Method for selectively separating aluminum and lithium from aluminum-lithium alloy waste

Abstract

The invention discloses a method for selectively separating aluminum and lithium from aluminum-lithium alloy waste, and belongs to the technical field of aluminum-lithium alloy waste recovery. The method comprises the steps that the surface of the aluminum lithium alloy waste is covered with molten salt, smelting is carried out in an inert atmosphere to obtain a melt, low-oxygen gas with the oxygen volume concentration being 3%-10% is introduced into the melt for oxidation, metal lithium in the melt is selectively oxidized and migrated into a molten salt layer on the surface of the melt to form lithium-rich slag, slag-metal separation is carried out, alloy liquid and lithium-rich salt slag are obtained, and the alloy liquid is subjected to heat treatment to obtain the aluminum lithium alloy waste. The alloy liquid can be subsequently quenched and tempered to be processed into regenerated aluminum alloy, the lithium-rich salt slag is rich in lithium oxide, a series of lithium products can be subsequently further processed and prepared, the aluminum-lithium alloy waste is used as the raw material, resource utilization of the alloy waste is achieved, meanwhile, high-value element lithium in the waste is recycled and extracted, the process technical route is simple and easy to implement, and the method is suitable for industrial production. The industrial application requirements are met.

Description

Technical Field

[0001] The invention relates to a method for treating aluminum-lithium alloy waste, and in particular to a method for selectively separating aluminum and lithium from aluminum-lithium alloy waste, belonging to the technical field of aluminum-lithium alloy waste recovery. Background Art

[0002] Aluminum-lithium alloy is a lightweight, high-strength material with significant advantages such as low density, high specific strength and specific stiffness. It also has excellent corrosion resistance, fatigue resistance and low-temperature performance, making it suitable for complex working environments such as aircraft fuselages and satellites. In addition to the aviation field, aluminum-lithium alloy is also used in automobiles, ships and electronic equipment. Its economic efficiency is significant, making it a key material for lightweight upgrades in modern industry. However, lithium is extremely chemically active, and waste is easily formed during the production and processing of aluminum-lithium alloy. In addition, aluminum-lithium alloy terminal products also face the problem of being scrapped when they reach their service life.

[0003] At present, the recycling process of aluminum-lithium alloy waste is mostly secondary smelting of conventional aluminum alloy waste. During the process, the alloy liquid is tempered and processed to become recycled aluminum alloy. For example, a Chinese patent (publication number: CN117587234A) discloses a method for continuous recycling of aluminum-lithium alloy waste, which specifically includes the following steps: Step S1: Obtain aluminum-lithium alloy scraps and fragments and perform pretreatment; Step S2: Obtain large scraps of aluminum-lithium alloy, and place the large scraps of aluminum-lithium alloy into a smelting furnace for melting to obtain a metal mother liquid; Step S3: Add a preset weight of aluminum-lithium alloy scraps and fragments to the metal mother liquid in batches, control the heating temperature and heating time of the metal mother liquid, and stir the metal mother liquid until the aluminum-lithium alloy scraps and fragments are completely melted to obtain a metal liquid; Step S4: When the weight of the metal liquid is ≥ the target weight, remove the scum in the metal liquid, pour part of the metal liquid into a casting device, use the remaining metal liquid as the metal mother liquid, and repeat step S3, which can effectively improve the recovery ratio and recovery efficiency of aluminum-lithium alloy scraps and fragments. A Chinese patent (publication number: CN111893335A) discloses a method for recycling aluminum-lithium alloy waste scraps, which uses a vacuum medium-frequency induction melting and casting process to recycle aluminum-lithium alloy waste scraps, recycles aluminum-lithium alloy waste scraps through two refining and multi-stage filtration, adds impurity removers to eliminate metal and non-metal inclusions introduced by some aluminum-lithium alloy waste scraps, and adds high-efficiency refiners to refine the grains of aluminum-lithium alloy regenerated ingots, thereby obtaining high-quality aluminum-lithium alloy regenerated ingots with high purity and grain refinement. In these smelting and regeneration methods, part of the lithium in the lithium-aluminum alloy will be oxidized into salt slag, and because refining agents, defoaming agents, etc. are added during the smelting process, the chemical composition of the salt slag is complex, the subsequent lithium extraction process is long and difficult, and the salt slag produced wastes resources and is also prone to secondary pollution.

[0004] In addition, there are methods for extracting lithium from aluminum-lithium alloy waste in the prior art. For example, a Chinese patent (publication number: CN119220817A) discloses a method for extracting lithium from aluminum-lithium alloy waste, wherein the aluminum-lithium alloy waste is dissolved with acid, and then the mixed solution obtained by dissolving is evaporated to obtain a crystal to be processed; the crystal to be processed is roasted so that the lithium and other metal elements in the crystal to be processed exist in different forms to obtain a roasted powder; the roasted powder is leached to obtain a leached mixed solution. This method dissolves the elements in the aluminum-lithium alloy waste into ions by acid, converts aluminum salts, magnesium salts, etc. in the crystal to be processed into oxides by roasting, and then leaches lithium into the solution by leaching to achieve the purpose of extracting lithium. This method requires a large amount of acid reagents and energy consumption, and the lithium leaching efficiency is only about 85%, and lithium-aluminum separation is not fully achieved. Summary of the invention

[0005] In view of the technical problems existing in the resource utilization of existing aluminum-lithium alloy waste, the purpose of the present invention is to provide a method for selectively separating aluminum and lithium from aluminum-lithium alloy waste. The method can achieve efficient separation of lithium in aluminum alloy waste and obtain alloy liquid and lithium-rich salt slag. The alloy liquid can be tempered and processed to regenerate aluminum alloy, and the lithium-rich salt slag can be further processed into high-value products such as lithium carbonate. The method does not require the use of refining agents, reduces costs, simplifies the composition of salt slag, and is conducive to the further recovery of lithium in the salt slag, providing a new way for the resource utilization, high value and large-scale utilization of aluminum-lithium alloy waste.

[0006] In order to achieve the above technical objectives, the present invention provides a method for selectively separating aluminum and lithium from aluminum-lithium alloy waste, the method comprising: covering the surface of the aluminum-lithium alloy waste with molten salt, smelting the waste in an inert atmosphere to obtain a melt, introducing a low-oxygen gas with an oxygen volume concentration of 3% to 10% into the melt for oxidation, selectively oxidizing the metallic lithium in the melt and migrating it to the molten salt layer on the surface of the melt to form lithium-rich slag, separating the slag and gold to obtain alloy liquid and lithium-rich salt slag.

[0007] The key to the technical solution of the present invention lies in: on the one hand, utilizing the difference in chemical activity between metallic aluminum and metallic lithium, and using low-oxygen gas to achieve selective oxidation of metallic lithium in the melt; on the other hand, utilizing the difference in physical properties such as density and compatibility between lithium oxide and the alloy liquid, achieving directional migration of lithium oxide to the upper part of the alloy liquid; thirdly, utilizing molten salt to capture lithium oxide products, it is possible to achieve directional enrichment of lithium oxide in the upper molten salt layer, which is helpful to achieve separation of metallic lithium and metallic aluminum.

[0008] As a preferred solution, the lithium content in the aluminum-lithium alloy waste is not higher than 15%, and the aluminum content is not lower than 80%. As a more preferred solution, the aluminum-lithium alloy waste includes at least one of the scrapped terminal aluminum-lithium alloy products, the waste generated during the production and processing of aluminum-lithium alloys, and the aluminum-lithium intermediate alloy waste. In general lithium alloys, every 1% increase in lithium can reduce the density by about 3%, and the elastic modulus can be increased by 10% to 16%. However, excessive lithium content can easily lead to an increase in the scrap rate during the smelting process. Generally, the lithium content in the finished aluminum-lithium alloy is not higher than 5%, and the lithium content in the aluminum-lithium intermediate alloy is not higher than 15%. Aluminum is the main alloy component in aluminum-lithium alloy waste. If the aluminum content in the aluminum-lithium alloy waste is too low, it means that a large amount of impurity components are mixed in the alloy, which will affect the subsequent smelting recovery efficiency and increase the smelting cost. The present invention preferably selects aluminum-lithium alloy waste with an aluminum content of not less than 80%.

[0009] As a preferred solution, the molten salt includes lithium chloride, sodium chloride and potassium chloride. As a more preferred solution, the molten salt is composed of the following mass percentage components: lithium chloride 1%~10%, potassium chloride 45%~55%, sodium chloride 40%~50%. The role of molten salt: on the one hand, after melting, the molten salt can be used as a protective layer to reduce the impact of the external environment on the alloy melt, such as oxidation; on the other hand, the use of molten salt to capture lithium oxides can achieve directional enrichment of lithium oxides in the upper molten salt layer, which is conducive to the selective extraction of lithium. Potassium chloride and sodium chloride are the main components of the molten salt, and the melting point is reduced by forming a complex salt, while the melting point of lithium chloride is relatively lower, and reducing the melting point also helps to improve the liquid phase fluidity of the molten salt. As a more preferred solution, the mass of the molten salt is 10%~80% of the mass of the aluminum-lithium alloy waste. The amount of molten salt added to the surface of the aluminum-lithium alloy waste is determined according to the lithium content in the lithium-aluminum alloy waste. When the lithium content is low, the amount added is relatively small, and when the lithium content is high, the amount added is relatively high. Too low an amount of addition will result in insufficient lithium enrichment, while too high an amount of addition will result in increased production costs. The mass of the molten salt is further 20% to 50% of the mass of the aluminum-lithium alloy waste.

[0010] As a preferred solution, the temperature of the melt is 700°C to 900°C. The smelting temperature is mainly adjusted according to the lithium content in the lithium aluminum alloy waste. When the lithium content is low, the smelting temperature is relatively high. Temperature is the main influencing factor of reaction kinetics. If the temperature is too low, the reaction progresses slowly, the smelting time is extended, and the production cost increases. If the temperature is too high, the production energy consumption increases, and it is easy to cause the volatilization of the molten salt phase.

[0011] As a preferred solution, the low-oxygen gas is composed of the following volume percentage components: 90% to 97% inert gas and 3% to 10% oxygen. The volume concentration of inert gas in the low-oxygen gas of the present invention is 90% to 97%, and the volume concentration of oxygen is 3% to 10%. In this low-oxygen gas environment, the chemical reaction equation is: 4Li+O2→2Li2O. If the proportion of oxygen is too high, it is easy to cause aluminum to be oxidized 4Al + 3O2→2Al2O3, which is difficult to achieve efficient separation of lithium and aluminum in lithium aluminum alloy waste, and will increase the amount of slag and increase losses. If the proportion of oxygen is too low, the reaction progresses slowly and the smelting efficiency is low.

[0012] As a preferred solution, the amount of low-oxygen gas introduced into the melt is to control the mass content of metallic lithium in the melt to be as low as 0.1% or less. When the mass content of metallic lithium in the melt is as low as 0.1%, further introduction of low-oxygen gas will easily lead to oxidation of metallic aluminum.

[0013] The inert atmosphere involved in the present invention is an argon atmosphere. Since both aluminum and lithium are highly active, aluminum will be oxidized in large quantities during the alloy waste smelting process under air conditions, and selective oxidation of lithium cannot be achieved, and the aluminum recovery rate drops sharply, and the amount of salt slag generated will also increase. In addition, the inert atmosphere cannot be replaced by a nitrogen atmosphere. The generation of aluminum nitride under nitrogen conditions also leads to aluminum loss and an increase in slag, resulting in a decrease in economic benefits and an increase in the difficulty of subsequent treatment of salt slag.

[0014] The lithium-rich slag of the present invention only needs to be soaked in water and then carbon dioxide is introduced or converted with sodium carbonate or potassium carbonate to form lithium carbonate precipitation.

[0015] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0016] (1) The present invention is based on the existing molten salt covering smelting aluminum alloy process, selectively oxidizes the lithium element in the aluminum-lithium alloy waste and enriches it in the upper molten salt layer. After the slag and gold are separated, the alloy liquid and lithium-rich salt slag can be obtained. This not only realizes the resource recovery of aluminum-lithium alloy waste, but also extracts the alloy element lithium. Subsequently, high-value lithium carbonate and other products can be prepared, which provides a new way for the resource recovery, high value and large-scale disposal and utilization of aluminum-lithium alloy waste, and solves the problem of difficulty in recovering and extracting alloy component lithium.

[0017] (2) The equipment used in the present invention is a smelting furnace used in the aluminum alloy industry. No new equipment is required. Compared with the traditional method of adding refining agents to remove impurities, low-concentration oxygen is used to selectively oxidize lithium and achieve directional enrichment. No refining agent is required. The technical route is simple to operate, which greatly simplifies the salt slag composition and salt slag generation, thereby reducing the production cost of the enterprise.

[0018] (3) The present invention makes full use of the difference in chemical activity between aluminum and lithium to achieve selective oxidation of lithium. At the same time, based on the difference in properties such as density, the directional enrichment of lithium oxide in the molten salt layer is achieved. The reaction process is flexibly controlled by temperature, gas composition, molten salt composition and addition amount, thereby achieving efficient separation between aluminum and lithium components. DETAILED DESCRIPTION

[0019] The following examples are intended to further illustrate the present invention, rather than to limit the scope of protection of the claims of the present invention.

[0020] Comparative Example 1

[0021] Compared with Example 1, the only difference is that the aluminum-lithium alloy scrap is smelted in a nitrogen atmosphere.

[0022] Due to the smelting in nitrogen atmosphere, aluminum nitride is significantly generated.

[0023] Final results: The lithium content in the alloy liquid was 0.10%, the aluminum nitride content in the salt slag was 14.7%, the aluminum oxide content was 0%, and the lithium recovery rate was 96.2%.

[0024] Comparative Example 2

[0025] Compared with Example 1, the only difference is that molten salt is added in an amount of 5% by mass of the alloy waste.

[0026] Due to the low amount of molten salt added, the directional migration of lithium oxide is insufficient, the smelting time is long, and part of the aluminum is oxidized.

[0027] Final results: The lithium content in the alloy liquid was 0.09%, the aluminum nitride content in the salt slag was 0%, the aluminum oxide content was 18.7%, and the lithium recovery rate was 95.8%.

[0028] Comparative Example 3

[0029] Compared with Example 1, the only difference is that a high oxygen content gas (oxygen volume concentration of 30%, argon volume concentration of 70%) is introduced.

[0030] Due to the high proportion of oxygen, aluminum is obviously oxidized.

[0031] Final results: The lithium content in the alloy liquid was 0.1%, the aluminum nitride content in the salt slag was 0%, the aluminum oxide content was 25.8%, and the lithium recovery rate was 96.2%.

[0032] Comparative Example 4

[0033] Compared with Example 1, the only difference is that the melting temperature is 670°C.

[0034] Due to the low smelting temperature, low gas utilization, long smelting time (needs to reach 35 minutes), and high energy consumption.

[0035] Final result: The metallic lithium content in the alloy liquid was 0.09%, the alumina content in the salt slag was 0%, and the lithium recovery rate was 95.3%.

[0036] Example 1

[0037] Taking a certain aluminum-lithium alloy waste (aluminum content 94.8%, lithium content 2.5%) as raw material, under argon atmosphere, molten salt (lithium chloride accounts for 1%, sodium chloride accounts for 50%, potassium chloride accounts for 49%) of the alloy waste mass was added and smelted at 800℃, and oxidizing gas (oxygen volume concentration 5%, argon volume concentration 95%) was introduced. The smelting time was 20 minutes. After the reaction was completed, the slag-liquid separation was achieved by slag removal. The metallic lithium content in the alloy liquid was 0.09%, the aluminum content of the salt slag was 0%, and the lithium recovery rate was 95.5%.

[0038] Example 2

[0039] Taking a certain aluminum-lithium alloy waste (aluminum content 94.8%, lithium content 2.5%) as raw material, under argon atmosphere, molten salt (lithium chloride accounts for 10%, sodium chloride accounts for 40%, potassium chloride accounts for 50%) of the alloy waste mass was added, and smelted at 900℃. Oxidizing gas (oxygen volume concentration 10%, argon volume concentration 90%) was introduced. The smelting time was 20 minutes. After the reaction was completed, the slag-liquid separation was achieved by slag removal. The metallic lithium content in the alloy liquid was 0.09%, the aluminum content of the salt slag was 0%, and the lithium recovery rate was 96.7%.

[0040] Example 3

[0041] Taking a certain aluminum-lithium alloy waste (aluminum content 93.6%, lithium content 3.7%) as raw material, under argon atmosphere, molten salt (lithium chloride accounts for 5%, sodium chloride accounts for 50%, potassium chloride accounts for 45%) of the alloy waste mass was added, and smelted at 700 ℃. Oxidizing gas (oxygen volume concentration 3%, argon volume concentration 97%) was introduced. The smelting time was 20 minutes. After the reaction was completed, the slag-liquid separation was achieved by slag removal. The metallic lithium content in the alloy liquid was 0.1%, the aluminum content of the salt slag was 0%, and the lithium recovery rate was 96.2%.

[0042] Example 4

[0043] Taking a certain aluminum-lithium intermediate alloy waste (aluminum content 93.3%, lithium content 2.1%) as raw material, under argon atmosphere, molten salt (lithium chloride accounts for 1%, sodium chloride accounts for 44%, potassium chloride accounts for 55%) of the alloy waste mass was added, and smelted at 800℃. Oxidizing gas (oxygen volume concentration 7%, argon volume concentration 93%) was introduced. The smelting time was 20 minutes. After the reaction was completed, the slag-liquid separation was achieved by slag removal. The metallic lithium content in the alloy liquid was 0.1%, the aluminum content of the salt slag was 0%, and the lithium recovery rate was 99.3%.

Claims

1. A method for selectively separating aluminum and lithium from aluminum-lithium alloy waste, characterized in that: The surface of aluminum-lithium alloy waste is covered with molten salt and smelted in an inert atmosphere to obtain a melt. A low-oxygen gas with an oxygen volume concentration of 3% to 10% is introduced into the melt for oxidation. The metallic lithium in the melt is selectively oxidized and migrated to the molten salt layer on the surface of the melt to form lithium-rich slag. The slag and gold are separated to obtain alloy liquid and lithium-rich salt slag.

2. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1, characterized in that: The lithium content in the aluminum-lithium alloy waste is not higher than 15%, and the aluminum content is not lower than 80%.

3. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1 or 2, characterized in that: The aluminum-lithium alloy waste includes at least one of scrapped terminal aluminum-lithium alloy products, waste generated during the production and processing of aluminum-lithium alloys, and aluminum-lithium intermediate alloy waste.

4. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1 or 2, characterized in that: The molten salt includes lithium chloride, sodium chloride and potassium chloride.

5. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 4, characterized in that: The molten salt is composed of the following components in mass percentage: 1% to 10% lithium chloride, 45% to 55% potassium chloride, and 40% to 50% sodium chloride.

6. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1 or 5, characterized in that: The mass of the molten salt is 10% to 80% of the mass of the aluminum-lithium alloy waste.

7. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1, characterized in that: The temperature of the melt is 700°C to 900°C.

8. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1, characterized in that: The low-oxygen gas is composed of the following components in volume percentage: 90% to 97% inert gas and 3% to 10% oxygen.

9. The method for selectively separating aluminum and lithium from aluminum-lithium alloy waste according to claim 1 or 8, characterized in that: The amount of the low-oxygen gas introduced into the melt is used to control the mass content of metallic lithium in the melt to be lower than 0.1%.