Mechanism of nitrate reduction by zero-valent iron: Equilibrium and kinetics studies
Mechanism of nitrate reduction by zero-valent iron: Equilibrium and kinetics studies
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DOI：
10.1016/j.cej.2011.12.074
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发表时间：
2012-02-15
影响因子：
15.1
通讯作者：
Niinae, Masakazu
中科院分区：
文献类型：
--
作者：
Suzuki, Tasuma;Moribe, Mai;Niinae, Masakazu
本研究的第一个目的是加深我们对零价铁（Fe-0）还原硝酸盐（NO3-）的机理的理解，特别是从电子供体到NO3-的电子转移过程（即，电子受体）在铁腐蚀产物的存在下。为了实现这一目标，进行了批实验，以研究几个变量的影响，包括水溶液的pH值，固液比，增强亚铁离子（Fe 2+）的浓度，和反应时间。实验结果表明，降低pH值或提高固液比均能提高NO3-的还原效率。此外，NO3-还原效率在近中性pH值的化学计量和动力学增强，通过增加在水相中的Fe 2+。这些实验数据一致地表明，NO3-直接从Fe-0接收电子（即，直接还原机制）通过铁腐蚀产物层（磁铁矿），而不是间接地经由H-2气体，其通过Fe-0和酸之间的反应产生（即，间接还原机理）。基于在近中性pH下NO3-还原效率通过增加Fe 2+而增强的观察，本研究的第二个目的是研究增加的Fe 2+的量和通过增加Fe 2+额外减少的NO3-的量之间的化学计量关系，最终目标是在接近中性的pH下有效地去除NO3-而不留下Fe 2 +在处理过的水中。实验结果表明，在接近中性的pH值下，只要Fe 2+在水相中增加，涂有铁腐蚀产物（磁铁矿）的Fe-0就能反复还原NO3-为铵离子;根据本研究推导出的化学计量关系，如果Fe 2+的加入量适当增加，则处理后水中NO3-和Fe 2+的浓度均降低至接近零。(C)2011爱思唯尔有限公司版权所有。
The first objective of this study was to deepen our understanding of the mechanism of nitrate (NO3-) reduction by zero-valent iron (Fe-0), especially the electron transfer process from electron donor(s) to NO3- (i.e., an electron acceptor) under the presence of iron corrosion products. To achieve this objective, batch experiments were performed to investigate the influence of several variables, including aqueous pH, the solid-liquid ratio, the concentration of augmented ferrous ion (Fe2+), and the reaction time. The experimental results showed that the NO3- reduction efficiency was enhanced by either decreasing the aqueous pH or increasing the solid-liquid ratio. Additionally, the NO3- reduction efficiency at near neutral pH was both stoichiometrically and kinetically enhanced by augmenting the Fe2+ in the aqueous phase. These experimental data consistently indicated that NO3- received electrons directly from Fe-0 (i.e., a direct reduction mechanism) through an iron corrosion product layer (magnetite), rather than indirectly via H-2 gas, which was produced by the reaction between Fe-0 and an acid (i.e., an indirect reduction mechanism).Based on the observation that the NO3- reduction efficiency at near neutral pH was enhanced by augmenting Fe2+, the second objective of this study was to investigate the stoichiometric relationship between the amount of augmented Fe2+ and the amount of NO3- additionally reduced by augmenting Fe2+ with the final goal of effectively removing NO3- at near neutral pH without leaving Fe2+ in the treated water. The experimental results demonstrated that Fe-0 coated with an iron corrosion product (magnetite) repeatedly reduced NO3- to ammonium ion at near neutral pH as long as the Fe2+ was augmented in the aqueous phase, and the concentrations of NO3- and Fe2+ in the treated water were both reduced to near zero if the proper amount of Fe2+ was augmented based on the stoichiometric relationship derived in this study. (C) 2011 Elsevier B.V. All rights reserved.