Preparation and properties of glass-ceramics from wastes (Kira) of silica sand and kaolin clay refining

Glass-ceramics were prepared from wastes generated from refining of silica sand and kaolin clay, called Kira. Several kinds of Kira were melted at 1300-1550 °C with additions of CaCO₃ and quenched in air or water to obtain glasses. The quenched glasses were ground to <48 mesh and used to prepare glass-ceramics. Crystallization of the parent glass occurred above 950 °C, producing wollastonite as a major crystalline phase which gradually transformed to pseudowollastonite above 1150 °C. The macroscopic appearance of the samples changed from transparent pale green glass to smooth-textured shiny white upon crystallization. The thermal expansion coefficient of the glass-ceramics was 5.2×10^-6/°C (30-380 °C). The four-point bending strengths of the as-fired glass-ceramics ranged from 76 to 86 MPa. Vickers microhardness was found to be 6.6-7.5 GPa. Since the chemical durability for acid and alkali was excellent in these glass-ceramics, they are considered to be candidates for applications such as building materials, ceramic tiles, etc.