Application of an Integrated Ion Exchange/Microfiltration Process for Water Defluoridation

Abstract High efficiency and key parameters have been established for an integrated water treatment (ion exchange/microfiltration) process for the removal of F– ions by using a finely disperse fraction (≤0.063 mm) of fluoride-selective resin Hydrolite ZG F 860 and a tubular microfiltration ceramic membrane created from clay materials by the Dumansky Institute of Colloid Chemistry and Water Chemistry of the National Academy of Sciences of Ukraine. It has been shown that the application of this process enables water defluoridation to the maximum permissible concentration (MPC) of F– ions in potable water at their initial concentration from 1.7 to 2.9 mg/dm3 (pH, 7.4–7.7; operating pressure, 0.75 MPa; process duration, up to 8 h) by adding 2–4 g/dm3 of fluoride-selective resin to the solution. To achieve permissible F– concentrations in potable water during its defluoridation under similar conditions at an initial F– concentration of 3.0–3.55 mg/dm3, it is necessary to add 5–10 g/dm3 of this resin to the solution to be treated. The obtained results can be explained by that F– ions are binded by the active aluminum groups present on the resin surface into stable complex aluminum fluoride compounds to remove F– ions and reduce their concentration in the water with the further retention of the ion-exchange resin by the ceramic membrane in the form of a finely disperse fraction. At the same time, the volumetric flux of the ceramic membrane continuously decreases from 0.44 to 0.04 m3/(m2 h) due to the significant clogging of pores by the fine resin fraction. The combination of microfiltration and ion exchange is a promising approach to the efficient defluoridation of natural waters due to that, during water treatment, not only the spent ion-exchange resin, but also mechanical impurities, fine suspended solids, colloidal and organic compounds, and microbiological contaminants are removed from them.