Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, USA.
Environ Sci Technol. 2010 Jan 1;44(1):170-6. doi: 10.1021/es9014597.
The heterogeneous reduction of U(VI) to U(IV) by ferrous iron is believed to be a key process influencing the fate and transport of U in the environment. The reactivity of both sorbed and structural Fe(II) has been studied for numerous substrates, including magnetite. Published results from U(VI)-magnetite experiments have been variable, ranging from no reduction to clear evidence for the formation of U(IV). In this contribution, we used XAS and high resolution (+/-cryogenic) XPS to study the interaction of U(VI) with nanoparticulate magnetite. The results indicated that U(VI) was partially reduced to U(V) with no evidence of U(IV). However, thermodynamic calculations indicated that U phases with average oxidation states below (V) should have been stable, indicating that the system was not in redox equilibrium. A reaction pathway that involves incorporation and stabilization of U(V) and U(VI) into secondary phases is invoked to explain the observations. The results suggest an important and previously unappreciated role of U(V) in the fate and transport of uranium in the environment.
亚铁离子将六价铀还原为四价铀被认为是影响铀在环境中归宿和迁移的关键过程。大量研究表明，无论是被吸附的还是结构内的二价铁都具有反应活性，其底物包括磁铁矿。发表的六价铀-磁铁矿实验结果变化很大，从没有还原到明显形成四价铀的证据都有。在本研究中，我们使用 X 射线吸收光谱（XAS）和高分辨率（+/低温）X 射线光电子能谱（XPS）来研究 U(VI)与纳米磁铁矿的相互作用。结果表明，U(VI)部分还原为 U(V)，但没有 U(IV)的证据。然而，热力学计算表明，平均氧化态低于 (V) 的 U 相应该是稳定的，这表明该系统没有处于氧化还原平衡状态。因此，我们提出了一个反应途径，涉及将 U(V)和 U(VI)掺入到次生相中并加以稳定，以此来解释观察到的现象。这些结果表明 U(V)在环境中铀的归宿和迁移中具有重要的、以前未被认识到的作用。
