Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

1 Publication
Stability and Molecular Speciation of Colloid-borne Uranium
Ulrich, K.-U.; Weiss, S.; Rossberg, A.; Foerstendorf, H.; Zänker, H.;
Mining on uranium ores in Eastern Germany produced 220,000 metric tons of uranium (U) in addition to ~5•108 metric tons of radioactive waste on 3000 dumps and 20 tailings, and leaving a total subsurface void volume of >1•108 m3 to be flooded. For a reliable assessment of the U migration, knowledge on the molecular speciation and complex stability is crucial. Starting from field studies and mesocosm-scaled simulation of a mine flooding scenario, we performed coprecipitation batch experiments with U(VI) and newly formed, initially colloidal 2-line ferrihydrite at different pH and ion matrix conditions. The talk presents major results of the colloid characterization, and of spectroscopic investigations on the molecular bonding of the colloid-borne U using Extended X-ray Absorption Fine Structure (EXAFS) and Attenuated Total Reflectance Infrared (ATR IR) spectroscopy. The influence of carbonate on the U(VI)-ferrihydrite surface complex formation will be discussed.
In addition, some U-loaded precipitates and a sediment sample from a uranium mine were subjected to consecutive leaching experiments and thermally induced aging. These experimental approaches aimed at determining the kinetics of U desorption processes and obtaining preliminary information on the long-term stability of U-binding. According to our results, part of the adsorbed uranium seems to be bound irreversibly within the bulk precipitate, especially when the U-sorbing ferrihydrite phase altered to hematite.
In summary, the presented results show that the interaction of U(VI) and highly reactive functional groups of colloidal and aggregated ferrihydrite surfaces can play a major role in lowering or delaying the release of toxic U from flooded uranium mines into adjacent groundwater aquifers or surface waters.
  • Lecture (Conference)
    Water Quality SuperGroup meeting at the School of Engineering & Applied Science, 31.03.2006, St. Louis, United States

Publ.-Id: 8358