Effect of bicarbonate and oxidizing conditions on U(IV) and U(VI) reactivity in mineralized deposits of New Mexico
Effect of bicarbonate and oxidizing conditions on U(IV) and U(VI) reactivity in mineralized deposits of New Mexico
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DOI：
10.1016/j.chemgeo.2019.07.007
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发表时间：
2019-10-05
期刊：
影响因子：
3.9
通讯作者：
Cerrato, Jose M.
中科院分区：
文献类型：
--
作者：
Avasarala, Sumant;Torres, Chris;Cerrato, Jose M.
采用光谱、显微镜和衍射技术，结合实验室实验，研究了碳酸氢盐和氧化剂对新墨西哥州普韦布洛拉古纳Jackpile矿铀（U）反应性及随后U（IV）和U（VI）矿物相溶解的影响。通过X射线荧光法（XRF）测定，本研究所获得的矿化存款固体样品中的铀浓度超过7000 mg kg（-1）。X射线光电子能谱（XPS）的结果表明，U（VI）和U（IV）以19：1的比例共存于未反应的固体样品的近表面区域。使用X射线衍射（XRD）和电子探针进行的分析检测到存在的coffinite（USiO 4）和铀-磷-钾（U-P-K）矿物相。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于强氧化条件下，但从与100%空气饱和的10 mM NaHCO 3溶液在pH 7.5下反应的样品中测量到最高的含水U浓度。X射线吸收光谱（XAS）分析表明，在碳酸氢盐（HCO 3-）存在下，固体样品中的U（IV）与溶解氧和次氯酸盐（OCl-）反应后，全部被氧化成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（含溶解氧）之间的反应可能导致水中U的大量流动，这与在Jackpile矿的Rio Paguate观察到的U浓度有关。从这次调查的结果提供了洞察碳封装的U-相在温和和强氧化条件下的反应性，具有重要意义的U回收，修复和风险暴露评估的网站。
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(-1), as determined by X-ray fluorescence (XRF). Results from X-ray photoelectron spectroscopy (XPS) suggest the co-existence 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 (USiO4) 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 NaHCO3 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 (HCO3-). 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.