Complexation study of NpO(sub 2)(sup +) and UO(sub 2)(sup 2+) ions with several organic ligands in aqueous solutions of high ionic strength

摘要

The acid dissociation constants, pK(sub a), and the stability constants for NpO2+ and UO2(2+) have been measured for certain organic ligands (acetate, (alpha)-hydroxyisobutyrate, lactate, ascorbate, oxalate, citrate, EDTA, 8-hydroxyquinoline, 1, 10-phenanthroline, and thenoyltrifluoroacetone) in 5 m (NaCl) ionic strength solution. The pK(sub a) values were determined by potentiometry or spectrometry. These methods, as well as solvent extraction with U-233 and Np-237 radiotracers, were used to measure the stability constants of the 1:1 and 1:2 complexes of dioxo cations. These constants were used to estimate the concentrations required to result in 10 % competition with hydrolysis in the 5 m NaCl solution. Such estimates are of value in assessing the solubility from radioactive waste of AnO2+ and AnO2(2+) in brine solutions in contact with nuclear waste in a salt-bed repository.