GB771144A - Improvements in or relating to the purification of zirconium tetrachloride - Google Patents

Abstract

Zirconium and hafnium tetrachlorides are purified by heating a fused mixture containing the impure tetrachlorides and a minor amount of at least one alkali metal chloride above the temperature at which the tetrachlorides vaporize and thereafter condensing the evolved purified tetrachlorides. Zirconium tetrachloride and attendant hafnium tetrachloride can thus be freed from metal and metalloid impurities and the content of zirconium oxy chloride decreased. The preferred fused starting mixture contains 88 per cent crude zirconium tetrachloride and 12 per cent potassium chloride which mixture melts at about 215 DEG C. Zirconium tetrachloride sublimes at about 331 DEG C. at atmospheric pressure. According to examples (1) a fused mixture of the zirconium tetrachloride and potassium chloride was heated to 500 DEG C. and the zirconium tetrachloride collected as a crystalline solid. The impurities in the zirconium tetrachloride were reduced from 3000 parts of metallic impurities per million to 193 parts per million. Further examples relate to distillation at 600 and 450 DEG C., and to the use of different alkali metal chlorides and proportions thereof and to the use of mixtures of alkali metal and alkaline earth metal chlorides. A further example (9) describes the re-employment of the fused salt residue after carrying out the zirconium tetrachloride distillation, which residue contains 27.5 parts of zirconium tetrachloride and 12 parts of potassium chloride. To such a residue further crude zirconium chloride is added and the mixture melted and purified zirconium tetrachloride recovered. The crude zirconium tetrachloride can be added to the fused salt residue after the latter has been cooled and pulverized, or while it is in liquid state. Alternatively the fused salt composition may be employed to scrub impurities from the crude tetrachloride. Thus a mixture containing 88 per cent zirconium tetrachloride and 12 per cent potassium chloride may be melted and crude zirconium tetrachloride introduced at about the same rate as purified zirconium tetrachloride is vaporized from the molten salt bath.