Fly ash (FA) from Zhundong coal combustion features high alkali/calcium content and a low Si/Al ratio, limiting its potential for conventional utilization. To enable its high-value application, six size-fractionated samples (FA1–FA6) were characterized via laser particle sizing, SEM-EDS, XRF, XRD, FT-IR, and TGA, to elucidate particle-size-dependent physicochemical and thermal properties. The results show that the size distribution centered at 48–150 μm (~71%). With decreasing size, the morphology shifted from irregular aggregates to smooth vitreous spheres. The chemical composition exhibits significant elemental segregation; the SiO2 content decreases with decreasing particle size, while active components such as CaO, MgO, and Fe2O3 are significantly enriched in fine particles. The thermal conversion behavior is regulated by particle size: The combustion reaction under an air atmosphere conforms to the second-order kinetic model, with the activation energy decreasing from 192.73 kJ·mol−1 for coarse particles (>150 μm) to 63.53 kJ·mol−1 for fine particles (<43 μm); under a nitrogen atmosphere, the weight loss originates from the removal of structural water and the decomposition of carbonates, and fine particles exhibit a higher pyrolysis activation energy (504.15 kJ·mol−1) in the high-temperature stage (850–940 °C) due to being rich in high-crystallinity carbonates. The results of this study elucidate the structure–activity relationship of “particle size-composition-activity” for Zhundong coal fly ash and propose a graded utilization scheme where coarse fractions are suitable for low-grade building fillers, while fine fractions can be used as feedstocks for coal pyrolysis catalysts and functional adsorbents, providing a theoretical basis for its targeted resource utilization based on particle size fractionation.
Gao et al. (Tue,) studied this question.