Zerovalent iron

Zerovalent iron (ZVI) is jargon^{[clarification needed]} that describes forms of iron metal that are proposed for use in groundwater remediation.^[1][2][3][4]

Model A

Model B

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Venn diagram showing the overlap between ZVIs and PRBs

ZVI operates by electron transfer from Fe⁰ toward some organochlorine compounds, a common class of pollutants. The remediation process is proposed to generate Fe²⁺ and Cl⁻ and halide-free organic products, all of which are relatively innocuous.^[5] Nanoscale ZVIs (nZVIs) are commonly used in remediation of chlorinated compounds and other pollutants.^[6]

Type of ZVI

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• Bulk Fe. Cast iron, consisting of scrap iron of construction grade, has been used as a reactive material for permeable reactive barriers (PRB) for groundwater remediation. Reactions are generally believed to occur on the Fe (oxide) surface; however, graphite inclusions can also serve as reaction sites.^[7]
• Nanoscale Fe. In addition to using macroscale iron in PRBs, nanoparticles (1-100 nm diameter) of zerovalent iron (nZVI) are effective.^[2]
• Zn. Zinc has shown much higher reactivity toward pentachlorophenol than iron. This indicates that zinc may be used as a replacement for ZVI in dechlorinating chlorinated phenols. Chlorinated phenols are sequentially dechlorinated and thus less-chlorinated phenols have been identified as a reduction product.^[8]

Type of contaminants treated

Treatment of many kinds of pollutants has been proposed, but few have been demonstrated in solving environmental challenges.

• Cadmium (Cd²⁺) is converted to immobile Cd metal.^[9]
• Chloramines are effectively reduced by ZVI.^[10]
• Nitrate reduction by iron powder is observed at pH ≤ 4.^[11] Ammonia is the end product. Using nanoscale iron, Nitrogen gas (N₂) is the product.^[12]
• Nitrated aromatics are reduced by bulk iron.^[7][13][14]
• Chlorinated pesticides such as DDT, DDD, and DDE. The rates of dechlorination are enhanced by the surfactant Triton X-114.^[15]

Further reading

• Tratnyek, P. G.; M. M. Scherer; T. J. Johnson; Matheson, L.J. (2003). Permeable reactive barriers of iron and other zerovalent metals. In: Tarr M. A. (ed.), Chemical Degradation Methods for Wastes and Pollutants; Environmental and Industrial Applications. Environmental Science and Pollution Control, Marcel Dekker, New York, pp 371–421. doi:10.1201/9780203912553.ch9