Electromotive Force Measurements on High-Temperature Sulfide Formation

Using formation cells with a sulfur vapor electrode, relative partial molar thermochemical properties are reported for the sulfide-rich region of the molten lead sulfide-lead chloride and silver sulfide-silver chloride systems. Negative deviations from Raoultian ideality observed in the former system and positive deviations in the latter are tentatively related to available molar conductance data. Most base metal reduction practices involve some stage in which solid or liquid sulfides are reacted with oxygen. As a result metal production is attended by the evolution of large volumes of sulfur dioxide. Sulfur dioxide emission could be eliminated "if it were possible to reduce the metal directly from the sulfide by a method which yields only the more easily handled elemental sulfur as a by-product It is known that base metal sulfides are soluble in chloride melts particularly those containing a cation common to the sulfide (1-4). Further, it has been found that such melts when dilute in sulfide (containing less than 0.1 mole fraction sulfide) are electrolytes (5, 6). As a result of such findings, one method of reducing base metal sulfide that has been proposed is fused salt electrolysis (7-9). In this process, the products of elec-trolysis are metal and sulfur gas. In previous publications, the reversibi l ity of a sulfur vapor electrode was demonstrated (10), and free en-ergies of formation of silver and lead sulfide were de-termined (11). This paper reports measurements, using this electrode, of partial molar properties in the lead sulfide-lead chloride and silver sulfide-silver chloride systems. This study was intended to supplement other investigations of the physical chemistry of sulfide-chloride melts carried out in this laboratory (1-6) and in particular establish any relationships which may exist between melt structure, as inferred from the thermodynamics, and the electrical conductance be-havior