Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 57 of 236
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The following is a summary of the significant conclusions from the data generated during
Task 2 of DOE Program DE-AC21-83MC30168, "Chemical Decontamination of Process
Equipment Using Recyclable Chelating Agents."
None of the elevated temperature (93*C) chelant-only solvent systems provided
acceptable uranium dissolution. This included the proprietary and commercially available
solvents evaluated in the program.
The combination of chelant, ammonium carbonate, and hydrogen peroxide at a pH of 9.0
(adjusted with ammonium hydroxide) was found to effect virtually 100% dissolution of the
uranium dioxide placed in the test flask, within the first two hours of exposure. The solvent was
effective in uranium dissolution at room temperature. Based on the results of the screening and
refinement test program, two solvent systems were concluded to provide optimum uranium
(1) EDTA, ammonium carbonate, and hydrogen peroxide: pH 9.0 with NH40H
(2) ammonium carbonate and hydrogen peroxide: pH 9.0 with NH40H.
Testing in this program indicated that the basic solvent systems were effective over a
wide range of concentrations. This can allow for tailoring the solvent for differing levels of
contamination and to minimize chemical usage. From the standpoint of uranium dioxide
dissolution, the carbonate-peroxide solvents (with or without EDTA) developed in this program
compared favorably with the HNO3 baseline tests.
Testing was performed to evaluate the possibility of using an oxidant other than hydrogen
peroxide in the solvent. This testing was performed to determine if application could be
simplified. Limited success was achieved with bromate and ferric chloride, however they did
not outperform the H202. Therefore, H202 became the oxidant of choice for the solvent.
The addition of corrosion coupons affected the uranium dioxide dissolution. This
necessitated an increase in the initial H202 concentration. The presence of the metal coupons
helped to catalyze the H202 decomposition which apparently resulted in a peroxide concentration
too low to effect complete dissolution. This will need to be factored into the solvent formulation
as it is being tailored for a specific application. Peroxide is an important variable that needs to
be carefully applied for optimum performance. This was evident from all of the testing covered
by this report.
The foaming tests were considered as a qualified success. From the limited data
generated in this phase of the program, it appeared that the EDTA/carbonate/peroxide solvent
developed in this program could be effectively applied in the foam state. The lack of a suitable
test coupon to bind the uranium dioxide for the foam tests limits the broad applicability of the
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Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994, report, July 1, 1995; United States. (https://digital.library.unt.edu/ark:/67531/metadc680875/m1/57/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.