Comparison of uranyl extraction mechanisms in an ionic liquid by use of malonamide or malonamide-functionalized ionic liquid

The extraction of uranyl from acidic (HNO3) aqueous solutions toward an ionic liquid phase, C-1-C-4-imTf(2)N (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 C-1 C-4 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 UO22+ versus 2 H+ for DMDBMA or versus C-1-C-4 -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.