Heterogeneous catalytic oxidation of neptunium(IV) in nitric acid solutions

Abstract

Summary Neptunium(IV), being quite stable in 0.5–3M HNO3, undergoes quick oxidation in the presence of 1 Pt/SiO2 catalyst. It was found that the catalytic oxidation of neptunium(IV) in nitric acid solutions proceeds even in the presence of anti-nitrous agent (such as NH2SO3H), though the rate of the reaction decreases to some extent. The kinetics of the heterogeneous catalytic oxidation of neptunium(IV) in nitric acid were studied for the following conditions: [HNO3] = 0.5–4.0M; [NH2SO3H] = 0 and 0.1M; T = 40–70°C; S/L = 0.025–0.1g/mL 1 Pt/SiO2. It was proposed that the mechanism of the neptunium(IV) oxidation is a result of the heterogeneous interaction of the Np(IV) aqua-ion with the nitronium ion NO2 + on the surface of the catalyst. The reaction deceleration and the increase of the apparent activation energy with the increase of the nitric acid concentration is explained by the complex formation of neptunium(IV) with nitrate ion.