Solidification and Stabilization of Heavy Metals in Municipal Solid Waste Incineration Fly Ash Using Nanoalumina by Alkali-Activated Treatment

Municipal solid waste incineration (MSWI) fly ash containing heavy metals is hazardous solid waste that requires safe disposal. Alkali-activated treatment can effectively improve the environmental safety of MSWI fly ash. Due to the low alumina content of MSWI fly ash, the addition of nanoalumina (NA) solves the defect to enhance the ability of solidification/stabilization (S/S) and maximize the utilization of MSWI fly ash. NA/MSWI fly ash solidified body was prepared by alkali-activated technology in this work. In this study, NA was added (0–3 wt.%) to explore its effects on mechanical properties and heavy metal immobilization efficiency of NA/MSWI fly ash solidified body. Research results revealed that when the addition of NA was 2 wt.%, the compressive strength of solidified bodies can significantly increase by 38.0% and 42.8% at 7 and 28 days, respectively. Meanwhile, the leaching concentration of heavy metals in NA/MSWI fly ash solidified body can noticeably reduce with the immobilization efficiency of above 99.5%. Adding NA promoted the ratio of stable state on Pb and Zn in solidified bodies. A series of microscopic characterization analyses indicated that NA stimulated gels and Friedel's salt formation, and N–A–S–H was also found in the NA/MSWI fly ash solidified body, enhancing S/S heavy metals by physical adsorption, physical encapsulation, and chemical bonding. Therefore, this study paves a potential new way for the application of nanomaterials in S/S MSWI fly ash through alkali-activated technology, and nanoalumina is a more promising candidate.