Abstract
Aqueous contaminant removal in the presence of metallic iron (e.g. in Fe 0/H 2O systems) is characterized by the large diversity of removing agents. This paper analyses the synergistic effect of adsorption, co-precipitation and reduction on the process contaminant removal in Fe 0/H 2O systems on the basis of simple theoretical calculations. The system evolution is characterized by the percent Fe 0 consumption. The results showed that contaminant reduction by Fe 0 is likely to significantly contribute to the removal process only in the earliest stage of Fe 0 immersion. With increasing reaction time, contaminant removal is a complex interplay of adsorption onto iron corrosion products, co-precipitation or sequestration in the matrix of iron corrosion products and reduction by Fe 0, Fe II or H 2/H. The results also suggested that in real world Fe 0/H 2O systems, any inflowing contaminant can be regarded as foreign species in a domain of precipitating iron hydroxides. Therefore, current experimental protocols with high contaminant to Fe 0 ratios should be revisited. Possible optimising of experimental conditions is suggested.
Highlights
Widespread groundwater contamination has prompted intensive efforts to find efficient and affordable remediation technologies
Contaminant removal is a complex interplay of adsorption onto iron corrosion products, co-precipitation or sequestration in the matrix of iron corrosion products and reduction by Fe0, FeII or H2/H
The ongoing discussion over the relative importance of adsorption and reduction on the process of contaminant removal in Fe0/H2O systems [3,9,10,11,12,13,14] illustrates the challenge in assessing the environmental relevance of laboratory results
Summary
Widespread groundwater contamination has prompted intensive efforts to find efficient and affordable remediation technologies. In the last two decades metallic iron (Fe0) has been extensively used in remediation schemes to effectively remove a wide variety of inorganic and organic contaminants in reactive barriers [3,4,5,6]. The process of H2O reduction by Fe0 obviously reduces the efficiency of the decontamination process (H2O as concurrent for contaminant) and increases the pH of the system, promoting the formation of iron hydroxides (Eq 6 and 7). Iron (hydr)oxides are good adsorbent for several contaminants (Eq 9). The ongoing discussion over the relative importance of adsorption and reduction on the process of contaminant removal in Fe0/H2O systems [3,9,10,11,12,13,14] illustrates the challenge in assessing the environmental relevance of laboratory results. The main goal is to purchase researchers with a solid guidance for purposeful experimental design for the investigation of Fe0/H2O systems
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