Home – Home – Jornals – Chemistry for Sustainable Development 2022 number 3

A method for producing biocomposite fertilizers with increased water resistance, based on the sequential impregnation of supports from pine bark with the solutions of urea and potassium dihydrophosphate is proposed. The structure of supports prepared from pine bark and fertilizers based on them was studied by means of scanning electron microscopy. The ability of biocomposite fertilizers based on pine bark supports to provide slow outwashing of mineral components with water for a long time was established. The treatment of fertilizers with water at room temperature for 15 days results in the removal of nitrogen, phosphorus and potassium by not more than 34.4, 74.3 and 58.4 wt. %, respectively (of the initial content), which evidences in favour of the prolonged action of biocomposite fertilizers based on pine bark. It is shown that the use of support obtained through extraction treatment of pine bark with organic solvents allows making a fertilizer with higher stability against nitrogen removal with water in comparison with the fertilizer based on the support prepared by treating pine bark with 1 % NaOH solution. Vegetation experiments on germination of Megion oat seeds revealed the same growth-promoting effect of biocomposite fertilizers based on supports obtained using different methods: the length of sprouts and roots increased by a factor of 1.5 in comparison with the reference experiment (water). The studies demonstrated the high potential of the developed fertilizers as an alternative to traditional water-soluble fertilizers and provided evidence of the possibility to obtain them using either original pine bark or wastes from its extraction processing.

The main properties of copper that determine its preferable application areas are high electrical conductance and thermal conductivity, as well as high stability against corrosion. The mechanical characteristics of metals may be affected by introducing trace additives of inert ceramic materials (modifying agents), which would be crystallization centres, altering micro- and macrostructure. For better wetting with the melt, ceramic particles are to be plated with metals through the joint treatment of ceramic powders and metals in planetary centrifugal activators. To study the effect of modification on copper properties, four molds were prepared to obtain cylindrical samples 30 mm in diameter, with different modifying agents: 1) B₄C/Cu/Cr, 2) (WC/TiC)/Cu/Cr, 3) ferrocerium MTs50Zh6 (an alloy of iron and a mixture of rare earth metals), 4) without additives. The amount of the active phase (ceramics and rare-earth metals) was 0.03 wt. % of the cast mass. It is discovered that samples 1 and 2 exhibit the smallest standard deviations of hardness from the mean values, which may be the sign of more uniform crystallization of the melt in the cases when B₄C and WC/TiC are used as modifying agents. Standard deviations for samples 1-4 with respect to HBW (Brinell hardness) are 1.90, 1.37, 6.29, 2.54, respectively, and with respect to HV (Vickers hardness) - 2.39, 2.89, 6.53, 5.28, respectively. The improvement of corrosion stability in comparison with non-modified sample after exposure for 43 h in 11 % HNO₃ solution was 9.3, 2.2, -10.9, 0.0 %, respectively, and after exposure for 127 h - 13.1, 15.4, 14.6, 0.0 %, respectively. The grain size of samples modified with ceramic refractory particles decreased by a factor of 2.4-3.0 in comparison with the reference sample, while the grain size of samples modified with rare-earth metals, on the contrary, increased by a factor of 1.5-1.7. The size of subgrains in all the modified samples was 1.3-5 times smaller than that in the reference sample.

Analysis of literature data in the field of synthesis and study of the physical and chemical properties of mono-, bi-, tri-, tetracyclic and adamantyl-containing esters of (meth)acrylic acids is systematized and presented in the review. The reactions under consideration involve the synthesis of these compounds by means of esterification of acids with cyclic alcohols, transesterification, as well as the addition of (meth)acrylic acids to unsaturated alicyclic hydrocarbons, etc. The main directions of the practical application of polycycloalkyl-containing (meth)acrylates are indicated. It is stressed that the functionalization of the double bond in norbornene-containing compounds makes it possible to obtain a wide class of functional derivatives with potential chemical activity. The results of studies carried out by the authors of this review on the addition of acrylic acids to the derivatives of cyclo- and polycycloolefins are presented. Studies on the synthesis of the derivatives of acrylic esters of cyclohexene, norbornene, dicyclopentadiene and tetracyclododecene containing hydroxyl, alkoxy, carboxyl, as well as siloxane, isocyanate and other nitrogen-containing groups are considered. It has been shown that these compounds are reactive monomers for obtaining practically valuable polymers used in many industrial areas.

Optimal parameters for determining As by the photometric method have been established. Results of arsenic determination in rocks and soils by means of photometry are presented. This method is distinguished by the low detection limit (0.1 g/t) and economic efficiency in comparison with other modern analytical methods (atomic absorption spectrometry, atomic emission spectrometry with inductively coupled plasma, and mass spectrometry with inductively coupled plasma). For rocks and soils containing organic matter, the applicability of the existing methods of acid decomposition and melting was evaluated. The results of As determination by means of photometry were compared with its certified contents in the State Standard Samples of rocks (SGKhM-1, SGKhM-3, SG-3, SZR-2, SKD-1, SGKh-1), and with the data obtained by means of mass spectrometry with inductively coupled plasma on volcanoclastic greywacke. The parameters of As determination by means of photometry were optimized. It is recommended to use the photometric method for mass determination of arsenic in rocks and soils.

Beneficiation of ilmenite ores from the Ha Tinh deposit (Vietnam) is studied by means of electromagnetic, electrostatic separation, and flotation. The dependences of the mass of the obtained magnetic fraction on the current strength and on benefication degree are determined for different numbers of the stages of magnetic separation. The conditions for the change in the concentration of the titanium product depending on the voltage on the electrodes in the process of electrostatic separation are studied. It is shown that separation brings the heavy magnetic fraction apart from the waste rock, while subsequent flotation provides a high efficiency of rutile separation from impurity components. For flotation concentration of the product after separation processes, it is established that process efficiency depends on titanium concentration in the product to be concentrated. As a result of beneficiation, ilmenite concentrate containing more than 50% TiO₂ is obtained, which meets the most stringent requirements of the market. The design of the laboratory facility and the fluorination reactor is described, as well as the materials used to manufacture them. The research methodology is described in detail. During the fluorination of the obtained concentrate with elemental fluorine, the dependences of conversion degree on the time and temperature of fluorination are investigated (S-shaped curves). It is determined that the process is complete (conversion degree is more than 98 %) within 5 min at 700 °C. The features of the fluorination of the obtained concentrate are analyzed on the basis of kinetic equations. The activation energy and preexponential factor in the Yander kinetic equation are determined. It is shown that fluorination kinetics are limited by diffusion processes (supply and removal of reagents) rather than by the rate of the chemical reaction itself.

Thorough investigation of the decomposition of eudialyte concentrate by means of sorption conversion in low-concentration sulphuric acid solutions is carried out. The effect of process conditions on the efficiency of decomposition of acid-soluble minerals from the concentrate and sorption of valuable metals and natural radionuclides from the concentrate by the sorbent is studied. It is shown that the sorption of rare earth elements, manganese, uranium and thorium, which are rather stable against hydrolysis under experimental conditions, is achieved within a broad range of process parameters. The optimal conditions for the sorption of zirconium (hafnium), niobium (tantalum) and titanium by the sorbent differ due to different hydrolytic stability of these elements in low-concentration acid solutions. The choice of optimal process conditions should be determined by economic reasonability because it is impossible to achieve a high recovery of all valuable components at the same time.

Two models of deconvolution of the first-order scattering Raman spectra of semi-coking solid products and initial coals of low metamorphism stage are compared. The results obtained by analyzing the spectra within both models are consistent with each other. It is shown that the I _D/ I _G parameter loses its informational value if additional functions describing the vibrations of C-C bonds with different types of carbon atom hybridization are used. Graphitization degree and the proportion of edge defects in graphite planes may be considered as the main numerical characteristics of imperfection in the carbon frame of low-metamorphised coal and the products of its pyrolysis.

Electron microscopy and X-ray fluorescence spectroscopy were used to study the effect of the cooling parameters of the melt obtained by reductive melting of the Chuktukon rare metal ore on the composition of the silicate and metal phases formed. The conditions for ore reduction and melt cooling are established, ensuring the predominant transition of iron, manganese, niobium and titanium into the metallic phase, and rare earth elements concentrating in the silicate phase, which is important for subsequent stages of ore processing. With relatively rapid cooling of the melt, the slag and metal parts of the system are homogeneous. In contrast, with a slow decrease in temperature, the formation of several phases with different chemical compositions is observed in both parts of the system.

The kinetics and mechanism of hydrogen evolution reaction on Mn₅Si₃ electrode in solutions x M H₂SO₄ + (0.5 - x ) M Na₂SO₄, where x = 0.5, 0.35, 0.20, 0.05, are studied by means of polarization and impedance measurements. It is established on the basis of direct- and alternating-current diagnostic criteria that hydrogen evolution reaction on manganese silicide (Mn₅Si₃) in sulphuric acid electrolyte proceeds via discharge - electrochemical desorption route. Both stages are irreversible, and the transfer coefficients of the stages are not equal. Adsorption of atomic hydrogen is described by the Langmuir isotherm. It is assumed that the hydrogen evolution reaction is complicated by the process of hydrogen absorption by the electrode material, proceeding with kinetic control (within the entire investigated potential range). The effect of a thin oxide film on the kinetics of hydrogen evolution on Mn₅Si₃ is noted at low cathodic polarizations. Keywords: manganese silicide Mn₅Si₃, hydrogen evolution reaction, sulphuric acid electrolyte, impedance

The production of many important carbon materials is currently based on the use of aromatic fractions of coal tar - a minor by-product in the production of metallurgical coke for the needs of ferrous metallurgy. Innovations to reduce the consumption of expensive metallurgical coke in blast furnace smelting and the priority development of the coke-free methods of steel production lead to a reduction in the output of coke-chemical products, which destabilizes the prospects for the production of important carbon materials, including those necessary for ferrous and non-ferrous metallurgy. The relevance of creating alternative methods for obtaining aromatic feedstock is substantiated. The potential of low-temperature coal processing by its thermosolvolysis with the production of concentrates of aromatic substances is shown. The possibility of their use as the raw material in the production of carbon anodes for the process of aluminum electrolysis is demonstrated.

To develop recommendations for the optimal consumption of food items considering the features of the Far North regions and the regional specificity of mineral composition, the content of 25 chemical elements was analyzed in the food items of local origin and those transported to the territory of the Magadan Region. It is determined that a portion of beef from cows grown in Magadan contains substantially higher amounts of calcium, sodium and phosphorus than beef samples brought from other regions. Locally produced beef liver contains higher concentrations of iron, iodine, manganese, and zinc. Locally produced pork contains significantly higher amounts of copper ( p = 0.01) and iron ( p = 0.1) in comparison with pork transported from other regions. Evaluation of microelement concentrations in vegetables in comparison with imported samples shows that local carrots contain higher selenium concentration, local cucumbers - higher potassium, copper, and manganese, beetroot is richer in selenium and zinc, with its portion being able to meet fully the daily demand for manganese. In all the analyzed vegetable samples imported from China, nickel content is higher than in local products. In addition, Chinese carrots contain reliably higher concentrations of boron and cobalt, tomatoes and cucumbers contain higher levels of chromium and vanadium, while silicon content is higher in vegetables from the Magadan Region. At the same time, neither of the examined samples exceeds the permissible levels of toxic elements.