GB987335A - Method of evaporating aluminium trihalides - Google Patents

Abstract

AlCl3 (or AlBr3) is evaporated from an electro-conductive molten salt mixture, containing at least one other metal salt, by A.C. heating. The salt mixture may contain a minimum of 50% mole AlCl3 and the other metal salt may be an alkali metal halide, e.g. NaCl. Evaporator 10 has thermal insulation 19 and refractory lining 11, which defines area 12 containing the molten mixture, in which are immersed electrodes 17 and 18 of graphite or a metal, e.g. mild or alloy steels. Solid AlCl3 falls from screw feeder 28 into the melt, and gaseous AlCl3 is removed through outlet 32 (not shown); the amount of AlCl3 in the melt remaining constant. Alternatively, AlCl3 may be supplied to the evaporator in molten admixture with another salt. Pressure may be at, above, or below atmospheric. This process may be incorporated into the sub-halide method of recovering Al, wherein crude Al is contacted with AlCl3 to give AlCl, which is withdrawn and decomposed to give pure Al and AlCl3. The AlCl3 is condensed to solid form, or absorbed in a molten salt mixture, and fed to the evaporator while non-condensable gases, e.g. H2, are exhausted. Specification 987,334 is referred to. <PICT:0987335/C1/1>ALSO:In the sub-halide method of recovering Al, wherein crude Al is contacted with AlCl3 (or AlBr3) to give AlCl, which is decomposed to give pure Al and AlCl3, this AlCl3 is condensed to solid form or absorbed in a molten salt mixture (non-condensable gases being exhausted), then fed into a melt containing AlCl3 with at least one other metal salt, and evaporated using A.C. heating. The melt may contain a minimum of 50 mole per cent AlCl3 and the salt may be an alkali metal halide, e.g. NaCl. Specification 987,334 is referred to.