Solubilities of Pb +2 , Bi +3 , Sb +3 , and Cu +1 sulfides in (NaCl+KCl+Na 2 S) melts

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Sb +3 and Cu !

Sulfides In (NaCI + KCI + Na2 S) Melts O. P. MOHAPATRA, C. B. ALCOCK, AND K. T. JACOB Solubilities of common m e t a l sulfides have been d e t e r m i n e d in the (NaCI + KCI) eutectic melt with and without NazS. A novel g a s - p h a s e equilibrium technique has been used for PbS, Bi~Ss, and Sb2Ss, and an improved liquid phase equilibrium technique for CuzS, which e l i m i nates the e r r o r s due to p h y s i c a l e n t r a p m e n t of the sulfide phase and s e g r e g a t i o n on quenchtrig, enabling p r e c i s e m e a s u r e m e n t s to be made. Solubilities in the (NaC1 + KC1) eutectic melt w e r e d e t e r m i n e d as a function of t e m p e r a t u r e in the rante 700* to 9500C, and were found to be s m a l l . The p a r t i a l m o l a r heats of mixing of the sulfides in the eutectic m e l t have been c a l c u l a t e d f r o m the solubility m e a s u r e m e n t s , to be 13.3, 31.4, 37.1, and 49.0 kca! for PbS(s), Sb2Ss(l), BI2Ss(/), and Cu2S(s), r e s p e c t i v e l y . Sodium sulfide addition was o b s e r v e d to enhance these s o l u b i l i t i e s , the effect being l a r g e s t for Cu2S followed by SO2Ss, Bi~Ss, and PbS. This effect is explained qualitatively. It was o b s e r v e d that FoS and SO2Ss obey H e n r y ' s law up to s a t u r a t i o n in (NaC1 + KC1 + Na2S) m e l t s .

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EXPERIMENTAL advent of s t r i c t pollution controls has e m p h a s i z e d the n e c e s s i t y for p r o c e s s e s that r e c o v e r sulfur in the Apparatus e l e m e n t a l f o r m f r o m sulfide o r e s . Homogeneous e l e c In the d i r e c t vapor phase equilibrium e x p e r i m e n t s , t r o l y s i s of sulfides d i s s o l v e d in the c o r r e s p o n d i n g chloH type quartz c e l l s of the design shown in Fig. l(a) were r i d e m e l t s to produce m e t a l s has been studied by Yang, used. The l i m b s of the cell w e r e filled with a mixture Pound, and Derge x and by Garbee and Flengas. 2 An a l of metal and metal sulfide* and alkali h a l i d e s , r e s p e c t e r n a t i v e method is to produce by e l e c t r o l y s i s a m o r e r e a c t i v e metal which then r e d u c e s the sulfide by h e t e r "~Except for Bi2Ss, in which ease pure Bi2 $3 alone was taken in one limb. ogeneous r e a c t i o n . F o r example, lead sulfide can be tively, evacuated to a pressure of I0 -s m m of mercury r e d u c e d on the cathode by e l e c t r o l y s i s of the (NaC1 using a rotary pump, and then sealed. Care was taken + KC1) eutecttc containing s m a l l amounts of sodium to ensure that at experimental temperatures the level sulfide, s The solubility of metal sulfides in these melts of the molten salt mixture and the solid sulfide in the might be expected to introduce significant e l e c t r o n i c respective limbs remained below the connecting capilcontribution to the conductivity and to provide a homolary. Equilibrium was established by vaporization of geneous reduction path. As a p a r t of a d e t a i l e d study of the sulfide from one lim

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