VACUUM CARBOTHERMIC REDUCTION OF ALUMINA

摘要

The current industrial production of aluminum from alumina is based on the electrochemical Hall-Heroult process, which has the drawbacks of high-greenhouse gas emissions, reaching up to 0.70 kg CO_(2-equiv) 1kg Al, and large energy consumption, about 0.055 GJIkg Al. An alternative process is the carhothermic reduction of alumina. Thermodynamic equilibrium calculations and experiments by induction furnace heating indicated that this reaction could be achieved under atmospheric pressure only above 2200 C. Lower required reaction temperatures can be achieved by alumina reduction under vacuum. This was experimentally demonstrated under simulated concentrated solar illumination and by induction furnace heating. By decreasing the CO partial pressure from 3.5 mbar to 0.2 mbar, the temperature required for almost complete readmit consumption could be decreased from 1800℃ to 1550 C. Deposits condensed on the relatively cold reactor walls contained up to 71 wt% of Al. Almost pure aluminum was observed as Al drops, while a gray powder contained 60-80% Al and a yellow-orange powder contained only Al_4C_3, Al-oxycarhides and Al_2O_3.