H<sub>2</sub> Gas Charging of Zero-Valent Iron and TCE Degradation
- 1 Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Canada
- 2 Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Canada.
Abstract
Granular zero-valent iron (ZVI) has been widely used to construct permeable reactive barriers (PRB) for the in situ remediation of groundwater contaminated with halogenated hydrocarbons. In the anaerobic condition of most groundwater flow systems, iron undergoes corrosion by water and results in hydrogen gas generation. Several studies have shown that some of the hydrogen gas generated at the iron/water interface can diffuse into the iron lattice. Hydrogen gas also can be an electron donor for dechlorination of chlorinated compounds. In this study, the possibility of hydrogen gas bound in the lattice of ZVI playing a role in dehalogenation and improving the degradation efficiency of ZVI was evaluated. Two different granular irons were tested: one obtained from Quebec Metal Powders Ltd (QMP) and the other from Connelly-GPM. Ltd. For each type of iron, two samples were mixed with water and sealed in testing cells. Since the rate of hydrogen entry varies directly with the square root of the hydrogen pressure, one sample was maintained for several weeks under near-vacuum conditions to minimize the amount of hydrogen entering the iron lattice. The other sample was maintained for the same period at a hydrogen pressure of over 400 kPa to maximize the amount of hydrogen entering the iron lattice. The degradation abilities of the reacted ironsand the original iron materials were tested by running several sets of batch tests. The results of this study show little to no improvement of inorganic TCE degradation reactions due to the presence of lattice-stored hydrogen in iron material. This is probably due to the high energiesrequired to release hydrogen trapped in the iron lattice. However, there are certain chemical compounds that can promote hydrogen release from the iron lattice, and there may be bacteria that can utilize lattice-bound hydrogen to carry out dechlorination reactions.
- W. A. Arnold and A. L. Roberts, “Pathways and Kinetics of Chlorinated Ethylene and Chlorinated Acetylene Reaction with Fe(0) Particles,” Environmental Science & Technology, Vol. 34, No. 9, 2000, pp. 1794-1805. doi:10.1021/es990884q
- W. S. Orth and R. W. Gillham, “Dechlorination of Trichloroethene in Aqueous Solution Using Fe0,” Environmental Science & Technology, Vol. 30, No. 1, 1996, pp. 66-71. doi:10.1021/es950053u
- L. J. Matheson and P. G. Tratnyek, “Reductive Dehalogenation of Chlorinatedmethanes Byiron Metal,” Environmental Science & Technology, Vol. 28, No. 12, 1994, pp. 2045-2053. doi:10.1021/es00061a012
- D. R. Burris, T. J. Campell and V. S. Manoranjan, “Sorption of Trichloroethylene and Tetrachloroethylene in a Batch Reactive Metallic Iron-Water System,” Environmental Science & Technology, Vol. 29, No. 11, 1995, pp. 2850-2855. doi:10.1021/es00011a022
- E. J. Reardon, “Zerovalent Irons: Styles of Corrosion and Inorganic Control on Hydrogen Pressure Buidup,” Environmental Science & Technology, Vol. 39, No. 18, 2005, pp. 7311-7317. doi:10.1021/es050507f
- P. Kedzierzawski, R. A. Oriani, J. P. Hirth, M. Smialowski, “Hydrogen Trapping in Iron and Iron Alloys,” Acta Metallurgicaet Materialia, Vol. 39, 1985, pp. 271-287.
- T. J. Carter and L. A. Cornish, “Hydrogen in Metals,” Engineering Failure Analysis, Vol. 8, No. 2, 2001, pp. 113-121. doi:10.1016/S1350-6307(99)00040-0
- A. Sieverts, “Absorption of Gases by Metals,” Zeitschrift für Metallkunde, Vol. 21, 1929, pp. 37-46.
- G. Schmitt, B. Sadlowsky and J. Noga, “Inhibition of Hydrogen Effusion from Steel—An Overlooked and Underestimated Phenomenon,” National Association for Corrosion Engineers, Orlando, 2000, p. 466.
- K. Ritter, M. S. Odziemkowski and R. W. Gillham, “An in Situ Study of the Role of Surface Films on Granular Iron in the Permeable Iron Wall Technology,” Contaminant Hydrology, Vol. 55, No. 1-2, 2002, pp. 87-111. doi:10.1016/S0169-7722(01)00187-5
- J. Gotpagar, S. Lyuksyutov, R. Cohn. E. Grulke and D. Bhattacharyya, “Reductive Dehalogenation of Trichloroethylene with Zero-Valent Iron: Surface Profiling Microscopy and Rate Enhancement Studies,” Langmuir, Vol. 15, No. 24, 1999, pp. 8412-8420. doi:10.1021/la990325x
- M. S. Odziemkowski and R. P. Simpraga, “Distribution of Oxides on Iron Materials Used for Remediation of Organic Groundwater Contaminants—Implications for Hydrogen Evolution Reactions,” Canadian Journal of Chemistry, Vol. 82, No. 10, 2004, pp. 1495-1506. doi:10.1139/v04-120