Brajendra Mishra

Materials sustainability for environment: Red-mud treatment

Bayer’s process revolutionized the extraction of aluminum from the bauxite ores. However, the hydrothermal extraction of alumina is associated with the generation of a byproduct, red-mud consisting of undissolved solids composed of iron oxides, sodium alumino silicates, titania, silica and rare earth elements. The accumulation of red-mud (or bauxite residue) in the world is 30 billion metric tons produced at a rate of 125 million tons per annum (2013). Utilization of red-mud for constructional purposes, wastewater treatment, metallurgical products, and pigments are listed. Metallurgical processing efforts of red-mud to generate various value added products such as pig iron, direct reduced iron slag wool, magnetite, titania, iron carbides are presented in the article.

Kinetic and Thermodynamic Study of Aluminum Recovery from the Aluminum Smelter Baghouse Dust

The recovery and utilization of metals from wastes are important for saving metal resources, as well as for protecting the environment. There are various types of solid wastes that have different origins and forms. Elemental and mineralogical composition of the wastes depends on the industry where they come from; therefore, the recovery processes for these materials are widely different. In general, the recovery of metals from ores and/or concentrates is carried out by extractive metallurgy methods comprising pyrometallurgy, hydrometallurgy, and electrometallurgy. In this research, sodium carbonate and sodium hydroxide leachings with different experimental conditions are tested for the aluminum dissolution. Also, a kinetic and thermodynamic study of sodium hydroxide leaching of the aluminum smelter baghouse dust is conducted. It is determined that when the solids content is 10xa0g/L, the overall reaction rate is controlled by pore diffusion and the activation energy is calculated to be about 4.8xa0kcal/mol. At temperatures below 100xa0°C, the stable form of the recovered compound after leaching is sodium aluminate.

Interfacial reaction and microstructure study of DSS/Cu/Ti64 diffusion-welded couple

In the present study, the interfacial reaction and microstructure behavior of diffusion-welded joints (DWJs) between duplex stainless steel (DSS) and Ti–6Al–4V alloy (Ti64) with copper interlayer were investigated. The joints were carried out at 825, 850, 875 and 900xa0°C temperature for 60xa0min under 4xa0MPa uniaxial pressure in vacuum. Welded joint was characterized by light microscopy and scanning electron microscopy using backscattered electron mode. Layer-wise Cu4Ti, Cu2Ti, Cu4Ti3, CuTi and CuTi2 intermetallic phases were formed at the Cu–Ti64 interface and the width of the intermetallic layers increases with increase in welding temperature. However, the DSS–Cu interface was completely free from intermetallics. The activation energy and interfacial energy of reaction phases was calculated at the interface. The activation energy values showed that the CuTi intermetallic grew faster than the other phases of the Cu–Ti-based reaction. However, CuTi2 phase first nucleates than the other Cu–Ti-based intermetallics due to its lowest interfacial energy. The highest joint tensile strength of ~u2009516xa0MPa (~u200979% of DSS) along with ~u20096.6% ductility was achieved at 875xa0°C processing temperature.

Mechanical and Corrosion Properties of Fe-Cr-Mn-C-N Austenitic Stainless Steels for Drill Collars

The mechanical and corrosion properties of air/water-quenched CN66 (0.28/0.38 wt pct, C/N) and CN71 (0.27/0.44 wt pct, C/N) steels after heat treatment were investigated. The carbon condensed area of the water-quenched alloys decreased compared with the air-cooled alloys, and lattice expansions occurred, resulting in a strained region. The values of UTS and elongation of water-quenched CN71 were increased as 105 MPa and 25.2 pct compared with the air-cooled CN71, and decreased sour corrosion resistance (1.8xa0×xa010−4 mm/year).

Effects of Cooling Rate on Precipitate Evolution and Residual Stresses in Al–Si–Mn–Mg Casting Alloy

The residual stresses with different heat treatment conditions have been measured and correlated with the microstructural behavior of AA365. 30 and 100xa0K/min cooling of AA365 inhibited the transformation of precipitates under 773xa0K, respectively. The alloy cooled at 30 and 100xa0K/min exhibited tensile residual stresses of 6.2 and 5.4xa0MPa, respectively, while the alloy cooled at 1 and 10xa0K/min showed compressive stresses of −u200912.8 and −u200910.3xa0MPa, respectively. The formation β′, β″, and other intermetallic compounds affected the compressive residual stresses, and that the fracture of the brittle intermetallic phases could reduce the extent of residual stresses in the lattice through plastic deformation.

Leaching Kinetics of Yttrium and Europium Oxides from Waste Phosphor Powder

AbstractPhosphor powder sample was characterized, and the leaching kinetics of yttrium, and europium in hydrochloric acid were investigated. Under optimized leaching conditions, 98% Y and 97% Eu were extracted, and a reaction curve was generated using the percentage of extraction as a function of time and temperature. Based on R2 values, shrinking spherical particle and shrinking core model were not applicable. SEM analysis also confirmed shrinking core behavior was not applicable due to the lack of core–shells in the leach residue. The kinetic data were best fitted by a logarithmic rate expression of the empirical model. Activation energy was calculated to be 77.49xa0kJ/mol for Y and 72.75xa0kJ/mol for Eu in the temperature range of 298–343xa0K.n

Recovery of Copper from Flue Dust Generated in e-Waste Processing Using Physicochemical Methods

A flue dust that contains valuable metals is generated during smelting operation for e-waste treatment. However, metal recovery from this flue dust has not been extensively studied. The flue dust can contain valuable metals such as gold, silver, copper, and iron. In this study, the flue dust from e-waste was investigated as the potential metal resource for obtaining valuable metals, including copper and iron, using physical and chemical methods. In the physical processes, size separation was performed, and the mass and composition of each fraction were analyzed. Major valuable elements of the flue dust are copper and iron with small levels of gold and silver in all size fractions. The iron is present mostly as magnetite, as determined by XRD. The magnetite was removed by magnetic separation, and the removal efficiency was about 90%. The chemical processes included leaching in various acid solutions (HNO3, H2SO4, and HCl) for copper recovery. The highest recovery efficiency of over 99% was obtained after 8xa0h in 1xa0M nitric acid and was optimized at a pulp density of 20xa0g/L and a stirring speed of 200xa0rpm at 20xa0°C temperature.

Effect of Cooling Rate on the Mechanical Properties of AA365 Aluminum Alloy Heat-Treated Under T4, T5, and T6 Conditions

The mechanical properties of AA365, an Al–Si–Mn–Mg alloy used in high-pressure die-casting of automotive parts, can be optimized for a proper application using different heat treatments. During a die-casting process including heat treatment, aluminum alloy cast components experience considerable changes in their mechanical properties due to the non-uniform cooling phenomena. The mechanical properties of AA365 with different cooling rates during T4, T5, and T6 heat treatments were investigated and analyzed by a statistical method using a design of experiments protocol to see which factor is most significant for mechanical properties. The factors used in this study are the type of heat treatment and cooling rate of each step. The microstructural analysis was conducted to observe the mechanism of mechanical property changes. The combination of heat treatment type and cooling rate enabled the control of ductility and strength properties in AA365.

Selective Reduction and Separation of Europium from Mixed Rare-Earth Oxides from Waste Fluorescent Lamp Phosphors

Nearly the entire worldwide production of europium is recovered, as a minor constituent, from mining bastnasite, monazite ore, or ion absorbing clays. However, this research indicates a process to recycle europium from waste lamp phosphors as a strategy meet the demand for europium. In this process, waste fluorescent lamp powder is retorted, sieved, leached, and precipitated to produce a mixed europium/yttrium rare earth oxide (REO). Europium is separated from yttrium by selectively reducing Eu(III) to Eu(II) using zinc powder and precipitating europium (II) sulfate from solution using sulfuric acid. Screening experiments were conducted observe the effect of pulp density, precipitation time, entrance pH, and stoichiometric ratio sulfate upon the grade and recovery of europium (II) sulfate. The best conditions to maximize grade and recovery of europium (II) sulfate were a 1 h precipitation time, 10× the stoichiometric ratio of sulfate, 100 g/L mixed REO, and the entrance pH equal to 3. The maximum grade of europium sulfate was 95.93%, and the maximum recovery was 73.32%.

Low Temperature Reduction of Hematite in Red-Mud to Magnetite

Red-mud, the residue generated from the Bayers processing of bauxite ore in Jamaica was subjected to a low temperature reduction process. Hematite (~60 m%) was reduced to magnetite employing a gas based mixture of CO, CO2 and N2 as a diluent. Extensive thermodynamic study was conducted to identify the stability region for magnetite. ‘Optimal conditions’ for the gas-phase reduction were determined to be: a processing temperature of 540 °C ± 10 °C, partial pressures CO(g) and CO2(g) each of 0.070 atm (bar) ± 0.001 atm (bar)/inert diluent-gas: N2(g), for a conversion-time of 30 min. Mathematical model for reduction based on unidirectional diffusion is also formulated in this paper.