A method and apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt

Abstract

This invention relates to a method and apparatus for preparing high-purity light metals by electrolysis of molten metal salt, belonging to the field of electrochemical metallurgy. It addresses at least one of the following problems in existing methods: low purity and large purity fluctuations, low current efficiency, high raw material purity requirements, poor stability in continuous production, and difficulties in recycling mediated metals. The method of this invention can stably obtain high-purity light metals without pre-purification of raw materials, while avoiding secondary oxidation reactions between the gas generated at the anode and the product light metal, significantly improving current efficiency. The dual-selective interface formed by the liquid metal layer-anode molten salt interface and the liquid metal layer-intermediate chamber molten salt interface effectively blocks impurity elements from entering the cathode molten salt and the liquid metal product layer above the cathode chamber, thereby improving the purity of the target light metal. Furthermore, raw materials can be replenished at any time during electrolysis without shutdown, enabling continuous large-scale production, effectively reducing energy consumption and carbon emissions, and making it suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of electrochemical metallurgy, and in particular to a method and apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt. Background Technology

[0002] Light metals such as lithium, magnesium, sodium, and aluminum are key materials for achieving lightweighting in new energy vehicles, aerospace, humanoid robots, and rail transportation. For example, lithium is the anode material for next-generation high-energy-density lithium metal batteries and an important component of lightweight structural materials such as aluminum-lithium alloys and magnesium-lithium alloys; magnesium, with its high specific strength, is known as the "lightest structural metal" and is already used in mass production for aerospace vehicles, new energy vehicles, and missile casings; sodium is the coolant for fast neutron reactors and the anode material for sodium-sulfur batteries; and aluminum is the second largest metallic structural material after steel.

[0003] Currently, the mainstream process for industrial magnesium production is the Pidgeon process (i.e., vacuum silicothermic reduction process). my country dominates global primary magnesium production with 91% of the global output, but its production process has always been characterized by high energy consumption per unit (4.5 t of standard coal / ton of magnesium), high carbon emission intensity (21.8 tons of CO2 / ton of magnesium), and low output per tank (only 30-40 kg). The latter leads to large-scale production relying on a large number of repetitive units, which seriously hinders the large-scale, automated, and green development of primary magnesium smelting. More importantly, due to the limitations of the current process, the primary magnesium produced by the Pidgeon process has low purity, many types of impurities, and large fluctuations in content. The purity of most products on the market can only reach 99.9% (China Materials Progress, 2020, 39(7-8): 576-584).

[0004] In contrast, aluminum, lithium, and sodium primarily employ molten salt electrolysis, with aluminum electrolysis boasting the largest production scale and most mature technology. Although the electrolysis systems differ for different metals, the electrolytic cell structure is generally similar: the electrolyte, anode, and cathode are housed in a single chamber. This single-chamber structure leads to a common problem: inert metal impurities generated from the corrosion and dissolution of raw materials and electrode materials are preferentially reduced into the metal product, lowering product purity. Therefore, aluminum electrolysis has strict requirements for the purity (≥98.5%) and impurity content of the raw alumina; even then, the purity of the produced primary aluminum is only 99.7%–99.9%. Similarly, the purity of industrially electrolyzed lithium metal is only 97.0%–99.0%. On the other hand, lithium and sodium mainly use chloride salts as raw materials, with metal deposited at the cathode and chlorine gas generated at the anode. Taking lithium as an example, the reduced lithium metal readily undergoes a re-oxidation reaction with chlorine gas, resulting in a current efficiency of only about 80%.

[0005] Patents CN202110499895.8, CN202110499605.X, and CN202111553856.8 propose a liquid alloy-mediated dual-chamber electrolytic cell structure, which enables the system to have excellent impurity interception capabilities, and can directly produce high-purity metals regardless of the degree of inert anode corrosion or the purity of the raw materials. However, the alloy components used also limit the further improvement of product purity to above 99.999%, and the bottom alloy is difficult to recycle due to the accumulation of impurities (Fe, Si, Ni). Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a method and apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt, so as to solve at least one of the problems of low purity and large purity fluctuation, low current efficiency, high raw material purity requirements, poor stability of continuous production, and difficulty in recycling mediated metals in existing methods.

[0007] In a first aspect, the present invention provides an apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt, comprising an electrolytic cell, wherein the electrolytic cell is provided with an anode chamber, an intermediate chamber and a cathode chamber arranged sequentially in a transverse direction, the anode chamber and the intermediate chamber are separated by a first partition, the intermediate chamber and the cathode chamber are separated by a second partition, the upper part of the anode chamber and the intermediate chamber are connected by a liquid metal layer, and the lower part of the intermediate chamber and the cathode chamber are connected by a cathode molten salt.

[0008] Furthermore, the lower end of the first partition is sealed and fixed to the bottom surface of the electrolytic cell, the upper end of the first partition is immersed in the liquid metal layer, the upper end of the second partition is sealed and fixed to the top surface of the electrolytic cell, and the lower end of the second partition is immersed in the cathode molten salt.

[0009] Furthermore, the anode chamber contains an anode, and the cathode chamber contains a cathode. The anode is connected to the positive terminal of the power supply via an anode conductive rod, and the cathode is connected to the negative terminal of the power supply via a cathode conductive rod. Preferably, the anode conductive rod and the cathode conductive rod are covered with protective sleeves.

[0010] Furthermore, an exhaust feeding device is fixedly connected to the top surface of the anode chamber. The lower end of the exhaust feeding device is an inverted funnel shape with a gradually increasing aperture. The upper end of the exhaust feeding device extends out of the top surface of the electrolytic cell, and a feeding port is provided at the upper end of the exhaust feeding device.

[0011] Furthermore, the side wall of the exhaust feeding device is provided with multiple through holes.

[0012] Secondly, the present invention provides a method for preparing high-purity light metals by liquid metal molten salt electrolysis based on the aforementioned device, comprising the following steps: S1: Add molten anode salt and light metal to the anode chamber and molten cathode salt to the cathode chamber. Under an inert atmosphere, heat the light metal to melt it. The light metal naturally floats on the upper surface of the molten anode salt and the molten cathode salt in the intermediate chamber to form a liquid metal layer. The upper end of the first partition is immersed in the liquid metal layer, and the lower end of the second partition is immersed in the molten cathode salt. The upper part of the anode chamber and the intermediate chamber are connected through the liquid metal layer, and the lower part of the intermediate chamber and the cathode chamber are connected through the molten cathode salt. Connect the anode and cathode to the positive and negative terminals of the power supply, respectively, and add electrolytic raw materials to carry out the electrolytic reaction. S2: During electrolysis, the target light metal ions in the anode molten salt are reduced at the interface between the liquid metal layer and the anode molten salt and enter the liquid metal layer; at the same time, the light metal atoms in the liquid metal layer are oxidized into ions at the interface between the liquid metal layer and the cathode molten salt in the intermediate chamber, enter the cathode molten salt, and migrate to the cathode for reduction under the action of the electric field. The products float on the upper layer of the cathode molten salt. Impurities in the raw material that are more reactive than the target light metal remain in the anolyte salt, while impurities that are more inert than the target light metal are reduced at the interface between the liquid metal layer and the anolyte salt and retained in the liquid metal layer. An oxidation reaction occurs at the anode to generate gas, which is discharged through the exhaust feeding device. During the electrolysis process, raw materials are added through the exhaust feeding device to achieve stable and continuous production.

[0013] Furthermore, the liquid metal layer and the target light metal are made of the same metallic element.

[0014] Furthermore, the target light metal is one of lithium, magnesium, sodium, and aluminum.

[0015] Furthermore, the density of the liquid metal is 0.25 to 0.95 times that of the anolyte or cathode molten salt.

[0016] Furthermore, it also includes step S3: regenerating the liquid metal layer enriched with impurities; Preferably, the liquid metal enriched with impurities is used as the anode for electrolysis, and high-purity light metal is obtained at the cathode. The obtained high-purity light metal is used as the raw material for the liquid metal layer, and the remaining impurities are discharged in the form of anode mud.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The apparatus of the present invention, through the cooperation of a first partition and a second partition, divides the electrolytic cell into an anode chamber, an intermediate chamber, and a cathode chamber. Active impurities in the raw material, due to their more negative electrode potential than the target light metal, cannot be reduced at the interface between the liquid metal layer and the molten anode salt and enter the liquid metal layer. While inert impurities, even if they can be reduced at the interface between the liquid metal layer and the molten anode salt and enter the liquid metal layer, cannot be oxidized at the interface between the liquid metal layer and the molten cathode salt in the intermediate chamber because their electrode potential is more positive than that of the light metal and enter the molten cathode salt. This dual interface effectively blocks both active and inert impurities from entering the molten cathode salt, thereby achieving high-purity preparation of the light metal at the cathode. In the apparatus of the present invention, the liquid metal mediated does not require the addition of additional inert metal. The dual selective interface formed by the liquid metal layer-anolyte salt interface and the liquid metal layer-intermediate chamber molten salt interface effectively blocks impurity elements from entering the molten cathode salt and also prevents them from entering the liquid metal product layer above the cathode chamber, thereby improving the purity of the target light metal. Furthermore, the device of the present invention can prevent the gas generated at the anode from entering the cathode chamber and undergoing a re-oxidation reaction with the product light metal, thereby effectively improving current efficiency.

[0018] 2. The upper end of the exhaust and feeding device of the present invention can not only discharge the gas generated by the anode reaction in a timely manner, but also replenish the electrolytic raw materials in the anode chamber at any time. The feeding operation can be completed without stopping the electrolysis, so as to achieve continuous and stable operation.

[0019] 3. The method of this invention can stably obtain high-purity light metals without pre-purifying the raw materials, while avoiding secondary oxidation reactions between the gas generated at the anode and the product light metals, thus significantly improving current efficiency. The dual selective interface formed by the liquid metal layer-anode molten salt interface and the liquid metal layer-intermediate chamber molten salt interface can effectively block impurity elements from entering the cathode molten salt and also prevent them from entering the liquid metal product layer above the cathode chamber, thereby improving the purity of the target light metal. Furthermore, raw materials can be replenished at any time during electrolysis without stopping operations, enabling continuous large-scale production, effectively reducing production energy consumption and carbon emissions, and making it suitable for industrial application.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1 This is a schematic diagram of the apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt according to the present invention.

[0023] Figure label: 1-First partition, 2-Second partition, 3-Liquid metal layer, 4-Anode, 5-Cathode, 6-Protective sleeve, 7-Exhaust and feeding device, 8-Anode molten salt, 9-Cathode molten salt, 10-Liquid metal product layer. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0025] In existing dual-chamber electrolysis systems, a "balance metal" (such as Cu, Sn, Bi, etc.) must be used to form an alloy with the target metal to ensure sufficient density, stable settling at the bottom of the tank, and clear stratification with the electrolyte. When light metals such as Mg and Li are involved, the alloy density decreases significantly, necessitating a substantial increase in the content of inert metal components to maintain stratification stability. Under fluctuating operating conditions, excessively low target metal concentration, concentration polarization, or excessively high current density, the inert components in the alloy are also easily oxidized and enter the cathode molten salt and reduced into the product, limiting further improvement in purity. For example, when preparing lithium metal using SnLi liquid alloy as the anode, Sn is the main impurity in the lithium product (content 1~0.05%), causing the lithium purity to fluctuate between 99.8~99.9% (Fullyliquid electrorefining: a highly efficient and selective approach for purelithium metal recovery from low-grade alloy. Green Chemistry, 2025, 27(44):14338-14349.).

[0026] On the other hand, taking electrolytic aluminum as an example, impurities from inert anodic corrosion are reduced at the molten salt / liquid alloy interface in the anode chamber, while only Al is dissolved through oxidation at the liquid alloy interface in the cathode chamber. Therefore, the target metal content in the alloy gradually decreases with electrolysis, leading to an increase in the alloy's melting point (for example, when the aluminum content in a copper-aluminum alloy decreases from 47% to 30%, the melting point rises from 593 °C to approximately 820 °C). This forces the system to operate at higher temperatures, further increasing energy consumption. Furthermore, the alloy medium is an Al-Cu alloy with an Al content of 40–75% to balance sufficient density (ensuring it sinks to the bottom of the tank) and a suitable melting point (reducing temperature fluctuations and maintaining good mass transfer). However, as electrolysis progresses, the reduction of impurities from inert anodic corrosion in the anode chamber gradually decreases the Al content in the bottom alloy, causing the alloy's melting point to rise, viscosity to increase, and mass transfer capacity to deteriorate.

[0027] If the above-mentioned dual-chamber electrolytic cell is used, and the target metal (such as Mg) is used as the liquid mediator, the Mg produced at the cathode will float to the top of the molten salt and re-dissolve into the mediator due to its low density. This will result in the cathode being unable to deposit metal products, current wastage, and current efficiency approaching zero.

[0028] In contrast, my country's production of high-purity magnesium is extremely limited. Currently, only a small amount of products meet the national standard Mg9995B (3N5B), while the higher purity Mg9995A, Mg9998, and Mg9999 are even scarcer (see "A Brief Analysis of the Importance of High-Purity Raw Materials - Taking Metallic Magnesium as an Example," China Materials Progress, 2020, 39(7-8): 576-558). Lithium, due to its extremely high chemical reactivity, readily reacts with crucible or container materials, making it difficult to economically achieve a purity of 99.99% using conventional refining methods (such as distillation).

[0029] A specific embodiment of the present invention, such as Figure 1 As shown, an apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt is disclosed, including an electrolytic cell. The electrolytic cell has an anode chamber, an intermediate chamber and a cathode chamber arranged sequentially in the transverse direction. The anode chamber and the intermediate chamber are separated by a first partition 1, and the intermediate chamber and the cathode chamber are separated by a second partition 2. The upper part of the anode chamber and the intermediate chamber are connected by a liquid metal layer 3, and the lower part of the intermediate chamber and the cathode chamber are connected by a cathode molten salt 9.

[0030] Compared with the prior art, the device of the present invention, through the cooperation of the first partition 1 and the second partition 2, divides the electrolytic cell into an anode chamber, an intermediate chamber, and a cathode chamber. In the anode chamber, active impurities in the raw material, due to their more negative electrode potential than the target light metal, cannot be reduced and enter the liquid metal layer 3 at the interface between the liquid metal layer 3 and the molten anode salt 8. While inert impurities, even if they can be reduced and enter the liquid metal layer 3 at the interface between the liquid metal layer 3 and the molten anode salt 8, cannot be oxidized and enter the molten cathode salt 9 at the interface between the liquid metal layer 3 and the molten cathode salt 9 in the intermediate chamber because their electrode potential is more positive than that of the light metal. This dual interface effectively blocks impurities more active than the light metal and inert impurities from entering the molten cathode salt 9, thereby achieving high-purity preparation of the light metal at the cathode by reducing the target metal ions. In the device of this invention, no additional inert metal is required for the target metal. The dual-selective interface formed by the interface between the liquid metal layer 3 and the anode molten salt 8 and the intermediate chamber molten salt effectively blocks impurity elements from entering the cathode molten salt 9 and also prevents them from entering the liquid metal product layer 10 above the cathode chamber, thereby improving the purity of the target light metal. Furthermore, the device of this invention can prevent the gas generated at the anode from entering the cathode chamber and undergoing a re-oxidation reaction with the product light metal, effectively improving current efficiency.

[0031] Specifically, the lower end of the first partition 1 is sealed and fixed to the bottom surface of the electrolytic cell, the upper end of the first partition 1 is immersed in the liquid metal layer 3, the upper end of the second partition 2 is sealed and fixed to the top surface of the electrolytic cell, and the lower end of the second partition 2 is immersed in the cathode molten salt 9.

[0032] Specifically, the anode chamber is provided with an anode 4, the cathode chamber is provided with a cathode 5, the anode 4 is connected to the positive terminal of the power supply through an anode conductive rod, and the cathode 5 is connected to the negative terminal of the power supply through a cathode conductive rod.

[0033] Preferably, the anode conductive rod and the cathode conductive rod are covered with a protective sleeve 6. Preferably, the protective sleeve 6 is made of a high-temperature resistant and corrosion-resistant insulating material.

[0034] More preferably, the insulating material includes materials such as boron nitride, silicon nitride, zirconium oxide, aluminum oxide, and magnesium oxide, which can be selected according to the specific type of the target light metal.

[0035] Specifically, an exhaust feeding device 7 is fixedly connected to the top surface of the anode chamber. The lower end of the exhaust feeding device 7 is an inverted funnel shape with a gradually increasing aperture. The upper end of the exhaust feeding device 7 extends out of the top surface of the electrolytic cell, and a feeding port is provided at the upper end of the exhaust feeding device 7.

[0036] Specifically, the anode rod covered with a protective sleeve 6 is located inside the exhaust feeding device 7, and the opening at the lower end of the exhaust feeding device 7 is located at the upper end of the anode.

[0037] Preferably, the lower end of the exhaust feeding device 7 is conical, and the upper end of the exhaust feeding device 7 is cylindrical, rectangular, or other irregular shape, as long as it can achieve exhaust.

[0038] Specifically, the side wall of the exhaust feeding device 7 is provided with multiple through holes. Preferably, the diameter of the through holes is 0.5~5mm, for example, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm. The through holes allow molten salt to pass through, and the surface tension of the bubbles prevents them from overflowing into the molten salt. Within the diameter range of this invention, the gas cannot pass through the through holes due to surface tension and floats upward away from the molten salt.

[0039] The upper end of the exhaust and feeding device 7 can not only discharge the gas generated by the anode reaction in a timely manner, but also replenish the electrolytic raw materials in the anode chamber at any time. The feeding operation can be completed without stopping electrolysis, so as to achieve continuous and stable operation.

[0040] In the device of the present invention, the electrolytic cell is divided into three parts by the first partition 1 and the second partition 2, namely the anode chamber, the intermediate chamber and the cathode chamber. The anode chamber is connected to the upper part of the intermediate chamber and the intermediate chamber is connected to the lower part of the cathode chamber. Combined with the low density of the light liquid metal, two liquid-liquid interfaces are formed on both sides of the liquid metal in the intermediate chamber, namely the anode molten salt / liquid metal and the liquid metal / cathode molten salt. This realizes the efficient transfer and selective oxidation and reduction of target metal ions, with low energy consumption and suitable for continuous industrial production.

[0041] It should be noted that the molten salt composition in the intermediate chamber and the cathode chamber of this invention is the same, both being cathode molten salt 9.

[0042] Another specific embodiment of the present invention discloses a method for preparing high-purity light metals by liquid metal molten salt electrolysis based on the above-mentioned device, comprising the following steps: S1: Add molten anode salt 8 and light metal to the anode chamber and molten cathode salt 9 to the cathode chamber. Under an inert atmosphere, heat to melt the light metal. The light metal naturally floats on the upper surface of molten anode salt 8 and molten cathode salt 9 in the intermediate chamber to form a liquid metal layer 3. The upper end of the first partition 1 is immersed in the liquid metal layer 3, and the lower end of the second partition 2 is immersed in the molten cathode salt 9. The upper part of the anode chamber and the intermediate chamber are connected through the liquid metal layer 3, and the lower part of the intermediate chamber and the cathode chamber are connected through the molten cathode salt 9. Connect the anode 4 and the cathode 5 to the positive and negative terminals of the power supply, respectively, and add electrolytic raw materials to carry out the electrolytic reaction. S2: During the electrolysis process, the target light metal ions in the anode molten salt are reduced and enter the liquid metal layer 3 at the interface between the liquid metal layer 3 and the anode molten salt 8; at the same time, the light metal atoms in the liquid metal layer 3 are oxidized into ions at the interface between the liquid metal layer 3 and the cathode molten salt 9 in the intermediate chamber and enter the cathode molten salt 9, and finally reduced and float on the upper layer of the cathode chamber molten salt. Impurities in the raw material that are more reactive than the target light metal remain in the anodic molten salt 8, while impurities that are more inert than the target light metal are reduced at the interface between the liquid metal layer 3 and the anodic molten salt 8 and retained in the liquid metal layer 3. The anode undergoes an oxidation reaction to generate gas, which is discharged along the exhaust feeding device 7. During the electrolysis process, raw materials are added through the exhaust feeding device 7 to achieve stable and continuous production.

[0043] The method of this invention can stably obtain high-purity light metals without pre-purifying the raw materials, while avoiding secondary oxidation reactions between the gas generated at the anode and the product light metals, thus significantly improving current efficiency. The dual-selective interface formed by the interface between the liquid metal layer 3 and the anode molten salt 8 and the interface between the liquid metal layer 3 and the intermediate chamber molten salt can effectively block impurity elements from entering the cathode molten salt 9 and also prevent them from entering the liquid metal product layer 10 above the cathode chamber, thereby improving the purity of the target light metal. Furthermore, the raw materials can be replenished at any time during the electrolysis process without stopping operations, enabling continuous large-scale production, effectively reducing production energy consumption and carbon emissions, and making it suitable for industrial application.

[0044] Specifically, the liquid metal layer 3 and the target light metal are the same metal element.

[0045] Preferably, the target light metal is one of lithium, magnesium, sodium, and aluminum.

[0046] Specifically, the density of the liquid metal is 0.25 to 0.95 times the density of the anode molten salt 8 or the cathode molten salt 9, for example, 0.25 times, 0.3 times, 0.35 times, 0.4 times, 0.45 times, 0.5 times, 0.55 times, 0.6 times, 0.65 times, 0.7 times, 0.75 times, 0.8 times, 0.85 times, 0.9 times, and 0.95 times.

[0047] Preferably, the anode molten salt 8 and the cathode molten salt 9 may be the same or different, and can be a chloride system, a fluoride system, or a chloride-fluoride mixed system, which can be flexibly selected according to the target metal, raw material type, and process requirements. The anode chamber molten salt focuses on the solubility of the target metal compound (such as oxides, chlorides, etc.), and can be selected as a fluoride system, a chloride system, or a mixed system; the intermediate chamber and cathode chamber molten salts focus on ionic conductivity and electrochemical stability, and can be selected according to the target metal as appropriate as a chloride system, a fluoride molten salt system, or a fluoride-chloride mixed molten salt system. The anode molten salt 8 or the cathode molten salt 9 must meet the following conditions: its density should be greater than the density of the target metal so that the liquid metal layer can float on the molten salt; its solubility for the target metal should be low to ensure that the liquid metal layer does not mix significantly with the molten salt or dissolve and lose its solubility; and the redox potential of the metal ions in the molten salt composition should be negative than the electrode potential of the target metal ions.

[0048] It should be noted that the inner wall of the electrolytic cell of the present invention, the outer layer of the first partition and the second partition are all provided with an insulating layer, and the material of the insulating layer is boron nitride, aluminum oxide, magnesium oxide, yttrium oxide, etc.

[0049] The following examples illustrate the composition of the anode molten salt 8 and the cathode molten salt 9 in this invention, as detailed below: Electrolytic Aluminum: Anode Molten Salt 8: Uses cryolite-based fluoride molten salt, with a mass percentage of 1.5%~8% alumina, 30%~80% cryolite, 0%~35% aluminum fluoride, 0%~30% potassium fluoride, 0%~20% sodium fluoride, 20%~50% barium fluoride, and 3%~6% calcium fluoride. A small amount of magnesium fluoride (1%~2%) and lithium fluoride (1%~10%) are added to fine-tune performance. The sum of the mass percentages of all components is 100%. Cathode Molten Salt 9: Can use an anode salt system (without adding alumina); or can use a fluoride-chloride molten salt, with a mass percentage of 45%~70% barium chloride, 0%~8% sodium chloride, 5%~20% sodium fluoride, 10%~30% aluminum fluoride, 0%~10% potassium chloride, and 0%~5% lithium chloride. The sum of the mass percentages of all components is 100%.

[0050] Electrolytic Magnesium: Anode Molten Salt 8: When using magnesium oxide as raw material, fluoride molten salt is mainly used, including magnesium fluoride, lithium fluoride, sodium fluoride, potassium fluoride, and calcium fluoride. A certain amount of sodium chloride, potassium chloride, lithium chloride, and calcium chloride can be added to adjust the physical properties. The sum of the mass percentages of each component is 100%. When using magnesium chloride as raw material, chloride molten salt is mainly used, including potassium chloride, lithium chloride, and sodium chloride. A certain amount of magnesium fluoride, lithium fluoride, potassium fluoride, and sodium fluoride can be added. The sum of the mass percentages of each component is 100%. Cathode Molten Salt 9: Regardless of the raw material used, magnesium fluoride, magnesium chloride, sodium chloride, potassium chloride, lithium chloride, calcium chloride, sodium fluoride, potassium fluoride, lithium fluoride, and calcium fluoride can be used to compose the molten salt composition according to the requirements of viscosity, conductivity, density, solubility, melting point, etc. The sum of the mass percentages of each component is 100%. Electrolytic sodium: The molten salts for both the anode and cathode chambers can be sodium chloride (must be added), calcium chloride, barium chloride, or strontium chloride. Certain amounts of sodium fluoride, potassium chloride, and sodium iodide can be added to adjust the properties of the molten salt. The sum of the mass percentages of all components must be 100%. Electrolytic lithium: The molten salts in the anode and cathode chambers are mainly lithium chloride (must be added), potassium chloride, strontium chloride, lithium iodide, potassium iodide, lithium bromide, and potassium bromide, with the sum of the mass percentages of each component being 100%.

[0051] Specifically, it also includes step S3: regenerating the liquid metal layer enriched with impurities.

[0052] Preferably, the regeneration process includes: using the liquid metal enriched with impurities as the anode to carry out an electrolytic reaction, obtaining a high-purity light metal at the cathode, using the obtained high-purity light metal as the raw material for the liquid metal layer, and discharging the remaining impurities in the form of anode sludge.

[0053] More preferably, the cathodes for electrolytic magnesium, lithium, etc., are made of low-carbon steel or stainless steel, while the cathodes for electrolytic aluminum are made of carbon blocks. The cathodes only need not to react with the reduced light metals.

[0054] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0055] Example 1 This embodiment of an apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt includes an electrolytic cell. The electrolytic cell is provided with an anode chamber, an intermediate chamber and a cathode chamber arranged sequentially in the transverse direction. The anode chamber and the intermediate chamber are separated by a first partition 1, and the intermediate chamber and the cathode chamber are separated by a second partition 2. The upper part of the anode chamber and the intermediate chamber are connected by a liquid metal layer 3, and the lower part of the intermediate chamber and the cathode chamber are connected by a cathode molten salt 9.

[0056] In the specific scheme, the lower end of the first partition 1 is sealed and fixed on the bottom surface of the electrolytic cell, the upper end of the first partition 1 is immersed in the liquid metal layer 3, the upper end of the second partition 2 is sealed and fixed on the top surface of the electrolytic cell, and the lower end of the second partition 2 is immersed in the cathode molten salt 9.

[0057] In a further embodiment, an anode 4 is disposed in the anode chamber, and a cathode 5 is disposed in the cathode chamber. The anode 4 is connected to the positive terminal of the power supply via an anode conductive rod, and the cathode 5 is connected to the negative terminal of the power supply via a cathode conductive rod. A protective sleeve 6 is fitted over the anode and cathode conductive rods.

[0058] The anode chamber is sealed to the top surface with an exhaust feeding device 7. The upper end of the exhaust feeding device 7 is cylindrical, and the lower end is a cone-shaped inverted funnel. The upper end of the cylinder extends out of the top surface of the electrolytic cell, and a feeding port is provided on the upper bottom surface of the cylinder. The anode rod, which is fitted with a protective sleeve 6, is located inside the exhaust feeding device 7. The opening of the cone-shaped structure at the lower end of the exhaust feeding device 7 is located at the upper end of the anode.

[0059] The cylindrical sidewall at the upper end of the exhaust feeding device 7 is provided with multiple through holes, and the diameter of the through holes is 2mm.

[0060] Example 2 This embodiment provides a method for preparing high-purity light metals using the apparatus of Example 1, such as... Figure 1 As shown, the light metal is Mg, and the process includes the following steps: S1: Add molten anode salt 8 and light metal to the anode chamber and molten cathode salt 9 to the cathode chamber. Heat to 850°C under argon protection to melt the light metal. The melting point of Mg is 650°C. The light metal floats naturally on the upper surface of molten anode salt 8 and molten cathode salt 9 to form a liquid metal layer 3. The upper end of the first partition 1 is immersed in the liquid metal layer 3, and the lower end of the second partition 2 is immersed in the molten cathode salt 9. The upper part of the anode chamber and the intermediate chamber are connected through the liquid metal layer 3, and the lower part of the intermediate chamber and the cathode chamber are connected through the molten cathode salt 9. Connect the anode 4 and the cathode 5 to the positive and negative terminals of the power supply, respectively. Add electrolytic raw materials to carry out the electrolytic reaction. The anode molten salt 8 comprises, by mass percentage: 15% MgF2, 30% LiF, 35% KF, and 20% BaF2. The density of the anode molten salt 8 is 2.50 g / cm³. 3 ; The cathode molten salt 9 comprises, by mass percentage: 35% MgCl₂, 30% KCl, and 35% BaCl₂. The density of cathode molten salt 9 is 2.05 g / cm³. 3 ; The raw material for the liquid metal layer 3 is metallic magnesium with a purity of 99.95%, and the electrolytic raw material is magnesium oxide. The density of the liquid metal layer 3 is 1.58 g / cm³. 3 ; Anode 4 is a graphite electrode, cathode 5 is a molybdenum rod, and protective sleeve 6 is made of boron nitride. S2: Electrolysis temperature is 760℃, anolyte current density is 0.8 A / cm³. 2 Cathode current density: 0.6 A / cm 2 The electrolysis time is 24 hours. During the electrolysis process, oxygen ions undergo a discharge reaction on the surface of the graphite anode, eventually generating carbon dioxide, which is discharged along the cylinder of the exhaust and feeding device; magnesium ions in the raw material enter the liquid metal layer 3 through the interface between the liquid metal layer 3 and the anode molten salt 8, are transferred through the liquid metal layer 3 in the intermediate chamber, and enter the cathode molten salt 9 through the interface between the liquid metal layer 3 in the intermediate chamber and the cathode molten salt 9, where they are reduced at the cathode 5 and float on the upper layer of the cathode chamber molten salt to form a liquid metal product layer 10; Impurities in the raw material that are more reactive than the target light metal remain in the anolyte salt 8, while impurities that are more inert than the target light metal are reduced and trapped in the liquid metal layer 3 at the interface between the liquid metal layer 3 and the anolyte salt 8.

[0061] In this embodiment, the MgCl2 contained in the cathode molten salt 9 is only used as a density and conductivity modifier, not as an electrolytic feedstock. The magnesium ions consumed in the electrolysis mainly come from the magnesium oxide feedstock in the anode chamber.

[0062] Example 3 This embodiment provides a method for preparing high-purity light metals, which is similar to that in Embodiment 2, except that the light metal is lithium and the electrolytic raw material is lithium chloride. The anode molten salt 8 and the cathode molten salt 9 are the same, and by mass percentage, they consist of: 45% LiCl and 55% KCl; the raw material for the liquid metal layer is lithium metal with a purity of 99.5%; The densities of anolyte salt 8 and cathode molten salt 9 are 1.64 g / cm³. 3 ; The density of liquid metal layer 3 is 0.51 g / cm³. 3 ; Anode 4 is a graphite rod, and cathode 5 is a stainless steel rod; In S1, the mixture is heated to 500°C under argon protection to completely melt the lithium (melting point 180.5°C). In S2, the electrolysis temperature is 500℃ and the anolyte current density is 0.5 A / cm². 2 Cathode current density: 0.4 A / cm 2 The electrolysis time is 24 hours. Chlorine gas is generated by the chloride ion discharge reaction at the anode and discharged along the cylinder of the exhaust and feeding device.

[0063] Example 4 This embodiment provides a method for preparing high-purity light metals, which is similar to that in Embodiment 2, except that the light metal is sodium and the electrolytic raw material is sodium chloride. The anodic molten salt 8 and the cathode molten salt 9 are the same, and by mass percentage they include: NaCl 55% and CaCl2 45%; the raw material for the liquid metal layer 3 is metallic sodium with a purity of 99.5%; The densities of anolyte salt 8 and cathode molten salt 9 are 1.95 g / cm³. 3 ; The density of liquid metal layer 3 is 0.82 g / cm³. 3 ; In S1, the sodium is heated to 550°C under argon protection to completely melt it (melting point 97.7°C). In S2, the electrolysis temperature is 550℃ and the anolyte current density is 0.6 A / cm². 2 Cathode current density 0.5 A / cm 2 The electrolysis time is 24 hours. Chloride ion discharge reaction occurs at the anode to generate chlorine gas, which is discharged along the cylinder of the exhaust and feeding device.

[0064] Example 5 This embodiment provides a method for preparing high-purity light metals, which is similar to that in Embodiment 2, except that the light metal is aluminum and the electrolytic raw material is aluminum oxide. The anolyte salt 8 comprises, by mass percentage: Na3AlF6 60%, BaF2 30%, and AlF3 10%. The density of the anolyte salt 8 is 2.55 g / cm³. 3 ; The cathode molten salt 9 comprises, by mass percentage: 20% Na3AlF6, 55% BaCl2, and 25% NaCl. The density of cathode molten salt 9 is 2.72 g / cm³. 3 ; The density of liquid metal is 2.3 g / cm³. 3 ; Anode 4 is a graphite electrode, and cathode 5 is a TiB2 coated cathode, with a TiB2 coating formed on the surface of the graphite substrate; In S1, the temperature is heated to 900°C under argon protection to completely melt the aluminum (melting point 660°C). In S2, the electrolysis temperature is 900℃ and the anolyte current density is 0.7 A / cm³. 2 Cathode current density: 0.6 A / cm 2 The electrolysis time is 24 hours. Oxygen ions undergo a discharge reaction on the surface of the graphite anode, eventually producing carbon dioxide, which is then discharged along the cylinder of the exhaust and feeding device.

[0065] Comparative Example 1 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that this comparative example uses a single-chamber electrolytic cell, i.e., the first partition 1 and the second partition 2 are not installed in the electrolytic cell, the electrolysis temperature is 760℃, and the anode current density is 0.8 A / cm². 2 Cathode current density: 0.6 A / cm 2 Electrolysis time is 24 hours.

[0066] Comparative Example 2 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that the electrolytic cell in this comparative example adopts the double-chamber structure of patent CN202111553856.8, the bottom of the cell is filled with liquid Cu-Mg alloy (Cu content 55 wt%), the electrolysis temperature is 760℃, and the current density is 0.8 A / cm². 2 Magnesium oxide is used as the electrolytic raw material, and the electrolysis time is 24 hours.

[0067] Comparative Example 3 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that the electrolytic cell in this comparative example adopts a double-chamber structure. A partition divides the electrolytic cell into an anode chamber and a cathode chamber. The lower end of the partition is sealed to the bottom of the electrolytic cell, and the upper end is connected to the top of the electrolytic cell through a communication port. The communication port is filled with a layer of liquid magnesium metal, and the upper end of the partition is immersed in the liquid metal layer. The electrolysis temperature is 760°C, and the current density is 0.8 A / cm². 2 Magnesium oxide is used as the raw material for electrolysis. During the electrolysis process, the magnesium generated by the reaction floats up and merges into the liquid magnesium metal layer above, so high-purity magnesium products cannot be obtained from the cathode.

[0068] Comparative Example 4 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that the electrolytic cell in this comparative example adopts the double-chamber structure of patent CN202111553856.8, the bottom of the cell is filled with liquid Cu-Mg alloy (Cu content 21 wt%), the electrolysis temperature is 760 ℃, and the current density is 0.8 A / cm². 2 Magnesium oxide was used as the electrolytic raw material. After 24 hours of electrolysis, no metallic magnesium was found at the cathode, and the bottom alloy was mixed with the molten salt without forming obvious stratification.

[0069] Comparative Example 5 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that the electrolytic cell in this comparative example adopts the double-chamber structure of patent CN202111553856.8, the bottom of the cell is filled with liquid Cu-Mg alloy (Cu content 32 wt%), the electrolysis temperature is 760 ℃, and the current density is 0.8 A / cm². 2Magnesium oxide was used as the electrolytic raw material. After 24 hours of electrolysis, the purity of magnesium at the cathode was 98.3% and the copper content was 1.5%. Copper-magnesium alloy droplets diffused into the molten salt at the interface between the cooled molten salt and the alloy.

[0070] Comparative Examples 2, 4, and 5 illustrate that when the alloy composition is not accurately controlled, the alloy and molten salt cannot stably separate into layers, which will affect the electrolysis effect and product purity.

[0071] Comparative Example 6 The method for preparing high-purity Mg in this comparative example is similar to that in Example 2, except that the electrolytic cell in this comparative example adopts the double-chamber structure of patent CN202111553856.8, the bottom of the cell is filled with liquid Cu-Mg alloy (Cu content 55wt%), a NiFeCu inert anode is used, the electrolysis temperature is 760 ℃, and the current density is 0.8 A / cm². 2 Magnesium oxide was used as the electrolytic raw material. After continuous electrolysis for 760 h, the voltage fluctuated and rose sharply. The copper content of the bottom alloy was found to have increased to 68%, and the viscosity of the alloy increased. After the temperature was raised to 870 °C, the voltage dropped and stabilized. The purity of the cathode magnesium decreased from the initial 99.96% to 99.76%.

[0072] Comparative Example 7 This comparative example describes a method for preparing high-purity Al using the dual-chamber structure described in patent CN202110499895.8. The bottom of the tank is filled with liquid Cu-Al alloy (Cu content 45wt%), the electrolysis temperature is 780 ℃, and the current density is 0.8 A / cm². 2 After adding 5 wt% Al2O3 raw material and electrolyzing continuously for 48 h, the voltage fluctuated and rose sharply, and then the electrolysis stopped.

[0073] This may be because the solubility of Al2O3 is oversaturated, and the undissolved Al2O3 deposits at the interface between the liquid alloy and the anode electrolyte, causing the electrolysis to be interrupted.

[0074] In contrast, when using Al as the mediating alloy in this invention, due to the high density of the electrolyte, the insoluble Al2O3 is suspended in the electrolyte. After continuous electrolysis for 48 hours, the voltage is stable and the purity of the cathode aluminum is also stable at 99.9999%.

[0075] Experimental Example 1 The light metals deposited at the cathodes of the examples and comparative examples were collected respectively. The purity and the total content of impurities with more negative redox potential and more positive redox potential compared with the light metals were detected by ICP-OES. The current efficiency was calculated, and the results are shown in Table 1.

[0076] Current efficiency is defined as the ratio of the actual mass of the target product deposited during electrolysis to the theoretical mass of the product calculated according to Faraday's law.

[0077] Calculation method: Calculate the theoretical mass of magnesium to be electrolyzed using the electrochemical equivalent of the target metal, electrolysis time, and current (for example: if the electrochemical equivalent of magnesium is 0.454 g / Ah, using a current of 1A and electrolysis for 1h, the theoretical mass of magnesium to be electrolyzed is 0.454 g / Ah × 1A × 1h = 0.454 g); the obtained mass of magnesium / the theoretical mass of magnesium electrolyzed is the current efficiency.

[0078] Table 1

[0079] Comparative Example 1 shows that without the use of a dual-interface barrier layer to block impurities, the purity of the electrolyzed magnesium can only reach 98.2%. Comparative Examples 2, 4, and 5 illustrate that when using a dual-chamber electrolytic cell, it is necessary to introduce an auxiliary metal to adjust the alloy density so that it can be well separated from the molten salt in order to achieve a higher purity of the cathode electrolyzed product. Comparative Example 3 uses a dual-chamber electrolytic cell but does not use the second partition 2 in this invention. The electrolyzed product floats to the light metal layer, and the product cannot be collected at the cathode.

[0080] This invention uses the target metal itself as the mediator layer, without introducing any other metal elements, thus avoiding contamination from external impurities at the source. Therefore, the purity of the product is significantly improved: Al purity can reach 99.9999% or higher, Mg purity can reach 99.999% or higher, Li purity can reach 99.99% or higher, and Na purity can reach 99.99% or higher. The current efficiency of the method of this invention is ≥86%.

[0081] Experiment Example 2: Verification of Continuous Production Using the method of Example 2, the operation time was 240 hours. The anode was replaced every 24 hours, magnesium oxide raw material was replenished every 8 hours through the exhaust feeding device cylinder, and the liquid magnesium was subjected to molten salt electrolytic refining treatment every 72 hours (temperature 760°C, anode current density 0.5A / cm², cathode current density 0.4A / cm², electrolysis time 4 hours).

[0082] Operational results show that the electrolytic cell operates stably, with cell voltage fluctuations within ±0.3V, and the purity of magnesium in the cathode product remains consistently above 99.999%. The magnesium recovered from molten salt electrolytic refining has a purity of 99.99%, and is returned to the electrolytic cell along with the replenished metallic magnesium; no degradation in the performance of the liquid magnesium was observed.

[0083] The same experiments were also conducted on other embodiments of the present invention, and the results were basically the same. Due to space limitations, they will not be listed one by one.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt, characterized in that, The device includes an electrolytic cell, which has an anode chamber, an intermediate chamber and a cathode chamber arranged sequentially in a transverse direction. The anode chamber and the intermediate chamber are separated by a first partition, and the intermediate chamber and the cathode chamber are separated by a second partition. The upper part of the anode chamber and the intermediate chamber are connected by a liquid metal layer, and the lower part of the intermediate chamber and the cathode chamber are connected by molten cathode salt.

2. The apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt according to claim 1, characterized in that, The lower end of the first partition is sealed and fixed to the bottom surface of the electrolytic cell, the upper end of the first partition is immersed in the liquid metal layer, the upper end of the second partition is sealed and fixed to the top surface of the electrolytic cell, and the lower end of the second partition is immersed in the cathode molten salt.

3. The apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt according to claim 1, characterized in that, The anode chamber contains an anode, and the cathode chamber contains a cathode. The anode is connected to the positive terminal of the power supply via an anode conductive rod, and the cathode is connected to the negative terminal of the power supply via a cathode conductive rod. Preferably, the anode conductive rod and the cathode conductive rod are covered with protective sleeves.

4. The apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt according to any one of claims 1-3, characterized in that, An exhaust feeding device is fixedly connected to the top surface of the anode chamber. The lower end of the exhaust feeding device is an inverted funnel shape with gradually increasing aperture. The upper end of the exhaust feeding device extends out of the top surface of the electrolytic cell and is provided with a feeding port at the upper end.

5. The apparatus for preparing high-purity light metals by electrolysis of liquid metal molten salt according to claim 4, characterized in that, The side wall of the exhaust feeding device is provided with multiple through holes.

6. A method for preparing high-purity light metals by electrolysis of liquid metal molten salt based on the apparatus of any one of claims 1-5, comprising the following steps: S1: Add molten anode salt and light metal to the anode chamber and molten cathode salt to the cathode chamber. Under an inert atmosphere, heat the light metal to melt it. The light metal naturally floats on the upper surface of the molten anode salt and the molten cathode salt in the intermediate chamber to form a liquid metal layer. The upper end of the first partition is immersed in the liquid metal layer, and the lower end of the second partition is immersed in the molten cathode salt. The upper part of the anode chamber and the intermediate chamber are connected through the liquid metal layer, and the lower part of the intermediate chamber and the cathode chamber are connected through the molten cathode salt. Connect the anode and cathode to the positive and negative terminals of the power supply, respectively, and add electrolytic raw materials to carry out the electrolytic reaction. S2: During electrolysis, the target light metal ions in the anode molten salt are reduced at the interface between the liquid metal layer and the anode molten salt and enter the liquid metal layer; at the same time, the light metal atoms in the liquid metal layer are oxidized into ions at the interface between the liquid metal layer and the cathode molten salt in the intermediate chamber, enter the cathode molten salt, and migrate to the cathode for reduction under the action of the electric field. The products float on the upper layer of the cathode molten salt. Impurities in the raw material that are more reactive than the target light metal remain in the anolyte salt, while impurities that are more inert than the target light metal are reduced at the interface between the liquid metal layer and the anolyte salt and retained in the liquid metal layer. An oxidation reaction occurs at the anode to generate gas, which is discharged through the exhaust feeding device. During the electrolysis process, raw materials are added through the exhaust feeding device to achieve stable and continuous production.

7. The method according to claim 6, characterized in that, The liquid metal layer and the target light metal are the same metal element.

8. The method according to claim 6, characterized in that, The target light metal is one of lithium, magnesium, sodium, and aluminum.

9. The method according to claim 6, characterized in that, The density of the liquid metal is 0.25 to 0.95 times that of the anodic or cathode molten salt.

10. The method according to any one of claims 6-9, characterized in that, It also includes step S3: regenerating the liquid metal layer enriched with impurities; Preferably, the liquid metal enriched with impurities is used as the anode for electrolysis, and high-purity light metal is obtained at the cathode. The obtained high-purity light metal is used as the raw material for the liquid metal layer, and the remaining impurities are discharged in the form of anode mud.

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