Elimination of fluoride ions in water for human consumption using hydroxyapatite as an adsorbent

In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD (R) has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of F-18 radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0-7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g.