Evolution of biochar structure and porosity with temperature and its impact on metal adsorption

Biochar were synthesised from wood biomass via slow pyrolysis at temperatures of 400, 500, and 600°C, denoted B400, B500, and B600, and evaluated for their capacity to remove Pb, Cu, and Zn from aqueous solutions. The investigation assessed the influence of pyrolysis temperature on biochar yield, physicochemical and chemical properties, pore development, and adsorption performance for these metals. Analytical techniques included proximate and ultimate analyses, Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopy (SEM), and batch adsorption experiments. Increasing pyrolysis temperature enhanced pore development and adsorption capacity while reducing biochar yield. The BET surface area increased from 50.7 m 2 /g in the feedstock to 265.2 m 2 /g for B600, with a corresponding rise in micropore volume from 0.03 to 0.13 cm 3 /g. SEM analysis revealed that higher temperatures promoted greater pore volume and induced structural modifications in the biochar. Adsorption equilibrium was achieved within 180–240 min, with biochar produced at 600°C (B600) demonstrating the highest performance. At pH 8, maximum removal efficiencies were approximately 90–95% for Pb, 85–90% for Cu, and 90–95% for Zn, corresponding to adsorption capacities of 4–5 mg/g for Pb and 3–4 mg/g for Cu and Zn. The adsorption efficiency order was Pb > Cu > Zn. Adsorption data closely fit the Langmuir isotherm model (R 2 ≈ 0.99), indicating monolayer adsorption on a uniform surface. Comparisons between pilot-scale Woodtek biochar (WTB) and laboratory-scale biochar (LSB) produced at 600°C showed comparable adsorption efficiencies and capacities. These findings suggest that scaling up biochar production does not compromise its effectiveness in removing heavy metals from water. Overall, the results highlight the potential of wood-derived biochar for large-scale remediation of heavy metals in contaminated water systems.