Enhancing the Rate of Magnesium Oxide Carbothermal Reduction by Catalysis, Milling, and Vacuum Operation

Catalysis, milling, vacuum operation, and their interactions were studied as methods for increasing the rate of carbothermal reduction (CTR) of hard-burned and soft-burned MgO powders. For CTR at 1550 °C and 10 kPa, pellets made with soft-burned MgO reached 90% conversion in 30 min without milling and achieved the same conversion in 5 min with 120 min of milling. Crystallite attrition of soft-burned MgO was not observed, and the increased reactivity was attributed to mixing and aggregate attrition. Catalytic additives improved the reactivity in the CTR of hard-burned MgO but decreased the rate of CTR for soft-burned MgO. Additives were shown to catalyze the gas–solid reaction pathway, and thermogravimetric analysis revealed that the rate of carbon oxidation by CO 2 was approximately 2 orders of magnitude higher than that of MgO reduction by CO; thus, the latter reaction was rate-limiting to the gas–solid reaction pathway.