The adsorption of fluoride from aqueous solutions by Fe, Mn, and Fe/Mn modified natural clinoptilolite and optimization using response surface methodology

Natural clinoptilolite was modified using iron, manganese, or iron-manganese for adsorption of fluoride from aqueous solutions. Natural and modified clinoptilolite samples were characterized by X-ray fluorescence spectrometry, scanning electron microscope, X-ray diffraction, and Brunauer–Emmett–Teller. For all modified clinoptilolite samples, the time required to reach equilibrium was determined as 5 hr. The effects of adsorbent dose, pH, and initial fluoride concentration for fluoride adsorption were determined using the Box–Behnken Design. Maximum fluoride removal efficiency was 80.23% at the solution pH of 11, iron-modified clinoptilolite amount of 1.08 g/50 ml and at the initial fluoride concentration of 2 mg/L. Fluoride adsorption on iron-modified clinoptilolite showed good compatibility with the Freundlich isotherm and the pseudo-second-order kinetic model. The adsorption capacity of iron-modified clinoptilolite was found to be 1.72 mg/g for the initial fluoride concentration of 50 mg/L. This study has shown that BBD is an effective and dependable method in determining the optimum conditions for fluoride adsorption. Practitioner points Response surface methodology is effective in determining the optimum conditions for fluoride adsorption using modified clinoptilolite. Fluoride adsorption on iron-modified clinoptilolite is well described Freundlich isotherm and follows pseudo-second-order kinetic model. Fluoride removal percentage not only depends on the adsorbent dose, but also depends on the initial fluoride concentrations. Regeneration process using acid solution is not very effective for desorption of iron-modified zeolite. The natural clinoptilolite is an effective and economical adsorbent for adsorption of fluoride.