Siberian Federal University

The ferrospheres recovered from industrial fly ash of Ekibastuz coal have been studied in the form of high-purity fractions. It is found that the main phase of ferrospheres is a ferrite spinel (46-49 %), in which a part of iron is replaced by Al and Mg, as evidenced by the lower lattice parameter as compared with magnetite. A major amount of the silicon, aluminum and a substantial amount of the iron are included in amorphous substance of ferrospheres constituting 41-42 % in the studied fractions. Three types of ferrospheres (dendritic, block-like and dendritic-block structure) constituting about 80 % of the studied fractions have been investigated by SEM-EDS. It was found that the gross compositions of these ferrospheres correspond to a relatively low melting (1100-1300 ºC) composition points located on the border areas of crystallization for wustite, fayalite, ferrous cordierite and hercynite in the FeO-Al2O3-SiO2 ternary diagram. The predominant type of globules is dendritic (48-63 %), they consist of a thin unidirectional individuals or branched crystalline Al, Mg-ferrite spinel. Dendritic crystals contain Mg 2-3 times and Al 1.1-2.1 times higher compared with the amorphous regions. Block-like ferrospheres having a similar composition with dendritic globules consist of large, high-iron blocks of ferrospinels, in which Mg and Al content in the 2-4 times lower than in the interblock amorphous substance. An important factor influencing the structure ferrospheres is the dispersion of their main precursor – siderite FeCO3