Static dissolution of uo2 in interstitial boom clay water

Static dissolution experiments were performed with unirradiated UO₂ in Boom Clay water. The objectives were (1) to measure the solubility of uranium species in Boom Clay water, with UO₂ as the solid phase, and (2) to assess the impact of dissolved organic matter and carbonate concentration on this solubility. The tests were supported by calculations with geochemical codes to indicate possibly solubility controlling solid phases. The tests were performed in anoxic and reducing conditions, at 20 and 25°C. The following conclusions could be drawn: (1) Within 2 months in anoxic conditions, the uranium concentrations appear to approach saturation. (2) The "near-saturation" concentrations are between 2.4 and 7.8×10^-7 M. (3) The influence of the carbonate concentration and humic acids on the uranium concentration was apparently small, but the interpretation is hampered by pH and Eh variations. (4) The concentrations tend to be higher than the concentrations found in literature for similar EH and/or pH conditions; this can probably be explained by small differences in experimental conditions. (5) The measured "near steadystate" uranium concentration in the real clay water agrees relatively well with the solubility calculated for uraninite. (6) Addition of sulfide species reduced the redox potential, but not the uranium concentrations, except in real Boom Clay water.