Solubility and sorption of redox-sensitive radionuclides (Np,Pu) in J-13 water from the Yucca Mountain site: comparison between experiment and theory |
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| Institution: | 1. ÚJV ?e?, a. s., Fuel Cycle Chemistry Department, Hlavní 130, ?e?, 250 68, Husinec, Czech Republic;2. SÚRAO, Dlá?děná 6, Prague 1, 110 00, Prague, Czech Republic;1. Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India;2. Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400094, India;3. Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India;4. Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India;1. Laboratory for Environmental and Oceanographic Research, Department of Marine Sciences, Texas A&M University, Building 3029, Galveston, TX, 77551, USA;2. School of Human Science and Environment, University of Hyogo, 1-1-12 Shinzaike-Honcho, Himeji, Hyogo, 670-0092, Japan;3. Department of Social Informatics, Graduate School of Informatics, Kyoto University, Kyoto, 606-8501, Japan;4. Division of Agroenvironmental Biology, Graduate School of Agriculture Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan;5. Savannah River National Laboratory, Aiken, SC, 29808, USA;6. Los Alamos National Laboratory, Los Alamos, NM, 87545, USA;1. Department of Natural Sciences and Mathematics, University of Charleston, Charleston, WV 25304, USA;2. Department of Chemistry, Marshall University, Huntington, WV 25755, USA;1. Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, PR China;2. University of Science and Technology of China, Hefei 230026, PR China;3. School for Radiological and Interdisciplinary Sciences (RAD-X), Soochow University, 215123 Suzhou, PR China;4. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, PR China;5. Faculty of Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia |
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| Abstract: | This study presents the characterization of Pu-bearing precipitates and the results from uptake studies of Np and Pu on inorganic colloidal particulates in J-13 water from the Yucca Mountain site. Plutonium solubilities determined experimentally at pH values of 6, 7, and 8.5 are about two orders of magnitude higher than those calculated using the existing thermodynamic database indicating the influence of colloidal Pu(IV) species. Solid phase characterization using X-ray diffraction revealed primarily Pu(IV) in all precipitates formed at pH 6, 7, and 8.5. The solubility controlling Pu-bearing solids precipitated at ambient temperature consisted of amorphous Pu(OH)4(s) with several Pu–O distances between 2.3 and 2.7 Å that are characteristic for Pu(IV) colloids. High temperature (90 °C) increased solid phase crystallinity and produced Pu(IV) solids that contained Pu oxidation state impurities. X-ray absorption spectroscopic studies revealed diminished Pu–O and Pu–Pu distances that were slightly different from those in crystalline PuO2(s). A Pu–O bond of 1.86 Å was identified that is consistent with the plutonyl(V) distance of 1.81 Å in PuO2+(aq). Hematite, montmorillonite, and silica colloids were used for uptake experiments with 239Pu(V) and 237Np(V). The capacity of hematite to sorb Pu significantly exceeded that of montmorillonite and silica. A low desorption rate was indicative of highly stable Pu-hematite colloids, which may facilitate Pu transport to the accessible environment. Neptunium uptake on all mineral phases was far less than Pu(V) uptake suggesting that a potential Pu(V)–Pu(IV) reductive sorption process was involved. The temperature effect on Pu solubility and pseudocolloid formation is also discussed. |
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