Mechanism of Np(VI) oxidation with ozone in alkaline solutions

Bubbling of an ozone-oxygen mixture containing 0.1-0.5 vol % ?3 at a rate of 15-20 l h -1 through 13 ml of a 2 × 10 -5-1 × 10 -4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O3 gas] 0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O 3 concentration in the gas phase increased to 1-4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1-5) × 10 -3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of ?3 with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O 3 + OH- = HO O 3 + OH- = HO 2 - + H 2, O 3 + O- 2 - + OH - + o 2, O 3 + OH 2 - + OH- = O 3 - + O 2 - + O 2H, and O 3 + O 2 - = O 3 - + O 2, followed by O 3 - + NpO2(OH)4 2- = O2 + NpO4(OH)2 3- + H 2O. In addition, HO 2 - reduces Np(VII) and Np(VI) and reacts with O 3 -. Certain contribution is made by the reaction Np(VI) + O3 = Np(VII) + O 3 -. The dependence of the Np(VII) accumulation rate on [O3 gas] 0.5 was interpreted in terms of the concept of heterogeneous-catalytic process. © Pleiades Publishing, Inc., 2012.