Production of lead via ammoniacal ammonium sulfate leaching
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AND
R. W. PICKERING
L a b o r a t o r y - s c a l e i n v e s t i g a t i o n s of a n o v e l h y d r o m e t a l l u r g i c a l p r o c e s s for lead p r o d u c t i o n a r e d e s c r i b e d . The p r o c e s s is b a s e d upon the s o l u b i l i t y of c e r t a i n o x i d i z e d lead compounds in aqueous a m m o n i a c a l a m m o n i u m s u lf at e (AAS) s o l u t i o n s . T h e r e a r e , e s s e n t i a l l y , five s t e p s in the p r o c e s s , v i z : p r e t r e a t m e n t to c o n v e r t lead in the r a w m a t e r i a l to a s u i t a b l e o x i d i z e d f o r m ; d i s s o l u t i o n of the lead compounds in an AAS solution at a m b i e n t t e m p e r a t u r e s and p r e s s u r e s ; r e c o v e r y of the lead f r o m s o l u t i o n by e l e c t r o l y s i s o r p r e c i p i t a t i o n ; c o n v e r s i o n of the p r o d u c t s of the p r e c e d i n g stage to s a l e a b l e p r o d u c t s ; t r e a t m e n t of so l u t i o n s to m a k e t h e m s u i t a b l e for r e c y c l i n g . This new p r o c e s s avoids m a n y of the d i f f i c u l t i e s of e x i s t i n g h y d r o m e t a l l u r g i c a l p r o c e s s e s f o r lead. P Y R O M E T A L L U R G I C A L m e t h o d s of p r o d u c i n g l e a d a r e w e l l known and w i d e l y p r a c t i c e d , but have l i m i t a t i o n s when low g r a d e o r c o m p l e x m a t e r i a l s m u s t be t r e a t e d . It is f o r the t r e a t m e n t of such m a t e r i a l s that h y d r o m e t a l l u r g i c a l m e t h o d s a r e of p a r t i c u l a r i n t e r e s t . Although h y d r o m e t a l l u r g i c a l p r o c e d u r e s f o r the c o n v e r s i o n of lead sulfide to l e a d sulfate have b e e n known f o r s o m e t i m e ~ it has only b e e n s i n c e the p r o p o s a l of p r e s s u r e oxidation p r o c e d u r e s 2 with high r e a c t i o n r a t e s that a c o m p l e t e h y d r o m e t a l l u r g i c a l lead p r o d u c tion p r o c e s s has a p p e a r e d f e a s i b l e . F o r m a t e r i a l s containing lead as l e a d s u l f a t e , v a r i ous s o l v e n t s have been s u g g e s t e d to enable the s e p a r a t i o n of l e a d sulfate f r o m u n d e s i r a b l e c o m p o n e n t s ; for e x a m p l e s o l u ti o n s of s o d i u m and c a l c i u m c h l o r id es , of alkanol and a l k y l e n e a m i n e s , and of a m m o nium acetate or acetic acid. The use of b r i n e s h a s b e e n t e s t e d on a s e m i c o m m e r i c a l s c a l e and i n v e s t i g a t e d in a c o n s i d e r a b l e amount of d e t a i l , s Some of the p r o b l e m s e n c o u n t e r e d in the use of b r i n e s a r e : the b r i n e solutions a r e c o r r o s i v e , thus r e q u i r i n g e x p e n s i v e m a t e r i a l s of c o n s t r u c t i o n ; the i n t e r m e d i a t e p r o d u c t , lead sponge o r l e a d h y d r o x i d e is c o n t a m i n a t e d with c h l o r i d e which m a k e s s u b s e q u e n t c o n v e r s i o n to s a l e a b l e p r
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