Up-cycling of vitrified bottom ash from MSWI into glass-ceramic foams by means of ‘inorganic gel casting’ and sinter-crystallization

The transformation of vitrified waste, such as bottom ash from municipal waste incineration, into cellular glass-ceramics is convenient, if the additional processing is simple and inexpensive. The present paper aims at presenting a possible route to achieve this goal, based on the recently proposed mechanical foaming of alkali-activated suspensions of waste glass powders, followed by sinter-crystallization at moderate temperatures (from 800 to 900 °C). Compared to previously studied glasses, in this experiment bottom ash-derived glass suspensions underwent progressive hardening at low alkali molarity and in limited times. The firing did not alter the open-celled structure that had developed upon low temperature foaming, owing to a significant crystallization. With an overall porosity of 80%, the optimized foams exhibited a remarkable compressive strength (>6 MPa). Finally, the process had no negative impact on the leaching of toxic elements, which remained well below the thresholds for inert materials.