Adsorption Equilibrium, Kinetics, and Thermodynamic Studies of Fluoride Adsorbed by Tetrametallic Oxide Adsorbent

This study investigated the performance of fluoride adsorption onto a specific tetrametallic oxide adsorbent Fe–Al–Ce-Ni (FACN) and the effect of temperature on adsorption performance. The adsorption performance was determined by adsorption equilibrium, kinetics, and thermodynamic parameters. The adsorption, kinetic, and thermodynamic parameters were compared alternatively. The fluoride adsorption capacity was obtained from four different adsorption isotherm models, namely, Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R), and Freundlich was found to best fit model. Fluoride removal rate using adsorption (0.27 min–1) was obtained faster than reactive adsorption (0.04 min–1). Several thermodynamic parameters such as enthalpy, Gibbs free energy, entropy (ΔS > 0), and adsorption activation energy were calculated which demonstrated the feasibility and spontaneity (ΔG < 0) and exothermic nature of (ΔH < 0) the fluoride adsorption process. The adsorption process was controlled by a physical mechanism, and the maximum adsorption capacity was found to be 250 mg/g. To our knowledge, this is the first report on the synthesis of tetrametallic oxide adsorbent for fluoride adsorption, and the feasibility of the adsorption process was ratified by three van't Hoff plots.