Synergism in the Solvent Extraction of Europium(III) with Thenoyltrifluoroacetone and CMPO in Methylimidazolium Ionic Liquids

The solvent extraction of Eu(III) from an aqueous chloride phase into hydrophobic ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides ([C₁C_nim⁺][Tf₂N⁻], n = 4, 6, 8 and 10), by β-diketone 2-thenoyltrifluoroacetone (HTTA) alone and in combination with N,N-diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO) was investigated. The interaction between the two extractants (acidic/neutral) in deuterochloroform has been studied by ¹H, ¹³C, ¹⁹F and ³¹P NMR spectra and NOESY experiments. ¹H and ¹⁹F Q-NMR analytical techniques were also applied for determination of [C₁C₄im⁺] and [Tf₂N⁻] entities transferred into the aqueous phase. Eu(III) was efficiently extracted by HTTA/[C₁C_nim⁺][Tf₂N⁻] and HTTA/CMPO/[C₁C_nim⁺][Tf₂N⁻] systems but a relatively small synergism was established. A cation extraction mechanism was proposed via the log–log slope analysis method. The effect of the IL cation alkyl chain length on the extraction process was studied as well.