Effect of reducing agents on the uranium concentration above uranium(IV) amorphous precipitate in Boom Clay pore water

The solubility of U(IV) amorphous precipitates was measured in Boom Clay water in the presence of reducing agents and under the in situ partial pressure of CO2(g) at 10-2.4 atm. Boom Clay pore water is of the sodium bicarbonate type (NaHCO3 ∝ 10-2 M) and contains about 100 mgl-1 of dissolved organic carbon. The total U concentration measured after two-months equilibrating time and the 0.45 μm filtration was about 10-6 M and higher. This concentration is about 3 orders of magnitude higher than literature data for U(IV) solubility and may suggest the existence of colloids and/or U(VI) species. The U concentration was found decreasing as a function of time within the experimental period. Further experiments are currently performed to evaluate the contribution of the colloids and the role of organic matter. (orig.)