title: Production of Hydroxyl radicals from oxygenation of simulated AMD due to CaCO3-induced pH increase.
abstract: Many karst areas are impacted by acid mine drainage (AMD) which is characterized by low pH, high concentrations of dissolved Fe(II) and toxic contaminants. During the flow of AMD in karst areas, the increase in pH facilitates the oxygenation of Fe(II). Whereas, the oxidizing capacity for Fe(II) oxygenation in AMD is poorly understood. In light of the recent finding that hydroxyl radicals (OH) can be produced from Fe(II) oxygenation, this study experimentally measured the cumulative concentrations of OH produced from oxygenation of simulated AMD (8.93 mM Fe2+, pH 3) in the presence of limestone (CaCO3). With the increase in CaCO3dosages from 0.67 to 2.78 g/L, Fe(II) oxidation rate increased accordingly, but the maximum concentration of cumulative OH appeared at the CaCO3dosage of 1.39 g/L, being 59.3 μM within 24 h. The production of OH was mainly attributed to the rise of AMD pH due to dissolution of limestone, rendering the appearance of adsorbed Fe(II) on the newly formed lepidocrocite and ferrihydrite and complexed Fe2+by carbonate (i.e., siderite). Oxygenation of these Fe(II) species was accountable for the production of OH. An appropriate pH (i.e., 5-6) was required for the moderate rate of Fe(II) oxidation, corresponding to the maximum production of OH. The OH produced from AMD oxygenation can concurrently oxidize the contaminants of arsenic and p-aminobenzenesulfonamide. Findings from this study suggest that the oxidizing impact of OH on contaminants transformation as well as organic carbon mineralization should be concerned for the oxygenation of AMD in karst areas.
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China; College of Resource and Environmental Engineering, Guizhou University, Huaxi District, Guiyang, 550025, PR China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China. Electronic address: yuansonghu622@cug.edu.cn.
authors.forename: Songhu
authors.initials: S
authors.lastname: Yuan
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China.
authors.forename: Peng
authors.initials: P
authors.lastname: Liao
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China.
authors.forename: Ao
authors.initials: A
authors.lastname: Qian
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China.
authors.forename: Xixiang
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, PR China.
authors.forename: Man
authors.initials: M
authors.lastname: Tong
authors.affiliation: Shanghai Synchrotron Radiation Facility, 239 Zhang Heng Road, Pudong New District, Shanghai, 201203, PR China.
authors.forename: Lina
authors.initials: L
authors.lastname: Li
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008906:Mining; D010084:Oxidation-Reduction
chemical_list: D017665:Hydroxyl Radical; D007501:Iron; D002119:Calcium Carbonate
keywords: Acid mine drainage; Contaminant transformation; Ferrous iron oxygenation; Hydroxyl radicals; Limestone