The oxidation of uranium(IV) ions by nitrous acid in 30% tri-butyl phosphate

V. S. Koltunov, Robin J. Taylor, V. I. Marchenko, O. A. Savilova,  and K. N. Dvoeglazov


The kinetics of the oxidation of U(IV) ions by nitrous acid in a 30% TBP solution have been determined. The rate equation was found to be:

-d[U(IV)]/dt = k2a([U(IV)][HNO2][HNO3][H2O])/([HNO3]23[HNO3][H2O]+β4[H2O]2),

where, k2a=0.405±0.055 M-1 min-1 at 55 °C (β3≈0.08; β4≈0.007) and the activation energy was E=112±17 kJ mol-1. The reaction mechanism appeared to involve interaction with the 1st hydrolysis product of U(IV)–UOH3+. The data is compared with a previous study of the nitric acid oxidation of U(IV) in 30% TBP. This reaction is autocatalytic due to the formation of nitrous acid during the reaction. The kinetics of the decomposition of HNO2 in 30% TBP (in the absence of U(IV)) have also been reported.

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Radiochimica Acta publishes original papers, review articles, and “rapid communications” (short articles of a more timely interest) on all chemical aspects of nuclear science and technology. The journal is geared toward scientists who are actively engaged in research work.