Removal of fluoride ions by batch electrodialysis

Suitability of conventional batch electrodialysis to fluoride removal from aqueous solutions has been investigated. The experiments were conducted with the use of laboratory installation PCCell BED-1 System at a constant current density (1.56 or 2.34 mA/cm2). The influence of initial fluoride and salt (NaCl) concentration, as well as the presence of organic matter on the process performance was studied. It was found that the separation efficiency increased upon decrease of initial fluoride content in model solutions. Permissible final concentration of fluorides in the product water (1.5 mg/dm3) was obtained for experiments with solutions of initial fluoride concentration equal to 5 mg F–/dm3 and 10 mg F–/dm3. The presence of humic acids in fluoride solutions subjected to electrodialysis treatment has no adverse effect on the defluorization and desalination efficiency. The calculated electrical energy demand depended on composition of fluoride solution and varied from 0.121 to 0.895 kWh/m3.