The reduction of sulfide minerals by hydrogen in the presence of lime
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C a l c i u m oxide f a v o r s g r e a t l y the r e d u c t i o n of m e t a l s u l f i d e s by H2 at 800"C. C o p p e r s u l f i d e s and c o p p e r - i r o n s u l f i d e s a r e r e d u c e d r a p i d l y to m e t a l s : Cu~q+H z+caO -- 2Cu+CaS+HzO CuS+H z+caO -- Cu+CaS+HzO CusFeS 4 + 4H 2 + 4CaO - - 5Cu + F e + 4CaS + 4H20 The r e d u c t i o n of c h a l c o p y r i t e t a k e s p l a c e a c c o r d i n g to a n y of the following r e a c t i o n s d e p e n d ing on the a m o u n t of CaO a d d e d : CuzS. FezS s + H z + CaO - - CuzS. 2 F e S + CaS + HzO CuzS. FezS ~ + 3H 2 + 3CaO - - CuzS + 2 F e + 3CaS + 3HzO CuzS. FezS s + 4Hz + 4CaO - - 2Cu + 2 F e + 4CaS + 4HzO G r a v i t y and m a g n e t i c m e t h o d s w e r e not s u c c e s s f u l in s e p a r a t i n g the r e a c t i o n p r o d u c t s . Howe v e r , l e a c h i n g b y d i l u t e HC1 was s u c c e s s f u l in e l i m i n a t i n g CaS and i r o n (as FeS a s w e l l a s m e t a l ) l e a v i n g behind CuzS c o n c e n t r a t e o r m e t a l l i c c o p p e r , r e s p e c t i v e l y . Reduction of m o l y b d e n i t e i s a l s o influenced by the p r e s e n c e of CaD, but that of p e n t l a n d i t e i s not. JLHE p r e s e n t t r e a t m e n t of c o p p e r s u l f i d e c o n c e n t r a t e s is b a s e d e x c l u s i v e l y on o x i d a t i o n s t e p s . F i r s t , a p a r t i a l r e m o v a l of s u l f u r by o x i d a t i o n r o a s t i n g , then f o r m a t i o n of m a t t e in the r e v e r b e r a t o r y f u r n a c e , then s l a g g i n g and c o n t r o l l e d o x i d a t i o n of the white m e t a l to b l i s t e r c o p p e r in the c o n v e r t e r . All t h e s e o p e r a t i o n s involve the f o r m a t i o n of SOs which c a u s e s e i t h e r p o l l u t i o n p r o b l e m s when e m i t t e d in the a t m o s p h e r e , o r e c o n o m i c p r o b l e m s if i t s r e c o v e r y is c o n s i d e r e d . A d i f f e r e n t a p p r o a c h to c o p p e r s m e l t i n g would be the r e d u c t i o n of s u l f i d e s , e . g . , b y Hz to m e t a l l i c c o p p e r . The r e d u c t i o n of m e t a l s u l f i d e s b y h y d r o g e n is t h e r m o d y n a m i c a l l y u n f a v o r a b l e . F o r the r e a c t i o n MS+Hz ~
M + HzS
[1]
the e q u i l i b r i u m c o n s t a n t K,-
PH2S PH 2
at 800~ i s t y p i c a l l y 2 x 10 -s to 6 • 10 -3 f o r Cu, Ni, Co, and F e s u l f i d e s ; i . e . , when the m e t a l s u l f i d e is h e a t e d u n d e r Hz a t m o s p h e r e in a c l o s e d c o n t a i n e r at that p a r t i c u l a r t e m p e r a t u r e , the amount of HzS f o r m e d , and c o n s e q u e n t l y the a m o u n t of m e t a l p r o d u c e d , a r e n e g l i gibly s m a l l when the s y s t e m is given enough t i m e to reach equilibrium. One way of i n c r e a s i n g the y i e l d of the m e t a l is b y shifting the e q u i l i b r i u m c o n t i n u o u s l y to the r i g h t . This can be a c h i e v e d b y r e m o v i n g H~S
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