Abstract Determining U oxidation state in contaminated (sub)surface soils and sediments is essential to depict the geochemical processes affecting U in natural media. This information is also mandatory to infer the mechanisms governing the mobilization and transfer of this toxic radionuclide to the environment. Here, in attempt to detect U(IV), U(V) and U(VI) in wetland soil samples contaminated by past mining activities, we have performed high-resolution fluorescence detected X-Ray absorption near edge structure (HERFD-XANES) measurements at the U M4-edge. Linear combination fitting (LCF) analysis of the spectra have been conducted using reference samples representative of the wetland geochemistry, in which U occurs as U-phosphate minerals and mononuclear U complexes. Our experimental constraints for HERFD measurements at low energy (3.7 keV) implied to limit the thickness of the Kapton® foil used to protect the samples, which lead to slow oxidation by air during the measurements. In this context, U(IV) appeared to partly oxidize into U(VI) and/or U(V) within a few tens of hours. Nano-crystalline reference samples showed contrasted oxidation pathways for U(IV), transforming into U(V)/U(VI)-uranate in biogenic nano-uraninite, and into U(VI)-uranyl in nano-U(IV)-rhabdophane. In the wetland soils samples, uranium was mainly present as U(IV) and U(VI) with detection of minor U(V) (

中文翻译：

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U M 边缘的 HERFD-XANES 光谱应用于重污染湿地土壤中 U 氧化态的分析

摘要 确定受污染（亚）表层土壤和沉积物中 U 的氧化态对于描述影响自然介质中 U 的地球化学过程至关重要。这些信息对于推断控制这种有毒放射性核素向环境迁移和转移的机制也是强制性的。在这里，为了检测受过去采矿活动污染的湿地土壤样品中的 U(IV)、U(V) 和 U(VI)，我们进行了高分辨率荧光检测 X 射线吸收近边缘结构 (HERFD-XANES)在 U M4 边缘测量。光谱的线性组合拟合 (LCF) 分析是使用代表湿地地球化学的参考样品进行的，其中 U 以 U-磷酸盐矿物和单核 U 复合物的形式出现。我们对低能量 HERFD 测量的实验限制 (3. 7 keV) 意味着限制用于保护样品的 Kapton® 箔的厚度，这会导致在测量过程中被空气缓慢氧化。在这种情况下，U(IV) 似乎在几十小时内部分氧化成 U(VI) 和/或 U(V)。纳米晶参考样品显示出对比的 U(IV) 氧化途径，在生物纳米铀矿中转化为 U(V)/U(VI)-铀酸盐，在纳米 U(IV)-中转化为 U(VI)-铀酰弹状体。在湿地土壤样品中，铀主要以 U(IV) 和 U(VI) 的形式存在，并检测到少量的 U(V) ( 纳米晶参考样品显示出对比的 U(IV) 氧化途径，在生物纳米铀矿中转化为 U(V)/U(VI)-铀酸盐，在纳米 U(IV)-中转化为 U(VI)-铀酰弹状体。在湿地土壤样品中，铀主要以 U(IV) 和 U(VI) 存在，并检测到少量 U(V) ( 纳米晶体参考样品显示出对比的 U(IV) 氧化途径，在生物纳米铀矿中转化为 U(V)/U(VI)-铀酸盐，在纳米 U(IV)-中转化为 U(VI)-铀酰弹状体。在湿地土壤样品中，铀主要以 U(IV) 和 U(VI) 存在，并检测到少量 U(V) (