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Abstract
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.”
ACKNOWLEDGMENT
The authors acknowledge the financial support of EU-project ENEXAL.
Notes
1AlO(OH), boehmite or diaspore minerals.
2Taking the HHV of graphite, 393.5 kJ/mol, as representative of coke.
3Theoretical process heat for changing equilibrium composition from 300 to 1400 K at 1 bar.
4Theoretical work for isothermal expansion at 1400 K of product gases from 1 bar to 10−7 bar.
5Assume fossil fuel both for process heat and for electricity generation.
6From partial WGS of CO to H2 to produce syngas.
7Assume process heat supplied by concentrated solar energy.
8Assume 90% chemical yield of methanol from syngas.
1Al(OH)3, gibbsite mineral.
2Taking the HHV of graphite, 393.5 kJ/mol, as representative of coke.
3Theoretical process heat for changing equilibrium composition from 300 to 1400 K at 1 bar.
4Theoretical work for isothermal expansion at 1400 K of product gases from 1 bar to 10−7 bar.
5Assume fossil fuel combustion both for process heat and for electricity generation.
6From partial WGS of CO to H2 for syngas production.
7Assume process heat supplied by concentrated solar energy.
8Assume 90% chemical yield of methanol from syngas.