Synthesis optimization and fluoride uptake properties of high capacity composite adsorbent for defluoridation of drinking water.

A novel low cost composite adsorbent has been successfully synthesized from waste eggshell (ES), alum, and chitin for removal of excess fluoride from drinking water. Synthesis of chitin based adsorbent (CBA) was optimized by varying different synthesis parameters such as alumina loading, ES:chitin ratio, calcination temperature, calcination time, shaking time, drying temperature, and washing time. CBA is a composite type material having heterogeneous phases of Ca(OH)₂, Al(OH)₃, Al₂O₃ encapsulated with carbon, Al(OH)₃ and Al₂O₃ deposited on carbon and Al₂O₃. Presence of multiple phases with prominent presence of crystalline as well as amorphous phases of alumina has been substantiated by using XRD and SEM analysis. The elemental composition of material and EDX also suggests composite nature of material with different phases. The SEM image of CBA reveals the presence of both coarse and fine particles with irregularly shaped particles of alumina agglomerates adhering to calcite particles of ES. Defluoridation performance was systematically studied for CBA, which has outperformed several reported adsorbents with its higher adsorption capacity of 30.3 mg g⁻¹. No significant influence on the percent fluoride removal was observed in presence of Cl⁻ [ABSTRACT FROM AUTHOR]