A thermodynamic study of dilute sulfur and Cu-S solutions in lead
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1.707
The activity coefficient of sulfur in l e a d , r e f e r r e d to pure h y p o t h e t i c a l liquid sulfur a s the s t a n d a r d state, is r e p r e s e n t e d by: o
log Ys = -0.1228
- -
-
2371 T -
The t e m p e r a t u r e dependence of the Cu-S f i r s t o r d e r i n t e r a c t i o n coefficient is given by:
log(_~sCU)_ 2070.9 T
0.5580
where ECu S i s defined a s
p In Ys~ lim
LYg- uJ N ,N o--o
K N O W L E D G E of the a c t i v i t y of s u l f u r in lead s o l u t i o n s at higher t e m p e r a t u r e s is r a t h e r l i m i t e d , b e c a u s e m o s t i n v e s t i g a t i o n s have b e e n d i r e c t e d t o w a r d s an u n d e r s t a n d i n g of the copper d r o s s i n g p r o c e s s . F o r s u c c e s s f u l a p p l i c a t i o n to s m e l t i n g p r o c e s s e s , hight e m p e r a t u r e data on the a c t i v i t y of s u l f u r in lead s o lutions is n e c e s s a r y , together with q u a n t i t a t i v e i n f o r m a t i o n on the i n t e r a c t i o n s of s u l f u r with the other m a j o r solute e l e m e n t s which a r e p r e s e n t in crude lead b u l l i o n , n a m e l y Cu, As, Sb, Ag, Fe, Zn, and s o m e t i m e s Sn and Bi. E x p e r i m e n t a l l y , the i n v e s t i g a t i o n of lead s o l u t i o n s at s m e l t i n g t e m p e r a t u r e s , 1100 ~ to 1200~ is ext r e m e l y difficult, if not i m p o s s i b l e , owing to the high vapor p r e s s u r e of lead. It is t h e r e f o r e n e c e s s a r y to d e t e r m i n e the activity coefficient of s u l f u r , and the v a r i o u s i n t e r a c t i o n c o e f f i c i e n t s , o v e r a range of lower t e m p e r a t u r e s so that r e l i a b l e e s t i m a t e s of the values of these coefficients at s m e l t i n g t e m p e r a t u r e s can be made. In the c l a s s of r e g u l a r solution developed by Hildeb r a n d , there is a z e r o e x c e s s e n t r o p y of solution, but a n o n z e r o enthalpy of solution, e4 In this case the p a r tial m o l a l heat of m i x i n g , ffI1 = R T In Yl, where Yl is R. M. GRANT, formerly Post-Graduate Student, Department of Miningand MetallurgicalEngineering,University of Queensland, Brisbane, Australia, is Assistant to the Research Superintendent, The Broken Hill Associated Smelters Pty. Ltd., Port Pirie, South Australia. B. RUSSELL, formerly Reader in Metallurgy, Department of Mining and MetallurgicalEngineering,University of Queensland, is Managing Director, Consolidated Mining Industries Ltd., Brisbane. Manuscript submitted June 16, 1969. METALLURGICALTRANSACTIONS
the a c t i v i t y coefficient of component 1 in a b i n a r y solution. If H1 is independent of t e m p e r a t u r e , R T In yl =-bN~ = - b ( 1 - N 1 ) 2. In dilute s o l u t i o n s , over the range of a p p l i c a b i l i t y of H e n r y ' s law, In Yl then b e c o m e s a function of t e m p e r a t u r e only, in the f o r m in ~1 = A + ( B / T ) . S t r i c t l y , the r e g u l a r solution model i s not an i n t e r n a l l y c o n s i s t e n
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