Sorption of lead in soil amended with coconut fiber biochar: Geochemical and spectroscopic investigations

In this study, we applied coconut fiber-derived biochar (CFB) to a lead (Pb)-contaminated soil (at 600 mg kg⁻¹) at 2% and 4% (w/w), in order to explore the efficacy and mechanism of CFB to immobilize Pb in soil during a 150-day incubation experiment. Our approach integrated various techniques namely micro-X-ray fluorescence, sequential extraction, X-ray absorption fine structure, scanning electron microscopy combined with energy dispersive X-ray spectroscopy to evaluate the Pb immobilization. Results indicated that the distribution of Pb in the studied soil was significantly affected by CFB application. The Pb content in organic matter bound fraction of the studied soil increased by 29.5% and 33.5% with 2% and 4% CFB, respectively, compared to control soil after 150-day of incubation. Lead-loaded humic acid (HA) and Pb₃(PO₄)₂ were higher in the biochar-amended soil (2% CFB) as compared with the control soil. The CFB particles possibly offer more binding sites of PO₄ ³⁻ and carboxylic functional groups than the binding sites of –FeO(OH), SiO₃ ²⁻, −Al₂O₃ and organic functional groups provided by the original soil particles alone (no biochar) for Pb. Overall, this study highlights that CFB can be a potential candidate to immobilize Pb for the restoration and remediation of Pb-contaminated soils.