SOLVENT-EXTRACTION OF ALKALINE-EARTH IONS WITH BENZOYLTRIFLUOROACETONE INTO CARBON-TETRACHLORIDE IN THE ABSENCE AND PRESENCE OF TETRABUTYLAMMONIUM ION OR TRIOCTYLPHOSPHINE OXIDE

The solvent extraction of Mg2+, Ca2+, Sr2+, and Ba2+ (M2+) in aqueous 0.1 mol dm-3 sodium nitrate solutions with benzoyltrifluoroacetone (Hbfa) in carbon tetrachloride was studied in both the absence and presence of tetrabutylammonium ion (tba+) or trioctylphosphine oxide (TOPO). It was found that not only the M(bfa)2 species, but also the tba+M(bfa)3- or the M(bfa)2(TOPO)n species (n is 1 to 3), were extracted by the addition of tba+ or TOPO, and that the extraction was very much enhanced. The equilibria for the extractions were treated as the over-all equilibrium of (i) extraction of the M(bfa)2 chelate and (ii) the association of the ion-pair of the reagents, tba+bfa-, or the TOPO molecules with the chelate in the organic phase. The separation of these four metal ions was improved by the addition of tba+. This was due to the fact that the chelates of smaller M2+ associated with the tba+bfa- better than those of larger M2+ in the organic phase.