Composition and Structure of Block-Type Ferrospheres Isolated from Calcium-Rich Power Plant Ash

• Published in: Inorganic materials Vol. 54; no. 2; pp. 187 - 194
• Main Authors: Anshits, N. N., Fedorchak, M. A., Zhizhaev, A. M., Sharonova, O. M., Anshits, A. G.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.02.2018; Springer Nature B.V
• Subjects: ALUMINIUM OXIDES; Aluminosilicates; Aluminum oxide; ANORTHITE; ASHES; CALCIUM; Calcium oxide; CALCIUM OXIDES; Chemistry; Chemistry and Materials Science; COAL; Crystallites; Electric power generation; FERRITE; Ferrites; Globules; Impurities; Industrial Chemistry/Chemical Engineering; Inhomogeneity; Inorganic Chemistry; IRON OXIDES; Magnesium oxide; MAGNESIUM OXIDES; MAGNETITE; MATERIALS SCIENCE; POWER PLANTS; PYRITE; QUARTZ; SCANNING ELECTRON MICROSCOPY; Silicon dioxide; SILICON OXIDES; SPHERES; Spinel; X ray spectrometers; ferrospheres with a blocky structure; formation paths
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168518020012

Polished sections of individual ferrospheres 30 to 40 μm in size, with single-block and blocky structures and a variable glass phase content, have been studied using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer system. The results demonstrate that the single-block globules consist of sintered magnetite crystallites containing Al 2 O 3 , MgO, and CaO as impurities and are formed from the pyrite of the initial coal. Characteristically, the ferrospheres with a variable glass phase content differ in the composition of local areas on polished sections of the globules, which attests to inhomogeneity of the melt droplets they formed from. We have identified groups of globules whose overall composition, as well as the composition of their local areas, meet general equations for the interrelation between the concentrations of their components: SiO 2 = f (FeO) and SiO 2 = f (Al 2 O 3 ). Comparison of the coefficients of the SiO 2 = f (Al 2 O 3 ) dependence for the globules with the silicate modulus (SiO 2 /Al 2 O 3 ) of the aluminosilicate mineral components of the coal indicates that the formation of this type of globules involves pyrite–anorthite or pyrite–albite associates containing quartz impurities. The composition of the spinel ferrite in the globules produced with the participation of anorthite comprises FeO, Al 2 O 3 , MgO, and CaO in concentrations of 85–96, 1.7–10, 0.1–1.8, and 0.3–2.8 wt %, respectively. In the albite-based globules, the respective concentrations are 81–92, 0.7–5.9, 1.0–5.7, and 2.2–5.6 wt %. The crystallite size and shape are determined by the size of the local melt areas where the total concentration of spinel-forming oxides exceeds 85 wt %.