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 ≈ 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+ ≈ 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.