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

Abstract

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 , Al 2 O 3 encapsulated with carbon, Al(OH) 3 and Al 2 O 3 deposited on carbon and Al 2 O 3 . 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 21 . No significant influence on the percent fluoride removal was observed in presence of Cl ions, respectively. CBA follows pseudo second order kinetic and fluoride adsorption mechanism was rather complex one, wherein both intraparticle diffusion and surface diffusion are involved in the rate-limiting step. Negligible leaching of Al 13 ions was observed. V C 2015 American Institute of Chemical Engineers Environ Prog, 34: 1576Prog, 34: -1585Prog, 34: , 2015