Short-process high-decomposition-rate coarse-grained low-alkali aluminum hydroxide and preparation method thereof

Abstract

The invention provides short-process high-decomposition-rate coarse-grained low-alkali aluminum hydroxide and a preparation method thereof, and relates to the technical field of sodium aluminate solution seed precipitation. The method specifically comprises the following steps: taking a small amount of circulating seed crystals and activating through a high-temperature refined sodium aluminate solution to obtain active seed crystals 1; adding an additive into the sodium aluminate solution to prepare an active seed crystal 2; the method comprises the following steps: adding an active seed crystal 1 and an active seed crystal 2 into a refined sodium aluminate solution for seed precipitation, then adding a large amount of circulating seed crystals for seed precipitation, regulating aluminate ions in the solution and selectively nucleating on the gibbsite crystal face through a specific seed precipitation temperature system and a stirring system, and strengthening particle agglomeration and growth, thereby obtaining the gibbsite crystal face nucleation-enhanced aluminum oxide crystal face nucleation-enhanced aluminum oxide crystal face nucleation-enhanced aluminum oxide crystal face nucleation-enhanced aluminum oxide crystal face nucleation-enhanced aluminum oxide crystal face. Gibbsite with large particle size and low alkali content is prepared under high decomposition rate, the decomposition rate is greater than 56%, and the alkali content of the product is (Na2O) lt; 0.16%, d50gt; and 60 [mu] m. The method has the advantages of short flow, high decomposition rate, low alkali content of the product, sand formation, and facilitation of stabilization of aluminum electrolyte components and promotion of the development of the fine alumina industry.

Description

Technical Field

[0001] The invention relates to the technical field of sodium aluminate solution seed separation, and in particular to a short-process high-decomposition rate coarse-grained low-alkali aluminum hydroxide and a preparation method thereof. Background Art

[0002] Sandy alumina is a key raw material for industrial aluminum electrolysis. Alumina comes from aluminum hydroxide (gibbsite). Seed decomposition (seed fractionation) of sodium aluminate solution is the main method for preparing sandy (coarse-grained) aluminum hydroxide. Coarse-grained alumina is conducive to dense phase transport, low alkali is conducive to the stability of aluminum electrolyte components, and is also conducive to the preparation of high-quality fine alumina. Therefore, the economical preparation of high-quality metallurgical grade alumina is imminent.

[0003] The seed separation process has always had disadvantages such as low decomposition rate, high alkali content of the product, and fine particle size. The preparation of coarse-grained low-alkali aluminum hydroxide at a high decomposition rate has always been a hot topic of research. Although many methods have been proposed to improve the decomposition rate, there is no economic solution to the contradiction between the decomposition rate and product refinement; there is no method to coordinate the decomposition rate, particle size and alkali content. This will affect the production cost and competitiveness of my country's alumina industry and aluminum electrolysis.

[0004] At present, the methods for improving the decomposition rate of sodium aluminate solution are as follows: (1) Adding additives for strengthening: ① Adding an inducer (10-800g per liter) and a propellant (10%-100% by volume) during the seeding, with an initial decomposition temperature of 40-80°C, a final temperature of 30-60°C, and a time of 20-30 hours (CN200910066001.5). When the decomposition time is 20 hours, the decomposition rate is 60.8%, but the d50 of aluminum hydroxide is 41.5μm. ② Using a crystallization aid CGM can increase the particle size of the aluminum hydroxide product, and the d50 of the product aluminum hydroxide is 68.74μm, but the decomposition rate is 50.88%, and the cost of the decomposition crystallization aid is high (CN201910086950.3). ③ Adding an aqueous solution containing 0.5%-20% sodium polyacrylate and polyacrylamide (CN00129877.1) can increase the decomposition rate of aluminum hydroxide during the decomposition of sodium aluminate solution, and the decomposition rate can reach about 60%, but the product particle size is fine. ④ Mixing Bayer semen with diethylene glycol (methanol) (CN201010577904.2; CN20218530882.9) changes the properties of the solution, and the decomposition rate can reach 70.7%, but the d50 of the product aluminum hydroxide is only 6.8μm, and the cost of recovering the additive is very high. (2) Adding active seed crystals for strengthening: ① Add active seed crystals (CN202311005503.3; CN201210191280X) in the middle stage of seed decomposition, and control the initial temperature of the seed to 65-80℃, the final temperature to 48-60℃, and the decomposition rate is less than 52% in 35-50h, so that Na 2O<0.15% of low sodium sand-like aluminum hydroxide, the decomposition rate did not increase significantly. ② Continuously grind aluminum hydroxide multiple times to obtain active seed crystals (CN202310551877.9), the decomposition rate can reach more than 52%, but the particle size of the aluminum hydroxide product and the sodium oxide impurity content of the product are not mentioned. (3) Optimize or multi-stage decomposition process: ① Grind aluminum hydroxide into a seed slurry with a particle size d50 of 2-15μm, add it to the decomposition mother liquor and then decompose it in two stages (CN201811465405.7) to strengthen the decomposition, and the product particle size d50 can reach about 50μm. ② Add lime to the mother liquor after seed decomposition to generate hydrated calcium aluminate precipitate, then decompose it with sodium carbonate solution, and finally decompose it with conventional seed crystals (CN200910243381.5), the total decomposition rate can reach 62% to 65%, but the particle size of the aluminum hydroxide product is not mentioned. ③ Song Dawei (Reference: Research on the production of coarse-grained aluminum hydroxide by Bayer process [D]. Northeastern University, 2022.) combined with the production data of Shanxi Alumina Plant, found that improving temperature control can improve agglomeration. When the agglomeration temperature is controlled at 78°C, the agglomeration effect is significantly enhanced. At the same time, it can effectively inhibit the secondary nucleation of fine particles and accelerate the particle size growth. After 24 hours of seeding, the product particle size d50 is 56μm, but the decomposition rate is less than 51%.

[0005] Therefore, although there have been many studies on strengthening and optimizing seeding processes, and complex active seed preparation processes have been proposed, there is no method to coordinate the decomposition rate, particle size and alkali content. How to improve the seeding decomposition rate and ensure that the product is coarse and low in alkali has always been a technical bottleneck that needs to be broken through in the global alumina industry production. Summary of the invention

[0006] The invention provides a short-process high-decomposition rate coarse-grained low-alkali aluminum hydroxide and a preparation method thereof, and aims to solve the outstanding contradiction between product particle size, alkali content and decomposition rate in the existing aluminum oxide industrial production technology.

[0007] In order to achieve the above-mentioned purpose, the embodiment of the present invention provides a short-process high-decomposition rate coarse-grained low-alkali aluminum hydroxide and a preparation method thereof. The method specifically comprises: taking a small amount of circulating seed crystals and activating them at high temperature through a high-temperature sodium aluminate solution (refined sodium aluminate solution) to obtain active seed crystals 1; adding additives to the refined sodium aluminate solution to prepare active seed crystals 2; then adding active seed crystals 1 and active seed crystals 2 in proportion to the refined sodium aluminate solution for seed separation, and then adding a large amount of circulating seed crystals for seed separation, and through a specific seed separation temperature system, regulating the aluminate ions in the solution and selectively nucleating on the gibbsite crystal surface, strengthening particle agglomeration and growth, and preparing gibbsite with coarse particle size and low alkali content at a high decomposition rate, the decomposition rate is greater than 56%, and the alkali content (Na 2O) <0.16%, d50>60μm. The method is simple in process and low in cost, ensures the product is sandy, is beneficial to stabilize the aluminum electrolyte composition and promote the development of fine alumina industry.

[0008] The embodiment of the present invention provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate, comprising the following steps:

[0009] S1, taking a small amount of circulating seed crystals and adding them into a high-temperature refined sodium aluminate solution (sodium aluminate solution, supersaturated sodium aluminate solution) for pretreatment to obtain active seed crystals 1;

[0010] S2, slowly adding the additive to the refined sodium aluminate solution, stirring (strong stirring at the beginning, and then reducing the stirring intensity) for a period of time, and then performing seed separation to obtain active seed crystals 2;

[0011] S3. Add active seed crystal 1 and active seed crystal 2 to the refined sodium aluminate solution, seed for a period of time, then add a large amount of circulating seed crystals for seeding, and follow a stirring system with a gradually decreasing stirring rate to prepare the coarse-grained low-alkali aluminum hydroxide.

[0012] Preferably, the sodium aluminate solution contains sodium oxide (Na 2 O k ) concentration is 140-165 g / L, caustic ratio (molar ratio of sodium oxide to aluminum oxide, α k ) is 1.4~1.55.

[0013] Preferably, in step S1, the high temperature is 85-100°C, and the pretreatment time is 10 min-2 h.

[0014] Preferably, in step S2, the additive includes at least one of sodium bicarbonate, hydrogen peroxide, aluminum sulfate, aluminum chloride, aluminum hydroxide gel, and ultrafine aluminum hydroxide; more preferably, the additive is sodium bicarbonate; the reaction temperature is less than 60°C, the reaction and seeding time is longer than 3h, and the median particle size of the active seed crystal 2 is d50<10μm.

[0015] Preferably, in step S3, the amount of active seed crystal 1 added is 20-100 g / L, the amount of active seed crystal 2 added is 0-5 g / L; and the amount of circulating seed crystal (industrial seed crystal) added is 400 g / L or more.

[0016] Preferably, in step S3, active seed crystals 1 and 2 are added and seeded at an initial seeding temperature of 75-85°C; circulating seed crystals are added and the temperature is lowered to 75°C, and then the temperature is evenly lowered to a final seeding temperature of 50-55°C.

[0017] Preferably, in step S3, active seed crystal 1 and active seed crystal 2 are added for 2 to 5 hours; and circulating seed crystal is added for 35 to 45 hours.

[0018] Preferably, in step S3, the initial seed temperature and the seed rate of the active seed crystal 1 are self-matched; when the amount of the active seed crystal 1 is not less than 40 g / L, the initial seed temperature is higher than 78° C., and the decomposition rate in the initial seeding period (2 to 5 hours of seeding) is less than 20%; or,

[0019] When the dosage of active seed crystal 1 is less than 40 g / L, the initial temperature of the seed is higher than 75° C., and the decomposition rate in the initial stage of the seed (2 to 5 hours of seeding) is less than 15%.

[0020] Preferably, in step S3, the total solid content of the solution at the end of the seeding is 500-800 g / L, and the decomposition rate at the end of the seeding is greater than 56%; the aluminum hydroxide (gibbsite) has a regular morphology, the coarse-grained gibbsite has small (001), (100) and (110) faces, and often has (101) and (112) faces, and Na 2 The O content is 0.10% to 0.16%, which significantly reduces the alkali content compared to industrial seed crystals (circulating seed crystals, sodium oxide content greater than 0.22%).

[0021] Based on a general concept of the invention, an embodiment of the present invention provides coarse-grained low-alkali aluminum hydroxide prepared by the above-mentioned preparation method.

[0022] The present invention is combined with the inventor's research results on the preparation of low-alkali sandy aluminum hydroxide by seed strengthening of sodium aluminate solution, and specifically found that:

[0023] (1) The activity of the seed crystal depends on the seed crystal size; the finer the particle size, the larger the specific surface area and the more active sites; high temperature pretreatment is conducive to significantly improving the activity of the circulating seed crystal.

[0024] (2) The activity of the seed crystal also depends on the surface defects of the seed crystal. The more active sites such as steps, hillocks, dislocations, and distortions there are, the better the activity of the seed crystal.

[0025] (3) The agglomeration rate is linearly related to the supersaturation and solid content of the solution. The temperature regime is coupled with the activity of the seed crystals to enhance the agglomeration of fine particles. To meet the requirements of particle agglomeration, the decomposition rate and the total amount of seed crystals need to be self-matched. To match the agglomeration, the stirring rate also decreases with the total solid content in the solution.

[0026] (4) Inhibiting the excessive growth of gibbsite (001), (100) and other crystal faces is beneficial to reducing the alkali content of sandy aluminum hydroxide (such as Figure 4 );

[0027] (5) By regulating the structure of aluminate ions and matching the crystal surface growth, coarse-grained low-alkali aluminum hydroxide with complete crystal surface growth and sufficient agglomeration can be precipitated (such as Figure 4 ).

[0028] The above solution of the present invention has the following beneficial effects:

[0029] (1) Short process. The present invention uses a high temperature (preferably >90°C) of a refined sodium aluminate solution to activate the seed crystals, and the activated slurry undergoes a seed separation process through heat exchange. This process is the same as the refined sodium aluminate solution cooling down and then entering the seed separation process, and no new process or process needs to be added.

[0030] (2) High decomposition rate. Compared with the traditional seed separation technology (seed separation rate is about 50%), the seed separation technology used in the present invention can increase the seed separation rate to more than 56%.

[0031] (3) The relationship between decomposition rate, product particle size and alkali content is solved in a coordinated manner. Traditional seed strengthening mainly focuses on improving the decomposition rate, does not solve the problem of particle size refinement, and pays little attention to the product alkali content. The present invention solves the problem of product refinement under high decomposition rate and reduces the alkali content of the product.

[0032] (4) High product quality. The aluminum hydroxide product prepared by the seed separation technology adopted by the present invention has a regular morphology and a low sodium oxide impurity content, and can obtain an aluminum oxide product with good physical and chemical properties suitable for modern aluminum electrolysis.

[0033] (5) Easy to industrialize. The active seed preparation method of the present invention is simple and requires little investment. The main equipment involved in the process is the same as that required by the traditional seed separation process, and no high-pressure and high-temperature equipment is required, so it is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 It is a schematic flow chart of a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to the present invention;

[0036] Figure 2 is the decomposition rate of the present invention and Na 2 The variation of O content over time;

[0037] Figure 3 is the particle size of the aluminum hydroxide product of embodiment 2 of the present invention;

[0038] Figure 4 This is a morphology diagram of the aluminum hydroxide product of Example 2 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0040] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0041] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0042] In view of the outstanding contradiction between product particle size, alkali content and decomposition rate in the existing alumina industrial production technology, an embodiment of the present invention provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate, comprising the following steps:

[0043] S1, taking a small amount of circulating seed crystals and adding them into a high-temperature refined sodium aluminate solution (sodium aluminate solution, supersaturated sodium aluminate solution) for pretreatment to obtain active seed crystals 1;

[0044] S2, slowly adding the additive to the refined sodium aluminate solution, stirring (strong stirring at the beginning, and then reducing the stirring intensity) for a period of time, and then performing seed separation to obtain active seed crystals 2;

[0045] S3. Add active seed crystal 1 and active seed crystal 2 to the refined sodium aluminate solution, seed for a period of time, then add a large amount of circulating seed crystals for seeding, and follow a stirring system with a gradually decreasing stirring rate to prepare the coarse-grained low-alkali aluminum hydroxide.

[0046] Preferably, the sodium aluminate solution contains sodium oxide (Na 2 O k ) concentration is 140-165 g / L, caustic ratio (molar ratio of sodium oxide to aluminum oxide, α k ) is 1.4~1.55.

[0047] Preferably, in step S1, the high temperature is 85-100°C, and the pretreatment time is 10 min-2 h.

[0048] Preferably, in step S2, the additive includes at least one of sodium bicarbonate, hydrogen peroxide, aluminum sulfate, aluminum chloride, aluminum hydroxide gel, and ultrafine aluminum hydroxide; more preferably, the additive is sodium bicarbonate; the reaction temperature is less than 60°C, the reaction and seeding time is longer than 3h, and the median particle size of the active seed crystal 2 is d50<10μm.

[0049] Preferably, in step S3, the amount of active seed crystal 1 added is 20-100 g / L, the amount of active seed crystal 2 added is 0-5 g / L; and the amount of circulating seed crystal (industrial seed crystal) added is 400 g / L or more.

[0050] Preferably, in step S3, active seed crystals 1 and 2 are added and seeded at an initial seeding temperature of 75-85°C; circulating seed crystals are added and the temperature is lowered to 75°C, and then the temperature is evenly lowered to a final seeding temperature of 50-55°C.

[0051] Preferably, in step S3, active seed crystal 1 and active seed crystal 2 are added for 2 to 5 hours; and circulating seed crystal is added for 35 to 45 hours.

[0052] Preferably, in step S3, the initial seed temperature and seed rate of the active seed crystal 1 are self-matched. When the amount of active seed crystal 1 is not less than 40 g / L, the initial seed temperature is higher than 78°C, and the decomposition rate in the initial seeding period (2 to 5 hours of seeding) is less than 20%; or,

[0053] When the dosage of active seed crystal 1 is less than 40 g / L, the initial temperature of the seed is higher than 75° C., and the decomposition rate in the initial stage of the seed (2 to 5 hours of seeding) is less than 15%.

[0054] Preferably, in step S3, the total solid content of the solution at the end of the seeding is 500-800 g / L, and the decomposition rate at the end of the seeding is greater than 56%; the aluminum hydroxide (gibbsite) has a regular morphology, the coarse-grained gibbsite has small (001), (100) and (110) faces, and often has (101) and (112) faces, and Na 2 The O content is 0.10% to 0.16%, which significantly reduces the alkali content compared to industrial seed crystals (circulating seed crystals, sodium oxide content greater than 0.22%).

[0055] Based on a general concept of the invention, an embodiment of the present invention provides coarse-grained low-alkali aluminum hydroxide prepared by the above-mentioned preparation method.

[0056] The following will describe the invention through specific embodiments.

[0057] Example 1 (Comparative Example)

[0058] This embodiment provides a method for preparing aluminum hydroxide, which specifically comprises the following steps:

[0059] According to the traditional seed separation process, 300 mL of refined sodium aluminate solution (αk: 1.4; Na2O k :155g / L;Al 2 O 3182.14g / L) is added to a 2000mL stainless steel tank, and the stainless steel tank is heated in a stainless steel water bath; 500g / L seed crystals (d50=55μm) are added, the stirring rate is fixed at 60r / min, the initial seed temperature is 62°C, the final seed temperature is 55°C, the stirring rate is 100r / min, and the seed time is 45h to prepare aluminum hydroxide. Among them, the seed decomposition rate is 50.12%, the total solid content is 640g / L, the sodium oxide content in the aluminum hydroxide is 0.27%, and the particle size D50 of the aluminum hydroxide product is 65μm. Although this embodiment solves the particle size problem, the decomposition rate is low and the product alkali content is high.

[0060] Comparative Example 1, the conventional seeding process, the following examples all adopt the following Figure 1 The process flow is shown.

[0061] Example 2

[0062] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0063] The method of this embodiment specifically includes the following steps:

[0064] Active seed preparation:

[0065] Active seed crystal 1: 20 g of circulating seed crystal was transferred to 200 mL of refined sodium aluminate solution (αk: 1.4; Na2O k :155g / L;Al 2 O 3 182.14 g / L), pretreated at 100 °C for 10 min to obtain active seed crystals 1, whose particle size d50 was 50 μm;

[0066] Active seed crystal 2: 40 g / L sodium bicarbonate was slowly added to 100 mL of refined sodium aluminate solution, and the mixture was reacted at 50° C. for 2 hours at a stirring rate of 500 r / min, and then seeded for 2 hours to obtain an active seed crystal 2 slurry. The particle size d50 of the active seed crystal 2 was 2 μm.

[0067] Synergistic strengthening of species:

[0068] 300 mL of refined sodium aluminate solution (αk: 1.4; Na2O k :155g / L;Al 2 O 3182.14g / L) was placed in a stainless steel tank (2000mL), and 60g / L active seed 1 and 1.5g active seed 2 were first added, the stirring rate was 100r / min, and the seeding was carried out at 80℃ for 4 hours, and the decomposition rate reached 18.2%; then 120g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 50r / min, the temperature was lowered to 75℃, and then the temperature was uniformly lowered to 50℃, and the seeding was carried out for 45h to prepare aluminum hydroxide. Among them, the seeding decomposition rate reached 60%, the total solid content was about 572g / L, and the product Na 2 The O impurity content is 0.16%, and the particle size d50 of the aluminum hydroxide product is 68μm.

[0069] Example 3

[0070] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0071] The method of this embodiment specifically includes the following steps:

[0072] Active seed preparation:

[0073] Active seed crystal 1: 20 g of circulating seed crystal was transferred to 200 mL of refined sodium aluminate solution (αk: 1.4; Na2O k :162g / L;Al 2 O 3 190.37 g / L), pretreated at 95 ° C for 60 min to obtain active seed 1, whose particle size d50 is 33 μm;

[0074] Active seed crystal 2: 15 mL of 10% hydrogen peroxide was slowly added to 100 mL of refined sodium aluminate solution, and the mixture was reacted at 40°C for 2 hours at a stirring rate of 500 r / min, and then seeded for 5 hours to obtain active seed crystal 2 slurry. The particle size d50 of active seed crystal 2 was 1.9 μm.

[0075] Synergistic strengthening of species:

[0076] 300mL refined sodium aluminate solution (αK: 1.4; Na2O k :162g / L;Al 2 O 3190.37g / L) was placed in a stainless steel tank (2000mL), and 60g / L active seed 1 and 1.5g active seed 2 were first added, the stirring rate was 100r / min, and the seeding was carried out at 80℃ for 4 hours, and the decomposition rate reached 15%; then 160g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 60r / min, the temperature was lowered to 75℃, and then the temperature was uniformly lowered to 53℃, and the seeding was carried out for 45h to prepare aluminum hydroxide. Among them, the seeding decomposition rate can reach 57.12%, the total solid content is about 689g / L, and the product Na 2 The O impurity content is 0.18%, and the particle size d50 of the aluminum hydroxide product is 80 μm.

[0077] Example 4

[0078] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0079] The method of this embodiment specifically includes the following steps:

[0080] Preparation of active seed crystals:

[0081] Active seed crystal 1: 10 g of circulating seed crystal was transferred to 200 mL of refined sodium aluminate solution (αk: 1.45; Na2O k :155g / L;Al 2 O 3 175.86 g / L), pretreated at 90 ° C for 60 min to obtain active seed 1, whose particle size d50 is 45 μm;

[0082] Active seed crystal 2: 5 mL of 40 g / L sodium bicarbonate and 10 mL of 20 g / L aluminum sulfate solution were slowly added to 100 mL of refined sodium aluminate solution, and the mixture was reacted at 40°C for 2 hours at a stirring rate of 500 r / min, and then seeded for 2 hours to obtain an active seed crystal 2 slurry. The particle size d50 of the active seed crystal 2 was 2.8 μm.

[0083] Synergistic strengthening of species:

[0084] 300mL refined sodium aluminate solution (αk: 1.45; Na2O k :155g / L;Al 2 O 3175.86g / L) was placed in a stainless steel tank (2000mL), 40g / L active seed 1 and 1.0g active seed 2 were first added, the stirring rate was 70r / min, and the seeding was carried out at 76℃ for 2 hours, and the decomposition rate reached 8%; then 120g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 60r / min, the temperature was lowered to 75℃, and then the temperature was uniformly lowered to 55℃, and the seeding was carried out for 45h to prepare aluminum hydroxide. Among them, the seeding decomposition rate reached 59.2%, the total solid content was about 570g / L, and the product Na 2 The O impurity content is 0.14% and the particle size d50 of the aluminum hydroxide product is 79 μm.

[0085] Example 5

[0086] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0087] The method of this embodiment specifically includes the following steps:

[0088] Active seed preparation:

[0089] Active seed crystal 1: 20 g of circulating seed crystal was transferred to 300 mL of refined sodium aluminate solution (αk: 1.4; Na2O k :155g / L;Al 2 O 3 182.14 g / L), pretreated at 100 °C for 30 min to obtain active seed 1, whose particle size d50 was 55.78 μm;

[0090] Synergistic strengthening of species:

[0091] Add 300 mL of refined sodium aluminate solution (αk: 1.4; Na2Ok: 155 g / L; Al 2 O 3 182.14g / L) was placed in a stainless steel tank (2000mL), 80g / L active seed 1 was added, the stirring rate was 100r / min, the temperature was 78°C, and the seed fraction reached 16.2%; 180g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 60r / min, and then the temperature was uniformly lowered to 55°C, and the seed fraction was 45h to prepare aluminum hydroxide. Among them, the seed fraction decomposition rate reached 56.5%, the total solid content was 760g / L, and the product Na 2 The O impurity content is 0.124%, and the particle size d50 of the aluminum hydroxide product is 87.23 μm.

[0092] Example 6

[0093] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0094] The method of this embodiment specifically includes the following steps:

[0095] Active seed preparation:

[0096] Active seed crystal 1: 20 g of circulating seed crystal was transferred to 200 mL of refined sodium aluminate solution (αk: 1.5; Na2O k :140g / L;Al 2 O 3 153.54 g / L), pretreated at 95 °C for 60 min to obtain active seed crystals 1, whose particle size d50 was 55 μm;

[0097] Active seed crystal 2: 15 mL of 40 g / L sodium bicarbonate and 5 g of ultrafine aluminum hydroxide powder were slowly added to 200 mL of refined sodium aluminate solution, and the mixture was reacted at 40°C for 2 hours at a stirring rate of 500 r / min, and then seeded for 4 hours to obtain an active seed crystal 2 slurry. The particle size d50 of the active seed crystal 2 was 1.5 μm.

[0098] Synergistic strengthening of species:

[0099] 500mL refined sodium aluminate solution (αk: 1.5; Na2O k :140g / L;Al 2 O 3 153.54g / L) was placed in a stainless steel tank (2000mL), and 60g / L active seed 1 and 1.5g active seed 2 were first added, the stirring rate was 100r / min, and the seeding time was 80℃ for 4 hours, and the decomposition rate reached 16.2%; then 300g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 50r / min, the temperature was cooled to 75℃, and then uniformly cooled to 50℃, the seeding time was 40h, and aluminum hydroxide was prepared. Among them, the seeding decomposition rate can reach 59.9%, the total solid content is about 740g / L, and the product Na 2 The O impurity content is 0.152%, and the particle size d50 of the aluminum hydroxide product is 79.3 μm.

[0100] Example 7

[0101] This embodiment provides a method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and a high decomposition rate.

[0102] The method of this embodiment specifically includes the following steps:

[0103] Preparation of active seed crystals:

[0104] Active seed crystal 1: 20 g of circulating seed crystal was transferred to 200 mL of refined sodium aluminate solution (αk: 1.4; Na2O k:155g / L;Al 2 O 3 182.14 g / L), pretreated at 100°C for 30 min to obtain active seed crystals 1, whose particle size d50 was 60 μm.

[0105] Active seed crystal 2: 60 g / L sodium bicarbonate was slowly added to 100 mL of refined sodium aluminate solution, and the mixture was reacted at 55°C for 1 hour at a stirring rate of 500 r / min, and then seeded for 4 hours to obtain active seed crystal 2 slurry. The particle size d50 of active seed crystal 2 was 3.5 μm.

[0106] Synergistic strengthening of species:

[0107] 500mL refined sodium aluminate solution (αK: 1.4; Na2Ok: 155g / L; Al 2 O 3 182.14g / L) was placed in a stainless steel tank, and 30g / L active seed 1 and 1.0g active seed 2 were first added, the stirring rate was 70r / min, and the seeding time was 4 hours at 76℃, and the decomposition rate reached 12.5%; then 250g of circulating seed (d50=85μm, sodium oxide content 0.22%) was added to the stainless steel tank, the stirring rate was 60r / min, the temperature was lowered to 75℃, and then the temperature was uniformly lowered to 50℃, and the seeding time was 40h to prepare aluminum hydroxide. Among them, the seeding decomposition rate reached 56.2%, the total solid content was about 660g / L, and the product Na 2 The O impurity content is 0.14%, and the particle size d50 of the aluminum hydroxide product is 82.3μm.

[0108] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate, characterized in that: The steps include: S1, taking a small amount of circulating seed crystals and adding them into a high temperature refined sodium aluminate solution for pretreatment to obtain active seed crystals 1; S2, slowly adding the additive to the refined sodium aluminate solution, stirring and reacting for a period of time, and then performing seed separation to obtain active seed crystals 2; S3. Add active seed crystal 1 and active seed crystal 2 to the refined sodium aluminate solution, seed for a period of time, then add a large amount of circulating seed crystals for seeding, and follow a stirring system with a gradually decreasing stirring rate to prepare the coarse-grained low-alkali aluminum hydroxide.

2. The method for preparing a short-process high-decomposition rate coarse-grained low-alkali aluminum hydroxide according to claim 1, characterized in that: The sodium aluminate solution has a sodium oxide concentration of 140 to 165 g / L and a caustic ratio of 1.4 to 1.

55.

3. The method for preparing a coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S1, the high temperature is 85-100°C, and the pretreatment time is 10 minutes to 2 hours.

4. The method for preparing a coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S2, the additive includes at least one of sodium bicarbonate, hydrogen peroxide, aluminum sulfate, aluminum chloride, aluminum hydroxide gel, and ultrafine aluminum hydroxide; the reaction temperature is less than 60°C, the reaction and seeding time is longer than 3 hours, and the particle size d50 of the active seed 2 is less than 10 μm.

5. The method for preparing a coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S3, the amount of active seed crystal 1 added is 20-100 g / L, the amount of active seed crystal 2 added is 0-5 g / L; the amount of circulating seed crystal added is 400 g / L or more.

6. The method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S3, active seed crystals 1 and 2 are added and seeded at an initial seeding temperature of 75-85°C; circulating seed crystals are added to cool the temperature to 75°C, and then uniformly cooled to a final seeding temperature of 50-55°C.

7. The method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S3, active seed crystal 1 and active seed crystal 2 are added for 2 to 5 hours; and circulating seed crystal is added for 35 to 45 hours.

8. The method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S3, when the amount of active seed crystal 1 is not less than 40 g / L, the initial temperature of the seed is higher than 78° C., and the initial decomposition rate of the seed is less than 20%; or When the dosage of active seed crystal 1 is less than 40 g / L, the initial temperature of the seed is higher than 75° C., and the initial decomposition rate of the seed is less than 15%.

9. The method for preparing coarse-grained low-alkali aluminum hydroxide with a short process and high decomposition rate according to claim 1, characterized in that: In step S3, the aluminum hydroxide has a regular morphology and a Na2O content of 0.10% to 0.16%; the total solid content of the solution at the end of the seeding is 500 to 800 g / L, and the decomposition rate at the end of the seeding is greater than 56%.

10. Coarse-grained low-alkali aluminum hydroxide prepared by the preparation method according to any one of claims 1 to 9.

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