Separation of hafnium from zirconium

摘要

In the separation of zirconium and hafnium by solvent extraction, an aqueous acidic phase containing hafnium and zirconium together with chloride ions is contacted with a water-immiscible ketone solvent phase, at least one of the phases containing thiocyanic acid, whereby the hafnium passes to the organic phase and is separated from the zirconium-containing aqueous phase. Ketones specified are methyl isobutyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, methyl isopropyl ketone and ethyl butyl ketone. Decomposition of the thiocyanate may be suppressed by adding butyl acetate in amounts between 20 and 25% by volume of the ketone. The zirconium and hafnium may be supplied as chloride, oxychloride, hydroxide or chlorate whilst the necessary chloride ions are provided in addition by recycled hydrochloric acid. The aqueous phase may be rendered acidic with any mineral acid but hydrochloric acid is preferred. If sulphate ions are present it is preferred that the hydrochloric acid present may be such as to give a chloride concentration from 0,5 to 2 molar. The sulphate anion may be present in amounts between 0,01 and 1 molar, and is normally added as ammonium sulphate, zirconium sulphate or sulphuric acid. The requisite thiocyanic acid, preferably in amounts between 1 and 3 molar, may be provided by ammonium thiocyanate or the acid itself. The hafnium taken up in the thiocyanate-containing organic phase may be removed by washing with 2 to 6 N sulphuric acid and this operation may be improved by scrubbing the effluent from the extraction step, prior to the sulphuric acid scrubbing step, with aqueous hydrochloric acid, preferably of 0,5 to 4 molar, which removes residual zirconium from the organic phase, the resulting zirconium containing aqueous phase being recycled to the feed to the extraction step. The hafnium-freed organic phase may be in part recycled to the extraction step and in part processed for thiocyanate recovery, for example by neutralizing with ammonium hydroxide and removing the thiocyanate-containing aqueous phase. The thiocyanate-free organic solvent may be employed to recover thiocyanate values remaining in the zirconium enriched aqueous product phase from the extraction step. Separation is preferably effected at 0 DEG to 5 DEG C. As shown in Fig. 1 of the drawings, a feed solution containing zirconium chloride, ammonium thiocyanate and hydroxide is fed through a line 14 to an extraction column 4, in admixture with zirconium-containing recycled hydrochloric acid fed through line 18. At the bottom of the column through line 16, is passed hexone (methyl isobutyl ketone) which, passing countercurrent in the aqueous phase, removes hafnium at the top of the column in the organic phase through line 17. The aqueous phase containing the zirconium is passed through a stripper column 5 where it flows countercurrent to fresh hexone entering through line 29 and the zirconium-containing aqueous phase is recovered through line 26. The hafnium-enriched organic phase leaving the extraction column 4 through line 17 is passed through a column 6 where it flows countercurrent to a hydrochloric acid solution entering at line 19 which takes up the zirconium in the aqueous phase for passage through line 18 to join the feed to extraction column 4. The hafnium-enriched, zirconium-depleted organic phase effluent from column 6 passes through line 20 to a hafnium recovery column 8 where it is stripped with sulphuric acid solution entering through line 25. The aqueous hafnium-enriched phase leaves through line 21 whilst the stripped hexone organic phase passes through line 22 in part to the thiocyanate recovery system through line 24 and in part for direct recycle through line 28 to the hexone input line at the base of the extraction column 4.