Adsorption characteristics and mechanism of modified chicken manure biochar on Cd(II)-Pb(II) compound polluted wastewater.

Biochar has been widely employed in heavy metal wastewater treatment due to its well-developed porosity. However, current studies lack efficient and environmentally friendly modification methods, especially for systems involving coexisting heavy metals. In this study, modified biochar was prepared from chicken manure via K₂FeO₄ modification, aiming to remove Cd(II)-Pb(II) compound polluted wastewater efficiently. Characterization results indicated that K₂FeO₄ treatment significantly increased the specific surface area (67.1 m²/g) and pore volume (0.08 cm³/g) of KFBC, and enriched its surface with oxygen-containing functional groups. The adsorption kinetics of Cd(II) and Pb(II) followed the pseudo-second-order model, while the isotherm data fit well with the Langmuir model. The maximum adsorption capacities were 141.24 mg/g for Cd(II) and 487.45 mg/g for Pb(II), considerably higher than those of the unmodified biochar. In both single and binary systems, the adsorption capacities increased with dosage, and the optimal adsorption occurred at pH 5-6. In the binary system, KFBC exhibited a strong preference for Pb(II), with a selectivity coefficient 4038 times that of Cd(II). After three adsorption-desorption cycles, KFBC retained adsorption capacities of 45.28 mg/g for Cd(II) and 171.09 mg/g for Pb(II). In real wastewater, KFBC achieved removal efficiencies of 84.62% for Cd(II) and 97.85% for Pb(II), while maintaining strong resistance to ionic interference. The removal mechanisms involved cation exchange, precipitation, complexation, electrostatic attraction, and cation-π interactions. This study not only proposes a high-performance adsorbent derived from chicken manure but also reveals its selective adsorption and anti-interference capability in binary systems, demonstrating promising environmental and practical application potential.