Preparation method of low-sodium aluminum hydroxide

Abstract

This application relates to a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps: adding a refined sodium aluminate solution to a first decomposition tank; adding aluminum hydroxide seed crystals to the first decomposition tank for further decomposition, such that the solid content of the solid-liquid mixture in the first decomposition tank is 700-750 g / L; sequentially subjecting the solid-liquid mixture in the first decomposition tank to a second to an (N-1)th decomposition tank for further decomposition; treating the solid-liquid mixture in the (N-1)th decomposition tank with a hydrocyclone, and discharging the underflow from the hydrocyclone, controlling the solid content of the underflow to be 750-800 g / L; obtaining aluminum hydroxide product from the underflow; and guiding the overflow from the hydrocyclone into an Nth decomposition tank, returning the solid-liquid mixture in the Nth decomposition tank to the first decomposition tank, wherein N is an integer not less than 3. This application achieves a low sodium oxide content in the aluminum hydroxide product while maintaining high production efficiency.

Description

Technical Field

[0001] This application relates to the aluminum industry, and in particular to the preparation of aluminum hydroxide. Background Technology

[0002] Calcined alpha-alumina products, as raw materials for industrial ceramics, are widely used in wear-resistant ceramics, ceramic glazes, refractory materials, polishing, electronic ceramics, glass substrates, and other industries. Especially with the increasing variety of industrial ceramics, the requirements for calcined alpha-alumina are gradually increasing, and the market is placing higher demands on its quality. 5G ceramics have strict requirements on the Na content of alpha-alumina raw materials. Since Na is not lost during the calcination of aluminum hydroxide to alumina, reducing the Na content in alpha-alumina requires reducing the Na content in aluminum hydroxide.

[0003] Currently, aluminum hydroxide production processes mostly employ a decomposition process involving seed washing, seed agglomeration, and crystal growth, and control at relatively high decomposition temperatures. This makes it difficult to maintain ideal production efficiency while ensuring low Na content. Even with acceptable production efficiency, aluminum hydroxide achieves a Na content of only 0.35%, which is unacceptable for α-alumina raw materials specifically used in 5G ceramics. Summary of the Invention

[0004] This application provides a method for preparing low-sodium aluminum hydroxide to solve the technical problem that existing aluminum hydroxide preparation processes are unable to maintain ideal production efficiency while ensuring low Na content.

[0005] This application provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0006] Add the refined sodium aluminate solution to the first decomposition tank;

[0007] Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 700-750 g / L.

[0008] The solid-liquid mixture in the first decomposition tank is sequentially decomposed into semen in the second to the (N-1)th decomposition tanks.

[0009] The solid-liquid mixture in the N-1th decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged, with the solid content of the underflow controlled to be 750-800 g / L;

[0010] Aluminum hydroxide product is obtained from the underflow;

[0011] The overflow from the hydrocyclone is directed into the Nth decomposition tank, and the solid-liquid mixture in the Nth decomposition tank is returned to the first decomposition tank.

[0012] Wherein, N is an integer not less than 3.

[0013] In some embodiments of this application, the caustic alkali concentration of the refined sodium aluminate solution is 145-150 g / L.

[0014] In some embodiments of this application, a refined sodium aluminate solution is added to a first decomposition tank, wherein the flow rate of the refined sodium aluminate solution is 370–400 m³ / h. 3 / h.

[0015] In some embodiments of this application, the time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 40-50 hours.

[0016] In some embodiments of this application, the temperature of the first decomposition tank is controlled at 71-72°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0017] In some embodiments of this application, the temperature of the Nth decomposition tank is 56–57°C.

[0018] In some embodiments of this application, the seed crystals are added once every half hour, with 2 tons added each time.

[0019] In some embodiments of this application, the particle size of the aluminum hydroxide crystals in the underflow is D50 = 75-85 μm.

[0020] In some embodiments of this application, the crystalline alkali content of aluminum hydroxide in the underflow is not higher than 0.16%.

[0021] In some embodiments of this application, the sodium oxide content of aluminum hydroxide in the underflow is not higher than 0.2%.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] The method for preparing low-sodium aluminum hydroxide provided in this application embodiment controls the solid content of the solid-liquid mixture in the first decomposition tank to be 700-750 g / L, resulting in a very low sodium oxide content in the aluminum hydroxide product; by controlling the solid content of the underflow to be 750-800 g / L, aluminum hydroxide products with suitable particle size are selected. By selecting the above parameters, it is possible to achieve a low sodium oxide content in the aluminum hydroxide product while also taking into account production efficiency. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart illustrating a method for preparing low-sodium aluminum hydroxide, as provided in an embodiment of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Unless otherwise specified, the terminology used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, 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 application pertains. In case of any conflict, this specification shall prevail.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0030] Existing aluminum hydroxide preparation processes face the technical challenge of maintaining ideal production efficiency while ensuring low Na content.

[0031] The technical solution provided in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0032] This application provides a method for preparing low-sodium aluminum hydroxide. Please refer to the following embodiments. Figure 1 The method includes the following steps:

[0033] S1: Add the refined sodium aluminate solution to the first decomposition tank;

[0034] S2: Add aluminum hydroxide seed crystals to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 700-750 g / L.

[0035] S3: The solid-liquid mixture in the first decomposition tank is sequentially decomposed into semen in the second to N-1 decomposition tanks;

[0036] S4: Treat the solid-liquid mixture in the N-1th decomposition tank with a hydrocyclone, and discharge the underflow from the hydrocyclone, controlling the solid content of the underflow to be 750-800 g / L;

[0037] S5: Obtain aluminum hydroxide product from the underflow;

[0038] S6: The overflow from the hydrocyclone is directed into the Nth decomposition tank, and the solid-liquid mixture in the Nth decomposition tank is returned to the first decomposition tank.

[0039] Wherein, N is an integer not less than 3.

[0040] Semen decomposition specifically refers to the process by which refined sodium aluminate solution precipitates aluminum hydroxide under the action of acid.

[0041] The solid content of the solid-liquid mixture affects the sodium oxide content of the aluminum hydroxide product. Specifically, a higher solid content results in smaller gaps between the seed crystals, making it less likely for sodium to be incorporated during crystallization. However, the solid content should not be too high, as this can lead to excessively large aluminum hydroxide particle sizes.

[0042] The sodium oxide content in aluminum hydroxide described in this application refers to the mass content of sodium in aluminum hydroxide after the sodium element is converted into sodium oxide.

[0043] Currently, most aluminum hydroxide production processes use a decomposition process involving seed washing, seed agglomeration, and crystal growth. This application adopts a process scheme that directly adds seed crystals for liquid decomposition. Combined with the relatively high solid content in the first decomposition tank, this reduces the sodium oxide content in aluminum hydroxide while maintaining production efficiency.

[0044] Setting up multiple decomposition tanks is a common technique in this field. The first to Nth decomposition tanks all contain high concentrations of sodium aluminate; therefore, the material in the Nth decomposition tank is generally returned to the first decomposition tank for continued production.

[0045] A hydrocyclone is used to separate aluminum hydroxide particles with a specific particle size. The hydrocyclone is typically located in the final tank, i.e., the tank preceding the Nth decomposition tank described in this application.

[0046] Those skilled in the art can implement step S5 in a conventional manner, such as by filtering.

[0047] This application achieves a very low sodium oxide content in the aluminum hydroxide product by controlling the solid content of the solid-liquid mixture in the first decomposition tank to 700-750 g / L; and selects aluminum hydroxide products with suitable particle size by controlling the solid content of the underflow to 750-800 g / L. By selecting the above parameters, it is possible to achieve a low sodium oxide content in the aluminum hydroxide product while also taking into account production efficiency.

[0048] In some embodiments of this application, the caustic alkali concentration of the refined sodium aluminate solution is 145-150 g / L.

[0049] The beneficial effect of controlling the caustic alkali concentration to 145-150 g / L is to increase the decomposition kinetics and the decomposition rate.

[0050] In some embodiments of this application, a refined sodium aluminate solution is added to a first decomposition tank, wherein the flow rate of the refined sodium aluminate solution is 370–400 m³ / h. 3 / h.

[0051] The flow rate of the refined sodium aluminate solution added is controlled at 370–400 m³. 3 The beneficial effect of / h is to extend the decomposition time and increase the decomposition rate.

[0052] In some embodiments of this application, the time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 40-50 hours.

[0053] The purpose of controlling the semen decomposition time to 40-50 hours is to maximize the yield of aluminum hydroxide with the target particle size.

[0054] In some embodiments of this application, the temperature of the first decomposition tank is controlled at 71-72°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0055] The beneficial effect of controlling the temperature of the first decomposition tank to 71-72°C is that it helps the crystals to grow slowly and nucleate, and introduces fewer impurities from the mother liquor.

[0056] In some embodiments of this application, the temperature of the Nth decomposition tank is 56–57°C.

[0057] The beneficial effect of setting the temperature of the Nth decomposition tank to 56-57°C is that the intermediate cooling gradient is small, the crystals grow slowly, and fewer impurities are introduced into the mother liquor.

[0058] In some embodiments of this application, the seed crystals are added once every half hour, with 2 tons added each time.

[0059] In some embodiments of this application, the particle size of the aluminum hydroxide crystals in the underflow is D50 = 75-85 μm.

[0060] The beneficial effect of controlling the particle size of aluminum hydroxide crystals in the underflow to D50 = 75-85 μm is that the seed crystals have high activity and suitable surface area, which is helpful for the modification research of downstream processes.

[0061] In some embodiments of this application, the crystalline alkali content of aluminum hydroxide in the underflow is not higher than 0.16%.

[0062] In some embodiments of this application, the sodium oxide content of aluminum hydroxide in the underflow is not higher than 0.2%.

[0063] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0064] Example 1

[0065] This embodiment provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0066] Add the refined sodium aluminate solution to the first decomposition tank;

[0067] Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 700g / L.

[0068] The solid-liquid mixture in the first decomposition tank is pumped into the second decomposition tank for semen decomposition.

[0069] The solid-liquid mixture in the second decomposition tank is pumped into the third decomposition tank for semen decomposition.

[0070] The solid-liquid mixture in the third decomposition tank is pumped into the fourth decomposition tank for semen decomposition. The solid-liquid mixture in the fourth decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged. The solid content of the underflow is controlled to be 750 g / L.

[0071] Aluminum hydroxide product is obtained from the underflow;

[0072] The overflow from the hydrocyclone is pumped into the fifth decomposition tank, and the solid-liquid mixture in the fifth decomposition tank is returned to the first decomposition tank.

[0073] The caustic alkali concentration of the refined sodium aluminate solution is 150 g / L.

[0074] A refined sodium aluminate solution is added to the first decomposition tank at a flow rate of 370 m³ / h. 3 / h.

[0075] The time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 50 hours.

[0076] The temperature of the first decomposition tank is controlled at 72°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0077] The temperature of the Nth decomposition tank is 56°C.

[0078] The seed crystals are added every half hour, with 2 tons added each time.

[0079] The particle size of the aluminum hydroxide crystals in the underflow is D50 = 75 μm.

[0080] The crystalline alkali content of aluminum hydroxide in the underflow is 0.16%.

[0081] The sodium oxide content of aluminum hydroxide in the underflow is 0.17%.

[0082] Example 2

[0083] This embodiment provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0084] Add the refined sodium aluminate solution to the first decomposition tank;

[0085] Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 750 g / L.

[0086] The solid-liquid mixture in the first decomposition tank is pumped into the second decomposition tank for semen decomposition.

[0087] The solid-liquid mixture in the second decomposition tank is pumped into the third decomposition tank for semen decomposition.

[0088] The solid-liquid mixture in the third decomposition tank is pumped into the fourth decomposition tank for semen decomposition. The solid-liquid mixture in the fourth decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged. The solid content of the underflow is controlled to be 800 g / L.

[0089] Aluminum hydroxide product is obtained from the underflow;

[0090] The overflow from the hydrocyclone is pumped into the fifth decomposition tank, and the solid-liquid mixture in the fifth decomposition tank is returned to the first decomposition tank.

[0091] The caustic alkali concentration of the refined sodium aluminate solution is 145 g / L.

[0092] A refined sodium aluminate solution is added to the first decomposition tank at a flow rate of 400 m³ / h. 3 / h.

[0093] The time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 40 hours.

[0094] The temperature of the first decomposition tank is controlled at 71°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0095] The temperature of the Nth decomposition tank is 57°C.

[0096] The seed crystals are added every half hour, with 2 tons added each time.

[0097] The particle size of the aluminum hydroxide crystals in the underflow is D50 = 85 μm.

[0098] The alkali content of aluminum hydroxide crystals in the underflow is 0.15%.

[0099] The sodium oxide content of aluminum hydroxide in the underflow is 0.2%.

[0100] Example 3

[0101] This embodiment provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0102] Add the refined sodium aluminate solution to the first decomposition tank;

[0103] Aluminum hydroxide seed crystals were added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank was 730 g / L.

[0104] The solid-liquid mixture in the first decomposition tank is pumped into the second decomposition tank for semen decomposition.

[0105] The solid-liquid mixture in the second decomposition tank is pumped into the third decomposition tank for semen decomposition.

[0106] The solid-liquid mixture in the third decomposition tank is pumped into the fourth decomposition tank for liquid decomposition. The solid-liquid mixture in the fourth decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged. The solid content of the underflow is controlled to be 790 g / L.

[0107] Aluminum hydroxide product is obtained from the underflow;

[0108] The overflow from the hydrocyclone is pumped into the fifth decomposition tank, and the solid-liquid mixture in the fifth decomposition tank is returned to the first decomposition tank.

[0109] The caustic alkali concentration of the refined sodium aluminate solution is 147 g / L.

[0110] A refined sodium aluminate solution is added to the first decomposition tank at a flow rate of 38 m³ / s. 3 / h.

[0111] The time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 45 hours.

[0112] The temperature of the first decomposition tank is controlled at 71°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0113] The temperature of the Nth decomposition tank is 57°C.

[0114] The seed crystals are added every half hour, with 2 tons added each time.

[0115] The particle size of the aluminum hydroxide crystals in the underflow is D50 = 77 μm.

[0116] The crystalline alkali content of aluminum hydroxide in the underflow is 0.16%.

[0117] The sodium oxide content of aluminum hydroxide in the underflow is 0.18%.

[0118] Example 4

[0119] This embodiment provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0120] Add the refined sodium aluminate solution to the first decomposition tank;

[0121] Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 700g / L.

[0122] The solid-liquid mixture in the first decomposition tank is pumped into the second decomposition tank for semen decomposition.

[0123] The solid-liquid mixture in the second decomposition tank is pumped into the third decomposition tank for semen decomposition.

[0124] The solid-liquid mixture in the third decomposition tank is pumped into the fourth decomposition tank for semen decomposition. The solid-liquid mixture in the fourth decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged. The solid content of the underflow is controlled to be 750 g / L.

[0125] Aluminum hydroxide product is obtained from the underflow;

[0126] The overflow from the hydrocyclone is pumped into the fifth decomposition tank, and the solid-liquid mixture in the fifth decomposition tank is returned to the first decomposition tank.

[0127] The caustic alkali concentration of the refined sodium aluminate solution is 145 g / L.

[0128] A refined sodium aluminate solution is added to the first decomposition tank at a flow rate of 370 m³ / h. 3 / h.

[0129] The time for the refined sodium aluminate solution to decompose semen in the first decomposition tank to the Nth decomposition tank is 47 hours.

[0130] The temperature of the first decomposition tank is controlled at 72°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0131] The temperature of the Nth decomposition tank is 57°C.

[0132] The seed crystals are added every half hour, with 2 tons added each time.

[0133] The particle size of the aluminum hydroxide crystals in the underflow is D50 = 85 μm.

[0134] The alkali content of aluminum hydroxide crystals in the underflow is 0.14%.

[0135] The sodium oxide content of aluminum hydroxide in the underflow is 0.17%.

[0136] Example 5

[0137] This embodiment provides a method for preparing low-sodium aluminum hydroxide, the method comprising the following steps:

[0138] Add the refined sodium aluminate solution to the first decomposition tank;

[0139] Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 750 g / L.

[0140] The solid-liquid mixture in the first decomposition tank is pumped into the second decomposition tank for semen decomposition.

[0141] The solid-liquid mixture in the second decomposition tank is pumped into the third decomposition tank for semen decomposition.

[0142] The solid-liquid mixture in the third decomposition tank is pumped into the fourth decomposition tank for semen decomposition. The solid-liquid mixture in the fourth decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged. The solid content of the underflow is controlled to be 750 g / L.

[0143] Aluminum hydroxide product is obtained from the underflow;

[0144] The overflow from the hydrocyclone is pumped into the fifth decomposition tank, and the solid-liquid mixture in the fifth decomposition tank is returned to the first decomposition tank.

[0145] The caustic alkali concentration of the refined sodium aluminate solution is 149 g / L.

[0146] A refined sodium aluminate solution is added to the first decomposition tank at a flow rate of 390 m³ / h. 3 / h.

[0147] The time for the refined sodium aluminate solution to flow from the first decomposition tank to the Nth decomposition tank for semen decomposition is 44 hours.

[0148] The temperature of the first decomposition tank is controlled at 72°C, and the temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

[0149] The temperature of the Nth decomposition tank is 57°C.

[0150] The seed crystals are added every half hour, with 2 tons added each time.

[0151] The particle size of the aluminum hydroxide crystals in the underflow is D50 = 75 μm.

[0152] The crystalline alkali content of aluminum hydroxide in the underflow is no higher than 0.16%.

[0153] The sodium oxide content of aluminum hydroxide in the underflow is no higher than 0.2%.

[0154] The sodium oxide content in Examples 1 to 5 is no higher than 0.2%, and it can be produced at 370m within 40 to 50 hours. 3 / h~400m 3 A production cycle can be completed with a flow rate of / h, which is highly efficient.

[0155] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0156] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, relational terms such as "first" and "second" are used merely 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 document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. For associations involving three or more related objects described using "and / or", it indicates that any one of the three related objects can exist alone, or at least two of them can exist simultaneously. For example, for A, and / or B, and / or C, it can mean that any one of A, B, and C exists alone, or any two of them exist simultaneously, or all three of them exist simultaneously. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0157] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing low-sodium aluminum hydroxide, characterized in that, The method includes the following steps: A refined sodium aluminate solution is added to the first decomposition tank. The caustic alkali concentration of the refined sodium aluminate solution is 145-150 g / L, and the addition flow rate of the refined sodium aluminate solution is 370-400 m³ / L. 3 / h; Aluminum hydroxide seed crystals are added to the first decomposition tank to decompose the liquid, so that the solid content of the solid-liquid mixture in the first decomposition tank is 700~750g / L; The solid-liquid mixture in the first decomposition tank is sequentially decomposed into semen in the second to the (N-1)th decomposition tanks. The solid-liquid mixture in the N-1th decomposition tank is treated with a hydrocyclone, and the underflow of the hydrocyclone is discharged, with the solid content of the underflow controlled to be 750~800g / L; Aluminum hydroxide product is obtained from the underflow; The overflow from the hydrocyclone is directed into the Nth decomposition tank, and the solid-liquid mixture in the Nth decomposition tank is returned to the first decomposition tank. Wherein, N is an integer not less than 3, the decomposition time of the refined sodium aluminate solution flowing from the first decomposition tank to the Nth decomposition tank is 40-50h, the temperature of the first decomposition tank is controlled at 71~72℃, and the temperature of the Nth decomposition tank is 56~57℃. The particle size of the aluminum hydroxide crystals in the underflow is D50 = 75~85μm, and the sodium oxide content of the aluminum hydroxide in the underflow is not higher than 0.2%.

2. The method for preparing low-sodium aluminum hydroxide according to claim 1, characterized in that, The temperatures of the first decomposition tank to the Nth decomposition tank decrease sequentially.

3. The method for preparing low-sodium aluminum hydroxide according to claim 1, characterized in that, The seed crystals are added every half hour, with 2 tons added each time.

4. The method for preparing low-sodium aluminum hydroxide according to claim 1, characterized in that, The crystalline alkali content of aluminum hydroxide in the underflow is no higher than 0.16%.

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