Method for preparing micron-sized magnesium hydroxide from low-grade bischofite and application of micron-sized magnesium hydroxide

Abstract

The invention discloses a method for preparing micron-sized magnesium hydroxide by utilizing low-grade bischofite and application of the micron-sized magnesium hydroxide. In the process of preparing a refined magnesium chloride solution by dissolving high-grade bischofite, low-grade bischofite (salty mud) generated by filter pressing is used as a raw material, water is added to dissolve the settled filtrate, an anionic surfactant and a chelating agent are added, the mixture and diluted ammonia water are synchronously dropwise added for co-precipitation crystallization, and the micron-sized magnesium hydroxide is obtained through suction filtration, washing and drying. Wherein the co-precipitation method is combined with SDBS and EDTA-2Na dual additives and alkali metal ions K < + > and Na < + > for cooperative regulation and control, nucleation and crystal growth are synchronously controlled, seed crystals do not need to be added, and the problems that in a traditional process, the product particle size distribution is wide, and the crystal shape is irregular are solved. Magnesium hydroxide has uniform particle size distribution (D50 = 1.60-1.80 [mu] m, D97lt, 5 [mu] m), the purity is greater than or equal to 99.3%, and the whiteness is gt; 97%. Meanwhile, solid waste magnesium resources are used as raw materials, solid waste resource utilization is achieved, and the method can be used in the high-end fields of medicine, food, flame-retardant materials and the like.

Description

Technical Field

[0001] This invention relates to the field of inorganic material preparation technology, specifically to a method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride and its application. Background Technology

[0002] During the development of magnesium resources in Qinghai Salt Lake, the dissolution of high-grade magnesium chloride (MgCl2) results in the formation of salt mud due to the enrichment of potassium and sodium salts. The washing filtrate from this mud is low-grade magnesium chloride (containing potassium). + +Na + 0.5-1.5 g / L, Ca 2+ 0.05-0.2 g / L, Fe 3+ : 10-50ppm, SiO2: 20-100ppm, Al 3+ (5-30ppm) Contains 35-40 g / L of magnesium ions. Its ammonia water comes from the brine-lime-ammonia process for producing magnesium hydroxide. Ammonia exists as an intermediate medium. Its circulation is achieved by cooling and condensing high-temperature ammonia gas during the heating, distillation and recovery process of ammonia, resulting in the separation of the gas and liquid phases of ammonia.

[0003] In traditional processes, low-grade magnesium chloride is wasted as the salt mud filter cake produced during the pressing process in the preparation of refined magnesium chloride solution, which is treated as general solid waste. Existing technologies attempt to recover magnesium ions from the salt mud washing filtrate, but the resulting magnesium hydroxide particles are large (D50 > 2μm), making it difficult to meet the demands of high-end applications. Traditional precipitation methods for preparing magnesium hydroxide suffer from problems such as large particle size (D50 > 40μm) and uneven distribution, failing to meet the requirements of high-end materials. Current technologies, by simply adjusting temperature, seed crystals, or reaction time, can only reduce D50 to 3μm, failing to overcome the 1-2μm technical bottleneck. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention utilizes the salt mud generated after pressure filtration during the preparation of refined magnesium chloride solution from high-grade hydrated magnesium chloride stone. This mud, after washing and settling, is used as raw material. A co-precipitation method is employed to simultaneously control nucleation and growth kinetics, achieving a low-cost method for preparing 1-2 μm small-particle-size, narrow-distribution magnesium hydroxide. The aim is to provide a method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride stone and its applications.

[0005] This invention protects a method for preparing micron-sized magnesium hydroxide using low-grade magnesium chloride. The method uses low-grade magnesium chloride (salt mud) produced during the preparation of refined magnesium chloride solution by dissolving high-grade magnesium chloride as raw material. After dissolving and settling the filtrate in water, anionic surfactants and chelating agents are added, and then diluted ammonia is added dropwise simultaneously for co-precipitation and crystallization. The resulting micron-sized magnesium hydroxide, with a D50 of 1.60~1.80 μm and a D97 < 5 μm, is obtained by filtration, washing, and drying. The low-grade magnesium chloride hexahydrate (salt mud) contains 40-60% magnesium chloride hexahydrate, 0.4-0.7% calcium ions, 3-5% potassium ions, 8-12% sodium ions, and 0.4-1% sulfate ions. Mg in the filtrate 2 ⁺35~40g / L, K + and Na + The sum of their contents is 0.5~1.5g / L, Ca 2+ The content is 0.05~0.2g / L, Fe 3+ Content is 10~50ppm, SiO2 content is 20~100ppm, Al 3+ The content is 5~30ppm.

[0006] Furthermore, the anionic surfactant is sodium dodecylbenzenesulfonate (SDBS); the chelating agent is disodium ethylenediaminetetraacetate (EDTA-2Na).

[0007] Furthermore, the specific preparation steps of the magnesium hydroxide are as follows: Step 1, Preparation of low-grade magnesium chloride: The salt mud produced by pressure filtration during the process of dissolving high-grade magnesium chloride to prepare refined magnesium chloride solution is the low-grade magnesium chloride, which is set aside for later use. Step 2, Low-grade magnesium chloride treatment: Dissolve the above-mentioned low-grade magnesium chloride in water and filter to remove suspended solids; the content of each element present in the filtrate after dissolution and filtration is Mg. 2 ⁺35~40g / L, K + and Na + The sum of their contents is 0.5~1.5g / L, Ca 2+ The content is 0.05~0.2g / L, Fe 3+ Content is 10~50ppm, SiO2 content is 20~100ppm, Al 3+ The content is 5~30ppm; Step 3, preparation of reaction solution: Add sodium dodecylbenzenesulfonate (SDBS) at 0.5-1% of the filtrate mass and disodium ethylenediaminetetraacetate (EDTA-2Na) at 5% of the filtrate mass to the low-grade magnesium chloride (salt mud) washing filtrate, stir until completely dissolved to obtain solution A; dilute with ammonia water to 2.5-3.0 mol / L for later use; Step 4, coprecipitation reaction: Mix solution A with diluted ammonia water at a molar ratio of Mg... 2+ Ammonia water in a ratio of 1:2 was simultaneously added dropwise to the reactor for co-precipitation reaction at a dropping rate of 0.5~1 mL / min. During the dropping process, the reactor was continuously stirred, and the temperature was controlled at 80~85℃, the pressure at 0.02~0.04 MPa, and the stirring speed at 250~300 rpm. Step 5, crystallization: After the addition is completed, maintain the temperature at 85℃ and the pressure at 0.04MPa, and continue stirring and keeping warm for 2 hours to crystallize and obtain crystallized slurry; Step 6, Post-processing: After vacuuming, the above crystallized slurry is washed with deionized water 2-4 times and dried at 100-110℃ to constant weight to obtain magnesium hydroxide with D50=1.60-1.80μm.

[0008] Furthermore, in step 4, a peristaltic pump is used for synchronous dripping.

[0009] Furthermore, in step 4, the reaction temperature is 85°C and the stirring speed is 300 rpm.

[0010] Furthermore, in step 6, the deionized water is washed three times and dried at 105°C to constant weight.

[0011] This invention also protects the application of the above method to prepare micron-sized magnesium hydroxide, which is used in the fields of medicine, food and flame retardant materials.

[0012] Compared with existing technologies, the present invention has the following beneficial effects: This invention utilizes low-grade magnesium chloride (salt mud) produced during the decomposition and filtration of high-grade magnesium chloride solution as raw material. The filtrate, after dissolution and sedimentation with water, is treated with anionic surfactants and chelating agents, and then simultaneously co-precipitated with diluted ammonia water. The resulting crystallization is achieved through filtration, washing, and drying to obtain micron-sized magnesium hydroxide. The co-precipitation method combines sodium dodecylbenzenesulfonate (SDBS) and disodium ethylenediaminetetraacetate (EDTA-2Na) as dual additives, along with alkali metal ions (K+). + and Na + This method employs synergistic regulation to simultaneously control nucleation and crystal growth, eliminating the need for seed crystals and resolving issues such as wide particle size distribution and irregular crystal shape in traditional processes. The resulting magnesium hydroxide particles exhibit precise and controllable size distribution (D50 = 1.60-1.80 μm, D97 < 5 μm), with a purity ≥ 99.3% and whiteness > 97%. Furthermore, this method utilizes solid waste magnesium resources as raw materials, achieving resource utilization and high-value-added magnesium hydroxide products, applicable to high-end fields such as pharmaceuticals, food, and flame-retardant materials. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a particle size distribution diagram of Example 1 of the present invention; Figure 3 This is a particle size distribution diagram of Example 2 of the present invention; Figure 4 This is a particle size distribution diagram of Example 3 of the present invention; Figure 5 This is a particle size distribution diagram for Comparative Example 1; Figure 6 This is a particle size distribution diagram for Comparative Example 2; Figure 7 SEM image of the product prepared in Example 1 of this invention; Figure 8 SEM image of the product prepared in Example 2 of this invention; Figure 9 SEM image of the product prepared in Example 3 of this invention; Figure 10 This is a SEM image of the product prepared in Comparative Example 1 of this invention; Figure 11 This is a SEM image of the product prepared in Comparative Example 2 of this invention. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1 A method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride. 1. Preparation of low-grade water-magnesium chloride In the process of dissolving high-grade magnesium chloride stone from western Qinghai magnesium industry to prepare refined magnesium chloride solution, the salt mud produced by pressure filtration is low-grade magnesium chloride stone, which is used for later use. In the low-grade magnesium chloride stone (salt mud), the content of magnesium chloride hexahydrate is 40~60%, the content of calcium ions is 0.4~0.7%, the content of potassium ions is 3~5%, the content of sodium ions is 8~12%, and the content of sulfate ions is 0.4~1%.

[0016] 2. Treatment of low-grade water with magnesium chloride The above-mentioned low-grade magnesium chloride was dissolved in water and filtered to remove suspended solids; the content of each element present in the filtrate after dissolution and filtration was as follows: Mg 2 ⁺38.91g / L, K + and Na + The sum of their contents is 0.5~1.5g / L, Ca 2+ The content is 0.05~0.2g / L, Fe 3+ Content is 10~50ppm, SiO2 content is 20~100ppm, Al 3+ The content is 5~30ppm; 3. Preparation of reaction solution Take 100 mL of the above filtrate, add 0.8 g sodium dodecylbenzenesulfonate (SDBS, accounting for 0.8% of the filtrate mass) and 5 g disodium ethylenediaminetetraacetate (EDTA-2Na, accounting for 5% of the filtrate mass), stir until completely dissolved to obtain solution A; dilute with ammonia water to 2.72 mol / L and set aside. 4. Coprecipitation reaction molar ratio Mg 2+ The ratio of ammonia to water is 1:2. Take 100 mL of solution A and 117.7 mL of diluted ammonia (2.72 mol / L), and add them to the reactor simultaneously using a peristaltic pump at a dropping rate of 1 mL / min. During the dropping process, the reactor is continuously stirred, and the temperature is controlled at 85℃, the pressure at 0.04 MPa, and the stirring speed at 300 rpm.

[0017] 5. Crystallization After the addition is complete, maintain the temperature at 85℃ and the pressure at 0.04MPa, and continue stirring and keeping warm for 2 hours to crystallize and obtain crystallized slurry.

[0018] 6. Post-processing After vacuuming, the crystallized slurry was washed three times with deionized water and dried at 105°C to constant weight to obtain magnesium hydroxide with D50 = 1.60~1.80μm (the test results of the product are shown in Table 1).

[0019] Table 1. Test results of the product in Example 1 Test items D50 D97 purity Chloride Whiteness result 1.601μm 4.899μm 99.35% 0.08% 97.5% Example 2 A method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride. The amount of sodium dodecylbenzenesulfonate (SDBS) added was adjusted to 0.5%, and the remaining steps were the same as in Example 1. The test results of the product are shown in Table 2.

[0020] Table 2. Test results of the product in Example 2 Test items D50 D97 purity Chloride Whiteness result 1.702μm 5.21μm 99.41% 0.07% 98.0% Example 3 A method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride. Adjust the reaction temperature to 80°C, and follow the same steps as in Example 1. The test results of the product are shown in Table 3.

[0021] Table 3. Test results of the product in Example 3 Test items D50 D97 purity Chloride Whiteness result 1.710μm 6.095μm 99.23% 0.08% 97.0% Comparative Example 1 Without the addition of SDBS and EDTA-2Na, the results were the same as in Example 1. The test results of the product are shown in Table 4.

[0022] Table 4 shows the test results of the product in Comparative Example 1. Test items D50 D97 purity Chloride Whiteness result 2.310μm 7.078μm 99.39% 0.07% 97.5% Comparative Example 2 In the coprecipitation step, the salt mud washing filtrate was added first, followed by the slow addition of ammonia water, which is non-coprecipitation. The rest is the same as in Example 1. The test results of the product are shown in Table 5.

[0023] Table 5. Test results of products in Comparative Example 2 Test items D50 D97 purity Chloride Whiteness result 3.551μm 14.20μm 99.35% 0.07% 98.0% Application Example 1 The average daily recovery of salt mud washing filtrate is 158.88 m³. 3 (Mg) 2+ Calculation based on content = 35.3 g / L: Daily recoverable Mg 2+ The mass is 158.88 × 10 3 L × 35.3 g / L = 5608.5 kg; based on the Mg content in magnesium hydroxide 2+ With a mass fraction (24.31 / 58.32) and a magnesium recovery rate of 85%, the mass of magnesium hydroxide produced is approximately 5608.5 kg × (58.32 / 24.31) × 85% ≈ 11.2 t / d. At the same time, it can save 48.8 t of water-magnesium chloride stone per day, reducing costs by 3908 yuan / d. The produced magnesium hydroxide has a particle size of 1-2 μm, meeting the UL-94V0 flame retardant requirements, and can be used in the field of flame retardant materials.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing micron-sized magnesium hydroxide using low-grade hydrated magnesium chloride, characterized in that, In the process of preparing refined magnesium chloride solution by dissolving high-grade magnesium chloride in water, low-grade magnesium chloride produced by pressure filtration is used as raw material. After dissolving and settling in water, the filtrate is mixed with anionic surfactant and chelating agent, and then co-precipitated and crystallized by simultaneous dropwise addition of diluted ammonia. After filtration, washing and drying, micron-sized magnesium hydroxide with D50 = 1.60~1.80μm and D97 < 5μm is obtained. The low-grade magnesium chloride hexahydrate contains 40-60% magnesium chloride hexahydrate, 0.4-0.7% calcium ions, 3-5% potassium ions, 8-12% sodium ions, and 0.4-1% sulfate ions. Mg in the filtrate 2 ⁺35~40g / L, K + and Na + The sum of their contents is 0.5~1.5g / L, Ca 2+ The content is 0.05~0.2g / L, Fe 3+ Content is 10~50ppm, SiO2 content is 20~100ppm, Al 3+ The content is 5~30ppm.

2. The method according to claim 1, characterized in that, The anionic surfactant is sodium dodecylbenzenesulfonate (SDBS); the chelating agent is disodium ethylenediaminetetraacetate (EDTA-2Na).

3. The method according to claim 1 or 2, characterized in that, The specific preparation steps for the magnesium hydroxide are as follows: Step 1, Preparation of low-grade magnesium chloride: The salt mud produced by pressure filtration during the process of dissolving high-grade magnesium chloride to prepare refined magnesium chloride solution is the low-grade magnesium chloride, which is set aside for later use. Step 2, Low-grade magnesium chloride treatment: Dissolve the above-mentioned low-grade magnesium chloride in water and filter to remove suspended solids; the content of each element present in the filtrate after dissolution and filtration is Mg. 2 ⁺35~40g / L, K + and Na + The sum of their contents is 0.5~1.5g / L, Ca 2+ The content is 0.05~0.2g / L, Fe 3+ Content is 10~50ppm, SiO2 content is 20~100ppm, Al 3+ The content is 5~30ppm; Step 3, preparation of reaction solution: Add sodium dodecylbenzenesulfonate (SDBS) at 0.5-1% of the filtrate mass and disodium ethylenediaminetetraacetate (EDTA-2Na) at 5% of the filtrate mass to the low-grade magnesium chloride filtrate, stir until completely dissolved to obtain solution A; dilute with ammonia water to 2.5-3.0 mol / L for later use; Step 4, coprecipitation reaction: Mix solution A with diluted ammonia water at a molar ratio of Mg... 2+ Ammonia water in a ratio of 1:2 is added dropwise to the reactor simultaneously at a rate of 0.5~1 mL / min. During the addition process, the reactor is continuously stirred while maintaining a temperature of 80~85℃, a pressure of 0.02~0.04 MPa, and a stirring speed of 250~300 rpm. Step 5, crystallization: After the addition is completed, maintain the temperature at 85℃ and the pressure at 0.04MPa, and continue stirring and keeping warm for 2 hours to crystallize and obtain crystallized slurry; Step 6, Post-processing: After vacuuming, the above crystallized slurry is washed with deionized water 2-4 times and dried at 100-110℃ to constant weight to obtain magnesium hydroxide with D50=1.60-1.80μm.

4. The method according to claim 3, characterized in that, In step 4, a peristaltic pump is used for synchronous dripping.

5. The method according to claim 4, characterized in that, In step 4, the reaction temperature is 85°C and the stirring speed is 300 rpm.

6. The method according to claim 3, characterized in that, In step 6, the deionized water is washed three times and dried at 105°C to constant weight.

7. An application of micron-sized magnesium hydroxide, characterized in that, The micron-sized magnesium hydroxide is prepared according to the method described in claim 1 or 2, and is used in the fields of medicine, food and flame retardant materials.

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