Kinetic Analysis of the Carbothermal Reduction of Magnesia in Vacuum

Carbothermal reduction of magnesium oxide is studied as an alternative method for the primary production of magnesium. The rate of the carbothermal thermal reduction of magnesium oxide (C + MgO → CO + Mg) was studied in the range of 1350-1650°C and 1-1000mBar. Near isothermal reaction conditions were achieved by dropping precursor pellets into a hot SiC crucible and measuring the produced carbon monoxide continuously via IR spectroscopy. A CSTR based model was used to correct for dispersion of the gas prior to measurement. SEM imaging reveals the dissolution of direct contact between magnesium oxide and carbon during the reaction. Operating at reduced system pressure was shown to initially increase the reaction rate, as compared to operating at higher system pressure, and subsequently reduce the reaction rate at higher conversion. Based on this work and other investigations into the carbothermal reduction of volatile metals, a kinetic model and mechanism is proposed.