A. G. Anshits

Composition and morphology of narrowly sized ferrospheres isolated from various types of fly ash

We report a systematic study of the interrelationship between the composition and microstructure of ferrospheres isolated from all known types of power plant fly ash. Our results demonstrate that the macro-component composition of narrow ferrosphere size fractions corresponds to the compositions of the phase boundaries between the primary crystallization fields of wüstite, fayalite, Fe-cordierite, and hercynite in the phase diagram of the FeO-SiO2-Al2O3 system. An increase in iron content leads to a monotonic variation in the main morphological species of the ferrospheres in the following sequence: porous, glassy, dendritic, skeletal-dendritic, and blocky. The relationships identified in this study allow one to find a fly ash source suitable for the preparation of functional materials of controlled composition and morphology.

Mössbauer Study of Magnetic Microspheres Isolated from Power Plant Fly Ash

The phase composition of magnetic microspheres isolated from Ekibastuz coal fly ash in six narrow size ranges is determined by Mössbauer spectroscopy. The major phase in the microspheres is nonstoichiometric, cation-substituted (Al, Mg, and Ti) magnetite. Their magnetic properties are shown to depend on the Fe content and cation distribution over the spinel sites.

Influence of the composition and structure of the glass-crystalline shell of cenospheres on helium permeability

We studied the interrelation between the composition, morphology, and helium permeability of the shell of narrow fractions of nonmagnetic nonperforated cenospheres extracted from cenosphere concentrates of fly ash of the sialic type with the use of technological stages of hydrodynamic, magnetic separation, sizing, and aerodynamic classification. For the interval of variation of Al2O3 content from 20 to 38 wt %, the regression equation [SiO2]/[Al2O3] = 5.06 − 0.1[Al2O3] is established, with the correlation coefficient equal to −0.98. It is found that, together with the growth in the concentration of Al2O3 in the indicated interval, the content of the originally mullite phase increases from 1.3 to 42.4 wt %, and this is accompanied by the growth of the helium permeability of the glass-crystalline shell of the cenospheres.

Polyfunctional microspherical materials for long-term disposal of liquid radioactive wastes

The possibility of immobilizing liquid radioactive wastes into polyfunctional microspherical materials of the block and powdered types is demonstrated. These materials are intended for reprocessing radioactive wastes of different compositions and make it possible to perform a multistage process of conditioning radioactive wastes under relatively mild conditions (at temperatures below 1000°C) with the conversion of water-soluble cesium and strontium compounds into water-insoluble mineral forms in the course of solid-phase transformations. Owing to the aluminosilicate composition of microspherical components of energy ashes (cenospheres), the cenospheres can serve as precursors of aluminosilicate granitoid minerals. Different techniques are proposed and conditions are experimentally determined for transforming precursors into final mineral-like materials of the predicted structure types chosen in the framework of the geoecological approach. The framework structures of aluminosilicates and phosphates thus formed can fix cesium and strontium in the crystal lattice and ensure the geochemical equilibrium between the matrix and incorporating granitoid rocks under conditions of long-term disposal.

Gas permeation properties of hollow glass-crystalline microspheres

Permeation of He, H2 and Ne was studied for hollow glass-crystalline microspheres. Microspheres demonstrated high permeability to helium with high selectivity for He/H2 and He/Ne owing to the composition and structure of their shells.

Composition and structure of the shells of aluminosilicate microspheres in fly ash formed on the combustion of Ekibastuz coal

A systematic study of the chemical and phase composition and structure of the shells of narrow fractions of nonmagnetic cenospheres separated from a concentrate of fly ash cenospheres from the combustion of pulverized SS (weakly caking coal) coal from the Ekibastuz Basin was carried out. It was found that the separated narrow fractions were characterized by a high Al2O3 content of 33–38 wt %. The phase composition included 57–73 wt % vitreous phase, 25–40 wt % mullite, and 1.2–2.5 wt % quartz. An increase in the average diameter, thickness, and porosity of the glass-crystalline shell of globules with the concentration of aluminum was observed. Globules of the following two types were identified in the obtained fractions: spherical globules with an annular structure and foamy globules with a network structure formed from different illite and kaolinite mineral precursors, respectively.

Nature of the active sites of ferrospheres in the oxidative condensation of methane

The catalytic properties of ferrospheres containing 76–97 wt % Fe2O3 in the oxidative condensation of methane were compared with their phase composition and the distribution of iron cations over the crystallographic positions of iron-containing phases in a steady state. It was established that the reaction route of methane oxidation changed at a Fe2O3 content of 89 wt %. Deep oxidation was the main reaction route on ferrospheres with a Fe2O3 content of <88.8 wt %. At a Fe2O3 content of ≥89 wt %, the yield of C2 hydrocarbons sharply increased and the contribution of deep oxidation decreased. The yield of C2 hydrocarbons correlated with the amount of defects in the structure of iron spinel, which are iron ions with the tetrahedral cation of Ca2+ and the octahedral cation vacancy among the nearest neighbors.

Composition of individual ferrospheres of different morphological types

We have studied the composition of three types of individual spheres differing in microstructure (single-block, platelike, and skeletal–dendritic spheres) in the–40 + 32 μm size fraction of ferrospheres containing 92.72 wt % FeO. The results demonstrate that the single-block spheres have the highest Fe content (95–97% FeO), a basicity factor Mb > 48, and an Fe/O atomic ratio of 0.68–0.71. They consist of block individuals of a partially martitized (oxidized to hematite) spinel ferrite. The platelike spheres feature high calcium content (11–12% CaO); lower basicity factor, Mb ≃ 20–21; and a higher degree of oxidation of Fe, with an Fe/O atomic ratio of 0.63–0.66. They consist of spinel ferrite blocks with large percentages of FeO (up to 90%) and MgO (up to 6%), surrounded by regions with a platelike structure, reduced FeO content (down to 57%), and high CaO content (up to 34%). The skeletal–dendritic spheres feature increased percentages of SiO2 (≃ 4.7 %) and Al2O3 (3.6–4.6%) and low basicity factor: Mb ≃ 10–11. They consist of unidirectional or branched crystalline spinel ferrite individuals with partial Mg2+ substitution for Fe2+, which prevents oxidation of the spinel to hematite, as evidenced by the large Fe/O atomic ratio: 0.72–0.73.

Mössbauer and magnetic study of microspheres extracted from fly ashes of power stations

Phase composition of six narrow size fractions of microspheres extracted from fly ashes of Ekibastuz coals has been determined by Mössbauer spectroscopy. The basic phase is defect magnetite substituted by Al, Mg, and Ti ions. The magnetic properties of microspheres depend on the content of iron and its distribution over spinel positions.

Single-Stage Aerodynamic Separation of Fly Ash Produced after Pulverized Combustion of Coal from the Ekibastuz Basin

The single-stage separation of fly ash from field 1 of the electrostatic precipitator of Reftinskaya GRES (Regional Thermal Power Plant), which burns coal from the Ekibastuz Basin, was performed by aerodynamic classification with the use of a flow of air. It was found that, at a constant airflow rate of 50 m3/h, the morphologically uniform fractions of small spherical particles with a narrow distribution, for which dmax was 2, 3, and 4 μm and d90 was 4, 6, and 8 μm, can be separated by decreasing the speed of the classifier rotor from 22000 to 10000 rpm. At a minimum speed of 2000 rpm, the target product of separation was a narrow fraction containing large particles, which were characterized by dmax of 109 μm and d90 of 205 μm. It was established that SiO2 and Al2O3 were the basic chemical components of the fractions obtained, and the total concentration of these components was as high as 86–91 wt %. With increasing the size of fractions with dmax from 2 to 116 μm, a decrease in the concentration of SiO2 and an increase in the amounts of Al2O3 and Fe2O3 were observed. The dependence of phase composition on the particle size was established for the small fractions: as dmax was increased in a range of 2–25 μm, a monotonic decrease in the concentration of a quartz phase and an increase in the concentration of mullite were observed; the concentration of a Fe-containing spinel phase also increased.