Vol 57, No 7 (2016)

A representative sample of zinc oxide from Dashteh Sefid mine was obtained and then mineral characterization studies were done. The results of mineralogical analysis showed that the main zinc-bearing minerals are smithsonite, hemimorphite and gangue minerals are quartz and dolomite. In the present paper, the effect of important factors including sodium sulfide, collector type (AC and AC/KAX), collector amount, sodium silicate, CMC dosage and frother type (MIBC and pine oil) were investigated. Design of experiment was carried out by the means of Design Expert 7 using Fractional Factorial 2^6–1. The results indicated that collector type, collector amount, CMC and frother dosage were the most effective factors controlling the zinc flotation recovery. For the zinc grade, it was found that all six parameters play a significant role. The maximum recovery and grade of zinc obtained 97.71% and 10.39% under the following optimum conditions: sodium sulfide, 5935.23 g/t; collector type, AC/KAX; collector amount, 654.09; sodium silicate, 300; CMC dosage, 600; frother type, MIBC. The result of two-stage cleaner flotation showed that zinc grade could be increased up to 16.2% with zinc recovery of 61.39%.

The influence of the PbO additive (up to 8.1 mol %) on the physicochemical properties of the KCl–PbCl₂ molten system is investigated. The primary crystallization temperatures of selected electrolyte compositions are determined. The temperature and PbO-content dependences of the conductance of electrolytes in cells with parallel electrodes are found by the impedance measurement method. The temperature dependence of density of the KCl–PbCl₂ equimolar melt containing up to 8.1 mol % lead oxide is measured by the Archimedean method, and the molar volumes are calculated. It is shown that the concentration dependence of the molar volume has an extreme form.

The results of electrochemical processing of the ZhS32-VI refractory alloy in nitric acid solutions are discussed. The main production idea involves the performance of an electrochemical process under the controlled value of the anodic potential. This procedure provides the preferential transfer of nickel, which is the alloy base, into the solution and the formation of the cathodic product or metallic nickel with a purity no lower than 95%. Experiments on the electrochemical dissolution of the mentioned alloy at various values of the anodic potential are performed. It is determined that the cathodic product contains at E_a = 1.05 V, %: Ni 94.9, Re 0.2, Co 4.7, and Cr 0.1. It is established that the incorporation of the chloride ion (20 g/L) into the nitric acid electrolyte exerts no substantial effect on process characteristics; notably, the amount of nickel in the anodic slime decreases from 2.4 to 1.6%, and no considerable increase in the nickel content in the cathodic product takes place. The exclusion is a considerable increase in the transfer rate of rhenium into the electrolyte; notably, the rhenium concentration in the nitric acid electrolyte after the 10-h production process is 1.26 g/L, and that in the nitric acid electrolyte with the addition of the chloride ion is 8.90 g/L. It is shown that the process performance of the electrochemical dissolution of Re-containing nickel-based refractory alloys under the controlled anodic potential E_a = 1.05 V in nitric acid electrolytes provides the formation of a nickel concentrate with a purity no lower than 95% in one stage and makes it possible to concentrate rhenium in the anodic slime.

The influence of tin (II) chloride additives on sorption of Rh(III) on the Purolite S920 ion exchange resin with isothiouronium groups, the Purolite S985 weak base anion exchange resin, and the Purolite A500 strong base anion exchange resin is investigated. It is established that the introduction of SnCl₂ leads to a substantial increase in selectivity of all tested ion exchange resins to Rh(III) and in the sorption rate of Rh(III) on S985 and S920 ion exchange resins. The optimal dosage of SnCl₂ (0.01 mol/L) at which the distribution coefficients of Rh(III) during sorption for all tested ion exchange resins reach maximal values is determined. It is shown that almost quantitative recovery of Rh(III) is attained when passing the multicomponent chloride solution of the composition (g/L) 0.2 Rh(III), 72.9 HCl, 53.5 NH₄Cl, 2.7 Al(III), 1.23 Fe(III) and 5.9 Sn(IV) with the SnCl₂ additive through the Purolite S920 ion exchange resin with isothiouronium groups. Desorption of Rh(III) from the Purolite S920 saturated ionite with the acidified thiourea solution is incomplete, no greater than 60%.

The heat-transfer coefficient h between a cylindrical cast made of AK7ch (A356) aluminum alloy and a no-bake mold based on a furan binder is determined via minimizing the error function, which reflects the difference between the experimental and calculated temperatures in the mold during pouring, solidification, and cooling. The heat-transfer coefficient is h_L = 900 W/(m² K) above the liquidus temperature (617°C) and h_S = 600 W/(m² K) below the alloy solidus temperature (556°C). The variation in the heat-transfer coefficient in ranges h_L = 900–1200 W/(m² K) (above the alloy liquidus temperature) and h_S = 500–900 W/(m² K) (below the solidus temperature) barely affects the error function, which remains at ~22°C. It is shown that it is admissible to use a simplified approach when constant h = 500 W/(m² K) is specified, which leads to an error of 23.8°C. By the example of cylindrical casting, it is experimentally confirmed that the heat-transfer coefficient varies over the casting height according to the difference in the metallostatic pressure, which affects the casting solid skin during its solidification; this leads to a closer contact of metal and mold at the casting bottom.

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al₃Sc (L1₂) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al₄Ca + Al₂Si₂Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al₂Si₂Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al₄Ca + Al₂Si₂Ca eutectic hardened without quenching is substantiated.

The mechanical mixing and subsequent compaction of a powder mixture consisting of carrier powder (electrolytic copper (Cu) with particle size of 20–100 μm) with nanopowder modifier compound (powders of silicon carbide (SiC)—50–70%, silicon nitride (Si₃N₄)—20–30%, sodium hexafluoroaluminate (Na₃AlF₆)—10–20%) with particle size of 70–100 nm obtained by azide technology of self-propagating high-temperature synthesis (SHS) were investigated. The mixtures containing 2.5, 5, 10, 15% of the modifier were investigated. Mechanical mixing was carried out for 30–45 min at speed of 150 rpm in a Pulverizette-5 planetary mill. An analysis of mixing of the raw powder components was performed. Some physicotechnological properties of the obtained powder mixtures, such as particle size distribution, density, bulk weight, and flowability, are determined. The formation of briquettes—the nanopowder pseudo-ligatures from powder mixtures of composition Cu–(SiC + Si₃N₄) with different concentration of modifier—was carried out by cold pressing. Compacting of the received mixtures of powders was carried out in cylindrical mold using a PSU-50 hydraulic press under pressure of 85–310 MPa. The dependence of the relative density and porosity of the briquettes on the pressure of pressing is determined. The microstructures of pseudo-ligatures pressed at maximum pressure of pressing are presented. Briquettes—nanopowder pseudo-ligatures with diameter of 25 mm, height up to 2 mm, weight of 5 g, with relative density of 53–85% and porosity of 15–47%—intended for subsequent input to aluminum melt with the aim of inoculation are obtained.

Peculiarities of the fabrication of ceramic porous and dense composite materials based on compounds of the Si–C–O–N system with the participation of chemical reactions and the formation of new phases are discussed. An analysis of comparatively new technologies is attempted in terms developed in earlier studies on the reaction sintering of silicon nitride, carbide, and oxynitride. It is shown that the approach to reaction sintering that includes the selection of promising reaction systems allowing for the bulk effect of reactions accompanying material formation can be extended to the fabrication of porous and highly porous materials. In contrast to the fabrication of dense materials, when reaction systems with positive bulk effects are used, the reaction systems with negative bulk effects can be used in the fabrication of highly porous materials.

Composites Al/Al₂O₃ (lamellar cermet matrix)–filler (discrete metallic fibers, duralumin chips, graphite particles, fused corundum grains, and technical alumina spherulites) are fabricated. To form the lamellar cermet matrix, industrially produced PAP-2 aluminum powder was used. This powder consists of scaled particles with stearin coating (the specific surface of the powder is 4.1322 m²/g, and its particle size varies from 0.03 to 10 μm). In order to form the composites, the following main process operations were used: heat treatment of the PAP-2 powder in air to burn out stearin from the particle surface and replace it with a passivating alumina film, mixing of the thus formed powder product with a filler, and compaction and reaction sintering of powder billets in the filtration burning mode in air. To fabricate the Al/Al₂O₃–C composite, a new approach based on the saponification chemical reaction of stearin is proposed. This reaction runs between stearin on the surface of aluminum particles and caustic soda, which is the product of hydrolysis of the diluted liquid glass introduced into initial powder. The reaction products (sodium stearate and glycerol) are decomposed during the subsequent heat treatment in air with the formation of a coke residue on the particle surface. The physicochemical properties of the composites were determined using standard and conventional procedures.

The specific surface and porous structure of viscose-based carbon fibers produced by the Krasnoyarsk Plant of Chemical Fibers are investigated by low-temperature nitrogen adsorption using an ASAP 2020 device. The dependence of their specific surface and character of the pore-size distribution on gas-phase activation modes in the carbon dioxide stream at a temperature of 900°C is shown. It is established that the adsorption surface of carbon fibers can rise from 0.3 to 1900 m²/g during the activation. It is revealed that the prolongation of the activation time leads to an increase in the specific fiber surface owing to the appearance of numerous new micropores and the development of the microporous structure.