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Pressure leaching of copper sulphides in perchloric acid solutions Loewen, Fred 1967

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THE PRESSURE LEACHING OF COPPER SULPHIDES IN PERCHLORIC ACID SOLUTIONS  BY FRED LOEWEN B . A . S c , U n i v e r s i t y o f B r i t i s h Golumbia, 1 9 6 4  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of METALLURGY  I  We a c c e p t t h i s  t h e s i s as conforming to the  standard required  from c a n d i d a t e s f o r the  degree o f MASTER OF APPLIED SCIENCE  THE UNIVERSITY OF BRITISH COLUMBIA May, 1967  In  presenting  for  an a d v a n c e d  that  thesis  Department  agree  that  of  of  this  thesis  D  a  t  e  for  permission.  T i , 1%7  for  may be g r a n t e d  M^Allnrgy  Sppfpnvhpr  of  Columbia  It  of  British  available  permission  representatives  his  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a '  freely  or  by  fulfilment  University  purposes  my w r i t t e n  Department  the  scholarly  publication  without  at  in p a r t i a l  s h a l l make i t  I further for  thesis  degree  the: L i b r a r y  study,  or  this  for  the  Columbia,  I  reference  and  extensive by  requirements  copying  gain  this  t h e Head o f my  is understood  financial  of  agree  shall  that not  be  copying allowed  - i i-  ABSTRACT  The chalcopyrite  l e a c h i n g of c o v e l l i t e  (CuS), c h a l c o c i t e  (CuFeS2) and b o r n i t e (Cu^FeS^) was  (Cu^S),  c a r r i e d out i n , a  s h a k i n g a u t o c l a v e i n p e r c h l o r i c a c i d s o l u t i o n s and u s i n g moderate p r e s s u r e s of  oxygen.. The  temperature  I t was at  approximately  105-140°C.  t h a t c o v e l l i t e , c h a l c o c i t e and b o r n i t e l e a c h  s i m i l a r r a t e s , w i t h c h a l c o p y r i t e b e i n g an order of  magnitude slower. i n t o two  found  range of i n v e s t i g a t i o n was  I t was  stages, f i r s t ,  a c t i v a t i o n energy  1.8  found  t h a t c h a l c o c i t e l e a c h i n g can be  the r a p i d t r a n s f o r m a t i o n to c o v e l l i t e w i t h  Kcal/mole,  These two  chalcocite  stages of l e a c h i n g were a l s o observed  Two for  Kcal/  No  such,  i n c o v e l l i t e or c h a l c o p y r i t e .  s e p a r a t e r e a c t i o n s were r e c o g n i z e d as o c c u r i n g s i m u l t a n e o u s l y  a l l f o u r m i n e r a l s d u r i n g the o x i d a t i o n p r o c e s s :  r e a c t i o n y i e l d i n g e l e m e n t a l s u l p h u r and s u r f a c e , and  of 11.4  i n bornite with  (or d i g e n i t e ) a p p e a r i n g as an i n t e r m e d i a t e s t e p .  t r a n s f o r m a t i o n s were observed  an  f o l l o w e d by a slower o x i d a t i o n stage  i d e n t i f i e d as c o v e l l i t e - d i s s o l u t i o n w i t h an a c t i v a t i o n energy mole.  divided  an e l e c t r o c h e m i c a l  c r e a t i n g p i t s on the m i n e r a l  a chemical r e a c t i o n producing sulphate.  The  first  reaction  dominates i n s t r o n g l y a c i d i c c o n d i t i o n s , b e i n g r e s p o n s i b l e f o r about. 85% of the s u l p h u r r e l e a s e d from the m i n e r a l , but the s u l p h a t e to elemental sulphur r a t i o i n s o l u t i o n increases with decreasing a c i d i t y . Above 120°C the g e n e r a l o x i d a t i o n p r o c e s s i s i n h i b i t e d by molten s u l p h u r c o a t i n g the m i n e r a l p a r t i c l e s ; i s not reduced  above t h i s  the s u l p h a t e p r o d u c i n g r e a c t i o n , however,  temperature.  - iii  For c h a l c o p y r i t e the a c t i v a t i o n e n e r g i e s p r o d u c i n g r e a c t i o n and and  11.0  mineral  for  -  the,sulphate  s o l u b i l i z e d were found to be 16.0  Kcal/mole, r e s p e c t i v e l y .  l e a c h p a r t i a l l y v i a the .formation  I t i s suggested t h a t c h a l c o p y r i t e  i s detected  may  of t r a n s i e n t c o v e l l i t e on the s u r f a c e  s i n c e i t s l e a c h i n g r a t e i s f a s t e r than t h a t f o r c h a l c o p y r i t e , tio covellite  Kcal/mole  after leaching.  but  - iv -  ACKNOWLEDGEMENT  S i n c e r e g r a t i t u d e i s extended t o P r o f e s s o r E r n e s t who p r o v i d e d  Peters  t h e i n s p i r a t i o n , i n f o r m a t i o n and i n s i g h t n e c e s s a r y i n  b r i n g i n g t h i s work t o i t s f i n a l  form.  Thanks a r e a l s o extended to Dr. I.H. Warren and Dr. H. Majima f o r h e l p f u l comments o f f e r e d d u r i n g the w r i t i n g o f t h i s  F i n a n c i a l support  thesis.  v i a a r e s e a r c h a s s i s t a n t s h i p from t h e  N a t i o n a l Research C o u n c i l o f Canada i s g r a t e f u l l y acknowledged.  TABLE OF CONTENTS Page INTRODUCTION  1  Scope o f t h i s work  3  EXPERIMENTAL 1. 2. 3. 4.  Materials E x p e r i m e n t a l Apparatus E x p e r i m e n t a l Procedure A n a l y t i c a l Methods  RESULTS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.  4 7 9 10  .  13  Phase changes d u r i n g l e a c h i n g L e a c h i n g massive specimens Formation o f s u l p h a t e from e l e m e n t a l sulphur E v o l u t i o n o f hydrogen s u l p h i d e and sulphur d i o x i d e .. Comparison o f l e a c h i n g r a t e s V a r i a t i o n of a c i d i t y V a r i a t i o n o f oxygen p r e s s u r e Temperature v a r i a t i o n •••• The c a t a l y t i c e f f e c t o f c u p r i c i o n s Leaching c h a l c o p y r i t e  DISCUSSION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.  4  . ...  41  Reproducibility of r e s u l t s Phase changes d u r i n g l e a c h i n g L e a c h i n g massive specimens The f o r m a t i o n df s u l p h a t e from e l e m e n t a l s u l p h u r .... E v o l u t i o n o f hydrogen s u l p h i d e and sulphur d i o x i d e .. Comparison o f l e a c h i n g r a t e s .. V a r i a t i o n of a c i d i t y V a r i a t i o n o f oxygen p r e s s u r e Temperature v a r i a t i o n . The c a t a l y t i c e f f e c t o f c u p r i c i o n s Leaching c h a l c o p y r i t e  CONCLUSIONS Suggestions f o r f u t u r e work.  13 14 15 18 18 24 24 31 35 35  ...  41 41 45 47 48 48 50 53 54 56 57  62 63  REFERENCES  65  APPENDIX - X-Ray D i f f r a c t i o n A n a l y s i s  67  LIST OF  TABLES  Table  Page  1  Chemical c o m p o s i t i o n  2  S p e c i f i c g r a v i t i e s and weights f o r equal  3  Temperatures and used  4  of Copper-Sulphide m i n e r a l s  corresponding  oxygen  L e a c h i n g C o v e l l i t e , C h a l c o c i t e and 4M  areas  pressures -  6 8  . . > 10  Chalcopyrite i n .  23  5  L e a c h i n g of C h a l c o c i t e at v a r i o u s a c i d i t i e s at 125°G.  26  6  L e a c h i n g of C h a l c o p y r i t e at t h r e e a c i d i t i e s at 125°C.  28  7  C h a l c o c i t e l e a c h i n g a t 110°C oxygen p r e s s u r e s  28  8  9  a c i d and  ....  B o r n i t e i n 1M a c i d  i n 1M a c i d . a t  Oxidation rates for leaching Chalcocite i n p e r c h l o r i c a c i d ........  three 1M  L e a c h i n g C h a l c o p y r i t e i n 1M a c i d f o r 2 hours ........  31 38  LIST OF FIGURES Figure  1  2  Page  S u r f a c e o f massive specimen o f C o v e l l i t e and a f t e r l e a c h i n g  before 16  S u r f a c e o f massive specimen.of C h a l c o p y r i t e and a f t e r l e a c h i n g  before 17  3  O x i d a t i o n curves f o r l e a c h i n g C o v e l l i t e i n 4M p e r chloric acid  4  Oxidation  r 19  curves f o r l e a c h i n g C h a l c o c i t e i n 4M  acid  . .  .....  20  5  Oxidation  curves f o r l e a c h i n g C h a l c o p y r i t e i n 4M a c i d  21  6  Oxidation  curves f o r l e a c h i n g B o r n i t e i n 1M a c i d ....  22  7  L e a c h i n g C h a l c o c i t e a t 125°C a t v a r i o u s a c i d i t i e s  ...  25  8  L e a c h i n g C h a l c o p y r i t e a t 125°C a t t h r e e a c i d i t i e s  ...  27  9  O x i d a t i o n curves f o r the l e a c h i n g o f C h a l c o c i t e i n . 1M a c i d a t 110°C a t v a r i o u s oxygen p r e s s u r e s ..  29  The e f f e c t o f oxygen p r e s s u r e on the l e a c h i n g r a t e o f C h a l c o c i t e i n 1M a c i d a t 110°C .  30  10  11.  12  13  14  15  C h a l c o c i t e leached temperaturee  in.lM perchloric acid,at • • • •  three • •  32  A r r h e n i u s p l o t f o r primary stage o f l e a c h i n g o f C h a l c o c i t e i n 1M a c i d  33  A r r h e n i u s p l o t f o r secondary stage o f l e a c h i n g o f . C h a l c o c i t e i n 1M a c i d  34  C h a l c o p y r i t e leached temperatures  i n 1M a c i d a t t h r e e • • • •.  36  The e f f e c t o f i n i t i a l c u p r i c a d d i t i o n s , o n the l e a c h i n g r a t e s o f C h a l c o c i t e and C h a l c o p y r i t e .......  16  Arrhenius  17  Arrhenius p l o t f o r sulphate l e a c h i n g i n 1M a c i d  18  Two p a i r s o f experiments: of oxygen consumption  37  p l o t f o r C h a l c o p y r i t e d i s s o l u t i o n i n . 1M a c i d 39 formation  from  Chalcopyrite ......40  A guide to r e p r o d u c a b i l i t y 42  The P r e s s u r e O x i d a t i o n of Copper S u l p h i d e s i n Perchloric Acid Solutions  INTRODUCTION  Most of the copper  i n the e a r t h ' s c r u s t appears  s u l p h u r or c o p p e r - i r o n - s u l p h u r compounds.  The  The  copper-  copper b e a r i n g s u l p h i d e  ore i s e a s i l y c o n c e n t r a t e d to the n e a r l y pure m i n e r a l w i t h gangue m a t e r i a l p r e s e n t .  as  little  c l a s s i c a l method of the r e c o v e r y of  by p y r o m e t a l l u r g y produces s u l p h u r d i o x i d e and  impure copper.  o l d e s t h y d r o m e t a l l u r g i c a l processes f o r the r e c o v e r y of copper,  copper  One  of the  involving  the l e a c h i n g of r o a s t e d c o n c e n t r a t e s w i t h s u l p h u r i c a c i d , a l s o produces sulphur d i o x i d e ^ \  More r e c e n t l y w i t h the i n t r o d u c t i o n o f p r e s s u r e  o x i d a t i o n l e a c h i n g s u l p h i d e s c o u l d be l e a c h e d without  roasting.  i s o x i d i z e d to s u l p h a t e i n ammoniacal l e a c h i n g and may  Sulphur  be r e c o v e r e d  as  ammonium s u l p h a t e  When s u l p h i d e s a r e s u b j e c t e d to o x i d a t i o n l e a c h i n g i n a c i d (4) media e l e m e n t a l s u l p h u r i s f r e q u e n t l y o b t a i n e d i n good y i e l d example almost  100%  of the m i n e r a l s u l p h u r i s o b t a i n e d i n the  s t a t e i n the o x i d a t i o n of p y r r h o t i t e ^ , g a l e n a ^ ' ^  and  .  For  elemental  sphalerite^ .  E l e m e n t a l s u l p h u r i s a l s o o b t a i n e d i n a c i d l e a c h i n g but i n poor y i e l d ( l e s s than 50%)  for p y r i t e ^ ' ^ . 1  With copper  sulphide minerals  the  p r o d u c t i o n of e l e m e n t a l s u l p h u r has a l s o been r e p o r t e d but i t s y i e l d does not appear to be r e l i a b l y h i g h . The  l e a c h i n g of copper  s t u d i e d i n v a r i o u s o x i d i z i n g media. used  sulphides i n acid  s o l u t i o n s have been  For example, Jackson and  c h l o r i d e s o l u t i o n s w i t h c h l o r i n e as an o x i d a n t .  Strickland  (12) Sullivan.  - 2 -  s t u d i e d the c h e m i s t r y and k i n e t i c s of copper acid f e r r i c for  s u l p h a t e as an o x i d a n t and  chalcopyrite.  sulphides leaching using  found much slower r a t e s ,  especially  F e r r i c s o l u t i o n s were a l s o used, as the o x i d i z i n g (13)  'agent  f o r the l e a c h i n g of c o v e l l i t e by Thomas and  l e a c h i n g of c h a l c o c i t e , c h a l c o p y r i t e and o x i d a n t was  s t u d i e d by W a r r e n ^ ^ 1  a c c o r d i n g to the order  and atmospheric  .  The  c o v e l l i t e u s i n g oxygen as  and r e c e n t l y by o t h e r s ' .  these s t u d i e s the r a t e of l e a c h i n g was agent  Ingraham  •^  the From  found to v a r y w i t h o x i d i z i n g 3+ Fe > C^; a t room temperature  =>  pressure, chlorine w i l l  o x i d i z e most s u l p h i d e s i n a  few  3+ hours, Fe  i n s e v e r a l days, w h i l e oxygen takes y e a r s .  At temperatures (17)  over 100°C oxygen w i l l o x i d i z e s u l p h i d e s i n a few hours of  .  In a l l  the t h r e e o x i d i z i n g media the f i n a l products of l e a c h i n g a r e  i.e.,  s u l p h a t e and  elemental sulphur.  similar,  T h i s i s c o n s i s t e n t w i t h the p r o p o s i t i o n  t h a t the r e d u c t i o n of the o x i d a n t i s r a t e c o n t r o l l i n g , and t h e r e f o r e t h a t the o x i d a t i o n of the m i n e r a l proceeds  a l o n g a path t h a t i s  p r e d i c t a b l e from thermodynamic c o n s i d e r a t i o n s . of  c u p r i c s o l u t i o n s w i t h e l e m e n t a l s u l p h u r i s not an e q u i l i b r i u m c o n d i t i o n ,  i n view of the f a c t t h a t the 3Cu ~ H  is  However, the c o e x i s t a n c e  +  4H 0 2  +  thermodynamically  4S°  equation 3CuS  +  S0=  +  8H  [1]  +  f a v o u r a b l e a t pH v a l u e s above -4,  a t 25°C.  p r o d u c t i o n of e l e m e n t a l s u l p h u r d u r i n g the d i s s o l u t i o n of copper m i n e r a l s , t h e r e f o r e , r e f l e c t s a thermodynamically a l l p r e v i o u s i n v e s t i g a t o r s have observed when copper  suppose t h a t both copper  sulphide  unstable condition; yet  t h a t elemental s u l p h u r i s formed  i s l e a c h e d by a c i d s o l u t i o n s from a l l copper  However, the c o n d i t i o n s of R e a c t i o n  The  sulphide minerals.  [1] a r e s u f f i c i e n t l y c o m p e l l i n g to  r e c o v e r y and  elemental sulphur formation w i l l  not  -  occur i n good y i e l d s i m u l t a n e o u s l y .  -  The deportment o f s u l p h u r t o  e l e m e n t a l s u l p h u r and s u l p h a t e d u r i n g a c i d l e a c h i n g o f copper m i n e r a l s , t h e r e f o r e , deserves  3  careful  sulphide .  investigation.  Scope o f t h i s Work  In t h i s work i t i s proposed  t o c a r r y the study o f the l e a c h i n g  of copper  s u l p h i d e s f u r t h e r , u s i n g p e r c h l o r i c a c i d , a n d oxygen as the  oxidant.  The f o u r m i n e r a l s , c o v e l l i t e , c h a l c o c i t e , c h a l c o p y r i t e and  bornite are investigated.  Answers as t o the r e l a t i v e r a t e s o f l e a c h i n g  among these f o u r m i n e r a l s and the deportment o f s u l p h u r as the product w i l l be attempted  on the b a s i s o f t h i s work and p r e v i o u s knowledge.  Kinetic  s t u d i e s o f these l e a d h o p e f u l l y t o the p r o p o s a l o f r e a c t i o n s t e p s by which the k i n e t i c mechanism o f the whole p r o c e s s takes p l a c e .  I d e n t i t y o f the a c i d chemically inert  i n the system.  ionized, strongly resistant lowest  tendency  i s irrelevant  i f the a c i d anions a r e  Perchloric acid  i s known to be c o m p l e t e l y  to r e d u c t i o n i n d i l u t e s o l u t i o n s and has the  to form metal complexes o f a l l known a n i o n s .  - 4 -  EXPERIMENTAL  Materials  Reagent grade c h e m i c a l s were used e x c l u s i v e l y . were made w i t h d i s t i l l e d w,ater.  A l l solutions  The p e r c h l o r i c a c i d used was  Baker  and Adamson, 60%.  The c o v e l l i t e , c h a l c o c i t e and b o r n i t e came from B u t t e , Montana and were s u p p l i e d by Ward's N a t u r a l S c i e n c e E s t a b l i s h m e n t , I n c . The c h a l c o p y r i t e used i n the ground form o r i g i n a t e d from Miyatamata, The s o l i d  Japan.  specimen of c h a l c o p y r i t e used f o r one r u n came from Rouyn,  Quebec and was a l s o s u p p l i e d by Ward's.  The c h a l c o p y r i t e from Japan was o b t a i n e d i n the ground c o a r s e r than 100 mesh.  The o t h e r m i n e r a l s were s u p p l i e d  a s s o c i a t e d w i t h minor amounts of gangue m a t e r i a l .  form,  i n massive chunks  The m a t e r i a l  fragments  were broken o f f w i t h p l i e r s o r hammer, crushed i n a mortar and p e s t l e and screened to s i z e f r a c t i o n s . f o r a l l the r u n s .  Enough of the m i n e r a l was ground  initially  Only -150 + 200 mesh* and -200 mesh s i z e f r a c t i o n s were  used.  When examining the ground m a t e r i a l m i c r o s c o p i c a l l y v e r y f i n e p a r t i c l e s , much s m a l l e r than the nominal p a r t i c l e s i z e were seen.  *  Mesh s i z e s r e f e r to T y l e r s t a n d a r d s c r e e n s .  This  - 5 c o u l d be c o n s i d e r e d as dust c l i n g i n g a weighed sample of -150  + 200  i n water and d r i e d , to f i n d a weight l o s s of 0.6%  to the l a r g e r p a r t i c l e s .  When  mesh m a t e r i a l was washed r e p e a t e d l y  the percentage  o f such dust i n the sample,  was o b t a i n e d .  Samples o f the ground m i n e r a l s were analyzed f o r copper, i r o n and s u l p h u r by Coast E l d r i d g e E n g i n e e r s and Chemists, and  f o r copper,  i r o n and " i n s o l u b l e s " by the author.  Limited,  The'insolubles"  were the m a t e r i a l t h a t would not d i s s o l v e i n hot, c o n c e n t r a t e d acid.  The r e s u l t  are presented  of the a n a l y s e s as w e l l as the formula  nitric  compositions  i n T a b l e 1.  X-ray  d i f f r a c t i o n p a t t e r n s * were made from -200 mesh m a t e r i a l .  The a n a l y s e s show c o n c l u s i v e i d e n t i f i c a t i o n  o f c o v e l l i t e and c h a l c o p y r i t e :  every l i n e on the p a t t e r n i s matched by a prominent l i n e on the index cards. of  A good i d e n t i f i c a t i o n  i s a l s o o b t a i n e d from  c h a l c o c i t e ; the o n l y extraneous  l i n e appearing  the X-ray  patterns  i s the dominant  of b o r n i t e , as the c h e m i c a l a n a l y s i s would i n d i c a t e .  line  A wide range i n .  (18) stoichiometry i s reported f o r chalcocite amounts o f a second  phase.  thus p r e c l u d i n g l a r g e  The p a t t e r n f o r the b o r n i t e sample i h c l u d e s  the t h r e e s t r o n g e s t l i n e s o f c o v e l l i t e ; however, the weakness o f these lines *  i n d i c a t e s t h a t c o v e l l i t e i s a minor c o n s t i t u e n t .  D-spacings w i t h i n t e n s i t i e s from x-ray d i f f r a c t i o n p a t t e r n s t o g e t h e r w i t h these v a l u e s o b t a i n e d from the index cards a r e p r e s e n t e d i n the Appendix.  Jable 1 - Chemical:: Cpmpp:5±t±^^  Coast'Eldridge. Cu Fe S Sum*  Miriera1  Cqawfc "-Efl d--,Jforroalized* Cu Fe S  Author Cu Fe-  Insol.  Cu  Formula Comp. Fe S  C o v e l l i t e (CuS)  62.8 2.49 31.7 97.0  64.7 2.6  32.7  61.9 2.84  1.67  66.4  33.6  Cahlcocite (Cu S)  63.8; 5.6?  67 .-6 6.0:  25.4  62.7 6.25.  2.60.  79.8  20.2  Chalcopyrite ,(CuFeS )  33.2 30.4 34.6 98". 2  33; 8 31.0  35.2  1.90,  34.5  30.5 35.0  Bornite (Cu FeS )  58.2 11-7 26.; 2 96.1  60.6 12.2.  27.2  3.15  63.3  11.1 25.6  2  2  5  4  25TQ  -94.5  *  Coast- E l d r i d g e . assays, a d j u s t e d to make. Cu. :k Fe +. S... = 100  *  Sum o f Cu.+ Fe + S  57.7 12.6.  i  - 7 -  To f a c i l i t a t e comparison of r e s u l t s among the approximately  equal s u r f a c e areas of m i n e r a l s were used.  g r a v i t i e s of the m i n e r a l samples were determined are r e c o r d e d i n T a b l e  Experimental  experiments  and  Specific  the v a l u e s o b t a i n e d  2."  Apparatus  The  r e a c t i o n v e s s e l was  manufactured by P r e s s u r e Products  a shaking, t i t a n i u m a u t o c l a v e , I n d u s t r i e s , Inc., of 117 ml c a p a c i t y  and a b l e to w i t h s t a n d 4500 p s i working p r e s s u r e .  The  shaking was  r e c i p r o c a l motion w i t h a s t r o k e of 1.4  266  cycles/minute.  A Flexitallic  inches and  a  s t a i n l e s s s t e e l gasket s e a l e d the a u t o c l a v e .  Heat was  p r o v i d e d by an e l e c t r i c a l r e s i s t a n c e h e a t e r wound  around the a i i t o c l a v e .  The  temperature  was  sensed by a t h e r m i s t o r l o c a t e d  i n a t i t a n i u m w e l l i n the l i d p r o j e c t i n g to the c e n t r e of the a u t o c l a v e . A Thermistemp temperature Co.,  controller  (Model 71, Y e l l o w S p r i n g s  Inc.) i n s e r i e s w i t h a v o l t a g e r e g u l a t o r c o n t r o l l e d the  temperature  w i t h i n 1/2°C  The  w i t h ±1°  average  cycles.  t o t a l p r e s s u r e i n the a u t o c l a v e was  kept c o n s t a n t by a  p r e s s u r e r e g u l a t o r (0-100 p s i range) which l e t oxygen gas,from i n t o the a u t o c l a v e as i t was Electrodynamics  Instruments  consumed.  a reservoir  A transducer (Consolidated  Corp., Model 4-311, 0-1000 p s i range) r e l a y e d a  s i g n a l p r o p o r t i o n a l to the p r e s s u r e of oxygen i n the r e s e r v o i r to a s t r i p chart recorder.  Thus the r i e of r e a c t i o n was  Sargent  measured by the oxygen,  consumption as r e g i s t e r e d by the p r e s s u r e drop i n the  reservoir.  - 8 -  Table 2 S p e c i f i c G r a v i t i e s and Weights f o r E q u a l Areas  Mineral  Specific  Dana  ( 1 9 )  Gravity  Smith  Weights f o r equal a r e a s * ( 2 0 )  Measured and used  Covellite  4.6  4.6-4.76  4.61  3.25 gm  Chalcocite  5.5-5.8  5.5-5.8  5.55  3.91  Chalcopyrite  4.1-4.3  4.1-4.3  4.26  3.00  Bornite  4.9-5.4  5.06-5.08  5.07  *  Assuming c u b i c  shape f a c t o r , A r e a = 475 cm  357  f o r -150 + 200 mesh m a t e r i a l .  - 9 -  The p r e s s u r e r e g u l a t o r was c a l i b r a t e d and found when t h e p r e s s u r e i n the a u t o c l a v e was 95 p s i g .  to read 100  A l l pressur  e s  mentioned  h e r e a f t e r a r e the c o r r e c t e d v a l u e s .  Experimental  Procedure  A l l runs were conducted  w i t h 70 ml o f s o l u t i o n .  A f t e r the a u t o c l a v e was s e a l e d i n p r e p a r a t i o n f o r a run, and h e a t i n g were s t a r t e d . 10 to 15 minutes,  When the working temperature  shaking  was r e a c h e d , i n  t h e oxygen was l e t i n t o the a u t o c l a v e t o i n i t i a t e t h e  run.  A t . t h e end o f t h e r u n the oxygen v a l v e to t h e a u t o c l a v e was c l o s e d , t h e heat was turned o f f , t h e i n s u l a t i n g cap was removed and wet towels were wrapped around the s e a l i n g nut to promote r a p i d Shaking was i n t e r m i t t a n t d u r i n g t h i s time. below 85°C, i n 10 t o 15 minutes,  cooling.  When the temperature  fell  the a u t o c l a v e was opened and the c o n t e n t s  removed by a s u c t i o n f l a s k .  Between runs, t h e a u t o c l a v e was washed w i t h 50% n i t r i c A  acid.  t e a - s p o o n f u l o f powdered s i l i c a was added i f a p r e c i p i t a t e was suspected  of  c o a t i n g the w a l l s o f the a u t o c l a v e .  w i t h s h a k i n g j i t was allowed nitric  The a u t o c l a v e was s e a l e d and  to reach some temperature  The  a c i d remained i n t h e a u t o c l a v e f o r no l e s s than 15 minutes.  Unless o t h e r w i s e s t a t e d a l l experiments psi  above 70°C.  gauge p r e s s u r e r e g a r d l e s s o f the temperature  were carried out a t 95  o f t h e run.  Therefore  because o f s o l u t i o n vapour p r e s s u r e and n i t r o g e n e n t r a i n e d i n the  -  a u t o c l a v e at the time of c l o s u r e the p r e s s u r e of-oxygen a u t o c l a v e v a r i e d w i t h temperature  as l i s t e d  10  -  i n the,  i n T a b l e 3.  Table 3 Temperatures and Corresponding  and Oxygen P r e s s u r e s Used  Temperature  Oxygen Press  105°C .  7.7.3 p s i .  110  73.8  115  69.9  120  65.4  125  60.3  130  54.6  140  41.0  Unless o t h e r w i s e stateclj the m i n e r a l charges were o f . t h e weights  listed  of a l l experiments  i n T a b l e 2.and of -150 + 200 mesh p a r t i c l e  size.  A n a l y t i c a l Methods  1.  The amount of sulphate i n s o l u t i o n was e s t i m a t e d by the (21)  s t a n d a r d barium  c h l o r i d e p r e c i p i t a t i o n and g r a v i m e t r i c d e t e r m i n a t i o n  From repeated d e t e r m i n a t i o n of the same s o l u t i o n s a r e p r o d u c a b i l i t y of ±1.7% was  found. 2.  The c o n c e n t r a t i o n of copper  a s t a n d a r d e l e c t r o p l a t i n g procedure  i n s o l u t i o n was determined (21) u s i n g p l a t i n u m cathodes  by  - 11 -  3.  The  amount of m i n e r a l leached, was  calculated  from  the weight l o s s of the .autoclave charge c o r r e c t e d f o r e l e m e n t a l content. to  The  elemental  s u l p h u r i n the r e s i d u e was  assumed-to be ..equal  the t o t a l s u l p h u r i n the consumed m i n e r a l minus t h a t determined  s u l p h a t e i n the s o l u t i o n . in  sulphur  the . f i l t e r  The  r e s i d u e was  paper b e f o r e weighing.  m i n e r a l l e a c h e d was no c o m p o s i t i o n  allowed  as  to dry o v e r n i g h t  T h i s e s t i m a t e of the amount of  used o n l y f o r the l e a c h i n g of c h a l c o p y r i t e i n which  change i n the m i n e r a l o c c u r s d u r i n g l e a c h i n g .  Several  t r i a l s . i n which m i n e r a l samples were shaken w i t h pure water i n the ;  a u t o c l a v e showed t h a t the r e p r o d u c i b i l i t y of the r e s i d u e r e c o v e r y method was  about ±0.5%. 4.  was  The amount of i r o n i n the o r i g i n a l m i n e r a l  e s t i m a t e d by the standard double  samples  p r e c i p i t a t i o n and g r a v i m e t r i c  (21) determination 5.  The  amount-of oxygen.consumed was  t r a c e produced on the r e c o r d e d c h a r t . used and  The  estimated  I t was  originally  intended  calibration.  to a n a l y z e f o r elemental  by washing'.the d r y r e s i d u e i n carbon d i s u l p h i d e to d i s s o l v e the filtering  to remove t h e , s o l i d r e s i d u e and  evaporate  to dryness  weighed beaker.  to l e a v e behind  the  r e l a t i o n s h i p between ml of oxygen  c h a r t r e a d i n g were e s t a b l i s h e d by a gas b u r e t t e 6.  from  letting  sulphur  sulphur,  the carbon d i s u l p h i d e  a c r u s t of sulphur i n a p r e -  The method c o n s i s t e d of immersing the r e s i d u e f o r about  an hour i n 30 ml carbon d i s u l p h i d e , and qualitative f i l t e r  paper.  d i s u l p h i d e decanted.  The  The  then d e c a n t i n g i t through  r e s i d u e was  r e s i d u e was  and washed w i t h about 10 ml of carbon  a g a i n immersed and  the  f i n a l l y p l a c e d i n the f i l t e r disulphide.  a carbon paper  A warmed watch-glass  was  -  p l a c e d over the f u n n e l to minimize to evaporate  evaporation.  The  12  f i l t r a t e was  -  allowed  overnight.  The most e l e m e n t a l s u l p h u r accounted  f o r was  about 90%.  The  amount of oxygen consumption and the r e p r o d u c a b i l i t y of s u l p h a t e d e t e r m i n a t i o n s between runs i n d i c a t e d t h a t the m i s s i n g s u l p h u r not s u l p h a t e .  A check w i t h potassium  permanganate i n d i c a t e d  of t r a n s i e n t s p e c i e s of s u l p h u r o x i d e i n s o l u t i o n . thought  t h a t the above procedure was  e l e m e n t a l s u l p h u r from the r e s i d u e .  inadequate No  was  the absence  T h e r e f o r e i t was  f o r e x t r a c t i n g a l l the  r e s u l t s from these " a n a l y s e s "  are r e p o r t e d here.  Other  i n v e s t i g a t o r s have encountered  a s i m i l a r problem  (22)  -  13  -  RESULTS  1.  Phase Changes During  Leaching  S i n c e c o v e l l i t e i s more s t a b l e towards o x i d a t i o n than o t h e r , copper of  s u l p h i d e m i n e r a l s i t s f o r m a t i o n as an i n t e r m e d i a t e d u r i n g o x i d a t i o n  c h a l c o p y r i t e , c h a l c o c i t e and b o r n i t e i s thermodynamically  possible.  To i n v e s t i g a t e t r a n s f o r m a t i o n s of c h a l c o c i t e and b o r n i t e d u r i n g l e a c h i n g these m i n e r a l s were each l e a c h e d i n . 1 M a c i d at_125°C f o r 30 minutes.  X-ray  d i f f r a c t i o n p a t t e r n s were taken of the r e s i d u e s a f t e r  washing w i t h carbon d i s u l p h i d e . of  both c h a l c o c i t e and  of  residual bornite.  covellite;  To. determine mesh m a t e r i a l , was  A  the p a t t e r n f o r b o r n i t e showed no  s i m i l a r changes i n c h a l c o p y r i t e , 3 gm of  l e a c h e d i n . l M a c i d a t l 2 0 ° C f o r 8 1/2  r e s i d u e , a f t e r the run, was s u l p h u r and  Both p a t t e r n s c o n s i s t e d of dominant  hours.  lines evidence  -200 The  washed w i t h carbon d i s u l p h i d e to remove elemental  an x-ray d i f f r a c t i o n p a t t e r n was  s i m i l a r sample of r e s i d u e was  made of the.unleached m a t e r i a l .  sent to Coast E l d r i d g e f o r c h e m i c a l  analysis.  The x-ray p a t t e r n r e v e a l e d no evidence of c o v e l l i t e or c h a l c o c i t e and  the c h e m i c a l a n a l y s i s showed the r e s i d u e had  w i t h i n the accuracy range of the i n i t i a l m a t e r i a l assay. for  a  composition  Further  evidence  no m i n e r a l t r a n s f o r m a t i o n i s t h a t the r e s i d u e s of a l l runs of  c h a l c o p y r i t e a f t e r b e i n g washed w i t h carbon d i s u l p h i d e were i d e n t i c a l i n appearance w i t h the i n i t i a l m a t e r i a l .  - 14  -  To determine whether c o v e l l i t e i s p r e c i p i t a t e d from a c u p r i c s o l u t i o n by was  elemental sulphur,  c h a l c o p y r i t e , 1 gm  shaken i n the .autoclave w i t h 0.3  s o l u t i o n a t 120°C f o r 3 hours. the m a t e r i a l p l u s  0.3  gm  gm  a c i d s o l u t i o n a t 120°C f o r 5 hours. event t h a t the  s u l p h u r i n 0.3  Another run was  s u l p h u r i n 2M  but  mesh m a t e r i a l ,  M cupric  perchlorate  performed w i t h 3 gm  of  cupric perchlorate—2M perchloric  The  c h a l c o p y r i t e was  f o r m a t i o n of c o v e l l i t e should be  of the m i n e r a l ,  of -200  to prevent.any l e a c h i n g  catalyzed  added i n on  the  the  surface  a nitrogen.atmosphere  was  maintained.  A f t e r the runs the c h a l c o p y r i t e was and  washed w i t h carbon d i s u l p h i d e .  were u n a l t e r e d .  removed by  filtration  Both the c h a l c o p y r i t e and  Barium c h l o r i d e added to the s o l u t i o n s v e r i f i e d  of  sulphate.,  2.  L e a c h i n g Massive Specimens  L a r g e s i n g l e specimens of c o v e l l i t e , c h a l c o c i t e and were p o l i s h e d  smooth on one  p a s t e f o r c o v e l l i t e and  side, using  c h a l c o c i t e and  flat  on the p o l i s h e d  absence  chalcopyrite  1 micron alumina s l u r r y on  surface.  The  a  S c r a t c h e s c o u l d be  observed  specimens were mounted i n a  c y l i n d e r of c a s t s u l p h u r r e i n f o r c e d w i t h t i t a n i u m w i r e to mount  specimens f i r m l y d u r i n g 110°C  the  f o r f i n a l p o l i s h 1 micron diamond  m e t a l l u r g i c a l p o l i s h i n g wheel f o r c h a l c o p y r i t e . microscopically  the,solutions  the run.  The  i n 1M p e r c h l o r i c a c i d f o r 4.8,  three 3 and  specimens were l e a c h e d at 6.5  hours r e s p e c t i v e l y .  the  - 15 -  For t h e c o v e l l i t e specimen, photomicrographs s u r f a c e b e f o r e and a f t e r l e a c h i n g a r e p r e s e n t e d  The  i n F i g u r e 1.  c h a l c o c i t e turned from grey t o b l a c k upon l e a c h i n g .  M i c r o s c o p i c examination throughout  taken of the  a t low m a g n i f i c a t i o n r e v e a l e d c r a c k s  the s u r f a c e of the specimen.  At low m a g n i f i c a t i o n t h e unleached showed i n c l u s i o n s o f two k i n d s :  surface of c h a l c o p y r i t e  grey, s o f t i n c l u s i o n s , probably  or c h a l c o c i t e , and hard, y e l l o w i n c l u s i o n s , p r o b a b l y p y r i t e . hardness  running  covellite  The  o f the i n c l u s i o n s r e l a t i v e to the m a t r i x i s e s t i m a t e d by the  d i f f i c u l t y o f removing s c r a t c h e s from them.  After leaching,the soft  i n c l u s i o n s were c o m p l e t e l y l e a c h e d out but the hard i n c l u s i o n s were unchanged. Photomicrographs taken a t 260X m a g n i f i c a t i o n a r e p r e s e n t e d  i n F i g u r e 2.  At lower m a g n i f i c a t i o n no change o f the m a t r i x was observed w i t h l e a c h i n g .  3.  Formation  o f Sulphate from E l e m e n t a l  To determine under the c o n d i t i o n s used  Sulphur.  whether e l e m e n t a l s u l p h u r o x i d i z e s to s u l p h a t e f o r l e a c h i n g a t e s t was made w i t h 0.5 gm o f s u l p h u r  p l u s one t e a s p o o n f u l o f s i l i c a  i n 0.36M c u p r i c p e r c h l o r a t e - 0.25M  p e r c h l o r i c a c i d s o l u t i o n a t 125°C.  A f t e r 2.3 hours the oxygen consumption was n e g l i g i b l e and a barium  c h l o r i d e t e s t r e v e a l e d t h a t no s u l p h a t e was p r e s e n t i n the s o l u t i o n .  - 16 -  After  Figure 1  Leaching  S u r f a c e of Massive Specimen of C o v e l l i t e b e f o r e and  after leaching 135X  - 17  Before  After  gure 2  -  Leaching  Leaching  S u r f a c e of Massive specimen of c h a l c o p y r i t e b e f o r e and  after leaching 260X  - 18 -  4.  E v o l u t i o n of Hydrogen S u l p h i d e and  To determine  Sulphur  Dioxide  whether hydrogen s u l p h i d e or s u l p h u r d i o x i d e  are p r o d u c t s of the o x i d a t i o n r e a c t i o n s c h a l c o p y r i t e , 6gm was  l e a c h e d i n 2M p e r c h l o r i c a c i d a t 120°C.  A f t e r 2 1/2  of -200  mesh,  hours,  when 0.0182 moles of oxygen had been consumed c o r r e s p o n d i n g to the o x i d a t i o n of about 30% of the m i n e r a l , the heat was the a u t o c l a v e c o o l below 100°C. i n the a u t o c l a v e was  turned o f f to l e t  With the oxygen l i n e c l o s e d the  allowed to bubble,  f o r about a minute each,  columns of s i l v e r n i t r a t e , 10 "*M potassium  permanganate and  gas through  distilled  water.  No  p r e c i p i t a t e was  formed i n the s i l v e r n i t r a t e which  the absence of hydrogen s u l p h i d e . its  f a i n t p i n k c o l o u r and  indicated  The permanganate s o l u t i o n r e t a i n e d  the pH of the d i s t i l l e d water remained  constant  i n d i c a t i n g the absence of s u l p h u r d i o x i d e .  5.  Comparison of L e a c h i n g Rates  C o v e l l i t e , c h a l c o c i t e and p e r c h l o r i c a c i d a t 110°C i n 1M a c i d a t the same  and  125°C and  c h a l c o p y r i t e were l e a c h e d i n 4M two  runs were conducted  with bornite  temperatures.  The oxygen consumption curves f o r these runs are p r e s e n t e d i n F i g u r e s 3, 4, 5 and  6.  A n a l y s e s of copper  a f t e r the runs a r e g i v e n i n T a b l e  4.  and  sulphate i n s o l u t i o n  600  T  Figure  3;  Leaching-:covellite  inr4M*-perchloric  acid  600  1  2  3  Time-Hours Fxgnre  4.  Lnea-dr±ng--chaicQC-ite--ln--.:4M%-acid.  Time-Hours Figure 5.  Leaching c h a l c o p y r i t e in-. 4M-acid.  600  Time-Hours F i g u r e 6.  L e a c h i n g . b o r n i t e i n 1M  acid  - 23 -  Table 4 L e a c h i n g 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 4M A c i d and B o r n i t e i n 1M A c i d f o r 6 Hours.  Mineral  Temp.  moles O2 consumed  moles'^Cu in soln.  moles SO4 in soln.  % S as SOf*  %"Cuin soln.  Covellite  110°C 125  .0079 .0112  .0111 .0165  .00145 .00172  13.0 10.4  34.7 51.5  Chalcocite  110 125  .0170 .0189  .0261 .0262  .00206 .00309  12.0 17.9  66.5 66.6  C h a l c o p y r i t e 110 125  .0015 .0040  .0007 .0017  N.D.* N.D.  N.D. N.D.  4.5 10.8  Bornite  .0277 .0160  .0277 .0178  .00248 :00340  10.3 24.2  84.5 54.1  110 125  *  The r e s i d u e s o f C h a l c o c i t e and B o r n i t e runs a r e assumed t o be e n t i r e l y transformed t o C o v e l l i t e .  ^  N.D. = not determined.  - 24 -  6.  Variation of A c i d i t y  A s e r i e s o f runs was  done in.which  c h a l c o c i t e was l e a c h e d  at 125°C i n p e r c h l o r i c a c i d r a n g i n g i n c o n c e n t r a t i o n from 0.1M t o 4M. The  l e n g t h s o f these runs were 5, 6 or 9 hours.  curves for. these runs a r e g i v e n i n . F i g u r e 7.  The oxygen consumption  The amounts o f s u l p h a t e and  copper i n s o l u t i o n and the f i n a l pH v a l u e s a r e p r e s e n t e d  After coated  i n Table 5.  the runs w i t h 0.1M and 0.25M a c i d a y e l l o w p r e c i p i t a t e  the i n s i d e o f the a u t o c l a v e and a l i g h t - b r o w n p r e c i p i t a t e was p r e s e n t  w i t h the unleached  mineral.  The amount o f p r e c i p i t a t e was much more  e x t e n s i v e a t the.O.lM tihan a t t h e 0..25M a c i d r u n .  C h a l c o p y r i t e , 9 gm o f -150 + 200 mesh, was l e a c h e d a t 125°C i n 0.25M, 1.0M and 4M a c i d f o r 6 hours each. for  these runs a r e g i v e n i n F i g u r e 8.  The oxygen consumption  The amount o f s u l p h a t e and copper  i n s o l u t i o n and the f i n a l pH v a l u e s a r e presented  7.  curves  i n T a b l e 6.  V a r i a t i o n o f Oxygen P r e s s u r e  Three experiments were performed u s i n g c h a l c o c i t e  i n 1M a c i d  at 110°C and a t oxygen p a r t i a l p r e s s u r e s i n the a u t o c l a v e o f 25, 42 and 74 p s i . The  l e n g t h s o f the runs were 5, 6 and 9 hours  The  respectively.  oxygen consumption curves f o r these runs a r e presented i n  F i g u r e 9. . These curves can b e d i v i d e d i n t o two p a r t s , r e p r e s e n t i n g an initial, The  r a p i d o x i d a t i o n . s t e p f o l l o w e d by a p e r i o d o f steady,  s l o p e s o f these curves a r e presented  p r e s s u r e o f oxygen i n F i g u r e 10.  slow o x i d a t i o n .  i n . T a b l e 7 and p l o t t e d  against  /  F i g u r e 7.  Leaching  Time-Hours of C h a l c o c i t e 125°C a t v a r i o u s  acidities.  -  -  Table Leaching  Chalcocite  -  5  in Perchloric  A c i d i t y D u r a t i o n moles 0 moles Cu moles SO4 consumed i n s o l n . i n s o l n . of r u n 2  26  Acid  at  125°C  %S as f i n a l p r e c i p i t a t e % Cu pH in soln. SO5*  4M  6 hr. 6  . 0189 . 0202  .0262 .0332  .00309 .00259  66.7 84.5  17.9 10.7  0 0  nil nil  2  5  .0210  .0261  .00625  66.5  36.3  0.5  nil  1  9  • 9327  .0327  .0113  83.2  47.5  1.1  nil  0.5  6 5  .0356 .0363  .0280 .0284  .0137 .0140  71.2 72.3  71.7 71.8  1.0 1.35  nil nil  0.25  6  .0465  .0272  N.D.  ppt  N.D.  2.3  ppt.  0.10  6  .0228  .00715  N.D.  ppt  N.D.  3.0  ppt.  N.D; *  = Not determined  Residue i s assumed to b e . e n t i r e l y  transformed to c o v e l l i t e .  - 28 -  Table 6 Leaching Chalcopyrite  Acidity  Moles- • 0'2- molee-Cu in soln. consumed  (9gm) at-125°C f o r 6 Hours  -moles- SO-^--. •%-Cu in soln. in soln.  X-S- • f i n a l . as pH SQ^  pr ec i-p i t a t e -  4M  .0217  .01475  .00220  31.3  7.2  0  nil  •1  .0265  .0116  .00488  24.6  20.4  0.5  ppt  0.25  .0178  .00839  .00261  17.9  15.1  1.2  ppt  Table 7 Chalcocite  L e a c h i n g a t 110 C i n 1M a c i d a t Three Oxygen P r e s s u r e s P  Pressure oxygen  Initial rate  Secondary rate  25 p s i  270 m l 0 / h r  53.8 m l 0 / h r  42  300  57.4  74  545-830  87.5  2  2  30  i  r  1  i  -  r  900  800 700  600  500  ^ 4 0 0 o  I n i t i a l ,  stage  rates  o  ^300 Hi  w200 CO  u 100  L J  L  J  L  I  90  o  80  Secondary  stage  rates  iA  e  3' c0  t-i  10  20  30 Oxygen  Figure  10  The  40 pressure  J  L  _L  J  50  60  70  80  L 90  (psi)  e f f e c t  of  oxygen  c h a l c o c i t e  i n  1M a c i d  pressure at  on  110°C.  the  l e a c h i n g  rate  of  - 31. -  8.  Temperature V a r i a t i o n  Three runs were done on c h a l c o c i t e i n 1M p e r c h l o r i c a c i d a t temperatures 9, 9 and  o f 110°C, 125°C and 140°C.  3 hours  The  l e n g t h s of these runs were .  respectively.  The r e s i d u e from the run a t 140°C was carbon disulphide a f t e r which 1.924  d r i e d and washed w i t h  gm o f i t were r e t u r n e d to the a u t o c l a v e  to be l e a c h e d i n 1M a c i d a t 140°C f o r 3 hours.  The oxygen consumption curves f o r these runs a r e . g i v e n i n F i g u r e 11.  The r a t e s were measured f o r each of the two  o x i d a t i o n and a r e p r e s e n t e d i n T a b l e 8_. of oxygen f o r the two i n F i g u r e s 12 and  stages of  The r a t e s d i v i d e d by p r e s s u r e  s t a g e s o f l e a c h i n g a r e shown on A r r h e n i u s p l o t s  13.  Table 8 O x i d a t i o n Rates f o r L e a c h i n g C h a l c o c i t e i n 1M P e r c h l o r i c  Temperature  Pressure 0 psi 2  Primary Stage L e a c h i n g Rate  Secondary  Acid  stage l e a c h i n g rate  110°C  74  490-540 m l 0 / h r .  90 m l 0 / h r .  125 C  60  425-475  140  1$.0 °C  41  340  150  9  2  2  - 32 -  i  r  Time-Hours F i g u r e 11.  C h a l c o c i t e leached  i n 1M p e r c h l o r i c a c i d a t t h r e e  temperatures.  Figure  13  Arrhenius  plot  for  secondary  stage of  leaching  of  chalcocite  i n 1M a c i d .  - 35 -  Three runs were done on c h a l c o p y r i t e , u s i n g 9 gm mesh, i n 1M a c i d a t temperatures of these runs were 11, curves  9.  6 and  of 110°C, 125°C and  3 hours r e s p e c t i v e l y .  f o r these runs are g i v e n i n F i g u r e  of -150  140°C. The  The  +200  lengths  oxygen consumption  14.  The C a t a l y t i c E f f e c t of. C u p r i c Ions  In o r d e r to t e s t f o r a c a t a l y t i c e f f e c t of c u p r i c i o n s on l e a c h i n g of copper s u l p h i d e s , c h a l c o c i t e was  l e a c h e d i n 0.5M  copper  p e r c h l o r a t e - 1M p e r c h l o r i c a c i d s o l u t i o n a t 125°C f o r 6 hours. run employed c h a l c o p y r i t e , 9 gm of -150+200 mesh, i n 0.5M perchlorate—0.5M a l s o 6 hours.  10.  The oxygen consumption curves  copper  f o r these runs t o g e t h e r w i t h  c u p r i c s a l t a d d i t i o n s are  presented  15.  Leaching C h a l c o p y r i t e  A s e r i e s of 2 hour runs was 3 gm of -200 The  Another  p e r c h l o r i c a c i d s o l u t i o n a t the same temperature f o r  c o n t r o l experiments l a c k i n g i n i t i a l i n Figure  mesh, i n 1M a c i d  conducted  with c h a l c o p y r i t e ,  i n the temperature range of 105°C to 130°C .  s o l u t i o n s were a n a l y z e d f o r s u l p h a t e and  the amount of m a t e r i a l  l e a c h e d was  c a l c u l a t e d from the weight of the r e s i d u e removed from the  autoclave.  One  of the s o l u t i o n s (from a run at 120°C) was  f e r r o u s content one hour a f t e r removal from the a u t o c l a v e . except  one  The  was  In a l l runs,  shown i n A r r h e n i u s p l o t s i n F i g u r e s _16_ and  f e r r o u s t i t r a t i o n showed t h a t 68% of the i r o n p r e s e n t  i n the f e r r o u s . s t a t e .  indicating  s u l p h a t e a n a l y s e s a t v a r y i n g amounts of m i n e r a l  l e a c h e d are g i v e n i n T a b l e 9 and The  analyzed f o r  at 130°C, the oxygen consumption curves were l i n e a r ,  constant r e a c t i o n r a t e s .  17.  the  in solution  - 36  1  0  1  1  2  I  r  3  4  -  1  5  —r  6  Time-Hours F i g u r e 14.  C h a l c o p y r i t e leached m i n e r a l used).  i n 1M a c i d at t h r e e temperatures,  (9gm  of  Time - Hours F i g u r e 15  The e f f e c t of I n i t i a l c u p r i c a d d i t i o n s on the l e a c h i n g r a t e s o f C h a l c o c i t e and C h a l c o p y r i t e .  - 38 Table 9 L e a c h i n g C h a l c o p y r i t e i n 1M A c i d f o r 2 Hours  Temperature  gm M i n e r a l leached  Moles SO^  (3 gm o f -200 mesh)  % S...aa...SQ._ 4  105°C 105  .476 .504  .000638 .000603  12.3% 11.0  110 110  .510 .545  .00078 .00111  14.0 18.7  115  .615  .00100  14.9  120 120  .750 .606  .001105 .00115  13.5 17.4  125  .648  .00143  20.2  130  .706  .001635  21.2  2.48  2.52  2.56 l/l  F i g u r e 16  2.60 x  10  2.64  3  A r r h e n i u s p l o t f o r C h a c b p y r i t e d i s s o l u t i o n i n 1M  acid  - 41 -  DISCUSSION  1.  R e p r o d u c i b i l i t y of R e s u l t s  F i g u r e 18,  showing the o x i d a t i o n curves of two  experiments, i n d i c a t e s the degree of r e p r o d u c i b i l i t y i n t h i s work. copper  p a i r s of  t h a t can be  expected  Some of the f a c t o r s , i n f l u e n c i n g oxygen consumption a r e :  e n t e r i n g the s o l u t i o n , the f o r m a t i o n of s u l p h a t e , t r a n s i e n t s p e c i e s  of s u l p h u r o x i d e b e i n g formed and o x i d i z e d , f e r r o u s i o n s o x i d i z i n g to f e r r i c , and may  i m p u r i t i e s i n the o r i g i n a l m i n e r a l r e a c t i n g .  Some.of these  be i n f l u e n c e d by minute v a r i a t i o n s i n v a r i a b l e s t h a t may  been c o n t r o l l e d .  Those experiments  of s u l p h u r are expected of the w e t t i n g and  not have  c a r r i e d out above the m e l t i n g p o i n t  to be l e s s r e p r o d u c i b l e than the o t h e r s because  s p r e a d i n g expected  of the l i q u i d  s u l p h u r and  the  r e s u l t i n g v a r i a t i o n i n area of anodic r e g i o n s .  2.  Phase Changes During  Leaching  In the l e a c h i n g of c h a l c o c i t e the f o r m a t i o n of o c c u r s r a p i d l y a c c o r d i n g to the  reaction:  Cu„S + 2H  Cu  +10 2 ^F°393  •>- 30.37  CuS +  ++  [2]  Kcal/mole*  The r a p i d s e l f - d i f f u s i o n of the cuprous i o n i n c h a l c o c i t e f o r the k i n e t i c s to be as f a s t as *  covellite  (23,24)  is  necessary  observed.  A l l thermodynamic data a r e taken from where noted.  Latimer  (25)  w i t h few  exceptions  Time-Hours Figure  18.  Two p a i r s o f e x p e r i m e n t s : oxygen consumption.  a guide  to  reproducibility  of  - 43  -  From the m a t e r i a l s a n a l y s i s (Table 1) i t i s c a l c u l a t e d t h a t i n the c h a l c o c i t e sample used the average f o r m a l v a l e n c e of copper i s +1.28. Reaction curve  For 3.91  gm  of c h a l c o c i t e to r e a c t to completion  [2] 224 ml of oxygen w i l l be consumed.  f o r the o x i d a t i o n of c h a l c o c i t e at 110°C  according  Examination of  to  the  i n F i g u r e 4 shows t h a t  t h i s i s near the v a l u e f o r the t r a n s i t i o n between the f a s t i n i t i a l r a t e , i d e n t i f i e d as c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n , and slower  the subsequent  o x i d a t i o n r a t e , i d e n t i f i e d as c o v e l l i t e d i s s o l u t i o n .  comparison of F i g u r e s 3 and  Also,  4 shows t h a t the c h a l c o c i t e curves  have  about the same shape as the c o v e l l i t e curves but are d i s p l a c e d upwards by about 200 ml.  T h i s i n d i c a t e s t h a t the c h a l c o c i t e - c o v e l l i t e  i s p r a c t i c a l l y completed i n 30 minutes and c o v e l l i t e o x i d a t i o n i s minor. conductor both  and  t h e r e f o r e one  c o v e l l i t e and  incompletely to go  elemental  Because c h a l c o c i t e i s a good  p a r t i c l e can be at o n l y one  Therefore  b e f o r e the next  time electrical  e l e c t r i c a l potential}  s u l p h u r w i l l not c o e x i s t on one  reacted c h a l c o c i t e .  to completion  that d u r i n g t h i s  transformation  p a r t i c l e of  the t r a n s f o r m a t i o n i s  o x i d a t i o n step begins.  expected  However,  because a l l the p a r t i c l e s of the charge w i l l not be i n e l e c t r i c a l  contact  a sharp  expected  d i s t i n c t i o n between the two  o x i d a t i o n steps should not be  w i t h powdered m a t e r i a l .  The  t r a n s f o r m a t i o n of c h a l c o c i t e to c o v e l l i t e produces  i n the m i n e r a l p a r t i c l e s as a r e s u l t of s h r i n k a g e molar volumes of c h a l c o c i t e and respectively. due  c o v e l l i t e are 28.7  T h i s would prevent  cracks  i n volume, s i n c e the cc/mole and  20.7  the r a t e of t r a n s f o r m a t i o n from  to a d i f f u s i o n b a r r i e r b e i n g e r e c t e d by the product  forming  on  cc/mole decreasing the  - 44 particles.  These c r a c k s a l s o i n c r e a s e s u r f a c e area and may  f o r the l e a c h i n g r a t e of c h a l c o c i t e at 110°C than the c o r r e s p o n d i n g  The  rate for c o v e l l i t e  Cu FeS 5  Cu FeS 5  with  + 4H  4  4  + 2H  AF°  2 9 g  + 0  +  +  »  2  + 10  4CuS + Cu*  responsible greater  (Figure 3).  c h a l c o c i t e from  the  t r a n s i t i o n r e a c t i o n s are o p e r a t i v e , + Fe"*"" + 2H 0 '  [3]  1  2  » - C u S + 3CuS + Fe** + H 0  2  2  of -80.05 and  The  ( F i g u r e 4) being  appearance of both c o v e l l i t e and  l e a c h i n g of b o r n i t e i n d i c a t e s , t h a t two  be  -  first  [4]  2  -47.79 Kcal/mole r e s p e c t i v e l y . *  r e a c t i o n i s the one  expected from a k i n e t i c  p o i n t of view because cuprous i o n s i n b o r n i t e are a b l e to d i f f u s e (28) much f a s t e r than the f e r r o u s ions  and  t h e r e f o r e are expected  a r r i v e i n s o l u t i o n at l e a s t as f a s t as the f e r r o u s i o n s . thermodynamic c a l c u l a t i o n s p r e d i c t t h a t i r o n should  to  However,  l e a c h out of b o r n i t e  at a lower o x i d a t i o n p o t e n t i a l than t h a t r e q u i r e d f o r copper d i s s o l u t i o n and  therefore Reaction  C h a l c o c i t e c o u l d be  [4] probably  occurs  formed a c c o r d i n g  even predominate..  to the l a t t e r r e a c t i o n o n l y i f the  r e d u c t i o n of oxygen i s r a t e - d e t e r m i n i n g . i n the p a r t i a l l y leached  and may  The  presence of c h a l c o c i t e  bornite i s consistent with (27)  o x i d a t i o n step f o r the m i n e r a l  , and  a reversible  i s t h e r e f o r e evidence f o r a  r a t e - c o n t r o l l i n g step i n v o l v i n g oxygen r e d u c t i o n r a t h e r . t h a n  mineral  CutFeS, + . 4H The+ r0 e a c t i o n oxidation  [5]  i s excluded because c h a l c o c i t e and r e a c t to form c o v e l l i t e , * Thermodynamic data  the end  elemental  r e s u l t being  sulphur  i n intimate  equivalent  f o r b o r n i t e comes form Majima and  contact  to R e a c t i o n Peters  ( 2 ft)  [3].  - 45  From p r e v i o u s  work done w i t h b o r n i t e i t i s r e p o r t e d  d i g e n i t e i s r a p i d l y formed when b o r n i t e - i s heated i n the range of 80°  to 1 5 0 ° C ^ \ 8  Digenite  -  that  temperature  i s s t a b l e above 105°C  and (29)  decomposes to c h a l c o c i t e and  c o v e l l i t e below t h i s temperature  T h i s work i s c o n s i s t a n t w i t h the r e s u l t s obtained transforming  l e a c h i n g a l t h o u g h the  reaction  CuFeS  + 2H-  + Fe^  has  a  AF°  here, i . e . , b o r n i t e  r e s u l t s show that c h a l c o p y r i t e does not  during  +  + 102  ». CuS  form  covellite  + S° + H 0  [6]  2  of -10.95 Kcal/mole at 120°C*  p o s s i b i ^ i t y that the f o r m a t i o n  T h i s does not  of c o v e l l i t e may  be an  exclude  i s f a s t e r than t h a t of c h a l c o p y r i t e would not be p r e s e n t  (comparing F i g u r e s  the  intermediate  i n the mechanism of l e a c h i n g , but because the l e a c h i n g r a t e of  3.  .  to c h a l c o c i t e . The  9  ,  3 and  step  covellite  5) the  former  i n o b s e r v a b l e amounts.  L e a c h i n g Massive Specimens  Examination of the photomicrographs of F i g u r e 1 f o r the of c o v e l l i t e r e v e a l s of l i g h t  that b e f o r e  leaching  the c o v e l l i t e contained  grey m a t e r i a l , p r o b a b l y c h a l c o c i t e or b o r n i t e ; the  a n a l y s i s suggests the presence of b o r n i t e .  After leaching  veins  chemical the  presence  of p i t s and  channels i n d i c a t e n o n u n i f o r m a t t a c k on the s u r f a c e of  covellite.  The  *  leaching  the  s c r a t c h marks s t i l l v i s i b l e show t h a t l i t t l e u n i f o r m  Thermodynamic data f o r c h a l c o p y r i t e i s taken from G o l o m z i k ^ * ^  attack  -  has o c c u r r e d .  46  -  The photographs show t h a t the p i t s were i n i t i a t e d a t  l o c a t i o n s of the o r i g i n a l l i g h t grey phase.  I f t h i s phase i s c h a l c o c i t e  or b o r n i t e , t h i s i s c o n s i s t e n t w i t h the f i n d i n g s d i s c u s s e d i n the above, s e c t i o n t h a t i f i n e l e c t r i c a l c o n t a c t then c o v e l l i t e should not l e a c h u n t i l c h a l c o c i t e and b o r n i t e have transformed  completely  to  covellite.  In the t r a n s f o r m a t i o n p r o c e s s the grey phase w i l l open up c r a c k s i n the mineral.  The p i t s and channels  l i g h t grey phase and  extend  over.a l a r g e r a r e a than the  original  t h i s i n d i c a t e s t h a t the r e g i o n a d j a c e n t to t h i s  phase becomes a n o d i c .  Nonuniform a t t a c k on e l e c t r i c a l conductors o c c u r r e n c e of e l e c t r o c h e m i c a l p r o c e s s e s ^ ^ . w i t h a c i d and oxygen the anodic and  i s i n d i c a t i v e of  I n the l e a c h i n g of  c a t h o d i c r e a c t i o n s may  the  covellite  be w r i t t e n  as f o l l o w s : CuS 2H  +  >-Cu + 10 2 On  may  migrate,  + S° + 2e  + +  + 2e  >  [7]  H2O  [8]  some c o r r o d i n g m a t e r i a l s the anodic and  c a t h o d i c areas  g i v i n g the appearance of g e n e r a l c o r r o s i o n .  However the  photographs show the areas were r e a s o n a b l y f i x e d d u r i n g the l e n g t h of t h i s run, w i t h R e a c t i o n [8]  [7]  i n i t i a t i n g and p r o p a g a t i n g p i t s , and  o c c u r i n g on the v i r t u a l l y unattacked  surface.  An e x p l a n a t i o n f o r t h i s  i s t h a t i n p i t s the c o n c e n t r a t i o n of oxygen i s expected on the f l a t  surface.  Therefore Reaction  the p i t s , whereas R e a c t i o n  [8]  d i f f u s i o n of oxygen and protons  [7]  Reaction  to be l e s s  would c o n t i n u e and  than  propagate  i s u n l i k e l y i n p i t s s i n c e i t i n v o l v e s the, to the s u r f a c e of the m i n e r a l .  - 47 -  S i n c e c h a l c o c i t e and b o r n i t e t r a n s f o r m to c o v e l l i t e d u r i n g the i n i t i a l  step o f l e a c h i n g , the d i s s o l u t i o n c h a r a c t e r i s t i c s o f  c o v e l l i t e d i s c u s s e d here should a l s o apply to the f i n a l l e a c h i n g o f c h a l c o c i t e and b o r n i t e .  During b l a c k and developed  l e a c h i n g the s o l i d specimen o f c h a l c o c i t e i t became c r a c k s on the s u r f a c e showing i t s t r a n s f o r m a t i o n to  c o v e l l i t e and a.simultaneous  shrinkage  i n volume.  The photomicrographs from l e a c h i n g the specimen of c h a l c o p y r i t e , F i g u r e 2, show t r a c e s o f l o c a l a t t a c k a t 260X m a g n i f i c a t i o n , however, c o n s i d e r i n g the slowness o f the l e a c h i n g o f c h a l c o p y r i t e the a v a i l a b l e evidence  4.  i s insufficient  Formation  of Sulphate  The  to exclude  the p o s s i b i l i t y o f g e n e r a l a t t a c k .  from Elemental  Sulphur  r e s u l t s i n d i c a t e t h a t w i t h oxygen and i n 0.25M p e r c h l o r i c  a c i d sulphur does not o x i d i z e to s u l p h a t e although S° + 30. +  H0 0  ^S07  + 2H  the r e a c t i o n [9]  +  — 2 I 4 has a /^F° o f -119.39 Kcal/mole a t 125°C.  Sulphur  t h a t o x i d i z e s t o s u l p h a t e through  c a t a y s i s by the  s u r f a c e of the m i n e r a l would not.be d i s t i n g u i s h a b l e from s u l p h a t e w i t h s u l p h u r o r i g i n a t i n g from the m i n e r a l  itself.  formation  -  5.  48  -  The E v o l u t i o n o f Hydrogen S u l p h i d e and Sulphur D i o x i d e  Hydrogen s u l p h i d e i s not a product of the l e a c h i n g even i n s o l u t i o n s o f 2M a c i d as p r e d i c t e d by thermodynamic  reaction  calculations,  s i n c e the r e a c t i o n .. H S  + Cu**  2  has a  >.  CuS + 2 H  [10]  +  ^ ° 2 9 8 °f -19.34 Kcal/mole F  and i s r a p i d i n the d i r e c t i o n as  written.  Sulphur d i o x i d e a l s o cannot be expected i n these s o l u t i o n s because  i t s o x i d a t i o n by oxygen i s r a p i d , a l t h o u g h the r e a c t i o n  CuS + 3 0 2  9  + 2H  >  +  has a or  6.  Cut* + '('  1  H~S0„ -*  A F ° 2 9 g °f -101.36 Kcal/mole.  [11] Sulphate f o r m a t i o n through  S0  H S0^ as an i n t e r m e d i a t e cannot be excluded. 2  Comparison of L e a c h i n g  Rates  From the o x i d a t i o n curves o f c o v e l l i t e , c h a l c o c i t e and of  F i g u r e s 3, 4, and  have a h i g h e r i n i t i a l  6,  a f t e r an i n i t i a l  s l o p e than the 110°C  c u r v e s , as expected, but have  steep s e c t i o n , assume c o n s t a n t s l o p e s .  the r e a c t i o n r a t e s a t 125°C can be a t t r i b u t e d the m i n e r a l and  thereby s t i f l i n g  s u l f u r i s 119 C. P  to l i q u i d  curves,  The decrease i n sulphur c o v e r i n g  the r e a c t i o n , s i n c e the m e l t i n g p o i n t  T h i s c o n c l u s i o n was  i n v e s t i g a t o r s ' ^ ' .  bornite  i t can be seen t h a t the curves f o r l e a c h i n g a t 125°C  c o n t i n u o u s l y d e c r e a s i n g s l o p e s over t h e i r range, whereas, the 110°C  of  2  a l s o reached by many p r e v i o u s  I f the anodic r e a c t i o n o c c u r s i n p i t s on the  m i n e r a l , s t i f l i n g of the r e a c t i o n i s e s p e c i a l l y  likely.  -  In the l e a c h i n g of c o v e l l i t e , F i g u r e f o r the steady r a t e s e c t i o n of the 110°C  3,  i t would be  and  expected  o x i d a t i o n curve to pass through  the o r i g i n , but b o r n i t e and/or c h a l c o c i t e i m p u r i t i e s i n the r e a c t r a p i d l y at f i r s t  -  49  covellite  a l i n e a r r a t e i s reached when o n l y  covellite  remains.  The curves but  c h a l c o c i t e curves are the same shape as the  d i s p l a c e d upwards by an amount n e c e s s a r y to produce  c h a l c o c i t e - c o v e l l i t e transformation, that the 110°C  as d i s c u s s e d  be  explained  formed d u r i n g  earlier.  by  the i n c r e a s e  i n surface  to be  fact  than f o r  the l e a c h i n g of  area of c h a l c o c i t e by  covellite,  the  cracks  the c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n .  I t i s i n c o r r e c t to compare the b o r n i t e o x i d a t i o n r i g o r o u s l y w i t h the o t h e r s noticed  the  The  steady l e a c h i n g r a t e f o r c h a l c o c i t e i s steeper  c o v e l l i t e , even though both can be c o n s i d e r e d may  covellite  from F i g u r e  s i n c e the a c i d i t i e s are d i f f e r e n t .  7 that there  l e a c h i n g c h a l c o c i t e i n 1M  curves  and  of s u l f a t e i s produced, and  4M  It i s  i s a s i g n i f i c a n t d i f f e r e n c e between acid.  The  t h a t the i r o n  f a c t that a v a r y i n g amount from b o r n i t e o x i d i z e s almost  c o m p l e t e l y to f e r r i c tend to make the oxygen consumption curves l e s s meaningful.  These f a c t o r s permit o n l y q u a l i t a t i v e i n t e r p r e t a t i o n s of  the  curves.  The  110°C  o x i d a t i o n curve i s steeper  f o r b o r n i t e than f o r  c h a l c o c i t e and  c o v e l l i t e p r o b a b l y because the g r e a t e r volume change d u r i n g  transformation  a m p l i f i e s the c r a c k s  of c h a l c o c i t e (or d i g e n i t e ) would be  and  p r o b a b l y because the  transformation  to c o v e l l i t e , s i n c e i t i s a secondary r e a c t i o n ,  spread over a l o n g e r  time p e r i o d  than the e q u i v a l e n t  transformation  - 50 -  in original chalcocite. of b o r n i t e i s probably  Thus the f i n a l  not o n l y the l e a c h i n g o f c o v e l l i t e but a  simultaneous t r a n s f o r m a t i o n a f t e r 1 hour i s s t e e p e r the same way.  steady r a t e f o r 110°C l e a c h i n g  to some e x t e n t .  The f a c t t h a t the 125°C curve  than the c h a l c o c i t e curve can be e x p l a i n e d i n  That i t i s l e s s s u b j e c t  to s t i f l i n g  may a g a i n be evidence t h a t the t r a n s f o r m a t i o n  by molten s u l f u r  i s spread  out over a l o n g e r .  period.  The  l e a c h i n g of c h a l c o p y r i t e ( F i g u r e 5) i s an order  slower than t h a t o f o t h e r  copper m i n e r a l s .  A f t e r s i x hours the oxygen  consumption w a s . s t i l l too s m a l l to d e t e c t s t i f l i n g by elemental at  125°C.  Apparently  other m i n e r a l s  fast i n i t i a l  of magnitude  r a t e s may be due to dust  sulphur  or t r a c e s o f  and a r e t h e r e f o r e not n e c e s s a r i l y c h a r a c t e r i s t i c o f  chalcopyrite.  7.  V a r i a t i o n of A c i d i t y  An  examination o f the o x i d a t i o n curves f o r l e a c h i n g chalcocite  i n p e r c h l o r i c a c i d of v a r y i n g s t r e n g t h s  ( F i g u r e 7) shows that t h e . t o t a l  oxygen consumption i n c r e a s e s from the 4M r u n t o a maximum a t the 0.25M r u n . The  sharp decrease i n r e a c t i o n r a t e a f t e r about one hour f o r the 4M and  2M cases may be a t t r i b u t e d to l i q u i d further leaching.  sulphur  c o a t i n g the m i n e r a l  T h i s phenomenon would normally  and i n h i b i t i n g  be expected t o be operative,  i n a l l runs i n t h i s s e r i e s .  From Table  5 i t i s seen that the decrease o f a c i d i t y  from  4M to 0.5M i s accompanied by an i n c r e a s e i n the y i e l d o f s u l p h a t e . i s not s u r p r i s i n g c o n s i d e r i n g t h a t sulphur  i s never produced when  This sulphides  - 51 -  a r e leached i n b a s i c s o l u t i o n s  (2 31) ' , and t h a t w i t h i n c r e a s i n g pH v a l u e s  e l e m e n t a l sulphur becomes l e s s s t a b l e .  The o b s e r v a t i o n t h a t the o x i d a t i o n  r a t e d u r i n g the l a t t e r h a l f o f each run i n c r e a s e s w i t h d e c r e a s i n g a c i d i t y l e a d s to the p o s s i b i l i t y  t h a t e i t h e r the s t i f l i n g o f the r e a c t i o n has been  e l i m i n a t e d , e.g., s u l p h u r i s b e i n g removed, or o t h e r r e a c t i o n s t h a t consume oxygen become i n c r e a s i n g l y dominant.  I t has a l r e a d y been shown t h a t s u l p h u r i s not removed by o x i d a t i o n to s u l p h a t e i n an a c i d , c u p r i c s o l u t i o n .  T h i s experiment/  was conducted i n 0.25M a c i d and i s not more f a v o u r a b l e a t h i g h e r acidities. directly  An a l t e r n a t i v e i s . f o r  the r e a c t i o n p r o d u c i n g  sulphate  to become dominant, and/or i s n o t , s u b j e c t - t o l i q u i d  stifling.  sulphur  Assuming c h a l c o c i t e i s completely converted t o c o v e l l i t e ,  the s u l p h a t e p r o d u c i n g r e a c t i o n i s CuS + 2 0  2  >-Cu  ++  + SO*  [12]  a r e a c t i o n which not o n l y consumes f o u r times as much oxygen as t h a t y i e l d i n g elemental s u l p h u r , b u t a l s o does not consume a c i d .  The s u g g e s t i o n t h a t R e a c t i o n  [12] may be o c c u r r i n g a t l o c a t i o n s  o t h e r than the anodic s i t e s a r i s e s from the p r o b a b i l i t y t h a t i t i s not s u b j e c t to sulphur s t i f l i n g .  I f t h i s i s the case the s u l p h a t i n g r e a c t i o n  may be c h e m i c a l i n n a t u r e and occur somewhat u n i f o r m l y on.the s u r f a c e of the m i n e r a l .  I t i s not l i k e l y  p a r t of the c a t h o d i c R e a c t i o n CuS + 4H 0 0 2?  »- Cu* Cu*  + SO. SO^  f o r s u l p h a t e to be formed as the c o u n t e r -  [ 8 ] , i e , to proceed  + 8H  +  + 8e  [13] A F  298  =  -  7  6  -  6  5  K  c  a  l  /  m  o  l  e  - 52 -  because o f the u n f a v o u r a b l e entropy changes i n v o l v e d when t h i s many water molecules  a r e taken up to y i e l d a s i n g l e s u l p h a t e i o n .  I t i s not n e c e s s a r y  f o r a heterogeneous c h e m i c a l  reaction  to e x h i b i t uniform a t t a c k on the s u r f a c e of a p a r t i c l e s i n c e p r e f e r m e n t i a l a d s o r p t i o n and s e l e c t i v e a c t i v i t i e s , and hence v a r y i n g r e a c t i o n r a t e s among c r y s t a l l a t t i c e planes o f d i f f e r e n t o r i e n t a t i o n haye been observed  i n some  (38)  systems  .  However the a t t a c k i s expected  to v a r y no more than the  o r i e n t a t i o n o f the exposed f a c e s and t h e r e f o r e , pronounced a t t a c k l e a d i n g to the c r e a t i o n o f p i t s i s not expected  prefer,rential  f o r chemical  processes. A chemical r e a c t i o n such as E q u a t i o n oxygen r a t h e r than water molecules  [12] i n v o l v e s m o l e c u l a r  and i s c o m p l e t e l y c h e m i c a l , i . e . , i t i s  not a s s o c i a t e d w i t h s e p a r a t e . a n o d i c or c a t h o d i c p r o c e s s e s .  However, i t may,  i n f a c t , takei.place i n s e v e r a l steps on the m i n e r a l s u r f a c e , i . e . CuS S0  + 0 = 2  Cu""" + S 0 1  2  (ads) + 0  2  1  (ads)  = 2  »^  S0  The amount o f copper  [14] [15]  = 4  i n s o l u t i o n f o r the runs i n which no  p r e c i p i t a t e was formed remained a p p r o x i m a t e l y T h i s i n d i c a t e s t h a t as R e a c t i o n correspondingly. of the i n i t i a l  c o n s t a n t as seen i n T a b l e 5.  [12] i n c r e a s e s R e a c t i o n  [7] must  I t i s a l s o seen t h a t w i t h d e c r e a s i n g a c i d i t y  s e c t i o n s o f the o x i d a t i o n curves a r e lowered  decrease  the slopes  (Figure 7).  Thus i t seems t h a t both the c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n and the subsequent c o v e l l i t e l e a c h i n g without  sulphate formation  consume a c i d ) d i m i n i s h i n r a t e w i t h d e c r e a s i n g a c i d i t y . curves f o r l e a c h i n g a t 0.25M and'O.lM a c i d  (reactions that The s l o p e s o f the  i n d i c a t e that sulphate formation  - 53  becomes important a f t e r some time has  elapsed,  perhaps when the  p r o d u c i n g r e a c t i o n i s n e a r l y stopped because of r i s i n g pH.  o  -  sulphur  liquid  r  sulphur  stifling. The  oxygen consumption curves f o r 6 hours of  c h a l c o p y r i t e i n 4M, curves of F i g u r e  The the h i g h e s t  1M  and  0.25M a c i d  7 f o r the f i r s t  4M  leaching  ( F i g u r e 8) are comparable .to the .  2 1/2  hours of l e a c h i n g c h a l c o c i t e .  curve shows the lowest f i n a l o x i d a t i o n r a t e i n d i c a t i n g  degree of s t i f l i n g by  a c i d has  the g r e a t e s t  sulphate  formation  final  sulfur.  The  curve f o r l e a c h i n g i n  s l o p e p r o b a b l y because i t has  (Table 3 ) .  I t may  be  the  of the t h r e e curves and a f t e r s i x hours but  oxygen consumption and See,  8.  be  show a moderate amount of s u l p h a t e  a longer  leaching  a much h i g h e r  highest  t h a t as a r e s u l t of the  l e a c h i n g r a t e of c h a l c o p y r i t e the curve at 0.25M a c i d may  slow  the  lowest  in solution  time would l e a d to more r a p i d percentage p r o d u c t i o n  of  sulphate.  f o r example, the c h a l c o c i t e curve ( F i g u r e 7) f o r the same a c i d i t y .  Oxygen P r e s s u r e V a r i a t i o n  From the oxygen consumption curves of F i g u r e 12 and rates plotted against  oxygen p r e s s u r e  on F i g u r e  13,  l e a c h i n g r e a c t i o n are dependent on the p r e s s u r e s vessel.  The  experiments are inadaquate f o r any  pressure  and  r e a c t i o n r a t e to be p o s t u l a t e d ;  adsorption  isotherm  the a d s o r p t i o n  r e a c t i o n r a t e s would be of f i r s t of l e a c h i n g r a t e s on p l o t t i n g of l o g  and  the  order  the p r e s s u r e  (rate/press  1  O2)  that  reaction  r e l a t i o n s h i p between oxygen  however, i f a Langmuir  i s incomplete and  i n oxygen p r e s s u r e .  of  that  The  for Arrhenius  plots.  80 the  dependence  of oxygen as found here j u s t i f i e s  v e r s u s 1/T  oxidation  covellite  of oxygen i n the  a p p l i e s , i t seems t h a t at below the p r e s s u r e of oxygen on the m i n e r a l  the  i t i s suggested  the r a t e of both the c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n  psi  1M  the  - 54  9.  -  Temperature V a r i a t i o n  The v e r s u s 1/T  a c t i v a t i o n energy o b t a i n e d  i s a p p r o x i m a t e l y 1.8  by p l o t t i n g l o g  (Rate/PC^)  Kcal/mole f o r the primary stage of  l e a c h i n g c h a l c o c i t e ( F i g u r e 12).  T h i s low  a c t i v a t i o n energy i n d i c a t e s  that the r e a c t i o n r a t e i s p r o b a b l y c o n t r o l l e d by d i f f u s i o n , e i t h e r as part.of  the c a t h o d i c  reaction,  i e . , d i f f u s i o n of oxygen or p r o t o n s through  a l i q u i d boundary l a y e r , or the d i f f u s i o n of cuprous i o n s through chalcocite l a t t i c e .  J o s t r e p o r t s an a c t i v a t i o n energy f o r the d i f f u s i o n  cal/i of cuprous i o n s i n c h a l c o c i t e as a p p r o x i m a t e l y 1 Kcal/mole source assigns a v a l u e  The  of about 5 Kcal/mole to  cathodic  e x h i b i t an e n t i r e l y d i f f e r e n t r a t e f o r each  g r e a t l y enhanced by  the s u r f a c e of the m i n e r a l to c u p r i c and  ; another  (24)  I t i s r e a s o n a b l e to expect t h a t the c a t h o d i c  p r o p o r t i o n a l to and  rapidly  this  (32)  r e a c t i o n i s s i m i l a r f o r both stages of  c h a l c o c i t e l e a c h i n g but may stage.  the  reaction rate i s  the a r r i v a l of cuprous i o n s  at  s i n c e the cuprous i o n s i n s o l u t i o n o x i d i z e  w i l l reduce adsorbed oxygen i n d o i n g so.  There i s  evidence f o r the occurance of t h i s f o r the l e a c h i n g of c h a l c o c i t e i n (12) f e r r i c solutions  .  When the c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n  i s complete the c a t h o d i c  r e a c t i o n must take p l a c e on the c o v e l l i t e  without the a i d of cuprous i o n s and  may  c o n t r o l the r a t e of the whole p r o c e s s . transformation l a y e r , the  occur at a r a t e slow enough to I f the c h a l c o c i t e - c o v e l l i t e  i s r a t e c o n t r o l l e d by d i f f u s i o n through a l i q u i d  transformation  r a t e should  surface  increase with a g i t a t i o n .  boundary  - 55 The a c t i v a t i o n energy stage of l e a c h i n g ( F i g u r e 13) d i s s o l u t i o n of c o v e l l i t e . Kcal/mole  of 11.4  Kcal/mole  f o r the  secondary  can be c o n s i d e r e d to be t h a t f o r the  T h i s v a l u e i s comparable w i t h t h a t of  r e p o r t e d elsewhere  f o r the a c t i v a t i o n energy  11.7  f o r the l e a c h i n g  (14) of  covellite  .  These v a l u e s a r e g r e a t e r than can be expected  l i q u i d phase d i f f u s i o n c o n t r o l l e d p r o c e s s .  When c o n s i d e r a t i o n of the  dependence of r a t e on oxygen p r e s s u r e . i s taken i n t o account, suggests  for a  t h a t the r a t e s of d i s s o l u t i o n of transformed  this  c o v e l l i t e are  t r o l l e d by heterogeneous p r o c e s s e s a t the s u r f a c e of the m i n e r a l .  conSuch  a p r o c e s s c o u l d be a p a r t of the c a t h o d i c r e a c t i o n ; f o r example, the a d s o r p t i o n of oxygen on the s u r f a c e of the m i n e r a l , the t r a n s f e r of e l e c t r o n s to the oxygen, the combination w i t h protons or the d e s o r p t i o n of r e a c t i o n products.  A r a t e c o n t r o l l i n g s t e p a t the' s u r f a c e would  infer  that the r a t e of m i n e r a l d i s s o c i a t i o n would be p r o p o r t i o n a l to the s u r f a c e a r e a of the m i n e r a l , a c o n c l u s i o n reached It  [8] a l t h o u g h  a c t i v a t i o n e n e r g i e s found are w i d e l y d i f f e r e n t .  the  apparent  In the i n i t i a l  stage i t  be t h a t the c h a l c o c i t e - c o v e l l i t e t r a n s f o r m a t i o n i s r a p i d enough to  the c a t h o d i c r e a c t i o n to speed c o n t r o l l e d by d i f f u s i o n ,  indue  up to the p o i n t were t h i s r e a c t i o n c o u l d be  (Both r e a c t i o n s must occur to the same d e g r e e ) .  but the subsequent c o v e l l i t e d i s s o l u t i o n may to  investigations^^  c o u l d be t h a t both stages of the l e a c h i n g of c h a l c o c i t e  are r a t e c o n t r o l l e d by the c a t h o d i c R e a c t i o n  may  by o t h e r  initial  be slow enough f o r d i f f u s i o n  keep up, making a c h e m i c a l step the slowest i n the whole p r o c e s s .  - 56 -  When p a r t o f the r e s i d u e o f the r u n a t 140°C was washed i n carbon d i s u l p h i d e and r e t u r n e d its  initial  to the a u t o c l a v e  o x i d a t i o n r a t e was g r e a t e r  from which i t came. the m i n e r a l  i s responsible  point of  Figure  than the f i n a l  leaching,  r a t e o f the r u n  T h i s i s f u r t h e r evidence t h a t molten sulphur  surface  above the m e l t i n g  for further  f o r i n h i b i t i n g l e a c h i n g a t temperatures  sulphur.  14 shows no evidence f o r more than one step  o x i d a t i o n of c h a l c o p y r i t e .  coating  The runs a t 125°C and 140°C show  i n the  stifling  of the r e a c t i o n a f t e r a time o f l e a c h i n g .  10.  The C a t a l y t i c E f f e c t o f C u p r i c  Ions  F i g u r e 15 shows t h a t t h e r e  i s p r o b a b l y no c a t a l y t i c ,  e f f e c t on the l e a c h i n g r a t e o f c k a l c o c i t e by the a d d i t i o n o f c u p r i c but  a large increase  the i n t e r m e d i a t e  i n the o x i d a t i o n r a t e o f c h a l c o p y r i t e e s p e c i a l l y i n  time p e r i o d o f l e a c h i n g i s observed.  The  oxygen consumption r a t e o f c h a l c o p y r i t e due to the i n i t i a l of c u p r i c s a l t s , exceeds the amount r e q u i r e d i n s o l u t i o n to f e r r i c It  increased addition  f o r complete o x i d a t i o n o f i r o n  an o x i d a t i o n c a t a l y z e d by c u p r i c i o n s  i s tempting to r e l a t e the c a t a l y t i c  (9 33 34) ' '  e f f e c t of cupric  on c h a l c o p y r i t e o x i d a t i o n to the w e l l e s t a b l i s h e d f e r r o u s - f e r r i c in solution. ferrous ferric  However i t i s d i f f i c u l t  to a s s o c i a t e  ions from s o l u t i o n w i t h i n c r e a s e d m i n e r a l content o f the s o l u t i o n i s kept constant  preventing  ions  oxidation  the d e p l e t i o n of o x i d a t i o n , and the  by h y d r o l y s i s , thus  i t a l s o from a f f e c t i n g the l e a c h i n g r a t e .  i s probably surface  ions,  A better  explanation  s u b s t i t u t i o n of i r o n by copper i n the m i n e r a l  lattice,  - 57 -  w i t h o r without s u p e r f i c i a l t r a n s f o r m a t i o n mineral  t o c o v e l l i t e , and the  s u r f a c e may then develop enhanced l e a c h i n g r a t e s more comparable  to c o v e l l i t e .  S u b s t i t u t i o n o f i r o n by copper on i r o n s u l p h i d e  i s w e l l known i n f l o t a t i o n p r a c t i c e  The  '  d i f f e r e n c e i n l e a c h i n g r a t e s i s expected t o d e c r e a s e  a f t e r some p e r i o d o f l e a c h i n g because copper from the m i n e r a l f o r c a t a l y s i s as l e a c h i n g  11.  Leaching  minerals  o£ \  M r  i s available  progresses.  Chalcopyrite  The  a c t i v a t i o n energies  f o r c h a l c o p y r i t e consumed and s u l p h a t e  produced a r e 11.0 Kcal/mole and 16.0 Kcal/mole r e s p e c t i v e l y as found from the A r r h e n i u s  p l o t s of Figures  f o r c h a l c o p y r i t e leached these a r e b e l i e v e d  16 and 17.  The p o i n t s on the graph  a t 120°C, 125°C and 130°C a r e i g n o r e d  to be too low as a r e s u l t o f l i q u i d  Evidence f o r the s u p p o s i t i o n  sulphur  because stifling.  t h a t the r a t e c o n t r o l l i n g mechanism  i s the same f o r the l e a c h i n g o f c h a l c o c i t e and c h a l c o p y r i t e may be from the s i m i l a r i t y o f t h e i r a c t i v a t i o n e n e r g i e s  construed  (11.4 and 11.0 K c a l / m o l e ) .  T h e i r v a s t l y d i f f e r e n t l e a c h i n g r a t e s i n t h i s case i n d i c a t e d i f f e r e n t cathodic  area  suggestion  f r a c t i o n s f o r these two m i n e r a l s ,  that they possess l i k e r a t e c o n t r o l l i n g steps  p r o p o s i t i o n that t h e i r c a t h o d i c step  and t h e r e f o r e , t h e  i n the p r o c e s s .  leads  t o the  r e a c t i o n s a r e s i m i l a r and the slowest  - 58 I t was p o i n t e d out b e f o r e t h a t i t i s thermodynamically  favourable  f o r c h a l c o p y r i t e t o c o n v e r t o f c o v e l l i t e d u r i n g l e a c h i n g , a c c o r d i n g to the r e a c t i o n CuFeS  =>. CuS + F e ^ + S° + 2e.  2  [16]  but because o f the f a s t e r l e a c h i n g r a t e o f c o v e l l i t e i t does not appear i n o b s e r v a b l e amounts. and  However m i c r o a r e a s  cover a c e r t a i n f r a c t i o n  o f c o v e l l i t e may be formed t e m p o r a r i l y  o f the m i n e r a l s u r f a c e i n dynamic e q u i l i b r i u m .  T h i s c o v e l l i t e may not be massive enough to form a s e p a r a t e phase.  Three  r e a c t i o n s may occur on t h e c o v e l l i t e , i e . , CuS + 2 0 CuS 4H The  +  ^Cu** + S0  2  [12]  = 4  ^Cu" "*" + S° + 2e  [7]  1  +0  2  + 4e  chemical R e a c t i o n  >.2H 0  [8]  2  [12] and the e l e c t r o c h e m i c a l R e a c t i o n  c o v e l l i t e , whereas, R e a c t i o n  [7] d e s t r o y  [8] i s t h e c a t h o d i c complement to R e a c t i o n s  [16] and [7] as w e l l as to t h e r e a c t i o n CuFeS which breaks  2  .  ^  Cut* + Fe"*^ + 2S° + 4e  c h a l c o p y r i t e i n t o i t s elements.  I f the c a t h o d i c R e a c t i o n covellite  [17]  [8] i s g r e a t l y enhanced on t h e  s u r f a c e , the c o v e l l i t e may c o n s t i t u t e a s m a l l f r a c t i o n  of the  t o t a l m i n e r a l s u r f a c e but be r e s p o n s i b l e f o r the b u l k o f the oxygen reduction.  When t h i s r e a c t i o n i s r a t e d e t e r m i n i n g ,  this  theory, t h e r e f o r e ,  l e a d s to equal a c t i v a t i o n e n e r g i e s f o r c h a l c o p y r i t e and the o t h e r t h r e e m i n e r a l s , s i n c e the r e a c t i o n occurs mainly on a c o v e l l i t e s u r f a c e i n a l l cases.  - 59 The temporary life,  c o v e l l i t e areas may be c a t h o d i c d u r i n g  their  and when they have d i s a p p e a r e d the c h a l c o p y r i t e s u r f a c e may a g a i n  be a n o d i c .  The d i f f e r e n c e i n a c t i v a t i o n e n e r g i e s f o r t h e l e a c h i n g o f c h a l c o p y r i t e between 11.0 Kcal/mole found here and 23 Kcal/mole found by (14) Warren  may p a r t i a l l y be due to t h e f o l l o w i n g f a c t o r s :  temperature range was employed  A different  f o r t h e two s t u d i e s — W a r r e n ' s work b e i n g  done i n a g e n e r a l l y h i g h e r temperature range.  A l s o , the copper i n s o l u t i o n  was measured as the r a t e o f r e a c t i o n by Warren; i n t h i s work the weight l o s s o f the m i n e r a l was used. The d i f f e r e n c e i n a c t i v a t i o n e n e r g i e s may be e x p l a i n e d by t h e c h a l c o p y r i t e - c o v e l l i t e p r o p o s i t i o n by r e a s o n i n g t h a t i f t h e c a t h o d i c r e a c t i o n has an a c t i v a t i o n energy o f 23 Kcal/mole on c h a l c o p y r i t e and 11 on c o v e l l i t e , and i f the net a r e a o f c o v e l l i t e on the c h a l c o p y r i t e s h r i n k s o r d i s a p p e a r s w i t h i n c r e a s i n g temperature, then a r i s e i n temperature would  force  the main f r a c t i o n o f the c a t h o d i c r e a c t i o n onto t h e c h a l c o p y r i t e and an a c t i v a t i o n energy o f 23 Kcal/mole would  then be observed a t h i g h e r temperatures.  At 120°C the wide s e p a r a t i o n between the two p o i n t s o f c h a l c o p y r i t e leached  ( F i g u r e 16) may i n d i c a t e t h a t s t i f l i n g by s u l p h u r may o r may not o c c u r  a t t h i s temperature.  T h i s i s r e a s o n a b l e because the m e l t i n g p o i n t o f s u l p h u r  i s li9°C and the temperature c o n t r o l l e r caused temperature c y c l e s o f ±1°C d u r i n g its  operation.  - 60 Because t h e a c t i v a t i o n energy f o r s u l p h a t e p r o d u c t i o n i s somewhat l a r g e r than t h a t f o r c h a l c o p y r i t e l e a c h i n g an i n c r e a s e i n the percentage  o f s u l p h a t e formed would be expected  and approximate  correlation  w i t h t h i s can be seen from T a b l e 9.  That  t h e p r o d u c t i o n of s u l p h a t e i s not i n h i b i t e d  above the m e l t i n g p o i n t of s u l p h u r may be deduced from t h e f a c t  t h a t the  p o i n t s above t h a t temperature do not f a l l below t h e l i n e on the A r r h e n i u s plot  ( F i g u r e 17) and a l s o t h a t t h e s c a t t e r f o r these p o i n t s i s l e s s  that f o r c h a l c o p y r i t e leached. f o r temperatures  Thus the percentages  o f s u l p h a t e produced  above 120°C i n c r e a s e s because the r e a c t i o n p r o d u c i n g  s u l p h a t e goes on u n i n h i b i t e d whereas the o v e r a l l r e a c t i o n p r o d u c i n g i s hindered.  than  T h i s i s evidence  f o r the o c c u r r e n c e  sulphur  o f t h e two r e a c t i o n s a t  d i f f e r e n t , s u r f a c e r e g i o n s f o r c h a l c o p y r i t e l e a c h i n g , as was a l s o s t a t e d f o r chalcocite leaching.  I f the r e a c t i o n y i e l d i n g s u l p h a t e i s c h e m i c a l then expected mineral.  i n nature i t i s  to occur,more o r l e s s u n i f o r m l y on the s u r f a c e o f t h e  Such a r e a c t i o n may be the one a l r e a d y d e s c r i b e d , i e . ,  CuS" + 2 0  ^  2  Cu""" + S 0 1  1  [12]  = 4  which would l e a d to the same s u l p h a t e p r o d u c i n g minerals.  r e a c t i o n f o r a l l four  A c h e m i c a l r e a c t i o n f o r s u l p h a t e f o r m a t i o n d i r e c t l y on  c h a l c o p y r i t e i s the f o l l o w i n g : CuFeS  2  + 40  ^.Cu " " + Fe "*" + 2 S 0 ~ 4  2  4  [18]  4  4  A l t e r n a t i v e l y a c h e m i c a l r e a c t i o n may occur which produces both and  sulphur  sulphate, i e . ,  CuFeS  2  +5/2" 0  + 2H -H>CU +  2  + +  + F e ^ + S0  4  + S° + H 0 2  [19]  - 61 -  Because the r a t e o f sulphur  production  i s reasonably  the r e a c t i o n may be p a r t l y c h e m i c a l and p a r t l y e l e c t r o c h e m i c a l . would r e q u i r e l e s s s t r i n g e n t atomic c o n f i g u r a t i o n s :during of the s u l p h a t e not  fast, This  the f o r m a t i o n  r a d i c a l s i n c e a l l steps o f the r e a c t i o n mechanism need  occur a t one l o c a t i o n .  I f sulphate  i s formed by an e l e c t r o c h e m i c a l  t o t a l r e a c t i o n may be s p l i t  into i t s cathodic  process, the  and anodic p a r t s , i e . , [8] [20]  In t h i s p r o c e s s the sulphur i n o x i d i z i n g to s u l p h a t e . and it  the h i g h  i s required  t o break up the water m o l e c u l e s  Because o f the s t a b i l i t y o f the water m o l e c u l e  c o n f i g u r a t i o n a l entropy r e q u i r e d  i s more l i k e l y  f o r the sulphur  i n the s o l u t i o n .  f o r r e a c t i o n withw.ater,  to o x i d i z e w i t h the oxygen d i s s o l v e d  T h i s makes the c h e m i c a l R e a c t i o n s  [12] or [18] more  likely.  From the v a s t l y d i f f e r e n t l e a c h i n g r a t e s observed f o r b o r n i t e and  c h a l c o p y r i t e i t i s suggested that the r o l e of i r o n i n these two  minerals  i s not merely c h e m i c a l but i n v o l v e s the s t r u c t u r e o f the m i n e r a l  so as t o produce two w i d e l y 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 . respect and  the p a r t played  p y r r h o t i t e (37)  i n ^ p i t e of being  In t h i s  by i r o n i n t h i s case i s p a r a l l e l t o that i n p y r i t e  - minerals  which d i s p l a y two d i f f e r e n t c h a r a c t e r i s t i c s  composed o f the same elements.  \  - 62 -  CONCLUSIONS  1.  The order  o f l e a c h i n g r a t e s f o r copper m i n e r a l s  slowest to the f a s t e s t was found to be i n the o r d e r ,  from the  chalcopyrite,  c o v e l l i t e , c h a l c o c i t e , and b o r n i t e . 2.  The l e a c h i n g o f c h a l c o c i t e and b o r n i t e can be d i v i d e d  i n t o two s t e p s :  first,  the t r a n s f o r m a t i o n  the d i s s o l u t i o n as c o v e l l i t e .  t o c o v e l l i t e , and second,  No t r a n s f o r m a t i o n s  occur i n the l e a c h i n g  of c o v e l l i t e o r c h a l c o p y r i t e . 3.  The major p o r t i o n o f the l e a c h i n g o f c o v e l l i t e i s by  non-uniform a t t a c k on i t s s u r f a c e r e s u l t i n g i n the c r e a t i o n o f p i t s . 4.  The p r o d u c t i o n  of sulphate  p r o d u c t s o f l e a c h i n g occur by two d i s t i n c t  and e l e m e n t a l sulphur as reactions.  that the r e a c t i o n y i e l d i n g e l e m e n t a l sulphur occuring  a t l o c a l i z e d areas on the m i n e r a l  y i e l d i n g sulphate  Evidence i n d i c a t e s  i s electrochemical  i n nature  and t h a t the r e a c t i o n  i s c h e m i c a l i n n a t u r e and t h e r e f o r e may occur  uniformly  on the s u r f a c e o f the m i n e r a l . 5.  The a c t i v a t i o n energy f o r the f i r s t  stage o f the l e a c h i n g  of c h a l c o c i t e was found to be 1.8 Kcal/mole; the r a t e was b e l i e v e d th^ in  to be  d i f f u s i o n c o n t r o l l e d , e i t h e r in the l i q u i d phase, o r by cuprous d i f f u s i o n the m i n e r a l .  *The second stage o f c h a l c o c i t e l e a c h i n g was thought t o be  c o n t r o l l e d by a step i n the c a t h o d i c energy o f 11.4 Kcal/mole. accompanying p r o d u c t i o n  For the l e a c h i n g o f c h a l c o p y r i t e and the  of sulphate  be 11.0 and 16 Kcal/mole.  r e a c t i o n mechanism, w i t h an a c t i v a t i o n  the a c t i v a t i o n e n e r g i e s  were found to  - 63  6.  For the l e a c h i n g of c h a l c o c i t e , the percentage  of  -  sulphur  appearing  as s u l p h a t e i n c r e a s e d w i t h d e c r e a s i n g a c i d i t y , b e i n g about  i n 4M and  71% i n 0.5M  acid.  A s i m i l a r e f f e c t i s expected  f o r the  14%  other  three minerals. 7.  The  presence  of c u p r i c i o n s i n s o l u t i o n c a t a l y z e s the  l e a c h i n g of c h a l c o p y r i t e but 8.  The  t h e i r e f f e c t i s not d e t e c t e d i n c h a l c o c i t e .  r e a c t i o n seems to be about f i r s t  o r d e r i n oxygen  p r e s s u r e a t lower, p r e s s u r e s , a l t h o u g h an a d s o r p t i o n i s o t h e r m form of dependence i s n o t , e x c l u d e d .  Suggestions  f o r F u t u r e Work  -  T h i s study has uncovered s e v e r a l areas of work which may usefully  be  followed.  1.-  I t should be determined  e l e c t r o c h e m i c a l or a c h e m i c a l p r o c e s s . oxygen-18 as the r e a c t a n t gas.  whether s u l p h a t e i s formed by T h i s c o u l d be done by  For example f o r c o v e l l i t e the  an  using chemical  reaction CuS + 2 0  »-  2  S0  + Cu""*"  =  1  4  would i n c l u d e o n l y oxygen-18 i n the s u l p h a t e , whereas, the e l e c t r o c h e m i c a l reactions 8H CuS  +  + 20 .+ 8e"  4H 0  2  + 4H 0—Cu"!" " + S 0  2  4  2  = 4  + 8H  +  +  would produce s u l p h a t e c o n t a i n i n g l i t t l e  8e~ oxygen-18.  - 64 -  2. sulphur  or  To d e t e r m i n e w h e t h e r  c o u l d be added i n i t i a l l y  to  sulphate  during 3.  is  leaching. reaction  the  Tests  w i t h the  r u n may b e  of  this  Experiments  massive  pH v a l u e  is  should  extent  of  sulphur-  its  i n which an  oxidation  specimens  electrical of  the  mineral  l e a c h i n g r a t e may e l u c i d a t e  the  l e n g t h of  run.  b u f f e r the  of minerals  or  s o l u t i o n at  on the  c h e c k e d by e x p e r i m e n t s  out  i n which the  The experiments  a pH c h a n g e  of  during  the  of  units  salt  during  system  can  be  l o w pH v a l u e s . sulphate  i n the  s o l u t i o n on t h e  r e s u l t i n g deportment  i n which sulphate  removed f r o m s o l u t i o n as  effect  d o n e , w i t h low a c i d i t y  several  The s u l p h u r i c a c i d - s u l p h a t e  Any e f f e c t  5.  be c a r r i e d  determined.  the  or  elemental  mechanism.  l e a c h i n g underwent  rate  out  on the  and e x t e n s i v e  to  m i n e r a l and t h e  can be c a r r i e d  The e f f e c t  a rising  used  formed from  noted.  imposed on p o l i s h e d ,  4. of  is  from sulphur o r i g i n a t i n g from the m i n e r a l r a d i o a c t i v e  35  potential  sulphate  it  is  of  sulphur could  added to  forms by an i n i t i a l  leaching  the  be  solution  initially  barium c h l o r i d e  addition. 6. leaching  The s u g g e s t i o n  and t h e  investigation. by low e n e r g y covellite  effect It  of  this  that  on t h e  may b e p o s s i b l e t o  electron  diffraction.  f o r m a t i o n on c h a l c o p y r i t e  expression calculated.  for  the  chalcopyrite  fraction  of  sulphate detect  surface  covellite  and c a t h o d i c  such c o v e l l i t e  By k n o w i n g and f o r  forms  its  covered  the  rate  during  reactions on  chalcopyrite  equations  dissolution, a by c o v e l l i t e  merits  for  mathematical  c o u l d be  -  65  -  REFERENCES  1.  L i d d e l l the  D.M.,  M e t a l s "  2.  Forward  3.  V i z s o l y i  of  McGraw-Hill  F.A.,  Trans.  A . ,  Veltman  24, 326 4.  "Handbook  Nonferrous  Turchaninov  Can. H.,  Inst. and  -  V.V.,  and  I s s l e d .  K.W.,  and  Sinakevich  I n s t .  Bruce  Redkikh  6.  Vizsolyi  A . ,  7.  Sherman  M.I.,  and  S t r i c k l a n d  8.  Forward  F.A.,  and  Veltman.H.,  9.  McKay  10.  Warren  11.  Jackson  12.  S u l l i v a n  13.  Thomas  G.,  14.  Warren  I.H.,  15.  Veltman  R.W.,  Veltman,H.,  D.R.,  and  I.H.,  Aust.  K . J . ,  and  J . D . ,  J .  Met.  5£,  F.A.,  363  Met.  of  (1953).  Soc.  Ingraham J .  P e l l e g r i n i  S . ,  of  C h a l c o c i t e  Meeting  of  AIME,  VizsoHyiA., Elemental  Conf.  presented  at  H., from  96th  J.T.,  and  Met.  AIME  _9,  58,  227,  795  77  215  (1955) (1963).  (1957).  (1959).  301  (1958).  (1956). AIME  212,  373  (1958).  (1933).  (1967) S c i .  346  Trans.  515  Min.  836  212,  Gos.  (1963).  Trans;  1 1 ,  Irkutsku  unpublished.  9_,  36  (1958). V . N . ,  Mackiw  Concentrates",  "Direct  paper  A c i d  presented  at  Pressure 95th  Annual  1966.  Veltman Sulphur  _7,  301  Metals  AIME  J . D . H . ,  T.R.  A p p l .  J .  Metals  S c i .  Tr.,  Inst.  F.A.,  Trans.  106,  1 1 ,  Can.  J . D . H . , J .  Nauchn.  Metal.  Trans.  A p p l .  AIME  A . S . ,  Forward  S t r i c k l a n d  Aust.  H.,  of  Trans.  and  and  Halpern .J . ,  Leaching  47  Min.  Forward  Downes  Woodcock  Recovery  (1945).  5.  17.  -  (1963).  Nauchn.  16.  Metallurgy  Warren  Annual  review  I.H.,  and  Chalcopyrite Meeting  a r t i c l e ,  by  of  Aust.  Mackiw  V . N . ,  Pressure  AIME, Inst.  "Copper  Leaching",  and paper  1967. Min.  Met.  Proc.  No.  198,  (1961).  18.  Gaudin  19.  Dana  20.  Smith  A . M . ,  E.S., O.C.,  M i n e r a l s " ,  and  "A  Dicke  Textbook  G., of  Econ.  Geol.  34,  49  Minerology",  4th  E d . ,  " I d e n t i f i c a t i o n  and  2nd  Nostrand  E d . ,  D.  Van  Q u a l i t a t i v e Co.  (1939). J .  Wiley.  Chemical  A n a l y s i s  of  - 66 -  21.  Vogel I . , "A Textbook o f Q u a n t i t a t i v e I n o r g a n i c A n a l y s i s - Theory and P r a c t i c e " , 2nd Ed., Longmans, Green and Co., pp. 401, 407, 518.  22.  Ingraham T.R., p r i v a t e  23.  Wagner J.B., and Wagner C ,  24.  Pavlyuchenko M.M., P o k r o v s k i i I . I . , and Tikhonov A.S. ,j D b k l . Akad. Nauk. B e l o r u s s k . SSR .9 (4) 235 (1965).  25.  Latimer W.M., "The O x i d a t i o n S t a t e s 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 s " , 2nd Ed., P r e n t i c e - H a l l , I n c . (1952).  26.  Majima H., and P e t e r s E., p r i v a t e  27.  G a r r e l s R.M., and C h r i s t C.L., " 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 u m " , Harper and Row (1965).  28.  Takeuchi T., and Nambu.M., Ganseki-kobutsu-koisho G a k k a i - s h i 3^6, 33 (1952).  29.  Edwards A.B., " T e x t u r e s o f the Ore M i n e r a l s " , 1 s t Ed., A u s t . I n s t . Min. Met.: Melbourne (1947).  30.  Golomzik A . I . , I z v . V y s s h i k h Uchebn Z a v e d e n i i T s v e t n . Met. 7 (2) 47 (1964).  31.  Majima H., and P e t e r s E., " O x i d a t i o n Rates o f S u l f i d e M i n e r a l s by Aqueous O x i d a t i o n a t E l e v a t e d Temperatures", paper presented a t 95th Annual Meeting o f AIME, 1966.  32.  J o s t W.,  33.  Huffman R.E., Davidson N., J . Amer. Chem. Soc. 7_8, 4836 (1956).  34.  George P., J . Chem. Soc. (London) 280, 4349 (1954).  35.  B u s h e l l C.H.G., Krauss C.J., and Brown G., T r a n s . Can. I n s t . Min. Met. 65, 185 (1962).  36.  B u s h e l l C.H.G., Krauss C.J., and Brown G., Trans. Can. I n s t .  communications J . Chem. Phys. .26, 1602 (1957).  communication.  " D i f f u s i o n " , p. 168, Academic P r e s s :  Min. Met. 64, 177  New York  (1952).  (1961).  37.  Hahne H., D o c t o r a l D i s s e r t a t i o n , Technishen U n i v e r s i t a t B e r l i n  38.  L a i d l e r K.J., "Chemical K i n e t i c s " , 2nd Ed., p. 304, McGraw H i l l  (1964). (1965).  -  67  APPENDIX  X-Ray D i f f r a c t i o n  Butte C o v e l l i t e d  A"  I /  Patterns  CuS Index I  m  d  I /  I  m  3.21  30  3.220  28  3.05  70  3.048  67  2.80  90  2.813  100  2.72  100  2.724  56  2.32  20  2,317  10  2.04  20  2.043  7  1.96  10  1.902  25  1.90  70  1.896  75  1.73  50  1.735  34  1.55  40  1.556  37  C h a l c o p y r i t e , Japan d  3.02  I/Ln  CuFeS^ d  Index I/I  100  3.03  100  2.63  5  2.63  5  1.87  20  1.865  40  1.86  40  1.854  80  1.59  20  1.591  60  m  -  - 68 -  Butte Bornite d  C u ^ e S ^ Index d  I/lm  3.30  30  3.32  30  3.16  50  3.16  30  3.02  10  2.94  20  2.81  20  2.74  50  2.75  30  2.51  30  2.52  30  1.94  100  1.94  100  1.65  5  1.65  10  Butte C h a l c o c i t e d  ^im  CuS Index d  ^Ita  3.048  67  2.813  100  2.724  56  Cu S 2  d  Index ^Im  3.40  10  3.412  25  3.335  40  3.330  . 50  3.16  10  3.181  75  3.07  10  3.051  75  2.95  100  2.950  75  2.85  10  2.864  50  2.65  10  2.665  75  2.55  10  2.560  50  2.51  10  2.528  75  2.39  50  2.401 2.398  100 100  2.32  10  2.328  50  2.02  10  2.206  50  1.96  60  1.972  100  1.94  30  1.94  100  1.87  70  1.879  100  1.80  30  1.795  50  Bornite d  l e a c h e d 30 m i n u t e s  C^S  Index  4.23  40  4.27  50  3.32  10  3.33  50  3.20  20  2.181  75  3.08  20  3.04  100  2.93  50  2.80  50  2.72  40  40  1.79  Bornite  2.930  100  leached 6  hours  d  -  Index  d  d  ^Im  1.89 -1.85  CuS  69  3.220  28  3.048  67  2.813  100  75  2.724  75  2.724  56  1.879  100  1.896  75  1.875  50  1.795  50  CuS  Index  Cu2S  d  d  4.25  10  4.27  3.32  80  3.330 3.311  3.21  20  3.220  28  3.04  100  3.048  67  2.93  60  2.930  75  2.81  30  2.813  100  2.72  30  2.724  56  1.90  30  2.724  75  1.87  80  1.73  10  1.735  Index  34  ^Im  50 .  50 75  3.181  75  1.908  75  1.879 1.875  100 50  Chalcocite  leached  30 m i n u t e s  1/  Cu S 2  Index  1/Im  Im  CuS d  70  Index 1/  Im  3.33  10  3.330  50  3.20  10  3.181  75  3.220  28  3.04  50  3.051  75  3.048  67  2.93  100  2.930  75  2.80  60  2.822  50  2.813  100  2.73  40  2.731  75  2.734  56  2.42  10  2.401  100  1.89  60  1.895  50  1.896  75  1.86  10  1.879 1.862  100 25  1.80  40  1.795  50  1.74  20  1.735  34  1.57  10  1.572  15  1.55  10  1.556  37  1.53  20  -  

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