CHARACTERIZATION OF CLAYS FROM “MINES MARITSA IZTOK” AS RAW MATERIALS FOR CERAMIC INDUSTRY

The chemical and phase compositions of the clays from coal mining were evaluated by XRF and powder XRD method, respectively. Hot Stage Microscope was used to estimate the thermal behaviour. In addition, the thermal losses of the clays after 1 h thermal treatment at different temperatures were measured. This preliminary analysis elucidates potential prospects for using some of clays as raw materials for ceramic industry. It seems that samples which are montmorillonite type are more plastic, while the others, where higher sand content is observed, and the drying shrinkage is negligible could be characterized as less plastic. The initial results for the thermal behaviour and the structure of a brick sample (obtained by mixing two types of clays) and a foamed geopolymer are also reported. The first sample shows a beginning of the firing shrinkage at about 1000°C, while the second demonstrates intensive bloating after 950°C, leading to specimen with about 56 % closed porosity. Finally, X - ray Computed Tomography and SEM was used to highlight the structure of some test samples.