Efficient removal of Pb²⁺ by iron-doped hydroxyapatite: Synthesis, adsorption, kinetics and mechanisms

This study reports the synthesis of an iron-doped modified hydroxyapatite (FeHAP-40) via an ultrasonic-microwave synergistic method, aiming to develop a high-performance adsorbent for Pb²⁺ removal from aqueous solutions. Material characterization was conducted using FT-IR, XPS, and XRD to clarify its structural and chemical properties. Systematic investigations were conducted on the effects of pH, temperature, initial concentration, and contact time on adsorption performance. Results demonstrated that Fe-HAP-40 achieved maximum adsorption capacity at pH 5, reaching equilibrium within 3 h. The Pb²⁺ adsorption behavior followed a proposed two-stage kinetic model, while the isotherm data fitted well with the Langmuir model, yielding a maximum adsorption capacity of 1012.27 mg/g. The adsorption mechanism primarily involved ion exchange, surface complexation, and dissolution-precipitation. These findings highlight the significant potential of FeHAP-40 as an efficient adsorbent for industrial heavy metal wastewater treatment.