Thermodynamic Investigation of MnAl<sub>2</sub>O<sub>4</sub> Spinel Precipitation Behavior in Manganese Containing-Slag Systems

In this study, the chemical equilibrium experiments were systematically conducted at 1673 K under an oxygen partial pressure of 10-13 atm to investigate the precipitation of MnAl2O4 spinel in the CaO–SiO2–MgO–FeO–MnO–Al2O3 slags. The results showed that with increasing Al2O3 content, Mn gradually transferred from the silicate liquid phase into the spinel phase. At 33.64 mol% Al2O3, the precipitation ratio of MnAl2O4 was approximately 80.32%, at which point the slag reached its solubility limit with respect to Al2O3. Therefore, 80.32% represented the maximum precipitation ratio attainable through Al2O3 control under the present experimental conditions. At this composition, comparison between water-quenching and slow cooling at 4 K/min revealed negligible differences in the crystal structure and composition of the spinel phase, indicating that MnAl2O4 precipitation predominately occurred during the high-temperature equilibration stage and remained stable upon cooling. In addition, with increasing Al2O3 content, the activity of MnO decreased, indicating its progressive consumption from the silicate melt and incorporation into the spinel phase.