title: Kinetics of uranium(VI) reduction by hydrogen sulfide in anoxic aqueous systems.
abstract: Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation modeling; product analysis by transmission electron microscopy (TEM) was also performed. The molar ratio of U(VI) reduced to sulfide consumed, and the TEM result suggested that the reaction stoichiometry could be best represented by UO2(2+) + HS- = UO2+ S* + H+. At pH 6.89 and total carbonate concentration ([CO32-]T) of 4.0 mM, the reaction took place according to the following kinetics: -d[U(VI)]/dt = 0.0103[U(VI)][S2-]T0.54 where [U(VI)] is the concentration of hexavalent uranium, and [S2-]T is the total concentration of sulfide. The kinetics of U(VI) reduction was found to be largely controlled by [CO32-]T (examined from 0.0 to 30.0 mM) and pH (examined from 6.37 to 9.06). The reduction was almost completely inhibited with the following [CO32-]T and pH combinations: [(> or = 15.0 mM, pH 6.89); (> or = 4.0 mM, pH 8.01); and (> or = 2.0 mM, pH 9.06)]. By comparing the experimental results with the calculated speciation of U(VI), it was found that there was a strong correlation between the measured initial reaction rates and the calculated total concentrations of uranium-hydroxyl species; we, therefore, concluded that uranium-hydroxyl species were the ones being reduced by sulfide, not the dominant U-carbonate species present in many carbonate-containing systems.
authors.affiliation: Department of Civil and Environmental Engineering, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Hua
authors.forename: Huifang
authors.initials: H
authors.lastname: Xu
authors.forename: Jeff
authors.initials: J
authors.lastname: Terry
authors.forename: Baolin
authors.initials: B
authors.lastname: Deng
mesh_terms: D000327:Adsorption; D000693:Anaerobiosis / Q000502:physiology*; D001711:Biotransformation; D002254:Carbonates / Q000494:pharmacology; D006862:Hydrogen Sulfide / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012990:Soil Pollutants, Radioactive / Q000378:metabolism; D014501:Uranium / Q000378:metabolism / Q000493:pharmacokinetics*; D017974:Uranium Compounds / Q000032:analysis; D014867:Water / Q000737:chemistry
chemical_list: D002254:Carbonates; D012990:Soil Pollutants, Radioactive; D017974:Uranium Compounds; D014867:Water; D014501:Uranium; D006862:Hydrogen Sulfide