Carbothermic production of aluminium

In a process for production of aluminium metal described in U.S. Pat. No. 4,099,959 carbon monoxide gas is evolved at very high temperature through reaction of aluminium carbide and alumina in a high temperature zone of the system. This gas is cooled by contact with a molten alumina slag at a lower temperature to cause back reaction of contained aluminium suboxide and Al vapor and consequent heat transfer to the contacted molten alumina slag. A body of molten alumina slag is maintained in a pretreatment zone, to which carbon and alumina feed are introduced and the carbon monoxide gas is led into the pretreatment zone. Excess slag, resulting from such introduction of feed and from gaseous back reaction, spills over into a low temperature zone of the system to augment the circulating slag stream.