title: Arsenic(III) and iron(II) co-oxidation by oxygen and hydrogen peroxide: divergent reactions in the presence of organic ligands.
abstract: 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.
authors.affiliation: Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia; College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China. Electronic address: zhaohui.wang@scu.edu.au.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.forename: Richard T
authors.initials: RT
authors.lastname: Bush
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry; D052918:Environmental Restoration and Remediation / Q000379:methods; D060587:Groundwater / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D008024:Ligands; D014874:Water Pollutants, Chemical; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D007501:Iron; D001151:Arsenic; D010100:Oxygen
keywords: Arsenic; EDTA; Fe(II) oxidation; Fenton reaction; Radical scavenger