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Vol 60, No 4 (2019)
- Year: 2019
- Articles: 16
- URL: https://journal-vniispk.ru/1067-8212/issue/view/13989
Mineral Processing of Nonferrous Metals
Studies on Beneficiation and Leaching Characteristics of Rare Earth Elements in Indian Red Mud
Abstract
Bauxite residue (red mud) is a process reject composed of undissolved bauxite phases during digestion in the Bayer process. Rare earth elements present in the bauxite residue could be a potential resource for the extraction of REEs (Sc, La, Ce). It is difficult to recover REEs directly from red mud due to its low concentration and the presence of major minerals. Large amounts of iron in leach solution create problems for further recovery processes, as iron and scandium have some common chemical characteristics. It is, therefore, advisable to remove iron from the mud as much as possible through physical beneficiation. In the present study, physical beneficiation using hydrocyclone, characterization and acid leaching has been exploited. The beneficiation process enhanced the REEs from 200 to 240 mg/kg at a yield of 43%, with a subsequent reduction in the iron oxide content from 37.5 to 29.2%. Further, leaching efficiencies of REEs and impurity (Fe) co-extraction were studied before and after physical beneficiation. It is evident from the data obtained that upgrading minimizes iron co-extraction, which improves the leaching efficiency of REEs.
335-340
Investigation into the Influence of Flocculants on Kinetic Parameters of Reducing Copper in an Aqueous Solution by Metallic Zinc
Abstract
A series of models is investigated for describing the reduction of copper by fine zinc powder in aqueous solutions. The experiments were performed in apparatuses with a magnetic stirrer at 15–50°C and stirring rates of 40–150 rpm. The influence of high-molecular flocculants such as nonionogenic magnafloc 333, cationic besfloc 6645, and anion besfloc 4034 on this process is investigated. These flocculants are applied under industrial conditions at the stage of hydrolytic purification of solutions and then enter the cementation purification along with the settled solution. Aqueous solutions of flocculants of 2.5 g/L with dosages of zinc dust of 2–4 g/L and flocculant of 50–200 mg/L are used in experiments. The copper content is determined quantitatively in initial and final solutions by spectrophotometric analysis with the preliminary transfer of copper into an ammonia complex. The experiment duration varied from 1 to 8 min. The degree of reduction of copper reduced from solutions was 10–90%. It is established that the process kinetics at low stirring rates can be described by the first-order equation. The kinetics of the heterogeneous reaction under study at high stirring rates in the presence of flocculants additives is most adequately described by the equation of the variation in the rate as the root square of the process duration. It is shown that the largest cementation rate constant is observed without adding surfactants. The cementation is retarded to a smaller degree in the presence of the anionic flocculant when compared with the cationic one, which agrees with the theory of electrochemical processes and shows that the discharge of copper cations under these conditions limits the cementation. The regularities of the process under study are retained with an increase in temperature. It is noted that the additions of high-molecular substances with a relative molecular mass of 20 million in an amount of 50–200 mg/L retard cementation. This fact should be taken into account under industrial conditions where cementation purification with the removal of copper and other impurities is performed from solutions containing flocculants.
341-347
Metallurgy of Nonferrous Metals
Development and Industrial Tests of the TiB2-Based Composite Material for Local Fractures Repairing of Electrolyzer Bottom Blocks
Abstract
The composition and fabrication technology of a repair mixture consisting of unmolded corundum with a TiB2–C composite coating wettable with aluminum for repairing local fractures of bottom blocks without interrupting electrolysis have been developed. The proposed technical solution makes it possible to decrease the bottom wear and prolong the service life of an aluminum electrolyzer by six months. To fabricate a repair mixture with an optimal composition, the titanium diboride powder with a refractory powderlike binder in ratio 50 : 50 (wt %) is used. Unmolded corundum is coated with this mixture of a binder and titanium diboride. This material is dried at 150°C and thermally treated in a carbon bed at t = 700–900°C. Calcination in a reducing gas atmosphere results in the formation of the TiB2–C composite material with a carbon content of 15–20 wt % on the unmolded corundum surface. The qualitative evaluation of the properties of the developed composite coating shows that it has rather high hardness, wear resistance, and adhesion to the base after calcination. To perform pilot tests, the repair mixture is poured with molten aluminum, which gives the platelike repair mass of the Al–TiB2–C composition. Pilot tests of the repair mass using an RA-400 operating electrolyzer at the pilot shop of OAO RUSAL-Sayanogorsk show that the bottom wear decreases within three months after the repair of the local fracture with uninterrupted electrolysis. This fact is evidenced by a 13% decrease in an average fracture depth with a stable current force of 4.7–4.8 kA/bloom after the repair. Thus, the local use of the repair mass retards the overall wear of the cathodic surface and makes it possible to prolong the service life of the electrolyzer.
348-353
Production of the Al–B Master Alloy by Aluminothermal Reduction of KBF4 and B2O3 in a Medium of the Molten Salt Flux
Abstract
The process of obtaining the Al–B master alloy by the aluminothermal reduction of KBF4 and B2O3 using fluoride fluxes KF–AlF3 and KF–NaF–AlF3 at 983 and 1123 К, respectively, and chloride-fluoride fluxes KCl–NaCl–KF at Т = 1173–1223 К have been studied. All experiments were carried out under the same conditions: the stirring rate of molten mixture was 400 rpm, the duration of synthesis was 30 min. The maximum amount of boron (1.5%) in the Al–B alloy was obtained using KBF4 (3% per B) as a boron-containing raw material in the KF–AlF3 medium with a molar (cryolite) ratio (CR) of KF/AlF3, equal to 1.3, at Т = 983 К, while the boron extraction degree does not exceed 75%. The comparable results were obtained in the experiments with the KF–NaF–AlF3 flux (CR = 1.5) at T = 1123 K. However, with an increase in the concentration of the loaded boron, the degree of its extraction significantly decreased, which is associated with the decomposition at a higher temperature not only KBF4, but also NaBF4, which is less thermally stable; the latter is formed as a result of an exchange reaction in the melt. Therefore, the use of sodium salts as a component of the flux is not recommended. The Al–B master alloys obtained by reducing the KBF4 in the fluoride fluxes were solid solutions of B in Al containing the intermetallic compound AlB2. The lowest amount of boron in aluminum with the minimum extraction degree was obtained in experiments with B2O3 in the molten KF–AlF3 with CR = 1.5. Nevertheless, the results of scanning electron microscopy indicate a uniform distribution of B along the Al matrix and the absence of intermetallic compounds; however, a large amount of Al2O3 was found, which is the product of B2O3 reactions with both the liquid Al and the flux (KF–AlF3).
354-362
Sulfidation Behaviour of Blast Furnace Dust at High Temperatures
Abstract
The sulfidation behaviour of blast furnace dust (BFD) with sulfur at high temperatures was investigated. The effects of the sulfur dosage, roasting temperature and time were studied on the basis of thermodynamic calculations. The results revealed that the Zn distribution ratio in ZnS increased from 13.28 to 92.01% after adopting the proposed process. The increase in the sulfur dosage, roasting temperature and time was conducive to the sulfidation of ZnO in the sample, but higher temperatures were not beneficial for sulfidation, which was ascribed to an accelerated volatilization rate of sulfur. The existence of carbon in the sample could decrease the O2 partial pressure, which is advantageous for the generation of ZnS. In addition, it was found that the generated FeO was sulfurized and then proceeded to form iron sulfides. The produced iron sulfides were further dissolved into ZnS to form (Zn, Fe)S compounds. The growth of ZnS particles largely depended upon the roasting temperature, and the growth was significantly accelerated when the temperature increased to 850°C. It is feasible that the sphalerite was transformed into wurtzite at higher temperatures.
363-371
Arsenic Removal from Cu–As-Containing Filter Cakes by Na2CO3 Leaching
Abstract
In the present study, a process for selective removal of arsenic from Cu–As-containing filter cakes using Na2CO3 leach was examined. When decreasing the weight percentage of arsenic in Cu–As-containing filter cakes, environmental problems can be eliminated while valuable metals will be recycled. The effect of α(Na2CO3) (where α represents excess coefficient), temperature, L/S ratio and leaching time were investigated. the optimal leaching conditions were achieved as follows: α(Na2CO3) = 2.7, L/S ratio 6 : 1 (mL/g), temperature 75°C, leaching time 3 h, where the leaching efficiency were 96.47% for As, 0.41% for Cu with final As and Cu concentrations of 11.72 and 0.02 g/L respectively. Further analysis showed that the Cu content in the leach residue increased to 51.42% with CuS as the major Cu phase. Notably, only 0.92% of As remained in the leach residue. The leaching solution was treated by sodium persulfate oxidation and arsenic precipitation which eliminated As 99%, leaving 0.5 mg/L As in the solution. Therefore, the proposed process is a viable method for the effective separation of Cu and As in Cu–As-containing filter cakes. Broadly, the results of this paper provide a reference for the treatment of arsenic sulfide from nonferrous metallurgy cyclic leaching process.
372-379
Physical Metallurgy and Heat Treatment
Heretophase Ceramics in the Hf–Si–Mo–B System Fabricated by the Combination of SHS and Hot Pressing Methods
Abstract
This work is devoted to the fabrication of heterophase powder and consolidated ceramics based on hafnium and molybdenum borides and silicides by combining self-propagating high-temperature synthesis (SHS) and hot pressing (HP). Composite ceramic HfB2–HfSi2–MoSi2 SHS powders are fabricated according to the magnesium-thermal reduction flowsheet from oxide raw materials, in which the combustion wave has temperatures of 1750–2119 K and rather high mss combustion rates of 8.4–9.3 g/s. The structure of synthesized SHS powders consists of relative coarse MoSi2 grains up to 10 μm in size, submicron elongated HfB2 grains mainly located inside the MoSi2 grains, and rounded Si precipitates. The composition with a lower boron concentration contains numerous polyhedral HfSi2 grains smaller than 10 μm in size. The resulting powders have an average particle size of ~6 μm with a maximal size up to 26 μm. The phase compositions of the ceramics consolidated by the HP method and synthesized SHS powders are identical. The microstructure of compact samples consists of faceted elongated HfB2 grains 0.5–10.0 μm in size, polyhedral HfSi2 and MoSi2 grains up to 8–10 μm in size, and silicon interlayers. The consolidated ceramics have a high structural and chemical homogeneity, low residual porosity of 1.1–1.7%, high hardness of 11.7–12.6 GPa, and thermal conductivity of 62–87 W/(m K).
380-389
Corrosion and Protection of Metals
Peculiarities of Corrosion of a Zinc Coating in Neutral Media in the Presence of Inhibitors Based on Benzotriazole, Cyclohexylamine, and Morpholine
Abstract
The influence of domestic nitrogen-containing corrosion inhibitors of the VNKh-L type on corrosion regularities of a zinc coating on steel in neutral media is investigated. This work is aimed at studying the surface structure of a corroding zinc coating, as well as the influence of conditions simulating the degradation of inhibitors during real operation on their protective properties. Mechanical activation in a ball planetary mill is used to simulate the deformation and thermal operational conditions of inhibitors. Corrosion of a zinc coating on steel is carried out in a sulfate–chloride medium simulating atmospheric corrosion and in a borate buffer solution. The concentration of inhibitors in the corrosion media was 0.2 wt %. The morphology of a corroded surface of a zinc coating is studied using a Philips SEM-515 scanning electron microscope (at an accelerating voltage of 10 kV) with an X-ray microprobe. Studies of the corrosion rate of zinc coating on St 08 are carried out by the indirect measurement of corrosion resistance with the help of a MONIKOR-1 corrosion meter. A borate buffer solution (Na2B4O7 + H3BO3, pH 6.6) and a solution simulating atmospheric corrosion (NaCl + Na2SO4, pH 6.0) are used as corrosion media. The corrosion rate of samples in corrosive media without an inhibitor is accepted 1. The exposure time of each sample in corrosive media is 3 h. The chemical composition of corrosion products is studied by the mirror reflection in the IR range. The IR spectra of the metal plate surface are recorded using an FSM-1202 IR Fourier spectrometer in a wavelength range of 450–4000 cm–1 with a resolution of 2 cm–1 and an accumulation of 100 scans. To record the reflection spectra, a mirror-reflection attachment with a 10° angle of incidence is used. The corrosion rate of zinc coating in sulfate–chloride and solvent media in the presence of inhibitors based on benzotriazole and cyclohexylamine is practically not decreased when compared with the corrosion rate in the same media without inhibitors. The addition of both initial and mechanically activated inhibitors based on morpholine and benzotriazole to the corrosion medium decreases the corrosion rate of iron when compared with the corrosion in the same media without inhibitors. The pitting corrosion of a zinc coating is observed in the presence of initial and mechanically activated inhibitors of both types in studied corrosion media. Herewith, the pitting depth is smaller than the zinc-coating thickness under these conditions.
390-400
Development of the Composition of a Magnesium Alloy for the Fabrication of Temporal Sealing Facilities Used in the Petroleum Industry
Abstract
The composition is developed and heat-treatment mode is determined for obtaining an intensely dissolving magnesium alloy for use as ball plugs in conditions of oil-well preparation, i.e., to seal various well sections with the subsequent and almost complete fracture of these balls in a short time (up to 11 h). It is revealed that the cause of a high dissolution rate of the Mg alloy, whose composition is close to high-strength ML6 alloy, is the increased nickel content in it (up to 0.19%). The compounds of this element are located along the grain boundaries, which leads to intense intercrystallite corrosion of the alloy in a medium containing chlorine ions. It is shown that an effective method for controlling the dissolution rate of the Mg alloy is the synthesis of coatings of various thicknesses on its surface by the plasma electrolytic treatment (PEO) in an aqueous solution containing 110 g/L of technical water glass. This method makes it possible to deposit coatings from 10 to 41 μm in thickness on the experimental magnesium alloy with an increased nickel concentration (~0.19%) in a short time period (from 10 to 20 min) with a low specified AC current density (4 A/dm2), which is the galvanostatic mode of PEO processes. The corrosion tests are performed in a 3% aqueous KCl solution at 93 ± 2°C, and PEO coatings are formed on the magnesium alloy using a capacitive setup. The conditions of the corrosion tests of materials used as ball plugs in sealing facilities of oil wells are similar to those presented by foreign researchers.
401-407
Production Processes and Properties of Powders
Volumetric Reduction of the FeCl2–CaCl2 Melt by Calcium Dissolved in Calcium Chloride
Abstract
The purpose of this study is to fabricate highly dispersed powder suitable for spheroidization with further application in additive technologies. The volumetric reduction of the FeCl2–CaCl2 melt by calcium dissolved in CaCl2 produced a fine iron powder. The process included three states, notably, the preparation of melts containing FeCl2 and Ca, their mixing, and high-temperature aging at 800°C for 1 h. Upon finishing the process, the solidified fusion cake is divided into top and bottom parts. The product from the top part has a specific surface of 7.60 m2/g, and that from the bottom part has a specific surface of 5.38 m2/g. The average particle size is 157 μm for the former and 124 μm for the latter. Ultrasonic dispersing is reduced to 26 μm and 71 μm, respectively. Quantitative X-ray phase analysis shows that the main phase of powder is metallic iron (more than 97 wt %). Thus, the originality of the research is due to the application of an intense volumetric reduction of iron from chloride melts by calcium dissolved in its chloride. The uniqueness of the study is due to its product, so far as the main part of reduced iron is arranged in the melt bulk in the form of linear aggregates 40–600 μm in length and 10–50 μm in diameter, which easily destruct by ultrasonic dispersal into separate crystals with an average size of 26 μm. The results of the study show the possibility of implementing the calcium-thermal production of fine iron powder.
408-412
Self-Propagating High-Temperature Synthesis
Self-Propagating High-Temperature Synthesis of (Al–2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC Nanostructured Composite Alloys Doped with Manganese Powder
Abstract
The influence of alloying with powder manganese on the preparation of nanostructured (Al‒2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC composite alloys with the application of the self-propagating high-temperature synthesis (SHS) of titanium carbide TiC nanoparticles from the Ti + C charge in a melt of matrix alloys is investigated. Powder metallic manganese in an amount of 2 wt % is preliminarily introduced into Al and Al–5%Cu matrix bases of composite alloys. This makes it possible to increase the ultimate tensile strength of the aluminum base from 81 MPa (for initial aluminum of the A7 brand) to 136 MPa and that of the aluminum–copper base to 169 MPa. It is revealed that, when alloying aluminum only with manganese, the SHS reaction proceeds weakly and incompletely, while the carbide phase size in the (Al‒2% Mn)–10% TiC alloy varies from a nanolevel to several microns. When adding 10% of the Na2TiF6 haloid salt into the SHS charge, the SHS process is intensified, but the resulting alloy contains numerous pores, inclusions of the unreacted charge, and coarse agglomerates of ceramic nanodimensional TiC particles. When using Ti + C and Ti + C + 10% Na2TiF6 SHS charges with coalloying matrix aluminum by copper and manganese, similar results are acquired. The difference is in the larger distribution uniformity of the nanodispersed TiC phase. The best results are attained with a decrease in the Na2TiF6 additive to 5% of the charge weight, which promotes the smoother and complete synthesis of preferentially nanodimensional TiC particles and the formation of the poreless homogeneous microstructure of the (Al–5% Cu–2% Mn)–10% TiC composite alloy with an ultimate tensile strength of 213 MPa and relative elongation of 6.6%.
413-421
SHS-Aided Joining of Ceramic Materials with the Ta Substrate
Abstract
Experiments on evaluating the possibility of joining ceramic materials with a Ta substrate under conditions of self-propagating high-temperature synthesis (SHS) are explored. The sample consists of tantalum foils and pellets Ti + 0.65C and 5T + 3Si, between which a Ti + 2B igniting tape is laid. The sample is installed on a boron nitride support. A chamotte brick plate (SiO2 + Al2O3) with a load of 3360 g placed on its top is placed on a sample to decrease the heat sink. The experiments are performed in a reaction chamber in argon under a pressure of 1 atm. The samples are preheated from the bottom, and the reaction is initiated from their butt. The sample temperature is measured using W–Re thermocouples. The temperature gradient over the sample thickness, depending on the heating rate, is 50–150 K/mm. The samples with strong joining of the tantalum foil with Ti + 0.65C, as well as between two pellets, are formed. The top foil is not welded to the 5Ti + 3Si pellet, which is explained by a rather low temperature (1600°C) at the interface. When studying the interface of the tantalum foil with titanium carbide, the formation of Ti–Ta and (Ta,Ti)C interlayers is found. The possibility of joining the tantalum foil with ceramic materials during SHS is shown by investigations. The main conditions of such joining are the presence of the liquid phase and correspondence of the combustion temperature of the Ti + 0.65C composition to the melting point of the tantalum substrate. These results can be useful when fabricating multilayered functional coatings and functionally graded materials.
422-425
Self-Propagating High-Temperature Synthesis of a Thin-Layer CuO–B–Glass System
Abstract
Experimental studies are performed and mathematical models of the wave synthesis and thermal explosion in a thin-layer CuO–B–glass system are constructed. It is established that the propagation of the combustion front occurs in a multisource mode and its rate depends on the reaction layer thickness (d) according to the parabolic law with a maximum at d = 4 × 10–4 m. An increase in the reaction layer thickness promotes the improvement of thermal explosion characteristics in this system, while its dilution with an inert component makes it possible to form copper coatings with high electrical conductivity. An X-ray phase analysis and optical microscopy showed that the coating consists of metallic copper drops fused together and surrounded by a boron–lead silicate glass melt. Coatings have high electrical conductivity comparable with that of metals. It is found that an increase in the layer thickness above 4 × 10–4 m leads to a considerable decrease in the propagation rate of the combustion wave front due to loosening the initial mixture under the effect of evaporation of water vapor and gases adsorbed on powders and, consequently, to a decrease in heat transfer in the combustion front. Such coatings are nonconductive. Mathematical models of the wave synthesis and thermal explosion in a thin-layer Cu–B–glass system are developed in a macroscopic approximation. Numerical calculations of the process dynamics are performed. Theoretical evaluations satisfactorily correspond to the experimental data. Thermal and thermokinetic process constants are determined by the inverse problem method. Experimental samples of film electric heaters with high electrical conductivity and operational temperature are fabricated based on the experimental data and mathematical models.
426-433
Refractory, Ceramic, and Composite Materials
Study into the Effect of the Amount of the Strengthening Phase in an Aluminum-Based Dispersion-Hardened Composite on Fracture Regularities
Abstract
The results of studying the static tensile strength of aluminum-based dispersion-hardened composite materials with various contents of the Al2O3 strengthening phase are given. The materials under study are fabricated according to a new in principle technology based on burning out the aluminum melt when interacting with oxygen or an oxygen–nitrogen mixture. The fractographic patterns of the static fracture surfaces were studied for the samples fractured at maximal stresses. It is established that samples with a low Al2O3 content have a poorly viscous fracture pattern mainly consisting of a single fibrous zone. A radial zone appears in the fractograph with a twofold increase in the amount of the solid phase, while the alternation of viscous fracture, according to the detachment and shear mechanism with the manifestation of a brittle cleavage fracture signs, is observed with a threefold increase in the Al2O3 content. An analysis of fracture profilograms of the samples containing 10 and 30% inclusions of the solid phase reveals no abrupt drop in the surface relief, but an absolutely different fracture character is herewith found. However, in both cases, the form of profilograms is not pronounced by any abrupt relief jumps or extreme profile values, which makes it possible to affirm the stability of fracture processes. This is not true for the fracture of the sample with 20% Al2O3, in which a rather significant one-time drop is observed. The features of varying the fracture surface profile and distinctions over the arrangement place and number of crack nucleation regions in the samples under study are revealed using optical microscopy.
434-440
Structure of a Diamond–Matrix Interface and Durability of a Diamond Tool Fabricated by the Metallization of Diamond with Chromium during Sintering of the WC–Co Briquette with Copper Impregnation
Abstract
The structure, as well as the elemental and phase compositions of the diamond–matrix interface of a diamond tool for abrasive wheel dressing, manufactured using a new hybrid technology, are studied. This technology combines the thermodiffusion metallization of diamond with chromium and sintering of a matrix based on a WC–6%Co carbide powder mixture with copper impregnation in a single cycle of the vacuum furnace operation. During matrix sintering, the compact arrangement of chromium powder particles around the diamond grains and the screening effect of the copper foil form favorable conditions that ensure the thermodiffusion metallization of diamond. Scanning electron microscopy, electron probe microanalysis, X-ray phase analysis, and Raman spectroscopy show that a metallized coating chemically bound with diamond is formed on the diamond surface in temperature-temporal modes and sintering conditions. The coating consists of chromium carbide and a solid solution of cobalt in chromium, which provides durable diamond retention in the copper-impregnated carbide matrix. Herewith, the matrix structure and microhardness, excluding the regions adjoining the diamond–matrix interface, remain the same as a matrix of a carbide powder mixture sintered in the absence of chromium. Comparative tests of similar diamond dressers show the high efficiency of the hybrid technology of formation of diamond-containing composites for tool application. It is shown that the specific productivity of a dresser prototype fabricated using the hybrid technology was 51.50 cm3/mg when dressing a grinding wheel made of green silicon carbide, which is 44.66% larger than a similar indicator of the same type of check dresser formed using the traditional method.
441-449
Investigation of Heat Source Models and Process Factors on Temperature and Residual Stress in GTAW of Aluminum Plates
Abstract
Heat source modeling is one of the most important problems in welding simulation and has a significant impact on temperature and residual stress fields. This paper first investigates accuracy of surface and volumetric heat fluxes for predicting temperature of the gas tungsten arc welding of aluminum plates, through the 3D finite element analysis. Comparing simulated and experimental temperatures shows that the volumetric model produces a more precise prediction of temperature at fusion zone, while temperature at locations far from the weld is independent of the heat source model. Next, this paper investigates the influence of different geometrical, technological, and material variables on the residual stress and the welding temperature, by using the Taguchi method. The results reveal that increase in the yield strength and the plate width lead to a higher residual stress. The yield strength is the most significant parameter, while the heat power and the plate length have insignificant impacts on the residual stress. Further, the order of factors based on their effect on the welding temperature is determined as time, distance, and thickness. The derived equations in this paper can be used to calculate the welding temperature and the residual stress in terms of design factors with high accuracy.
450-462