| This communication challenges the concept that nanoscale metallic iron (nano-Fe0) is a strong reducing agents for contaminant reductive transformation. It is shown that the inherent relationship between contaminant removal and Fe0 oxidative dissolution which is conventionally attributed to contaminant reduction by nano-Fe0 (direct reduction) could equally be attributed to contaminant removal by adsorption and co-precipitation. For reducible contaminants, indirect reduction by adsorbed FeII 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-Fe0 than for micro-Fe0 in the short term. However, because of the increased reactivity, nano-Fe0 will deplete in the short term. No more source of reducing agents (FeII, H, H2) will be available in the system. Therefore, the efficiency of nano-Fe0 as a reducing agent for environmental remediation is yet to be demonstrated. |
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