Electrodialytic remediation of municipal solid waste incineration fly ash as pre-treatment before geopolymerisation with coal fly ash

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste and needs to be disposed of according to strict regulations. By disposal, valuable resources in the MSWI fly ash is lost, and other solutions are sought for. The effect of electrodialytic remediation (ED) as a pre-treatment for removing heavy metals from MSWI fly ash before using the treated ash in geopolymerization with coal fly ash was explored. ED pre-treatment for MSWI fly ash increased the Si reactivity and the Si/Al ratio. The mixture of 80% coal fly ash and 20% ED treated fly ash with 8 M NaOH (L/S 0.37 mL/g) was found optimal, with a resulting compressive strength of 15.3 MPa, which was higher than the reference coal fly ash geopolymer. The leaching concentrations of Pb, Zn, Cr, Cu and Ni were below 0.02 mg/L with Mn and Cd at 0.023 and 0.027 mg/L, respectively. The enhanced mechanism for ED treated MSWI fly ash in geopolymer was confirmed by FTIR analysis and SEM images. The resistance against extreme leaching environments for treated fly ash geopolymer was stronger than raw fly ash geopolymer, and physical encapsulation of geopolymeric gels contributed to the heavy metal immobilization.