EFFECT OF SEVERAL QUARTERNARY AMMONIUMS ON THE SOLVENT-EXTRACTION OF EUROPIUM(III) 2-THENOYLTRIFLUOROACETONATE ANIONIC COMPLEX INTO CHLOROFORM

The solvent extraction of europium (III) in aqueous 0.1 mol dm-3 sodium chloride or sodium nitrate solutions with 2-thenoyltrifluoroacetone (Htta) into chloroform was measured in the absence and presence of tetraethylammonium, tetrapropylammonium, tetrapentylammonium, or tetradecyldimethylbenzylammonium (base+). The addition of quarternary ammoniums enhanced the extraction, except for tetraethylammonium. This enhancement could be explained in terms of the extraction of the ternary complex, the Eu(tta)4-base+, in addition to the Eu(tta)3 complex. The difference in the enhancement of extraction with a different quarternary ammonium at a certain total concentration was much smaller than that expected from the difference in the size. This could be explained in terms that although the extraction of the anionic complex should be better when the size of the base+ is larger, its concentration in the aqueous phase at equilibrium is lower because it is extracted with the other anions in the aqueous phase better than a smaller base+. It was also found that the formation equilibrium of the ternary complex, the Eu(tta)4-base+, by association of the neutral complex, Eu(tta)3, with the ion-pair, tta-base+, in the organic phase is essentially not affected by the size of the base+.