Extraction equilibrium of lanthanoids(III) in ionic liquid synergistic extraction systems; Effect of -diketones on the extracted species

Okamura, Hiroyuki   ; Hatakeyama, Mizuki*; Nagatani, Hirohisa*; Nishiyama, Yoshio*; Shimojo, Kojiro   ; Naganawa, Hirochika  ; Imura, Hisanori*

In the separation of lanthanoids (Lns), the synergistic extraction systems have been widely investigated to enhance the extractability and separability. Recently, a method of extraction equilibrium analysis for Ln(III) in the ionic liquid (IL) synergistic extraction system with 2-thenoyltrifluoroacetone (Htta)-trioctylphosphine oxide (TOPO) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was reported. In this study, the extraction equilibrium of Ln in the benzoylacetone (Hba)-TOPO system exhibiting higher Ln separability than the Htta-TOPO system was investigated. The effect of -diketones on the extracted species and the relationship between the extracted species and Ln separability were clarified. A three-dimensional non-linear analysis of log -log [ba]-log [TOPO] was applied in the Hba-TOPO synergistic extraction system, and both Ln(ba)(TOPO) and Ln(ba)(TOPO) were found as the extracted species. The formation of 1:1:4 dicationic complex was not observed in the Htta-TOPO synergistic extraction system, indicating that the extracted species is dependent on the acidity of -diketone. Consequently, it was suggested that the formation of the highly hydrophobic 1:1:4 complex is a factor of higher Ln separability.