Preparation of a cost-effective modified red mud-based adsorbent and its defluoridation performance

In order to solve the critical issues of the environmental risks and waste valorization of industrial solid waste red mud (RM), it was pretreated with H₂SO₄/H₂O₂ to obtain activated red mud (RM1). Subsequently, cerium (Ce) was loaded onto RM1 via a liquid-phase deposition method to develop a novel modified red mud-based adsorbent (Ce/RM1). The surface morphology and structure of Ce/RM1 were investigated via SEM, XRD, FTIR, and BET. Batch adsorption tests were conducted to evaluate the effects of initial solution pH value, contact time, adsorbent dosage, and coexisting anions on the defluoridation efficiency of Ce/RM1. The results show that the specific surface area of Ce/RM1 (157.643 m²·g⁻¹) is 8.518 times higher than that of RM. The highest fluoride removal rate (95.4%) can be achieved at initial pH of 5, adsorbent dosage of 1 g·L⁻¹, initial fluoride ions concentration of 10 mg·L⁻¹, and adsorption time of 30 min. The final fluoride ions concentration is 0.46 mg·L⁻¹, being much lower than the guideline fluoride emission limit of the WHO (1.50 mg·L⁻¹). The adsorption behaviors of fluoride ions on Ce/RM1 are better fitted with Langmuir isotherm and Pseudo-second-order kinetic model, and the maximum adsorption capacity is 14.1864 mg·g⁻¹. Ce/RM1 exhibits effective removal of fluoride ions in actual industrial wastewater treatment, and the final fluoride ions concentration is below 1 mg·L⁻¹ after adsorption. The present work establishes an integrated strategy that achieves both waste RM valorization and deep treatment of fluoride-containing wastewater.