Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 10 of 236
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Under contract to the U. S. Department of Energy, the Babcock & Wilcox Company is
developing a chemical decontamination process using chelating agents to remove uranium
compounds and other actinide species from process equipment. The overall goal of the program
is to develop a solvent capable of selectively chelating uranium; an additional requirement of the
process is the ability to control corrosion of the base metal during decontamination. In cases
where reuse of the equipment is a possibility, corrosion must be controlled at a low rate.
However, if contamination has migrated into the grain boundaries of the base metal, a more
aggressive solvent is required to corrode away base metal and expose radioactive species for
removal. Another objective of the program is to recycle the chelating solvent, thereby
minimizing the generation of secondary waste streams.
The project is divided into Phase I: "Lab Scale/Small Pilot Proof of Concept," and Phase
II: "Field Demonstration." Phase I encompasses Task 1: "NEPA Study"; Task 2: "Chelate
Chemistry/Process Optimization," the goal of which is to identify promising chelating solvents
and optimize application parameters for maximum effectiveness; Task 3: "Solvent
Recycle/Contaminant Reduction," the objective of which is to develop a process to break the
chelant-metal bond and make chelant available for reuse; Task 4: "Bench Scale Tests," to
evaluate the developed solvent system under dynamic test conditions; and Task 5: "Pilot Plant
Study," involving application of the process to equipment actually contaminated in service. This
report describes chelant screening and refinement testing performed under Task 2 of the
As a first part of this task, a literature search was conducted to select organic chelating
agents for screening. Due to the limited availability and high cost of many of the identified
candidates, screening tests were initiated using three readily available chelating agents: EDTA
(ethylenediaminetetraacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), and
DTPA (diethylenetriaminepentaacetic acid). Additionally, several proprietary formulations of
chelating solvents, provided by Environmental Scientific Incorporated (ESI), were evaluated.
Screening tests were performed by placing a known weight of uranium dioxide in a three-liter
test flask, then adding a known volume of test solvent to the flask and holding at carefully
controlled conditions. Solvent was analyzed periodically to evaluate the extent of uranium
dissolution. Monel, nickel and carbon steel coupons were included in some tests to evaluate
Each of the candidate chelants was initially subjected to several screening tests at 93*C
(200*F), run at varying pH's and utilizing several different additives. Dissolution results for
this high temperature testing were unacceptable. A decision was then made to test chelants in
conjunction with hydrogen peroxide and carbonate salts; the combination of peroxide and
carbonate has been applied to the dissolution of uranium compounds in the mining industry. The
combination of chelant, ammonium carbonate, and hydrogen peroxide, adjusted to a pH of 9.0
with ammonium hydroxide and applied at room temperature, was found to effect virtually 100%
dissolution of available UO2 within the first two hours of exposure. Results were equivalent for
EDTA, HEDTA, and DTPA.
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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/m1/10/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.