Volatilization and leaching behavior of heavy metals in MSW incineration fly ash in a DC arc plasma furnace

Three fly ash samples collected from different waste incinerators were vitrified using a direct current arc plasma furnace at 1250-1400 °C. The influence of water-wash extraction and wrapping pretreatment on the volatilization and leaching behavior of heavy metals was investigated. Results showed: After thermal arc plasma treatment, the volume reduction and weight loss of fly ash were in the range of 68.7-82.2% and 23.8-56.7%, respectively. The residual fractions (wt.%) of heavy metals in slag are in the following sequence: Cr < Ni < Cd < Pb < Cu < Zn. Water-washing could reduce the volatilization rate of heavy metals due to some volatile salts removed by washing, while wrapping of fly ash could most effectively resist heavy metals against volatilizing, especially for Zn and Ni. The possible CaO - Al2O3 - SiO2 (CAS) ratio for successful melting of fly ash is suggested to be CaO in range of 20-48%, Al2O3 in range of 10-15%, and SiO2 in range of 40-65%. Moreover, toxicity characteristic leaching procedure results showed that the leaching of heavy metals in slags was much lower than the standard limit of toxicity characteristic leaching procedure (TCLP).