Effect of FeO and Al 2 O 3 on the MgO Solubility in CaO–SiO 2 –FeO–Al 2 O 3 –MgO Slag System at 1823 K

The MgO solubility in CaO–SiO 2 –FeO–Al 2 O 3 –MgO quinary slag system at 1823 K was measured to evaluate the effect of FeO and Al 2 O 3 on the MgO solubility. It was found that the MgO solubility was decreased with higher optical basicity, FeO concentration, and increased with higher Al 2 O 3 concentration. The MgO solubility was affected by activity coefficient of Mg 2+ ( $\gamma _{{\rm Mg}_{{\rm 2 + }} } $ ). Increase of the activity coefficient of Mg 2+ ( $\gamma _{{\rm Mg}_{{\rm 2 + }} } $ ) with higher FeO or lower Al 2 O 3 decreased the MgO solubility. The increment in MgO solubility is remarkably reduced beyond a critical $X_{{\rm Al}_{2} {\rm O}_{{\rm 3}} } /(X_{{\rm Al}_{2} {\rm O}_{{\rm 3}} } + X_{{\rm FeO}} )$ ratio. The significant decrease of the increment of MgO solubility is caused by the change of the molten slag structure. The excess stability function of Al 2 O 3 and the Fourier transform infrared (FT‐IR) analysis were applied to indirectly verify the existence of the spinel structure in the CaO–SiO 2 –FeO–Al 2 O 3 –MgO slag system.