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 ([C-n mim][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. (C) 2011 Elsevier B.V. All rights reserved.