Characterization of bottom ash of Pliocene lignite as ceramic composites raw material by petrographic, SEM/EDS and Raman microspectroscopical methods

An investigation has been carried out into the changes occurring in the organic and mineral matter of lignite during combustion and the effect of bottom ash characteristics on making fired-ceramic composites and lightweight heat-resistant concretes. In addition to examination of physico-chemical properties using XRD, XRF, SEM/EDS and Raman microspectroscopy, detailed petrographic studies were performed, including texture and microstructure analysis of feed coal and bottom ash, with special reference to a novel approach for bottom ash reuse in the production of ceramic composites. The results of the petrographic study show correlation of the low rank coal composition with bottom ash optical texture, providing information on the active surface gasified by oxygen, as well as the origin of char particles of woody origin that participated in the combustion process. The bottom ash microstructure is directly related to the reactivity of the porous residue and the properties of the ceramic composites produced, which include density, absorbency, porosity and firing compression strength. In particular, the reduction in density indicates an increased potential of thermal insulation of fired-ceramic composites containing up to 50% bottom ash, and lightweight heat-resistant concretes containing up to 75% bottom ash. The results of the study indicate the positive contribution that can be made by using petrography as a complementary method to study the organic phases, and SEM/EDS and Raman microspectroscopy to analyse the chemical composition of the inorganic phases, when studying bottom ash utilization, and the promising potential for bottom ash to be recycled in making ceramic composites.