Gravity-flotation gold-bearing ore concentration

The paper focuses on the study of the gold-bearing ore dressability. According to technological research, the average gold content is 11.88 g/t. The silver content is insignificant – 2.43 g/t. Main ore minerals in the sample are pyrite and pyrrhotite. According to mineralogical and X-ray structural analysis, the average content of these minerals in the ore is about 6 % (in total). Main rock-forming minerals of the original ore are: quartz (60.1 %), quartz-chlorite-mica aggregates (3.8 %), carbonates (7.1 %). According to the study results, it was found that the gold recovery in the GRG test was 72.75 % with a total concentrate yield of 1.34 % and a content of 664.78 g/t. At the same time, the gold content in tailings was 3.29 g/t. A stage test showed that it is advisable to use a two-stage scheme for ore processing by gravity technology only. The first stage is in the grinding cycle with the 60–70 % ore size, and the second stage is with the final classifier overflow size of 90 % –0.071 mm. Centrifugal separation has high performance as a free gold recovery operation in the grinding cycle. A concentrate with a gold content of 2426 g/t was obtained with a yield of 0.31 % and a recovery of 63.74 %. The beneficiation of first stage tailings ground to 90 % –0.071 mm at the KC-CVD concentrator (modeling) made it possible to extract gold into a total gravity concentrate (KC-MD + KC-CVD) of 87.25 % with a concentrate yield of 22.63 %. The gold content in tailings was 1.97 g/t. The results of gravity and flotation concentration of the original ore indicate the feasibility of using a combined gravity-flotation technological scheme. In a closed experiment of the initial ore beneficiation according to the gravity-flotation scheme at a natural pH of the pulp (without adding acid), the following products were obtained: gravity concentrate with a gold content of 2426 g/t at a yield of 0.31 % and recovery of 64.06 %; flotation concentrate (after the II cleaning) with a gold content of 122 g/t at a yield of 2.90 % and recovery of 33.01 %; the total gold recovery in the gravity-flotation concentrate was 94.07 % with a yield of 3.21 % and an Au content of 345.87 g/t, the gold content in the flotation tailings was 0.72 g/t.

Study on the kinetics of process for obtaining cobalt nanopowder by hydrogen reduction under isothermal conditions

The kinetics of metallic cobalt nanopowder synthesizing by hydrogen reduction from Co(OH)2 nanopowder under isothermal conditions were studied. Co(OH)2 nanopowder was prepared in advance by chemical deposition from aqueous solutions of Co(NO3)2 cobalt nitrate (10 wt.%) and NaOH alkali (10 wt.%) at room temperature, pH = 9 under continuous stirring. The hydrogen reduction of Co(OH)2 nanopowder under isothermal conditions was carried out in a tube furnace in the temperature range from 270 to 310 °C. The crystal structure and composition of powders was studied by X-ray phase analysis. The specific surface area of samples was measured using the BET method by low-temperature nitrogen adsorption. The average particle size of powders was determined by the measured specific surface area. Particles size characteristics and morphology were investigated by transmission and scanning electron microscopes. Kinetic parameters of Co(OH)2 hydrogen reduction under isothermal conditions were calculated using the Gray–Weddington model and Arrhenius equation. It was found that the rate constant of reduction at t = 310 °C is approximately 1.93 times higher than at 270 °C, so the process accelerates by 1.58 times for 40 min of reduction. The activation energy of cobalt nanopowder synthesizing from Co(OH)2 by hydrogen reduction is ~40 kJ/mol, which indicates a mixed reaction mode. It was shown that cobalt nanoparticles obtained by the hydrogen reduction of its hydroxide at 280 °C are aggregates of equiaxed particles up to 100 nm in size where individual particles are connected to several neighboring particles by contact isthmuses.

Using shell-type tuyeres at Pierce–Smith horizontal converters of the Nadezhda Metallurgical Plant

Since 2015 the processing capacity reconfiguration at the Polar Branch of MMC Norilsk Nickel (hereinafter PB) sets new goals for conventional pyrometallurgical processes of smelting and converting. The design flowsheet of Kolesnikov Nadezhda Metallurgical Abstract: Plant (hereinafter NMP) provided for «cross-converting» when copper matte was first processed in one converter to produce blister copper followed by nickel matte processing to yield copper-nickel converter matte bypassing the discharge of dry coagulated slag. This flowsheet allowed for converter heat balance optimization, decreasing the formation of refractory reverts and significant extension of the converter campaign. PB Nickel Plant shutdown resulted in copper processing elimination at NMP and switching the converters to the conventional nickel converting flowsheet. In turn, it gave rise to the need for solutions to extend converter campaign while maintaining the possibility to process large amounts of nickel slag from the second converting stage at the PB Copper Plant. For this purpose the series of lab experiments were carried out to develop the technology and design documentation for the system to supply oxygen-enriched air (up to 45 %) to horizontal converters using shell-type tuyeres. In addition, literature data were analyzed on this topic along with the experience of smelters in this area. Process design calculations were done. The efforts were taken in cooperation with the PB engineering personnel and Laboratory of Pyrometallurgy of LLC «Gipronickel Institute». The use of reduced diameter shell-type tuyeres to inject the oxygen-air mixture was found to decrease the converter blowing and off-gas volumes. The decline in off-gas quantity leads to reduced heat load on the converter mouth and flue duct system, as well as to lowered converter dust entrainment. The use of oxygen-enriched blowing implies the higher smelt heating rate. Excess heat compensation requires timely charging of cold reverts and flux. In emergencies (if cold reverts are not available) the oxygen content of the blowing has to be reduced until switching over to air blowing. The series of the above efforts will offer a possibility to use the shell-type tuyeres keeping the converter off-gas temperature at the current level. Thus continuous monitoring and efficient control will ensure the off-gas temperature and volume at the inlets of gas cooling and cleaning systems not exceeding the limiting values. The introduction of the reduced diameter shell-type tuyeres for air-oxygen mixture injection does not require any upgrade of the existing gas cooling and cleaning systems. Moreover, switching to these tuyeres will reduce gas load on the flue duct system and heat load on the water-cooled dust cap, lower dust entrainment and non-recoverable dust losses after the gas cleaning system.

Investigation of the stress-strain state and microstructure transformation of copper busbars in the deformation zone during continuous extrusion

The paper describes an extensive study of features peculiar to physical and mechanical processes occurring in metal in the deformation zone during the continuous extrusion of Cu-ETP rectangular busbars 10×60 mm in size. Finite element computer simulation was used to obtain the values of extrusion power parameters. It was noted that moment and force values increase to the point of filling the press chamber free space with metal reaching a maximum of 12.26 kN·m and 1.54 MN, respectively. The stress-strain state analysis of metal in the deformation zone made it possible to obtain distribution fields of accumulated plastic strain, strain rate intensity and average stresses, and to build the graph of metal temperature variation over time during extrusion. Maximum levels of accumulated plastic strain and compressive stresses are observed in the contact zone of the workpiece with the press container abutment. The most intense metal deformation heating also occurs there. The comparison of modeling and microstructural study results indicate that a significant portion of the cast structure grinding work occurs at the entrance to the deformation zone and at the abutment zone subjected to the highest level of compression stresses. Metal deformation during the die passage leads to an oriented crystal structure formed with a grain size of 25–30 μm. Sample hardness measurement results are consistent with the results of structure analysis in the studied areas of the deformation zone. When the workpiece passes through the compression container abutment section, deformation heating occurs, which leads to a decrease in hardness from 93 to 67 HV. After the metal passes through the die, recrystallization processes continue in it leading to a slight increase in grain size and, accordingly, a decrease in hardness from 79 to 74 HV, which continues until the busbar contacts a cooling medium.

Research of process factors increasing metal yield during aluminum waste remelting

The article presents the results of research determining the most effective technologies for increasing metal yield in the processing of aluminum-containing waste. In particular, peculiarities of the processes of melting aluminum alloys were analyzed using complex methods of furnace and off-furnace processing of charge material containing an increased amount of shovelling scrap and swarf. Studies on the impact of charge preparation and aluminum remelting technology were carried out in SAT-0,16 and IAT-0,4 furnaces on the АК12М2 alloy. Experiments proved that batchwise loading 20 kg of swarf briquette preheated to 300–400 °C into the SAT-0,16 furnace with the addition of flux (composition: NaCl – 50 %; KCl –35 %, Na3AlF6 – 15 %) in the amount of 3 % of total metal mass is the most efficient technology. This technology makes it possible to achieve a metal yield of about 94 %. The study of the remelting technology influence on IAT-0,4 furnace metal yield showed that the greatest effect can be obtained in case of furnace charge (95 kg swarf briquette) by batches of 2 kg into the 7 kg liquid bath with modifier flux (composition: NaCl – 62 %; KCl – 13 %, NaF – 25 %) added in the amount of 2 % from the total metal mass. This technology provides up to 93.5 % of metal yield. Data from 10 series of 5–9 melts were also analyzed with the comparison of metal yield results depending on the mass of briquetted swarf charged into the furnace. A histogram of the change in the porosity of AK12M2 and AK9 samples depending on the content of swarf in the charge (from 0 to 45 %) during remelting. It was found that an increase in the content of swarf in the charge, all other things being equal, leads to an increase in the average porosity score, which indicates the need for additional refining of such melts.

In memory of Evgeny Nikolaevich Selivanov

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Fluoride processing of oil hydrocarbon cracking catalyst with REE concentrate extraction

It is proposed to use a spent cracking catalyst of petroleum hydrocarbons containing 1 wt.% of rare earth element (REE) oxides as an alternative REE feed source. The study covers the process of removing silicon in the form of ammonium hexafluorosilicate (NH4)2SiF6 by sintering an oil cracking catalyst sample with NH4F and subsequent (NH4)2SiF6 sublimation to produce an aluminum-containing concentrate of rare earth elements. The orthogonal central compositional planning of the experiment was used to study the effect of three factors: sublimation temperature (350 to 400 °С), duration (40 to 80 min), and weight of the catalyst fluorinated sintered mass (5 to 10 g) on the (NH4)2SiF6 sublimation completeness. Results obtained in the experiment were used to build a second-order model, which correlate with experimental data. The dynamics of (NH4)2SiF6 sublimation removal was determined for sublimation durations of τ = 10, 20, 40 and 80 min at processing temperatures of 350, 375 and 400 °C. The (NH4)2SiF6 removal degree values calculated based on the second-order model for τ = 44, 48, 52, 56, 60, 64, 68, 72, and 76 min fit well the experimental curves. Spectra of fluorinated catalyst samples before and after sublimation were studied using X-ray phase analysis and IR spectroscopy. The data of IR spectroscopy and X-ray phase analysis are in good agreement and show that (NH4)2SiF6, (NH4)3AlF6 and unreacted NH4F are present in the catalyst with NH4F sintered mass, and only aluminum compounds are detected – NH4AlF4 and AlF3 after sublimation. These data indicate the completeness of the sublimation removal of silicon from the catalyst and NH4F sintered mass with NH4AlF4 and AlF3 aluminum compounds only observed after sublimation. REE concentration is 15 % due to silicon removal.

Joint metallothermic reduction of titanium and rare refractory metals of V group

The features of phase formation during the joint aluminothermic reduction of titanium, niobium, tantalum, vanadium from their oxides using methods of thermodynamic modeling, differential thermal and X-ray phase analysis were studied. Computer thermodynamic modeling made it possible to predict the optimal temperature conditions in the metallothermic process, composition and ratio of reagents in the charge, behavior of elements and sequence of phase formation. Thermodynamic calculations were supplemented by differential thermal studies using the combined scanning calorimetry method to identify the kinetic and thermochemical components of the process. An analysis of theoretical and experimental data allowed us to establish that the interaction of aluminum with titanium dioxide proceeds through the stage of titanium monoxide formation and features by the formation of TixAly intermetallic compounds of various compositions (TiAl3, TiAl, Ti2Al) depending on the Al and TiO2 ratio in the charge. When titanium dioxide is partially replaced by niobium, tantalum and vanadium oxides, the metallothermic process during interactions in the Al–TiO2–Nb2O5, Al–TiO2–Ta2O5 and Al–TiO2–V2O5 systems has a similar nature, enters the active phase once liquid aluminum appears, is accompanied by exothermic effects and features by the priority formation of titanium aluminides and binary and ternary intermetallic aluminum compounds with Group 5 rare refractory metals – AlNb3, Al3Nb, Al3Ta, Al3(Ti1–х, Taх), Al3(Ti0,8V0,2). The joint conversion of titanium dioxide and rare refractory metal pentoxides during the reduction process is carried out through sequential and parallel stages of the formation of simple and complex element oxides with low oxidation states.

Computer simulation of the technology for AK4-1 alloy die forging production for an internal combustion engine piston

The process of hot die forging of AK4-1 aluminum alloy billets for the piston of an internal combustion engine (ICE) for an unmanned aerial vehicle (UAV) was simulated using the Deform-3D software package. The object of research was an ICE piston mounted on one of the UAV types of Russian production. Simulation was performed using the following parameters: tooling and billet temperature was 450 °C, ambient temperature was 20 °C, punch speed was 5 mm/s, and Siebel friction index was 0.4. Rigid plastic medium was chosen as a material model. The number of elements (6000) was selected so that at least 3 elements fit in the narrowest section of the part. Thus, as illustrated by the piston die forging, computer simulation in the Deform-3D software makes it possible to develop hot die forging processes for making aluminum alloy billets for UAV ICE pistons. At the same time, computer simulation can be used to evaluate the power parameters of the hot die forging process, study the nature of billet forming in die forging, make necessary adjustments to the virtual process, and develop the design of a die forging tool in order to select the most effective process solutions when designing a real process. The described computer simulation technique can be extended to other aluminum alloy die forgings.

Influence of surface hardening by combined thermal force impacts on VT22 titanium alloy fatigue life and damage

The study covers the influence of electromechanical surface treatment (EMT), non-abrasive ultrasonic finishing (NAUF), their complex influence with subsequent aging on the fatigue life and surface microhardness changes. Samples for research were made of VT22 transition alloy rods after standard thermomechanical treatment. EMT was carried out by sample surface rolling with a roller and applying a high density current between them. As a result, surface thermomechanical treatment was carried out with the local fast surface heating and cooling. NAUF were implemented by shock treatment with an ultrasonic emitter striking on the treated surface. This revealed 1.8 times higher fatigue life when loading by rotational bending (with amplitude of 0.5σв) for samples after NAUF in comparison with the untreated initial state together with a slight increase in microhardness (up to 16 %). EMT reduces microhardness and fatigue life by almost 20 % and 70 %, respectively. EMT + NAUF complex processing has an insignificant effect on microhardness, but it increases fatigue life by 40 % with respect to EMT. Aging at 450 °C for 5 hours increases microhardness after EMT by 30–40 % with a simultaneous increase in fatigue life by 2 times. The aging of samples subjected to EMT + NAUF revealed virtually no increase in microhardness, but increased fatigue life by almost 3 times (as compared to EMT). According to fractography results, the reduction in fatigue life after EMT is associated with a reduction in the crack initiation stage, which virtually excludes this stage of fatigue damage accumulation from the overall sample fatigue life.