The reversibility of the reaction CaCO₃ ⇄ CaO+CO₂

Abstract The reversibility of the reaction CaCO 3 ⇌ CaO+CO 2 has been examined through a large number of cycles (up to 40), mainly at 866 °C. The decomposition to the oxide is always 100% but the reactivity of the oxide so formed to carbon dioxide falls off markedly after a rapid initial reaction. There is a large increase in surface area on going from the non‐porous calcium carbonate to the oxide and this is due to the formation of pores, mostly very small (< 4 nm). The fast component of the back reaction is a surface reaction and the subsequent slow reaction is controlled by the slow diffusion of carbon dioxide through the newly formed carbonate layer. The reversibility of the reaction decreases with the number of cycles, rapidly at first and then more slowly: the first effect is probably due to loss of pore volume in the oxide and the second to sintering of the carbonate.