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Kristin M. Brown, H.I.T. June 5, 2013

Geochemical Modeling of Uranyl (UO 2 2+ ) Sorption to Ferrihydrite Colloids at a Colorado test site. Kristin M. Brown, H.I.T. June 5, 2013. Uranium in the environment. Uranium occurs naturally and is a common contaminant in the environment Anthropogenic Causes Weapons Production

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Kristin M. Brown, H.I.T. June 5, 2013

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  1. Geochemical Modeling of Uranyl (UO22+) Sorption to Ferrihydrite Colloids at a Colorado test site Kristin M. Brown, H.I.T. June 5, 2013

  2. Uranium in the environment • Uranium occurs naturally and is a common contaminant in the environment • Anthropogenic Causes • Weapons Production • Nuclear Energy • Leaching from Mine tailings • Scientific/Other Uses

  3. What are colloids? • Colloids are very small particles • 1 mm or less in diameter • Important surface properties that larger particles do not

  4. Ferrihydrite colloid determination IN Lab • [FeII]gwfiltration [FeII]m solution • [FeII]gw – [FeII]m = [FeII]colloid • [FeII]gw + O2filtration [FeII]m2 • [FeII]gw– [FeII]m2 = [FeII]colloid oxide

  5. Uranium sorption Determination in lab [UVI]gw+ O2filtration [UVI]m2 [UVI]gw ≈ [UVI]m2 Laboratory Data: Uncertainty ± 10% [0.035mg/L] ≈ [0.0343mg/L]

  6. Laboratory data

  7. Conceptual Model • Colloids are present • Fe-Oxide Colloids are known to sorb to Uranium • Carbonate and Sulfate Uranium complexes are not charged and do not sorb. • Does UO22+ sorb in this system (i.e at the Colorado Test Site)?

  8. Hypothesis (i.e. The Story) • Uranium Ion Does Not Sorb to Ferrihydrite Colloids at the Colorado Test Site • The Model Basis was water data from the Colorado test site and the results were compared to the Laboratory Results

  9. Colorado Test Site

  10. Colorado Test Site • Between 1924-1958 the area hosted Vanadium and Uranium ore processing facilities and mill tailings • Uranium Mill Tailings located on a flood plain of the Colorado River • Groundwater flows through unconsolidated Quaternary floodplain deposits that are often coated by iron oxide minerals

  11. General site Model Not to Scale

  12. Basis water parameters

  13. Reactants • Run 1 – Initial pH set at 7.13 • Log fugacity slid from -6 to -1 • Run 2 – Log Fugacity held constant at -2.5 (an average groundwater value) • pH slid from 7.1 to 9.0

  14. Uo22+ versus fugacity co2Run 1

  15. Sorbed fraction vsphRun 1

  16. Sorbed fraction vsfCo2RUN 1

  17. Uo2 versus phRun 2 Fixed Log Fugacity (-2.5)

  18. RUN 2 – Sorbed Fraction VS pH

  19. Conclusions • Uranium sorption is highly dependent on the amount of carbonate in the system. • Based on the modeling and laboratory results Uranium sorption does not occur at the Colorado Test Site.

  20. Thanks! kbrown2@osmre.gov (303) 293-5048

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