The Preparation and Contact Drying Performance of Encapsulated Microspherical Composite Sorbents Based on Fly Ash Cenospheres.

Sorption technologies are essential for various industries because they provide product quality and process efficiency. New encapsulated microspherical composite sorbents have been developed for resource-saving contact drying of thermolabile materials, particularly grain and seeds of crops. Magnesium sulfate, known for its high water capacity, fast sorption kinetics, and easy regeneration, was used as an active moisture sorption component. To localize the active component, porous carriers with an accessible internal volume and a perforated glass-crystalline shell were used. These carriers were created by acid etching of cenospheres with different structures isolated from fly ash. The amount of magnesium sulfate included in the internal volume of the microspherical carrier was 38 wt % for cenospheres with ring structures and 26 wt % for cenospheres with network structures. Studies of the moisture sorption properties of composite sorbents on wheat seeds have shown that after 4 h of contact drying the moisture content of wheat decreases from 22.5 to 14.9-15.5 wt %. Wheat seed germination after sorption drying was 95 ± 2%. The advantage of composite sorbents is the encapsulation of the desiccant in the inner volume of perforated cenospheres, which prevents its entrainment and contamination and provides easy separation and stable sorption capacity in several cycles.

Characterization of Silicate Glass/Mullite Composites Based on Coal Fly Ash Cenospheres as Effective Gas Separation Membranes.

Membrane technology is a promising method for gas separation. Due to its low energy consumption, environmental safety, and ease of operation, membrane separation has a distinct advantage over the cryogenic distillation conventionally used to capture light inert gases. For efficient gas recovery and purification, membrane materials should be highly selective, highly permeable, thermally stable, and low-cost. Currently, many studies are focused on the development of high-tech materials with specific properties using industrial waste. One of the promising waste products that can be recycled into membrane materials with improved microstructure is cenospheres-hollow aluminosilicate spherical particles that are formed in fly ash from coal combustion during power generation. For this purpose, based on narrow fractions of fly ash cenospheres containing single-ring and network structure globules, silicate glass/mullite composites were prepared, characterized, and tested for helium-neon mixture separation. The results indicate that the fragmented structure of the cenosphere shells with areas enriched in SiO2 without modifier oxides, formed due to the crystallization of defective phases of mullite, quartz, cristobalite, and anorthite, significantly facilitates the gas transport process. The permeability coefficients He and Ne exceed similar values for silicate glasses; the selectivity corresponds to a high level even at a high temperature: αHe/Ne-22 and 174 at 280 °C.

Anomalous Diffusion of Helium and Neon in Low-Density Silica Glass.

The diffusion properties of low-density non-porous silica glasses (expanded silica glasses) were researched with the aim of searching for the molecular structure of membrane materials intended for the effective separation of helium-neon gas mixtures. It has been shown on a large number (84) of computer models of such glasses that there are molecular structures of silica in which various helium and neon diffusion mechanisms are simultaneously implemented: superdiffusion for helium and subdiffusion for neon. This makes it possible to significantly (by 3-5 orders of magnitude) increase the helium permeability of such glasses at room temperature and maintain a high selectivity for the separation of helium and neon (at the level of 104-105) at the same time.

Composition-Structure Relationship and Routes of Formation of Blocklike Ferrospheres Produced by Pulverized Combustion of Two Coal Types.

The composition-structure relationship of blocklike ferrospheres (FSs) isolated from fly ash produced during the combustion of two different types of coal was studied systematically by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Monoblock globules were shown to consist of large sintered crystallites of Mg, Mn ferrospinel, which are formed from excluded siderite particles containing isomorphic impurities of magnesium and manganese carbonates. The common groups of globules for which the gross composition of polished sections corresponds to the general equations for the relationship of the concentrations SiO2 = f(Al2O3) and CaO = f(SiO2) were highlighted from FSs of two series. These globules are formed during the thermochemical transformation of associates of siderite, quartz, calcite, and anorthite, which have a silicate modulus of SiO2/Al2O3 equal to 1.18, which corresponds to the coefficients in the general equations of the relationship SiO2 = f(Al2O3). SEM analysis of polished cross-sections of the globules of selected FS groups demonstrates that the crystallite size of ferrospinel decreases, while the content of the glass phase increases with the declining FeO concentration in individual globules. The crystallite size and shape are found to depend on the size of the local melt area where the concentration of spinel-forming oxides is >85 wt %. The observed increase in the glass-phase content is attributed to the broadening of the liquation zone in the FeO-Fe2O3-SiO2 system as the oxidative potential increases and to the higher content of [Fe3+O2]- and [Fe3+ 2O5]4- ferrite complexes in calcium-rich melts.

Magnetic Fractions of PM2.5, PM2.5-10, and PM10 from Coal Fly Ash as Environmental Pollutants.

Characterization of magnetic particulate matter (PM) in coal fly ashes is critical to assessing the health risks associated with industrial coal combustion and for future applications of fine fractions that will minimize solid waste pollution. In this study, magnetic narrow fractions of fine ferrospheres related to environmentally hazardous PM2.5, PM2.5-10, and PM10 were for the first time separated from fly ash produced during combustion of Ekibastuz coal. It was determined that the average diameter of globules in narrow fractions is 1, 2, 3, and 7 µm. The major components of chemical composition are Fe2O3 (57-60) wt %, SiO2 (25-28 wt %), and Al2O3 (10-12 wt %). The phase composition is represented by crystalline phases, including ferrospinel, α-Fe2O3, ε-Fe2O3, mullite, and quartz, as well as the amorphous glass phase. Mössbauer spectroscopy and magnetic measurements confirmed the formation of nanoscale particles of ε-Fe2O3. Stabilization of the ε-Fe2O3 metastable phase, with quite ideal distribution of iron cations, occurs in the glass matrix due to the rapid cooling of fine globules during their formation from mineral components of coal.

Methane oxidation over A-site ordered and disordered Sr(0.8)Gd(0.2)CoO(3-δ) perovskites.

A tetragonal phase Sr0.8Gd0.2CoO3-δ with ordered Gd(3+)/Sr(2+) ions and oxygen vacancy sites is found to be about five times less active in the reaction of methane combustion than a quenched cubic perovskite phase with randomly distributed (disordered) Gd(3+)/Sr(2+) ions over the A-sites of the crystal lattice.