Sodium iodide modified-red mud for efficient adsorptive removal of methylene blue from wastewater: isotherm modeling and adsorption

Abstract

The discharge of synthetic dyes and the improper disposal of industrial red mud (RM) pose serious environmental challenges worldwide. This study introduces an innovative adsorbent, RMI, synthesized by functionalizing raw red mud with sodium iodide (NaI) to remove methylene blue (MB) from aqueous solutions effectively. Comprehensive characterization using XRD, TG, DTG, SEM, and BET analysis confirmed the enhanced structural and surface properties of the RMI composites. Batch adsorption experiments revealed that RMI-5 achieved a maximum MB removal capacity of 245.2 mg g⁻¹ under optimal conditions. The adsorption process followed pseudo-second-order kinetics (R² = 0.99), suggesting that chemisorption is the dominant mechanism, while the Langmuir isotherm model best described the equilibrium behaviour. Thermodynamic analysis showed that MB adsorption was spontaneous and exothermic. The primary adsorption mechanisms include hydrogen bonding, electrostatic attraction, and pore diffusion. These findings demonstrate the high efficiency and sustainability of NaI-modified red mud as a low-cost, high-performance adsorbent for dye-contaminated wastewater treatment. Hence, this study illustrates the efficient elimination of contaminants, particularly methylene blue, from aqueous solutions with NaI-modified red mud composites. The results underscore the potential for practical applications in water treatment technologies for dye elimination and other pollutant remediation techniques.