Vol 61, No 9 (2025)

A comparative study of the catalytic activity of composites based on few-layer graphene structures decorated with Pt nanoparticles obtained as a result of low-voltage and plasma-assisted electrochemical dispersion of platinum electrodes towards oxygen reduction reaction was carried out. The prospects of oxygen reduction reaction electrocatalyst synthesis via electrochemical sputtering of platinum under the action of anodic-cathodic electrolytic plasma were shown.

Comparative investigation of potentiometric characteristics was carried out for coatings electropolymerized from phosphate buffer and HEPES buffer solutions or deep eutectic solvents, such as reline and mixture of citric acid, glucose and water. Both the effect of media acidity on sensor potential and the potentiometric response reversibility were evaluated for all the coatings synthesized. The solid contact potentiometric sensor array was developed for the determination of easily oxidizing organic compounds: hydroquinone, dopamine, quercetin and ascorbic acid. Analytical characteristics of such easily oxidizing organic compounds determination were established. According to the media pH the analytes can perform as either single-charged ions demonstrating the slopes close to Nernstian values or reducing agents influencing on polymer redox forms ratio in modifying coating. The coatings synthesized from deep eutectic solvents showed a wider linear range of determined concentrations. Also, they had better sensitivity comparing with those electrodeposited from aqueous media. The solid contact potentiometric sensors were tested for analytes determination in real samples of cosmetics, pharmaceuticals and biologically active additives with 92–107% recovery.

In this work, the electrochemical behavior of dysprosium, neodymium, and lanthanum ions and their co-reduction with nickel ions on tungsten and nickel electrodes in the eutectic melt KCl–NaCl–CsCl at a temperature of 823 K have been studied. It was found that the electroreduction of Ln³⁺ ions proceed reversibly in one three electron stage up to the polarization rates of 0.2 V/s. At the combined content of lanthanide and nickel ions, the voltampere dependences show the reduction waves of nickel ions at potentials of –0.12… –0.3 V and of lanthanide ions at potentials of –2.13… –2.18 V relative to the chlorosilver reference electrode. Besides these waves on voltammetryograms there are three recovery waves in the region of potentials: –1.68… –1.77 V; –1.95… –2.0 V; –2.13… –2.18 V. The appearance of these waves is connected with the joint electroreduction of lanthanide and nickel ions on the metallic nickel previously separated on the tungsten electrode with a certain depolarization and formation of intermetallic phases of lanthanides and nickel of different composition Ln_xNi_y. The chronopotentiograms of the open circuit revealed plateaus of potential delay corresponding to dissolution of separate phases of intermetallides. Electrolysis in potentiostatic condition at potentials –1.7… –2.1 V and at a certain ratio of concentrations of lanthanide and nickel chlorides the phases of intermetallic compounds LnNi₅, Ln₂Ni₇, Ln₂Ni₃, LnNi₃, LnNi₂ were obtained. The synthesized samples of lanthanide and nickel intermetallides were characterized by X-ray phase analysis and scanning electron microscopy. The EMF values for Ln_xNi_y intermetallic compounds in two-phase coexisting states at 823 K have been measured. The relative partial moles of the Gibbs free energy and activity of lanthanide in Ln_xNi_y intermetallic compounds were calculated from the EDS values.

An analysis of the composition of brass metallurgical waste was carried out using X-ray fluorescence analysis (XRF). The results showed that the copper content in the slag reaches 15 wt. %, and the zinc content – 83 wt. %. Sulfuric acid leaching was performed to separate zinc from the metallurgical dust. Optimal process parameters were selected: leaching duration – 60 minutes, sulfuric acid concentration – 0.1 M. After sulfuric acid leaching, the acid solution was subjected to electrochemical treatment to recover copper and zinc, and the copper cake (copper in unoxidized form) was subjected to copper-ammonia leaching for 40 minutes. The concentration of copper in the copper-ammonia solution reached 35 g/L. At the final stage, solvent extraction of copper from the copper-ammonia leach solutions was carried out, for which the most effective extractant was selected. Extractants of different nature and classes were studied: D2EHPA (a strong acidic organophosphorus extractant), DХ510А and LIX54 (belonging to the class of β-diketones). The concentration of extractants ranged from 50 to 100%, the diluent was kerosene. Copper stripping from the copper-ammonia extract was performed using 2M sulfuric acid. The best extractant was found to be LIX54 at 50% concentration in kerosene. The final stage was copper electrowinning from the stripping solutions at a current density of 3 A/dm², with a current efficiency of 65%. Based on the conducted research, a process flowsheet was developed for the recovery of copper and zinc from brass metallurgical dust.