The kinetics of dissolution of bornite in acidified ferric sulfate solutions
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S i n t e r e d d i s k s of s y n t h e t i c b o r n i t e w e r e d i s s o l v e d in a c i d i f i e d f e r r i c sulfate s o l u t i o n s at t e m p e r a t u r e s r a n g i n g f r o m 5~ to 94~ The d i s s o l u t i o n o c c u r s in two s t a g e s ; in the f i r s t a nons t o i c h i o m e t r i c b o r n i t e with up to 25 pct d e f i c i e n c y of c o p p e r i s f o r m e d . In the s e c o n d , the nons t o i c h i o m e t r i c b o r n i t e is c o n v e r t e d to c h a l c o p y r i t e and e l e m e n t a l s u l f u r , which a c c u m u l a t e s on the disk s u r f a c e . At t e m p e r a t u r e s b el o w 35~ the r e a c t i o n f o l l o w s p a r a b o l i c k i n e t i c s and stops at the n o n s t o i c h i o m e t r i c b o r n i t e s t a g e . At higher t e m p e r a t u r e s it co n t i n u es through to c h a l c o p y r i t e and f o ll o w s l i n e a r k i n e t i c s . Both the p a r a b o l i c and l i n e a r p r o c e s s e s have a c t i v a tion e n e r g i e s of 5 to 6 kcal p e r m o l e . At h i g h e r t e m p e r a t u r e s the s e n s i t i v i t y of the r e a c t i o n r a t e to c h a n g e s in s t i r r i n g v e l o c i t y i n d i c a t e s c o n t r o l by diffusion through the liquid boundary l a y e r . N a t u r a l and s y n t h e t i c b o r n i t e d i s s o l v e by the s a m e p r o c e s s and at e s s e n t i a l l y the s a m e rate.
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the mining of sulfide c o p p e r o r e s , l a r g e t o n n a g e s , a p p r o x i m a t e l y 250,000 tons p e r day, ~ of l o w - g r a d e waste r o c k a r e p r o d u c e d in the o p e r a t i o n s . R e c e n t l y , t h e r e has been g r o w i n g i n t e r e s t ''z in r e c o v e r i n g s o m e of the c o p p e r c o n t a i n e d in this waste r o c k by h e a p - l e a c h i n g . In a c o m m e r c i a l o p e r a t i o n , a c i d is s p r a y e d on the s u r f a c e of the w a s te r o c k and it t r i c k l e s through the p il e , r e a c t i n g s l o w l y with the v a r i o u s m i n e r a l s . Oxidic c o p p e r m i n e r a l s a r e d i s s o l v e d rapidly by the a c i d a l o n e , but c o p p e r sulfide m i n e r a l s r e q u i r e the p r e s e n c e of an oxidizing agent to p r o m o t e t h e i r d i s s o l u t i o n . In h e a p - l e a c h i n g p r a c t i c e , the oxidizing agent is g e n e r a l l y the f e r r i c s u l fate f o r m e d by the action of a i r and a c i d on v a r i o u s i r o n m i n e r a l s which a r e i n e v i t a b l y p r e s e n t in the heap. The a c i d - f e r r i c sulfate solution o x i d i z e s and d i s s o l v e s the copper s u l f i d e s . The c o p p e r - b e a r i n g s o l u t i o n s a r e c o l l e c t e d at the bottom of the heap for c o n v e n t i o n a l p r o c e s s i n g to r e c o v e r the c o p p e r . Although c o p p e r h e a p - l e a c h i n g has b e e n p r a c t i c e d for many y e a r s , much s t i l l r e m a i n s unknown c o n c e r n ing the c h e m i s t r y of d i s s o l u t i o n o
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