Immobilizatiaon of heavy metals in municipal solid waste incineration fly ash with red mud-coal gangue

In this research, Bayer red mud (RM) and coal gangue (CG) bend with a ratio of 8:2 was prepared as a geopolymer precursor (RG) through mechanochemistry-alkali activation. It was used for municipal solid waste incineration (MSWI) fly ash solidification/stabilization (S/S). TCLP test, sequential extraction test, long-term immersion test and compressive strength test were used to evaluate the effectiveness and stability of the geopolymer S/S regent. Meanwhile, XRD, SEM–EDS and FTIR were applied for characterization of the geopolymer S/S solid samples. The results showed that more than 99.6% of the heavy metals in geopolymer S/S solid could be immobilized when the RG content exceeded 60%. The S/S effectiveness decreased in the order of Pb > Zn > Cr > Cd. Total content of heavy metals controlled the TCLP leaching behavior, while the availability and diffusivity of heavy metals controlled the long-term leaching behavior. According to XRD results, the MSWI FA can participate in the hydration process to generate Ca-based and Al/Si-based products, thus has double effects to the geopolymerization. In consequence, most heavy metals in the geopolymeric S/S solid were successfully immobilized in the hydration phases and geopolymer structure, transformed from the available fractions into the stable fractions, and the long-term security of heavy metals in RM–CG–MSWI FA ternary system geopolymer was safe.