Speciation of uranium(VI) extracted from acidic nitrate media by TODGA into molecular and ionic solvents

Maria Boltoeva, Clotilde Gaillard, Sylvia Georg, Vasilii K. Karandashev, Alexander N. Turanov

Index: 10.1016/j.seppur.2018.04.003

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Abstract

The speciation of uranium(VI) extracted by a molecular extractant N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and a hydrophobic ionic liquid (IL), namely 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][Tf2N], mixture from acidic nitrate media in 1,2-dichloroethane (DCE), and, for comparison, with only TODGA dissolved in DCE or IL has been studied by UV-vis and EXAFS spectroscopy. Our results confirm that the extraction in the conventional system occurs via a common solvation mechanism, at high acidity the extracted complex was identified as [UO2(NO3)2(TODGA)]. The addition of hydrophobic bistriflimide anions (Tf2N-) in the aqueous phase or IL in the organic phase results in a formation of another uranyl complex, in which two tridentate TODGA ligands directly coordinate metal cation and two NO3- and/or Tf2N- anions are expulsed in the outer sphere and act as charge balancing ions. When pure IL is used as diluent for TODGA ligand, the extracted uranyl complex has the same composition and stoichiometry as in the previous case, [UO2(TODGA)2]2+.