Interaction of Ozone with Actinides and Lanthanides in Aqueous Solutions

Abstract

Specific features of the interaction of O3 in aqueous media with f-elements in a wide range of pH values are considered. In neutral solutions, O3 splits-off an O atom, which becomes the beginning of a chain process of O3 decomposition. NO3–, HSO4–, OH– anions initiate the decomposition by forming complexes with O3. The products of the subsequent transformations are OH, HO2, HO3, and H2O2. Phosphate and carbonate ions and HNO3 react with OH radicals and block the chain process. The peroxynitric acid formed from HNO3 serves both as an oxidizing agent and, as a result of hydrolysis, as reducing agent. In solutions of 1 M NaHCO3 or Na2CO3, ozone forms a complex with CO32– and its stability grows. In the alkaline medium, O3 is converted to O3–, but reducing agents are formed in the alkaline solution at a high concentration of O3 in the gas phase. The reactions of O3 with Ce, U, Np, Pu, Am, Bk, Ce, Tb, and Pr ions are analyzed. The reactions occur via a preliminary formation by cations of anion complexes and then complexes with O3. The formation constant of the Pu(IV) complex with O3 in a 4 M HNO3 solution is estimated to be 4.5 × 105 M–1. U(IV) and Pu(III) in an HClO4 solution, Np(IV) and Pu(IV) in an HNO3 solution, Np(IV) and Am(III) in a NaHCO3 solution are oxidized by ozone with transfer of the O. atom, Ce(III) and Bk(III) in an HNO3 solution, U(IV) and Am(III) in a solution of heteropolyanions, Np(IV, V) in a Na2CO3 solution, Np(V,VI), Pu(V, VI), and Am(V,VI) in alkaline media are oxidized with charge transfer to O3 or O3–.