GB220359A - Process of separating hafnium and zirconium - Google Patents

Abstract

The separation of hafnium from zirconium is effected by partially precipitating the oxides from the mixed salts or by partially converting the mixed oxides into other compounds or by a combination of both processes, hafnium being more basic than zirconium. In any case it is important to remove impurities such as titanium, niobium, tantalum aluminium and iron before the fractional separation, the removal being effected by means known for the purification of zirconium from those impurities. The mineral may be fused with potassium bifluoride or sodium bisulphate to obtain mixed double fluorides or mixed sulphates. Impurities are removed and a base such as ammonia or sodium hydrate or a salt having a similar action such as sodium acetate or thiosulphate is added in such proportion that part only of the zirconium and hafnium are precipitated as hydroxides, the mother-liquor being richer in hafnium than the original solution and the precipitate poorer; the precipitate is dissolved in acid and again partially precipitated to obtain a purer zirconium hydroxide, and the mother-liquor is partially precipitated again to obtain a mother-liquor still richer in hafnium and so on until the separation is carried far enough, when the hafnium solution is precipitated with excess of reagent or hydrolyzed by superheated steam, and the oxide may be converted into chloride and reduced to hafnium or an alloy of hafnium and zirconium by any method known for reducing zirconium chloride, for instance by sodium vapour. Alternatively, a solution of zirconium and hafnium salts is precipitated with excess of reagent or hydrolyzed with superheated steam to obtain the mixed hydroxides, and the precipitate is fractionated by incompletely dissolving in an acid such as hydrochloric acid, the solution being richer in hafnium than the original solution, and these operations being repeated as often as desired. In another alternative a solution of mixed zirconium and hafnium salts is partially precipitated by a reagent, and the mother-liquor which is proportionately richer in hafnium is then completely precipitated, the mixture of hydroxides treated with a deficiency of acid to obtain a solution enriched in hafnium, the operations being repeated as above described. In another modification a mixture of the oxides or hydroxides of hafnium and zirconium is partially converted into chlorides by means of carbon tetrachloride and chlorine, the chlorides containing more hafnium than the original mixture. The chlorides may be again converted into the oxides.