Silica nanoparticles for the removal of fluoride from aqueous solution: equilibrium, isotherms, kinetics, and thermodynamics

Fluorine is one of the most active and electronegative elements of the periodic table that exists in different amounts and sizes in water, soil, and plants. The excessive use of this substance can cause many problems. The research work was an experimental laboratory study aimed to investigate the fluoride removal from aqueous solutions by silica nanoparticles. The effect of different variables such as pH (3-11), adsorbent dose (0.2-2 g/L), contact time (2-120 min), different concentrations of fluoride (2-10 mg/L), and temperature (283, 293, 303, and 313 K) were determined in batch condition. Also, kinetics, thermodynamics, and isotherms process were studied. The results of this study showed that maximum adsorption capacity in optimum conditions (pH = 3, the adsorbent dose of 0.2 g/L, the contact time of 10 min, and the initial concentration of 10 mg/L) was found to be 8.40 mg/g. Also, the adsorption process was an endothermic and spontaneous as well as the Dubinin-Radushkevich isotherm and pseudo-second-order kinetic is more consistent with adsorbing fluoride by the silica nanoparticles. This study indicated that silica nanoparticles can be used in optimum conditions as an effective, usable and inexpensive adsorbent for the fluoride removal in aqueous solutions which values are higher than the standard level.