College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China.
College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China; Department of Chemistry, University of Science and Technology of China, Hefei 230026, China.
Water Res. 2019 Aug 1;159:233-241. doi: 10.1016/j.watres.2019.04.061. Epub 2019 May 8.
Groundwater pH is one of the most important geochemical parameters in controlling the interfacial reactions of zero-valent iron (ZVI) with water and contaminants. Ball milled, microscale ZVI (mZVI) efficiently dechlorinated TCE at initial stage (<24 h) at pH 6-7 but got passivated at later stage due to pH rise caused by iron corrosion. At pH > 9, mZVI almost completely lost its reactivity. In contrast, ball milled, sulfidated microscale ZVI (S-mZVI) didn't experience any reactivity loss during the whole reaction stage across pH 6-10 and could efficiently dechlorinate TCE at pH 10 with a reaction rate of 0.03 h. Increasing pH from 6 to 9 also enhanced electron utilization efficiency from 0.95% to 5.3%, and from 3.2% to 22%, for mZVI and S-mZVI, respectively. SEM images of the reacted particles showed that the corrosion product layer on S-mZVI had a puffy/porous structure while that on mZVI was dense, which may account for the mitigated passivation of S-mZVI under alkaline pHs. Density functional theory calculations show that covered S atoms on the Fe(100) surface weaken the interactions of HO molecules with Fe surfaces, which renders the sulfidated Fe surface inefficient for HO dissociation and resistant to surface passivation. The observation from this study provides important implication that natural sulfidation of ZVI may largely contribute to the long-term (>10 years) efficiency of TCE decontamination by permeable reactive barriers with pore water pH above 9.
地下水 pH 值是控制零价铁 (ZVI) 与水和污染物界面反应的最重要地球化学参数之一。球磨后的微尺度 ZVI（mZVI）在 pH 值为 6-7 时能在初始阶段（<24 小时）有效地脱氯三氯乙烯（TCE），但由于铁腐蚀导致 pH 值升高，随后会发生钝化。在 pH 值>9 时，mZVI 几乎完全失去了反应活性。相比之下，球磨后的硫化微尺度 ZVI（S-mZVI）在整个 pH 值为 6-10 的反应阶段都没有经历任何反应活性损失，并且可以在 pH 值为 10 时以 0.03 h 的反应速率有效地脱氯 TCE。将 pH 值从 6 增加到 9 还分别将 mZVI 和 S-mZVI 的电子利用率从 0.95%提高到 5.3%，从 3.2%提高到 22%。反应后颗粒的 SEM 图像表明，S-mZVI 上的腐蚀产物层具有蓬松/多孔结构，而 mZVI 上的腐蚀产物层则致密，这可能是 S-mZVI 在碱性 pH 值下钝化程度减轻的原因。密度泛函理论计算表明，Fe(100)表面覆盖的 S 原子削弱了 HO 分子与 Fe 表面的相互作用，使硫化 Fe 表面不利于 HO 解离，并能抵抗表面钝化。本研究的结果表明，ZVI 的自然硫化可能在 pH 值大于 9 的可渗透反应性屏障中对 TCE 污染的长期（>10 年）去除效率有很大贡献。
