Comparison of the removal behavior of fluoride by Fe3+ modified geomaterials from water

In the present work geomaterials (Fe3+ modified clinoptilolite (C-Fe), Fe3+ modified clinoptilolite heated at 200 degrees C (C-Fe 200), montmorillonite (M) and Fe3+ modified montmorillonite heated at 200 degrees C (M-Fe 200)) were studied to evaluate their efficiency on the removal of fluoride from water. Clinoptilolite (C) and montmorillonite (M) were treated with Fe3+ under reflux conditions and heated at 200 degrees C in order to improve their adsorption properties. They were characterized before and after fluoride adsorption by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Adsorption experiments were carried out in batch systems considering the effect of contact time, initial concentration of fluoride and initial pH. Experimental data were well adjusted to pseudo-second order kinetic model that assumes chemical interaction between adsorbent and adsorbate. Fluoride adsorption on C-Fe and M-Fe 200 were well described by a linear isotherm equation where the adsorption capacity increases as the initial fluoride concentration increases. The adsorption of fluoride by C-Fe 200 was described by Freundlich model that suggests a multilayer adsorption and the isotherm of M was well fitted to Sips model indicating a heterogeneous surface of the material. The adsorption capacities of the materials followed the order: M > C-Fe > C-Fe 200 approximate to M-Fe 200. Finally, the possible mechanism of fluoride adsorption was also discussed.