Chlorine removal from MSWI fly ash by thermal treatment: Effects of iron/aluminum additives

The high content of alkali chlorides in municipal solid waste incineration (MSWI) fly ash limit its resource reuse due to the potential environmental risks. In this paper, with superheated steam as the gasifying agent and inducer, chlorides in fly ash were removed by thermal treatment within a moderate temperature range. Thermal treatment experiments were performed under different conditions: temperature (500-800°C), steam addition (mass ratio of steam to fly ash = 0.25-1) and residence time (0.5-3 hr). Iron and aluminum powders were added to fly ash to improve the chlorine removal efficiency. Water-soluble chlorides included NaCl and KCl, and insoluble chlorides mainly included Ca(OH)Cl. The heating process with the addition of water steam was more efficient than that without steam in terms of the removal performance of water-soluble chlorides. The removal efficiency of soluble chlorides reached 75.25% for a mass ratio of 1:1 after 1-hr thermal treatment at 700°C. When the residence time was increased above 1 hr, the total dechlorination efficiency was not increased dramatically. Moreover, adding iron and aluminum powder into the fly ash improved the removal of water-insoluble chlorides, and the total dechlorination efficiency was increased by 11.41%-16.64%.