Fluoride removal by Donnan dialysis with anion exchange membranes

The removal of fluoride from diluted solution with Neosepta AHA anion exchange membrane has been studied by Donnan dialysis. The effects of concentration, pH, and accompanying anion on feed phase and receiving phase composition were investigated. Neosepta AHA anion exchange membrane was used for the removal of fluoride and the flux of fluoride with respect to the concentration, pH, and the effect of the counter-ions (HCO3−, Cl−, SO4−2) were obtained between 34–136.10−7 (m.mol.cm−2.s−1). The effect of the fluoride flux increased with increasing of concentration on the feed phase. The flux of fluoride was found to be higher at higher pH in the feed phase. In addition, the accompanying counter-anions also influenced the flux of fluoride and the order of flux was founded as HCO3−>Cl−>SO4−2. The results obtained for AHA membrane were compared with Neosepta AFN and polysulfone SB-6407 membranes. The transport efficiencies of the membranes were found to be in the order AFN>AHA>SB-6407.

The results show that anion exchange membranes allow defluoridation, particularly the AFN, which is the most efficient membrane with respect to AHA and SB-6407. It was observed that the receiver phase composition of hydrogen carbonate ions, compared to other ions, was the most efficient parameter for fluoride transport. This can be explained by considering the basic characterization of hydrogen carbonate ions. The flux value for both membranes was different and the flux of AFN was higher by about 4-fold than that of AHA. This is due to the different structure of the membrane. Ion concentration has effect and the fluoride flux increased with the increasing of concentration on the feed phase. It was observed that the influence of pH on the flux of fluoride is negligibly small. In addition, the accompanying ions also influence the flux of fluoride and the order of HCO3−>Cl−>SO4−2.