(385g) Enhancing the Rate of Magnesium Oxide Carbothermal Reduction By Catalysis, Mechanical Milling, and Vacuum

Primary magnesium metal production by carbothermal reduction of magnesium oxide can be an efficient alternative over current silicothermic reduction methods. Catalyst addition, mechanical milling, and vacuum reduction were investigated as methods to increase the reactivity of precursor pellets. When using hard burn magnesia (0.6 m²/g), catalyst addition and mechanical milling of powders prior to pelletization increased pellet reactivity during reduction at 1550°C and 1 kPa. Further increasing vacuum in the reaction chamber to 0.1 kPa resulted in catalyst addition having no effect on the reaction rate. When using soft burn magnesia (147 m²/g), mechanical milling showed increased reactivity, but catalyst addition hindered the reaction rate. Catalysis was determined to proceed by a gas-solid reaction pathway, with CO₂ as the likely reaction intermediate, and not by the direct solid-solid reaction of carbon with magnesium oxide. For catalyst addition to improve the reactivity of pellets, the catalysis of the gas-solid reaction pathway must outweigh any hindrance to the solid-solid reaction pathway.