Mixed-ligand chelate extraction of thorium(IV) and uranium(VI) with thenoyltrifluroacetone and various imidazoles

Abstract

The synergistic extraction of thorium(IV) and uranium(VI) has been studied using mixtures of thenoyltrifluoroacetone (Htta) and various imidazoles such as imidazole (Imz), 2-methylimidazole (2-Meimz), benzimidazole (Bimz) or 2-pyridylbenzimidazole (2-Pybimz). The extraction data have been analysed by both graphical and theoretical methods by taking into account chemical mass action principles. The results demonstrate that these metal ions are extracted into chloroform as Th(tta)4 and UO2(tta)2 with Htta alone and as Th(tta)4 · nS and UO2(tta)2 · nS in the presence of imidazoles (where n = 1 and 2 for thorium(IV) and n = 1 for uranium(VI); S represents imidazole). The equilibrium constants of the above extracted complexes have been deduced by non-linear regression analysis. The addition of an imidazole to the metal chelate system enhances the extraction efficiency of these metal ions. The complexation strength of these metal ions with various imidazoles follows the order: Imz > 2-Meimz > Bimz > 2-Pybimz.