Metallic iron for environmental remediation: Learning from electrocoagulation

The interpretation of processes yielding aqueous contaminant removal in the presence of elemental iron (e.g. in Fe-0/H2O systems) is subject to numerous complications. Reductive transformations by Fe-0 and its primary corrosion products (Fe-II and H/H-2) as well as adsorption onto and co-precipitation with secondary and tertiary iron corrosion products (iron hydroxides, oxyhydroxides, and mixed valence Fe-II/Fe-III green rusts) are considered the main removal mechanisms on a case-to-case basis. Recent progress involving adsorption and co-precipitation as fundamental contaminant removal mechanisms have faced a certain scepticism. This work shows that results from electrocoagulation (EC), using iron as sacrificial electrode, support the adsorption/co-precipitation concept. It is reiterated that despite a century of commercial use of EC, the scientific understanding of the complex chemical and physical processes involved is still incomplete. (C) 2009 Elsevier B.V. All rights reserved.