Crystallization–Foaming Coupling in Foam Glass-Ceramics from Multi-Source Coal Power Wastes

The large-scale disposal of coal fly ash (CFA), coal bottom ash (CBA), and desulfurization gypsum (DG) from coal-fired power plants poses serious environmental challenges, driving the need for high-value utilization strategies. In this study, we propose a synergistic approach to prepare foam glass-ceramics from CFA, CBA, and DG via a sintering-foaming method. The effects of sintering temperature (1200–1230 °C) and DG content (0–5 wt.%) on phase composition, pore structure, and overall material properties were systematically investigated. The optimal sample, obtained at 1220 °C with 2 wt.% DG exhibits outstanding comprehensive performance: a bulk density of 1.0030 g/cm3, porosity of 62.09%, compressive strength of 9.66 MPa, and thermal conductivity of 0.6156 W/(m·K). Additionally, it demonstrates excellent chemical stability, with acid resistance exceeding 96% and alkali resistance over 98%, while the leaching concentrations of heavy metals (Pb, Cr, Cu, Zn) remain far below regulatory limits. Mechanistic analysis reveals a crystallization–foaming coupling effect. At an appropriate DG content (2 wt.%), a synergy is established: bubble formation provides heterogeneous nucleation sites that promote crystal precipitation, while moderate crystallization increases melt viscosity and stabilizes the pore structure. Conversely, excessive DG (3–5 wt.%) reduces melt viscosity, leading to bubble coalescence and rupture, suppressed crystallization, and consequently deteriorated material properties. This work provides a theoretical foundation for the synergistic utilization of multiple power plant wastes and the structure–property regulation of foam glass-ceramics.