Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 33 of 236
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Test 34 was a baseline test using the basic solvent system formulated with air saturated
water. The solvent was formulated and stirred overnight in the open to ensure air saturation.
This lowered the initial pH of the solvent to 8.85. The test was carried out at room
temperature. After two hours of exposure it was visually evident that essentially no dissolution
was occurring. In addition, the two hour sample contained only 81 ppm of dissolved uranium.
After the two hour sample, 20 mL of a 30% H2O2 solvent was injected into the test flask.
Uranium dissolution appeared to occur immediately. The dissolved uranium increased to 1652
ppm for the three hour sample. The 20 mL injection of 30% H202 was performed after the four
hour sample and again after five hours of exposure with continued uranium dissolution. The
H202 concentration at the end of the test was 0.343% and greater than 99% uranium dioxide
dissolution was achieved. This test verified the effectiveness of the H202 as an oxidant in this
system, even at a relatively low concentration.
Tests 35 through 39 all used sparging of the solvent. Test 25 used an air sparge (typical
plant compressed air). Tests 36 through 39 all used an oxygen sparge (from a compressed gas
tank containing oxygen). For all of the sparging tests, the gas was bubbled through the solvent
by means of a glass frit. All of these tests were performed without corrosion coupons.
The initial tests (35 and 36) were applied at room temperature. Overall effectiveness was
very low. From fossil chemical cleaning experience (References 26 and 27) oxygen sparged
solvents for copper dissolution are normally applied at higher temperatures. Tests 37, 38, and
39 were therefore performed at progressively higher temperatures (32.2*C, 43.3*C, and 65.6*C
respectively) to evaluate this parameter. The results of these tests are shown graphically in
Figure 4 and can be found in Appendices B and C. The increase in temperature only marginally
improved the performance. None of the oxygen sparged systems showed acceptable uranium
At this point in the program, the alternate oxidant tests were temporarily put on hold to
evaluate some additional proprietary solvent formulations (Tests 40 - 42 which will be presented
later). The oxidant tests were restarted at Test 43. The solvent system used for Test 43 was
similar to that used in Test 39 (EDTA/carbonate/65.6*C/oxygen sparge).. Sodium nitrite
(NaNO2) at 5 g/L was also added to the formulation. Sodium nitrite is used as an additive to
accelerate the rate of oxidation in some standard copper dissolution solvents (References 28 and
29). Corrosion coupons were mistakenly included in the test.
Test 43 showed improved performance, as compared to Test 39 (approximately 39%
uranium dissolution). At first glance this was attributed to the addition of the sodium nitrite.
However, there was also a considerable amount of dissolved iron in solution (about 1000 ppm
by the end of the test) from corrosion of the coupons. Because of the oxygen sparge, the
dissolved iron would be expected to be complexed and in the ferric state. The ferric:EDTA
complex is also known to be a strong oxidizing agent (Reference 29). Therefore, it was
uncertain if the improved uranium dissolution was due to the sodium nitrite or the presence of
the ferric:EDTA complex.
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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/m1/33/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.