SOLVENT-EXTRACTION OF ANIONIC CHELATE COMPLEXES OF LANTHANUM(III), EUROPIUM(III), LUTETIUM(III), SCANDIUM(III), AND INDIUM(III) WITH 2-THENOYLTRIFLUOROACETONE AS ION-PAIRS WITH TETRABUTYLAMMONIUM IONS

The solvent extraction of lanthanum(III), europium(III), lutetium(III), scandium(III), and indium(III) in 0.1 mol dm-3 sodium nitrate solutions with 2-thenoyltrifluoroacetone (Htta) in the absence and presence of tetrabutylammonium ions (tba+) into carbon tetrachloride was measured. The extraction of lanthanum(III), europium(III), and lutetium(III) was greatly enhanced by the addition of tba+; this could be explained in terms of the extraction of a ternary complex, M(tta)4-tba+. However,the extractions of scandium(III) and indium(III) were nearly the same when tba+ was added. The data were treated on the basis of the formation equilibrium of the ternary complex from the neutral chelate, M(tta)3, with the extracted ion-pairs of the reagents, tta-tba+, in the organic phase. It was concluded that the degree of association of M(tta)3 with the ion-pair, tta-tba+, is greater in the order La(tta)3 almost-equal-to Eu(tta)3>Lu(tta)3, or that the stability of the ternary complex in the organic phase is higher in the order La(tta)4-tba+ almost-equal-to Eu(tta)4-tba+>Lu(tta)4-tba+. This is similar to those of adduct metal chelates of Htta with tributylphosphate (TBP) in synergistic extraction systems.