Diffusion and phase transformations during the reaction between ferrosilicon and CaO·MgO under vacuum

Abstract Metal magnesium is mainly produced from the calcined dolomite by the vacuum silicothermic process. However, it requires a high energy input. An improved process was proposed in which the magnesium was produced from pre-prepared pellets. In this work, diffusion and phase transformations in the pre-prepared pellets during the reduction process were investigated. The results suggested that the reduction ratio is remarkably increased as the reduction temperature increased or the dolomite/ferrosilicon molar ratio decreased. Only Si diffused into dolime, which caused the reduction reactions and Fe might not have been involved in the reactions. The liquid Ca-Si alloy was produced. CaSi was an important intermediate product to produce CaSi2 and Ca vapor. Both CaSi2 and Ca vapor were the effective reducing agents for MgO. This process for Mg production includes both solid–liquid and solid–gas reactions. A plausible reactions route was proposed based on experimental and thermodynamic analyses.