THE SEPARATION OF EUROPIUM FROM A MIDDLE RARE-EARTH CONCENTRATE BY COMBINED CHEMICAL-REDUCTION, PRECIPITATION AND SOLVENT-EXTRACTION METHODS

The chemical reduction of pure europium(III) chloride solutions was in vestigated using reagents comprising reactive metals (Zn and Mg), meta l amalgams (Zn-Hg, Na-Hg and Eu-Hg), metal hydride (NaBH,) and nitroge nous reductants (N,H, and NH,OH). Using 100% excess of reducing agent and of ammonium sulphate, efficient precipitation of europium(II) sulp hate was obtained with the metal amalgams (99.7-99.9%) and with zinc m etal (99.8%), whereas only partial precipitation was obtained with mag nesium metal (69%), and no precipitation was observed with the other r eagents. Application of the method to synthetic rare earth chloride so lutions containing europium 7.5, neodymium 5, samarium 35 and gadolini um 20 g dm(-3) gave efficient precipitation of europium(II) sulphate w ith zinc and europium amalgams, but no selective precipitation with so dium amalgam. Reduction of an authentic middle rare earth chloride sol ution with zinc amalgam gave 97.5% recovery of europium(II) sulphate c ontaining (as a percentage of the total rare earths) europium 92, sama rium 3.5, neodymium 2, cerium 1, praseodymium 0.6 and gadolinium 0.5%. Conversion of the europium(II) sulphate to europium(II) chloride, fol lowed by re-precipitation of the sulphate increased the europium conte nt only to 96.5%, whereas replacement of the reprecipitation by solven t extraction of the trivalent rare earth impurities into solutions of commercial organophosphorus or carboxylic acids in xylene increased th e europium content to >99.98%. The zinc ions introduced into the middl e rare earth mother liquor during the reduction procedure can be remov ed by solvent extraction into a commercial phosphine oxide (Cyanex 925 ), without loss of rare earth values.