Removal of fluoride ions from aqueous solutions using protonated cross-linked chitosan particles

Protonated cross-linked chitosan particles (PCP) were used to remove fluoride from aqueous solution. PCP were characterized using FTIR, XRD and SEM. Adsorption isotherms, the effects of adsorbent dosage, pH, contact time and co-existing anions on adsorption process, and the regeneration ability of PCP were investigated. The optimum pH value was achieved at 7. The equilibrium was attained in 40 min. The presence of co-existing anions weakened fluoride adsorption on PCP, especially the high valence anions such as sulfate. The equilibrium data fitted well with Langmuir and Freundlich isotherm models, and the maximum monolayer adsorption capacity was 8.10 mg g−1 at room temperature. 0.1 M HCl was identified as the best eluent. Electrostatic attraction was the main driving force for fluoride adsorption.