Zerovalent iron

Venn diagram showing the overlap between ZVIs and PRBs

Zerovalent iron (ZVI) describes forms of iron metal that are proposed for use in the environmental remediation of contaminated soil and groundwater. ^{[1] [2] [3] [4]}

Model A

Model B

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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]
• Perchloroethylene (PCE) and trichloroethylene (TCE), common industrial solvents, and their degradation products dichloroethylene (DCE) and vinyl chloride, can be reduced to ethylene and ethane using ZVI as a reagent. This can be applied to the remediation of soils contaminated with these chlorinated organic solvents, commonly found at dry cleaning facilities. ^[16]

Notes

1. Fu, Fenglian; Dionysiou, Dionysios D.; Liu, Hong (February 2014). "The use of zero-valent iron for groundwater remediation and wastewater treatment: A review". Journal of Hazardous Materials. 267: 194–205. Bibcode:2014JHzM..267..194F. doi:10.1016/j.jhazmat.2013.12.062. PMID   24457611.
2. Li, Xiao-qin; Elliott, Daniel W.; Zhang, Wei-xian (December 2006). "Zero-Valent Iron Nanoparticles for Abatement of Environmental Pollutants: Materials and Engineering Aspects". Critical Reviews in Solid State and Materials Sciences. 31 (4): 111–122. Bibcode:2006CRSSM..31..111L. doi:10.1080/10408430601057611.
3. Stefaniuk, Magdalena; Oleszczuk, Patryk; Ok, Yong Sik (March 2016). "Review on nano zerovalent iron (nZVI): From synthesis to environmental applications". Chemical Engineering Journal. 287: 618–632. Bibcode:2016ChEnJ.287..618S. doi:10.1016/j.cej.2015.11.046.
4. Gillham, Robert W.; Vogan, John; Gui, Lai; Duchene, Michael; Son, Jennifer (2010). "Iron Barrier Walls for Chlorinated Solvent Remediation". In Situ Remediation of Chlorinated Solvent Plumes. SERDP/ESTCP Environmental Remediation Technology. pp. 537–571. doi:10.1007/978-1-4419-1401-9_16. ISBN   978-1-4419-1400-2.
5. Tratnyek, Paul, and Rick Johnson. "Remediation with Iron Metal."^{[ verification needed ]} Center for Groundwater Research. Oregon Health and Science University, 04 Feb. 2005.
6. Karn, Barbara; Kuiken, Todd; Otto, Martha (December 2009). "Nanotechnology and in Situ Remediation: A Review of the Benefits and Potential Risks". Environmental Health Perspectives. 117 (12): 1823-1831. Bibcode:2009EnvHP.117.1813K. doi:10.1289/ehp.0900793. PMC   2799454 . PMID   20049198.
7. Jafarpour, Benham; Imhoff, Paul T.; Chiu, Pei C. (January 2005). "Quantification and modelling of 2,4-dinitrotoluene reduction with high-purity and cast iron". Journal of Contaminant Hydrology. 76 (1–2): 87–107. Bibcode:2005JCHyd..76...87J. doi:10.1016/j.jconhyd.2004.08.001. PMID   15588574.
8. Kim, Y-H.; Carraway, E. R. (December 2003). "Dechlorination of chlorinated phenols by zero valent zinc". Environmental Technology. 24 (12): 1455–1463. Bibcode:2003EnvTe..24.1455K. doi:10.1080/09593330309385690. PMID   14977141.
9. Boparai, Hardiljeet K.; Joseph, Meera; O’Carroll, Denis M. (February 2011). "Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles". Journal of Hazardous Materials. 186 (1): 458–465. Bibcode:2011JHzM..186..458B. doi:10.1016/j.jhazmat.2010.11.029. PMID   21130566.
10. Bedner, Mary; MacCrehan, William A; Helz, George R (May 2004). "Making chlorine greener: investigation of alternatives to sulfite for dechlorination". Water Research. 38 (10): 2505–2514. Bibcode:2004WatRe..38.2505B. doi:10.1016/j.watres.2004.03.010. PMID   15159154.
11. Huang, Chin-Pao; Wang, Hung-Wen; Chiu, Pei-Chun (August 1998). "Nitrate reduction by metallic iron". Water Research. 32 (8): 2257–2264. Bibcode:1998WatRe..32.2257H. doi:10.1016/S0043-1354(97)00464-8.
12. Choe, Seunghee; Chang, Yoon-Young; Hwang, Kyung-Yub; Khim, Jeehyeong (October 2000). "Kinetics of reductive denitrification by nanoscale zero-valent iron". Chemosphere. 41 (8): 1307–1311. Bibcode:2000Chmsp..41.1307C. doi:10.1016/S0045-6535(99)00506-8. PMID   10901263.
13. "2,4-DIAMINOTOLUENE". Organic Syntheses. 11: 32. 1931. doi:10.15227/orgsyn.011.0032.
14. "o-Aminobenzaldehyde, Redox-Neutral Aminal Formation and Synthesis of Deoxyvasicinone". Organic Syntheses. 89: 274. 2012. doi:10.15227/orgsyn.089.0274.
15. Sayles, Gregory D.; You, Guanrong; Wang, Maoxiu; Kupferle, Margaret J. (December 1997). "DDT, DDD, and DDE Dechlorination by Zero-Valent Iron". Environmental Science & Technology. 31 (12): 3448–3454. Bibcode:1997EnST...31.3448S. doi:10.1021/es9701669.
16. Navarra, Wanda; Sacco, Olga; Rescigno, Raffaella; Daniel, Christophe; Vaiano, Vincenzo; Pisano, Domenico; Brancato, Bruno; Casertano, Francesco; Raiola, Mario; Venditto, Vincenzo (July 2023). "Remediation of perchloroethylene contaminated groundwater using Fe0/ZnS embedded in a highly porous polymer: Experimental results on pilot-scale photoreactor and kinetic modeling analysis for industrial scale-up". Catalysis Communications. 180 106699. doi:10.1016/j.catcom.2023.106699.

Further reading

• Tratnyek, Paul (2003). "Permeable Reactive Barriers of Iron and Other Zero-Valent Metals". In Tarr, Matthew A. (ed.). Chemical Degradation Methods for Wastes and Pollutants. Environmental Science & Pollution. Vol. 26. pp. 371–421. doi:10.1201/9780203912553. ISBN   978-0-8247-4307-9.