Composition and structure of the shells of fly ash cenospheres from the combustion of coal of the Kuznetsk Basin

The chemical and phase composition and the structure of the shells of the narrow fractions of nonmagnetic and magnetic unperforated cenospheres in fly ash from the combustion of coal of the Kuznetsk Basin were studied. It was found that the fractions of nonmagnetic cenospheres were characterized by a low Fe2O3 content of 2.6-3.5 wt %, and they consisted of globules with uniform smooth or relief surfaces and shells with different degrees of porosity. The average diameter, thickness, and porosity of the vitrocrystalline shells of cenospheres decreased with increasing the aluminum content of the nonmagnetic fractions; in this case, the concentration of the crystalline phase of quartz as two modifications with different lattice parameters decreased. The narrow fractions of magnetic cenospheres contained 3-21 wt % Fe2O3, and they contained globules with a thick porous shell, on the external surface of which the heterogeneous regions of a ferrospinel phase were detected. The amount of the ferrospinel phase in the magnetic cenospheres increased with the iron content; in this case, an increase in the size of its crystallites and a decrease in the degree of magnesium and aluminum substitution for iron were observed.