Kinetics of fluoride removal from drinking water by ion exchange method

High concentrations of fluoride occurring naturally in ground or drinking water cause the bone disease fluorosis among local populations. Therefore, lowering of fluoride to a certain concentration in drinking water is required. One of the various methods applied for this purpose is ion exchange method. In this study, a strong basic ion exchange resin, Purolite-250, having the chemical form R-N(CH3)(2)C2H4Cl, was used for removing fluoride ions. In the experimental runs, fluoride solutions in various concentrations were prepared to remove fluoride ions at harmful levels to human health in some drinking waters and temperature, the ratio of resin/water, fluoride concentration, pH and the stirring speed were selected as influencing parameters. Fluoride removal increased with increasing ratio of resin/water and stirring speed, but decreased with increasing temperature and fluoride concentration. During ion exchange, the pH of solutions decreased about 0.1 pH units, attributable to the fact that fluoride ion was more basic than chloride ion. It was found that the removal of excess quantities of fluoride in drinking water is possible by ion exchange methodology with removal rates up to 70 % for 5 ppm of fluoride at 20 C and 400 rpm. The used resin was regenerated by a 4 % (in wt) solution of sodium chloride. On the other hand, it was investigated that the kinetics of fluoride removal from drinking water by ion exchange fitted well to a second order reaction equation as follows.