Processing High Level Waste: Spectroscopic Characterization of Redox Reactions in Supercritical Water Page: 1 of 2
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Project ID Number: 54828
Project Title: Processing High Level Waste: Spectroscopic Characterization of Redox
Reactions in Supercritical Water
Principal Investigator: Charles A. Arrington, Jr.
Greenville, SC 29613
Undergraduate Students: Six undergraduate students from Furman have worked on this project at
Los Alamos National Laboratory during the summers of 1996, 1998, and 1999.
We are engaged in a collaborative research effort with Los Alamos staff scientists Steven
Buelow and Jeanne Robinson, staff members in group CST-6. The work proposed by these LANL staff
scientists is directed towards the destruction of complexants and oxidation of chromium and technetium
by hydrothermal processing in near critical or supercritical aqueous solutions. Our own work has been
focused on a careful kinetic study of oxidation reactions of hydrogen peroxide with chromium
hydroxide. This reaction occurs readily at ambient temperatures.
Research Progress and Implications
Most of the work during the third year of the grant was carried out at Los Alamos National Lab.
During the summer of 1999 the PI and two undergraduate students from Furman worked for 10 weeks at
Los Alamos National Laboratory. Ginger Denison, a senior, and Shane Golden, a junior, continued the
research during the current academic year at Furman. Both students will return for summer research at
Los Alamos in the summer of 2000. Ginger is going to graduate school at Indiana University.
Ginger carried out an extensive set of experiments using UV-visible spectroscopy to low the
production of chromate ion, Cr042-, the product of oxidation of Cr(OH)4 by H202 in basic solutions.
The reactions were carried out under pseudo first order conditions with OH- and H202 present in
excess. The rate of reaction was found to depend on the aging of the chromium hydroxide solutions,
getting slower the longer the solution ages before reaction. We attribute this behavior to oligomerization
of the chromium hydroxide solution. The decay of chromium hydroxide concentration with time cannot
be fit to a single exponential function. We get good fits of the data to two or three exponential
functions. Such behavior is consistent with different degrees of polymerization leading to forms of the
hydroxide that react at different rates- slower rates at higher degrees of polymerization. The rate of
reaction was found to decrease with increasing concentration of hydroxide ion under our experimental
conditions. The rate initially increased with increasing hydrogen peroxide concentration, but at the
higher concentrations of H202 the rate of reaction decreases. The reaction was carried out over a
temperature range from 15 to 25 0C. The Arrhenius plot of these data gives an activation energy of
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Arrington, Charles A., Jr. Processing High Level Waste: Spectroscopic Characterization of Redox Reactions in Supercritical Water, report, June 1, 2000; Greenville, South Carolina. (digital.library.unt.edu/ark:/67531/metadc786816/m1/1/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.