Pilot trial of upcycling of MSWI fly ash into mineral wool: Effects of fluxing agents on vitrification, viscosity and heavy metal immobilization

Upcycling municipal solid waste incineration fly ash (MSWI-FA) into mineral wool offers a sustainable solution for both safe disposal and resource recovery of hazardous waste. Given the high calcium and low silica, alumina and magnesia content of MSWI-FA, the addition of fluxing agents (SiO₂, Al₂O₃, and MgO) is essential for optimizing vitrification and material properties. This study employs a four-factor, three-level orthogonal experimental design to systematically examine how these fluxing agents influence vitrification, melt viscosity, and heavy metal immobilization. Results indicate that SiO₂ content above 30 wt% and Al₂O₃ content between 10 and 15 wt% act as effective network formers, promoting the formation of Q² and Q³ silica tetrahedra, and enhancing heavy metal retention, albeit with higher melt viscosity and production temperatures. Conversely, MgO and MSWI-FA function as network modifiers, disrupting Si-O-Si and Si-O-Al bonds, thereby reducing viscosity, lowering fiberization temperature, and broadening the operation window for mineral wool formation. Pilot trials using four-roller centrifugal spinning confirm that the optimized MSWI-FA-derived mineral wool exhibits excellent thermal and fire-resistant properties, and economic assessment confirms its positive economic benefits, underscoring its potential for large-scale application. Collectively, these findings provide new insights into the structural influence of fluxing agents and substantiate the feasibility of producing high-quality mineral wool from MSWI-FA through controlled vitrification.