Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 152313, USA.
Environ Sci Technol. 2010 May 1;44(9):3455-61. doi: 10.1021/es902924h.
Nanoscale zerovalent iron (NZVI) that was aged in simulated groundwater was evaluated for alterations in composition and speciation over 6 months to understand the possible transformations NZVI could undergo in natural waters. NZVI was exposed to 10 mN of various common groundwater anions (Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), and HCO(3)(-)) or to dissolved oxygen (saturated, approximately 9 mg/L). Fresh and exposed NZVI samples, along with Fe-oxide model compounds, were then analyzed using synchrotron radiation X-ray absorption spectroscopy (XAS) to yield both relative oxidation state, using the X-ray absorption near edge structure (XANES), and quantitative speciation information regarding the types and proportions of mineral species present, from analysis of the extended X-ray absorption fine structure (EXAFS). Over 1 month of aging the dissolved anions inhibited the oxidation of the NZVI to varying degrees. Aging for 6 months, however, resulted in average oxidation states that were similar to each other regardless of the anion used, except for nitrate. Nitrate passivated the NZVI surface such that even after 6 months of aging the particles retained nearly the same mineral and Fe(0) content as fresh NZVI. Linear least-squares combination fitting (LCF) of the EXAFS spectra for 1 month-aged samples indicated that the oxidized particles remain predominantly a binary phase system containing Fe(0) and Fe(3)O(4), while the 6 month aged samples contained additional mineral phases such as vivianite (Fe(3)(PO(4))(2).8H(2)O) and iron sulfate species, possibly schwertmannite (Fe(3+)(16)O(16)(OH,SO(4))(12-13).10-12H(2)O). The presence of these additional mineral species was confirmed using synchrotron-based X-ray diffraction (XRD). NZVI exposed to water saturated with dissolved oxygen showed a rapid (<24 h) loss of Fe(0) and evolved both magnetite and maghemite (gamma-Fe(2)O(3)) within the oxide layer. These findings have implications toward the eventual fate, transport, and toxicity of NZVI used for groundwater remediation.
纳米零价铁（NZVI）在模拟地下水中老化，以研究其在 6 个月内组成和形态的变化，从而了解 NZVI 在天然水中可能发生的转化。NZVI 暴露于 10 mN 的各种常见地下水阴离子（Cl(-)、NO(3)(-)、SO(4)(2-)、HPO(4)(2-)和 HCO(3)(-)）或溶解氧（饱和，约 9 mg/L）中。然后，使用同步辐射 X 射线吸收光谱（XAS）分析新鲜和暴露的 NZVI 样品以及铁氧化物模型化合物，以获得相对氧化态，使用 X 射线吸收近边结构（XANES），以及关于存在的矿物种类的类型和比例的定量形态信息，来自扩展 X 射线吸收精细结构（EXAFS）的分析。在 1 个月的老化过程中，溶解的阴离子在不同程度上抑制了 NZVI 的氧化。然而，经过 6 个月的老化，除了硝酸盐外，无论使用哪种阴离子，平均氧化态都相似。硝酸盐使 NZVI 表面钝化，即使经过 6 个月的老化，颗粒仍保留与新鲜 NZVI 几乎相同的矿物和 Fe(0)含量。对 1 个月老化样品的 EXAFS 光谱进行线性最小二乘法组合拟合（LCF）表明，氧化颗粒仍然主要是含有 Fe(0)和 Fe(3)O(4)的二元相系统，而 6 个月老化的样品含有其他矿物相，如磷铁矿（Fe(3)(PO(4))(2).8H(2)O)和铁硫酸盐物种，可能是水铁矿（Fe(3+)(16)O(16)(OH,SO(4))(12-13).10-12H(2)O）。使用基于同步加速器的 X 射线衍射（XRD）证实了这些额外矿物相的存在。暴露于溶解氧饱和水中的 NZVI 表现出 Fe(0)的快速（<24 h）损失，并在氧化物层内演化出磁铁矿和磁赤铁矿（γ-Fe(2)O(3)）。这些发现对用于地下水修复的 NZVI 的最终命运、迁移和毒性具有重要意义。
