The paper proposes a method for quick estimation of the average floatability of minerals according to the kinetic experiment, without finding the flotation spectrum where first moments of distribution are calculated by the coefficients of the polynomial approximation of the kinetic curve in the logarithmic form. An example of copper-nickel ore demonstrated that this method is effective in the multiparameter problem of comparative assessment of reagents. The ten parameters assessed included the average floatability of target minerals (chalcopyrite and pentlandite), pyrrhotite and rock; flotation selectivity coefficients of target minerals relative to pyrrhotite and rock; levels of copper and nickel losses with bulk flotation tailings. Interdependencies of parameters were visualized using diagrams showing the effect of flotation reagents on the groups of parameters: average floatability, selectivity coefficients, metal losses and selectivity relative to rock. The influence of butyl xanthate, aerofloat, diesel fuel, as well as gangue depressants – carboxymethyl cellulose (CMC) and acidified water glass (with a total consumption of collectors, diesel fuel, acidified water glass and CMC of 130 g/t, 5–10 g/t, 200 g/t, and 500 g/t, respectively) on the estimated parameters under collective flotation conditions was determined. It was found that the addition of aerofloat and diesel fuel to the main reagent collector – xanthate – increases the flotation selectivity of pentlandite and chalcopyrite relative to pyrrhotite and rock-forming component. The introduction of acidified water glass into the reagent scheme increases the flotation selectivity of nickel and copper sulfides relative to the rock. CMC additives impair the selectivity of copper flotation. The quantitative effects of each individual parameter were taken into account in the integral rating assessment of the prospects of using reagent combinations for copper-nickel ore by a set of ten parameters. The method proposed can be further used for the mass comparative evaluation of flotation reagents.

The study covers physical and chemical regularities of zinc sulfide concentrate oxygen pressure leaching in sulfuric acid. The effect of lignosulfonate concentration (C_LSN = 0.2÷0.8 g/dm³), leaching time (τ = 20÷120 min), temperature (T = 393÷423 K), and oxygen partial pressure (РО₂= 0.3÷0.7 MPa) on the degree of zinc and iron extraction into the solution and on the cake grain-size distribution was established. It was shown that lignosulfonate additive intensifies zinc and iron extraction into the solution. Maximum extraction of zinc and iron was 89 and 37 %, respectively, for 120 min of leaching at C_LSN = 0.6÷0.8 g/dm³. The differential rate law with respect to lignosulfonate was 0.3 for sphalerite, and 0.9 for iron sulfides. A controversial influence of rising temperature on the process under investigation was found. Temperature elevation from 413 to 423 K leads to a decrease in zinc extraction by 3–4 % due to the formation of sulfur-sulfide aggregates over 150 μm in size. The calculated values of apparent activation energy (Е_а) of sphalerite and iron sulfide leaching in the presence of lignosulfonate were 30 and 45 kJ/mole, respectively. It was found out that an increase in oxygen partial pressure from 0.3 to 0.5 MPa has a positive influence on leaching and increases extraction of zinc and iron by 22 and 27 %, respectively. However, an increase in oxygen partial pressure up to 0.7 MPa in the presence of lignosulfonate after 40 min of leaching led to a decrease in leaching rate, possibly as a result of lignosulfonate destruction. It was found that differential rate laws with respect to oxygen are 1.2 for sphalerite and 2.5 for iron sulfides.

Fine dusts of copper smelting production are a valuable raw material for the extraction of heavy non-ferrous, noble and rare metals. A feature of dusts is the high content of arsenic in them, which must be removed from the production cycle in the form of a product suitable for safe storage. The most rational way is the combined technology for processing copper smelting production dusts including low-temperature dust roasting (calcination) in order to distill arsenic into a separate product and to break up poorly soluble sulfide and ferrite zinc and copper compounds. The chemical and phase composition of Ausmelt technology dusts is presented. Thermodynamic calculations of reactions occurring during the dust roasting were carried out in order to study the behavior of copper, zinc, arsenic and iron compounds when roasted in the temperature range of 20–1000 °C, features of solid phase formation and composition, optimization of arsenic roasting and distillation conditions. It was established that dust calcination allows the conversion of poorly soluble sulfides and ferrites of zinc and copper into acidsoluble oxides and sulfates. Thermodynamic parameters were determined for the sulfuric acid leaching of individual cinder compounds. The results of laboratory studies showed that the calcination temperature of 550 °C provides the most satisfactory results of arsenic conversion to sublimates (more than 95 %) as well as copper and zinc recovery into the solution during sulfuric acid leaching (more than 90 %). The initial acidity of solutions of 50 g/dm³ and solution temperature of 60°C are sufficient to achieve high values of copper and zinc recovery into the solution.

The paper provides the results of experiments on the hydrometallurgical processing of finely dispersed technogenic raw materials for primary aluminum production in Soderberg cells (case study of the Irkutsk Aluminum Smelter) – aged sludge. The components of this sludge are dust from electrostatic precipitators (79.7 %), wet gas cleaning sludge (4.4 %) and coal froth flotation tailings (15.8 %). According to the grain-size analysis carried out, aged sludge sample particles have a size of –50 μm. According to the chemical composition analysis of the sludge sample, main components in it are carbon, cryolite, chiolite with a small amount of other compounds (corundum, ralstonite, spodumene, fluorite). Fluorine leaching experiments were carried out with a 2 % sodium hydroxide solution at a stirrer speed of ~1020 rpm. Using the mathematical planning of a three-factor experiment, it was found that the maximum concentration of fluorine in the solution (15.844 g/dm³) is achieved with the following optimal parameters of fluorine alkaline leaching: temperature of 90 °C, liquid-to-solid ratio of 9 : 1, and time of 90 min. The multidimensional polynomial equation was obtained for fluorine alkaline leaching from aged sludge. Cryolite was obtained from fluorine-containing solutions (by the reaction of sodium fluoride interaction with sodium bicarbonate and an aluminate solution), which was confirmed by X-ray phase analysis data.

The paper provides the results obtained in the study of the features of metallic platinum, rhodium and iridium dissolution in hydrochloric acid solutions under hydrothermal autoclave conditions. Hydrogen peroxide was used as an oxidizing agent. Solid and liquid phases were brought into contact after reaching a predetermined temperature, which is critically important in the study of rhodium black and platinum plate dissolution kinetics due to the high rates of these processes. The concentrations of metals in solutions were determined by atomic absorption spectroscopy and inductively coupled plasma mass spectrometry. The forms of rhodium, iridium, and platinum chlorocomplexes in solutions were determined using the spectrophotometric method. As a result of the experiments, the conditions of platinum plate and rhodium quantitative dissolution (in the form of affined powder and a plate) were determined and it was shown that at 210 °C in 6M hydrochloric acid as a medium with the addition of 5 vol.% hydrogen peroxide, iridium taken in the form of affined powder went into the solution by 50 % within more than 50 h, while the platinum plate dissolved completely at 130 °C in about 120 min. Kinetic data analysis using the shrinking core model showed that rhodium black and affined rhodium and iridium powders dissolve under autoclave conditions in a kinetic mode. The results obtained can be used both in analytical chemistry for the quantitative determination of inert platinum metals and in refining production to improve the technology for processing raw materials containing platinum group metals (PGMs) and to optimize approaches to the synthesis of pure chlorocomplex compounds of PGMs.

The study covers the free linear shrinkage of samples from PLA, HIPS, and ABS filaments used for FDM 3D printing in the ranges of extrusion operating temperatures (t). It was found that the PLA filament features by shrinkage values in the range of 0.2–0.6 % at Δt =200÷220 °С. HIPS filaments (Δt = 220÷240 °С) and ABS filaments (Δt = 240÷270 °С) have a shrinkage of 0.3–0.8 %. Linear shrinkage values must be taken into account when designing mathematical models of the future cast product. The influence of the print density d_р (degree of internal structure filling) on the ash residue A when burning out samples obtained from the studied filaments was investigated. It was shown that the A value also increases with an increase in d_р (5–15–30 %). The PLA filament has minimum A values (0.19–0.48 %). It was concluded that the PLA filament features the highest processability in the FDM 3D printing of casting patterns for casting into refractory ceramic molds (RCM) in terms of the set of free linear shrinkage and ash residue indicators. Clusters were made by FDM 3D printing from the PLA filament to produce «Nozzle» castings by casting into RCMs. Clusters were used to form RCMs. When burning out the clusters from RCMs, it was found that some RCMs cracked under linear heating. This was due to excessive pressure exerted by the expanding filament when heated to its softening temperature, and pressure exerted by gas emitted during the subsequent filament burn-out. The proportion of cracked RCMs increased with an increase in the heating rate. A stepwise mode of RCM heating combined with RCM calcination was developed in order to prevent cracking. There was no RCM cracking when clusters were removed in the stepwise mode. Experimental «Nozzle» castings were obtained from BrA9ZH3L bronze. The casting quality met the design documentation requirements.

Laser cladding featuring by a minimal thermal impact on the substrate is an advanced method of restoring the working dimensions of parts operated under wear conditions. Ni–Cr–B–Si system coatings can be used in parts operated at high temperatures. The research was aimed to study the influence of heating and subsequent cooling conditions during high-temperature treatment on the structural phase state formation features of the coating obtained by PG-SR2 powder laser cladding (chemical composition, wt.%: 14.8Cr; 2.1B; 2.9Si; 2.6Fe; 0.48C; the rest is Ni), and properties achieved in this process (hardness and tribological properties when sliding on the fixed corundum abrasive). Samples with the clad layer were heated at 1050 °С (holding for 1 h) with subsequent cooling in water (which made it possible to record structural transformations under high-temperature heating), in air, in a muffle furnace and in a vacuum furnace. It was shown that the cooling rate during the high-temperature treatment of the laser clad PG-SR2 coating has a significant effect on the formed structure and properties. High-temperature heating leads to a partial diffusive dissolution of Ni₃B nickel borides and Cr₂₃C₆ chromium carbides in a solid solution and a corresponding decrease in hardness, an increase in abrasive wear intensity and friction coefficient. Cooling rate deceleration from 1050 °C when samples are cooled in air, muffle and vacuum furnaces leads to the release of CrB chromium borides and Ni₃Si nickel silicides that were absent in the clad coating structure. High-strength CrB borides with hardness equal to or even higher than that of the corundum abrasive limit the development of the microcutting mechanism during abrasive wear. Large chromium carbides and borides formed during slow cooling in the furnace form wear-resistant frame-like structures. This leads to an increase in hardness and abrasive wear resistance to levels that exceed the features of the original clad coating.