U3O8 oxides and UO3 hydroxides and oxide hydrates and peroxides

Hydrates or hydroxides have been confirmed primarily for the hexavalent uranium. Of the tetravalent uranium, the compound UO2·xH2O is known, the water content of which varies according to the conditions of preparation and drying. Studies of its formation, preparation, structure, magnetic susceptibility and chemical reactions are reviewed. Recent investigations have shown that a hydrate of U3O8 probably does not exist and the compound designated in the literature as U3O8xH2O is a hydrate of composition UO2.86nH2O (where n = 0.5 and 1.5). Investigations of this compound's formation, preparation, optical properties, thermal stability and solubility are reviewed. The existence of four hydrates or hydroxides of uranium trioxide has been confirmed. They are UO3nH2O, where n = 0.5, 0.8, 1 and 2. They may be prepared by breaking down UO4·xH2O by hydrolysis of uranyl salts or hydrothermally from UO3. Hydrothermal investigations in the range 250C to 3300C, resulting in a phase diagram for the UO22+-UO3-H2O system, are reviewed. (UK)