A method for preparing boehmite
The preparation method of boehmite was optimized by using a two-stage hydrothermal reaction, which solved the problems of wide particle size distribution and poor dispersibility in the preparation of boehmite, and realized efficient and environmentally friendly boehmite production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAMEN ZIJIN NEW ENERGY & NEW MATERIAL TECH CO LTD
- Filing Date
- 2025-08-20
- Publication Date
- 2026-07-03
AI Technical Summary
Existing methods for preparing boehmite have problems such as wide particle size distribution, poor dispersibility, insufficient regularity of the product, harsh reaction conditions, and poor environmental friendliness.
Using aluminum hydroxide as the single aluminum source, combined with a two-stage hydrothermal reaction with a temperature difference of ≥50℃, rapid nucleation is achieved first at high temperature, followed by slow growth at low temperature, optimizing crystallization and avoiding crystal agglomeration or excessive growth.
It significantly improves the crystallization rate, dispersibility and particle size distribution uniformity of boehmite, simplifies the process, reduces production costs and improves environmental friendliness.
Smart Images
Figure CN120793981B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of inorganic materials technology, and in particular to a method for preparing boehmite. Background Technology
[0002] Boehmite is an aluminum hydroxide mineral (γ-AlOOH), belonging to the hydroxyl oxides of aluminum, and is commonly found in bauxite. Boehmite has a layered crystal structure with hydroxyl groups located between the layers and aluminum atoms occupying octahedral sites. This structure gives it a high specific surface area and good thermal stability, making it widely used in lithium-ion battery separators, metal catalyst supports, adsorbent materials, and ceramic materials.
[0003] Traditional methods for synthesizing boehmite mainly include precipitation, sol-gel, and hydrothermal methods. Among these, the hydrothermal method has become the mainstream industrial method due to its advantages of simple operation and high product purity. However, existing hydrothermal methods still have certain problems: the product has a wide particle size distribution, poor dispersibility, and insufficient regularity. Furthermore, the use of multiple additives often leads to impurity residues. Additionally, the reaction conditions are harsh (e.g., high temperature and high pressure) and environmentally unfriendly (e.g., difficult waste recovery). For example, Chinese patent CN113860342A discloses a method for preparing high-purity parallelepiped boehmite. This method uses aluminum hydroxide and γ-alumina as aluminum sources, ammonia as a pH adjuster, and employs a two-stage heating process to prepare boehmite. Although this method produces boehmite with high purity and crystallinity, its dispersibility is poor, and the washing aids and ammonia used in the preparation process cannot be recycled, increasing production costs and posing environmental pollution risks.
[0004] Therefore, further optimization of the boehmite preparation method is of great practical significance. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for preparing boehmite.
[0006] The technical solution adopted in this invention is as follows:
[0007] This invention provides a method for preparing boehmite, comprising the following steps:
[0008] S1. Mix aluminum hydroxide, water and grinding aid and grind to obtain a slurry;
[0009] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to a first temperature and kept at that temperature for a first time. Then, the temperature is lowered to a second temperature and kept at that temperature for a second time. After the reaction is completed, the slurry is naturally cooled to room temperature to obtain the boehmite.
[0010] The difference between the first temperature and the second temperature is not less than 50°C.
[0011] This invention proposes a method for preparing boehmite, using aluminum hydroxide as the sole aluminum source and combining it with a two-stage hydrothermal reaction with a temperature difference ≥50℃ to optimize crystallization. First, rapid nucleation occurs at a first temperature (high temperature) to ensure a sufficient number of crystal nuclei; then, slow growth occurs at a second temperature (low temperature) to prevent crystal agglomeration or overgrowth, thereby significantly improving the crystal transformation rate, dispersibility, and particle size distribution uniformity of boehmite. This preparation method is characterized by simple raw materials, easy operation, and environmental friendliness, making it suitable for large-scale industrial production.
[0012] Preferably, in step S1, before mixing, the aluminum hydroxide is further activated by calcining at 150–300°C for 1–6 hours.
[0013] Preferably, in step S1, the grinding aid is selected from one or a combination of two or more of oleic acid, stearic acid, ethylene glycol, polyethylene glycol, propylene glycol and triethanolamine.
[0014] Preferably, in step S1, the weight ratio of aluminum hydroxide, water and grinding aid is 5-10:20-100:1.
[0015] Preferably, in step S1, the grinding is ball milling or sand milling, and the grinding time is 0.5 to 8 hours.
[0016] Preferably, in step S2, the first temperature is 200-300℃, and the first heat preservation time is 0.5-3h.
[0017] Preferably, in step S2, the second temperature is 140-250°C, and the second heat preservation time is 2-30 hours.
[0018] Preferably, in step S2, after the natural cooling to room temperature, a post-processing is further included, which includes: filtering the obtained hydrothermal reaction product to obtain a filter cake and a filtrate, drying and grinding the filter cake to obtain the boehmite, and returning the filtrate to step S1 for slurry preparation.
[0019] Preferably, the drying temperature is 30–100°C and the time is 4–12 hours. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the boehmite preparation process in Example 1;
[0021] Figure 2 The XRD pattern of boehmite prepared in Example 1;
[0022] Figure 3 SEM image of boehmite obtained in Example 1;
[0023] Figure 4SEM image of boehmite obtained in Example 1;
[0024] Figure 5 SEM image of boehmite prepared in Comparative Example 1;
[0025] Figure 6 The image shows a SEM image of boehmite prepared in Comparative Example 2. Detailed Implementation
[0026] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.
[0027] This invention provides a method for preparing boehmite, comprising the following steps:
[0028] S1. Mix aluminum hydroxide, water and grinding aid and grind to obtain a slurry;
[0029] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to the first temperature and kept at that temperature for the first time. Then, the temperature is lowered to the second temperature and kept at that temperature for the second time. After the reaction is completed, the slurry is naturally cooled to room temperature to obtain boehmite.
[0030] The difference between the first temperature and the second temperature shall not be less than 50°C.
[0031] This invention employs a two-stage hydrothermal reaction with a temperature difference ≥50℃. The first temperature is higher than the second temperature. Boehmite rapidly nucleates at the first temperature stage and grows slowly at a low temperature at the second temperature stage, thereby generating boehmite with high purity, good dispersibility, adjustable particle size, narrow particle size distribution, and regular shape. If only the first temperature is used for high-temperature hydrothermal reaction, the following problems will occur: (1) The crystal nucleus formation rate is fast, but the growth is uncontrolled. After a large number of crystal nuclei are generated instantaneously, they are prone to collision and fusion, forming large-sized agglomerates, which significantly reduces the dispersibility of boehmite; (2) The particle size is difficult to control, and the atoms do not have time to stack in an orderly manner, resulting in a wide particle size distribution and poor morphological regularity of boehmite. If only the second temperature is used for low-temperature hydrothermal reaction, since the low temperature cannot provide enough energy for nucleation, the number of crystal nuclei formed is small and the speed is slow, resulting in a low crystallization rate of boehmite. For example, the temperature difference between the first temperature and the second temperature can be any value among 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc., without any particular restrictions.
[0032] In a preferred embodiment, step S1 further includes activating the aluminum hydroxide before mixing by calcining at 150–300°C for 1–6 hours. In this invention, pre-activating the aluminum hydroxide enhances its reactivity. Activated aluminum hydroxide is easier to grind and refine, and more readily converts to boehmite in subsequent hydrothermal reactions, thus increasing the crystallization rate. For example, the activation treatment can be 150°C × 6 hours, 180°C × 5 hours, 200°C × 4 hours, 220°C × 3 hours, 250°C × 2 hours, 270°C × 2 hours, 300°C × 1 hour, etc., without particular limitation.
[0033] In a preferred embodiment, in step S1, the grinding aid is selected from one or a combination of two or more of oleic acid, stearic acid, ethylene glycol, polyethylene glycol, propylene glycol, and triethanolamine. In this invention, the grinding aid has dual functions of aiding grinding and dispersing: during the grinding stage, the grinding aid assists in the refinement of aluminum hydroxide particles, thus playing a role in grinding; during the hydrothermal reaction stage, the grinding aid continuously adsorbs onto the particle surface, playing a dispersing role, effectively inhibiting particle agglomeration and improving dispersibility, eliminating the need for the additional addition of a dispersant.
[0034] In a preferred embodiment, in step S1, the weight ratio of aluminum hydroxide, water, and grinding aid is 5–10:20–100:1. In this invention, selecting the above ratio helps ensure the grinding effect of aluminum hydroxide and meets the requirements of the subsequent hydrothermal reaction, thereby ensuring the high dispersibility and purity of the obtained boehmite. For example, the weight ratio of aluminum hydroxide, water, and grinding aid can be 5:20:1, 5:25:1, 6:40:1, 7:50:1, 8:60:1, 9:70:1, 10:80:1, 10:100:1, etc., but is not limited to the listed values.
[0035] In a preferred embodiment, in step S1, the grinding is performed by ball milling or sand milling, and the grinding time is 0.5 to 8 hours. In this invention, ball milling or sand milling can refine the particle size of aluminum hydroxide, increase its specific surface area, provide more reactive sites for the subsequent hydrothermal reaction, and promote the complete progress of the reaction. For example, the grinding time can be any value from 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc., without particular limitation.
[0036] In a preferred embodiment, in step S2, the first temperature is 200–300°C, and the first holding time is 0.5–3 hours. In this invention, the high-temperature hydrothermal stage at the first temperature is the core step for rapid and uniform nucleation of boehmite. Its reaction conditions directly affect the quantity and quality of crystal nuclei, thereby affecting the performance of boehmite. If the first temperature is too high or the first holding time is too long, excessive nucleation leads to crystal nuclei collision and agglomeration. Furthermore, the rapid atomic migration at high temperatures causes disordered growth, resulting in decreased dispersibility, wider particle size distribution, and poorer morphological regularity. If the first temperature is too low or the first holding time is too short, the nucleation motive force is insufficient, the number of crystal nuclei is too small, and a large amount of unconverted raw material forms heterogeneous crystals in the subsequent low-temperature growth stage, resulting in insufficient crystal conversion rate and uneven particle size distribution. For example, the first temperature can be any value among 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the first heat preservation time can be any value among 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc., without any particular restrictions.
[0037] In a preferred embodiment, in step S2, the second temperature is 140–250°C, and the second holding time is 2–30 hours. In this invention, the low-temperature hydrothermal stage of the second temperature is a key step in optimizing the integrity of the crystal structure through low-temperature "slow growth," building upon the high-temperature nucleation stage. If the second temperature is too high or the second holding time is too long, the crystal will overgrow or fuse, disrupting the uniformity of the particle size distribution; if the second temperature is too low or the second holding time is too short, the crystal growth will be incomplete, resulting in a loose crystal structure, increased defects, decreased crystallinity, and a disordered morphology. For example, the second temperature can be any value from 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, etc.; the second holding time can be any value from 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 22 hours, 26 hours, 30 hours, etc., without any particular limitation.
[0038] For further examples, when the first temperature is 250℃, the second temperature can be 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, etc.; when the first temperature is 280℃, the second temperature can be 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, etc. The high-temperature-low-temperature two-stage hydrothermal reaction design of this invention enables high-performance control of boehmite.
[0039] In a preferred embodiment, step S2 further includes post-processing after natural cooling to room temperature. Post-processing includes: filtering the obtained hydrothermal reaction product to obtain a filter cake and filtrate; drying and grinding the filter cake to obtain boehmite; and returning the filtrate to step S1 for slurry preparation. In this invention, the filtrate from the hydrothermal reaction in step S2 can be directly reused in the slurry preparation of step S1. On the one hand, the filtrate is highly compatible with the initial slurry raw material components, and reuse will not affect the stability of the system, achieving efficient resource recycling and significantly reducing production costs. On the other hand, since the entire process requires no additional additives (such as dispersants, crystallizing agents, pH adjusters, etc.), no impurities are introduced. Unlike traditional hydrothermal methods, washing and purification are unnecessary, simplifying the process flow, improving production efficiency, and reducing wastewater discharge at the source, significantly enhancing the environmental friendliness of the process.
[0040] In a preferred embodiment, the drying temperature is 30–100°C, and the drying time is 4–12 hours. In this invention, drying reduces the water content of boehmite, which is beneficial for improving its dispersibility and stability. For example, the drying treatment can be 30°C for 12 hours, 50°C for 10 hours, 80°C for 6 hours, 100°C for 4 hours, etc.
[0041] Example 1
[0042] See Figure 1 A method for preparing boehmite includes the following steps:
[0043] S1. 10g of aluminum hydroxide is activated by calcining at 220℃ for 3 hours and then naturally cooling to room temperature to obtain activated aluminum hydroxide.
[0044] Activated aluminum hydroxide, 50g water, 1g polyethylene glycol and 1g triethanolamine were mixed and ball-milled at 500rpm for 4h to obtain a slurry;
[0045] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to 250℃ and kept at that temperature for 1 hour, then the temperature is lowered to 160℃ and kept at that temperature for 8 hours. After the reaction is completed, it is naturally cooled to room temperature to obtain the hydrothermal reaction product.
[0046] The hydrothermal reaction products are post-processed, including filtration to obtain filter cake and filtrate. The filter cake is dried at 80°C for 6 hours and ground to obtain boehmite. The filtrate is returned to step S1 for slurry preparation.
[0047] The XRD pattern of the boehmite obtained in this embodiment is as follows. Figure 2 As shown, the boehmite obtained in this embodiment has sharp characteristic peaks (black), and its peak positions (red) highly match those of the standard card, indicating that the boehmite obtained by the method of this invention has high crystallinity; the SEM image of the boehmite obtained in this embodiment is shown below. Figure 3 and Figure 4As shown, the boehmite prepared in this embodiment has a uniform particle size, basically has a blocky structure, regular morphology, and high dispersibility.
[0048] Example 2
[0049] A method for preparing boehmite includes the following steps:
[0050] S1. 10g of aluminum hydroxide is activated by calcining at 220℃ for 3 hours and then naturally cooling to room temperature to obtain activated aluminum hydroxide.
[0051] Activated aluminum hydroxide, 50g of water and 1.5g of ethylene glycol were mixed and ball-milled at 500rpm for 6h to obtain a slurry;
[0052] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to 280℃ and kept at that temperature for 1 hour, then the temperature is lowered to 160℃ and kept at that temperature for 8 hours. After the reaction is completed, it is naturally cooled to room temperature to obtain the hydrothermal reaction product.
[0053] The hydrothermal reaction products are post-processed, including filtration to obtain filter cake and filtrate. The filter cake is dried at 80°C for 6 hours and ground to obtain boehmite. The filtrate is returned to step S1 for slurry preparation.
[0054] Example 3
[0055] A method for preparing boehmite includes the following steps:
[0056] S1. 10g of aluminum hydroxide is activated by calcining at 200℃ for 5h and then naturally cooling to room temperature to obtain activated aluminum hydroxide.
[0057] Activated aluminum hydroxide, 50g water, 0.5g stearic acid and 1g polyethylene glycol were mixed and ball-milled at 500rpm for 4h to obtain a slurry;
[0058] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to 250℃ and kept at that temperature for 1 hour, then the temperature is lowered to 180℃ and kept at that temperature for 8 hours. After the reaction is completed, it is naturally cooled to room temperature to obtain the hydrothermal reaction product.
[0059] The hydrothermal reaction products are post-processed, including filtration to obtain filter cake and filtrate. The filter cake is dried at 80°C for 6 hours and ground to obtain boehmite. The filtrate is returned to step S1 for slurry preparation.
[0060] Example 4
[0061] A method for preparing boehmite includes the following steps:
[0062] S1. 10g of aluminum hydroxide is activated by calcining at 200℃ for 3 hours and then naturally cooling to room temperature to obtain activated aluminum hydroxide.
[0063] Activated aluminum hydroxide, 50g water, 1g propylene glycol and 1g polyethylene glycol were mixed and ball-milled at 500rpm for 4h to obtain a slurry;
[0064] S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to 230℃ and kept at that temperature for 2 hours, then the temperature is lowered to 160℃ and kept at that temperature for 8 hours. After the reaction is completed, it is naturally cooled to room temperature to obtain the hydrothermal reaction product.
[0065] The hydrothermal reaction products are post-processed, including filtration to obtain filter cake and filtrate. The filter cake is dried at 80°C for 6 hours and ground to obtain boehmite. The filtrate is returned to step S1 for slurry preparation.
[0066] Example 5
[0067] The difference between this embodiment and Embodiment 1 is that the aluminum hydroxide in step S1 is not activated. The remaining steps remain unchanged.
[0068] Example 6
[0069] The difference between this embodiment and Embodiment 2 is that "10g aluminum hydroxide, 50g water" is replaced with "12g aluminum hydroxide, 90g water". The remaining steps remain unchanged.
[0070] Example 7
[0071] The difference between this embodiment and Embodiment 2 is that "10g aluminum hydroxide, 50g water" is replaced with "15g aluminum hydroxide, 150g water". The remaining steps remain unchanged.
[0072] Comparative Example 1
[0073] The difference between this comparative example and Example 1 is that in step S2, "first heat to 250°C and hold for 1 hour, then cool down to 160°C and hold for 8 hours" is replaced with "heat to 250°C and hold for 9 hours". The remaining steps remain unchanged.
[0074] The SEM image of the boehmite prepared in this comparative example is shown below. Figure 5 As shown, the boehmite prepared in this comparative example exhibits obvious agglomerates, reduced dispersibility, and poorer particle size uniformity and morphological regularity.
[0075] Comparative Example 2
[0076] The difference between this comparative example and Example 1 is that in step S2, "first heat to 250°C and hold for 1 hour, then cool down to 160°C and hold for 8 hours" is replaced with "heat to 160°C and hold for 9 hours". The remaining steps remain unchanged.
[0077] The SEM image of the boehmite prepared in this comparative example is shown below. Figure 6As shown, the boehmite prepared in this comparative example has fewer crystal nuclei and incomplete crystallization.
[0078] Comparative Example 3
[0079] The difference between this comparative example and Example 2 is that in step S2, "first heat to 280°C and hold for 1 hour" is replaced with "first heat to 310°C and hold for 1 hour". The remaining steps remain unchanged.
[0080] Comparative Example 4
[0081] The difference between this comparative example and Example 2 is that in step S2, "heating to 280°C and holding for 1 hour" is replaced with "heating to 190°C and holding for 1 hour". The remaining steps remain unchanged.
[0082] Comparative Example 5
[0083] The difference between this comparative example and Example 2 is that in step S2, "cool down to 160°C and keep warm for 8 hours" is replaced with "cool down to 260°C and keep warm for 8 hours". The remaining steps remain unchanged.
[0084] Comparative Example 6
[0085] The difference between this comparative example and Example 2 is that in step S2, "cool down to 160°C and keep warm for 8 hours" is replaced with "cool down to 130°C and keep warm for 8 hours". The remaining steps remain unchanged.
[0086] Performance tests were conducted on Examples 1-7 and Comparative Examples 1-6, and the test results are recorded in Table 1.
[0087] The testing method is as follows:
[0088] The particle size distribution and polydispersity index (PDI) of the samples were determined using a laser particle size analyzer based on the principle of dynamic light scattering. The particle size range was expressed by the formula (D). 90 -D 10 ) / D 50 calculate.
[0089] Table 1
[0090] Crystallization rate (%) purity(%) Particle size range Multi-dispersion index Example 1 98.8 99.8 1.46 0.13 Example 2 98.6 99.7 1.55 0.14 Example 3 98.1 99.5 1.61 0.18 Example 4 98.5 99.6 1.58 0.15 Example 5 95.7 98.9 1.78 0.26 Example 6 98.7 99.7 1.59 0.16 Example 7 98.3 99.5 1.58 0.13 Comparative Example 1 91.7 94.5 2.96 0.46 Comparative Example 2 75.8 91.9 3.95 0.61 Comparative Example 3 81.6 87.4 2.99 0.49 Comparative Example 4 84.5 93.0 3.71 0.56 Comparative Example 5 90.0 93.2 3.12 0.52 Comparative Example 6 90.9 94.8 2.44 0.33
[0091] As shown in Table 1, the boehmite prepared in each embodiment of the present invention exhibits excellent crystal transformation rate, purity, dispersibility, and particle size distribution uniformity. Comparing Example 1 and Comparative Examples 1-2, it is evident that single high-temperature hydrothermal treatment easily leads to agglomeration and difficulty in controlling particle size, resulting in poor boehmite dispersibility and decreased particle size uniformity; single low-temperature hydrothermal treatment results in low boehmite crystal transformation rate and wide particle size distribution. Comparing Example 2 and Comparative Examples 3-4, it is evident that excessively high temperatures in the high-temperature hydrothermal treatment stage lead to numerous secondary phases and intense crystal nucleus collisions, resulting in low boehmite purity and poor dispersibility; excessively low temperatures in the high-temperature hydrothermal treatment stage result in insufficient nucleation, slightly more residual raw materials, low boehmite purity, and large particle size differences. Comparing Example 2 and Comparative Examples 5-6, it is evident that excessively high temperatures in the low-temperature hydrothermal treatment stage lead to excessive crystal growth, mainly affecting particle size uniformity and dispersibility; excessively low temperatures in the low-temperature hydrothermal treatment stage result in incomplete crystal growth, mainly affecting particle size uniformity.
[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing boehmite, characterized in that, Includes the following steps: S1. Mix aluminum hydroxide, water and grinding aid and grind to obtain a slurry; S2. The slurry is subjected to a hydrothermal reaction. First, the temperature is raised to a first temperature and kept at that temperature for a first time. Then, the temperature is lowered to a second temperature and kept at that temperature for a second time. After the reaction is completed, the slurry is naturally cooled to room temperature to obtain the boehmite. The difference between the first temperature and the second temperature is not less than 50°C; The first temperature is 200~300℃, and the first heat preservation time is 0.5~3h; The second temperature is 140~250℃, and the second heat preservation time is 2~30h.
2. The method for preparing boehmite as described in claim 1, characterized in that, In step S1, prior to the mixing, the aluminum hydroxide is further activated by calcining at 150-300°C for 1-6 hours.
3. The method for preparing boehmite as described in claim 1, characterized in that, In step S1, the grinding aid is selected from one or a combination of two or more of oleic acid, stearic acid, ethylene glycol, polyethylene glycol, propylene glycol and triethanolamine.
4. The method for preparing boehmite as described in claim 1, characterized in that, In step S1, the weight ratio of aluminum hydroxide, water, and grinding aid is 5~10:20~100:
1.
5. The method for preparing boehmite as described in claim 1, characterized in that, In step S1, the grinding is ball milling or sand milling, and the grinding time is 0.5~8h.
6. The method for preparing boehmite as described in claim 1, characterized in that, In step S2, after the natural cooling to room temperature, a post-processing is also included. The post-processing includes: filtering the obtained hydrothermal reaction product to obtain a filter cake and a filtrate. The filter cake is dried and ground to obtain the boehmite. The filtrate is returned to step S1 for slurry preparation.
7. The method for preparing boehmite as described in claim 6, characterized in that, The drying temperature is 30~100℃, and the time is 4~12h.