Abstract: Anatase titanium dioxide nanoparticles were employed for the adsorption of fluoride ions from aqueous solution. The process was studied in details by varying the pH value, adsorption time and temperature. The results showed that equilibrium was reached within 2.0 min at room temperature. The adsorption efficiency was over 97% at pH 2.0~10.0. Adsorbed fluoride ions were desorbed with 0.1 mol/L NaOH within 3.0 min, while the desorption efficiency could be up to 96%. The kinetic experimental data properly correlate with the second-order kinetic model. The apparent activation energy was calculated to be 6.85 kJ/mol. The overall rate process is mainly controlled by the intraparticle diffusion, while the boundary layer resistance cannot be ignored. The adsorption data could be well interpreted by the Langmuir and Dubinin-Radushkevich adsorption isotherms. The mean energy of adsorption was 4.26 kJ/mol at room temperature. The results show that ΔH0＞0 and ΔG0＜0 for the adsorption reaction, indicating that the adsorption process is a spontaneous and endothermic reaction. The co-existed ions such as HCO-3 and PO3-4, had greater effects on adsorption of fluoride ions. Removal efficiency of nano-TiO2 for fluoride ions obtained by dynamic adsorption is close to that obtained by the static adsorption.

Key words: fluorine ions, nano-TiO2, adsorption, dynamics, thermodynamics