Method for purifying solid aluminium electrolysis products
By using solid-state aluminum electrolysis, the density difference of the electrolyte is used to separate the molten aluminum and the electrolyte liquid, which solves the problems of high energy consumption, high pollution and low efficiency in the existing high-purity aluminum purification process, and realizes high-efficiency and low-cost high-purity aluminum production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHENGZHOU XUANHUA TECH CO LTD
- Filing Date
- 2022-06-20
- Publication Date
- 2026-07-24
AI Technical Summary
Existing high-purity aluminum purification processes suffer from high energy consumption, significant pollution, long processes, and low efficiency. In particular, the three-layer liquid electrolytic refining method and the segregation method are characterized by high energy consumption, environmental pollution, and low efficiency in the high-purity aluminum purification process.
The solid-state aluminum electrolysis method involves inserting aluminum electrode plates into a molten electrolyte for electrolysis, scraping off the aluminum cathode plate product and pressing it into a cake shape, covering it with powdered electrolyte, heating and melting it, separating the molten aluminum and electrolyte liquid by utilizing density differences, and then casting it into ingots after vacuum melting to obtain high-purity aluminum ingots.
It achieves efficient purification of high-purity aluminum, reduces oxidation loss, lowers production costs, and features a short, pollution-free process with recyclable and reusable electrolyte.
Smart Images
Figure CN117265597B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for purifying solid aluminum electrolysis products, belonging to the field of aluminum preparation technology. Background Technology
[0002] High-purity aluminum possesses superior electrical and thermal conductivity, ductility, reflectivity, corrosion resistance, and weaker magnetic permeability compared to primary aluminum. Components made from high-purity aluminum play a crucial role in low-temperature electromagnetic fields. As a material with both high technological content and added value, high-purity aluminum is also frequently used in high-tech research fields. For example, it is used in rolling aluminum foil for electrolytic capacitors and computer components. Furthermore, due to its excellent reflectivity, high-purity aluminum is also used in lighting materials. In the aerospace field, due to the special nature of the work, the requirements for materials are extremely high. Aerospace vehicles require metals or alloys with high strength, good toughness, and excellent fatigue resistance, all of which high-purity aluminum possesses.
[0003] Generally, aluminum with a purity (aluminum content) greater than 99.9% is called high-purity aluminum. Currently, there are two main high-purity aluminum refining processes: the three-layer electrolytic refining method and the segregation method. The three-layer electrolytic refining method uses fluorides with melting points higher than metallic aluminum as the electrolyte, purifying the aluminum in a liquid state. This method has advantages such as high output, high purity, and good quality; however, it consumes a lot of energy, requires significant investment per unit of production capacity, and involves high labor intensity for workers. Furthermore, because the electrolyte used is a fluoride, it is also quite environmentally harmful. The segregation method has higher purification efficiency, but the process is longer and the purification effect is poorer.
[0004] In view of this, it is indeed necessary to propose a purification method for solid aluminum electrolysis products to solve the above problems. Summary of the Invention
[0005] The purpose of this invention is to provide a method for purifying solid aluminum electrolysis products, which can improve the purity of aluminum.
[0006] To achieve the above objectives, the present invention provides a method for purifying solid aluminum electrolysis products, mainly comprising the following steps:
[0007] Step 1: Insert multiple aluminum electrode plates into the molten electrolyte to serve as at least one aluminum anode plate and at least one aluminum cathode plate, and electrolyze by passing direct current through them.
[0008] Step 2: Scrape off the product from the surface of the aluminum cathode plate, and press the scraped product to obtain a cake-shaped product.
[0009] Step 3: Place the cake-shaped product into the aluminum melting furnace and cover the top of the cake-shaped product with powdered electrolyte;
[0010] Step 4: Heat the cake-shaped product and the powdered electrolyte until they are completely melted to obtain an upper electrolyte liquid and a lower aluminum liquid.
[0011] Step 5: Scoop out the upper layer of electrolyte liquid, cool the lower layer of aluminum liquid, and then vacuum melt it. After the melting is completed, cast it into ingots to obtain high-purity aluminum ingots.
[0012] As a further improvement of the present invention, the molten electrolyte is formed by mixing and heating at least two electrolyte raw materials, wherein the electrolyte raw materials include AlCl3 and one or more of NaCl, KCl, LiCl, CaCl2 and MgCl2.
[0013] As a further improvement of the present invention, the mass percentage of AlCl3 in the electrolyte raw material is 55-85%.
[0014] As a further improvement of the present invention, the distance between the aluminum anode plate and the aluminum cathode plate is 3-8 cm.
[0015] As a further improvement of the present invention, the current density during electrolysis with direct current is 30-200 mA / cm². 2 .
[0016] As a further improvement of the present invention, in step 2, the product on the aluminum cathode plate is scraped off every 1-7 hours.
[0017] As a further improvement of the present invention, in step 2, the product scraped off the surface of the aluminum cathode plate is pressed under a pressure of 20-300 MPa. In step 3, the electrolyte is cooled and crushed to form powder. The particle size of the electrolyte is 50 μm-3 mm, and the thickness of the electrolyte covering the surface of the cake-shaped product is 2-30 mm.
[0018] As a further improvement of the present invention, in step 4, the temperature at which the cake-shaped product and the electrolyte are heated and melted is 660-900°C.
[0019] As a further improvement of the present invention, in step 5, the vacuum degree of the vacuum melting is 0.1-3 Pa and the temperature is 690-780℃.
[0020] The beneficial effects of this invention are: this invention can achieve complete separation of high-purity aluminum and electrolyte, and can obtain high-purity aluminum with higher purity. Since high-purity aluminum is easily oxidized during the smelting process, this invention utilizes the difference in density between the two melts to reduce the degree of oxidation of high-purity aluminum during the smelting process, thereby significantly increasing the yield of high-purity aluminum. At the same time, the process flow of this invention is short and pollution-free, and the electrolyte used in the preparation process can be recycled and reused in the electrolysis process, reducing the production cost of high-purity aluminum. Attached Figure Description
[0021] Figure 1 This is a schematic flowchart of the purification method for solid aluminum electrolysis products of the present invention. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0023] It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.
[0024] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0025] like Figure 1 As shown, this invention discloses a method for purifying solid aluminum electrolysis products, mainly targeting aluminum with a purity greater than 99.70%. This invention can obtain high-purity aluminum with even higher purity, and mainly includes the following steps:
[0026] Step 1: Insert multiple aluminum electrode plates into the molten electrolyte to serve as at least one aluminum anode plate and at least one aluminum cathode plate, and electrolyze by passing direct current through them.
[0027] Step 2: Scrape off the product from the surface of the aluminum cathode plate, and press the scraped product to obtain a cake-shaped product.
[0028] Step 3: Place the cake-shaped product into the aluminum melting furnace and cover the top of the cake-shaped product with powdered electrolyte;
[0029] Step 4: Heat the cake-shaped product and the powdered electrolyte until they are completely melted to obtain an upper electrolyte liquid and a lower aluminum liquid.
[0030] Step 5: Scoop out the upper layer of electrolyte liquid, cool the lower layer of aluminum liquid, and then vacuum melt it. After the melting is completed, cast it into ingots to obtain high-purity aluminum ingots.
[0031] Steps 1 through 5 will be described in detail below.
[0032] In step 1, two or more mixed electrolyte raw materials are added to the electrolytic cell and heated to melt at 120-600℃ to obtain a molten electrolyte. The electrolyte raw materials include AlCl3, NaCl, KCl, LiCl, CaCl2, and MgCl2. It should be noted that since AlCl3 must be present in the electrolyte raw materials to ensure the presence of aluminum ions, the mixed electrolyte raw materials include AlCl3 and one or more of NaCl, KCl, LiCl, CaCl2, and MgCl2. However, since AlCl3 sublimates when heated to 177℃, other chloride salts need to be added to ensure the stable presence of AlCl3 during high-temperature melting. Other chloride salts do not react chemically with AlCl3 and can adjust the melting point and vapor pressure of the mixed electrolyte raw materials to achieve electrolyte stability. Preferably, the mass percentage of AlCl3 in the mixed electrolyte raw material is 1-95%, and the mass percentage of other chloride salts is 5-99%. More preferably, the mass percentage of AlCl3 in the mixed electrolyte raw material is 55-85%, and the mass percentage of other chloride salts is 15-45%.
[0033] During electrolysis, current flows from a DC power source through the aluminum anode plate, across the molten electrolyte, into the aluminum cathode plate, and finally back to the DC power source, forming a circuit. Electrochemical reactions occur in the molten electrolyte between the two aluminum electrode plates. The distance between the aluminum anode and cathode plates is 1-20 cm, preferably 3-8 cm. Reducing the distance between the electrodes improves current efficiency. The DC current density at the anode is 10-700 mA / cm². 2 Preferably 30-200 mA / cm 2 Therefore, by reducing the current, the purity of the cathode aluminum product can be improved.
[0034] It should be noted that multiple electrode groups can coexist in the electrolytic cell and react simultaneously. An aluminum anode plate and an aluminum cathode plate can be paired to form an electrode group. Multiple electrode groups are arranged in a straight line in the electrolytic cell, and the spacing between connected electrode groups is 3-8 cm. The specific setting can be made as needed and is not limited here.
[0035] In addition, the aluminum electrode plate is obtained by processing aluminum plates with a content of more than 99.70%.
[0036] In step 2, the product scraped from the surface of the aluminum cathode plate is pressed under a pressure of 20-300 MPa. The resulting cake-shaped product can greatly reduce the surface area in contact with the outside world, thereby effectively reducing the degree of oxidation of the metal during the smelting process in subsequent steps.
[0037] In step 3, the cake-shaped product is a mixture of aluminum and electrolyte, with a high proportion of aluminum and a low proportion of electrolyte. During the smelting process, the electrolyte in the cake-shaped product is insufficient to effectively protect the aluminum, resulting in significant aluminum burn-off and oxidation. To avoid aluminum loss, a certain amount of electrolyte needs to be added to isolate it from air and prevent aluminum oxidation and burn-off. It should be noted that the electrolyte obtained in step 1 can be used here. After cooling, the electrolyte is broken down into powder with a particle size of 50μm-3mm. It is important to note that the particle size of the powdered electrolyte should not exceed 3mm to ensure sufficient and interconnected pores, preventing aluminum burn-off during smelting. Since the volume of the electrolyte solution formed after melting will significantly decrease, to prevent aluminum oxidation, the thickness of the powdered electrolyte covering the surface of the cake-shaped product needs to be 2-30mm. If the thickness is less than 2mm, the electrolyte solution formed after melting will be too thin to completely cover the remaining metal in the cake-shaped product.
[0038] In step 4, the heating and melting temperature of the cake-shaped product and the electrolyte is 660-900℃. It should be noted that the electrolyte melts at a temperature below 660℃, while aluminum begins to melt above 660℃. Due to the lower melting temperature of the electrolyte, the electrolyte melts first, forming a liquid protective layer on the surface of the remaining metal in the cake-shaped product, which reduces the oxidation loss of aluminum during the smelting process. As the temperature rises, the cake-shaped product also begins to melt. Due to the density difference—the aluminum liquid has a higher density than the electrolyte liquid—the aluminum liquid and the electrolyte liquid gradually separate during the melting process, with the aluminum liquid at the bottom and the electrolyte liquid at the top, achieving effective separation.
[0039] In step 5, the upper electrolyte solution can be recycled after being scooped out. The vacuum degree of vacuum melting is 0.1-10 Pa, and the temperature is 660-900℃. The vacuum degree is preferably 0.1-3 Pa, and the temperature is preferably 690-780℃. In this way, the vacuum conditions can be used to further remove residual impurities such as sodium and chlorine from the aluminum. Finally, the aluminum content of the high-purity aluminum ingot obtained by casting can reach 99.995%.
[0040] The following is a detailed description with reference to specific examples.
[0041] Example 1 specifically includes the following steps:
[0042] After electrolyzing the aluminum anode plate and aluminum cathode plate, the aluminum cathode plate is removed, the product on the surface of the aluminum cathode plate is scraped into a container, and pressed on an 80 MPa press to obtain a cake-shaped product.
[0043] The obtained cake-shaped product is placed in an aluminum melting furnace, and a 1 cm thick layer of powdered electrolyte is added to the top. The mixture is heated to 210°C. Since the electrolyte has a low melting point, it begins to melt at around 210°C. After melting, it coats the surface of the remaining metal in the cake-shaped product. The mixture is then heated to 720°C to completely melt the metal. The resulting liquid has an electrolyte liquid on the top and a metal liquid layer on the bottom.
[0044] The upper layer of electrolyte solution is scooped out, and the bottom molten metal is cooled and then vacuum-melted at a vacuum degree of 0.1 Pa and a temperature of 690 °C to remove residual sodium, chlorine and other impurities. After the melting is completed, the metal is cast into ingots to obtain high-purity aluminum ingots.
[0045] Example 2 specifically includes the following steps:
[0046] After electrolyzing the aluminum anode plate and aluminum cathode plate, the aluminum cathode plate is removed, the product on the surface of the aluminum cathode plate is scraped into a container, and pressed on a 120 MPa press to obtain a cake-shaped product.
[0047] The obtained cake-shaped product is placed in an aluminum melting furnace, and a 2cm thick layer of powdered electrolyte is added on top. The mixture is heated to 300°C. Since the electrolyte has a low melting point, it begins to melt at around 300°C. After melting, it coats the surface of the remaining metal in the cake-shaped product. The mixture is then heated to 750°C to completely melt the metal. The resulting liquid has an electrolyte liquid on top and a metal liquid layer on the bottom.
[0048] The upper layer of electrolyte solution is scooped out, and the bottom molten metal is cooled and then vacuum-melted at a vacuum degree of 0.5 Pa and a temperature of 720 °C to remove residual sodium, chlorine and other impurities. After the melting is completed, ingots are cast to obtain high-purity aluminum ingots.
[0049] Example 3 specifically includes the following steps:
[0050] After electrolyzing the aluminum anode plate and aluminum cathode plate, the aluminum cathode plate is removed, the product on the surface of the aluminum cathode plate is scraped into a container, and pressed on a 20 MPa press to obtain a cake-shaped product.
[0051] The obtained cake-shaped product is placed in an aluminum melting furnace, and a 3cm thick layer of powdered electrolyte is added on top. The mixture is heated to 250°C. Since the electrolyte has a low melting point, it begins to melt at around 250°C. After melting, it coats the surface of the remaining metal in the cake-shaped product. The mixture is then heated to 750°C to completely melt the metal. The resulting liquid has an electrolyte liquid on top and a metal liquid layer on the bottom.
[0052] The upper layer of electrolyte solution is scooped out, and the bottom molten metal is cooled and then vacuum-melted at a vacuum degree of 1 Pa and a temperature of 700 °C to remove residual impurities such as sodium and chlorine. After the melting is completed, the metal is cast into ingots to obtain high-purity aluminum ingots.
[0053] Example 4 specifically includes the following steps:
[0054] After electrolyzing the aluminum anode plate and aluminum cathode plate, the aluminum cathode plate is removed, the product on the surface of the aluminum cathode plate is scraped into a container, and pressed on a 300 MPa press to obtain a cake-shaped product.
[0055] The obtained cake-shaped product is placed in an aluminum melting furnace, and a 3cm thick layer of powdered electrolyte is added on top. The mixture is heated to 300°C. Since the electrolyte has a low melting point, it begins to melt at around 300°C. After melting, it coats the surface of the remaining metal in the cake-shaped product. The mixture is then heated to 900°C to completely melt the metal. The resulting liquid has an electrolyte liquid on top and a metal liquid layer on the bottom.
[0056] The upper layer of electrolyte solution is scooped out, and the bottom molten metal is cooled and then vacuum-melted at a vacuum degree of 10 Pa and a temperature of 900 °C to remove residual impurities such as sodium and chlorine. After the melting is completed, ingots are cast to obtain high-purity aluminum ingots.
[0057] In summary, this invention enables complete separation of high-purity aluminum and electrolyte, resulting in higher purity aluminum. Since high-purity aluminum is highly susceptible to oxidation during smelting, this invention utilizes the density difference between the two melts to reduce the degree of oxidation during smelting, thereby significantly increasing the yield of high-purity aluminum. Furthermore, this invention features a short and pollution-free process, and the electrolyte used in the preparation process can be recycled and reused during electrolysis, reducing the production cost of high-purity aluminum.
[0058] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims
1. A method for purifying solid aluminum electrolysis products, characterized in that: The main steps include: Step 1: Insert multiple aluminum electrode plates into the molten electrolyte to serve as at least one aluminum anode plate and at least one aluminum cathode plate, and electrolyze by passing direct current through them. Step 2: Scrape off the product from the surface of the aluminum cathode plate, and press the scraped product to obtain a cake-shaped product. Step 3: Place the cake-shaped product into the aluminum melting furnace and cover the top of the cake-shaped product with powdered electrolyte; Step 4: Heat the cake-shaped product and the powdered electrolyte until they are completely melted to obtain an upper electrolyte liquid and a lower aluminum liquid. Step 5: Scoop out the upper layer of electrolyte liquid, cool the lower layer of aluminum liquid, and then vacuum melt it. After the melting is completed, cast it into ingots to obtain high-purity aluminum ingots.
2. The purification method for solid aluminum electrolysis products according to claim 1, characterized in that: The molten electrolyte is formed by heating and melting a mixture of at least two electrolyte raw materials, including AlCl3 and one or more of NaCl, KCl, LiCl, CaCl2 and MgCl2.
3. The purification method for solid aluminum electrolysis products according to claim 2, characterized in that: The mass percentage of AlCl3 in the electrolyte raw material is 55-85%.
4. The purification method for solid aluminum electrolysis products according to claim 1, characterized in that: The distance between the aluminum anode plate and the aluminum cathode plate is 3-8 cm.
5. The method for purifying solid aluminum electrolysis products according to claim 1, characterized in that: The current density during electrolysis with direct current is 30-200 mA / cm². 2 .
6. The method for purifying solid aluminum electrolysis products according to claim 1, characterized in that: In step 2, the product on the aluminum cathode plate is scraped off every 1-7 hours.
7. The method for purifying solid aluminum electrolysis products according to claim 1, characterized in that: In step 2, the product scraped off the surface of the aluminum cathode plate is pressed under a pressure of 20-300 MPa. In step 3, the electrolyte is cooled and crushed to form powder. The particle size of the electrolyte is 50 μm-3 mm, and the thickness of the electrolyte covering the surface of the cake-shaped product is 2-30 mm.
8. The method for purifying solid aluminum electrolysis products according to claim 1, characterized in that: In step 4, the temperature at which the cake-like product and the electrolyte are heated and melted is 660-900℃.
9. The method for purifying solid aluminum electrolysis products according to claim 1, characterized in that: In step 5, the vacuum degree of the vacuum melting is 0.1-3 Pa and the temperature is 690-780℃.