Characterization of Ferrospheres Recovered from High-Calcium Fly Ash

Abstract

Eight fractions of ferrospheres in a range of sizes from 0.4 to 0.02 mm recovered from high-calcium fly ash have been studied. The major component composition of obtained fractions can be described by two linear regression equations, [CaO] = 54.50 – 0.54­[FeO] and [SiO2] = 27.71 – 0.29­[FeO] with the correlation coefficients of −0.96 and −0.88, respectively. On the basis of SEM-EDS study of the structure of 540 ferrospheres, it was found that the fraction −0.04 + 0.032 mm contains the individual globules with block-like, plate-like, and dendritic structures in concentrations of 60, 10–13, and 13–15%, respectively. The block-like globules containing 94–95 wt % FeO mainly consist of intergrown blocks (“single-block type”) of the ferrospinel which is subjected to partial martitization in regions with CaO content more than 0.9 wt %. The composition of the local sites of the plate-like globules containing 79–90 wt % FeO and 3.5–14.0 wt % CaO are characterized by the general dependence [CaO] = 87.4 – 0.93­[FeO] with the correlation coefficient −0.96. These globules consist of the fragments of the “core–shell” type with the size ranging from 3 to 6 μm. The composition of the core with the block-like structure corresponds to a region of ferrospinel crystallization on the phase diagram Fe x O y –CaO system. The composition of the shell with a plate-like structure corresponds to a region of the crystallization of the Fe2O3, CaFe2O4, and CaFe4O7 phases. The composition of the local sites of the dendritic individual globules containing ∼90 wt % FeO and 4.8–5.5 wt % SiO2 are characterized by the general dependence [SiO2] = 61.3 – 0.63­[FeO] with the correlation coefficient −0.94. It was shown that the structure of ferrospinel aggregates depends on the concentrations of Al2O3 and MgO.

Advances in Methods for Recovery of Ferrous, Alumina, and Silica Nanoparticles from Fly Ash Waste

“…Whereas class C fly ash is not suitable for high sulfate conditions, limited to low fly ash content concrete mixes are mainly used for the residential construction. Goodzari and Sanei [40] and Olga Sharonova et al [40].…”

“…The mineralogy and composition of fly ash is not constant, rather it varies from place to place, parent coal source, operating parameters and temperature of TPPs [42], the extent of coal preparation and cleaning, furnace design, usual climate storage [43] and handling. The mineralogical properties determine the crystalline phases of the fly ash, and their composition varies from 15-45% in the fly [40] and Olga Sharonova et al [40]. Goodzari and Sanei [40] and Olga Sharonova et al [40].…”

“…The mineralogical properties determine the crystalline phases of the fly ash, and their composition varies from 15-45% in the fly [40] and Olga Sharonova et al [40]. Goodzari and Sanei [40] and Olga Sharonova et al [40].…”

Structure–Composition Relationship of Platelike Ferrospheres in Calcium-Rich Power Plant Ash

“…The combustion of various types of coal is accompanied by the formation of homogeneous ferrospheres with blocky, skeletal, dendritic, and platelike structures, differing in the size and shape of crystallites of Fe-containing phases and the concentration of glass phase [1][2][3][4][5][6][7][8][9]. The formation of the individual globules is the result of thermochemical transformations of aluminosilicate, Fe,Ca,Mg-containing minerals in the carbon matrix, which ensures the formation of lowtemperature divalent iron-based eutectics [10].…”

“…5 [6]. There is contradictory information about their composition [2,6,9]. Without determining the chemical composition of the globules, their structure was inter-preted in terms of the formation of needle-like anorthite (CaAl 2 Si 2 O 8 ) crystallites, with magnetite (Fe 3 O 4 ) and jacobsite (MnFe 2 O 4 ) crystallites in between [2].…”