Phase equilibria of FeO_x-SiO₂-Al₂O₃ slag system at 1200 °C and pO₂ of 10^−8.6 atm

The increasing concentrations of metallic Al or Al₂O₃ in secondary copper resources like electronic wastes motivate research into the slag chemistry of high-Al₂O₃ iron silicate slags for optimizing the industrial smelting process. In this study, the effect of Al₂O₃ in slag on the phase equilibria of the FeO_x-SiO₂-Al₂O₃ slag system was experimentally investigated at 1200 °C and pO₂ of 10^−8.6 atm. The high-temperature experiments were undertaken in silica and spinel crucibles in a controlled CO–CO₂ gas atmosphere, followed by rapid quenching and Electron Probe Microanalysis. The equilibrium compositions of liquid slags in the tridymite primary phase field, spinel primary phase field, and the three-phase invariant point were determined. The 1200 °C isothermal section was constructed for the FeO_x-SiO₂-Al₂O₃ system, and the results showed that Al₂O₃ can dissolve in the liquid slags to a maximum concentration of 17 wt%. The present experimental results were compared with the predictions by MTDATA and FactSage. It was found that the present experimentally determined liquid domain agreed well with the calculations by FactSage except the invariant point. However, the present isotherm in the spinel primary phase field of spinel displayed lower Al₂O₃ concentrations. The present results help regulating fluxing strategies of FeO_x-SiO₂-Al₂O₃ slags and optimizing smelting operations of recycling high-alumina concentration copper resources.