Abstract
Material from the electric arc furnace smelting of municipal solid waste incineration (MSWI) bottom ash was easily converted into highly porous glass-ceramics by a combination of inorganic gel casting and sinter-crystallization at 1000 °C. In particular, the gelation of aqueous suspensions of fine glass powders, transformed into “green” foams by intensive mechanical stirring, occurred with a limited addition of alkali activator (1 M NaOH). The products coupled the stabilization of pollutants with good mechanical properties (e.g., compressive strength approaching 4 MPa). Interestingly, they could be used also as raw material for new glass-ceramic foams, obtained by the same gel casting and sintering method, with no degradation of chemical stability. Limitations in the crushing strength, derived from the limited viscous flow densification of semi-crystalline powders, were overcome by mixing powders from recycled foams with 30 wt% soda-lime glass. The new products finally featured an even higher strength-to-density ratio than the foams from the first cycle.
Highlights
Porous glass-ceramics were developed by firstly mixing at 400 rpm fine powders of vitrified bottom ash to an alkaline solution of 1 M NaOH
In the case of recycled Vitrified BA (VBA)/Soda-Lime Glass (SLG), the interaction of fine powders of soda-lime glass and fired vitrified bottom ash during the thermal treatment determined a pronounced precipitation of wollastonite (CaSiO3, Powder Diffraction File (PDF)#84-0655), coupled with more intense nepheline traces
Treating municipal solid waste incineration (MSWI) Bottom Ash (BA) through submerged arc furnace (SAF) favors the generation of an amorphous mineral precursor, which represents around 65–68 wt% of BA and a rich Fe-Cu metal phase, in an amount of 9–12 wt%
Summary
The novelty of this study concerns, first, the application of the latter “inorganic gel casting” approach to the vitrified material from bottom ash smelting, using an alkali activator at a low molarity (1 M NaOH). The manufacturing of durable products from waste-derived glass does not strictly represent a “permanent” solution, since nothing can be said about the same products in the end-of-life condition. It will be demonstrated, that the approach is so flexible to be applicable even to powders from crushed foams, especially by the addition of recycled soda-lime glass.
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