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Nitrate degradation by iron oxide: Mechanisms, kinetics, and the role of iron oxide coatings
Abstract
Nitrate reduction by zero-valent iron (Fe0, or ZVI) under different conditions was investigated through batch and column studies. The research focuses on the mechanisms of ZVI as a reactive media and particularly, on the iron corrosion products and their roles on the reactivity of ZVI. The loss of Fe0 reactivity due to the formation of various iron oxide coatings is a major concern in using ZVI processes for in-situ remediation. The study demonstrates that under anoxic conditions, Fe0 can rapidly reduce nitrate at acidic conditions. At near neutral pH, a magnetite (Fe3O4) coating will form on Fe0 and stop nitrate reduction reaction; however, the magnetite-coated Fe0 can be re-activated in the presence of Fe2+(aq.) and achieve a fast nitrate reduction. A relationship was established as 0.75 mole Fe2+ for 1 mole NO3−-N transformation, indicating that Fe2+ may have a role other than as a reducing agent. Surface-bound Fe(II), detected in large amounts in the test, might be the actual effective species. The kinetic study indicates that both nitrate and Fe2+ may follow a Langmuir adsorption on surface reactive sites. A two-layer semiconductor mechanism is proposed to explain the unique roles played by the magnetite coating and the surface-complex Fe(II) in re-activating Fe0 at near-neutral pH conditions. This research provides new insights on the complicated interactions among Fe0, its surface (hydr)oxides, surface-complexed Fe(II), aqueous Fe2+, and the targeted contaminants. The finding that magnetite-coated Fe0 can be re-activated by adding Fe2+ and the theory proposed here to explain the mechanism contribute to the development of new technologies for overcoming the passivation of ZVI barriers in field applications.
Subject Area
Environmental engineering|Civil engineering
Recommended Citation
Huang, Yongheng, "Nitrate degradation by iron oxide: Mechanisms, kinetics, and the role of iron oxide coatings" (2002). ETD collection for University of Nebraska-Lincoln. AAI3074082.
https://digitalcommons.unl.edu/dissertations/AAI3074082