Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 36 of 236
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The results of Tests 45, 47, and 48 are shown graphically in Figure 5. Overall
effectiveness was similar between all of the bromate solvents tested. Overall uranium dissolution
was in the 70-80% range, which was an improvement over the other alternate oxidants tested.
However, results were still less than that achieved with the H202. A decision was made at this
time to concentrate all further testing with the H202 system. Although limited success was
achieved with bromate and ferric chloride, application temperature had to be increased to about
66*C. These additives also had the potential of complicating the secondary waste stream. The
H202 was very effective at room temperature, and has already been stated, does not cause a
secondary waste problem. There was still the concern of handling H202. However, H202 has
been successfully used in numerous large scale chemical cleaning projects. Therefore, the
engineering of the H202 delivery system is well understood.
6.3 Process Optimization
At this point in the program the decision was made to concentrate efforts on optimization
of the basic EDTA-carbonate-peroxide solvent system. The base solvent selected was as
follows:
100 g/L EDTA
15 g/L (NH4)2CO3
15 g/L H202
pH 9.0
Room Temperature Application
This was the solvent tested and proved to be effective in Test 32. The results of Test 34
indicated that the H202 concentration could be lowered with no loss in efficiency. It was thought
that other constituents could also be lowered. The next sequence of testing methodically lowered
the individual solvent constituents and evaluated the uranium dioxide dissolution effectiveness.
Tests 51, 52, and 53 examined lower initial H202 concentrations. The initial H202
concentration was lowered to 10 g/L (Test 51), then to 5 g/L (Test 52) and then 2.5 g/L (Test
53). Essentially 100% uranium dissolution was achieved in all three tests (see Appendices B and
C for the data). In all cases dissolution was rapid, essentially all occurring prior to the first
sample (taken after 1 hour). The temperature rise from the exothermic reactions was relatively
small for all tests (from about 22*C to about 28*C).
For the next series 'of tests, the Test 53 solvent became the new baseline:
100 g/L EDTA
15 g/L (NH4)2CO3
2.5 g/L H202
pH 9.0
Room Temperature Application-28-
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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/m1/36/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.