Method for preparing low-sodium aluminum hydroxide by two-stage method

Abstract

The invention provides a method for preparing low-sodium aluminum hydroxide through a two-stage method, and belongs to the field of aluminum hydroxide production. The method comprises the following steps: adding a first aluminum hydroxide seed into a sodium aluminate solution, and carrying out first-stage decomposition to obtain first mixed slurry; carrying out solid-liquid separation on the first mixed slurry to obtain first low-sodium aluminum hydroxide and separated mother liquor; adjusting the alpha k of the separated mother liquor to a second set alpha k; adding a second aluminum hydroxide seed into the separated mother liquor to perform second-stage decomposition to obtain second mixed slurry; and carrying out solid-liquid separation on the second mixed slurry to obtain second low-sodium aluminum hydroxide. According to the present invention, the sodium aluminate solution is subjected to the first-stage decomposition, such that the sodium aluminate solution is purified, the solution alpha k is increased, and the saturation degree of the solution is reduced so as to produce the aluminum hydroxide with the high purity during the second-stage decomposition, such that the technology of synchronously producing the two low-sodium aluminum hydroxide in the same process is achieved. Therefore, the impurity ion content of the metallurgical-grade aluminum hydroxide is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of aluminum hydroxide production, and in particular to a method for preparing low-sodium aluminum hydroxide by a two-stage process. Background Art

[0002] The high-temperature alumina on the domestic market is made from metallurgical-grade aluminum hydroxide or alumina, and is prepared using a calcination process.

[0003] However, the process scale of metallurgical-grade alumina is large, and refined control is difficult to achieve. It is difficult to meet the requirements of metallurgical-grade alumina while meeting the requirements of high-temperature alumina during production. When metallurgical-grade aluminum hydroxide is used as the raw material for high-temperature alumina, high-quality production of metallurgical-grade aluminum hydroxide can be achieved, and the stability of high-temperature alumina indicators and its quality can be improved. However, the existing metallurgical-grade aluminum hydroxide has a high content of impurity ions. Impurity ions may introduce unnecessary defects during the preparation process of high-temperature alumina, affecting the quality and performance of the product. At the same time, the presence of impurity ions may also affect the crystal phase transformation and particle size distribution of high-temperature alumina, thereby affecting its application effect. Therefore, how to reduce the impurity ion content of metallurgical-grade aluminum hydroxide is a technical problem that urgently needs to be solved. Summary of the invention

[0004] The present application provides a two-stage method for preparing low-sodium aluminum hydroxide to solve the following technical problem: how to reduce the impurity ion content of metallurgical-grade aluminum hydroxide.

[0005] The present application provides a two-stage method for preparing low-sodium aluminum hydroxide, the method comprising:

[0006] Adding a first aluminum hydroxide seed to a sodium aluminate solution having a first set αk to perform a one-stage decomposition under a first set condition to obtain a first mixed slurry;

[0007] Performing solid-liquid separation on the first mixed slurry to obtain a first low-sodium aluminum hydroxide and a separation mother liquor;

[0008] adjusting αk of the separated mother liquor to a second setting αk;

[0009] adding a second aluminum hydroxide seed to the separated mother liquor having a second set αk to perform a two-stage decomposition under a second set condition to obtain a second mixed slurry; and

[0010] The second mixed slurry is subjected to solid-liquid separation to obtain a second low-sodium aluminum hydroxide.

[0011] Optionally, the first setting αk is 1.5-2.2.

[0012] Optionally, the particle size D50 of the first aluminum hydroxide seeds is 50 μm to 100 μm, and the mass concentration of the first aluminum hydroxide seeds is 100 g / L to 300 g / L.

[0013] Optionally, the first setting condition includes at least one of the following: the seeding temperature is 70°C to 85°C, and the seeding time is 4h to 12h.

[0014] Optionally, the mass concentration of Al2O3 in the sodium aluminate solution is 80g / L to 180g / L.

[0015] Optionally, the particle size D50 of the first low-sodium aluminum hydroxide is 70 μm to 100 μm, and the mass fraction of sodium oxide in the first low-sodium aluminum hydroxide is less than 0.15%.

[0016] Optionally, the second setting αk is 1.8-2.8.

[0017] Optionally, the particle size D50 of the second aluminum hydroxide seeds is 30 μm to 60 μm, and the mass concentration of the second aluminum hydroxide seeds is 500 g / L to 900 g / L.

[0018] Optionally, the second setting condition includes at least one of the following: the seeding temperature is 60°C to 75°C, and the seeding time is ≥40h.

[0019] Optionally, the particle size D50 of the second low-sodium aluminum hydroxide is 40 μm to 60 μm, and the mass fraction of sodium oxide in the second low-sodium aluminum hydroxide is less than 0.10%.

[0020] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0021] The present application provides a method for preparing low-sodium aluminum hydroxide by a two-stage method, the method comprising: adding a first aluminum hydroxide seed to a sodium aluminate solution having a first set αk, so as to perform a first-stage decomposition under a first set condition to obtain a first mixed slurry; performing solid-liquid separation on the first mixed slurry to obtain a first low-sodium aluminum hydroxide and a separation mother liquor; adjusting the αk of the separation mother liquor to a second set αk; adding a second aluminum hydroxide seed to the separation mother liquor having a second set αk, so as to perform a two-stage decomposition under a second set condition to obtain a second mixed slurry; and performing solid-liquid separation on the second mixed slurry to obtain a second low-sodium aluminum hydroxide. By performing a one-stage decomposition on the sodium aluminate solution, the sodium aluminate solution is purified, the impurity content of the solution is reduced, and the αk of the solution is increased, and the saturation of the solution is reduced, thereby producing aluminum hydroxide with higher purity in the two-stage decomposition, and realizing the technology of simultaneously producing two characteristic low-sodium aluminum hydroxides in the same process. Thereby reducing the impurity ion content of metallurgical grade aluminum hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 A schematic flow chart of a two-stage method for preparing low-sodium aluminum hydroxide provided in an embodiment of the present application;

[0025] Figure 2 This is a SEM image of the first low-sodium aluminum hydroxide product provided in Example 1 of the present application;

[0026] Figure 3 This is an SEM image of the second low sodium aluminum hydroxide product provided in Example 1 of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0028] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0029] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0031] Figure 1 A schematic flow chart of a two-stage method for preparing low-sodium aluminum hydroxide provided in an embodiment of the present application.

[0032] See also Figure 1 The present application provides a two-stage method for preparing low-sodium aluminum hydroxide, the method comprising:

[0033] S1, adding a first aluminum hydroxide seed to a sodium aluminate solution having a first set αk to perform a first-stage decomposition under a first set condition to obtain a first mixed slurry;

[0034] It should be noted that αk is the caustic ratio, which is the molar ratio of NaOH to Al2O3 in the sodium aluminate solution, reflecting the strength of the alkalinity of the solution.

[0035] In some embodiments, the method for preparing the sodium aluminate solution comprises:

[0036] The αk of Bayer process semen, re-dissolved semen or sintered process semen is adjusted to the first set αk to obtain the sodium aluminate solution; wherein the αk range of Bayer process semen, re-dissolved semen or sintered process semen is 1.30-1.80, and the Al2O3 concentration range is 80g / L-180g / L.

[0037] In some embodiments, the first setting αk is 1.5-2.2.

[0038] The first setting αk is limited to 1.5-2.2, and the solution usually has a high stability, which is conducive to the subsequent decomposition reaction. In the range of 1.5-2.2, the decomposition rate is moderate, neither too fast to cause uneven product particle size, nor too slow to affect production efficiency. At the same time, the caustic ratio within this range is also helpful to generate aluminum hydroxide products with moderate particle size and stable quality. Exemplarily, the first setting αk can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, etc.

[0039] In some embodiments, the first setting αk is 1.6-2.1.

[0040] In some embodiments, the first setting αk is 1.7-2.0.

[0041] In some embodiments, the particle size D50 of the first aluminum hydroxide seeds is 50 μm to 100 μm, and the mass concentration of the first aluminum hydroxide seeds is 100 g / L to 300 g / L.

[0042] The particle size of aluminum hydroxide seeds is one of the important factors affecting the decomposition rate. Aluminum hydroxide seeds with moderate particle size can provide more surface area, which is conducive to the adsorption and crystallization of aluminum ions in the sodium aluminate solution on its surface, thereby accelerating the decomposition rate. Within the particle size range of 50μm to 100μm, the decomposition rate of aluminum hydroxide seeds is moderate, which will not be too fast to cause uneven product particle size, nor too slow to affect production efficiency. At the same time, the particle size of aluminum hydroxide seeds will also affect the particle size distribution of the product. Within the particle size range of 50μm to 100μm, aluminum hydroxide products with moderate particle size and uniform distribution can be obtained to meet the needs of subsequent processes. Exemplarily, the particle size D50 of the first aluminum hydroxide seed can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc., and the mass concentration of the first aluminum hydroxide seed can be 100 g / L, 110 g / L, 120 g / L, 150 g / L, 180 g / L, 200 g / L, 220 g / L, 250 g / L, 280 g / L, 300 g / L, etc.

[0043] In some embodiments, the particle size of the first aluminum hydroxide seeds is 70 μm to 80 μm, and the mass concentration of the first aluminum hydroxide seeds is 180 g / L to 220 g / L.

[0044] In some embodiments, the first set condition includes at least one of the following: the seeding temperature is 70° C. to 85° C., and the seeding time is 4 h to 12 h.

[0045] The seeding temperature in the first setting condition is limited to 70℃~85℃. As the temperature increases, the decomposition rate of the sodium aluminate solution will gradually accelerate. This is because high temperature can increase the movement speed of molecules in the solution and promote the adsorption and crystallization of aluminum ions on the surface of aluminum hydroxide seeds. However, if the temperature is higher than 85℃, it may also cause impurities in the solution to precipitate, affecting the purity of the product. The seeding time is limited to 4h~12h. As time goes on, the decomposition reaction will be more sufficient and the product yield will increase accordingly. However, if the seeding time is longer than 12h, it may lead to uneven particle size distribution of the product and even agglomeration. Exemplarily, the seeding temperature of a decomposition stage can be 70℃, 72℃, 75℃, 78℃, 80℃, 85℃, etc., and the seeding time can be 4h, 6h, 8h, 10h, 12h, etc.

[0046] In some embodiments, the first set condition includes at least one of the following: the seeding temperature is 75° C. to 80° C., and the seeding time is 6 h to 10 h.

[0047] In some embodiments, the mass concentration of Al2O3 in the sodium aluminate solution is 80 g / L to 180 g / L.

[0048] S2, performing solid-liquid separation on the first mixed slurry to obtain a first low-sodium aluminum hydroxide and a separation mother liquor;

[0049] Through steps S1 and S2, the sodium aluminate solution is preliminarily decomposed and purified, the αk of the solution is increased, and its saturation is reduced, providing conditions for the subsequent production of aluminum hydroxide with higher purity.

[0050] In some embodiments, the particle size D50 of the first low-sodium aluminum hydroxide is 70 μm to 100 μm, and the mass fraction of sodium oxide in the first low-sodium aluminum hydroxide is less than 0.15%.

[0051] The sodium oxide content of the first low-sodium aluminum hydroxide product is less than 0.15%, and the product particle size D50 is 70-100 μm, which can be used as metallurgical grade aluminum hydroxide. For example, the particle size D50 of the first low-sodium aluminum hydroxide can be 70 μm, 75 μm, 80 μm, 90 μm, 95 μm, 100 μm, etc.

[0052] S3, adjusting the αk of the separated mother liquor to the second set αk;

[0053] In some embodiments, the second setting αk is 1.8-2.8.

[0054] By limiting the second setting αk to 1.8 to 2.8, the precipitation conditions of the impurity components can be better controlled to avoid their precipitation too early or too late. This helps to reduce the content of impurities in the product and improve the purity of the product. Exemplarily, the second setting αk can be 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, etc.

[0055] In some embodiments, the second setting αk is 2.0-2.6.

[0056] In some embodiments, the second setting αk is 2.2-2.4.

[0057] S4, adding a second aluminum hydroxide seed to the separated mother liquor with a second set αk to perform a two-stage decomposition under a second set condition to obtain a second mixed slurry; and

[0058] In some embodiments, the particle size D50 of the second aluminum hydroxide seeds is 30 μm to 60 μm, and the mass concentration of the second aluminum hydroxide seeds is 500 g / L to 900 g / L.

[0059] Limiting the particle size D50 of the second aluminum hydroxide seed to 30 μm to 60 μm can ensure that the seed particles have a suitable surface area and activity, which is conducive to the adsorption and crystallization of aluminum ions in the sodium aluminate solution on the seed surface. At the same time, the appropriate particle size can also reduce the crystal agglomeration and crushing phenomenon, and obtain a second mixed slurry with uniform particle size distribution. Limiting the mass concentration of the second aluminum hydroxide seed to 500 g / L to 900 g / L can ensure that there are enough seed particles to participate in the reaction during the second stage decomposition process, thereby improving the decomposition rate and product yield. At the same time, the appropriate mass concentration can also avoid the agglomeration and uneven reaction caused by too dense seed particles. Exemplarily, the particle size D50 of the second aluminum hydroxide seed is 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc., and the mass concentration of the second aluminum hydroxide seed can be 500 g / L, 600 g / L, 700 g / L, 800 g / L, 900 g / L, etc.

[0060] In some embodiments, the particle size D50 of the second aluminum hydroxide seeds is 40 μm to 50 μm, and the mass concentration of the second aluminum hydroxide seeds is 600 g / L to 800 g / L.

[0061] In some embodiments, the second set condition includes at least one of the following: the seeding temperature is 60°C to 75°C, and the seeding time is ≥40h.

[0062] Limiting the seeding temperature to 60°C to 75°C can ensure that the two-stage decomposition process is carried out at an appropriate temperature, which is neither too high to cause impurity precipitation and product degradation, nor too low to cause the decomposition rate to be too slow. Limiting the seeding time to ≥40h can ensure that the decomposition reaction is fully carried out to obtain high-quality aluminum hydroxide products. Exemplarily, the seeding temperature of the two-stage decomposition can be 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, etc., and the seeding time can be 40h, 45h, 50h, 55h, 60h, 65h, etc.

[0063] In some embodiments, the second set condition includes at least one of the following: the seeding temperature is 65° C. to 70° C., and the seeding time is ≥ 50 h.

[0064] In some embodiments, the particle size D50 of the second low-sodium aluminum hydroxide is 40 μm to 60 μm, and the mass fraction of sodium oxide in the second low-sodium aluminum hydroxide is less than 0.10%.

[0065] The particle size of the second low-sodium aluminum hydroxide product is 40 μm to 60 μm, and the mass fraction of sodium oxide is less than 0.10%, which meets the requirements of high-temperature aluminum oxide raw materials.

[0066] S5. Perform solid-liquid separation on the second mixed slurry to obtain a second low-sodium aluminum hydroxide.

[0067] Through steps S3 to S5, the sodium aluminate solution that has been preliminarily purified is further decomposed to produce low-sodium aluminum hydroxide with a lower impurity ion content, thereby improving the quality of the product.

[0068] In summary, the two-stage method for preparing low-sodium aluminum hydroxide in the present application has the following significant advantages:

[0069] (1) Improve product quality: Through the two-stage decomposition process, two specifications of low-sodium aluminum hydroxide products can be prepared, and their sodium oxide content is less than 0.15%, which meets the needs of different fields for high-quality aluminum hydroxide. The particle size distribution of the product is optimized. The particle size D50 of one product is 70-100μm, which is suitable for use as metallurgical grade aluminum hydroxide; the particle size of the other product is 40-60μm, which meets the requirements of high-temperature alumina raw materials.

[0070] (2) Optimize resource utilization: The two-stage decomposition process efficiently utilizes the sodium aluminate solution, making fuller use of the aluminum element in the solution and reducing resource waste. By adjusting the caustic ratio (αk) and decomposition conditions, the technology of simultaneously producing two characteristic low-sodium aluminum hydroxides in the same process is realized, which improves production efficiency.

[0071] (3) Environmental protection and sustainability: This method reduces the generation of wastewater, waste gas and solid waste, meeting the requirements of environmental protection and sustainability. By optimizing the decomposition conditions, energy consumption and emissions are reduced, which is conducive to achieving green and low-carbon production.

[0072] (4) Technological innovation and guidance: This invention reveals the relationship between aluminum hydroxide and sodium oxide and temperature, solid content, causticity ratio, etc., and provides technical guidance for the high-quality transformation of metallurgical-grade alumina to fine alumina. This method has been verified to be feasible and reliable through long-term research, production and application evaluation practice, providing new ideas and technical paths for the preparation of aluminum hydroxide.

[0073] (5) Economic benefits: High-quality low-sodium aluminum hydroxide products have higher added value and market competitiveness, which can bring better economic benefits to enterprises. By optimizing production processes and resource utilization, production costs are reduced and the profitability of enterprises is improved.

[0074] The two-stage method for preparing low-sodium aluminum hydroxide in the present application shows significant advantages in terms of product quality, resource utilization, environmental protection and sustainability, technological innovation and guidance, and economic benefits, providing new technical support and solutions for the preparation of aluminum hydroxide and the development of fine alumina.

[0075] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0076] According to the technology of this patent, the same conclusion is obtained for Bayer process semen, re-dissolved semen and sintered semen. Therefore, as an embodiment, this patent takes Bayer process semen as raw material for example. The composition of Bayer process semen is shown in Table 1.

[0077] Table 1 Bayer process semen composition

[0078] NT AO NC αk 170.01 168.53 21.45 1.45

[0079] Example 1

[0080] (1) One-stage decomposition

[0081] 1000ml of Bayer process semen was measured and adjusted with homemade Bayer process mother liquor (αk was 3.2), αk was adjusted to 1.75, transferred into a 2L beaker and placed in a water bath, the temperature was controlled at 77°C, seeds (particle size d50 was 75.31μm) were added after reaching the temperature, the solid content was controlled at 200g / l, the decomposition time was 8h, and the slurry was separated after the decomposition was completed. The mother liquor was retained as the second-stage decomposition raw material, and the separation filter cake was not washed (the cyclic decomposition was continued). Then 1000ml of semen was measured, αk was adjusted to 1.75, and the separation filter cake was added to continue the decomposition. After 7 cycles, the slurry was separated and washed to obtain a sample. The first-stage decomposition was completed to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.143 and a particle size d50 of 97.32μm.

[0082] (2) Two-stage decomposition

[0083] Measure 1000ml of the retained mother liquor of the first stage, add homemade Bayer process mother liquor (αk is 3.2) to adjust, αk is adjusted to 2.2, transfer into a 2L beaker and put into a water bath, control the temperature at 68°C, add seeds (particle size d50 is 42.67μm) after reaching temperature, control the solid content at 750g / l, decompose for 50h, and after the decomposition is completed, the slurry is separated, and the separated filter cake is not washed (continue to circulate decomposition), and then measure 1000ml of semen, adjust αk to 2.2, add the second stage filter cake to continue decomposition, and after 7 cycles, the slurry is separated and washed to obtain a sample, and the second stage decomposition is completed to obtain a second low sodium aluminum hydroxide product with a Na2O content of 0.079% and a particle size d50 of 58.46μm.

[0084] Figure 2 This is a SEM image of the first low-sodium aluminum hydroxide product provided in Example 1 of the present application; Figure 3 This is a SEM image of the second low sodium aluminum hydroxide product provided in Example 1 of the present application. Figure 2 and Figure 3 It can be seen that the particle size distribution of the low-sodium aluminum hydroxide product is uniform, and the particle size of the second low-sodium aluminum hydroxide product is significantly smaller than that of the first low-sodium aluminum hydroxide product.

[0085] Comparative Example 1

[0086] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0087] The remaining steps of the first-stage decomposition are exactly the same as those of Example 1, except that αk is not adjusted and the Bayer process stock solution is directly used, i.e., αk is 1.45. After 7 cycles, the material is discharged and washed to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.27% and a particle size of 110.23 μm.

[0088] The remaining steps of the second-stage decomposition are exactly the same as those of Example 1, except that αk is adjusted to 1.6. After 7 cycles of decomposition, filtration and washing are performed, and samples are analyzed to obtain a second low-sodium aluminum hydroxide product with a Na2O content of 0.19% and a particle size of 45.74 μm.

[0089] Comparative Example 2

[0090] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0091] The remaining steps of the first decomposition are exactly the same as those of Example 1, except that the decomposition time is shortened to 3 h, to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.18% and a particle size of 81.44 μm.

[0092] The remaining steps of the second-stage decomposition are exactly the same as those of Example 1, except that the decomposition time is shortened to 20 hours, and a second low-sodium aluminum hydroxide product with a Na2O content of 0.12% and a particle size of 48.55 μm is obtained.

[0093] Comparative Example 3

[0094] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0095] The remaining steps of the first decomposition are exactly the same as those of Example 1, except that the decomposition temperature is adjusted to 65° C., to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.21% and a particle size of 109.34 μm.

[0096] The remaining steps of the second-stage decomposition are exactly the same as those of Example 1, except that the decomposition temperature is adjusted to 50° C. to obtain a second low-sodium aluminum hydroxide product with a Na2O content of 0.23% and a particle size of 49.37 μm.

[0097] Comparative Example 4

[0098] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0099] The remaining steps of the first decomposition are exactly the same as those of Example 1, except that the decomposition solid content is adjusted to 400 g / l to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.141% and a particle size of 82.33 μm.

[0100] The remaining steps of the second stage decomposition are exactly the same as those of Example 1, except that the decomposition solid content is adjusted to 400 g / l to obtain a second low sodium aluminum hydroxide product with a Na2O content of 0.093% and a particle size of 71.27 μm.

[0101] Comparative Example 5

[0102] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0103] The remaining steps of the first decomposition are exactly the same as those of Example 1, except that the αk of the decomposed sodium aluminate solution is adjusted to 2.2 to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.123% and a particle size of 82.45 μm.

[0104] The remaining steps of the second-stage decomposition are exactly the same as those of Example 1, except that the αk of the decomposed sodium aluminate solution is adjusted to 2.8 to obtain a second low-sodium aluminum hydroxide product with a Na2O content of 0.075% and a particle size of 47.88 μm.

[0105] Comparative Example 6

[0106] This comparative example is further modified as follows based on the contents disclosed in Example 1:

[0107] The remaining steps of the first decomposition are exactly the same as those of Example 1, except that the decomposition solid content is adjusted to 80 g / l to obtain a first low-sodium aluminum hydroxide product with a Na2O content of 0.17% and a particle size of 134.22 μm.

[0108] The remaining steps of the second stage decomposition are exactly the same as those of Example 1, except that the αk of the decomposed sodium aluminate solution is adjusted to 2.8 to obtain a second low-sodium aluminum hydroxide product with a Na2O content of 0.079% and a particle size of 58.46 μm.

[0109] The sample indicators of Example 1 and Comparative Examples 1 to 6 are summarized in Table 1.

[0110] Table 1 Sample indicators of Example 1 and Comparative Examples 1 to 6

[0111]

[0112]

[0113] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0114] In the examples of the present application, after long-term research, production and application evaluation practice, the relationship between aluminum hydroxide, sodium oxide and temperature, solid content, causticity ratio, etc. is revealed. Through continuous research, practice and re-research, the technology of simultaneously producing two characteristic low-sodium aluminum hydroxides in the same process is realized. The sodium oxide content of both products is less than 0.15%. One of the products has a particle size D50 of 70μm to 100μm, which can be used as metallurgical grade aluminum hydroxide, and the other product has a particle size of 40μm to 60μm, which meets the requirements of high-temperature alumina raw materials.

[0115] In the embodiments of the present application, two processes are embedded in a set of processes to simultaneously produce aluminum hydroxides with two different characteristics, thereby supporting the quality improvement of high-temperature alumina; at the same time, it is beneficial to start the research and development of high-temperature alumina from special raw materials, and then integrate calcination and grinding technology, which can improve the technical content of high-temperature alumina.

[0116] In the examples of the present application, research experiments found that by preliminarily decomposing the sodium aluminate solution, the sodium aluminate solution was purified, the solution αk was increased, and its saturation was reduced, which made it more suitable for producing aluminum hydroxide with higher purity, and was beneficial for preparing high-quality aluminum hydroxide raw materials to support the quality improvement of fine alumina.

[0117] In the embodiments of the present application, a two-stage decomposition process is configured according to the law of change of solution impurities during the decomposition of the sodium aluminate solution, and two specifications of low-sodium aluminum hydroxide are obtained differently. The sodium aluminate solution is efficiently utilized, making the production of aluminum hydroxide more green and low-carbon. At the same time, the quality of the aluminum hydroxide product is improved. The present invention has a technical guiding role in the high-quality transformation of metallurgical-grade alumina to fine alumina.

[0118] In the embodiment of the present application, decomposition is carried out at a higher temperature in one stage to obtain aluminum hydroxide with a sodium oxide content of 0.15%. The solution is purified by the first decomposition, and the impurity content of the solution is reduced. Continuing the decomposition can produce low-sodium aluminum hydroxide with a lower impurity ion content, and the sodium oxide content of the product is less than 0.1%.

[0119] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing low-sodium aluminum hydroxide by a two-stage process, the method comprising: Adding a first aluminum hydroxide seed to a sodium aluminate solution having a first set αk to perform a one-stage decomposition under a first set condition to obtain a first mixed slurry; Performing solid-liquid separation on the first mixed slurry to obtain a first low-sodium aluminum hydroxide and a separation mother liquor; adjusting the αk of the separated mother liquor to a second setting αk; adding a second aluminum hydroxide seed to the separated mother liquor having a second set αk to perform a two-stage decomposition under a second set condition to obtain a second mixed slurry; as well as The second mixed slurry is subjected to solid-liquid separation to obtain a second low-sodium aluminum hydroxide.

2. The method according to claim 1, characterized in that The first setting αk is 1.5-2.

2.

3. The method according to claim 1, characterized in that The particle size D50 of the first aluminum hydroxide seeds is 50 μm to 100 μm, and the mass concentration of the first aluminum hydroxide seeds is 100 g / L to 300 g / L.

4. The method according to claim 1, characterized in that The first setting condition includes at least one of the following: the seeding temperature is 70° C. to 85° C., and the seeding time is 4 hours to 12 hours.

5. The method according to claim 1, characterized in that The mass concentration of Al2O3 in the sodium aluminate solution is 80g / L to 180g / L.

6. The method according to claim 1, characterized in that The particle size D50 of the first low-sodium aluminum hydroxide is 70 μm to 100 μm, and the mass fraction of sodium oxide in the first low-sodium aluminum hydroxide is less than 0.15%.

7. The method according to claim 1, characterized in that The second setting αk is 1.8-2.

8.

8. The method according to claim 1, characterized in that The particle size D50 of the second aluminum hydroxide seeds is 30 μm to 60 μm, and the mass concentration of the second aluminum hydroxide seeds is 500 g / L to 900 g / L.

9. The method according to claim 1, characterized in that: The second setting condition includes at least one of the following: the seeding temperature is 60° C. to 75° C., and the seeding time is ≥ 40 hours.

10. The method according to claim 1, characterized in that The particle size D50 of the second low-sodium aluminum hydroxide is 40 μm to 60 μm, and the mass fraction of sodium oxide in the second low-sodium aluminum hydroxide is less than 0.10%.

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