Process for producing aluminum hydroxide micro powder by rapidly decomposing active seed crystal at high temperature

Abstract

The invention discloses a process for producing aluminum hydroxide micro powder by quickly decomposing active seed crystal at high temperature, which comprises the following steps: preparing active seed crystal: mixing a certain amount of purified and refined sodium aluminate solution with carbon dioxide gas according to a specific mass ratio, and reacting in a high-speed stirring state to generate amorphous aluminum hydroxide microcrystal nuclei; an additive is added into the reaction system, the additive is a mixture of polyethylene glycol and lauryl sodium sulfate, the mass ratio of polyethylene glycol to lauryl sodium sulfate is 1: (1-2), and the addition amount of the additive is 0.5-1% of the mass of the aluminum salt; continuously stirring for 10 minutes to obtain an active seed crystal suspension; and after activating the seed crystal, quickly decomposing the seed crystal with a sodium aluminate solution at high temperature to obtain aluminum hydroxide micro powder. The purity of the prepared aluminum hydroxide micro-powder reaches up to 99.5% or above, the particle size distribution is uniform, the aluminum hydroxide micro-powder can be quickly decomposed and generated within a short time, and the production cost is reduced.

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 aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals. Background Technology

[0002] Aluminum hydroxide micro powder has the advantages of being non-toxic, non-corrosive, stable, not producing toxic gases at high temperatures, and inexpensive. It can be used as a flame retardant and shows broad application prospects in many industries such as chemical, ceramic, and electronic industries.

[0003] Currently, the main processes for preparing aluminum hydroxide micronized powder include the Bayer process, carbonization process, hydrothermal process, and seeding process. The Bayer process, as the mainstream method for industrial production of aluminum hydroxide, has significant drawbacks: its production cycle is lengthy, energy consumption is high, and it generates a large amount of waste residue, placing a heavy burden on the environment. While the carbonization process can reduce energy consumption to some extent, the purity of the product is difficult to guarantee, and the particle size distribution is uneven, greatly limiting product quality and application range. The hydrothermal process produces aluminum hydroxide micronized powder with high purity and uniform particle size; however, it requires stringent equipment and has high production costs, making large-scale industrial production difficult. The seeding process uses a supersaturated sodium aluminate solution as raw material, adding seed crystals to promote aluminum hydroxide precipitation. During the seeding process, the particle size of aluminum hydroxide exhibits a polarized phenomenon: fine particles gradually coarsen through agglomeration and crystal growth, while coarse particles become finer due to secondary nucleation and abrasion and cracking of coarse aluminum hydroxide particles. This periodic coarsening and refining process results in uneven particle size distribution, affecting product quality and application effectiveness.

[0004] With the market demand for aluminum hydroxide micronized powder continuing to rise, and the requirements for its quality and performance becoming increasingly stringent, existing preparation processes can no longer meet production needs. There is an urgent need to develop a new process to overcome existing technical challenges and achieve high-quality, efficient, environmentally friendly, and low-cost production of aluminum hydroxide micronized powder. Summary of the Invention

[0005] Traditional aluminum hydroxide micron powder preparation processes suffer from long production cycles, high energy consumption, and unstable product quality, severely hindering the industry's development. Given the increasingly stringent environmental requirements and rising energy costs, developing novel aluminum hydroxide micron powder preparation processes is of great significance. This invention proposes a high-temperature rapid decomposition process for producing aluminum hydroxide micron powder using active seed crystals, aiming to overcome existing technological bottlenecks. Through the design of the active seed crystals and precise control of the high-temperature rapid decomposition process, the production cycle can be shortened, energy consumption reduced, and product purity and particle size uniformity improved, thereby enhancing product market competitiveness and meeting market demand for high-quality aluminum hydroxide micron powder. To achieve the above objectives, this invention provides the following technical solution:

[0006] A process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals includes the following steps:

[0007] S1, Preparation of active seed crystals: Sodium aluminate solution and carbon dioxide gas are mixed at a specific mass ratio and reacted under high-speed stirring at a stirring speed of 3000-8000 rpm to generate amorphous aluminum hydroxide microcrystal nuclei; then an additive, which is a mixture of polyethylene glycol and sodium dodecyl sulfate, is added to the reaction system; stirring is continued for 0.5-1 hour to obtain an active seed crystal suspension.

[0008] Preferably, the sodium aluminate solution is obtained by purifying the crude sodium aluminate solution from the sintering process and performing deep desiliconization to obtain a refined solution with an AK value of approximately 1.27.

[0009] Preferably, the composition and content of the purified sodium aluminate solution are as follows: in step S1, the AL2O3 concentration in the sodium aluminate solution is 20-65 g / L; more preferably, the AL2O3 concentration in the sodium aluminate solution is 40-50 g / L.

[0010] Preferably, in step S1, the mass ratio of alumina to carbon dioxide gas in the sodium aluminate solution is in the range of 1:1.0 to 1.2, more preferably 1:0.8 to 1.0, and even more preferably 1:0.9 to 0.95.

[0011] Preferably, in step S1, the mass ratio of polyethylene glycol to sodium dodecyl sulfate in the additive is 1:1 to 2, and the amount of additive added is 0.5 to 1% of the mass of alumina in the sodium aluminate solution.

[0012] Preferably, in step S1, the stirring speed is 3000-8000 rpm; more preferably, the stirring speed is 4500-6000 rpm.

[0013] Preferably, in step S1, the reaction temperature is controlled at 20-40°C and the reaction time is 10-30 minutes. More preferably, the reaction temperature is controlled at 30-35°C and the reaction time is 10-15 minutes.

[0014] Preferably, the polyethylene glycol is PEG-300.

[0015] Preferably, the final pH value of the reaction solution between the sodium aluminate solution and carbon dioxide gas is 9.5–11; more preferably, the pH value is 10–10.5. Sodium dodecyl sulfate, as a surfactant, adsorbs onto specific crystal faces of aluminum hydroxide, promoting the formation of microcrystal nuclei with uniform particle size and regular morphology, avoiding the formation of coarse particles. Simultaneously, under high-speed stirring, it can reduce the gas-liquid interfacial tension, promote the dispersion of carbon dioxide bubbles, and improve the reaction efficiency of the sodium aluminate solution with CO2, indirectly affecting the crystal nucleus formation rate. PEG-300, as a nonionic surfactant, adsorbs onto the particle surface through hydrogen bonding, forming a polymeric protective film; sodium dodecyl sulfate, as an anionic surfactant, provides electrostatic repulsion. The combination of these two surfactants produces a synergistic stabilizing effect, significantly improving the dispersibility and stability of the suspension.

[0016] S2, Seed activation treatment: After filtering and washing the above active seed suspension to remove impurities, place the active seed in a room temperature environment for activation treatment for 12 to 72 hours to promote the generation of more active sites on the seed surface.

[0017] S3, High-Temperature Rapid Decomposition: The activated seed crystals are fed into a high-temperature decomposition device at a ratio of 1:10 to 20 of the mass of alumina in the sodium aluminate solution to be decomposed. The decomposition is carried out rapidly at a high temperature of 80 to 90°C for 10 to 30 minutes to obtain aluminum hydroxide micro powder product.

[0018] S4, Post-processing: Wash and dry the aluminum hydroxide micro powder product, and classify it if necessary to obtain the finished aluminum hydroxide micro powder with uniform particle size and narrow distribution.

[0019] The finished aluminum hydroxide micro powder has a purity of ≥99.5% and an average particle size between 0.5 and 3 μm.

[0020] In this invention, sodium dodecyl sulfate performs the following functions:

[0021] 1. The core functions of surfactants include:

[0022] Dispersion and stabilization: The molecular structure contains hydrophilic sulfonate groups and lipophilic alkyl chains, which can be adsorbed on the surface of aluminum hydroxide microcrystal nuclei. Through electrostatic repulsion (anionic groups make the particles negatively charged) and steric hindrance (alkyl chains extend to form a protective layer), particle agglomeration is inhibited, ensuring uniform dispersion of the seed crystals.

[0023] Regulating crystal growth: Selective adsorption on specific crystal planes of aluminum hydroxide affects crystal growth kinetics, promotes the formation of microcrystal nuclei with uniform particle size and regular morphology, and avoids the formation of coarse particles.

[0024] Enhanced gas-liquid mass transfer: High-speed stirring can reduce the interfacial tension between gas and liquid, promote the dispersion of carbon dioxide bubbles, improve the reaction efficiency of sodium aluminate solution with CO2, and indirectly affect the crystal nucleation rate.

[0025] 2. Synergistic effect with polyethylene glycol (PEG):

[0026] PEG, as a nonionic surfactant, adsorbs onto the particle surface through hydrogen bonding, forming a polymeric protective film; SDS, as an anionic surfactant, provides electrostatic repulsion. The combination of these two surfactants produces a synergistic stabilizing effect, significantly improving the dispersibility and stability of the suspension.

[0027] A mass ratio of 1:1 to 2 may optimize the adsorption layer structure of the two surfactants on the particle surface, balancing steric hindrance and electrostatic repulsion.

[0028] Experimental comparisons in this invention revealed that sodium dodecyl sulfate is more suitable for this system: its linear structure and strong hydrophilic sulfate ions can provide stable electrostatic repulsion and steric hindrance, and the synergistic effect after being combined with PEG is significant, making it suitable for preparing highly dispersible active seed crystals.

[0029] Sodium dodecylbenzenesulfonate, as another surfactant, has the following limitations: its branched and benzene ring structures may lead to a decrease in dispersion efficiency, and it is not stable enough under acidic conditions. If the pH of the system fluctuates greatly, it can easily affect the quality of the seed crystals.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention achieves rapid preparation of aluminum hydroxide micro powder by optimizing the preparation and decomposition conditions of active seed crystals, thereby improving production efficiency, reducing production costs, and ensuring that the product has excellent characteristics of high purity and uniform particle size.

[0032] 2. In the process of preparing active seed crystals, this invention adds special additives, which can effectively regulate seed crystal growth, promote the formation of active sites on the seed crystal surface, and enhance seed crystal activity, thereby significantly accelerating the high-temperature decomposition reaction rate and greatly shortening the production cycle.

[0033] 3. The optimized high-temperature decomposition conditions of this invention enable aluminum hydroxide micro powder to be rapidly decomposed and generated in a short time, reducing investment and energy consumption by 30% to 40% compared to traditional processes.

[0034] 4. Through precise control of the entire process, the present invention produces aluminum hydroxide micro powder with a purity of over 99.5%, uniform particle size distribution, and an average particle size between 0.5 and 3 μm. Furthermore, by making fine adjustments, products with different particle size grades can be produced, fully meeting the quality requirements of different industries for aluminum hydroxide micro powder.

[0035] 5. The raw materials used in this process are widely available and inexpensive, and the wastewater and waste residue generated during the production process are returned to the alumina production process, which is environmentally friendly and has good economic and social benefits. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] Example 1

[0039] (1) Preparation of active seed crystals: 1000 mL of crude sodium aluminate solution obtained by sintering was purified and deeply desiliconized to obtain a refined solution with an AK of approximately 1.27 and an Al2O3 concentration of 50 g / L. 500 mL of this solution was placed in a 1000 mL beaker (a carbonation reaction tank was used in large-scale production). Under high-speed stirring, carbon dioxide gas (liquid carbon dioxide becomes a gas with a purity of over 99% after depressurization) was slowly added. The flow rate of carbon dioxide gas (converted to mass) was controlled at 2.5 g / min (i.e., the mass ratio of alumina to total carbon dioxide introduced was 1:1). The reaction temperature was controlled to not exceed 35℃, and the reaction was carried out for 10 minutes. The pH value at the final gas-liquid reaction point was controlled to be 10, generating amorphous aluminum hydroxide crystal nuclei. Then, a mixture of 0.08 g of polyethylene glycol PEG-300 and 0.08 g of sodium dodecyl sulfate was added to the reaction system, and stirring was continued for 0.5 hours to obtain an active seed crystal suspension.

[0040] In the preparation of aluminum hydroxide, crude sodium aluminate solution is used for purification; quicklime (calcium oxide) or hydrated lime (calcium hydroxide) is added for desilication treatment, followed by filtration and purification to obtain a refined sodium aluminate solution. This is a common method in the field and will not be elaborated upon here. The method provided in published patent CN101182019A can be referenced.

[0041] (2) Seed activation treatment: After filtering and washing the active seed suspension to remove impurities, place the active seed at room temperature for activation treatment and leave it for 12 hours to promote the generation of more active sites on the seed surface.

[0042] (3) High-temperature rapid decomposition: The activated active seed crystals and the refined sodium aluminate solution to be decomposed are mixed at a mass ratio of 1:10 to form a uniform slurry. The slurry is then transported to a high-temperature decomposition device (with a stirring decomposition tank) and rapidly decomposed at a high temperature of 80-90℃ for 10 minutes to obtain aluminum hydroxide micro powder product.

[0043] (4) Post-processing: The aluminum hydroxide micro powder product is washed and dried to obtain a finished aluminum hydroxide micro powder with uniform particle size. The purity of the finished product is 99.6% and the average particle size D50 is 0.5μm.

[0044] Example 2

[0045] (1) Preparation of active seed crystals: 1000 mL of crude sodium aluminate solution obtained by sintering was purified and deeply desiliconized to obtain a refined solution with an AK of approximately 1.27 and an Al2O3 concentration of 45 g / L. 500 mL of this solution was placed in a 1000 mL beaker, and carbon dioxide gas was slowly added under high-speed stirring (the mass ratio of alumina to total carbon dioxide introduced was 1:1.1, and the carbon dioxide was controlled by a flow meter at a rate of 3.1 g / min). The reaction temperature was controlled to not exceed 30 °C, and the reaction was carried out for 8 minutes. The pH value of the gas-liquid reaction endpoint was controlled to be 10.5, generating amorphous aluminum hydroxide crystal nuclei. Then, a mixture of 0.1 g of polyethylene glycol PEG-300 and 0.12 g of sodium dodecyl sulfate was added to the reaction system, and stirring was continued for 1 hour to obtain an active seed crystal suspension.

[0046] (2) Seed activation treatment: After filtering and washing the active seed suspension to remove impurities, place the active seed at room temperature for activation treatment for 24 hours to promote the generation of more active sites on the seed surface.

[0047] (3) High-temperature rapid decomposition: The activated active seed crystals and the refined sodium aluminate solution to be decomposed are mixed at a mass ratio of 1:15 to form a uniform slurry. The slurry is then transported to a high-temperature decomposition device and rapidly decomposed at a high temperature of 80-90℃ for 20 minutes to obtain aluminum hydroxide micro powder product.

[0048] (4) Post-processing: The aluminum hydroxide micro powder product is washed and dried to obtain a finished aluminum hydroxide micro powder with uniform particle size. The purity of the finished product is 99.7% and the average particle size D50 is 1.5μm.

[0049] Example 3

[0050] (1) Preparation of active seed crystals: 1000 mL of crude sodium aluminate solution obtained by sintering was purified and deeply desiliconized to obtain a refined solution with an AK of approximately 1.27 and an Al2O3 concentration of 47 g / L. 500 mL of this solution was placed in a 1000 mL beaker, and carbon dioxide gas (the mass ratio of alumina to total carbon dioxide introduced was 1:1.2, and the carbon dioxide was controlled by a flow meter at a rate of 3.5 g / min) was slowly added under high-speed stirring at 4500–6000 rpm. The reaction temperature was controlled to not exceed 30 °C, and the reaction was carried out for 8 minutes. The pH value at the final gas-liquid reaction point was controlled to be 10.5, generating amorphous aluminum hydroxide crystal nuclei. Then, a mixture of 0.12 g of polyethylene glycol PEG-300 and 0.14 g of sodium dodecyl sulfate was added to the reaction system, and stirring was continued for 1 hour to obtain an active seed crystal suspension.

[0051] (2) Seed activation treatment: After filtering and washing the active seed suspension to remove impurities, the active seed is placed at room temperature for activation treatment and left for 36 hours to promote the generation of more active sites on the seed surface.

[0052] (3) High-temperature rapid decomposition: The activated active seed crystals and the refined sodium aluminate solution to be decomposed are mixed at a mass ratio of 1:20 to form a uniform slurry. The slurry is then transported to a high-temperature decomposition device and rapidly decomposed at a high temperature of 80-90℃ for 30 minutes to obtain aluminum hydroxide micro powder product.

[0053] (4) Post-processing: The aluminum hydroxide micro powder product is washed and dried to obtain a finished aluminum hydroxide micro powder with uniform particle size. The purity of the finished product is 99.6% and the average particle size D50 is 2.0 μm.

[0054] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals, characterized in that, The steps include: S1, Preparation of active seed crystals: Sodium aluminate solution is mixed with carbon dioxide gas and reacted under high-speed stirring at a speed of 3000-8000 rpm to generate amorphous aluminum hydroxide microcrystal nuclei; then an additive, a mixture of polyethylene glycol and sodium dodecyl sulfate, is added to the reaction system; stirring is continued to obtain an active seed crystal suspension. S2, Seed activation treatment: After filtering and washing the above active seed suspension to remove impurities, place the active seed in a room temperature environment for activation treatment for 12 to 72 hours to promote the generation of more active sites on the seed surface. S3, High-Temperature Rapid Decomposition: The activated active seed crystals are mixed with the sodium aluminate solution to be decomposed to form a uniform slurry. The slurry is then transported to a high-temperature decomposition device and decomposed at a high temperature of 80-90°C for 10-30 minutes to obtain aluminum hydroxide micro powder product.

2. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the concentration of Al2O3 in the sodium aluminate solution is 20–65 g / L.

3. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the mass ratio of alumina to carbon dioxide gas in the sodium aluminate solution ranges from 1:1.0 to 1.

2.

4. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the final pH value of the reaction solution between sodium aluminate solution and carbon dioxide gas is 9.5-11.

5. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the mass ratio of polyethylene glycol to sodium dodecyl sulfate in the additive is 1:1 to 2, and the amount of additive added is 0.5 to 1% of the mass of alumina in the sodium aluminate solution.

6. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the reaction temperature is controlled at 20-40℃ and the reaction time is 0.5-1 hour.

7. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S1, the polyethylene glycol is of type PEG-300.

8. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, In step S3, the activated seed crystals are added at a ratio of 1:10 to 20 of the mass of alumina in the sodium aluminate solution to be decomposed.

9. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, It also includes S4, post-processing: washing and drying the aluminum hydroxide micro powder product to obtain the finished aluminum hydroxide micro powder.

10. The process for producing aluminum hydroxide micro powder by high-temperature rapid decomposition of active seed crystals according to claim 1, characterized in that, The finished aluminum hydroxide micro powder has a purity of ≥99.5% and an average particle size between 0.5 and 3 μm.