A Study of Solid-Liquid Phase Equilibria of Pu(VI) and U(VI) in Aqueous Carbonate Systems

Abstract

Solubility products of PuO2CO3(s) and UO2CO3(s) are determined in 0.1 M NaC1O4 at 22 1 C under 100%, 1 % and 0.03% CO2. The carbonate precipitates of Pu(VI) and U(VI), prepared under 100% CO2 at neutral pH, are characterized by powder diffraction measurement, IR spectroscopy and UV spectroscopy. The solubility experiment is carried out in different CO[formula omitted] concentrations and pH. The speciation of PuO[formula omitted] and UO[formula omitted] in equilibrium Solutions is made by UV spectroscopy and the total concentrations of Pu(VI) and U(VI) are determined by liquid scintillation spectrometry and ICP-AES, respectively. The concentration correlation of [M[formula omitted]] vs. [CO[formula omitted]] gives a slope of negative unity, while [MO[formula omitted]] vs. pH shows a slope of 2 irrespective of CO2 partial pressure. The fact concludes that the present experiment comprises solid-liquid phase equilibrium reactions with only MO2CO3(s). The solubility products converted to zero ionic strength are found to be [formula omitted]=-14.84+0.10 for PuO2CO3(s) and log Ksp=-14.22+0.14 for UO2CO3(s). © 1993, Walter de Gruyter. All rights reserved.