Adsorption of fluoride from aqueous solution by using hybrid adsorbent fabricated with Mg/Fe composite oxide and alginate via a facile method

Present study deals with the fluoride removal from aqueous solution by using hybrid adsorbent fabricated with Mg/Fe composite oxide and alginate via simple blending method. The fluoride adsorption capacity of the resulting hybrid adsorbent was systematically evaluated with batch adsorption experiments in various operation parameters including initial pH, adsorbent dose, co-existing anions, contact time and temperature. The results indicated the hybrid adsorbent kept good adsorption performance for fluoride over a broad pH range and even in the presence of co-existing anions. With adsorbent dose of 10 g/L, 96.6% of fluoride ion can be reduced from aqueous solution of 10 mg/L at natural pH. The adsorption of fluoride onto the adsorbent is found to be a multi-step rate-limiting reaction with exothermic nature and follows pseudo-second order kinetics. Thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) coupled with energy dispersive spectrum (EDS) and Fourier transform-infrared spectroscopy (FT-IR) were employed to characterize the hybrid material and explore the possible adsorption mechanism. It is suggested that ligand exchange and electrostatic interaction played an important role in the process of fluoride adsorption. Regeneration of adsorbent was also conducted, and 83.3% of the original fluoride removal rate was maintained after three regeneration cycles.