Green preparation of magnetic biochar for the effective accumulation of Pb(II): Performance and mechanism

[Display omitted] •Magnetic biochar (MBC) was prepared by the co-pyrolysis of wheat straw and hematite.•The prepared MBC800-120 exhibited an excellent Pb(II) adsorption capacity (190.42 mg/g).•The magnetic biochar can be recycled easily.•The formation of PbOHCl and the surface complexation enhanced the Pb(II) removal. Magnetic biochar (MBC) was prepared by the pyrolysis of wheat straw and natural hematite in nitrogen. The effect of the pyrolysis temperature and time was considered. The as-prepared MBCs were characterized by using XRD, FTIR, BET, XPS, and a magnetic susceptibility device. The performance of the prepared MBCs on the removal of Pb(II) was evaluated. The effect of the contact time, pH value, and initial Pb(II) concentration on the adsorption capacity of Pb(II) by the MBCs was investigated. The results show that porous MBCs were successfully prepared by the pyrolysis method. The pyrolysis temperature and time controlled the pore structure, surface area, valence state of iron and magnetic susceptibility of the prepared MBCs. The prepared MBC800-120 exhibited the best Pb(II) adsorption capacity (196.91 mg/g). Moreover, the former still displayed excellent solid-liquid separation efficiency by magnetic separation due to strong magnetism. The hydrolysis-induced precipitation of PbOHCl and the surface complexation by the active sites on the surface of biochar and corroded iron were proposed as the main removal mechanisms. The experimental results provide a novel method for preparing magnetic carbon material and enhancing the comprehensive utilization of biomass and hematite.