Synthesis and application of amine-functionalized MgFe2O4-biochar for the adsorption and immobilization of Cd(II) and Pb(II)

Biochar composites have been widely applied to wastewater and soil remediation due to their advantages of high efficiency, controllability and recyclability. Many studies have demonstrated the application potential of biochar, but little is known about the process and mechanism of surface functionalization of biochar. In this study, an amine-functionalized magnesium ferrite-biochar composite (MgFe2O4–NH2@sRHB) was first synthesized by coprecipitation and then used as a remediation agent to remove heavy metals from aqueous solution and immobilize heavy metals in polluted soils. The results revealed the performance and mechanisms for MgFe2O4–NH2@sRHB to remove or immobilize heavy metals from wastewater or in polluted soils. In wastewater treatment, the mechanisms primarily involved complexation and ion exchange as well as pore filling and electrostatic attraction, and Cd(II) and Pb(II) were adsorbed through a monolayer on the surface of MgFe2O4–NH2@sRHB, with the maximum adsorption capacity reaching 195.50 and 198.93 mg g−1, respectively. In the treatment of soils polluted by heavy metals, MgFe2O4–NH2@sRHB facilitated the transformation of exchangeable Cd to residual and Fe-Mn bound Cd. The addition of 1% MgFe2O4–NH2@sRHB decreased the concentration of exchangeable Cd from 21.0% to 15.2%, 14.8%, 14.8% and 14.6% after 7, 14, 21 and 35 days of treatment, respectively. Electrostatic attraction, precipitation and complexation contributed substantially to the immobilization of heavy metals in the soil. This study provides a new type of biochar composite that can effectively remove and immobilize heavy metals in wastewater and soil at the same time.