Removal of Fluoride Ions from Water by Kolmé Clay

The present study was carried out with Kolmé clay in Liptako. X-rays diffraction results suggest that kaolinite was the predominant phase in this clay. The zero charge point of the pHpzc clay is about 7.1. The adsorption value and the percentage of fluoride ion removal by the clay increase up to a contact time of 1 h. Beyond this value, however, the fluctuation varies very little. This adsorption value increases with the fluoride ion concentration of the solution. However, it decreases considerably as the pH increases. The process of elimination of fluoride ions is done in three steps, including the diffusion of fluoride ions on the surface of the clay, the migration of fluoride ions from the surface of the clay to the active intra-particle sites and finally the chemisorption of fluoride ions on the active sites. The study of the sorption equilibrium of fluoride ions for the different concentrations indicates that the adsorption process appears to be both monolayer and multilayer and corresponds well to the Langmuir and Freundlich models. The fluoride ion adsorption kinetics can be fitted to the first and pseudo second order Lagergren models. The different velocity constants reflect a slow diffusion of fluoride ions, so this clay can be used in water defluorination.