Thermodynamics of converting lead sulfide
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Jr., PEI-CHEH
CHEN,
P. PALANISAMY,
AND
D. H. R. SARMA
Available t h e r m o d y n a m i c data on the P b - S - O s y s t e m a r e r e v i e w e d and collated to e s t a b l i s h a q u a n t i t a t i v e e q u i l i b r i u m model for p r o c e s s e s of c o n v e r t i n g and d i r e c t s m e l t i n g of PbS c o n c e n t r a t e s to lab. The t h e r m o d y n a m i c p r o p e r t i e s of lab-S liquid s o l u t i o n s a r e well r e p r e s e n t e d by an e m p i r i c a l m o d e l which t r e a t s t h e s e s o l u t i o n s as " r e g u l a r " m i x t u r e s of liquid lab and liquid labS. The c a l c u l a t i o n s and e q u i l i b r i u m d i a g r a m s for the lab-S-O s y s t e m show that c l o s e c o n t r o l of oxygen a c t i v i t y and t e m p e r a t u r e will be r e q u i r e d for a s u c c e s s f u l lead c o n v e r t i n g p r o c e s s , and that in fact a m u l t i s t a g e c o u n t e r c u r r e n t p r o c e s s should be a d v a n t a g e o u s .
T H E c a l c u l a t i o n s , d i a g r a m s , and i n t e r p r e t a t i o n s s u m m a r i z e d in this p a p e r w e r e developed by the a u t h o r s as p a r t of a g r a d u a t e - l e v e l c o u r s e in m e t a l l u r g i c a l p r o c e s s design. The o b j e c t i v e s of this study w e r e a) to e s t a b l i s h a t h e r m o d y n a m i c model for a c o n t i n u o u s p r o c e s s of c o n v e r t i n g g a l e n a c o n c e n t r a t e s to a c r u d e lead p r o d u c t and b) to r e l a t e the t h e r m o d y n a m i c model to the p r o c e s s d e s i g n . T i m e for e x p e r i m e n t a t i o n was not a v a i l a b l e , so that the work involved o r g a n i z i n g and c o l l a t i n g t h e r m o d y n a m i c data f r o m a v a r i e t y of s o u r c e s in the l i t e r a t u r e . THE
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The principal over-all reaction in converting lead sulfide to m e t a l m a y be w r i t t e n PbS + 0 2 ~ Pb + S O 2
[i]
and involves a system of at least three components: Pb, S, and O. For a practical and rapid converting process, SO 2 will evolve spontaneously at about atmospheric pressure, so that Pso2 = I atmosphere is taken as a fixed thermodynamic condition for m a n y of the subsequent calculations and diagrams. W h e n this procedure is followed, the thermodynamic control of the process m a y be thought of in terms of two primary variables, oxygen activity and temperature. In this work the oxygen activity is measured by equivalent CO 2 / C O r a t i o . Fig. 1 is an e q u i l i b r i u m d i a g r a m for the lab-S-O s y s t e m with PSO2 = 1 a t m o s p h e r e . The lower t e m p e r a t u r e p o r t i o n of the d i a g r a m is b a s e d on data r e c o m m e n d e d by Kellogg and Basu, ~ whose work should be c o n s u l t e d for m o r e c o m p l e t e u n d e r s t a n d i n g of the v a r i e t y of g a s - s o l i d r e a c t i o n s which a r e of both p r a c t i c a
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