Effect of bis(methylimidazolium) ionic liquid on the extraction of actinides and lanthanides with bis(carbamoylmethylphosphine oxide) extractant from nitric acid solutions

A novel bis(methylimidazolium) ionic liquid 3,3′-(pentane-1,5-diyl) bis(1-methylimidazolium) bis(trifluoromethanesulfonul)imide [C${}_5$(mim)${}_2$][Tf${}_2$N]${}_2$ has been synthesized. Its effect on the extraction of U(VI), Th(IV), Am(III), and lanthanides(III) from nitric acid solutions with a polydentate neutral bis(carbamoylmethylphosphine oxide) ligand L containing two bidentate fragments Ph${}_2$P(O)CH${}_2$C(O)NH-, interconnected by 4,7,10-trioxatridecane spacer through amide nitrogen atoms has been investigated. The efficiency of the extraction of metal ions with solutions of L in 1,2-dichloroethane (DCE) significantly increases in the presence of [C${}_5$(mim)${}_2$][Tf${}_2$N]${}_2$. A synergistic effect in the extraction of metal ions in this system has been explained with the high hydrophobicity of the Tf${}_2$N${}^{-}$ anions, which are involved in the formation of extracted complexes as counterions. The value of the synergistic effect decreases with increasing acidity of the aqueous phase. The influence of the composition of the aqueous and organic phases on the efficiency of the extraction of metal ions into the organic phase is considered, and the stoichiometry of the extracted complexes is determined. The effect of the HTf${}_2$N coextraction with L on the extraction of metal ions in the L - [C${}_5$(mim)${}_2$][Tf${}_2$N]${}_2$ system is discussed. The synergistic effect in the extraction of Ln(III) from 3 M HNO${}_3$ solutions with the mixture of L and [C${}_5$(mim)${}_2$][Tf${}_2$N]${}_2$ in DCE is higher than that in the L - [C${}_4$mim][Tf${}_2$N] - DCE system.