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

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

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 = k_2a([U(IV)][HNO₂][HNO₃][H₂O])/([HNO₃]²+β₃[HNO₃][H₂O]+β₄[H₂O]²),

where, k_2a=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 1^st 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.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 92, 07/2004
Pages: 387 - 394

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