Exothermic, sluggish biphasic extraction of uranyl through polygonal bipyramidal chloroacetamide complexes in ionic liquid

Abstract

An exothermic, spontaneous, highly efficient, sluggish biphasic extractive mass transfer of uranyl ion have been reported from aqueous acidic solution using chloroacetamide ligands into highly viscous ionic liquid involving UO2(NO3)(Chloroacetamide)2+ species predominantly following diffusion controlled ‘cation exchange’ mechanism. The O-donor of chloroacetamide monodentate ligand and O-donor of the bidentate NO3− were coordinated to the UO22+ ion. The average U−OUO2 bond distance is found to be the shortest (1.788 Å), followed by U−Ochloroacetamide (2.439 Å and 2.446 Å for L1 and L2) and U–ONO3 (2.511 Å). The donation of electron density from the O-donors to the central U atom was evidenced by lowering of positive charge (∼0.28) on U atom from [UO2(H2O)5]2+ to UO2(NO3)(Chloroacetamide)2+ complexes. In these uranyl complexes, the contributions from the electrostatic and orbital interaction were found to be ∼73.7–75.2 % and 22.4–23.9 %, respectively of the total contribution, which was estimated as −518.9 and −582.2 kcal mol−1. The ionic liquid based solvent systems exhibited moderate radiolytic stability and good back extract ability using aqueous carbonate complex. The regeneration ability has been clearly demonstrated for five consecutive cycles consisting of one extraction and three back extraction cycles without much compromise on the performance (reduction in DU values were within 5–10 %).