Effects of dissolved oxygen on formation of corrosion products and concomitant oxygen and nitrate reduction in zero-valent iron systems with or without aqueous Fe2+.

Abstract Batch tests were conducted in zero-valent iron (ZVI or Fe 0 ) systems to investigate oxygen consumption and the effect of dissolved oxygen (DO) on formation of iron corrosion products, nitrate reduction, the reactivity of Fe 0 , the role Fe 2+ (aq) played, and the fate of Fe 2+ . The study indicates that without augmenting Fe 2+ (aq), neither nitrate nor DO could be removed efficiently by Fe 0 . In the presence of Fe 2+ (aq), nitrate and DO could be reduced concomitantly with limited interference with each other. Unlike nitrate reduction, DO removal by Fe 0 did not consume Fe 2+ (aq). A two-layer structure, with an inner layer of magnetite and an outer layer of lepidocrocite, may be formed in the presence of DO. When DO depleted, the outer lepidocrocite layer was transformed to magnetite. The inner layer of magnetite, even in a substantial thickness, might not impede the Fe 0 reactivity as much as the thin interfacial layer between the oxide coating and liquid. Surface-bound Fe 2+ may greatly enhance the electron transfer from the Fe 0 core to the solid–liquid interface, and thus improve the performance of the Fe 0 process.