Reduction of Fluorine in Water Using Clay Mixed with Hydroxyapatite
Auphedeous Y. Dang-i, Apea O. Boansi, Mary-Magdalene Pedevoah

Abstract
There was a gradual increase in the adsorption capacity of the Clay-HAp (C-HAp) mixture for the fluoride ions as time increased. A maximum adsorption capacity of 0.995mg/g and fluoride removal of 99.5% of the initial fluoride concentration was observed at the time (30 min) of the maximum adsorption. C-HAp mixture showed that the equilibrium concentration of fluoride decreased with increasing adsorbent dose. The maximum adsorption capacity was found to be 18.409 mg/g for the adsorbent dose of 1.25 g/L. The fluoride removal efficiency remained the same from pH 2-4 and increased steadily to pH 6, hence maximum adsorption was observed at pH of 6. As the initial fluoride concentration increased, the adsorption capacity of the C-HAp also increased. . The equilibrium data for the adsorption fitted the Freundlich more than Langmuir isotherm models. The adsorption mechanism was analyzed for pseudo first and second order reactions. The values of correlation coefficient (R2 = 1.00, 0.9999 and 1.00) of the second order model for the three concentrations (5.0, 10.0 and 15.0 mg L-1) were equal or closer to unity than the first order model.

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