Abstract: To alleviate environmental pollution caused by the accumulation of agricultural solid waste, spent Pleurotus ostreatus substrate was used as raw material to prepare biochar at pyrolysis temperatures ranging from 300 to 800 ℃. The biochars were characterized using SEM-EDS, BET, and FTIR techniques. The results showed that as the pyrolysis temperature increased, the pH of the biochar initially rose and then declined, the output capacity decreased, the carbon content increased while the oxygen content decreased, and aromaticity was enhanced. When the pyrolysis temperature ranged from 300 to 750 ℃, the number of pores gradually increased and their arrangement became uniform as the pyrolysis temperature rose; however, at 800 ℃, the porous structure collapsed, resulting in reduced specific surface area and pore volume. The intensity of functional group vibrations weakened at higher temperatures, and the CaCO₃ content in biochar produced at 750 ℃ increased, promoting the precipitation of heavy metal ions. The results of heavy metal wastewater treatment by biochar prepared at 750 ℃ showed that the adsorption rate of Pb²⁺ and Cd²⁺ reached 97.63% and 92.01%, respectively, when the biochar dosage was 4 g/L, showing excellent adsorption performance.

Key words: spent Pleurotus ostreatus substrate, biochar, pyrolysis temperature, heavy metal, lead, cadmium, water body, adsorption