Water balance and magnesium control in electrolytic zinc plants using the E.Z. selective zinc precipitation process
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MANY
m o d e r n e l e c t r o l y t i c zinc p l a n t s r e j e c t i r o n a s j a r o s i t e o r g o e t h i t e p r e c i p i t a t e s . The s i m u l t a n e o u s need to m a x i m i z e zinc r e c o v e r y and to p r o d u c e e n vironmentally acceptable precipitates necessitates inc r e a s i n g l y m o r e e f f i c i e n t washing of t h e s e m a t e r i a l s . C o n s e q u e n t l y the zinc plant c i r c u i t w a s h w a t e r input is i n c r e a s e d and the d i s c h a r g e of c o m p o n e n t s such a s m a g n e s i u m and c h l o r i n e with m o t h e r l i q u o r e n t r a i n e d in l e a c h r e s i d u e s and in p r e c i p i t a t e s is d e c r e a s e d . T h u s t h e r e is an i n c r e a s i n g t e n d e n c y for e l e c t r o l y t i c zinc p l a n t s to e x p e r i e n c e w a t e r b a l a n c e and m a g n e s i u m control problems. The S e l e c t i v e Zinc P r e c i p i t a t i o n (SZP) p r o c e s s d e v e l o p e d and p a t e n t e d by the E l e c t r o l y t i c Zinc Company of A u s t r a l a s i a L i m i t e d (EZ) m a y be u s e d to a c h i e v e s i m u l t a n e o u s l y w a t e r b a l a n c e and m a g n e s i u m c o n t r o l . 1 T h i s p a p e r o u t l i n e s the v e r s a t i l i t y of the SZP t e c h nology and is p a r t i c u l a r l y c o n c e r n e d with a q u a n t i t a t i v e a s s e s s m e n t , using m a t h e m a t i c a l m o d e l s , of v a r i o u s m o d e s of i n t e g r a t i n g the p r o c e s s into e l e c t r o l y t i c zinc plant c i r c u i t s . THE S E L E C T I V E ZINC P R E C I P I T A T I O N PROCESS The SZP p r o c e s s i n v o l v e s the p r e c i p i t a t i o n of b a s i c zinc sulfate f r o m zinc sulfate l i q u o r s using l i m e s t o n e , l i m e , o r c a l c i n e . The r e s u l t a n t b a s i c zinc sulfate p r e c i p i t a t e is s e p a r a t e d f r o m the t r e a t e d zinc d e p l e t e d l i q u o r by a conventional s o l i d - l i q u i d s e p a r a t i o n step, t y p i c a l l y by f i l t r a t i o n . W a t e r b a l a n c e and m a g n e s i u m c o n t r o l m a y be a c h i e v e d by e i t h e r d i s c a r d i n g the p r o c e s s f i l t r a t e o r by using it to wash p r e c i p i t a t e s in a c l o s e d c i r c u i t o p e r a t i o n . The p r o c e s s f i l t e r cake c o n t a i n i n g the b a s i c zinc sulfate is u s e d a s a n e u t r a l i z i n g agent in o t h e r p a r t s of the zinc plant c i r c u i t .
I. G. MATTHEW, O. M. G. NEWMAN, and D. J. PALMER are Superintendent, Senior Research Officer, and Research Officer, respectively, Risdon Research Department, Electrolytic Zinc Company of Australasia Limited, Hobart, Tasmania, 7001, Australia. Manuscript submitted June 18, 1979. METALLURGICAL TRANSACTIONS B
The R i s d o n SZP P l a n t EZ has o p e r a t e d the SZP p r o c e s s at i t s R i s d o n P l a n t in T a s m a n i a s i n c e S e p t e m b e r , 1971.e The R i s d o n o p e r ation i n v o l v e s r e a c t i n g finely g
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