Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
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DOI：
10.3390/geosciences9020081
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发表时间：
2019-02
期刊：
影响因子：
2.7
通讯作者：
P. Bots;A. Veelen;J. Mosselmans;C. Muryn;R. Wogelius;K. Morris
中科院分区：
文献类型：
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作者：
P. Bots;A. Veelen;J. Mosselmans;C. Muryn;R. Wogelius;K. Morris
在核燃料循环的许多方面，镎和铀是重要的放射性核素，并且经常存在于需要长期管理的放射性废物中。了解这些锕系元素的环境行为和流动性，对于支持含有这些放射性核素的废物的补救战略和安全评估至关重要。通过将最先进的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（VI）相反，镎（V）与磁铁矿的相互作用不会受到碳酸氢盐的影响。铀与磁铁矿表面的相互作用导致XAS和XPS信号主要由U（VI）的表面络合物，而磁铁矿表面上的镎主要由Np（IV）物种。紫外-可见光谱的水溶液中的Np（V）物种之前和之后的相互作用与磁铁矿显示不同的形态，由于碳酸盐的存在。有趣的是，在碳酸氢盐的存在下，与磁铁矿平衡后，一个未知的水性NpO 2+物种检测使用紫外-可见光谱，我们假设这是一个三元复合物的Np（V）与碳酸盐和（可能）的铁物种。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，在有和没有碳酸氢盐的情况下，Np（V）与磁铁矿的相互作用通过表面介导的还原机制进行。总体而言，所呈现的结果突出了铀和镎与磁铁矿相互作用之间的差异，并重申了水相中存在的碳酸氢盐的潜在重要性。
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 NpO2+ 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.