PNNL

Abstract

Immobilization of hexavalent uranium [U(VI)] by hydrogen sulfide (H2S)-treated soil was investigated using laboratory column experiments to assess the potential of applying in situ gaseous reduction (ISGR) under vadose conditions to uranium remediation. Soil from the Hanford Formation in the U. S. Department of Energy (DOE) Hanford Site, Washington was used in this study. The impact of water chemistry and soil treatment on U(VI) immobilization and the role of gas humidity on soil treatment were investigated. Uranium immobilization results revealed that sorption of U(VI) from deionized water was much stronger than sorption from the simulated Hanford ground water. Gas treated soil was shown to have the potential for immobilizing U(VI) from the simulated ground water, however. In addition, soil treatment output indicated that humidity enhanced the soil reduction. In the first 20 pore volumes, the soil treated with moisturized H2S gas can effectively immobilize more than 80% of the mobile U(VI). Remobilization of uranium upon reoxidation of the sediment was relatively insignificant, at least in the short term, apparently owing to the adsorption or incorporation of uranium into poorly crystallized hydrous ferric oxide products.