title: Zero-valent iron for the abatement of arsenate and selenate from flowback water of hydraulic fracturing.
abstract: Zero-valent iron (ZVI) was tested for the removal of 150 μg L-1As(V) and 350 μg L-1Se(VI) in high-salinity (ionic strength 0.35-4.10 M) flowback water of hydraulic fracturing. Over 90% As(V) and Se(VI) was removed by 2.5 g L-1ZVI in Day-14 flowback water up to 96-h reaction, with the remaining concentration below the maximum contaminant level for As(V) and criterion continuous concentration for Se(VI) recommended by US EPA. The kinetics of As(V) and Se(VI) removal followed a pseudo-second-order rate expression with the observed rates of 4.51 × 10-2-4.91 × 10-1and 3.48 × 10-2-6.58 × 10-1h-1(with 0.5-10 g L-1ZVI), respectively. The results showed that Se(VI) removal significantly decreased with increasing ionic strength, while As(V) removal showed little variation. Common competing anions (nitrate, bicarbonate, silicate, and phosphate), present in shallow groundwater and stormwater, caused marginal Se(VI) desorption (2.42 ± 0.13%) and undetectable As(V) desorption from ZVI. The competition between As(V) and Se(VI) for ZVI removal depended on the initial molar ratio and surface sites, which occurred when the Se(VI) concentration was higher than the As(V) concentration in this study. The characterization of As(V)- and Se(VI)-loaded ZVI by X-ray diffraction and Raman analysis revealed that ZVI gradually converted to magnetite/maghemite corrosion products with lepidocrocite in flowback water over 30 days. Similar corrosion compositions were confirmed in aerobic and anaerobic conditions regardless of the molar ratio of As(V) to Se(VI). The high reactivity and stability of ZVI showed its suitability for in-situ prevention of As(V) and Se(VI) migration due to accidental leakage, spillage, or overflow of flowback water.
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Season S
authors.initials: SS
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. Electronic address: dan.tsang@polyu.edu.hk.
authors.forename: Daniel C W
authors.initials: DCW
authors.lastname: Tsang
authors.affiliation: Environmental and Water Resources Engineering, Department of Civil and Environmental Engineering, Imperial College London, South Kensington, London, SW7 2AZ, UK.
authors.forename: Nigel J D
authors.initials: NJD
authors.lastname: Graham
authors.affiliation: Korea Biochar Research Center & School of Natural Resources and Environmental Science, Kangwon National University, Chuncheon, 24341, South Korea.
authors.forename: Yong Sik
authors.initials: YS
authors.lastname: Ok
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China. Electronic address: yujief@hit.edu.cn.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Feng
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Xiang-Dong
authors.initials: XD
authors.lastname: Li
mesh_terms: D001149:Arsenates / Q000737:chemistry*; D001639:Bicarbonates / Q000737:chemistry; D003343:Corrosion; D005290:Ferric Compounds / Q000737:chemistry; D000067071:Hydraulic Fracking; D007220:Industrial Waste; D007501:Iron / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D064586:Selenic Acid / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods; D014961:X-Ray Diffraction
chemical_list: D001149:Arsenates; D001639:Bicarbonates; D005290:Ferric Compounds; D007220:Industrial Waste; D009566:Nitrates; D010710:Phosphates; D017640:Silicates; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D007501:Iron; D064586:Selenic Acid; C025657:arsenic acid
keywords: Arsenic; Hydraulic fracturing; Ionic strength; Permeable reactive barrier; Selenium; Zero-valent iron