Mössbauer Studies of Narrow Fractions of Fly Ash Formed after Combustion of Ekibastuz Coal

Abstract

Nuclear gamma-resonance spectroscopy on 57Fe nuclei, X-ray diffraction, and scanning electron microscopy have been used to study the narrow fractions of fly ash formed after combustion of the Ekibastuz coal. Two groups of samples of magnetic (ferrospheres) and non-magnetic type have been separated by granulometric and magnetic separation. A number of regularities associated with the granules size of fly ash have been established. According to the data of Mössbauer spectroscopy, a decrease in the magnetically ordered contribution has been identified with the growth of the particle size. After magnetic separation, iron in ferrospheres was found mainly in the structure of Fe3O4/γ-Fe2O3 and α-Fe2O3. The dominant phase was Fe3O4 (60–77%), the amount of which decreases with the growth of the grain size. With the growth of the particle size, the ratio of [Fe]tetra/[Fe]octa positions occupancy in Fe3O4 approaches 0.5; the structure of magnetite tends to the stoichiometric composition. α-Fe was found in the composition of ferrospheres, and a mechanism of its formation was proposed. The main components of the non-magnetic fractions of fly ash are mullite, hercynite, and silicate glass.