The sulphide capacity of CaO-SiO2-Al2O3-MgO(-FeO) smelting reduction slags

The effects of MgO and FeO contents on the sulphide capacity of Corex slags were investigated at 1773 K using gas/slag equilibrium technique as a fundamental study for stabilising Corex operational conditions. The gradual substitution of MgO for CaO at a fixed basicity [B = {(%CaO)+(%MgO)}/(%SiO₂)] decreased the sulphide capacities of CaO-SiO₂-Al₂C₃-MgO slags. The addition of FeO into the CaO-SiO₂-Al₂O₃-MgO slags at the fixed (%CaO)/(%SiO₂) ratio, MgO and Al₂O₃ contents significantly increased the sulphide capacities. The sulphide capacity decreased according to the increasing Al₂O₃ content at the fixed (%CaO)/(%SiO₂) ratio, MgO and FeO content. Based on the previously reported and present values of sulphide capacities, the sulphide capacity as a function of slag composition on the mole fraction base at 1773 K was expressed by the formula of log C_S = X_CaO – 3.89 X_SiO2 – 3.18 X_Al2O₃ – 0.55 X_MgO + 2.43 X_FeO – 2.61. In addition, the relationship between the sulphide capacity and optical basicity could be represented as the formula of log C_S = 12.51 A – 12.24 and the theoretical optical basicity of FeO was found be 0.94 from the correlation. The effect of FeO on the sulphur distribution ratio was estimated using the present sulphide capacity values and the oxygen activity in liquid iron, which could be determined with the help of Fe/FeO equilibrium. FeO activity in slag was well described by the quadratic formalism based on the regular solution model. The sulphur distribution ratio according to FeO content varies in an opposite way, compared with that of the sulphide capacity.