Mineralogy and Surface Properties of Melting Slag of MSWI Fly Ash in Swirling Furnace

The pilot-scale thermal treatment experiment of municipal solid waste incinerator fly ash was carried out by swirling melting furnace. The melting characteristics of fly ash were examined in terms of chemical composition, mineralogy, morphology, leaching behavior of heavy metals. The experimental results indicate that the fly ash mainly consists of silicates, and major crystalline phases of fly ash are CaCO₃, NaCl, KCl, Ca₁₂Al₁₄O₃₃, CaSO₄, SiO₂, and Ca₂SiO₄, melted slag are glassy amorphous product in 1400°C. The ratio of volume reduction of fly ash reaches 87%. The analysis Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDS) show that fly ash particles undergo significant changes of morphology and chemical compositions in slag due to melting reaction. The large amount of SiO₂ and silicate with Si-O network structures in melted slag, most of heavy metals would be fixed into these network structures. The toxicity characteristic leaching procedure (TCLP) leaching concentrations of the heavy metals in all slag, met the maximum EPA regulatory limit values. Thus, Swirling melting is efficient for heavy metals stabilization in MSWI fly ash.