Conversion to glass-ceramics from glasses made by MSW incinerator fly ash for recycling

Glasses were made using fly ash from municipal solid waste (MSW) incinerators with the addition of SiO2, MgO and TiO2. The glasses were then converted to glass-ceramics for further recycling to construction materials. The optimum heat-treatment schedule for the ceramitization of glasses was 720 °C for 90 min for nucleation and 870 °C for 10 h for crystal growth. Diopside (CaMgSi2O6) was formed as a major crystalline phase. The glass-ceramics showed good mechanical properties with a hardness of 6,730 MPa, fracture toughness of 1.86 Mpa m1/2 and bending strength of 127 MPa. Glasses and glass-ceramics with a composition of 20SiO2–5MgO–75fly ash–2TiO2 (all given in wt.%) showed an excellent resistance against leaching of heavy metal ions in water. The amount of heavy metal ions leached after 18 h at 23 °C was well below regulation with Cd2+ <0.04 ppm, Cr3+ <0.004 ppm, Cu2+ <0.03 ppm and Pb2+ <0.15 ppm, respectively.