A method for three-layer liquid refining of high purity aluminum

Abstract

The present application relates to non-ferrous metal technical field, especially to a kind of three-layer liquid refining high-purity aluminum method, comprising: using anion as fluoride ion and containing sodium ion, potassium ion, containing aluminum ion perfluorinated electrolyte molten salt;The quantity of sodium ion in perfluorinated electrolyte molten salt is controlled ≤ the quantity of aluminum ion, and the content of potassium ion obtains the best conductivity and current efficiency.This application introduces potassium ion in perfluorinated electrolyte molten salt, and by controlling the quantity of sodium ion in perfluorinated electrolyte molten salt ≤ the quantity of aluminum ion, and the content of potassium ion, obtains higher conductivity and current efficiency, overcomes the defects of low conductivity and high energy consumption in prior art.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting industry technology, and in particular to a method for refining high-purity aluminum using a three-layer liquid process. Background Technology

[0002] Three-layer electrolytic aluminum refining can be divided into fluorinated / chlorinated systems and perfluorinated systems based on electrolyte composition. The fluorinated / chlorinated system (BaCl2-NaCl-NaF-AlF3) has good conductivity, a low melting point, and low density, and is widely used in aluminum electrolytic refining in my country. However, BaCl2 and NaCl in this system are prone to hydrolysis, requiring drying before use. Furthermore, the HCl and HF in the products are highly corrosive to equipment, and the system also produces accumulated BaClF precipitate, which is extremely detrimental to continuous production. The perfluorinated system, on the other hand, does not contain chlorine, effectively avoiding the inherent problems of fluorinated / chlorinated systems such as BaClF formation. However, it suffers from low conductivity, high energy consumption, and low aluminum yield, making its widespread application difficult. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a method for refining high-purity aluminum using a three-layer liquid process, which solves at least one of the problems existing in the prior art, such as high corrosiveness to equipment, difficulty in continuous production, low electrical conductivity, high energy consumption, and low aluminum yield.

[0004] The objective of this invention is mainly achieved through the following technical solutions:

[0005] A method for refining high-purity aluminum using a three-layer liquid process includes:

[0006] The molten salt of perfluorinated electrolyte is used, and the anions are fluoride ions, sodium ions, potassium ions, and aluminum ions.

[0007] To achieve optimal conductivity and current efficiency, the amount of sodium ions in the perfluorinated electrolyte molten salt should be controlled to be less than or equal to the amount of aluminum ions, and the potassium ion content should also be controlled.

[0008] Preferably, the potassium ions are added to the perfluorinated electrolyte molten salt in the form of KF, and the weight percentage of KF in the perfluorinated electrolyte molten salt is 1% to 10%.

[0009] Preferably, the molar ratio of sodium ions to aluminum ions satisfies: 0.55 to 1.0.

[0010] Preferably, the cations in the perfluorinated electrolyte molten salt also include Ba. 2+ Ca 2+ and Li + .

[0011] Preferably, the mass percentage composition of the raw materials for the perfluorinated electrolyte molten salt satisfies the following:

[0012] 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, with the remainder being NaF and AlF3.

[0013] Preferably, the K in the perfluorinated electrolyte molten salt + It is added in the form of KF, wherein the KF meets the following requirements: purity > 98.5%, loss on ignition < 1%, total oxides < 0.2%, and total other impurities < 0.3%.

[0014] Preferably, the anode is a copper-aluminum alloy with a copper content of 35%-75% and the remainder being aluminum; the cathode is an aluminum rod with a purity of 99.99%-99.999%.

[0015] Preferably, the electrolyte molten salt level between the anode and cathode is 4.0 cm to 10 cm.

[0016] A perfluorinated electrolyte molten salt for refining high-purity aluminum using a three-layer liquid process, used in the aforementioned three-layer liquid refining method for high-purity aluminum, is prepared from the following raw materials in the indicated mass percentages:

[0017] 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.55–1.0.

[0018] A high-purity elemental aluminum is prepared by the above method, with an aluminum purity ≥ 99.95%.

[0019] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0020] (1) This invention achieves higher conductivity and current efficiency by introducing potassium ions into the perfluorinated electrolyte molten salt and controlling the amount of sodium ions in the perfluorinated electrolyte molten salt to be less than or equal to the amount of aluminum ions and the content of potassium ions, thus overcoming the shortcomings of low conductivity and high energy consumption in the prior art; the purity of high-purity aluminum is ≥99.95%, and the current efficiency is ≥78%; the primary crystallization temperature is 650℃~750℃, and the density is 2.6g / cm³. 3 ~2.9g / cm 3 Its electrical conductivity is 1.1 S / cm to 1.5 S / cm.

[0021] (2) By controlling the ratio of sodium ions and aluminum ions in the perfluorinated electrolyte molten salt, the present invention achieves the initial crystallization temperature of the perfluorinated electrolyte molten salt at 750°C, preferably below 740°C, thereby reducing energy consumption and cost.

[0022] (3) This invention uses a perfluorinated electrolyte molten salt that does not contain chlorine, overcoming the limitations of the Ba electrolyte process. 2+ With F - Cl- The formation of BaClF precipitate leads to a decrease in electrode conductivity, resulting in a defect that prevents continuous production.

[0023] Other features and advantages of the invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained from the embodiments described and the accompanying drawings. Attached Figure Description

[0024] Figure 1a A schematic diagram of the electrode and electrolytic molten salt setup for three-layer aluminum refining;

[0025] Figure 1b A schematic diagram of the electrode and electrolytic molten salt setup for aluminum ore smelting;

[0026] Figure 2 This is a graph showing the primary crystallization temperature in Example 1;

[0027] Figure 3 This is a graph showing the primary crystallization temperature in Example 2;

[0028] Figure 4 This is a graph showing the primary crystallization temperature in Example 3;

[0029] Figure 5 This is a graph showing the primary crystallization temperature in Example 4;

[0030] Figure 6 This is a graph showing the primary crystallization temperature in Example 5;

[0031] Figure 7 The primary crystallization temperature test diagram is shown in Comparative Example 1;

[0032] Figure 8 The primary crystallization temperature test results are shown in Comparative Example 2.

[0033] Figure 9 The image shows the primary crystallization temperature test results in Comparative Example 3.

[0034] Figure label:

[0035] Cathode 01a; Anode 01b; Finished aluminum product 02; Electrolyte molten salt 03. Detailed Implementation

[0036] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the present invention.

[0037] It should be noted that although both three-layer liquid aluminum refining and aluminum ore smelting can use molten salt as an electrolyte to electrolyze and produce elemental aluminum, the two processes are completely different:

[0038] 1. Electrode setup: such as Figure 1a As shown, the three-layer aluminum refining process uses an electrode arrangement from bottom to top: anode 01b, electrolyte molten salt 03, and cathode 01a. The finished aluminum product 02 is located between the electrolyte molten salt 03 and the cathode 01a. In the three-layer solution, the alloy acts as the anode at the bottom, the electrolyte molten salt is in the middle, and the space above allows for aluminum deposition. After energizing, the current flows from the anode busbar through the anode aluminum rod to the bottom carbon block, through the anode alloy and electrolyte, and finally out through the cathode aluminum liquid. Figure 1b As shown, aluminum ore smelting employs a bottom-to-top electrode arrangement of cathode 01a, molten electrolyte 03, and anode 01b. The finished aluminum product 02 is positioned between molten electrolyte 03 and cathode 01a. In aluminum ore smelting, the electrolyte is injected into the electrolytic cell, and carbon anodes and cathodes are inserted for electrolysis. The alumina in the raw material is decomposed into aluminum ions and oxygen ions. The aluminum ions are reduced to metallic aluminum at the cathode and deposited at the bottom of the electrolytic cell.

[0039] 2. Different sources of aluminum: The aluminum in aluminum ore smelting comes from the added aluminum ore; the aluminum in three-layer liquid refining comes from the anode aluminum;

[0040] 3. Different reaction processes:

[0041] Aluminum ore smelting reaction process:

[0042] Cathode: Al³⁺ + 3e⁻ = Al;

[0043] Anode C+2O 2- ==CO2 + 4e - .

[0044] Three-layer liquid aluminum refining reaction process:

[0045] Cathode: Al³⁺ + 3e⁻ = Al;

[0046] Anode Al-3e-==Al3+.

[0047] 4. The product separation processes are different:

[0048] The density of Al, a product of aluminum ore smelting, is greater than that of the electrolyte molten salt, and it sinks to the bottom of the electrolyte molten salt.

[0049] The density of the aluminum product Al produced by the three-layer liquid refining process is less than that of the electrolyte molten salt, so it floats to the bottom of the electrolyte molten salt surface.

[0050] As can be seen from the above, there are significant differences in the two types of raw materials, reacting ions, and reaction processes. The composition of the electrolyte molten salt in aluminum ore smelting products is quite different from that in three-layer liquid refining of aluminum. They belong to two independent technical fields. The composition of the electrolyte molten salt in the two systems is quite different, and the adjustment of their composition is unpredictable in their respective systems, making it difficult to learn from each other.

[0051] On one hand, this invention discloses a method for refining high-purity aluminum using a three-layer liquid process, comprising:

[0052] The molten salt of perfluorinated electrolyte is used, and the anions are fluoride ions, sodium ions, potassium ions, and aluminum ions.

[0053] To achieve optimal conductivity and current efficiency, the amount of sodium ions in the perfluorinated electrolyte molten salt should be controlled to be less than or equal to the amount of aluminum ions, and the potassium ion content should also be controlled.

[0054] It should be noted that perfluorinated electrolyte molten salts can be obtained by mixing metal salts of fluorine. The electrolyte solution is obtained by ionizing the cations and anions in the molten salt at high temperature. The anions in the perfluorinated electrolyte molten salt include F. - And complex anions formed by fluorine and metal ions.

[0055] It should be noted that the applicant's research found that the addition of potassium ions to the perfluorinated electrolyte molten salt helps to improve the conductivity of the perfluorinated electrolyte molten salt and the current efficiency of electrolytic aluminum. However, neither too high nor too low potassium ion content can achieve better conductivity and current efficiency than perfluorinated electrolyte molten salt without potassium ions.

[0056] The applicant's further research revealed that when the number of sodium ions in the perfluorinated electrolyte molten salt is less than or equal to the number of aluminum ions, it is beneficial for the perfluorinated electrolyte molten salt containing potassium ions to obtain better conductivity and current efficiency.

[0057] Compared with the prior art, the present invention achieves higher conductivity and current efficiency by introducing potassium ions into the perfluorinated electrolyte molten salt and by controlling the amount of sodium ions in the perfluorinated electrolyte molten salt to be less than or equal to the amount of aluminum ions and the content of potassium ions, thus overcoming the defects of low conductivity and high energy consumption in the prior art.

[0058] Specifically, potassium ions are added to the perfluorinated electrolyte molten salt in the form of KF, and the weight percentage of KF in the perfluorinated electrolyte molten salt is: 1% to 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0059] Preferably, the molar ratio of sodium ions to aluminum ions satisfies: 0.55 to 1.0, such as 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.88, 0.90, 0.95 or 1.0.

[0060] It should be noted that the ratio of sodium ions to aluminum ions also affects the primary crystallization temperature. An excessively high primary crystallization temperature will result in excessively high electrolysis temperatures, increasing energy consumption and costs. A molar ratio of sodium ions to aluminum ions between 0.55 and 1.0 helps to control the primary crystallization temperature below 750℃.

[0061] Compared with existing technologies, this invention controls the primary crystallization temperature of perfluorinated electrolyte molten salt to within 750°C by controlling the ratio of sodium ions and aluminum ions in the perfluorinated electrolyte molten salt, thereby reducing energy consumption and cost.

[0062] Preferably, the cations in the perfluorinated electrolyte molten salt also include Ba. 2+ Ca 2+ and Li + .

[0063] It should be noted that Ca 2+ It helps to form the furnace sides, while Ba 2+ Ca 2+ It is also an important density regulator, adjusting the density of the perfluorinated electrolyte molten salt to be greater than that of elemental aluminum, thereby achieving the separation of aluminum from the electrolyte molten salt; Li + On the one hand, it helps aluminum ions and fluoride ions form copolymer complexes; on the other hand, Li + These are small-radius, highly mobile ions that experience minimal resistance during movement and can move rapidly in molten salt systems. Their addition improves the fluidity and ionic conductivity of ions in the system, enhances the conductivity and current efficiency of perfluorinated electrolyte molten salts, and lowers the primary crystallization temperature.

[0064] It should be further explained that the furnace lining is a ring of solid electrolyte blocks formed by the molten electrolyte solidifying along the inner wall of the tank. This ring, continuously varying in thickness, constitutes the tank space within which the electrochemical and physicochemical reactions of aluminum electrolysis take place, realizing the electrolysis process. The furnace lining is an excellent heat and electrical insulation material. A well-shaped furnace allows for high and concentrated current density, smooth flow of electrolyte and molten aluminum, and easy gas removal, all of which contribute to achieving high current efficiency.

[0065] In one specific embodiment, the mass percentages of the raw materials used to prepare the perfluorinated electrolyte molten salt satisfy the following:

[0066] 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, with the remainder made up by NaF and AlF3 in a molar ratio of 0.55–1.0.

[0067] The applicant's research found that the addition of potassium ions helps improve the conductivity of perfluorinated electrolyte molten salts and the current efficiency of aluminum electrolysis; however, excessively high or low potassium ion content does not result in better conductivity and current efficiency compared to perfluorinated electrolyte molten salts without potassium ions. The molar ratio of sodium ions to aluminum ions has a significant impact; a ratio of 0.55 to 1.0 helps control the primary crystallization temperature below 750℃. The ratio of sodium ions to aluminum ions also affects the primary crystallization temperature; excessively high primary crystallization temperatures lead to excessively high electrolysis temperatures, increasing energy consumption and costs. The addition of lithium fluoride can lower the primary crystallization temperature and improve conductivity.

[0068] Calcium fluoride is used to form the furnace lining; barium fluoride is a weighting agent used to adjust the density of the molten salt.

[0069] Specifically, the mass ratio of BaF2 can be 16%, 17%, 18%, 19%, 20%, 21%, or 22%.

[0070] The mass ratio of LiF can be 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%;

[0071] The mass ratio of KF can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%;

[0072] The molar ratio of NaF to AlF3 can be 0.55, 0.58, 0.60, 0.68, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.95, or 1.0.

[0073] Preferably, the mass ratio of BaF2 can be 16%-20%.

[0074] The mass ratio of LiF can be 2%-6%.

[0075] The mass ratio of KF can be 2%-5%.

[0076] Compared with existing technologies, this invention uses a perfluorinated electrolyte molten salt that does not contain chlorine, overcoming the problems of Ba in the electrolysis process. 2+ With F - Cl - The formation of BaClF precipitate leads to a decrease in electrode conductivity, resulting in defects that prevent continuous production.

[0077] Preferably, the molar ratio of NaF to AlF3 is 0.75-1.0.

[0078] Specifically, the K of perfluorinated electrolyte molten salts + It can be added in the form of KF, and the KF specifications must meet the following requirements: KF purity > 98.5%, loss on ignition < 1%, total oxides < 0.2%, and total other impurities < 0.3%.

[0079] Preferably, the current density during electrolysis is 0.3 A / cm². 2 ~0.9A / cm 2 The electrode distance is 1cm to 5cm, and the electrolyte molten salt level between the anode and cathode is 4.0cm to 10cm.

[0080] Electrolyte levels are related to electrolyte conductivity. If the electrolyte level is too low, the total amount of charge in the electrolyte is insufficient, reducing conductivity and current efficiency. If the electrolyte level is too high, the resistance between the two electrodes increases, which also reduces conductivity and current efficiency. Electrolyte levels within the above range are sufficient to ensure normal experiments in exploring current efficiency under different electrode spacings.

[0081] On the other hand, this invention discloses a three-layer liquid refining perfluorinated electrolyte molten salt for high-purity aluminum, prepared from the following raw materials by mass percentage:

[0082] 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, with the remainder being NaF and AlF3.

[0083] Preferably, the molar ratio of NaF to AlF3 is 0.55 to 1.0.

[0084] Specifically, perfluorinated electrolyte molten salts can be prepared by uniformly mixing the above raw materials in a molten state.

[0085] Specifically, the primary crystallization temperature of the perfluorinated electrolyte molten salt is 650℃~750℃, and its density is 2.6g / cm³. 3 ~2.9g / cm 3 Its electrical conductivity is 0.5 S / cm to 1.5 S / cm.

[0086] Thirdly, the present invention also discloses a high-purity aluminum element prepared by the above method, with a purity ≥99.95%.

[0087] Fourthly, the present invention also discloses a method for measuring the primary crystallization temperature of an electrolyte molten salt, the step-cooling curve method, which utilizes the release or absorption of latent heat and the abrupt change in heat capacity during phase transformation of metals and alloys during heating and cooling to obtain the phase transformation temperature in the metal or alloy. The method includes:

[0088] S1: Place the electrolyte in a crucible inside the sealed chamber of the physical property determination furnace, heat it up, and accurately measure the sample temperature inside the crucible using a thermocouple;

[0089] S2: Heat the electrolyte molten salt to a completely molten state, stir evenly to preheat it thoroughly inside and out;

[0090] S3: Maintain sufficient temperature, for example, for 60 minutes, to ensure uniform temperature inside and outside the electrolyte molten salt, and cool slowly, for example, at a rate of 1℃ / min, to obtain a curve of temperature change over time.

[0091] S4: The temperature of the inflection point or plateau in the curve is the initial crystallization temperature of the electrolyte.

[0092] To further illustrate the technical solution of the present invention, the following embodiments and comparative examples are provided:

[0093] Example 1

[0094] This embodiment discloses a perfluorinated electrolyte molten salt with the following mass composition ratio: 20% BaF2, 16% CaF2, 2% LiF, 2% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.65.

[0095] Using the method described above, with a horizontal molten salt electrolyte at a depth of 8 cm and a cooling rate of 1 °C / min, the initial crystallization temperature of the perfluorinated electrolyte molten salt was measured to be 688 °C. (Specific details are as follows...) Figure 2 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing technical methods, is 2.756 g / cm³. 3 The electrical conductivity is 1.1 S / cm.

[0096] This embodiment discloses a three-layer liquid refining method for high-purity aluminum, which is used to prepare high-purity aluminum and uses the perfluorinated electrolyte molten salt of this embodiment.

[0097] The anode is made of a copper-aluminum alloy with a copper content of 42% and an aluminum content of 58%.

[0098] The cathode uses an aluminum rod with a purity of 99.99%. During electrolysis, the anode alloy is placed at the bottom, and the electrolyte molten salt between the anode and cathode is at a level of 8 cm.

[0099] At an electrolysis temperature of 780℃ and a current density of 0.45 A / cm² 2 Prepared with a polar distance parameter of 3.5 cm.

[0100] The purity of high-purity aluminum prepared using the above method is 99.97%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 78%.

[0101] Example 2

[0102] This embodiment discloses a perfluorinated electrolyte molten salt with the following mass composition ratio: 20% BaF2, 16% CaF2, 3% LiF, 3% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.75.

[0103] Using the method described above, with a horizontal molten salt electrolyte at a depth of 10 cm and a cooling rate of 1 °C / min, the initial crystallization temperature of the perfluorinated electrolyte molten salt was measured to be 653 °C. (Specific details are as follows...) Figure 3 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing technical methods, is 2.7 g / cm³. 3 The electrical conductivity is 1.15 S / cm.

[0104] This embodiment discloses a three-layer liquid refining method for high-purity aluminum, which is used to prepare high-purity aluminum and uses the perfluorinated electrolyte molten salt of this embodiment.

[0105] The anode is made of a copper-aluminum alloy with a copper content of 35% and an aluminum content of 65%.

[0106] The cathode uses an aluminum rod with a purity of 99.995% and an electrode spacing of 5cm. During electrolysis, the anode alloy is placed at the bottom, and the electrolyte molten salt between the anode and cathode is 10cm horizontally.

[0107] At an electrolysis temperature of 780℃ and a current density of 0.5 A / cm² 2 Prepared below.

[0108] The purity of high-purity aluminum prepared using the above method is 99.98%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 80%.

[0109] Example 3

[0110] This embodiment discloses a perfluorinated electrolyte molten salt with the following mass composition ratio: 16% BaF2, 18% CaF2, 4% LiF, 4% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.85.

[0111] Using the method described above, with a horizontal molten salt electrolyte at a depth of 8 cm and a cooling rate of 1 °C / min, the initial crystallization temperature of the perfluorinated electrolyte molten salt was measured to be 673 °C. (Specific details are as follows...) Figure 4 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing methods, is 2.52 g / cm³. 3 The electrical conductivity is 1.2 S / cm.

[0112] This embodiment discloses a three-layer liquid refining method for high-purity aluminum, which is used to prepare high-purity aluminum and uses the perfluorinated electrolyte molten salt of this embodiment.

[0113] The anode is made of a copper-aluminum alloy with a copper content of 75% and an aluminum content of 25%.

[0114] The cathode uses an aluminum rod with a purity of 99.998% and an electrode spacing of 3cm. During electrolysis, the anode alloy is placed at the bottom, and the electrolyte molten salt between the anode and cathode is at a horizontal level of 8cm.

[0115] At an electrolysis temperature of 750℃ and a current density of 0.55 A / cm²2 Prepared below.

[0116] The high-purity aluminum prepared using the above method has a purity of 99.99% and a current efficiency (the ratio of actual aluminum production to theoretical aluminum production) of 84%.

[0117] Example 4

[0118] This embodiment discloses a perfluorinated electrolyte molten salt with the following mass composition ratio: 18% BaF2, 18% CaF2, 5% LiF, 2% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.9.

[0119] Using the method described above, with a horizontal molten salt electrolyte at a depth of 8 cm and a cooling rate of 1 °C / min, the initial crystallization temperature of the perfluorinated electrolyte molten salt was measured to be 696 °C. (Specific details are as follows...) Figure 5 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing methods, is 2.64 g / cm³. 3 The electrical conductivity is 1.25 S / cm.

[0120] This embodiment discloses a three-layer liquid refining method for high-purity aluminum, which is used to prepare high-purity aluminum and uses the perfluorinated electrolyte molten salt of this embodiment.

[0121] The anode is made of a copper-aluminum alloy with a copper content of 46% and an aluminum content of 54%.

[0122] During electrolysis, an aluminum rod with a purity of 99.992% was used as the cathode, and the molten salt level of the electrolyte between the anode and cathode was 8 cm; the electrolysis temperature was 780℃, and the current density was 0.35 A / cm². 2 Prepared with a polar distance parameter of 3.5 cm.

[0123] The purity of high-purity aluminum prepared using the above method is 99.96%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 83%.

[0124] Example 5

[0125] This embodiment discloses a perfluorinated electrolyte molten salt with the following mass composition ratio: 20% BaF2, 16% CaF2, 6% LiF, 2% KF, and the remainder being NaF and AlF3 in a molar ratio of 1.

[0126] Using the method described above, with a horizontal molten salt electrolyte at a depth of 8 cm and a cooling rate of 1 °C / min, the initial crystallization temperature of the perfluorinated electrolyte molten salt was measured to be 717 °C. (Specific details are as follows...) Figure 6 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing technical methods, is 2.62 g / cm³. 3 The electrical conductivity is 1.32 S / cm.

[0127] This embodiment discloses a three-layer liquid refining method for high-purity aluminum, which is used to prepare high-purity aluminum and uses the perfluorinated electrolyte molten salt of this embodiment.

[0128] The anode is made of a copper-aluminum alloy with a copper content of 41% and an aluminum content of 59%.

[0129] During electrolysis, an aluminum rod with a purity of 99.993% was used as the cathode, and the molten salt level of the electrolyte between the anode and cathode was 8 cm; the electrolysis temperature was 770℃, and the current density was 0.35 A / cm². 2 Prepared with a polar distance parameter of 5 cm.

[0130] The purity of high-purity aluminum prepared using the above method is 99.95%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 90%.

[0131] Comparative Example 1

[0132] This comparative example uses the same method as Example 1 to prepare high-purity aluminum, except that KF is not added to the electrolyte molten salt, and the remaining steps and conditions are the same as in Example 1.

[0133] The primary crystallization temperature of the perfluorinated electrolyte molten salt, measured according to the aforementioned method, is 702℃. (Specific details are as follows...) Figure 7 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing methods, is 2.6 g / cm³. 3 The electrical conductivity is 1.1 S / cm.

[0134] The purity of high-purity aluminum prepared using the above method is 99.50%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 72%.

[0135] Comparative Example 2

[0136] This comparative example uses the same method as Example 1 to prepare high-purity aluminum, except that 12% KF by mass is added to the electrolyte molten salt, and the remaining steps and conditions are the same as in Example 1.

[0137] The primary crystallization temperature of the perfluorinated electrolyte molten salt, measured according to the aforementioned method, is 650℃. Specifically, as follows... Figure 8 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing technical methods, is 2.45 g / cm³. 3 The electrical conductivity is 0.75 S / cm.

[0138] The purity of high-purity aluminum prepared using the above method is 99.56%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 70%.

[0139] Comparative Example 3

[0140] This comparative example uses the same method as Example 1 to prepare high-purity aluminum, except that the molar ratio of NaF to AlF3 is 1.15, and the remaining steps and conditions are the same as in Example 1.

[0141] The primary crystallization temperature of the perfluorinated electrolyte molten salt, measured using the aforementioned method, is 767℃. (Specific details are as follows...) Figure 9 As shown; the density of the perfluorinated electrolyte molten salt, measured using existing methods, is 2.56 g / cm³. 3 The electrical conductivity is 0.7 S / cm.

[0142] The purity of high-purity aluminum prepared using the above method is 99.51%, and the current efficiency (the ratio of actual aluminum production to theoretical aluminum production) is 63%.

[0143] The results show:

[0144] The high-purity aluminum prepared in Examples 1-5 of this invention has a purity ≥99.95%, a current efficiency ≥78%, a primary crystallization temperature of 650℃~750℃, and a density of 2.6g / cm³. 3 ~2.9g / cm 3 Its electrical conductivity is 1.1 S / cm to 1.5 S / cm.

[0145] Comparing Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1 without the addition of KF, the primary crystallization temperature is significantly increased, while the current efficiency and the purity of high-purity aluminum are reduced. This indicates that KF has a significant effect on reducing the primary crystallization temperature and increasing the conductivity and current efficiency.

[0146] Comparing Example 1 and Comparative Example 2, it can be seen that adding excessive KF in Comparative Example 2 reduces conductivity and current efficiency, indicating that adding KF within a limited range helps to improve conductivity and current efficiency.

[0147] Comparing Example 1 and Comparative Example 3, it can be seen that in Comparative Example 3, the molar ratio of NaF to AlF3 is greater than 1, the initial crystallization temperature increases, and the conductivity and current efficiency decrease. This indicates that when the molar ratio of NaF to AlF3 is ≤1, it helps to improve the conductivity and current efficiency.

[0148] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for refining high-purity aluminum using a three-layer liquid process, characterized in that, include: The molten salt of perfluorinated electrolyte is used, and the anions are fluoride ions, sodium ions, potassium ions, and aluminum ions. To achieve optimal conductivity and current efficiency, the amount of sodium ions in the perfluorinated electrolyte molten salt should be controlled to be less than or equal to the amount of aluminum ions, and the potassium ion content should also be controlled.

2. The method for refining high-purity aluminum using a three-layer liquid process according to claim 1, characterized in that, The potassium ions are added to the perfluorinated electrolyte molten salt in the form of KF, and the weight percentage of KF in the perfluorinated electrolyte molten salt is 1% to 10%.

3. The method for refining high-purity aluminum using a three-layer liquid process according to claim 2, characterized in that, The molar ratio of sodium ions to aluminum ions satisfies the condition: 0.55 to 1.

0.

4. The method for refining high-purity aluminum using a three-layer liquid process according to claim 3, characterized in that, The cations in the perfluorinated electrolyte molten salt also include Ba. 2+ Ca 2+ and Li + .

5. The method for refining high-purity aluminum using a three-layer liquid process according to claim 4, characterized in that, The mass percentage composition of the raw materials for the perfluorinated electrolyte molten salt satisfies the following: 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, with the remainder being NaF and AlF3.

6. The method for refining high-purity aluminum using a three-layer liquid process according to claim 5, characterized in that, The KF must meet the following requirements: purity > 98.5%, loss on ignition < 1%, total oxides < 0.2%, and total other impurities < 0.3%.

7. The method for refining high-purity aluminum using a three-layer liquid process according to any one of claims 1-6, characterized in that, The anode is a copper-aluminum alloy with a copper content of 35%-75% and the remainder being aluminum; the cathode is an aluminum rod with a purity of 99.99%-99.999%.

8. The method for refining high-purity aluminum using a three-layer liquid process according to claim 7, characterized in that, The electrolyte molten salt level between the anode and cathode is 4.0 cm to 10 cm.

9. A three-layer liquid refining perfluorinated electrolyte molten salt for high-purity aluminum, characterized in that, The method for refining high-purity aluminum using a three-layer liquid process according to any one of claims 1-8 is prepared from the following raw materials in the following mass percentages: 16%–22% BaF2, 14%–18% CaF2, 1%–8% LiF, 1%–10% KF, and the remainder being NaF and AlF3 in a molar ratio of 0.55–1.

0.

10. A high-purity elemental aluminum, characterized in that, The high-purity aluminum is prepared by the three-layer liquid refining method according to any one of claims 1-8, and the purity of the elemental aluminum is ≥99.95%.

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