The effect of CaF2 on the magnesium production with silicothermal process

• A new method of experiment on the silicothermal reaction was proposed.
• Accurate extents of magnesium reduction were obtained.
• Box-Lucas fitting was given based on the kinetic equation of solid-state reaction.
• The influence of CaF2 content on the silicothermal diffusion process was linear.

Calcium fluoride (CaF2) was widely used in magnesium production as a surfactant. In this paper, the effect of CaF2 content on the silicothermal process was investigated. Experiments were carried out on briquettes made from mixture of calcined dolomite, ferrosilicon (Fe·Si) and CaF2. Briquettes with a thickness of about 2 mm were used to reduce the effect of heat transfer on the reaction. The extent of magnesium reduction with different experimental temperatures, CaF2 content and reaction time was proposed. The experimental temperature ranged from 1323 K to 1473 K, and the CaF2 content was 0%–3%. The results showed that the increase of CaF2 content leads to the decrease of reaction time and the increase of reaction rate. In addition, a Box-Lucas fitting of magnesium reduction was proposed in order to describe the influence factors of reduction extent, in which the temperature, CaF2 content and reaction time were independent variables. It was indicated that the CaF2 influenced the diffusion process instead of the reduction process, which could be explained with the mathematical expression reasonably.