A chloride molten salt electrolyte and a method for producing aluminum by low-temperature electrolysis

Abstract

This application discloses a chloride molten salt electrolyte comprising the following components by weight percentage: KCl 10%~15%; LiCl 25%~35%; MgCl2 0.5%~1%; CaCl2 1%~2%; AlCl3 3%~7%; with the balance being NaCl. The chloride molten salt electrolyte of this application has low cost, a low initial crystallization temperature, and high conductivity, and can effectively suppress AlCl3 volatilization and ensure Al³⁺... + With ample supply, the problem of reduced current efficiency caused by AlCl3 volatilization is avoided, enabling efficient and low-cost electrolytic production of aluminum at a low temperature of around 700 ℃.

Description

Technical Field

[0001] This application relates to the field of aluminum electrolysis technology, and in particular to a chloride molten salt electrolyte and a method for producing aluminum by low-temperature electrolysis. Background Technology

[0002] The traditional Hall-Héroult electrolytic aluminum process uses a molten cryolite-alumina system as the electrolyte, with operating temperatures reaching approximately 950°C. This method suffers from drawbacks such as high energy consumption and significant CO2 and PFC emissions due to carbon anode consumption.

[0003] The theoretical decomposition voltage of aluminum production by aluminum chloride molten salt electrolysis is about 1.8V, and the operating temperature can be reduced to about 700℃. The carbon anode is not consumed and is inert, and there is no CO2 or PFC emission. It is considered one of the carbon-free aluminum smelting technology routes.

[0004] The related technology, Alcoa Smelting Process (ASP), uses an electrolyte system of 5±2% AlCl3-53% NaCl-42% LiCl, and carbon materials as the anode and cathode (bipolar electrodes). The electrolytic cell has a multi-chamber structure with stacked layers. However, this process still has defects such as severe AlCl3 volatilization, high electrolyte cost, easy expansion and damage of the cathode, and inability to replace the anode.

[0005] Therefore, how to produce aluminum more efficiently and at a lower cost under low-temperature conditions of around 700 ℃ remains a technical problem that urgently needs to be solved. Summary of the Invention

[0006] By utilizing one or more embodiments of the present application, a chloride molten salt electrolyte and a method for producing aluminum by low-temperature electrolysis solve one of the technical problems of how to efficiently and cost-effectively produce aluminum by electrolysis at low temperatures of around 700 °C.

[0007] A first aspect of this application provides a chloride molten salt electrolyte, characterized in that it comprises the following components in weight percentages: KCl 10%~15%; LiCl 25%~35%; MgCl2 0.5%~1%; CaCl2 1%~2%; AlCl3 3%~7%; with the balance being NaCl.

[0008] In some embodiments, the chloride molten salt electrolyte comprises 10%~12% KCl; 28%~32% LiCl; 0.5%~0.7% MgCl2; 1.3%~1.7% CaCl2; 34%~6% AlCl2; and 48%~53% NaCl.

[0009] In some embodiments, the weight ratio of CaCl2 to MgCl2 is (2~3):1.

[0010] In some embodiments, the initial crystallization temperature of the chloride molten salt electrolyte is 566°C to 660°C; and / or, The chloride molten salt electrolyte has a conductivity of 2.36 S·cm at 700°C. - ¹~2.55 S·cm - ¹; and / or, The kinematic viscosity of the chloride molten salt electrolyte at 700°C is less than 1.5 cm² / s.

[0011] A second aspect of this application provides a method for producing aluminum by low-temperature electrolysis, comprising the following steps: The chloride molten salt electrolyte is placed in an electrolytic cell and electrolyzed by passing direct current to obtain aluminum; wherein the temperature of the electrolysis reaction is 700℃~750℃.

[0012] In some embodiments, the electrolytic cell includes at least one cathode and at least one anode, the anode and the cathode being arranged vertically alternately and spaced apart.

[0013] Optionally, the anode and the cathode are arranged at equal intervals, and / or, The distance between the anode and the cathode is 20 mm to 35 mm.

[0014] In some embodiments, the cathode of the electrolytic cell is a TiB2 ceramic cathode.

[0015] Optionally, the TiB2 ceramic cathode is sintered from a green body comprising TiB2 powder, carbon powder, and sintering aids; wherein the carbon content in the green body is ≤20%, the TiB2 content in the green body is ≥80%, the sintering aid content in the green body is 2-5%, and the content of Fe, Ni, Cu, and Zr in the sintering aids is less than or equal to 0.01%.

[0016] In some embodiments, the anode of the electrolytic cell is a cermet inert anode, and the current density of the anode is less than or equal to 0.4 A / cm² during the first hour of the electrolytic reaction, and less than or equal to 0.8 A / cm² after the first hour of the electrolytic reaction.

[0017] Optionally, the cermet inert anode is a nickel ferrite-based cermet anode, wherein the metal phase of the nickel ferrite-based cermet anode is at least one of nickel-copper alloy, elemental nickel, and elemental iron, and the content of the metal phase in the nickel ferrite-based cermet anode is ≤30%, and the total content of elemental iron in the metal phase is ≤2%.

[0018] Optionally, the method further includes adding anhydrous aluminum chloride to the chloride molten salt electrolyte during the electrolysis reaction, wherein the oxygen content of the anhydrous aluminum chloride is less than 2%.

[0019] In some embodiments, the anode of the electrolytic cell is a graphite anode, and the anode current density is controlled below 1.5 A / cm².

[0020] Optionally, the method further includes adding anhydrous aluminum chloride to the chloride molten salt electrolyte during the electrolysis reaction, wherein the oxygen content of the anhydrous aluminum chloride is less than 0.03%.

[0021] Optionally, the graphite anode is a replaceable anode, and the method further includes replacing the anode when the cell voltage rises to 8V.

[0022] Compared with the prior art, the technical solution provided in this application has the following beneficial effects: The chloride molten salt electrolyte of this application uses NaCl as the main material, and also adds 3%~7% AlCl3 to provide Al 3 + AlCl3 is volatile; when the AlCl3 content exceeds 7%, the volatilization rate increases significantly. However, the AlCl3 content is also a key indicator of Al... 3+ The provider of AlCl3, when the content is below 3%, will trigger Na... + Li + K + Alkali metals discharge, thus reducing current efficiency. To ensure Al³⁺... + To supply and avoid alkali metal discharge, maintain relatively high current efficiency, and avoid excessive volatilization, the chloride molten salt electrolyte of this application introduces 1%~2% CaCl2 and 0.5%~1% MgCl2. 2+ With a large ionic radius and high charge, it can react with Cl. - Formation of stable [CaCl4] 2- Complexing ions reduces free Cl- - The concentration of CaCl2 is adjusted to inhibit AlCl3 volatilization. When the CaCl2 content is below 1%, the complexing effect is weak and the inhibition is not significant. When the CaCl2 content exceeds 3%, the primary crystallization temperature of the electrolyte increases significantly. Mg 2+ Can with Cl - [MgCl4] is formed.2- Complex ions, with [CaCl4] 2- Synergistic reinforcement of free Cl - The effect is not obvious when the MgCl2 content is below 0.5%, and the MgCl2 content is more than 2%, which easily leads to electrolyte hydrolysis. In addition, replacing LiCl with KCl reduces the LiCl content from 42% in the traditional ASP process to 25%~35%, significantly reducing the cost of the electrolyte. Although the chloride molten salt electrolyte of this application introduces KCl with a higher melting point, the LiCl content is still maintained above 25%, and the synergistic effect of AlCl3, CaCl2, and MgCl2 allows the initial crystallization temperature of the chloride molten salt electrolyte of this application to be controlled in a relatively low temperature range below 660℃. The conductivity at 700℃ can reach more than 2.36 S / cm, and the electrolyte has good fluidity in the molten state, with a kinematic viscosity of less than 1.5 cm² / s at 700℃, which meets the requirements of electrolysis. The chloride molten salt electrolyte of this application has low cost, low initial crystallization temperature and high conductivity, and can effectively inhibit AlCl3 volatilization and ensure Al³⁺. + With ample supply, the problem of reduced current efficiency caused by AlCl3 volatilization is avoided, enabling efficient and low-cost electrolytic production of aluminum at a low temperature of around 700 ℃. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and disclosure, and together with the description serve to explain the principles of this application and disclosure.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of an aluminum chloride electrolytic cell structure according to some embodiments of this application; Among them, 1 is the furnace tube of the pit-type heating furnace, 2 is the stainless steel crucible, 3 is the corundum crucible, 4 is the aluminum chloride electrolyte melt, 5 is the gas inlet pipe, 6 is the thermocouple with corundum protective sleeve, 7 is the exhaust pipe, 8 is the furnace tube sealing cover, 9 is the electrode guide rod, 10 is the lifting device, 11 is the sealing sleeve, 12 is the corundum protective sleeve, 13 is the anhydrous aluminum chloride feeding funnel made of corundum, 14 is the corundum castable, 15 is the vertical plate anode, 16 is the vertical plate cathode, and 17 is the support pad.

[0026] Figure 2This is a schematic diagram of an aluminum chloride electrolytic cell structure according to some other embodiments of this application; Among them, 21 is the cathode current collector rod, 22 is the furnace tube of the pit-type heating furnace, 23 is the stainless steel crucible, 24 is the corundum casting material, 25 is the corundum crucible, 26 is the aluminum chloride electrolyte melt, 27 is the gas inlet pipe, 28 is the thermocouple with corundum protective sleeve, 29 is the flue pipe, 30 is the furnace tube sealing cover, 31 is the sealing ferrule, 32 is the screw feeder, 33 is the electrode guide rod, 34 is the lifting device, 35 is the aluminum outlet plug, 36 is the corundum protective sleeve, 37 is the corundum casting material, 38 is the vertical plate anode, 39 is the vertical plate cathode, 40 is the cathode ramming paste, 41 is the graphite block, and 42 is the support pad. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0029] Any specific numerical values ​​disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed herein.

[0030] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0031] Unless otherwise stated, "%" in this article refers to weight percentage.

[0032] In this article, "AlCl3" refers to anhydrous AlCl3.

[0033] In this article, "high-purity graphite" refers to graphite with a purity of ≥99.99%.

[0034] The specific reasons for the aforementioned defects in the Alcoa Smelting Process (ASP) aluminum electrolysis are as follows: 1. The high LiCl content in the 5±2%AlCl3-53%NaCl-42%LiCl electrolyte system used in this process leads to its high cost.

[0035] 2. The electrolyte components used in this process are highly volatile, especially the AlCl3 component, which has a high saturated vapor pressure, resulting in significant electrolyte loss due to volatilization, high raw material consumption, and difficulty in stabilizing and controlling the electrolyte components.

[0036] 3. This process uses graphite as the cathode. On one hand, graphite has poor wettability with molten aluminum. On the other hand, using graphite as the cathode requires a higher AlCl3 content in the electrolyte. If the AlCl3 content is too low, alkali metal ions (Na+) will proliferate. + Li + K + (etc.) will preferentially enter the lattice of graphite material during cathode discharge, forming intercalation compounds, leading to cathode expansion and damage; and if the AlCl3 content is too high, electrolyte volatilization will be very serious.

[0037] 4. This process uses graphite as the anode, and the electrolytic cell has a multi-chamber structure with stacked layers. The anode cannot be replaced, and the raw material AlCl3 must be high-purity anhydrous aluminum chloride, with an oxygen content in the electrolyte of less than 0.03%. If the electrolyte contains water or other oxides, oxygen ions will be introduced. The discharge voltage of oxygen ions on the carbon anode is lower than that of chloride ions, so they will preferentially discharge and react with carbon to generate CO2, causing the carbon anode to be consumed. This renders the "bipolar, stacked, non-replaceable anode" electrolytic cell ineffective. Furthermore, the preparation and storage costs of high-purity anhydrous aluminum chloride are extremely high, further hindering the industrialization of aluminum chloride electrolysis.

[0038] First aspect Some embodiments of this application provide a chloride molten salt electrolyte comprising the following components in weight percentage: KCl 10%~15%; LiCl 25%~35%; MgCl2 0.5%~1%; CaCl2 1%~2%; AlCl3 3%~7%; with the balance being NaCl.

[0039] Of the components mentioned above, NaCl has extremely low cost, low vapor pressure, and high conductivity, but also a high melting point. KCl has low density, excellent separation properties with molten aluminum, and slightly lower conductivity than NaCl. LiCl has the lowest melting point, highest conductivity, and lowest viscosity, but its cost is relatively high. CaCl2 has extremely strong thermal stability and can suppress the volatilization of AlCl3, but its conductivity is relatively low. MgCl2 provides the best viscosity adjustment for molten chloride electrolytes, which helps ensure good fluidity of the chloride electrolyte, while also suppressing the volatilization of AlCl3, and it is also inexpensive.

[0040] Specifically, AlCl3 is volatile; when the AlCl3 content exceeds 7%, the volatilization rate increases significantly. However, the AlCl3 content is also a key indicator of Al... 3+ The provider of the ion, when the AlCl3 content is below 3%, will trigger Na + Li + K + Alkali metals discharge, thus reducing current efficiency. To ensure Al³⁺... + To supply and avoid alkali metal discharge, maintain relatively high current efficiency without excessive volatilization, the chloride molten salt electrolyte provided in this application embodiment introduces 1%~2% CaCl2 and 0.5%~1% MgCl2. 2+ With a large ionic radius and high charge, it can react with Cl. - Formation of stable [CaCl4] 2- Complexing ions reduces free Cl- - The concentration of CaCl2 is adjusted to inhibit AlCl3 volatilization. When the CaCl2 content is below 1%, the complexing effect is weak and the inhibition is not significant. When the CaCl2 content exceeds 3%, the primary crystallization temperature of the electrolyte increases significantly. Mg 2+ Can with Cl - [MgCl4] is formed. 2- Complex ions, with [CaCl4] 2- Synergistic reinforcement of free Cl - The binding effect is not obvious when the MgCl2 content is below 0.5%, and when the MgCl2 content exceeds 2%, it is easy to trigger electrolyte hydrolysis.

[0041] The chloride molten salt electrolyte in this application uses NaCl as the main material, and also adds 3%~7% AlCl3 to provide Al. 3+ Furthermore, 1%~2% CaCl2 and 0.5%~1% MgCl2 are used to suppress the volatilization of AlCl3, ensuring the stability of Al³⁺. +Sufficient supply. Furthermore, replacing LiCl with KCl reduces the LiCl content from 42% in the traditional ASP process to 25%~35%, significantly lowering electrolyte costs. Although the chloride molten salt electrolyte provided in this application introduces KCl with a higher melting point, the LiCl content remains above 25%, and the synergistic effect of AlCl3, CaCl2, and MgCl2 allows the initial crystallization temperature of the chloride molten salt electrolyte provided in this application to be controlled within a relatively low temperature range below 660℃. At 700℃, the conductivity can reach above 2.36 S / cm, and the electrolyte exhibits good fluidity in the molten state, with a kinematic viscosity of less than 1.5 cm² / s at 700℃, meeting electrolysis requirements and effectively suppressing AlCl3 volatilization.

[0042] In some embodiments, the chloride molten salt electrolyte comprises 10%–12% KCl; 28%–32% LiCl; 0.5%–0.7% MgCl₂; 1.3%–1.7% CaCl₂; 4%–6% AlCl₃; and 48%–53% NaCl. Within this range, the components of the chloride molten salt electrolyte, with AlCl₃ providing Al... 3+ With a more stable concentration, this electrolyte can achieve higher current efficiency when used in the electrolysis of chloride molten salts to produce aluminum.

[0043] In some specific embodiments, the chloride molten salt electrolyte includes 10% KCl; 30% LiCl; 0.5% MgCl2; 1.5% CaCl2; 35% AlCl; and 53% NaCl. When this electrolyte is used for the electrolytic production of aluminum using chloride molten salt, the current efficiency can reach over 88%.

[0044] In some implementations, the weight ratio of CaCl2 to MgCl2 is (2~3):1, for example, 2:1, 2.5:1, or 3:1. Within this weight ratio range, the volatilization of AlCl3 can be more effectively suppressed, ensuring the preservation of Al... 3+ The concentration is stable and the supply is sufficient.

[0045] In some embodiments, the above-mentioned chlorides are all anhydrous chlorides or chlorides dried to a water content of less than 0.1%.

[0046] In some embodiments, the primary crystallization temperature of the chloride molten salt electrolyte is 566°C to 660°C. Understandably, the primary crystallization temperature of the chloride molten salt electrolyte can be 566°C, 568°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, and any value between them or a range between any two values.

[0047] The conductivity of the chloride molten salt electrolyte at 700℃ is 2.36 S·cm. - ¹~2.55 S·cm - ¹. Understandably, the conductivity of chloride molten salt electrolytes at 700 °C can be 2.36 S·cm. - ¹、2.48 S·cm - ¹、2.40 S·cm - ¹、2.45S·cm - ¹、2.50 S·cm - ¹、2.55 S·cm - ¹and any values ​​between them and the range between any two values.

[0048] The kinematic viscosity of chloride molten salt electrolytes at 700°C is less than 1.5 cm² / s. Understandably, the kinematic viscosity of chloride molten salt electrolytes at 700°C can be less than 1.5 cm² / s, less than 1.3 cm² / s, or less than 1.1 cm² / s.

[0049] Second aspect Some embodiments of this application provide a method for producing aluminum by low-temperature electrolysis, including the following steps: The chloride molten salt electrolyte of any embodiment of the first aspect is placed in an electrolytic cell, and an electrolytic reaction is carried out by passing a direct current to obtain aluminum; wherein the temperature of the electrolytic reaction is 700℃~750℃.

[0050] This method for producing aluminum by low-temperature electrolysis is based on the aforementioned chloride molten salt electrolyte. The specific characteristics of the chloride molten salt electrolyte can be found in the above embodiments. Since this method employs some or all of the technical solutions described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions in the above embodiments, which will not be elaborated upon here. It is particularly noteworthy that the low-temperature electrolysis method for producing aluminum provided in this application has high current efficiency, reaching over 75%, which is superior to the traditional ASP process. Furthermore, the AlCl3 consumption during electrolysis is low, essentially close to the theoretical value.

[0051] It should be noted that the electrolysis reaction temperature is controlled at 700℃~750℃. Within this temperature range, the chloride molten salt electrolyte melt has good fluidity and low viscosity, and does not cause severe volatilization of AlCl3. Experiments have shown that electrolysis operates relatively stably within this temperature range, and the voltage does not fluctuate significantly. In addition, it can also prevent scaling on the cathode surface.

[0052] In some embodiments, the electrolytic cell includes at least one cathode and at least one anode, with the anode and cathode arranged vertically in an alternating pattern and spaced apart, which facilitates anode replacement. Optionally, the anode and cathode are arranged at equal intervals. Further optionally, the electrode distance between the anode and cathode is 20 mm to 35 mm, for example, it can also be 22 mm, 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, or 34 mm.

[0053] In some implementations, the vertically staggered arrangement of the anode and cathode can be achieved in two ways. The first way is as follows: Figure 1 As shown, the anode 15 is connected to the electrode rod 9 and is inserted into the electrolytic cell from above, with electricity output from above the electrolytic cell; the second method is as follows... Figure 2 As shown, the cathode 39 is connected to the graphite block 41 at the bottom of the electrolytic cell, and electricity is drawn from the bottom or side of the electrolytic cell. The first method results in a simple and easy-to-implement electrolytic cell structure, but the cathode electrode rod 9 is immersed in the electrolyte melt, and despite protection, it is still prone to breakage. Therefore, the operating time is short, making it suitable for small-scale, short-cycle electrolysis experiments in the laboratory with a total DC current ≤100A. The second method results in a more complex electrolytic cell structure, but the cathode current collector 21 is isolated from the electrolyte melt by the graphite block 41, making it less susceptible to corrosion and allowing for long-term operation. Therefore, it is suitable for slightly larger-scale laboratory experiments with currents >100A and for industrial-scale electrolytic cells.

[0054] In some embodiments, the electrode rods (9, 33) are made of 310S, which is a high-chromium (25%), high-nickel (20%) austenitic heat-resistant stainless steel.

[0055] The electrode conductors (9, 33) were protected using corundum protective sleeves (12, 36) and corundum castables (16, 37), and experiments showed good results. For the anode electrode conductors, since the anode portion is exposed to the electrolyte melt, the anode conductors only face corrosion from the electrolyte atmosphere and chlorine. The combined use of corundum sleeves and corundum castables provides good sealing and prevents reaction with the chloride electrolyte atmosphere and chlorine, effectively isolating them and enabling long-cycle electrolysis operation. However, for the cathode electrode conductors, since the cathode is submerged in the electrolyte melt, the cathode electrode conductors not only face corrosion from the electrolyte atmosphere and chlorine but are also partially immersed in the electrolyte melt. The corundum sleeves and corundum castables are also partially immersed in the electrolyte melt. Although the chloride electrolyte has low solubility for corundum (alumina) and slow dissolution corrosion, penetration still occurs. When the electrolyte melt penetrates and contacts the internal electrode conductors, they will still be corroded. Therefore, this method can support the protection of the cathode electrode rod for tens to hundreds of hours, making it suitable for short-cycle electrolysis tests.

[0056] It should be noted that, as Figure 1 and Figure 2 Specific embodiments of the vertically staggered arrangement of the anode and cathode shown can be found in patent applications 202310009797.0 and 2025104485334. In some embodiments, the cathode of the electrolytic cell is a TiB2 ceramic cathode. The TiB2 ceramic cathode effectively avoids expansion and breakage caused by alkali metal penetration into the cathode, resulting in a more stable operation of the electrolytic cell during the electrolysis reaction. Simultaneously, the TiB2 ceramic cathode has good wettability with molten aluminum, reducing secondary dissolution losses of aluminum and further improving current efficiency.

[0057] In some embodiments, the TiB2 ceramic cathode is sintered from a blank comprising TiB2 powder, carbon powder, and sintering aids. It can be commercially available hot-pressed TiB2 ceramic or self-cooled and sintered TiB2 ceramic. A method for preparing self-cooled and sintered TiB2 ceramic can be found in patent application number 202310047908.7.

[0058] In some alternative embodiments, the TiB2 ceramic cathode is sintered from a green body comprising TiB2 powder, carbon powder, and sintering aids; wherein the carbon content in the green body is ≤20%, the TiB2 content in the green body is ≥80%, and the sintering aid content in the green body is 2-5%, wherein the content of Fe, Ni, Cu, and Zr in the sintering aids is less than or equal to 0.01%. This TiB2 ceramic cathode exhibits better resistance to alkali metal penetration. The content of the sintering aid elements is ≤0.01%, which avoids the risk of aluminum penetrating into the cathode reacting with it, leading to cathode expansion and cracking.

[0059] In some embodiments, the anode of the electrolytic cell is a cermet inert anode. During the initial one hour of the electrolytic reaction, the anode current density is less than or equal to 0.4 A / cm², and after one hour of the electrolytic reaction, the anode current density is less than or equal to 0.8 A / cm². When using a cermet inert material as the anode, the anode current density should not be too high, especially the initial anode current density. Anode current density less than or equal to 0.4 A / cm² during the initial one hour of the electrolytic reaction and less than or equal to 0.8 A / cm² after one hour of the electrolytic reaction can effectively prevent anode effects and ensure stable operation of the electrolytic cell.

[0060] In some optional embodiments, the cermet inert anode is a nickel ferrite-based cermet anode. In the nickel ferrite-based cermet anode, the ceramic phase is a nickel ferrite matrix, forming the material's framework, with the metallic phase filling the ceramic framework. The metallic phase of the nickel ferrite-based cermet can be at least one of a nickel-copper alloy, elemental nickel, or elemental iron. Optionally, the content of the metallic phase in the nickel ferrite-based cermet anode is ≤30%, and more preferably, the total content of elemental iron in the metallic phase is ≤2%.

[0061] In some embodiments, the method further includes adding anhydrous aluminum chloride to the chloride molten salt electrolyte during the electrolysis reaction. When the anode of the electrolytic cell is a cermet inert anode, the oxygen content of the anhydrous aluminum chloride is less than 2%. When the anode of the electrolytic cell is a cermet inert anode, the oxygen ion potential is higher than the chloride ion potential, and the oxygen content of the added anhydrous aluminum chloride is within this range, so that no significant precipitation or scaling will occur at the cathode of the electrolytic cell.

[0062] In some implementations, the anode of the electrolytic cell is a graphite anode, and the anode current density is controlled below 1.5 A / cm², which can effectively prevent the anode effect and ensure the stable operation of the electrolytic cell.

[0063] In some embodiments, the method further includes adding anhydrous aluminum chloride to the chloride molten salt electrolyte during the electrolysis reaction. When the anode of the electrolytic cell is a graphite anode, the oxygen content of the anhydrous aluminum chloride is less than 0.03%. When the anode of the electrolytic cell is a graphite anode, the oxygen ion potential is lower than the chloride ion potential, and oxygen ions will preferentially precipitate and react with the carbon anode to generate CO2 or CO, leading to anode consumption. The lower the oxygen content in the anhydrous aluminum chloride added during the electrolysis reaction, the slower the carbon anode is consumed. However, since the anode is replaceable, a small amount of oxygen can be allowed in the anhydrous aluminum chloride, which to some extent reduces the requirements for high-purity anhydrous aluminum chloride.

[0064] In some embodiments, the anode of the electrolytic cell is a graphite anode, which is replaceable. When the anode of the electrolytic cell is a graphite anode, the oxygen ion potential is lower than the chloride ion potential, and oxygen ions will preferentially precipitate and react with the carbon anode to generate CO2 or CO, leading to anode consumption. Setting the anode as a replaceable anode can solve the problem of anode consumption.

[0065] In some implementations, the anode is replaced when the tank voltage rises to 8V.

[0066] Example To better understand this application, the following description, in conjunction with embodiments, further illustrates this application. However, the scope of protection claimed in this application is not limited to the scope of the embodiments.

[0067] In the following examples, unless otherwise specified, all experimental instruments, raw materials, and quantities involved are commercially available products or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0068] Unless otherwise specified, the specific parameters used in each step of the material preparation process in each embodiment and comparative example are the same.

[0069] Example 1 On a 100A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 1 As shown, an electrolyte with an initial composition of 15% KCl - 35% LiCl - 1% MgCl2 - 2% CaCl2 - 7% AlCl3 - 40% NaCl was used for electrolysis experiments. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 5 kg of the electrolyte was placed in a corundum crucible 3 and heated and kept at a constant temperature inside the furnace tube 1 of a pit-type heating furnace, and sealed by the furnace tube 1 and the sealing cover 8. During the heating, holding, electrolysis, and cooling processes, dry N2 gas at a flow rate of 0.8 L / min was continuously introduced for protection. The specific structure of the electrolytic cell and the materials of related structures are as follows: There are two flat cathodes 16, which are made of commercially available hot-pressed TiB2 ceramic with a carbon content of 20% and a TiB2 content of 80%. The dimensions of cathode 16 are width × thickness × height = 56mm × 20mm × 50mm.

[0070] There is one flat anode 15, made of high-purity graphite. The dimensions of anode 15 are width × thickness × height = 56mm × 20mm × 80mm.

[0071] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 20 mm between them.

[0072] Two 310S stainless steel rods with a diameter of 8mm are used as electrode guide rods 9 on each electrode, and the guide rods are protected by corundum tubes 12 and corundum castable 14. Both the anode and cathode are inserted into the electrolytic cell from above, and the electrode guide rods 9 pass through the furnace tube sealing cover 8 and are led out of the cell.

[0073] The anode 15 is partially exposed about 20 mm above the chloride electrolyte melt 4, while the cathode 16 is submerged about 10 mm inside the chloride electrolyte melt 4.

[0074] During the electrolysis process, the electrolysis temperature is gradually increased from 700℃ to around 720℃ and then stabilized. The DC current is 100A, and the anode current density is approximately 1.5A / cm³. 2 Anhydrous aluminum chloride powder was manually added through funnel 13 at a rate of 65g every half hour. During electrolysis, the voltage remained relatively stable at around 3.919V for the first 2 hours. Afterward, the voltage experienced several slow but continuous increases. The voltage decreased slightly after the manual addition of anhydrous aluminum chloride powder, then gradually increased again. Around the 6-hour mark, an anodic effect occurred, causing the voltage to rise rapidly to 30V, which recovered after restarting the DC power supply. The amount of anhydrous aluminum chloride added every half hour was then increased to 75g, and the voltage remained relatively stable at 4.15V. Electrolysis continued for 10 hours, at which point the DC power was disconnected to stop operation. The anode and cathode were then raised away from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 252g of aluminum blocks. The current efficiency was 75%, and the AlCl3 consumption was approximately 5.48kg / kg-Al (5.48kg of AlCl3 raw material is required to produce 1kg of metallic aluminum). The electrodes were ultrasonically washed with water. The hot-pressed TiB2 ceramic cathode remained intact, without expansion or cracking, and was encased in an aluminum shell. The high-purity graphite anode remained intact overall, with localized pitting corrosion.

[0075] Example 2 On a 100A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 1 As shown, an electrolyte with an initial composition of 10% KCl - 25% LiCl - 0.5% MgCl2 - 1% CaCl2 - 3% AlCl3 - 60.5% NaCl was used for electrolysis experiments. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 5 kg of the electrolyte was placed in a corundum crucible 3 and heated and kept at a constant temperature inside a pit-type heating furnace tube 1, and sealed by the furnace tube 1 and the sealing cover 8. During the heating, holding, electrolysis, and cooling processes, dry N2 gas at a flow rate of 0.8 L / min was continuously introduced for protection. The specific structure of the electrolytic cell and the materials of related structures are as follows: There are two flat cathodes 16, which are made of commercially available hot-pressed TiB2 ceramic with a carbon content of 15% and a TiB2 content of 85%. The cathode 16 has dimensions of width × thickness × height = 56mm × 20mm × 50mm.

[0076] There is one flat anode 15, which is made of high-purity graphite. The dimensions of anode 15 are width × thickness × height = 56mm × 20mm × 80mm.

[0077] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 20 mm between them.

[0078] Two 310S stainless steel rods with a diameter of 8mm are used as electrode guide rods 9 on each electrode, and the guide rods are protected by corundum tubes 12 and corundum castable 14. Both the anode and cathode are inserted into the electrolytic cell from above, and the electrode guide rods 9 pass through the furnace tube sealing cover 8 and are led out of the cell.

[0079] The anode 15 is partially exposed to the chloride electrolyte melt by about 20 mm, and the cathode 16 is submerged in the electrolyte melt 4 by about 10 mm.

[0080] During the electrolysis process, the electrolysis temperature was gradually increased from 720℃ to around 748℃ and then stabilized. The DC current was 80A, and the anode current density was approximately 1.2A / cm³. 2 Anhydrous aluminum chloride powder was manually added through funnel 13, with 62g added every half hour. After electrolysis started, the voltage showed a continuous upward trend. After manually adding anhydrous aluminum chloride powder, the voltage stabilized at around 3.59V, followed by slight fluctuations. After 4 hours, the voltage increased slightly but remained relatively stable at around 3.941V. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised away from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 239g of aluminum blocks. The current efficiency was 89%, and the aluminum chloride consumption was 5.19 kg / kg-Al (5.19 kg of AlCl3 raw material is required to produce 1 kg of metallic aluminum). The electrodes were ultrasonically washed with water. The hot-pressed TiB2 ceramic cathode remained intact, without expansion or cracking, and was covered with an aluminum shell. The high-purity graphite anode remained intact overall, with localized pitting corrosion.

[0081] Example 3 On a 100A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 1 As shown, an electrolyte with an initial composition of 15% KCl - 30% LiCl - 0.5% MgCl2 - 1.5% CaCl2 - 5% AlCl3 - 48% NaCl was used for electrolysis experiments. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 5 kg of the electrolyte was placed in a corundum crucible 3 and heated and kept at a constant temperature inside a pit-type heating furnace tube 1, and sealed by the furnace tube 1 and the sealing cover 8. During the heating, holding, electrolysis, and cooling processes, dry N2 gas at a flow rate of 0.8 L / min was continuously introduced for protection. The specific structure of the electrolytic cell and the materials of related structures are as follows: There are two flat cathodes 16, which are made of self-cooled and sintered TiB2 ceramic with a carbon content of 0.26% and a TiB2 content of 87%, with the balance being a sintering aid free of Ni, Fe, Cu, and Zr. The cathode 16 has dimensions of width × thickness × height = 56mm × 20mm × 50mm.

[0082] There is one flat anode 15, which uses nickel ferrite-based cermet as the anode, with a metal phase content of 30% and an Fe element content of less than 2% in the metal phase composition. The dimensions of anode 15 are width × thickness × height = 56mm × 20mm × 80mm.

[0083] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 20 mm between them.

[0084] Two 310S stainless steel rods 9 with a diameter of 8mm are used as electrode guides for each electrode, and the guides are protected by corundum tubes 12 and corundum castable 13. Both the anode and cathode are inserted into the electrolytic cell from above, and the electrode guides 9 pass through the furnace tube sealing cover 8 and are led out of the cell.

[0085] The anode 15 is partially exposed to the chloride electrolyte melt by about 20 mm, and the cathode 16 is submerged in the electrolyte melt 4 by about 10 mm.

[0086] During the electrolysis process, the electrolysis temperature was gradually increased from 710℃ to around 736℃ and then stabilized. The initial DC current was 53A, and the anode current density was approximately 0.8A / cm³. 2 Anhydrous aluminum chloride powder was manually added through funnel 13, with 28g added every half hour. After electrolysis started, the voltage showed a slow and continuous upward trend. After manually adding anhydrous aluminum chloride powder, the voltage would decrease rapidly but would quickly and continuously rise again, reaching over 8V. Therefore, after 3 hours of startup, the DC current was reduced to 26.5A, i.e., the anode current density was approximately 0.4A / cm³. 2 The voltage remained stable at around 3.28V and did not increase further. After 6 hours, the current increased to 40A, which is approximately 0.6A / cm³. 2The voltage remained stable at around 3.44V with slight fluctuations, gradually increasing to around 3.521V after 8 hours. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised and removed from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 107.2g of aluminum blocks. The average current efficiency was 80%, and the aluminum chloride consumption was 5.22 kg / kg-Al (5.22 kg of AlCl3 raw material is required to produce 1 kg of metallic aluminum). The electrodes were ultrasonically washed with water. The self-cooled and sintered TiB2 ceramic cathode remained intact, without expansion or cracking, and had an aluminum shell covering its surface. The cermet anode remained intact overall, but had a very thin film. XRD analysis showed that the main component was NiFe2O4, suggesting that the metallic chloride electrolyte had been corroded.

[0087] Example 4 On a 100A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 1 As shown, an electrolyte with an initial composition of 10% KCl - 30% LiCl - 0.5% MgCl2 - 1.5% CaCl2 - 5% AlCl3 - 53% NaCl was used for electrolysis experiments. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 5 kg of the electrolyte was placed in a corundum crucible 3 and heated and kept at a constant temperature inside a pit-type heating furnace tube 3, and sealed by the furnace tube 1 and the sealing cover 8. During the heating, holding, electrolysis, and cooling processes, dry N2 gas at a flow rate of 0.8 L / min was continuously introduced for protection. The specific structure of the electrolytic cell and the materials of related structures are as follows: There are two flat cathodes 16, which are made of self-cooled and sintered TiB2 ceramic with a carbon content of 0.26% and a TiB2 content of 87%, with the balance being a sintering aid free of Ni, Fe, Cu, and Zr. The cathode 16 has dimensions of width × thickness × height = 56mm × 20mm × 50mm.

[0088] There is one flat anode 15, which uses nickel ferrite-based cermet as the anode, with a metal phase content of 15% and an Fe element content of less than 2% in the metal phase composition. The dimensions of anode 15 are width × thickness × height = 56mm × 20mm × 80mm.

[0089] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 20 mm between them.

[0090] Two 310S stainless steel rods with a diameter of 8mm are used as electrode guide rods 9 on each electrode, and the guide rods are protected by corundum tubes 12 and corundum castable 13. Both the anode and cathode are inserted into the electrolytic cell from above, and the electrode guide rods 9 pass through the furnace tube sealing cover 8 and are led out of the cell.

[0091] The anode 15 is partially exposed to the chloride electrolyte melt by about 20 mm, and the cathode 16 is submerged in the electrolyte melt 4 by about 10 mm.

[0092] During the electrolysis process, the electrolysis temperature was gradually increased from 715℃ to around 745℃ and then stabilized. Initially, the DC current was 26.5A over the first hour, with an anode current density of approximately 0.4A / cm³. 2 The DC current was then 40A, and the anode current density was approximately 0.6A / cm². 2 Anhydrous aluminum chloride powder was manually added through funnel 13, with 40g of anhydrous aluminum chloride added every half hour. After electrolysis started, the voltage stabilized at 3.436V within 1 hour. After 1 hour, the voltage increased due to the increased current, stabilizing at around 3.495V. After 8 hours, the voltage gradually increased to around 3.56V. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised and removed from the electrolyte melt, and the well-type heating furnace was stopped. After natural cooling, the crucible and electrodes were removed, yielding 116.8g of aluminum blocks. The average current efficiency was 90%, and the aluminum chloride consumption was 5.13kg / kg-Al (5.13kg of AlCl3 raw material was required to produce 1kg of metallic aluminum). The electrodes were ultrasonically washed with water. The self-cooled and sintered TiB2 ceramic cathode was intact, without expansion or cracking, and had an aluminum shell covering its surface. The metal ceramic anode was intact overall, but had a very thin film. XRD analysis showed that the main component was NiFe2O4, suggesting that the metallic chloride electrolyte was corroded.

[0093] Example 5 On a 200A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 2 As shown, an electrolyte with an initial composition of 10% KCl - 30% LiCl - 0.5% MgCl2 - 1.5% CaCl2 - 5% AlCl3 - 53% NaCl was used in the electrolysis experiment. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 20 kg of the electrolyte was placed in a specially assembled corundum crucible 25 and heated and kept at a constant temperature inside the furnace tube 22 of a pit-type heating furnace. The furnace tube 22 and the sealing cap 30 were used to achieve a seal. During the heating, holding, and cooling processes, dry N2 gas at a flow rate of 1.8 L / min was continuously introduced for protection.

[0094] There are two flat cathodes 39, which are made of commercially available hot-pressed sintered TiB2 ceramic with a carbon content of 15% and a TiB2 content of 85%. The cathodes 39 are connected to the graphite block 41 at the bottom of the corundum crucible 25 by cathode paste tamping 40, and the exposed part has dimensions of width × thickness × height = 80mm × 30mm × 170mm.

[0095] There is one flat anode 38, which is made of high-purity graphite. The dimensions of anode 38 are width × thickness × height = 80mm × 55mm × 200mm.

[0096] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 35 mm between them.

[0097] Two 12mm diameter 310S stainless steel rods are used as electrode guide rods 33, and corundum tubes 36 and corundum castings 37 are used to protect the guide rods. The anode 38 is inserted into the electrolytic cell from above, and the guide rod passes through the sealing cover 30 and is led out of the cell.

[0098] The anode 38 is partially exposed about 50 mm above the chloride electrolyte melt, and the bottom of the anode 38 is 50 mm from the bottom of the electrolytic cell. The cathode 39 is submerged about 30 mm below the electrolyte melt 26.

[0099] During the electrolysis process, the electrolysis temperature was gradually increased from 716℃ to around 745℃ and then stabilized. The DC current was 200A, and the anode current density was approximately 0.83A / cm³. 2 Anhydrous aluminum chloride powder was automatically added via a screw feeder 32, once every 5 minutes, at a rate of approximately 300g per hour. After electrolysis started, the initial voltage stabilized at around 3.831V, subsequently showing a trend of first decreasing (around 3.54V) and then gradually increasing (to 4.36V). Electrolysis lasted for 260 hours, at which point the DC power was disconnected to stop operation, and the anode was removed from the electrolyte melt, stopping the well-type furnace heating. During this period, approximately 1.42kg of aluminum was manually removed once every 24 hours. After natural cooling, the crucible and electrodes were removed, yielding a total of 15341g of aluminum blocks, with an average current efficiency of 88% and an aluminum chloride consumption of 5.08kg / kg-Al (5.08kg of AlCl3 raw material is required to produce 1kg of metallic aluminum). The cathode remained intact. During the electrolysis process, samples of the anhydrous aluminum chloride automatically fed by the feeder were taken, and the oxygen content was analyzed using an oxygen-nitrogen analyzer, finding it to be 2.12%.

[0100] Example 6 On a 200A-class vertical aluminum chloride electrolytic cell, the structure is as follows: Figure 2As shown, an electrolyte with an initial composition of 10% KCl - 30% LiCl - 0.5% MgCl2 - 1.5% CaCl2 - 5% AlCl3 - 53% NaCl was used in the electrolysis experiment. The initial crystallization temperature of the chloride electrolyte with different compositions was measured using the step-cooling curve method, and the conductivity at 700℃ was measured using the Continuously Varying Cell Constant method (results are shown in Table 1). Approximately 20 kg of the electrolyte was placed in a specially assembled corundum crucible 25 and heated and kept at a constant temperature inside the furnace tube 22 of a pit-type heating furnace. The furnace tube 22 and the sealing cap 30 were used to achieve a seal. During the heating, holding, and cooling processes, dry N2 gas at a flow rate of 1.8 L / min was continuously introduced for protection.

[0101] There are two flat cathodes 39, which are made of commercially available hot-pressed sintered TiB2 ceramic with a carbon content of 15% and a TiB2 content of 85%. The cathodes 39 are connected to the graphite block 41 at the bottom of the corundum crucible 25 by cathode paste tamping 40, and the exposed part has dimensions of width × thickness × height = 80mm × 30mm × 170mm.

[0102] There is one flat anode 38, which uses nickel ferrite-based cermet as the anode, with a metal phase content of 15% and an Fe element content of less than 2% in the metal phase composition. The dimensions of anode 38 are width × thickness × height = 80mm × 55mm × 200mm.

[0103] The electrodes are arranged in a "cathode-anode-cathode" configuration with equal spacing and a distance of 35 mm between them.

[0104] Two 12mm diameter 310S stainless steel rods are used as electrode guide rods 33, and corundum tubes 36 and corundum castable 37 are used to protect the guide rods. The anode 38 is inserted into the electrolytic cell from above, and the electrode guide rods 33 pass through the sealing cover 30 and are led out of the cell.

[0105] The anode 38 is partially exposed about 50 mm above the chloride electrolyte melt, and the bottom of the anode 38 is 50 mm from the bottom of the electrolytic cell. The cathode 39 is submerged about 30 mm inside the electrolyte melt 26.

[0106] During electrolysis, the electrolysis temperature was gradually increased from 712℃ to approximately 748℃ and then stabilized. The initial DC current was 100A for the first hour, with an anode current density of approximately 0.415 A / cm³. 2 The DC current was then increased to 200A, with an anode current density of approximately 0.83A / cm². 2Anhydrous aluminum chloride powder was automatically added via a screw feeder 32, once every 5 minutes, at a rate of approximately 298g per hour. After electrolysis started, the initial voltage stabilized at around 3.45V, rising to 200A and then stabilizing at 4.06V. Subsequently, the voltage generally showed a trend of first decreasing (around 3.75V) and then gradually increasing (to 3.92V). Electrolysis lasted for 288 hours, at which point the DC power was disconnected to stop operation, and the anode was removed from the electrolyte melt, and the pit furnace heating was stopped. During this period, approximately 1.42kg of aluminum was manually removed once every 24 hours. After natural cooling, the crucible and electrodes were removed, yielding a total of 17200.8g of aluminum blocks, with an average current efficiency of 89% and an aluminum chloride consumption of 5.05kg / kg-Al. The cathode could not be removed because it was connected to the graphite block inside the crucible. The cermet anode was removed and ultrasonically washed. The anode showed no overall change, but a very thin film formed on its surface. XRD analysis showed that the main component was NiFe2O4, suggesting that the metallic chloride electrolyte was corroded. During the electrolysis process, anhydrous aluminum chloride, which is automatically fed by the feeder, is sampled, and the oxygen content is analyzed using an oxygen-nitrogen analyzer to be 2.08%.

[0107] Comparative Example 1 The preparation method is basically the same as that in Example 1, except that an electrolyte with an initial composition of 15% KCl - 35% LiCl - 1.5% MgCl2 - 1.5% CaCl2 - 7% AlCl3 - 40% NaCl is used.

[0108] During the electrolysis process, the electrolysis temperature was gradually increased from 698℃ to approximately 716℃ and then stabilized. The DC current was 100A, and the anode current density was approximately 1.5A / cm³. 2 Anhydrous aluminum chloride powder was manually added through funnel 13, with 65g of anhydrous aluminum chloride added every half hour. During electrolysis, the voltage remained relatively stable at around 3.912V for the first 2 hours. Afterward, the voltage repeatedly showed a slow but continuous increase. The voltage decreased slightly after the manual addition of anhydrous aluminum chloride powder, then gradually increased again. Around 6 hours, an anodic effect occurred, with the voltage rapidly rising to 30V, which recovered after restarting the DC power supply. Then, the amount of anhydrous aluminum chloride added every half hour was increased to 80g, and the voltage remained relatively stable at 4.165V. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised away from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 246g of aluminum blocks. The current efficiency was 73%, and the AlCl3 consumption was approximately 5.77kg / kg-Al (5.77kg of AlCl3 raw material is required to produce 1kg of metallic aluminum). The electrodes were ultrasonically washed with water. The hot-pressed TiB2 ceramic cathode remained intact, without expansion or cracking, and was encased in an aluminum shell. The high-purity graphite anode remained intact overall, with localized pitting corrosion.

[0109] Comparative Example 2 The preparation method is basically the same as that in Example 1, except that an electrolyte with an initial composition of 15% KCl - 35% LiCl - 0.5% MgCl2 - 2.5% CaCl2 - 7% AlCl3 - 40% NaCl is used.

[0110] During the electrolysis process, the electrolysis temperature was gradually increased from 705℃ to approximately 724℃ and then stabilized. The DC current was 100A, and the anode current density was approximately 1.5A / cm³. 2 Anhydrous aluminum chloride powder was manually added through funnel 13, with 65g added every half hour. During electrolysis, the voltage remained relatively stable at around 3.943V for the first 2 hours. Afterward, the voltage repeatedly showed a slow but continuous increase. The voltage decreased slightly after the manual addition of anhydrous aluminum chloride powder, then gradually increased again. Around 6 hours, an anodic effect occurred, with the voltage rapidly rising to 30V, which recovered after restarting the DC power supply. Then, the amount of anhydrous aluminum chloride added every half hour was increased to 80g, and the voltage remained relatively stable at 4.173V. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised away from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 258g of aluminum blocks. The current efficiency was 77%, and the AlCl3 consumption was approximately 5.50kg / kg-Al (5.50kg of AlCl3 raw material is required to produce 1kg of metallic aluminum). The electrodes were ultrasonically washed with water. The hot-pressed TiB2 ceramic cathode remained intact, without expansion or cracking, and was encased in an aluminum shell. The high-purity graphite anode remained intact overall, with localized pitting corrosion.

[0111] Comparative Example 3 The preparation method is basically the same as that in Example 1, except that an electrolyte with an initial composition of 15% KCl - 35% LiCl - 0.5% MgCl2 - 2% CaCl2 - 7% AlCl3 - 40.5% NaCl is used.

[0112] During the electrolysis process, the electrolysis temperature was gradually increased from 702℃ to approximately 722℃ and then stabilized. The DC current was 100A, and the anode current density was approximately 1.5A / cm³. 2Anhydrous aluminum chloride powder was manually added through funnel 13, with 65g of anhydrous aluminum chloride added every half hour. During electrolysis, the voltage remained relatively stable at around 3.932V for the first 2 hours. Afterward, the voltage repeatedly showed a slow but continuous increase. The voltage decreased slightly after the manual addition of anhydrous aluminum chloride powder, then gradually increased again. Around 6 hours, an anodic effect occurred, with the voltage rapidly rising to 30V, which recovered after restarting the DC power supply. Then, the amount of anhydrous aluminum chloride added every half hour was increased to 80g, and the voltage remained relatively stable at 4.158V. Electrolysis continued for 10 hours, then the DC power was disconnected to stop operation. The anode and cathode were raised away from the electrolyte melt, and the well-type furnace heating was stopped. After natural cooling, the crucible and electrodes were removed, yielding 262g of aluminum blocks. The current efficiency was 78%, and the AlCl3 consumption was approximately 5.42kg / kg-Al (5.42kg of AlCl3 raw material is required to produce 1kg of metallic aluminum). The electrodes were ultrasonically washed with water. The hot-pressed TiB2 ceramic cathode remained intact, without expansion or cracking, and was encased in an aluminum shell. The high-purity graphite anode remained intact overall, with localized pitting corrosion.

[0113] Table 2 lists the electrolysis conditions and operating results of Examples 1-6 and Comparative Examples 1-3 above.

[0114] Table 1

[0115] Table 2

[0116] The above experiments show that: (1) when the anode is a graphite anode, if the current density is 1.5 A / cm 2 or more than 1.5A / cm 2 If the voltage gradually increases and becomes unstable, an anode effect will occur; if the current density is 1.5 A / cm², the voltage will gradually increase and become unstable. 2 The voltage is generally stable, mainly due to the slight increase in voltage caused by anode consumption; (2) When the anode is a nickel ferrite metal ceramic anode, if the initial current density is 0.8A / cm 2 or more than 0.8A / cm 2 The voltage will gradually increase and become unstable; if the initial current density is less than 0.415 A / cm², the voltage will also gradually increase and become unstable. 2 Later, the current density was further increased to 0.6 A / cm. 2 or 0.8A / cm 2 The voltage remains stable; (3) The amount of volatilization is related to the initial crystallization temperature of the electrolyte and the electrolysis temperature. At the same electrolysis temperature, the lower the initial crystallization temperature, the greater the amount of volatilization, the more AlCl3 is consumed, and the lower the current efficiency. For example, Example 1 and Comparative Examples 1, 2, and 3.

[0117] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

[0118] Although preferred embodiments have been described in this specification, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this specification.

[0119] Obviously, those skilled in the art can make various modifications and variations to this specification without departing from its spirit and scope. Therefore, if such modifications and variations fall within the scope of the claims and their equivalents, this specification is also intended to include such modifications and variations.

Claims

1. A chloride molten salt electrolyte characterized in that, It includes the following components by weight percentage: KCl 10%~15%; LiCl 25%~35%; MgCl2 0.5%~1%; CaCl2 1%~2%; AlCl3 3%~7%; the balance is NaCl.

2. The chloride molten salt electrolyte according to claim 1, characterized in that, It includes KCl 10%~12%; LiCl 28%~32%; MgCl2 0.5%~0.7%; CaCl2 1.3%~1.7%; AlCl3 4%~6%; and NaCl 48%~53%.

3. The chloride molten salt electrolyte according to claim 1, characterized in that, The weight ratio of CaCl2 to MgCl2 is (2~3):

1.

4. The chloride molten salt electrolyte according to any one of claims 1 to 3, characterized in that, The primary crystallization temperature of the chloride molten salt electrolyte is 566℃~660℃; and / or, The conductivity of the chloride molten salt electrolyte at 700°C is 2.36 S-cm - 1 2.55 S-cm - 1 and / or, The kinematic viscosity of the chloride molten salt electrolyte at 700°C is less than 1.5 cm² / s.

5. A method for producing aluminum by low-temperature electrolysis, characterized in that, Includes the following steps: The chloride molten salt electrolyte according to any one of claims 1 to 4 is placed in an electrolytic cell and electrolyzed by passing direct current to obtain aluminum; wherein the temperature of the electrolysis reaction is 700℃ to 750℃.

6. The method for producing aluminum by low-temperature electrolysis according to claim 5, characterized in that, The electrolytic cell includes at least one cathode and at least one anode, wherein the anode and the cathode are arranged vertically in an alternating manner and spaced apart.

7. The method for producing aluminum by low-temperature electrolysis according to claim 6, characterized in that, The anode and the cathode are arranged at equal intervals, and / or, The distance between the anode and the cathode is 20 mm to 35 mm.

8. The method for producing aluminum by low-temperature electrolysis according to claim 6, characterized in that, The cathode of the electrolytic cell is a TiB2 ceramic cathode.

9. The method for producing aluminum by low-temperature electrolysis according to claim 8, characterized in that, The TiB2 ceramic cathode is made by sintering a green body comprising TiB2 powder, carbon powder and sintering aids; wherein the carbon content in the green body is ≤20%, the TiB2 content in the green body is ≥80%, the sintering aid content in the green body is 2-5%, and the content of Fe, Ni, Cu and Zr in the sintering aids is less than or equal to 0.01%.

10. The method for producing aluminum by low-temperature electrolysis according to any one of claims 5 to 9, characterized in that, The anode of the electrolytic cell is a metal-ceramic inert anode. During the initial 1 hour of the electrolytic reaction, the current density of the anode is less than or equal to 0.4 A / cm², and after 1 hour of the electrolytic reaction, the current density of the anode is less than or equal to 0.8 A / cm².

11. The method for producing aluminum by low-temperature electrolysis according to claim 10, characterized in that, The cermet inert anode is a nickel ferrite-based cermet anode, wherein the metal phase of the nickel ferrite-based cermet anode is at least one of nickel-copper alloy, elemental nickel, and elemental iron, and the content of the metal phase in the nickel ferrite-based cermet anode is ≤30%, and the content of elemental iron in the metal phase is ≤2%.

12. The method for producing aluminum by low-temperature electrolysis according to claim 10, characterized in that, Also includes: During the electrolysis reaction, anhydrous aluminum chloride is added to the chloride molten salt electrolyte, wherein the oxygen content of the anhydrous aluminum chloride is less than 2%.

13. The method for producing aluminum by low-temperature electrolysis according to any one of claims 5 to 9, characterized in that, The anode of the electrolytic cell is a graphite anode, and the anode current density is controlled below 1.5 A / cm².

14. The method for producing aluminum by low-temperature electrolysis according to claim 13, characterized in that, Also includes: During the electrolysis reaction, anhydrous aluminum chloride is added to the chloride molten salt electrolyte, wherein the oxygen content of the anhydrous aluminum chloride is less than 0.03%.

15. The method for producing aluminum by low-temperature electrolysis according to claim 13, characterized in that, The graphite anode is a replaceable anode, and the method further includes replacing the anode when the cell voltage rises to 8V.

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