Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy.
Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy.
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使用塔菲尔分析和电化学阻抗谱了解硝酸盐与零价铁的反应。
DOI：
10.1021/es049259y
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发表时间：
2005
影响因子：
11.4
通讯作者：
Farrell,James
中科院分区：
文献类型：
--
作者：
Mishra,Dhananjay;Farrell,James
本研究探讨了硝酸盐（NO3-）与零价铁（ZVI）介质的条件下，相关的地下水处理，使用可渗透反应屏障（PRB）的反应机理。在间歇式反应器中测定了NO3-与自由腐蚀的铁丝以及与阴极或阳极极化的铁丝的反应速率。采用Tafel分析和电化学阻抗谱（EIS）研究了铁表面发生的反应。通过腐蚀铁还原NO3-导致接近化学计量的NO2-产生，其在没有添加Fe（II）的情况下没有可测量的反应。增加NO3-浓度导致增加的腐蚀电流。然而，EIS和塔菲尔分析表明，有很少的直接还原NO3-在ZVI表面，尽管存在水减少。这种行为可以归因于在铁表面上形成微孔氧化物，其阻止NO3-和NO2-的还原，但不阻止水的还原。这一发现与之前的观察结果一致，即NO3-阻碍了ZVI对有机化合物的还原。亚硝酸盐浓度大于4 mM导致铁的阳极钝化，但没有观察到钝化与NO3-浓度高达96 mM。这表明，钝化氧化物防止NO3-还原对阳离子迁移是可渗透的。由于与Fe（0）的反应可以被排除为NO3-和NO2-还原的机制，因此与涂覆在铁表面的含Fe（II）的氧化物的反应是最可能的反应机制。这表明，短期批量测试需要很少的营业额在铁表面上的反应位点可能高估长期的NO3-去除率，因为钝化的影响是不明显的，在批量测试进行高初始Fe（II）NO3-的比例。
This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevant to groundwater treatment using permeable reactive barriers (PRB). Reaction rates of NO3-with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3-by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3-concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3-at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3-and NO2-but did not block water reduction. This finding is consistent with previous observations that NO3-impedes reduction of organic compounds by ZVI. Nitrite concentra tions greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3-concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3-reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded as the mechanism for NO3-and NO2-reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3-removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3-ratios.