Distribution of chloride in municipal solid waste incineration bottom ash

Chloride content is a critical problem for the reuse of incineration bottom ash as raw material in cement. The effect of dechlorination procedure largely depends on the existence form of the chlorides. However, limited information about the distribution and identity of chlorides in bottom ash can be obtained by bulk analysis methods. In this paper, the investigation towards a more comprehensive understanding about chloride in bottom ash was carried out by means of optical microscopy and scanning electron microscopy. Two types of bottom ashes with different cooling methods were studied. It was revealed that chloride was mainly contained by the glass in the air-cooled bottom ash and, moreover, a strong association between chloride and calcium was disclosed. Water quenching altered the morphology of ash particle and formed fragile phase, which concentrated relatively high content of chloride. The crystalline chloride of Friedel's salt was also identified in the water-quenched bottom ash.