A kinetic model for the oxidation of U(IV) to U(VI) with O-2: Determination of stability constants via oxidation kinetic experiments

The oxidation of U(IV) to IJ(VI) with molecular oxygen in acidic aqueous Na ClO4 (I = 0.5 M) solutions at different temperatures was studied. It was fo und that the reaction kinetics is a combination of a first-order reaction a nd an autocatalytic reaction. The speciation of tetravalent uranium is impo rtant since it was found that the two first hydrolysed uranium(IV) species are the reactive species under the conditions studied. One problem in inter preting the results comes from the lack of thermodynamic data. However. oxi dation kinetic experiments may be a method for determining stability consta nts for redox sensitive tetravalent actinides. The stability constants for the formation of the first two hydrolysed complexes of U(IV) are reported i n this work, e.g. log*beta (1) (I = 0.5 M, T = 303.15 K) = -1.39 +/-0.42, a s compared to the literature value of -1.39 +/-0.20.