Vol 59, No 5 (2018)

The possibility of using an inorganic sorbent of iron oxyhydrate (IOH) for the removal of F^– ions from process solutions of zinc production is considered. The synthesis method of IOH is chosen. The results of scanning electron microscopy and X-ray phase analysis are presented. The possibility in principle of using ion-exchange resins as carriers modified by IOH is considered. The formation of an active substance on anion-exchange and cation-exchange resins is investigated. It is shown that the strongest composite sorbents are formed when using strong acidic cation-exchange resins with sulfonate groups. The method of IOH incorporation into the structure of carrier materials and the formation of composite sorbents is described. The KU-2×8 cation exchanger is recommended as the composite basis. To form IOH crystals of the β-modification distributed over the ion-exchanger grain bulk, iron-saturated cation exchangers are held in the sodium chloride solution with a concentration of 2.5 g/dm³ for 24 h at 85°C. Anion exchangers are held in the iron(III) sulfate solution with the sodium chloride additive for 24 h at t = 85°C. Herewith, the formation of IOH films on the surface of sorbent grains is observed. The fluorine was sorbed in a static mode from a model solution with the concentration of F^– = 100 mg/dm³ at t = 60°C. The sorption on the AV-17×8 anion exchanger is performed at t = 20°C. Adsorbed fluorine is desorbed by the 0.1 M NaOH solution at t = 60°C for 2 h. The synthesized KU-2×8-IOH composite sorbent has a capacity of 0.7–1.1 mg/g with respect to fluorine and can be regenerated with the formation of easily utilizable fluorine-containing eluate.

The paper reports spontaneous and electrochemical dissolution of polymetallic alloy obtained from electrowaste. Effectiveness of chloride, carbonate and sulfate ammoniacal solutions was compared. Leaching process was conducted with and without addition of cupric ions. It resulted in the transfer of primarily copper (over 90%) and negligible amounts of zinc, lead, nickel and iron to the electrolyte, but the rate of the spontaneous dissolution was low. The best condition of the alloy leaching was obtained in the presence of Cu²⁺ ions in ammonium-carbonate solution. Anodic dissolution of the alloy led to unfavorable distribution of metals among the slime, electrolyte and cathodic deposit, but the highest dissolution rate in the chloride bath was found. Copper can be selectively recovered on the cathode from all electrolytes.

Alumina refineries in China continue to face challenges in achieving clean and efficient utilization of high-sulfur bauxite. Disulfide ions, \({\text{S}}_{2}^{{2 - }},\) in FeS₂ can be considered as active components in the Bayer process for alumina production, but they lead to corrosion of the equipment used in the processing of bauxite. Our research investigates the transformation rules of \({\text{S}}_{2}^{{2 - }}\) in bauxite during roasting, and the impact of digestion conditions on the digestion efficiency of the roasted ore and \({\text{S}}_{2}^{{2 - }}\) distribution. The results revealed that the onset temperature of kaolinite dehydration was approximately 700°C. The standard Gibbs free energy of all other reactions, including pyrite oxidation at 500–750°C, was negative. Dehydration began at 433.0°C, attained its maximum rate at 508.5°C, and ended at 593.0°C. Roasting pre-treatment removed approximately 95% of the sulfide, promoted digestion of alumina in bauxite, and reduced the active sulfur content by ~27%.

The analysis of certain trends in the development of the rare-earth-element (REE) world market is presented allowing for changes in the commerce and industrial policy of China and REE-consumption tendencies. The main characteristics of modern REE markets are considered and the volume of the world production, world trade, and prices are evaluated. The market dynamics for 2000–2020 is described and main indices and prices are forecasted to 2020. The review of modern world REE reserves, production, and trade over main countries is given. The prices and main REE buyers, as well as the consumption forecast, are presented. Prospects of the domestic REE market allowing for the fulfillment of the subprogram “Development of the Industry of Rare and Rare-Earth Metals” of the State Program of the Russian Federation “Development of Industry and an Increase in Its Competitiveness” are evaluated. The purpose of the subprogram was the development of the competitive rare-earth industry of a complete fabrication cycle to satisfy the needs of the domestic defense-industry complex, civil branches of industry, and output to foreign markets. The necessity of fulfilling this subprogram, making it possible to change the market conditions and the development of production of REEs in the territory of the Russian Federation, is noted, including by normative, nontariff, and technical regulations. Loparite and apatite remain the main sources of the REE raw materials in Russia for industrial processing for the nearest period, and the REE production from apatite will increase. It is emphasized that the prospects of REE development in the Russian Federation consist mainly of the development of new enterprises consuming REE production rather than in an increase in production of primary products.

A comparative study on the influence of fabrication methods of AlTi4 master alloys on the grain size of Al₃Ti intermetallic compounds is performed. It is found that an increase in the cooling rate during the solidification from 10–15 K/s (the crystallization in a hot cast iron mold and plate 30 mm in thickness) to 60–65 K/s (the crystallization in a cold cast iron chill mold; the rod 20 mm in diameter and 170 mm in length) promotes an increase in length and thickness of needle crystals of intermetallic compounds almost twofold (from 397 × 23 to 215 × 13 μm). Herewith, a decrease in electrical conductivity and an increase in the master alloy density in the solid state are observed. The modification of the master alloy melt by the addition of magnesium in an amount of 0.5 wt % determines the formation of homogeneous fine needles of intermetallic compounds 98 × 3 μm in size. The magnesium addition insignificantly decreases electrical conductivity and density when compared with the AlTi4 master alloy crystallized at the same cooling rate (60–65 K/s). The grain refinement of aluminum of the A97 grade and AK9ch alloy (the Al–Si–Mg system) by these foundry alloys with the same amount of introduced titanium (0.01 wt %) exert hereditary influence on the density and electrical conductivity, as well as on the marcograin (A97) and aluminum dendrites (AK9ch). The maximal modifying effect is characteristic of the AlTi4 master alloy containing magnesium in an amount of 0.5 wt %. Its introduction into the alloy promotes the formation of aluminum dendrites of 10 μm in size in an amount of 1427 pieces/mm² in the alloy structure. When modifying the AK9ch alloy by the master alloy crystallized with cooling rates of 10–15 K/s, dendrites 28 μm in size in an amount of 672 pieces/mm² are formed in the alloy structure. It is proposed to use the determination procedures of density and electrical conductivity for the express evaluation of the modifying efficiency of master alloys.

Aluminum-based metal glasses are a promising new family of materials. However, the influence of thermal treatment on the structure and properties of amorphous alloys of the Al–Y–Ni–Co system is still not studied in detail. In this work, amorphous ribbons of the Al₈₅Y₈Ni₅Co₂ alloy are formed by quenching on a rotating copper disc. The influence of annealing in vacuum at temperatures from 100 to 500°C for 30 min on the structure and hardness of these ribbons is investigated. To investigate the variations occurring in their structure after thermal treatment, scanning electron microscopy, X-ray structural analysis, and differential scanning calorimetry are used. To investigate the influence of annealing on mechanical properties of ribbons, the Vickers microhardness is measured. Conclusions on the variation in hardness depending on the structure of ribbons of the Al₈₅Y₈Ni₅Co₂ alloy are made based on these results. It is established that their microhardness increases with an increase in temperature, reaching the maximal value of 575 ± 7 HV after annealing at 350°C, and then decreases with a further increase in the thermal-treatment temperature. It is shown that ribbons of the Al₈₅Y₈Ni₅Co₂ alloy remain totally amorphous after annealing at t ≤ 250°C for 30 min, and crystalline phases are absent in the structure. An abrupt increase in hardness after annealing at 350°C is associated with the formation of nanocrystals of the aluminum solid solution 10–30 nm in size in an amorphous matrix surrounded by the residual amorphous matrix, while its further decrease is caused by an increase in the size of these crystals and the appearance of Al₃Yand Al₁₉Ni₅Y₃ intermetallic compounds in the structure.

Strongly basic anion exchange resins, Amberlite IRA 400 and IRA 900, have been tested to remediate Cr(VI) from a model as well as from the untreated chromite mine effluent samples. For an initial concentration of 50 ppm Cr(VI), IRA 400 was found to adsorb Cr(VI) completely in less than 6 min of contact time and was efficient in a larger range of pH (1–6); however IRA 900 was able to remediate 97% Cr(VI) in the pH range 4.5–5 in less than 10 min. A cumulative loading of 112.9 and 115.2 mg/g of Cr(VI) was obtained with Amberlite IRA 400 and IRA 900, respectively from a feed of 200 ppm Cr(VI). A close adherence to the Freundlich isotherm during the adsorption reflected the strong chemical interaction of Cr⁶⁺ ions with the quaternary functional group on the resins. The adsorption process followed the pseudo second-order kinetics. The experiments were further carried out in glass columns with 10 L chromite mine effluent samples. Almost complete sorption of Cr(VI) from the effluent was achieved using 0.5% (w/v) IRA 400 and 2% (w/v) IRA 900, at a resin bed height of 7 cm and flow rate of 10 mL/min. Desorption studies in column show that 200–500 mL solutions of 15–30% (w/v) NaOH eluted the Cr(VI) completely from the metal laden Amberlite IRA 400 and IRA 900 resins.

The results of the investigation into the formation of amorphous structures in the Cu–Ti system and their subsequent crystallization under the effect of high-energy ball milling (HEBM) are presented. To form amorphous Cu–Ti powders, powders of copper (MPS-V grade with average particle size d = 45–100 μm, GOST (State Standard) 4960–75) and titanium (PM99.95, d = 2.0–4.5 μm, TU (Technical Specifications) 48-19-316–80) are selected as the initial components. The HEBM of Cu + Ti powder mixtures is performed using an Aktivator-2S laboratory planetary ball mill (at revolution rates of discs of 694 rpm and drums of 1388 rpm) for 1–30 min. The investigations into the surface morphology and micro-, nano-, and atomic crystalline structure of activated Cu + Ti powder mixtures are fulfilled by X-ray structural analysis (XSA) using a DRON-3M diffractometer, scanning electron microscopy using a Zeiss Ultra+ microscope (Germany) with the application of energy dispersive analysis, and high-resolution transmission electron microscopy (TEM) using a Titan microscope (United States). The determination of thermal characteristics of phase transformations (temperature, heat of reaction, and amorphous-to-crystalline transition) are performed by differential scanning calorimetry using a DSC 204 F1 device in the mode of linear heating to 450°C at a rate of 20 K/min. The Cu–Ti amorphous powders were fabricated using HEBM for 20 min. The XSA data evidence that the fraction of the amorphous phase in the material was 93%. The TEM investigations showed that the material preferentially consists of the amorphous phase with an insignificant content of nanocrystalline regions 2–8 nm in size. It is found that the Cu–Ti amorphous phase crystallizes in a temperature range of 336–369°C, and the heat of reaction is 79.78 J/g.

This article is devoted to investigating polycrystalline diamond compacts (PDCs), which find broad application in drilling, tool-and-die, and building branches of industry. They are a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various granulometric compositions and shapes and forms a strong hard skeleton. A cermet phase serves as a binder. The presence of catalyst metals in a diamond layer of bilayer PDC composite materials lowers their operational properties, because the difference in thermal expansion coefficients between diamond grains and catalyst can lead to material cracking in the cutting process, while a high temperature when fabricating the diamond tool and its operation in the cutting zone can lead to the reverse diamond–graphite phase transition. In order to increase wear-resistance characteristics of diamond PCD composites formed using catalyst metals (cobalt and tungsten), etching of metals from the surface of the tool working zone is performed by two methods, notably, electrochemical and chemical. Electrochemical etching is performed in sulfuric acid with various current modes and concentration, and chemical etching is performed in a mixture of hydrochloric and nitric acids and a mixture of fluoric and nitric acids. The distribution of the chemical composition over the depth of PCD samples after etching is performed using scanning electron microscopy. It is established that electrochemical etching is more active kinetically, while chemical etching is promising for industrial application. Abrasive tests of PCD samples before and after etching show the absence of a noticeable effect of both electrochemical and chemical etching of their abrasive ability.

New-generation superalloys based on Ni intermetallics possess high thermomechanical stability at high temperatures and are widely used in modern industry. The fabrication of such materials by self-propagating high-temperature synthesis (SHS) is advantageous over traditional metallurgical technologies due to the use of the chemical-reaction energy. The development of coatings and pads based on the NiAl intermetallic on the surface of tungsten articles during SHS is of great practical interest. In this work, experiments on the interaction of the W substrate and the Ni–Al-based melt are performed in the SHS mode. When the W substrate connects with the NiAl intermetallic during SHS, the gradient welded joint 200–400 μm in thickness having a complex structure occurs. The Ni and Al melt is formed during the SHS reaction, and surface layers of the W substrate diffuse into it. The crystallization of the dendrites of the tungsten-based phase (84‒86 at % W and 16–14 at % Ni) and dendrites of the pseudobinary NiAl-based eutectic (β phase), in which precipitates of W-containing phase smaller than 50 nm in size and needle Ni₃Al inclusions (γ') are present, occurs during cooling in the near-surface layer. The W + Ni + Ni₃Al (α + γ + γ') containing the solid solution particles based on Ni₃Al intermetallics of about 100 nm in size is revealed in the transient layer. The modification of the W substrate is modified with the formation of globular precipitations of W (α phase) in it, which considerably increases the surface area.