Electrowinning Of Metals Research Articles

Revealing the Surface and In-Depth Operational Performances of Oxygen-Evolving Anode Coatings: A Guideline for the Synthesis of Inert Durable Anodes in Metal Electrowinning from Acid Solutions

The electrochemical performances of an oxygen-evolving anode produced by the reactivation of waste Ti substrate by a typical IrO2-Ta2O5 coating are correlated to the textural (non)uniformities of the coating and its exhaustion state. Coating degradation is considered operational loss of the activity in a metal electrowinning process. It was found that (pseudo)capacitive performances can vary over the coating surface by 20–30% and depend on the type of dynamics of the input perturbation: constant through cyclic voltammetry (CV) or discontinuous time-dependent through electrochemical impedance spectroscopy (EIS). CV-EIS data correlation enabled profiling of the capacitive properties through the depth of a coating and over its surface. The correlation was confirmed by the findings for the analysis of coating activity for an oxygen evolution reaction, finally resulting in the reliable proposition of a mechanism for the operational loss of the anode. It was found that the less compact and thicker coating parts performed better and operated more efficiently, especially at lower operational current densities.

Electrowinning of Light Metals from Molten Salts Electrolytes

Light metals such as lithium, sodium, potassium, magnesium and aluminium are produced by molten salts electrolysis. Aluminium is by far the largest in terms of production volumes. Magnesium is currently produced by silicothermic reduction of MgO according to the Pidgeon process. Titanium is also regarded as a very attractive light metal with excellent properties. The current Kroll process is energy intensive and requires lots of work as well as low productivity. Ongoing research focuses on developing a process based on electrolysis in molten salts.The main reason for large carbon footprint during electrowinning of metals from molten salts is the source of electricity due to the fact that China is the largest producer where generation of electricity is based on coal. In the Hall-Heroult process for producing aluminium the use of carbon anodes is an additional important cause for increased CO2 emissions. The use of carbon anodes also leads to the formation of perfluoro carbon (PFC) gases CF4 and C2F6 which are powerful greenhouse gases. The search for an inert oxygen evolving anode has been going on for many decades and if successful it will improve the carbon footprint significantly. The possibility to use alloys with iron, nickel and copper has been popular recently. Magnesium is produced by the Pidgeon process which is based on silicothermic reduction of MgO. However, electrolysis in molten chloride electrolytes using MgCl2 as feedstock used to be the main process for producing magnesium for many years until around 2000. Electrowinning is better in terms of environmental issues and carbon footprint but the Pidgeon process is more profitable. The production processes for alkali metals by electrolysis in molten chloride electrolytes may be improved by using alkali metal oxides as raw materials and inert oxygen evolving anodes, where tin oxide is a strong candidate and is commercially available. Electrolysis to produce titanium is very challenging mainly because of the existence of several stable valencies of dissolved titanium species. Electrodeposition of titanium based alloys by co-deposition of alloying elements may be a new and interesting alternative.

Sustainable Semi-Continuous Rare Earth Alloy Production in Chloride Based Molten Salts

Rare earth elements have numerous uses ranging from green energy to defense applications. Nd metal production uses a neodymium/lithium fluoride molten salt with a consumable carbon anode where dissolved neodymium oxide and carbon are converted to neodymium metal and CO2. In addition to producing CO2, the process releases PFCs, making it environmentally unsustainable. We have shown that neodymium chloride can be electrolyzed to produce Nd metal at the cathode and chlorine gas at the anode. The chlorine can be recycled in the conversion of the neodymium oxide (from ore) to neodymium chloride. In our process, the anode is non-consumable which allows for continuous processing without producing deleterious greenhouse gases. Chloride rare earth electrowinning historically suffered from low Coulombic efficiency obtained in lab-scale efforts (10-50%). The electrolytic reduction of neodymium chloride is a two-step reaction where a stable intermediate (Nd2+) is formed,1-2 The intermediate species can diffuse away from the cathode resulting in efficiency losses. Further, anodic overpotentials for the chlorine evolution reaction are significant due to the somewhat sluggish kinetics and poor wetting characteristics of the salt on traditional graphite anodes. Solid metal electrowinning in molten salts tends to produce rough deposits which trap significant salt impurities necessitating downstream purification. However, producing liquid metal allows for easy density separation from the salt, leading to a purer as-deposited product as well as faster metal deposition kinetics (i0 ~ 1 A/cm2) which reduces the effects of Nd2+ out diffusion, and chlorine evolution kinetics (i0 ~ 0.2 A/cm2) because of the higher temperature. In this talk, we report our work on improvements to Coulombic efficiency (~85%), and a stable anode that catalyzes chlorine evolution. The combination of improved Coulombic efficiency and reduced anode overpotentials results in low specific energy consumption (~3 kWh/kg) and thus lower operating costs. We will also report on efforts to produce liquid metal in the form of an NdFe alloy at ~800 °C which can be collected semi-continuously at rates of >1 A/cm2. References : R. Akolkar, J. Electrochem. Soc., 169, 043501 (2022). D. Shen and R. Akolkar, J. Electrochem. Soc., 164, H5292–H5298 (2017). Holcombe et al., ACS Sustainable Chem. Eng. 2024, 12, 10, 4186–4193, (2024). Holcombe et al., Holcombe et al 2024 Electrochem. Soc. Interface 33 49, (2024). Rohan Akolkar. System and Process for Sustainable Electrowinning of Metals. US Patent 20230279572. Sept. 2023 Portions of this work were performed by LLNL under Contract DE-AC52-07NA27344.

Electrowinning of Light Metals from Molten Salts Electrolytes

Light metals such as lithium, sodium, potassium, magnesium and aluminium may be produced by molten salts electrolysis. Aluminium is produced by the Hall-Heroult process by electrolysis in molten salts. It is by far the largest in terms of production volumes and for metals second only to iron and steel, but it carries a very high carbon footprint mainly due to the wide-spead use of electricity based on based on coal. Magnesium is currently produced by silicothermic reduction of MgO according to the Pidgeon process. However, electrolysis in molten chloride electrolytes using MgCl2 as feedstock may return as it is more sustainable. The current Kroll process for producing titanium is energy intensive and requires lots of work as well as having very low productivity. Sodium is produced by electrolysis in a chloride electrolyte. This process may be improved by using sodium oxide as raw material and inert oxygen evolving anode.

IrO2 nanoparticles supported on submicrometer-sized TiO2 as an efficient and stable coating for oxygen evolution reaction

The sluggish kinetics of the oxygen evolution reaction (OER) refers to the major contributor to the energy losses in electrowinning of metals. Improving the stability in the long term and activity of the electrocatalyst for OER take on a critical significance in reducing the energy consumption. An efficient and stable OER electrode (named as Ti/SMST/IrO2 electrode) was prepared in this study by supporting IrO2 nanoparticles on the surface of the submicrometer-sized TiO2 (SMST) interlayer. The obtained results indicated that the IrO2 nanoparticles approximately 14 nm in size were supported onto the submicrometer-sized TiO2 particles’ surface and exhibited a cactus-like morphology. The Ti/SMST/IrO2 electrode with the SMST interlayer prepared at 450 °C exhibited the highest electrocatalytic activity in terms of OER for its largest active surface area. This electrode showed an overpotential of 350 mV at a current density of 50 mA cm−2 and displayed a remarkable electrochemical stability of 443 h at a high current density of 2 A cm−2 in H2SO4 solution without significant change in OER activity. The prepared Ti/SMST/IrO2 electrode with high electrocatalytic performance is considered one of the promising electrodes for OER.

Intermetallic compounds as oxygen evolving anodes for metal electrowinning: Electrochemical dealloying and effects of scale in practical electrochemistry

Electrochemical dealloying has recently been highlighted as a promising technique for developing active electrodes for water electrosplitting. Intermetallic compounds of a base metal with passive film-forming element are effective oxygen evolution anodes for metal electrowinning. Cobalt- manganese-silicon alloys and titanium-nickel intermetallics are demonstrated as examples and related to the proposed paradigm of electrochemical dealloying. These systems illustrate the effects of scale in practical electrochemistry, where ‘scale’ has multiple meanings: the transition to practise; formation of surface deposits; and the evolution of the interface in extended use. In the case of cobalt-silicon-manganese alloys, the microstructure of the metal is critical. A highly porous surface layer is developed, within which the active phase is ‘nanostrands’ of cobalt metal in ‘nanoconfinement’ within a slowly-dissolving silicide matrix. Within the confined environment, a saturated solution of cobalt salt causes a salt film over the cobalt metal under which an oxygen-evolving cobalt anodic oxide is stabilised. In the case of TiNi, a nickel-rich surface forms over a thin titanium anodic oxide. Oxygen evolution occurs by field-assisted electron tunnelling to the surface nickel titanium oxide states. Field-driven ion migration both leads to these active states and leads to a slow dissolution of the metal. There is a useful range of composition between 51 and 55 wt% Ni (46 – 50 at%) which balances ductility against dissolution rate: excess titanium leading to a continuous phase of Ti2Ni results in a very brittle material; separation of TiNi3 leads to more rapid dissolution. In practise however, intrusion of oxygen during casting of large plates segregated Ti as the oxide Ti4Ni2O leading to separation of TiNi3 . The more rapid dissolution of this phase, in association with formation of MnO2 from Mn salts present in plant electrolyte, led in association with oxidation of cobalt salts to deposition of an adherent surface scale under which the solution became strongly acidic. The accelerated anode dissolution led to an under-scale of TiO2 which further increased acidification. Impractically rapid destruction of the anode resulted. The work illustrates how mass-transport and microstructure in the evolving interphase between electrode and electrolyte can interact in subtle ways important for practical application.

Unveiling the contribution of catalytic particles to the electrochemical performance of a Pb-dispersed particle composite anode for nonferrous metal electrowinning

Incorporating oxygen evolution catalytic particles into the Pb matrix via a powder mixing-pressing-sintering process is an effective strategy to develop efficient lead-dispersed particle (Pb-DP) composite anodes for nonferrous metal electrowinning. Catalytic particles are demonstrated to significantly reduce the anodic potential of Pb-DP anodes. However, the intrinsic contribution of catalytic particles to the electrochemical performance of Pb-DP anodes remains obscure. Herein, Pb-DP anodes with different dispersed particles (chemically inert Si or C, catalytic Co3O4 or MnCo2O4) were prepared. The anodic potential, microstructure and phase composition of the oxide layer, and oxygen evolution behavior of these Pb-DP anodes were investigated and compared with those of the Pure-Pb anode (prepared without dispersed particles). The results showed that compared with the Pure-Pb anode, Pb-Si and Pb-C anodes present similar microstructures and phase compositions of the oxide layer. However, they exhibit a larger Tafel slope for the oxygen evolution reaction (OER). Although the incorporation of catalytic particles (Co3O4 and MnCo2O4) reduced the thickness and specific surface area of the oxide layer and inhibited PbO2 growth, the presence of Co3O4 and MnCo2O4 significantly reduced the Tafel slope and charge transfer resistance (Rct) of the OER. Consequently, the anodic potentials of Pb-Co3O4 and Pb-MnCo2O4 are approximately 45 mV and 69 mV lower than that of Pure-Pb, respectively. It is demonstrated that the lower anodic potential of the Pb-Co3O4 and Pb-MnCo2O4 composite anodes originates from the catalytic activity of the dispersed particles rather than the physical effect of the dispersed particles.

Incorporating an Efficient Oxygen Evolution Catalyst of MnCo2O4.5 into a Pb Matrix as an Energy-Saving Anode for Metal Electrowinning

Based on the outstanding catalytic activity and stability of Mn-Co bimetallic oxides toward oxygen evolution in acidic solutions, MnCo2O4.5 was incorporated into a Pb matrix through a powder pressing-sintering process to obtain a Pb-MnCo2O4.5 composite anode. The results show that compared with the Pb anode that was made via the powder pressing-sintering process (PS-Pb), the oxide layer formed on the Pb-MnCo2O4.5 anode presented a higher flatness, compactness, and β-PbO2 concentration. Consequently, Pb-5.0MnCo2O4.5 presented a stable anodic potential of 1.235 V, approximately 170 mV lower than that of the PS-Pb anode. In the case of lower MnCo2O4.5 content (≤2.5%), the Pb-MnCo2O4.5 composite anode exhibited a smaller Tafel slope (70.39 ∼ 79.59 mV dec−1) and a lower charge transfer resistance (0.437 ∼ 0.676 Ω cm2). The fresh Pb-5.0MnCo2O4.5 composite anode showed a self-corrosion density of 0.25 mA cm−2, approximately 14.3% of that tested on the PS-Pb anode. However, Co2+ and Mn2+ were detected in the electrolyte during 72 h of electrowinning with the Pb-MnCo2O4.5 composite anode. In summary, the Pb-MnCo2O4.5 composite anode has the potential to reduce the energy consumption of the metal-electrowinning process. Nonetheless, it is necessary to evaluate the influence of dissolved Co2+ and Mn2+ on the cathodic process before commercial application.

Electroanalytical measurements of lanthanum (III) chloride in molten calcium chloride and molten calcium chloride and lithium chloride

Cyclic voltammetry (CV), square wave voltammetry (SWV) and other electroanalytical methods have been applied to molten chloride salts to study metal ion behavior. These studies have been useful for understanding and optimizing the electrowinning of metals. Notable ions that have been studied are rare earth and actinide metal ions in LiCl-KCl salts. However, the behavior of lanthanum (La3+) ions in some molten chlorides or chloride mixtures (e.g., CaCl2) has not been studied. CV experiments were conducted to evaluate La3+ behavior in CaCl2-LiCl and CaCl2 and were compared to La3+ behavior in LiCl-KCl and CaCl2-NaCl eutectics from other studies. The electrochemical reaction was checked for reversible, quasi-reversible, and irreversible transitions in scan rate by examining the relationship between the scan rate applied and the peak current and potential for La3+ reduction. Properties such as diffusion coefficient (Do) and electrons exchanged (n) were calculated from data. The electrochemical setup was also checked for radial diffusion based on the calculated La3+ diffusion coefficient and electrode radius, which led to the observation that natural convection possibly affected the La3+ reduction peak at low scan rates. For more accurate electroanalytical measurements of La3+ reduction, CV curves with and without LaCl3 added to CaCl2 and CaCl2-LiCl were compared to establish baselines for the La3+ reduction peak. The impact of resistance (IR) compensation on the La3+ reduction peak was also explored. Techniques and practices that improved electroanalytical measurements include placing the electrolytic cell in a Faraday cage, distancing electrodes from the heating coils, and melting the chlorides twice prior to measurements.

Electroanalytical Measurements of Lanthanum (III) Chloride in Molten Calcium Chloride and Molten Eutectic Calcium Chloride and Lithium Chloride

Cyclic voltammetry (CV), square wave voltammetry (SWV) and other electroanalytical methods have been applied to molten chloride salts to study metal ion behavior. These studies have been useful for understanding and optimizing the electrorefining and electrowinning of metals. Notable ions that have been studied are rare earth (RE) and actinide metals in eutectic KCl-LiCl salts. However, the behavior of lanthanum (La3+) ions (a RE metal commonly used as a glass additive, component in electric motor vehicle batteries, etc.) in some molten chlorides or chloride mixtures, such as CaCl2, has not been studied. To facilitate the study of La3+ ion behavior, electroanalytical measurements in molten salts require improved experimental techniques to perform appropriate measurements. CV experiments were conducted to evaluate La3+ behavior in eutectic LiCl-CaCl2 and CaCl2 and are compared to La3+ behavior in LiCl-KCl and CaCl2-NaCl eutectics from other studies. The electrochemical reaction was checked for reversible, quasi-reversible, and irreversible transitions in scan rate by examining the relationship between the scan rate applied and the peak current and potential for La3+ reduction. Properties such as diffusion coefficient (Do) and electrons exchanged (n) are calculated from data demonstrating reversible or irreversible behavior. The electrochemical setup was also checked for radial diffusion via error measurements for semi-infinite linear diffusion, which led to the observation that natural convection possibly effected the La3+ reduction peak at low scan rates. For more accurate electroanalytical measurements of La3+ reduction, CVs with and without LaCl3 added to CaCl2 and eutectic CaCl2-LiCl were compared to establish baselines for the La3+ reduction peak. The impact of resistance (IR) compensation on the La3+ reduction peak is also explored. Techniques and practices that optimized electroanalytical performance include placing the electrolytic cell in a Faraday cage, distancing electrodes from the heating coils, and melting the chlorides twice prior to measurements.

Preparation and performance of an Al/TiB2 + 10%Ti4O7/β-PbO2 as a composite anodic material for electrowinning of non-ferrous metals

Electrodes are the key material in the electrolysis of non-ferrous metals, and their selection and preparation can be a difficult problem in the hydrometallurgical industry. In this paper, starting from the selection of electrode materials and structural design, an Al/TiB2 + 10%Ti4O7-coating composite material was prepared by plasma spraying technology, and a β-PbO2 coating was prepared by electrochemical deposition. The phase composition of the coating was analyzed by X-ray diffractometer, and the structure of the coating was observed by scanning electron microscopy. Results show that the electrode prepared by electrodeposition at a current density of 0.03 A cm−2 has a more compact structure and more uniform grain size. Through steady-state polarization curve, cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy, the electrochemical performance of the electrode was studied. Through porosity measurements, it was found that the composite electrode material prepared by the plasma spraying method under the parameters of a spraying power of 36 kW, powder feeding rate of 30 g/min, spraying distance of 105 mm, and argon gas flow rate of 2.6 m3/h greatly reduces the charge resistance in the double-layer structure on the electrode surface, thereby accelerating the charge transfer rate. Plasma spraying and electrochemical deposition have been used to successfully prepare Al/TiB2 + 10%Ti4O7/β-PbO2 composite electrode materials with good corrosion resistance and electrochemical catalytic activity. Compared to Ti/β-PbO2 and Pb-(0.5 wt%)Ag/β-PbO2, the corrosion resistance and polarization potential increased by 83.6% and 93.0% and negatively shifted by 517.37 mV and 587.12 mV, respectively, and the catalytic activity was also significantly improved.

The role of ZnFe2O4 in the electrochemical performance of Pb-ceramic composite anode in sulfuric acid solution

The nonferrous metal electrowinning process is energy intensive due to the sluggish dynamics of the oxygen evolution reaction (OER) on the anode. Developing novel anode materials with high OER activity and stability is imperative. Herein, we propose a novel Pb-ceramic composite anode by introducing ZnFe2O4. In this work, Pb-ZnFe2O4 and PS-Pb anodes were prepared through powder pressing and sintering processes. The effects of ZnFe2O4 particles on the phase composition, surface morphology and inner structure of the oxide layer formed on Pb-ZnFe2O4 anodes were investigated. Furthermore, the role of ZnFe2O4 in the anodic potential and stability of Pb-ZnFe2O4 anodes was discussed. The results show that as the ZnFe2O4 content increases, the oxide layer formed on Pb-ZnFe2O4 anodes exhibits higher surficial compactness, higher integrity, and much smaller thickness. ZnFe2O4 exhibits a trivial impact on the oxygen evolution dynamics. However, the anodic potential of the Pb-ZnFe2O4 anode declines as the ZnFe2O4 content increases, which could be attributed to the higher compactness and smaller thickness of the oxide layer. As the ZnFe2O4 content increases, the weight loss of the Pb-ZnFe2O4 composite anode increases, suggesting the unsatisfactory stability of Pb-ZnFe2O4, which could be attributed to the inevitable dissolution of ZnFe2O4 particles, smaller thickness of the oxide layer and larger porosity of the substrate. Although Pb-ZnFe2O4 composite anodes have the potential to reduce energy consumption, their unsatisfactory stability limits the feasibility of Pb-ZnFe2O4 anodes in the electrowinning industry.

Rapidly Solidified Pb-Sn-Ca-Ag Alloy for Electrowinning Anode

Electrowinning of metals from aqueous solutions has been used for over a century. It is the main recovery method for zinc, gold, silver, copper and cobalt. Lead alloys for anode are widely used because their desirable characteristics like low cost, reducing of power consumption and longer life time. So that the aim of the present work is to study the effect of addition of Ag and rapid solidification using melt spinning technique on the structure, physical and electrochemical properties of Pb-Sn-Ca alloys to be used as anode for electrowinning cell. Six rapidly solidified alloys of Pb-10Sn-2.5Ca-xAg (x = 0, 0.5, 1, 1.5, 2, 2.5 wt.%) were produced by melt-spinning technique. X-ray diffraction analysis and differential scanning calorimetry have been carried out. Also, mechanical, electrical and electrochemical properties were measured. Here we show that adding of Ag to Pb-10Sn-2.5Ca improves its mechanical properties. This is shown in the increase of Young's modulus and micro creep behavior as well as enhancement of corrosion resistance and electrical conductivity. Among the prepared rapidly solidified alloys, the Pb-10Sn-2.5Ca-1.5Ag in wt.% is considered as the one with the best composition to be used as anode for electrowinning cell.

Electrochemical Study of Dysprosium in Fused LiCl–KCl Eutectic for Production of High Purity Metal

High purity rare earth metals are essential for research and use as high-performance materials. Even a minute amount of impurities can have significant influence on physical and chemical properties of metals, so some special properties of rare earth materials are exhibited only when they are in the state of high purity. Molten salts are promising reaction media for extractive metallurgy. In particular, molten chlorides are good electrolytes for selective dissolution or deposition of pure reagents; using molten salts provides a promising route for treatment of raw materials. In addition, molten salts proved to be suitable media for metal electrowinning and electrorefining. Available experience in high-temperature electrochemistry allows producing metals in the solid form. One of the advantages of molten salts is their variety. So, it is possible to find a solvent, which chemical and electrochemical characteristics are suitable to carry out a given process.The goal of this work was studying the mechanism of electrochemical reduction of dysprosium ions in molten LiCl–KCl eutectic for production of high purity dysprosium metal.The cathodic reduction of Dy(III) ions was studied on inert molybdenum electrode in the temperature range of 723–843 K under inert atmosphere. Cyclic voltammograms contained one cathodic peak at–3.19±0.11 V and the corresponding anodic peak at –2.95±0.11 V vs. chlorine reference electrode, Fig. The cathodic peak potential was not constant and shifted to the negative values with increasing scan rate. The cathodic peak current was directly proportional to the square root of the polarization rate. It was found that increasing scan rate led to an expected increase of irreversibility of the cathode process. The number of electrons (n) of the electrode reaction for reduction of Dy(III) ions was determined by square-wave voltammetry and the calculated value was equal to 2.93±0.05. According to the theory of linear sweep voltammetry the redox system Dy(III)/Dy(0) is irreversible and controlled by the rate of the charge transfer.So, cathodic reduction of dysprosium ions proceeded in one three-electron electrochemical step at the potential of –3.19 V versus the Cl–/Cl2 reference electrode:DyCl6 3– + 3 e– = Dy + 6 Cl–.Temperature dependence of Dy(III)/Dy couple apparent standard potential was determined by chronopotentiometry at the zero current. The experimental values are described by the linear equation: E*Dy/Dy(III) = –(3.401±0.009) + (6.2±0.1)∙10–4∙T.The apparent standard Gibbs energy change, enthalpy, and entropy of dysprosium trichloride formation from the elements in fused LiCl–KCl eutectic and activity coefficient of DyCl3 were calculated.The influence of different parameters on the composition of the cathode product was investigated. It was found that for fine purification of dysprosium from its impurities, the electrolysis should be carried out in two stages, in which the first stage is the purification electrolysis, and the second one is the base electrolysis.The reported study was funded by Russian Foundation for Basic Research according to the research project No. 20-03-00743.Figure. Typical cyclic voltammograms for the reduction of dysprosium trichloride on molybdenum electrode (S = 0.14 cm2) in fused LiCl–KCl eutectic at 723 K. m(DyCl3) = 4.1∙10–2 mol/kg. Scan rates, V s−1: 1 – 0.075; 2 – 0.2; 3 – 0.5. Figure 1

Effect of the grain size of YSZ ceramic materials on corrosion resistance in a hot molten salt CaCl2-CaF2-CaO system

The hot corrosion behaviour of YSZ specimens sintered at 1500 °C (6 and 11 h) and 1600 °C (11 h) was evaluated in CaCl2-CaF2-CaO molten salt at 1150 °C. YSZ sintered at 1600 °C for 11 h exhibited the lowest corrosion, whereas YSZ sintered at 1500 °C for 6 h showed the most corrosion, with a grain size dependency. XRD analysis showed that all YSZ contained mainly CaZrO3 with a small t-ZrO2 peak. To use SOM anodes for the electrowinning of various metals, the corrosion resistance of YSZ can be improved by adjusting the grain size instead of adding stabilizers.

Preparation and electrochemical properties of Al-based composite coating electrode with Ti4O7 ceramic interlayer for electrowinning of nonferrous metals

Electrode materials with an Al-based coating and a Ti4O7 ceramic interlayer were prepared by plasma spraying to obtain improved electrochemical properties. RuO2–TiO2 coatings doped with Sn, Ta and Ir, or La were prepared by thermal decomposition. The results indicate that good bonding between Al and Ti4O7 was obtained by plasma spraying. The dopants affected the electrochemical performance by changing the surface morphology of the active coatings. The addition of Sn not only improved the electrocatalytic activity in the chlorine evolution reaction but also inhibited the electrocatalytic activity in the oxygen evolution reaction. The electric potential distribution on the surface of the electrode materials with an Al-based coating and a Ti4O7 ceramic interlayer was more uniform than that of a Ti/RuO2–TiO2 anode. The results of electrowinning tests revealed that an Al/Ti4O7/RuO2–TiO2–SnO2 anode exhibited the best anodic performance with lower energy consumption, a longer accelerated lifetime, more deposition of Co as a product, and greater efficiency.

Processes for the Electrowinning of Metals and Oxygen from Lunar Regolith

One of the great goals of manned space flight is the colonization of the moon. It can serve as a rocket launch pad for deep space missions, or for the development of new processes under reduced gravity. Tourism can also be a worthwhile goal. For the scientific and economic development of the moon, large quantities of different materials are necessary, which cannot be transported from the earth for cost reasons. This concerns materials for the construction of accommodation for astronauts and other infrastructures. Regolith, the easily available upper powdery layer of the Moon, can be used to build houses, roads, etc. For this purpose, processes such as additive manufacturing are under investigation. In addition, pure metals like iron or aluminium for the construction of tools and machines as well as oxygen as breathing air and fuel are needed. These can also be obtained from regolith. Regolith consists of the oxides of silicon, iron, titanium, aluminium, magnesium and other materials. By means of a combined process, the components of regolith are chemically dissolved and electrochemically extracted as metal (cathodic process) and oxygen (anodic process). The aim is to develop an almost closed process for the electrowinning of metal and oxygen, which only requires the regolith without any additional consumables. The process is based on the use of so-called Ionic Liquids (IL), which are transported once from the earth. IL serve as solvents for the chemical dissolution of the oxides. In addition, they are also the electrolyte for the electrochemical production of metal and oxygen. Ionic liquids are salts that are present in liquid form at room temperature or slightly higher temperatures and are very stable electrochemically. In addition, they have a very low vapour pressure. Since Ionic Liquids do not participate directly in the electrochemical reaction, they are not consumed. This is a great advantage compared to the known aqueous electrochemical processes, in which hydrogen is often produced as a by-product at the cathode. This consumes the water as electrolyte. In addition, the electrochemical production of aluminum, an important raw material in the regolith, from aqueous electrolytes is not possible. The oxygen obtained, can be used as breathing air. In addition, in combination with water it can also be further processed electrochemically to hydrogen peroxide, H2O2. H2O2 can be used as fuel for mobility on the moon, but also as fuel for other rockets, e.g. for deep space missions. The lecture presents the principle and discusses first results. Figure 1

Oxygen evolution behaviours of novel porous MnxSiy electrodes for metal electrowinning

In this study, three types of novel porous MnxSiy oxygen electrodes for metal electrowinning were prepared by elemental powders reactive synthesis. The electrocatalytic activity and corrosion resistance of the porous MnxSiy electrodes were evaluated. The results demonstrated that the electrodes with lower silicon content presented lower potential during a 24-h polarization period and that the corrosion resistance of MnxSiy electrodes was enhanced as the Si content increased. Among these prepared oxygen electrodes, the porous Mn5Si3 electrode exhibited the highest catalytic activity towards oxygen evolution reaction (OER) in 1.63 mol l−1 sulfuric acid solutions. The influence of the electrode active surface on electrocatalytic activity was also studied, and the results showed that large active surface greatly promoted the electrocatalytic performance of the electrodes. The porous MnxSiy electrodes were also tested in conditions which simulate industrial zinc electrowinning and compared to conventional Pb and Pb-Ag (0.8 wt%) anodes. The current efficiency of porous Mn5Si3 electrode reached 85.7%, which was comparable to that of Pb and Pb-Ag (0.8 wt%) anodes. Moreover, the zinc cathode exhibited much lower impurity content. Besides, the addition of Mn2+ ions was also found to result in blockage of pores and increase of potential.

Oxygen evolution and corrosion behaviours of the porous Mn5Si3 electrode in sulfuric acid

In this study, the porous Mn5Si3 electrodes for metal electrowinning were developed through elemental powders reactive synthesis. The powder size of raw materials and sintering temperature have been changed to study the effect of these fabrication parameters on the pore structure and the electrochemical performance of the porous Mn5Si3 electrodes. The effect of Mn ions on the corrosion behaviours of the porous Mn5Si3 electrodes has also been investigated. The results indicated that lower sintering temperature in the investigated range led to higher porosity, smaller average pore size and better catalytic activity for oxygen evolution reaction (OER). This phenomenon can be attribute to the larger active surface area of this pore structure. The average pore size increased with the incremental of powder size of Si, however, it appeared that porosity and catalytic activity were almost unchanged, which indicated that pore size has a weak effect on the catalytic activity. Presence of Mn ions in solutions can improve the corrosion resistance of the porous Mn5Si3 electrodes, for Mn ions help form an oxide film on the surface of the electrodes, blocking continuous dissolution of the inside Mn5Si3.

Mathematical modeling and simulation of the reaction environment in electrochemical reactors

Abstract An electrochemical reactor, enabling controlled flow and capable of including a varied range of forms of electrodes, is important in the studies of electrochemical processes, such as energy production and storage, electrosynthesis of chemicals, electrowinning of metals, purification of water, wastewater treatment, remediation of soils, and so on, before the process development and scale-up. Here, we reviewed recent advances in modeling and simulation of the reaction environment in many electrochemical reactors used in multiple applications. The importance of computational fluid dynamics simulations to study existing reactors and to design novel reactor geometries and some components of existing cells is discussed. Aspects include the effect of electrolyte velocity on the flow dispersion, mass transport rates, and current distribution.