Formation of excited uranyl ion in oxidation of U(IV) with xenon trioxide in aqueous H2SO4 and HClO4 solutions: III. Kinetic mode of self-accelerated reaction

Abstract

Self-acceleration was revealed for chemiluminescent radical-chain oxidation of U(IV) with xenon trioxide in aqueous HClO4 solutions in a reactor made of Teflon (instead of conventionally used glass). In oxidant excess, U(IV) oxidation with XeO3 follows the first-order kinetics only at low (under 10−6 M) concentrations of U(IV) in solution. Self-acceleration is observed at relatively high concentrations of the reactants, when the contribution of the heterogeneous decay of the radicals to chain termination substantially decreases and that of the degenerate branching reactions to the U(IV) oxidation mechanism increases. Oxidation of U(IV) with XeO3 demonstrates a critical phenomenon, uncommon for liquid-phase radical-chain processes: a minor increase in the concentrations of the reactants is responsible for transition from a steady-state mode to self-acceleration of the redox process.