A novel class of hydrophobic ionic liquids based on quaternary ammonium cation and bearing phosphoryl groups was synthesized. The preliminary results of U(VI) extraction from aqueous solution into the ionic liquid are presented.

The extraction of U(VI) by tributylphosphate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide), C₄-mimTf₂N, has been studied as a function of TBP and HNO₃ initial concentrations. Extraction measurements have been completed by UV-vis spectroscopy in order to get insights into the extraction mechanism. The proposed chemical model describes the data through a fit of uranyl distribution ratios, while some other suggestions are unable to do so. In this model, uranyl extraction is proposed to proceed via cation exchange at low initial acidities ([UO₂(TBP)_n]²⁺ versus C₄-mim⁺ and H⁺) and via anion exchange at high HNO₃ concentrations ([(UO₂(NO₃)₃(TBP)_m]⁻ versus Tf₂N⁻). By contrast to the usual TBP/dodecane organic phase, the IL system does not favor the neutral species UO₂(NO₃)₂(TBP)₂, and TBP does not extract nitric acid.

The extraction of uranyl from acidic (HNO₃ ) aqueous solutions toward an ionic liquid phase, C₁–C₄–imTf₂N (1-methyl,3-butylimidazolium Tf₂N), has been investigated as a function of initial acid concentration and ligand concentration for two different extracting moieties: a classical malonamide, N,N′-dimethyl-N,N′-dibutylmalonamide (DMDBMA) and a functionalized IL composed of the Tf₂N⁻ anion and an imidazolium cation on which a malonamide pattern has been grafted (FIL-MA). The extraction mechanism, as demonstrated through the influence of added C₁–C₄–imCl or added LiTf₂N in the aqueous phase, is slightly different between the DMDBMA and FIL-MA extracting agents. Modeling of the extraction data evidences a double extraction mechanism, with cation exchange of UO₂ ²⁺versus 2 H⁺ for DMDBMA or versus C₁–C₄ -im⁺ and H⁺ for FIL-MA at low acidic values, and through anion exchange of [UO₂(NO₃)₃]⁻versus Tf₂N⁻ for both ligands at high HNO₃ concentrations. The FIL-MA molecule is more efficient than its classical DMDBMA parent.