College of Environment, Zhejiang University of Technology , Hangzhou 310014, China.
School of Public Health, Oregon Health & Science University 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.
Environ Sci Technol. 2017 Nov 7;51(21):12653-12662. doi: 10.1021/acs.est.7b03604. Epub 2017 Oct 18.
In water treatment processes that involve contaminant reduction by zerovalent iron (ZVI), reduction of water to dihydrogen is a competing reaction that must be minimized to maximize the efficiency of electron utilization from the ZVI. Sulfidation has recently been shown to decrease H formation significantly, such that the overall electron efficiency of (or selectivity for) contaminant reduction can be greatly increased. To date, this work has focused on nanoscale ZVI (nZVI) and solution-phase sulfidation agents (e.g., bisulfide, dithionite or thiosulfate), both of which pose challenges for up-scaling the production of sulfidated ZVI for field applications. To overcome these challenges, we developed a process for sulfidation of microscale ZVI by ball milling ZVI with elemental sulfur. The resulting material (S-mZVI) exhibits reduced aggregation, relatively homogeneous distribution of Fe and S throughout the particle (not core-shell structure), enhanced reactivity with trichloroethylene (TCE), less H formation, and therefore greatly improved electron efficiency of TCE dechlorination (ε). Under ZVI-limited conditions (initial Fe/TCE = 1.6 mol/mol), S-mZVI gave surface-area normalized reduction rate constants (k') and ε that were ∼2- and 10-fold greater than the unsulfidated ball-milled control (mZVI). Under TCE-limited conditions (initial Fe/TCE = 2000 mol/mol), sulfidation increased k and ε ≈ 5- and 50-fold, respectively. The major products from TCE degradation by S-mZVI were acetylene, ethene, and ethane, which is consistent with dechlorination by β-elimination, as is typical of ZVI, iron oxides, and/or sulfides. However, electrochemical characterization shows that the sulfidated material has redox properties intermediate between ZVI and FeO, mostly likely significant coverage of the surface with FeS.
在涉及零价铁 (ZVI) 减少污染物的水处理过程中，水还原为氢气是一个竞争反应，必须最小化以最大限度地提高 ZVI 的电子利用效率。最近的研究表明，硫化可以显著降低 H 的形成，从而大大提高（或选择性提高）污染物还原的整体电子效率。迄今为止，这项工作主要集中在纳米级 ZVI (nZVI) 和溶液相硫化剂（例如，连二亚硫酸盐、连二硫酸盐或硫代硫酸盐）上，这两者都对大规模生产用于现场应用的硫化 ZVI 提出了挑战。为了克服这些挑战，我们开发了一种通过球磨 ZVI 与元素硫来硫化微尺度 ZVI 的方法。得到的材料（S-mZVI）表现出降低的聚集、Fe 和 S 在整个颗粒中的相对均匀分布（不是核壳结构）、与三氯乙烯 (TCE) 的增强反应性、较少的 H 形成，因此大大提高了 TCE 脱氯的电子效率（ε）。在 ZVI 受限条件下（初始 Fe/TCE = 1.6 mol/mol），S-mZVI 的比表面积归一化还原速率常数（k'）和 ε 分别比未硫化的球磨对照（mZVI）高约 2 倍和 10 倍。在 TCE 受限条件下（初始 Fe/TCE = 2000 mol/mol），硫化使 k 和 ε 分别增加约 5 倍和 50 倍。由 S-mZVI 降解 TCE 的主要产物是乙炔、乙烯和乙烷，这与β-消除脱氯一致，与 ZVI、铁氧化物和/或硫化物典型情况一致。然而，电化学特性表明，硫化材料具有介于 ZVI 和 FeO 之间的氧化还原性质，很可能是表面被大量的 FeS 覆盖。
