Efficiency of calcium carbonate from eggshells as an adsorbent for cadmium removal in aqueous solution

The presence of heavy metals in water resources brings hazard to health and the environment consid-ering that most of these cannot be degraded and may result in bioaccumulation in the food chain. Its removal from aqueous solution can relatively be done through adsorption, a known technique that efficiently reduces heavy metal concentration. This study investigated the applicability and efficiency of waste chicken eggshells as an adsorbent for the removal of Cadmium (Cd) heavy metal in aqueous so-lution. The adsorbent dose, contact time and initial concentration were the chosen variables of the study that were optimized through the Central Composite Design of the Response Surface Methodology using Design Expert 7.0 software. The result of the study showed that the chicken eggshells as an adsorbent could remove Cd in an aqueous solution up to 73%. The optimum adsorption capacity was 146 mg g(-1 )obtained at 150 mg L-1 initial concentration, 75 min contact time, 0.75 g adsorbent dose, and pH 6 at room temperature. Heterogeneous adsorption occurred during the process as revealed by isotherm studies with Freundlich model emerged having a higher coefficient of determination (R-2 = 0.91) than the Langmuir model (R-2 = 0.86). Overall, the study demonstrated that the chicken eggshell that is generally considered as wastes in large quantities could become an economically advantageous raw material for the removal of carcinogenic Cd from the water body. (C) 2018 Chinese Institute of Environmental Engineering, Taiwan. Production and hosting by Elsevier B.V.