Department of Civil, Environmental and Construction Engineering, Texas Tech University, Texas, USA.
Environ Sci Process Impacts. 2020 Mar 1;22(3):759-770. doi: 10.1039/c9em00593e. Epub 2020 Feb 19.
Recent studies on the use of controlled sulfur amendment to improve the reactivity and selectivity of zerovalent iron (ZVI) in reductive dechlorination reactions have generated renewed interest in ZVI-based remediation materials. However, existing studies have focused on the reactions between trichloroethene (TCE) and lab-synthesized ZVI, and the applicability of sulfidation to ZVIs with different material characteristics for reductive dechlorination of chloroethenes such as tetrachloroethene (PCE) and cis-dichloroethene (cis-DCE) has not been systematically examined. In this study, four ZVI materials from commercial sources having different sizes and morphological and compositional characteristics were subjected to various sulfidation treatments and were assessed in batch reactions with PCE, TCE, or cis-DCE. Sulfur amendment induces modest increases in PCE degradation rates and steers reactions towards a cleaner pathway that has minimum accumulation of partially dechlorinated intermediates. In the case of cis-DCE, bifurcating outcomes were observed that include enhancement effects for two high-purity ZVIs and inhibitory effects for two ZVIs possessing low levels of metal impurities. Further investigations based on controlled metal dosing reveal that the trace metals commonly present in cast iron or recycled metal scraps, such as Cu and Ni, can act as adventitious catalysts for cis-DCE reduction. Sulfidation results in poisoning of these catalytic ingredients and accounts for the adverse effect observed with a subset of ZVIs. Collectively, this study confirms enhanced degradation of highly chlorinated ethenes (PCE and TCE) by sulfidation of ZVIs from diverse origins; nonetheless, the effects of sulfidation can be highly variable for the less chlorinated ethenes due to differences in the material characteristics of ZVI and the predominant dechlorination pathways.
最近的研究表明，通过控制硫磺添加来提高零价铁（ZVI）在还原脱氯反应中的反应性和选择性，重新引起了人们对基于 ZVI 的修复材料的兴趣。然而，现有的研究主要集中在三氯乙烯（TCE）与实验室合成的 ZVI 之间的反应，以及硫磺添加对具有不同材料特性的 ZVI 用于还原脱氯三氯乙烯（PCE）和顺式-二氯乙烯（cis-DCE）等氯代烯烃的适用性尚未得到系统的研究。在这项研究中，来自商业来源的四种具有不同大小、形态和组成特性的 ZVI 材料经过不同的硫化处理，并在与 PCE、TCE 或 cis-DCE 的批处理反应中进行了评估。硫磺添加可适度提高 PCE 的降解速率，并使反应朝着更清洁的途径进行，最大限度地减少部分脱氯中间产物的积累。对于 cis-DCE，观察到分叉的结果，包括两种高纯度 ZVI 的增强效应和两种金属杂质含量低的 ZVI 的抑制效应。基于受控金属剂量的进一步研究表明，通常存在于铸铁或回收金属废料中的痕量金属，如 Cu 和 Ni，可以作为 cis-DCE 还原的偶然催化剂。硫化会导致这些催化成分中毒，这解释了部分 ZVI 观察到的不良影响。总的来说，这项研究证实了通过来自不同来源的 ZVI 的硫化可以增强高度氯化的乙稀（PCE 和 TCE）的降解；然而，由于 ZVI 的材料特性和主要脱氯途径的差异，硫磺添加对较少氯化的乙稀的影响可能非常大。
