[en] High amounts of sulfur dioxide (SO₂) are produced by burning of fossil fuels in air in excess, a pollutant agent which, once reaching the atmosphere, transforms in sulfuric acid . One solution of diminishing the SO₂ releases is injection of powder limestone in the oven. The reaction CaCO₃ = CaO + CO₂ gives rise to porous calcium oxide grains which react with SO₂ in the presence of oxygen. As a result, calcium sulphate is formed by the reaction CaO + SO₂ + 1/2O₂ = CaSO₄. This technology is convenient for thermal power plants due to small investments and simple operation. However,the desulfurization degree is reduced and the process kinetics is still unelucidated. In this work, the kinetics of the second reaction is studied by thermogravimetry with CAHN TG-121 device. Conversion-time kinetic diagrams were generated for five granulometric classes of Ca CO₃ with an average diameter of 25-900 μm. The measurements were carried out at 973 K - 1173 K and gas flow speeds of 0.023 - 0.0277 m/s. The kinetic parameters of the external mass transfer, solid crust diffusion and chemical reaction were determined. The influence of external mass transfer in all operation conditions is insignificant. The influence of solid crust diffusion is dominant even for the smallest particles (25 μm). Therefore, the process is described by a combined macrokinetics reaction-diffusion model, where the resistance to the diffusion is about 80% of the total resistance. Complementary structure determinations using structural models are required for the solid undergoing the reaction in order to rigorously identify the enhancing factors of the process. (authors)