Removal of Fe³⁺ ions from polluted water using heat-pretreated and H₃PO₄ modified oyster shells

Oyster shells pretreated by calcination at 500 °C and chemically modified with H₃PO₄ were used in this study to enhance surface reactivity for efficient removal of Fe³⁺ ions from polluted water. Characterization by SEM, XRD, and FTIR confirmed significant structural and chemical changes, including the formation of phosphate-containing compounds. Batch adsorption experiments revealed that modified oyster shells exhibited high Fe³⁺ removal efficiency, achieving near-complete removal (~100%) within 120 minutes. Kinetic modeling indicated that the adsorption process followed pseudo-second-order and Bangham models, suggesting chemisorption and intraparticle diffusion as dominant mechanisms. Isotherm analysis showed the best fit with Sips and Redlich–Peterson models, reflecting heterogeneous surface adsorption behavior. The removal of Fe³⁺ ions effectiveness of modified oyster shells as a low-cost, sustainable, and eco-friendly adsorbent for Fe³⁺ remediation, providing a promising approach to heavy metal pollution.