Ceramics-Silikáty 68, (3) 378 - 388 (2024)

To reveal the specific reason for the bubble release and expansion of municipal solid waste incineration fly ash (MSWI FA) during polymerisation, the chemical composition and source of the emitted gas were studied at length in this paper. To further explore the advantage of an alkali washing pre-treatment for MSWI FA, the influence and mechanism of the alkali washing pre-treatment on the macroscopic mechanical properties, microscopic pore structure and heavy metal leaching of geopolymers have been investigated. The results show that the emerging bubbles are mainly H₂ and NH₃ released by the reaction of elemental aluminium and ammonium salts from MSWI FA with alkali, respectively. The alkaline washing pre-treatment can ensure the volume stability of the geopolymers by releasing bubbles in advance, which is conducive to improving the strength of hardened paste and hindering the leaching of heavy metals. Although the alkaline washing process cannot significantly remove heavy metal ions directly, it can remove almost all the soluble chlorine salts and has a certain significance for the development of the overall compressive strength.