Study on the theoretical and mechanism of CaF₂-catalyzed vacuum carbothermal reduction of MgO

Abstract

The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF₂ as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium (VCTRM). This study investigates the thermodynamic theory and catalytic mechanism of CaF₂ in the VCTRM process. Catalytic reduction experiments and molecular dynamics simulations were conducted to gain a comprehensive understanding of the process. Thermodynamic calculations indicate that in vacuum carbothermal reduction, the primary reaction occurs between MgO and C. Analysis shows that CaF₂'s catalytic action primarily involves F⁻, Ca²⁺, and melt eutectic. Our experiments demonstrate that the addition of CaF₂ significantly increases the reduction rate. Furthermore, the mass loss rate increases with both the quantity of CaF₂ added and the holding time, stabilizing at additions over 5%. Experiments conducted at temperatures above the melting point of CaF₂ exhibited a pronounced catalytic effect. The resultant magnesium showed optimal structure and crystallization, with a purity of 87.84%. Notably, while CaF₂ remained in the residue, it was not detected in the condensate, confirming its catalytic role. Molecular dynamics simulations revealed that molten CaF₂ sabotages the structure of magnesium oxide, with F⁻ dispersing onto the surface of MgO, thus enhancing the reaction between MgO and C to form CO. However, no chemical reaction was observed between C, MgO, and CaF₂. The occurrence of the carbothermal reduction reaction at high temperatures depends on the concentration of the reducing agent C, with CaF₂ influencing the reaction rate. This research elucidates the theoretical and mechanistic foundations of CaF₂-catalyzed VCTRM, aligning with the green energy-saving concept and significantly advancing the green and efficient VCTRM process.