Sorption behavior of fluoride ions from aqueous solutions by hydroxyapatite

摘要

The effects of pH, contact time, fluoride-ion concentration, and the dose of sorbent on the sorption of fluoride ions by hydroxyapatite were studied. Equilibrium was reached in 16h of contact time and the maximum sorption of fluoride ions was in the pH_(eq) range between 5 and 7.3. The highest efficiency in the sorption system was determined by using 0.01 g of hydroxyapatite and 25 mL of solution. The pseudo-second order model described the kinetic sorption processes, and the Freundlich model, the sorption isotherm process. These results indicated that the mechanism was chemisorption on a heterogeneous material. Fluoride ions were partially desorbed using an alkaline solution.