Characteristics of Heavy Metals Partition during Melting Process of MSWI Fly Ash

The partition characteristics of heavy metals during melting process of MSWI fly ash was carried out using a microscale furnace between 1100 and 1400°C under different melting time and basicity conditions. Experimental results indicated that the fixation rates of Ni, Cr, Cu and As were up to the maximum at 1200°C. This is attributed to inorganic materials in solid residue took place chemical reaction and transformed into the salt layer. The produced crystal prevented the evaporation of heavy metals and their volatile chlorides. Temperature changes had slimly impact on the volatilization rates of Pb, Cd and Hg with the exception of Zn. There are marked differences that the melting time affects the behavior of various heavy metals. The fixation rates of Ni and Cr increase with increasing melting time prolonging in duration. On the contrary, the proportion of Cu and As in the slag was decreasing. With melting time increasing, the fixation rate of Ni, Cr, Cu and As in samples tended to level off after melting for 90 min. The volatilization rates of Pb, Cd, Hg were on a high level above 95% and nearly complete volatilization in 30 min. The proportions of heavy metals remaining in the melted slag were affected by the basicity (CaO/SiO₂). High basicity redounded to fixation of Ni, Cr, Cu and As. There were slightly impacts on volatilization of Pb, Cd, Hg and Zn with the basicity changes of fly ash. Low basicity produced a remarked effect on volatilization of Zn. The leaching test on 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.