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.

Graphical abstractIn this study, protonated cross-linked chitosan particles (PCP) were prepared. Chitosan was molded in membranes, membranes were cross-linked, and then protonated, the resultant membranes were ground to obtain particles of 200-mesh size. These particles were very stable and can remove fluoride from aqueous solution due to big specific surface area and many positive charges. Besides, PCP would have good subsidence, and could be separated from solution rapidly after adsorption. Batch experiments were conducted to evaluate adsorption capacity and to determine the regeneration feasibility of PCP.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► PCP was prepared with chitosan membrane cross-linked and protonated. ► This adsorbent has good subsidence. ► The maximum amount of fluoride adsorbed was 8.10 mg g−1 at 20 °C. ► The equilibrium data fitted with Langmuir and Freundlich isotherm models well. ► The adsorption of fluoride onto this adsorbent was attributed to physical adsorption.