Equilibrium and kinetics of adsorption of fluoride onto zirconium impregnated cashew nut shell carbon

Zirconium impregnated cashew nut shell carbon was studied to assess its capacity for the adsorption of fluoride from aqueous solutions. The dependence of the adsorption of fluoride on the pH of the solution has been studied to achieve the optimum pH value and a better understanding of the adsorption mechanism. The influence of addition of the co-existing ions on the adsorption of fluoride was also studied. Adsorption isotherms have been modeled by Langmuir, Freundlich and Redlich–Peterson equations and their constants were determined. Pseudo-first- and second-order equations were used to describe the adsorption rate of fluoride and adsorption rate constant was calculated. A mechanism involving three stages, viz.; external surface adsorption, intra-particle diffusion and final equilibrium has been proposed for the adsorption of fluoride onto adsorbent material. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of sorption. 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.