Competitive Reduction of Nitrate Nitrite

Treating mixed contaminants with zerovalent iron (Fe0) for environmental remediation requires a thorough understanding of the competition among electron acceptors. The authors conducted aqueous batch tests to determine competitive reduction of nitrate, nitrite, and nitrobenzene by Fe0 under varying conditions. Results indicate that nitrate reduction by Fe0 was accompanied by substantial Fe0 oxidation by water. Nitrite and nitrobenzene were concomitantly reduced by Fe0, forming a lepidocrocite (γ-FeOOH) coating on the Fe0 grains. When present together, nitrite and nitrobenzene reduction proceeded without apparent interference from nitrate. Nitrate reduction, however, did not occur in the presence of nitrite or nitrobenzene. Adding aqueous Fe(II) facilitated nitrate reduction by Fe0, but not until the lepidocrocite coating on the Fe0 grains was transformed to magnetite (Fe3O4), a process that is significantly accelerated by surface-bound Fe(II). This study illustrates the relative reactivity of Fe0 towards specific compounds and the related formation and compositional evolution of the iron oxide coating in Fe0-water systems.