A preparation process of high-purity magnesium silicate

Abstract

The invention discloses a preparation process of high-purity magnesium silicate, which belongs to the field of preparation process of magnesium silicate; the process, including the preparation process of magnesium silicate, is as follows: S1: magnesium sulfate solution and sodium silicate solution are configured separately; S2: an appropriate amount of water is added to the reactor, and then urea is added according to the ratio of water: urea=20-30:1, and stirring and mixing is made into a urea solution; S3: the sodium silicate solution and magnesium sulfate solution in the S1 step are slowly added dropwise to the reactor of the S2 step according to the ratio of n(Si):n(Mg)=5-6:1, stirred and heated, and after the dropwise addition is completed, the reaction is carried out for aging, filtering and collecting the filter cake, and the filter cake is rinsed and dried to obtain a finished product. The process is carried out by adding the reactants dropwise to the urea solution and gradually increasing the solution pH value by heating, so that the rate of the reaction is gradually increased, thereby reducing the occurrence of coprecipitation and improving product purity; at the same time, the filtration time of the process is short and the yield is high, which enhances its applicability in large-scale manufacturing.

Description

Technical Field

[0001] The present invention relates to the field of preparation technology of magnesium silicate, and more particularly to a preparation technology of high-purity magnesium silicate. Background Art

[0002] Magnesium silicate is already a mature chemical product, widely used in medicine, food, environment and other fields, and is closely related to human life; therefore, the safety issue of magnesium silicate has become particularly important, and the most concerning safety factor is the purity of magnesium silicate.

[0003] Currently, there are two main methods for producing magnesium silicate: precipitation and hydrothermal. Because the hydrothermal method requires more demanding equipment and conditions than the precipitation method, precipitation is typically used to produce magnesium silicate. However, magnesium silicate produced by precipitation may contain certain impurities, which can affect its performance and safety, particularly in food applications (magnesium silicate used in food must strictly adhere to GB 1886.62-2015, the "National Food Safety Standard for Food Additive Magnesium Silicate") and pharmaceutical applications. Magnesium silicate's high BET surface area provides improved flowability and anti-caking properties, while also providing more adsorption sites, enhancing its anti-caking and adsorption properties in food and pharmaceutical applications.

[0004] Coprecipitation occurs when a precipitate precipitates from a solution and certain coexisting soluble substances also precipitate. This can affect the purity of the precipitate and cause it to form fine particles. These fine particles can clog the filter, making filtration difficult. The main causes of this phenomenon include surface adsorption, mixed crystals, or entrapment. Magnesium silicate, as an adsorbent with strong adsorption capacity, exhibits a more pronounced coprecipitation phenomenon, especially coprecipitation caused by entrapment. Encapsulation refers to the coprecipitation caused by the rapid precipitation rate, where impurities or mother liquor adsorbed on the precipitate surface do not have time to leave and are covered by the subsequently grown precipitate, thereby becoming encapsulated within the precipitate.

[0005] In order to solve this problem, a Chinese patent with publication number CN2021109976832 published on March 21, 2023 discloses a preparation method and application of a magnesium silicate adsorbent. This solution reduces the adsorption on the surface of magnesium silicate by washing the filter cake with water, but the effect on removing embedded and mixed crystals is general.

[0006] Therefore, it is necessary to provide a preparation process for magnesium silicate, which can solve the co-precipitation doping problem and the slow filtration speed problem caused by the precipitation method for synthesizing magnesium silicate. Summary of the Invention

[0007] In response to the problems existing in the prior art, the object of the present invention is to provide a preparation process for high-purity magnesium silicate. The technical solution is to add magnesium sulfate solution and sodium silicate solution to urea solution in a certain proportion, and heat and stir the solution to gradually increase the pH of the solution, thereby gradually accelerating the formation rate of magnesium silicate, reducing the probability of impurity co-precipitation, and thus improving the purity of magnesium silicate.

[0008] To solve the above problems, the present invention adopts the following technical solutions.

[0009] A preparation process of high-purity magnesium silicate, including the following preparation process of magnesium silicate:

[0010] S1: prepare magnesium sulfate solution with a mass concentration of 14%-25% and sodium silicate solution with a mass concentration of 33%-35% respectively;

[0011] S2: Add 200-300g of water to the reactor, then add urea in a ratio of water: urea = 20-30:1, and stir to mix to form a urea solution;

[0012] S3: Slowly add the sodium silicate solution and magnesium sulfate solution prepared in step S1 to the reactor in step S2 at a ratio of n(Si):n(Mg)=5-6:1, while stirring and heating. After the addition is completed, keep warm, age, filter, and collect the filter cake;

[0013] S4: Rinse and dry the filter cake in step S3 to obtain a finished product.

[0014] Furthermore, in step S1, the content of sodium silicate is sodium oxide ≥ 15%, and silicon dioxide ≥ 30%; the content of magnesium oxide in magnesium sulfate is 4-6%.

[0015] Furthermore, the mass concentration of the urea solution in step S2 is 3%-5%.

[0016] Furthermore, in step S3, the sodium silicate solution and the magnesium sulfate solution are added at a rate of 6.67-10 mL / min.

[0017] Furthermore, in step S3, the solution is heated until boiling.

[0018] Furthermore, the heat preservation and aging time in step S3 is 1-2 hours.

[0019] Furthermore, the filtration time in step S3 is 13-15 minutes.

[0020] Furthermore, the flushing operation in step S4 is to use a washing liquid to flush the filter cake and collect the flushing liquid; and use the washing liquid to flush until the flushing liquid is mixed with the barium chloride solution and is no longer turbid.

[0021] Furthermore, the washing liquid is deionized water.

[0022] Furthermore, in step S4, the drying temperature is 60-80° C., and the drying time is 36-72 hours.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] 1. This solution slowly drops a sodium silicate solution and a magnesium sulfate solution into a urea solution. The initial pH of the urea solution is neutral, and the reaction is not yet activated. When the urea solution is heated, the urea begins to decompose, producing ammonia and carbon dioxide. This decomposition process causes the pH of the solution to gradually increase. When the pH exceeds 7, the reaction between sodium silicate and magnesium sulfate is activated, forming magnesium silicate. The carbon dioxide generated by the decomposition of urea helps improve the mixing uniformity of the solution, effectively preventing incomplete or uneven reactions. As the heating process continues, the pH of the solution further increases, which not only promotes the decomposition of urea but also accelerates the magnesium silicate formation reaction, helping to reduce impurity contamination during the coprecipitation process. In addition, the addition rate of the magnesium silicate solution and sulfuric acid solution is controlled at 6.67-10 mL / min to ensure uniformity and efficiency of the reaction, thereby obtaining high-purity magnesium silicate.

[0025] Second, this method involves adding sodium silicate solution and magnesium sulfate solution dropwise to a urea solution at a ratio of n(Si):n(Mg) = 5-6:1. Heating and stirring are performed during the addition. This ensures a more complete reaction, thereby increasing the purity of the magnesium silicate. Furthermore, the magnesium silicate prepared by this method exhibits excellent filterability and adsorption properties. DETAILED DESCRIPTION

[0026] The present invention will be further described below:

[0027] Example 1:

[0028] Magnesium sulfate with a 5% magnesium oxide content was added to water to prepare an 18.97% magnesium sulfate solution. Sodium silicate with a 16% sodium oxide content and a 31% silicon dioxide content was added to water to prepare a 34.15% sodium silicate solution. 200g of water and 10g of urea were added to a 500ml three-necked flask and stirred until uniformly mixed, yielding a 4.76% urea solution. Subsequently, the prepared sodium silicate solution and magnesium sulfate solution were added dropwise to the urea solution at a rate of 6.67mL / min, with a ratio of n(Si):n(Mg) = 6:1. At the start of the addition, the stirrer was turned on and the heater was turned on to raise the temperature to boiling. After the addition was complete, the solution was aged at 100°C for 2 hours, filtered for 15 minutes, and the filter cake was collected. The filter cake was rinsed with deionized water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 70°C for 36 hours to obtain the finished product.

[0029] Example 2:

[0030] Magnesium sulfate with a 5.89% magnesium oxide content was added to water to prepare a 24.84% magnesium sulfate solution. Sodium silicate with a 16% sodium oxide content and a 30% silicon dioxide content was added to water to prepare a 31.3% sodium silicate solution. 250g of water and 10g of urea were added to a 500ml three-necked flask and stirred until uniformly mixed, yielding a 3.85% urea solution. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the urea solution at a ratio of n(Si):n(Mg) = 5.5:1 at a rate of 6.67mL / min. At the start of the addition, the stirrer was turned on and the heater was turned on to raise the temperature to boiling. After the addition was complete, the solution was aged at 100°C for 1 hour, filtered for 15 minutes, and the filter cake was collected. The filter cake was rinsed with deionized water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding wet magnesium silicate. The obtained wet magnesium silicate product was dried at 70° C. for 48 h to obtain a finished product.

[0031] Example 3:

[0032] Magnesium sulfate with a 4.5% magnesium oxide content was added to water to prepare a magnesium sulfate solution with a mass concentration of 22.51. Sodium silicate with a 15% sodium oxide content and a 33% silicon dioxide content was added to water to prepare a sodium silicate solution with a mass concentration of 30.69%. 300g of water and 10g of urea were added to a 500ml three-necked flask and stirred until uniformly mixed, resulting in a 3.23% urea solution. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the urea solution at a ratio of n(Si):n(Mg) = 5:1 at a rate of 6.67mL / min. At the start of the addition, the stirrer was turned on and the heater was turned on to heat the solution to boiling. After the addition was complete, the solution was aged at 100°C for 1 hour, filtered for 15 minutes, and the filter cake was collected. The filter cake was rinsed with deionized water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 80°C for 72 hours to obtain the finished product.

[0033] Example 4:

[0034] Magnesium sulfate with a 4.5% magnesium oxide content was added to water to prepare a magnesium sulfate solution with a mass concentration of 22.51. Sodium silicate with a 15% sodium oxide content and a 33% silicon dioxide content was added to water to prepare a sodium silicate solution with a mass concentration of 30.69%. 300g of water and 10g of urea were added to a 500ml three-necked flask and stirred until uniformly mixed, resulting in a 3.23% urea solution. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the urea solution at a ratio of n(Si):n(Mg) = 5:1 at a rate of 10mL / min. At the start of the addition, the stirrer was turned on and the heater was turned on to heat the solution to boiling. After the addition was complete, the solution was aged at 100°C for 1 hour, filtered for 15 minutes, and the filter cake was collected. The filter cake was rinsed with deionized water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 80°C for 72 hours to obtain the finished product.

[0035] Example 5:

[0036] Magnesium sulfate with a 4.5% magnesium oxide content was added to water to prepare a magnesium sulfate solution with a mass concentration of 22.51. Sodium silicate with a 15% sodium oxide content and a 33% silicon dioxide content was added to water to prepare a sodium silicate solution with a mass concentration of 30.69%. 300g of water and 10g of urea were added to a 500ml three-necked flask and stirred until uniformly mixed, resulting in a 3.23% urea solution. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the urea solution at a ratio of n(Si):n(Mg) = 5:1 at a rate of 8.52mL / min. At the start of the addition, the stirrer was turned on and the heater was turned on to heat the solution to boiling. After the addition was complete, the solution was aged at 100°C for 1 hour, filtered for 15 minutes, and the filter cake was collected. The filter cake was rinsed with deionized water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 80°C for 72 hours to obtain the finished product.

[0037] Comparative Example 1:

[0038] Magnesium sulfate with a 5% magnesium oxide content was added to water to prepare a magnesium sulfate solution with a mass concentration of 18.97%. Sodium silicate with a 16% sodium oxide content and a 31% silicon dioxide content was added to water to prepare a sodium silicate solution with a mass concentration of 34.15%. 100 g of water was added to a 500 ml three-necked flask. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the water at a ratio of n(Si):n(Mg) = 5:1 at a rate of 6.67 mL / min. At the start of the addition, the stirrer was turned on and 1 M sodium hydroxide was added dropwise. After the addition was complete, the mixture was incubated at 100°C for 2 hours, filtered for 33 minutes, and the filter cake was collected. The filter cake was rinsed with water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 80°C for 72 hours to obtain the finished product.

[0039] Comparative Example 2:

[0040] Magnesium sulfate with a 5% magnesium oxide content was added to water to prepare a 24.84% magnesium sulfate solution. Sodium silicate with a 16% sodium oxide content and a 30% silicon dioxide content was added to water to prepare a 31.3% sodium silicate solution. 50 g of water was added to a 500 ml three-necked flask. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the water at a rate of 6.67 mL / min in a ratio of n(Si):n(Mg) = 5.5:1. At the start of the addition, the stirrer was turned on and 1 M sodium hydroxide was added dropwise. After the addition was complete, the mixture was incubated at 100°C for 1 hour, filtered for 40 minutes, and the filter cake was collected. The filter cake was rinsed with water until the wash solution, mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 70°C for 48 hours to obtain the finished product.

[0041] Comparative Example 3:

[0042] Magnesium sulfate with a 5% magnesium oxide content was added to water to prepare a 22.3% magnesium sulfate solution. Sodium silicate with a 16% sodium oxide content and a 30% silicon dioxide content was added to water to prepare a 30.12% sodium silicate solution. 100g of water and 0.4g of sodium hydroxide were added to a 500ml three-necked flask and stirred to prepare a 0.4% sodium hydroxide solution. Subsequently, the prepared sodium silicate and magnesium sulfate were added dropwise to the sodium hydroxide solution at a ratio of n(Si):n(Mg) = 5.5:1 at a rate of 6.67mL / min. The stirrer was turned on at the beginning of the addition. After the addition was complete, the mixture was incubated at 100°C for 1 hour, filtered for 33 minutes, and the filter cake was collected. The filter cake was rinsed with water until the wash solution, when mixed with the barium chloride solution, was no longer turbid, yielding a wet magnesium silicate product. The resulting wet magnesium silicate product was dried at 60°C for 36 hours to obtain the finished product.

[0043] Comparative Example 4

[0044] To a 500ml three-necked flask, add 50ml of water, 0.4g (1.6mmol) of Mg(NO₃)₂·6H₂O, and urea, and stir to obtain a mixed solution. Add 100g of magnesium sulfate to the mixed solution, and sonicate for 20 minutes. The sonicated solution and solids are then transferred to a 0.7ml hydrothermal reactor, heated to 100°C for 5 hours, filtered, and the solids collected. A certain amount of sodium silicate is weighed to prepare a 0.7mmol sodium silicate solution with a mass concentration of 27%. The sodium silicate solution and solids are placed in a 70ml hydrothermal reactor, heated to 160°C for 8 hours, cooled to room temperature, washed several times with deionized water, and dried at 80°C for 30 minutes to obtain the finished product.

[0045] Experimental Example 1

[0046] The magnesium silicate prepared in the examples and comparative examples of the present invention was analyzed for magnesium silicate content, and the specific analysis results are shown in Table 1.

[0047] Table 1 Analysis results of the content of magnesium silicate prepared in Examples and Comparative Examples

[0048] ;

[0049] As shown in Examples 1-3 and Comparative Examples 1-3, adding sodium silicate and magnesium sulfate dropwise to a urea solution (water:urea = 20-30:1) at a ratio of n(Si):n(Mg) = 5-6:1 significantly reduces the time required for the filtration step and effectively controls other impurities in the magnesium silicate to below 0.6%, thereby improving the overall purity of the product. Conventional methods generally contain impurities of 3-5% or even higher. Therefore, this method can effectively reduce impurities in the generated magnesium silicate. Furthermore, this solution is simple to operate, has low energy consumption, and offers high yields in industrial production.

[0050] It can be seen from Examples 1 to 3 and Comparative Example 4 that the magnesium silicate prepared by the method provided in this scheme has a lower impurity content and a higher magnesium oxide content than the magnesium silicate prepared by the hydrothermal method in Comparative Example 4. Since the adsorption of magnesium silicate depends on the magnesium oxide content, when the magnesium oxide content of magnesium silicate is high, the adsorption effect of magnesium silicate is better. Therefore, the adsorption effect of magnesium silicate prepared in Comparative Example 4 is significantly lower than that of magnesium silicate prepared in Example.

[0051] From Example 1, Example 4, and Example 5, it can be seen that when the droplet acceleration rate is 6.67 mL / min, the impurity content of magnesium silicate is the lowest and the magnesium oxide content is the highest; when the droplet acceleration rate is lower than 6.67 mL / min or higher than 10 mL / min, the impurity content of magnesium silicate will significantly increase, and the magnesium oxide content in magnesium silicate will significantly decrease, thereby affecting the adsorption effect of magnesium silicate.

[0052] Experimental Example 2:

[0053] The magnesium silicate prepared in the examples of the present invention and the comparative examples was subjected to performance tests, and the specific results are shown in Table 2:

[0054] Table 2 Performance test results of magnesium silicate prepared in Examples and Comparative Examples

[0055] ;

[0056] As shown in Table 2, the process provided by the present invention not only significantly improves product yield, reaching over 93%, but also increases the BET specific surface area of ​​magnesium silicate, thereby enhancing the adsorption efficiency of the magnesium silicate particles. Furthermore, this method shortens filtration time during the preparation process, making this process applicable to industrial production.

[0057] It can be seen from Examples 3 to 5 that: when other conditions remain unchanged, it can be seen from Example 3 that when the dropping rate is 6.67 mL / min, the impurity content of magnesium silicate is 0.50%, and the BET specific surface area is 323.00 m² / g; it can be seen from Example 5 that when the dropping rate is 8.52 mL / min, the impurity content of magnesium silicate is 0.49%, and the BET specific surface area is 357.00 m² / g; it can be seen from Example 4 that when the dropping rate is 10 mL / min, the impurity content of magnesium silicate is 0.53%, and the BET specific surface area is 313.00 m² / g; therefore, the optimal dropping rate is 6.67 mL / min.

Claims

1. A process for preparing high-purity magnesium silicate, characterized in that: The preparation process including magnesium silicate is as follows: S1: prepare magnesium sulfate solution with a mass concentration of 14%-25% and sodium silicate solution with a mass concentration of 33%-35% respectively; S2: Add 200-300g of water to the reactor, then add urea in a ratio of water: urea = 20-30:1, and stir to mix to form a urea solution; S3: Slowly add the sodium silicate solution and magnesium sulfate solution prepared in step S1 to the reactor in step S2 at a ratio of n(Si):n(Mg)=5-6:1 while stirring and heating. After the addition is completed, keep warm, age, filter, and collect the filter cake; the sodium silicate solution and magnesium sulfate solution are added at a rate of 6.67-10 mL / min; S4: Rinse and dry the filter cake in step S3 to obtain a finished product.

2. A process for preparing high-purity magnesium silicate according to claim 1, characterized in that: In step S1, the content of sodium silicate is sodium oxide ≥ 15%, and silicon dioxide ≥ 30%; the content of magnesium oxide in magnesium sulfate is 4-6%.

3. A process for preparing high-purity magnesium silicate according to claim 1, characterized in that: In the step S3, the solution is heated until boiling.

4. A process for preparing high-purity magnesium silicate according to claim 1, characterized in that: The heat preservation and aging time in the step S3 is 1-2 hours.

5. The process for preparing high-purity magnesium silicate according to claim 1, wherein: The filtration time in the S3 step is 13-15 minutes.

6. A process for preparing high-purity magnesium silicate according to claim 1, characterized in that: The rinsing operation in step S4 is to rinse the filter cake with a washing liquid and collect the washed liquid; and to rinse with the washing liquid until the washed liquid is mixed with the barium chloride solution and is no longer turbid.

7. A process for preparing high-purity magnesium silicate according to claim 6, characterized in that: The washing liquid is deionized water.

8. The process for preparing high-purity magnesium silicate according to claim 1, wherein: In step S4, the drying temperature is 60-80° C. and the drying time is 36-72 hours.