The short-term reduction of uranium by nanoscale zero-valent iron (nZVI): role of oxide shell, reduction mechanism and the formation of U(V)-carbonate phases
The short-term reduction of uranium by nanoscale zero-valent iron (nZVI): role of oxide shell, reduction mechanism and the formation of U(V)-carbonate phases
复制标题
DOI：
10.1039/c7en00024c
复制
发表时间：
2017-06
期刊：
影响因子：
--
通讯作者：
Sergey Tsarev;Richard N. Collins;E. Ilton;A. Fahy;T. Waite
中科院分区：
文献类型：
--
作者：
Sergey Tsarev;Richard N. Collins;E. Ilton;A. Fahy;T. Waite
纳米级零价铁（nZVI）是一种潜在的铀污染地下水修复剂，然而，对导致铀固定化的过程还没有一个完整的机理认识。在这项研究中，短期缺氧反应的U（VI）与新鲜的，（缺氧）老化和腐蚀的nZVI颗粒进行了研究，在水的条件下，有利于形成化学稳定的U（VI）-Ca-CO 3三元水溶液络合物。U（VI）和nZVI之间的反应的第一阶段被分配到表面U（VI）-碳酸盐络合物的形成的吸附过程。老化的nZVI去除U（VI）比新鲜或腐蚀的nZVI更快，据推测，U还原最初发生通过转移一个电子从Fe（II）在nZVI表面氧化层。还原为U（V）的证据是通过X射线光电子能谱和使用U LIII边缘X射线吸收光谱测定的U-O键距分别为2.05和2.27获得的，这与在U（V）/U（VI）碳酸盐矿物wyartite中观察到的U（V）位点相似。扫描透射电子显微镜也表明，U是作为一个纳米颗粒相反应后一天，而不是一个表面复合物。如先前研究所观察到的，进一步还原为U（IV）似乎是速率限制性的，并且与这种亚稳定的U-碳酸盐相转化为晶质铀矿（UO 2）相一致。
Nanoscale zero-valent iron (nZVI) is a potential remediation agent for uranium-contaminated groundwaters, however, a complete mechanistic understanding of the processes that lead to uranium immobilization has yet to be achieved. In this study, the short-term anoxic reaction of U(VI) with fresh, (anoxic) aged and corroded nZVI particles was investigated under aqueous conditions conducive to the formation of thermodynamically stable U(VI)–Ca–CO3 ternary aqueous complexes. The first stage of the reaction between U(VI) and nZVI was assigned to sorption processes with the formation of surface U(VI)-carbonate complexes. Aged nZVI removed U(VI) faster than either fresh or corroded nZVI and it is hypothesized that U reduction initially occurs through the transfer of one electron from Fe(II) in the nZVI surface oxide layer. Evidence for reduction to U(V) was obtained through X-ray photoelectron spectroscopy and by determination of U–O bond distances of ∼2.05 A and 2.27 A, using U LIII-edge X-ray absorption spectroscopy, which are similar to those observed for the U(V) site in the mixed U(V)/U(VI) carbonate mineral wyartite. Scanning transmission electron microscopy also demonstrated that U was present as a nanoparticulate phase after one day of reaction, rather than a surface complex. Further reduction to U(IV), as observed in previous studies, would appear to be rate-limiting and coincident with the transformation of this meta-stable U-carbonate phase to uraninite (UO2).