A method for producing high-purity alumina from a bayer process sodium aluminate solution

Abstract

The application discloses a method for preparing high-purity alumina from a Bayer-process sodium aluminate solution, which comprises the following steps: heating and liquefying excessive industrial aluminum hydroxide and liquid alkali to obtain a sodium aluminate solution; adding crystal seeds to pre-decompose and purify the sodium aluminate solution to obtain a high-purity sodium aluminate solution; diluting part of the high-purity sodium aluminate solution, adding crystal seed initiators and high-molecular dispersants to prepare an active crystal seed slurry; adding the active crystal seed slurry to the remaining high-purity sodium aluminate solution to perform seed decomposition, and sampling in the early, middle and late stages of seed decomposition, respectively, and then performing solid-liquid separation to obtain superfine pure aluminum hydroxide; and then performing low-temperature activation roasting, detergent washing, high-temperature secondary calcination and dispersion depolymerization to obtain high-purity alumina powder. The method does not need to add a purifying agent, cooperatively removes impurities through resolubilization and pre-decomposition, realizes multi-grade product production through seed decomposition and sampling at different times, and returns all materials to a Bayer-process system, and realizes zero discharge of hazardous waste. The product has a purity of greater than or equal to 99.99%, a medium particle size of less than 5 microns, and is suitable for high-end ceramic and ceramic substrate fields.

Description

Technical Field

[0001] This invention belongs to the field of fine alumina preparation technology, specifically relating to a method for preparing high-purity alumina from sodium aluminate solution using the Bayer process. Background Technology

[0002] High-purity alumina (Al2O3 content ≥ 99.99%) has become a core basic material in the fields of electronic substrates, new energy batteries, biomedicine and high-end catalysts due to its high purity, high hardness, high strength, high temperature resistance and excellent chemical stability.

[0003] Currently, the mainstream processes for large-scale preparation of high-purity alumina include the activated aluminum powder method, aluminum alkoxide hydrolysis method, ammonium aluminum sulfate pyrolysis method, and modified Bayer process. Among them, the modified Bayer process has attracted much attention due to its wide availability of raw materials and relatively low theoretical cost. This method typically uses industrial sodium aluminate solution as raw material, and deeply removes silicon, iron, and organic matter by adding purifying agents (such as decolorizing agents and impurity removers), followed by seeding or carbonization, sodium removal, and calcination to obtain the product.

[0004] However, existing technologies generally suffer from the following insurmountable drawbacks:

[0005] (1) Risk of introducing impurities: In order to achieve the purification purpose, chemical agents (purifying agents, sodium removal agents) must be added to the solution. This not only increases the production cost, but also poses the risk of agent residue or introduction of new impurities, making it difficult for the purity of the final product to consistently reach 4N level or above (≥99.99%).

[0006] (2) Lengthy process flow: For example, patent CN201710703297.1 discloses a method that requires multiple steps such as decolorization, pressure desiliconization, and hydrothermal desodiumization. Such processes not only require large equipment investment and high energy consumption, but also impose strict requirements on equipment materials for pressure and hydrothermal conditions, which is not conducive to industrial promotion.

[0007] (3) Bottleneck of purification efficiency: For example, the co-precipitation method proposed in patent CN201811585906.9 relies only on simple seed adsorption, which is difficult to effectively remove trace impurities, resulting in high residual amount of intermediate products and large fluctuations in product purity.

[0008] (4) Poor environmental protection and coupling, leading to unstable product purity: The purification slag produced by existing processes has a complex composition and can usually only be disposed of after harmless treatment, making resource utilization impossible. More importantly, since most high-purity alumina production enterprises do not have a large-scale metallurgical-grade alumina production system, the low-concentration alkaline waste liquid generated cannot be contained and absorbed by the large system and must undergo complex purification treatment separately before it can be recycled within the process. This not only significantly increases the purification cost and environmental pressure, but also inevitably causes the accumulation and fluctuation of trace impurities in the waste liquid during repeated purification and recycling. This fluctuation is directly transmitted to the product, often resulting in the inability to maintain the purity of high-purity alumina products at the 4N level for a long period of time.

[0009] In summary, the existing modified Bayer process is trapped in a technical paradox: adding a purifying agent introduces new impurities, while not adding one results in incomplete purification. Furthermore, the resulting sludge is difficult to utilize as a resource, and the waste liquid requires repeated purification and recycling, leading to frequent fluctuations in product purity. Therefore, developing a method that requires no external purifying agent, has a short process, produces high and stable product purity, and enables low-cost, pollution-free material recycling of sludge and waste liquid with the metallurgical-grade alumina production system is a pressing technical challenge. Summary of the Invention

[0010] In view of the above, it is necessary to provide a method for preparing high-purity alumina from sodium aluminate solution using the Bayer process, in order to solve the problems of complex preparation process, insufficient product purity, uncontrollable product morphology and activity, and difficulty in handling process waste and residue in the existing technology, thereby providing a low-cost, pollution-free, and easily industrially applicable high-purity alumina production process.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A method for preparing high-purity alumina from sodium aluminate solution using the Bayer process includes the following steps:

[0013] S1: Redissolution: Excess industrial aluminum hydroxide and liquid alkali are mixed and heated to 100-150℃ to liquefy, yielding a sodium aluminate solution; the α-value of the sodium aluminate solution is controlled. k The concentration of caustic alkali (N) is 1.4-1.7. K The concentration is 80-160 g / L, and then filtered to obtain a sodium aluminate solution;

[0014] S2: Pre-decomposition self-purification: Seed crystals are added to the sodium aluminate solution obtained in S1 for pre-decomposition purification treatment to remove silicon, iron, zinc and organic impurities from the solution. After filtration, a high-purity sodium aluminate solution and purification residue are obtained; the purification residue is returned to the metallurgical grade alumina production system.

[0015] S3: Preparation of active seed crystals: Take 5-10% of the total volume of the high-purity sodium aluminate solution obtained in S2 and dilute it. Then add the seed initiator and polymeric dispersant and stir to react to obtain the active seed crystal slurry.

[0016] S4: Segmented seeding: Add the active seed slurry described in S3 to the remaining high-purity sodium aluminate solution in S2 to decompose the seed crystals. Take samples at the early, middle and late stages of seeding to obtain seed slurries with different purities and particle sizes. After filtering and washing the seed slurries with different purities and particle sizes, ultrafine pure aluminum hydroxide and seed mother liquor are obtained.

[0017] S5: Two-stage calcination and washing: The pure aluminum hydroxide obtained in S4 is activated and calcined at 400-900℃, and then a detergent is added for thorough washing to remove impurities, resulting in high-purity amorphous active alumina; the high-purity amorphous active alumina is then calcined a second time at 1000-1500℃, and after dispersion and depolymerization, high-purity alumina powder is obtained.

[0018] In this invention, further, in step S1, based on controlling the solution target α k Based on the ingredients, the industrial aluminum hydroxide is added in excess by 10-30%.

[0019] In this invention, further, in step S2, the seed crystal is one or a mixture of industrial aluminum hydroxide powder and a self-made active seed crystal slurry, and its addition amount is 1-25 g / L; the temperature of the pre-decomposition and purification treatment is 65-95℃, and the pre-decomposition rate is 2-15%. In this invention, the self-made active seed crystal slurry refers to the active seed crystal slurry prepared by the method described in step S3 above, that is, by diluting 5-10% of the total volume of high-purity sodium aluminate solution, adding a seed initiator and a polymeric dispersant, and then stirring to react.

[0020] In this invention, further, in step S3, the seed initiator is at least one of sodium bicarbonate, hydrogen peroxide, and aluminum nitrate, added at an amount of 30-120 g / L; the polymeric dispersant is one or a mixture of polyvinyl alcohol, polyethylene glycol, and polyvinyl maleic anhydride, added at an amount of 0.01-0.5 g / L; the N2 content of the diluted solution... K It is 40-80g / L.

[0021] In this invention, further, in step S4, the initial temperature of seed decomposition is 65-90℃, the final temperature of decomposition is 55-65℃, the decomposition time is 6-48h, and the decomposition rate is greater than 35%; the early stage of seeding is 6-12h, the middle stage of seeding is 12-24h, and the late stage of seeding is 24-48h.

[0022] In this invention, further, in step S5, the detergent is at least one of nitric acid, acetic acid, citric acid, ethylenediaminetetraacetic acid, and ammonium bicarbonate, and the amount added is 0.5-10% of the mass of pure aluminum hydroxide. The washing is performed 1-3 times, and finally rinsed with high-purity water.

[0023] In this invention, further, in step S2, the temperature of the pre-decomposition and purification treatment is 70-80℃, and the pre-decomposition rate is 5-10%.

[0024] In this invention, further, in step S3, the amount of seed initiator added is 40-60 g / L; the amount of polymeric dispersant added is 0.05-0.1 g / L; the reaction temperature for preparing the active seed slurry is 25-50℃, and the time is 0.5-2 h.

[0025] In this invention, further, in step S5, the activation calcination temperature is 400-800℃ and the time is 1-4h; the secondary calcination temperature is 1200-1400℃ and the time is 1-6h.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] 1. This invention uses metallurgical-grade industrial aluminum hydroxide directly as raw material, eliminating the need to purchase high-purity aluminum sources. The purification slag (containing impurity aluminum hydroxide), low-concentration seed mother liquor, and washing liquid generated during the process all possess the material characteristics for direct return to the Bayer process alumina production system as recycled process materials, requiring no additional treatment. This achieves zero hazardous waste discharge throughout the entire process and significantly reduces raw material and environmental treatment costs. Furthermore, the process conditions of this invention are mild (atmospheric pressure, temperature ≤150℃), using conventional chemical equipment, and have high system compatibility with existing metallurgical alumina production lines, facilitating technological upgrades for existing enterprises and demonstrating excellent industrialization prospects.

[0028] 2. This invention achieves deep removal of various impurities, including silicon, iron, zinc, calcium, and organic matter, from sodium aluminate solution without adding any chemical purifying agents. This is achieved through the synergistic effect of a dual purification mechanism: "physical adsorption of excess aluminum hydroxide during redissolution" and "pre-decomposition co-precipitation of seed crystals." Specifically, in the redissolution stage, the adsorption sites of excess aluminum hydroxide preferentially capture some impurity ions, inhibiting their entry into the solution. In the pre-decomposition stage, the high surface energy of active seed crystals and newly formed aluminum hydroxide induces residual impurities to precipitate out in the form of co-precipitate. Single adsorption or precipitation methods are difficult to effectively remove multiple impurities with different properties simultaneously. However, this invention achieves deep purification through the temporal coupling and mechanistic complementarity of the above two steps, avoiding the risks of purifying agent residue and the introduction of new impurities from the source. This overcomes the technical contradiction in existing technologies where "adding purifying agents introduces new impurities, while not adding them results in incomplete purification."

[0029] 3. This invention employs a self-made active seed slurry for high-temperature seed decomposition. Under optimized seeding conditions (initial temperature 65-90℃, final temperature 55-65℃), aluminum hydroxide grains grow well with smooth surfaces, significantly reducing sodium ion adsorption and entrainment. The resulting precursor does not require the complex hydrothermal sodium removal process of traditional methods to meet high-purity requirements, greatly simplifying the process. Furthermore, this invention uses time-phased sampling at the early, middle, and late stages of the seeding process, utilizing the natural differences in purity and particle size at different times to directly obtain precursors of different grades. Combined with the "low-temperature activation calcination - deep washing with detergent - high-temperature secondary calcination" process, not only is further deep removal of residual impurities achieved, but the crystal transformation and sintering activity of the final α-Al2O3 powder can also be directionally controlled. Through the above process, the product purity consistently reaches over 99.99% (4N grade) with a medium particle size of less than 5μm, meeting the stringent requirements for high-purity alumina materials in high-end ceramic substrates, new energy battery separator coatings, and other fields. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of a method for preparing high-purity alumina from sodium aluminate solution using the Bayer process, provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] In this invention, the "self-made active seed crystal slurry" refers to a slurry prepared by diluting 5-10% of the total volume of high-purity sodium aluminate solution, adding seed crystal initiator and polymeric dispersant, and then stirring to obtain the slurry.

[0033] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the embodiments are all commercially available.

[0034] Unless otherwise specified, the percentage sign "%" in this invention refers to the mass percentage; however, the percentage of a solution, unless otherwise specified, refers to the number of grams of solute contained in 100 mL of solution.

[0035] The weight parts mentioned in this invention can be weight units known in the art such as μg, mg, g, kg, or multiples thereof, such as 1 / 10, 1 / 100, 10 times, 100 times, etc.

[0036] like Figure 1 As shown, the method for preparing high-purity alumina from sodium aluminate solution using the Bayer process of the present invention comprises the following process flow: using industrial aluminum hydroxide and liquid alkali as raw materials, the solution undergoes resolution, filtration, pre-decomposition self-purification (purification slag is returned to the metallurgical system), and solid-liquid separation sequentially to obtain a high-purity sodium aluminate solution. The obtained high-purity sodium aluminate solution is divided into two streams: a portion is diluted and initiator / dispersant is added to prepare active seed crystals; the other stream is mixed with the prepared active seed crystals for seed crystal decomposition, and samples are taken at different times during the early, middle, and late stages of seed crystal decomposition, and then filtered and washed to obtain ultrafine pure aluminum hydroxide and seed crystal mother liquor. The ultrafine pure aluminum hydroxide undergoes low-temperature activation calcination, deep washing with detergent, high-temperature secondary calcination, and dispersion depolymerization sequentially to finally obtain high-purity alumina.

[0037] The specific implementation method is as follows:

[0038] Example 1:

[0039] This embodiment proposes a method for preparing high-purity alumina from sodium aluminate solution using the Bayer process, comprising the following steps:

[0040] (1) Redissolution: 20% excess industrial aluminum hydroxide and liquid alkali are stirred and liquefied at 110℃, and the solution α is controlled. k The concentration of caustic alkali is 1.55 N. K The concentration is 150 g / L. The solution reaches the target α. k Then, it was immediately filtered and separated to obtain a sodium aluminate solution.

[0041] (2) Pre-decomposition self-purification: Add 10 g / L of self-made active seed slurry (prepared in advance according to step S3) to the above sodium aluminate solution, and stir slowly at 90℃ for 1 h, controlling the decomposition rate to 5%. Utilize the adsorption and co-precipitation effect of the active seed crystals and newly precipitated aluminum hydroxide to remove impurities such as iron, calcium, copper, and organic matter from the solution. After stirring, use a plate and frame filter press for two circulation filtrations to obtain a high-purity sodium aluminate solution. The filter residue is Al(OH)3, a gibbsite phase with a purity of 99.88% and a particle size of 1.3 μm, which can be used as an ultrafine aluminum hydroxide powder product or directly returned to the metallurgical alumina production system as a seed crystal.

[0042] (3) Preparation of active seed crystals: Take 5% of the total volume of the high-purity sodium aluminate solution obtained by the above pre-decomposition and self-purification, dilute it to a caustic alkali concentration of 40 g / L, add 120 g / L of sodium bicarbonate and 0.05 g / L of polyethylene glycol polymeric dispersant, and react for 2 h at a temperature of 30℃ and a stirring speed of 200 r / min to obtain an active seed crystal slurry.

[0043] (4) Segmented seeding: All the remaining high-purity sodium aluminate solution from the pre-decomposition and self-purification process was added to the prepared active seed slurry. The initial seeding temperature was controlled at 70℃, the final seeding temperature at 55℃, and the stirring speed at 100r / min. Seeding was carried out for 48 hours. Samples were taken at 12h, 24h, and 48h during the seeding process. After filtration using a plate and frame filter press, the samples were washed with high-purity water in a counter-current manner until neutral to obtain aluminum hydroxide of different purities.

[0044] (5) Two-stage calcination and washing: Aluminum hydroxide precursors of different purities were activated and calcined at 500℃ for 4 hours to obtain activated alumina with high specific surface area. The alumina was washed for 1 hour at 50℃ and 100 r / min with 2% nitric acid by mass, and finally rinsed with pure water. The washed and dried activated alumina was then calcined a second time at 1300℃ for 2 hours. After calcination, it was dispersed and depolymerized using an air jet mill to obtain different products. The performance parameters are shown in Table 1.

[0045] Table 1 Performance Parameters

[0046]

[0047] As shown in Table 1, the product particle size is finer but the purity is slightly lower in the early stage of seeding (12h); the product purity is highest (99.998%) in the middle stage of seeding (24h), and the particle size is moderate; the product purity is lower than that in the middle stage of seeding (48h), and the particle size is too coarse.

[0048] Example 2

[0049] This embodiment proposes another method for preparing high-purity alumina from sodium aluminate solution using the Bayer process, including the following steps:

[0050] (1) Redissolution: 10% excess industrial aluminum hydroxide and liquid alkali are stirred and liquefied at 140℃, and the solution α is controlled. k The concentration of caustic alkali (N) is 1.57. K The concentration is 140 g / L. The solution reaches the target α. k Then, it was immediately filtered and separated to obtain a sodium aluminate solution.

[0051] (2) Pre-decomposition self-purification: Add 3 g / L of self-made active seed slurry (prepared in advance according to step S3) to the above sodium aluminate solution, and stir slowly at 70℃ for 1 h, controlling the decomposition rate to 10%. Utilize the adsorption and co-precipitation effect of the active seed crystals and newly precipitated aluminum hydroxide to remove impurities such as iron, calcium, copper, and organic matter from the solution. After stirring, perform two circulation filtrations using a plate and frame filter press to obtain a high-purity sodium aluminate solution. The filter residue is Al(OH)3, a gibbsite phase with a purity of 99.79% and a particle size of 2.0 μm, which can be directly returned to the metallurgical alumina production system for use as seed crystals.

[0052] (3) Preparation of active seed crystals: Take 5% of the total volume of the high-purity sodium aluminate solution obtained by the above pre-decomposition and self-purification, dilute it to a caustic alkali concentration of 40 g / L, add 80 g / L sodium bicarbonate and 0.05 g / L polyethylene glycol polymeric dispersant, and react for 2 h at a temperature of 50℃ and a stirring speed of 200 r / min to obtain an active seed crystal slurry.

[0053] (4) Segmented seeding: All the remaining high-purity sodium aluminate solution from the pre-decomposition and self-purification process was added to the prepared active seed slurry. The initial seeding temperature was controlled at 75℃, the final seeding temperature at 55℃, and the stirring speed at 100 r / min. Seeding was carried out for 48 hours. Samples were taken at 12h, 24h, and 48h during the seeding process. After filtration using a plate and frame filter press, the samples were washed with high-purity water in a reverse manner until neutral to obtain aluminum hydroxide of different purities.

[0054] (5) Two-stage calcination and washing: Aluminum hydroxide precursors of different purities were activated and calcined at 800℃ for 4 hours to obtain activated alumina with high specific surface area. The alumina was then washed for 4 hours at 40℃ and 100 r / min with 2% ammonium bicarbonate by stirring, and finally rinsed with pure water. The washed and dried activated alumina was then calcined a second time at 1300℃ for 2 hours. After calcination, it was dispersed and depolymerized using an air jet mill to obtain different products. The performance parameters are shown in Table 2.

[0055] Table 2 Performance parameters of product in Example 2

[0056]

[0057] As shown in Table 2, consistent with the trend in Example 1, the product purity was highest (99.996%) and the particle size was moderate during the mid-stage of seeding (24h).

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that excess resolution control and pre-decomposition purification are not performed. Specifically, in step S1, industrial aluminum hydroxide is not used excessively (according to the target α). k (Precise ingredient proportioning), and the pre-decomposition and purification treatment in step S2 is omitted. The remaining steps are the same as in Example 1.

[0060] Redissolved (not excessive): according to target α k =1.55 Precise ingredient mixing, industrial aluminum hydroxide and liquid alkali are liquefied by stirring at 110℃, N K =150g / L, after filtration, sodium aluminate solution is obtained.

[0061] Pre-decomposition self-purification: This step is omitted.

[0062] Preparation of active seed crystals, segmented seeding, two-stage calcination and washing: same as in Example 1.

[0063] Product performance parameters are shown in Table 3.

[0064] Table 3 Performance parameters of Comparative Example 1

[0065]

[0066] As shown in Table 3, without remelting excess control and pre-decomposition purification, the product purity cannot reach 99.99% (4N) or higher.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that the two calcinations are omitted; instead, a single high-temperature calcination followed by washing is performed. Specifically, the activation roasting step is omitted, and the aluminum hydroxide precursor is directly subjected to high-temperature calcination, followed by washing. The remaining steps are the same as in Example 1.

[0069] Resolution, pre-decomposition self-purification, preparation of active seed crystals, and segmented seeding: Same as Example 1.

[0070] Two-stage calcination and washing (modified to one-stage calcination): The aluminum hydroxide precursors of different purities obtained from the segmented seeding were directly calcined at 1300℃ for 4 hours. After calcination, they were washed with 2% ammonium bicarbonate at 40℃ and 100r / min stirring speed for 4 hours. Finally, they were rinsed with pure water, dried, and then dispersed and depolymerized by an air jet mill to obtain different products. The performance parameters are shown in Table 4.

[0071] Table 4 Performance parameters of Comparative Example 2

[0072]

[0073] As shown in Table 4, without adopting the two-step calcination process of "low-temperature activation roasting followed by acid washing", the product purity cannot be stably maintained above 99.99%.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that no detergent was added during the washing process. Specifically, after activation and calcination, the product was washed only with pure water, without any chemical detergents. The remaining steps were the same as in Example 1.

[0076] Resolution, pre-decomposition self-purification, preparation of active seed crystals, and segmented seeding: Same as Example 1.

[0077] Two-stage calcination and washing (without detergent): The aluminum hydroxide precursors of different purities obtained by the segmented seeding were activated and calcined at 500℃ for 4 hours, then washed with pure water only (without any detergent), dried, and then calcined a second time at 1300℃ for 2 hours. After dispersion and depolymerization by air jet mill, different products were obtained. The performance parameters are shown in Table 5.

[0078] Table 5 Performance parameters of Comparative Example 3

[0079]

[0080] Table 5 shows that after activation and calcination, without deep washing with detergent and only rinsing with pure water, although the purity of some samples approached the 4N threshold, the purity stability was poor, and the residual sodium ion content in the product was significantly higher than in Example 1, resulting in reduced sintering activity. This indicates that detergent treatment is a necessary step to achieve stable high purity and excellent sintering activity.

[0081] In summary, the technical solution of this invention, through the synergistic effect of "redissolution excess control + pre-decomposition self-purification," "time-separated sampling during the seeding process," and "two-stage calcination and washing," can stably prepare high-purity α-Al2O3 powder with a purity ≥99.99% and controllable particle size. The results of Comparative Examples 1-3 further demonstrate that each key technical feature (redissolution excess, pre-decomposition purification, two calcinations, and detergent washing) is a necessary technical means to achieve high purity and cannot be omitted.

[0082] The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention.

Claims

1. A method for preparing high-purity alumina from sodium aluminate solution using the Bayer process, characterized in that, Includes the following steps: S1: Redissolution: Excess industrial aluminum hydroxide and liquid alkali are mixed and heated to 100-150℃ to liquefy, yielding a sodium aluminate solution; the α-value of the sodium aluminate solution is controlled. k The concentration of caustic alkali (N) is 1.4-1.

7. K The concentration is 80-160 g / L, and then filtered to obtain a sodium aluminate solution; S2: Pre-decomposition self-purification: Seed crystals are added to the sodium aluminate solution obtained in S1 for pre-decomposition purification treatment to remove silicon, iron, zinc and organic impurities from the solution. After filtration, a high-purity sodium aluminate solution and purification residue are obtained; the purification residue is returned to the metallurgical grade alumina production system. S3: Preparation of active seed crystals: Take 5-10% of the total volume of the high-purity sodium aluminate solution obtained in S2 and dilute it. Then add the seed initiator and polymeric dispersant and stir to react to obtain the active seed crystal slurry. S4: Segmented seeding: Add the active seed slurry described in S3 to the remaining high-purity sodium aluminate solution in S2 to decompose the seed crystals. Take samples in the early, middle and late stages of seeding to obtain seed slurries with different purities and particle sizes. After filtering and washing, the seed slurries of different purities and particle sizes were respectively obtained as ultrafine pure aluminum hydroxide and seed mother liquor. S5: Two-stage calcination and washing: The pure aluminum hydroxide obtained in S4 is activated and calcined at 400-900℃, and then a detergent is added for thorough washing to remove impurities and obtain high-purity amorphous active aluminum oxide. The high-purity amorphous active alumina is then calcined again at 1000-1500℃, and after dispersion and deagglomeration, high-purity alumina powder is obtained.

2. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S1, the control solution target α is used. k Based on the ingredients, the industrial aluminum hydroxide is added in excess by 10-30%.

3. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S2, the seed crystal is one or a mixture of industrial aluminum hydroxide powder and self-made active seed crystal slurry, and the amount added is 1-25 g / L; the temperature of the pre-decomposition and purification treatment is 65-95℃, and the pre-decomposition rate is 2-15%.

4. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S3, the seed initiator is at least one of sodium bicarbonate, hydrogen peroxide, and aluminum nitrate, added at a concentration of 30-120 g / L; the polymeric dispersant is one or a mixture of polyvinyl alcohol, polyethylene glycol, and polyvinyl maleic anhydride, added at a concentration of 0.01-0.5 g / L; the N2 content of the diluted solution... K It is 40-80g / L.

5. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S4, the initial temperature for seed decomposition is 65-90℃, the final temperature for decomposition is 55-65℃, the decomposition time is 6-48h, and the decomposition rate is greater than 35%; the early stage of seeding is 6-12h, the middle stage of seeding is 12-24h, and the late stage of seeding is 24-48h.

6. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S5, the detergent is at least one of nitric acid, acetic acid, citric acid, ethylenediaminetetraacetic acid, and ammonium bicarbonate, and the amount added is 0.5-10% of the mass of pure aluminum hydroxide. The washing is performed 1-3 times, and finally rinsed with high-purity water.

7. The method for preparing high-purity alumina according to claim 3, characterized in that: In step S2, the temperature of the pre-decomposition and purification treatment is 70-80℃, and the pre-decomposition rate is 5-10%.

8. The method for preparing high-purity alumina according to claim 4, characterized in that: In step S3, the amount of seed initiator added is 40-60 g / L; the amount of polymeric dispersant added is 0.05-0.1 g / L; the reaction temperature for preparing the active seed slurry is 25-50℃, and the time is 0.5-2 h.

9. The method for preparing high-purity alumina according to claim 1, characterized in that: In step S5, the activation calcination temperature is 400-800℃ and the time is 1-4h; the secondary calcination temperature is 1200-1400℃ and the time is 1-6h.

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