AluminumAluminum–scandiumScandium master alloysMaster alloy are highly demanded products used to create multi-functional aluminum alloysAluminum alloys and composites. A high cost of Al-Sc master alloysMaster alloy stops the automotiveAutomotive industry from using them widely. This research investigates the possibility to produce Al-ScAl-Sc master alloysMaster alloy via electrolysisElectrolysis of the LiF-AlF3-Sc2O3 melt. The kinetic parameters of the aluminumAluminum and scandiumScandium electrowinningElectrowinning were studied by means of voltammetryVoltammetry, stationary polarization, and electrolysisElectrolysis tests. The apparent limiting current density for co-deposition of AluminumAluminum and ScandiumScandium on tungsten cathodeCathode was in the range from 1.28 to 1.97 A.cm–2 in the temperature range from 860 to 940 °C. Based on the electrochemical measurements, the parameters for galvanostatic electrolysisElectrolysis were selected and electrolysisElectrolysis tests were carried out to obtain Al-Sc master alloysMaster alloy. The microstructureMicrostructure of the obtained Al-Sc master alloysMaster alloy was studied. It was possible to obtain Al-Sc alloysAl-Sc alloys with the concentration of Sc 0.68 wt.%.

The current three-layer aluminium refining process consumes a great amount of energy. Due to the need to save energy and because of a great interest to the recycling of off-grade aluminium scrap, the effort of developing a process for thin-layer refining of metals is of relevance today. This paper examines the kinetics of thin-layer refining in a single-capillary cell. Experiments were conducted in a cell with a capillary with the diameter of 1.5 mm and the length of 1 mm, with NaCl – KCl – AlF3 (3 wt.%) used as electrolyte and an aluminium-coated tungsten rod – as reference electrode. Electrochemical measurements were made by means of chronopotentiometry. The design current density i limits varied between 0.70 and 1.62 A/cm2 at the total voltage of ~0.2 V, whereas the mass-transfer coefficient was about 3.3·10–5 m/s at the temperature of 890 oC. Based on the results of the experiments it was concluded that the capillary cell can be used to obtain reproducible polarization curves in thin layers of ion melts. This enables to broaden the range of studied salt systems and metals aimed at implementing the thin-layer refining process. The il values obtained suggest that the refining process has high performance. However, reduction of alkaline metals together with aluminium may affect the process stability and the purity of the resulting metal. The thin-layer electrolyte system offer potential. However, before it can be adopted on a commercial scale, more research is needed in order to define optimum process parameters, which include current density, dimensions of capillaries and electrolyte composition.This research was funded by the Krasnoyarsk Krai Foundation Supporting Research and Engineering under the following project: Energy-Efficient Production of High-Purity Metals. Application Code: 2020092506647.

The anodic behaviour of pre-oxidised and non-oxidised Cu−Al-based anodes (Cu−10Al and Cu−9.8Al−2Mn) in KF−AlF3−Al2O3 melts was studied through galvanostatic and potentiodynamic polarization techniques. The alloy compositions were oxidised for a short-term (8 h) at 700 °C, followed by galvanostatic polarization for 1 h at 800 °C with an applied current density of 0.4 A/cm2. The potentiodynamic curves were recorded with a sweep rate of 0.01 V/s. XRD analysis was conducted on frozen melt samples collected on the surface of the anode, and SEM observation was performed on the anode after the experiment to study the phases of the scales formed on the alloys. All the anode materials had a steady potential between 2.30 and 2.50 V(vs Al/AlF3). The corrosion rates of the anodes were calculated from the data acquired through potentiodynamic polarization. It was seen that pre-oxidised anodes possess a low corrosion rate compared to those without pre-oxidation treatment.

New methods of liquid metals refining and separation operated with low energy consumption and environmental impact are highly desirable nowadays. This work presents an approach of Al refining and extraction from scrap in a thin layer of the multiple-pore molten salt electrochemical system, which appears promising. The new single-capillary cell design with a quasi-reference electrode on the TiB2 substrate was used to study the kinetics of aluminium reduction and dissolution in a narrow 1 mm-diameter channel filled with KF-AlF3 (1.1 < [KF]/[AlF3] < 1.5 mole/mole) or equimolar NaCl-KCl with N wt.% of AlF3 (3 < N < 20) at 700-850 degrees C. It was found that the chloride-based melts are more preferable than the fluoride mixtures due to the much bigger electrode potential window between Al and Alkali metal (1.3 vs. 0.4 V), higher apparent limiting currents (0.9 vs. 0.3 A cm(-2)) and lower overvoltage (4-16 vs. 66-247 mV at 0.1 A cm(-2)) resulted from the diffusion kinetics dominance. However, anodic dissolution of aluminium in NaCl-KCl-AlF3 may be chemical reaction-controlled with the exchange current density of 105 mA cm(-2), and the reaction order of 0.34 observed in the experiment. The temperature drastically affected the whole kinetics picture with the activation energy for alkali metal reduction found to be 94.762 kJ mole(-1). The preferable temperature for liquid metal refining was found to be 800 degrees C. The cathodic process in the KF-AlF3 melt has mixed kinetics. It possesses surprisingly low apparent diffusion limiting current (0.3 A cm(-2) at 800 degrees C and [KF]/[AlF3] = 1.1 mole/mole) and chemical reaction control at higher [KF]/[AlF3] (with exchange current density of 50 mA cm(-2) and the reaction order of 0.08 at [KF]/[AlF3] = 1.5 mole/mole). It may happen due to the co-deposition of Al and K with the evolution of solid cryolite. The composition of the melt plays a crucial role in refining performance. The optimal [KF]/[AlF3] for Al refining is 1.2 mole/mole. It allows operating at a current density not higher than 0.4 A cm(-2) with a thickness of a thin-layer system less than 60 mu m. The preferable AlF3 concentration in the NaCl-KCl-AlF3 composition is 10%. It allows operating at 1.4 A cm(-2) with a thickness of 22 mu m or lower. (c) 2020 Elsevier Ltd. All rights reserved.

Liquid bipolar electrodes (LBE) were proposed for the extraction of noble metals from spent catalysts by the electrometallurgical method with the production of aluminium and oxygen. The two-sectioned electrolysis cell divided by the LBE for the one-step extraction was designed. The first section acts as the aluminium reduction cell; the second one plays the role of the aluminium refinery cell. The noble metals are collected in the LBE, while the carrier (Al2O3) is decomposed to oxygen and aluminium which is transferred through the second section to be collected in the cathode. The effect of the spent catalysts content in the melt on the electrode processes and carrier dissolution kinetics was studied for molten fluoride systems at 800 °C. The dissolution rate lays in the range from 0.0123 to 0.0291 g kg−1 s−1. The extraction of Pt to the LBE reached more than 99%. This method can be applied for the treatment of catalyst based on γ-Al2O3 carrier with a minor content of other oxides (SiO2, Fe2O3, MgO, TiO2, CeO2).

Electrochemical decomposition of spent catalyst dissolved in molten salts is a promising approach for the extraction of precious metals from them. This article reports the results of the study of aluminum electrowinning from the xLiF–(1-x)AlF3 melt (x = 0.64; 0.85) containing 0–5 wt.% of spent petroleum Pt/γ-Al2O3 catalyst on a tungsten electrode at 740–800 °C through cyclic voltammetry and chronoamperometry. The results evidence that the aluminum reduction in the LiF–AlF3 melts is a diffusion-controlled two-step process. Both one-electron and two-electron steps occur simultaneously at close (or same) potentials, which affect the cyclic voltammograms. The diffusion coefficients of electroactive species for the one-electron process were (2.20–6.50)∙10−6 cm2·s–1, and for the two-electron process, they were (0.15–2.20)−6 cm2·s−1. The numbers of electrons found from the chronoamperometry data were in the range from 1.06 to 1.90, indicating the variations of the partial current densities of the one- and two-electron processes. The 64LiF–36AlF3 melt with about 2.5 wt.% of the spent catalysts seems a better electrolyte for the catalyst treatment in terms of cathodic process and alumina solubility, and the range of temperatures from 780 to 800 °C is applicable. The mechanism of aluminum reduction from the studied melts seems complicated and deserves further study to find the optimal process parameters for aluminum reduction during the spent catalyst treatment and the primary metal production as well.

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF–AlF3 and equimolar NaCl–KCl with 10 wt.% AlF3 addition at 720–850 °C. The cathodic process on the vertical liquid aluminium electrode in NaCl–KCl (+10 wt.% AlF3) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6∙10−3 cm.s−1 to 13.1∙10−3 cm.s−1 in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 kJ.mol−1. In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF–36AlF3 melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm−2 or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6–7 kWh.kg−1. The resistance fluctuated between 0.9 and 1.4 Ω during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.

Secondary aluminum production is required for the conservation of the environment. It can significantly reduce greenhouse gas emissions and energy consumption and reduce the consumption of alumina, a source of primary aluminum. Secondary aluminum production requires sorting processes for the metal scrap before starting the refining process. Salt slags generated from both primary and secondary aluminum production need to be recycled/treated as they are considered hazardous byproducts. This review paper discusses the methods used for sorting and refining aluminum waste and managing and utilizing slag cakes/slag from recycling techniques.

Electrochemical behaviour of aluminium ions from the Pt/γ-Al2O3 spent catalyst in the eutectic [LiF (63.6 wt.%)–AlF3 (36.4 wt.%)]eutectic−5 wt.% CaF2 melt was studied by the means of cyclic voltammetry, chronopotentiometry and chronoamperometry methods. Tungsten rod (diameter 2 mm) was used as a working electrode. The XRD method was used to study the composition of melt collected near the working electrode and the spent catalyst. The aluminium reduction kinetics was studied concerning varying parameters like spent catalyst content in the melt and the temperature. The reduction of Al3+ ions on the tungsten electrode changed from diffusion-controlled to quasi-reversible process. The charge transfer coefficient and the diffusion coefficient were calculated from the data obtained from the above-mentioned methods. The estimated diffusion activation energy was 117.85 kJ.mole−1.

The liquid metal refining industry has a demand for new technologies operated at low energy consumption and environmental impact nowadays. This work addresses an approach for Al purification and extraction from scrap in a thin layer of the multiple-capillary molten salt electrochemical system. The two types of single-capillary cells with quasi-reference electrodes were used to study the kinetics of aluminium reduction and dissolution in a narrow (Ø x length) 1 × 1 and 1 × 5 mm channel filled with liquid LiF-AlF3 or equimolar NaCl-KCl with the AlF3 addition at 850 °C. A multiple-capillary Al refinery process can be designed to significantly reduce the specific energy consumption. The new refinery process can be performed at high current densities. The single-capillary electrolysis can be used for kinetics studies. Thin-layer cells should be operated at a thickness no more than 5 mm to compensate the high resistance which may vary in the range from 0.7 to 2.5 Ω at this capillary length. The 64LiF-36AlF3 melt can be used as an electrolyte for the thin-layer electrolysis due to the high electrical conductivity, the wide potential window between Al and Li reduction, and the low liquidus temperature.

Among different “novel” technologies for eco–friendly aluminium production with zero greenhouse gas emissions, the electrolysis of alumina suspension (or slurry) based on halide melts deserves more attention than it got recently. The original idea of the slurry was first proposed by Theodor R. Beck and has been modified and developed basically by Petr V. Polyakov. This paper presents a comprehensive analysis of the current status of this technology, future opportunities, and the new experimental results, which have not been published yet. This overview covers the properties of high-temperature suspensions, including sedimentation behaviour and apparent electrical conductivity; anodic process on oxygen-evolving electrodes, including the polarization characteristics and the bubble behaviour at vertical anodes; cathodic process on wettable substrates; primary electrolysis results; and the general considerations touching upon the possible cell designs and the thermal balance. The future scope of the technology and possible applications are discussed.

In the past several decades, many technologies to recover platinum group metals (PGMs) and rhenium (Re) from electronic waste and spent catalysts have been developed and published. The reasons for the rising interest in this area are: (1) The abundance of these elements in the earth’s crust is < 10 −3 ppm (~ 6.6 × 10 4 tons worldwide); (2) global demand for PGMs is > 590 tons; (3) electronics and catalyst industries consume > 90 pct of precious metals (about 65 pct of Pd, 45 pct of Pt and 84 pct of Rh are used in catalytic converters); (4) properties of PGMs and Re (resistance to corrosion and oxidation, high melting temperatures, electrical conductivity and catalytic activity) are of great commercial interest. Even though several comprehensive reviews on the recovery of precious metals from spent catalysts have recently been published, several developments were not focused by the scientific community. The reviews divide the technologies into hydro- and pyrometallurgical ones. However, the variety of different approaches requires a more detailed classification. This article is an overview of the recently reported works and a comparison of different technologies in terms of extraction efficiency, environmental friendliness, and capital and operational expenditures. A new electrochemical method, which is now under development, is also presented.

SEM-EDX image of the oxide layer on the surface of the 90Cu–Al anode after the electrolysis process.

Cu-based alloys have been considered as promising candidates (along with the Fe-Ni alloys) for the inert anodes material in aluminium reduction cells with low-temperature electrolytes. However, low purity of aluminium due to the contamination by anode corrosion products is a problem yet to be solved. Introduction of alumina suspension as an electrolyte has been presented recently as a possible solution for providing commercial purity aluminium produced with the metallic anode. An attempt to characterize the CuAl-based anodes electrochemical performance in KF-AlF3-Al2O3 melts and suspensions has been made and presented. The effects of the suspension (or melt) properties, the anode composition and the temperature on the electrochemical behaviour of the anode and the kinetics of the oxide layer formation during polarization are studied. The 90Cu-10Al anode in the KF-AlF3-Al2O3 suspension with the cryolite ratio 1.3 and the dispersed phase volume fraction not more than 0.12 is found to be the good option for further investigations.

The article addresses the properties of melts and alumina suspensions based on the molten KF-AlF3-Al2O3 system, the kinetics of alumina dissolution and the rheological properties that determine the sedimentation stability. The study of such suspensions has become topical due to the prospects of their use as electrolytes in the production of aluminium using carbon-free anodes. The effects of the temperature, the particle size and the phase composition of the dispersed material and its volume fraction in the suspension on the dissolution kinetics and the sedimentation velocity are studied. The experiments were carried out over the melts with cryolite ratios 1.3 and 1.5 in the range of 750-850 degrees C. Three different types of aluminium oxide were used. The Reynolds numbers for sedimentation have indicated the Stokesian regime. Typical alumina dissolution rates were in the range of 0.028-0.167 g kg(-1) s(-1), which is close to the values reported previously. Sedimentation velocities were in the range of (0.05-3.61).10(-2) m/s, which is several times higher than those obtained previously for phi = 0.24-0.32 at 700 degrees C. It is shown that mechanical activation of alumina increases the performance of the suspension in terms of the sedimentation stability and the dissolution rate increasing.

Anodic processes on Cu?10Al electrode in molten KF?AlF3?Al2O3 (saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio (CR= x(KF)/x(AlF3)), temperature and particle volume fraction (φ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions (φ=0.12, 0.15) at 750 ℃ with 0.4 A/cm2 current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions (φ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of φ in the suspension. The results suggest that the Cu?10Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 ℃.

This update includes the literature related to the inert anodes which were published in the past decade. The metallic anodes are widely regarded as promising candidates to replace the carbon anodes due to its attractive properties like good electrical conductivity, easy to manufacture and high resistance to high thermal shocks. The metals have been tested in pure state and alloy (binary, ternary) form. The oxide scale formed on the anode surface acts as a barrier between the electrolyte and the anode, which protects the anode from being dissolved. The layer of molten fluorides is formed between the scale and the metal anode after a certain time of polarization, and the oxide scale acts as a bipolar electrode. Metal like Cu is reduced at the internal side of the scale. This paper elaborates the effects of various parameters on the performance of the anode. Cu-based alloys (Cu - Ni - Fe and Cu - Al) have shown promising results and could perform well in low-temperature electrolytes. It has been well established that the Cu content in Cu - Ni - Fe and Cu - Al alloys plays a major role in the metal dissolution as the CuO/Cu2O scales formed on the outer layer act as a sacrificial one. The corrosion rate of an anode can be reduced by decreasing the operating temperature, which is possible by using the KF - AlF3 melts. The use of suspensions can increase the purity of the produced metal by stopping the anode products to come in contact with cathode metal. Many industries including RUSAL and ELYSIS are still conducting a considerable amount of research to develop an inert anode and are expecting to have a carbon-free cell in the nearest future.

China is short of high grade bauxite for the production of smelting grade alumina. With the massive exploitation of potassium containing bauxite in China, the produced Bayer alumina contains a non-negligible content of potassium oxide. When this kinde of alumina is used as the raw material for aluminum electrolysis, the potassium would cause multiple effects to the cell performance. In this paper, the potassium concentrations of fresh alumina, secondary alumina, aluminum fluoride, anode, electrolyte, anode cover, cathode block, carbon lining, silicon carbide block and product aluminum et al. in 160 kA and 200 kA prebaked aluminum reduction cells were tested and a potassium balance model was preliminarily given. Initial results showed that most of the potassium was brought into the cell by the potassium containing impurities in the fresh alumina. The only effective way for potassium removal from the cell was through the carbon residue though nearly 80 wt% of the potassium would stay and enrich in different positions of the cell.

Bath of the aluminum reduction cell (as a cell itself) is a dissipative system. Important parameters of its welfare among others are: proper volume, shape, potential distribution in the anode-cathode space (ACS), direction and value of the electrolyte velocity. Using indicator (SrCl2) introduction, volume of the electrolyte V is determined. Derivation ∂V/∂I = 10 dm3/kA is found. Bath velocity (2–15 cm/s) and its direction using thermographic and hydrodynamic methods are ascertained. Velocities distribution is given.