Spectroscopic evidence for uranium bearing precipitates in vadose zone sediments at the Hanford 300-area site
Environmental Science & Technology
By: Y. Arai, M.A. Marcus, N. Tamura, J.A. Davis, and J.M. Zachara
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Abstract
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 (Washington) 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: (i) U discrete grains associated with Cu and (ii) areas with intermediate U concentrations on grains and grain coatings. Metatorbernite (Cu[UO2]2[PO 4]2??8H2O) and uranophane (Ca[UO 2]2[SiO3(OH)]2?? 5H 2O) at some U discrete grains, and muscovite at U intermediate concentration areas, were identified in synchrotron-based micro-X-ray diffraction. Scanning electron microscopy/energy dispersive X-ray analyses revealed 8-10 ??m size metatorbernite particles that were embedded in C-, Al-, and Si-rich coatings on quartz and albite grains. In ??- and bulk-X-ray absorption structure (??-XAS and XAS) spectroscopy analyses, the structure of metatorbernite with additional U-C and U-U coordination environments was consistently observed at U discrete grains with high U concentrations. The consistency of the ??- and bulk-XAS analyses suggests that metatorbernite may comprise a significant fraction of the total U in the sample. The entrapped, micrometer-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. ?? 2007 American Chemical Society.
Suggested Citation
Arai, Y., Marcus, M., Tamura, N., Davis, J., and Zachara, J., 2007, Spectroscopic evidence for uranium bearing precipitates in vadose zone sediments at the Hanford 300-area site: Environmental Science & Technology, v. 41, no. 13, p. 4633-4639, https://doi.org/10.1021/es062196u.
ISSN: 1520-5851 (online)
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Spectroscopic evidence for uranium bearing precipitates in vadose zone sediments at the Hanford 300-area site |
| Series title | Environmental Science & Technology |
| DOI | 10.1021/es062196u |
| Volume | 41 |
| Issue | 13 |
| Publication Date | June 01, 2007 |
| Year Published | 2007 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Environmental Science and Technology |
| First page | 4633 |
| Last page | 4639 |