Improvements in or relating to subhalide distillation process for the recovery of aluminium

In the subhalide process for the preparation of aluminium, the mixture of aluminium monohalide and trihalide (chloride or bromide) obtained by passing aluminium trihalide over heated aluminium ores, is cooled, heated or scrubbed by advancing the gas through a confined region and bringing the gas into contact with a molten mixture of salts. The salt mixture may contain one or more alkali metal or alkaline earth metal halides of the same halogen as the aluminium trihalide and aluminium trihalide if desired. Sodium chloride saturated with aluminium chloride is preferably used. The aluminium halide gas passes over the molten salt mixture in a modified splash condenser, good contact being ensured by projecting droplets countercurrently into the gas stream by means of a rotating wheel (Fig. 1) or in a second apparatus by two vertically mounted screws in separate compartments, the gas passing through them in series (Fig. 2). The salt mixture is kept at the required temperature by circulation through a heat exchanger, which is pressurized to ensure constant saturation of the sodium chloride with aluminium chloride. Molten aluminium which forms in the salt mixture is removed either by filtration or by allowing it to settle out in a settling tank. In the examples, heating and cooling the aluminium chloride is carried out in the range 200 DEG to 500 DEG C.