On the Dissolution Behavior of Sulfur in Ternary Silicate Slags

Sulfur dissolution behavior, in terms of sulfide capacity (C _S), in ternary silicate slags (molten oxide slags composed of MO – NO – SiO₂, where M and N are Ca, Mn, Fe, and Mg), is discussed based on available experimental data. Composition dependence of the sulfur dissolution, at least in the dilute region of sulfur, may be explained by taking into account the cation–anion first-nearest-neighbor (FNN) interaction (stability of sulfide) and the cation–cation second-nearest-neighbor (SNN) interaction over O anion (oxygen proportions in silicate slags). When the Gibbs energy of a reciprocal reaction MO + NS = MS + NO is positive, the sulfide capacity of slags with virtually no SiO₂ or low SiO₂ concentration decreases as the concentration of MO increases. However, in some slags, as SiO₂ concentration increases, replacing NO by MO at a constant SiO₂ concentration may increase sulfide capacity when the basicity of NO is less than that of MO. This phenomenon is observed as rotation of iso-C _S lines in ternary silicate slags, and it is explained by simultaneous consideration of the stability of sulfide and oxygen proportions in the silicate slags. It is suggested that a solution model for the prediction of sulfide capacity should be based on the actual dissolution mechanism of sulfur rather than on the simple empirical correlation.