Various technological options such as thermal treatment, physical/chemical separation, and stabilization/solidification (S/S) techniques are now available for the treatments of fly ash [3]. For example, MSWI fly ash treatment by solidification with Portland cement is widely used in China before fly ash goes to landfill dis- posal. This treatment technology increases the volume and weight of fly ash and consumes a large amount of cement and land resources. Moreover, slow release of heavy metals from the treated ash was found in a wet environment, thus making it still hazardous to the environment [4–6]. Thermal treatment of MSWI fly ash is costly and leads to the subsequent negative impact on environ- ment because of volatilisation of heavy metals from fly ash during vitrifying and melting processes [7–9]. Physical/chemical separa- tion methods have been applied to extract heavy metals from fly ash and achieved the limited success