Halloysite and coconut shell biochar magnetic composites for the sorption of Pb(II) in wastewater: Synthesis, characterization and mechanism investigation

Halloysite/biochar was prepared by co-pyrolysis at different temperatures using coconut shell and halloysite as raw materials. Magnetic adsorbents were prepared through ball-mill extrusion with Fe 3 O 4 and the halloysite/biochar and the capacity of the adsorbents to adsorb Pb(II) from water was evaluated and compared. The effects of pH, contact time, and initial Pb(II) concentration on the adsorption capacity of the magnetic adsorbents for Pb(II) were investigated. The pseudo-second-order ( R 2 =0.9999) and Langmuir isothermal models ( R 2 =0.9906) fit the experimental data well. The prepared samples denotes as MBM-HBC700 exhibited the highest Pb(II) adsorption capacity (833.33 ± 16.71 mg·g -1 ), and the removal efficiency of Pb(II) by the magnetic adsorbents was above 90% after four adsorption–desorption cycles. Complexation, cation exchange, cation–π interaction, precipitation, pore filling and electrostatic adsorption have been proposed as the main removal mechanisms. After applying MBM-HBCs to simulated electroplating wastewater, the contents of Pb(II), Cu(II), Zn(II), and Cr(VI) were significantly lower than the discharge standard of China. The magnetic adsorbents prepared in this study have wide application prospects in the treatment of Pb(II) in wastewater, thus providing a new approach for promoting waste recycling and utilization.