In the desulfurization of gas resulting from the burning of coal generally are used limestone sorbents that react readily with SO2, depositing it in the ash. The literature also seeks to explanations about the mechanism involved and the changes that occur in the particles during the reaction. In this process TGA studies provide important information for the simulation of the atmosphere and process control. This study analyzed the curves TGA/DTA and TGA derivative curves for two Brazilian limestones: calcitic and dolomitic. There was a different behavior in oxy-combustion for sorbents containing higher content of impurities. Calcination profile to dolomitic marble in TGA curves was clearly distinguished into two steps. The calcination of dolomitic marble generates a compact microstructure, but with a few large pores on the surface that favors the exit of the gases from calcite decomposition. The absence of these impurities in calcitic marble favored cracks in the surface due to the pressure of CO2 the particle, resulting in a large and uniform porosity. (C) 2013 Elsevier B.V. All rights reserved.