Aluminothermic Reduction Process Research Articles

Control of Silica Gel Formation in the Acidic Leaching of Calcium Aluminate Slags with Aqueous HCl for Al Extraction

The present research article investigates the extraction of aluminum (Al) from an engineered CaO-Al2O3-SiO2 slag by leaching with aqueous HCl under atmospheric pressure conditions. The slag is the by-product of an aluminothermic reduction process to produce metallurgical-grade silicon (Si) in a more sustainable way compared to conventional carbothermic reduction. One major challenge in the acidic leaching of aluminosilicate materials, like the slag treated in this study, is the possibility of SiO2 gel formation during the leaching process. Extensive SiO2 gel formation can make the separation of pregnant leach solution (PLS) from the leached residue impossible. Consequently, any acid leaching of aluminosilicate materials must be optimized for avoidance of these gelation phenomena. The present study first explores the leaching behavior of the calcium aluminosilicate slag in relation to the S/L ratio, with all other hydrometallurgical factors remaining stable (20.2% wt. HCl solution, 80 °C, optimized stirring rate), to determine at which value of this parameter SiO2 gelation occurs. After determining the optimum S/L ratio for this system, an analysis of the behavior of Si in the PLS is presented, and the mechanism of SiO2 gelation is explained based on critical assessment of these results against data provided from the scientific literature. It was found that the value of the pH of the PLS and the concentration of dissolved CaCl2 and AlCl3 are critical factors for the formation of filterable amorphous SiO2. Under the optimum leaching conditions, PLS containing 37 g/L Al was obtained with concurrent avoidance of gelation phenomena.

Low-oxygen Ti-6Al-4V alloy powder synthesized by an aluminothermic reduction combined with deoxidation process

A novel aluminothermic reduction combined with deoxidation process was developed in this research to prepare low-oxygen Ti-6Al-4V alloy powder. First, with Al and Al-V alloy powders as reducing agents and additives, crude Ti-6Al-4V alloy powder was fabricated by reduction-vacuum distillation using Na2TiF6 as a titanium source. The aluminothermic reduction process was investigated by TG-DSC technique, and the thermal kinetic parameters of the reaction process were calculated by the Kissinger method. The oxygen content of the crude Ti-6Al-4V alloy powder with a coral-like porous structure was detected as 0.366 %. Furthermore, the existential states of the oxygen contained in the crude product powder was analyzed using XPS. The results indicated that the oxygen existed in three chemical states: metal oxides, defective oxygen, and adsorbed oxygen. Therefore, the deoxygenation of the crude Ti-6Al-4V alloy powder with calcium as a deoxidizer was carried out at 900 °C. As a result, the final Ti-6Al-4V powder with an oxygen content of approximately 822 ppm could be obtained. The contents of Ti, Al, V, Fe, and O in the obtained Ti-6Al-4V powders met the requirements of GB/T 3620.1−2016. This work had demonstrated the feasibility of preparing Ti-6Al-4V alloy powder by the novel aluminothermic reduction combined with deoxidation process.

Aluminium extraction from a calcium aluminate slag using sodium carbonate based on the critical examination of the patented industrial Pedersen process

The extraction of aluminium from calcium aluminate phases by leaching with Na2CO3 solutions has been researched intermittently for more than a hundred years. In the 21st century, this process has gained a renewed interest for the design of novel metallurgical methods. The Pedersen Process has been the only known successful industrial scale application of calcium aluminate leaching to date. The engineering principles that ensured plant operations remained, until recently, unknown. These principles are critically assessed for the first time, based on recently retrieved patents submitted at the time the Pedersen process was in operation. The findings of the previous analysis were used for an experimental study with the two goals: (i) to validate the principles applied in the industrial Pedersen process and (ii) to apply these principles in designing an optimized leaching process for calcium aluminate slags originating from alternative Al sources. The calcium aluminate slag used in this study is the by-product of an aluminothermic reduction process for Si production along with an 8% (w/w) Na2CO3 aqueous solution. Results confirmed the majority of the assumed principles. All the tested leaching conditions produced Al extraction in the range of 75% - 95% (w/w).

Photocatalytic and eletrocatalytic activity of black TiO 2 nanotube arrays by aluminothermic reduction

The black TiO2 nanotubes arrays were prepared by anodizing and aluminothermic reduction process. The prepared samples were characterized by X-ray diffraction (XRD), SEM, UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). The photochemical/electrical catalytic activity of the samples before and after blackening treatment was tested. Comparing with the raw TiO2, the macrostructure of the black TiO2 nanotube arrays changes a little, and the tubal walls become a little thicker and rough. The photocatalytic hydrogen production rate has an obvious enhancement (from 8.9 µmol cm−2 h−1 to 22.8 µmol cm−2 h−1) after the blackening treatment and the electrocatalytic H2 evolution rate is also improved with a lower onset potential. The increment of trivalent Ti3+ on the surface is confirmed by XPS and presented by the colour changing of the samples (from white colour to black). The hybrid energy band gap and reduced charge transfer barrier are proved to be essential in promoting the catalytic properties of the black TiO2 nanotube arrays.

Low Temperature Aluminothermic Reduction of Natural Sepiolite to High-Performance Si Nanofibers for Li-Ion Batteries.

Nanostructure silicon is one of the most promising anode materials for the next-generation lithium-ion battery, but the complicated synthesis process and high cost limit its large-scale commercial application. Herein, a simple and low-cost method was proposed to prepare silicon nanofibers (SNF) using natural sepiolite as a template via a low-temperature aluminum reduction process. The low temperature of 260°C during the reduction process not only reduced the production cost but also avoided the destruction of the natural sepiolite structure caused by the high temperature above 600°C in the traditional magnesium thermal reduction process, leading to a more complete nanofiber structure in the final product. For the first time, the important role of Mg-O octahedral structure in the maintenance of nanofiber structure during the process of low-temperature aluminothermic reduction was verified by experiments. When used as an anode for lithium-ion batteries, SNF yield a high reversible capacity of 2005.4 mAh g−1 at 0.5 A g−1 after 50 cycles and 1017.6 mAh g−1 at 2 A g−1 after 200 cycles, remarkably outperforming commercial Si material. With a low-cost precursor and facile approach, this work provides a new strategy for the synthesis of a commercial high-capacity Si anode.

Thermodynamics, kinetics and mechanism analysis of aluminothermic reduction for preparing Al-Zr alloy

In this study, we investigated the thermodynamics and kinetics of the aluminothermic reduction of ZrO2. The results of thermal analysis and isothermal heat treatment showed that the aluminothermic reduction of ZrO2 was an exothermic reaction that occurred at . 958.8°C. The aluminothermic reduction process does not produce metal Zr, but when the stoichiometric number of Al:ZrO2 was 13:3, Al3Zr and Al2O3 can be obtained by the reaction. The activation energy of the reaction was 1589.89 kJ/mol, and the reaction order was 1.90. The aluminothermic reduction process and mechanism of ZrO2 in the presence of potassium cryolite as the molten salt medium was also studied. The results showed that ZrO2 dissolved in potassium cryolite molten salt and participated in the reduction reaction in the form of Zr–O–F complex ions, while the by–product Al2O3 also dissolved in potassium cryolite to further promote the formation of the Al–Zr alloy.

Manganese and Aluminium Recovery from Ferromanganese Slag and Al White Dross by a High Temperature Smelting-Reduction Process.

The recovery of Mn and Al from two industrial waste of ferromanganese and aluminum production processes was investigated via implementing a high temperature smelting—aluminothermic reduction process. The experiments were carried out with or without CaO flux addition, and two dross qualities. It was observed that the prepared mixtures of the materials yield homogeneous metal and slag products in terms of chemical composition and the distribution of phases. However, the separation of produced metal phase from the slag at elevated temperatures occurs when a higher amount of CaO is added. Viscosity calculations and equilibrium study indicated that the better metal and slag separation is obtained when the produced slag has lower viscosity and lower liquidus. It was found that the process yields Al-Mn-Si alloys, and it is accompanied with complete recovery of Mn, Si and Fe and the unreacted Al in the process. Moreover, the quality of metal product was less dependent on the slightly different dross quality, and the concentration of minor Ca in metal is slightly increased with significant increase of CaO in the slag phase.

Reaction mechanism and kinetics of ferrotitanium preparation by aluminothermic reduction of CaTiO3

A ferrotitanium alloy production process by aluminothermic reduction and using perovskite as materials was studied in laboratory. The thermodynamics of the Al-CaO, Al-CaO-CaTiO3, Al-CaO-Fe-CaTiO3 system was calculated and the reduction process of CaTiO3 to prepare ferrotitanium was investigated. The Freeman-Carroll method was used to analyze the kinetics of aluminothermic reduction process. The results show that ferrotitanium alloys can be produced by aluminothermic reduction using perovskite as material. In the reduction process, the reduction reaction of TiO2 in CaTiO3 by aluminum proceeds at 1000–1100 ℃, and the formation temperature of ferrotitanium alloy is between 1400 ℃ and 1500 ℃. CaO not only acts as a slag-forming agent in the reaction process, but also participates in the reduction reaction process. The apparent activation energy and the reaction order at the reduction peak decrease with the increasing of heating rate which indicates that the reaction is easier with the increase of heating rate.

Matryoshka-type carbon-stabilized hollow Si spheres as an advanced anode material for lithium-ion batteries

Silicon (Si) is regarded as the potential anode for lithium-ion batteries (LIBs), due to the remarkable theoretical specific capacity and low voltage plateau. However, the rapid capacity decay resulting from volume variation and slow electron/ion transportation of Si limit its practical application. Here, matryoshka-type carbon-stabilized hollow silicon spheres (Si/C/Si/C) are synthesized by an aluminothermic reduction and calcination process. The Si/C/Si/C anode materials prepared at 500 °C (Si/C/Si/C-500) exhibit unique structures, in which amorphous region and porous structure are preserved in the Si layers. The anode based on Si/C/Si/C-500 displays an initial specific capacity of 2792 mAh/g at a current density of 100 mA/g. At 1000 mA/g, this anode retains a reversible capacity of 1673 mAh/g, 86.9% of the initial capacity after 200 cycles. Such synthetic strategy can be employed to fabricate other high-capacity anode materials with large volume variation during charge/discharge process

Aluminothermic Reduction of Manganese Oxide from Selected MnO-Containing Slags.

The aluminothermic reduction process of manganese oxide from different slags by aluminum was investigated using pure Al and two types of industrial Al dross. Two types of MnO-containing slags were used: a synthetic highly pure CaO-MnO slag and an industrial high carbon ferromanganese slag. Mixtures of Al and slag with more Al than the stoichiometry were heated and interacted in an induction furnace up to 1873 K, yielding molten metal and slag products. The characterization of the produced metal and slag phases indicated that the complete reduction of MnO occurs via the aluminothermic process. Moreover, as the Al content in the charge was high, it also completely reduced SiO2 in the industrial ferromanganese slag. A small mass transport of Ca and Mg into the metal phase was also observed, which was shown to be affected by the slag chemistry. The obtained results indicated that the valorization of both Al dross and FeMn slag in a single process for the production of Mn, Mn-Al, and Mn-Al-Si alloys is possible. Moreover, the energy balance for the process indicated that the energy consumption of the process to produce Mn-Al alloys via the proposed process is insignificant due to the highly exothermic reactions at high temperatures.

Mechanism and kinetic analysis of vacuum aluminothermic reduction for preparing TiAl intermetallics powder

This work investigates the mechanism and kinetics of an aluminothermic reduction process using Na2TiF6 as the raw material for preparing TiAl alloy powder. The experiment was carried out at 1100 °C with a 3:7 M ratio of Na2TiF6 to Al. Quasispherical TiAl alloy powder with an oxygen content of 0.32% could be achieved after vacuum ball milling of the reduction product. The thermal analysis results demonstrated that the aluminothermic reduction reaction was an exothermic process. Moreover, the kinetic parameters and the equation for the exothermic reaction rate of the reduction process were calculated by a thermoanalytical technique. According to XRD, SEM, and EDS analyses, the reduction mechanism and the evolution process of the products were discussed. Experimental evidence indicated that TiAl3 and TiF3 could be generated as intermediate products during reduction. TiAl could be produced through further reduction reactions between TiAl3 and TiF3.

Molten-Salt-Assisted Synthesis of Bismuth Nanosheets for Long-term Continuous Electrocatalytic Conversion of CO2 to Formate.

Two-dimensional (2D) monometallic pnictogens (antimony or Sb, and bismuth or Bi) nanosheets demonstrate potential in a variety of fields, including quantum devices, catalysis, biomedicine and energy, because of their unique physical, chemical, electronic and optical properties. However, the development of general and high-efficiency preparative routes toward high-quality pnictogen nanosheets is challenging. A general method involving a molten-salt-assisted aluminothermic reduction process is reported for the synthesis of Sb and Bi nanosheets in high yields (>90 %). Electrocatalytic CO2 reduction was investigated on the Bi nanosheets, and high catalytic selectively to formate was demonstrated with a considerable current density at a low overpotential and an impressive stability. Bi nanosheets continuously convert CO2 into formate in a flow cell operating for one month, with a yield rate of 787.5 mmol cm-2 h-1 . Theoretical results suggest that the edge sites of Bi are far more active than the terrace sites.

Molten‐Salt‐Assisted Synthesis of Bismuth Nanosheets for Long‐term Continuous Electrocatalytic Conversion of CO2to Formate

AbstractTwo‐dimensional (2D) monometallic pnictogens (antimony or Sb, and bismuth or Bi) nanosheets demonstrate potential in a variety of fields, including quantum devices, catalysis, biomedicine and energy, because of their unique physical, chemical, electronic and optical properties. However, the development of general and high‐efficiency preparative routes toward high‐quality pnictogen nanosheets is challenging. A general method involving a molten‐salt‐assisted aluminothermic reduction process is reported for the synthesis of Sb and Bi nanosheets in high yields (>90 %). Electrocatalytic CO2reduction was investigated on the Bi nanosheets, and high catalytic selectively to formate was demonstrated with a considerable current density at a low overpotential and an impressive stability. Bi nanosheets continuously convert CO2into formate in a flow cell operating for one month, with a yield rate of 787.5 mmol cm−2 h−1. Theoretical results suggest that the edge sites of Bi are far more active than the terrace sites.

Influence of Carbon Content on Aluminothermic Reduction of Ilmenite During Hot Pressing

Al2O3-TiCN-Fe composites were successfully prepared by hot pressing using natural ilmenite, aluminum, and carbon. The process of aluminothermic reduction of ilmenite and the influence of carbon on the phase evolution, synthetic products, microstructure, and properties were investigated using x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and mechanical analysis. The XRD results showed that the reduction process of the FeTiO3-2Al system was a gradual deoxygenation process. In the FeTiO3-2Al-xC systems, carbon participates in the reduction reaction to form TiN, which gradually transforms to TiCN. The carbon content had a great influence on the presence of titanium oxides during the reaction. In addition, the grain size of Al2O3, TiCN, and Fe phases became smaller as the carbon content was increased. When the carbon content was 0.88 mol, the synthesized products achieved comprehensive mechanical properties, i.e., bending strength and Vickers hardness of 375 MPa and 15.5 GPa, respectively.

Aluminothermic Reduction Process Under Nitrogen Gas Pressure for Preparing High Nitrogen Austenitic Steels

The aluminothermic reduction casting process under nitrogen gas pressure to make austenitic Cr-Mn-N (Ni-free) and Cr-N (Ni/Mn-free) high nitrogen stainless steels was investigated. Thermodynamic simulation of the redox reaction depending on process parameters was performed. As a result, the optimal ratio of aluminum to oxygen in the initial powder mixture to obtain the highest yield of metal product with minimal aluminum nitride contamination was predicted to be slightly greater than the stoichiometric ratio of 1.125. Microstructures of aluminothermic 26Cr1N and 23Cr9Mn1N steels, prepared taking into account the results of thermodynamic simulation, were investigated by X-ray diffraction, metallography, and transmission electron microscopy. The as-cast microstructure was a pseudo-pearlite (layered ferrite-nitride mixture) in 26Cr1N steel and a ferrite-austenite with signs of discontinuous austenite decomposition in 23Cr9Mn1N steel. After hot forging and subsequent water quenching from 1200 °C, the microstructure was fully austenitic in both steels. Tensile tests of quenched 23Cr9Mn1N steel showed a combination of high strength (ultimate strength of 1324 MPa) and ductility (elongation of 27 pct). The results illustrate that the aluminothermic casting process for producing high nitrogen steel is competitive with the commonly used methods, such as pressure electroslag remelting, both in terms of cost and mechanical properties of manufactured steel.

A low-cost and energy-saving preparation method for silicon derived from rice husks and lithium ion battery applications

Rich husks are used as the raw material for preparation of silicon nanoparticles from an aluminothermic reduction process. The synthetic process is conducted on a low temperature condition, avoiding the large energy consumption resulting from high temperature operation course. The fabricated silicon has a porous structure with average particle size of approximately 30 nm. The unique structure triggers pronounced electrochemical behavior for Li alloy/de-alloy reaction. The material delivers an initial discharge and charge capacity of 3844.7 mAh g−1 and 3144.4 mAh g−1 at the current density of 100 mA g−1. With the current density increasing to 6 A g−1 and 8 A g−1, the material shows a reversible capacity of 860.1 mAh g−1 and 413.4 mAh g−1, respectively. The low material fabrication cost and satisfactory electrochemical performance make the low temperature aluminothermic reduction to be a promising route for silicon fabrication for next-generation lithium-ion battery.

Effect of Mg Concentration on the Aluminothermic Reduction of Mn2O3 Particles Obtained from Cathodes of Discharged Alkaline Batteries: Mathematical Modeling and Experimental Results

This paper aimed at studying the effect of magnesium concentration in molten aluminum produced from beverage cans on the process of aluminothermic reduction of Mn2O3 particles obtained from the cathodes of discharged alkaline batteries. The experimental results were analyzed by using thermodynamic fundamentals and kinetic modeling, while the characterization of the reaction products obtained allowed the mechanism of the process to be described. It was found that the addition of magnesium improves the wettability of solid particles by molten aluminum, thus increasing the reaction and its subsequent incorporation into the molten aluminum solution of Mn released from the reduction reaction. This work was carried out using several initial magnesium concentrations; 1.0, 2.0, 3.0, and 4.0 wt %, under a constant temperature of 1073 K, a constant treatment time of 240 min, and a constant agitation speed of 200 rpm. The results show that the higher the initial magnesium concentration in the molten alloy, the higher the speed of the chemical reduction reaction of the Mn2O3 particles.

Direct preparation of V-Al alloy by molten salt electrolysis of soluble NaVO3 on a liquid Al cathode

Vanadium-aluminum (V-Al) alloy, the master alloy for the well-known Ti-6Al-4V alloy, is mainly produced via aluminothermic reduction process of V2O5 over the past decades. However, the reaction rate is too fast and it is difficult to control the product quality. Moreover, the utilization of aluminum is very low due to the production of Al2O3. In this work, a new method is proposed to prepare V-Al alloys by molten salt electrolysis of soluble NaVO3 on a liquid aluminum (Al) cathode in molten NaCl-KCl melt. The results show that VO3− ions can be reduced to metallic V-Al alloys on the liquid Al cathode during electrolysis process. Furthermore, thermodynamic and electrochemical analysis indicate that the reduction of VO3− ions on the liquid Al cathode results from the combined effect of electroreduction and aluminothermic reduction. In this process, the liquid Al can not only reduce VO3− ions to V, but also to combine with vanadium to form V-Al alloys. However, unlike the traditional aluminothermic reduction process, alumina produced due to the aluminothermic reduction will be in-situ electro-reduced to aluminum, which will be helpful to increase the utilization of aluminum. As a result, when the electrolysis voltage is enough large, VO3− ions will be completely reduced. Al3V alloy without alumina can be obtained.

Production of calcium metal by aluminothermic reduction of Egyptian limestone ore

ABSTRACTCalcium metal was successfully produced from Egyptian limestone ore under vacuum using aluminium as a reducing agent. The aluminothermic reduction process of CaO by aluminium metal was followed up by collected amounts of produced calcium metal. The progress of the reduction process was investigated by the phase analysis of produced reaction residues through X-ray diffraction. The technical parameters affecting the reduction progress were investigated such as reductant stoichiometry, reduction temperature and reduction time. Maximum metallic yield (30%) was obtained by using charge containing 19.4% aluminium powder reduced at 1300°C for 90 min under vacuum (10−3 mbar). The reduction residues composed mainly of unreacted calcium oxide, tri-calcium aluminate (3CaO·Al2O3), mayenite (12CaO·7Al2O3) and traces of calcium aluminide (CaAl4). The probable reaction sequences of the aluminothermic reduction of calcium oxide were also discussed.

Preparation of Al-Ti Master Alloy by Electrochemical Recovery of Titanium-Reducing Slag in Molten Salts

An electrochemical method for the preparation of an Al-Ti master alloy in Al electrolysis melts of Na3AlF6-Al2O3-LiF at 980°C was investigated. The Ti-reducing slag (5.24 wt.% Ti in the Ti-reducing slag) was obtained from the aluminothermic reduction of Na2TiF6. The cold test (i.e., the aluminothermic reduction process without applying any voltages) result revealed the capability of the Al cathode to reduce the Ti slag, and the recovery rate could reach 45.8% at 980°C over 3.5 h with the addition of 10 wt.% Ti-reducing slag. In contrast, the recovery rate of Ti after electrolysis at 3.0 V could reach 99.2%. Thus, the electrochemical treatment for Ti-reducing slag is a cooperative process involving aluminothermic and electrochemical reduction reactions. Electrochemical analysis indicated that the Ti ions are reduced to metallic Ti according to Ti4+ → Ti3+ → Ti. An Al-Ti alloy layer could be prepared on the external surface of the Mo electrode after electrolysis with the addition of 12 wt.% Ti-reducing slag.