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Changes in uranium speciation through a depth sequence of contaminated Hanford sediments
Jeffrey G Catalano1, James P McKinley, John M Zachara
1Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA. catalano@anl.gov
Environmental Science & Technology
|May 11, 2006
Summary
Uranium in Hanford site sediments was studied to understand its groundwater plume. Remediation removed calcite-bound uranium, leaving sorbed uranium and metatorbernite to control future plume behavior.
Area of Science:
- Environmental Science
- Geochemistry
- Nuclear Waste Management
Background:
- Hanford site's 300 A Process Ponds received uranium-containing waste.
- This resulted in a significant uranium groundwater plume.
Purpose of the Study:
- Investigate uranium solid-phase speciation in sediments.
- Understand geochemical processes affecting the uranium plume's fate and transport.
Main Methods:
- Sediment analysis across a depth sequence (pond base to groundwater).
- Utilized chemical, mineralogical, electron microprobe, X-ray microprobe, and X-ray absorption fine structure spectroscopy.
Main Results:
- Near-surface sediments: Uranium coprecipitated with calcite (from over-neutralization).
- Intermediate depths: Metatorbernite precipitated.
- Deeper vadose zone/groundwater: Uranium predominantly sorbed onto phyllosilicates.
Conclusions:
- Calcite-containing sediments removed during remediation.
- Future uranium fate and transport controlled by desorption from phyllosilicates and metatorbernite dissolution.