Vol 59, No 3 (2018)

A hydroxylated xanthate salt (HXS) was synthesized from ethanol, carbon disulfide, and NaOH. The flotation responses of chalcopyrite and molybdenite when HXS was used as a novel depressant were investigated using bench-scale flotation tests. The bench-scale flotation results indicate that HXS strongly influenced the flotation of chalcopyrite and had little effect on the flotation of molybdenite. These results can be attributed to a significant improvement in the molybdenite/chalcopyrite selectivity surface index after the addition of HXS. The synthesized HXS contained both solid-philic and hydrophilic groups. The molybdenum recovery achieved using HXS was 9.91% higher than that obtained using sodium hydrosulfide, and better separation was achieved. Compared with sodium hydrosulfite, the chemical oxygen demand, sulfates and five-day BOD decreased significantly using the alternative depressant. This HXS is therefore a potential depressant for use in copper-molybdenum separation.

The removal of As, Sb, and Bi impurities from copper electrolyte is a primary objective of copper electrorefineries. The present experimental work demonstrates that the presence of Sb₂O₃ facilitates efficient and fast removal these impurities (with removal rates of 38.50, 98.50, and 99.00% for As, Sb, and Bi) through the formation of antimonate (AsSbO₄/Sb₂O₄/BiSbO₄), which plays a critical role in the self-purification of copper electrolyte. However, the antimonate which is a valuable metallurgical by-product contained high contents of As and Sb. The thermal decomposition of the antimonate was characterized by TG/DTA, a new method was proposed for recovering the target components, As, Sb, Bi, and to regenerate Sb₂O₃ with a two-stage roasting process under argon atmosphere. According to the results of XRD, SEM-EDS and ICP-MS, AsSbO₄ decomposed during the first stage roasting at 800°C over 2 h, affording As with a recovery rate of 98.80%. During the second stage, decomposition of BiSbO₄ and Sb₂O₄ at 1200°C over 2 h resulted in 99.01, 95.14% recovery rates for Sb, Bi.

The basis of the concentrate is sodium hexahydroxoantimonate or mineral mopungite. Upon reduction of the concentrate with coke, ground antimony containing 0.34% arsenic was obtained. To reduce the arsenic content in the rough metal to 0.1% and exclude the stages of antimony refining from arsenic, reductive melting is proposed in the presence of lead compounds. Because of the smelting reduction of the antimonate concentrate in the presence of sodium plumbite or lead oxide, a rough antimony with an arsenic content of 0.07–0.1% was obtained. The process of reductive smelting of the antimonate concentrate on black antimony was carried out in an oven with silicate heaters in alundum crucibles with batches of charge of 100–150 grams. The content of impurities and the base metal in antimony was determined by chemical and atomic absorption methods. The form of arsenic in the concentrate was determined by X-ray phase analysis. The analysis was carried out on an automated diffractometer DRON-3 with CuK_α radiation, ß-filter. The concentration of arsenic in the slag phase in the form of lead diarsenate Pb₂As₂O₇ is shown. Thermal gravimetric analysis of the smelting reduction process of the antimonate concentrate was studied on the Q-1000/D derivatograph of the F. Paulik, J. Paulik and L. Erdey systems of the “MOM” company. Thermogravimetric researches of process of recovery melting of the furnace charge consisting of an antimony concentrate, lead oxide and coke as a result of which it is established that process of formation of metal antimony proceeds in the range of temperatures 445–950°C are conducted.

The substitution method of recovering gold from thiosulfate-ethylenediamine (en)-Cu²⁺ leaching solution using copper powder was studied. The effects of reaction time, stirring speed, pH, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature on gold recovery were systematically examined. The experimental results showed that reaction time, stirring speed, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature have a significant influence on the recovery rate of gold, whereas the pH has little effect. A high gold recovery rate of 95.38% was achieved in 0.2 mol/L thiosulfate at 40°C after 40 min with a stirring speed of 400 rpm, pH of 11, en/Cu²⁺ molar ratio of 6, and Cu/Au⁺ mass ratio of 150. A kinetic study revealed that the reduction of gold-thiosulfate complex ions (Au(S₂O₃)₂^3-) on the surface of copper powder follows a first-order kinetics model with an apparent activation energy of 39.82 kJ/mol.

In order to control the crystallization of metals consciously with the purpose of forming the specified ingot microstructure, various physical fields are used. They vary the internal state of the melt and, consequently, the crystallization kinetics when affecting the melt. In this article, the thermodynamic and kinetics of the crystallization of aluminum under melt processing with the magnetic field is described. A rather simple experimental setup which makes it possible to investigate the magnetic-field effect on the melts of aluminum or other metals and alloys is designed. It consists of several main units: (1) the electrical furnace, (2) the water-cooled copper crystallizer combined with an electromagnetic coil, (3) mechanical facility for the rapid motion of a crucible with the aluminum melt, (4) the monitoring and control system of the melt temperature, and (5) the electronic part for recording and processing information. It is established experimentally that the magnetic field varies the temperature of the melt–crystal phase equilibrium, latent heat of the phase transition, and supercooling temperature of the melt during crystallization. It is shown that the variation in these parameters leads to a decrease in the radius of critical nuclei and an increase in their nucleation rate. The temperature–temporal dependences of crystallization are found. It is established experimentally that the crystallization time shortens under the aluminum melt treatment with the magnetic field. The analysis of aluminum samples formed under the magnetic-field effect showed that their structure is finer grained when compared with the samples not subjected to such treatment.

Isothermal sections of the diagram of the Al–Fe–Si–Zr alloy at temperatures of 450 and 600°C, as well as polythermal sections at concentrations of silicon up to 2 wt % and zirconium up to 1 wt %, are analyzed using computational methods with the help of Thermo-Calc software. It is shown that the favorable phase composition consisting of the aluminum solid solution (Al), the Al₈Fe₂Si phase, and Zr (which completely enters the composition of the solid solution (Al) during the formation of the cast billet) can be attained in equilibrium conditions at silicon concentrations of 0.27–0.47 wt %. To implement the above-listed structural components in nonequilibrium conditions and ensure that Zr enters the (Al) composition, experimental ingots were fabricated at an elevated cooling rate (higher than 10 K/s). A metallographic analysis of the cast structure of experimental samples revealed the desired structure with contents of 0.25 wt % Si and 0.3 wt % Zr in the alloy. The microstructure of the Al–1% Fe–0.3% Zr–0.5% Si alloy also contains the eutectic (Al) + Al₈Fe₂Si; however, the Al₈Fe₂Si phase partially transforms into Al₃Fe. The structure of the alloy with 0.25 wt % Si in the annealing state at 600°C contains fragmented particles of the degenerate eutectic (Al) + Al₈Fe₂Si along the boundaries of dendritic cells. It is established that the Si: Fe = 1: 2 ratio in the alloy positively affects its mechanical properties, especially hardness, without substantially lowering the specific conductivity during annealing, which is explained by the formation of the particles of the Al₈Fe₂Si phase of the compact morphology in the structure. Moreover, silicon accelerates the decay of the solid solution by zirconium, which is evidenced by the experimental plots of the dependence of hardness and resistivity on the annealing step. The best complex of properties was shown by the Al–1% Fe–0.3% Zr–0.25% Si alloy in the annealing stage at 450°C with the help of the optimization function at specified values of hardness and resistivity.

A model of the melt impregnation of metal powder under low-frequency vibration is presented in the form of mathematical dependences. The influence of factors such as the powder dispersity, its wetting with the melt, melt viscosity, and conditions and parameters of the vibration treatment are considered. The results of simulation are confirmed by the experimental data found using vibration treatment and without it. Recommendations on the selection of amplitude-frequency parameters are elaborated.

This article is devoted to the investigation into the combustion kinetics and mechanism of reaction mixtures in Zr–Si–B and Zr–B systems formed according to the forced SHS-pressing of compact ceramic materials, as well as to studying their heat resistance. It is shown that dependences of the combustion temperature and rate on the initial temperature (T₀) for compositions in the Zr–Si–B system are linear; i.e., staging of chemical reactions of formation of zirconium diboride and disilicide remains invariable with an increase in T₀. The values of effective activation energy of SHS process, which evidence the leading role of the reaction interaction of zirconium with boron and silicon in the melt, are calculated. Staging of chemical transformations in the combustion wave of the Zr–Si–B system is investigated: initially the ZrB₂ phase is formed by crystallization from the melt, and then the ZrSi₂ phase appears with a delay of 0.5 s; unreacted Si crystallizes after 1 s. The phase composition of synthesis products, in which the main component is ZrB₂ diboride, and zirconium disilicide, Si, and ZrB₁₂ boride are contained depending on the composition of the reaction charge, is investigated. Compact samples having high hardness and low residual porosity are fabricated according to forced SHS-pressing technology. High-temperature oxidation of SHS samples results in the formation of SiO₂–ZrO₂–B2O₃ oxide films and ZrSiO₄ complex oxide on their surface depending on the composition, which serve the effective diffusion barrier and lower the oxidation rate.

Tungsten deposition from a gaseous mixture of its hexafluoride with hydrogen on the surface of a porous billet of thoriated tungsten makes it possible to fasten the particles of peripheral layers and its core between each other, as well as to form a more plastic shell on the surface capable of relaxing stresses appearing during rotary forging, thus preventing the destruction of semifinished products. This procedure makes it possible to perform the rotary forging of a pilot batch of insufficiently sintered billets of thoriated tungsten, which would be destroyed if treated uncoated. The improvement of manufacturing properties can be used when fabricating similar tungsten-based compositions (of W(La₂O₃) and W(Y₂O₃)), as well as for other types of deformation. These results can be applicable for (i) lowering the sintering–welding temperature of bars (and rods) of dispersion-strengthened tungsten-based compositions, thereby reducing power consumption and increasing the overhaul period of equipment; (ii) increasing the sizes of semifinished products using the existing equipment thereby increasing the production process productivity and expanding the range of output products; (iii) producing less environmentally hazardous thoriated tungsten products, multiply reducing the radiation exposure of operators; and (iv) using composite cathodes in arc xenon lamps, thereby increasing their service life by a factor of 2–3.

The results of the predictive calculation of thermodynamic properties (enthalpy, entropy, and heat capacity) of boron silicide required for a thermodynamic analysis of the Si–B–Cl–H system performed with the help of the TERRA software complex are presented. Cases of the formation of condensed phases SiB₄ and SiB₆ in the reaction mixture are considered. To evaluate process parameters (temperature, pressure, and ratio of initial reagents) of deposition from the gas phase of silicon borides, thermodynamic calculations of the Si B–Cl–H system formed by SiCl₄, BCl₃, and H₂ for a temperature range of 1000–2200 K and pressure range of 0.00001–0.1 MPa are performed. It is shown that the thermodynamic stability of higher chlorides in the Si–B–Cl system drops with a decrease in pressure and the fraction of lower chlorides increases; i.e., initial silicon and boron chlorides destruct. However, no condensed phases SiB₄ and SiB₆ is formed, because their formation requires the introduction of hydrogen. It is determined that, varying the parameters of chemical deposition from the gas phase, it is possible to fabricate both single-phase and multiphase coatings. The results found in this study are of scientific and practical interest for developers of various production processes (gas-phase, liquid-phase, etc.) of silicon borides.

The possibility of using binders of the Next100 type alloyed with nickel and modified with WC, ZrO₂, and hBN nanoparticles for fabricating a cutting tool based on superhard materials and intended for steel and cast iron machining is shown. It is established that alloying the binder with nickel makes it possible to increase its impact viscosity by a factor of 2.5 and substantially improve the resistance of tool segments during operation. An increase in binder strength by 100–150 MPa and hardness by 5–7 HRB is provided due to the introduction of WC, ZrO₂, and hBN into it. The adhesion of cubic boron nitride to a binder increases in the presence of WC nanoparticles. The optimal ratio of diamond single crystals and cubic boron nitride in a working layer, at which maximal service characteristics of the tool are attained, is determined to be 75: 25. The formation of nanoclusters of amorphous boron at the interface of cubic boron nitride and a binder and dissolution of a small amount of nitrogen in binder components during hot compaction are revealed.