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July 30, 2010 7 of 24 <br />O. R <br /> I• Aalimad NO wlthW ale. <br />n <br /> 2. V4 elm alt in aallated faak. <br /> <br /> 2 S. 3A elm air 1nPaahuta tank. <br />d <br /> <br />06 <br />0 3 4. flop" pulp 1e aaratlan Num <br />. end 120 Olm ale. <br />0.04 <br />Tim*, now* <br />14 <br />Figure 5. Effect of Aeration During Uranium Leaching (Clevenger and Eisenhauer, <br />1958) <br />Studies have also been performed to evaluate the dissolution of uranium that has recently <br />precipitated under reducing conditions. Scientists at the Pacific Northwest National Laboratory <br />(PNNL) conducted laboratory experiments and computer simulations to assess the potential of <br />uranium mobility associated with the in situ redox process considered for remediation of uranium. <br />The process involved adding a reductant to sediment which would then accumulate uranium by <br />eduction and precipitation. Specifically, the scientists evaluated the uranium release to solution <br />that occurs when the reduced/precipitated uranium is reoxidized. The researchers determined that <br />the precipitated uranium would be remobilized when the sediment was "oxidized by groundwater <br />containing dissolved oxygen and other oxidants" and they found that "the release rate of uranium <br />into solution was found to be controlled mainly by the oxidation/dissolution rate of the U6+ <br />precipitate (half-life 200 hours)" (Szecsody, et al., 1998). <br />Experiments at PNNL also indicated that increasing the contact time between the U6+ precipitates <br />and the reduced sediment results in a slower U6+ oxidation rate, which, in turn, would lower the <br />concentration of re-mobilized U6+ in an oxidizing environment (Szecsody, et al., 1998). The <br />implications of these experiments for the Schwartzwalder Mine are significant. The precipitation