XAFS and micro-XAFS at the PNC-CAT beamlines

Heald, S. M.; Brewe, Dale; Stern, Edward A.; Kim, K. H.; Brown, F. C.; Jiang, Dawei; Crozier, E. D.; Gordon, R. A.

doi:10.1107/s090904959801677x

Cited by 103 publications

(85 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For solid-phase measurements by electron-beam and x-ray-beam methods, the sediment subsamples were imbedded in epoxy, wafered using a diamond saw, and prepared as 100-µm-thin sections on fused-quartz slides. Measurements were made at the Argonne National Laboratory Advanced Photon Source on the Pacific Northwest Consortium Collaborative Access Team (PNC-CAT) beamline (Heald et al 1999). The primary x-ray beam was focused using Kirkpatrick-Baez mirrors to a 6-7 µm diameter on the sample surface.…”

Section: Instrumental Analysismentioning

confidence: 99%

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Zachara¹,

Brown²,

Christensen³

et al. 2007

View full text Add to dashboard Cite

Executive SummaryUranium (U) is an important risk-driving contaminant at the Hanford Site. Over 200,000 kg have been released to the vadose zone over the course of site operations, and a number of vadose zone and groundwater plumes containing the uranyl cation [UO 2 2+ , U(VI)] have been identified. U is recognized to be of moderate-to-high mobility, conditions dependent. The site is currently making decisions on several of these plumes with long-lasting implications, and others are soon to come.Uranium is one of nature's most intriguing and chemically complex elements. The fate and transport of U(VI) has been studied over the long lifetime of the Hanford Site by various contractors, along with the Pacific Northwest National Laboratory (PNNL) and its collaborators. Significant research has more recently been contributed by the national scientific community with support from the U.S. Department of Energy's (DOE) Office of Science through its Environmental Remediation Sciences Division (ERSD). This report represents a first attempt to integrate these findings into a cohesive view of the subsurface geochemistry of U at the Hanford Site. The objective is to inform all interested Hanford parties about the in-ground inventory of U and its geochemical behavior. This report also comments on the prospects for the development of a robust generic model to more accurately forecast future U(VI) migration at different Hanford waste sites, along with further research necessary to reach this goal.To accomplish the report objectives, the environmental geochemistry of U at the Hanford Site is discussed in terms of both the vadose and saturated zone, to the extent that it is known. Hexavalent uranium [U(VI)] is the dominant valence form of U under the predominantly oxidizing subsurface conditions at the Hanford Site, and the researchers' analyses consequently emphasize this species. The nature and concentration of background U in Hanford subsurface sediments is identified to place contaminant U(VI) concentrations and behavior in perspective to the natural system. In-ground U-waste inventories are quantified and characterized with regard to source term, to the extent possible, and the most important sites from an inventory perspective are identified. The U-isotopic content of various waste streams are discussed from the perspective of waste-source tracking. The geochemical attenuation processes responsible for slowing the rate of subsurface U migration, relative to the transporting water front, are illustrated through careful consideration of both field characterization studies of existing U vadose-zone and groundwater plumes, and laboratory studies of derived contaminated and uncontaminated sediments. Both empirical and more mechanistic models of these attenuation processes are considered as well as the parameters that define attenuation magnitude. Attention is given to the behavior of contaminant U(VI) that has been in contact with Hanford sediments for extended periods (circa 10-50 years), as long contact imparts unique characte...

show abstract

Section: Instrumental Analysismentioning

confidence: 99%

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Zachara¹,

Brown²,

Christensen³

et al. 2007

View full text Add to dashboard Cite

show abstract

“…The x-ray microprobe measurements were performed at the PNC-CAT insertion device beamline (Heald et al 1999) and at the GSE-CARS beamline, both at the ANL Advanced Photon Source (APS). Focusing was achieved using Kirkpatick-Baez mirrors.…”

Section: D322 Experimental Proceduresmentioning

confidence: 99%

Field Investigation Report for Waste Management Area S-SX Volume 1 & 2 [SEC 1 Thru 6]

Knepp¹

2002

View full text Add to dashboard Cite

“…The XANES analyses were performed at the PNC-CAT and GSE-CARS undulator beamlines, Sectors 20 and 13, respectively, at the Advanced Photon Source, Argonne National Laboratory (Heald et al 1999, Newville et al 1999, in prep., Sutton & Rivers 1999.…”

Section: Samples and Techniques Of Their Characterizationmentioning

confidence: 99%

Chemical Speciation of Gold in Arsenopyrite

Cabri¹,

Newville

Gordon

et al. 2000

The Canadian Mineralogist

Self Cite

137

View full text Add to dashboard Cite

The speciation of Au in gold-bearing arsenopyrite (FeAsS) from four gold deposits (Olympiada, Sentachan, São Bento and Sheba) was determined by micro-X-ray absorption near-edge structure (XANES) on grains well characterized microscopically and by electron-microprobe and secondary-ion mass spectrometry analyses and images. "Invisible" gold in arsenopyrite occurs in two apparently mutually exclusive chemical forms: chemically bound and elemental. Arsenopyrite from the Sentachan, São Bento and Sheba deposits contains chemically bound gold. With comparable constituent electronegativities and a white-line feature in the XANES indicating unoccupied Au 5d-states, but absorption-edge positions comparable to Au 1+ species, the bonding is interpreted as being covalent rather than ionic. The invisible gold in arsenopyrite from the Olympiada deposit, on the other hand, occurs as very small particles of Au 0 , probably less than a few nanometers in diameter. Micro-XANES data for the Olympiada and Sentachan arsenopyrite support earlier results obtained by 197 Au Mössbauer spectroscopy on arsenopyrite concentrates. In some arsenopyrite crystals, the gold concentration is closely related to growth zoning. This feature represents conditions during crystallization and does not correlate with the chemical form of the gold. Similarly, selenium, where present, correlates with gold in some deposits and not in others, irrespective of the gold speciation. The finding of two types of invisible gold in arsenopyrite from different deposits has beneficial implications for extractive metallurgy.

show abstract

XAFS and micro-XAFS at the PNC-CAT beamlines

Cited by 103 publications

References 0 publications

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Field Investigation Report for Waste Management Area S-SX Volume 1 & 2 [SEC 1 Thru 6]

Chemical Speciation of Gold in Arsenopyrite

Contact Info

Product

Resources

About