Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 35 of 236
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Note that the corrosion coupons experienced relatively high corrosion rates as compared
to the earlier tests:
C1018 - 4.391 mils (112 m)
N200 - 0.937 mils (24 m)
M400 - 0.973 mils (24.7 m)
Note further that the corrosion loss was uniform. This was an early indication that temperature
control could be used to cause uniform corrosion of base metal, if required to- expose
contamination buried deep in the components.
Test 44 was performed in an attempt to clarify the results of Test 43. The corrosion
coupons were eliminated from Test 44. All other parameters were the same as for Test 43. The
results of Test 44 more nearly duplicated Test 39 than Test 43 (see Appendices B and C for
details). Comparing Tests 39, 43, and 44, it was concluded that the improved results from Test
43 were the result of the ferric:EDTA complex rather than the addition of the sodium nitrite.
This was evaluated further in Test 46 (Test 45 will be discussed later).
Test 46 used 100 g/L EDTA, 15 g/L ammonium carbonate, and 3 g/L ferric chloride
(FeCl3). The initial pH of the solvent was 9.0 and the application temperature was 65.6*C
(150*F). An oxygen sparge was also used. Test 46 clearly demonstrated the benefits of the
ferric:EDTA complex as an oxidizing agent. Greater than 60% uranium dissolution was
achieved. The results of the various oxygen sparge tests are graphically compared in Figure 4.
Note that even with the ferric:EDTA complex initially present in the solvent, uranium
dissolution effectiveness was still lower than the basic H202 system.
A final test of the ferric:EDTA solvent system was performed in Test 50. Test 50 was
the same as Test 46 with the exception that air sparging was substituted for the oxygen sparge.
Air sparging would be easier to utilize than oxygen sparging in actual application. The results
of Test 50 are also shown graphically in Figure 4. Not surprisingly, the oxygen sparge resulted
in improved dissolution over the air sparge in this system. Note however, that the air
sparge/ferric:EDTA system (Test 50) outperformed the systems using oxygen sparging and no
Test 49 rounded out the data on oxygen sparging. This was a 24 hour oxygen sparge at
relatively low temperatures (35*C maximum temperature). Test 49 was used to determine, if
given enough residence time (which could be engineered into a delivery system) if the oxygen
sparge concept could be utilized. Results were poor.
Tests 45, 47 and 48 evaluated potassium bromate as the oxidant. Potassium bromate is
a standard oxidant used in copper dissolution solvents for fossil boiler chemical cleanings. The
potassium bromate chemical cleaning solvents are typically applied at about 66*C. Therefore,
these tests were also applied at this temperature. Test 45 utilized the basic solvent system with
40 g/L potassium bromate (KBrO3). Test 48 also used the same basic solvent system with a
lower concentration of potassium bromate (25 g/L). Test 47 used the same solvent as Test 48
with the addition of oxygen sparging throughout the test.
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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/m1/35/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.