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Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface

机译：磁铁矿（111）表面的（V）和铀（VI）反应

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Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron-based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO 2 + species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.
机译：ept和铀在核燃料循环的许多方面都是重要的放射性核素，经常存在于需要长期管理的放射性废物中。了解这些act系元素的环境行为和迁移性，对于支持含这些放射性核素的废物的补救策略和安全评估至关重要。通过将最新的X射线技术（基于同步加速器的掠入射XAS和XPS）与湿化学技术（ICP-MS，液体闪烁计数和UV-Vis光谱）相结合，我们确定与铀相反（ VI），n与磁铁矿的相互作用不受碳酸氢盐的影响。铀与磁铁矿表面的相互作用导致XAS和XPS信号由U（VI）的表面配合物控制，而磁铁矿表面上的n则由Np（IV）物质控制。与磁铁矿相互作用之前和之后，水溶液中Np（V）物种的UV-Vis光谱显示，由于碳酸盐的存在，形成了不同的形态。有趣的是，在与磁铁矿平衡后存在碳酸氢盐的情况下，使用UV-Vis光谱法检测到未知的NpO 2 +水溶液，我们假设它是Np（V）与碳酸盐和（可能）铁物种的三元络合物。无论如何，在水相（Np（V））和磁铁矿（111）表面（Np（IV））上的Np形态表明，在有或没有碳酸氢盐的情况下，Np（V）与磁铁矿的相互作用都是通过表面介导的还原进行的机制。总体而言，提出的结果突出了铀和n与磁铁矿相互作用的区别，并重申了水相中存在的碳酸氢盐的潜在重要性。

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