Chinese research into utilisation of coal waste in ceramics, refractories and cements

Disposal of coal mine waste (gangue) presents a serious environmental problem. In the present paper, applications of siliceous and kaolinitic gangues in ceramics, refractories and cementing materials are reviewed. Coal gangue series mullite, superfine beta-SiC and Si3N4 powder have been prepared from siliceous gangue and carbon black, anthracite or bituminous coal. Using kaolinitic gangue with few impurities as raw materials, Al2O3-SiC and sialon-SiC composite powders, and sialon series powders including beta-sialon, O-sialon and X phase have also been synthesised successfully. Kaolinitic gangue has been used to produce porous ceramics, cordierite, cordierite-mullite insulating brick, anorthite lightweight brick and other lightweight aggregates. Calcined coal gangue had high activity of volcanic ash and may be used as a cement admixture. Alkali activation is another effective method of improving the strength of coal gangue based alkaline cementitious materials.