Management of huge quantities of fly ash and bottom ash produced from lignite combustion in power generation units is nowadays of great environmental concern. The use of these industrial solid wastes in the development of value-added materials is a significant subject. Microwave sintering can be an efficient, economic and valuable approach for the processing of powdery materials for ceramics manufacturing, because microwave processes, with their selective and volumetric heating, can enhance the solidification efficiency and reduce the processing time considerably thereby leading to energy savings. In the present research, microwave sintering of Class C (high-Ca) lignite combustion fly ash and bottom ash towards ceramic microstructures development is investigated. For microwave processing, fly ash, bottom ash and mixtures of them were cold pressed to form a series of disc-shaped specimens. Microwave sintering of the ash specimens was carried out at 1000 οC for 10, 20 or 30 minutes in a special purpose microwave (2.45 GHz) system designed for rapid laboratory heating of materials. The microstructures produced were characterized by means of XRD, SEM-EDX analyses and density measurements, and the effectiveness of the sintering process was evaluated. The experimental results are encouraging, as reasonably dense ceramic microstructures mainly composed of gehlenite, quartz and kyanite are achieved after rapid sintering (30 minutes) of the compacted ash specimens using microwave radiation. Several experimental parameters, including ash particle size and shape, green density of the compressed powders, and sintering time appear to influence the consolidation efficiency by microwave heating

Keywords: Microwave sintering, Ceramics, High-Ca fly ash, Bottom ash, Valorization