Thermodynamic model for the solubility of PuO2(am) in the aqueous Na+-H+-OH--CI--H2O-ethylenediaminetetraacetate system

The solubility of PuO2(am) was determined in the aqueous Na+-H+-OH--Cl--H2O -ethylenediaminetetra-acetate (EDTA) system as a function of pH (1 to 13.5) and EDTA concentrations (0.00001 to 0.093 M) to determine PuEDTA complexes important in a wide range of pH values acid EDTA concentrations. The solub ility studies were carried out as a function of time and show, as expected, that steady-state/equilibrium in this system is reached rapidly (< 7 days) . The aqueous Pu oxidation states were determined by X-ray absorption near edge spectroscopy and solvent extraction. The aqueous Pu(IV) concentrations in equilibrium with PuO2(am) at fixed concentrations of EDTA (0.0001 or 0. 001 M) as a function of pH, and at fixed pH (<similar to>9), and as a funct ion of EDTA were interpreted using the Fitter ion-interaction model. The mo del was developed based on a subset of the experimental data and was valida ted against the remaining, more extensive data not used in model developmen t. The log K-0 values for the formation of Pu(OH)(x)EDTA(x-) according to t he generalized reaction (Pu4+ + xOH + EDTA(4-) reversible arrow Pu(OH)(x)ED TA(-x)) were determined to be 36.44 +/- 0.35, 44.78 +/- 0.35, and 49.80 +/- 0.35 for x = 1, 2, and 3, respectively, when log K-0 of -56.85 for (PuO2(a m) + 2H(2)O reversible arrow Pu4+ +4OH ) is used.