Fluoride removal in water using Kaolin and Eggshell powder blend adsorbents

Abstract

Fluoride contamination in water has emerged as a significant global concern due to its adverse health effects when consumed in excess. This study is focused on developing an eco-friendly, cost-effective adsorbent for fluoride removal using eggshells and kaolin. Adsorbent blends were prepared by mixing kaolin and eggshell powder in six different ratios, namely; 100:0, 80:20, 65:35, 50:50, 35:65, and 20:80. Cylindrical-shaped pellets were produced from each of the blends and subjected to the thermal treatment at 950 oC. Fluoride adsorption capacities of the pellets were investigated at different pH conditions (from pH 2 to pH 10) for a 5 ppm fluoride solution with 1 g of adsorbent dosage and 60 minutes of contact time. Pellets with a 50:50 ratio (CKE3) were found to be the most effective adsorbent considering the adsorption capacity and stability at all the studied pH conditions. At pH 6, CKE3 showed an adsorption capacity of 0.06 mg/g in comparison to 0.02 mg/g of kaolin-only pellets. XRD analysis indicated that CaCO3 in the adsorbent has converted to CaO after the calcination. Further batch experiments were carried out with CKE3 for adsorbent dosage, pH, contact time, and initial fluoride concentration. An adsorbent dosage of 4 g was capable of resulting a 53% removal of fluoride for a 5 ppm solution after 60 minutes of contact time. The pseudo-second-order kinetic model exhibited the best fit in the kinetic study. The isotherm data were studied for Langmuir and Freundlich models and the results were satisfactorily fitted with Langmuir isotherm.