Veniamin S. Boldyrev

Non-stoichiometric tungsten carbide WC_1−x layers (~20 mm thickness) were used as a reductant substrate to deposit palladium nanoparticles under open-circuit conditions in aqueous solutions. The prepared Pd(WC_1−x)/TEG electrodes (TEG—thermally expanded graphite) were studied by a complex of modern physical methods: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman Spectroscopy. The reduction of Pd(II) species to the metallic state was confirmed by XPS and XRD. The coherent scattering domain (CSD) for Pd particles was determined using the Scherrer formula (peak broadening analysis) with the LaBeil profile fitting the XRD pattern. It was ca. 16 nm, which would correspond to a specific surface area of palladium of 30.9 m²·g⁻¹, assuming a spherical shape of its particles. According to electrochemical studies, the specific area of palladium is significantly lower (8.5 m²·g⁻¹ in 0.1 M PdCl₂ after 2 h of deposition), which is due to the inevitable coalescence of metal nanoparticles during the currentless deposition process. Pd(WC_1−x) composites demonstrated high catalytic activity in the hydrogen evolution reaction (HER) and formic acid oxidation reaction (FAOR). Thus, currentless deposition can be considered as a relatively simple method for producing electrode catalysts.

The processes of metal extraction from ores, in which metals can often be found as part of oxides and sulphides, involve stages of chemical or electrochemical dissolution. Few publications can be found in the literature that describe detailed research studies looking into how the surface phenomena of d-metal oxides are linked to the acid-base properties and the dissolution mechanics. Consequently, it would be of relevance to establish kinetic relationships of the processes related to the extraction of metals from lean ores and secondary raw materials, leaching and beneficiation, surface etching and purification. This paper describes the results of a study that relied on potentiometric titration in an aqueous solution of potassium chloride to understand the dissolution kinetics of zirconium dioxide suspension. Titration curves were produced for different concentrations of the background electrolyte and pH values and a relationship was established between ZrO2 dissolution kinetics and pH of the medium. Acid-base equilibrium constants were calculated at the metal oxide/electrolyte solution interface. The obtained results were used to analyze the distribution of surface particles that form as a result of hydrogen ions adsorption and desorption. Interpretation of the experimental relationships was based on comparison with theoretical calculations. The authors simulated the dissolution process. The paper demonstrates that metal oxides dissolve in stages, and adsorption complexes form in the process, the composition of which is linked to the surface charge. These findings could be useful when studying the kinetics of d-metal oxides, as well as in practical applications related to the dissolution of transition metal oxides in electrolyte solutions.

The study of the kinetic features of the dissolution of chromium is relevant in connection with its wide application in steels and alloys, strength and corrosion-resistant coatings, in electronic engineering and many other industries. In connection with the depletion and decrease in the reserves of chromium-containing ores, the creation of new highly efficient technologies for their processing is of paramount importance. Along with topical issues of optimization of technologies for chemical etching, leaching and enrichment of chromium-containing ores, the development of combined chemical-electrochemical methods, the development of the theory and practice of electrochemical methods of processing mineral raw materials are promising. The paper presents the results of studying the features of the anodic behavior of chromium in an acidic environment. An aqueous solution of sulfuric acid was used as a working solution. The dependence of the kinetics of dissolution of the anodic dissolution of chromium on the acidity of the electrolyte was established by the potentiodynamic method. Based on the analysis of experimental and thermodynamic data, it was concluded that the process proceeded in stages with the formation of chromium hydroxo complexes, and the mechanism of its anodic dissolution. The data obtained expand the understanding of the electrochemical behavior of chromium and can be taken into account when developing regimes for leaching chromiumcontaining ores and processes associated with the dissolution of chromium in acidic media.

As part of the work, studies of the quality of wastewater from alcohol production were carried out; the main characteristics were determined, such as the charge of dispersed particles and the content of organic compounds and fats. A comparison is made of the effectiveness of titanium salts, traditional aluminum, and iron-containing coagulants. It has been established that titanium salts are much more effective than traditional reagents, but their high cost significantly limits the scope of their application. The possibility of increasing the efficiency of traditional coagulants by adding various titanium salts in an amount of up to 10% of the mass has been proved. It has been established that the addition of titanium compounds to aluminum or iron-containing coagulants makes it possible to increase the cleaning efficiency by an average of 10–20% while a significant reduction in the dose of reagents is possible, which will have a positive effect on the cost of the cleaning process. It was found that the addition of titanium salts to a coagulant based on aluminum sulfate allows not only an increase in the cleaning efficiency but also further intensifies the processes of sedimentation and filtration of coagulation sludge, which will significantly reduce the size of the treatment equipment and reduce capital costs.

The kinetics of dissolution of the commercial powdered Co₃O₄ cobalt oxide in an aqueous H₂SO₄ solution of various concentrations is experimentally studied. Electron microscopy and X-ray diffraction analysis are used to study the effect of the initial state of the surface structure of the cobalt oxide on the kinetic characteristics of dissolution. The shape and sizes of Co₃O₄ particles and the character of their surface distribution are determined. The ICDD powder material database is used to identify the structure of the oxide samples, and the Co₃O₄ oxide is found to be represented by the α form of cubic symmetry. Kinetic curves are constructed and the kinetic parameters of the process are calculated. The results obtained can serve as a contribution to the generalization of the experimental material accumulated to determine the laws of dissolution of the oxide phases of cobalt and other transition metals in acid electrolytes of various compositions.

This team of authors presents the development of an algorithm and its practical application in the software for solving the problems of automatizing the calculation of principal characteristics for powder painting chambers. The algorithm enables a developer to consider several design solutions to select an optimal variant with consideration for the initial data. The application of this algorithm and the software on its basis is illustrated with the design works of NPO Lakokraspokrytie.