Preparation of magnetic biochar from macadamia nutshell pretreated by FeCl3-assisted mechanochemical activation for adsorption of heavy metals

Magnetic biochar is an inexpensive and easily recoverable adsorbent material for heavy metals. This study involved the preparation of magnetic biochar (MCA-BC) by solvent-free pyrolysis of macadamia nutshell pretreated with FeCl3-assisted mechanochemical activation (MCA) to remove Cu2+ and Pb2+. MCA-BC exhibited a serrated lamellar structure with abundant functional groups, which has outstanding adsorption performance for Cu2+ and Pb2+ and can be recycled 5 times with a 70% removal rate. Langmuir isotherms models (Qmax = 339.78 and 200.44 mg⋅g-1 for Cu2+ and Pb2+, respectively) and pseudo-second-order kinetics models were aptly used for the adsorption process. The adsorption mechanisms included pore filling, electrostatic adsorption, complexation and coordination reactions. This study has provided a novel synthetic pathway for the FeCl3-assisted MCA coupled with pyrolysis to prepare magnetic macadamia nutshell biochar, which has great potential for treating heavy metal wastewater.