Controlling Role of CaClOH in the Process of Dechlorination for Municipal Solid Incineration Fly Ash Utilization

The existence of high chlorine components in municipal solid waste incineration fly ash (IFA) has become a key bottleneck in the utilization of IFA as building materials. In this work, the chlorides in IFA were classified as alkali chlorine, calcium chloride, and calcium aluminum chloride, whereas CaClOH was the dominant phase of calcium chloride. For the first time, the effects of CaClOH on chlorine elimination for IFA-derived products by water-washing treatment or high-temperature treatment were carefully examined. The results indicated that IFA chlorine removal was closely linked to CaClOH phase dissolution, decomposition, volatilization, and transformation. CaClOH was easily removed by water washing and had excellent thermostability, even at 1300 °C. As shown in the results of XRD and XRF, the siliceous component would combine with CaClOH to volatilize as SiCl4, whereas the aluminous component would react with CaClOH to form chlorine-fixed and stable calcium aluminum chloride phases. The calcium aluminum chloride instead of CaClOH was in favor of the transformation of residual chlorine from soluble chlorine to chemically fixed chlorine. Therefore, the detoxification mechanism of chlorine for IFA could be summarized as washing dechlorination, volatilization dechlorination, and chemical fixation. As an application, the synergistic treatment of IFA with siliceous/aluminous materials could greatly reduce risks from soluble chlorine, while IFA-derived products were used as building materials.