Upcycling municipal solid wastes to self-foaming glass-ceramics by chemical additive-free and rapid low-temperature sintering

Incinerated sewage sludge ash (ISSA) and waste glass (WG) produced in large quantities from municipal solid wastes are either not recycled or are used in relatively low-value applications. Here, we reported a scalable strategy to rapidly convert them, along with waste paper (WP), into novel foamed glass-ceramics (FGCs) by low-temperature sintering, considerably reducing environmental impact and manufacturing cost. The Fe₂O₃ in ISSA and cellulose in WP were used as precursors to trigger the self-foaming process at low temperatures by carbon-enhanced ferric reduction when WG formed the softened matrix without chemical additives. This study analyzed the foaming mechanism, physical properties of FGCs, and variable importance assisted by thermodynamics and machine learning. The resulting FGCs with 20 wt% ISSA content and 10 wt% WP addition exhibited the excellent properties of a geometric density of 0.76 ± 0.02 g/cm³, volume water absorption of 14.35 ± 2.48%, and compressive strengths of 7.15 ± 0.88 MPa by a short holding (5 min) at a low firing temperature of 850 °C. The successful synthesis and mechanistic study provide new insights into the development of waste-derived high-performance FGCs.