Formation of a sol of mixed U(IV) ? U(VI) hydroxide in aqueous solutions with pH 1.5-4

Article abstract of DOI:10.1134/S1066362208040036

Addition of a Cs₂UCI₆ sample to solutions with pH 1.5 - 4, saturated with argon and containing 1 × 10^-4-0.1 MUO ₂(CIO₄)_2' results in the appearance of U(V), so that U(IV), U(V), and U(VI) occur in an equilibrium. However, after a certain induction period, black colloidal particles containing U(IV) polymer start to form. With an increase in pH from 1.5 to 4 or in temperature, the induction period becomes shorter. Under anaerobic conditions, the colloidal solution is stable for more than a month. Centrifugation at 8000 rpm (5500g) allows separation of the colloidal particles from the liquid phase. The colloid slowly dissolves in mineral acids saturated with argon or in a K₂CO ₃ solution, whereas precipitates of individual freshly prepared U(IV) and U(VI) hydroxides dissolve rapidly. Short UV irradia-of a UO ₂(ClO₄)₂ solution saturated with argon and containing ethanol (pH 2.5) results in the appearance of U(V) which then disproportionates, and U(IV) forms with U(VI) a black colloid similar to that arising on mixing U(IV) and U(VI) solutions.