Remediation of Lead-Contaminated Soil Using Biochar-Nanoscale Zero-Valent Iron Composite

A novel biochar-supported nanoscale zero-valent iron composite (BC-nZVI) was synthesized and systematically evaluated for lead immobilization in contaminated soil. Material characterization revealed uniform distribution of nZVI particles on the biochar surface, with XRD analysis confirming successful integration through characteristic Fe0 peaks at 2θ = 44.7° and 65.0°. Surface charge analysis showed a point of zero charge at pH 6.5 for BC-nZVI, indicating enhanced stability compared to bare nZVI (pH 7.5). The composite exhibited superior performance in lead immobilization compared to unmodified biochar, with sequential extraction showing significant reduction in acid-extractable lead (from 790.3 to 278.4 mg/kg) and increased residual fraction (from 415.3 to 949.4 mg/kg). Column leaching studies under simulated acid rain (pH 4.7) demonstrated 76.4% reduction in cumulative lead leaching over 30 days. The immobilization mechanism involved multiple pathways including surface complexation, precipitation, and incorporation into crystal structures, as evidenced by XPS analysis showing Pb–O–Fe bond formation. The enhanced performance was attributed to the synergistic combination of biochar’s high surface area and nZVI’s reactive properties.