Process for producing high-whiteness aluminum hydroxide micropowder through decomposition at high temperature and low seed crystal ratio
By employing a high-temperature, low-seed ratio decomposition process and deep desilication and decolorization, the problems of seed dependence and high energy consumption in traditional processes have been solved, enabling the production of high-whiteness, ultra-fine particle size aluminum hydroxide micropowder to meet the demands of the high-end market.
Patent Information
- Application Number
- CN202510753179.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-06
- Publication Date
- 2025-10-28
AI Technical Summary
Traditional aluminum hydroxide micron powder production processes suffer from problems such as high seed ratio dependence, wide particle size distribution, insufficient whiteness, and high energy consumption, making it difficult to meet the high-end market's demand for high whiteness and ultra-fine particle size.
A high-temperature, low-seed ratio decomposition process is adopted. α-Al(OH)3 seeds are prepared and decomposed by stirring at 75-85℃. Polyethylene glycol is added as a dispersant to control particle size distribution and whiteness, shorten the decomposition time, and carry out deep desilication, decolorization and post-treatment.
It has enabled the production of aluminum hydroxide micro powder with high whiteness and ultra-fine particle size, reducing production load and energy consumption, improving product purity and quality, and meeting the needs of high-end applications.
Smart Images
Figure CN120841547A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of inorganic non-metallic material preparation technology, and in particular relates to a process for producing high-whiteness aluminum hydroxide micro powder by high-temperature low seed ratio decomposition. Background Technology
[0002] Aluminum hydroxide micronized powder, due to its low smoke, non-toxicity, and flame-retardant properties, is widely used in the preparation of flame-retardant polymer materials, ceramic raw materials, and catalysts. Traditional production processes often employ a sodium aluminate solution decomposition method, controlling the particle size and morphology of the product by adjusting parameters such as decomposition temperature, seed crystal addition amount, and stirring speed. Liu Yanling et al., in their paper "A Two-Stage Seeding Method for Preparing Aluminum Hydroxide Micronized Powder," proposed a two-stage decomposition process using self-decomposing seeds to prepare aluminum hydroxide micronized powder. The decomposition conditions are: a seed ratio of 3%–25% in the first stage and 0.5%–8% in the second stage; a seed slurry pH of 8–10; an αk value of 1.45–1.55 for the refined sodium aluminate solution; a mass concentration of 90–140 g / L for both the first and second stages; no heating during the first stage decomposition; a second-stage decomposition temperature of 50–60℃; and decomposition times of 2–5 hours for the first stage and 2–20 hours for the second stage.
[0003] However, the preparation of aluminum hydroxide in the prior art has the following problems:
[0004] (1) High seed ratio dependence: Traditional processes require the addition of a large number of seed crystals (the mass ratio of seed crystals to alumina in sodium aluminate solution is usually 3 to 6:1), which leads to a large seed crystal circulation volume, high production load, increased cost, and seed crystal residue affecting product purity.
[0005] (2) Wide particle size distribution: Secondary nucleation is prone to occur during the decomposition process, resulting in uneven particle size distribution and affecting the performance of downstream applications;
[0006] (3) Insufficient whiteness: Decomposition at medium temperature (65-70℃ in the first tank and 45-50℃ in the last tank) can easily cause phase transformation of impurities, making it difficult for the whiteness (L value) of the product to exceed 95.
[0007] (4) High energy consumption: Low temperature decomposition process (<60℃) has a long cycle, generally requiring more than 48 hours, while high temperature decomposition (>80℃) is prone to agglomeration and requires complex post-processing.
[0008] With the increasing demands for performance of aluminum hydroxide micropowder in fields such as electronic ceramics and 5G communication materials (e.g., D50≈1μm, whiteness>96), traditional processes can no longer meet the needs of the high-end market. Summary of the Invention
[0009] To overcome the shortcomings of existing technologies, this invention provides a high-temperature, low-seed-ratio decomposition process for producing high-whiteness aluminum hydroxide micropowder. This method, employing high-temperature, low-seed-ratio decomposition, produces high-whiteness, ultrafine-particle-size aluminum hydroxide micropowder, suitable for fields with stringent requirements for aluminum hydroxide purity and particle size distribution, such as electronic ceramics, catalyst supports, flame retardants, and high-end coatings. The technical solution provided by this invention is as follows:
[0010] A process for producing high-whiteness aluminum hydroxide micropowder through high-temperature, low-seed ratio decomposition includes the following steps:
[0011] S1, Seed preparation: Preparation of α-Al(OH)3 seed crystals;
[0012] S2, add the α-Al(OH)3 seed crystals prepared in step S1 to the sodium aluminate solution, stir and decompose at 75-85℃, and add synergistic additives simultaneously.
[0013] S3, after the reaction is complete, post-processing is carried out, including centrifugation, washing and drying, to obtain the product.
[0014] Preferably, in step S1, the α-Al(OH)3 seed crystals have a particle size of D50 = 0.8–1.2 μm. Preferably, ammonium bicarbonate is used as a precipitant to prepare spherical α-Al(OH)3 seed crystals with a particle size of D50 = 0.8–1.2 μm.
[0015] Preferably, in step S1, the seed crystal is prepared by: preparing an aluminum hydroxide solution, using ammonium bicarbonate as a precipitant, and drying the resulting precipitate to obtain a white aluminum hydroxide powder.
[0016] Preferably, in step S2, the sodium aluminate solution contains an Al2O3 concentration of 80–150 g / L and a caustic ratio of 1.2–1.6.
[0017] Preferably, in step S2, the sodium aluminate solution undergoes deep desilication and decolorization, followed by impurity removal through membrane or belt filtration to control the Fe content to <0.005% and improve the whiteness of the product.
[0018] Preferably, in step S2, the amount of α-Al(OH)3 seed crystals added to the sodium aluminate solution is 1-10%.
[0019] In step S2, a constant temperature decomposition of 75-85℃ is used, which is 15-20℃ higher than the traditional process.
[0020] Preferably, in step S2, the stirring speed is 150 to 1000 rpm.
[0021] Preferably, in step S2, the decomposition time is 10 to 60 minutes, and even more preferably 30 to 60 minutes, which is dozens of times faster than the traditional process of 48 hours.
[0022] Preferably, in step S2, 0.1 to 0.5 wt% of polyethylene glycol is added as a synergistic additive. Polyethylene glycol acts as a dispersant and can effectively inhibit agglomeration. Further, polyethylene glycol 2000 to 4000 is used.
[0023] Preferably, in step S3, the post-processing includes: high-speed centrifugal separation, or first ceramic membrane concentration and filtration followed by belt filtration separation, washing and drying to obtain the product.
[0024] Preferably, the product particle size distribution SPAN value is <0.6;
[0025] Whiteness L value > 96.2, Fe content < 0.003%;
[0026] Decomposition rate > 48%.
[0027] Compared with the prior art, the beneficial effects of the present invention include:
[0028] 1. This invention provides a high-temperature, low-seed ratio decomposition process for producing high-whiteness aluminum hydroxide micro powder, which increases the decomposition temperature, reduces the amount of seed crystals added (1-10%), lowers the production load, and improves product purity.
[0029] 2. The aluminum hydroxide micro powder product obtained by this invention has a concentrated particle size distribution, which improves product quality;
[0030] 3. The aluminum hydroxide micro powder product obtained by this invention has higher whiteness;
[0031] 4. The preparation process provided by this invention greatly shortens the production cycle, reduces energy consumption, and reduces the complexity of post-processing. Attached Figure Description
[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0033] Figure 1 Here is a SEM image of the product from Example 1;
[0034] Figure 2 The image shown is a SEM image of product 2 in Comparative Example 2. Detailed Implementation
[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.
[0037] In existing technologies, the preparation of aluminum hydroxide suffers from problems such as high seed ratio dependence, affecting product purity; wide particle size distribution leading to uneven particle size distribution; insufficient whiteness; and high energy consumption. This invention provides the following technical solution:
[0038] A process for producing high-whiteness aluminum hydroxide micropowder through high-temperature, low-seed ratio decomposition includes the following steps:
[0039] S1, Seed preparation: Preparation of α-Al(OH)3 seed crystals;
[0040] S2, add the α-Al(OH)3 seed crystals prepared in step S1 to the sodium aluminate solution, heat and stir, and add additives to react;
[0041] S3, after the reaction is complete, post-processing is carried out, including centrifugation, washing and drying, to obtain the product.
[0042] In some embodiments, in step S1, the α-Al(OH)3 seed crystal size is D50 = 0.8 μm, and in another embodiment, the α-Al(OH)3 seed crystal size is D50 = 1.2 μm.
[0043] In some embodiments, in step S1, the seed crystal is prepared by: preparing an aluminum hydroxide solution, using ammonium bicarbonate as a precipitant, and drying the resulting precipitate to obtain a white aluminum hydroxide powder.
[0044] In some embodiments, in step S2, the sodium aluminate solution contains an Al2O3 concentration of 80–150 g / L and a caustic ratio of 1.2–1.6.
[0045] In some embodiments, in step S2, the sodium aluminate solution undergoes deep desilication and decolorization, followed by impurity removal through membrane or belt filtration to control the Fe content to <0.005% and improve the whiteness of the product.
[0046] In some embodiments, in step S2, the amount of α-Al(OH)3 seed crystals added to the sodium aluminate solution is 1-10%.
[0047] In some embodiments, step S2 involves isothermal decomposition at 75–85°C, which is 15–20°C higher than the traditional process.
[0048] In some embodiments, in step S2, the stirring speed is 150 to 1000 rpm.
[0049] In some embodiments, the decomposition time in step S2 is 10 to 60 minutes.
[0050] In some embodiments, in step S2, 0.1 to 0.5 wt% of polyethylene glycol is added as a dispersant to inhibit agglomeration; the polyethylene glycol used has a molecular weight of 2000 to 4000.
[0051] In some embodiments, in step S3, the post-processing includes: high-speed centrifugal separation, or first ceramic membrane concentration and filtration followed by belt filtration separation, washing and drying to obtain the product.
[0052] Particle size distribution SPAN value < 0.6;
[0053] Whiteness L value = 96.2, Fe content < 0.003%;
[0054] Decomposition rate > 48%.
[0055] This invention aims to solve the above problems through the following innovative means:
[0056] (1) Reduce the seed ratio: Break through the traditional reliance on high seed ratio, reduce raw material consumption, energy consumption and impurity introduction; reduce the addition of seed crystals, reduce production load and improve product purity.
[0057] Furthermore, this invention achieves efficient induced nucleation through seed crystal size and surface modification; the seed crystal size directly affects its specific surface area and surface energy. Smaller particle size results in a larger specific surface area, more surface active sites, and easier adsorption of aluminate ions (Al(OH)4). - This accelerates the nucleation process. According to research and industrial practice, efficient induced nucleation can be achieved when the seed crystal size is typically controlled within the range of 200-500 nm.
[0058] (2) Optimize particle size distribution: α-Al(OH)3 seed crystals provide growth interface → consume solution supersaturation → inhibit secondary nucleation → particles grow uniformly on seed crystal surface → interface effect maintains monodispersity → regulate thermodynamics and kinetics to achieve preparation of ultrafine aluminum hydroxide particles;
[0059] In addition, this invention utilizes the synergistic effect of temperature and stirring speed to balance the decomposition rate and particle size control.
[0060] Furthermore, the present invention uses polyethylene glycol as an additive. Polyethylene glycol inhibits particle agglomeration through steric hindrance effect, while avoiding the introduction of impurity ions by traditional dispersants (such as sodium hexametaphosphate).
[0061] The product obtained by this invention has a concentrated particle size distribution, which improves product quality.
[0062] (3) Improve whiteness: SiO2 in sodium aluminate solution will form aluminosilicate impurities (such as sodium silicate slag). This can be achieved by adding lime milk (Ca(OH)2) or desiliconizing agent (such as MgO) to precipitate silicon as calcium silicate slag (CaO·SiO2·xH2O) or magnesium silicate slag, thereby reducing the SiO2 concentration in the solution (<0.01g / L). Strictly control the pH at the neutralization endpoint (usually 9-10) to avoid local over-alkaliness leading to the dissolution and recrystallization of aluminum hydroxide, forming irregular particles and adsorbing impurities. Moderate stirring (such as 100-200rpm) can promote uniform mixing of the solution, prevent local oversaturation leading to impurity encapsulation, and improve the whiteness of the product.
[0063] (4) Energy saving and consumption reduction: shortening the decomposition cycle, reducing the complexity of post-processing, and reducing post-processing costs.
[0064] Terminology Explanation:
[0065] αk means:
[0066] SPAN value of diameter distribution:
[0067] Whiteness L-value: This is a core indicator for measuring the brightness of an object, representing lightness. It ranges from 0 (absolute black) to 100 (ideal white). The higher the L-value, the brighter and closer to white the object's surface (such as white paper or the high whiteness of ceramic surfaces). The lower the L-value, the darker and closer to black the object's surface (such as dark fabrics or charcoal materials).
[0068] The decomposition rate indicates the degree to which aluminum oxide decomposes into aluminum hydroxide in sodium aluminate solution, and the calculation formula is:
[0069]
[0070] The aluminum content refers to the concentration of aluminum oxide in the solution, expressed in g / L.
[0071] Example 1: Preparation of seed crystals:
[0072] Aluminum hydroxide was dissolved in sodium hydroxide solution to obtain sodium aluminate solution. The solution composition was C[Al₂O₃] 110 g / L and C[NaO₂] 100 g / L. The volume was measured per cubic meter. 3The mixture was pumped into the decomposition bed and a CO2 mixture (35% v / v%) was introduced for 50 minutes. After aeration, the reaction slurry was separated and washed with high-purity water, while ammonium bicarbonate was added as a precipitant. The resulting precipitate was dried to obtain a white aluminum hydroxide powder. XRD analysis showed that the obtained white powder was α-Al(OH)3 crystalline phase; scanning electron microscopy showed that it was spherical.
[0073] D50 = 1.0 μm.
[0074] Example 2,
[0075] Take 1000ml of sodium aluminate solution with an Al2O3 concentration of 85g / L and αk = 1.25, add lime milk (mixed according to a mass ratio of calcium oxide to silicon dioxide in the solution of 1.5:1), heat to 150℃ in a high-pressure reactor and keep warm for 1 hour, with simultaneous stirring at a speed of 150 rpm, to deeply desiliconize and decolorize, and then filter and purify to obtain a pure sodium aluminate solution. Add 6g of α-Al(OH)3 seed crystals prepared in Example 1 to a beaker containing sodium aluminate solution. The seed crystal ratio (the ratio of the alumina content of the seed crystals to the mass ratio of alumina in the solution) is 1:15. Heat the solution to 80°C and stir at 300 rpm for 60 minutes to decompose the alumina. Simultaneously add 0.3wt% polyethylene glycol 4000. Separate the product using a centrifuge (3000 rpm) or a combination of membrane filtration and belt filter. The mother liquor recovery rate is >90%. Wash the product with deionized water until the conductivity is <50 μS / cm, and flash dry at 120°C. Test results:
[0076] D50 = 1.05 μm, particle size distribution SPAN value < 0.6;
[0077] Whiteness L value = 96.2, Fe content < 0.003%;
[0078] Decomposition rate > 48%.
[0079] The product is high-whiteness aluminum hydroxide micro powder, which meets the relevant indicator requirements.
[0080] Comparative Example 1 (Traditional Process):
[0081] Take 1000ml of sintered sodium aluminate solution with Al2O3 concentration of 85g / L and αk = 1.25, and a seed ratio (the ratio of alumina to the mass of alumina in the solution when seed crystals are added) of 4:1, i.e., add 340g of Bayer process aluminum hydroxide seed crystals. The initial decomposition temperature is 65℃, the final temperature is 45℃, the stirring speed is 1 rpm for 3 minutes, the decomposition time is 48 hours, and the decomposition rate is 48%. After solid-liquid separation, the product is washed and dried. The test results are: product D50 = 25μm, whiteness L value = 86.5. The product is ordinary aluminum hydroxide, which is an intermediate product of metallurgical alumina.
[0082] Comparative Example 2
[0083] The same preparation method as in Example 2 was used, except that polyethylene glycol 4000 was not added.
[0084] SEM images of the products obtained in Example 2 and Comparative Example 2 are shown below. Figure 1 and Figure 2 As shown, polyethylene glycol can be effectively used as an additive to inhibit particle agglomeration.
[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A process for producing high-whiteness aluminum hydroxide micropowder through high-temperature, low-seed ratio decomposition, characterized in that, Includes the following steps: S1, Seed preparation: Preparation of α-Al(OH)3 seed crystals; S2, add the α-Al(OH)3 seed crystals prepared in step S1 to the sodium aluminate solution, stir and decompose at 75-85℃, and add synergistic additives simultaneously. S3, after the reaction is complete, post-processing is carried out, including centrifugation, washing and drying, to obtain the product.
2. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S1, the α-Al(OH)3 seed crystals have a particle size of D50 = 0.8–1.2 μm.
3. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S1, the seed crystals are prepared by preparing an aluminum hydroxide solution, using ammonium bicarbonate as a precipitant, and drying the resulting precipitate to obtain a white aluminum hydroxide powder.
4. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, the sodium aluminate solution contains an Al2O3 concentration of 80–150 g / L and a caustic ratio of 1.2–1.
6.
5. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, the sodium aluminate solution undergoes deep desilication and decolorization, followed by impurity removal through membrane or belt filtration.
6. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, the amount of α-Al(OH)3 seed crystals added to the sodium aluminate solution is 1-10%.
7. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, the stirring speed is 150-1000 rpm.
8. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, the decomposition time is 10 to 60 minutes.
9. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S2, 0.1-0.5 wt% of polyethylene glycol is added as a synergistic additive; further, polyethylene glycol 2000-4000 is used.
10. The process for producing high-whiteness aluminum hydroxide micropowder by high-temperature, low-seed ratio decomposition according to claim 1, characterized in that, In step S3, the post-processing includes: high-speed centrifugal separation, or first ceramic membrane concentration and filtration followed by belt filtration separation, washing and drying to obtain the product.