Том 57, № 4 (2016)

This paper deals with filtration of very-fine size ground brecciated calcitic limestone ore slurry using flocculant chemicals. Screening of flocculants was carried out using capillary suction time (CST). Optimization of the neutral slurry filtration behaviour was carried out using a commercial non-ionic type polyacrylamide based synthetic flocculant. Response surface methodology and central composite rotatable design was used for model development and optimization of the filtration process. Critical filtration parameters such as applied vacuum, cake thickness and flocculant dosage were optimized. A correlation coefficient of 0.97 was obtained both for filtration rate and percent cake moisture. The analysis of variance of the determined model indicated that linear effects, interaction effects, quadratic effects, linear terms of all the three variables and some interaction among them are more significant for the filtration rate and cake moisture percent. The optimum filtration rate of 742 kg/(h m²) was obtained at the optimum conditions with cake moisture of 22.3%.

The electrothermal process of magnesium metal production is a promising route, where large sized internally heated reactor is used for magnesium production resulting in less energy and labour intensive and high space-time yield process. However, the dissolution behavior of dolime in the electrothermal slag has been found critical for the process optimization. In this paper, the dissolution kinetics of the dolime in the slag was discussed. Quaternary slag (CaO-Al₂O₃-SiO₂-MgO) was prepared having basicity CaO/SiO₂ ≥ 1.8 and Al₂O₃/SiO₂ ≥ 0.26 for dolime dissolution studies by static hot dip method. Prior to the experiments, FactSage calculations were carried out varying temperatures and slag compositions. In the kinetic studies, dolime particles 10–15 mm size was added in slag melted at 1450, 1500 and 1550°C and samples were taken at various time intervals. The chemical analysis of slag sample was carried out to investigate the dissolution kinetics to establish the rate expression. The activation energy for the process was calculated for different models used in study and was found to be in the range of 130–270 kJ/mol. SEM analysis was done for surface analysis of reacted particles. This study would be helpful in optimizing the dolime charging rate during pilot scale trials for electrothermal magnesium production at CSIR-NML, Jamshedpur.

Leaching of zinc from indium-bearing zinc ferrite (IBZF) under microwave heating (MH) has been investigated. The result showed microwave intensified the leaching reaction of IBZF in the MH process. Microwave had a great nonthermal effect on the leaching reaction. The effective collision and the H₂SO₄ activation under the action of microwave belonged to the nonthermal microwave effect. Particle size of IBZF in the range from 45 to 150 μm almost had no effect on the zinc leaching in the MH process. Leaching temperature and leaching time had important effects on the zinc leaching. Zinc leaching in the MH process obeyed the unreacted shrinking core model very well, and the activation energy was 73.747 kJ/mol. The kinetic equation was \(1 - (1 - x)^{1/3} = 8.82 \times 10^8 e^{ - 73.747 \times 10^3 /RT} t\). The ratio of frequency factor of K_0(In)/K_0(Zn) was up to 4.69, indicating the effect of microwave intensification on the indium leaching was greater than that on the zinc leaching.

A novel pyrometallurgical route was used to reduce the lead paste to obtain metallic lead with different additions of sodium carbonate at 850°C in a silicon carbide crucible. The process allows to obtain a high recovery of metallic lead in a single step and a slag constituted mainly by lead silicate. Products obtained were characterized by atomic absorption, X-ray powder diffraction and SEM-EDS techniques. A thermodynamic study was carried out with the software FactSage to determinate the compounds formation to the experimental conditions. High amounts of Na₂CO₃ and SiC promoted the formation of a lead sulfide compound which decreased the lead recovery.

Cobalt is an essential engineering metal among the less abundant metals found in the earth crust with wide range of applications. However due to the scarcity of resources, it is required to produce the metal in a cost effective manner to meet the supply demands. Cobalt is produced by electrodeposition from chloride or sulphate media, the latter being a widely used method. The use of additives in the electrolytic bath during electrodeposition from sulphate solutions can not only solve issues related to current efficiencies, but also result in production of uniform, smooth and bright deposits of the metal. The present work investigates the effect of Tween 80 a non-ionic additive, on the electrodeposition of cobalt. The concentration of the additive Tween 80 was varied over a range of 1–50 mg/L to evaluate the changes in current efficiency, specific energy consumption and quality of electrodeposited cobalt metal. The results indicated that, apart from increasing the current efficiency, the additive produced bright cobalt deposits. A maximum current efficiency of 98.1% was achieved with 20 mg/L Tween 80 in the electrolytic bath. X-ray diffraction studies have revealed that <100> direction is the most preferred orientation of crystal growth during cobalt electrodeposition. However it is shifted to <110> at higher concentrations (50 mg/L) of the additive. Scanning electron micrographs indicate that smooth, compact and uniform deposits of cobalt are obtained at 20 mg/L beyond which there is deterioration in the quality of deposits. Cyclic voltammetric studies indicated polarization of the cathode in the presence of Tween 80. This behaviour was also reflected in the decrease of the rate of electron transfer as evident from exchange current density (i₀) values.

Wastes generated from the Bayer’s process serve as valuable resources for aluminum, vanadium, gallium, etc. This work aims to develop a environmentally acceptable and low-cost chemical leaching-cumpurification method for the recovery of vanadium sludge of Indian alumina plant (10–12% V₂O₅) and synthesize vanadium pentaoxide. The efficiency of leaching was evaluated by various lixiviants like acidified water, H₂SO₄, soda and NaOH against variation in pulp density and temperature. Maximum extraction (96%) vanadium was achieved using acidified water leaching at above ambient temperature in 1 h with 200 g/L pulp density following diffusion control model. Finally, the vanadium rich leach liquor was purified by steps of adsorption/precipitation etc., to remove with iron and silica to get vanadium pentaoxide. A high purity product of 99% V₂O₅ was obtained by allowing the adsorption at acidic pH followed by desorption and precipitation at 90°C.

A new aluminum matrix composite reinforced with B₄C particles was manufactured using different stirring speeds and time. Stirring speeds of 600 and 700 rpm and stirring time of 5, 10, and 15 minutes were chosen for casting the aluminum-B₄C composites The effects of these parameters on the microstructure and mechanical properties of the produced composites were analyzed using reflected light microscopy (RLM), scanning electron microscopy (SEM and FESEM), image analysis, density measurement, and tensile test. Image analysis of the as-cast microstructures revealed that longer stirring speeds and time resulted in higher reinforcement content in the as-cast microstructure and consequently the sample under 700 rpm stirring speed with 15 min total stirring time had incorporated most of the added B₄C particles. Interface characterization performed by FESEM showed that the added Ti and Zr had accumulated at the interface. Tensile test results revealed that higher stirring speed and longer stirring time resulted in the reduction of ultimate tensile strength and total elongation for 700 rpm stirring speed. It was concluded that a 700 rpm stirring speed with 15 min stirring time could produce a composite sample with the incorporation of most of the added particles distributed almost uniformly throughout the microstructure.

Present studies account the feasibility studies on isothermal oxidation of W–Cu hard metal electrical contractor scraps for recycling by roasting-leaching method. This was investigated as one of main processes to produce friable oxidized product amenable to subsequent leaching process. Oxidation is facilitated using scrap turnings instead of solid W–Cu contactor rods. The alloy oxidizes to Cu_xO, WO_x and CuWO₄ upon heating in the temperature range 400–1000°C under oxygen flow. Apart from oxidized W and Cu phases, significant amount of Cu nuggets formed initially at 450°C that rose gravimetrically up to 750°C, and then disappeared at higher temperature. The maximum weight gain was about 22% compared to initial weight when oxidation was carried out at 750°C. Oxidation beyond the temperature of 750°C corresponded to significant loss of tungsten by evaporation of WO₂ · (OH)₂ gaseous product. Thermal oxidation of W–Cu metal electrical contractor tip scraps produced porous and friable oxidized product of W and Cu.

In this study, the CuAl–TiC composite materials were produced using hot pressing process. Effect of TiC grain size (0.2, 4 and 20 μm) on some properties of these materials was investigated experimentally. Production of CuAl–TiC composites was carried out under pressure of 35 MPa, at 700°C, and for a sintering time of 5 minutes. SEM-MAP studies showed that the TiC grains were relatively homogeneously distributed in the CuAl matrix. Microstructure analysis revealed that the composite materials consist of Cu, Al, Cu₉Al₄, CuAl₂ and TiC phases. With the decreasing of TiC grain size, the hardness, transverse rupture strength, relative density and sintered density of composites increased.