2010-08-31_ENFORCEMENT - M1977300

Home Browse Search

July 30, 2010 6 of 24 MINE POOL CHEMISTRY IS SIGNIFICANTLY AFFECTED BY OXYGENATION The e bullet point on Mr. David Bird's rebuttal testimony (before the MLRB on July 12, 2010) states that it is "speculation" that dewatering would create oxidizing conditions in the mine pool and mobilize uranium that would otherwise remain stable and insoluble in the flooded mine. Further, Mr. Bird states that "it is unknown what chemical effect dewatering will have on the mine pool. " The concept that uranium is more mobile in oxidizing conditions and less mobile under reducing conditions is well established and irrefutable. Uranium solubility under oxidizing conditions has been studied for decades with respect to uranium solution mining. Uranium deposits form in reducing environments. The classic uranium roll front deposit occurs where dissolved uranium in oxidized waters moves through a sandstone aquifer and precipitates from solution upon encountering the reducing conditions. The precipitation of uranium minerals occurs when the oxygen content decreases along extensive oxidation-reduction (redox) interfaces. Solution mining of uranium deposits uses the same concept (in reverse) to dissolve uranium by adding a complexing agent (such as carbonate) and an oxidant (such as hydrogen peroxide, H2O2). The oxidant serves to dissolve the uranium and the complexing agent helps to keep it in solution until the uranium-enriched solution can be pumped to the surface for mineral extraction. The effect of oxidation on uranium solubility is clearly shown in Figure 5. Researchers working on behalf of the U.S. Atomic Energy Commission (Department of Energy) demonstrated that uranium solubility increased significantly with oxygen/aeration (lines 2 through 4 in Figure 5) than without oxygen/aeration (line 1). Further, as shown in Lines 2 through 4 in Figure 5, increasing oxygen increases the leaching of uranium.