Photochemical Oxidation of Americium in Dilute Nitric Acid Solution with the Addition of Ozone

Abstract

A trial to oxidize americium (Am) from the trivalent to the hexavalent form in dilute nitric acid solution was undertaken by emitting light from a deuterium lamp as well as by blowing ozone into the solution. It was found out that trivalent Am in dilute nitric acid solution (～0.1 N) can be photooxidized to its hexavalent form by a deuterium lamp which emits lines below 170 nm. Photooxidation, however, cannot be effected unless the oxidation rate exceeds the rate of autoreduction of Am which is caused by radicals and ions formed by alpha radiolysis. Ozone was introduced into the solution to maintain Am in its hexavalent form because ozone, which does not oxidize Am³⁺ to Am⁶⁺ in acid media, readily oxidizes Am^{5 +} to Am⁶⁺ in HNO₃ solution. Photooxidation can be effectively carried out by a combination of photolysis and ozone. Its oxidation rate was about 5%/h in 0.1 N nitric acid solution at 65°C. The oxidation rate decreased with increasing nitric acid concentration.