Abstract
This communication challenges the concept that nanoscale metallic iron (nano-Fe 0) is a strong reducing agents for contaminant reductive transformation. It is shown that the inherent relationship between contaminant removal and Fe 0 oxidative dissolution which is conventionally attributed to contaminant reduction by nano-Fe 0 (direct reduction) could equally be attributed to contaminant removal by adsorption and co-precipitation. For reducible contaminants, indirect reduction by adsorbed Fe II or adsorbed H produced by corroding iron (indirect reduction) is even a more probable reaction path. As a result, the contaminant removal efficiency is strongly dependent on the extent of iron corrosion which is larger for nano-Fe 0 than for micro-Fe 0 in the short term. However, because of the increased reactivity, nano-Fe 0 will deplete in the short term. No more source of reducing agents (Fe II, H and H 2) will be available in the system. Therefore, the efficiency of nano-Fe 0 as a reducing agent for environmental remediation is yet to be demonstrated.
Highlights
Increased soil and groundwater contamination has prompted researchers to investigate affordable and efficient strategies for environmental protection
One recent innovative possibility has been the use of microscale granular metallic iron, initially for reductive dechlorination of halogenated carbons [1,2,3,4]
Contaminant reduction via surface-mediated reaction is likely to occur but the discussion of its extent is a complex issue. It is the intension of this communication to draw the attention of the scientific community on this key issue for nanoscale Fe0 injected into the subsurface for groundwater remediation
Summary
Increased soil and groundwater contamination has prompted researchers to investigate affordable and efficient strategies for environmental protection. The whole dynamic process of Fe0 oxidative dissolution coupled to iron hydroxide precipitation and crystallization at pH > 4.5 is responsible of contaminant removal and sequestration [12,13]. In this dynamic process, contaminant reduction via surface-mediated reaction (by Fe0, adsorbed FeII or adsorbed H) is likely to occur but the discussion of its extent is a complex issue. Contaminant reduction via surface-mediated reaction (by Fe0, adsorbed FeII or adsorbed H) is likely to occur but the discussion of its extent is a complex issue It is the intension of this communication to draw the attention of the scientific community on this key issue for nanoscale Fe0 injected into the subsurface for groundwater remediation
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