonate . This then causes 4 c a t a l y z e d h y p o c h l o r i t e decomposi t ion before C u 1 1 1 p r e c i p i t a t i o n moles of Carbonate added Figure 45: Effect of Carbonate Addition on Calcium Precipitation from Solution. 120. E Q. cL CD a CL o .o. A - NaOCl --: • C u. • 10 g/1 [co3=] A 5 g/1 [C03=] (pH .9.0, 35°C) A>.: N 80 TIME minutes 120 160 -6 8 CD CO 1 4 E ^ CO O) O O CO V2 Z Figure 46: Copper dissolution and NaOCl Decomposition during Covellite/Molybdenite leaching at pH 9.0, with varied [C03~JT> 4̂ 03 160 8 T 1 — 1 1 1 ' 1 I 40 80 120 160 TIME minutes Figure 47: Copper Dissolution and NaOCl Decomposition during Chalcocite/Molybdenite Leaching at pH 9.0 (10 g/1 [C0 3 =] ). - 150 - (Figure 48, Table L V I ) . A s i m i l a r run w i t h double the amount o f carbon- 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 decom- p o s i t i o n fo r over 4 hours (Figure 12b, Table X V I I I ) . Leaching i n the presence o f l a r g e r amounts o f carbonate 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 to c o p p e r 1 1 1 p r e c i p i t a t i o n and 0C1 decompos i t ion , as w e l l as p r even t ing CuMoO^ and CaMoO^ fo rma t ion . 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 . Va r ious beaker experiments were done to i n v e s t i g a t e the e f f e c t i v e n e s s o f these reagents 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 to carbonate , thereby p reven t ing copper d i s s o l u t i o n . Sodium meta s i l i c a t e , N a ^ i O ^ - S H ^ O was found to be most e f f i c i e n t i n t h i s r e spec 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 each was subsequent ly c a r r i e d out i n 2- the presence o f 1 g/1 SiO^ • Almost 99% Mo recovery was ob ta ined (Figure 49, Table L V I I ) . No copper was de tec ted i n s o l u t i o n and the h y p o c h l o r i t e main ta ined a constant va lue 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 in the presence of Na„SiO„. - 153 - A d d i t i v e [Ca] i n s o l n . A d d i t i v e [Ca] ppt ( g / D (ppm) (Moles) (Moles) Ra t io — 94.12 — 2 . 3 5 x l 0 ~ 2 [ C 0 3 2 - ] : 2 - 2+ CO^ :Ca^ 0.25 90.31 4 . 1 6 6 x l 0 ~ 3 9 . 5 0 x l 0 ~ 4 4.39:1 0.50 53.17 8 . 3 3 x l 0 ~ 3 1 . 0 2 x l 0 ~ 3 8.17:1 1.00 18.8 1 . 6 6 x l 0 ~ 2 1 . 8 8 x l 0 ~ 3 8.83:1 [ S i 0 3 2 - ] : 0.25 20.03 3 . 2 8 x l 0 ~ 3 1 . 8 5 x l 0 ~ 3 1.77:1 1.00 3.45 1 . 3 1 x l 0 ~ 2 2 . 2 6 x l 0 ~ 3 5.04:1 [ P 0 4 3 - ] : 0.25 53.17 3 . 1 6 x l 0 ~ 3 1 . 0 2 x l 0 ~ 3 3.09:1 1.00 25.20 1 . 2 7 x l 0 ~ 2 1 . 7 0 x l 0 ~ 3 7.47:1 Table 9: E f f e c t o f SiO , CO and P 0 4 (sodium s a l t s ) on Calc ium 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 . - 154 - CHAPTER 4 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 Leaching o f Copper Su lph ide 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 behaviour 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 ea f f i rmed Ismay 1 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 copper rougher concen t ra t e s , t ha t a c e r t a i n amount o f copper was r a p i d l y ex t r ac t ed by the 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 hydroxide which i s the 73 -9 s t a b l e specxes a t pH 9 . 0 , as g iven by Pourba ix i s 8.0 x 10 which i s s e v e r a l orders o f magnitude l e s s than the observed exper imenta l va lue -3 of 10 M. I t thus seemed l i k e l y t ha t complexing o f some k i n d was o c c u r r i n g . Copper, i n common w i t h o ther elements o f the f i r s t t r a n s i t i o n s e r i e s , i s capable o f forming aqueous complexes w i t h a l a r g e number o f an ions , but these are more l i m i t e d on the a l k a l i n e s ide of n e u t r a l i t y than i n a c i d s o l u t i o n s . The most common a t h igher pH l e v e l s are ammonia and cyan ide , but the o n l y components present i n the system under study were c h l o r i d e (as CI and as 0C1 ) and carbonate , as w e l l as su lph ide con- t a i n e d i n the copper ores which would be expected to o x i d i z e to su lpha te , 2- SO^ , i n h y p o c h l o r i t e s o l u t i o n . To determine i f one o r more o f these spec ies 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 , r e l e v a n t l i t e r a t u r e was reviewed and i t was found: i ) C e r t a i n c u p r i c c h l o r i d e complexes are known to e x i s t , but - 155 - 39,40 are found predominant ly i n a c i d s o l u t i o n . i i ) 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 but 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 spec ies i s r e l a t i v e l y u n s t a b l e . Va r ious re fe rences to Cu - 0C1 complexes were found but none con ta ined d e f i n i t e p roof t ha t such a complex cou ld be made. i i i ) B i v a l e n t copper can combine w i t h v a r i o u s in t e rmed ia t e s u l - phur o x i d a t i o n spec ies t o form a number o f s a l t s , such as CuS„0 ' 4H„0 , z 6 2 79 CuS^Og, some o f which are s o l u b l e i n aqueous s o l u t i o n . i v ) Cupr 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 i n a l k a l i n e s o l u t i o n . Thus carbonate seemed to be the most l i k e l y complexing agent a t a pH va lue o f 9 . 0 , and the f a c t t ha t the l e a c h i n g s o l u t i o n s showed such s t rong b lue c o l o u r a t i o n fo r the amounts o f copper they con ta ined was 27 30 31 i n l i n e w i t h obse rva t ions 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 lue c o l o u r . Al though s l i g h t v a r i a t i o n s i n the amount o f copper d i s s o l v e d occur red between the th ree 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 case , i m p l y i n g t ha 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 resen t , suggests t ha t t h i s va lue represented the maximum amount o f copper which 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 and carbonate c o n c e n t r a t i o n . For a t o t a l carbonate content o f 10 ^ M, De Zoubov e t a l . show the s o l u b i l i t y o f c o p p e r 1 1 to be 4.0 x 10 ^ M a t pH 9 . 0 , where i t e x i s t s as - 15'6 - the cupr ica rbona te i o n CuCCO^)^ (F igure 51 ) . Th i s i s s l i g h t l y lower than the va lue ob ta ined i n t h i s study and suggests t h a t carbonate 2- may not be the o n l y complexing agent f o r copper . Assuming tha t C u ( C 0 3 ) 2 forms the major complex s p e c i e s , however, and tha t a l l the su lph ide 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 to su lpha te , the r e a c t i o n can be de sc r i bed by the equa t ion : CuS + 4NaOCl + 2NaOH + 2HCC>3~ >- 2- C u ( C 0 3 ) 2 + 4NaCl + N a 2 S 0 4 + 2H 2 0 (55) The reasons why such apparen t ly random v a r i a t i o n s i n the copper content occur red throughout a l e a c h i n g run , or why a b l a c k p r e c i p i t a t e was depos i t ed from f i l t e r e d s o l u t i o n s on s tand ing o v e r n i g h t , were not immediate ly apparent . 4 . 1 . 2 Removal o f Carbonate from the System Experiment confirmed tha t the carbonate bu 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 3/Na 2CC> 3 mix ture was r e p l a c e d by sodium hydroxide s o l u t i o n . This would seem to be an important 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 process which 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 porphyry copper o r e s . The s o l u b i l i t y o f copper i n carbonate s o l u - t i o n s has been over looked by a number o f o ther workers i n c l u d i n g Shapi ro 14 and Kulenkeva who c la imed t ha t i n a carbonate system, any meta l s u l - ph ides o the 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 carbonates; - 15-7 - and Bhappu and Scheiner e t a l . ' ' both o f whom suggested hypo- c h l o r i t e l e a c h i n g i n the presence o f carbonate would g ive 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 carbonate , and hence any s o l u b l e copper , from the system i s o f f s e t by the observed e f f e c t s on the h y p o c h l o r i t e . The sma l l amounts o f copper d i s s o l v e d i n the carbonate buf fe red case consumed very l i t t l e h y p o c h l o r i t e and no fu r t he r l o s s of s t r e n g t h was observed fo r up to four hours l e a c h i n g . On the o ther hand, l e a c h i n g w i t h no carbonate caused r a p i d decomposi t ion o f the h y p o c h l o r i t e , accompanied by a drop i n the pH of the s o l u t i o n , n e c e s s i t a t i n g the a d d i t i o n o f sodium hydroxide as an e x t e r n a l bu f f e r component. Sodium h y p o c h l o r i t e i s a s t rong ox idan t and i t i s l i k e l y t ha t the sur faces o f the copper mine ra l s are r a p i d l y o x i d i z e d on con tac t w i t h i t . A t pH 9.0 and w i t h no complexing agent p re sen t , the copper p r e c i p i t a t e s as a hydroxide on the m i n e r a l su r face , thereby p r e v e n t i n g any copper d i s s o l u t i o n : CuS + 4NaOCl + 2Na0H >- Cu(OH) 2 + NaS0 4 + 4NaCl (56) The f a c t t h a t molybdeni te and c h a l c o p y r i t e have approximate ly 25 equal o x i d a t i o n r a t e s suggested to Stumpf and Berube t ha t a s e l e c t i v e molybdenum l e a c h was not p o s s i b l e , but these authors seem to have ove r - looked 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 spec ies i n a l k a l i n e s o l u t i o n . The format ion o f a surface hydroxide i s presumably the cause o f the observed h y p o c h l o r i t e decompos i t ion : ox ides and hydroxides o f v a r i o u s t r a n s i t i o n me ta l s , i n c l u d i n g copper, are known to be a c t i v e c a t a l y s t s / - 158 - 43-51 fo r the heterogeneous decomposi t ion o f h y p o c h l o r i t e s o l u t i o n s . Decomposit ion can occur e i t h e r to oxygen and c h l o r i d e o r to c h l o r i d e and c h l o r a t e . The former r e a c t i o n i s g e n e r a l l y thought to 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 epor ted by P rokopch ik , h o w e v e r , ^ t h a t some c h l o r a t e i s produced a t h igh pH v a l u e s , and t ha t i n the presence o f copper hydroxide c a t a l y s t s t h i s r e a c t i o n becomes more predominant as the pH i s lowered . Thus at pH 9.0 a r a t i o o f C1C> 3:0 2 o f about 3:1 was ob ta ined . Sodium c h l o r a t e i s undes i r ab l e i n a h y p o c h l o r i t e system 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 egenera t ion o f the l i x i v i a n t . The p r o d u c t i o n o f NaClO^ i n l a r g e amounts would the re fore n e c e s s i t a t e s o l u - t i o n treatment t o remove i t ; f o r example, u s i n g S 0 2 r e d u c t i o n , as 20 repor ted i n the U . S . Bureau o f Mines p roces s . C h l o r a t e has a l s o been shown to i n t e r f e r e w i t h the subsequent recovery o f molybdenum from l e a c h - 23 24 i n g s o l u t i o n s . ' 4 . 1 . 4 Decomposit ion Products During the Leaching o f Copper Sulphide 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 decomposi t ion i n the present study was found to vary from m i n e r a l t o m i n e r a l . The f a c t t ha t c h l o r a t i v e decomposi t ion inc reased w i t h r e spec t to time du r ing c h a l c o c i t e l e a c h i n g , but 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 a s s o c i a t e d w i t h t h e i r r e l a t i v e c a t a l y t i c r a t e s , c o n s i d e r i n g tha t c h a l c o - c i t e produced a much s lower r a t e o f decomposi t ion than the o ther two. In no case was a C 1 0 : 0 2 r a t i o o f any th ing approaching the 3:1 r epor t ed by Prokopchik a t pH 9.0 found to e x i s t . The most obvious reason f o r the observed d i f f e r e n c e s i n c a t a l y t i c - 159 - decomposi t ion 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 surface a rea , s i n c e the r e a c t i o n i s heterogeneous. C a l c u l a t i o n s fo r the o v e r a l l surface area 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 ive va lues o f 33,300 cm and 2 27,000 cm r e s p e c t i v e l y (Appendix B ) . The d i f f e r e n c e i s the re fore i n - s u f f i c i e n t t o account f o r the 6:1 r a t i o observed between the r a t e s o f decomposi t ion g iven by CuS and C ^ S . Furthermore, the use o f s y n t h e t i c copper su lph ides i n d i c a t e d a cons tant r a t e o f NaOCl decomposi t ion fo r both 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 of copper hydrox ide , w i t h t ha t observed dur ing 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 be ing caused by some s o r t o f "promoted c a t a l y s i s . " Both these mine ra l s were found to con t a in t r aces 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 than the cor responding copper s a l t s , and i t i s known t h a t n e g l i g i b l e amounts o f both 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 h y p o c h l o r i t e decompos i t ion . ' ' Chirnoaga a l s o r epor t ed t h a t the a c t i o n o f 'm ixed ' 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 . Th i s was confirmed 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 t he re fo re suggested tha t the enhanced r a t e s o f decomposi t ion observed i n the present study are caused by the combined a c t i o n of copper and n i c k e l hydroxide c a t a l y s t s , g i v i n g a f a s t e r r a t e than would be produced by copper a lone . The presence o f carbonate 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 su r f ace : complexing a s m a l l amount o f o x i d i z e d copper as 2- the cupr i - ca rbona te i o n , C u ( C 0 2 ) 3 , p revents format ion o f a hydroxide c a t a l y s t , and the s o l u b l e copper spec ies does not i n i t s e l f ac t as a - 160 - c a t a l y s t , so t ha t no h y p o c h l o r i t e decomposi t ion o c c u r s . 4.1.5 Sodium H y p o c h l o r i t e Leaching o f Massive Samples o f Copper Sulphide M i n e r a l s Experiments u s ing massive samples were c a r r i e d out to o b t a i n more i n f o r m a t i o n , bo th 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 , about the nature o f surface r e a c t i o n s o c c u r r i n g d u r i n g l e a c h i n g . C o v e l l i t e was found to 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 than c h a l c o c i t e , whether o r not carbonate was present i n the system. C u 2 S n a s been shown to l e a c h i n a two stage process i n a c i d s o l u t i o n , w i t h the second 80,81 stage resembl ing 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 . I t i s 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 which occurs on exposure to h y p o c h l o r i t e s o l u t i o n s , there i s a d i f f e r e n c e between the o x i d a t i o n behaviour o f c h a l c o c i t e and c o v e l l i t e . Th i s would represent a more fundamental cause f o r the d i f f e r e n c e s i n the r a t e s o f NaOCl decomposi t ion noted above. The patchy whi te areas present on the c o v e l l i t e surface a f t e r 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 carbonate s o l u t i o n s f o r shor t pe r iods p robab ly i n d i c a t e su lphate format ion a l though why e lementa l s u l - phur should be p resen 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 Faulkenber ry r epor t ed tha t e lementa l su lphur cou ld be produced dur ing the o x i d a t i o n o f aqueous su lph ide s o l u t i o n s by hypoch lo r - i t e whenever the r a t i o o f S:0C1 was l e s s than 1:4. In a l l o ther cases 2- su lpha t e , SO^ , was the o n l y end p roduc t . I t i s thus p o s s i b l e t ha t h y p o c h l o r i t e d e p l e t i o n occur red i n l o c a l i z e d areas o f the m i n e r a l su r f ace , enab l i ng sma l l amounts o f su lphur to be formed. - 161 - Green d e p o s i t s produced on both c o v e l l i t e and c h a l c o c i t e sur faces a f t e r longer 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^. Th i s substance forms the s t a b l e phase i n the Cu-CO^-I^O system at pH 9.0 (Figure 2 ) . Fu r the r o x i d a t i o n o f the m i n e r a l surface a f t e r the s a t u r a t i o n p o i n t f o r the cupr i - ca rbona te spec ies 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 carbonate , copper hydroxide forms on the m i n e r a l surface as a l i g h t green, powdery d e p o s i t . Mic ro -p robe a n a l y s i s confirmed t ha t both depos i t s had a s i g n i f i c a n t l y i nc reased Cu:S surface r a t i o , due t o a l a r g e i nc r ea se i n the copper content a t the su r f ace . The appearance o f a b l a c k d e p o s i t on top o f both green substances 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 su r f ace , accompanied by a l o s s of b lue 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 taken to be ana lo - gous t o the 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 ob ta ined du r ing the l e a c h i n g o f CuS and Cu 2 S powders. Subsequent l e a c h - 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 carbonate i n the system, 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 Prokopchik and o thers on the mechanism of h y p o c h l o r i t e decomposi t ion i n the presence of copper hydroxide c a t a - l y s t s , together w i t h ex tens ive a n a l y s i s o f the compounds made by the a c t i o n of NaOCl on copper s a l t s a t pH 9.0 (Sec t ion 3.2.1) l e d to the c o n c l u s i o n tha t these b l a c k substances are t r i - v a l e n t copper compounds. 4 . 1 . 6 V a r i a t i o n o f the T o t a l Carbonate Content Dur ing Leaching A lower amount o f carbonate i n the l e a c h i n g system caused l e s s - 162 - copper to 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 p e r i o d o f t ime . Th i s t ime p e r i o d , and the copper c o n c e n t r a t i o n i n s o l u t i o n were found to be p r o p o r t i o n a l to the con ta ined carbonate . The r a p i d drop i n copper c o n c e n t r a t i o n which subsequent ly o c c u r r e d , accompanied by simultaneous h y p o c h l o r i t e decomposi t ion can be exp l a ined by assuming sodium h y p o c h l o r i t e i s capable o f o x i d i z i n g copper to the t r i - v a l e n t s t a t e , and t ha 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 complexing a c t i o n o f carbonate u n t i l such time as a s o l i d copper1"'"'1' compound i s able to nuc lea te and p r e c i p i t a t e on the m i n e r a l su r f ace . Th i s then becomes an a c t i v e c a t a l y s t fo r h y p o c h l o r i t e decompos i t ion . In the absence o f any carbonate , the hydroxide formed on the m i n e r a l surface i s the re fo re a copper*1"1" compound r a t h e r than normal c u p r i c hydrox ide , Cu(OH) 2 , and h y p o c h l o r i t e decomposi t ion presumably occurs by the mechanism o u t l i n e d by Prokopchik ( a p p l i c a b l e to pH va lues below 1 2 . 0 ) : C10~ + 2Cu(OH) 2 + H2<3 > C l ~ + 2Cu(OH) 3 (57) 4Cu(OH) 3 >• 4Cu(OH) 2 + ° 2 + H 2 ° ( 5 8 ) (4Cu(OH) 3 + CIO" >• 4Cu(OH) 2 + C10 3 ~ + 2H 20) (59) The o b s e r v a t i o n t h a t exposure of a sma l l surface area o f copper to a h y p o c h l o r i t e s o l u t i o n w i t h minimal a g i t a t i o n , r e s u l t s i n format ion o f c o p p e r 1 1 hydroxide before d e p o s i t i o n o f the b l a c k c o p p e r * 1 1 hydroxide i l l u s t r a t e s s tep ( 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 carbonate accompanying h y p o c h l o r i t e decomposi t ion amounted to about 0.06 g/1 Cu. - 163 - I f the t o t a l surface area of m i n e r a l p resent i s taken to be 33,000 cm 2 fo 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 , then i t can be shown tha t t h i s 60 ppm copper i s s u f f i c i e n t to form a mono-molecular l a y e r cove r ing the e n t i r e surface (Appendix B ) . A n a l y s i s showed tha t the compound made i n the presence o f carbonate 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 1 1 1 carbonate , r a t he r than 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 carbonate p r e sen t . The b l a c k p r e c i p i t a t e observed to be depos i t ed from f i l t e r e d l e a c h s o l u - t i o n s i s the re fo re a copper 1 1" 1" carbonate and i s presumably the same substance which coats the m i n e r a l surface 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 con tac t w i t h m i n e r a l samples. The f a c t t ha t t h i s compound and the t r i - v a l e n t hydroxide apparen t ly c a t a l y z e the decomposi t ion o f hypo- c h l o r i t e a t the same r a t e i s not too s u r p r i s i n g ; but the reason why c h a l c o c i t e , c o v e l l i t e and s y n t h e t i c copper su lph ide s t i l l produce d i f f e r - ent r a t e s o f decomposi t ion a f t e r l o s s o f copper from a carbonate system, when i t i s assumed t ha t the e n t i r e surface i s covered by a C u 1 1 1 ca rbon- ate l a y e r i n each case , i s l e s s o b v i o u s . I t c o u l d w e l l be t ha t c a t a l y s i s 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 sur face and a l though the e n t i r e sur face i s covered by Cu1"'""'", o n l y c e r t a i n areas produce c a t a l y - s i s . Any area i n which adso rp t ion can occur more r e a d i l y than i n o ther sur rounding areas 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 f o r c a t a l y s i s . 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 va lue 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 to 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 compound, 74 d e s c r i b e d as hydra ted C u 2 0 3 - V a r i o u s o the r s tud i e s have shown tha t copper1"1" s a l t s can be o x i d i z e d to the +3 o x i d a t i o n s t a t e i n the presence 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 though most o f t h i s work was c a r r i e d out at - 16 4 - pH l e v e l s g r e a t e r than 9 . 0 . ^ 2 ' ^ ' ^ 2 i n f a c t Prokopchik s p e c i f i c a l l y s t a t e s t ha t t r i - v a l e n t copper compounds cannot be made a t pH l e s s than 11 .5 , and the b l a c k product so ob ta ined i s merely dehydrated c o p p e r 1 1 hydrox ide . The present s tudy would seem to d i spu te t h i s v iew. In t h e i r paper acknowledging the ex i s t ence o f cup r i - ca rbona te ions and the r o l e they 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 e t a l . do not cons ide r the p o s s i b i l i t y tha t a t s u f f i c i e n t l y h igh redox p o t e n t i a l s a t r i - v a l e n t copper - carbonate complex spec ies cou ld e x i s t , r a t he r than the C u 2 ° 3 s o l i d substance shown i n the r e l e v a n t Eh-pH diagrams (F igure 3 ) . I t i s u n l i k e l y t ha t these workers used s u f f i c i e n t l y s t rong 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 , but i t seems p e r f e c t l y reasonable t o assume t h a t a complexing agent f o r c o p p e r 1 1 i s e q u a l l y capable o f h o l d i n g copper^^^ in s o l u t i o n , g iven tha t the aqueous medium has a s u f f i c i e n t l y h igh p o t e n t i a l which the h y p o c h l o r i t e s o l u t i o n does. Equa t ion 55 c o u l d then be m o d i f i e d : CuS + 4NaOCl + 3NaOH + 3HC0 ~ >-3- C u ( C 0 3 ) 3 + N a 2 S 0 4 + 4NaCl + 3H 2 0 (60) The C u 3 + i o n i s not g e n e r a l l y thought o f as be ing s t a b l e i n s o l u - t i o n : i t s h a l f l i f e has been suggested by Magee and Wood^ 3 to be o f the 66 64 65 o rder of 25 seconds. However, L i s t e r , M a l a t e s t a , Malaprode, Berka et a l . ^ and o t h e r s , have a l l shown tha t complexing agents such as t e l l u r a t e s and pe r ioda t e s w i l l s t a b i l i z e copper1"1""1" i n s o l u t i o n . T r i - v a l e n t cuprates are a l s o known to 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 ' but these substances occur on ly a t h igher pH v a l u e s . Due t o i t s re levance t o the presen t s tudy , i t i s i n t e r e s t i n g to note L i s t e r ' s o b s e r v a t i o n tha t any copper present i n s o l u t i o n i n an - 165 - uncomplexed s t a t e , as Cu(OH)^ f o r example, showed c a t a l y t i c a c t i v i t y towards 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 ions to the system prevented any such decompos i t ion . Th i s i s i n l i n e w i t h the o b s e r v a t i o n 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 - carbonate com- p l e x d i d not produce any h y p o c h l o r i t e decompos i t ion , but as soon as any s o l i d m a t e r i a l p r e c i p i t a t e d the decomposi t ion r e a c t i o n was c a t a l y z e d he terogeneous ly . 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 Concen t ra t ion The f a c t t ha t more copper c o u l d e x i s t i n l each ing s o l u t i o n s con- t a i n i n g 7 - 8 g/1 h y p o c h l o r i t e i n the presence o f carbonate , than tha t thermodynamical ly 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 carbonate and no o x i d a n t , suggests t ha t more copper can e x i s t as a C u 1 1 1 complex than f o r the cor responding C u 1 1 complex. Th i s was a l s o i l l u s t r a t e d i n experiments done i n the absence o f h y p o c h l o r i t e (see be low) . The inc rease i n s o l u b l e copper caused by an inc rease i n 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 i s thus a r e l a t e d phenomenon: the presence o f c h l o r i d e i s known to i nc rease the s o l u b i l i t y o f c e r t a i n meta l s a l t s and i n the present study t h i s was found to apply to c a l c i u m i n r e l a t i o n to another p a r t o f the work (Sec t ion 4 . 3 . 4 . 2 ) . I t seems l i k e l y the re fo re t h a t copper i s an analogous case , and t ha t w h i l e carbonate i s the p r i n c i - p a l complexing agent, c h l o r i d e inc reases both 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 longer n u c l e a t i o n time to C u 1 1 1 p r e c i p i t a t i o n . - 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 su lph ide carbonate l e a c h - 2- i n g system showed q u i t e c l e a r l y t ha t l e s s copper e x i s t e d as the CutCO^)^ spec ies than as CuCCO^)^ 3 . I t was a l i t t l e s u r p r i s i n g tha 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 ca rbona te /b ica rbona te , but t h i s i s p robab ly 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 o f the copper d u r i n g a g i t a t i o n . I t i s s i g n i f i c a n t t ha t the d i s s o l v e d copper content o f these 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 to t h a t con ta ined by the l e a c h i n g s o l u t i o n s a f t e r decomposi t ion o f the h y p o c h l o r i t e . I t was a s c e r t a i n e d t h a t a t the h ighe r va lues o f t o t a l carbonate (5.0 g / 1 ; 7.5 g/1 and 10.0 g/1) a second ' p l a t e a u ' l e v e l cor responding to the C u 1 1 carbonate complex e x i s t e d before t h i s a l s o decomposed, l e a v i n g no copper i n s o l u t i o n . At lower va lues o f con ta ined carbonate the 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-s tage" cu rve . The reason why a s m a l l drop i n the copper content 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 observed i n a l l experiments c a r r i e d out i n the presence o f carbonate 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 not known p r e c i s e l y . I t c o u l d be a r e s u l t o f super- s a t u r a t i o n by the very 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 m i n e r a l su r face , n e c e s s i t a t i n g p r e c i p i t a t i o n o f a sma 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 . While i t i s c l e a r t ha t the b l a c k p r e c i p i t a t e put down from hypo- 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 i s an o x i d i z e d form o f the ma lach i t e p r e c i p - i t a t e d from copper*"1" carbonate s o l u t i o n s , the appearance o f e i t h e r substance, 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 - Ismay's hypothes i s t ha t the substance cou ld be a p a r t i a l l y o x i d i z e d su lphur spec ies was d i smissed by showing t ha t the same amount o f copper was d i s s o l v e d i n the presence o f carbonate 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 su lph ide or copper s u l p h a t e . I t i s now c l e a r , however, t ha t copper*'1*"'" was a l s o produced i n t h i s study dur ing 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 , but presumably s m a l l , amount o f carbonate b u f f e r a t pH 9 . 0 , because the curves ob ta ined were ve ry s i m i l a r to 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 c h a l c o c i t e l e a c h i n g . Observat ions made d u r i n g copper su lphate a g i t a t i o n i n carbonate s o l u t i o n s bare a s t rong resemblance t o those i n s i m i l a r 28 31 experiments c a r r i e d out by P i c k e r i n g and Appleby and Lane. These workers found t ha t m i x i n g Na^CO^/NaHCO^ s o l u t i o n s w i t h copper su lphate or copper ace ta te produced a deep b lue s o l u t i o n which subsequent ly p r e c i p i - t a t ed e i t h e r a greeen powder, CuCOH^CO^, or w e l l de f ined b lue c r y s t a l s assumed to 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 observed i n the present work i s almost c e r t a i n l y m a l a c h i t e . Appleby noted t ha t p r e c i p i t a t i o n o f the double s a l t cou ld not be a c c e l e r a t e d by " seed ing , " 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*"''"'" to h y p o c h l o r i t e s o l u t i o n s , o r as ma lach i t e t o copper** carbonate , gave l o s s o f copper and fu r the r p r e c i p i t a t i o n w i t h i n a ve ry shor t t ime . Th i s would seem to conf i rm tha t the observed p r e c i p i t a t i o n can . o n l y occur a f t e r n u c l e a t i o n of a s m a l l amount o f s o l i d has taken p l a c e , and t ha t t h i s i s the slow step o f the p r o c e s s . F i l t e r e d s o l u t i o n s take longer to put down a p r e c i p i t a t e than the cor responding l e a c h i n g s o l u t i o n s i n con tac t w i t h a m i n e r a l because the m i n e r a l surface can p rov ide - 168 - favourable s i t e s on which n u c l e i can form. N u c l e a t i o n g e n e r a l l y occurs when the s u p e r - s a t u r a t i o n o f the separating phase has reached a c e r t a i n va lue such t ha t the a c t i v a t i o n b a r r i e r has been surmounted. The free energy o f format ion o f a nucleus c o n s i s t s o f two terms: 3 A G . = ~ V° M I n - + 4T7r Z : 3V a 0 where a / a o i s the c o n c e n t r a t i o n r a t i o or degree o f s u p e r s a t u r a t i o n V = molecu la r volume 3 = i h t e r f a c i a l energy r = r ad ius The second term represents the work necessary t o c rea te a new su r f ace , i . e . f o r the format ion o f a new phase, w h i l e the f i r s t takes account o f the energy i n v o l v e d i n making new bonds. Th i s assumes the n u c l e i to be s p h e r i c a l . As the degree o f supe r sa tu r a t i on i n c r e a s e s , then AG_. w i l l decrease , and t h i s u s u a l l y r e s u l t s i n sma l l e r n u c l e i forming by a decrease i n r a d i u s , r . The term d e s c r i b i n g the r a t e o f format ion o f c r y s t a l n u c l e i , J , can be expressed: A G_ J = A - — a -exp kT where A represents the e f f i c i e n c y o f i o n i c o r molecu la r c o l l i s i o n s . Homogeneous n u c l e a t i o n i s a ve ry slow process which r a r e l y occurs 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 ac t as ' c a t a l y s t s ' fo r n u c l e a t i o n - 169 - by reduc ing the energy b a r r i e r presented by AG, thus i n d u c i n g heterogen- 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 fo r n u c l e a t i o n may be def ined by the express ion k = t c * " - 1 * where n = number o f ions r e q u i r e d t o form a c l u s t e r o f c r i t i c a l s i z e c = c o n c e n t r a t i o n o f s o l u t i o n 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 i n c o r p o r - a t i o n o f f o r e i g n p a r t i c l e s i n t o a n u c l e a t i o n s i t e . 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 presence o f v a r y i n g amounts o f carbonate under o therwise i d e n t i c a l c o n d i t i o n s , f o l l o w s an almost l i n e a r r e l a t i o n - sh ip w i t h carbonate c o n c e n t r a t i o n . 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 1 1 1 has occur red l e a v i n g a s o l u t i o n c o n t a i n i n g a copper* 1 - carbonate 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 o f ma lach i t e a f t e r another i n d u c t i o n p e r i o d fo r the n u c l e a t i o n o f copper** c r y s t a l s . A p p l e b y ' s sugges t ion t ha t de layed p r e c i p i t a t i o n occurs due t o a very slow ra t e o f c r y s t a l l i z a - 31 t i o n , thus appears t o be reasonab le . H i s o b s e r v a t i o n tha 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 3 ) 2 , may be an i n d i c a t i o n tha t s o l u t i o n s decomposing to g i v e m a l a c h i t e , Cu(OH) (CO^) , are more supe r - sa tu ra t ed . The reason f o r the 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 (Sec t ion 3 . 1 . 1 ) , i s p robably p r e c i p i t a t i o n o f XXX 28 some copper p r i o r to a n a l y s i s . P i c k e r i n g noted tha t excess water c o u l d induce p r e c i p i t a t i o n o f the s o l i d compound. 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 turned 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 the re fo re i n d i c a t e a lower copper con- t en t than was a c t u a l l y present on i n i t i a l removal o f the sample. 4 . 2 . 1 A n a l y s i s o f C o p p e r 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 to c a r r y out any meaningful 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 by the a c t i o n o f sodium hypo- c h l o r i t e on copper1"1" s a l t s a t pH 9 . 0 . The b l a c k compound so formed was assumed to be the same as t ha 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 , which he subsequently complexed w i t h pe r ioda t e or t e l l u r a t e t o g ive a t r i - v a l e n t copper s a l t . He presumedthe i n i t i a l m a t e r i a l was a copper"'""'""1" h y d r o x i d e . S i m i l a r l y i n the p resen t study the gas evolved 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 taken to 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 Cu1""''"" v C u * 1 : 2Cu(OH) 3 + 4HC1 y 2 C u C l 2 + 5 ^ 0 + ho^ 3+ - 2+ Cu + e > Cu (61) The presence 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 of a mercury column. Compounds made i n the absence o f carbonate d i d not c o n t a i n carbon d i o x i d e . - 171 - The r e s u l t s c o n s i s t e n t l y showed, however, t ha t i n s u f f i c i e n t oxygen was presen t f o r the b l a c k powder to 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 ha t 25 - 30% a v a i l a b l e oxygen e x i s t e d . Whi le the percentage of copper1"'""'" d i d i nc rease s l i g h t l y w i t h pH, there was no s i g n i f i c a n t change i n appearance o f the compound when prepared 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 ther 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^, occurs as a red compound, and t ha t i t s format ion i s c a t a l y z e d by the presence o f barium and ca l c ium i o n s . In the present s tudy, a d d i t i o n o f these ions to s o l u t i o n s con- 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 t o the f i n a l p roduc t , and no red m a t e r i a l was ever de t ec t ed . I t i s t he re fo re proposed t ha t the b l a c k compound produced i s a mixed copper ox ide or 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 a c t u a l l y r e p r e - sen t ing the m a j o r i t y . The f a c t tha t i t i s b l a c k would support t h i s 72 v i ew: t h i s i s a c h a r a c t e r i s t i c o f mixed o x i d e s . Delhez a l s o r epor ted o b t a i n i n g a mix ture o f copper""""1""1" and copper 1"'", w i t h the t r i - v a l e n t s t a t e aga in amounting to no more than 30% o f the t o t a l , but h i s compound was e x c l u s i v e l y r e d . I t should be noted however t ha t he was u s i n g s o l u t i o n s s i g n i f i c a n t l y more concent ra ted i n h y p o c h l o r i t e than 0.1 M, a t a h ighe r pH l e v e l and w i t h a g rea te r i o n i c s t r eng th than i n t h i s case . I t i s q u i t e l i k e l y t ha t he ob ta ined a mix ture o f the two d i f f e r e n t o x i d e s : 30% C u 2 ° 3 + 70% CuO which appeared r e d , w h i l e the b l a c k compound des- c r i b e d here i s a c t u a l l y a mixed va lence s t a t e compound c o n s i s t i n g o f Cu^O^ and CuO toge the r . Assuming a mix ture o f 75% copper"'""'" and 25% I I I 2+ 3+ copper the r a t i o Cu :Cu would be 3 : 1 . - 172 - Cu-O, + 3CuO "-Cu^Cv (62) 2 3 3 6 Th i s g ive s a compound having an o x i d a t i o n s t a t e o f 2 . 4 . By fu r the r analogy w i t h D e l h e z ' s work, and from the r e s u l t s ob ta ined by i n f r a - r e d spectrophotometry, i t appears t ha t the compound f l u c t u a t e s between an ox ide and a hyd rox ide . Thus i t c o u l d c o n s i s t of Cu(OH) 3 and Cu(OH) 2 g i v i n g a compound such as Cu^(OH) w i t h an o x i d a t i o n s t a t e o f 2 . 5 . T h i s would have a copper content o f about 60% which f i t s the exper imenta 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 fu r t he r confirmed tha t the compound i s o n l y p a r t i a l l y C u 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 to be c u p r i c o x i d e . No r epor t ed X - r a y d i f f r a c t i o n data fo r copper1"'""'" compounds was found. I t i s p o s s i b l e t h a t C u 2 ° 3 1 S amorphous, i n which case no d i f f r a c t i o n peaks would be de t ec t ed . 4 . 2 . 2 P r e c i p i t a t i o n o f copper 1 1" 1" i n the presence o f carbonate X - r a y t e s t s c a r r i e d out 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 carbonate s o l u t i o n s showed peaks cor responding to both ma lach i t e and c u p r i c o x i d e , con f i rming i t to be a mix ture o f a carbonate and an o x i d e . There were a l s o some u n i d e n t i f i e d peaks which cou ld represent the d i f f e r e n c e between Cu1""" carbonate and the Cu""*"'"'"" s a l t . I n f r a - r e d s t u d i e s and l imewater t e s t s suggested fu r t he r t ha t t h i s compound was a t l e a s t p a r t i a l l y a carbonate . The n u c l e a t i o n t imes i n v o l v e d i n i t s p r e p a r a t i o n are not l i n e a r w i t h respec t to carbonate c o n c e n t r a t i o n s . The c o n d i t i o n s o f temperature, a g i t a i t o n e t c . were not mainta ined p e r f e c t l y cons tant d u r i n g p r e p a r a t i o n o f each sample however, as they were i n the l e a c h i n g exper iments . I t was again shown tha t ' s e e d i n g ' would induce p r e c i p i t a t i o n o f the compound. Both o x i d e / h y d r o x i d e and carbonate samples were found to c a t a l y z e the h y p o c h l o r i t e decomposi t ion r e a c t i o n a t approximate ly the same r a t e , when added i n equal amounts to a 0.1 M s o l u t i o n . This i s to be expected, because both compounds c o n t a i n approximate ly the same amount o f copper 1 1" 1", and i t has been shown by L i s t e r , - 3 ^ P r o k o p c h i k ^ 4 and D e l h e z ^ 2 t ha t Cu"""1""" i s the a c t i v e c a t a l y s t f o r decompos i t ion . When none i s present i n i t i a l l y o x i d a t i o n o f Cu""""1" must take p l a c e before the r e a c t i o n o c c u r s , thereby 2+ 3+ s e t t i n g up a Cu / C u o x i d a t i o n - r e d u c t i o n c y c l e . Th i s i s presumably why c u p r i c ox ide showed a s lower r a t e o f decomposi t ion under i d e n t i c a l c o n d i t i o n s . 4.3 Sodium H y p o c h l o r i t e Leaching o f Molybden i t e , MoS,, Leaching molybdeni te 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 a t 2- . pH 9.0 d i d not i n i t i a l l y y i e l d 100% molybdenum as MoO^ i n s o l u t i o n . Examinat ion o f l e a c h re s idues r evea l ed the presence o f i r o n , copper, z i n c and s i l i c a , as w e l l as l e a d molybdate which i s i n s o l u b l e . Thus the assumption o f 100% MoS^ was a f a l s e one, and spec t ro scop i c a n a l y s i s o f unleached samples r evea l ed a t l e a s t a 3% i m p u r i t y con ten 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 i n excess o f 97%, con f i rming Ismay's f i n d i n g s t h a t molybdeni te leaches r a p i d l y and comple te ly a t pH 9 .0 , 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 0.1 M OC1 . H y p o c h l o r i t e consumption was found to correspond to the - 174 - p r e v i o u s l y r epor ted s t o i c h i o m e t r i c MoS 2 + 9NaOCl + 6NaOH : —* Na 2 Mo0 4 + 9NaCl + 2Na 2 S0 4 + 3H 2 0 (63) 4 . 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 molybdeni te and copper su lph ide mine ra l s a t pH 9.0 I t has a l r eady been r epor t ed i n con junc t ion w i t h the l e a c h i n g behaviour o f copper su lph ide m i n e r a l s , t ha t carbonate 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 bes ides tha t o f a b u f f e r i n g reagent . In a d d i t i o n to a c t i n g as a complexing 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 to a f f e c t molybdenum e x t r a c t i o n . When excluded from the system, the l e v e l o f molybdenum e x t r a c t i o n dropped from 98% to o n l y 76 - 84%. The a c t u a l depress ion was a f u n c t i o n o f the p a r t i c u l a r m i n e r a l be ing l eached . I t was p o s t u l a t e d t ha t copper molybdate compounds were i n t e r f e r i n g w i t h molybdenum e x t r a c t i o n , but i t was r a t h e r s u r p r i s i n g tha t the case i n which no copper was present i n s o l u t i o n showed the g rea te s t molybdenum l o s s . O x i d a t i o n o f molybdeni te i n the presence o f CuS0 4 s o l u t i o n suggest- ed fu r t he r t ha 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 not 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 which no copper had been d i s s o l v e d . 4 . 3 . 2 Leaching o f molybdeni te and copper su lph ides a t pH 5.5 Experiments were c a r r i e d out i n a c i d i c s o l u t i o n s to see i f an - 175 - - 176 - improved molybdenum y i e l d cou ld be ob t a ined , 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 . -2 Copper e x i s t s i n s o l u t i o n to a maximum c o n c e n t r a t i o n o f 10 M 2+ as the Cu i o n a t pH 5 . 5 . T h i s f a c t proved very d e t r i m e n t a l to molyb- 2+ denum e x t r a c t i o n . Cu ions can combine w i t h the molybdate spec ies 2- MoO^ 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 su lph ide m i n e r a l can be i n t e r p r e t e d as p r e c i p i t a t i o n o f t h i s molybdate s a l t . The presence o r o therwise o f carbonates 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 tha t had been observed i n a l k a l i n e s o l u t i o n s . The o n l y de t ec t ab l e d i f f e r e n c e between a carbonate and non-carbonate l e a c h i n the experiments a t pH 5.5 was a s l i g h t l y h ighe r copper content i n the former case . The f a c t tha t such a s m a l l i nc rease i n pH, a va lue of 6 . 0 , r e s u l t e d i n the carbonate be ing ab le to suppress format ion o f copper molybdate, 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 iven by De Zoubov e t a l . showing the ex i s t ence o f the s t a b l e copper carbonate compounds and complex ions fo r the Cu-H^O-CO^ system (Figure 3 ) . The Cu(C0 3 ) aq . molecule e x i s t s as a s o l u b l e spec ies a t pH l e v e l s between 5.0 and 7.0 dependent on the t o t a l carbonate content o f the s o l u t i o n . At the l e v e l used here (10 g/1 HCO^ E 1.6 x 10 1 M t c 0 3 ] T ) i t i s s t a b l e a t pH va lues 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 (Figure 51 ) . Thus 2+ l e a c h i n g a t pH 5.5 puts copper a t the s t a b i l i t y boundary between Cu / CujCO^) aq . The exper imenta l r e s u l t s i n d i c a t e d tha t copper i s o n l y com- p lexed by carbonate to a very s m a l l degree, shown by the sma l l i nc r ea se i n d i s s o l v e d copper, and tha 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 to prevent - 177 - copper molybdate fo rma t ion . An inc rease i n pH to 6.0 puts copper i n t o the r e g i o n where Cu(CC>3) aq . i s s t a b l e i n s o l u t i o n , thereby p reven t ing a r e a c t i o n w i t h the molybdate. Leaching i n the absence of carbonate , 2+ 2- however, enables Cu and MoO^ to combine as b e f o r e . The observed r a p i d decomposi t ion o f the h y p o c h l o r i t e was presumed to be caused by copper molybdate c a t a l y s i s , sugges t ing again t ha 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 excess h y p o c h l o r i t e decomposi t ion was observed. 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 decreases to 1.6 x 10 M. Th i s i s s t i l l s u f f i c i e n t to g ive a 60% l o s s o f the molybdenum, coupled w i t h an even g rea te 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 which h y p o c h l o r i t e most r e a d i l y decomposes to c h l o r a t e . These f i n d i n g s would seem to ques t i on 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 process 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 con junc t ion w i t h t h i s i n v e s t i - g a t i o n t ha t a minimum of copper s o l u b i l i t y occurs a t pH 7.0 i s i n i t s e l f a l i t t l e dubious s ince t h i s i s shown to occur f o r CuO and Cu(0H) 2 a t a 73 va lue o f 9 . 0 , and i s not g r e a t l y mod i f i ed by the presence o f c h l o r i d e s . Secondly , 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 Cu(OH) 2 C0 3 or CuC^CO^ which Scheiner e t a l . c l a i m as be ing r e s p o n s i b l e for 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 cupr i - ca rbona te 2- i o n , C u ( C 0 3 ) 2 appears to be the o n l y spec ies which can impart s i g n i f i c a n t s o l u b i l i t y to copper a t pH va lues above 9 . 0 . Scheiner mentions the compound copper molybdate as be ing 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 epo 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 , but does not appear to have s tud ied the c o n d i t i o n s fo r i t s fo rma t ion . In t h i s e l e c t r o o x i d a t i o n process the pH i s a l lowed to r i s e du r ing l e a c h i n g by the a d d i t i o n o f sodium carbonate on a semi-cont inuous b a s i s . In the l i g h t o f present f i n d i n g s any copper molybdate which d i d form, would be i n the i n i t i a l s tages o f a run 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 the U . S . Bureau o f Mines s tudy , however, i s the f a c t t ha t c h a l c o p y r i t e i s unaf fec ted by h y p o c h l o r i t e , but t h a t c h a l c o c i t e i s o x i d i z e d to a c e r t a i n ex ten t g i v i n g s o l u b l e copper compounds which are capable o f combining w i t h the molybdate i ons to form i n s o l u b l e copper molybdate. In the p resen t study no d i f f e r e n c e i n the l e a c h i n g behaviour of the d i f - f e ren t copper su lph ide mine ra l s exposed to h y p o c h l o r i t e s o l u t i o n s has been de tec t ed , except 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 decompos i t ion . Furthermore, and i n c o n t r a s t t o S c h e i n e r ' s s tatement, i t i s i n the presence o f the s o l u b l e copper compound C u ( C 0 3 ) 2 aq . t ha t copper molybdate format ion 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 carbonate o r a t pH <6.0 can a r e a c t i o n w i t h molybdate ions occu r . T h i s should h o l d t rue f o r any copper m i n e r a l i n t roduced i n t o the 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 concent ra tes 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 presence o f carbonate , and i n a l i m i t e d pH r e g i o n o f =6.0 - 7 . 5 . T h i s would not g ive any improve- ment i n molybdenum s e l e c t i v i t y over t ha t a t pH 9.0 i n the presence o f carbonate , and would have the added disadvantage o f p roduc ing l a r g e amounts of sodium c h l o r a t e . Ba r r and coworkers have shown tha t t h i s represents 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 process and t ha t - 179 - i t a l s o i n t e r f e r e s w i t h subsequent molybdenum recove ry . ' T h e i r sugges t ion o f l e a c h i n g a t pH va lues o f 4 .0 - 5.0 to overcome the c h l o r a t e problem, i s h a r d l y p r a c t i c a l on account o f the s t a b i l i t y o f copper molyb- date i n . t h i s r e g i o n . 4 .3 .3 Copper molybdate The s imple molybdate, CuMoO^, i s not w e l l documented i n the l i t e r a t u r e . I t i s known to be i n s o l u b l e , i n common w i t h most o ther 82 t r a n s i t i o n meta l molybdate s a l t s . Zel ikman quotes t h i s s o l u b i l i t y as 0.017 M which i s s l i g h t l y h ighe r than t ha t found i n the present work o f 0.00783 M. X - r a y data fo r a number o f copper molybdate spec ies has been pub- l i s h e d . The one cor responding c l o s e l y to d i f f r a c t i o n pa t t e rn s ob ta ined i n t h i s study (Table 8 ) , i s the hydrated spec ies Cu 3 (MoO^) 2 (OH) 2 which occurs i n nature as the m i n e r a l L i n d g r e n i t e . Data f o r o ther :copper molybdates are shown i n Table 10: Species dA (1) dA (2) dA (3) CuMoO,, 4 3.72 3.36 2.71 CuMoO. 4 3.05 3.30 3.53 Cu 2 Mo0 5 3.54 3.45 3.32 C u 3 M o 2 ° 9 3.44 2.63 3.39 C U 4 - x M O 3 0 1 2 3.42 3.31 2.65 C U 4 - x M ° 3 ° 1 2 3.42 2.64 2.76 C U 6 M ° 4 ° 1 5 3.38 2.89 2.63 ( T h i s study 3.52 4.20 2.53 ) ( C u 3 ( M o 0 4 ) 2 ( O H ) 2 3.50 4.15 2.67 ) Table 10: S t ronges t X - r a y Peaks fo r Va r ious Copper Molybdate Species - 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 decomposi t ion 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 confirmed by a g i t a t i n g copper 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 . Th i s i s a fu r the r reason fo r p reven t ing ' i n - s i t u ' format ion o f the compound even i n s m a l l amounts du r ing molybdeni te l e a c h i n g . An Eh-pH diagram f o r the Cu-H^O-MoO^ system was cons t ruc t ed to conf i rm the 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 - i t e s o l u t i o n s . In F i g u r e 52 the s o l i d spec ies cons idered are Cu, C ^ O , CuO, CuMo0 4 and C u 2 0 3 , and i n F i g u r e 53, Cu, C u 2 0 , Cu(OH) 2 , CuMo0 4 and C u 2 0 3 . In both diagrams the d i s s o l v e d spec ies have been taken as C u + , 2+ 3+ — 2— 2— — Cu , Cu , Cu0 2 H , Cu0 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 substances when the a c t i v i t i e s o f copper con- t a i n i n g ions i n s o l u t i o n are 10 ^ M, and o f molybdenum spec ies are 10 1 M. C o n s i d e r i n g the s o l i d spec ies to be o x i d e s , F igu re 52 shows tha 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 to 8 .65 , 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 to 2.4 V . Thus a t pH 9.0 there should be no i n t e r f e r e n c e w i t h molybdenum e x t r a c t i o n from CuMo0 4 forma- t i o n . An inc rease i n copper c o n c e n t r a t i o n would decrease the pH l i m i t f o r CuMo0 4 s t a b i l i t y , w h i l e decreas ing molybdenum a c t i v i t y would inc rease i t (and v i c e v e r s a ) . In F i g u r e 53, i n which the hydroxides are shown as the s t a b l e 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 to a pH va lue o f 9 .18 . As the hydroxide i s the meta-s tab le 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 tha t CuMo0 4 format ion cou ld pose a problem to a l e a c h a t pH 9 . 0 . I t a l s o shows c l e a r l y why a molybdeni te - copper su lph ide l e a c h would not be f e a s i b l e - 181 - Figure 52: Eh-pH diagram for the system Cu-H20 - M o0 4 (oxide species). (Activities of copper ions 10 _ 6M and acti v i t i e s of molybdenum ions 10 _ 1M). \ - 182 - Figure 53:. Eh-pH diagram for the system Cu-H20 - M Q O ^ (hydroxide system). (Activities of copper ions 10~ 6 M and ac t i v i t i e s of molybdenum ions 1 0 _ 1 M ) . - 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 ha t copper format ion would not be encountered i n a c i d s o l u t i o n s due t o the h ighe r redox po ten- t i a l o f the +3 s t a t e . Al though copper molybdate c o u l d the re fo re e x i s t a t pH 9.0 from a thermodynamic p o i n t o f v i ew , the 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 carbonate , together w i t h r e s u l t s ob ta ined from l e a c h i n g w i t h s y n t h e t i c copper su lph ides and a t pH 10.0 (Sec t ion 3 . 3 . 4 ) , confirmed t h a t copper i t s e l f was not the p r i n c i p a l cause o f poor molybdenum recovery a t t h i s pH v a l u e . In a d d i t i o n t o t h i s , ag ing 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 to 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 ) 2 , and the f a c t tha t some molybdenum dropped out o f s o l u t i o n i n i t i a l l y but reappeared on s tand ing or 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 to which copper su lphate 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 Cu(OH) 2 . 4 .3 .4 S o l u b i l i t y o f c a l c i u m i n h y p o c h l o r i t e s o l u t i o n s A combinat ion o f these v a r i o u s f a c t o r s brought to l i g h t the f a c t t h a t o the r elements , con ta ined i n the copper su lph ide mine ra l s under s tudy as i m p u r i t i e s , c o u l d be capable o f forming i n s o l u b l e molybdates and thus 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 which one o r more elements were r e s p o n s i b l e i n the present case , as w e l l as to determine i f any o ther 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 the r ore samples, the f o l l o w i n g f a c t o r s were taken i n t o c o n s i d e r a t i o n : 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 spec ies which i s thermodynamical ly s t a b l e a t pH 9 . 0 . i i ) whether h y p o c h l o r i t e o x i d a t i o n leads to the 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 . i i i ) whether the element i s l i k e l y to 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 the r eg ions o f s t a b i l i t y o f the s imple molybdates o f elements known to be con ta ined i n the copper su lph ide mine ra l s under s tudy, Eh-pH diagrams were cons t ruc ted f o r the f o l l o w i n g systems: Ca -H 2 0-Mo0 4 F e - H 2 0 - M o 0 4 "Pb-H 2 0-Mo0 4 Cd-H 0-MoO„ 2 4 Zn-H 2 0-Mo0 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 taken as 10 ^ M i n a l l cases , and t ha t o f the meta l c o n t a i n i n g -6 -4 spec ies i s {10 } except fo r l e a d , where {10 } was found to more appro- p r i a t e . F i g u r e 54: c a l c i u m molybdate: The diagram drawn up f o r c a l c i u m 2+ spec ies and t h e i r i n t e r a c t i o n w i t h molybdate, shows t ha t the Ca i o n 2+ has a much l a r g e r zone o f s t a b i l i t y than the cor responding r e g i o n f o r Cu 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 spec ies CaO, c a l c i u m molybdate i s s t a b l e up to a pH o f 19.14, w h i l e for the hydroxide system the molybdate would extend to 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 value 2- o f 14.2 before d i s s o l u t i o n i n t o p lumbi te i o n s , HPbO^ , o c c u r s . 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 pH, to 2.0 V a t pH 0. Thus a t a va lue o f 9 . 0 , the p o t e n t i a l a t which PbMoO^ decomposes to g ive PbO^ i s 0.92 V and t h i s molybdate should not be s t a 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 w i t h a p r e d i c t e d va lue of 1.2 V below pH va lues 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 which 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 than 0.4 V and up t o a pH va lue o f 1 8 . 6 . The w h i t e , amorphous z i n c hydroxide was cons idered as the s t a b l e ox ide phase i n s e t t i n g up the diagram, and i t i s apparent t h a t the molybdate i s more s t a b l e thermo- 2+ - 2 - dynamica l l y than Zn , Zn(OH) 2 , HZnC>2 and ZnC>2 u n t i l d i s s o l u t i o n o f t h i s f i n a l spec ies occurs a t pH 1 8 . 0 . F i g u r e 57: i r o n molybdate: I ron i s o f major i n t e r e s t w i t h respec t to i t s i n t e r a c t i o n w i t h molybdate, be ing present 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 , Cu^FeS^, as w e l l as a common i m p u r i t y i n c h a l c o c i t e and c o v e l l i t e . I t i s u n l i k e l y however tha t f e r rous i r o n 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 , thus FeMoO^ should not pose a problem. Th i s i s confirmed i n the Eh-pH diagram; FeMoO^ i s s t a b l e up to a pH o f 10 .8 , but the maximum p o t e n t i a l i t can w i th s t and i s 1.2 V , a t pH 2 . 4 , and a t pH 9.0 decomposi t ion t o F e ( 0 H ) 3 would occur a t l e s s than 0.5 V . 92 Zel ikman mentions theex is tence o f a f e r r i c molybdate compound, Figure 55: Eh-pH diagram for the system Pb-H„0-MoO^ (Activities of lead ions 10~^M, act i v i t i e s of molybdenum ions 10_^M). PH Figure 56: Eh-pH diagram for the system Zn-Ĥ O-MoÔ . (Activities of zinc ions 10~^M, and activities of molybdenum ions ^ Q - I J M ) • ' Figure 57: Eh-pH diagram for the system Fe-H„0 MoÔ  (Activities of ferr i c and ferrous ions 10"%, ana ac t i v i t i e s of molybdenum ions 10 _ 1M). - 19 0 - Fe^(MoO^) and notes 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 c e r t a i n c o n d i t i o n s . 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 q u i t e commonly found i n nature but i s not a source o f molybdenum m e t a l . No thermodynamic data fo r such an i r on 1 1 " ' " molybdate compound c o u l d be found and i t has not been i n c l u d e d i n the Eh-pH diagram shown. F i g u r e 58: cadmium molybdate: Cadmium and z i n c have s e v e r a l chemica l s i m i l a r i t i e s and are found i n c l o s e a s s o c i a t i o n i n many ore b o d i e s . The present 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 molybdates form under s i m i l a r c o n d i t i o n s : 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 ions 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 molybdeni te l e a c h i n g . 2- The s t a b i l i t y boundary between the s imple molybdate i o n MoO^ and polymolybdate s p e c i e s , de sc r i bed as HMoO^ , occurs a t pH 6 . 0 . Above t h i s v a l u e , combinat ion w i t h meta l c a t i o n s 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 imple 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 t i s p o s s i b l e t ha t a complex molybdate spec ies w i l l form the s t a b l e s p e c i e s . 2 - On the o the 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^ i n e q u i l i b r i u m w i t h HMoO^ , a s imple molybdate may s t i l l p r e c i p i t a t e . Exper imenta l r e s u l t s fo r molybdeni te - copper su lph ide l e a c h i n g c a r r i e d out a t pH 5.5 suggests 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 format ion o f the s imple molybdate CuMoO^. The exact nature o f molyb- denum spec ies a t low pH va lues i s not known. MoO^ i s the s t a b l e spec ies a t h igher p o t e n t i a l s below pH 3 .0 . MoC>2 p r e c i p i t a t e s a t a p o t e n t i a l o f 0.4 V (pH 0 . 0 ) , dec reas ing to -0 .1 V at pH 6.0 and -0 .55 a t pH 1 0 . 0 . Between these two spec ies molybdenum probab ly e x i s t s i n the +5 o x i d a t i o n 9 s t a t e . - 191 - Figure 58: Eh-pH diagram for the system Cd-Ĥ O-MoÔ . (Activities of cadmium ions 10~^M and act i v i t i e s of molybdenum ions 10_1M) - 19 2 - In con junc t ion .with these 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 molybdates, the f o l l o w i n g data was accumulated f o r the s o l u b i l i t y o f a number of molybdate compounds: Compound S o l u b i l i t y (g Mo0 4 /1) Source PbMo0 4 1.2 x l o " 6 83 SrMoCK 4 3.0 x l o " 4 83 CaMoO„ 4 a) 5.0 x 1 0 ~ 4 ; b) 1.3 x 10~ 3 a) 83; b) 82 BaMo0 4 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 Ag 2 Mo0 4 3.86 x 10 3 83 ZnMoO. 4 a) 3.70 x 10 ; b) 5.0 x 10  2 a) 82; b) 83 Of the above elements bar ium, s t ron t ium and s i l v e r were not con- s i d e r e d because i t was not f e l t they would be present 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 to cause molybdenum l o s s e s . From the remainder i t appears from the Eh-pH diagrams tha t l e a d and i r o n are both 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 cus sed above. Th i s was borne out e x p e r i m e n t a l l y : samples o f ga l ena , PbS and p y r i t e , F e S 2 were leached 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 copper / molybdenum mine ra l s and no l e a d o r i r o n whatsoever was de tec ted i n s o l u t i o n . Copper molybdate can be de sc r i bed as a b o r d e r l i n e case w i t h respec t - 193 - to l e a c h i n g a t pH 9.0 s ince the thermodynamic boundary occurs a t pH 8.65 fo r the oxide and 9.2 f o r the hydroxide ' ; but the f a c t t ha t both these s a l t s are i n s o l u b l e should prevent any molybdate fo rma t ion . As noted p r e v i o u s l y , the presence o f carbonate imparts a c e r t a i n degree o f s o l u b i l i t y to copper i n a l k a l i n e s o l u t i o n , and exper imenta l r e s u l t s suggested tha t a copper - carbonate a s s o c i a t i o n occur red i n preference to CuMoO^ fo rma t ion . The r e l e v a n t e q u i l i b r i a a r e : C u 2 + + 2 C 0 3 2 ~ v==^ C u ( C 0 3 ) 2 2 ~ l o g k = 9.83 2+ 2- Cu + Mo0 4 v = ^ CuMo0 4 l o g k = -2.027 I t was observed , however, t ha t l e a c h i n g i n the presence o f s m a l l amounts o f carbonate d i d r e s u l t i n some copper molybdate format ion (Sec t ion 3 . 3 . 4 . 3 ) , sugges t ing t ha t l e s s carbonate produced a weaker C u - C 0 3 bond. Z i n c , cadmium and c a l c i u m are a l l undes i r ab 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 spec ies a t pH 2- 9.0 and hence t o combine w i t h Mo0 4 and p r e c i p i t a t e . I t has been shown tha 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 fo 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 . However, i t i s not l i k e l y t ha t e i t h e r z i n c or cadmium would be present i n more than t r ace amounts i n most copper - molybdenum ore bod ie s , and a n a l y s i s c e r t a i n l y showed tha t i n s u f f i c i e n t amounts were presen t to account 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 exper iments . By a process 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 above f a c t o r s i t was concluded tha t c a l c i u m was the element p r i m a r i l y respons- i b l e f o r the observed poor molybdenum r e c o v e r i e s . Th i s would r e a d i l y - 19.4 - e x p l a i n the l o s s o f molybdenum from combined copper su lph ide molybdeni te experiments i n the absence o f carbonate . Ca lc ium was present as an i m p u r i - t y i n a l l th ree m i n e r a l samples used; i t can e x i s t as a s o l u b l e spec ies a t pH 9 . 0 , and has a ve ry i n s o l u b l e molybdate s a l t . In the presence o f carbonate , 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 . The f a c t tha t copper i s a l s o d i s s o l v e d i n the l a t t e r case i s c o i n c i d e n t a l . 2+ 2 - ^ Ca + MoO. l o g k = -7 .38 4 S 2+ 2 — Ca + CO., l o g k = -8 .55 3 S 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 to g ive 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 molybdenite and c a l c i u m c h l o r i d e , except i n the presence o f carbonate bu f fe 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 presence o f carbonate and copper su lph ide mine ra l s was s l i g h t l y below the l e v e l s ob ta ined f o r l e a c h i n g molybdeni te a lone , 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 f o l l o w i n g f a c t o r s : i ) format ion o f s m a l l amounts o f copper molybdate, even i n 2- the presence o f s o l u b l e Cu(C0. j ) 2 , i i ) 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 carbonate , i i i ) s l i g h t s o l u b i l i t y o f CaCO^ due t o the presence o f c h l o r i d e , enab l i ng CaMoO^ to form i n sma 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 unfavour- ab le f o r an a l k a l i n e l e a c h i n g process i n which the p o t e n t i a l feed m a t e r i a l i s a copper - rougher concen t ra te , which would unavoidably con t a in 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 the copper - molybdenum - 195 - meta l v a l u e s . The problems o f such gangue m a t e r i a l s be ing 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 capable o f forming i n s o l u b l e molybdates would pose an even g rea te r t h r e a t to an ' i n - s i t u ' l e a c h i n g process where good s e l e c - t i v i t y o f meta l va lues i s a n e c e s s i t y . I t i s i n t e r e s t i n g to note Bhappu's comments i n t h i s r e s p e c t : he s t a t e s t ha t e i t h e r a b a s i c carbonate - 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 capable o f d i s s o l v i n g molybdenum from mixed su lph ide - ox ide o r e s , but t ha t an a l k a l i l e a c h would be p r e f e r a b l e 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 to 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 presence o f carbonate to suppress molybdate format ion 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 mine ra l s l i k e l y to be a s s o c i a t e d w i t h copper - molybdenum porphyry ores were cons idered to be c a l c i t e and gypsum, and a b r i e f rev iew o f the geology o f porphyry type depos i t s confirmed t h i s : C h a l c o p y r i t e , molybdenite and p y r i t e are the most commonly o c c u r r i n g mine ra l s i n such ore b o d i e s . Other su lph ides found i n a s s o c i a t i o n w i t h these three i n c l u d e b o r n i t e , c h a l c o c i t e , ga l ena , s p h a l e r i t e , c o v e l l i t e , 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 . The most abundant gangue m a t e r i a l i s quar tz but magnet i te , t ou rma l ine , hemati te and f l u o r i t e are a l s o common. 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 quar tz or tourmal ine d i s t r i b u t i o n s . In most ore depos i t s they occur i n the youngest rocks p re sen t , and represent l a t e stage v e i n i n g which i s the re fo re u s u a l l y p o s t - o r e . C a l c i t e , together w i t h z e o l i t e can in te rg row w i t h the su lph ide mine ra l s and i s a l s o found, w i t h gypsum i n v e i n s and f r ac tu re f i l l i n g s i n the q u a r t z . F ib rous gypsum can a l s o be p resen t as vugs i n the main l a t e stage qua r t z - su lph ide 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 - va ry c o n s i d e r a b l y between d i f f e r e n t ore b o d i e s . In some cases both metals are con ta ined w i t h i n the c e n t r a l core o f a d e p o s i t , w h i l e i n o thers the copper e s p e c i a l l y i s found i n the ou te r zones, and the re fo re i n a s s o c i a - t i o n w i t h q u a r t z , s e r i c i t e , p y r i t e e t c . The molybdeni te i s o f t en unsystem- a t i c a l l y d i s t r i b u t e d throughout the ore body and can c ross cut the areas i n which c a l c i t e and gypsum are found. Of the molybdenum-bearing porphyry copper ores mined i n B r i t i s h Columbia, depos i t s a t Bethlehem Copper, Lornex , V a l l e y Copper, Ox Lake, Brenda and the ' J . A . ' ore body are a l l known to c o n t a i n c a l c i t e and/or gypsum i n c l o s e p r o x i m i t y t o the metal s u l p h i d e s . In the s o - c a l l e d 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 mine ra l s are l e s s common, but i n the Boss Mountain depos 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 quar tz and c l a y mine ra l s con ta ined i n the ore b o d i e s . 4 4 . 3 . 4 . 1 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 mine ra l s Having e s t a b l i s h e d t ha t c a l c i t e and gypsum are l i k e l y gangue mater- i a l s i n low grade copper-molybdenum o r e s , experiments were c a r r i e d out i n which samples o f these mine ra l s were leached i n h y p o c h l o r i t e s o l u t i o n s under i d e n t i c a l c o n d i t i o n s t o those used f o r molybdeni te . 2+ I t was confirmed tha t both mine ra l s y i e l d Ca i n s o l u t i o n i n the presence o f h y p o c h l o r i t e , and t ha t the amounts e x t r a c t e d were s u f f i c i e n t to account f o r the observed molybdenum l o s s e s du r ing copper su lph ide - molybdeni te l e a c h i n g . 4 . 3 . 4 . 2 E f f e c t o f 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 s o l u b i l i t y Samples o f c a l c i t e and gypsum leached i n the presence 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 ha t c a l c i u m s o l u b i l i t y i nc reases as a f u n c t i o n o f [CI ] and t ha t the r e s u l t s were i n good agreement w i t h l i t e r a t u r e va lues (Table 1 1 ) . S t ronger h y p o c h l o r i t e s o l u t i o n s can thus be expected to e x t r a c t more c a l c i u m . I d e n t i c a l r e s u l t s were ob ta ined whether 0C1 o r an e q u i v a l e n t amount o f NaCl a lone were used. Th i s d i d not support the sugges t ion made i n con junc t ion w i t h the exper imenta l obse rva t i on t h a t c a l c i u m sulphate i s 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 , namely t ha t t h i s was due t o c a l c i u m complexing agents con ta ined i n a commercial b l e a c h . Furthermore, an assurance was ob ta ined from the manu- f a c t u r e r s o f JAVEX t h a t the p roduc 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 water . The reason fo r the i nc r ea sed 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 to an i nc rea sed i o n i c s t r e n g t h . The thermodynamic s o l u b i l i t y product fo r c a l c i u m sulphate i s d e r i v e d from the equa t ion : 2+ 2 -CaS0 4 *xH 2 0 ===== Ca + S 0 4 + xH^O . - 198 - i ) Calc ium sulphate C h l o r i d e Content [Ca] D i s s o l v e d [Ca] D i s s o l v e d (Moles C l~) (Experiment) g/1 (Reported) g/1 Source 0.0 0.712 0.666 85 0.825 86 0.2 1.326 1.068 85 1.224 87 0.5 1.528 1.532 87 1.442 88 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 i i ) Ca lc ium carbonate C h l o r i d e Content [Ca] D i s s o l v e d [Ca] D i s s o l v e d Source (Moles CI ) (Experiment) g/1 (Reported) g/1 0.0 0.016 0.022 85 0.014 86 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 Table 11: Comparison o f Exper imenta l and L i t e r a t u r e Values f o r S o l u b i l i t y o f i ) CaSC~>4 and i i ) CaCCy 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 St rengths - 199 - f o r which k sp = t m C a 2 + ] [ m S 0 4 2 " ] [ 6 C a 2 + ] ^ S O ^ [ a H 2 0 ] X where m„ , m„ „ are i ho l a l concen t r a t i ons Ca S0„ 4 &n ' &cr\ a r e a c t i v i t y c o e f f i c i e n t s 4 x = number o f moles o f water a = water a c t i v i t y i n the s o l u t i o n . 2+ 2 - S 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 4 from the Debye Huckel e x p r e s s i o n : - A z l o g 6 1 1 + B / l where i o n i c s t r eng th I = 4 m CaSo 4 = m NaCl z = charge on i o n i A , B are cons tants then l o g k = l o g k + 2 - x l o g aT T „ S P S P 1+ B/F H 2 ° Assuming t ha t m 2+ = m 2-Ca. bu 4 I 3 * then , l o g S = l o g S° + 4A j - - — l o g a n 1+B12 2 H 2 where S = m o l a l s o l u b i l i t y fo CaSC>4 a t any i o n i c s t r e n g t h , I 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 the re fo re tha t S i nc reases w i t h an i nc r ea se i n m, n l l NaCl and hence o f i o n i c s t r e n g t h , I . - 200 - 4 . 3 . 4 . 3 Removal o f c a l c i u m from l e a c h i n g s o l u t i o n s The minimum ca rbona te : ca l c ium r a t i o fo r e f f e c t i v e p r e c i p i t a t i o n o f CaCo^ and p reven t ion o f c a l c i u m molybdate format ion was found to be 2- 2+ 3.19 M [CO^ ] : 1 M [Ca ] • For the amount o f c a l c i u m conta ined i n the c o v e l l i t e m i n e r a l under s tudy , 0.058 g / 1 , t h i s gave a minimum carbonate requirement o f 0.55 g / 1 . However, l e a c h i n g w i t h t h i s va lue o f t o t a l 2- I I I [CO^ ] a t pH 9.0 gave almost ins tantaneous p r e c i p i t a t i o n o f copper and r a p i d decomposi t ion o f the sodium h y p o c h l o r i t e , as noted e a r l i e r . I nc reas ing the carbonate above the s t o i c h i o m e t r i c requirement 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 copper1"1"''', but gave more copper i n s o l u t i o n i n i t i a l l y . The f a c t t ha t the presence o f molybdeni te seeming- l y decreased t h i s i n d u c t i o n p e r i o d i s p robab ly due to the lower hypo- c h l o r i t e content 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 2 to 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 . The s m a l l degree o f copper molybdate format ion which occur red a t lower carbonate l e v e l s has been p o i n t e d out p r e v i o u s l y to be d e t r i m e n t a l to molybdenum recovery and an undes i r ab l e c a t a l y s t f o r h y p o c h l o r i t e decompos i t ion . There would seem to be two a l t e r n a t i v e s the re fo re f o r the e x t r a c t i o n o f molybdenum from molybdeni te - copper su lph ide concen t r a t e s : i ) to l e a c h i n the presence o f l a r g e amounts o f carbonate bu f f e r reagents and hence to p r e c i p i t a t e c a l c i u m , as w e l l as o ther s o l u b l e i m - p u r i t i e s such as z i n c and cadmium, as i n s o l u b l e carbonate s a l t s and to prevent any copper molybdate p r e c i p i t a t i o n . A t the same time a s m a l l percentage of the copper would be d i s s o l v e d . Th i s would enable a l l the molybdenum to be e x t r a c t e d before n u c l e a t i o n o f copper1"'"''" and decomposi t ion - 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 occu r , but would probably n e c e s s i t a t e a copper - molybdenum sepa ra t ion s tep p r i o r to molybdenum recovery from the s o l u t i o n . i i ) to l e a c h w i t h no carbonate i n the system, and thereby to ob- t a i n complete s e l e c t i v i t y o f molybdenum over copper , but to decompose a l l the h y p o c h l o r i t e reagent as a r e s u l t o f heterogeneous copper c a t a l y s i s . Th i s would n e c e s s i t a t e constant r egenera t ion o f the l e a c h i n g s o l u t i o n . In case ( i i ) an a l t e r n a t i v e suppressant f o r c a l c i u m would have to 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 f e a s i b l e . Leaching c h a l c o p y r i t e and molybdeni te toge ther i n the presence o f s i l i c a t e i n f a c t showed t ha t ve ry good molybdenum r e c o v e r i e s were ob t a ined , coupled 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 . Copper m e t a - s i l i c a t e , CuSiO^, i s known to e x i s t , and such a compound c o u l d form a t the m i n e r a l surface i n preference to Cu(0H) 2 and/or Cu(0H) 3 and thus prevent r a p i d c a t a l y t i c decomposi t ion o f the h y p o c h l o r i t e . Whi le the use o f s i l i c a t e appears to be a ve ry v i a b l e a l t e r n a t i v e f o r l e a c h i n g a t pH 9 .0 , i t should be noted: i ) S i l i c a t e s and polymolybdates can combine i n a c i d s o l u t i o n s and problems c o u l d be i n c u r r e d du r ing subsequent molybdenum recovery i f s i l i c a t e was p resen t i n the l e a c h i n g s o l u t i o n s . i i ) S i l i c a t e reagents are l i k e l y to be more expensive than carbonates . The most favourable process thus seems to be one i n c o r p o r a t i n g l e a c h i n g i n the presence o f sodium carbona te /b icarbona te a t pH 9 .0 , p r o - v i d e d a s u i t a b l e method f o r copper - molybdenum sepa ra t i on a f t e r l e a c h i n g can be found. - 202 - CHAPTER 5 5.1 Conc lus ions 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 su lph ide - molybdeni te concent ra tes can be r a p i d l y and comple te ly ob ta ined 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 carbonate bu f f e r reagen ts . 2) Under these c o n d i t i o n s the sur faces o f the copper mine ra l s ac t as c a t a l y s t s fo r the heterogeneous decomposi t ion o f sodium hypoch lo r - i t e due t o the format ion o f an ox ide o r hydroxide s a l t o f t r i - v a l e n t copper on the m i n e r a l s u r f a c e . 3) A l k a l i n e carbonate s o l u t i o n s are capable o f d i s s o l v i n g s m a l l amounts o f copper as copper - carbonate complexes which are cons ide r ab ly 2+ more s o l u b l e than the Cu i o n alone a t pH va lues above 7 . 0 . I t i s suggested t h a t the presence 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 enables the copper to e x i s t as a t r i - v a l e n t cup r i - ca rbona t e s p e c i e s , and tha t p r e c i p i t a t i o n o f a s o l i d carbonate compound c o n t a i n i n g up to 30% o f the copper i n the +3 o x i d a t i o n s t a t e occurs a f t e r a s u i t a b l e n u c l e a t i o n p e r i o d has passed . T h i s t ime p e r i o d and the o r i g i n a l copper content 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 carbonate concen t r a t i on i n the system. 4) So lub l e i m p u r i t y elements which 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 to good molybdenum e x t r a c t i o n . Calc ium i s suggested as be ing 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 su lph ide - molybdeni te l e a c h i n g p r o c e s s . The presence of carbonate i n the system would prevent c a l c i u m molybdate format ion 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 carbonate , and a s i m i l a r mechanism would apply t o z i n c and cadmium i m p u r i t i e s . The use o f s i l i - ca tes 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 - out 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 complexing, but may prove d e t r i m e n t a l t o subsequent molybdenum recove ry . 6) Lead and i r o n do not e x i s t as s o l u b l e spec ies 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 not 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 minor 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 to copper molybdate fo rma t ion . T h i s compound i s a c a t a l y s t f o r h y p o c h l o r i t e decomposi t ion and has a s o l u b i l i t y o f about 1.25 g/1 as CuMoO^. 7) Leaching 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 presence o f carbonate and above a pH va lue o f 6 .0 , because t h i s i s the 2+ r e g i o n i n which the c u p r i c i o n , Cu , i s complexed by carbonate an ions , and copper molybdate format ion i s the re fo re p reven ted . 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 to be the most favourable f o r sodium c h l o r a t e fo rma t ion . 8) Leaching 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 presence 2- o f s u f f i c i e n t l y l a r g e amounts o f carbonate (25 g/1 [CO^ ] f o r example) would g ive good molybdenum e x t r a c t i o n w i t h approximate s t o i c h i o m e t r i c consumption o f the l i x i v i a n t ; but would e n t a i l s imultaneous d i s s o l u t i o n o f a c e r t a i n amount o f copper . Th i s copper would p robab ly r e q u i r e separat ion - 204 - from the molybdenum before the recovery s tage . To minimize sodium h y p o c h l o r i t e decomposi t ion such a s epa ra t i on s tep should be made before I I I . • . copper p r e c i p i t a t i o n can o c c u r . 5.2 Suggest ions f o r Future Work Fu r the 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 areas r e l a t i n g to the p resen t s tudy: i ) A more d e t a i l e d study o f the surface r e a c t i o n s o c c u r r i n g between h y p o c h l o r i t e and d i f f e r e n t copper su lph ide mine ra 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 observed i n the r a t e s o f c a t a l y z e d decompos i t ion . i i ) F u r t h e r a n a l y s i s o f the carbonate 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 t i o n s , to 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 copper spec ies p r e sen t . P o l a r o g r a p h i c techniques would probably g i v e d i f f e r e n t h a l f wave p o t e n t i a l s f o r copper carbonate complexes i n the +2 and +3 o x i - d a t i o n s t a t e s . i i i ) A n a l y s i s o f s o l i d compounds thought to c o n t a i n t r i - v a l e n t c o p p e r proved to be somewhat d i f f i c u l t due t o a l a c k o f p u b l i s h e d da ta f o r s tandard compounds. I f pure samples o f Cu^O^ or (""^(CO^)^ c o u l d be manufactured, 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 u s c e p t i b i l i t i e s , s o l u b i l i t y data e t c . c o u l d be u s e f u l l y o b t a i n e d . i v ) Leaching was found to be most s u c c e s s f u l i n a l k a l i n e s o l u t i o n s . I t would the re fo re be l o g i c a l to r e sea rch i n t o ways o f r e c o v e r i n g molyb- denum from l e a c h s o l u t i o n s wi thout l ower ing pH. The i d e a l method would - 205 - be one o f so lven t e x t r a c t i o n o r i o n exchange ope ra t i ng a t pH 9 . 0 . This would g ive copper - molybdenum sepa ra t ion and molybdenum recovery i n a s i n g l e stage and would prevent unnecessary c h l o r a t e format ion by m a i n t a i n - i n g an a l k a l i n e system throughout the p roces s . v) Use o f t y p i c a l copper rougher concent ra tes •as feed m a t e r i a l would i l l u s t r a t e the f e a s i b i l i t y o f t h i s type o f process more c l e a r l y ; and show whether o r not the suggested c o n d i t i o n s are optimum f o r good molybdenum r e c o v e r y . F l o t a t i o n s t u d i e s on the l e a c h i n g t a i l s c o u l d a l s o be u s e f u l l y pursued. - 206 - REFERENCES 1. Kummer, J . T . : Molybdenum, U . S . B u . Mines M i n e r a l Commodity P r o f i l e , May 1979. 2. World M i n i n g Annual Review, 1978; p . 84. 3. S u t u l o v , A . : Molybdenum and Rhenium 1778-1977; U n i v e r s i t y o f Concepcion, C h i l e , 1976. 4 . Su ther land Brown, A . ( E d . ) : Porphyry Depos i t s o f the Canadian C o r d i l l e r a ; CIM s p e c i a l volume 15, 1976. 5. S h i r l e y , J . F . : World M i n i n g , J u l y 1978, p . 46, and A p r i l 1974, p . 44. 6. Her lund , R .W. : Quat. Colorado School o f Mines ; 56, No. 3, 1961. 7. Johnstone, S . J . ; Johnstone M . G . : M i n e r a l s fo r Chemical and A l l i e d I n d u s t r i e s , J . W i l e y I n c . , New York , 1961. 8. Baes, Mesmer: The H y d r o l y s i s o f C a t i o n s , J . W i l e y L t d . , New York , 1976, p . 248. 9. R e i d , D . C . : M.A . S c . T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia , September 1979. 10. A p i a n , F . F . ; McKinney W . A . ; P e r n i c h e l e , A . D . ( E d s . ) : S o l u t i o n Min ing Symposium, AIME, New Y o r k , 1974. 11 . Cox, H; S c h e l l i n g e r , A . K . : Eng. M i n . J o u r n a l , 159, 1958, p . 101. 12. Dresher , W . H . ; Wadsworth, M . E . ; F a s s e l , W . M . : J . M e t a l s , June 1956, p . 794. 13 . I o r d i n o v , K . V . ,- Ze l ikman, A . N . : Khim, I . Ind . ( S o f i a ) , 33, 1961, p . 171-175. 14. Shap i ro , K . A . ; Kulenkava , B . B . : Tsve t . M e t . , 36_, No. 9, 1963, p . 8 8 . 15 . Bhappu, R . B . ; Reynolds , D . H . ; Stahmann, W . S . : I n t . Symp. on U n i t Processes i n Hydrometa l lu rgy , AIME, D a l l a s , 1963, p . 95. 16. Choppin, A . R . ; Fau lkenbe r ry , L . C . : J . Am. Chem. S o c , 59_, 1937, p . 2203. - 207 - 17. Bhappu, R . B . ; Reynolds , D . H . ; Roman, R . J . ; Schwab, D . A . : New Mexico B u . M i n . Res. C a i r e . , 81_, (60-5101e) , 1965, p . 165. 18. Ze l ikman, A . N . : O x i d a t i o n o f Molybdeni te by S o l u t i o n s o f H y p o c h l o r i t e . " M o l i b d e n , " Moscow M e t a l l u r g u j a , 1970. 19. Sche ine r , B . J . ; L inds t rom, R . E . : U . S . B u . Mines Tech. Progress Repor t , No. 47, J a n . 1972. 20. L inds t rom, R . E . ; Sche ine r , B . J . : U . S . B u . Mines , RI 7802, 1973. 21. Sche ine r , B . J . ; L inds t rom, R . E . ; P o o l D . L . : U . S . Bu . Mines , RI 8145, 1976. 22. Sche ine r . B . J . ; H e i g , R . A . ; P o o l D . L . : Paper No. 87, CIM Conference, Vancouver, B . C . , 1977. 23. B a r r , D . S . ; L inds t rom, R . E . ; Hendr ix , J . L . ; I n t . J . M i n . P r o c , 2_, 1975, p . 303-320. 24. B a r r , D . S . ; Sche ine r , B . J . ; Hendr ix , J . L . : I n t . J . M i n . P r o c , 4_, 1977, p . 83-88. 25. Stumpf, A . ; Berube, Y . : AIME T r a n s . , 254, 1973, p . 305. 26. Warren, I . H . ; Ismay, A . ; K i n g , J . : CIM Annual Volume 1977, p . 11-21 . 27. D e v i l l e , Ann. Chim. P h y s . , [ i i i ] , 3_3, 1851, p . 104. 28. P i c k e r i n g , S . U . : J . Chem. S o c , 9_5, 1909, p . 1409. 29. Reynolds , Trans . Chem. S o c , 73.' 1898, p . 266. 30. Wood, Jones: P r o c . Camb. P h i l . S o c , 1_4, 1907, p . 174. 31 . Appleby , M . P . ; Lane, K.W. : J . Chem. S o c , 113, 1918, p . 609. 32. M e i t e s , L . : J . Am. Chem. S o c , 72, 1950, p . 188. 33. Hsu, C . T . : J . A p p l . Chem., 6_, 1956, p . 84. 34. S c a i f e , J . F . : Can. J . Chem., 35_, 1957, p . 1332. 35. G a r r e l s , R . M . ; C h r i s t , C . H . : S o l u t i o n s , M i n e r a l s and E q u i l i b r i a , Harper and Row, New York , 1965. 36. De Zoubov, N . ; Van Muylder , J . ; Van Lee r , P . ; Pou rba ix , M . : CEBELCOR R . T . No. 133, 1965. 37. S c h i n d l e r , P . ; R e i n e r t , M . ; Gamsjager, H . : H e l v . Chim. A c t a , 51 , (8 ) , 1968, p . 1845. - 208 - 38. Stumm, W.; Morgan, J . J . : Aqua t i c Chemis t ry ; Wi l ey I n t e r s c i e n c e , 1971. 39. B i a n c h i , G . ; L o n g h i , P . : C o r r o s i o n Sc i ence , 1_3_, 1973, p . 853. 40. Van Muylder , J . ; de Zoubov, N . ; Pourba ix , M . : CEBELCOR, R . T . No. 101, J u i l l e t 1962. 41 . D 'Ans , J . ; Freund, H . E . : Z . E l e k t r o c h e m . , 61 , 1957, p . 10-81 . 42. L i s t e r , M.W. : Can. J . Chem., 34_, 1956, p . 465 . ' 43. B e l l , N . M . : Z . Anorg . Chem., 82_, 1913, p . 145. 44. Hofmann, K . A . ; R i t t e r , K . : Ber Deutsch. Chem. G e s . , 47, 1914, p . 2233 (Chem. Abs £ 3275) . 45. Chi rnoaga , E . : J . Chem. S o c , 1926, p . 1693. 46. Lewi s , J . R . : J . Phys . Chem., 32_, 1928, p . 243 and p . 1808. 47. G l ikman , T.S.: ;. D a i n , B . Y a : Zhur . Obshchei K h i m i i , 11, 1941, p . 190. 48. A y r e s , G . H . ; Booth , M . H . : J . Am. Chem. S o c , 77_, 1955, p . 825. 49. L i s t e r , M.W. : Can. J . Chem., 34_, 1956, p . 479. 50. F o e r s t e r , F . ; Dorch, P . : Z . E l e k t r o c h e m . , 23_, 1917. 51. P rokopch ik , A . : C a t a l y t i c Decomposit ion o f H y p o c h l o r i t e and C h l o r i t e ; Academy o f Sc i ece of USSR Ins t . Chem. and Chem. Technology, 1964. 52. Massey, A . G . : Chapter 27 (Copper) i n Comprehensive Inorgan ic Chemistry o f the Elements , Pergamon P r e s s , Oxford , 1973 ( V o l . 3 ) . 53. C o t t o n , F . A . ; W i l k i n s o n , G . : Advanced Inorgan ic Chemis t ry , Wi l ey I n t e r s c i e n c e , New Y o r k , (3rd E d i t i o n ) , 1972. 54. Sneed, M . C . ; Maynard, J . L . ; B r a s t e d , R . C . : Comprehensive Inorgan ic Chemis t ry , V o l . 11 , VanNostrand, 1954. 55. Crum: Annale der Chemie Pharmacie Von L i e b i g , 55, 1845, p . 213. 56. Moser, L : Z . Am. Chem., 54_, 1907, p . 121. 57. S c a g l i a r n i , T o r e l l i , : G a r r . Chim. I t a l . , 51, 1921, p . 225 (Chem. Abs . 16_ 536) . 58. M u l l e r , S p i t z e r , : Z . Anorg . Chem. 54, 1907, p . 417 and p . 121. 59. A l d r i d g e , Miss J . ; Appleby , M . P . : J . Chem. S o c , 121, 1922, p . 238. - 209 - 60. Lepore,. A . : Annales a s soc . q u i n . y . form. Uruguay, 48^ 1946, p . 5. 61 . Scho lde r , R. ; Voelskow, U . : Z . Ann. Chem., 266, 1951, p . 256. 62. P rokopch ik , A . ; Norkus, P . K . : Russ . J . I n o r g . Chem., 4, No. 6, 1959, p . 611. ~~ 63. M a g e e , J . S . ; Wood, R . H . : Can. J . Chem., 43, 1965, p . 1234. 64. M a l a t e s t a , L . : G a r r . Chim. I t a l . , 1941, p . 580. 65. Malaprade, L . : Compte. Rend . , 204, 1937, p . 979. 66. L i s t e r , M.W. : Can. J . Chem., 31̂ , 1953, p . 638. 67. Jensov.sky, L . : Z . Ann. U . A l l egem. Chem., 307, 1960, p . 208. 68. B e r k a , A . : "Compounds of T r i v a l e n t Copper ," Newer Redox T i t r a n t s , Chapter 3, Pergamon P r e s s , 1965. 69. Gadd, K . F . ; Hunns, A . B . ; R ichardson , M . A . : Educa t ion i n Chemis t ry , 164, 1977, p . 145. 70. M e y e r s t e i n , D . : I n o r g . Chem., 10 (3 ) , 1971, p . 638. 71. Shams E l . D i n , A . M . ; Abd, E l Wahab, F . M . : Eleckrochem. A c t a , 9_, 1964, p . 113. 72. Delhez:, R. : 'Sur L ' e x i s t a n c e de l ' o x y d e de C u i v r e ( I I I ) ' ; I - I V , B u l l . Soc. Royale Sc iences L i e g e ; 28 (9,10) 1959, p . 234; 30 (9 ,10 ) , 1961, p . 446; 30_ (9 ,10 ) , 1961, p . 531; 31_ (1-2 , 1962, p . 108) . 73. Pourba ix , M . : A t l a s o f E l e c t r o c h e m i c a l E q u i l i b r i a i n Aqueous S o l u t i o n s , Pergamon P r e s s , 1966. 74. Delhez , R . ; Depommier, C ; Van Muylder , J . : CEBELCOR, R . T . No. 100, J u i l . 1962. 75. La t ime r , W . M . : O x i d a t i o n S ta tes o f the Elements and t h e i r P o t e n t i a l s i n Aqueous S o l u t i o n ; P r e n t i c e H a l l , N . Y . , 1952. 76. Ismay, A . : M . A . S c . T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia , 1976. 77. ASTM, D2022-64, 1970, p . 285. 78. Thompson, R . M . : Department o f Chemis t ry , U n i v e r s i t y o f B r i t i s h Columbia , Pe r sona l Communication. 79. P a s c a l e , P . : Nouveau T r a i t e De Chimie M i n e r a l e , ( I I I ) , Masson and C l e . , 1956, p . 297-30. - 210 - 80. Warren, I . H . : A u s t . J . A p p l . S c i e n c e , 9_, 1958, p . 36. 81 . K i n g , J . A . ; B u r k i n , A . R . ; F e r r e i r a , R . C . H . : Leaching and Reduct ion i n Hydrometa l lurgy (A.R. B u r k i n , E d . ) , IMM, London, 1975, p . 36. 82. Ze l ikman, A . N . ; Prosenkova, T . E . : Zhur. Neorg. K h i m . , 6_, 1961, p . 212. 83. Cl imax Molybdenum Company (AMAX): Molybdenum Chemica l s , Chemical da ta s e r i e s , B u l l . Cdb - 16, January 1973. 84. V a s s i l e v , C . : Compt. Rend, de l 'Acadamie Bulgare des Sc i ences , Tome, 18, No. 2, 1965. 85. S e i d e l , A . : S o l u b i l i t i e s o f Inorgan ic and Organic Compounds, 4th E d . , Am. Chem. S o c , 1958. 86. Chemical Rubber Company, Handbook o f Chemistry and P h y s i c s , C l e v e l a n d , Oh io . 87. M a r s h a l l , W . L . ; S l u s h e r , Ruth; Jones , E . V . : J . Chem. Eng. Data , 9_, No. 2, 1964, p . 187. 88. Furby , E . ; Glueckauf , E. ,- McDonald, L . A . : D e s a l i n a t i o n , 4_, 1968, p . 264. 89. Densmore, D . : B r i s t o l Meyers Canada L t d . , Vancouver, B . C . Pe r sona l Communication. 90. Gaudin, A . : P r i n c i p l e s o f M i n e r a l D r e s s i n g , McGraw H i l l , 1939. 91 . Zharkova, L . A . ; Gerasimov, Y a , I . : Zhur . F i z Khim, 35, 1961, p . 2291. 92. Ze l ikman , A . N . : Russ. J . I n o r g . Chem., 1_, No. 12, 1956, p . 2778. - 211 APPENDIX A Tables o f Exper imenta l Resu l t s Table I : NaOCl l e a c h i n g o f c o v e l l i t e i n the presence o f carbonate buf fe r s (Figures 6,8) Temp. 35°C,- pH 9 .0 , A g i t a t i o n 748 rpm, [NaOCl] 7.68 g / 1 , CuS 10 g , NaHC0 3 14.15 g , N a 2 C ° 3 1 - 0 1 9- Time [Cu] [NaOCl] (mins) ppm g/1 5 133 5.64 10 133 15 125 20 127 5.60 30 127 45 127 60 121 5.62 90 126 120 128 150 130 5.64 - 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 carbonate buf fe r s (F igures 6,8) Temp 35°C, A g i t a t i o n 720 rpm, [NaOCl] 7.8 g / 1 , pH 9 .0 , Cu 2 S 10 g , NaHC0 3 14.15 g , N a 2 C 0 3 1.01 g Time [Cu] [NaOCl] (mins) ppm g/1 5 122.5 7.08 10 122 15 115 6.07 30 116 45 118 6.10 60 118 90 113 6.05 120 118 150 115 6.07 ) / - 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 presence o f carbonate bu f fe r s (Figures 6,8) Temp 35°C, A g i t a t i o n 803 rpm, [NaOCl] 8.13 g ' / l , pH 9 .0 , CuFeS 2 10 g , NaHC0 3 14.15 g , N a 2 C 0 3 1.01 g . Time [Cu] [NaOCl] '(mins) ppm 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 7.22 120 95 150 101 180 104 7.20 210 106 - 214 - Table I V : E f f e c t o f s epa ra t i ng 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 (Figure 7) Temp 35°C, A g i t a t i o n 760 rpm, [NaOCl] 8.0 g / 1 , pH 9 .0 , CuFeS 2 10 g , NaHC0 3 14.15 g , N a 2 C 0 3 1.01 g . Time [Cu] s l u r r y [Cu] f i l t e r e d s o l n (mins) ppm 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 - 215 - Table V : E f f e c t o f s epa ra t i ng 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 Cu^S i n NaOCl (Figure 7 ) . Temp 35°C, A g i t a t i o n 782 rpm, NaOCl 7.45 g / 1 , pH 9 . 0 , Cu 2 S 10 g , NaHC0 3 14.15 g , N a 2 C 0 3 1.01 g . Time [Cu] s l u r r y [Cu] f i l t e r e d s o l n (mins) ppm 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 -216 - Table V I : 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 bu f f e r s (Figures 9,11) Temp 35°C, A g i t a t i o n 784 rpm, pH 9 . 0 , [NaOCl] 7.61 g / 1 , CuS 10 g . Time [Cu] [NaOCl] [NaC10 3] NaC10 3 (mins) ppm g/1 g/1 % 0 0.05 7.61 0.179 5 0.29 5.93 0.304 13.70 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 - 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 carbonate bu f fe r s (F igure s 9,11) Temp 35°C, A g i t a t i o n 780 rpm, pH 9 . 0 , [NaOCl] 7.69 g / 1 , Cu 2 S 10 g . Time (mins) [Cu] ppm [NaOCl] g / i [NaCIO ] g / i NaCIO % 0 0.13 7 .69 0.304 5 0.19 6.98 0.340 8.73 10 6.60 0.358 9.21 20 0.20 6.30 0.429 17.70 30 5.63 0.501 21.22 45 0.25 5.03 0.633 22.81 60 4.53 0.716 20.20 80 0.21 3.91 100 3.30 0.859 23.42 120 0.19 2.78 0.913 23.03 150 2.18 0.922 23.31 180 0.23 1.56 - 218 - Table V I I I : NaOCl l e a c h i n g of c h a l c o p y r i t e i n the absence o f carbonate bu f fe r s (Figures 9.11) Temp 35°C, A g i t a t i o n 785 rpm, pH 9 . 0 , [NaOCl] 7.73 g / 1 , CuFeS 10 g . Time [Cu] [NaOCl] [NaC10 3] NaCIO (mins) ppm g/1 g/1 % 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 20.2 100 0.10 - 219 - Table I X : Microprobe examinat ion 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, pH 9 . 0 , [NaOCl] 7.06 g/1 2 P o l i s h e d Cu„S sur face 3.2 cm Area S Count Before Cu Count Before Cu/S R a t i o S Count A f t e r Cu Count A f t e r Cu/S R a t i o 7287 81631 11.18 4873 71025 14.58 7963 74964 9.41 4429 70794 15.98 5699 71766 12.59 4463 70688 15.84 1 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 2 7232 82722 11.44 8072 78918 9.78 7243 82370 11.37 8030 79544 9.91 7220 82314 10.95 8459. 76290 8.88 - 220 - Table X : Microprobe examinat ion o f massive c o v e l l i t e , before 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, pH 9 . 0 , [NaOCl] 8.1 g / 1 , P o l i s h e d 2 CuS sur face 4.5 cm . Area S Count Cu Count Cu/S S Count Cu Count Cu/S Before Before R a t i o A f t e r A f t e r R a t i o 14161 67660 4.78 10338 67705 6.55 14132 67131 4.75 10434 67189 6.44 1 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 2 13932 66553 4.78 28605 52541 1.84 14111 66321 4.69 29641 50942 1.72 13400 64360 4.80 13352 64230 4.81 A f t e r CuCl„ Wash A 12751 64821 4.71 13748 64491 4.69 3 13704 66909 4.88 00541 79590 147.11 (Green Deposi t ) 13826 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 , CuS i n the absence o f carbonate (Figure 10) Temp 35°C, A g i t a t i o n 821 rpm, pH 9 .0 , [NaOCl] 7.67 g/1 CuS 10.0 g . Time [Cu] [NaOCl] (mins) ppm 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 - 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 , C u 2 S > -*-n t n e absence o f carbonate (Figure 10) Temp 35°C, A g i t a t i o n 806 rpm, pH 9 .0 , [NaOCl] 7.14 g / 1 , Cu 2 S 10.0 g . Time [Cu] [NaOCl] (mins) ppm 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 0.55 g/1 [CO ] 1.0 g/1 [C0 3 ] 2 .0 g/1 [C0 3 ] 5.0 g/1 [C0 3 ] 7.5 g/1 [C0 3 ] 10.7 g/1 [C0 3] (mins) [Cu] NaOCl [Cu] NaOCl [Cu] NaOCl [Cu] NaOCl [Cu] NaOCl [Cu] NaOCl ppm g / i ppm g / i ppm g / i ppm g / i ppm g / i ppm g / i 0 7.82 0.19 7.67 7.66 0.2 7.44 7.45 0.9 7.85 5 5.6 6.94 14.5 6.84 21.5 7.05 46.4 6.43 84.0 6.69 119.2 7.07 10 5.0 5.48 3.0 6.24 12.0 6.69 44.1 76.8 119.3 6.31 20 1.3 3.38 3.9 4.29 12.0 6.59 40.3 6.43 77.4 6.64 114.3 30 3.8 1.13 3.3 1.32 13.0 6.39 38.0 77.8 105.8 45 2.5 — 3.5 0.38 7.5 4.96 37.6 6.47 80.0 113.7 60 2.5 — 3.4 -- 4.5 0.52 29.0 5.53 77.2 6.62 117.2 6.32 90 1.5 0.09 20.2 0.25 75.0 6.69 116.5 120 17.3 — 67.2 6.65 116.2 6.31 140 41.8 4.71 107. 3 180 42.1 — 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 (Figures 12,13) - 224 - Time 1.0 g/1 l c o 3 2 - ] 2.0 g/1 [co 3 2 - ] 5.0 g/1 [co 3 2 - ] (mins) [Cu] ppm [NaOCl] g / i [Cu] ppm [NaOCl] g / i [Cu] ppm [NaOCl] g / i 0 8.12 7.89 8.06 5 2.93 7.67 8.5 7.52 10 1.00 7.52 8.0 7.52 40.8 7.59 20 1.55 7.14 8.0 30 0.85 6.92 6.3 7.52 7.52 45 0.33 6.39 38.3 60 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 2.3 3.30 22.0 4.35 240 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 (Figures 14,15) I - 225 - Table XV: NaOCl l e a c h i n g o f s y n t h e t i c copper su lph ides w i t h 5 g/1 [CO.,""* ] (F igures 16,17) pH i > ) .0 , Temp 35 °C, A g i t a t i o n 821 rpm CuS Cu 2 S Time (mins) [Cu] ppm [NaOCl] g / i [Cu] ppm [NaOCl] g / i 0 7.67 7.14 5 46.6 7.52 44.8 15 44.8 43.8 7.07 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 - 226 - Table X V I : NaOCl l each o f c o v e l l i t e i n the presence o f 5 g/1 [CO ] and 20 g/1 [NaOCl] (Figure 18) Temp 35°C, pH 9 .0 , A g i t a t i o n 800 rpm, CuS 10 g , NaHCO 6.5165 g , N a 2 C 0 3 0.4720 g . Time [Cu] [NaOCl] (mins) ppm g/1 0 19.17 2 106 18.04 10 117 25 109 40 103 16.54 60 97 155 94 13.53 195 49 5.86 205 28 3.35 225 22 0.75 265 22 - 227 - Table X V I I : A g i t a t i o n o f c o v e l l i t e i n the presence o f NaHCO^/Na^CO^ ± NaCl (Figure 19) Temp 35°C, A g i t a t i o n 817 rpm, pH 9 . 0 , CuS l O g , NaHC0 3 14.15 g , Na2CC>3 1.01 g . Time Carbonate o n l y Carbonate and 14.0 g/1 NaCl (mins) [Cu] ppm [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 leaching of c o v e l l i t e i n the presence of 10 g/1 [ C 0 3 2 ~ ] , and Na2MoQ4 (Figure 20) Temp 35°C, [NaOCl] 7.82 g/1, Agit a t i o n 803 rpm, pH 9.0, NaHC03 14.15 g, Na 2C0 3 1.01 g, CuS 10 g, Na^MoO„ 2 4 1.538 g = 0.6 g/1 Mo. Time [Cu] [NaOCl] [Mo] Mo % (mins) ppm g / i g / i 0 7.82 0.66 100 5 136 6.76 0.63 95.5 20 133 60 133 6.54 0.63 95.5 120 131 6.54 180 133 6.52 0.65 98.5 255 132 6.50 270 118 4.96 0.65 98.5 290 85 1.65 305 66 0.60 0.61 92.0 360 64 — 410 20 — 0.65 98.5 440 9 - 229 - Table X I X : Sodium h y p o c h l o r i t e decomposi t ion i n the presence o f t r i -v a l e n t copper s a l t s (Figure 21) Temp 35 copper °C, A g i t a t i o n 700 - samples: 2 g . • 760 rpm, pH 9 .0 , Time (mins) I l l copper ox ide [NaOCl] g/1 I I I copper carbonate [NaOCl] g/1 c u p r i c o x i d e , CuO [NaOCl] g/1 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 45 — 0.20 6.35 60 — 6.00 90 5.45 - 230 - Table XX: NaOCl o x i d a t i o n o f molybdeni te (F igure 22) Temp 35°C, pH 9 .0 , A g i t a t i o n 780 rpm, [NaOCl] 7.7 g / 1 , MoS 2 0.3 g . Time [Mo] Mo e x t r a c t e d [NaOCl] (mins) ppm % g/1 0 — — 7.70 5 168 93.3 6.83 10 168 93.3 15 169 93.8 20 170 94.4 6.82 30 170 94.4 45 170 94.4 60 169 93.8 6.82 - 231 - Table X X I : NaOCl o x i d a t i o n o f ' reagent grade ' 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 , MoS 2 1.0 g Reagent grade MoS^ 98% + MoS„ 2 Time (mins) [Mo] g / i Mo e x t r n . "O [NaOCl] g / i [Mo] g / i Mo e x t r n . % [NaOCl] g / i 0 8.54 8.72 5 0 .535 89.3 5.62 0.375 62.5 6.91 10 0 .535 89.3 0.531 88.5 6.05 20 0 .535 89.3 5.60 0.587 97.9 5.68 30 0 .536 89.3 0.587 97.9 45 0 .536 89.3 5.59 0.584 97.9 5.00 60 0 .536 89.3 5.59 0.587 97.9 4.65 - 232 - Table X X I I : NaOCl o x i d a t i o n of molybdenite and c o v e l l i t e , w i t h and wi thou t carbonate buf fe r s (F igure 25) Temp 35°C, A g i t a t i o n 800 rpm, pH 9 . 0 , MoS 2 0.3 g CuS 10.0 g (10 g/1 t o t a l carbonate) MoS 2 , CuS + NaHCO^/Na 2 C ° 3 M o S 2 , CuS + NaOH Time [Mo] Mo e x t r [Cu] [NaOCl] [Mo] Mo e x t r . [Cu] [NaOCl] (mins) ppm % ppm g / i ppm % ppm g / i 0 — — — 7.37 — — — 7.43 5 160 88.9 110 132 73.3 0.25 4.44 10 160 88.9 108 4.89 132 73.3 0.30 3.01 20 160 88.9 106 133 73.8 0.27 1.13 30 160 88.9 104 4.66 133 73.8 0.23 0.38 45 160 88.9 107 133 73.8 0.32 — 60 160 88.9 103 4.04 133 73.8 0.27 — - 233 - Table X X I I I : NaOCl o x i d a t i o n o f molybdeni te and c h a l c o c i t e , w i t h and wi thou t carbonate buf fe r s (F igur e 26) Temp 35°C, A g i t a t i o n 785 rpm pH 9 . 0 , MoS 2 0. 3 g , Cu 2 S 10.0 g (10 g/1 t o t a l carbonate) MoS 2 , Cu 2 S + NaHC0 3 /Na 2 C ° 3 M o S 2 , Cu 2 S + NaOH Time [Mo] Mo e x t r . [Cu] [NaOCl] [Mo] Mo e x t r . [Cu] [NaOCl] (mins) ppm % ppm g / i ppm % ppm g / i 0 — — 7.89 — — — 7.35 5 159 88.5 96.0 139 77.2 0.13 6.50 10 169 89.2 93.0 4.61 139 77.2 0.13 6.35 20 160 89.0 94.0 139 77.2 0.25 6.02 30 162 89.9 93.0 4.53 139 77.2 0.25 5.57 45 162 89.9 90.0 139 77.2 0.25 4.95 60 162 90.0 89.0 4.44 139 77.2 0.23 3.60 - 234 - Table XXIV: NaOCl o x i d a t i o n o f molybdenite and c h a l c o p y r i t e w i t h and wi thou t carbonate buf fe r s (Figure 27) Temp 3 4 . 9 ° C , A g i t a t i o n 792 rpm, pH 9 . 0 , MoS 2 0.3 g , CuFeS 10.0 g (10 g/1 t o t a l ca rbona te ) . MoS 2 , CuFeS 2 + NaHC0 3 /Na 2 C ° 3 MoS 2 CuFeS 2 + NaOH Time [Mo] Mo e x t r . [Cu] [NaOCl] [Mo] Mo e x t r . [Cu] [NaOCl] (mins) ppm % ppm g / i ppm Q. "6 ppm g / i 0 — — 7.50 — — — 7.13 5 154 86.1 106 5.32 143 79.4 0.53 4.51 10 156 86.6 100 144 80.0 0.41 4.17 20 156 86.6 98 5.30 142 78.8 0.32 2.82 30 158 87.8 98 144 80.0 0.32 1.97 45 158 87.8 94 5.25 144 80.0 0.27 0.94 60 158 87.8 99 5.20 144 80.0 0.11 — - 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 wi thou t carbonate bu f fe r s Temp 35°C, A g i t a t i o n 780 rpm, pH 9 .0 , CuFeS 2 10 g , MoS 0 5 g (reagent grade) MoS^ o n l y MoS 2 , CuFeS 2 + NaOH MoS 2 , CuFeS 2 + [co 3 2-] Time (mins) [Mo] g / i Mo e x t r . 0. ~o [NaOCl] g / i [Mo] g / i Mo e x t r . % [NaOCl] g / i [Mo] g / i Mo e x t r . % [NaOCl] g / i 0 24.55 — — 20.32 — — 20.21 5 2.67 89.0 11.32 2.54 84.7 8.32 2.64 87.5 7.37 10 2.66 88.7 2.54 84.7 4.62 2.64 87.5 20 2.68 89.3 11.30 2.54 84.7 2.83 2.62 87.5 7.28 30 2.67 89.0 2.54 84.7 1.56 2.62 87.3 45 2.67 89.0 11.27 2.54 84.7 0.34 2.62 87.3 7.26 60 2.67 89.0 11.25 2.54 84.7 — 2.64 87.5 - 236 - Table XXVI : NaOCl o x i d a t i o n o f molybdenite i n the presence o f copper su lphate s o l u t i o n Temp 3 5 . 1 ° C , NaOCl 7.5 g / 1 , A g i t a t i o n 792 rpm, pH 9 .0 , MoS 2 0.3 g , CuS0 4 0.4 g/1 = 0.1 g/1 Cu Time Cu added [Cu] i n s o l n [Mo] Mo e x t r d . (mins) ppm ppm ppm % 5 — — 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 60 100 0.11 132 73.5 - 237 - Table X X V I I : 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 , A g i t a t i o n 821 rpm, pH 9 . 1 , CuS 10.0 g , Na 2 Mo0 4 2.15g= 0.1 g Mo, [NaOCl] 7.63 g/1 Time Mo added [Mo] i n s o l n Mo i n s o l n [Cu] (mins) ppm ppm % 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 molybdeni te a t pH 5.5 (Figure 28) Temp 35°C, A g i t a t i o n 880 rpm, pH 5 .4 , [NaOCl] 6.92 g / 1 , Mo S 2 1.0 g Time [Mo] Mo e x t r a c t e d [NaOCl] (mins) g/1 % g / 1 0 — — 6.92 5 0.550 91.6 10 0.563 93.8 2.71 20 0.548 91.3 30 0.563 93.8 2.53 45 0.564 94.0 60 0.563 93.8 2.21 - 239 - Table XXIX: NaOCl o x i d a t i o n o f molybdeni te and c h a l c o p y r i t e a t pH 5.5 (Figure 29) Temp 35°C, A g i t a t i o n 803 rpm, pH 5 .55 , [NaOCl] 6.54 g / i CuFeS 2 10 g , MoS 2 0. 3 g . MoS 2 , CuFeS 2 + NaOH M o S 2 , CuFeS 2 + 10 g NaHC0 3 Time [Mo] ppm Mo e x t r . % [Cu] ppm [Mo] ppm Mo e x t r . % [Cu] ppm 5 142 78.8 — 146 82.2 — (CuFeS 2 added) 10 4.1 2.27 12.9 0.2 0.10 37.5 20 4.5 2.50 8.7 0.3 0.16 33.7 30 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 - 240 - Table XXX: NaOCl oxidation of molybdenite and c o v e l l i t e at pH 5.5 (no carbonate)(Figure 30 a) Temp 35°C, Agi t a t i o n 802 rpm, pH 5.45, [NaOCl] 6.17 g/1 CuS 10.0 g, MoS2 0.3 g. Time [Mo] Mo extracted [Cu] [NaOCl] (mins) ppm % ppm g/1 5 141 78.3 — 5.55 (CuS added) 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 - 241 - Table X X X I : NaOCl o x i d a t i o n o f molybdeni te and c o v e l l i t e a t pH 5 . 5 , w i t h sodium b ica rbona te (Figure 30 b) Temp 3 4 . 9 ° C , A g i t a t i o n 800 rpm, pH 5 .50 , [NaOCl] 6.92 g/1 CuS 10 g , Mo S 0.3 g , NaHCO 10.0 g . Time [Mo] Mo e x t r a c t e d [Cu] [NaOCl] (mins) ppm % ppm g/1 5 153 85.0 — 6.92 (CuS added) 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 - 242 - Table XXXII: NaOCl leaching of chalcopyrite at pH 5.5 with and without bicarbonate i n the system Temp 35°C, A g i t a t i o n 805 rpm, pH 5.40, [NaOCl] 7.2 g/1, CuFeS 2 10 g, NaHC03 9.28 g. CuFeS 2 only CuFeS 2 + HCO3- Time [Cu] [NaOCl] [Cu] [NaOCl] (mins) ppm g / i ppm g / i 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 — - 243 - Table XXXIII: NaOCl leaching of molybdenite and chal c o c i t e at pH 6.5, with bicarbonate i n the system (Figure 31 a) Temp 35°C, A g i t a t i o n 880 rpm, pH 6.5, [NaOCl] 6.92 g/1 Cu 2S 10 g, MoS2 1.0 g, NaHC03 10 g. Time [Mo] Mo extracted [Cu] [NaOCl] (mins) g/1 % ppm g/1 0 — — 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 - Table XXXIV: NaOCl l e a c h i n g o f molybdeni te and c h a l c o c i t e a t pH 6 . 5 , w i t h no carbonate present (Figure 31 b) Temp 35°C, A g i t a t i o n 880 rpm, pH 6 . 5 , [NaOCl]7.52 g / 1 , Mo S 2 l . O g , Cu 2 S 10 g Time [Mo] Mo e x t r a c t e d [Cu] [NaOCl] (mins) g/1 % ppm 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 - Table XXXV: NaOCl leaching of molybdenite and cupric sulphide at pH 6.0 i n the presence of carbonate (Figure 32) Temp 35°C, A g i t a t i o n 803 rpm, pH 6.5, [NaOCl] 7.04 g/1, CuS 10.0 g, MoS2 1.0 g, NaHC03 10.0 g Time [Mo] Mo extracted [Cu] [NaOCl] (mins) g/1 % ppm 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 2.63 60 0.560 93.3 24.9 100 0.560 93.3 25.0 2.56 - 246 - Table XXXVI: NaOCl leaching of molybdenite and cupric sulphide at pH 6.0, with no carbonate present Temp 35°C, A g i t a t i o n 857 rpm, pH 6.5, [NaOCl] 6.39 g/1, CuS 10.0 g, MoS2 1.0 g. Time [Mo] Mo extracted [Cu] [NaOCl] (mins) g/1 % ppm 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 - Table XXXVII: NaOCl leaching of molybdenite and chalcopyrite at pH 7.0 with bicarbonate present (Figure 33 a) Temp 35°C, A g i t a t i o n 785 rpm, pH 7.0, [NaOCl] 6.5 g/1, CuFeS 2 10 g, MoS2 1.1 g, NaHC03 10 g Time [Mo] Mo extracted [Cu] [NaOCl] (mins) g/1 % ppm 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 molybdeni te and c h a l c o p y r i t e a t pH 7 .0 , no carbonate (Figure 33 b) Temp 35°C, A g i t a t i o n 785 rpm, pH 7 . 0 , [NaOCl] 6.54 g / 1 , CuFeS 2 10 g , MoS 2 1.0 g . Time [Mo] Mo e x t r a c t e d [Cu] [NaOCl] (mins) g ' / l % ppm 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 1.96 120 0.195 32.50 0.7 205 0.203 33.75 0.5 1.94 - 249 - Table IXL: NaOCl decomposition i n the presence of copper molybdate at pH 5.5 (Figure 35) Temp 35°C, A g i t a t i o n 792 rpm, pH 5.40, [NaOCl] 6.84 g/1, Cu Mo04 2 g. Time [NaOCl] [NaCIO ] (mins) g/1 g/1 0 6.84 — 10 6.39 0.109 20 5.30 0.785 30 4.14 1.430 45 2.31 1.480 - 250 - Table XL: Determina t ion o f the s o l u b i l i t y o f copper molybdate a t pH 5.0 (Figure 34) pH 5.0 N a 2 M o 0 4 - 2 H 2 0 4.13 g = 0.096 g/1 Mo CuSO 4 -5H 2 0 6.22 g 5 0.064 g/1 Cu Mo added Mo i n s o l n Cu i n s o l n Mo pptd Cu pptd ( M o l e s ) x l O 2 ( M o l e s ) x l O 2 ( M o l e s ) x l O 2 (Moles)xlO (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 molybdenite and c o v e l l i t e pH 10 .0 , w i t h carbonate (Figure 37 a) Temp 3 5 . 1 ° C , A g i t a t i o n 789 rpm, pH 1 0 . 0 , [NaOCl] 7.54 g / 1 , MoS 2 0.3 g , CuS 10.0 g, N a 2 C 0 3 5.37 g , NaHC0 3 7.24 g . Time [Mo] Mo e x t r n . [NaOCl] (mins) ppm % g/1 5 148 82.2 6.63 10 150 83.3 20 154 85.5 6.43 30 158 87.8 45 160 88.9 6.25 60 164 91.1 6.23 - 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 molybdeni te . and c o v e l l i t e a t pH 10.0 w i t h no carbonate (Figure 37 b) Temp 35°C, A g i t a t i o n 790 rpm, pH 10 .0 , [NaOCl] 7.61 g / 1 , CuS 10 g , MoS 0.3 g . Time [Mo] Mo e x t r n . [Cu] [NaOCl] (mins) ppm % ppm g / i 5 142 78.9 0.5 6.01 10 142 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 - 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 su lph ide a t pH 9 .0 , w i t h no carbonate (Figure 36) Temp 35°C, Agitat ion 808 rpm, pH 9 .0 , [NaOCl] 33.32 g / 1 , MoS 2 5 g , Cu 2 S 10 g . Time [Mo] Mo e x t r n . [NaOCl] (mins) g/1 % g/1 5 2.66 88.67 10 2.65 88.30 19.36 20 2.66 88.67 30 2.66 89.0 10.53 45 2.68 89.0 70 2.68 89.0 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 su lph ide a t pH 9 .0 , w i t h 10 g/1 carbonate (Figure 36) Temp 35°C, A g i t a t i o n 803 rpm, pH 9 .0 , [NaOCl] 33.08 g / 1 , MoS 2 5 g , Cu 2 S 10 g . Time [Mo] Mo e x t r n . [NaOCl] (mins) g/1 % g/1 5 2.68 89.01 20.14 10 2.68 89.01 20 2.70 90.00 19.36 30 2.72 90.67 45 2.72 90.67 16.16 60 2.72 90.67 13.90 - 255 - Table 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 carbonate (F igure 38) Temp 35°C, A g i t a t i o n 799 rpm, pH 9 . 0 , [NaOCl] 7.74 g / 1 , Cu samples 10 g- CuFeS 2 C U 2 S CuS Time [Ca] [Cu] [Ca] [Cu] [Ca] [Cu] (mins) ppm ppm ppm ppm ppm 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 - 256 - Table X L V I : NaOCl l e a c h i n g o f MoS^ and Cu^S i n the presence o f 0.1 g/1 c a l c ium as C a C l ^ s o l u t i o n Temp 35°C, A g i t a t i o n 821 rpm, pH 9 . 0 , [NaOCl] 8.0 g / 1 , M o S 2 1 g (reagent g rade ) , Cu 2 S 10 g , C a C l 2 0.3703 g = 0.1 g Ca . Time [Ca] [Mo] Mo e x t r . Mo p p t d . Ca p p t d . (mins) ppm g/1 % (x 10 M) (x 10 4M) 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 molybdeni te and c h a l c o c i t e i n the presence o f CaCl^, and Na^CO^/NaHCO^ Temp 3 4 . 9 ° C , A g i t a t i o n 820 rpm, pH 9 .0 , [NaOCl] 7.89 g / 1 , MoS 2 1.0 g , CU 2 S 10 g , C a C l 2 0.3703 g, NaHCt>3 14 .15 g , N a 2 C 0 3 1.01 g- Time [Mo] Mo e x t r . [Ca] [mins) g / i % ppm 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 - 258 - Table X L V I I I : NaOCl l e a c h i n g o f molybdeni te and c a l c i t e w i t h no carbonate (Figure 40) Temp 3 4 . 9 ° C , A g i t a t i o n 805 rpm, pH 9 .0 , [NaOCl] 9.5 g / 1 , MoS 2 1 g , CaC0 3 10 g . Time [Mo] Mo e x t r n . [Ca] (mins) g/1 % 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 igure 39) Temp 35°C, A g i t a t i o n 780 rpm, pH 9 . 0 , [NaOCl] 6.69 g/1 CaCO., 10 g = 4 g Ca Time [Ca] Ca e x t r . (mins) ppm % 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 - 260 - .: 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 , CaSO^*%Hn0 a t pH 9.0 (Figure 39) 4 2 Time [Ca] Ca e x t r n . [NaOCl] (mins) g / i Q, "O 5 1.81 60.2 7.89 10 1.87 62.1 20 1.89 63.0 7.89 30 1.89 63.0 50 1.90 64.5 7.94 70 1.90 64.5 Temp 35°C, A g i t a t i o n 805 rpm, pH 9 . 0 , [NaOCl] 8.01 g / 1 , C a S O ^ H ^ O 10 g L I : i ) CaSo 4-J5H 20 Time 0 g/1 NaCl 12 g/1 NaCl 28 g/1 NaCl 40 g/1 NaCl 58.5 g/1 NaCl 86.8 g/1 NaCl 117 g/1 NaCl (mins) [Ca] g/1 [Ca] g/1 [Ca] g/1 [Ca] g/1 [Ca] g/1 [Ca] g/1 [Ca] g/1 10 0.435 0.960 1.394 1.860 2.06 20 1.548 1.684 1.864 2.012 2.08 30 0.659 1.314 40 1.688 2.012 2.10 50 1.528 1.868 60 0.712 1.326 1.686 2.10 90 0.712 1.326 1.528 1.690 1.860 2.012 L I I : i i ) CaC0 3 Time (mins) 0 g/1 NaCl [Ca] ppm 13 g/1 NaCl [Ca] ppm 20 g/1 NaCl [Ca] ppm 35 g/1 NaCl [Ca] ppm 40 g/1 NaCl [Ca] ppm 80 g/1 NaCl [Ca] ppm 10 6.5 12.25 16.80 21.50 43.20 35.75 20 14.50 18.30 33.50 55.05 30 15.5 15.25 34.75 48.75 56.80 45 16.0 15.50 49.00 58.60 60 16.5 16.00 35.0 49.00 60.30 55.00 Tables L I , L I I : 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 concen t r a t i on on ca l c ium d i s s o l u t i o n from i ) c a l c i u m sulphate i i ) c a l c ium carbonate (Figure 41-44) pH 9 .0 , Temp 35°C, A g i t a t i o n 780 - 860 rpm - 262 - Table L I I I : E f f e c t o f carbonate on ca l c ium content i n h y p o c h l o r i t e s o l u t i o n s (Figure 45) pH 9 .0 , Temp 35°C, NaOCl 8.0 g/1 [ C 0 3 2 ] T added [ C O ^ - ] [Ca] [Ca] [Ca] p p t d . g/1 (moles) ppm (moles) (moles) 0 — 1.750 0.0438 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 . 8 x l 0 ~ 4 0.0434 25.00 0.417 0.005 9 . 3 x l 0 ~ 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 molybdeni te w i t h 5 g/1 carbonate (Figure 46) Temp 35°C, A g i t a t i o n 821 rpm, pH 9 . 0 , [NaOCl] 8.77 g / 1 , CuS 10 g , MoS 2 1 g , [ C 0 3 2 " ] T 5 g/1 Time [NaOCl] [Cu] [Mo] Mo e x t r n . (mins) g/1 ppm 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 91.0 120 — 5.0 0.540 90.0 - 264 - Table LV: NaOCl l e a c h i n g o f molybdeni te and c o v e l l i t e i n the presence o f 10 g/1 carbonate (Figure 46) Temp 35°C, A g i t a t i o n 803 rpm, pH 9 .0 , [NaOCl] 7.5 g/1 2 - MoS 2 1.0 g , CuS 10 g , [C0 3 ] 10.7 g / 1 . Time [Cu] [Mo] Mo e x t r n . [NaOCl] (mins) ppm g/1 % 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 carbonate (Figure 48) Temp 35°C, A g i t a t i o n 785 rpm, pH 9 . 0 , CuS 10 g , Na 2 Mo0 4 0.5 g = 0.35 g [Mo], NaHC0 3 0.46 g , N a 2 C 0 3 6.52 g , [NaOCl] 7.5 g / 1 . Time [Cu] [Mo] Mo i n s o l n [NaOCl] (mins) ppm g/1 % 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 (Figure 47) Temp 35°C, A g i t a t i o n 803 rpm, pH 9 .0 , MoS 1.0 g , 2- Cu 2 S 10 g , [C0 3 ] T 10.68 g / 1 . Time [Cu] [Mo] Mo e x t r n . [NaOCl] (mins) ppm g/1 % g/1 0 — — — 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 o 2 ~ added to the system, pH 9.0 (Figure 49T Temp 35°C, A g i t a t i o n 803 rpm, [NaOCl] 8.4 g / 1 , MoS 2 1 g , CuFeS 2 10 g , N a 2 S i 0 3 3.29 g , pH 9 . 0 . Time [Cu] [Mo] Mo e x t r n . [NaOCl] (mins) ppm g/1 % g/1 10 0.25 0.579 96.5 5.04 20 0.13 0.579 96.5 30 0.17 0.583 97.2 5.04 60 0.22 0.590 98.4 90 0.15 0.593 98.9 5.04 - 268 - APPENDIX B B . l C a l c u l a t i o n o f surface areas f o r ground m i n e r a l samples The s p e c i f i c surface (surface per u n i t we igh 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 : n = x 2 k - l k - l S * l = 6hk . *2 " X I *2 A (k - l ) k k A V x x X 2 " X l 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 = cons tant A = s p e c i f i c g r a v i t y For copper su lph ide minera l s ground to pass a -200 mesh screen: x^ = 5 x 10 cm x 2 = 0.0074 cm 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 sur face area o f a cube f o r same screen s i z e ) k = 1.02 A = 5.6 - 5.8 (Cu 2S) = 4.5 - 4.6 (CuS) Cu^S 6 x 1.75 x 1.02 - 0 . 0 0 7 4 ( 0 - ° 2 ) - (5 x 1 0 ~ 8 ) 0 " 0 2 2 -1 UT021 ~ , -8,1.02 c m g 2 5.65 x 0.02 0.0074 v ' - (5 x 10 ) = 94.779 x 28.632 c m 2 g - 1 2 -1 = 2713.71 cm g - 269 - 6 x 1.75 x 1.02 • 0 . 0 0 7 4 ( ° - 0 2 ) - (5 x 10 8 ) ° - 0 2 2 -1 C U S ~ 4.60 x 0.02 0 . 0 0 7 4 ( 1 - ° 2 ) - (5 x I O " 8 ) 1 ' 0 2 " ? 116.41 x 28.632 c m 2 g - 1 = 3333.05 c m V 1 2 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 surface area 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 surface area o f 33,330 2 cm . 90 (Er ro r o f c a l c u l a t i o n can be 30 - 50%) B . 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 sur face a f t e r c o p p e r 1 1 1 format ion Radius o f copper molecule = copper p r e c i p i t a t e d = Avagadro ' s number = Number o f Cu molecules T o t a l area o f Cu Thi s compares w i t h a surface area 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 cm f o r a 10 g sample of c o v e l l i t e . 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 i s thus 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 s u r f a c e . o - a 1A = 10 cm 60 ppm = 0 . 0 6 g/1 23 6 x 10 0.06 , l n 2 3 = ,- x 6 x 10 63. D = 5.660 x 1 0 2 1 = 5.669 x 1 0 2 1 x 10~ 8 = 5.669 x 1 0 1 5 c m 2 . 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 = JgCl^aq) + H 2 0 E = 1.59 + 0.0591 { l o g (HC10) - Jglog ( C l 2 ) - pH} - 270 - 2) *SCl 2(aq) + e C l " E = 1.40 + 0.0591 {%log ( C l 2 ) - l o g (Cl )} (1) + (2) 3) HC10 + H + + 2e = C l ~ + H 2 0 E = 1.49 + 0 , ° ^ 9 1 { l og (HC10) - l o g ( C l ) - pH} 4) HC10 = HCIO H + + CIO" E° = 1.49 (2) - (4) + (1) : 5) CIO + 2 H + + 2e = C l " + H 2 0 E = 1.738 + ° ' 0 ^ 9 1 ( l o g (CIO ) - l o g ( C l ) - 2pH> a t pH 9.0 E = 1.738 + { 0 - 0 5 2 9 1 ) • (-18) = 1.738 - 0.532 E = 1.206 V - 271 - APPENDIX C React ions and e q u i l i b r i a p e r t a i n i n g to p o t e n t i a l - pH diagrams for v a r i o u s meta l molybdate systems shown i n F igu re s 52-58 C.1 Cu-H^O-MoO^ system C . l . l Substances cons idered . O x i d a t i o n Number Species AG° (kcal ) Source o f Data 0 Cu° — +1 Cu 2 0 -34.98 73 +1 C u + +12.00 73 +2 CuO -30.40 73 +2 Cu(OH) 2 -85 .30 73 +2 CuMo0 4 -202.70 91 +2 ^  2 + Cu +15.53 73 +2 2-Cu0 2 -43 .50 73 +2 Cu0 2 H -61.42 73 +3 C U 2 ° 3 -41.50 74 +3 CuO - -26.87 74 +3 r, 3 + Cu +72.50 74 (+4 Mo0 3 -120.00) 73 (+6 HMoO„~ 4 -161.95) 73 (+6 MoO 2 ~ 4 -213.60) 73 +6 CuMoO. 4 -205.42 35 A c t i v i t y o f copper c o n t a i n i n g spec ies i n s o l u t i o n s has been taken as 10 ^ M, and t ha t o f molybdenum c o n t a i n i n g spec ies as 10 1 M. 272 C . 1 . 2 Two d i s s o l v e d substances + 2+ 1) Cu ->Cu + e 2+ E = 0.153 + 0.0591 l o g ^ (Cu +) E = 0.153 2) C u + + 2H 2 0 >-HCu02 + 3H + + e" E = 1.733 - 0.1773 pH + 0.0591 l o g ( H C u ° 2 - i - (Cu ) E = 1.733 - 0.1773 pH + 2- „ + 3) Cu + 2H 2 0 >Cu°2 + + e E = 2.510 - 0.2364 pH + 0.0591 l o g - ^ ^ - 2 — - (Cu ) E = 2.510 - 0.2364 pH 4) C u 2 + + 2H 2 0 >flCu02 + 3 H + l o g ( H C U ° 2 - ^ - = -2 .72 + 3pH; pH = 8.91 (Cu + ) 2 - + 5) HCu0 2 > Cu°2 + H 2- l o g - ^ ^ 2 ] - = -39.88 + 4 pH; pH = 13.15 (HCu0 2~) ^ , 2 + 3+ 6) Cu • Cu + e 3+ E = 2.475 + 0.0591 l o g U ; E = 2.475 (Cu ) 2- 7) Cu0 2 Cu0 2 + e (CuO ) E = 0.721 + 0.0591 l o g ; E = 0.721 (Cii02 ) - 273 - 8) HCu0 2 > C u 0 2 + 6 E = 1.498 - 0.0591 pH + 0.0591 l o g E = 1.498 - 0.0591 pH (Cu0 2 ) (HCu0 2~) 9) C u 2 + + 2H 2 0 =*CuO + 4 H + + e" (CuO ) E = 3.078 - 0.2364 pH + 0.0591 l o g ( C u 2 + ) E = 3.078 - 0.2364 pH 3+ - + 10) Cu + 2H.0 >-Cu0o + 4H (Cu0 2 ) l o g * — = -10.28 + 4 pH; pH = 2.57 ( C u 3 + ) C .1 .3 One s o l i d substance and one d i s s o l v e d substance + 2+ 11) Cu 2 0 + 2H >-2Cu + H 2 0 + 2e 2+ E = 0.203 + 0.0591 pH + 0.0591 l o g (Cu ) E = -0.152 + 0.0591 pH 12) Cu 2 0 + 3H 2 0 + 4 H + + 2e »- 2HCu02~ + 4 H + + 2e~ E = 1.783 - 0.1182 pH + 0.0591 l o g (HCu0 2~) E = 1.428 - 0.118 pH 2+ 13) Cu ->Cu + 2e 2+ E = 0.337 + 0.0295 l o g (Cu ) ; E = 0.337 274 . 2 + + 14) a) Cu + H 2 0 CuO + 2H 2+ l o g (Cu ) = 7.89 - 2 pH; pH = 6.93 2+ + b) Cu + 2H 2 0 > Cu(OH) 2 + 2H 2+ l o g (Cu ) = 9.071 - 2 pH; pH = 7.54 15) a) CuO + H 2 0 y HCu0 2 ~ + H + l o g (HCu0 2~) = -18.83 + pH; pH = 12.83 b) Cu(OH) 2 > C u 0 2 + 2 H + l o g (Cu0 2 ) = -30 .80 + 2 pH; pH = 12.4 2- + 16) CuO + H 2 0 Cu0 2 + 2H l o g (CuO 2 ) = -31.98 + pH; pH = 12.99 2+ + -17) Cu + 3H 2 0 >• C u 2 0 3 + 6H + 2e E = 1.783 - 0.1182 pH + 0.0591 l o g (HCu0 2 ) E = 1.428 - 0.118 pH 18) a) CuO + H 2 0 • C u 0 2 _ + 2 H + + 2 e _ E = 2.609 - 0.1182 pH + 0.0591 l o g (Cu0 2~) E = 2.254 - 0.118 pH b) Cu(0H) 2 > C u 0 2 ~ + 2 H + + 2 e " E = 1,267 - 0.118 pH - 0 ' ° 2 9 1 l o g (Cu0 2~) E = 1.149 - 0.118 pH - 275 - ' 3 + + 19) Cu + 3H 2 0 y C u 2 0 3 + 6H 3+ l o g (Cu ) = -6 .09 + 3 pH; pH = -0 .3 20) C u 2 ° 3 + H 2 ° 2 C u 0 2 ~ + 2 H + l o g (Cu0 2~) = -16.31 + pH; pH = 10.31 2- 2- + 21) Cu0 2 + Mo0 4 + 4H y CuMo0 4 + 2H 2 0 2 - 2- 4 pH = 67.18 - 0.0591 l o g ( (Cu0 2 ) • (Mo0 4 )'); pH = 10.815 2 - + 22) Cu0 2 H + Mo0 4 + 3H y CuMo0 4 + 2H 2 0 2- 3 pH = 49.06 - 0.0591 l o g ((CuC^H ) • (Mo0 4 ) ) ; pH = 9.99 3+ 2- 23) CuMo0 4 y Cu + Mo0 4 + e E = 3.026 + 0.0591 l o g ( ( C u 3 + ) • ( M o C ^ 2 - ) ) E = 2.671 2- + -24) CuMoO„ + 2H O y CuO„ + MoO„ + 4H + e 4 2 2 4 2- E = 3.626 - 0.236 pH + 0.0591 l o g ( (Cu0 2 )•(MoO ) E = 3.271 - 0.236 pH C .1 .4 Two s o l i d substances 25) 2Cu + H 2 0 y Cu 2 0 + 2 H + + 2e~ 0.471 - 0.0591 pH 26) a) Cu + H 2 0 y CuO + 2H + + 2e~ E = 0.570 - 0.0591 pH - 276 - b) Cu + 2H 2 0 y Cu(OH) 2 + 2H + + 2e~ E = 0.609 - 0.0591 pH 27) a) Cu 2 0 + H 2 0 y 2CuO + 2H + + 2e~ E = 0.669 - 0.0591 pH b) Cu 2 0 + 3H 2 0 y 2Cu(OH) 2 + 2 H + + 2e~ E = 0.741 - 0.0591 pH 2- + 28) C u 2 0 + 2Mo0 4 + 2H • 2CuMo0 4 + H 2 0 + 2e E = 0.35 + 0.0591 pH - 0.029 l o g (MoO 2 ~) E = 0.379 + 0.0591 pH 2- + 29) a) CuO + Mo0 4 + 2H > CuMo0 4 + H 2 0 2 pH = 17.23 - 0.0591 l o g (MoO 2 ~) pH = 8.62 2- + b) Cu(OH) 2 + Mo0 4 + 2H CuMo0 4 + 2H 2 0 2 pH = 18.46 - 0.0591 l o g (MoO^ 2 - ) pH = 9.25 30) a) CuO + H2Q > C u 2 ° 3 + 2 H + + 2 e " E = 1.648 - 0.0591 pH b) 2Cu(OH) 2 y C u 2 0 3 + H 2 0 + 2H* + 2e~ E = 1.572 - 0.0591 pH - 277 - 31) 2CuMo04 + 3H 2 0 2- + Cu„0^ + 2MO0,, + 6H + 2e 2 3 4 E = 2.658 - 0.0197 pH - 0.0197 l o g (MoC>4 ) 2.677 - 0.0197 pH 32) Cu + MoO 2- 4 * CuMoO„ + 2e 4 E = 0.0589 - 0.0591 l o g (Mo0 4 ) E = 0.118 C. 2 C a - H 2 0 - M o 0 4 system C . 2 . 1 Substances cons idered O x i d a t i o n Number Species AG (kcal) Source o f Data -2 0 +2 +2 +2 +2 +4 ( +4 ( +6 ( +6 +6 CaH 2 Ca CaO Ca(OH) CaMoO„ n 2 + Ca C a 0 2 Mo0 2 MoO„ 3 HMoO ~ 4 MoO. 2 ~ -35 .80 -144.40 -157.64 -345.80 -132.18 -143.00 -120.00 ) -161.95 ) -213.60 ) -205.42 73 73 73 91 73 73 73 73 73 35 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 spec ies 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 spec ies as I O - 1 M. 278 - C . 2 . 2 One s o l i d substance and one d i s s o l v e d substance 2+ + 1) a) Ca + H 2 0 y CaO + 2H l o g ( C a 2 + ) = 32.63 - 2pH; pH = 19.315 b) C a 2 + + H 2 0 • Ca(OH) 2 + 2 H + 2+ l o g (Ca ) = 22.91 - 2 pH; pH = 14.45 2) CaH„ > C a 2 + + 2H + + 4e~ 2 E = -1 .045 - 0.0295 pH - 0.0148 l o g ( C a 2 + ) E =. -1 .134 - 0.0295 pH 2+ 3) Ca y Ca + 2e 2+ E = -2 .866 - 0.0295 l o g (Ca ) ; E = -3 .043 C . 2 . 3 Two s o l i d substances 4) CaH 2 y Ca + 2 H + + 2e" E = 0.776 - 0.0591 pH 5) a) CaH 2 + H 2 0 y CaO + 4 H + + 4e~ E = -0 .563 - 0.0591 pH b) CaH 2 + 2H 2 0 y Ca(OH) 2 + 4 H + + 4e -0 .706 - 0.0591 pH 6) a) Ca + H 2 0 y CaO + 2 H + + 2e E = -1 .902 - 0.0591 pH - 279 - b)r Ca + 2H 2 0 >-Ca(OH)2 + 2H + + 2e~ E = -2 .189 -. 0.0591 pH 2- 7) Ca + MoO. > CaMoO„ + 2e 4 4 0.0591 2-E = -3.044 - - l o g (Mo0 4 ) ; E = - 3 . 0 . 1 4 2- + 8) a) CaO + Mo0 4 + 2H >• CaMo0 4 + H 2 0 2 pH = 38.36 + l o g (Mo0 4 2 ~) pH = 19.15 2- + b) Ca(OH) 2 + Mo0 4 + 2H • CaMo0 4 + 2H 2 0 2- 2 pH = 28.99 + l o g (Mo0 4 ) pH = 14.00 2- + 9) CaH„ + MoO. y CaMoO„ + 2H + 4e 2 4 4 E = -1.134 - 0.0295 pH - 0.0148 l o g (Mo0 4 E = -1 .192 - 0.0295 pH 2- + 10) CaMoO. + 2H_0 y CaO„ + MoO„ + 4H 4 2 2 4 2 - 4 pH = 81.09 - l o g (Mo0 4 ) pH = 20.52 11) a) CaO + H 2 0 y C a ° 2 + 2 H + + 2 e _ E = 1.260 - 0.0591 pH b) Ca(OH) 2 + H 2 0 y C a 0 2 + 2 H + + 2e~ E = 1.547 - 0.0591 pH 2- . - 280 - C.3 Pb-H^O-MoO^ system C . 3 . 1 Substances cons idered O x i d a t i o n „ . AG° Source Species , Number (kcal ) o f Data 0 Pb — 73 +2 PbO -45.25 91 +2 PbMo0 4 -205.42 73 +2 P b 2 + -5 .81 73 +2 HPb0 2 ~ -81.00 73 +2.67 Pb ,0„ -147.6 73 3 4 +3 P b 2 ° 3 -98 .42 73 +4 P b 0 2 -52 .34 73 +4 P b 4 + +72.30 73 +4 PbO 2 ~ -66.34 73 2-+4 PbO, -67 .42 73 4 ( +4 Mo0 2 -120.00 ) 73 ( +6 Mo0 3 -161.95 ) 73 ( +6 HMo04- -213.60 ) 73 +6 M o O . 2 - -205.42 35 -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 spec ies i n s o l u t i o n taken as 10 M, and o f molybdenum c o n t a i n i n g spec ies as 10 M. S tab le b i - v a l e n t ox ide cons idered to be anhydrous plumbous o x i d e , PbO. 281 C . 3 . 2 Two d i s s o l v e d substances 2+ - + 1) Pb + 2H 2 0 y HPb0 2 + 3H l o g ( H P b ° 2 ) = -28.02 + 3 pH; pH = 9.34 ( P b 2 + ) 4+ 2 - + 2) Pb + 3H 2 0 y P b 0 3 + 6H (PbO 2"~) l o g — = -23.06 + 6 pH; pH V= 3.84 ( P b 4 + ) 2- 4- + 3) P b 0 3 + H 2 0 y P b 0 4 + 2H (PbO 4 " ) l o g r - j - = -40.87 + 2 pH; pH = 20.44 (PbO ) 2+ 4+ 4) Pb y Pb + 2e 4+ E = 1.694 + 0.0295- l o g ( } ( P b 2 + ) E° = 1.694 2+ 2- + - 5) Pb + 3H O y PbO + 6H + 2e 2- (PbO ) E = 2.375 - 0.177 pH = 0.0295 l o g - ( P b 2 + ) 2 - + -6) HPbO + H O y PbO + 3H + 2e Z Z j> (Pb0 3 ")' E = 1.547 - 0.0886 pH + 0.0295 l o g _ (HPb0 2 ) E = 1.547 - 0.0886 pH - 282 C . 3 . 3 Two s o l i d substances 7) Pb + H 2 0 y PbO + 2 H + + 2e" E = 0.248 - 0.0591 pH 8) 3PbO + H 2 0 y P b 3 0 4 + 2 H + + 2e" E = 0.972 - 0.0591 pH 9) 2 p b 3 ° 4 + H 2 ° 3 P b 2 ° 3 + 2 H + + 2 e ~ E = 1.228 - 0.0591 pH 10) P k 3 0 4 + 2H 2 0 > 3Pb0 2 + 2 H + + 2e~ E = 1.127 - 0.0591 pH 11) p b 2 0 3 + H 2 0 — -> 2Pb0 2 + 2 H + + 2e~ E = 1.093 - 0.0591 pH 2- 12) Pb + MoO, y PbMoO, + 2e 4 4 E = -0.672 + l o g (Mo0 4 2 ~) E = -0 .613 2 - + - 13) PbMo0 4 + 2H 2 0 y P b 0 2 + Mo0 4 + 4H + 2e E = 1.99 - 0.1182 pH + 0.0591 l o g (MoO^") E = 1.931 - 0.1182 pH 2- + 14) 3PbMo0 4 + 4H 2 0 y P b 3 0 4 + 3Mo0 4 + 8H + 2e E = 3.724 - 0.236 pH + 3(0.0591) l o g (MoO^" E = 3.547 - 0.236 pH - 283 C.3 .4 One s o l i d substance and one d i s s o l v e d substance 2+ + 15) Pb + H 2 0 y PbO + 2H 2+ l o g (Pb ) = 12.65 - 2 pH; pH = 8.325 16) PbO + H 2 0 y HPb0 2 ~ + H + l o g (HPb0 2 ) = -15.36 + pH; pH = 11.36 4+ + 17) Pb + 2H 2 0 > P b 0 2 + 4H l o g ( P b 4 + ) = -8.26 - 4 pH; pH = -1.065 2- + 18) P b 0 2 + H 2 0 -> P b 0 3 + 2H 2- l o g (PbO. ) = -31.22 + 2 pH; pH = 13.66 2+ 19) Pb • Pb + 2e E = -0.126 + 0.0295 l o g ( P b 2 + ) E = -0.244 20) Pb + 2H 2 0 y HPb0 2 + 3H + + 2e" E = 0.702 - 0.0886 pH + 0.0295 l o g (HPb0 2 ) E = 0.584 - 0.0886 pH 2+ + - 21) 3Pb + 4H 2 0 y P b 3 0 4 + 8H + 2e E = 2.094 - 0.2364 pH - 0.0886 l o g ( P b 2 + ) E = 2.448 - 0.2364 pH 22) 3HPb0 2~ + H + —~-y P b ^ + 2H 2 0 + 2e~ E = -0 .390 ••+ 0.295 pH - 0.0886 l o g (HPbO^) - 284 - E = -0.0356 + 0.0295 pH 23) P b 2 + + 2H 2 0 — -> Pb0 2 + 4 H + + 2e~ E = 1.449 - 0.1182 pH - 0.0295 l o g ( P b 2 + ) E = 1.567 - 0.1182 pH 24) HPb0 2 ~ + M o 0 4 2 ~ + 3 H + • PbMo0 4 + 2H2<3 l o g (HPb0 2~) = -46.33 + 3pH; pH = 14.11 4+ 25) PbMo0 4 y Pb + 4e E = 3.347 - 0.0147 l o g ( P b 4 + ) E = 3.288 2 - 2- + - 26) PbMo0 4 + 3H 2 0 >- P b 0 3 + Mo0 4 + 6H • + 2e E = 2.915 - 0.177 pH + 0.0295 l o g (PbO 2 ~) E = 2.797 - 0.177 pH - 285 - C. 4 Zn-H^O-MoO^ system C . 4 . 1 Substances cons idered O x i d a t i o n Number Species AG° Source (kcal) o f Data 0 +2 +2 +2 +2 +2 +2 ( +4 ( +6 ( +6 +6 Zn Zn(OH)„ ZnMoO„ * 2 + Zn HZn0 2 ~ ZnO 2 ~ 2 + ZnOH Mo0 2 Mo0 3 HMoO.~ ' 4 M o O 2 ~ -76.94 -294.40 -35.18 -110.90 -93.03 -78 .70 -120.00 ) -161.95 ) -213.60 ) -205.42 73 91 73 73 73 73 73 73 73 73 35 A c t i v i t y o f z i n c c o n t a i n i n g spec ies taken to be 10 ^ M, and o f molybdenum c o n t a i n i n g spec ies as 10 -1 M. S t a b l e ox ide cons idered to be z i n c hydroxide Zn(OH) 2 (orthorhombic) C . 4 . 2 Two d i s s o l v e d substances 1) Z n 2 + + H 2 0 • ZnOH + + H + (7nOH~'~ ̂ l o g = -9 .67 + pH; pH = 9.67 ( Z n + ) + - + 2) ZnOH + H 2 0 > HZn0 2 + 2H (HZn0 2~) l o g — = -17.97 + 2 pH; pH = 8.98 (ZnOH ) - 286 - 2+ - + 3) Zn + 2H 2 0 y HZnC>2 + 3H (HZn0 2~) l o g — = -27.63 + 3 pH; pH = 9.21 (Zn + ) 2- + 4) HZnO y ZnO + H 2- (Zn0 2 ) l o g = -13 .11 + pH; pH = 13.11 (HZn0 2 C . 4 . 3 Two s o l i d spec ies 5) Zn + 2H 20 >- Zn (OH) + 2H + + 2e E = -0 .439 - 0.0591 pH 2- + 6) Zn(OH) 2 + Mo0 4 + 2H • ZnMo0 4 + 2H 20 2- 2 pH = 91.84 + l o g (Mo0 4 ) pH = 45.42 2- 7) Zn + Mo0 4 + 2e >- ZnMo0 4 2- E = -1 .929 - 0.0295 l o g (Mo0 4 ) E = -1 .899 C .4 .4 One s o l i d substance and one d i s s o l v e d substance 8) Zn(OH) 2 + H 20 *• HZn0 2~ + H + l o g (HZn0 2 ) = -16.68 + pH; pH = 10.68 - 287 - 2- + 9) HZnC- + MoO. + 3H y ZnMoO„ + 2H„0 2 4 4 2 2- 3 pH = 66.94 - l o g ((HZn0 2 ) • ( M o 0 4 )) pH = 20.31 2- 2- + 10) ZnO„ + MoO, + 4H y ZnMoO, + 2H~0 2 4 4 2 2- 4 pH = 80.04 - l o g ( (Zn0 2 )•(MoO )) pH = 18.51 2+ 11) Zn y Zn + 2e E = -0 .763 + 0.0295 l o g ( Z n 2 + ) ; E = -0 .94 2- + - 12) Zn + H 2 0 y Zn0 2 + 4H + 2e E = 0.441 - 0.1182 pH + 0.0295 l o g (Zn0 2 2 ~) E = 0.264 - 0.1182 pH 2+ + 13) Zn + 2H 2 0 y Zn(OH) 2 + 2H 2+ l o g (Zn ) = 10.96 - 2 pH; pH = 8.48 14) Zn + 2H 2 0 y HZn0 2 ~ + 3 H + + 2e~ E = 0.054 - 0.0886 pH + 0.0295 l o g (HZn0 2~) E = -0.123 - 0.0886 pH - 288 - C. 5 Fe-H^O-MoO^ system C . 5 . 1 Substances cons idered O x i d a t i o n „ . AG° Source Species Number (kca l ) o f Data 0 Fe +2 Fe(OH) -58 .88 73 2+ +2 Fe -20 .30 73 +2 HFe0 2 ~ -90.63 73 +2 FeMoO, -235.30 91 4 +3 Fe(OH). -161.93 73 3+ +3 Fe -2 .53 73 +3 Fe(OH) + -106.20 73 2+ +3 FeOH -55.91 73 ( +4 Mo0 2 -120.00 ) .73 ( +6 Mo0 3 -161.95 ) 73 ( +6 HMoO -213.60 ) 73 +6 MoO„ ~ -205.42 35 V +6 FeO„ -111.69 73 4 A c t i v i t y o f i r o n c o n t a i n i n g spec ies i n s o l u t i o n taken as 10 ^ M, and o f molybdenum spec ies as 10 M. Ferrous and f e r r i c hydrox ides , Fe(OH) 2 and Fe(OH) have been used as the s t a b l e o x i d e s . C . 5 . 2 Two d i s s o l v e d spec ies 2+ - + 1) Fe + 2H 2 0 ——* HFe0 2 + 3H < (HFeO ) l o g = -31.58 + 3 pH; pH = 10.53 ( F e 2 + ) - 289 - 3+ 2+ + 2) Fe + H 2 0 FeOH + H 2+ l o g ( F e ° " ) =•- -2 .43 + pH; pH = 2.43 (Fe J ) 3) F e O H 2 + + H 2 0 —>• F e ( O H ) 2 + + H + l o g ( F e ( ° H ) 2 } = -4 .69 + pH; pH = 4.69 (Fe(OH) 2 + ) . , 2 + 3+ 4) Fe Fe + e ( F e 3 + ) E = 0.771 + 0.0591 l o g (Fe^ ) E = 0.771 5) F e 2 + + H 2 0 >: F e ( O H ) 2 + + H + + e" (Fe (OH) 2+. E = 0.914 - 0.0591 pH + 0.0591 l o g ( F e 2 + ) E = 0.914 - 0.059 pH 6) F e 2 + + 2H 9 0 ^-r* Fe (OH) + + 2 H + + e~ 2 + (Fe(OH) ) E = 1.91 - 0.1182 pH + 0.0591 l o g ( F e 2 + ) E = 1.91 - 0.1182 pH 7) HFeO + H + — F e (OH) + + e~ + (Fe(OH) 2 ) E = -0 .675 + 0.0591 pH + 0.0591 l o g : (Fe0 2H~) E = -0.675 + 0.0591 pH 2- + - 8) HFe0 2 + 2H 2 0 — F e 0 4 + 5H + e (Fe0 4 2 ~) E = 1.001 - 0.0738 pH + 0.0148 l o g (HFe0 2 E = 1.001 - 0.0738 pH - 290 - 3+ 2- + -9)' Fe + 4H 2 0 — F e 0 4 + 8H + 3e (FeO ") E = 1.700 - 0.1580 pH + 0.0197 l o g - ( F e 3 + ) E = 1.700 - 0.1580 pH 10) F e ( O H ) 2 + + 3H 2 0 ——> F e 0 4 2 ~ + 7 H + + 3e~ (FeO 2 ~) E = 1.652 - 0.1379 pH + 0.0197 l o g (Fe(OH) 2 + ) E = 1.652 - 0.1379 pH + 2- + -11) Fe(OH) 2 + 2H 2 0 —y F e 0 4 + 6H + 3e E = 1.559 - 0.1182 pH + 0.0197 l o g ( F e ° 4 ) 1.559 - 0.1182 pH (Fe(OH) 2 + ) C .5 .3 Two s o l i d substances 12) Fe + 2H 2 0 y Fe(OH) 2 + 2 H + + 2e~ E = -0 .047 - 0.0591 pH 13) Fe + 3H 2 0 y Fe (OH) + 2 H + + 2e~ E = 0.059 - 0.0591 pH 14) Fe(OH) 2 + H 2 0 >-Fe(OH) 3 + 2 H + + 2e~ E = 0.271 - 0.0591 pH 2-15) Fe + MoO, + 2e >• FeMoO, 4 4 2- E = -0.648 - 0.0295 l o g (Mo0 4 ) E = -0.6185 2- + 16) Fe(OH) 2 + Mo0 4 + 2H >- FeMo0 4 + 2H 2 0 291 - 2 -2 pH = 61.804 + l o g (MoO ) 4 pH = 30.402 17) FeMo0 4 + 3H 2 0 y Fe (OH) 3 + 3 H + + MoO 2 ~ + e~ E = 1.637 - 0.1773 pH + 0.0591 l o g (MoO 2 ~) E = 1.578 - 0.1773 pH C . 5 . 4 One s o l i d substance and one d i s s o l v e d substance 18) F e 2 + + 2H 2 0 y Fe(OH) 2 + 2 H + l o g ( F e 2 + ) = 13.29 - 2pH pH = 9.645 19) Fe(OH) 2 y HFe0 2 ~ + H + l o g (HFe0 2 ) = -18 .30 + pH pH • = 12.30 20) F e 3 + + 3H 0 y Fe (OH) + 3H + 3+ l o g (Fe ) = 4.84 - 3 pH pH = 3.613 2+ + 21) Fe (OH) + 2H O y Fe (OH) + 2H l o g (Fe(OH) 2 + ) = 2.41 - 2 pH pH = 4.205 22) F e ( O H ) 2 + + H 2 0 • >-Fe(OH) 3 + H + - 292 l o g (Fe(OH) 2 + ) = -2 .28 - pH pH = 4.28 2+ 23) Fe y Fe + 2e E = -0 .440 + 0.0295 l o g ( F e 2 + ) E = -0.617 24) Fe + 2H 2 0 ^ HFe0 2 + 3 H + + 2e~ 2+ E = 0.493 - 0.0886pH + 0.0295 l o g (Fe ) E = 0.316 - 0.0886 pH 3+ 25) Fe B j Fe + 3e E = -0.037 + 0.0197 l o g ( F e 3 + ) ; E = -0.1552 2+ + -26) Fe + 3H 2 0 • Fe(OH) + 3H + e E = 1.057 - 0.1773 pH - 0.0591 l o g ( F e 2 + ) E = 1.4116 - 0.1773 pH 27) HFe0 2 + H 2 0 -y 2Fe(OH) 3 + e -0.810 - 0.0591 l o g (HFe0 2 ) ; E = -0.4356 2- + 28) FeMo0 4 + 2H 2 0 y HFe0 2 + Mo0 4 + 3H 3 pH = 38.46 + l o g ( (HFe0 2 ~) - (Mo0 4 2 ~) ) pH = 10.82 3+ 2-29) FeMoO. 4- Fe + MoO, + e 4 4 2- E = 1.186 + 0.0591 l o g (Mo0 4 ) ; E = 1.127 - 293 - r 2-H 2 —• "I-30.) FeMoO + H O y Fe (OH) + MoO + H + e E = 1.326 - 0.0591 pH + 0.0591 l o g ( (FeOH 2 + ) (Mo0 4 2 *) ) E = 0.971 - 0.0591 pH + + - 2-31) FeMo0 4 + 2H 2 0 y Fe(OH) 2 + 2H + e + Mo0 4 E = 1.599 - 0.1182 pH + 0.0591 l o g ((FeOH + )• ( M o 0 4 2 - ) ) E = 1.244 - 0.1182 pH C.6 Cd-H 2 Q-MoQ 4 system C . 6 . 1 Substances cons idered O x i d a t i o n „ . AG° Source Species ,, _ „ , Number (kcal) o f Data 0 Cd — 73 2 Cd(OH) 2 -56.44 73 2 CdMoO„ ' -283.30 91 2+ 4 2 Cd -18.58 73 2 HCdO ~ -86 .50 73 6 M o O „ 2 - -205.42 35 4 A c t i v i t y o f cadmium c o n t a i n i n g spec ies i n s o l u t i o n taken as 10 6 M, and t ha t o f molybdenum spec ies as 10 1 M. ' I n a c t i v e ' cadmium hydrox ide , Cd(OH) 2 , has been used as the oxide s p e c i e s . - 294 C . 6 . 2 Two d i s s o l v e d spec ies 1) C d 2 + + 2H 2 0 HCd0 2 + 3H + (HCdO ) l o g — = -33.34 - 3 pH; pH = 11.11 (CcT ) C . 6 . 3 Two s o l i d spec ies 2) Cd + H 2 0 >- Cd(OH) 2 + 2 H + + 2e~ E = 0.05 - 0.0591 pH 2- + 3) Cd(OH) 2 + Mo0 4 + 2H • CdMo0 4 + 2H 2 0 2- 2 pH = 65.73 + l o g (MoC>4 ) pH = 32.365 2-4) Cd + MoO, + 2e > CdMoO, 4 4 2- E = -0 .713 - 0.0295 l o g (Mo0 4 ) ; E = -0.684 C . 6 . 4 One s o l i d substance and one d i s s o l v e d substance 5) C d 2 + + 2H 2 0 >-Cd(OH) 2 + 2 H + l o g ( C d 2 + ) = 13.81 - 2 pH; pH = 9.905 6) Cd(OH) 2 > HCd0 2 + H + l o g (HCd0 2 ) = -19.54 + pH; pH = 13.54 7) Cd y C d 2 + + 2e~ E = -0.403 + 0.0295 l o g ( C d 2 + ) ; E = -0 .508 - 295 - 8) Cd + 2H 20 y HCd0 2~ + 3H + + 2e~ E = 0.583 - 0.0886 pH + 0.0295 log (HCd02 E = 0.406 - 0.0886 pH 2- + 9) CdMo04 + 2H 20 • y HCd0 2 + MoC>4 + 3H log (HCd02~) - 3 pH = -43.69 pH = 12.564 C.8 Molybdenum species ( a l l systems) C.8.1 Substances considered Oxidation „ . AG° Source Species „ ,\ _ „ ^ Number (kcal) of Data 0 Mo +3 Mo 3 + -13.80 73 +4 Mo02 -120.00 73 +6 Mo0 3 -161.95 73 +6 MoO,2" -205.42 73 4 +6 HMoO ~ -213.60 73 4 A c t i v i t y of dissol v e d species taken as 10 "*" M. Hexa- valent oxide considered to be molybdic t r i o x i d e , MoO^ C.8.2 Two d i s s o l v e d substances 2- + 1) HMoO. y MoO. + H 4 4 2-, (MoO ) l o g — = -6.00 + pH; pH = 6.0 (HMoO ) 296 C .8 .3 One s o l i d substance and one d i s s o l v e d substance 2) Mo0 3 + H 2 0 K HMo0 4~ + H + l o g (HMo04 ) = -3 .70 + pH; pH = 2.70 3+ 3) Mo y Mo + 3e E = -0 .200 + 0.0197 l o g ( M o 3 + ) ; E = -0.2197 2- + 4) Mo + 4H 2 0 y Mo0 4 + 8H + 6e 2- E = 0.154 - 0.0788 pH + 0.0098 l o g (Mo0 4 E = 0.144 - 0.0788 pH 3+ + -5) Mo + 2H 2 0 y Mo0 2 + 4H + e E = 0.311 - 0.2364 pH - 0.0591 l o g (Mo 3 + ) E = 0.370 - 0.2364 pH 3+ + -6) Mo + 3H 2 0 y Mo0 3 + 6H + 3e E = 0.317 - 0.1182 pH - 0.0197 l o g (Mo 3 + ) E = 0.337 - 0.1182 pH 7) Mo0 2 + 2H 2 0 y HMo04 + 3 H + + 2e~ 0.429 - 0.0886 pH + 0.0295 l o g (HMo04 ) E = 0.399 - 0.0886 pH 2- + 8) Mo0 2 + 2H 2 0 y Mo0 4 + 4H + 2e 2- E = 0.606 - 0.1182 pH + 0.0295 l o g (Mo0 4 ) E = 0.577 - 0.1182 pH - 297 - C .8 .4 Two s o l i d substances 9) Mo + 2H 2 0 > Mo0 2 + 4 H + + 4e~ E = -0 .072 - 0.0591 pH 10) Mo0 2 + H 2 0 y Mo0 3 + 2 H + + 2e E = 0.320 - 0.0591 pH C

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
United States 14 7
Japan 7 0
Iran 7 6
Germany 3 14
Hong Kong 2 0
Canada 2 0
China 1 0
India 1 0
Poland 1 0
City Views Downloads
Unknown 11 20
Tokyo 7 0
Ashburn 7 0
Tucson 5 5
Fredericton 2 0
Redmond 2 0
Tai Hang 2 0
Beijing 1 0
Farsi 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items