A method for extracting lithium in hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide

Abstract

The application discloses a method for extracting lithium in hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide, and the method comprises the following steps: hydrothermally treating the lithium-containing aluminum hydroxide with an acidic solution to realize extraction of lithium elements and preparation of lithium carbonate, and simultaneously, aluminum elements are directly converted into boehmite through hydrothermal separation. Compared with the traditional acid leaching method for adjusting pH and segmenting precipitation, the method has the advantages of lower acid consumption, no need for secondary separation of aluminum gel in the leaching solution, and a more simple operation process, and can directly prepare sheet-shaped boehmite with uniform morphology and excellent crystallinity, and effectively avoids the loss of lithium elements caused by aluminum-lithium co-precipitation in the traditional process. Compared with the conventional hydrothermal leaching process, the lithium extraction rate of the method can reach more than 95%, and the boehmite can be directly used as a finished product, and there is no need to return the hydrated aluminum oxide obtained through the conventional hydrothermal method to the system for processing after being resolubilized into sodium aluminate solution. The method has the advantages of significantly reduced energy consumption, simplified process links, and outstanding industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of lithium and aluminum ion separation and boehmite hydrothermal synthesis in inorganic material preparation, specifically involving a method for simultaneously extracting lithium ions and preparing battery-grade lithium carbonate during the hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide. Background Technology

[0002] Boehmite (γ-AlOOH) is a key inorganic functional material. Due to its unique crystal structure, high specific surface area, and excellent thermal stability, it is widely used in lithium-ion battery separator coatings, catalyst supports, ceramic materials, and many other fields. There are numerous methods for its preparation, among which the hydrothermal method using aluminum hydroxide as a raw material has become the mainstream technical route for industrial production and laboratory preparation of high-quality boehmite due to its advantages such as process controllability, high product purity, and uniform morphology.

[0003] During the development and utilization of bauxite resources, some bauxite contains associated lithium. After processing using processes such as the Bayer process, lithium accumulates in the form of lithium ions in the aluminum hydroxide raw material, forming lithium-containing aluminum hydroxide. When this type of aluminum hydroxide is used to prepare boehmite via hydrothermal conversion, lithium ions in the system are gradually released into the hydrothermal mother liquor during the hydrothermal reaction. Direct discharge or recycling of this mother liquor not only results in a significant waste of lithium resources, but the accumulation of lithium ions also affects the efficiency and performance of subsequent boehmite preparation, such as causing crystal morphology distortion and decreased purity, thereby impacting the stable operation of the hydrothermal process.

[0004] Lithium, a strategically scarce resource, is a core raw material for high-end fields such as lithium-ion batteries, nuclear fusion devices, and aerospace materials. With the rapid development of the new energy industry, global demand for lithium resources continues to rise, highlighting the growing imbalance between supply and demand. Traditional lithium extraction mainly relies on brine lake extraction and ore extraction technologies: brine lake extraction is significantly limited by geographical environment and climate conditions, and suffers from long processing cycles and difficulties in impurity separation; ore extraction faces challenges such as high energy consumption, severe environmental pollution, and low resource utilization. Therefore, developing new technologies and processes for extracting lithium from non-traditional lithium resources has become a core direction for alleviating lithium resource supply pressure.

[0005] Currently, there are existing technologies for extracting lithium carbonate from sodium aluminate solutions derived from aluminum ore with high lithium content in central my country, such as the method disclosed in CN107500318A "Method for Extracting Lithium Carbonate from Sodium Aluminate Solution in Alumina Plants". However, the product after hydrothermal treatment needs to be redissolved into sodium aluminate solution, and the separated lithium leachate contains aluminum colloid, which needs to be neutralized with inorganic acid before separation. Moreover, the lithium extraction rate is low, the process is cumbersome and the efficiency is limited. CN110627095B "A Method for Extracting Lithium from Alumina Production Process and Preparing Battery-Grade Lithium Carbonate" discloses a microwave desorption method for extracting lithium from lithium-rich aluminum hydroxide. The desorbed extract contains a large number of aluminum ions, which causes lithium loss during the separation of aluminum and lithium. Furthermore, in the pilot-scale stage, the microwave reactor has the risk of uneven microwave field distribution and microwave leakage, which reduces the extraction rate in industrial applications. Summary of the Invention

[0006] This invention provides a method for extracting lithium ions from lithium-containing aluminum hydroxide and simultaneously preparing high-quality boehmite.

[0007] This invention utilizes an acid-hydrothermal reaction to directionally convert aluminum in lithium-containing aluminum hydroxide into highly crystalline platy boehmite, while simultaneously allowing lithium to selectively leach into the solution, achieving efficient separation of aluminum and lithium. The lithium-containing solution is then concentrated, purified, and precipitated to obtain battery-grade lithium carbonate. This method achieves a lithium extraction rate of over 95%, and the process is simple and easily implemented industrially.

[0008] This invention enables the simultaneous extraction of lithium ions and the preparation of battery-grade lithium carbonate during the acid-hydrothermal preparation of boehmite. The specific technical solution is as follows:

[0009] Lithium-containing aluminum hydroxide is added to an acidic solution and subjected to a hydrothermal reaction at 150℃~180℃. After the reaction, the product is filtered, washed, and dried to obtain a solid product of platy boehmite. Lithium ions enter the solution phase after the hydrothermal reaction. The lithium extraction solution is then evaporated and concentrated, and calcium and magnesium impurity ions in the solution are removed to obtain a refined lithium extraction solution. A saturated sodium carbonate solution is added to the refined solution, and battery-grade lithium carbonate is precipitated by a water bath reaction.

[0010] Preferably, the lithium extraction solution is evaporated and concentrated to a lithium content ≥6g / L.

[0011] Preferably, the acidic solution is any one of acetic acid solution, oxalic acid solution, or phosphoric acid solution. The concentration of the acidic solution is 0.1–0.5 mol / L, preferably 0.2–0.4 mol / L.

[0012] Preferably, the solid content of the lithium-containing aluminum hydroxide in the reaction system is 100-300 g / L. The hydrothermal reaction time is 2h to 6h, preferably 3h to 5h.

[0013] Preferably, the impurity removal process specifically involves: adding oxalic acid as a calcium removal agent, with the amount of oxalic acid added being 2 to 3 times the molar amount of calcium ions in the concentrate; adjusting the pH of the system to 12 using sodium hydroxide to remove magnesium ions from the concentrate; and carrying out the removal of calcium and magnesium ions in a water bath at 55 to 75°C for a reaction time of 1 to 2 hours.

[0014] Preferably, the concentration of the saturated sodium carbonate solution in the lithium precipitation process is 250 g / L, the water bath temperature is controlled at 85°C, and the reaction time is 2 h. The lithium precipitation process can be further enhanced by adding finely ground lithium carbonate as seed crystals and sodium dodecylbenzenesulfonate as a seed crystal growth promoter to reduce impurity adsorption on the crystal surface and intergranular impurity inclusion.

[0015] Preferably, the particle size D50 of the lithium-containing aluminum hydroxide is 5 μm. Grinding pretreatment of the raw materials helps to improve the hydrothermal reaction efficiency and lithium leaching rate.

[0016] Simultaneous extraction of lithium ions and preparation of battery-grade lithium carbonate during the hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide aligns with the concept of resource recycling and responds to the development needs of the new energy industry. This has significant practical implications and broad prospects for industrial application in promoting the green and high-value development of the aluminum and lithium industries.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. High-efficiency aluminum-lithium separation: Through acidic hydrothermal treatment, aluminum is directionally converted into boehmite, and lithium is selectively leached into the solution phase, completing the aluminum-lithium separation in one step and avoiding the loss of lithium caused by aluminum-lithium co-precipitation in traditional processes.

[0018] 2. High lithium extraction rate: The lithium extraction rate can reach over 95%, which is significantly higher than that of conventional hydrothermal extraction processes (approximately 70%), achieving efficient recovery of lithium resources.

[0019] 3. Excellent product quality: The obtained boehmite is a plate-like crystal with high crystallinity and uniform morphology, which can be directly used as a functional material such as lithium battery separator coating; the obtained lithium carbonate has a purity of over 99.5%, which meets the battery-grade lithium carbonate standard.

[0020] 4. Simple process flow: There is no need for secondary separation of aluminum glue in the leaching solution, which simplifies the operation process and reduces acid consumption and energy consumption.

[0021] 5. Strong industrial adaptability: It has a wide process parameter window, is easy to connect with existing boehmite production lines, and has good prospects for industrial application. Attached Figure Description

[0022] Figure 1The process flow diagram for lithium extraction during the hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide provided by this invention.

[0023] Figure 2 Scanning electron microscope (SEM) image of the platy boehmite prepared by acid hydrothermal method in Example 1.

[0024] Figure 3 The image shows a scanning electron microscope (SEM) image of lithium carbonate prepared from the hydrothermal leachate of Example 1 after concentration, impurity removal, and purification.

[0025] Figure 4 Scanning electron microscope image of boehmite prepared hydrothermally without acid in Comparative Example 1.

[0026] Figure 5 A photograph of the residue after acetic acid leaching in Comparative Example 2. Detailed Implementation

[0027] The present invention will be further described in detail and completely below with reference to specific embodiments. The specific embodiments disclosed in this patent are merely exemplary interpretations of the scope of protection of the claims and are not intended to exhaustively limit the scope of protection. Any technical implementation scheme formed by equivalent substitution, simple modification, parameter adjustment, etc., without departing from the core concept of the technical solution contained in the claims of this patent should be included within the scope of protection of this patent.

[0028] like Figure 1 As shown, the method of the present invention includes the following steps: A method for extracting lithium during the hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide includes the following steps: 1) Add lithium-containing aluminum hydroxide to an acidic solution and carry out a hydrothermal reaction at 150℃~180℃ to leach lithium into the solution phase, and separate aluminum after hydrothermal conversion to form platy boehmite. 2) Evaporate and concentrate the lithium extraction solution, add impurity removal agent to remove calcium and magnesium ions from the solution to obtain a purified solution; in this step, it is preferable to evaporate and concentrate the lithium extraction solution to a lithium content ≥6g / L, so as to efficiently remove calcium and magnesium impurities.

[0029] 3) Add saturated sodium carbonate solution to the purified solution, and precipitate battery-grade lithium carbonate through a water bath reaction.

[0030] This invention, based on the process characteristics of hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide, completely separates lithium and aluminum during the hydrothermal reaction crystal transformation in one step, and extracts lithium ions from the hydrothermal mother liquor to prepare lithium carbonate, thus possessing the dual value of resource recovery and process optimization. This technical route uses lithium-containing aluminum hydroxide as raw material. After acid hydrothermal treatment, the hydrothermal mother liquor undergoes enrichment, concentration, purification, and precipitation crystallization processes to convert low-concentration lithium ions into high-value-added lithium carbonate. This process not only achieves efficient recovery of lithium resources and enhances the comprehensive utilization value of aluminum hydroxide resources, but also reduces the adverse effects of the hydrothermal mother liquor on subsequent production, realizing the synergistic development of boehmite preparation and lithium extraction.

[0031] The lithium-containing aluminum hydroxide described in this invention is typically an intermediate product obtained from the production of alumina from lithium-containing bauxite using the Bayer process. Its lithium abundance is usually between 300 and 50,000 ppm. Raw material aluminum hydroxide with lower abundance is not industrially viable from the current cost perspective.

[0032] In this invention, the hydrothermal reaction has a significant synergistic effect. Compared with non-hydrothermal conditions (e.g., holding at 70°C), the latter has low lithium leaching and severe aluminum dissolution. Therefore, the hydrothermal process is indispensable for selective lithium leaching and inhibiting aluminum dissolution.

[0033] The introduction of acidic substances in the hydrothermal reaction also plays a crucial role, promoting lithium leaching while inhibiting excessive aluminum dissolution. Comparative experiments show that without acidic substances, the lithium extraction rate is only about 70%, while adding acidic substances can increase it to about 95%, confirming its necessity. The acidic substances in this invention are typically acetic acid, oxalic acid, or phosphoric acid. Preferred embodiments of this invention use acetic acid and oxalic acid. Acids stronger than phosphoric acid have been proven unsuitable for this invention. However, it is readily understood that the acidic solution in this invention is not limited to these three acids; other organic acids with similar acidity, such as malonic acid, malic acid, and succinic acid, can also be used if material availability is not a concern. The concentration of the acidic solution is 0.1~0.5 mol / L, preferably 0.2~0.4 mol / L. More acidic substances have not shown an improving effect.

[0034] The solid content of the hydrothermal reaction system is best controlled between 100 and 300 g / L, preferably within the range of 100–200 g / L. Excessive solid content will result in an overly thick slurry that is difficult to handle; excessively low solid content will reduce production efficiency.

[0035] Example 1 Lithium-containing aluminum hydroxide with a lithium content of 15212 ppm was ground to a particle size D50 of 5 μm (original particle size D50 was 25 μm). It was added to a reaction vessel at a solid content of 150 g / L, followed by the addition of 0.3 mol / L acetic acid solution. The mixture was heated to 170 °C and subjected to a hydrothermal reaction for 4 h. After the reaction was completed, the system was filtered and washed. The resulting precipitate was platy boehmite. Figure 2 The filtrate was found to contain 750 ppm lithium and 1 ppm aluminum residue. The boehmite contained 610 ppm lithium, and the lithium extraction rate was 96.0%.

[0036] The lithium-containing leachate obtained in (1) was evaporated and concentrated. The concentration of each ion in the concentrated solution was: Li 6946 ppm, Ca 282 ppm, and Mg 44 ppm. The concentrated solution was placed in a 65°C water bath and oxalic acid (twice the molar amount of calcium ions in the concentrated solution) was added. The mixture was stirred for 2 hours to precipitate calcium ions. Then, sodium hydroxide was added to adjust the pH to 12, and the solution was kept in a 65°C water bath for 2 hours to precipitate magnesium ions. After filtration, a lithium precipitation and impurity removal solution was obtained. The solution was tested and found to contain 47 ppm Ca and 2 ppm Mg. Commercially available lithium carbonate (3.75 g / L) with fined particle size and sodium dodecylbenzene sulfonate were used as seed crystals and seed crystal growth promoters, respectively. The solution was added to a 250 g / L saturated sodium carbonate solution at 85°C. The above lithium precipitation and impurity removal solution was then slowly added dropwise and reacted in a water bath for 2 hours. After the reaction was completed, the solution was filtered, washed, and dried to obtain battery-grade lithium carbonate products. See [link to relevant documentation]. Figure 3 The purity of the sample was tested and found to be 99.57%, which meets the quality requirements for battery-grade lithium carbonate.

[0037] Example 2 Lithium-containing aluminum hydroxide with a lithium content of 16856 ppm was ground to a particle size D50 of 5 μm (original particle size D50 was 25 μm). It was added to a reaction vessel at a solid content of 100 g / L, followed by the addition of 0.2 mol / L acetic acid solution. The mixture was heated to 160 °C and subjected to a hydrothermal reaction for 5 h. After the reaction, the system was filtered and washed. The resulting precipitate was platy boehmite, and its scanning electron micrograph is similar to... Figure 2 The results were basically the same; the filtrate contained 538 ppm lithium and 3 ppm aluminum residue, while the boehmite contained 238 ppm lithium, and the lithium extraction rate reached 98.6%.

[0038] The lithium-containing leachate obtained in (1) was evaporated and concentrated. The concentration of each ion in the concentrated solution was: Li 6298 ppm, Ca 530 ppm, and Mg 94 ppm. The concentrated solution was placed in a 70°C water bath environment, and oxalic acid (the amount added was twice the molar amount of calcium ions in the concentrated solution) was added. The mixture was stirred for 1 h to precipitate calcium ions. Then, sodium hydroxide was added to adjust the pH value to 12, and the solution was kept in a 70°C water bath for 1 h to precipitate magnesium ions. After filtration, a lithium precipitation and impurity removal solution was obtained. The solution was tested and found to contain 38 ppm Ca and 8 ppm Mg. Commercially available lithium carbonate (3.75 g / L) with fined particle size and sodium dodecylbenzene sulfonate were used as seed crystals and seed crystal growth promoters, respectively. They were added to a 250 g / L saturated sodium carbonate solution at 85°C. Then, the above lithium precipitation and impurity removal solution was slowly added dropwise, and the solution was reacted in a water bath for 2 h. After the reaction was completed, the solution was filtered, washed, and dried to obtain a battery-grade lithium carbonate product. Its scanning electron microscope image and Figure 3 They are essentially the same, and their purity is tested to be 99.62%, which meets the quality requirements for battery-grade lithium carbonate.

[0039] Example 3 Lithium-containing aluminum hydroxide with a lithium content of 15699 ppm was ground to a particle size D50 of 5 μm (original particle size D50 was 25 μm). It was added to a reaction vessel at a solid content of 200 g / L, followed by the addition of 0.4 mol / L acetic acid solution. The mixture was heated to 180℃ and subjected to a hydrothermal reaction for 3 hours. After the reaction, the system was filtered and washed. The resulting precipitate was flaky boehmite. Analysis showed that the filtrate contained 952 ppm lithium, 5 ppm residual aluminum, and 201 ppm lithium in the boehmite, with an extraction rate of 98.7%.

[0040] The lithium-containing leachate obtained in (1) was evaporated and concentrated. The concentrations of each ion in the concentrated solution were: Li 7200 ppm, Ca 371 ppm, and Mg 49 ppm. The concentrated solution was placed in a 60°C water bath and oxalic acid (twice the molar amount of calcium ions in the concentrated solution) was added. The mixture was stirred for 1.5 h to precipitate calcium ions. Then, sodium hydroxide was added to adjust the pH to 12, and the solution was kept in a 60°C water bath for 1.5 h to precipitate magnesium ions. After filtration, a lithium-precipitated impurity-removed solution was obtained. The solution was tested and found to contain 48 ppm Ca and 4 ppm Mg. Commercially available lithium carbonate (3.75 g / L) with fined particle size and sodium dodecylbenzenesulfonate were used as seed crystals and seed crystal growth promoters, respectively, and added to a 250 g / L saturated sodium carbonate solution at 85°C. Then, the above-mentioned lithium precipitation and impurity removal solution was slowly added dropwise, and the reaction was carried out in a water bath for 2 hours. After the reaction was completed, the product was filtered, washed, and dried to obtain battery-grade lithium carbonate. The purity of the product was tested to be 99.57%, which meets the quality requirements of battery-grade lithium carbonate.

[0041] Example 4 Lithium-containing aluminum hydroxide with a lithium content of 18036 ppm was ground to a particle size D50 of 5 μm (original particle size D50 was 25 μm). It was added to a reaction vessel at a solid content of 250 g / L, followed by the addition of 0.4 mol / L oxalic acid solution. The mixture was heated to 160 °C and subjected to a hydrothermal reaction for 4 h. After the reaction, the system was filtered and washed. The resulting precipitate was platy boehmite, and its scanning electron micrograph is similar to... Figure 2 The results were basically the same; the filtrate contained 1392 ppm lithium and 6 ppm aluminum residue, while the boehmite contained 195 ppm lithium, with an extraction rate of 98.9%.

[0042] The lithium-containing leachate obtained in (1) was evaporated and concentrated. The concentration of each ion in the concentrated solution was: Li 6882 ppm, Ca 381 ppm, and Mg 51 ppm. The concentrated solution was placed in a 75°C water bath and oxalic acid (the amount added was twice the molar amount of calcium ions in the concentrated solution) was added. The mixture was stirred for 1.5 h to precipitate calcium ions. Then, sodium hydroxide was added to adjust the pH to 12 and the solution was kept in a 75°C water bath for 1.5 h to precipitate magnesium ions. After filtration, a lithium precipitation and impurity removal solution was obtained. The solution was tested and found to contain 27 ppm Ca and 33 ppm Mg. Commercially available lithium carbonate (3.75 g / L) with fined particle size and sodium dodecylbenzene sulfonate were used as seed crystals and seed crystal growth promoters, respectively. The solution was added to a 250 g / L sodium carbonate saturated solution at 85°C. Then, the above lithium precipitation and impurity removal solution was slowly added dropwise and the solution was reacted in a water bath for 2 h. After the reaction was completed, the solution was filtered, washed, and dried to obtain a battery-grade lithium carbonate product. Its scanning electron microscope image and Figure 3 They are essentially the same, and their purity is tested to be 99.62%, which meets the quality requirements for battery-grade lithium carbonate.

[0043] Example 5 Lithium-containing aluminum hydroxide with a lithium content of 12875 ppm was ground to a particle size D50 of 5 μm (original particle size D50 was 25 μm). It was added to a reaction vessel at a solid content of 300 g / L, followed by the addition of 0.3 mol / L phosphoric acid solution. The mixture was heated to 150 °C and subjected to a hydrothermal reaction for 6 h. After the reaction, the system was filtered and washed. The resulting precipitate was platy boehmite, and its scanning electron micrograph is similar to... Figure 2 The results were basically the same; the filtrate contained 1224 ppm lithium and 7 ppm aluminum residue, while the boehmite contained 171 ppm lithium, with an extraction rate of 98.7%.

[0044] The lithium-containing leachate obtained in (1) was evaporated and concentrated. The concentration of each ion in the concentrated solution was: Li 7721 ppm, Ca 393 ppm, and Mg 47 ppm. The concentrated solution was placed in a 55°C water bath and oxalic acid (twice the molar amount of calcium ions in the concentrated solution) was added. The mixture was stirred for 2 hours to precipitate calcium ions. Then, sodium hydroxide was added to adjust the pH to 12 and the solution was kept in a 55°C water bath for 2 hours to precipitate magnesium ions. After filtration, a lithium precipitation and impurity removal solution was obtained. The solution was tested and found to contain 47 ppm Ca and 0 ppm Mg. Commercially available lithium carbonate (3.75 g / L) with fined particle size and sodium dodecylbenzene sulfonate were used as seed crystals and seed crystal growth promoters, respectively. A 250 g / L sodium carbonate saturated solution was added at 85°C. The above lithium precipitation and impurity removal solution was then slowly added dropwise and reacted in a water bath for 2 hours. After the reaction was completed, the solution was filtered, washed, and dried to obtain a battery-grade lithium carbonate product. Its scanning electron microscope image and Figure 3 They are essentially the same, and their purity is tested to be 99.59%, which meets the quality requirements for battery-grade lithium carbonate.

[0045] Comparative Example 1: The lithium content in lithium-containing aluminum hydroxide is 15212 ppm, and its particle size D 50 The material was milled from 25 μm to 5 μm and added to the reactor at a solid content of 150 g / L. No acid was added as the reaction medium. The mixture was heated to 170 °C and hydrothermally reacted for 4 hours. After the reaction, the system was filtered and washed. The resulting precipitate was boehmite. (See [link to relevant documentation]). Figure 4 The filtrate contained 518 ppm lithium and 48 ppm aluminum residue, requiring further separation of the aluminum colloid. The boehmite contained 4518 ppm lithium, with a lithium extraction rate of only 70.3%, far lower than that of the acid-assisted hydrothermal lithium extraction process. This indicates that without acid, the aluminum-lithium separation is poor, with a large amount of lithium remaining in the solid phase.

[0046] Comparative Example 2: The lithium content in lithium-containing aluminum hydroxide is 15212 ppm, and its particle size D 50 The material was milled from 25 μm to 5 μm and added to a reaction vessel at a solid content of 150 g / L. Then, 0.3 mol / L acetic acid was added, and the mixture was leached at 70°C for 4 hours. After the reaction, the system was filtered and washed, and the leaching filtrate and the leached solid were collected separately. (See [reference needed]). Figure 5 The filtrate contained 495 ppm lithium and 925 ppm aluminum, indicating a significant amount of aluminum leaching, necessitating further separation of the large amount of aluminum colloid. The lithium content in the solid after leaching was 4455 ppm, with a lithium extraction rate of 70.7%, indicating that the lithium extraction efficiency did not reach a breakthrough. This demonstrates that low-temperature leaching under normal pressure cannot achieve selective aluminum-lithium separation, and the large amount of aluminum leaching complicates subsequent processing.

[0047] Table 1 Comparison of process conditions and results between each embodiment and comparative example

[0048] As shown in Table 1, the lithium extraction rate using the acidic hydrothermal treatment process of this invention (Examples 1-5) all reached over 96%, far exceeding the approximately 70% of the comparative examples. The low residual lithium content in the boehmite product indicates thorough aluminum-lithium separation. The low residual aluminum content in the filtrate eliminates the need for secondary aluminum gel separation, making the process simple and efficient. Comparative Example 2 shows that even in an acidic medium, if the hydrothermal temperature is not reached, a large amount of aluminum dissolves, making selective separation impossible.

[0049] In summary, this invention achieves efficient separation of aluminum and lithium from lithium-containing aluminum hydroxide through acidic hydrothermal treatment, and prepares high-quality flake boehmite in one step and recovers lithium resources to prepare battery-grade lithium carbonate, which has significant technical advantages and industrial application value.

Claims

1. A method for extracting lithium during the hydrothermal preparation of boehmite from lithium-containing aluminum hydroxide, comprising the following steps: 1) Add lithium-containing aluminum hydroxide to an acidic solution and carry out a hydrothermal reaction at 150℃~180℃ to leach lithium into the solution phase, and separate aluminum after hydrothermal conversion to form platy boehmite. 2) The lithium extraction solution is evaporated and concentrated, and a purification agent is added to remove calcium and magnesium ions from the solution to obtain a purified solution; 3) Add saturated sodium carbonate solution to the purified solution, and precipitate battery-grade lithium carbonate through a water bath reaction.

2. The method according to claim 1, wherein the acidic solution is any one of acetic acid solution, oxalic acid solution, and phosphoric acid solution.

3. The method according to claim 1, wherein the concentration of the acidic solution is 0.1~0.5 mol / L, preferably 0.2~0.4 mol / L.

4. According to the method of claim 1, the solid content of the lithium-containing aluminum hydroxide in the reaction system is 100~300g / L.

5. According to the method of claim 1, in step 2), the lithium extraction solution is evaporated and concentrated to a lithium content ≥ 6 g / L.

6. The method according to claim 1, wherein the impurity removal process specifically comprises: adding oxalic acid as a calcium removal agent, wherein the amount of oxalic acid added is 2 to 3 times the molar amount of calcium ions in the concentrate; adjusting the pH of the system to 12 using sodium hydroxide to remove magnesium ions from the concentrate; the removal processes of calcium and magnesium ions are both carried out under water bath conditions of 55 to 75°C, and the reaction time is 1 to 2 hours.

7. The method according to claim 1, wherein the concentration of the saturated sodium carbonate solution is 250 g / L, the lithium precipitation water bath temperature is 85°C, and the reaction time is 2 h.

8. The method according to claim 1, characterized in that, Step 3) describes the lithium precipitation process by adding finely sized lithium carbonate as seed crystals and sodium dodecylbenzenesulfonate as a seed crystal growth promoter.

9. The method according to claim 1, characterized in that, The particle size D50 of the lithium-containing aluminum hydroxide is 5 μm.

10. The method according to claim 1, characterized in that, The boehmite obtained after the hydrothermal reaction has a lithium content of less than 250 ppm and a lithium extraction rate of more than 95%.

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