Isotherm Evaluation and Performance Assessment of Bone Biochar at Varied Dosages for the Simultaneous Removal of PAHs and Heavy Metals

Abstract

The co-contamination of soils with polycyclic aromatic hydrocarbons (PAHs) and heavy metals arising from petroleum exploration and spill incidents poses significant remediation challenges due to differences in their physicochemical behavior and environmental persistence. This study investigated the effectiveness of bone biochar (BB), produced through pyrolysis of cattle bone at 400 °C for 2 h, for the simultaneous removal of sixteen priority PAHs and selected heavy metals (Cd, Cr, Ni, and Pb) from crude oil–contaminated soil. Physicochemical characterization using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed a porous carbonaceous structure enriched with crystalline hydroxyapatite phases, providing multiple adsorption sites. Batch remediation experiments were conducted using biochar dosages ranging from 2 to 10 g per 50 g of contaminated soil over a 21-day incubation period. Removal efficiencies increased significantly with dosage, achieving maximum reductions of 89.75% for total PAHs and 89.51% for Ni at 10 g amendment, alongside substantial removal of Cd, Cr, and Pb. Adsorption equilibrium data were evaluated using Langmuir, Freundlich, and Temkin isotherm models. The Langmuir model provided the best fit for PAHs (R² = 0.988), Cd (R² = 0.978), and Pb (R² = 0.989), indicating predominantly monolayer adsorption behavior, whereas the Freundlich model better described Cr (R² = 0.788) and Ni (R² = 0.920), suggesting heterogeneous surface adsorption. The results demonstrate that bone biochar is an efficient and sustainable adsorbent for multi-contaminant soil remediation, with performance strongly governed by amendment dosage and contaminant-specific adsorption mechanisms