Improvements in or relating to the purification of halide salts obtained from metal halide reduction processes

摘要

The impure chloride, bromide or iodide of a reducing metal recovered from the reduction of a metal halide with said reducing metal is purified by treating in the molten state with gaseous chlorine, bromine or iodine, respectively, to form and remove volatile halides of metal impurities in said halide. The purified halide may if desired be electrolysed to give back the reducing metal and halogen, the latter then being used to halogenate one of the metals having a volatile halide, and the halide reduced to give the desired metal and the impure halide. Metals which may be thus produced are titanium, zirconium, niobium, molybdenum, tantalum and tungsten, the two first-mentioned being referred to in detail. Reducing metals referred to are alkali metals (sodium, potassium, lithium), alkaline earth metals (calcium, strontium, barium) and magnesium. Mixtures of a halide of more than one reducing metal may be used also. A temperature of 750-1050 DEG C. is generally applicable in the case of chlorides, e.g. magnesium chloride, the temperature being high enough to ensure sufficient vapour pressure of the volatile halide, but not high enough for attack on the material of the reactor or vaporization of the halide to be purified. In the examples, electrical heating is used to melt the halide. The halogen may be preheated. Halogenation may be effected by passing the halogen into a molten bath of the halide, or by contact as a flowing film, spray or in a packed tower &c., and may be batchwise or continuous. Specifications 479,014, [Group II], and 632,564 are referred to.