Novel multi-stage aluminium production: part 2 – experimental investigation on carbosulphidation of Al₂O₃ using H₂S and sodiothermic reduction of Al₂S₃

In this paper, experimental investigation on the carbosulphidation of alumina (Al₂O₃) for aluminium (Al) production and the sodiothermic reduction of aluminium sulphide (Al₂S₃) are presented. Hydrogen sulphide (H₂S) was used as a reductant and source of sulphur. This work is the second of two-parts paper series. The experimental investigations of the Stage-1 process (Al₂O₃ carbosulphidation) were carried out at 1100–1600°C using a laboratory scale horizontal tube resistance-furnace. H₂S gas, diluted with argon (5% H₂S and 95% Ar), was reacted with pellets of a mixture of γ-Al₂O₃ and C powders (1:6 molar ratio) to produce Al₂S₃. The effects of gas injection rate, pelletizing pressure, temperature and reaction time on the conversion of Al₂O₃ to Al₂S₃ were investigated. The X-ray diffraction results confirmed the formation of Al₂S₃(s) in the reaction product above 1400°C. The conversion of Al₂O₃ to Al2S3 was found to be 99.5% at 1600°C and 12 h. The kinetics analysis of alumina sulphidation using Ginstling-Brounshtein diffusion model suggested the overall reaction was controlled by the diffusion of H₂S gas through the reaction product (liquid Al₂S₃). The activation energy of the alumina sulphidation reaction was calculated to be 148.5 kJ mol⁻¹. It has also been demonstrated in this study that Al can be extracted from Al₂S₃ by sodiothermic reduction using Na or NaH. In the case of Na, a level of Al conversion of 75% has been observed for reaction at 290°C.