Mechanism of solid–liquid reaction in magnesium smelting by silicothermic process

The reaction pathways and phase transitions during primary magnesium production via silicon reduction of CaO·MgO under vacuum conditions were examined using thermodynamic calculations, X-ray diffraction (XRD), electron probe microanalyzer scanning (EPMA), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analysis. The findings suggest that the actual chemical reaction involves Si interacting with CaO in dolime to form CaSi2, which subsequently serves as a reducing agent to reduce MgO, resulting in magnesium vapor. Solid–solid reactions occur in pellets at temperatures below 1028 °C, whereas solid–liquid reactions take place above this temperature. The solid–liquid reaction notably enhances the reaction rate. In addition, the limited hydration reactivity of the slag from the silicothermic process is attributable to the formation of large MgO particles through the solid–liquid reaction.