Preparation method of ultralow-sodium flake alumina

Abstract

The invention discloses a preparation method of ultralow-sodium flake alumina, relates to the technical field of inorganic non-metallic material preparation, and solves the problems of high roasting temperature and high sodium content in the flake alumina preparation process, aluminum hydroxide is used as an aluminum source, is mixed with a composite molten salt system, is roasted at 720-860 DEG C, and is mixed with a sodium removal agent for wet grinding to obtain the ultralow-sodium flake alumina. And centrifugally washing and drying to obtain the ultralow-sodium flake alumina. By utilizing the synergistic effect of the composite fluoride salt, the roasting temperature of the flaky alumina prepared by the molten salt method is reduced, the roasting temperature is lower than the temperature of the traditional molten salt method, meanwhile, the sodium content in the flaky alumina is preliminarily reduced, and the sodium content in the flaky alumina is finally reduced by combining the sodium removal agent wet grinding and centrifugal washing twice sodium removal and multi-effect synergism. The sodium content of the finished product is less than 0.05 wt.%.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material preparation technology, and relates to a method for preparing ultra-low sodium flake alumina. Background Technology

[0002] As a functional material with a special two-dimensional structure, lamellar alumina has radial dimensions down to the micrometer level and longitudinal dimensions down to the nanometer level. Its unique high aspect ratio and scaly microstructure give lamellar alumina multiple excellent properties of micro and nano materials, including high hardness, high melting point, excellent thermal conductivity and good light reflection characteristics. It has been widely used in many key fields such as refractory materials, ceramic toughening and modification, pearlescent pigments, and high-performance thermally conductive fillers.

[0003] In practical industrial applications, residual Na2O impurities in flake alumina significantly reduce the material's density and adversely affect the electrical insulation and other properties of the products, severely restricting its application in high-end product sectors. Therefore, developing efficient production technologies for flake alumina with ultra-low sodium content has become a core technological challenge that urgently needs to be overcome in this field.

[0004] Currently, researchers both domestically and internationally have conducted extensive research on the preparation technology of sheet-like alumina. Mainstream technical routes include high-temperature solid-state methods, hydrothermal synthesis methods, mechanical ball milling methods, sol-gel methods, and molten salt methods. Related published patents present diverse technical solutions, for example: 1. Patent application CN117819582A discloses a method for preparing sheet-like alumina using aluminum sol and controlling its thickness. This method involves mixing aluminum sol, molten salt, and a morphology modifier to prepare a suspension, which is then dried and calcined at 1000~1350℃ for 1~5 hours to achieve crystal transformation; 2. Patent application CN119080042A discloses a high aspect ratio alumina sheet and its preparation method. This method proposes preparing an aluminum source slurry using aluminum hydroxide and sodium oxide, mixing it with additives, and then subjecting it to a hydrothermal reaction and drying to obtain a precursor powder, which is then reacted with molten salt at 1100℃. Alumina flakes with an aspect ratio >40 can be prepared by calcination and purification at ~1350℃. 3. Patent application CN116041984B discloses a self-weathering flaky alumina and its preparation method. This method uses aluminum sulfate as the aluminum source, adds a certain amount of cerium chloride heptahydrate, potassium sulfate, and other auxiliaries, dissolves them in deionized water to obtain solution A, and dissolves sodium sulfate dodecahydrate and sodium carbonate in deionized water to obtain solution B. Solution B is added dropwise to solution A at 60~80℃ to obtain a white gel. After calcination at 1100~1300℃, flaky alumina with an average particle size of 5~65μm and a thickness of 0.2~0.8μm is obtained. Through gel preparation and calcination at 1100~1300℃, a product with an average particle size of 5~65μm and a thickness of 0.2~0.8μm is obtained.

[0005] However, in the above-disclosed technical solutions, the preparation of flake alumina relies on a high-temperature calcination process of 1000~1350℃ to achieve a complete transformation of the alumina crystal structure. This not only leads to high production energy consumption costs but also low energy utilization efficiency in the process. Furthermore, when aluminum hydroxide is used as the aluminum source in the current flake alumina preparation, sodium in the Bayer process exists mainly in four forms: attached alkali, intercrystalline alkali, lattice alkali, and chemical alkali. While attached alkali can be removed by adjusting the washing water temperature and dosage, the other three forms of sodium cannot be removed by water washing. Therefore, the sodium content of metallurgical-grade aluminum hydroxide produced by the Bayer process is at least 0.20 wt.%. Of course, some existing technologies replace aluminum hydroxide with other aluminum sources, but sodium salts are added in the subsequent molten salt or sol-gel process for preparing flake alumina, and there is no subsequent deep desodium removal step. The introduction of raw materials and the addition of molten salt during the preparation process result in a high sodium content in the flake alumina.

[0006] Existing research on the preparation of ultra-low sodium flake alumina by molten salt method is relatively scarce, making it difficult to meet the dual requirements of low sodium content and low cost for high-end applications.

[0007] Therefore, developing a new technology for preparing sheet-like alumina that combines low-temperature energy-saving characteristics with low-sodium conversion effect is of great academic value and industrial significance for breaking through existing technological bottlenecks and expanding its application in high-end fields. Summary of the Invention

[0008] To address the above shortcomings, this invention provides a method for preparing ultra-low sodium flake alumina, solving the problems of high calcination temperature and high sodium content in the product during the flake alumina preparation process. Through the synergistic effect of fluoride salt calcination, wet milling with a sodium-removing agent, and centrifugal washing, the sodium content in the flake alumina is reduced. The specific technical solution is as follows: A method for preparing ultra-low sodium flake alumina involves using aluminum hydroxide as the aluminum source, mixing it with a composite molten salt system, calcining it at 720–860°C, then mixing it with a desodiumning agent and deionized water and ball milling it. After centrifugation, washing, and drying, the ultra-low sodium flake alumina is obtained.

[0009] Preferably, the preparation method of the ultra-low sodium flake alumina specifically includes the following steps: (1) Mix aluminum hydroxide and the composite molten salt system evenly to obtain a mixture; (2) The mixture from step (1) is placed in a crucible and heated to 720-860°C for calcination to obtain the calcined material; (3) After washing the roasting material from step (2), add sodium removal agent and deionized water, and wet grind to obtain wet-ground slurry; (4) The wet grinding slurry from step (3) is centrifuged, washed, and dried to obtain the low-sodium flake alumina.

[0010] Preferably, in step (1), the mass ratio of aluminum hydroxide to composite molten salt is 100:(1.5-13).

[0011] Preferably, in step (1), the composite molten salt system is composed of composite fluoride salts.

[0012] Preferably, the composite fluoride salt is two or three of aluminum fluoride, potassium fluoride, lithium fluoride and ammonium fluoride, and their mass ratio is 1:(1-20) or 1:(1-20):(1-50).

[0013] Preferably, in step (2), the heating rate is 10-40℃ / min, the calcination temperature is 720-860℃, and the calcination time is 1-3h.

[0014] Preferably, in step (3), the desodiuming agent is at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid, and the amount of desodiuming agent added is 0.3 to 2.0 wt. of the roasted material.

[0015] Preferably, in step (3), the liquid-to-solid ratio of the wet mill is (4-7):1, the ball-to-material ratio is (7-10):1, the wet milling speed is 200 r / min to 300 r / min, and the wet milling time is 20-30 min.

[0016] Preferably, in step (4), the centrifugal washing is carried out by liquid-solid separation, the centrifuge speed is 2000-3500 r / min, and the number of centrifugal washing cycles is 3-5.

[0017] Preferably, in step (4), the drying method is blower drying, the drying temperature is 90-110℃, and the time is 2-3 hours.

[0018] The present invention achieves at least the following beneficial effects: 1. This invention utilizes the synergistic effect of composite fluoride salts to reduce the calcination temperature of molten salt method for preparing flake alumina. The calcination temperature is lower than that of the traditional molten salt method. At the same time, the sodium content in the flake alumina is initially removed. Then, combined with wet grinding and centrifugal washing with a sodium removal agent, sodium is removed twice, and finally the purpose of deep sodium removal is achieved. The sodium content of the finished product is <0.05 wt.%.

[0019] 2. This invention first uses a composite molten salt to form a eutectic. At the same calcination temperature, the molten salt system has better fluidity and higher activity, making the mass transfer and chemical reaction between reactants more rapid and complete. This allows the reaction and crystal growth to proceed at a lower phase transition temperature than the traditional γ-Al2O3 to α-Al2O3 transition. Secondly, the volatility of fluoride salts at high temperatures is utilized to promote the transport of fluoride ions in the gas phase, achieving the growth of lamellar alumina structures. Simultaneously, the fluoride salts react with the lattice bases and intercrystalline bases in aluminum hydroxide during the high-temperature process to form slightly water-soluble sodium fluoride. After washing with water to remove sodium fluoride, the sodium content of the lamellar alumina is reduced. Combined with weak acid wet milling and centrifugal washing, the sodium content of the product is further reduced. Moreover, the wet milling process avoids the damage to the morphology of lamellar alumina caused by dry milling and ball milling, effectively improving the dispersibility of calcined lamellar alumina. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a process flow diagram for preparing ultra-low sodium flake alumina according to the present invention; Figure 2 This is a SEM image of the ultra-low sodium flake alumina prepared according to the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] Lamellar alumina, with its unique two-dimensional structure, possesses excellent properties similar to micro and nanomaterials due to its large aspect ratio and scaly microstructure. It exhibits high hardness, high melting point, high thermal conductivity, and good light reflection properties, and is widely used in refractory materials, ceramic toughening, pearlescent materials, and thermally conductive fillers. However, in practical applications, the presence of Na₂O leads to a decrease in material density and also affects the electrical properties of the finished product. Therefore, developing an ultra-low sodium lamellar alumina production technology is an urgent problem to be solved in this field.

[0025] Based on this, the inventors continued to conduct in-depth research and exploration in this field. During the literature review, the inventors discovered that there are many existing documents on the preparation technology of sheet alumina. For example, patent application CN117819582 discloses a method for preparing sheet alumina using aluminum sol and controlling its thickness (calcination temperature of 1000~1300℃), patent application CN119080042A discloses a thin sheet of alumina with a high aspect ratio and its preparation method (calcination temperature of 1100~1350℃), and patent application CN116041984B discloses a sheet alumina with self-weathering function and its preparation method (calcination temperature of 1100~1300℃).

[0026] However, after considering the problems existing in current flake alumina production technologies, the inventors found that all the above technical solutions achieve alumina crystal transformation through high-temperature calcination, with a calcination temperature range of 1000~1350℃, resulting in high energy consumption. Furthermore, the flake alumina produced by the above methods and other existing technologies has a relatively high sodium content. Currently, there is limited research on the preparation of ultra-low sodium flake alumina using the molten salt method. Therefore, developing a lower-temperature, lower-sodium preparation method is of significant value. After extensive innovative design and failed experiments, the inventors of this application have developed the technical solution of this invention: A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite molten salt system (composite fluoride salt) are mixed evenly at a mass ratio of 100:(1.5~13) to obtain a mixture; (2) The mixture from step (1) is placed in a crucible and heated to 720-860°C at a rate of 10-40°C / min and kept warm for calcination for 1-3 hours to obtain calcined material; (3) After washing the calcined material from step (2), add 0.3 to 2.0 wt.% of sodium removal agent and deionized water to the calcined material, and wet grind it at a speed of 200 r / min to 300 r / min for 20 to 30 minutes to obtain a wet grinding slurry; (4) The wet grinding slurry from step (3) is centrifuged and washed 3 to 5 times using a liquid-solid separation method. The centrifuge speed is 2000 to 3500 r / min. The material is then placed in an oven at 90 to 110°C and dried for 2 to 3 hours to obtain ultra-low sodium flake alumina.

[0027] Specifically, in step (1), the composite fluoride salt is two or three of aluminum fluoride, potassium fluoride, lithium fluoride, and ammonium fluoride, and their mass ratio is 1:(1-20) or 1:(1-20):(1-50); in step (3), the desodiuming agent is at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid; the liquid-solid ratio of wet milling is (4-7):1, and the ball-to-material ratio is (7-10):1.

[0028] Example 1 A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite fluoride salt are mixed evenly at a mass ratio of 100:10 to obtain a mixture; the composite fluoride salt is aluminum fluoride and ammonium fluoride in a mass ratio of 1:1. (2) The mixture from step (1) is placed in a crucible and then sent into a muffle furnace. The temperature is raised to 860°C at a rate of 24°C / min and kept at the temperature for 2 hours to obtain the calcined material. (3) After washing the calcined material from step (2), add 2.0 wt.% of the desodiuming agent and deionized water to the calcined material, place it in a ball mill jar, add agate balls and wet mill for 20 minutes at 200 r / min to obtain a wet mill slurry; the desodiuming agent is nitric acid and hydrochloric acid in a mass ratio of 1:2; the liquid-solid ratio of wet milling is 4:1 and the ball-material ratio is 7:1; (4) The wet grinding slurry from step (3) was centrifuged and washed three times using a liquid-solid separation method. The centrifuge speed was 3500 r / min. The material was then placed in an oven at 110°C and dried for 2 hours to obtain the ultra-low sodium flake alumina.

[0029] The alumina obtained in Example 1 has an aspect ratio greater than 12 and a sodium content of 0.04 wt.%.

[0030] Example 2 A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite fluoride salt are mixed evenly at a mass ratio of 100:13 to obtain a mixture; the composite fluoride salt is aluminum fluoride, potassium fluoride and ammonium fluoride in a mass ratio of 1:20:50. (2) The mixture from step (1) is placed in a crucible and then placed in a muffle furnace. The temperature is raised to 750°C at a rate of 27°C / min and kept at the temperature for 3 hours to obtain the calcined material. (3) After washing the calcined material from step (2) with water, add 0.3 wt.% of the desodiuming agent and deionized water to the calcined material, place it in a ball mill jar, add agate balls and wet mill for 30 min at 300 r / min to obtain wet mill slurry; the desodiuming agent is nitric acid, hydrochloric acid and phosphoric acid in a mass ratio of 2:1:1; the liquid-solid ratio of wet milling is 7:1 and the ball-material ratio is 10:1; (4) The wet grinding slurry from step (3) was centrifuged and washed 5 times using a liquid-solid separation method. The centrifuge speed was 2000 r / min. The material was placed in an oven at 90°C and dried for 3 hours to obtain the low-sodium flake alumina.

[0031] The alumina obtained in Example 2 has an aspect ratio greater than 15 and a sodium content of 0.03 wt.%.

[0032] Example 3 A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite fluoride salt are mixed evenly at a mass ratio of 100:2.5 to obtain a mixture; the composite fluoride salt is aluminum fluoride, lithium fluoride and ammonium fluoride in a mass ratio of 1:15:12. (2) The mixture from step (1) is placed in a crucible and heated to 720°C at a rate of 10°C / min and kept warm for 3 hours to obtain the calcined material. (3) After washing the calcined material from step (2) with water, add 1.0 wt.% of desodiuming agent and deionized water to the calcined material, place it in a ball mill jar, add agate balls and wet mill, and wet mill at 300 r / min for 30 min to obtain wet mill slurry; the desodiuming agent is phosphoric acid with an acid concentration of 1.0%, the liquid-solid ratio of wet milling is 7:1, and the ball-material ratio is 8:1; (4) The wet grinding slurry from step (3) was centrifuged and washed 4 times using a liquid-solid separation method. The centrifuge speed was 2800 r / min. The material was placed in an oven at 100°C and dried for 2.5 h to obtain the low-sodium flake alumina.

[0033] The alumina obtained in Example 3 has an aspect ratio greater than 15 and a sodium content of 0.012 wt.%.

[0034] Example 4 A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite molten salt system (composite fluoride salt) are mixed evenly at a mass ratio of 100:1.5 to obtain a mixture. The composite fluoride salt is aluminum fluoride and ammonium fluoride at a mass ratio of 1:20. (2) The mixture from step (1) is placed in a crucible and heated to 820°C at a rate of 10°C / min and kept warm for 3 hours to obtain the calcined material. (3) After washing the calcined material from step (2) with water, add 0.5 wt.% of the desodiuming agent and deionized water to the calcined material, and wet grind at 220 r / min for 22 min to obtain a wet grinding slurry. The desodiuming agent is nitric acid, sulfuric acid, phosphoric acid and citric acid in a mass ratio of 2:3:1:1. The liquid-solid ratio of the wet grinding is 5:1 and the ball-material ratio is 8:1. (4) The wet grinding slurry from step (3) was centrifuged and washed three times using a liquid-solid separation method. The centrifuge speed was 2500 r / min. The material was then placed in an oven at 95°C and dried for 3 hours to obtain ultra-low sodium flake alumina.

[0035] The alumina obtained in Example 4 has an aspect ratio greater than 12 and a sodium content of 0.02 wt.%.

[0036] Example 5 A method for preparing ultra-low sodium flake alumina specifically includes the following steps: (1) Aluminum hydroxide and composite molten salt system (composite fluoride salt) are mixed evenly at a mass ratio of 100:13 to obtain a mixture. The composite fluoride salt is aluminum fluoride, potassium fluoride and ammonium fluoride in a mass ratio of 1:1:1. (2) The mixture from step (1) is placed in a crucible and heated to 860°C at a rate of 40°C / min and kept warm for 1 hour to obtain the calcined material. (3) After washing the calcined material from step (2) with water, add 1.5 wt.% of desodiuming agent and deionized water to the calcined material, and wet grind at 280 r / min for 28 min to obtain wet grinding slurry. The desodiuming agent is hydrochloric acid, sulfuric acid, phosphoric acid and citric acid in a mass ratio of 3:1:1:2. The liquid-solid ratio of wet grinding is 6:1 and the ball-material ratio is 9:1. (4) The wet grinding slurry from step (3) is centrifuged and washed 5 times using a liquid-solid separation method. The centrifuge speed is 2000-3500 r / min. The material is placed in an oven at 90-110℃ and dried for 2-3 hours to obtain ultra-low sodium flake alumina.

[0037] The alumina obtained in Example 5 has an aspect ratio greater than 12 and a sodium content of 0.015 wt.%.

[0038] Comparative Example 1 The difference from Example 1 is that the temperature of the heat preservation and roasting in step (2) is 550°C, while other conditions remain unchanged.

[0039] The microstructure of the material obtained in Comparative Example 1 showed flaky and blocky particles, indicating that the composite fluoride salt system composed of aluminum fluoride and ammonium fluoride did not react completely at this temperature, and the sodium content of the calcined material was 0.28 wt.%.

[0040] Comparative Example 2 The difference from Example 1 is that: in step (3), no molten salt (complex fluoride salt) was added, that is, no fluoride salt was added, and aluminum hydroxide was directly roasted, while other conditions remained unchanged.

[0041] The microstructure of the material obtained in Comparative Example 2 is a bulk structure. That is, in the absence of a liquid medium provided by molten salt, the crystallization process of alumina cannot grow in an oriented manner and can only form thermodynamically stable equiaxed particles. At the same time, the sodium content of the calcined alumina without the participation of fluoride salt is 0.35 wt.%.

[0042] Comparative Example 3 The difference from Example 1 is that the fluoride salt is a single fluoride salt, containing only aluminum fluoride, while other conditions remain unchanged.

[0043] The microstructure of the sample obtained in Comparative Example 3 still retains the particle agglomeration of aluminum hydroxide, with micropores on the surface and unreacted fluoride salts. The sodium content of the calcined material is 0.24 wt.%.

[0044] Comparative Example 4 The difference from Example 1 is that no sodium removal agent was added during the wet milling process, while other conditions remained the same.

[0045] The alumina obtained in Comparative Example 4 had poor dispersibility, with a large number of stacked sheets, an aspect ratio greater than 12, and a sodium content of 0.17 wt.%.

[0046] Comparative Example 5 The difference from Example 1 is that wet milling was not performed; instead, deionized water was continuously added for vacuum filtration and cleaning of the calcined material. After cleaning until the pH value of the supernatant layer in the funnel was neutral, it was dried for 2-3 hours. Other conditions remained unchanged.

[0047] The microstructure of the sheet-like alumina prepared by the filtration and washing method in Comparative Example 5 showed that the sheet distribution was relatively concentrated, with many overlapping layers, an aspect ratio greater than 12, and a sodium content of 0.20 wt.%.

[0048] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing ultra-low sodium flake alumina, characterized in that, Using aluminum hydroxide as the aluminum source, it is mixed with a composite molten salt system and calcined at 720–860°C. Then, it is mixed with a sodium removal agent and deionized water and wet-milled. After centrifugation, washing, and drying, the ultra-low sodium flake alumina is obtained.

2. The method for preparing ultra-low sodium flake alumina according to claim 1, characterized in that, Specifically, the following steps are included: (1) Mix aluminum hydroxide and the composite molten salt system evenly to obtain a mixture; (2) The mixture from step (1) is placed in a crucible and heated to 720-860°C for calcination to obtain the calcined material; (3) After washing the roasted material from step (2), add sodium removal agent and deionized water and mix and wet grind to obtain wet grinding slurry; (4) The wet grinding slurry from step (3) is centrifuged, washed, and dried to obtain the ultra-low sodium flake alumina.

3. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (1), the mass ratio of aluminum hydroxide to the composite molten salt system is 100:(1.5-13).

4. The method for preparing ultra-low sodium flake alumina according to claim 2 or 3, characterized in that, In step (1), the composite molten salt system is composed of composite fluoride salts.

5. The method for preparing ultra-low sodium flake alumina according to claim 4, characterized in that, The composite fluoride salt is two or three of aluminum fluoride, potassium fluoride, lithium fluoride and ammonium fluoride, and their mass ratio is 1:(1-20) or 1:(1-20):(1-50).

6. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (2), the heating rate is 10-40℃ / min, the calcination temperature is 720-860℃, and the calcination time is 1-3h.

7. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (3), the desodiuming agent is at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid, and the amount of desodiuming agent added is 0.3 to 2.0 wt. of the roasted material.

8. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (3), the liquid-to-solid ratio of the wet mill is (4-7):1, the ball-to-material ratio is (7-10):1, the wet mill speed is 200 r / min to 300 r / min, and the wet milling time is 20-30 min.

9. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (4), the centrifugal washing is carried out by liquid-solid separation, the centrifuge speed is 2000-3500 r / min, and the number of centrifugal washing cycles is 3-5.

10. The method for preparing ultra-low sodium flake alumina according to claim 2, characterized in that, In step (4), the drying method is blower drying, the drying temperature is 90-110℃, and the time is 2-3 hours.

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