Summary
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]2+β3[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.
© 2004 Oldenbourg Wissenschaftsverlag GmbH