Remediation of lead-contaminated soil by Fe-Mn-Ni layered double hydroxide composite biochar

• LDH/CSB500 achieved a Pb(II) adsorption capacity of 474.69 mg/g. • Synergistic mechanisms like ion exchange and complexation enhanced Pb(II) removal. • 3.Flake-like structure improved adsorption performance and stability. This study investigated the remediation of lead (Pb)-contaminated soil using Fe-Mn-Ni layered double hydroxide composite biochar (LDH/CSB). The results demonstrated that LDH/CSB application significantly increased soil pH, electrical conductivity (EC), and total organic carbon (TOC) content. The elevation of soil pH enhanced Pb precipitation as insoluble hydroxides (e.g., Pb(OH) 2 ), while increased TOC provided abundant oxygen-containing functional groups (e.g., carboxyl and hydroxyl groups) to immobilize Pb through complexation and surface adsorption. The high specific surface area (up to 78.70 m²/g) and layered structure of LDH/CSB further facilitated Pb binding, transforming mobile fractions (acid-soluble and reducible Pb) into stable forms (oxidizable and residual Pb). Toxicity characteristic leaching procedure (TCLP) tests confirmed a 53.80% reduction in Pb leachability, highlighting reduced bioavailability and ecological risks. This work underscores the potential of LDH/CSB as a sustainable and efficient material for Pb-contaminated soil remediation, with broader applications in heavy metal-polluted environments. Future studies should focus on optimizing field-scale application parameters and evaluating long-term stability.