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JAFFERALI,

JEAN-MARIE

VANSEVEREN,

JEAN

VEREECKEN,

The anodic d i s s o l u t i o n of Cuss in s u l f u r i c acid so l u t i o n s was studied under g a l v a n o s t a t i c and p o t e n t i o s t a t i c conditions. The anodic p r o d u c t s w e r e studied by m i n e r a l o g i c a l and X - r a y d i f f r a c t i o n m e t h o d s . In e v e r y c a s e , the f o r m a t i o n of a digenite Cul.sS l a y e r is obs e r v e d at the s u r f a c e of Cu2S a c c o r d i n g to 5Cu2S ~

5Cul.8S + Cu ++ + 2e

A c o p p e r c o n c e n t r a t i o n g r a d i e n t a p p e a r s through the digenite l a y e r whose t h i c k n e s s r e m a i n s constant as soon as a Cul.~S l a y e r a p p e a r s at its own s u r f a c e a c c o r d i n g to 3Cul.8S ~ 4Cu1.1S + Cu ++ + 2e If the e l e c t r o l y s i s conditions a r e such that the anodic p o t en t i al r e m a i n s low, the next r e action to o c c u r is 10Cul.~S ~

l l C u ++ + 10S + 22e

But if under g a l v a n o s t a t i c conditions, the c u r r e n t d e n s i t y is high enough at a given t e m p e r a t u r e to r e a c h the s h a r p r i s e in anodic potential, o r if under p o t e n t i o s t a t i c conditions the p o t e n t i a l is kept high, two o t h e r r e a c t i o n s a r e p o s s i b l e : 10Cux.IS ~

lOCuS + Cu ++ + 2e

f o l l o w e d by C u S - - Cu ++ + S + 2e M o r e o v e r , at high anodic p o t e n t i a l , the following r e a c t i o n o c c u r s a l s o to s o m e extent CuS + 4 H z O - - Cu +§ + SO~ + 8H + + 8e r e s u l t i n g in a d e c r e a s e in anodic c u r r e n t e f f i c i e n c y f o r the c o p p e r d i s s o l u t i o n . F r o m a m o r e p r a c t i c a l point of v i e w , it was shown that it is p o s s i b l e to d ep l et e v i r t u a l l y c o m p l e t e l y the c o p p e r content of the anode ( r e s i d u e at l e s s than 0.5 pct C u ) k e e p i n g t h e e l e c t r o d e p o t e n t i a l at a low v a l u e ( l e s s than + 650 m V / E N H ) . P r o v i d i n g the t e m p e r a t u r e is high enough (75~ at l e a s t) , the m e a n c u r r e n t d e n s i t y r e m a i n s n e a r to 2 A / d m s, a s u i t a b l e v a l u e to obtain good cathodic d e p o s i t s . T H E usual way to win c o p p e r f r o m sulfide o r e s cons i s t s of c o n c e n t r a t i n g by flotation, s m e l t i n g the c o n c e n t r a t e s to obtain a c o p p e r m a t t e , c o n v e r t i n g to b l i s t e r c o p p er , f i r e r e f i n i n g and c a s t i n g i m p u r e c o p p e r into anodes, and e l e c t r o l y t i c r e f i n i n g . If the t e c h n i c a l and e c o n o m i c a l f e a s i b i l i t y of c a s t i n g the c o p p e r m a t t e into anodes and e l e c t r o r e f i n i n g t h e m into p u r e e l e c t r o l y t i c c o p p e r could be d e m o n s t r a t e d , two o p e r a t i o n s of the c l a s s i c a l p r o c e s s could be e l i m inated. The idea is not new: M a r c h e s e I p a t e n t e d such a p r o c e s s as e a r l y as 1882. A t t e m p t s to d e v