Effect of Al 2 O 3 substitution for SiO 2 on fluorosilicate glass-ceramics fabricated from fluoride-containing sludge

Abstract 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·m1/2. 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.