It has been documented that contaminants could be degraded by hydroxyl radicals (center dot OH) produced upon oxygenation of Fe(II)-bearing sediments. However, the dependence of contaminant degradation on sediment characteristics, particularly Fe(II) species, remains elusive. Here we assessed the impact of the abundance of Fe(II) species in sediments on contaminant degradation by center dot OH during oxygenation. Three natural sediments with different Fe(II) contents and species were oxygenated. During 10 h oxygenation of 200 g/L sediment suspension, 2 mg/L phenol was negligibly degraded for sandbeach sediment (Fe(II): 9.11 mg/g), but was degraded by 41 and 52 for lakeshore (Fe(II): 9.81 mg/g) and farmland (Fe(II): 19.05 mg/g) sediments, respectively. center dot OH produced from Fe(II) oxygenation was the key reactive oxidant. Sequential extractions, X-ray diffraction, Mossbauer, and X-ray absorption spectroscopy suggest that surface-adsorbed Fe(II) and mineral structural Fe(II) contributed predominantly to center dot OH production and phenol degradation. Control experiments with specific Fe(II) species and coordination structure analysis collectively suggest the likely rule that Fe(II) oxidation rate and its competition for center dot OH increase with the increase in electron-donating ability of the atoms (i.e., O) complexed to Fe(II), while the center dot OH yield decreases accordingly. The Fe(II) species with a moderate oxidation rate and center dot OH yield is most favorable for contaminant degradation.
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