Phase equilibria in the FeO–Fe2O3–SiO2 system: Experimental measurement and thermodynamic modeling

Knowledge about the phase equilibria of the FeO–Fe2O3–SiO2 system is very important for the resource utilization of waste slag. To solve the controversy over the calculated isothermal section at 1723 K in the literature, key experiments were carried out using equilibrium/quenching, X-ray diffraction (XRD) and electron probe microanalysis (EPMA). According to the present experiments, the existence of the three-phase region liquid + spinel (Fe3O4) + tridymite (SiO2) at 1723 K was confirmed. The ionic two-sublattice model (Fe+2, Si+4)P(O−2, Va, SiO4−4, SiO2, FeO1.5)Q was used to describe the liquid phase. The FeO–Fe2O3–SiO2 system was then critically evaluated by means of the CALPHAD (CALculation of PHAse Diagram) method in view of phase diagram and thermodynamic data. A new and improved self-consistent set of thermodynamic parameters for the FeO–Fe2O3–SiO2 system is obtained, and the calculated results show good agreement with the experimental data. The present thermodynamic modeling is of interest for the comprehensive recycling of solid waste resources.