Experimental Analysis of Heavy Metals Behavior during Melting Process of Fly Ashes from MSWI under Different Atmospheres

Fly ashes from municipal solid waste incinerator were melted using a micro-scale furnace at 1100 to 1400°C. The behaviors of several heavy metals had been systematically measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). This study investigated leaching characteristics of melted slag. Experimental results showed that the fixation rates of Cr, Ni, Cu and As in melted samples would increase with the elevation of their melting point at oxidizing atmosphere. Several volatile heavy metals are readily emitted during melting process. The volatilization rates of lead, cadmium and mercury with low boiling points reached over 95% at oxidizing atmosphere. The reducing atmosphere would be propitious to enhancing the fixation rates of chromium, nickel, copper and arsenic. It is confirmed that mercury, cadmium, and zinc are more easily vaporized under reducing atmosphere, but the volatilization of lead would be inhibited at the same condition. The volatilization rate of zinc was very low due to easily forming the nonvolatile compounds, like Zn₂SiO₄, ZnSiO₃, and ZnAl₂O₄. Due to the volatilization rate of lead being inhibited, it was less than 50% at 1100-1400°C. The leaching test on all the melted slag samples showed that the fly ashes were successfully detoxified to meet of the limits toxicity characteristic leaching procedure (TCLP) in China and United States.