Avasarala Sumant, Torres Chris, Ali Abdul-Mehdi S, Thomson Bruce M, Spilde Michael N, Peterson Eric J, Artyushkova Kateryna, Dobrica Elena, Lezama-Pacheco Juan S, Cerrato José M
Department of Civil, Construction, & Environmental Engineering, MSC01 1070, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Department of Chemical and Biological Engineering, MSC01 1120, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Chem Geol. 2019 Oct 5;524:345-355. doi: 10.1016/j.chemgeo.2019.07.007. Epub 2019 Jul 8.
We investigated the effect of bicarbonate and oxidizing agents on uranium (U) reactivity and subsequent dissolution of U(IV) and U(VI) mineral phases in the mineralized deposits from Jackpile mine, Laguna Pueblo, New Mexico, by integrating laboratory experiments with spectroscopy, microscopy and diffraction techniques. Uranium concentration in solid samples from mineralized deposit obtained for this study exceeded 7000 mg kg, as determined by X-ray fluorescence (XRF). Results from X-ray photoelectron spectroscopy (XPS) suggest the coexistence of U(VI) and U(IV) at a ratio of 19:1 at the near surface region of unreacted solid samples. Analyses made using X-ray diffraction (XRD) and electron microprobe detected the presence of coffinite (USiO) and uranium-phosphorous-potassium (U-P-K) mineral phases. Imaging, mapping and spectroscopy results from scanning transmission electron microscopy (STEM) indicate that the U-P-K phases were encapsulated by carbon. Despite exposing the solid samples to strong oxidizing conditions, the highest aqueous U concentrations were measured from samples reacted with 100% air saturated 10 mM NaHCO solution, at pH 7.5. Analyses using X-ray absorption spectroscopy (XAS) indicate that all the U(IV) in these solid samples were oxidized to U(VI) after reaction with dissolved oxygen and hypochlorite (OCl) in the presence of bicarbonate (HCO ). The reaction between these organic rich deposits, and 100% air saturated bicarbonate solution (containing dissolved oxygen), can result in considerable mobilization of U in water, which has relevance to the U concentrations observed at the Rio Paguate across the Jackpile mine. Results from this investigation provide insights on the reactivity of carbon encapsulated U-phases under mild and strong oxidizing conditions that have important implication in U recovery, remediation and risk exposure assessment of sites.
我们通过将实验室实验与光谱学、显微镜和衍射技术相结合，研究了碳酸氢盐和氧化剂对新墨西哥州拉古纳普韦布洛杰克皮勒矿矿化矿床中铀（U）反应性以及随后U(IV)和U(VI)矿相溶解的影响。通过X射线荧光（XRF）测定，本研究获得的矿化矿床固体样品中的铀浓度超过7000 mg/kg。X射线光电子能谱（XPS）结果表明，在未反应固体样品的近表面区域，U(VI)和U(IV)以19:1的比例共存。使用X射线衍射（XRD）和电子微探针进行的分析检测到了硅铀矿（USiO）和铀-磷-钾（U-P-K）矿相的存在。扫描透射电子显微镜（STEM）的成像、绘图和光谱结果表明，U-P-K相被碳包裹。尽管将固体样品暴露在强氧化条件下，但在pH值为7.5的100%空气饱和10 mM NaHCO₃溶液反应的样品中测得的最高水相铀浓度。使用X射线吸收光谱（XAS）进行的分析表明，在碳酸氢盐（HCO₃⁻）存在下，这些固体样品中的所有U(IV)在与溶解氧和次氯酸盐（OCl⁻）反应后都被氧化为U(VI)。这些富含有机物的沉积物与100%空气饱和碳酸氢盐溶液（含有溶解氧）之间的反应，会导致水中的铀大量迁移，这与杰克皮勒矿对岸的里奥帕瓜特河观测到的铀浓度有关。这项研究的结果为碳包裹的铀相在温和及强氧化条件下的反应性提供了见解，这对铀的回收、修复以及场地风险暴露评估具有重要意义。
