Department of Civil Engineering, McGill University, Montreal, Canada.
Department of Civil Engineering, McGill University, Montreal, Canada.
Water Res. 2015 Jul 1;78:144-53. doi: 10.1016/j.watres.2015.04.009. Epub 2015 Apr 14.
Direct injection of reactive nanoscale zerovalent iron particles (NZVI) is considered to be a promising approach for remediation of aquifers contaminated by chlorinated organic pollutants. In this study we show that the extent of sulfidation of NZVI enhances the rate of dechlorination of trichloroethylene (TCE) compared to that by unamended NZVI, and the enhancement depends on the Fe/S molar ratio. Experiments where TCE was reacted with NZVI sulfidated to different extents (Fe/S molar ratios 0.62-66) showed that the surface-area normalized first-order TCE degradation rate constant increased up to 40 folds compared to non-sulfidated NZVI. Fe/S ratios in the range of 12-25 provided the highest TCE dechlorination rates, and rates decreased at both higher and lower Fe/S. In contrast, sulfidated NZVI exposed to water in the absence of TCE showed significantly lower hydrogen evolution rate (2.75 μmol L(-1) h(-1)) compared to that by an unamended NZVI (6.92 μmol L(-1) h(-1)), indicating that sulfidation of NZVI suppressed corrosion reactions with water. Sulfide (HS(-)) ions reacted rapidly with NZVI and X-ray photoelectron spectroscopy analyses showed formation of a surface layer of FeS and FeS2. We propose that more electrons are preferentially conducted from sulfidated NZVI than from unamended NZVI to TCE, likely because of greater binding of TCE on the reactive sites of the iron sulfide outer layer. Resuspending sulfidated NZVI in sulfide-free or sulfide containing solutions altered the TCE degradation rate constants because of changes in the FeS layer thickness. Sulfidated NZVI maintained its high reactivity in the presence of multiple mono and divalent ions and with polyelectrolyte coatings. Thus, sulfide ions in groundwater can significantly alter NZVI reactivity.
直接注入反应性纳米零价铁颗粒（NZVI）被认为是修复受氯化有机污染物污染的含水层的一种很有前途的方法。在这项研究中，我们表明，NZVI 的硫化程度增强了其与未改性 NZVI 相比对三氯乙烯（TCE）的脱氯速率，并且这种增强取决于 Fe/S 摩尔比。在 TCE 与硫化程度不同的 NZVI（Fe/S 摩尔比为 0.62-66）反应的实验中，发现表面面积归一化的 TCE 降解一级速率常数比未硫化的 NZVI 增加了高达 40 倍。Fe/S 比在 12-25 范围内提供了最高的 TCE 脱氯速率，而在更高或更低的 Fe/S 下，速率会降低。相比之下，在没有 TCE 的情况下暴露于水中的硫化 NZVI 的析氢速率（2.75 μmol L(-1) h(-1)）明显低于未改性的 NZVI（6.92 μmol L(-1) h(-1)），这表明 NZVI 的硫化抑制了与水的腐蚀反应。硫离子（HS(-)）与 NZVI 迅速反应，X 射线光电子能谱分析表明形成了一层 FeS 和 FeS2 的表面层。我们提出，与未改性的 NZVI 相比，更多的电子优先从硫化的 NZVI 传导到 TCE，这可能是因为 TCE 在铁硫化外层的反应性位点上的结合更强。由于 FeS 层厚度的变化，将硫化的 NZVI 重新悬浮在无硫或含硫溶液中会改变 TCE 降解速率常数。在存在多种单价和二价离子和聚电解质涂层的情况下，硫化的 NZVI 保持其高反应性。因此，地下水中的硫离子可以显著改变 NZVI 的反应性。
