Waste-derived glass-ceramic products with novel functionalities

Vitrification of waste is an effective method to produce a safe waste-based material. However, this process is only economical viable if the vitrified residue is further valorised into new materials, such as glass-ceramics. In this PhD thesis, vitrified residues, such as a glass from the gasification/vitrification of solid recovered fuel (‘Plasmastone’) and vitrified MSWI bottom ash, were converted into safe building materials with high-added values, by sinter-crystallisation. Dense glass-ceramics (with properties comparable to those of commercial tiles) as well as lightweight aggregates (developed to increase the thermal insulation of cement-based products) were produced mainly with mixtures of Plasmastone with soda-lime glass. Furthermore, highly porous inorganic materials for thermal and acoustic insulation were developed by alkali activation, followed by gel-casting and sinter-crystallisation of vitrified residues or partially crystallised residues (e.g. polishing stoneware residue and plasma processed asbestos-containing waste). In specific conditions, soda-lime glass was also added in order to improve hardening and sintering by viscous flow, as in the case of glasses prone to crystallisation, such as Plasmastone, and of partially crystallised residues. Interestingly, the addition of waste glass enabled to recycle powders of vitrified bottom ash-based glass-ceramics into even stronger foams. In addition, the chemical stability of Plasmastone/soda-lime glass foams was considered a critical point, due to high leaching of heavy metals. This was adjusted by using boro-alumino-silicate glass instead of soda-lime-glass or by firing in nitrogen. Besides stabilisation of heavy metals, firing in an inert atmosphere also promoted functionalities in Plasmastone-based porous glass-ceramics: foams fired at low temperature exhibited shielding properties, whereas foams fired at a higher temperature presented dielectric characteristics. A waste-derived glass-ceramic exhibiting multifunctionalities (e.g. insulation coupled with shielding properties) is essential to justify costs and environmental impact of the firing treatment