Aluminum hydroxide seed crystal as well as preparation method and application thereof

Abstract

The invention discloses an aluminum hydroxide seed crystal and a preparation method and application thereof, and relates to the technical field of aluminum oxide production and inorganic material preparation. The preparation method comprises the following steps: desiliconizing a sintering method sodium aluminate solution, then adding aluminum sulfate which is 0.05-0.15 time of the molar weight of sodium aluminate in the solution at 20-40 DEG C, stirring, introducing carbon dioxide gas, reacting for 10-20 minutes, filtering and washing to obtain a seed crystal; and mixing disodium ethylene diamine tetraacetate and sodium potassium tartrate tetrahydrate according to a mass ratio of 1: (1-2) to obtain an additive, adding the seed crystal into the additive solution, activating at 70-90 DEG C for 2-2.5 hours, and filtering and drying to obtain the high-activity aluminum hydroxide seed crystal. The activity of the prepared seed crystal is greatly improved compared with that of a traditional seed crystal.

Description

Technical Field

[0001] This invention relates to the field of alumina production and inorganic material preparation technology, and particularly to an aluminum hydroxide seed crystal, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Alumina or high-whiteness aluminum hydroxide micro powder has a wide range of applications due to its unique physicochemical properties. Aluminum hydroxide seed crystals are the raw materials for producing alumina or high-whiteness aluminum hydroxide micro powder.

[0004] Sintering is one of the important methods for producing alumina. The process involves mixing bauxite with auxiliary raw materials such as sodium carbonate (Na₂CO₂) and limestone (CaCO₃) in a specific ratio and calcining them. This converts the alumina (Al₂O₃) in the bauxite into soluble sodium aluminate (NaAlO₂), from which aluminum is extracted as a sodium aluminate solution, yielding a sintered sodium aluminate solution. However, the sintered sodium aluminate solution still requires the addition of aluminum hydroxide seed crystals for seed decomposition for at least 48 hours to prepare aluminum hydroxide. Summary of the Invention

[0005] Based on the current state of technology, the purpose of this invention is to provide an aluminum hydroxide seed crystal, its preparation method and application. The aluminum hydroxide seed crystal is prepared by using sodium aluminate solution obtained by sintering as raw material, and by steps such as desilication, seed induction and seed activation. It has the characteristics of low impurities and high activity.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, a method for preparing aluminum hydroxide seed crystals includes the following steps:

[0008] S1. After desiliconizing the sodium aluminate solution by sintering, stir at 20-40°C and then introduce carbon dioxide gas to react for 10-20 minutes. Filter and wash to obtain seed crystals.

[0009] S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate are mixed in a mass ratio of 1:(1~2) as additives. After adding seed crystals to the additive solution, the mixture is activated at 70~90℃ for 2~2.5h, filtered and dried to obtain aluminum hydroxide seed crystals.

[0010] Secondly, the aluminum hydroxide seed crystals obtained by the above-mentioned method for preparing aluminum hydroxide seed crystals.

[0011] Thirdly, the aforementioned aluminum hydroxide seed crystals are used in the preparation of high-whiteness aluminum hydroxide micro powder or alumina.

[0012] The beneficial effects of the present invention are as follows:

[0013] 1. During the seed crystal induction process, by precisely controlling the amount of carbon dioxide introduced, as well as the reaction temperature and time, the growth process of the seed crystals can be regulated, resulting in uniform seed crystal size and significantly improved seed crystal activity. Furthermore, the use of a special additive solution in the seed crystal activation step can form a large number of active sites on the seed crystal surface, further enhancing seed crystal activity. Compared to seed crystals prepared by traditional methods, the seed crystals prepared by this invention exhibit significantly improved activity.

[0014] 2. The entire preparation process is simple, easy to operate, and has a wide range of raw material sources and low cost. Moreover, it can make full use of the solution resources in the sintering process, which has good economic and environmental benefits and is suitable for large-scale industrial production. Detailed Implementation

[0015] 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.

[0016] 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.

[0017] The reagents or compounds involved in the following specific embodiments include:

[0018] Disodium ethylenediaminetetraacetate, also known as EDTA-2Na, CAS No.: 139-33-3.

[0019] Sodium potassium tartrate, also known as Rochelle salt or Rochelle salt, CAS No.: 304-59-6.

[0020] One or more embodiments of the present invention provide a method for preparing aluminum hydroxide seed crystals, comprising the following steps:

[0021] S1. Desiliconize the sodium aluminate solution obtained by sintering, then react with carbon dioxide gas at 20-40℃ for 10-20 minutes after rapid stirring, and then filter and wash to obtain seed crystals.

[0022] S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate are mixed in a mass ratio of 1:(1~2) as additives. After adding seed crystals to the additive solution, the mixture is activated at 70~90℃ for 2~2.5h, filtered and dried to obtain aluminum hydroxide seed crystals.

[0023] Sintering can prepare sodium aluminate solutions with high purity, but some silicon impurities are still present. Desiliconization can further improve the purity of sodium aluminate solutions. Then, seed crystals are induced to form under the action of carbon dioxide. After that, the seed crystals are activated by additives to obtain low-impurity and high-activity aluminum hydroxide seed crystals.

[0024] Optionally, in S1, the desilication method includes: heating the sintered sodium aluminate solution to 150-180°C, adding lime or lime slurry and stirring for 60-120 minutes, and then filtering to obtain a refined sodium aluminate solution.

[0025] Optionally, in S1, after desilication, a flocculant is added, and the mixture is stirred at 70-80°C for 15-30 minutes to generate a precipitate. The solution is then filtered to further reduce the impurity content.

[0026] Optionally, in S1, the flocculant includes one or more of polyaluminum chloride and ferrous ammonium sulfate, which can reduce the content of elements such as Si, Na, and Fe.

[0027] Optionally, in S1, the concentration of sodium aluminate in the solution is 20–85 g / L, preferably 60–80 g / L.

[0028] Optionally, in S1, the flow rate of carbon dioxide introduced into each liter of sodium aluminate solution is 5-12 L / min. During the process, the acidic substances formed by sodium aluminate and carbon dioxide neutralize each other and induce seed crystal formation.

[0029] Optionally, in S1, the temperature is controlled at 20-40°C, preferably 30-40°C, during the introduction of carbon dioxide gas.

[0030] Optionally, in S2, the mass concentration of the additive solution is 5–10 g / L. EDTA-2Na exposes hydroxyl active sites through chelation, while potassium sodium tartrate enhances surface adsorption capacity through coordination and hydrogen bonding. Both activate the seed crystals by reducing surface energy and promoting aluminum species migration. The additive enables the formation of more active sites on the seed crystal surface, increasing the number of unsaturated coordination ion sites (such as Al) on the aluminum hydroxide seed crystal surface. 3+ O 2- The hydroxyl functional groups are the core reaction sites for crystal growth, thereby enhancing the activity of the seed crystal.

[0031] Optionally, in S2, the filtration and drying method includes: filtering the activated seed crystals, washing them until neutral, and then drying them at 60–90°C for 2–4 hours to obtain aluminum hydroxide seed crystals.

[0032] One or more embodiments of the present invention provide aluminum hydroxide seed crystals prepared by the above-described method.

[0033] Optionally, the particle size range of the aluminum hydroxide seed crystals is 1.5 to 2.5 μm.

[0034] Optionally, the impurity content of the aluminum hydroxide seed crystals is 0.4 to 0.6 wt%.

[0035] One or more embodiments of the present invention provide the application of the above-mentioned aluminum hydroxide seed crystals in the preparation of high-whiteness aluminum hydroxide micro powder or alumina.

[0036] Example 1

[0037] An aluminum hydroxide seed crystal, the preparation method of which includes:

[0038] S1. Take 1000 mL of a sodium aluminate solution with a concentration of 80 g / L from the sintering process, and filter it to remove suspended impurities. Since SiO2 still has a certain solubility in alkaline solutions, the filtered sodium aluminate solution from the sintering process was found to contain silicon in the form of SiO2, with a mass concentration of 2 g / L. The filtered solution was then subjected to deep desilication. The desilication process included: placing the solution in a heating device and heating it to 150°C; while stirring, adding lime milk (calcium hydroxide) to the solution, with the amount of calcium hydroxide added being 1 times the mass of silicon in the solution, i.e., 2 g / L; stirring for 60 min to allow the silicon impurities to precipitate. Next, three solid-liquid separation and filtration processes were performed to remove silicon impurities, resulting in a pretreated refined sodium aluminate solution. The pretreated sodium aluminate solution was cooled to 35°C. A 30% (w / w) aluminum sulfate solution was added to the solution according to a molar ratio of 1:0.1 (sodium aluminate to aluminum sulfate molar ratio of 0.5:0.1). After stirring evenly, carbon dioxide gas was introduced at a flow rate of 8 L / min, and the reaction temperature was maintained at 35°C for 3 hours to induce the formation of aluminum hydroxide seeds. The dispersion containing the seeds was filtered and washed to obtain the seeds.

[0039] S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate in a mass ratio of 1:1.5 were prepared as additives and dissolved in water to obtain an additive solution with a mass concentration of 5 g / L. Seed crystals and additive solution were mixed in a mass ratio of 100:1 and stirred at 150 r / min for 1.5 h at 55 °C to complete the activation treatment. The activated seed crystals were obtained by filtration and washed until neutral. Then, they were dried at 70 °C for 4 h to obtain the high-activity aluminum hydroxide seed crystal product.

[0040] The application of highly active aluminum hydroxide seeds in the preparation of high-whiteness aluminum hydroxide micro powder in this embodiment includes:

[0041] Take 16g of the highly active aluminum hydroxide seed crystals obtained in this example and add them to 1000mL of a refined sodium aluminate solution with an ak value of 1.50 (the concentration of alumina in the sodium aluminate solution is 160g / L). Under the conditions of stirring at 100r / min, initial decomposition temperature of 70℃, final temperature of 70℃, and decomposition for 30min, the decomposition rate is 50%, and high white aluminum hydroxide micro powder is obtained.

[0042] Furthermore, alumina was prepared using the high-whiteness aluminum hydroxide micro powder obtained in this embodiment as a raw material.

[0043] Example 2

[0044] An aluminum hydroxide seed crystal, the preparation method of which includes:

[0045] S1. Take 1200 mL of a sintering sodium aluminate solution with a concentration of 60 g / L, filter it to remove suspended impurities; the filtered sintering sodium aluminate solution is found to contain silicon in the form of SiO2 with a mass concentration of 1.8 g / L. Perform deep desilication on the filtered solution. The desilication process includes: placing the solution in a heating device and heating it to 180°C; adding lime milk (calcium hydroxide) to the solution while stirring, with the amount of calcium hydroxide added being 1 times the mass of silicon in the solution, i.e., 1.8 g / L; stirring for 120 min to allow silicon impurities to precipitate; then performing three solid-liquid separation filtrations to remove silicon impurities, obtaining a purified sodium aluminate solution; then heating the purified sodium aluminate solution... At 70°C, add 2g of polyaluminum chloride (flocculator) under stirring, continue stirring for 25min to agglomerate small particulate impurities, and then filter three times to complete the pretreatment. Cool the pretreated sodium aluminate solution to 32°C, and add 25% aluminum sulfate solution according to the molar ratio of alumina content in sodium aluminate solution to alumina content in aluminum sulfate solution of 1:0.08 (molar ratio of sodium aluminate to aluminum sulfate is 0.5:0.08). After stirring evenly, introduce carbon dioxide gas at a flow rate of 6L / min, maintain the reaction temperature at 32°C, and react for 3.5h to induce the formation of aluminum hydroxide seed crystals. Filter and wash the dispersion containing the seed crystals to obtain the seed crystals.

[0046] S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate in a mass ratio of 1:1.2 were prepared as additives and dissolved in water to obtain an additive solution with a mass concentration of 7 g / L. Seed crystals and additive solution were mixed in a mass ratio of 80:1 and stirred at 200 r / min at 52℃ for 1.8 h to complete the activation treatment. The activated seed crystals were obtained by filtration and washed until neutral. Then, they were dried at 75℃ for 4.5 h to obtain the high-activity aluminum hydroxide seed crystal product.

[0047] The application of highly active aluminum hydroxide seeds in the preparation of high-whiteness aluminum hydroxide micro powder in this embodiment includes:

[0048] Take 8g of the highly active aluminum hydroxide seed crystals obtained in this example and add them to 1000mL of a refined sodium aluminate solution with an ak value (caustic ratio) of 1.50 (the concentration of alumina in the sodium aluminate solution is 160g / L). Under the conditions of stirring at 100r / min, initial decomposition temperature of 70℃, final temperature of 70℃, and decomposition for 60min, the decomposition rate is 50%, and high white aluminum hydroxide micro powder is obtained.

[0049] Furthermore, alumina was prepared using the high-whiteness aluminum hydroxide micropowder obtained in this embodiment.

[0050] Example 3

[0051] An aluminum hydroxide seed crystal, the preparation method of which includes:

[0052] S1. Take 800 mL of a sintering sodium aluminate solution with a concentration of 40 g / L, filter it to remove suspended impurities; the filtered sintering sodium aluminate solution contains silicon in the form of SiO2 with a mass concentration of 1.5 g / L. Perform deep desilication on the filtered solution. The desilication process includes: placing the solution in a heating device and heating it to 165°C; adding lime milk (calcium hydroxide) to the solution while stirring, with the amount of calcium hydroxide added being 1.2 times the mass of silicon in the solution, i.e., 1.8 g / L; stirring for 90 min to allow silicon impurities to precipitate; then performing three solid-liquid separation filtrations to remove silicon impurities, obtaining a purified sodium aluminate solution; then heating the purified sodium aluminate solution to... At 75℃, 1.2g of ferrous ammonium sulfate (flocculator) was added under stirring conditions, and the mixture was kept warm and stirred for 18min to agglomerate small particulate impurities. The mixture was then filtered three times to complete the pretreatment. The pretreated sodium aluminate solution was cooled to 38℃. A 25% aluminum sulfate solution was added to the solution according to the molar ratio of alumina content in the sodium aluminate solution to that in aluminum sulfate, which was 1:0.12 (the molar ratio of sodium aluminate to aluminum sulfate was 0.5:0.12). After stirring evenly, carbon dioxide gas was introduced at a flow rate of 9L / min, and the reaction temperature was maintained at 38℃ for 2.5h to induce the formation of aluminum hydroxide seed crystals. The dispersion containing the seed crystals was filtered and washed to obtain the seed crystals.

[0053] S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate in a mass ratio of 1:1.8 were prepared as additives and dissolved in water to obtain an additive solution with a mass concentration of 9 g / L. Seed crystals and additive solution were mixed in a mass ratio of 60:1 and stirred at 300 r / min at 58℃ for 1.8 h to complete the activation treatment. The activated seed crystals were obtained by filtration and washed until neutral. Then, they were dried at 85℃ for 3.5 h to obtain the high-activity aluminum hydroxide seed crystal product.

[0054] Comparative Example

[0055] High-whiteness aluminum hydroxide micropowder was prepared by using 500g of aluminum hydroxide from the Bayer process decomposition tank as a common seed crystal. The method included: adding it to 1000mL of a refined sodium aluminate solution with an ak value of 1.50 (the concentration of aluminum oxide in the sodium aluminate solution was 160g / L). Under the conditions of stirring at 100r / min, initial decomposition temperature of 70℃, final temperature of 50℃, and decomposition for 48 hours, the decomposition rate was 50%.

[0056] Performance testing

[0057] The particle size of the highly active aluminum hydroxide seeds obtained in each example and comparative example was detected by laser particle size analysis. It was found that the particle size range of Example 1 was 0.3-0.8 μm, the particle size of Example 2 was 0.4-0.8 μm, and the particle size of Example 3 was 0.2-0.4 μm.

[0058] The particle size of the high-whiteness aluminum hydroxide micronized powder products obtained in each example and comparative example was determined using laser particle size analysis. The results showed that the particle size range of Example 1 was 2–3 μm, that of Example 2 was 2.5–3.5 μm, and that of Example 3 was 1.5–2.5 μm. The particle size distribution was concentrated, meeting the requirements for high-whiteness aluminum hydroxide micronized powder. The particle size range of the comparative examples was 1–100 μm, indicating that the high-whiteness aluminum hydroxide product obtained by decomposition using highly active seed crystals had a fine particle size, with a particle size D50 of 1–3.5 μm.

[0059] The impurity content of the high-whiteness aluminum hydroxide micropowder products obtained in each embodiment and comparative example was detected by ICP (inductively coupled plasma analysis). The results showed that the impurity content of the product obtained in Example 1 was less than 0.2 wt%, the impurity content of the product obtained in Example 2 was less than 0.3 wt%, and the impurity content of the product obtained in Example 3 was less than 0.1 wt%. This indicates that the technical solution of the present invention can effectively control the impurity content, especially reducing elements such as Si, Na, and Fe in the product. The impurity content of the product obtained in the comparative example was 0.45%, indicating that the high-activity seed crystals used in the embodiments decomposed rapidly, and the impurity elements precipitated / carried out were less than those from ordinary seed crystal decomposition.

[0060] The evaluation method for seed activity is as follows: Under the premise that other process parameters and decomposition rates are basically the same in the process of obtaining high white aluminum hydroxide micro powder, the seed with less seed addition and / or shorter decomposition time has higher activity. Based on the activity of ordinary seed in the comparative example, the amount of active seed added in Example 1 is only 3.2% of that of ordinary seed, but the decomposition time to achieve the same decomposition rate is only 1 / 96 of that of ordinary seed; based on the activity of traditional seed in Comparative Example 2, the amount of active seed added in Example 1 is only 1.6% of that of ordinary seed, but the decomposition time to achieve the same decomposition rate is only 1 / 48 of that of ordinary seed; This shows that the seed activity of the present invention has been significantly improved, which can significantly reduce the amount of seed added, the amount of seed recycled, significantly shorten the decomposition time, and greatly reduce the cost.

[0061] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing aluminum hydroxide seed crystals, characterized in that, The following steps are involved: S1. After desiliconizing the sodium aluminate solution by sintering, add aluminum sulfate at 20-40℃ in a volume of 0.05-0.15 times that of sodium aluminate in the solution. Stir and then pass carbon dioxide gas through to react for 10-20 minutes. Filter and wash to obtain seed crystals. S2. Disodium ethylenediaminetetraacetate and sodium potassium tartrate are mixed in a mass ratio of 1:(1~2) as additives. After adding seed crystals to the additive solution, the mixture is activated at 70~90℃ for 2~2.5h, filtered and dried to obtain aluminum hydroxide seed crystals.

2. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, In S1, the desilication method includes: heating the sintering sodium aluminate solution to 150-180°C, adding lime or lime slurry and stirring for 60-120 minutes, and then filtering to obtain a refined sodium aluminate solution.

3. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, In S1, after desilication, flocculant is added, and the mixture is stirred at 70-80℃ for 15-30 minutes. After precipitation, the solution is obtained by filtration.

4. The method for preparing aluminum hydroxide seed crystals according to claim 3, characterized in that, The flocculant includes one or more of polyaluminum chloride and ferrous ammonium sulfate.

5. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, The concentration of sodium aluminate in the solution is 20–85 g / L, preferably 60–80 g / L.

6. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, In S1, the flow rate of carbon dioxide introduced into each liter of sodium aluminate solution is 5-12 L / min; Alternatively, during the introduction of carbon dioxide gas, the temperature can be adjusted to 20–40°C, preferably 30–40°C.

7. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, In S2, the mass concentration of the additive solution is 5–10 g / L.

8. The method for preparing aluminum hydroxide seed crystals according to claim 1, characterized in that, In S2, the filtration and drying method includes: filtering the activated seed crystals, washing them until neutral, and then drying them at 60-90°C for 2-4 hours.

9. An aluminum hydroxide seed prepared by a method according to any one of claims 1-8.

10. The application of the aluminum hydroxide seed crystal as described in claim 9 in the preparation of high-whiteness aluminum hydroxide micro powder or alumina.