Polarized x-ray-absorption spectroscopy of the uranyl ion: Comparison of experiment and theory

Hudson, Eric A.; Allen, P. G.; Terminello, Louis J.; Denecke, Melissa A.; Reich, Tobias

doi:10.1103/physrevb.54.156

Cited by 166 publications

(168 citation statements)

References 30 publications

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“…A single Eo for all sets of backscattering atoms was used. Fixed values for CN and R values for transdioxo uranium MS paths (1: UdOaxdUdOax2; 2: Ud Oax)Oax2; and 3: UdOaxdUdOax) were calculated based on the fit-derived values for axial shells (11). The other CN, σ 2 , and R values were allowed to vary unless otherwise mentioned in the text.…”

Section: Methodsmentioning

confidence: 99%

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

Arai

Marcus

Tamura

et al. 2007

Environ. Sci. Technol.

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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% pCO 2 . 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) O) 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 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 was 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, 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.

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Section: Methodsmentioning

confidence: 99%

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

Arai

Marcus

Tamura

et al. 2007

Environ. Sci. Technol.

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“…Plutonium EXAFS Spectral Fits 282 Figure 7 shows EXAFS spectra fits in both k-space and r-space with the accompanying fit parameters given in Table 4 283 This effect has been observed in the past for the uranyl moiety [40]. For the MS path, R MS was set to 2R Oax , and the MS Debye-Waller (DW) factor was constrained to be twice the single-scattering (SS) DW factor (σ 2 MS = 2σ 2 SS ) as was done in previous studies with uranyl [40].…”

Section: 4mentioning

confidence: 99%

“…For the MS path, R MS was set to 2R Oax , and the MS Debye-Waller (DW) factor was constrained to be twice the single-scattering (SS) DW factor (σ 2 MS = 2σ 2 SS ) as was done in previous studies with uranyl [40]. was chosen for the model instead of a possible Pu-Mn path because of statistical reasons; it is simply more probable that plutonium will encounter a surface binding site which contains a distal iron atom as opposed to a distal manganese, assuming that site reactivity is similar for the two metal sites.…”

Section: 4mentioning

confidence: 99%

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Schwaiger

Booth

et al. 2010

Ract

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SummaryPlutonium(VI) sorption on the surface of well-characterized synthetic manganese-substituted goethite minerals (Fe 1-x Mn x OOH) was studied using X-ray absorption spectroscopy. We chose to study the influence of manganese as a minor component in goethite, because goethite rarely exists as a pure phase in nature. Manganese X-ray absorption near-edge structure measurements indicated that essentially all the Mn in the goethite existed as Mn(III), even though Mn was added during mineral synthesis as Mn(II). Importantly, energy dispersive X-ray analysis demonstrated that Mn did not exist as discrete phases and that it was homogeneously mixed into the goethite to within the limit of detection of the method. Furthermore, Mössbauer spectra demonstrated that all Fe existed as Fe(III), with no Fe(II) present. Plutonium(VI) sorption experiments were conducted open to air and no attempt was made to exclude carbonate. The use of X-ray absorption spectroscopy allows us to directly and unambiguously measure the oxidation state of plutonium in situ at the mineral surface. Plutonium X-ray absorption near-edge structure measurements carried out on these samples showed that Pu(VI) was reduced to Pu(IV) upon contact with the mineral. This reduction appears to be strongly correlated with mineral solution pH, coinciding with pH transitions across the point of zero charge of the mineral. Furthermore, extended X-ray absorption fine structure measurements show evidence of direct plutonium binding to the metal surface as an inner-sphere complex. This combination of extensive mineral characterization and advanced spectroscopy suggests that sorption of the plutonium onto the surface of the mineral was followed by reduction of the plutonium at the surface of the mineral to form an inner-sphere complex. Because manganese is often found in the environment as a minor component associated with major mineral components, such as goethite, understanding the molecular-level interactions of plutonium with such substituted-mineral phases is important for risk assessment purposes at radioactively contaminated sites and long-term underground radioactive waste repositories. Previous work by Kaplan et al.[4] using laboratory and lysimeter studies showed that > 95% of plutonium migrating from a purposefully placed solid Pu IV (NO 3 ) 4 source remained within 1.25 cm of the source over an 11 year period under natural environmental conditions at the Department of Energy (DOE) Savannah River Site (SRS).Such work on large-scale environmental systems is an important part in uncovering essential components of the soil and mineral composition that controls plutonium redox chemistry. However, individual sorption and redox processes must also be tested on well-characterized model mineral phases that properly represent individual environmental In nature, manganese is rarely found as a pure mineral phase. It is often found as a minor component associated with major mineral phases, such as goethite. As a model to these environmental minerals, we have synthesiz...

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“…In the case of a split equatorial shell (observed only in the U(VI)-humic standard), r 2 of the two shells were constrained to be the same value to avoid correlation problems between N and r 2 . In the case where the data allow fitting intermediate-and long-range order, the MS Pu profiles, which reflect the nuclear fallout of the sixties (Pu activity) and the contribution of the Chernobyl accident ( path U-O ax -U-O ax -U (4 legged axial path at 180°) was included in the fits as described previously Hudson et al, 1996). The shift in the threshold energy, E 0 , was allowed to vary as a global parameter but was constrained to be the same value in the different shells.…”

Section: Data Processing and Evaluationmentioning

confidence: 99%

Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)

Regenspurg

Margot-Roquier

Harfouche

et al. 2010

Geochimica et Cosmochimica Acta

104

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Very high concentrations of uranium (up to 4000 ppm) were found in a natural soil in the Dischma valley, an alpine region in the Grisons canton in Switzerland. The goal of this study was to examine the redox state and the nature of uranium binding in the soil matrix in order to understand the accumulation mechanism. Pore water profiles collected from Dischma soil revealed the establishment of anoxic conditions with increasing soil depth.

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Polarized x-ray-absorption spectroscopy of the uranyl ion: Comparison of experiment and theory

Cited by 166 publications

References 30 publications

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

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

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)

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