Extraction of the uranyl ion from the aqueous phase into an ionic liquid by diglycolamide

Extraction of the uranyl ion, UO22+, in an aqueous solution was carried out using N,N,N′,N′-tetrabutyl-3-oxapentanediamide (TBDA) and N,N,N′,N′-dimethylDibutyl-3-oxapentanediamide (MBDA) as extractants in an ionic liquid (IL) of 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6], n = 4, 6, and 8). The extraction efficiency for UO22+ ion in imidazolium-type ILs was found to be higher than that in chloroform under the same conditions. The extraction mechanism was deduced by the slope analysis and extraction tests. The UO22+ extraction most likely occurs by a mechanism involving a cation-exchange. The conventional log-log plot analysis of the extraction equilibrium data reveals that UO22+ ion is extracted as cation complexes in a 1:2 ratio of UO22+ to extractant. These complexes were characterized by their IR spectral data.

Research highlights
► A solvent extraction system based on combining imidazolium-based ILs and diglycolamides to extract uranyl ions from aqueous phase was firstly investigated.
► Solutions of diglycolamide in these ILs provide efficient extraction of UO22+ cation from aqueous solutions under low acidity conditions that give negligible extraction with traditional organic solvents chloroform.
► The extraction mechanism has been studied by slope analysis and extraction tests and these confirmed that the metal extraction proceeds via a cation-exchange mechanism.
► The conventional log-log plot analysis of the extraction equilibrium data reveals that the uranyl ions are extracted as cation complexes characterized by a metal/ligand ratio of 1:2.
► IR spectral data of the extracted complexes were used to further clarify the nature of the complexes.