Processing of High Level Waste: Spectroscopic Characterization of Redox Reactions in Supercritical Water - Final Report Page: 2 of 4
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NO. 589 D0.5
13:46 FURMAN CHEMISTRY 4 1626402882085265548
The first two weeks of the summer program were spent setting up the Raman spectrometer system with
a high temperature-high pressure cell. Initial experiments examined the reaction of nitrate anion with organic
species such as ethanol and acetate anion. These early experiments gave erratic results because of high levels of
scattered light from the Raman cell caused by particle formation at high temperatures.
Beginning with the third week we began working more directly with Dr. Buelow and a post doctoral
fellow and graduate student who were working on his EMSP project. This goal of this project is to find ways of
removing Cr(II) compounds from Hanford tank wastes before the solids are formed into glass ingots for
permanent storage. High chromium content results in imperfect, cracked glass ingots.
Our efforts began with an examination of spectroscopic methods for characterization of solids formed
when Cr(IJI) solutions are made basic. The chemistry of chromium in basic solutions is amazingly complex
with hydroxides and oxides present in varying degrees of oligomerization, It is important to learn how the
history of the sample affects the distribution of products, especially the temperature of the solution and its pH.
A number of experiments were carried out on seven samples prepared in the laboratory. These samples were
prepared by Dr. Ding, the post doctoral fellow, following literature procedures to make Cr(OH)3, CrO(OH), and
Cr203. Other samples were prepared then calcined at various temperatures up to 700 C. we determined that
infrared spectra of the samples in KBr pellets provided the most reliable diagnostic information in a short time.
Both Raman spectra and X-ray photoelectron spectra provided some structural information but were not as
useful as JR spectra. The IR spectra indicated the presence and relative amounts of Cr(OH)3, Cr203, and
CrO42~. We also observed a band attributed to carbonate, which forms when carbon dioxide is absorbed from
the atmosphere by the basic solution.
Along with these spectroscopic characterization studies we began experiments on the dissolution and
oxidation of chromium (III) compounds. All of the samples prepared by Dr. Ding were treated by several
different methods. Visible spectra of samples treated with DI water and filtered showed the presence of
chromate in the water for samples calcined at 200 0C or higher. None of the Cr(I) compounds dissolved. The
same samples were stirred with aqueous solutions of oxalic acid. No additional solubility was noted with oxalic
All of the samples showed rapid reaction with basic hydrogen peroxide solutions with formation of
yellow supernatant solutions, Quantitative results were obtained for the fraction of each sample dissolved in
this treatment. Infrared spectra of the remaining solid showed that everything except Cr203 was dissolved in
A number of experiments were conducted to determine if Cr(IU) compounds could be oxidized by N03V
in high temperature water. These reactions were carried out in the high temperature Raman cell. In none of the
experiments did we observe a decrease in the intensity of the nitrate band at 1050 cm 1. nor did we see the
chromate band at 850 cm~1 grow in. The dark green color of the solutions reduced the intensity of scattered
Raman light, and formation of solids above 300 oC blocked the laser beam at the lower diamond window.
Dana Olsen followed the change in pH as Cr(NO3)3 was added to NaOH solutions of in an attempt to
learn something about the stoichiometry of chromium hydroxide formation. She found that in the early stages
more than 4 hydroxides reacted with chromium. The final stoichiometry was convincingly close to the 1:3 ratio
expected for Cr(OH)3.
Robb Lanning studied the kinetics of the reaction of Cr(1II) with basic hydrogen peroxide by following
the change in pH- as the reaction proceeds. The data he generated at different concentrations of reactants
convince us that the reaction is complex and not easily interpreted in terms of a simple order rate equation.
In the course of Robb's experiments we noted that the addition of NaOH to H202 resulted in the
reduction of the 0-0 stretch band and appearance of a new band, which we tentatively assign to the H02-
anion. We have been unable to find a literature reference to the Raman spectrum of this species. We will carry
out the experiment with D202 to confirm this assignment.
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Arrington, C. A., Jr. Processing of High Level Waste: Spectroscopic Characterization of Redox Reactions in Supercritical Water - Final Report, report, November 15, 2000; Greenville, South Carolina. (digital.library.unt.edu/ark:/67531/metadc715181/m1/2/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.