Novel multi-stage aluminium production: part 1 – thermodynamic assessment of carbosulphidation of Al₂O₃/bauxite using H₂S and sodiothermic reduction of Al₂S₃

A novel multi-stage Al production through a carbosulphidation of Al₂O₃, followed by a sodiothermic reduction of Al₂S₃, was proposed. In Stage-1, alumina (or bauxite) is reduced to Al₂S₃ in the presence of carbon and H₂S. In Stage-2, Al₂S₃ is reduced to Al through reactions with Na or NaH. The thermodynamic analysis predicted Al₂S₃ to be the main intermediate Al-compound when H₂S is reacted with Al₂S₃ and C at 1000-2000°C at 1 atm. Al₂S₃ formation was predicted to be low at 1100-1300°C at 1 atm (0.1 moles/mole Al₂O₃) but increased with increasing temperature (0.96 moles/mole Al₂O₃ at 1800°C). The thermodynamic analysis of sodiothermic reduction predicted that Al metal can be extracted from Al₂S₃ below 800°C at 1 atm. The Na₂S produced can be hydrolysed to form H₂S and NaOH. H₂S can be re-used and the Na can be reproduced from NaOH and put back into the process.