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A. Landgren, H. Ramebäck

A kinetic model for the oxidation of U(IV) to U(VI) with O₂: Determination of stability constants via oxidation kinetic experiments

The oxidation of U(IV) to U(VI) with molecular oxygen in acidic aqueous NaClO₄ (I=0.5 M) solutions at different temperatures was studied. It was found that the reaction kinetics is a combination of a first-order reaction and an autocatalytic reaction. The speciation of tetravalent uranium is important since it was found that the two first hydrolysed uranium(IV) species are the reactive species under the conditions studied. One problem in interpreting the results comes from the lack of thermodynamic data. However, oxidation kinetic experiments may be a method for determining stability constants for redox sensitive tetravalent actinides. The stability constants for the formation of the first two hydrolysed complexes of U(IV) are reported in this work, e.g. log ^*β₁ (I = 0.5;M, T = 303.15;K)= 1.39±0.42, as compared to the literature value of -1.39±0.20.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 89, 02/2001
Pages: 075

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