Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 27 of 236
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5.4 Room Temperature/Oxidizing Tests
As presented in the preceding, the high temperature reducing conditions were ineffective
in dissolving uranium. Therefore, a decision was 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 (oxidation of uranium
to the +6 valence state by peroxide, followed by complexation with carbonate, References 21-
23), and to the dissolution of copper compounds in the chemical cleaning industry. The testing
was performed at room temperature, due, in part to the known potential for violent reaction
between peroxide and organic materials. In addition, it is easier to maintain oxidizing conditions
with H202 at lower temperatures.
The first test in this series (Test 27) used DTPA at about 100 g/L with the addition of
about 30 g/L ammonium carbonate ((NH4)2CO3). Hydrogen peroxide (H202) was added to the
solvent at a concentration of about 3% and the solvent was pumped into the reaction flask. Note
that the H202 was added just prior to injection to the reaction flask. No corrosion coupons were
used in this testing. It is known that low temperature H202/chelate solutions are essentially non-
corrosive (References 3 and 24).
Table 1 summarizes the analytical data from Test 27 (this same data can be found in
Appendices B and C). In Test 27, the pH dropped from the original 9.0 to 8.43 due to the
addition of the low pH H202 solution (30% H202 at a pH of 5.5 was used for the peroxide
addition). The pH remained essentially constant for the remainder of the exposure.
Temperature increased from 23.9*C (75*F) to a maximum of 35.3*C (95.6*F). This peak in
temperature occurred 1.5 hours after the start of the test. The free DTPA (i.e. uncomplexed
DTPA) decreased due to chelation with the uranium and also from decomposition reactions
caused by the H202. The test was terminated after four hours due to the very rapid dissolution.
Analytical results and visual observations indicated that essentially complete dissolution of the
UO2 occurred within the first hour of exposure. Post test weight loss of the deposit indicated
greater than 99% dissolution.
Analytical Data From Test 27
Low Temperature/Oxidizing Test Sequence
after addition = 99.7 g/L
Elapsed . Free
Time [DTPA] [Uranium] Temperature
(Hours) pH (g/L) (ppm) (*C)
0* 9.00 110.8 - 23.9
1 8.43 38.2 3470 34.8
2 8.43 12.7 - 3492 34.6
4 8.41 6.4 3542 30.7
* - l Hour analysis just pnor to addition of concentrated H202 solution - [D
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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/m1/27/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.