CO2 capture in a calcium looping (CaL) system is one of the most promising technologies for climate change mitigation. The main reactors in these systems (carbonator and calciner) operate in conditions where the reaction of CaO with the SO2 resulting from the combustion of coal is inevitable. This work reports on the sulphation of CaO under a range of variables that are typical of reactors in CaL systems. Furthermore it is demonstrated that the number of calcination carbonation cycles changes the sulphation patterns of the CaO from heterogeneous to homogeneous in all the limestones tested. For 50 carbonation calcination cycles and for particle sizes below 200 mu m, the sulphation pattern is in all cases homogeneous. The sulphation rates were found to be first order with respect to SO2, and zero with respect to CO2. Steam was observed to have a positive effect only in the diffusion through the product layer controlled regime, as it leads to an improvement in the sulphation rates and effectiveness of the sorbent. Most of the experimental results of sulphation of highly cycled sorbents under all conditions can be fitted by means of the Random Pore Model (RPM) assuming that the kinetics and diffusion through the product layer of the CaSO4 are the controlling regimes. (C) 2015 Elsevier Ltd. All rights reserved.