Effects of ionic strength on the kinetics for UO2 oxidation

The effect of ionic strength on the kinetics of UO2 oxidation by H2O2 in aqueous solution has been studied using powder suspensions, where the concentration of H2O2 was monitored as a function of time. Experiments were performed at 0 and 10 mM HCO3-. NaCl and Na2SO4 were used to adjust the ionic strength. At 0 mM HCO3- (where the kinetics is influenced by both oxidation and dissolution) the rate constant for the reaction increases with increasing ionic strength while at 10 mM HCO3- (where the kinetics is independent of the dissolution of oxidized UO2) the rate constant is virtually independent of ionic strength. This implies that dissolution of oxidized UO2 in the absence of HCO3- is ionic strength dependent. As expected, the reaction between H2O2 and UO2 is not affected by ionic strength since H2O2 has no charge. This finding also implies that peroxymonocarbonate (HCO4-) cannot be an important oxidant under the present conditions.