Influence of calcination temperature on equine bone hydroxyapatite structure and lead adsorption efficiency
Douae Touareb, Souhayla Latifi, Sarah Saoiabi, Lamiaa Habraji, Othmane Hammani, Khalil Azzaoui, Shehdeh Jodeh, Sobhi Yaghi, Rachid Sabbahi, B. Hammouti, Sanaâ Saoiabi, Sanaâ Saoiabi, Sanaâ Saoiabi
Abstract
Lead (Pb²⁺) contamination in aquatic environments represents a serious global threat due to its toxicity, persistence, and non-biodegradable nature. In this study, hydroxyapatite (HA) was synthesized from equine scapula bone and investigated as a low-cost, sustainable adsorbent for Pb²⁺ removal from aqueous media. HA was thermally treated at 100 °C, 500 °C, and 900 °C to assess the effect of calcination on physicochemical and adsorption properties. Characterization techniques including XRD, FTIR, SEM/EDX, TGA and XRF confirmed structural and compositional evolution with temperature. Among the samples, HA-500 exhibited the highest adsorption performance, achieving 99% Pb²⁺ removal and a maximum capacity of 50 mg/g under optimal conditions (0.25 g dose, 20 mg/L initial Pb²⁺ concentration). Kinetic studies followed a pseudo-second-order model (R² > 0.999), and equilibrium data were best described by the Freundlich isotherm (R² = 0.9839), indicating multilayer adsorption on heterogeneous surfaces. Thermodynamic analysis revealed that Pb²⁺ adsorption is spontaneous and exothermic, with negative Gibbs free energy values and positive entropy changes, confirming increased randomness at the solid-liquid interface. Furthermore, regeneration studies showed that HA-500 retained 73% of its efficiency after three cycles. These findings demonstrate the potential of equine bone as a novel bio-based source of hydroxyapatite for efficient and sustainable heavy metal remediation.