Photochemical reactions of uranyl ion in nitric acid — quantum yields of photoemission and photoreduction with ethanol

Abstract Photochemical reactions of uranyl ion (UO 2 2+ ) in nitric acid have been investigated from the viewpoint of applications of photochemical reactions to nuclear fuel reprocessing. The emission quantum yield of excited uranyl ion in nitric acid was determined by comparison with the fluorescence of quinine in sulfuric acid as a reference. It was found that the yield is of the order of 10 −3 and strongly dependent on the concentration of nitric acid. The emission is also strongly affected by the presence of additives, and their quenching parameters were determined. To evaluate the absolute concentrations of the uranyl ion in the presence of a quencher, a simple method using emission measurements is proposed. Quantum yields of the photochemical reduction of uranyl ion, U VI to U IV , with ethanol in nitric acid were determined under various conditions. On the basis of the concentration dependences of nitric acid and ethanol, and effects of oxygen and concomitant ions such as [H + ] and [NO 3 − ], the mechanism of the photochemical reduction is discussed.