Sustainable Remediation Using Metallic Iron: Quo Vadis?

Dear Colleagues,

During the past three decades, groundwater remediation using permeable reactive barriers (PRBs) containing metallic iron (Fe⁰) has become a well-established technology. However, many uncertainties exist regarding their design, suggesting that Fe⁰ PRBs is still an innovative technology.

Research on Fe⁰ PRBs started in the early 1990s and has boomed in the past three decades. Sufficient data and observations have been accumulated to establish the science of the Fe⁰/H₂O system. To explain the initial observation that there were losses of chlorinated organic contaminants from aqueous solutions in contact with a variety of metals (including Fe⁰), it was proposed that reductive dechlorination was the main cause, with electrons coming from the metal body. In the meantime, Fe⁰ is described in the literature as “reservoir of electrons” for contaminant transformation. However, considering Fe⁰ as source of electrons for dissolved species, including O₂, contradicts the century-old knowledge that, under environmental conditions, the Fe⁰ surface is covered by a non-conductive oxide scale, hindering any electron transfer from the Fe⁰ body. This state of affairs implies that abiotic reductive transformations in Fe⁰/H₂O systems are mediated by secondary reducing agents such as Fe^II species, Fe^II/Fe^III species, and H₂. Biotic transformations are also reported, using Fe^II or H₂ as electron sources. In other words, the still widely accepted operating mode of Fe⁰/H₂O systems seems not to have a scientific basis. The other evidence against this operating mode is that its establishment was not based on any holistic approach since the essence of aqueous iron corrosion is by water and is found in trace amounts (humidity). Clearly, the conversion of data and observations into knowledge constitutes a great challenge for the Fe⁰ research community.

This Special Issue welcomes papers highlighting: (i) established or innovative Fe⁰ materials for water treatment; (ii) models and research tools applied to advancing the understanding of the Fe⁰/H₂O system; and (iii) case studies, conceptual frameworks, viewpoints, and field applications. Special attention is given (but is not limited) to the assessment of operation modes of innovative materials (e.g., composites) and their sustainability under field conditions. The objective is to give state-of-the-art knowledge of the development of Fe⁰ PRBs-based recent advances in understanding the operating mode of the Fe⁰/H₂O system, and in particular, the view that Fe⁰ is not a stand-alone reducing agent under environmental conditions.

Dr. Chicgoua Noubactep
Dr. Marius Gheju
Guest Editors

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