Effect of the MgO/SiO2 ratio on MgO–silica binders solidifying MSWI fly ash

To improve the effect of MgO–SiO₂ binders solidifying municipal solid waste incineration fly ash (MSWI FA), MSWI FA solidified bodies with five MgO/SiO₂ ratios (0.41 ~ 3.77) were investigated. The leaching behavior of solidified bodies was evaluated by leaching toxicity tests and pH-dependent experiments. In addition, hydration products in solidified bodies were analyzed by thermodynamic modeling and microstructure characterizations. The results showed that the variation in the MgO/SiO₂ ratio had a significant effect on the leaching toxicity of the solidified bodies, because it affected the leachate pH and the composition of the hydration products of the solidified bodies. The acid and alkali resistance of the MSWI FA was enhanced through solidification with MgO–SiO₂ binders. MgO can improve the alkalinity of the solidified bodies and facilitate the chemical precipitation of heavy metals. Moreover, silica fume, an industrial waste, can serve as a cost-effective measure. Overall, MgO–SiO₂ binders demonstrated great potential as promising candidates for encapsulating MSWI FA.