A comprehensive review of functionalized biochar for antimony soil remediation

Antimony (Sb) is a highly toxic metalloid extensively released from mining, smelting, and industrial activities, resulting in widespread soil contamination and posing serious risks to ecosystems and human health. Biochar, a low-cost and environmentally friendly porous carbon material, has shown strong potential for the remediation of Sb-contaminated soils. This review summarizes recent advances in the application of pristine and modified biochar for Sb soil remediation, with a focus on both direct and indirect mechanisms. Particular emphasis is placed on biochar modification strategies, which significantly enhance Sb removal efficiency and stability. Metal oxide-doped biochars (Fe, Mn, Ce) and nanomaterial composites (nZVI, TiO 2 ) achieve superior Sb immobilization, with Fe-modified biochar reaching adsorption capacities up to 64.0 mg·g -1 and reducing exchangeable Sb from 15% to 2% in soil systems. Moreover, the synergistic remediation using biochar combined with functional microorganisms is discussed where biochar serves as a microbial carrier and electron shuttle, upregulating Sb(III) oxidation genes ( anoA ) by 12.9-36.2% while suppressing Sb (V) reduction pathways ( arsC downregulation), ultimately reducing Sb bioavailability by 35-93% and plant accumulation by 40-61%. Finally, key challenges and future research directions toward multifunctional biochar design and field-scale validation are proposed.