Hydroxyl radical (.OH) plays a crucial role in the fate of redox-active substances in the environment. Production of .OH has often been related to Fe(II) oxygenation. The oxidation of ligand-complexed Fe(II), structural Fe(II) in minerals and adsorbed Fe(II) on solids can be coupled to the transformation of O2 to .OH through the Haber-Weiss mechanism. However, .OH production from the oxygenation of dissolved Fe2+ is largely overlooked. This study demonstrated that .OH can be produced from oxygenating dissolved Fe2+ under circumneutral pH conditions. Solution pH (6.0~7.0) greatly influenced Fe2+ oxidation and .OH production. The maximum concentration of cumulative .OH was 2.5 μM for 5 h oxygenation of 0.357 μM Fe2+ at pH 6.5. Under the tested pH conditions, the Fe3+ produced quickly hydrolyzed to form lepidocrocite mainly and ferrihydrite. The presence of Fe(III) hydroxides accelerated Fe2+ oxidation by the adsorption and variation of coordination structure. The enhancement by adsorption was explicitly confirmed by the increase in cumulative .OH to 5.5 and 7.0 μM with the respective addition of lepidocrocite and ferrihydrite into Fe2+ solution at pH 6.5. The Fe(III) hydroxides generated in situ play the controlling role in .OH production.

Production of .OH from oxygenation of Fe2+ under near-neutral conditions

253rd National Meeting (2017)

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