Selective separation of heavy lanthanoids by the synergistic ionic-liquid extraction with -diketones and a hydrophobic neutral ligand

Okamura, Hiroyuki   ; Takagi, Hitomi*; Isomura, Taku*; Hatakeyama, Mizuki*; Morita, Kotaro*; Nagatani, Hirohisa*; Imura, Hisanori*

Synergistic ionic-liquid extraction systems with several -diketones such as 2-thenoyltrifluoroacetone, 2-naphthoyltrifluoroacetone, benzoylacetone, and acetylacetone have been investigated for the selective extraction of heavy lanthanoids(III) (Ln(III)) in the presence of trioctylphosphine oxide as a hydrophobic neutral ligand in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as an ionic liquid (IL). Equilibrium analysis of Eu(III) indicated the formation of highly extractable cationic ternary complexes, followed by the ion exchange into the IL phase in all the systems studied. The extractability of heavier Ln(III) was selectively enhanced by the novel synergistic effect found in the present IL systems. This effect results in the significant improvement of the separation among Ln(III).