Stabilization of fluorine-containing industrial waste by production of sintered glass-ceramics

Calcium hydroxide is normally used to neutralize acid fumes escaping from furnaces for glass and ceramic manufacturing, leading to huge amounts of waste material known as “exhausted lime”. The presence of calcium fluoride greatly complicates the use of this waste as Ca-rich secondary raw material. The present study is aimed at the development of a new type of glass-ceramics, allowing a significant fixation of fluorine (maintained as CaF2 or in form of calcium silicon oxyfluorides), by direct sintering of exhausted lime mixed with clay and recycled glass from dismantled cathode ray tubes. The low softening temperature of recycled glass allowed a substantial viscous flow at relatively low temperature. Sintered glass-ceramic samples of optimized composition (glass/clay/waste weight proportion equal to 50/30/20), featured a water absorption below 2%, a good specific strength and, above all, a substantially unchanged F content, compared to the starting mixture. The obtained glass-ceramics could be used as low cost tiles, especially for insulation purposes, exploiting the residual porosity (30-40%).