Water washing can remove chlorides from municipal solid waste incineration fly ash but with high consumptions of energy and reagents for the following wastewater treatment. In this study, a novel method named delayed bubbling washing (water washing first and then CO2 bubbling washing) was proposed to promote the chlorine dissolution. The mechanisms were considered as the less shell formed outside ash particles and the reaction between CaClOH and H2CO3 during washing. However, for single-stage washing, the incomplete dehydration of washed ash greatly weakened the chloride removal effect. Three-stage countercurrent washing addressed this issue well with the best bubbling position in the first stage. Through the combination of delayed bubbling washing and three-stage countercurrent washing, the chlorine content in the product was lowered to 0.85% at a liquid–solid ratio of 2.5 mL/g, the cost of wastewater treatment was reduced by 23%, the byproduct of NaCl was reduced by 14.5%, and the CO2 emission was reduced by 23 kg/ton of ash.

Utilization of municipal solid waste incineration fly ash (MSWI-FA) can avoid land occupation and environmental risks of landfill. In this paper, MSWI-FA was used to prepare alkali activated cementitious materials (AACMs) after two-step pretreatment. The ash calcination at 450 °C removed 93% of dioxins. The alkali washing with 0.2 g NaOH/g ash removed 89% of chlorine and retained almost 100% of calcium. The initial setting time of AACMs was too short to detect for 20% of MSWI-FA addition, and the prepared block had extensive cracks and expansion for CaClOH and CaSO4 inside. Alkaline washing pretreatment increased the initial setting time by longer than 3 min with 30% ash addition and eliminated the cracks and expansion. The significance of the factors for compressive strength followed the modulus of alkali activator > silica fume amount > alkaline washing MSWI fly ash (AW-MSWI-FA) amount. When the activator modulus was 1.2, 1.4 and 1.6, the blocks with 30% of AW-MSWI-FA had a compressive strength of up to 36.73, 32.61 and 16.06 MPa, meeting MU15 grade. The leaching test shows that these AACM blocks were not hazardous waste and almost no Zn, Cu, Cd, Pb, Ba, Ni, Be and Ag were released in the leaching solution.