03-Mar-2001

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GeoSoilEnviroCARS

X-ray Absorption Spectroscopy at GSECARSMatt Newville, Steve Sutton, Peter Eng, Mark Rivers

Pu speciation in Yucca Mountain Tuff

Sr coordination in coral used as a paleothermometer

• Selected Applications:

Design Team: Glenn Waychunas (LBNL), Gordon Brown (Stanford), Paul Bertsch (SREL, U Georgia), Francois Farges (U Marne la vallee, Paris)

XANES

EXAFS

As speciation and distribution in Bangladesh groundwater sediments

Cu speciation and coordination in hydrothermal fluid inclusions

Eu oxidation state distribution in apatites

Cr oxidation state in Hanford core samples

Au speciation and coordination in ore deposits

Mn, Cu, Zn speciation around plant hyphae and roots

Pb speciation in biofilms on mineral surfaces

• Techniques:

near-neighbor distances and coordination numbers

chemical speciation and oxidation state

Micro-Beamspatial sensitivity at the micron scale, high sensitivity

V oxidation state in meteoric fassaite

03-Mar-2001

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GeoSoilEnviroCARS

GSECARS Fluorescence and XAFS Microprobe StationBeamline13-ID-C is a world-class micro-beam facility for x-ray fluorescence (XRF) and x-ray absorption spectroscopy (XAS) studies:

Focusing: Horizontal and Vertical Kirkpatrick-Baez mirrors

Incident Beam:Monochromatic x-raysfrom LN2 cooled Si (111)

Sample Stage: x-y-z stage, 0.1m resolution

Fluorescence detector:16-element Ge detector [shown], Si(Li) detector,Lytle Detector, or Wavelength Dispersive

Spectrometer at 90o to incident beam

Data Collection:Flexible software for x-y mapping, traditional XAFS scans, XAFS scans vs. sample position.

Optical Microscope:(5x to 50x) with external video system

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Double Focused Undulator Beam

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FWHW = 0.85 microns

FWHW = 0.80 microns

Flux Density Gain = 113,000

De-mag = 787

Source Size = 700m FWHM

Ideal focus = 0.88m FWHM

De-mag = 324

Source Size = 96m FWHM

Ideal focus = 0.30m FWHM

rad RMS Slope Error100mm long Rh Coated Si Mirrorf1 = 55m f2 = 0.07m

= 5mradEntrance Aperture = 350 m

1.2rad RMS Slope Error

100mm long Rh Coated Si Mirrorf1 = 55m f2 = 0.17m

= 5mradEntrance Aperture = 350 m

The table-top Kirkpatrick-Baez mirrors use a four-point bender and flat, trapezoidal mirror to dynamically form an ellipsis. They will focus a 300x300m beam down to 1x1m - a flux density gain of 105.

With a typical working distance of 100mm, and an energy-independent focal distance and spot size, they are ideal for micro-XRF and micro-EXAFS.

We use Rh-coated silicon for horizontal and vertical mirrors to routinely produce 3x3m beams for XRF, XANES, and EXAFS.

Kirkpatrick-Baez focusing mirrors

03-Mar-2001

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GeoSoilEnviroCARS

Zn Cu

Fe Mn

Metals distribution at Root/Soil Interface

Metal oxide dust was introduced to a forest topsoil resulting in 5000 ppm Zn and 2500 ppm Cu in the soil.

These XRF maps show the distribution of Zn, Cu, Fe and Mn near a barley root growing in the contaminated soil. Close to a Zn oxide particle, the root is strongly enriched in Zn.

Arrows mark regions where Zn -XAFS spectra were collected.

Andreas Scheinost, Ruben Kretzschmar (ETH Zurich)

stelecortex

Mn-richFe-rich

Zn-rich

Optical microscope image of root

Cu-rich

03-Mar-2001

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Zn EXAFS and speciation at Rhizosphere

The Zn-rich and Cu-rich areas consist of Zn oxide. The remaining areas lack a strong second shell, and show tetrahedral Zn-O coordination, suggesting that Zn dissolved from the oxide is sorbed by the root cortex and by Fe and Mn hydroxides.

03-Mar-2001

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GeoSoilEnviroCARS

Cr redox in Boreholes below Hanford Waste TanksSam Traina, Isao Yamakawa (Ohio State Univ.), Gordon Brown, Jeff Warner, Jeff Catalano (Stanford Univ.)

Borehole samples collected from the vadose zone under leaking waste tanks, containing highly alkaline fluids.

Radioactive (~10 Ci/g Cs-137) soil sections were embedded in epoxy, and sent for synchrotron analysis during January, 2001.

XRF mapping and Cr XAS were studied at GSECARS, bulk Cr XAS SSRL beamline 11-2, and Cs and Cr XAS at PNC-CAT (APS 20-ID)

Chromium Barium Iron

300 x 300 m

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GeoSoilEnviroCARS

Cr redox in boreholes below Hanford Waste Tanks

Hanford Soil Chromium Redox State

Prelminary analysis of the Cr XANES from a few different core samples shows some variability of the Cr6+ / Cr3+ ,ratio, but fairly significant reduction of Cr6+ to Cr3+.

Cr EXAFS measurements are still being processed (but seem to be typical Cr3+-oxide)

03-Mar-2001

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GeoSoilEnviroCARS

Cu speciation in Hydrothermal Fluid InclusionsJohn Mavrogenes, Andrew Berry (Australian National University)

Cu 25oC

Cu 495oC

Fe 25oC

Fe 495oC

Understanding the metal complexes trapped in hydrothermal solutions is key to understanding the formation of ore deposits.

XRF and XAFS are important tools for studying the chemical speciation and form of these fluid inclusions.

65m

Cu and Fe-rich fluid inclusions in granites were examined at room temperature and elevated temperatures by XRF mapping and XAFS.

Expectation: chalcopyrite precipitate at low temperature would dissolve into solution at high temperature.

Result: uniform Cu2+ solution at low temperature, not associated with Fe, and Cu1+ at high temperatures, with a less uniform spatial distribution.

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GeoSoilEnviroCARS

A complication in measuring fluorescence and EXAFS in many natural samples is the prescence of fluorescence lines from other elements near the line of interest: The resolution of a solid-state fluorescence detector (~150eV) is sometimes not good enough to resolve nearby fluorescence lines

The Wavelength Dispersive Spectrometer has much better resolution (~20eV) than a solid-state detector, and a much smaller solid angle. It uses a Rowland circle, not electronics, to select energies of interest.

It needs the brightness of an undulator, but complements the Ge detectors, and allows XRF and even EXAFS on systems with overlapping fluorescence lines.

High Resolution X-ray Fluorescence and EXAFS

03-Mar-2001

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Sector Zoning of Rare Earth Elements in Apatites John Rakovan (Miami University)

Eu is the only REE showing no zonation, but it has two valence states and two ionic sizes that straddle the size of Ca2+.

Is there a partitioning of Eu based on valence state/ionic size?

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77.3577.5577.7577.9578.1578.35

Linescan distance (mm)

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270.000000

320.000000

370.000000

420.000000

470.000000

520.000000

570.000000

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Subsector boundry

011 subsector 001 subsector

011 vicinal face

001 vicinal face

011 vicinal face.Apatites have a high affinity for Rare Earth Elements (REE), and

are often used to study petrogenesis. Heterogeneities in crystal surface structure during apatite growth can strongly alter REE incorporation.

Most REE show sectoral zoning in apatite based on ionic size. Ions larger than Ca2+ (La3+) preferring growth along the 001 face, and those smaller than Ca2+ (Sm3+) preferring the 011 face

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Sector Zoning of Rare Earth Elements in Apatites

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Energy (keV)

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Since Eu has two valence states with different ionic sizes (Eu2+ / 1.2 Å, Eu3+ / 1.3 Å), it was suggested that there may be a valence/ionic size variation in different growth zones.

The bad news: There is way too much Mn in the apatite to separate from the Eu fluorescence line with a solid state detector.

Using the high resolution WDS and the microprobe, we measured the Eu XANESon several spots in the different sectors, and across a <011> / <001> boundary.

Result: We see almost no change at all in Eu2+ / Eu3+ across the zone boundary: the ratio is ~17% Eu2+ throughout the apatite.

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Eu sorption on Fe/Cr oxides

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k2 4 6 8 10

-Fe2O3

-Fe1.93Cr0.07O3

-Cr2O3

-Fe1.69Cr0.31O3

Eu2O3(s)

Eu precipitate

0.1M Eu liquid

(k)

x k

3

Chia Chen, Sam Traina (Ohio State Univ.)

The local structure and coordination chemistry of sorbed species at mineral-water interfaces greatly influence their stability -- XAFS plays a key role in understanding the interactions interactions between sorbent and surface.

The sorption of Eu on minerals such as Fe-and Cr-oxides is especially relevant to DOE concerns, as Eu is a common fission product and a chemical analog of Am.

Several model Eu on Fe/Cr oxide sorption samples were made to determine the local structure of sorbed Eu as a function of Cr concentration, pH, and sample aging.

There is way too much Fe/Cr for a solid-state detector.

The Eu LIII edge can’t be used: it gives only 150 eV of

EXAFS before the Fe K-edge

These EXAFS measurements were made with the Eu LII

edge, monitoring the Eu L fluorescence line with the Wavelength Dispersive Spectrometer.

Bulk EXAFS that requires an undulator.

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GeoSoilEnviroCARS

Eu sorption on Fe/Cr oxides: Results

.Sample CN R 2 E0 CN R 2

-Fe2O3 7.8 2.39 0.008 -3.59 1.0 3.47 0.0025-Fe1.93Cr0.07O3 9.4 2.43 0.014 -1.44 0.4 3.45 0.0025-Fe1.69Cr0.31O3 9.0 2.42 0.01 -2.04 0.7 3.59 0.0025

-Cr2O3 8.9 2.41 0.01 -3.30 0.9 3.53 0.0025

Eu liquid 9.1 2.43 0.007 -1.89

Eu2O3(s) 7.0 2.31 0.01 -5.79 9.0 3.62 0.0081

Eu ppt 9.0 2.43 0.01 -1.36 1.9 3.21 0.0087

1st Shell 2nd Shell

R+Å0 2 4 6

Fou

rier

Tra

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rm M

agni

tude -Fe2O3

-Fe1.93Cr0.07O3

-Cr2O3

-Fe1.69Cr0.31O3

Eu2O3(s)

Eu precipitate

0.1M Eu liquidEu are sorbed to the Fe/Cr oxide surfaces.

Cr substitution for Fe does not impact the sorbed Eu surface structures.

No significant aging effects were seen.