Transcript No Slide Title

X-ray Microprobe for Fluorescence and Absorption Spectroscopy
Matt Newville, Steve Sutton, Mark Rivers
Chemical composition, speciation, and local atomic structure
for elements in heterogeneous materials at a micron scale.
•Techniques:
X-ray Fluorescence
Chemical composition, elemental correlations, 2dimensional mapping, fluorescence tomography
(1ppm)
XANES
Chemical speciation / oxidation state
(10ppm)
EXAFS
Near-neighbor distances and coordination
environment of selected element.
(100ppm)
• Applications:
Environmental Sciences:
Speciation, mobility, and bio-availability of metals
in soils, plant tissues, and at mineral surfaces.
Planetary Sciences
Elemental abundance and correlations and
oxidation state of metals in meteorites.
Geochemistry:
Elemental partitioning and metal speciation in
hydrothermal fluids.
GeoSoilEnviroCARS
2002-02-28
GSECARS Fluorescence and XAFS Microprobe Station
Beamline13-ID-C is a world-class micro-beam facility for x-ray fluorescence
(XRF) and x-ray absorption spectroscopy (XAS) studies:
Incident Beam:
Monochromatic x-rays
from LN2-cooled Si
(111)
Sample Stage: x-y-z(-q) stage, 1mm resolution
Fluorescence detector:
16-element Ge
detector [shown],
Ion Detector, or
Wavelength Dispersive
Spectrometer
Optical Microscope:
(5x to 50x) with
external video system
Data Collection:
Flexible software for
x-y mapping, XAFS,
tomography scans.
GeoSoilEnviroCARS
Focusing: Horizontal and Vertical Kirkpatrick-Baez mirrors
2002-02-28
Metal Speciation in Hydrothermal Fluid Inclusions
John Mavrogenes, Andrew Berry (Australian National University)
Hydrothermal ore deposits are the main
source of Cu, Au, Ag, Pb, Zn, and U.
Metal complexes in high-temperature, highpressure solutions are transported until
cooling, decompression, or chemical reaction
cause precipitation and concentration in
deposits.
To further understand the formation of these
deposits, the nature of the starting metal
complexes need to be determined.
XRF and XAFS are important spectroscopic
tools for studying the chemical speciation and
form of these metal complexes in solution.
This is challenging to do at and above the
critical point of water (22MPa, 375oC).
Fluid inclusions from hydrothermal deposits
can be re-heated and used as sample cells for
high temperature spectroscopies.
GeoSoilEnviroCARS
Natural Cu and Fe-rich brine fluid inclusions in quartz
from Cu ore deposits from New South Wales,
Australia were examined at room temperature and
elevated temperatures by XRF mapping and XAFS.
2002-02-28
Cu Speciation in Hydrothermal Fluid Inclusions: XRF Maps
John Mavrogenes, Andrew Berry (Australian National University)
Natural Cu and Fe-rich brine fluid inclusions in
quartz from Cu ore deposits were examined at
room temperature and elevated temperatures by
XRF mapping:
Cu 25oC
Fe 25oC
Cu 495oC
Fe 495oC
Cu and Fe Ka fluorescence intensities were
recorded as a function of x-y position across a
fluid inclusion by moving the sample in 5mm steps
with an x-ray beam of 5mm x 5mm.
Initial Expectation: chalcopyrite (CuFeS2)
would be precipitated out of solution at low
temperature, and
would dissolve into
solution at high temperature. We would study
the dissolved solution at temperature
XRF mapping showed that a uniform solution at
room temperature was becoming less uniform at
temperature.
This was reversible.
GeoSoilEnviroCARS
2002-02-28
Cu Speciation in Hydrothermal Fluid Inclusions: XAFS
John Mavrogenes, Andrew Berry (Australian National University)
XAFS measurements at low and high temperature were
also very different, with a very noticeable differences in
the XANES indicating a change in speciation
Low temp: Cu2+
O
2.35Å
Cu2+
High temp: Cu1+
O
Cl
2.09Å
Cu1+
1.96Å
Low temp
High temp
EXAFS from the high temperature phase
(below) is also consistent with the model of
Fulton et al: Cu1+ with Cl (or S) at 2.09Å,
These results are consistent with Fulton et al [Chem Phys
Lett. 330, p300 (2000)] study of Cu solutions near critical
conditions: Cu2+ solution at low temperature, and Cu1+
associated with Cl at high temperatures.
GeoSoilEnviroCARS
2002-02-28