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Dhanpat Rai, H. Bolton, Dean A. Moore, Nancy J. Hess, Gregory R. Choppin

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

The solubility of PuO₂(am) was determined in the aqueous Na⁺ H⁺-OH^--Cl^--H₂O-ethylenediaminetetraacetate (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 and EDTA concentrations. The solubility 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 (∼9), and as a function of EDTA were interpreted using the Pitzer ion-interaction model. The model was developed based on a subset of the experimental data and was validated against the remaining, more extensive data not used in model development. The log K⁰ values for the formation of Pu(OH)_xEDTA^x- according to the generalized reaction (Pu⁴⁺ + xOH+EDTA^4- ↔ Pu(OH)_xEDTA^-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;K⁰ of -56.85 for (PuO₂(am)+2H₂O harr; Pu⁴⁺+4OH^-) is used.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 89, 02/2001
Pages: 067

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