Composition of Individual Microspheres in a Finely Dispersed Fraction from Fly Ash after the Pulverized Combustion of Ekibastuz Coal

Abstract—A systematic study of the compositions of individual microspheres with sizes of <2.5 μm in a fine fraction of fly ash after the pulverized combustion of Ekibastuz coal was carried out using scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM–EDS). It was established that individual ash microspheres with diameters of <1 and 1–2.5 μm from aerosol particle classes PM₁ and PM_1–2.5, respectively, form several groups depending on SiO₂, Al₂O₃, and FeO contents, and various mineral precursors participated in the formation of these groups. Microspheres of group (1), in the compositions of which SiO₂ + Al₂O₃ > 90 wt % and FeO < 3 wt %, were formed with the participation of NH₄-illite and montmorillonite. Isomorphic mixtures of mixed-layer minerals of the illite–montmorillonite series with a low degree of cationic substitution with iron took part in the formation of microspheres of group (2) containing SiO₂ + Al₂O₃ > 90 wt % and FeO = 3–6 wt %. Mineral precursors of microspheres of group (3), SiO₂ + Al₂O₃ < 90 wt % and FeO to 11 wt %, were mixed-layer illite–montmorillonites with a high degree of cationic substitution with iron and Fe³⁺ included into interlayer sites.