Calcination of CaCO 3 is a process of producing CaO - a widely used substance in high temperature applications. However, the efficiency of the process depends on the variable involved and the assumption made. Therefore, this paper aims to illustrate the effects of few variables on calcination and carbonation reaction of CaCO 3 via thermo-gravimetric analyzer (TGA) in order to optimize the process. In the present work, cockle shells were used as CaCO 3 sources. The experimental variables i.e. particle size, heating rate, calcination and carbonation temperature were employed. A minimum of two runs of experiments for each variable were conducted and the standard deviation for all of the runs are found to be less than 1. Analysis of XRD, XRF and EDX indicates the conversion of CaCO 3 in cockle shells to CaO after calcination. The optimum adsorptive capacity of synthesized CaO for CO 2 at the optimum conditions is 0.72 kg CO 2/kg CaO. © 2012 Elsevier Ltd. All rights reserved.