Synthesis of magnetic biochar co-doped with sulfur, iron, and manganese via a novel modification method for simultaneous Cd and Pb remediation

Abstract

In this study, a manganese (Mn)/ iron (Fe) bimetallic sulfide-modified magnetic biochar composite derived from hardwood sawdust (S-M-KAC) was synthesized via a stepwise activation-magnetization-sulfidation method for the simultaneous remediation of water and soil contaminated by cadmium (Cd) and lead (Pb). In a single-contaminant system, metal adsorption by potassium permanganate (KMnO₄)-activated biochar (KAC), magnetized KMnO₄-activated biochar (M-KAC), and S-M-KAC followed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacities for Cd(II) in water were in the order of S-M-KAC (127.37 mg/g) > M-KAC (36.95 mg/g) > KAC (31.04 mg/g), whereas for Pb(II), the adsorption capacity was greatest for S-M-KAC (290.17 mg/g), followed by M-KAC (148.05 mg/g) and KAC (67.85 mg/g). In the binary system, S-M-KAC retained more than 80 % of its maximum adsorption capacities from the single-contaminant systems, making it the most effective adsorbent for remediating Cd/Pb-contaminated water. In addition, the stabilization efficiencies for soil Cd and Pb across four biochar treatments increased consistently with higher adsorbent application rates and longer treatment periods compared to the control. The stabilization efficiencies followed the order of S-M-KAC > M-KAC > KAC > BC. These findings highlight the significant potential of S-M-KAC for practical remediation of water and soil contaminated by Cd and Pb.