Efficient Fluoride Removal Using Cerium-Modified Red Mud: Adsorption Mechanism, Interference Resistance and Environmental Safety

A cerium-modified red mud adsorbent (Ce-RM) was prepared from industrial red mud waste by acid activation, cerium-salt treatment and calcination, and applied to fluoride removal from aqueous solutions. Batch adsorption tests examined the effects of initial fluoride concentration, pH, adsorbent dosage, contact time and coexisting ions. SEM, BET, XRD, FTIR and XPS were used to characterize the morphology, pore structure, crystalline phases and surface chemistry of Ce-RM and relate these features to fluoride uptake. Ce-RM removed more than 97% of fluoride at an initial F– concentration of 20 mg·L–1, pH 3 and a dosage of 0.4 g·L–1, with an equilibrium adsorption capacity of about 56 mg·g–1. The adsorption kinetics followed the pseudo-second-order model. The equilibrium data fitted both Langmuir and Freundlich models, with Freundlich giving the better fit, indicating heterogeneous surface adsorption dominated by multilayer uptake with partial monolayer adsorption. FTIR and XPS results suggested that ligand exchange, Ce–F complexation and electrostatic attraction contributed to fluoride removal. Real wastewater tests showed good resistance to interference, supporting Ce-RM as a promising waste-derived adsorbent for fluoride-containing industrial wastewater.