Remobilization of U and Se reductively immobilized on iron oxide surfaces
(English)Manuscript (preprint) (Other academic)
In this work we have studied the possible remobilization of U and Se reductively immobilized on iron oxide surfaces experimentally. Samples consisting of reductively immobilized U and Se (carefully characterized in previous studies) we exposed to aqueous solutions containing HCO3- and HCO3- and H2O2. HCO3- increases the solubility of U(VI) and H2O2 will oxidize U(IV) to U(VI). Exposure to a HCO3- solution revealed a transient increase in the uranium concentration which can probably attributed to detachment of loosely bound UO2 particles upon addition of the new solution. Upon addition of H2O2, the concentrations of U and Se increased fairly rapidly indicating that oxidative dissolution is taking place. The rate of uranium release was well in line with what could be expected from the kinetics of oxidative dissolution of UO2 by H2O2. The Se/U ratio increases with leaching time approaching the overall original composition of the immobilized surface. Hence, oxidative dissolution of the immobilized U and Se is not congruent. Furthermore, the iron oxide surface exposed to the solution after oxidative removal of the immobilized Se and U, appears to be less reactive towards Se and U in solution compared to the original oxide surface. Consequently, the oxidative remobilization process has also affected the iron oxide. These findings suggest that oxidative re-mobilization of reductively immobilized redox sensitive radionuclides is aprocess of potential impact in a deep geological repository for spent nuclear fuel.
IdentifiersURN: urn:nbn:se:kth:diva-27179OAI: oai:DiVA.org:kth-27179DiVA: diva2:375332
QC 201012082010-12-072010-12-072010-12-08Bibliographically approved