Abstract
Contact time, pH, fluoride concentration, and sorbent dose effects on the removal of fluoride ions by a carbonaceous material obtained from pyrolysis of sewage sludge (CM) were evaluated. Equilibrium was reached after 18 h of contact time and the maximum sorption was found at pHeq = 7.06 ± 0.08, which corresponds to the zero charge point of the CM. The highest efficiency in the sorption system for fluoride removal (2.84 ± 0.03 mg F− \( g_{{CM}}^{{ - 1}} \)) was found with 0.4 gCM L−1 and with 20 gCM L−1, 82.2 ± 0.5% of fluoride was removed. The kinetic data of the process could be fitted to the pseudosecond order and the intraparticle mass transfer diffusion models, whereas isotherm to the Langmuir–Freundlich equation. These results indicate that the mechanism is chemisorption on a heterogeneous material. Fluoride ions were best partially desorbed using a bicarbonate ions solution and the material was partially regenerated by using a solution of HCl (pH = 1).
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