A kinetic study on the pressure leaching of sphalerite
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l e a c h i n g of s p h a l e r i t e (ZnS) at e l e v a t e d t e m p e r a t u r e s and p r e s s u r e s has b e e n the object of s e v e r a l i n v e s t i g a t i o n s .1-8 The o v e r a l l r e a c t i o n of the p r o c e s s is ZnS + H2SO4 + 1 / 2 0 2 = ZnSOa + H20 + S.
[1]
It was r e p o r t e d as e a r l y a s 1956 by B j o r l i n g 1 that the r e a c t i o n p r o c e e d e d so slowly that it was i m p r a c t i c a l to e x t r a c t z i n c f r o m z i n c sulfide u n l e s s n i t r i c acid was a l s o p r e s e n t as a p r o m o t e r . The n i t r i c acid, B j o r l i n g stated, p r e s e n t s obvious d i f f i c u l t i e s i n the s u b s e q u e n t e l e c t r o l y s i s . He concluded that b e c a u s e of t h e s e d i f f i c u l t i e s and the added p r o b l e m s of r e c o v e r ing s u l f u r f r o m the l e a c h r e s i d u e , " a c i d d e c o m p o s i tion of z i n c b l e n d e is u n f a v o r a b l e . " However B j o r l i n g , F o r w a r d and V e l t m a n z in 1959 s u c c e s s f u l l y l e a c h e d ZnS at 110 to 115~ at oxygen p a r t i a l p r e s s u r e s f r o m 10 to 60 p s i . S u b s e q u e n t l y , r e s e a r c h w o r k done by Mackiw and V e l t m a n , 3 and V e l t m a n and O ' K a n e 4 e n a b l e d the g r e a t i m p r o v e m e n t of the p r o c e s s and the r e d u c t i o n of l e a c h r e t e n t i o n t i m e . The r e a c t i o n m e c h a n i s m was p r o p o s e d to be ZnS + H2SO4 = ZnSO4 + H2S
[2]
H2S + Fe2(SO4)s = 2 FeSO4 + H2SO4 + S
[3]
2 FeSO4 + H2SO4 + 1 / 2 0 2 = Fe2(SO4)3 + H20.
[4]
L i t t l e e x p l a n a t i o n was m a d e r e g a r d i n g the p r o p o s e d m e c h a n i s m and no e x p e r i m e n t a l v e r i f i c a t i o n was r e ported. The c o n t r i b u t i o n f r o m E x n e r , G e r l a c h , and P a w l e k s f r o m the I n s t i t u t e for M e t a l l u r g y of the T e c h n i c a l U n i v e r s i t y , B e r l i n , and l a t e r p u b l i s h e d by P a w l e k 6 p r o p o s e s an e n t i r e l y d i f f e r e n t m e c h a n i s m for the d i s s o l u t i o n of ZnS. Z i n c b l e n d e (ZnS) was c h o s e n in t h e i r i n v e s t i g a t i o n of the k i n e t i c s of the r e a c t i o n . An e l e c R. J. JAN is Process Engineer, AMAX Nickel Refining Company, Briathwaite, LA 70040. M. T. HEPWORTH,formerly with University of Denver, is now with AMAX Extractive MetallurgicalLaboratories, Golden, CO 80401. V. G. FOX is with Air Products and Chemicals, Allentown, PA. Manuscript submitted September 30, 1974. METALLURGICALTRANSACTIONSB
t r o c h e m i c a l m o d e l was p r o p o s e d i n which l e a c h i n g of zinc i s analogous to the c o r r o s i o n of m e t a l s . Anodic and cathodic p a r t i a l r e a c t i o n s o c c u r at the s o l i d s u r f a c e s , s e p a r a t e d l o c a l l y f r o m each o t h e r . The anodic r e a c t i o n is given a s : ZnS = Zn +2 + SO + 2 e - .
[5]
On the o t h e r hand, the cathodic r e d u c t i o n of c h e m i
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