GB800426A - Improvements in methods for separating and purifying zirconium and hafnium - Google Patents

Abstract

<PICT:0800426/III/1> Zirconium and hafnium are separately recovered from an ore or a complex substance containing them by forming from the substance or ore an aqueous and acid solution of zirconium and hafnium and contacting this solution with a solvent which is an alkyl phosphate or acetate or an alkyl-aryl phosphate or acetate, whereby the zirconium is extracted from the aqueous solution whereas hafnium remains therein, and thereafter separating the solvent and the aqueous solution from which the zirconium and hafnium respectively are recovered. Suitable solvents are mono-, di- or tributyl phosphate, trioctyl phosphate, butyl phenyl phosphate, butyl acetate or isoamyl acetate or mixtures thereof, diluted if desired with other solvents such as petroleum ether which have no action on zirconium or hafnium. The initial aqueous acid solution is preferably a 1.5-3N nitric acid solution and the concentration of zirconium and hafnium in the solution is preferably lower than 0.2 molar. The presence of a salt such as an alkali or alkaline earth metal nitrate, for example sodium nitrate, in the aqueous acid solution may enhance extraction. After the contact of the aqueous acid solution with the solvent, which is preferably effected in countercurrent, the zirconium or hafnium dissolved in the solvent may be recovered by washing with an aqueous solution containing a complexing agent such as oxalic acidic or hydrofluoric acid or salts thereof, and such aqueous solution may also contain a precipitating body such as an alkali metal or ammonium carbonate and if desired a surfaceactive substance such as octyl alcohol to prevent the formation of an emulsion. As shown in the drawing, a mixing tank A0 is fed with the zirconium source material, nitric acid and sodium nitrate so as to form an aqueous solution containing 10 grammes of zirconium per litre with a concentration of nitric acid of substantially 2.5N. A1 indicates a second mixing tank fed with nitric acid and sodium nitrate, which mixed solution is fed to the top of an extracting column 1. Through the middle of this column 1, the solution from the mixing tank A0 is fed and to the bottom of the column is fed a mixture of tributyl phosphate (PTB) and petroleum ether (EP) which are separately fed to a tank S0 and from thence to the bottom of the column 1. The solvent from the tank S0 flows countercurrent to the zirconium containing solution fed from tank A0 and having taken up zirconium, then flows countercurrent in the upper half of the column to the solution of sodium nitrate and nitric acid fed from tank A1. The solvent phase leaves column 1 and passes to the base of column 2 where the zirconium is extracted from the solvent by countercurrent washing with an aqueous solution of a substance forming a complex with zirconium, for example M/3 ammonium acetate solution coming from source SOLr. The spent solvent leaving the top of column 2 may be returned to the solvent tank S0, whilst the aqueous solution containing the zirconium leaves the bottom of the column 2 to pass to a solvent extraction column 3 where the last traces of solvent are removed by washing the aqueous solution with benzine or carbon tetrachloride. The pure purified zirconium containing aqueous solution is finally treated in a vessel 7 with sodium carbonate whereby zirconia free from hafnium is precipitated and recovered. The aqueous solution coming from the base of column 1, containing almost all the hafnium is acidified in a mixing tank H1 with nitric acid to a final acidity of 5-7N and then passed to a solvent extraction column 4 where the hafnium is extracted from the aqueous solution with the organic solvent coming from tank S0 entering the bottom of column 4. The residual aqueous phase is discarded and the hafnium containing solvent leaving the top of column is passed to a further column 5 where the hafnium is transferred to a nitric acid solution supplied from the tank A1, such nitric acid solution then passing to a column 6 where the last traces of solvent are removed by benzine or carbon tetrachloride washing. The aqueous and purified solution of hafnium is finally passed to a mixing tank 8 where the hafnium values are precipitated with a solution of sodium carbonate. The solvent leaving the top of column 5, which may still contain a small amount of zirconium, may be re-cycled to the solvent tank S0 for re-use in the process.