Adhesion of anode slime on anode surface in electrolytic refining of lead
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d e m a n d for high p u r i t y m e t a l s is i n c r e a s i n g r e cently. Much has b e e n said about the p r o d u c t i o n t e c h n i q u e s of p u r e r grade of lab by B e t t s p r o c e s s . A d h e s i o n of anode s l i m e on the anode s u r f a c e p l a y s the m o s t i m p o r t a n t r o l e in m a i n t a i n i n g the p u r i t y of lab at 99.99 pct. In e l e c t r o l y s i s , the i m p u r i t i e s i n c l u d e d in the anode m u s t r e m a i n a s an a d h e r e n t s l i m e l a y e r on the anode s u r f a c e b e c a u s e d r o p p i n g of the s l i m e into the s o l u t i o n c a u s e s an e x c e s s i v e c o n t a m i n a t i o n due to m e c h a n i c a l or e l e c t r o c h e m i c a l d e p o s i t i o n of i m p u r i ties on the cathode. The f o r m a t i o n of a p o r o u s s l i m e l a y e r is a l s o a p r a c t i c a l n e c e s s i t y to p r e v e n t a n a b n o r m a l r i s e i n the cell voltage. T h e r e l a t i o n b e t w e e n the n a t u r e of a d h e s i o n and i m p u r i t i e s in the anode has not b e e n made c l e a r and the a d h e s i o n is c o n t r o l l e d by e x p e r i e n c e at p r e s e n t . T h e p u r p o s e of the p r e s e n t study is to r e v e a l the f a c t o r s r e s p o n s i b l e for a d h e s i o n and to c o n t r i b u t e to the r a t i o n a l i m p r o v e m e n t of the practical operations. EXPERIMENTAL E l e c t r o l y t i c lab, Bi, Sb, Ag and As of 99.99 pct p u r i t y w e r e used. Anodes w e r e p r e p a r e d by m e l t i n g t h e s e m e t a l s in a graphite c r u c i b l e and c a s t i n g in an i r o n mold. T h e s u r f a c e l a y e r of the c a s t i n g was cut off by m a c h i n i n g , and the d e n d r i t i c s t r u c t u r e was d e s t r o y e d by c o l d - r o l l i n g . The anodes thus o b t a i n e d w e r e a n n e a l e d i n a s t r e a m of a r g o n at 250~ for 5 h and s u b s e q u e n t l y f u r n a c e - c o o l e d o r w a t e r quenched. The e l e c t r o l y t e contained 80 g/1 of lab, 100 g/1 of f r e e HeSiF6 and 3 g/1 of glue. E l e c t r o l y s i s was c a r r i e d out at 30~ and 1 A / d m 2 for 26 h, with an e l e c t r o d e s p a c i n g of 30 m m . T h e d i m e n s i o n s of the anode and cathode a r e 40 x 80 • 5 m m and 40 • 80 x 0.5 m m , r e s p e c t i v e l y . F o r a c o m p a r i s o n of the f o r m of the Bi s l i m e with the Bi deposited by the r e d u c t i o n of Bi ions by m e t a l l i c lab, a n a t t e m p t was made to drop the Bi s o l u t i o n on the TOKIAKI TANAKA, Member AIME, is Professor, Department of Metallurgical Engineering, Faculty of Engineering, Hokkaido University, 060 Sapporo, Japan. Manuscript submitted December 13, 1976. METALLURGICALTRANSACTIONSB
s u r f a c e of a p u r e lab anode d u r i n g e l e c t r o l y s i s . In this c a s e , the Bi s o l u t i o n c o n t a i n i n g 5.2 g Bi/1, 100 g f r e e HeSiF6/I was s u p p l i e d through a tip of L - s h a p e d polye t h y l e n e pipe i m m e r s
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