Obtainment of glass-ceramic composites based on clay, recycled glass and fluorine-containing industrial waste

Calcium hydroxide is normally used in fume abatement systems, in furnaces for glass and ceramic manufacturing to neutralize acidic substances leading to huge amounts of waste material. The concern is the presence of calcium fluoride which complicates the usage of this waste as Ca-rich secondary raw material. Since fluorine escapes easily, the aim of the present study is to determine optimum conditions for the fixation of fluorine in glass-ceramic material. As a consequence, processing involved low temperature direct sintering instead of melting. Clay and recycled glass from dismantled cathode ray tubes were used as binder and promoter of viscous flow sintering. Waste/glass/clay compositions of 20 wt%/70 wt%/10 wt%, 20/60/20 and 20/50/30 were tested. Samples processed at 800-1100°C were subjected to physical and microstructural characterization. The optimized composition (20/50/30) has resulted in lower than 2% water absorption and most of the fluorine was observed to retain in the form of CaF2 and calcium silicon oxyfluorides. These results could be exploited for the manufacturing of low cost tiles, or insulating panels.