Effect of Atmosphere on HCl Releasement during MSWI Fly Ash Thermal Treatment

Municipal solid waste incineration (MSWI) fly ash constitutes a hazardous waste. Melting disposal has been verified to be prospective for stabilizing heavy metals and dioxins. Release of contaminant HCl during MSWI fly ash thermal treatment leads to potential environmental risks. The behavior and transformation of chlorine are critical to the disposal strategy of MSWI fly ash. In this study, the pathway of HCl formation in MSWI fly ash thermal treatment under complex atmosphere was revealed. Results show that CaOHCl in fly ash was first decomposed to CaCl 2 , CaO and H 2 O below 550°C, which provides H for HCl generation. Then, CaCl 2 , NaCl or KCl were reacted with H 2 O to release HCl, during which process H 2 O and O 2 promote HCl formation, CO inhibit HCl production since H 2 O is consumed in water-gas reaction. The initial temperature of HCl generation affected by the concentration of H 2 O in the atmosphere. When temperature up to 1250°C, almost all NaCl or KCl were volatilized, HCl mainly from the reaction of chlorine-containing minerals with H 2 O, such as Ca 19.2 Mg 2.8 (Si 0.75 Al 0.75 ) 8 O 36 Cl 2 , Ca 4 (SiO 4 )(SO 4 )Cl 2 and Ca 10 (SiO 4 ) 3 Cl 2 in N 2 , CO and air atmosphere separately. Moreover, in a reducing atmosphere, metals are more easily chlorinated by HCl, resulting in further consumption of HCl. The order of atmosphere for reducing HCl emissions should be CO>N 2 >Air>>H 2 O.