Effect of Cation-Cation Complexes on Uranium(IV) Oxidation with Oxygen in Aqueous Solutions

• Published in: Radiochemistry (New York, N.Y.) N.Y.), 2023-02, Vol.65 (1), p.21-27
• Main Authors: Shilov, V. P., Fedoseev, A. M.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Bicarbonates; Cations; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Disproportionation; Kinetics; Nuclear Chemistry; Oxidation; Oxygen; Reaction kinetics; Sulfuric acid; Uranium dioxide
• ISSN: 1066-3622; 1608-3288
• DOI: 10.1134/S1066362223010034

The reported data on the kinetics of U(IV) oxidation with oxygen in HClO 4 and H 2 SO 4 solutions, in near neutral media, and in bicarbonate solutions were analyzed. In acidic solutions at [U(IV)] = 0.005–0.02 M, the reaction rate –d[U(IV)]/d t = k [U(IV)][O 2 ][H + ] n , n varied from –1 to –2 with an increase in ionic strength from 0.5 to 4. UOH 3+ and U(OH) 2 2+ ions react with O 2 , which brings about the appearance of UO 2 + and HO 2 . UO 2 + disproportionates and together with HO 2 participates in a chain reaction. An increase in [H + ] and [SO 4 2– ] reduces the proportion of UOH 3+ and U(OH) 2 2+ , accelerates U(V) disproportionation, and slows down oxidation. UO 2 2+ , U(OH) 2 2+ , and USO 4 2+ ions bind UO 2 + into complexes, which inhibits U(IV) oxidation. At [U(IV)] > 0.02 M, the reaction slows down. In solutions of pH > 1.5, the reaction of U(OH) 2 2+ with O 2 is accelerated by U(VI) ions; they form a complex with U(IV). The complex turns into U(V), which reacts with O 2 faster than U(IV). In bicarbonate solutions, the kinetics of the oxidation reaction depends on [U(IV)]. The addition of U(VI) speeds up the process.