The effects of washing solvents on the properties of ceramsite and heavy metal immobilization via the cosintering of municipal solid waste incineration fly ash and Cr-containing waste glass

Various washing solvents are being extensively researched to remove chlorides from municipal solid waste incineration fly ash (FA) and they have significant impacts on the recycling and reutilization of FA. The cosintering of FA and waste glass (WG) containing chromium (Cr) was explored in this study, as well as the effects of washing solutions (water [W-FA], phosphoric acid [P-FA], and sodium carbonate [Na-FA]) on the treated FA compositions, ceramsite characteristics, and heavy metals speciation. The findings demonstrated that washing process increased calcium oxide (CaO) content while reducing soluble salt level. The particle strength increased from 290.50 N to 926.78 N at 800–1050 °C, while increased from 228.68 N to 820.23 N when WG increased from 20% to 60%. Raw-FA ceramsite had a lower sintering temperature than treated FA ceramsite due to the higher particle strength and lower water absorption rate. At 1000 °C, the acid-soluble fraction of Cr of Na-FA and P-FA ceramsite was 64.72% and 9.07%, showing a promoted and inhibited effect on Cr leaching, respectively. The ecological risk index for P-FA and Na-FA ceramsite, both of which were produced at 1100 °C, were 30.61 and 46.68, respectively, indicating low environmental risk. Wollastonite was the dominating mineral phase in W-FA and Na-FA ceramsite, whereas chlorapatite and halite predominated in P-FA and Raw-FA ceramsite. Chlorine in P-FA ceramsite was combined with phosphates and calcium to generate stable minerals. Washing pretreatment reduced the environmental risk of ceramsite, and introduction of phosphorus could enhance heavy metal immobilization.