Evaluation of Raw and Calcined Eggshell for Removal of Cd 2+ from Aqueous Solution

The potential use of egg shell and calcined egg shell as adsorbent was evaluated and compared to remove Cd2+ from aqueous solution. The samples were characterized using Thermogravimetry and Differential Thermal Analysis (TG/DTA), Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD), Energy Dispersive X-ray Spectrometer (EDX) and BET Surface Analyzer. The batch-type adsorption experiment was conducted by varying diverse variables such as contact time, pH, initial Cd2+ concentrations and adsorbent dosage. The results showed that, under the initial Cd2+ concentrations ranged from 25 to 200 mg g-1, the removal efficiencies of Cd2+ by egg shell powder (ESP) were decreased steadily from 96.72% to 22.89% with increase in the initial Cd2+ concentration at 2.5 g of dosage and 8 h of contact time. However, on the contrary to this, calcined egg shell powder (CESP) showed removal efficiencies above 99% regardless of initial Cd2+ concentration. The difference in the adsorption behavior of Cd2+ may be explained due to the different pH values of ESP and CESP in solution. Cd2+ seems to be efficiently removed from aqueous solution by using the CESP with a basicity nature of around pH 12. It was also observed that an optimum dosage of ESP and CESP for nearly complete removal of Cd2+ from aqueous solution is approximately 5.0 g and 1.0 g, respectively. Consequently, Cd2+ is more favorably adsorbed on CESP than ESP in the studied conditions. Adsorption data were applied by the pseudo-first-order and pseudo-second-order kinetics models and Freundlich and Langmuir isotherm models, respectively. With regard to adsorption kinetics tests, the pseudo-second-order kinetics was more suitable for ESP and CESP. The adsorption pattern of Cd2+ by ESP was better fitted to Langmuir isotherm model. However, by contrast with ESP, CESP was described by Freundlich isotherm model well.