The role of petrography on the thermal decomposition and burnability of limestones used in industrial cement clinker

The present research examines the influence of the petrographic features on the thermal decomposition and burnability of three limestones, the main raw materials for Portland cement-making. A detailed characterisation of the limestones has been performed by means of optical microscopy and X-Ray Powder Diffraction. The carbonate thermal decomposition was conducted under isothermal conditions by means of in situ High Temperature X-Ray Powder Diffraction and the heated samples were further investigated by Scanning Electron Microscopy. Three kiln feeds were then prepared and submitted to burning trials and the temperature of occurrence of the main clinker phases was investigated as well as the content of the uncombined CaO in the heated samples was determined by using the Franke method. The results attest that the microfabric, a combination of depositional and diagenetic features, drives the kinetics of the thermal decomposition of the selected limestones as well as it appears to influence the temperature of crystallisation of the main clinker phases and the uncombined CaO content in the final clinker. In particular, the limestone with the lowest micrite to sparite ratio (1) exhibits the lowest Apparent Activation Energy (E a ) value and the highest rate of calcination and (2) requires a lower temperature for observing the clinker phases crystallisation and has the lowest content of uncombined CaO in the final clinker, thus reflecting a high burnability of the limestone.