Removal of Pb(II) from Water by Potassium Permanganate-Modified Areca Fiber Biochar: Performance and Mechanism

Heavy metal contamination, particularly lead (Pb) pollution in aquatic environments, poses serious threats to ecosystems and human health, necessitating the development of efficient and cost-effective adsorbents. In this study, potassium permanganate-modified areca fiber biochar (PAFB) is successfully synthesized for Pb(II) removal from aqueous solutions. Characterization results confirm the successful loading of MnO2 nanoparticles and the introduction of abundant –OH, –COOH, and Mn–OH active sites onto the biochar surface. Batch adsorption experiments reveal that Pb(II) removal by PAFB is highly pH- and temperature-dependent, with optimal performance at pH = 6.0 and 25 °C. The adsorption process follows the pseudo-second-order kinetic model (R2 = 0.9997) and the Freundlich isotherm model (R2 = 0.9363), indicating chemisorption-dominated adsorption on heterogeneous surfaces. Thermodynamic analysis confirmed the spontaneous and endothermic nature of the adsorption process. The maximum adsorption capacity reaches 45.62 mg/g at 25 °C, comparable to or higher than that of many similar biochar-based adsorbents. Mechanistic analysis revealed that Pb(II) removal by PAFB proceeds via a synergistic electrostatic attraction–surface complexation mechanism, wherein Pb(II) forms inner-sphere complexes with –OH, –COOH, and ≡Mn–OH groups, as evidenced by FTIR and XPS analyses. The Pb4f spectrum exclusively displayed Pb(II) complexation peaks without detectable Pb0 precipitates, confirming the immobilization of Pb(II) as amorphous surface complexes. Moreover, PAFB maintains an 87.00% removal efficiency after four regeneration cycles, demonstrating excellent reusability. This study provides an environmentally friendly adsorbent for Pb(II) removal, showing promising potential for heavy-metal-contaminated wastewater treatment.