The application of multiple advanced chloride removal methods to synthesized Friedel's salt and municipal solid waste incineration bottom ash

Abstract

To recycle municipal solid waste incineration bottom ash as a cement raw material, it is important to reduce the Cl concentration in the ash. However, the reduction of chlorides by washing only has limited success due to the presence of insoluble Friedel's salt (FS) in the ash. Although some studies on the decomposition of FS and the application of advanced chloride removal methods to bottom ash have been reported, few studies have compared the effects of different removal methods. Moreover, due to the complex ash composition, it is also necessary to compare the effects on different ashes and pure FS. Therefore, in this study, we applied five advanced chloride removal methods to synthesized FS and two types of bottom ash (FS-High and FS-Low), and compared the effects. For both FS and bottom ash, all methods promoted chloride dissolution more than washing only. For FS, aging was the most effective method, with a Cl removal ratio of 73%. In contrast, for ash FS-High, aging increased the Cl removal ratio to 80% and decreased the Cl content to 2800 mg/kg. The FS-derived peak observed in an X-ray diffraction analysis disappeared following aging. For ash FS-Low, acid washing increased the Cl removal ratio to 64% and decreased the Cl content to 1800 mg/kg. The treatment with the highest removal ratio in each ash had the lowest pH. There was a significant correlation between pH and the Cl removal effect. The Cl remaining after the application of the methods was likely associated with Na.

Keywords: Advanced chloride removal method; Bottom ash; Cement; Chloride; Friedel’s salt; Washing.