Interaction of Ozone with Actinides and Lanthanides in Aqueous Solutions

Specific features of the interaction of O 3 in aqueous media with f -elements in a wide range of pH values are considered. In neutral solutions, O 3 splits-off an O atom, which becomes the beginning of a chain process of O 3 decomposition. NO 3 – , HSO 4 – , OH – anions initiate the decomposition by forming complexes with O 3 . The products of the subsequent transformations are OH, HO 2 , HO 3 , and H 2 O 2 . Phosphate and carbonate ions and HNO 3 react with OH radicals and block the chain process. The peroxynitric acid formed from HNO 3 serves both as an oxidizing agent and, as a result of hydrolysis, as reducing agent. In solutions of 1 M NaHCO 3 or Na 2 CO 3 , ozone forms a complex with CO 3 2– and its stability grows. In the alkaline medium, O 3 is converted to O 3 – , but reducing agents are formed in the alkaline solution at a high concentration of O 3 in the gas phase. The reactions of O 3 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 O 3 . The formation constant of the Pu(IV) complex with O 3 in a 4 M HNO 3 solution is estimated to be 4.5 × 10 5 M –1 . U(IV) and Pu(III) in an HClO 4 solution, Np(IV) and Pu(IV) in an HNO 3 solution, Np(IV) and Am(III) in a NaHCO 3 solution are oxidized by ozone with transfer of the O . atom, Ce(III) and Bk(III) in an HNO 3 solution, U(IV) and Am(III) in a solution of heteropolyanions, Np(IV, V) in a Na 2 CO 3 solution, Np(V,VI), Pu(V, VI), and Am(V,VI) in alkaline media are oxidized with charge transfer to O 3 or O 3 – .