Pacific Northwest National Laboratory , 902 Battelle Boulevard, Richland, Washington 99354, United States.
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
Environ Sci Technol. 2017 Aug 1;51(15):8635-8642. doi: 10.1021/acs.est.7b02278. Epub 2017 Jul 20.
Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (FeO). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, CrO, and Cr(OH) phases. Spinel (modeled as FeO), goethite (α-FeOOH), and feroxyhyte (δ-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (FeO) and chromite (FeCrO).
锝（Tc）仍然是一个优先修复的关注点，因为存在持续的挑战，包括由于被固定的 Tc 的快速再氧化而导致的迁移，以及竞争共存的混合污染物，例如 Cr(VI)，它们抑制 Tc(VII)的还原和掺入到稳定的矿物相中。在这里，Fe(OH)(s) 被研究为克服这些挑战的综合解决方案，它既是还原剂（Fe(II)），也是固定剂，用于形成掺入 Tc 的磁铁矿（FeO）。痕量金属分析表明，Tc(VII)和 Cr(VI)从溶液中同时去除；然而，Cr(VI)的完全去除和还原比混合 Tc(VII)的去除/还原更早实现。通过 XANES 对最终磁铁矿固相的体相氧化态分析表明，大部分 Tc 是 Tc(IV)，这与 XPS 测量结果相符。此外，EXAFS 结果表明，Tc(IV)成功地但部分地掺入到磁铁矿八面体位置中。Cr XPS 分析表明 Cr 被还原为 Cr(III)，并形成了 Cr 掺入的尖晶石、CrO 和 Cr(OH)相。在所有反应后的最终固相样品中，XRD 分析检测到尖晶石（模拟为 FeO）、针铁矿（α-FeOOH）和纤铁矿（δ-FeOOH）。Tc(IV)的掺入对尖晶石晶格结构几乎没有影响。在 Cr(III)存在下的 Fe(OH)(s)反应导致形成了一种尖晶石相，它是磁铁矿（FeO）和铬铁矿（FeCrO）之间的固溶体。
