This paper evaluates a novel sorbent for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater (FWW). A series of iron-biochar (Fe-BC) composites with different Fe/BC impregnation mass ratios (0.5:1, 1:1, and 2:1) were prepared by mixing forestry wood waste-derived BC powder with an aqueous FeCl3 solution and subsequently pyrolyzing them at 1000 °C in a N2-purged tubular furnace. The porosity, surface morphology, crystalline structure, and interfacial chemical behavior of the Fe-BC composites were characterized, revealing that Fe chelated with CO bonds as COFe moieties on the BC surface, which were subsequently reduced to a CC bond and nanoscale zerovalent Fe (nZVI) during pyrolysis. The performance of the Fe-BC composites was evaluated for simultaneous removal of potentially toxic elements (Cu(II), Cr(VI), Zn(II), and As(V)), inherent cations (K, Na, Ca, Mg, Ba, and Sr), hetero-chloride (1,1,2-trichlorethane (1,1,2-TCA)), and total organic carbon (TOC) from high-salinity (233 g L-1 total dissolved solids (TDS)) model FWW. By elucidating the removal mechanisms of different contaminants, we demonstrated that Fe-BC (1:1) had an optimal reducing/charge-transfer reactivity owing to the homogenous distribution of nZVI with the highest Fe0/Fe2+ ratio. A lower Fe content in Fe-BC (0.5:1) resulted in a rapid exhaustion of Fe0, while a higher Fe content in Fe-BC (2:1) caused severe aggregation and oxidization of Fe0, contributing to its complexation/(co-)precipitation with Fe2+/Fe3+. All of the synthesized Fe-BC composites exhibited a high removal capacity for inherent cations (3.2-7.2 g g-1) in FWW through bridging with the CO bonds and cation-π interactions. Overall, this study illustrated the potential efficacy and mechanistic roles of Fe-BC composites for (pre-)treatment of high-salinity and complex FWW.

Department of Civil and Environmental Engineering Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong China

Department of Civil and Environmental Engineering Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong China; State Key Laboratory of Urban Water Resource and Environment Harbin Institute of Technology Harbin 150090 China

Department of Earth and Atmospheric Sciences University of Alberta Edmonton Alberta T6G 2E3 Canada

Department of Environmental Science Zhejiang University Hangzhou 310058 China

Environmental and Water Resources Engineering Department of Civil and Environmental Engineering Imperial College London South Kensington London SW7 2AZ UK

Faculty of Environmental Sciences Czech University of Life Sciences Kamýcká 129 165 00 Prague Suchdol Czech Republic

Korea Biochar Research Center O Jeong Eco Resilience Institute Division of Environmental Science and Ecological Engineering Korea University Seoul 02841 Republic of Korea

School of Environmental Science and Engineering Huazhong University of Science and Technology Wuhan 430074 China

School of Environmental Science and Engineering Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240 China

State Key Laboratory of Urban Water Resource and Environment Harbin Institute of Technology Harbin 150090 China

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