Red mud-chitosan composite for dye pollution control: A low-cost solution for industrial waste valorization in developing countries

A novel composite adsorbent (CS-4) was synthesized by integrating industrial waste red mud with chitosan, demonstrating exceptional congo red (CR) dye removal efficiency (98.36 %) and a high adsorption capacity of 684.79 mg/g. The adsorption performance was systematically evaluated through equilibrium, kinetic, and thermodynamic analyses. Among tested isotherm models, the Freundlich equation (R² = 0.9895, at 298K) exhibited superior correlation with experimental data, revealing the dominance of multilayer adsorption on the heterogeneous CS-4 surface. Kinetic studies identified pseudo-second-order behavior (R² = 0.9858, at 298K), emphasizing chemisorption mechanisms including electrostatic attraction, hydrogen bonding, π-π interactions, and pore diffusion. Thermodynamic calculations confirmed the process spontaneity (ΔG < 0) and endothermic characteristics (ΔH > 0) of the process. The composite's hierarchical porosity (BET surface area = 39.53 m²/g) and regenerability (92 % efficiency retained after five cycles) underscore its dual environmental benefit, valorizing hazardous RM waste while addressing dye pollution. These findings validate the dual environmental benefit of valorizing industrial waste while addressing dye pollution.