EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The present paper deals with investigations conducted on waste glasses as components of new sustainable binders. Waste glasses include materials from the melting of inorganic waste (such as fly ash from coal combustion, red mud from refining of aluminum-rich minerals, etc.) as well as cullet from the dismantling of common articles. In fact, strict recycling is not always feasible, for risks of contaminations or degradation of properties (e.g. fractions of soda-lime container glass enriched in heterogeneous contaminants, pharmaceutical container glass, opal glass, etc.). A stable semi-crystalline geopolymer-like gel could be obtained either by producing a highly reactive CaO-Na2O-Fe2O3-Al2O3-SiO2 glass, from the melting of a waste mixture, and subjecting it to alkali activation, by means of an aqueous solution comprising just NaOH (8M). As an alternative, similar gels could be obtained by mixing cullet with reactive alumino-silicate residues, consisting of basalt powders, and operating the activation with an alkaline solution of lower molarity (NaOH not exceeding 3M). Finally, a further form of stable gel could be obtained even by direct reaction with pure water, operating on a waste glass of particular composition (Ca- and Al-rich CaO-Al2O3-SiO2 glass), deriving from a carbothermal approach, enabling the conversion of most Fe2O3 and extraction of molten iron.