Experimental determination of contaminant metal mobility as a function of temperature time and solution. 1998 annual progress report Page: 2 of 3
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Experimental Determination of Contaminant Metal
Mobility as a Function of Temperature Time and Solution
Susan Carroll, Lawrence Livermore National Laboratory
Carol Bruton, Lawrence Livermore National Laboratory
Peggy O'Day, Arizona State University
Nita Sahai, Arizona State University
The objective of this work is to determine the fundamental data needed to predict the behavior of 90Sr
at temperature and time scales appropriate to thermal remediation. Our approach combines
macroscopic sorption/precipitation and desorption/dissolution kinetic experiments which track changes
in solution composition with direct molecular characterization of Sr in the solid phase using x-ray
absorption spectroscopy. These experiments will be used to identify mechanistic geochemical reactions
and their thermochemical properties that will be incorporated into geochemical computer codes.
Research Progress and Implications
As of May 1998, we have completed most of our static sorption experiments as a function of
temperature (25, 60, and 80*C), solution pH (4 to 10), initial Sr concentrations (10-7 to 10-3 M), and
partial pressure of CO2 (100% N2 or atmospheric CO2). We chose to study goethite, kaolinite, gibbsite,
and amorphous silica because iron and aluminum (oxy)hydroxides, aluminosilicate clays, and quartz
are key components in soils, sediments, and aquifers. We have completed x-ray absorption analysis
of Sr sorption to kaolinite and goethite at 25*C, initial Sr of 10-3 M, and pH 9.
Strontium sorption to goethite, kaolinite, and amorphous silica is dependent on solution pH, with
little or no sorption between pH 4 and 7, and increasing sorption from pH 8 to 10. No sorption
occurred at the gibbsite-water interface from pH 4 to 10. Strontium removal from solution is catalyzed
by reactions at the goethite, kaolinite, and amorphous silica surfaces, because minimal amounts of Sr
where removed from solution without these solids in waters supersaturated with respect to strontianite
(SrCO3). Strontium sorption from 10-3 M Sr solutions at pH 10 and atmospheric CO2 was greater to
amorphous silica (100%), than goethite (50%) and kaolinite (20%). Strontium sorption to kaolinite
and goethite is not dependent on temperature from 25 to 80*C.
The dominant surface complexes, as determined by x-ray absorption spectroscopy (XAS), are
outersphere hydrated-Sr complexes at the kaolinite-water interface and both outersphere hydrated-
Sr complexes and reactive multinuclear Sr-carbonate complexes. For all of the kaolinite samples
identical x-ray absorption spectra were obtained, yielding 6 to 9 first neighbor O atoms at an average
distance of 2.60 A. If innersphere or multinuclear complexes form we would expect to see second
neighbor Al, Si, or Sr atoms in the x-ray absorption spectra. Outersphere hydrate-Sr complexes at the
kaolinite-water interface appear to be very stable. Spectra from sorption experiments aged for two
months showed only outersphere hydrated-Sr complexes. In solutions supersaturated with respect to
strontianite, we had expected multinuclear Sr-carbonate surface complexes to form as the samples
Strontium complex formation at the goethite-water interface consists of disordered multinuclear
Sr-carbonate complexes in atmospheric CO2 experiments and outersphere hydrated-Sr complexes in
C02 free experiments. The multinuclear Sr-carbonate complex consists 6 to 9 first neighbor O atoms
at 2.60A, 1 second neighbor Fe atom at 2.04 A, and 7 to 8 second neighbor Sr atoms at 4.1A and 2
second neighbor Sr atoms at 4.88 A. Interestingly, aging the goethite experiments with initial
EMSP Project Summaries
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Carroll, S.; Bruton, C.; O'Day, P. & Sahai, N. Experimental determination of contaminant metal mobility as a function of temperature time and solution. 1998 annual progress report, report, June 1, 1998; United States. (https://digital.library.unt.edu/ark:/67531/metadc624502/m1/2/: accessed July 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.