High-temperature treatment and partial vitrification of fine-grained municipal solid waste incineration bottom ash: Mineralogical and chemical behaviour and reuse potential

Finest grain-size fractions of municipal solid waste incineration bottom ash (MSWI-BA) represent a critical barrier to ash valorisation because they are commonly enriched in soluble salts and potentially toxic elements. This study evaluates whether thermal treatment can reduce the short-term leachability and improve the reuse potential of fine-grained MSWI-BA from the Parma Waste-to-Energy (WtE) plant by linking mineralogical and microstructural evolution to EN 12457–2 batch-leaching behaviour. The 0–2 mm fraction and selected finer sub-fractions were thermally treated at selected temperatures up to 1200 °C and characterised by XRF, ICP-MS, XRD with quantitative phase analysis, Raman spectroscopy, SEM-EDS, and leaching tests. The untreated ash consists mainly of an amorphous/glassy aluminosilicate matrix with secondary carbonates, hydrates, and sulfate- and chloride-bearing phases, whereas the finest fractions show higher concentrations of alkalis, soluble salts, and other minor phases bearing potentially ecotoxic elements. Thermal treatment causes progressive dehydration, decarbonation, recrystallization and, above approximately 1000 °C, the formation of a Ca-silicate glass–ceramic assemblage containing pyroxene and wollastonite. Above approximately 1050–1100 °C, the amorphous fraction increases again, indicating partial vitrification. This evolution is accompanied by a marked decrease in electrical conductivity and in the release of chloride, sulfate, alkalis, and several regulated elements. Among the conditions investigated, the 1100–1150 °C range with a 1 h holding time provides the clearest environmental upgrading and supports consideration of the treated fines as candidate secondary raw-material precursors. Long-term durability, industrial feasibility, off-gas management, and end-use performance remain to be established.