Magnetic Fractions of PM_2.5, PM_2.5-10, and PM₁₀ from Coal Fly Ash as Environmental Pollutants

Characterization of magnetic particulate matter (PM) in coal fly ashes is critical to assessing the health risks associated with industrial coal combustion and for future applications of fine fractions that will minimize solid waste pollution. In this study, magnetic narrow fractions of fine ferrospheres related to environmentally hazardous PM_2.5, PM_2.5-10, and PM₁₀ were for the first time separated from fly ash produced during combustion of Ekibastuz coal. It was determined that the average diameter of globules in narrow fractions is 1, 2, 3, and 7 μm. The major components of chemical composition are Fe₂O₃ (57-60) wt %, SiO₂ (25-28 wt %), and Al₂O₃ (10-12 wt %). The phase composition is represented by crystalline phases, including ferrospinel, α-Fe₂O₃, ε-Fe₂O₃, mullite, and quartz, as well as the amorphous glass phase. Mössbauer spectroscopy and magnetic measurements confirmed the formation of nanoscale particles of ε-Fe₂O₃. Stabilization of the ε-Fe₂O₃ metastable phase, with quite ideal distribution of iron cations, occurs in the glass matrix due to the rapid cooling of fine globules during their formation from mineral components of coal.