Activity and Activity Coefficient of Iron Oxides in the Liquid FeO-Fe₂O₃-CaO-SiO₂ Slag Systems at Intermediate Oxygen Partial Pressures

At present, there is a scarcity of data on the activities of iron oxides in the FeO-Fe₂O₃-CaO-SiO₂ slag system at intermediate oxygen partial pressures and temperatures relevant to sulfide smelting and nonferrous metallurgy. The present study provides relevant data at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10⁻⁹ and 10⁻⁴ atm. The experiments were carried out by equilibrating the slag in a CO-CO₂ gas mixture in a platinum crucible, after which the phases of all the experimental samples, including the platinum foil, were analyzed by electron probe microanalysis (EPMA). Where only liquid phase or liquid phase and tridymite (SiO₂) were observed, wet chemical analysis was used to determine the ratio of (mass pct Fe²⁺)/(mass pct Fe³⁺). Activity and activity coefficients for FeO (liquid) and FeO_1.33 (solid) were calculated. Tendencies of the effect of the (CaO/SiO₂) ratio, temperature, and oxygen partial pressure on these thermochemical quantities are discussed in this article.