Kinetics and thermodynamics of silver cyanide adsorption on activated charcoal
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A C T I V A T E D c h a r c o a l has b e e n used s i n c e the late 1800s to a d s o r b gotd and s i l v e r f r o m c h l o r i d e o r cyanide s o l u t i o n s . A c t i v a t e d c h a r c o a l is p r e p a r e d for this p u r p o s e by s t e a m a c t i v a t i o n which p r o d u c e s a high s u r f a c e a r e a (1200 m2/g) and a high p o r o s i t y (0.6 ~ 0.9). A c t i v a t e d c h a r c o a l is c o m p r i s e d of r i g i d c l u s t e r s of c r y s t a l l i t e s . C a r b o n a t o m s on the edges of c r y s t a l l i t e s b e c o m e highly r e a c t i v e s i n c e these a t o m s have u n s a t i s f i e d v a l e n c i e s . A d i v e r s i t y of oxygen c o n t a i n i n g f u n c t i o n a l groups f o r m on t h e s e r e a c t i v e s i t e s . The active s i t e s for a d s o r p t i o n a r e c o n s i d e r e d to come f r o m these oxygen c o n t a i n i n g f u n c t i o n a l g r o u p s . The c h a r c o a l c o n t a i n s m a c r o p o r e s , t r a n s i t i o n p o r e s , and m i c r o p o r e s . T h e l a r g e s u r f a c e a r e a of the c h a r c o a l is m o s t l y obtained f r o m the m i c r o p o r e s whose d i a m e t e r r a n g e s f r o m 10 to 204. The l a r g e s u r f a c e a r e a , high p o r o s i t y , and the s t r u c t u r e of the c h a r c o a l give a t r e m e n d o u s opportunity for c e r t a i n a d s o r b a t e s to a d s o r b on the c h a r c o a l s u r f a c e . T h i s i n v e s t i g a t i o n is c o n c e r n e d with the k i n e t i c s and t h e r m o d y n a m i c s of the a d s o r p t i o n p r o c e s s of s i l v e r on c h a r c o a l . EXPERIMENTAL The c h a r c o a l used was coconut c h a r c o a l obtained f r o m Calgon C o r p o r a t i o n , A c t i v a t e d C a r b o n D i v i s i o n . T h e c h a r c o a l was 10 • 30 m e s h s i z e with a s u r f a c e a r e a of 1150 to 1250 m2/g as d e t e r m i n e d by N2 ads o r p t i o n u s i n g the BET method. S a m p l e s w e r e p r e p a r e d by s e p a r a t i n g u n i f o r m size p a r t i c l e s (16 x 20 mesh) by s i e v i n g the o r i g i n a l c h a r c o a l s u p p l i e d f r o m Calgon C o r p o r a t i o n . The bulk of the e x p e r i m e n t s were c a r r i e d out u s i n g 2 g of 16 • 20 m e s h s i z e p a r t i c l e s except for c a s e s where o t h e r w i s e i n d i c a t e d . S i l v e r cyanide s o l u t i o n s were p r e p a r e d by d i s s o l v i n g 2 g of s i l v e r m e t a l powder into a s o l u t i o n c o n t a i n i n g a known q u a n t i t y of s o d i u m cyanide. Oxygen was b u b b l e d E. H. CHO is Assistant Professor, Department of Mineral Process Engineering,West Virginia University, Morgantown, WV 26506, and C. H. PITT is Professor, Department of Metallurgy and Metallurgical Engineering,University of Utah, Salt Lake City, UT. Manuscript submitted August 28, 1978. METALLURGICALTRANSACTIONSB
into the s o l u t i o n and the s o l u t i o n was s t i r r e d d u r i n g the d i s s o l u t i o n . F i g u r e 1 s
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