Processes Affecting Nitro Reduction by Iron Metal: Mineralogical Consequences of Precipitation in Aqueous Carbonate Environments

摘要

In aqueous systems, zero-valent iron metal is readily oxidized by many substances to ferrous iron. These reactions may be considered as corrosion processes in which oxidation of Fe(0) to Fe(2+) is the anodic half-reaction. In anoxic pure aqueous media the only available cathodic half-reactions involve H(+) and H2O as electron acceptors (oxidants). Rapid corrosion requires more favorable cathodic reactions, of which the reduction of dissolved O2 is certainly the most important. However, other electron acceptors offer additional cathodic reactions that can contribute to iron corrosion. Possible oxidants of primary interest in groundwater remediation include anthropogenic contaminants such as chlorinated solvents, nitro aromatic compounds, and chromate. In addition, most contaminated waters contain substantial amounts of secondary solutes that are also oxidants relative to iron metal and, therefore, must be considered in any process-level interpretation of field performance. Among these solutes, carbonate is certainly one of the most important.