The effect of replacing cement with high-calcium fly ash (HCFA), represented by 4 fractions (Fr1–Fr4) from 4 electrostatic precipitators of the ash collectors at the Krasnoyarsk TPP-2, on the properties of cementing slurry was studied. The parameters of flowability, thickening, and compressive strength of specimens containing Fr1–Fr4 fractions from 100 to 20% were determined. Optimal compositions of cement slurries containing Fr3 fraction from 20, 30 to 40% were proposed.

A systematic study of the relationship between the composition and structure of skeletal-dendritic ferro-spheres isolated from fly ash formed in the combustion of Ekibastuz coal, carried out by means of scanning elec-tron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), allowed us to establish the general routes of their formation and the peculiarities of the influence of mineral precursors on their structure. The groups of globules were distinguished exhibiting a linear correlation between the content of silicon, iron and al-uminium oxides in the gross composition of the polished sections. It is shown that the investigated ferrospheres are formed from the melt droplets of the general FeO-SiO2-Al2O3-CaO system during their cooling and crystal-lization of individual phases. The formation of melt droplets occurs due to the sequential transformation of dis-persed products from thermal conversion of mineral precursor associates, such as siderite, quartz, calcite and aluminosilicate components in the carbon matrix. The aluminosilicate precursor determining the structure of globules is hydromica of illite group. The crystallization of the ferrospinel of skeletal-dendritic globules occurs due to the "seed" of Al,Mg-ferrospinel, which is formed as a result of the thermochemical transformation of the illite of the initial coals. The observed general trend to changes in the structure of ferrospheres from coarse-grained crystalline skeletal type to fine-crystalline skeletal-dendritic globules is explained by a decrease in the content of the main spinel-forming oxides FeO, Al2O3 and MgO in the melt microdroplets.

The dispersed fractions of industrial high-calcium fly ash (HCFA), selectively collected in the form of fractions 1-4 (Fr1-Fr4) on fields 1-4 of the electrostatic precipitators of the ash collecting unit at the Krasnoyarsk TPP-2, are systematically characterized. The fluidity parameters of ash mortars prepared from 100 % of each of the fractions at a ratio of water/binder = 0.5 were determined. It has been established that the value of fluidity de-creases with an increase in the specific surface area of the fractions from Fr1 to Fr4. The parameters of ce-ment-ash mortars with the replacement of cement by 50 and 20 % of each of the four fractions were determined. It has been established that at a 20 % HCFA content, the fluidity of cement-ash mortars of all fractions meets the requirements of GOST 1581-2019 for oil well cements. The samples based on finely dispersed fractions Fr3 and Fr4 meet the requirements for compressive strength on the second day of hardening. The specimens of ash-cement composites with high strength, more than 50 MPa for the 28th day of hardening, were prepared on the basis of the Fr4 fraction. In particular, high compressive strength (62-90 MPa) has been achieved for com-posite cements containing 80 and 90 % of the Fr4 fraction of HCFA in the presence of the superplasticizer Melflux 5581 F, which promotes efficient dispersion of finely dispersed HCFA in the liquid phase, faster and more com-plete interaction of active components with the formation of hardening hydrated phases. The addition of 5 % microsilica, which promotes the formation of an additional amount of calcium hydrosilicates, made it possible to achieve an increase in strength up to 108 MPa. The results obtained show that finely dispersed HCFA can be used as the components of oil well cements to improve the flowability of cement-ash slurries and improve the strength properties of highly filled ash-cement composite materials.

The combination of factors was established for using high-calcium fly ash (HCFA) as a binder material of high early and long-term strength: (1) high dispersity of microspherical HCFA, 90% <10 mu m; (2) the positive effect of polycarboxylate superplasticizer, that allowed to use water/binder = 0.25; (3) formation of finely mixed hydrate phases such as portlandite, ettringite, calcium carboaluminate hydrates and cryptocrystalline calcium hydrosilicates. X-ray powder diffraction quantitative phase analysis of initial HCFA and hydration products in high-strength specimens was performed, which contributes to understanding phase transformations of HCFA during hydration and to improving the properties of the binder. (C) 2019 Elsevier Ltd. All rights reserved.

The high-calcium fly ashes (HCFA) of Krasnoyarsk TPP-2, Russia were studied. The HCFA were selected from each of the 4 fields of the electrostatic precipitator. It was determined that the size distribution, chemical and quantitative phase composition vary significantly from 1st to 4th EF field. The fine high-calcium fly ash (d(90) < 10 microns) selected from the fourth field of electrostatic precipitator was the source for high strength specimens. In the composition with a superplasticizer at a water:binder ratio of W/B = 0.25 the specimens were made and then cured from 1 to 120 days, with their compressive strength increasing from 17 to 72 MPa. The strength of these specimens is comparable to the strength of specimens based on Portland cement PC 42.5 N without superplasticizer. The methods of simultaneous thermal analysis (STA) and quantitative X-ray phase analysis (XRD) were used to study phase transformations of high-calcium fly ash in the process of hydration curing. The major newly formed phases are ettringite 3CaO center dot Al2O3 center dot 3CaSO(4)center dot 32H(2)O, as well as calcium carboaluminate hydrates Ca4Al2(OH)(13)(CO3)0.5 center dot 4H(2)O and Ca4Al2(OH)(12)CO3 center dot 5H(2)O with low crystallinity. The new phases can form a wide range of solid solutions by replacing Al (3+) with Fe (3+). The more the curing age was, the more transformations of calcium silicate amorphous substance contribute to form cryptocrystalline calcium hydrosilicates that increased the initial and long- term strength of the material. The phase transformations and strength indicators allow to use fine high-calcium fly ash of coal-fired power plants as an independent cementing material in modern technologies for producing building materials, in particular, in the technology of self-compacting composite concrete (SCC). The proposed alternative to cement contributes to the solution of a complex environmental problem: (1) in the heat power engineering the accumulation of fine ash particles can be lowered with consequent reduction of the pollution of water, soil and atmosphere with thin dust particles, and (2) in the construction materials industry a part of the cement can be replaced by the fine HCFA, that will save energy and natural resources.

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 %.

The composition was studied of calcium aluminosilicate microspheres of three morphological types in high-calcium fly ash from combustion of brown coal from the Kansk-Achinsk basin in slag-tap boilers at temperatures from 1400 to 1500°С and sampled in the first field of electrostatic precipitators at the Krasnoyarsk Cogeneration Power Station no. 2 (TETs-2). Gross compositions and the composition of local areas were determined using a scanning electron microscopy technique and an energy-dispersive analysis with full mapping of globules. With a high content of basic oxides O ох (68 to 79 wt %) and a low content of acid oxides K ох (21 to 31 wt %), type 1 microspheres are formed. They consist of heterogeneous areas having a porous structure and crystalline components in which the content of CaO, SiO 2 , or Al 2 O 3 differs by two to three times and the content of MgO differs by seven times. With a lower content of O ох (55 to 63 wt %) and an elevated content of K ох (37 to 45 wt %), type 2 microspheres are formed. They are more homogeneous in the composition and structure and consist of similar crystalline components. Having a close content of O ох (46 to 53 wt %) and K ох (47 to 54 wt %), type 3 microspheres, which are a dense matter consisting of amorphous substance with submicron- and nanostructure of crystalline components, are formed. The basic precursor in formation of high-calcium aluminosilicate microspheres is calcium from the organomineral matter of coals with various contribution of Mg, Fe, S, or Na from the coal organic matter and Al, Fe, S, or Si in the form of single mineral inclusions in a coal particle. On the basis of the available data, the effect was analyzed of the composition of a CaO–MgO–Al 2 O 3 –SiO 2 –FeO system on the melting and viscous properties of the matter in microspheres and formation of globules of different morphology. The results of this analysis will help to find a correlation with properties of microspheres in their use as functional microaggregates in cement or polymeric composite materials, or in the production of ceramic membranes or zeolite sorbents.

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.

In processing a heavy oil feedstock, an urgent problem is to find new and less expensive, primarily cracking, catalysts. We have studied the activity of redox catalysts based on ferrospheres from energy ashes in the cracking of two types (paraffinic and asphaltenic) of heavy oil and paraffinic crude oil under autoclave conditions. It was found that at 450 °C and in the presence of 10 wt % of ferrospheres, the selectivity toward liquid products for paraffinic and asphaltenic feedstock achieves 95–96 % and 72 %, respectively. Compared with the thermal cracking, this catalytic system provides the composition of liquid products with the higher content of light products and higher percent of the gasoline fraction. The influence of ferrospheres is most pronounced in the cracking of paraffinic feedstock: compared with thermal cracking, the content of light fractions in the products of petroleum cracking increases by ~20 % and achieves 67 %, while in the products fuel oil cracking, the ratio of the gasoline fraction increases 14-fold. During the cracking, we detected changes in the phase composition and structural characteristics of ferrospheres, formation of surface carbonaceous deposits with different reactivity in the combustion, and accumulation of sulfur compounds from petroleum feedstock.

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.

Finding new low-cost catalysts, especially ones that can be used in cracking, is a problem of great interest in the refining of heavy oils. The activity of redox catalysts based on coal fly ash ferrospheres is examined for the cracking of two types of heavy oils (paraffin and asphaltenic), and for paraffin oil residue under autoclave conditions. It is established that at 450°C and with 10 wt % of ferrospheres, the selectivity of the formation of liquid products can be as high as 95–96% for paraffin oil and 72% for asphaltenic oil. The content of light products and the gasoline fraction increases in liquid products in comparison to thermal cracking. The effect of ferrospheres is most pronounced in the cracking of paraffin oil: the light fraction in the oil cracking products grows by approximately 20% relative to those obtained after thermal cracking, reaching almost 67%; the gasoline fraction in the light products of oil residue cracking grow by 14 times. The phase composition and structural characteristics of ferrospheres change during cracking, carbon compounds with different combustion reactivity are deposited on their surfaces, and concentrated sulfur compounds from heavy oils are observed.

This paper reports on the results of the investigation of fly ashes from pulverized combustion of coals of two ranks, i.e., the B2 (sub C) rank, which is taken from Fields 1−4 of the electrostatic precipitators at the BSDPS -1 (the Bfa series), and the T (sa) rank, which is taken from Fields 1 and 2 of the electrostatic precipitators at the MPP-22 (the Mfa series). It has been shown that fly ashes of the Bfa series have a lower bulk density and a higher dispersity and a unimodal particle size distribution. The size of particles increases along the gas-and-dust flow, in particular from the Field 1 to the Field 2 of the electrostatic precipitators. Fly ashes of the Mfa series are characterized by a higher density, a substantially lower dispersity, a bimodal particle size distribution and have rather close size characteristics for ashes from the Fields 1 and 2 of the electrostatic precipitators. The use of the aerodynamic separation has made it possible to obtain three products from fly ashes of both series which differ significantly in the bulk density and size of particles. Combination of selective sampling and aerodynamic separation of fly ashes from pulverized combustion of coals are promising techniques for manufacturing ash products with a controlled density and dispersity.