Effect and mechanism of nano-alumina on early hydration properties and heavy metals solidification/stabilization of alkali-activated MSWI fly ash solidified body

Municipal solid waste incineration (MSWI) fly ash has serious pollution. It needs to be solidification/stabilization (S/S) to sanitary landfill as quickly as possible. In order to achieve the objective, the early hydration properties of alkali-activated MSWI fly ash solidified body were investigated in this paper. Meanwhile, nano-alumina was utilized as an agent to optimize the early performance. Therefore, the mechanical properties, environmental safety, hydration process and mechanisms of heavy metals S/S were explored. The results showed that after adding nano-alumina, the leaching concentration of Pb and Zn in solidified bodies after 3 d curing was significantly reduced by 49.7-63% and 65.8-76.1%, respectively, and the compressive strength was enhanced by 10.2-55.9%. Nano-alumina improved the hydration process, and the predominant hydration products in solidified bodies were C-S-H gels and C-A-S-H gels. Meanwhile, nano-alumina could obviously increase the most stable chemical speciation (residual state) ratio of heavy metals in solidified bodies. Pore structure data showed that, due to the filling effect and pozzolanic effect of nano-alumina, the porosity has been reduced and the ratio of harmless pore structure has been increased. Therefore, it can be concluded that solidified bodies mainly solidify MSWI fly ash by physical adsorption, physical encapsulation and chemical bonding.