Biomass conversion of waste oyster shells into calcium phosphate/carbonate adsorbents for efficient manganese removal

Abstract The effective removal of manganese (Mn 2+ ) from water is essential to reduce pollution and protect public health. This study focused on developing a low‐cost adsorbent using Pacific milk oyster shells, which were treated through preheating and phosphatization. This process resulted in a mixture of calcium phosphate and carbonate with improved adsorption properties. We evaluated the characteristics of the waste oyster shells using techniques such as scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and adsorption analysis. Phosphatized oyster shells (POS) showed peaks of both hydroxyapatite and calcite. This material demonstrated a high adsorption capacity of 76.92 mg g −1 , which outperforms many natural and treated adsorbents. The kinetics of adsorption were best explained by a pseudo‐second‐order (PSO) model, indicating that chemisorption is the primary mechanism at work. Given its cost‐effectiveness, high efficiency, and environmental sustainability, this adsorbent appears to be a promising solution for manganese removal in water treatment applications. Future studies should investigate its performance in real wastewater systems and explore possibilities for regeneration and reuse.