Application of freeze concentration for fluoride removal from water solution

A study on fluoride removal by freeze concentration was conducted using deionized and added dissolved substances to the water samples. Fluoride removal characteristics were evaluated in a batch system with reference to changes in freezing temperature, initial concentration, freezing rate and total dissolved solids (TDS). Fluoride removal was found to be freeze temperature-dependent and the optimal temperature range was −15 °C to approximately −20 °C. Fluoride removal rate ranged from 50 to 75% for added dissolved substances to water and from 75 to 85% for deionized water spiked with fluoride, which gives a more satisfactory result. The decline of salinity was consistent with the decline of fluoride concentrations. However, from the perspective of fluoride removal rate, TDS played an inverse role in the fluoride removal efficiency. The removal efficiency by freeze concentration was finally validated using the high fluoride groundwater samples collected from 5 monitoring wells in the field, which showed a good correlation. Our results show that freeze concentration is possible to develop as a feasible technology for fluoride removal from aqueous environment in remote and small areas.