Chemistry, Vol 10, No 2 (2017)

The composition and structure of ferrospheres formed by industrial combustion of Ekibastuz coal

Olga Mykhaylovna Sharonova, Marina Anatol'evna Fedorchak, Elena Valentinovna Mazurova

Abstract


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 (1100-1300oC) 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. Blokc-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.