Iron-mediated reductive transformations : investigation of reaction mechanism
Iron-mediated reductive transformations : investigation of reaction mechanism
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DOI：
10.1021/es9505210
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发表时间：
1996-01
影响因子：
11.4
通讯作者：
E. J. Weber
中科院分区：
文献类型：
--
作者：
E. J. Weber
拟议使用零价铁修复受污染的地下水已促使大量实验室和现场研究评估该处理工艺的普遍适用性 (1-7)。目前正在推行两种类型的处理方案，涉及使用原位反应屏障或地上反应器。为了在修复过程中使用零价铁，有必要彻底了解还原转化的反应机制。本研究涉及的反应机制的主要问题是零价铁的还原是否是表面介导的过程。由此产生的对铁修复技术的正确设计的影响可能是重大的。如果零价铁的还原是一个表面介导的过程，那么可以假设，目标污染物向铁表面的传输将是许多处理方案中的限速步骤。这项工作的大部分推动力来自 Matheson 和 Tratnyek (8) 的工作，他们提出了缺氧 Fe0-H2O 系统中还原脱卤的几种途径。这些反应途径涉及铁金属表面零价铁的直接电子转移或与铁腐蚀产物溶解的 Fe2+ 或 H2 的反应。由于 Fe2+ 或 H2 的直接还原通常是非常缓慢的反应，因此通常需要通过催化剂（可能是铁表面）活化这些物质才能轻松进行还原。剩下的一个关键问题是还原是否发生在铁表面，涉及零价铁的直接电子转移或铁腐蚀产物的络合，或者通过释放水溶性还原剂在水相中发生。
The proposed use of zero-valent iron for remediating contaminated groundwater has prompted numerous laboratory and field studies to assess the general applicability of this treatment process (1-7). Two types of treatment schemes are currently being pursued that involve the use of either in situ reactive barriers or above-ground reactors. In order to use zero-valent iron in remediation processes, a thorough understanding of the reaction mechanisms for the reductive transformations is necessary. The primary question concerning the reaction mechanism that this study addresses is whether reduction by zero-valent iron is a surface-mediated process. The resulting implications concerning the proper engineering of iron remediation technologies can be significant. If reduction by zero-valent iron is a surface-mediated process, it can probably be assumed that transport of the contaminant of interest to the iron surface will be the rate-limiting step in many treatment scenarios.Much of the impetus for this work has come from the work of Matheson and Tratnyek (8), who have proposed several pathways for reductive dehalogenation in anoxic Fe0-H2O systems. These reaction pathways involve either direct electron transfer from zero-valent iron at the surface of the iron metal or reaction with dissolved Fe2+ or H2, which are products of iron corrosion. Because direct reduction by either Fe2+ or H2 is generally a very slow reaction, activation of these species by catalysts (perhaps the iron surface) is generally required for facile reductions to occur. A key question that remains is whether reduction occurs at the iron surface, involving either direct electron transfer by zero-valent iron or complexation of a product of iron corrosion, or in the aqueous phase by release of a water-soluble reductant.