Melting characteristics during the vitrification of MSW incinerator fly ash by swirling melting treatment

Pilot tests of fly ash were investigated in a 0.2 MW swirling melting furnace at 1250–1400 °C. The properties of raw fly ash and melted slag were investigated in terms of their chemical and mineralogical composition, particle size distribution, thermal analysis and microstructure, heavy metals distribution and leaching toxicity. Experimental results indicated that over 85 % particle sizes of raw ash sample were below 149 μm. At 1350 °C the main identified compounds were the silicates and aluminates (CaAl₂Si₂O₈, Ca₃Si₂O₇, CaSiO₃, and Ca(Al,Si)₂O₄). The main compositions of melted slag at 1400 °C contained large amounts of dark glassy materials was completely the formation of more amorphous structure (Si–O), and heavy metals were immobilized in the silicate network matrix. The heavy metals Cr and Ni were shown a high solidification rate and reached about over 90 and 83 % in the slag. The achieved immobilization efficiency as judged by the US EPA test was 38–45 % for Co, Mn, Cu, and Pb. It can be seen that the solidification rates of As, Zn, and Hg remain about 20, 23 and 2 %, respectively. TCLP of heavy metals of vitrified slag met the regulatory thresholds of US EPA and China Standard.