Ultrafine aluminum hydroxide and its preparation method and application

Abstract

The present invention discloses an ultrafine aluminum hydroxide and a preparation method and application thereof. The preparation method of the ultrafine aluminum hydroxide of the present invention is mainly designed to use the ultrafine aluminum hydroxide produced in the original process as the raw material of the seed slurry, and by controlling the caustic ratio of the seed semen, the dissolution temperature and the seed temperature in the preparation process, and selecting a mechanical vapor recompression evaporator for concentration evaporation and a double cone vacuum dryer for vacuum drying, so that the method not only has the technical effects of high raw material utilization, energy saving, high production efficiency, etc., but also can obtain ultrafine aluminum hydroxide that meets the production standards, and thus the method is suitable for actual large-scale industrial production, transportation and application.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic materials, and in particular to ultrafine aluminum hydroxide and a preparation method and application thereof. Background Art

[0002] With the increasing degree of industrialization, the requirements for ultrafine aluminum hydroxide products are becoming more and more stringent. Ultrafine aluminum hydroxide products generally refer to aluminum hydroxide materials with a particle size of 0.5 to 2.0 μm, which are often used as adsorbents and fillers.

[0003] At present, among the numerous methods for preparing ultrafine aluminum hydroxide, they can be mainly divided into physical methods and chemical methods. The physical method refers to the deformation and rupture of solid blocks or particles under the action of external forces to produce finer particles. The chemical method includes microemulsion method, metal alkoxide method, supergravity method, solid phase method, sodium aluminate solution carbon fractionation method, seed decomposition method, etc. The seed decomposition method, that is, the sodium aluminate solution seed decomposition method, has the advantages of a wide source of raw materials, low production cost, and good product quality. It is one of the mainstream processes for producing ultrafine aluminum hydroxide. However, with the improvement of economic level and people's environmental awareness, the requirements for industrial production have also been further improved. It is not only required to produce ultrafine aluminum hydroxide products with good comprehensive performance and meet the standards, but also required that the production process meet the requirements of low cost, green environmental protection, and high comprehensive utilization rate of raw materials.

[0004] Therefore, it is urgent to research and develop a method for preparing an ultrafine aluminum hydroxide product that is economical, environmentally friendly, has a high degree of resource utilization, and has low storage and transportation costs. Summary of the invention

[0005] In order to overcome the problems existing in the prior art of ultrafine aluminum hydroxide preparation, such as high production cost, low raw material utilization rate, use of many types of raw materials, easy environmental pollution, and difficulty in dispersing solid particles during large-scale preparation, one of the purposes of the present invention is to provide a method for preparing ultrafine aluminum hydroxide by a physical-chemical combined seed separation method, which uses its own product as a seed after grinding with a nano sand mill.

[0006] A second object of the present invention is to provide an ultrafine aluminum hydroxide product obtained by the above preparation method.

[0007] A third object of the present invention is to provide an application of the above-mentioned ultrafine aluminum hydroxide product.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] In a first aspect, the present invention provides a method for preparing ultrafine aluminum hydroxide comprising the following steps:

[0010] 1) mixing industrial grade aluminum hydroxide and sodium hydroxide solution, and dissolving by heating to obtain original seed fraction semen;

[0011] Adding the first aluminum hydroxide seed slurry to the original seed separation semen to perform seed separation to obtain an original mother liquor and ultrafine aluminum hydroxide;

[0012] 2) The original mother liquid in step 1) is concentrated and evaporated to obtain a product having a specific gravity of 1.3 g / cm 3 ~1.5g / cm 3 Circulating mother liquor;

[0013] The ultrafine aluminum hydroxide described in step 1) is slurried with water, and then ground and refined to obtain a circulating aluminum hydroxide seed slurry;

[0014] 3) mixing the circulating mother liquor described in step 2) with industrial-grade aluminum hydroxide and heating and dissolving again to obtain a circulating seed fraction semen having a caustic ratio of 1.40 to 1.60;

[0015] Adding the circulating aluminum hydroxide seed slurry to the circulating seed separation semen for seed separation to obtain mother liquor and ultrafine aluminum hydroxide;

[0016] The aluminum hydroxide in the circulating aluminum hydroxide seed slurry in step 2) and step 3) is in granular form, and the particle size D 50 It is 300~500nm.

[0017] Preferably, the method for preparing the ultrafine aluminum hydroxide comprises the following steps:

[0018] 1) industrial grade aluminum hydroxide and sodium hydroxide aqueous solution are mixed, heated for dissolution, diluted, cooled to 50° C. to 65° C., and plate and frame filter pressed to obtain original seed semen;

[0019] Adding the first aluminum hydroxide seed crystal slurry to the original seed separation semen to perform seed separation and diaphragm filter pressing to obtain the original mother liquor and ultrafine aluminum hydroxide;

[0020] 2) The mother liquor is treated by compression evaporation system and salt removal to obtain a specific gravity of 1.3g / cm 3 ~1.5g / cm 3 Circulating mother liquor;

[0021] The ultrafine aluminum hydroxide and water are mixed by slurrying, and processed by a nano sand mill for 90 minutes to 160 minutes to obtain a circulating aluminum hydroxide seed slurry;

[0022] 3) mixing the circulating mother liquor described in step 2) with industrial-grade aluminum hydroxide, dissolving by heating, diluting, cooling to 50° C. to 65° C., and filtering by plate and frame pressure to obtain a circulating seed fraction semen having a caustic ratio of 1.40 to 1.60;

[0023] Adding the circulating aluminum hydroxide seed slurry to the circulating seed separation semen to perform seed separation and diaphragm filter pressing to obtain a mother liquor and a filter cake;

[0024] The filter cake is treated in a double cone vacuum dryer and broken up to obtain ultrafine aluminum hydroxide;

[0025] The aluminum hydroxide in the circulating aluminum hydroxide seed slurry in step 2) and step 3) is in granular form, and the particle size D 50 300~500nm;

[0026] Step 2) and step 3) can be run multiple times, and the number of runs n of the process of step 2) and step 3) is 1 to 500 times, and n is a positive integer;

[0027] When the number of operations n=1, the mother liquor in step 2) is the original seed fractionated semen in step 1), and the ultrafine aluminum hydroxide in step 2) is the ultrafine aluminum hydroxide in step 1);

[0028] When the number of runs n≥2, in the nth run, the mother liquor in step 2) uses the recycled seed semen prepared in step 3) in the n-1th run, and the ultrafine aluminum hydroxide in step 2) uses the ultrafine aluminum hydroxide prepared in step 3) in the n-1th run.

[0029] Preferably, the sodium hydroxide solution in step 1) is industrial liquid alkali, which is a mixture of sodium hydroxide and water, and the content of sodium hydroxide solute in the industrial liquid alkali is 28wt.% to 32wt.%.

[0030] Preferably, the industrial-grade aluminum hydroxide in step 1) is a light yellow fine sand-like powder; the aluminum hydroxide content in the industrial-grade aluminum hydroxide is ≥98%, and the silicon dioxide content is ≤0.04%; the particle size D of the industrial-grade aluminum hydroxide is 50 It is 200μm~400μm.

[0031] Preferably, the heating dissolution in step 1) and step 3) is carried out by heating by introducing steam, and the temperature of the heating dissolution is 95°C to 115°C.

[0032] Preferably, the causticity ratio of the original semen in step 1) is 1.45-1.60.

[0033] Preferably, the Al2O3 content of the original semen in step 1) is 134 g / L to 138 g / L.

[0034] Preferably, the caustic soda content of the original semen in step 1) is 120 g / L to 135 g / L.

[0035] Preferably, the plate and frame filter press in step 1) and step 3) is an automatic hydraulic plate and frame filter press.

[0036] Preferably, the membrane filter press in step 1) and step 3) uses a high-pressure membrane filter press.

[0037] Specifically, the manufacturer of the high-pressure diaphragm filter press is Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd.

[0038] Preferably, the model of the high-pressure diaphragm filter press is XAMYG30 / 800-GB.

[0039] Preferably, after the membrane filtration in step 1) and step 3), the method further comprises the steps of multi-stage countercurrent washing with water until the pH value of the effluent is ≤8, and pressing.

[0040] Preferably, the preparation method of the first aluminum hydroxide seed slurry in step 1) comprises: mixing the aluminum hydroxide product and water in a mass ratio of 1:2.5 to 1:3.5, and then cyclically grinding with a nano sand mill for 90 minutes to 120 minutes to obtain the first aluminum hydroxide seed slurry,

[0041] Wherein, the particle size D of the aluminum hydroxide product is 50 The aluminum hydroxide of the first aluminum hydroxide seed slurry has a particle size of D 50 Aluminum hydroxide particles with a size of 300 to 500 nm.

[0042] Preferably, the model of the aluminum hydroxide product is MARTINAL OL-104LEO.

[0043] Preferably, the particle size D of the ultrafine aluminum hydroxide in step 1) is 50 1.5~2.5μm.

[0044] Preferably, the process parameters of the compression evaporation system in step 2) are as follows: gauge pressure of 0.1 MPa to 0.4 MPa, and temperature of 90° C. to 108° C.

[0045] Preferably, the equipment selected for the compression evaporation system treatment in step 2) is a mechanical vapor recompression evaporator.

[0046] Preferably, when the number of repeated cycles n≥2, the amount of the ultrafine aluminum hydroxide used in step 2) is 0.2wt% to 0.5wt% of the ultrafine aluminum hydroxide prepared in step 3).

[0047] Further preferably, when the number of operations n≥2, in the nth operation, the mass of the ultrafine aluminum hydroxide used in step 2) accounts for 0.2wt% to 0.5wt% of the ultrafine aluminum hydroxide prepared in step 3) in the n-1th operation.

[0048] Preferably, the mass ratio of ultrafine aluminum hydroxide to water in step 2) is 1:2.5 to 1:3.5.

[0049] Preferably, the specific gravity in step 3) is 1.3 g / cm 3 ~1.5g / cm 3 The mass ratio of circulating mother liquor to industrial-grade aluminum hydroxide is 6:1 to 7:1.

[0050] Preferably, the amount of industrial-grade aluminum hydroxide used in step 3) is 400kg to 600kg.

[0051] Preferably, the causticity ratio of the circulating semen in step 3) is 1.45-1.55.

[0052] Preferably, the seeding in step 3) is carried out under the condition that the seed rate of the liquid system is 0.15% to 0.22%.

[0053] Specifically, in the liquid system, the seed rate is calculated as follows: "Seed rate (%) = the number of moles of aluminum hydroxide seeds / (the number of moles of aluminum oxide in the seed solution × 2) × 100% = the amount of Al(OH)3 in the liquid system / (the amount of Al2O3 in the liquid system × 2) × 100%"; that is, seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%.

[0054] Preferably, the seeding time in step 1) and step 3) is 16 to 24 hours.

[0055] Preferably, the seeding in step 1) and step 3) is carried out at a temperature of 50°C to 65°C.

[0056] Preferably, the process parameters of the double-cone vacuum dryer in step 3) are as follows: vacuum degree is -0.05MPa to -0.10MPa (gauge pressure or vacuum degree), and temperature is 170°C to 190°C.

[0057] Preferably, in step 3), the filter cake is treated in a double-cone vacuum dryer to obtain a filter cake with a water content of ≤0.3 wt%.

[0058] Preferably, in step 3), the breaking up is carried out by using an ultra-fine airflow pulverizer.

[0059] Preferably, step 1), step 2) and step 3) further include a stirring step.

[0060] In a second aspect, the present invention provides an ultrafine aluminum hydroxide prepared by the preparation method described in the first aspect.

[0061] Preferably, the ultrafine aluminum hydroxide is in granular form, and the particle size D 50 It is 1.6μm~2.2μm.

[0062] Preferably, the bulk density of the ultrafine aluminum hydroxide is 0.35 g / cm 3 ~0.45g / cm 3 .

[0063] Preferably, the oil absorption value of the ultrafine aluminum hydroxide is 25 mL linseed oil / 100 g to 30 mL linseed oil / 100 g.

[0064] Preferably, the whiteness of the ultrafine aluminum hydroxide is ≥99.5%.

[0065] Preferably, the conductivity of the ultrafine aluminum hydroxide is less than 50S / m.

[0066] Preferably, the ultrafine aluminum hydroxide has a heat-resistant decomposition temperature of 225°C to 240°C.

[0067] In a third aspect, the present invention provides the use of the ultrafine aluminum hydroxide described in the second aspect in insulating materials or flame retardant materials.

[0068] Preferably, the insulating material is rubber or plastic.

[0069] The beneficial effects of the present invention are as follows: the preparation method of the ultrafine aluminum hydroxide of the present invention not only has the advantages of strong overall process controllability, multiple recycling, high raw material utilization rate, low cost, energy saving and environmental protection, but also the ultrafine aluminum hydroxide prepared has the characteristics of concentrated particle size distribution, large bulk density, high whiteness, oil absorption value, low conductivity, and good heat resistance, which is convenient for actual large-scale industrial production, transportation and application. Specifically:

[0070] (1) The method for preparing ultrafine aluminum hydroxide of the present invention is a method suitable for large-scale preparation, which uses the ultrafine aluminum hydroxide product prepared in its own process as a seed crystal, thereby saving the time for grinding the slurry in the process of grinding the seed crystal slurry and the time and cost for purchasing additional aluminum hydroxide products, thereby achieving the technical effects of improving production efficiency, saving energy, and reducing preparation costs;

[0071] (2) The method for preparing ultrafine aluminum hydroxide of the present invention can not only make the decomposition rate of sodium aluminate higher by controlling the decomposition temperature and the caustic ratio, but also ensure that the prepared product meets the "particle size D 50 =1.6~2.2μm, whiteness ≥99.5%, conductivity <50S / m, thermal decomposition temperature ≥225℃”, thereby further achieving the technical effect of high raw material utilization and reduced preparation cost;

[0072] (3) By selecting a mechanical vapor recompression evaporator and a double-cone vacuum dryer, the present invention can further reduce the energy consumption and production cost in the preparation process of the present invention compared with the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 The present invention is a process flow chart for preparing ultrafine aluminum hydroxide. DETAILED DESCRIPTION

[0074] The present invention is further described in detail below through specific examples.

[0075] The preparation process flow chart of the ultrafine aluminum hydroxide of the present invention is as follows: Figure 1 shown.

[0076] Depend on Figure 1 It can be seen that the present invention designs a method for preparing ultrafine aluminum hydroxide by an environmentally friendly physical-chemical combined seed separation method, which uses a ground and refined ultrafine sodium hydroxide product as a seed.

[0077] Specifically, the present invention firstly uses industrial-grade aluminum hydroxide and liquid alkali (30wt.% sodium hydroxide aqueous solution) to obtain a seed semen (i.e., sodium aluminate solution) with a caustic ratio of 1.40 to 1.60 and a plankton requirement of ≤0.01g / L by beating and mixing, heating and dissolving, cooling, and plate-frame filter pressing; then, the seed semen and D 50 Aluminum hydroxide with a diameter of 300 to 500 nm (made by grinding commercially available industrial-grade aluminum hydroxide) was used as a seed crystal, and after seed separation and membrane filtration, a mother liquor and D 50 It is an ultrafine aluminum hydroxide product with a size of 1.6 to 2.2 μm.

[0078] After that, the present invention designs to evaporate and concentrate the mother liquor and remove the salt to obtain a specific gravity of ≥1.35g / cm 3 The circulating mother liquor is mixed with industrial-grade aluminum hydroxide instead of liquid alkali to obtain the same production standard fine liquor (i.e. the sodium aluminate solution with the above-mentioned caustic ratio of 1.40-1.60 and the requirement of suspended matter ≤0.01g / L); a very small part of the ultrafine aluminum hydroxide product obtained in the first or previous process is weighed (the very small part refers to 0.25wt%-0.45wt% of the ultrafine aluminum hydroxide product obtained in the previous process), and D is obtained through a short-time grinding and refinement process. 50 The active seed crystals are 300 to 500 nm in size; finally, the ultrafine aluminum hydroxide product (D 50 The active crystal seeds that are ground and refined into 1.6-2.2 μm are mixed with the seed separation semen obtained again, and the ultrafine aluminum hydroxide product is obtained again through seed separation and diaphragm filtration, thus realizing the technical effect of comprehensive utilization of raw materials in production and no waste alkali discharge.

[0079] Obviously, compared with the existing preparation methods, this preparation method not only improves the utilization rate of raw materials and greatly reduces the cost, but also the key quality indicators of the prepared products are good and the application prospects are broad.

[0080] Since the improvement of the present invention is that the ultrafine aluminum hydroxide product and circulating mother liquor are obtained for the first time by using the process as experimental raw materials, the embodiments of the present invention mainly describe in detail the preparation method using the ultrafine aluminum hydroxide product and circulating mother liquor as experimental raw materials.

[0081] Unless otherwise specified, the fractions in the present invention are all mass fractions; the caustic ratios, Na2O K The content (i.e., caustic soda content) and Al2O3 content are measured with reference to the detection and analysis method of conventional sodium aluminate solution and the conventional method in the production standard for preparing aluminum hydroxide by the Bayer process; M, M0 and M1 in the present invention all represent the caustic ratio.

[0082] It should be noted that, except for the use of purchased aluminum hydroxide to grind crystal seeds and fresh liquid caustic soda as raw materials, the other process parameters and steps used in the first production of ultrafine aluminum hydroxide products are similar to the process of using recycled crystal seeds and recycled mother liquor to produce ultrafine aluminum hydroxide products.

[0083] The method for preparing the ultrafine aluminum hydroxide product for the first time in the present invention (i.e., the step of preparing the ultrafine aluminum hydroxide product for the first time in Examples 1 to 4 and Comparative Examples 1 to 3) specifically comprises the following steps:

[0084] 1) Preparation of seed crystals: 6 L of pure water (i.e., 6 kg of pure water) was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 2 kg of aluminum hydroxide (model: MARTINAL OL-104LEO, D 50 :1.7~2.1μm) for slurrying (until the slurry color is uniform), and then the slurry is transferred to a nano sand mill (a 200-mesh filter is set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 100min to obtain a slurry containing aluminum hydroxide seeds (the slurry after grinding is tested with a Malvern 3000 laser particle size analyzer, and the seed particle size D in the slurry is measured). 50 300~500nm);

[0085] 2) Preparation of seed semen: add 1979L of industrial grade liquid alkali (i.e. 30wt.% sodium hydroxide aqueous solution) to the dissolution tank, start stirring, add 1000kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105°C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4800L, continue stirring and cool down;

[0086] After the temperature of the dissolving liquid drops to 60°C, use an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) to filter and obtain 4800L of semen (Na2O K The content of is 128.5g / L, the content of Al2O3 is 136.5g / L, M=1.55);

[0087] 3) Preparation of seed slurry: Place the seed semen in step 2) in a seed tank, turn on stirring and heating, control the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1), stir and mix, control the seed rate to 0.2%, and obtain the seed slurry after 20 hours of seeding;

[0088] 4) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 3) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3 , filter plate size: 800×800mm, model: XAMYG30 / 800-GB) for filtration, and then multi-stage countercurrent washing with pure water until the pH value of the effluent is lower than 8, and pressing to obtain 6120L of filtrate and filter cake;

[0089] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, dried to a moisture content of ≤0.3wt%), and then broken up by an ultra-fine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 508kg of ultrafine aluminum hydroxide product was obtained.

[0090] Steps 1) to 5) recorded in the preparation method in the embodiment are all processes that can be recycled multiple times. In order to briefly explain and highlight the invention point of the present invention is the improvement of the recycling process, a specific operation cycle process is recorded in the embodiment, and the dosage and parameters of various raw materials in this operation process are tested and recorded. However, it cannot be limited to the effect that the process can be operated multiple times on the grounds that only one specific operation step is recorded in the embodiment. Moreover, in order to facilitate the comparison of the energy consumption difference of a single cycle, the energy consumption recorded in each embodiment and comparative example is the actual energy consumption value of a single cycle in that cycle process as shown in the recorded content, and the actual energy consumption value of a single time does not include the energy consumption of the first preparation process.

[0091] Example 1

[0092] This embodiment provides a method for preparing ultrafine aluminum hydroxide, comprising the following steps:

[0093] 1) Preparation of seed crystals: 5.5L of pure water was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 1.8kg of the first homemade ultrafine aluminum hydroxide product (D 50 The slurry was 1.6-2.2 μm) and beaten (until the slurry color was uniform) to obtain a preliminary slurry, and then the preliminary slurry was transferred to a nano sand mill (a 200-mesh filter was set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 100 minutes to obtain a slurry containing aluminum hydroxide seeds (the slurry after grinding was tested with a Malvern 3000 laser particle size analyzer to measure the seed particle size D in the slurry). 50 is 420nm);

[0094] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained from the first preparation of the product is placed in a mechanical vapor recompression evaporator (MVR evaporation system), the temperature is set to 90°C to 108°C, the pressure is 0.1MPa to 0.4MPa (gauge pressure), and the liquid after compression evaporation treatment and salt removal is controlled to obtain a liquid with a specific gravity of 1.35g / cm 3 of circulating mother liquor (2271L);

[0095] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 450 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4311 L, continue stirring and cool down;

[0096] After the temperature of the dissolving liquid drops to 60°C, use an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) was filtered to obtain 4311L of seed semen (Na2O in seed semen K The content is 128.5g / L, the Al2O3 content is 136.5g / L, M=1.55);

[0097] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 0.2%. After 20 hours of seeding, obtain the seed slurry;

[0098] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3, filter plate size: 800×800mm, model: XAMYG30 / 800-GB) for filtration, and then multi-stage countercurrent washing with pure water until the pH of the effluent is lower than 8, and pressing to obtain 4933L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0099] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, vacuum degree: -0.09MPa) until the moisture content was ≤0.3wt%, and then broken up by an ultra-fine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 458kg of ultrafine aluminum hydroxide product was obtained;

[0100] Wherein, the caustic ratio of the circulating mother liquor in step 2) is M0=3.1, Na2O K The content is 243.9g / L, and the Al2O3 content is 129.6g / L; the calculation formula of the seed rate in step 4) is:

[0101] Seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%;

[0102] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0103] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0104] The processes from step 1) preparing the seed crystal to step 5) preparing the ultrafine aluminum hydroxide product are all processes that can be recycled multiple times;

[0105] The filtrate in step 5) of this embodiment was taken and analyzed, and it was found that the Na2O in the filtrate K The content is 112.3g / L, the Al2O3 content is 57.7g / L, and the caustic ratio M1=3.2;

[0106] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of seed separation in this embodiment is 51.6%, calculated by the formula: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 464.4 kg;

[0107] The product test results obtained in the above steps (i.e., a single cycle) are detailed in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this embodiment is statistically analyzed by a water meter, an electricity meter, and a steam flow meter, including: 2.89 t of water, 174 kW·h of electricity, and 0.96 t of hot steam (in order to facilitate the preparation process and parameters specifically involved in the energy consumption of a single cycle, the above steps do not record the first or last step of obtaining the ultrafine aluminum hydroxide product).

[0108] It should also be noted that the preparation method of ultrafine aluminum hydroxide in this embodiment actually also includes:

[0109] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0110] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, step 1) needs to replace the "ultrafine aluminum hydroxide product prepared in the previous process" with the "ultrafine aluminum hydroxide product prepared in the first process" to prepare the crystal seed; step 2) replaces the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the previous process" with the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the first process" and then concentrates it to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0111] Other things to control: Seed particle size D in the slurry containing aluminum hydroxide seeds 50 350nm~450nm, liquid density of circulating mother liquid ≥1.35g / cm 3 The caustic ratio of the seed separation fluid is 1.45-1.55, the seed rate of step 3) is 0.15%-0.22%, and the obtained ultrafine aluminum hydroxide product D 50 =1.6~2.2μm, and the temperature in the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, the equipment and its parameters are consistent with the above records; the average energy consumption after a period of circulation operation is shown in Table 2 (in order to maintain the above parameters unchanged, liquid alkali is occasionally added to the circulating mother liquor, but the key process parameters that need to be controlled are still as mentioned above).

[0112] Example 2

[0113] This embodiment provides a method for preparing ultrafine aluminum hydroxide, comprising the following steps:

[0114] 1) Preparation of seed crystals: 4.5L of pure water was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 1.5kg of the ultrafine aluminum hydroxide product (D 50The slurry was 1.6-2.2 μm) and beaten (until the slurry color was uniform) to obtain a preliminary slurry, and then the preliminary slurry was transferred to a nano sand mill (a 200-mesh filter was set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 100 minutes to obtain a slurry containing aluminum hydroxide seeds (the slurry after grinding was tested with a Malvern 3000 laser particle size analyzer to measure the seed particle size D in the slurry). 50 is 450nm);

[0115] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained from the first preparation of the product is placed in a mechanical vapor recompression evaporator (MVR evaporation system), the temperature is set to 90°C to 108°C, the pressure is 0.1MPa to 0.4MPa (gauge pressure), and the liquid after compression evaporation treatment and salt removal is controlled to obtain a liquid with a specific gravity of 1.35g / cm 3 of circulating mother liquor (2501L);

[0116] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 500 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4822 L, continue stirring and cool down;

[0117] After the temperature of the dissolution solution dropped to 60°C, an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) to filter and obtain 4822L of seed semen (Na2O in seed semen K The content is 128.3 g / L, the Al2O3 content is 136.8 g / L, M=1.54);

[0118] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 0.15%. After 20 hours of seeding, obtain the seed slurry;

[0119] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3 , filter plate size: 800×800mm, model:

[0120] XAMYG30 / 800-GB) for filtration, multi-stage countercurrent washing until the pH of the effluent is lower than 8, and pressing to obtain 5691L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0121] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, vacuum degree: -0.09MPa) until the moisture content was ≤0.3wt%, and then broken up by an ultra-fine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 527kg of ultrafine aluminum hydroxide product was obtained;

[0122] Wherein, the caustic ratio of the circulating mother liquor in step 2) is M0=3.06, Na2O K The content is 247.4g / L, and the Al2O3 content is 133g / L; the calculation formula of the seed rate in step 4) is:

[0123] Seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%;

[0124] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0125] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0126] Steps 1) to 5) are processes that can be recycled multiple times;

[0127] The filtrate in step 5) of this embodiment was taken and analyzed, and it was found that the Na2O in the filtrate K The content is 108.7g / L, the Al2O3 content is 53.5g / L, and the caustic ratio M1=3.34;

[0128] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of seed separation in this embodiment is 53.8%, calculated by the formula: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 543 kg;

[0129] The product test results obtained in the above steps (i.e., a single cycle) are detailed in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this embodiment is statistically analyzed by a water meter, an electricity meter, and a steam flow meter, including: 3.53 tons of water, 199.2 kW·h of electricity, and 1.08 tons of hot steam (in order to facilitate the preparation process and parameters specifically involved in the energy consumption of a single cycle, the above steps do not record the first or last step of obtaining the ultrafine aluminum hydroxide product).

[0130] It should also be noted that the preparation method of ultrafine aluminum hydroxide in this embodiment actually also includes:

[0131] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0132] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, step 1) needs to replace the "ultrafine aluminum hydroxide product prepared in the previous process" with the "ultrafine aluminum hydroxide product prepared in the first process" to prepare the crystal seed; step 2) replaces the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the previous process" with the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the first process" and then concentrates it to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0133] Other things to control: Seed particle size D in the slurry containing aluminum hydroxide seeds 50 350nm~450nm, liquid density of circulating mother liquid ≥1.35g / cm 3 The caustic ratio of the seed separation fluid is 1.45-1.55, the seed rate of step 3) is 0.15%-0.22%, and the obtained ultrafine aluminum hydroxide product D 50 =1.6~2.2μm, and the temperature during the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, equipment and its parameters are consistent with the above records.

[0134] Example 3

[0135] This embodiment provides a method for preparing ultrafine aluminum hydroxide, comprising the following steps:

[0136] 1) Preparation of seed crystals: 5.3 L of pure water was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 1.75 kg of the first homemade ultrafine aluminum hydroxide product (D 50 The slurry was 1.6-2.2 μm) and beaten (until the slurry color was uniform) to obtain a preliminary slurry, and then the preliminary slurry was transferred to a nano sand mill (a 200-mesh filter was set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 110 minutes to obtain a slurry containing aluminum hydroxide seeds (the ground slurry was tested with a Malvern 3000 laser particle size analyzer to measure the seed particle size D in the slurry). 50 is 400nm);

[0137] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained from the first preparation of the product is placed in a mechanical vapor recompression evaporator (MVR evaporation system), the temperature is set to 90°C to 108°C, the pressure is 0.1MPa to 0.4MPa (gauge pressure), and the liquid after compression evaporation treatment and salt removal is controlled to obtain a liquid with a specific gravity of 1.35g / cm 3of circulating mother liquor (2317.5L);

[0138] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 465 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105 ° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4737 L, continue stirring and cool down;

[0139] After the temperature of the dissolving liquid drops to 60°C, use an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) to filter and obtain 4737L of seed semen (Na2O in seed semen K The content is 122.6 g / L, the Al2O3 content is 130.6 g / L, M=1.54);

[0140] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 0.18%. After 20 hours of seeding, obtain the seed slurry;

[0141] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3 , filter plate size: 800×800mm, model: XAMYG30 / 800-GB) for filtration, multi-stage countercurrent washing until the effluent pH is lower than 8, and pressing to obtain 4933L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0142] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, vacuum degree: -0.09MPa) until the moisture content was ≤0.3wt%, and then broken up by an ultra-fine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 536kg of ultrafine aluminum hydroxide product was obtained;

[0143] Wherein, the caustic ratio of the circulating mother liquor in step 2) is M0=3.04, Na2O K The content is 250.6 g / L, and the Al2O3 content is 135.7 g / L; the calculation formula of the seed rate in step 4) is:

[0144] Seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%;

[0145] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0146] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0147] Steps 1) to 5) are processes that can be recycled multiple times;

[0148] The filtrate in step 5) of this embodiment was taken and analyzed, and it was found that the Na2O in the filtrate K The content is 105.8g / L, the Al2O3 content is 51.9g / L, and the caustic ratio M1=3.2;

[0149] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of seed separation in this embodiment is 55.6%, calculated by the formula: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 545.4 kg;

[0150] The product test results obtained in the above steps (i.e., a single cycle) are detailed in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this embodiment is statistically analyzed by a water meter, an electricity meter, and a steam flow meter, including: 3.43 tons of water, 212.8 kW·h of electricity, and 1.12 tons of hot steam (in order to facilitate the preparation process and parameters specifically involved in the energy consumption of a single cycle, the above steps do not record the first or last step of obtaining the ultrafine aluminum hydroxide product).

[0151] It should also be noted that the preparation method of ultrafine aluminum hydroxide in this embodiment actually also includes:

[0152] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0153] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, step 1) needs to replace the "ultrafine aluminum hydroxide product prepared in the previous process" with the "ultrafine aluminum hydroxide product prepared in the first process" to prepare the crystal seed; step 2) replaces the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the previous process" with the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the first process" and then concentrates it to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0154] Other things to control: Seed particle size D in the slurry containing aluminum hydroxide seeds 50 350nm~450nm, liquid density of circulating mother liquid ≥1.35g / cm3 The caustic ratio of the seed separation fluid is 1.45-1.55, the seed rate of step 3) is 0.15%-0.22%, and the obtained ultrafine aluminum hydroxide product D 50 =1.6~2.2μm, and the temperature during the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, equipment and its parameters are consistent with the above records.

[0155] Example 4

[0156] This embodiment provides a method for preparing ultrafine aluminum hydroxide, comprising the following steps:

[0157] 1) Preparation of seed crystals: 5.5L of pure water was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 1.8kg of the first homemade ultrafine aluminum hydroxide product (D 50 The preliminary slurry was 1.6-2.2 μm) for slurrying (until the slurry color was uniform), and then the preliminary slurry was transferred to a nano sand mill (a 200-mesh filter was set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 100 minutes to obtain a preliminary slurry, and a slurry containing aluminum hydroxide seeds was obtained (the slurry after grinding was tested with a Malvern 3000 laser particle size analyzer, and the seed particle size D in the slurry was measured). 50 is 380nm);

[0158] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained from the first preparation of the product is placed in a mechanical vapor recompression evaporator (MVR evaporation system), the temperature is set to 90°C to 108°C, the pressure is 0.1MPa to 0.4MPa (gauge pressure), and the liquid after compression evaporation treatment and salt removal is controlled to obtain a liquid with a specific gravity of 1.35g / cm 3 of circulating mother liquor (2244.3 L);

[0159] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 450 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4311 L, continue stirring and cool down;

[0160] After the temperature of the dissolution solution dropped to 60°C, an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) to filter and obtain 4311L of semen (Na2O K The content is 128.5g / L, the Al2O3 content is 136.5g / L, M=1.55);

[0161] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 0.2%. After 20 hours of seeding, obtain the seed slurry;

[0162] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3 , filter plate size: 800×800mm, model: XAMYG30 / 800-GB) for filtration, multi-stage countercurrent washing until the effluent pH is lower than 8, and pressing to obtain 4933L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0163] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, vacuum degree: -0.09MPa) until the moisture content was ≤0.3wt%, and then broken up by an ultra-fine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 458kg of ultrafine aluminum hydroxide product was obtained;

[0164] Wherein, the caustic ratio of the circulating mother liquor in step 2) is M0=3.05, Na2O K The content is 238.3g / L, and the Al2O3 content is 128.4g / L; the calculation formula of the seed rate in step 4) is:

[0165] Seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%;

[0166] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0167] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0168] Steps 1) to 5) are processes that can be recycled multiple times;

[0169] The filtrate in step 5) of this embodiment was taken and analyzed, and it was found that the Na2O in the filtrate K The content is 112.3g / L, the Al2O3 content is 57.7g / L, and the caustic ratio M1=3.2;

[0170] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of seed separation in this embodiment is 51.6%, calculated by the formula: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 464.4 kg;

[0171] The product test results obtained in the above steps (i.e., a single cycle) are detailed in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this embodiment is statistically analyzed by a water meter, an electricity meter, and a steam flow meter, including: 2.89 t of water, 174 kW·h of electricity, and 0.96 t of hot steam (in order to facilitate the preparation process and parameters specifically involved in the energy consumption of a single cycle, the above steps do not record the first or last step of obtaining the ultrafine aluminum hydroxide product).

[0172] It should also be noted that the preparation method of ultrafine aluminum hydroxide in this embodiment actually also includes:

[0173] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0174] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, step 1) needs to replace the "ultrafine aluminum hydroxide product prepared in the previous process" with the "ultrafine aluminum hydroxide product prepared in the first process" to prepare the crystal seed; step 2) replaces the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the previous process" with the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the first process" and then concentrates it to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0175] Other things to control: Seed particle size D in the slurry containing aluminum hydroxide seeds 50 350nm~450nm, liquid density of circulating mother liquid ≥1.35g / cm 3 The caustic ratio of the seed separation fluid is 1.45-1.55, the seed rate of step 3) is 0.15%-0.22%, and the obtained ultrafine aluminum hydroxide product D 50 =1.6~2.2μm, and the temperature during the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, the equipment and its parameters are consistent with the above records; the average energy consumption after a period of circulation operation is shown in Table 2.

[0176] Comparative Example 1

[0177] This comparative example provides a method for preparing ultrafine aluminum hydroxide, which is mainly different from Example 1 in that the causticity ratio of the seed semen is relatively low at 1.25, and specifically comprises the following steps:

[0178] 1) Preparation of seed crystals: 7.1L of pure water was added to the pulping tank, and after the stirring device of the pulping tank was turned on, 2.38kg of the first homemade ultrafine aluminum hydroxide product (D 50 The slurry was 1.6-2.2 μm) and beaten (until the slurry color was uniform) to obtain a preliminary slurry, and then the preliminary slurry was transferred to a nano sand mill (a 200-mesh filter was set inside the sand mill to intercept the grinding medium zirconium beads) for cyclic grinding for 120 minutes to obtain a slurry containing aluminum hydroxide seeds (the ground slurry was tested with a Malvern 3000 laser particle size analyzer to measure the seed particle size D in the slurry). 50 is 420nm);

[0179] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained by the first preparation of the product is placed in a mechanical vapor recompression evaporator (MVR evaporation system), and the temperature is set to 90°C to 108°C and the pressure is set to 0.1MPa to 0.4MPa (gauge pressure) for evaporation and concentration. At the same time, the liquid after compression evaporation and salt removal is controlled to obtain a liquid with a specific gravity of 1.35g / cm 3 of circulating mother liquor (2300L);

[0180] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 725 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 105 ° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4311 L, continue stirring and cool down;

[0181] After the temperature of the dissolving liquid drops to 60°C, use an automatic hydraulic plate and frame filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 3m 3 , filter plate size: 500×500mm, number of filter plates: 8, model: XMY3 / 500-UB) to filter and obtain 4600L of semen (Na2O K The content is 128.7g / L, the Al2O3 content is 169g / L, M=1.25);

[0182] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 55±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 0.2%. After 20 hours of seeding, obtain the seed slurry;

[0183] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) was filtered through a high-pressure diaphragm filter press (manufacturer: Huizhou Zhongsheng Environmental Protection Equipment Co., Ltd., filtration area: 30m 3, filter plate size: 800×800mm, model: XAMYG30 / 800-GB) for filtration, multi-stage countercurrent washing until the effluent pH is lower than 8, and pressing to obtain 5380L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0184] The filter cake was dried in a double cone vacuum dryer (drying temperature: 180°C, vacuum degree: -0.09MPa) until the moisture content was ≤0.3wt%, and then crushed in an ultrafine air flow mill (required D 100 ≤8μm, D 50 =1.6~2.2μm), and 733kg of ultrafine aluminum hydroxide product was obtained;

[0185] Among them, the caustic ratio of the circulating mother liquor in step 2) is 3.2, Na2O K The content is 257g / L, and the Al2O3 content is 132g / L; the calculation formula of the seed rate in step 4) is:

[0186] Seed rate (%) = n (Al (OH) 3) / 2n (Al 2 O 3) × 100%;

[0187] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0188] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0189] Steps 1) to 5) are processes that can be recycled multiple times;

[0190] The filtrate in step 5) of this comparative example was tested and analyzed, and it was found that the Na2O in the filtrate K The content is 109.9g / L, the Al2O3 content is 52.5g / L, and the caustic ratio M1=3.44;

[0191] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of seed separation in this comparative example is 63.7%, and the calculation formula is: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 758 kg;

[0192] The product test results obtained in the above steps (i.e., a single cycle) are shown in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this comparative example is calculated by using a water meter, an electricity meter, and a steam flow meter, including: 5t of water, 320kW·h of electricity, and 1.58t of hot steam.

[0193] It should also be noted that the preparation method of the ultrafine aluminum hydroxide in this comparative example actually also includes:

[0194] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0195] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, step 1) needs to replace the "ultrafine aluminum hydroxide product prepared in the previous process" with the "ultrafine aluminum hydroxide product prepared in the first process" to prepare the crystal seed; step 2) replaces the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the previous process" with the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product in the first process" and then concentrates it to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0196] Other things to control: Seed particle size D in the slurry containing aluminum hydroxide seeds 50 350nm~450nm, liquid density of circulating mother liquid ≥1.35g / cm 3 The caustic ratio of the seed separation liquid is 1.25, the seed rate of step 3) is 0.15% to 0.22%, and the obtained ultrafine aluminum hydroxide product D 50 =1.6~2.2μm, and the temperature in the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, the equipment and its parameters are consistent with the above records; the average energy consumption after a period of circulation operation is shown in Table 2 (in order to maintain the above parameters unchanged, liquid alkali is occasionally added to the circulating mother liquor, but the key process parameters that need to be controlled are still as mentioned above).

[0197] Comparative Example 2

[0198] This comparative example provides a method for preparing ultrafine aluminum hydroxide, which differs from Example 1 in that: industrial-grade aluminum hydroxide is used instead of homemade ultrafine aluminum hydroxide product as seed crystal raw material, and the preparation of seed crystal takes 400 minutes; the circulating mother liquor is obtained by evaporating and concentrating with a four-effect forced circulation evaporator; the filter cake is dried and mechanically dispersed with a flash dryer to obtain ultrafine aluminum hydroxide, which specifically comprises the following steps:

[0199] 1) Preparation of seed crystals: In a pulping tank, 20 kg of industrial grade aluminum hydroxide (particle size D 50 =200~400μm) and pure water in a mass ratio of 1:3 to obtain a preliminary slurry, and then the preliminary slurry is transferred to a nano sand mill and circulated for 400min to obtain 80kg of slurry containing aluminum hydroxide seeds; (the particle size D of the slurry containing aluminum hydroxide seeds is tested by Malvern 3000 laser particle size analyzer 50 =1.1 μm, and this slurry is a reserve raw material for seed crystals);

[0200] 2) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained by the first preparation of the product is placed in a four-effect forced circulation evaporator for concentration, and the temperature of the four-effect forced circulation evaporator is set to 70°C to 90°C and the pressure is -0.1 to 0.1 MPa (gauge pressure). After four-effect forced circulation evaporation treatment and salt removal, the liquid with a specific gravity of 1.36 g / cm 3 of circulating mother liquor (2283L);

[0201] 3) Preparation of seed semen: Add the circulating mother liquor in step 2) into the dissolution tank, start stirring, add 535 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution treatment at a temperature of 100 ° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4187 L, continue stirring and cool down;

[0202] After the temperature of the dissolution liquid dropped to 65°C, it was filtered using an automatic hydraulic plate-frame filter press to obtain 4187L of semen (Na2O K The content is 135g / L, the Al2O3 content is 158.6g / L, M=1.40);

[0203] 4) Preparation of seed slurry: Place the seed semen in step 3) in a seed tank and start stirring. After controlling the temperature of the seed semen to 50±5°C, add the slurry containing aluminum hydroxide crystal seeds in step 1) and stir to mix. Control the seed rate to 2%. After 16 hours of seeding, obtain the seed slurry;

[0204] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) is filtered with a vertical plate and frame filter press, and then multi-stage countercurrent washing is performed with pure water until the pH of the effluent is lower than 8, and then pressed to obtain 5433L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0205] The filter cake is dried with a flash dryer (drying temperature: 130℃~220℃, dried to a moisture content of ≤0.3wt%, the heat source of the flash dryer is natural gas combustion), and then broken up with a mechanical breaker (requires D 100 ≤8μm, D 50 =1.8~2.5μm), and obtain 487kg of ultrafine aluminum hydroxide product;

[0206] Wherein, the caustic ratio of the circulating mother liquor in step 2) is M0=2.96, Na2O K The content is 247.6g / L, and the Al2O3 content is 137.8g / L; the calculation formula of the seed rate in step 4) is:

[0207] Seed rate (%) = n (Al (OH) 3) / 2n (Al 2 O 3) × 100%;

[0208] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0209] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0210] Steps 1) to 5) are processes that can be recycled multiple times;

[0211] The filtrate in step 5) of this comparative example was tested and analyzed, and it was found that the Na2O in the filtrate K The content is 104.5g / L, the Al2O3 content is 63.9g / L, and the caustic ratio M1=2.69; after calculation and preliminary analysis, it can be known that the decomposition rate of sodium aluminate in the overall process of the seed separation in this comparative example is 48%, and the calculation formula is: decomposition rate=(1-M / M1)×100%, and the theoretical output of ultrafine aluminum hydroxide product is 487.6kg;

[0212] The product test results obtained in the above steps (i.e., a single cycle) are shown in Table 1. The energy consumption of a single cycle (i.e., step 1) to step 5) of this comparative example is calculated by a water meter, an electricity meter, and a steam flow meter, including: 8.77 tons of water, 146.1 kW·h of electricity, 1.705 tons of steam, and 58.5 Nm of natural gas. 3 (In order to facilitate the identification of the specific preparation processes and parameters involved in the energy consumption of a single cycle, the above steps do not record the first or last steps of preparing the ultrafine aluminum hydroxide product).

[0213] It should also be noted that the preparation method of the ultrafine aluminum hydroxide in this comparative example actually also includes:

[0214] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0215] When the preparation of the crystal seed in step 1) to the preparation of the ultrafine aluminum hydroxide product in step 5) is repeated multiple times, the industrial-grade aluminum hydroxide is continued to be used as the crystal seed raw material in step 1), and the preparation of the crystal seed takes 400 minutes; in step 2), the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product for the first time" is replaced by "the mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product for the last time" and then concentrated to obtain a new circulating mother liquor" to prepare the ultrafine aluminum hydroxide;

[0216] Others need to be controlled: The preparation of the seed crystal takes 400 minutes, and the liquid density of the circulating mother liquor is 1.36g / cm 3 The caustic ratio of the seed fraction is 1.40, the seed rate of step 3) is 2%, and the obtained ultrafine aluminum hydroxide product D 50=1.8~2.5μm, and the temperature in the circulation process, multi-stage countercurrent washing until the effluent pH is lower than 8, the equipment and its parameters are consistent with the above records; the average energy consumption after a period of circulation operation is shown in Table 2 (in order to maintain the above parameters unchanged, liquid alkali is occasionally added to the circulating mother liquor, but the key process parameters that need to be controlled are still as mentioned above).

[0217] Comparative Example 3

[0218] This comparative example provides a method for preparing ultrafine aluminum hydroxide, which is different from Example 1 in that: the preparation of the seed crystal is carried out by chemical method; the mother liquor is evaporated and concentrated by a four-effect forced circulation evaporator to obtain a circulating mother liquor; the filter cake is dried by a flash dryer; and the method specifically comprises the following steps:

[0219] 1) Preparation of circulating mother liquor: The mother liquor containing sodium hydroxide and sodium aluminate obtained by the first preparation of the product is placed in a four-effect forced circulation evaporator for concentration, and the temperature of the four-effect forced circulation evaporator is set to 70°C to 90°C and the pressure is -0.1 to 0.1 MPa (gauge pressure). After four-effect forced circulation evaporation treatment and salt removal, the liquid with a specific gravity of 1.36 g / cm 3 of circulating mother liquor (2325L);

[0220] 2) Preparation of seed semen: Add the circulating mother liquor in step 1) into the dissolution tank, start stirring, add 428 kg of industrial grade aluminum hydroxide, and use steam heating to control the dissolution process at a temperature of 100° C. After the solid is completely dissolved, turn off the heating device, add tap water to dilute to a total liquid volume of 4043 L, continue stirring and cool down;

[0221] After the temperature of the dissolution liquid dropped to 65°C, it was filtered using an automatic hydraulic plate-frame filter press to obtain 4043 L of semen (Na2O K The content is 138.2g / L, the Al2O3 content is 142.3g / L, M=1.60);

[0222] 3) Preparation of seed crystals: Take 5% (i.e. 200 L) of the total volume of the seed semen in step 2) as the seed semen, add it to the seed tank, start stirring, add the same volume (200 L) of 100 g / L sodium bicarbonate solution dissolved in advance, note that the sodium bicarbonate solution must be added slowly with flow adjustment, and the addition time is controlled to be about 40 minutes, and then continue to age for 2 hours to obtain a slurry containing aluminum hydroxide seeds, which is used as seed crystals for standby use;

[0223] 4) Preparation of seed slurry: about 3843L of the remaining seed liquid (minus the seed liquid used to prepare the seed slurry) in step 2) is placed in a seed tank, and stirred. After controlling the temperature of the seed liquid to 53±5°C, the slurry containing aluminum hydroxide seeds in step 3) is added, stirred and mixed. After 16 hours of seeding, a seed slurry is obtained;

[0224] 5) Preparation of ultrafine aluminum hydroxide product: The seed slurry in step 4) is filtered with a high-pressure diaphragm filter press, and then multi-stage countercurrent washing is performed with pure water until the pH of the effluent is lower than 8, and then pressed to obtain 5126L of filtrate (for the preparation of circulating mother liquor for the next process) and filter cake;

[0225] The filter cake is dried with a flash dryer (drying temperature: 130-220°C, dried to a moisture content of ≤0.3wt%, the heat source of the flash dryer is hot steam), and then dispersed with a mechanical disperser (requires D 100 ≤8μm, D 50 =1.6~2.5μm), and 416kg of ultrafine aluminum hydroxide product was obtained;

[0226] Wherein, the caustic ratio of the circulating mother liquor in step 1) is M0=3.11, Na2O K The content is 240.3g / L, and the Al2O3 content is 127.1g / L;

[0227] The calculation formula of the seed rate in step 4) is:

[0228] NaAlO2+NaHCO3+H2O→Al(OH)3↓+Na2CO3

[0229] Seed rate (%) = n(Al(OH)3) / [2×n(Al2O3)]×100%

[0230] =(100×200 / 84) / [2×(142.3×3843 / 102]×100%

[0231] =2.2%;

[0232] Wherein, n(Al(OH)3) represents the molar number of aluminum hydroxide seed crystals; n(Al2O3) represents the molar number of aluminum oxide in the seed semen”;

[0233] Steps 1) to 5) are processes that can be recycled multiple times;

[0234] The washing liquid for the multi-stage countercurrent washing in step 5) is 70° C. pure water;

[0235] The filtrate in step 5) of this comparative example was tested and analyzed, and it was found that the Na2O in the filtrate KThe content is 106.4g / L, the Al2O3 content is 57.2g / L, and the caustic ratio M1=3.06;

[0236] According to calculation and preliminary analysis, the decomposition rate of sodium aluminate in the overall process of the seed separation in this comparative example is 47.7%, and the calculation formula is: decomposition rate = (1-M / M1) × 100%, and the theoretical output of ultrafine aluminum hydroxide product is 420kg;

[0237] The product test results obtained in the above steps (i.e., a single cycle) are shown in Table 1 (the particle size of the product is D 50 =1.87μm), the energy consumption of a single cycle (i.e., step 1) to step 5)) of this comparative example is calculated by water meter, electricity meter, and steam flow meter, including: 4.6 tons of water, 146kW·h of electricity, and 2.2 tons of steam.

[0238] It should also be noted that the preparation method of ultrafine aluminum hydroxide in this embodiment actually also includes:

[0239] The first step of obtaining the ultrafine aluminum hydroxide product (see above);

[0240] When the preparation of the circulating mother liquor from step 1) to step 5) of the preparation of the ultrafine aluminum hydroxide product is repeated multiple times, the seed semen for preparing the seed crystals in step 3) is 5% of the seed semen of this cycle, and the 100 g / L sodium bicarbonate solution is the auxiliary raw material prepared and used immediately; in step 1), the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product last time" is used to replace the "mother liquor containing sodium hydroxide and sodium aluminate obtained by preparing the product for the first time" and then the mother liquor is concentrated to obtain a new circulating mother liquor to prepare the ultrafine aluminum hydroxide;

[0241] The rest needs to be controlled: the caustic ratio of the seed semen remains unchanged, the particle size of the ultrafine aluminum hydroxide product remains unchanged, the temperature during the circulation process remains unchanged, the specific gravity of the circulating mother liquor remains unchanged, multi-stage countercurrent washing is performed until the effluent pH is lower than 8, and the equipment and its parameters are consistent with the above records; the average energy consumption after a period of circulation operation is shown in Table 2.

[0242] Product Reviews

[0243] The ultrafine aluminum hydroxide products prepared by using the circulating mother liquor and circulating seed crystals in Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to performance tests, and the measured product parameters are shown in Table 1.

[0244] Table 1 Product parameters of ultrafine aluminum hydroxide in Examples 1 to 4 and Comparative Examples 1 to 3

[0245]

[0246] Note: The particle size D in Table 1 50It was measured using a Malvern 3000 laser particle size analyzer;

[0247] The whiteness in Table 1 was measured using a whiteness meter;

[0248] The conductivity in Table 1 is measured with reference to "YS / T 704-2009 Determination of conductivity of aluminum hydroxide analysis method for fillers";

[0249] The oil absorption values ​​in Table 1 are determined according to the standard of GB / T 5211.15-2014 General test methods for pigments and extenders Part 15 Determination of oil absorption;

[0250] The bulk density in Table 1 was measured using a density cup;

[0251] The thermal decomposition temperatures in Table 1 were measured using a thermogravimetric analyzer.

[0252] It can be seen from Table 1 that the ultrafine aluminum hydroxide products prepared in Examples 1 to 4 of the present invention not only have a particle size that meets D 50 =1.6~2.2μm, whiteness ≥99.5%, conductivity <50S / m, heat-resistant decomposition temperature ≥225℃, and also has the advantages of low oil absorption value (oil absorption value ≤30mL linseed oil / 100g), large bulk density, etc., and its application in rubber and plastic system has excellent flame retardant properties, mechanical properties, and insulation properties. In addition, the ultrafine aluminum hydroxide products in Examples 1 to 4 have the advantage of low oil absorption value. Applying them as fillers in rubber or plastic will obtain rubber or plastic liquids with lower viscosity, better fluidity, and easier operation, thereby improving the processability of the rubber and plastic system. The ultrafine aluminum hydroxide products in Examples 1 to 4 have the advantage of large bulk density, which can save the cost of transportation and warehousing in practical applications, so the products and preparation methods of the present invention are very suitable for promotion and practical application. Since the ultrafine aluminum hydroxide products in Examples 1 to 4 have the advantage of low oil absorption value, applying them as fillers in rubber and plastic will obtain rubber and plastic liquids with low viscosity, good fluidity, and easy operation, thereby improving the processability of the rubber and plastic system. Since the ultrafine aluminum hydroxide products in Examples 1 to 4 have the advantage of a larger bulk density, they can save transportation and storage costs in practical applications.

[0253] Cost evaluation of production processes

[0254] The production processes of Example 1 and Comparative Examples 1 to 3 were cycled for the same time, and the production cost of the products produced during this time was calculated. The cost evaluation of the production processes of different processes is shown in Table 2.

[0255] Table 2 Cost evaluation table of product production process of Example 1 and Comparative Examples 1 to 3

[0256]

[0257]

[0258] Note: The liquid caustic soda raw materials in the examples and comparative examples in Table 2 are the average loss of liquid caustic soda after 20 cycles of production, mainly including the loss of liquid caustic soda in the slag during the filtration process and the concentration and salt removal process; in addition, the cost data are the actual consumption in the examples and comparative examples converted into data per ton of product. The unit price of raw materials is calculated according to the current market price, and fixed assets, labor costs, and management and sales costs are all calculated on the same scale.

[0259] From the energy consumption calculated in the embodiments and comparative examples, it can be seen from Table 2 that the raw materials and energy consumption in the ultrafine aluminum hydroxide preparation method of Example 1 are lower than those in Comparative Examples 2 and 3, the operating cost of the overall process is low, the utilization rate of raw materials is high, and it also has the advantages of environmental protection, greenness and economy.

[0260] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing ultrafine aluminum hydroxide, characterized in that: The preparation method comprises the following steps: 1) mixing industrial grade aluminum hydroxide and sodium hydroxide solution, and dissolving by heating to obtain original seed semen; wherein the caustic ratio of the original seed semen is 1.45-1.60, and the Al2O3 content of the original seed semen is 134g / L-138g / L; The first aluminum hydroxide seed slurry is added to the original seed separation semen for seed separation to obtain the original mother liquor and ultrafine aluminum hydroxide; wherein the seeds in the first aluminum hydroxide seed slurry are particles with a diameter of D 50 Aluminum hydroxide particles of 300 to 500 nm; 2) The original mother liquid in step 1) is concentrated and evaporated to obtain a product having a specific gravity of 1.3 g / cm 3 ~1.5g / cm 3 Circulating mother liquor; The ultrafine aluminum hydroxide described in step 1) is slurried with water, and then ground and refined to obtain a circulating aluminum hydroxide seed slurry; 3) mixing the circulating mother liquor described in step 2) with industrial-grade aluminum hydroxide and heating and dissolving again to obtain a circulating seed fraction semen having a caustic ratio of 1.40 to 1.60; Adding the circulating aluminum hydroxide seed slurry to the circulating seed separation semen for seed separation to obtain mother liquor and ultrafine aluminum hydroxide; The aluminum hydroxide in the circulating aluminum hydroxide seed slurry in step 2) and step 3) is in granular form, and the particle size D 50 The diameter of the nanostructured particles is 300 to 500 nm; the seeding time in step 1) and step 3) is 16 to 24 hours; the seeding in step 3) is carried out under the condition that the seed rate of the liquid system is 0.15% to 0.22%; the seeding in step 1) and step 3) is carried out under the condition that the temperature is 50°C to 65°C.

2. The method for preparing ultrafine aluminum hydroxide according to claim 1, characterized in that: The preparation method comprises the following steps: 1) industrial grade aluminum hydroxide and sodium hydroxide aqueous solution are mixed, heated for dissolution, diluted, cooled to 50° C. to 65° C., and plate and frame filter pressed to obtain original seed semen; Adding the first aluminum hydroxide seed crystal slurry to the original seed separation semen to perform seed separation and diaphragm filter pressing to obtain the original mother liquor and ultrafine aluminum hydroxide; 2) The mother liquor is treated by compression evaporation system and salt removal to obtain a specific gravity of 1.3g / cm 3 ~1.5g / cm 3 The circulating mother liquor is obtained by slurrying and mixing the ultrafine aluminum hydroxide and water, and treating the mixture with a nano sand mill for 90 minutes to 160 minutes to obtain a circulating aluminum hydroxide seed slurry; 3) mixing the circulating mother liquor described in step 2) with industrial-grade aluminum hydroxide, dissolving by heating, diluting, cooling to 50° C. to 65° C., and filtering by plate and frame pressure to obtain a circulating seed fraction semen having a caustic ratio of 1.40 to 1.60; Adding the circulating aluminum hydroxide seed slurry to the circulating seed separation semen to perform seed separation and diaphragm filter pressing to obtain a mother liquor and a filter cake; The filter cake is treated in a double cone vacuum dryer and broken up to obtain ultrafine aluminum hydroxide; The aluminum hydroxide in the circulating aluminum hydroxide seed slurry in step 2) and step 3) is in granular form, and the particle size D 50 300~500nm; Step 2) and step 3) can be run multiple times, and the number of runs n of the process of step 2) and step 3) is 1 to 500 times, and n is a positive integer; When the number of operations n=1, the mother liquor in step 2) is the original seed fractionated semen in step 1), and the ultrafine aluminum hydroxide in step 2) is the ultrafine aluminum hydroxide in step 1); When the number of runs n≥2, in the nth run, the mother liquor in step 2) uses the recycled seed semen prepared in step 3) in the n-1th run, and the ultrafine aluminum hydroxide in step 2) uses the ultrafine aluminum hydroxide prepared in step 3) in the n-1th run.

3. The method for preparing ultrafine aluminum hydroxide according to claim 2, characterized in that: When the number of repeated cycles n≥2, the amount of the ultrafine aluminum hydroxide used in step 2) is 0.2wt% to 0.5wt% of the ultrafine aluminum hydroxide prepared in step 3).

4. The method for preparing ultrafine aluminum hydroxide according to claim 2, characterized in that: The heating dissolution in step 1) and step 3) is heated by introducing steam, and the temperature of the heating dissolution is 95°C to 115°C.

5. The method for preparing ultrafine aluminum hydroxide according to claim 2, characterized in that: The causticity ratio of the circulating semen in step 3) is 1.45 to 1.

55.

6. The method for preparing ultrafine aluminum hydroxide according to claim 2, characterized in that: The mass ratio of the circulating mother liquor and the industrial-grade aluminum hydroxide described in step 3) is 6:1 to 7:1.

Images