Phase transformations in clays and kaolins produced by thermal treatment in chlorine and air atmospheres

a study of the phase transformations generated by chlorine during the calcination of clays and kaolins is presented. the original samples and residues of the thermal treatment carried out in air and chlorine atmospheres are analyzed at different calcination times and temperatures. sample characterization was performed by x-ray diffraction (xrd), scanning electron microscopy (sem) and x-ray microanalysis (epma). the results indicate that in samples of kaolin and ball clays the α -alumina phase (corundum) appears in the first chlorination stage. this phase disappears at longer chlorination times due to the volatilization of alcl3. it is also observed that the kaolinite calcination in chlorine atmosphere favors the formation of the mullite phase. other crystalline phases present in minerals, such as anatase and iron oxides, practically disappear after the samples chlorination.