Mechanism of growth of MgO and CaCO3 during a dolomite partial decomposition

The kinetics of the dolomite partial decomposition into MgO and CaCO3 have been investigated using isothermal and isobaric thermogravimetry (T = 953 K, CO2 pressure in the range 0.025–0.4 atm). The characterization of the reaction products using XRD, SEM and XPS indicated that fine particles of MgO are formed at the surface of the initial dolomite needles. The elucidation of the mechanism of growth and of the rate-limiting step was based on a series of experiments devoted first to verify the steady-state assumption (by coupling thermogravimetry to calorimetry), second to verify the existence of a rate-limiting step, and third to determine the variations of the areic growth reactivity, ϕ, in mol m− 2 s− 1, as a function of CO2 pressure. A growth mechanism in eight elementary steps, involving interface and diffusion steps has been proposed. By comparing the experimental results to the possible rate laws calculated from the mechanism on the assumption of a rate-limiting step, it was found that the growth of MgO and CaCO3 can be controlled by the diffusion of magnesium through the MgO phase surface.