Effect of a Solvent on the Extraction of the Europium(III) 2-Thenoyltrifluoroacetonate Anionic Complex as Ion-Pairs with Tetrabutylammonium Ions

Abstract

Abstract The solvent extraction of europium(III) in aqueous 0.1 mol dm−3 sodium nitrate or sodium chloride solutions with 2-thenoyltrifluoroacetone (Htta) into chloroform, toluene, and 4-methyl-2-pentanone (MIBK) was studied in both the absence and presence of tetrabutylammonium ions (tba+); the results were compared with those into carbon tetrachloride. When the diluent was chloroform or toluene, the extraction was greatly enhanced by the addition of tba+, just as with carbon tetrachloride. This could be explained in terms of the extraction of the Eu(tta)4−tba+ species, in addition to the Eu(tta)3 species. However, this did not occur in the MIBK system, and was explained in terms of stable solvates with MIBK, which interfere with the addition of tta−tba+ ion-pairs on the Eu(tta)3 species. The enhancement due to the extraction of Eu(tta)4−tba+ was not very much different from that in the other solvent systems. This could be explained by assuming that although the amount of tta−tba+ in the organic phase was smaller in the order chloroform > toluene > carbon tetrachloride, the degree of association of this ion-pair with the Eu(tta)3 in the organic phase was larger in the inverse order, and that these two opposite tendencies canceled each other out. The results were compared with the synergistic enhancement of the extraction of europium(III) with Htta by organophilic neutral ligands, such as tributylphosphate.