Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 39 of 236
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temperature rise. The final H202 concentration was 1200 ppm. In this case, the elimination of
the EDTA did not significantly alter the solvent's performance.
The final two tests in the optimization phase (Tests 60 and 61) increased the uranium
dioxide concentration to 12 g/L (30 grams of UO2 in the 2.5 liters of solvent). Test 60 used the
carbonate only solvent evaluated in Test 59. Results at the higher UO2 concentration were good,
but there was a slight fall off in efficiency (about 98.5% of the UO2 added was dissolved). Like
the other solvent applications, almost all of the dissolution appeared to occur over the first two
hours of exposure. The results of this test (see Appendices B and C for details) indicated that
the limits of this particular solvent.were being reached. Note, however that this test used the
low peroxide and carbonate concentration.
For Test .61, the EDTA was added back into the formulation:
50 g/L EDTA
10 g/L (NH4)2CO3
2.5 g/L H202
Room Temperature Application
Again, 12 g/L of UO2 was added to the test flask. Corrosion coupons were once again included
in the test flask (as previously stated, corrosion coupons had not been used in the previous
optimization studies). Dissolution was good, but unexpectedly lower than Test 60 (about 94%
UO2 dissolution). A small amount of corrosion occurred to the Monel 400 coupon (0.5 gm)
with the 1018 carbon steel and the Nickel 200 coupons experiencing no weight loss. This small
amount of dissolved metal (confirmed by the metals analyses - see Appendix B) would not be
expected to cause a drop in chelating capacity. However, it was also noted that the peroxide
concentration dropped to below 0.1 % by the first hour of exposure. This relatively rapid loss
of H202 was thought to be the cause of the slight drop in dissolution efficiency in Test 61. More
discussion on this theory will be presented in Section 6.5.
This completed this phase of the process optimization testing. The remaining
optimization tests were performed with corrosion coupons. These final optimization tests will
be presented in more detail in Section 6.5 of this report.
6.4 Miscellaneous Tests
As already stated, the original test plan allowed for three solvents to be carried forward
into the refinement phase of the program, and ESI-600 had been selected for limited testing.
A reformulation of this solvent, and also of ESI-603, were supplied by the manufacturer along
with a request for re-evaluation of their performance. None of the proprietary formulations
matched the performance of the basic solvent systems. The tests of the proprietary solvent
systems are included in this section for completeness.
The original plan also included baseline tests with nitric acid (HNO3). It is known that
uranium is highly soluble in nitric acid and it is the solvent of choice in the reprocessing of
uranium fuel. Therefore, HNO3 was considered as the appropriate baseline for judging the rate
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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/m1/39/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.