Composition and Morphology of Fly Ash Cenospheres Produced from the Combustion of Kuznetsk Coal

The chemical and phase composition, morphology, and shell structure of narrow fractions of nonmagnetic and magnetic low-density nonperforated cenospheres separated from fly ash concentrates produced via the pulverized combustion of coal from the Kuznetsk Basin (Russia) have been studied. Narrow fractions of nonmagnetic cenospheres contain 2.6–3.5 wt % Fe2O3 and include globules with a uniform smooth or relief surface and shells with different degrees of porosity. For nonmagnetic cenospheres, the aluminum concentration increase leads to an increase in the mullite phase content and a decrease in the average sphere diameter, glass-crystalline shell thickness and porosity, and the crystalline quartz content. The quartz phase comprises two modifications with different lattice parameters. The narrow fractions of magnetic cenospheres contain 3–21 wt % Fe2O3 and include globules with thick porous shells covered by heterogeneous regions of ferrospinel on their outer surface. In magnetic cenospheres, an increase in the iron concentration leads to an increase in the ferrospinel phase content and crystallite size, accompanied by a decrease in the degree of substitution of magnesium and aluminum for iron.