Defluorination of wastewater by calcium chloride modified natural zeolite

Natural zeolite was chemically modified using calcium chloride to enhance its fluoride removal capability. Batch adsorption experiments were conducted to examine and optimize various operational conditions such as adsorbent dose, contact time, pH, effect of co-ions, and initial fluoride concentrations. Maximum fluoride adsorption capacity of CaCl2 modified-zeolite (CZ) was 1.766 mg g− 1 at an initial fluoride concentration of 100 mg L− 1. Kinetic study reveals that the fluoride adsorption by CZ follows both pseudo-second order kinetic and intra-particle diffusion models. The experimental data fitted well to both Langmuir and Freundlich adsorption isotherm. The ΔG0 and ΔH0 values suggest that the fluoride adsorption by CZ is spontaneous and endothermic in nature. Studies were also performed to understand the effect of some co-existing anions present in aqueous solutions. Results of this study demonstrated the effectiveness and feasibility of CZ for removal of fluoride ions from aqueous solution.

Research highlights
► CaCl2-modified natural zeolite (CZ) removes fluoride efficiently from wastewater;
► Operational conditions are optimized;
► Fluoride adsorption fits to both Langmuir and Freundlich adsorption isotherm;
► Fluoride adsorption by CZ is spontaneous and endothermic.