文摘
The oxidative dissolution of uranium(IV) dioxide powder at room temperature in aqueouscarbonate media has been investigated. Kinetic studies evaluating the efficacy of various oxidants,including K2S2O8, NaOCl, and H2O2, for dissolving UO2 in alkaline solution have been performed,with H2O2 exhibiting the most rapid initial dissolution at 0.1 M oxidant concentrations. Thisresult is due in part to the ability of peroxide to act as both an oxidant and a ligand underalkaline conditions. A spectrophotometric titration was used to confirm peroxide coordinationto the U(VI) metal center. The disappearance of characteristic absorbance maxima associatedwith UO2(CO3)34- (e.g., 448.5 nm) and a subsequent change in solution coloration upon titrationwith hydrogen peroxide indicated a change in speciation. Optimization of the hydrogen peroxideconcentration indicated that the initial rate of uranium oxidation increased with increasingperoxide concentration, with a maximum reaction rate estimated at about 0.9 M peroxide. Inaddition, the effects of both the carbonate countercation and the carbonate concentration werealso studied. It was determined that for 40 mg UO2 0.5 M Na2CO3 was the most propitiouschoice, exhibiting both a high initial dissolution rate and the highest UO2 dissolution capacityamong the systems studied.
