Synergistic extraction of uranium(VI) by bis(2,4,4-trimethylpentyl) phosphini acid in the presence of neutral oxo-donors

Abstract

Summary The extraction behavior of uranium(VI) from nitric acid solutions has been investigated using mixtures of bis(2,4,4-trimethylpentyl)phosphinic acid (HBTMPP) and trialkylphosphine oxide (Cyanex 923 = TRPO), triphenylphosphine oxide (TPhPO) or tributylphosphate (TBP). The results demonstrate that uranium(VI) is extracted into xylene as UO2(BTMPP)2 with HBTMPP alone and as UO2(BTMPP)2·S (where S = TRPO, TPhPO or TBP) in the presence of neutral oxo-donors. The extraction equilibrium constants of the above extracted complexes have been deduced by non-linear regression analysis with the aid of suitable chemically based model developed taking into account aqueous phase complexation of metal ion with inorganic ligands and all plausible complexes extracted into the organic phase. The addition of a neutral oxo-donor to the metal chelate system significantly enhances the extraction efficiency of uranium(VI). Complexation strength of uranium(VI) with neutral oxo-donors follows the order: TRPO > TPhPO > TBP, which is also the basicity sequence of these ligands. The IR spectral studies of the extracted complexes were used to further clarify the nature of the extracted complexes.