Effect of Initial FeO Content and CaO:SiO₂ Ratio on the Reduction Smelting Kinetics of the CaO-SiO₂-MgO_satd.-FeO Slag System

The effect of the initial FeO content and CaO:SiO₂ ratio (CaO mass pct/SiO₂ mass pct) on the reduction smelting of FeO with carbon flake addition is investigated in the CaO-MgO_satd.-SiO₂-FeO slag system at 1823 K (1550 °C). Carbon rapidly reacted with FeO in the molten slag, causing both foaming and compositional changes in the slag. As FeO is reduced, the MgO saturation is modified, and solid precipitants, including MgO and other complex oxides, were observed, which significantly affected the slag properties, including the viscosity and foaming behavior. The solid-phase fraction and viscosity were estimated from changes in the measured FeO content over time using the thermochemical software FactSage. The iron recovery, which is distinguished from the amount of reduced Fe droplets, showed opposite behavior to the measured maximum foaming height and modified foaming index. According to the FeO mass transfer coefficient considering slag foaming at various initial FeO contents and CaO:SiO₂ ratios, the reduction rate was optimal at higher initial FeO contents and a CaO:SiO₂ ratio of 2.0, which did not correspond to the optimal iron recovery at an initial FeO content of 44 mass pct and above and a CaO:SiO₂ ratio of 1.2. The results showed that slag foaming may increase the reduction kinetics, but the slag composition needs to be optimized for greater iron recovery.