Vacuum Carbothermic Reduction of Bauxite Components: A Thermodynamic Study

The possibility of direct vacuum carbothermic reduction of bauxite minerals to metallic aluminum at a temperature of 1400–1500 K and a pressure of 10−7 bar is examined by thermochemical equilibrium calculations on AlO(OH) (boehmite and diaspore) and Al(OH)3 (gibbsite) in the absence and presence of SiO2, TiO2, and FeO(OH). Carbon monoxide and hydrogen coproduced by the reaction may be used as combustion fuel or further processed to liquid hydrocarbons. The vacuum carbothermic reduction of iron-rich calcined bauxite was studied for Al2O3–Fe2O3–C mixtures at 10−4, 10−5, and 10−6 bar, indicating narrow temperature ranges at which the equilibrium for the release of gaseous Al is favored relative to gaseous Fe. Alternatively, for iron-rich bauxite, a preliminary step of iron-removal would be necessary. The proposed process could potentially decrease energy consumption and greenhouse gas emissions, and avoid the production of “red mud.”