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首页> 外文期刊>RSC Advances >Uranium speciation in weathered granitic waste rock piles: an XAFS investigation
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Uranium speciation in weathered granitic waste rock piles: an XAFS investigation

机译：风化花岗岩废石堆中的铀形态：XAFS调查

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Investigation of uranium migration in the waste piles of granite rock in the Limousin region of France is vital for developing strategies which address related environmental issues. Despite the fact that the concentration of uranium is far below the lower end of the cut off level in these piles, the large volume of rocks – which measure in the hundreds of metric tons – and their conditions of repository make this type of waste a source of concern for the international community. In this work, X-ray absorption spectroscopy techniques (XAFS) were employed in order to identify the speciation of uranium in the different categories of samples collected from various regions of the rock piles which had undergone 50 years of weathering. The samples, such as weathered granite, arena and technosoils, were studied in order to probe the transformation of the U bearing complex. XANES indicates U( VI ) valence with uranyl species in all samples. Using a linear combination analysis and shell fitting approach, distinct speciation of uranium was observed in the different categories of samples. In the weathered rock and arena samples with relics of magmatic U minerals, uranyl phosphates comparable to autunite are shown to be dominantly linked with monodentate PO _(4) ~(3?) . However, the samples collected from technosoils are found to have a mixture of U-phosphate and U-clay minerals (phyllosilicates and silicates). Irrespective of the collection location, all the samples were found to contain U( VI )-oxo species The equatorial O ligands occur as two shells with an average separation of 0.14–0.21 ?. Moreover, all the samples have an Al/Si/P shell around 3.1 ?. A detailed EXAFS curve fit analysis shows that disorder afflicts the entire range of samples which can be attributed to either inhomogeneous binding sites on the disordered clay minerals or to the presence of a mixture of uranium-bearing minerals. XAFS investigations highlight the uranyl overriding forms of U (as U sorbed on clay minerals and secondary uranyl phosphates or silicates) contribute to the retention of U, even in oxidizing conditions known to enhance the mobility of U.
机译：对法国利穆赞地区花岗岩岩废料堆中的铀迁移进行调查对于制定解决相关环境问题的战略至关重要。尽管事实上铀的浓度远低于这些堆中的截止水平的下限，但大量的岩石（数百公吨）及其储藏条件使这类废物成为了一种来源。国际社会的关注。在这项工作中，使用X射线吸收光谱技术（XAFS）来确定从经历了50年风化的岩堆各个区域收集的不同类别样品中的铀形态。研究了诸如风化花岗岩，竞技场和技术土等样品，以探测含U合物的转变。 XANES表示所有样品中具有铀酰种类的U（VI）价。使用线性组合分析和壳拟合方法，在不同类别的样品中观察到了不同的铀形态。在风化的岩石和竞技场样品中含有岩浆U矿物的遗迹，可证明与金铁矿相当的磷酸铀酰磷酸酯主要与单齿PO _（4）〜（3？）相关。但是，发现从技术土壤中收集的样品含有U-磷酸盐和U-粘土矿物（页硅酸盐和硅酸盐）的混合物。不论收集地点如何，所有样品均含有U（VI）-氧代物种。赤道O配体以两个壳的形式存在，平均间隔为0.14-0.21？。而且，所有样品都具有约3.1Ω的Al / Si / P壳。详细的EXAFS曲线拟合分析表明，无序现象影响了整个样本范围，这可能归因于无序粘土矿物上不均匀的结合位点，或者归因于含铀矿物混合物的存在。 XAFS研究表明，即使在已知增强U迁移性的氧化条件下，U的铀基重载形式也是如此（因为U吸附在粘土矿物和仲铀酰磷酸或硅酸盐上）。

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