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 ◦C. Fluoride adsorption capacities of the pellets were investigated at different pH conditions (from pH 2 to pH 10) for a 5 mg/L fluoride solution with 1 g of adsorbent dosage and 60 min 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 compared to 0.02 mg/g of kaolin-only pellets. XRD, TGA-DSC, EDX and SEM analysis were used to characterize the adsorbent. XRD analysis showed that the raw adsorbent contained phases of CaCO3 and kaolinite, whereas the calcined material comprised Ca(OH)2 and metakaolinite. 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 in a 53% removal of fluoride for a 5 mg/L solution after 60 min of contact time. Pseudo-first-order and pseudo-second-order kinetic models were applied in the study, and pseudo-second-order exhibited the best fit. The isotherm data were studied for Langmuir and Freundlich models, and the results were satisfactorily fitted with Langmuir isotherm.