SOLVENT-EXTRACTION OF THE TRIVALENT LANTHANIDES AND YTTRIUM BY MIXTURES OF 3,5-DIISOPROPYLSALICYLIC ACID AND NEUTRAL ORGANOPHOSPHORUS COMPOUNDS

Neutral organophosphorus compounds containing a phosphoryl or thiophos phoryl group were found to cause appreciable synergistic shifts in the pH50 values for the extraction of the trivalent lanthanides and yttri um from chloride media by solutions of 3,5-diisopropylsalicylic acid ( DIPSA) in xylene. For the series of compounds with R = n-butyl, the sy nergistic effect increases in the order (RO)3PS < (RO)3PO < (RO)2RPO < (RO)R2PO < R3PO. The synergistic effects are greater for lutetium(III ) than for lanthanum(III) and, as a result, the separation across the lanthanide series (pH50La-pH50Lu) increases from only 0.17 pH unit for 0.25 M DIPSA alone to, for example, 0.85 pH unit for a mixture of 0.2 5 M DIPSA and 0.25 M triisobutylphosphine oxide (TIBPO). Mixtures of D IPSA and TIBPO give somewhat better separation factors between the lig ht and middle lanthanide fractions (beta(Nd)Sm = 3.0) than the commerc ial Versatic 10 acid (beta(Nd)Sm = 2.6), and separation factors compar able to those of the latter extractant between the heaviest lanthanide s (thulium to lutetium).