For the Republic of Kazakhstan as a country with developed mining and processing sectors, a topical issue is to develop the areas of knowledge aimed at improving and refining methods and technologies for comprehensive mineral processing including for the more complete extraction of precious metals. The necessity of these studies is determined by the high loss of precious metals during their processing and separation and the need to improve the process of their concentration. Advances in the field of carbon nanomaterials offer great prospects for improving existing technologies for the precious metal extraction from waste solutions and pulps. This paper covers the comprehensive studies into the influence of the solution flow rates, pH and the presence of ions of other metals on the extraction of gold on a carbon nanostructured material consisting of rice husk with its further regeneration and reuse. It was found that the highest gold (III) ion recovery is observed at pH ~ 2. The gold recovery efficiency was studied in the combined presence of copper, nickel and silver. The dependence of the electrochemical reduction sorption of gold on the flow rate of solutions was investigated. It was found that the optimal solution flow rate is 10 ml/min. The sorption capacity of a sorbent based on carbonized rice husk was calculated. The investigation of electrochemical sorption/desorption of gold (III) ions showed that the desorption process runs better in an acetone + water + NaOH mixture with a desorption degree of 96 %. This demonstrates the possibility of regenerating the electrode carbon material for reuse. The results obtained can be used to optimize the processes of extraction of precious metals from their solutions.

The paper provides the results of experimental studies on the development of a method for obtaining titanium-containing bar ligature, the study of its structure and modifying ability. The distinctive features of the new technology are the use of titanium sponge and/or titanium shavings as titanium raw materials, the primary alloying of aluminum with titanium, and then boron, titanium introduction in two stages: initially, 2/3 of titanium metal raw materials are dissolved in the aluminum melt, and the remaining amount is introduced after the potassium tetrafluoroborate reduction. Titanium sponge pre-impregnation with halide-containing flux and the use of a briquetted KBF4 + Al-powder mixture are also provided. The experimental technology for Al–Ti–B melt preparation is described, titanium and boron extraction into the ligature is calculated, ligature microstructure is investigated, and chemical and molecular compositions of resulting slags are determined. Deformation processing for bar ligature production was carried out by the method of direct extrolling that smoothed over cast structure defects. It was found that the use of high-speed crystallization-deformation in the combined direct extrolling process makes it possible to obtain alloying bars of a given diameter at minimal energy consumption with the required set of mechanical and operational properties. A quantitative modifying ability assessment of the experimental cast-iron ligature and the deformed cast-iron rod obtained by the direct extrolling method was carried out in comparison with the mass-produced cast-iron ligature produced by KBM Affilips (the Netherlands/Belgium). Based on theoretical and experimental studies, the composition and technology for producing Al–Ti–B modifying ligature using titanium sponge and/or shavings and potassium tetrafluoroborate containing 3.0±0.3 % titanium and 1.0±0.2 % boron as alloying additives have been developed that meet the aluminum ligature composition requirements.

In the mechanical engineering, antifriction tin bronzes are used for the manufacture of friction parts. For example, the C92900 bronze has found use in aircraft braking system components. One of the ways to improve the properties of leaded tin bronzes is to increase the cooling rate during solidification. This paper studies the effect of the cooling rate and changes in the content of alloying elements within the limits established by the C92900 bronze industry standard OST 1 90054-72. In order to provide different cooling rates, the prepared alloys were casted into molds made of resin-bonded sand, steel and graphite with cooling rates 0.4, 5.0, and 14.6 °C/s, respectively. The influence of the cooling rate and the bronze composition on the freezing range, macrostructure, microstructure, thermal conductivity, mechanical, and tribological properties were investigated. Differential thermal analysis demonstrated that the upper-limit alloying of C92900 bronze leads to a decrease of the solidus temperature by 40 °C, which should be considered during deformation processing and heat treatment. An increase in the cooling rate during C92900 bronze ingot solidification provides a significant grain refinement and changes the amount, size and morphology of phases. For example, in case of metallic and graphite mold casting, the size of lead particles decreases, and its circularity increases. The change in the Sn content within the range established by the industrial standard has a significant effect on the γ-(Cu,Ni)₃Sn intermetallic phase fraction. The increase in the cooling rate has no significant effect on the C92900 bronze thermal conductivity but increases hardness by 30 HB as well as cooling rate and yield strength and ultimate tensile strength. Wear tests carried out in accordance with the «shaft – partial insert» scheme in a kerosene medium using a steel counterbody showed that an increase in the cooling rate during solidification leads to an increase in the bronze wear rate from ~0.4·10^–8 to ~1.2·10^–8. The change in the bronze composition within the industrial standard range has practically no effect on the wear rate but leads to a slight increase of the coefficient of friction.

The study covers the effect of Melt Superheating Treatment (MST) for Al–Sn alloys. To determine the optimal superheating temperature, the authors measured the temperature dependences of the kinematic viscosity, electrical resistivity, density and surface tension of Al–Sn melts with tin contents of 10, 20, 30, 40, and 50 wt.%. According to the measurement results, the temperature t* was determined for each Al–Sn alloy sample. Heating to this temperature breaks down the micro-inhomogeneous state and leads to the heterogeneous liquid – homogeneous liquid structural transition. Melt superheating (MST) results in a decrease in melt viscosity. It was found that the temperature t* rises with increasing tin concentration in the Al–Sn melt. An increase in the tin content in the Al–Sn melt also leads to a decrease in the absolute values of kinematic viscosity and surface tension, while the electrical resistivity and density increase accordingly. Thus, the Melt Superheating Treatment (MST) mode for Al–Sn alloys was determined. The effect of MST of Al–50wt.%Sn melt on the microstructure and mechanical properties of the ingot was studied in order to determine the structural sensitivity to the degree of melt overheating, and to find a new strategy to improve the shaping ability of the Al–Sn alloy two-phase structure. The results demonstrated that the method of resistivity and viscosity determination are more sensitive and effective for melt superheating temperature (MST mode) evaluation. In addition, the desired modified Al–Sn ingot structure can be formed under normal casting conditions; MST can contribute to the modified ingot structure formation by increasing the solidification time and decreasing the average solidification rate by reducing melt viscosity after superheating.

The paper provides results on the further development of a method for calculating heat emissions during plastic strain in its instantaneous deformation zone in the course of cold pilgering of pipes, such as the ones that affect the working tool deflection in coldpilgering mills and mechanical properties of wrought pipe metal. It was determined that a decrease in the cross-sectional depth of the coldpilgering mill die groove due to thermal distortions (thermal effect) caused by plastic strain of a pipe in the instantaneous deformation zone is in direct proportion to the distance of the die groove longitudinal section considered to the roll barrel edge. It was found that sections located closer to the roll barrel receive thermal distortion of a lesser degree. A method is proposed for thermal distortion compensation in roll-pass design calculation. Experiments on applying marks on the roll barrel surface near the groove taper showed that the maximum galling of marks takes place directly near tapers. This indicates the local nature of thermal expansion. Dependencies are presented to determine the value of tool geometry variation depending on the heating temperature. The presented dependencies were tested experimentally and were introduced as a basis for developing the method of calculating the transversal die groove parameters for the cold-pilgering mill taking into account local thermal expansion in the instantaneous deformation zone. The inferred law allows taking into account the influence of cold pilgering peculiarities on the variation of the die groove cross-section geometry in the cold-pilgering mill, pipe dimensions and performance parameters.

Multicomponent eutectic alloys developed in recent years based on the Al–Ca system have high practical application prospects due to their low density, high corrosion resistance, good processability when casting, and high formability in the as-annealed state. Alloy hardening is achieved by doping with Mn, Fe, Zr, Sc and other elements. Obtaining an ultrafine-grained state in aluminum alloys by the methods of severe plastic deformations, e.g. equal channel angular pressing (ECAP), significantly increases the complex of their mechanical properties. In this regard, the purpose this paper was aimed to study the effect of warm ECAP on the structure, mechanical properties and thermal stability of the eutectic aluminum alloy, wt.%: Al–3.5Ca–0.9Mn–0.5Fe–0.1Zr–0.1Sc. The ECAP process was carried out on as-cast alloy specimens with a diameter of 20 mm (temperature 400 °C, route BC, channel intersection angle 110°, number of passes N = 6). It is shown that as a result of ECAP, a developed substructure with high-density dislocations and released nanosized Al₆(Mn, Fe), and Al₃Sc particles is formed in the alloy, as well as primary coarse Al₆(Mn, Fe) particles and eutectic Al₄Ca particles are reduced in size. Such a change in the structure during ECAP leads to the significant hardening of the alloy: its strength properties increased by 1.5–2.0 times, and relative elongation decreased by 1.3 times in the longitudinal section sample and slightly changed in the «transverse» section sample as compared to the initial condition.

EP741NP alloy samples featuring various types of defects with the volume fraction varying from 0.31 to 0.65 % were produced by the method of selective laser melting (SLM) at various process conditions. The structure of SLM samples was investigated using optical and scanning electron microscopy, and mechanical properties were determined by tensile tests. All investigated SLM samples featured by low strength characteristics due to the metastable single-phase structure formation, as well as structural defects in the form of cracks. To improve mechanical properties, various types of post-processing were carried out including hot isostatic pressing (HIP), heat treatment according to the «solution + aging» (HT) type, and comprehensive processing combining HIP and HT. According to the research results, the influence of various post-processing types on the microstructure and properties of SLM samples were determined. It was established that the use of HIP contributes to a decrease in porosity to 0.04 %, structure recrystallization, and the precipitation of a strengthening intermetallic phase based on Ni₃Al (γ ′-phase) in the form of large particles of different sizes forming agglomerates. HT leads to the structure recrystallization and precipitation of a finely dispersed γ ′-phase uniformly distributed in the alloy matrix. In this case, strength characteristics of samples after HIP and HT are approximately at the same level (σв ~ 1250÷1290 MPa), however, the ductility of samples after HT is significantly lower. This is associated with the retention of defects in the structure in the form of cracks and large pores. The maximum increase in mechanical characteristics (σ up to 1460 MPa, δ up to 21.3 %) was recorded during comprehensive post-processing (HIP + HT) that ensures defect elimination and optimal alloy structure formation.