Effect of Al₂O₃ substitution for SiO₂ on fluorosilicate glass-ceramics fabricated from fluoride-containing sludge

The safe disposal and resource utilization of industrial fluoride-containing sludge represent a critical environmental challenge. In this study, high-performance fluorcanasite glass-ceramics were successfully synthesized from industrial sludge via a melt-quenching followed by heat treatment method. The effects of equimolar substitution of Al₂O₃ for SiO₂ on the phase composition on the glass network structure, crystallization behavior, mechanical properties, and fluoride leaching were systematically investigated. Structural analyses revealed that lower Al₂O₃ content (1-1.5 mol%) favored the formation of layered Q³ units, promoting the precipitation of an interlocking lath-like fluorcanasite main phase at 800 °C. Conversely, higher Al2O3 substitution (>2 mol%) induced the precipitation of xonotlite. The optimized fluorcanasite glass-ceramic (1 mol% Al₂O₃) exhibited exceptional mechanical performance, achieving a maximum flexural strength of 296.71 ± 22.18 MPa, an elastic modulus of 75.33 ± 0.03 GPa, and a fracture toughness of 1.00 ± 0.14 MPa·m^1/2. Furthermore, the fluorcanasite crystalline phase effectively immobilizes F- ions, and its layered structure enhances chemical durability. This work provides a promising method for the resource utilization of fluoride-containing sludge.