Dense glass-ceramics by fast sinter-crystallization of mixtures of waste-derived glasses

Dense glass-ceramics were obtained by cold pressing and sinter-crystallization of a glass originated from the plasma gasification of municipal solid waste ("Plasmastone") mixed with recycled soda-lime glass and kaolin clay. The optimum mixture featured 45% Plasmastone/45% soda-lime glass/10% kaolin clay and it was sintered according to a fast heat treatment (30 minutes at 1000 degrees C with heating and cooling rates of approximately 40 degrees C/min), mimicking that of industrial ceramic tiles. The fast treatment avoided extensive crystallization during heating, promoting the viscous flow. In this way, dense glass-ceramics with a water absorption below 0.7% could be produced. The developed tiles presented mechanical properties comparable to those of commercial ceramic tiles. Finally, the environmental impact assessment performed on these materials showed that the leaching of hazardous elements was particularly limited. Microprobe analyses indicated that heavy metals were incorporated in newly formed crystals, consisting mainly of hedenbergite, wollastonite, and iron oxide-rich "islands" surrounded by residual glass. The results show that Plasmastone, combined with recycled soda-lime glass and kaolin clay, may be converted in building materials, with a possible commercial exploitation.