Efficient phosphate removal from water with red mud‐derived <scp>LDH</scp> ‐biochar as a strategy for sludge and industrial waste valorization

Abstract BACKGROUND Excess phosphate in aquatic systems accelerates eutrophication and poses serious ecological risks. However, the adsorption performance of many existing adsorbents is limited by low capacity, slow kinetics, and instability arising from inconsistent or low‐quality feedstocks. To address these challenges, a sustainable hybrid adsorbent was developed by integrating magnesium–iron–aluminum layered double hydroxides (LDHs) with sludge‐derived biochar, using Fe 3+ and Al 3+ ions recovered from red mud as LDH precursors. RESULTS The Mg–Fe/Al LDH@biochar composite demonstrated a maximum phosphate adsorption capacity of 119.7 mg/g at 308 K and pH 4. More than 80% of phosphate was removed within the first 10 min, and the adsorption kinetics followed the pseudo‐second‐order model with a high rate constant and an excellent correlation coefficient. Isotherm fitting showed strong agreement with the Freundlich model, indicating heterogeneous multilayer adsorption. Structural analyses confirmed the formation of a lamellar LDH phase with abundant active metal sites, supporting uptake mechanisms dominated by electrostatic attraction, anion exchange, ligand substitution, and surface precipitation. CONCLUSION This study presents an efficient and sustainable strategy for phosphate removal, demonstrating high adsorption capacity, rapid kinetics, and stable performance. The use of red‐mud‐derived metal ions and municipal sludge for composite synthesis provides a feasible pathway for solid‐waste valorization and promotes environmentally responsible water‐treatment technologies. © 2026 Society of Chemical Industry (SCI).