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 Al2O3, 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: SiO2 = f(FeO) and SiO2 = f(Al2O3). Comparison of the coefficients of the SiO2 = f(Al2O3) dependence for the globules with the silicate modulus (SiO2/Al2O3) 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, Al2O3, 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 %.

This paper presents a systematic SEM–EDS study of polished sections of individual skeletal and dendritic ferrospheres in the–0.04 + 0.032 mm size fraction, isolated from fly ash from the combustion of brown coal from the Berezovskoe field. The ferrospheres are characterized by a wide range of variations in the macrocomponent composition of local areas. We have identified groups of globules whose overall composition as well as the composition of local areas on their polished sections can be represented by general equations for component concentrations: SiO2 = f(FeO), SiO2 = f(Al2O3), and CaO = f(SiO2). Such equations make it possible to identify the nature of the mineral precursors involved in the formation of the globules. FeO-rich skeletal ferrospheres with low CaO concentration originate from the thermochemical transformation of pyrite and illite associates. Skeletal and dendritic ferrospheres with monotonically increasing CaO and SiO2 concentrations are formed from pyrite and montmorillonite associates, with the participation of a melt containing quartz and decomposition products of Ca-humates of the initial coal. Skeletal and dendritic spinel ferrite crystallization is due to a magnesium aluminate spinel “seed,” resulting from the thermal transformation of illite and montmorillonite from the parent coal. The observed increase in glass phase concentration and the change from the skeletal type of crystallization to a dendritic in the ferrospheres containing ≤64 wt % FeO and ≥6.5 wt % CaO are due to the low concentration of the spinel-forming cations Fe2+ and Fe3+ in the melt and the increase in the percentage of [Fe3+O2]− and [Fe23+ O5]4− ferrite complexes with an increase in the degree of oxidation of the melt.

Magnetic Ni(2+)-zeolite/ferrosphere and Ni(2+)-silica/ferrosphere beads (Ni-ferrosphere beads - NFB) of a core-shell structure were synthesized starting from coal fly ash ferrospheres having diameters in the range of 0.063-0.050 mm. The strategy of NFB fabrication is an oriented chemical modification of the outer surface preserving the magnetic core of parent beads with the formation of micro-mesoporous coverings. Two routes of ferrosphere modification were realized, such as (i) hydrothermal treatment in an alkaline medium resulting in a NaP zeolite layer and (ii) synthesis of micro-mesoporous silica on the glass surface using conventional methods. Immobilization of Ni(2+) ions in the siliceous porous shell of the magnetic beads was carried out via (i) the ion exchange of Na(+) for Ni(2+) in the zeolite layer or (ii) deposition of NiO clusters in the zeolite and silica pores. The final NFB were tested for affinity in magnetic separation of the histidine-tagged green fluorescent protein (GFP) directly from a cell lysate. Results pointed to the high affinity of the magnetic beads towards the protein in the presence of 10 mM EDTA. The sorption capacity of the ferrosphere-based Ni-beads with respect to GFP was in the range 1.5-5.7 mg cm(-3).

An affine sorbent of the “core–shell” type was prepared on the basis of fly ash ferrospheres with the aluminosilicate glass phase content of 41 wt % as a magnetic core. The synthesis of the functional coating included four steps: the steam treatment of the fraction, the synthesis of a mesoporous silica coating on the ferrospheres surface, the surface activation by boiling in an alkaline medium, and the subsequent immobilization of Ni 2+ ions on the surface of modified ferrospheres by impregnation. The modified ferrospheres were characterized by the methods of simultaneous thermal analysis, infrared spectroscopy, X-ray diffraction, and low-temperature nitrogen adsorption. It was found that the obtained sorbent was characterized by an acceptable strength of binding of the functional shell and the sorption capacity with respect to the green fluorescent protein of up to 6.7 mg/cm 3 . The stability of the sorbent in repeated use was studied. It was established that the sorption capacity after the seventh cycle was stabilized at the level of 70% of the initial capacity.

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 M b > 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, M b ≃ 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 SiO 2 (≃ 4.7 %) and Al 2 O 3 (3.6–4.6%) and low basicity factor: M b ≃ 10–11. They consist of unidirectional or branched crystalline spinel ferrite individuals with partial Mg 2+ substitution for Fe 2+ , which prevents oxidation of the spinel to hematite, as evidenced by the large Fe/O atomic ratio: 0.72–0.73.

Изучен состав трех типов индивидуальных глобул, отличающихся характером микроструктуры (моноблочные, пластинчатые, скелетно-дендритные), во фракции ферросфер –40 + 32 мкм с содержанием 92.72 мас. % FeO. Установлено, что моноблочные глобулы имеют наиболее высокое содержание железа (95–97% FeO) и величину модуля основности Mo > 48 при соотношении Fe/O (ат.) 0.68–0.71. Они состоят из блочных индивидов частично мартитизованной (окисленной до гематита) феррошпинели. Пластинчатые глобулы отличаются высоким содержанием кальция (11–12% CaO), меньшей величиной Mo 20 21 и более окисленным состоянием железа: Fe/O (ат.) 0.63–0.66. Они состоят из блочных участков феррошпинели с высоким содержанием FeO (до 90%) и MgO (до 6%), окруженных участками пластинчатой структуры с пониженным содержанием FeO (до 57%) при высоком содержании CaO (до 34%). Cкелетно-дендритные глобулы имеют повышенное содержание SiO2 ( 4.7 мас. %), Al2O3 (3.6–4.6%) и низкую величину Mo 10 11; образованы однонаправленными или разветвленными кристаллическими индивидами феррошпинели с частичным замещением Fe2+ на Mg2+, препятствующим окислению шпинели до гематита, что подтверждается высоким отношением Fe/O (ат.) 0.72–0.73.

The effect of the concentration of mineral components in brown coal on the process of their thermal oxidative degradation was studied by differential thermogravimetry and scanning microcalorimetry. It was found that the process parameters depend on the concentrations of metal cations in the samples.