COMPLEXATION STUDY OF NPO2-LIGANDS IN AQUEOUS-SOLUTIONS OF HIGH IONIC-STRENGTH( AND UO22+ IONS WITH SEVERAL ORGANIC)

The acid dissociation constants, pK(a), and the stability constants fo r NpO2+ and UO22+ have been measured for certain organic ligands [acet ate, alpha-hydroxyisobutyrate, lactate, ascorbate, oxalate, citrate, E DTA, 8-hydroxyquinoline, 1,10-phenanthroline, and thenoyltrifluoroacet one] in 5 m (NaCl) ionic strength solution. The pK, values were determ ined by potentiometry or spectrometry. These methods, as well as solve nt 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. S uch estimates are of value in assessing the solubility from radioactiv e waste of AnO(2)(+) and AnO(2)(2+) in brine solutions in contact with nuclear waste in a salt bed repository.