Development by co-grinding of a magnetic activated carbon/hydroxyapatite composite: Cu(II) adsorption potential and regeneration performance

This study investigates the efficiency of copper ions adsorption from aqueous solutions using magnetized marine-derived materials. Three adsorbents were synthesized: magnetized activated carbon (MCA) obtained from brown algae of the Sargassaceae family, magnetized hydroxyapatite (MHAP) derived from purple sea urchins, and a magnetized composite (MCO) combining organic and inorganic matrices with a mass ratio of 1:1 were prepared via the co-grinding method. The adsorbents were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), BET surface area analysis, and X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). FTIR Fe–O bands, the XRD magnetic-phase peak near 35°, and SEM–EDX evidence of iron-rich particles collectively confirm the successful magnetization of the materials. The BET surface areas were 218.08 m2.g−1(MCA), 80.25 m2.g−1 (MHAP), and 145.24 m2.g−1(MCO). Kinetic data followed the pseudo-second-order model (R2 > 0.999), and a thermodynamic study showed that copper adsorption is a spontaneous and endothermic process for all materials. Isotherms for MHAP and MCO fitted well with the Langmuir model, while the Freundlich and Temkin models better described MCA. Error analysis using χ2 and RMSE confirmed the high reliability of the model fits. Among the tested adsorbents, MCO showed the highest copper adsorption capacity (106.83 mg/g ± 0.084), followed by MHAP and MCA. Desorption using 0.1 N HCl demonstrated good material stability and reusability over four cycles. Overall, these findings indicate that magnetized marine adsorbents particularly the magnetic composite are promising, cost-effective, and environmentally friendly candidates for the removal of copper ions from contaminated water.