GB833103A - Improvements in or relating to the separation of zirconium and hafnium compounds - Google Patents

Abstract

<PICT:0833103/III/1> Zirconium and hafnium tetrachlorides are separated from mixtures thereof by subjecting the mixture to fractional distillation in a fractionating zone, in which the temperature of the hot end of the zone is in the range 455 DEG to 520 DEG C., and the absolute pressure is not less than 97% or more than 103% of that indicated by the equation: <FORM:0833103/III/1> where Pmm Hg is the pressure in millimetres of mercury, and TK DEG is the absolute temperature of the hot end of the zone. The pressures corresponding to this formula range from 5.69 X 104 mm. Hg to 2.23 X 104 mm. Hg. Zirconium tetrachloride of reduced hafnium content is removed from the hot end, and enriched hafnium tetrachloride from the low temperature end. The process may be carried out in a column of at least 30 theoretical plates. The temperature at the hot end being between 460 DEG C. and 512 DEG C. and the still head above the column being cooled to not below 440 DEG C. to provide a liquid reflux, pure hafnium tetrachloride being recovered from the top of the column and pure zirconium tetrachloride from a lower part. In an example (illustrated by Fig. 2), an impure zirconium tetrachloride, containing 1.6% hafnium tetrachloride, was introduced into the boiler 24 in an argon atmosphere, and then argon was introduced into the whole system to a pressure of about 19,400 mm. Hg. The whole system was then heated, and the column 17 and boiler 29 were filled with halide vapour and some liquid, the argon being removed via valve 7. The pressure in the system was maintained at 28,180-28,440 mm. Hg by heating the boiler 29 by means of heater 33. The top of the column is maintained at about 440 DEG C., and a continuous separation may be achieved, pure zirconium tetrachloride being withdrawn either as liquid through 26 or as vapour through 30, and a fraction rich in hafnium collected in 14a or withdrawn via 14b. The condenser 8 provides a reflux liquid for the column, and the hafnium fraction is condensed by condenser 9. The whole apparatus is jacketed so that suitable temperature controlling liquids, such as molten salts, may be circulated.