Remediation of Pb contaminated soil with recovered P-laden engineered biochar: Effects on Pb speciation and soil...

This study investigates the concept of using engineered biochar to reclaim phosphorus (P) in water and subsequent reuse of recovered P-laden engineered biochar for remediation of lead (Pb) contaminated soil. Hickory wood biochar (BC) was loaded with Mg oxides/hydroxides (EBC) via wet-impregnation pretreatment and Mg/Fe layered double hydroxides (LDH) via co-precipitation, respectively. Both engineered biochar types demonstrated effective P adsorption, with maximum capacities of 196.0 mg P/g for EBC and 88.3 mg P/g for LDH. The recovered P-laden biochar (EBC-P and LDH-P) were incubated with a Pb contaminated soil for four months, and changes in labile Pb content, Pb speciation, and soil microbial community were monitored. EBC-P and LDH-P significantly reduced extractable Pb (CaCl₂ and TCLP methods) by over 95% stabilization efficiency. Soil XRD spectra indicated gradual crystallization of hydroxypyromorphite within the first month, yet this Pb mineral phase was not detected in later months by XANES. Pb was consistently bonded on biochar surfaces across all treatments. Biochar applications also altered the soil microbial community structure, increasing the relative abundance of taxa (e.g., Bacillus strains) in association with increased soil pH and reduced Pb toxicity. This change suggests enhanced microbial functionalities to cope with environmental stresses such as pH and heavy metals as well as assimilation and generation of precursor metabolites. Ultimately, this study provides a technical foundation for evaluating P-enriched engineered biochar as a sustainable strategy for remediating Pb-contaminated soils.