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2003 NSLS Users' Meeting
Processes in Environmental Sciences
Location: Bldg. 555 - Chemistry Department, Hamilton Seminar Room
Date: May 19, 2003
Organizer: Thorsten Schaefer (Institute for Nuclear Waste Management, Germany) and Mark Fuhrmann (BNL)
Description: Reliable long-term prediction of heavy
element mobility in natural multi-component systems or construction of intelligent reactive
barrier systems for waste confinement requires a fundamental process
understanding. Application of a combination of macro- and
microscopic techniques including EXAFS, XANES, FTIR, XRD, XRF and
soft X-Ray microscopy can provide atomic scale chemical information
as well as information of nano- to microscopic spatial distribution
in complex matrixes. New single crystal approaches on well defined
crystallographic planes furthermore gives insight in redox-kinetics
and sorption relevant mineral surfaces. The scope of this workshop
will be to give a discussion platform as well as an overview of
recent applications of synchrotron based techniques to elucidate
important pathways in natural and anthropogenic influenced
environmental systems.
Schedule:
| 8:30-8:45 a.m. |
Opening Remarks - T. Schaefer and M.
Fuhrmann |
| 8:45-9:30 a.m. |
Dr. B. Lanson, CNRS, Grenoble,
France
“Crystal-chemistry
of Poorly Crystalline Minerals as a Tool to Understand the Fate
of Heavy Metals in the Environment”
The
structure of heavy metal sorbed synthetic birnessites (MeBi)
was studied to improve our understanding of the interactions
between naturally ubiquitous manganese oxides (buserite/birnessite)
and environmentally important heavy metals (Me) including Pb,
Cd, and Zn. MeBi samples were prepared by equilibrating at
pH4 a Na-buserite (NaBu) suspension in presence of the desired
aqueous metal and studied using a trial-and-error fitting
analysis of powder X-ray diffraction (XRD) data, selected area
electron diffraction, as well as powder and polarized extended
X-ray absorption fine structure spectroscopy. All cations
sorbed on well-defined crystallographic sites without evidence
for sorption on layer edges or surface precipitation.
The
influence of the nature of Me cations on layer stacking
sequence, as well as on location and coordination of Me is
assessed. Results are compared with the speciation of heavy
metals in contaminated soil environments.
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| 9:30-10:15 a.m. |
Dr. K. Dardenne, INE, Karlsruhe,
Germany
“Application
of Synchrotron Radiation Methods to Actinide/Lanthanide Speciation”
Long-term safety
analysis for radioactive waste repositories requires
predictions on a geological time scale. The development of
reliable models describing geochemical behaviour and transport
phenomena of actinides released into the environment requires
the understanding of actinide mobilization-immobilization
processes on a molecular scale. Speciation techniques using
synchrotron radiation, such as X-ray absorption fine structure
spectroscopy (XAFS), are of particular importance as
speciation/spectroscopic methods because many are elemental
specific and often applicable without prior sample
preparation, separation or dissolution steps, thereby
minimizing possible speciation changes.
Typical
examples of XAFS applied for determining the coordination of
actinides (or chemically homologue lanthanides) complexed with
humic substances, sorbed onto amorphous iron hydroxides and
their transformation products, in polynuclear hydrolysis
products and eigencolloids are shown. Soft X-ray NEXAFS
investigations at the ionization energy of C, O and/or Fe (L
edges), combined with microscopic imaging for characterizing
the interaction of actinides with humic/inorganic colloids are
presented.
Combined
with complementary spectroscopy/microscopy studies these
investigations give us an insight view into actinide
coordination structures, their reactions in solution, in the
solid state and at the water-solid interface, as well as the
reaction mechanisms involved.
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| 10:15-10:45 a.m. |
Coffee Break |
| 10:45-11:30 a.m. |
Dr. E.A. Ghabbour, and Dr.
G. Davies, Northeastern
University, US
“XAFS Studies of Tight Metal Binding by
Solid Humic Acids”
Amorphous
brown solid humic acids (HAs) in sediments and soils retain
water and selectively bind organic solutes and metals. Their
binding of nutrient (Fe and Mn) and toxic (Cd and Pb) metals
affects metal transport rates and bioavailability.1
The most tightly bound metal is in the clay or mineral
attached to HA. Organically bound metal resists brief water
washing and exceeds clay- or mineral-bound metal. The most
weakly bound metal is easily washed away and likely is trapped
in electrostricted water. Isotherm studies2,3 indicate
a common HA binding site A for Cu(II), Fe(III), Mn(II), Co(II),
Mg and other metals; a peat-derived HA has another site B for
Cu(II), Fe(III) and Co(II) binding and a third very weak site
C for Cu(II) binding. We need to know how these tight binding
sites differ. In particular, can XAFS 1) structurally
distinguish sites A and B and 2) be used to confirm
inner-sphere tight metal binding? |
| 11:30-12:15 p.m. |
Dr. R. Kretzschmar, ETH,
Zurich, Switzerland
“Spatial
Distribution and Speciation of Pb and Zn in Contaminated Soils”
Contamination
of soils with heavy metals is a worldwide problem and can pose
serious threats to soil quality and ecosystem health. Zn is an
essential plant nutrient but it can also become phytotoxic at
elevated concentrations. Pb is less toxic to plants, but is
highly toxic to humans and animals. Risk assessment and
development of soil remediation or stabilization strategies
requires knowledge about the spatial distribution and chemical
speciation of heavy metals in soils. In the first part, we
will present a study on the slow formation and dissolution of
Zn precipitates in soils using a combination of column
experiments and XAFS spectroscopy (NSLA, Beamline X11A). In
the second part, we will discuss a field study on the spatial
distribution and speciation of Pb in shooting range soils as
affected by preferential water flow. The spatial distribution
and speciation of Pb was studied at the cm-scale by grid
sampling and bulk XRF and XAFS spectroscopy, and at the
micrometer scale around corroding Pb bullets using μ-XRF
and μ-XANES
spectroscopy (NSLS, Beamline X26).
|
| 12:15-01:15 p.m. |
Lunch Break at workshop location |
| 01:15-02:00 p.m. |
Dr. U. Neuhausler, ESRF, France
“Scanning
Fluorescence X-ray Microscopy Using keV Radiation – A Unique
Tool for High Resolution Elemental Mapping and Spectroscopy in
Environmental Science”
Pioneered
in the soft X-ray ‘water window’ energy range at the X1A
beamline of the NSLS, scanning X-ray microscopy using Fresnel
zone plate lenses evolved within the last decade into the 2
– 8 keV photon energy range, thanks to progress made in
nanofabrication technology and to the advent of new 3rd
generation synchrotron sources.
Therefore,
many medium-light element K – absorption edges (Si,
P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co) and L,M –
edges of higher-Z materials (Sn, Ag, I, Pt, Au) can now be accessed with simultaneously high spectral (down to
10-4) and spatial resolution (sub-500 nm) to
address new scientific questions.
Amongst
the broad spectrum of application fields, we will focus on
work done at the ID 21 beamline of the ESRF on environmental
science related projects. As examples, we will present high
resolution elemental mapping combined with XANES-spectroscopy
of sulfur in soils and marine sediment as well as organotin-clay
mineral interactions studies. |
| 02:00-02:45 p.m. |
Dr. E. Elzinga, S.U.N.Y. at
Stony Brook
“EXAFS Studies of Uranyl and Metal
Interactions with Calcite”
Carbonate
minerals play an important in controlling the solubility,
bioavailablity and mobility of trace contaminant compounds in
calcareous sediments and aquifers. The
transfer of trace elements from solution to the solid phase in
such systems may proceed via a number of mechanisms, which
include adsorption reactions, coprecipitation, and bulk
precipiation. Elucidating these mechanisms by resolving the
metal bonding characteristics at the molecular scale is
crucial for the development of mechanistic models describing
the behavior of contaminants in natural systems. In the
studies presented here, EXAFS spectroscopy was used to study
metal-calcite interactions. Specific systems include divalent
metal-calcite adsorption and coprecipitation studies, and the
way in which the adsorption step controls metal partitioning
between structurally non-equivalent growth steps on calcite
growth faces. In another study, EXAFS and luminescence
spectroscopy was used to characterize the local structure
around U(VI) adsorbed at the calcite surface following uptake
from pre-equilibrated calcite-saturated solutions.
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| 02:45-03:15 p.m. |
Coffee Break |
| 03:15-03:40 p.m. |
Dr. B. Twining,
S.U.N.Y. at Stony Brook
“Quantification
and Localization of Trace Metals in Marine and Freshwater
Protists Using a Synchrotron X-ray Fluorescence Microprobe”
The
accumulation of trace metals by planktonic protists influences
the growth of primary producers, metal biogeochemical cycling,
and metal bioaccumulation in aquatic food chains.
Despite their importance, unequivocal measurements of
trace elements in natural plankton cells have not been possible
to date. We have used the 2-ID-E microprobe at APS to measure
trace elements in single-celled aquatic microbes.
This microprobe employs zoneplate optics to produce the
sub-micron spatial resolution and low background
fluorescence required to produce trace element maps of natural
aquatic protists. Sample
preparation protocols have been developed and tested to ensure
that cellular constituents are not altered during mounting,
and spectral modeling techniques are employed to account for
the frequent overlap of adjacent fluorescence peaks and
non-uniform detector response. SXRF element maps can be
combined with STXM and epifluorescence microscopy images to
measure cellular C, identify functional cell types, and
correlate cell structures with spatial patterns in trace
element fluorescence.
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| 03:40-04:00 p.m. |
Dr. M. Nachtegaal, S.U.N.Y. at
Stony Brook
“NEXAFS
Spectroscopic Studies of Humic Substances and their Metal
Binding Affinity”
The
release of potentially toxic (radioactive) metals in the
environment is of worldwide concern. Due to its high specific
surface area and cation exchange capacity (CEC), humic
substances (HS) play a significant role in the retention and
mobility of these metals in the environment. Despite extensive
and important studies, the metal binding mechanisms and
affinity of HS are still not well understood. HS interact with
their environment through their functional groups. Using near
edge X-ray absorption fine structure (NEXAFS) spectroscopy,
the valence level of unoccupied molecular orbitals of the
carbon containing functional groups can be probed. We found
shifts in the relative position of these valence bands upon
reaction with MnII and CuII. These shifts could be explained
by considering electron density shifts from the carboxyl
functional group to Mn and from Cu to the carboxyl group. |
| 04:00-04:25 p.m. |
C. Eng, S.U.N.Y. at
Stony Brook
“Effectiveness
of Citric Acid As a Remedial Technique on Uranium Contaminated
and Corroded Carbon Steels”
We investigated the association of
uranium with 1010 carbon steel before and after
decontamination using a citric acid/hydrogen peroxide cleaning
method developed by A.J. Francis and C. Dodge. Synchrotron
infrared microspectroscopy (SIRMS) was one of the main
surface characterization techniques we used to study the
interaction of uranium species with the steel surfaces and
establish the effectiveness of the cleaning technique.
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| 04:25-04:50 p.m. |
S. J. White, S.U.N.Y. at
Stony Brook
“Influence
of Elevated Soil-CO2 on Mineral Weathering and Soil
Biogeochemistry, Mammoth Mountain, CA”
The
accumulation of carbon dioxide (CO2) in the
atmosphere is an increasing cause of concern. In an effort to
slow the accumulation of CO2 in the atmosphere,
scientists and engineers are researching possibilities to
sequester CO2 as it is emitted from industrial
processes by piping it into underground reservoirs. One
of the critical facets for terrestrial carbon sequestration
research is to determine how CO2 will react if it
escapes from the reservoirs and reaches shallow zones. Mammoth
Mountain, California, is an area that has been exposed to high
soil-CO2 levels since an earthquake in 1989 that
triggered magmatic degassing. This long-term exposure to
elevated soil-CO2 provides a natural laboratory by
which we can study interactions between CO2 and
minerals in the shallow zone. This talk examines the
differences in plant growth modification, plant metal uptake,
solution chemistry, and soil surface chemistry of areas
affected by high soil-CO2 and areas at ambient
soil-CO2.
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| 05:30-06:00 p.m. |
Round-Table Discussion and Closing
Remarks |
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Adjourn |
Register: Please register for the meeting and workshops (including speakers) at
http://www.nsls.bnl.gov/users/meeting/2003/registration/
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