Study on the Adsorption Performance of Hydroxyapatite-Loaded Biochar for Cu

Hydroxyapatite-loaded biochar (HAP–biochar) composites were synthesized using corn straw biochar (CSB) and chicken manure biochar (CMB) to improve Cu²⁺ removal from aqueous solutions. Composites with varying biochar:HAP ratios were prepared and characterized by SEM, which confirmed uniform HAP dispersion and enhanced porosity. Systematic testing identified the composition corresponding to biochar:HAP = 3:1 (designated CSB-1.5 and CMB-1.5; HAP ≈ 25 wt%) as optimal. Under pH 5.0 and an adsorbent dose of 0.05 g, CSB-1.5 and CMB-1.5 achieved maximum Cu²⁺ capacities of 82.06 and 98.09 mg·g⁻¹, respectively. Kinetic and isotherm analyses indicated that adsorption followed a pseudo- second-order model (R² ≈ 0.99) and was dominated by chemisorption via ion exchange and surface complexation; Elovich fitting supported heterogeneous surface behavior. Compared to single-component HAP or pristine biochar, the optimized composites combine improved HAP dispersion, abundant functional groups, and robust pore networks, delivering high removal efficiency and material stability. These features make the optimized HAP–biochar composites promising, low-cost adsorbents for practical heavy-metal remediation.