Spectroscopic and Diffraction Study of Uranium Speciation in Contaminated Vadose Zone Sediments from the Hanford Site, Washington State

Journal Article · Sat May 15 04:00:00 EDT 2004 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es049963e· OSTI ID:860051

Catalano, Jeffrey G; Heald, Steve M; Zachara, John M; Brown, Jr, G E

Contamination of vadose zone sediments under tank BX-102 at the Hanford site, Washington, resulted from the accidental release of 7-8 metric tons of uranium dissolved in caustic aqueous sludge in 1951. We have applied synchrotron-based X-ray spectroscopic and diffraction techniques to characterize the speciation of uranium in samples of these contaminated sediments. U LIII-edge X-ray absorption fine structure (XAFS) spectroscopic studies demonstrate that uranium occurs predominantly as a uranium-(VI) silicate from the uranophane group of minerals. XAFS cannot distinguish between the members of this mineral group due to the near identical local coordination environments of uranium in these phases. However, these phases differ crystallographically, and can be distinguished using X-ray diffraction (XRD) methods. As the concentration of uranium was too low for conventional XRD to detect these phases, X-ray microdiffraction (?XRD) was used to collect diffraction patterns on {approx}20 ?m diameter areas of localized high uranium concentration found using microscanning X-ray fluorescence (?SXRF). Only sodium boltwoodite, Na(UO2)(SiO3OH)?1.5H2O, was observed; no other uranophane group minerals were present. Sodium boltwoodite formation has effectively sequestered uranium in these sediments under the current geochemical and hydrologic conditions. Attempts to remediate the uranium contamination will likely face significant difficulties because of the speciation and distribution of uranium in the sediments.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 860051
• Report Number(s): PNNL-SA-42813; EY3542301
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 10 Vol. 38; ISSN ESTHAG; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ABSORPTION
CONTAMINATION
DIFFRACTION
DISTRIBUTION
FINE STRUCTURE
FLUORESCENCE
SEDIMENTS
SILICATE MINERALS
SILICATES
SLUDGES
SODIUM
TANKS
URANIUM
URANIUM MINERALS
URANOPHANE
X-RAY DIFFRACTION