Adsorption Isotherms on Fluoride Removal: Batch Techniques

The ability of cynodon dactylon based thermally activated carbon to remove fluoride from aqueous solution has been investigated. The batch adsorption studies were carried out at neutral pH as the functions of contact time, adsorbent dose, adsorbate concentration, temperature and effect of co-anions, which are commonly present in water. The rate of adsorption was rapid during initial 105 minutes and attained equilibrium. Adsorption isotherms have been modeled by Langmuir, Freundlich, Temkin and Redlich–Peterson isotherms. The data indicate that prepared adsorbent surface sites are heterogeneous in nature and that fits into a heterogeneous site binding model. The present system followed the Redlich–Peterson isotherm as well as Langmuir adsorption isotherm model. The enthalpy change (∆H°) and entropy change (∆S°) for the adsorption reaction are calculated as +8.725 kJ/mol and +0.033 J/mol K respectively. The adsorption is endothermic in nature. Instrumental analysis XRD, FT-IR and SEM gives the conformation about the fluoride binding ability of adsorbent. Field studies were carried out with the fluoride containing water sample collected from a fluoride-endemic area in order to test the suitability of the sorbent at field conditions and obtained good success rate.