Spectroscopic Evidence for Uranium Bearing Precipitates in Vadose Zone Sediments at the Hanford 300-Area Site

Journal Article · Sun Jul 01 04:00:00 EDT 2007 · Environmental Science & Technology, 41(13):4633-4639

DOI:https://doi.org/10.1021/es062196u· OSTI ID:920945

Arai, Yuji ^[1]; Marcus, Matthew A. ^[2]; Tamura, Nobumichi ^[2]; Davis, James A. ^[3]; Zachara, John M. ^[4]

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1. Clemson Univ., SC (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. United States Geological Survey, Menlo Park, CA (United States)
4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Uranium(U) solid-state speciation in vadose zone sediments collected beneath the former North Process Pond (NPP) in the 300-Area of the Hanford site (WA, USA) was investigated using multi-scale techniques. In 30-day batch experiments, only a small fraction of total U (~7.4%) was released to artificial groundwater solutions equilibrated with 1% pCO₂. Synchrotron-based micro X-ray fluorescence spectroscopy analyses showed that U was distributed among at least two types of species: 1) U discrete grains associated with Cu, and 2) areas with intermediate U concentrations on grains and grain coatings. Metatorbernite (Cu[UO₂]₂[PO₄]₂•8H₂O) and uranophane (Ca[UO₂]₂[SiO₃(OH)]₂•5H₂O) at some U discrete grains, and muscovite at U intermediate concentration areas were identified in synchrotron-based micro X-ray diffraction. SEM/EDS analyses revealed 8-10 µm size metatorbernite particles that were embedded in C-, Al-, and Si-rich coatings on quartz and albite grains. In μ- and bulk-X-ray Absorption Structure (μ-XAS and XAS) spectroscopy analyses, the structure of metatorbernite with additional U-C and U-U coordination environments were consistently observed at U discrete grains with high U concentrations. The consistency of the μ- and bulk-XAS analyses suggests that metatorbernite may comprise a significant fraction of the total U in the sample. The entrapped, micron-sized metatorbernite particles in C, Al, and Si rich coatings, along with the more soluble precipitated uranyl carbonates and uranophane, likely control the long-term release of U to water associated with the vadose zone sediments.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 920945
• Report Number(s): PNNL-SA--57346; 830403000
• Journal Information: Environmental Science & Technology, 41(13):4633-4639, Journal Name: Environmental Science & Technology, 41(13):4633-4639 Journal Issue: 13 Vol. 41; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ABSORPTION
BEARINGS
COATINGS
FELDSPARS
FLUORESCENCE SPECTROSCOPY
MUSCOVITE
PONDS
QUARTZ
SEDIMENTS
SPECTROSCOPY
URANIUM
URANOPHANE
URANYL CARBONATES
X-RAY DIFFRACTION