Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia; College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
Chemosphere. 2013 Nov;93(9):1936-41. doi: 10.1016/j.chemosphere.2013.06.076. Epub 2013 Jul 20.
Iron-catalyzed oxidation of As(III) to As(V) can be highly effective for toxic arsenic removal via Fenton reaction and Fe(II) oxygenation. However, the contribution of ubiquitous organic ligands is poorly understood, despite its significant role in redox chemistry of arsenic in natural and engineered systems. In this work, selected naturally occurring organic ligands and synthetic ligands in co-oxidation of Fe(II) and As(III) were examined as a function of pH, Fe(II), H2O2, and radical scavengers (methanol and 2-propanol) concentration. As(III) was not measurably oxidised in the presence of excess ethylenediaminetetraacetic acid (EDTA) (i.e. Fe(II):EDTA<1:1), contrasting with the rapid oxidation of Fe(II) by O2 and H2O2 at neutral pH under the same conditions. However, partial oxidation of As(III) was observed at a 2:1 ratio of Fe(II):EDTA. Rapid Fe(II) oxidation in the presence of organic ligands did not necessarily result in the coupled As(III) oxidation. Organic ligands act as both iron speciation regulators and radicals scavengers. Further quenching experiments suggested both hydroxyl radicals and high-valent Fe species contributed to As(III) oxidation. The present findings are significant for the better understanding of aquatic redox chemistry of iron and arsenic in the environment and for optimization of iron-catalyzed arsenic remediation technology.
铁催化氧化砷（III）为砷（V）可以通过芬顿反应和 Fe(II)氧化有效地去除有毒的砷。然而，尽管有机配体在自然和工程系统中砷的氧化还原化学中具有重要作用，但普遍存在的有机配体的贡献仍了解甚少。在这项工作中，研究了在 co-oxidation 中选择的天然存在的有机配体和合成配体 Fe(II)和 As(III)，作为 pH、Fe(II)、H2O2 和自由基清除剂（甲醇和 2-丙醇）浓度的函数。在过量乙二胺四乙酸（EDTA）（即 Fe(II):EDTA<1:1）存在下，As(III)没有被测量到氧化，这与在相同条件下中性 pH 下 O2 和 H2O2 对 Fe(II)的快速氧化形成对比。然而，在 Fe(II):EDTA 的 2:1 比例下观察到了 As(III)的部分氧化。在有机配体存在下，Fe(II)的快速氧化不一定导致耦合的 As(III)氧化。有机配体既可以作为铁形态调节剂，也可以作为自由基清除剂。进一步的猝灭实验表明，羟基自由基和高价态的 Fe 物种都有助于 As(III)氧化。本研究结果对于更好地理解环境中铁和砷的水相氧化还原化学以及优化铁催化的砷修复技术具有重要意义。
