Kinetic analysis has been performed on TG and DTG diagrams of the forward reaction MnCO3⇌ MnO + CO2, recorded at different pressures of CO2 ranging form 2.6. 10−4 Pa to 26.6 kPa. The results obtained show that this reaction follows a first-order kinetic law, independently of the CO2 pressure used in carrying out the experiments. On the other hand, the activation energy increases on increase of the CO2 pressure, from 117 kJ/mol up to an asymptotic value of 292 kJ/mol at about 26.6 Pa. This finding cannot be explained by considering the influence of the reverse reaction of formation of MnCO3, for under the described experimental conditions the ratio
to zero. A mechanism that takes into account the adsorption of CO2 on the phase boundary has been proposed in order to interpret the results.