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

Abstract

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 UO₂²⁺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.