The association of uranium with organic matter in Holocene peat: An experimental leaching study |
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| Institution: | 1. University of Utah, Civil & Environmental Engineering, 110 S. Central Campus Drive, Suite 2000, Salt Lake City, UT 84112, United States;2. Simpson Gumpertz & Heger, 41 Seyon Street, Building 1, Suite 500, Waltham, MA 02453, United States;1. Nuclear Science and Technology Development Center, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsingchu 30013, 325, Taiwan, ROC;2. Center for Energy and Environmental Research, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsingchu 30013, 325, Taiwan, ROC;3. Institute of Nuclear Engineering and Science, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsingchu 30013, 325, Taiwan, ROC;1. School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China;2. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China;1. Qingdao Institute of Marine Geology, CGS, Qingdao 266071, China;2. Laboratory for Marine Mineral Resource, Qingdao Pilot National Laboratory for Marine Science and Technology, Qingdao 266071, China;3. Guangzhou Marine Geological Survey, Guangzhou 510760, China;4. Qingdao Geological Exploration Institute of China Metallurgical Geology Bureau, Qingdao 266071, China |
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| Abstract: | Uraniferous peat was sampled from surface layers of a Holocene U deposit in northeastern Washington State. Dried, sized, and homogenized peat that contained5980 ±307 ppm U was subjected to a variety of leaching conditions to determine the nature and strength of U-organic bonding in recently accumulated organic matter. The results complement previous experimental studies of U uptake on peat and suggest some natural or anthropogenic disturbances that are favorable for remobilizing U. The fraction of U leached in 24 h experiments at 25°C ranged from 0 to 95%. The most effective leach solutions contained anions capable of forming stable dissolved complexes with uranyl (UO2+2) cation. These included H2SO4 (pH= 1.5) and concentrated (0.01M) solutions of sodium bicarbonate-carbonate (pH= 7.0–10.0), or sodium pyrophosphate (pH= 10). Effective leaching by carbonate and pyrophosphate in the absence of added oxidant, and the insignificant effect of added oxidant (as pressurized O2) strongly suggest that U is initially fixed on organic matter as an oxidized U(VI) species. Uranium is more strongly bound than some other polyvalent cations, based on its resistance to exchange in the presence of large excesses of dissolved Ca2+ and Cu2+. Measurements of the rate of U leaching indicate faster rates in acid solution compared to carbonate solution, and are consisten with simultaneous attack of sites with different affinities for U. Sulfuric acid appears a good choice for commercial extraction of U from mined peat.In situ disturbances such as overliming of peat soils, addition of fertilizers containing pyrophosphate, or incursions of natural carbonate-rich waters could produce significant remobilization of U, and possibly compromise the quality of local domestic water supplies. |
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