Method for reducing pH value of calcium silicate prepared from sodium silicate and lime milk

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk. The method comprises the following steps: reacting a sodium silicate aqueous solution with lime milk to generate calcium silicate slurry, adding ammonium molybdate into the slurry, simultaneously introducing carbon dioxide to adjust the pH value to 9.5-10.5, adding a compound acidic modifier, carrying out ultrasonic treatment, and finally treating the slurry to obtain calcium silicate. According to the method, through reasonable step design and raw material selection, the pH value of calcium silicate can be effectively reduced, and the problem that the pH value of a traditional method fluctuates greatly is solved. Meanwhile, the particle size distribution of the calcium silicate can be optimized by the method, so that the particles are finer and more uniform, and the specific surface area and the reaction activity of the calcium silicate are improved. In addition, the method disclosed by the invention is simple to operate, low in cost, good in economical efficiency and environmental protection property, and suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk. Background Art

[0002] Calcium silicate is an important inorganic chemical raw material, widely used in building materials, ceramics, coatings, papermaking and other fields.

[0003] In the production process of calcium silicate, pH control is a crucial link. Calcium silicate is usually produced by the reaction of sodium silicate (Na2SiO3) and lime milk (Ca(OH)2), and the calcium silicate produced in this reaction has a high pH value. Too high a pH value of calcium silicate will not only affect its performance, but may also have an adverse effect on downstream applications. For example, in cement production, if the pH value of calcium silicate is too high, it may lead to reduced adhesion of the product, thereby affecting the strength and durability of the cement. In the production of ceramics and coatings, too high a pH value will affect the dispersibility of calcium silicate and its compatibility with other ingredients, resulting in poor product stability.

[0004] Traditional methods for reducing the pH value of calcium silicate usually involve the addition of acidic substances, such as dilute acids or acidic salts, to reduce its pH value to the desired range through neutralization reactions. However, these methods have some significant shortcomings. First, the cost of using acidic substances is high, especially in large-scale production, the consumption of acid will lead to a significant increase in production costs. Secondly, the addition of acidic substances may introduce some unnecessary impurities, affecting the purity and performance of the final product. More importantly, excessive use of acidic substances may have an adverse effect on the reaction system, and may also cause the pH value of calcium silicate to be too low, affecting its stability, and may even affect the crystal structure and particle size distribution of calcium silicate, thereby affecting the physical properties of the product.

[0005] In addition, traditional pH adjustment methods are often cumbersome to operate, requiring more time and steps. Especially in large-scale production, frequent pH monitoring and adjustment will increase operational difficulty and labor costs. In addition, these methods mostly rely on manual adjustment, which is prone to operational errors and leads to unstable final product quality.

[0006] Therefore, there is an urgent need for a more efficient, economical and easy-to-operate method for reducing the pH value of calcium silicate. Summary of the invention

[0007] The purpose of the present invention is to provide a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk. The present invention has simple steps, can effectively reduce the pH value of calcium silicate slurry, and improve product quality and production efficiency.

[0008] In order to achieve the above object, the present invention provides the following technical solutions: A method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk comprises the following steps: (1) reacting a sodium silicate aqueous solution with lime milk to generate a calcium silicate slurry, filtering and washing the calcium silicate slurry to obtain a calcium silicate filter cake; (2) mixing the calcium silicate filter cake with water to obtain a slurry; (3) adding ammonium molybdate to the slurry of step (2) and simultaneously introducing carbon dioxide to perform carbon separation treatment; (4) When the pH value of the slurry drops to 9.5-10.5, add a compound acid modifier and perform ultrasonic treatment; (5) After the ultrasonic treatment is completed, the slurry is separated, washed, and dried to obtain calcium silicate.

[0009] Furthermore, in step (1), the mass concentration of the sodium silicate aqueous solution is 5-20%; the mass concentration of calcium hydroxide in the lime milk is 10-30%; the mass ratio of the sodium silicate aqueous solution to the lime milk is 1:0.8-1.5; the reaction temperature is 30-100°C, and the reaction time is 15-90 min.

[0010] Furthermore, in step (2), the mass ratio of the calcium silicate filter cake to water is 1:5-15.

[0011] Furthermore, in step (3), the mass of the ammonium molybdate is 0.1-0.3% of the slurry; and the ventilation rate of the carbon dioxide is 0.5-2.0 L / min.

[0012] In step (3), the combined action of ammonium molybdate and carbon dioxide can refine the calcium silicate crystals and adjust the acidity. Ammonium molybdate promotes the refinement of calcium silicate crystals through the interaction between its molybdenum ions and calcium ions, preventing the crystals from growing too fast, thereby avoiding excessively large particles or aggregation. At the same time, the addition of carbon dioxide further adjusts the pH value of the slurry to 9.5-10.5. This process has a regulating effect on the crystal structure and particle morphology of calcium silicate, especially by adjusting the pH value to optimize the stability of the precipitation and the dispersibility of the precipitate. In addition, the acidification effect of carbon dioxide can reduce the pH value of the slurry, reduce the solubility of silicate ions, thereby creating a more suitable precipitation environment, and indirectly promote the formation and crystallization process of calcium silicate.

[0013] Furthermore, the mass of the compound acidic modifier in step (4) is 2-20% of the calcium silicate.

[0014] Furthermore, the compound acid modifier in step (4) is a composition of aluminum sulfate 18hydrate, sodium citrate and magnesium chloride, with a mass ratio of 1:0.5-1:0.2-0.6.

[0015] Furthermore, the power of the ultrasonic treatment in step (4) is 200-500W, and the time is 5-15 minutes.

[0016] In step (4), the addition of the compound acidic modifier can further fine-tune the pH value and optimize the uniformity of the calcium silicate particles. The aluminum ions provided by aluminum sulfate 18hydrate can promote the stability and precipitation of crystals, sodium citrate can enhance the stability of the solution through its chelation effect, avoid excessive crystallization, and improve the dispersibility of particles, and the magnesium ions provided by magnesium chloride can promote the directional precipitation of calcium silicate and control the size and uniformity of the particles. The synergistic effect of the three substances in the compound acidic modifier effectively promotes the optimization of particle size, ensuring the uniformity of the precipitate and the refinement of the particles.

[0017] Ultrasonic treatment further improves the dispersibility of calcium silicate particles in the slurry and optimizes the morphology of the crystals. After ultrasonic treatment, the calcium silicate particles are finer and more uniform, which helps the subsequent separation and drying process to proceed smoothly, and ultimately obtains a higher quality calcium silicate product.

[0018] In addition, it is worth noting that the best performance is usually achieved when the pH value of calcium silicate is reduced to a range of 9-10. When the pH value of calcium silicate is higher than 10, too high a pH value may affect the dispersibility, compatibility and adhesion of calcium silicate with other components, and too low a pH value may affect the stability of calcium silicate and reduce the reactivity of calcium silicate. In the prior art, when using a strong acidic substance to reduce the pH value of calcium silicate, the pH value often drops too low. Therefore, the present invention uses carbon dioxide in the process of reducing the pH value, but carbon dioxide can easily lead to unstable pH value. When a single carbon dioxide is used to adjust the pH value, it is very likely that the pH value of the final product will deviate from the expected control range. In the present invention, ammonium molybdate is added while introducing carbon dioxide. With the help of carbon dioxide, ammonium molybdate can further stabilize and refine the pH value, avoiding fluctuations caused by relying solely on carbon dioxide. The addition of ammonium molybdate can stabilize the pH value of the system within the range of 9.5-10.5 after step (3) is completed. The addition of compound acid modifiers can help to further reduce the pH value within a controllable range, and can also further optimize the reaction environment by slowly releasing acidic components to ensure the uniformity and stability of calcium silicate particles.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are: The present invention provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk. The method can effectively reduce the pH value of calcium silicate through reasonable step design and raw material selection, and can control the pH value within the range of 9-10, thereby avoiding the problem of large pH value fluctuations in traditional methods. At the same time, the method of the present invention can also optimize the particle size distribution of calcium silicate, making its particles finer and more uniform, thereby increasing its specific surface area and reaction activity. In addition, the method of the present invention is simple to operate, low in cost, has good economy and environmental protection, and is suitable for large-scale production. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the raw materials used in the examples are common commercially available products.

[0022] Example 1 This embodiment provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, comprising the following steps: (1) respectively preparing a sodium silicate aqueous solution with a mass concentration of 10% and a lime milk with a mass concentration of 25%, mixing the sodium silicate aqueous solution and the lime milk in a mass ratio of 1:1, reacting in a water bath at 80° C. for 30 minutes, stirring continuously during the reaction to ensure that the reaction proceeds fully, and generating a calcium silicate slurry; after the reaction, filtering the calcium silicate slurry with a vacuum filtration device, collecting a filter cake, and washing the filter cake with deionized water for 4 times to reduce the sodium oxide content in the filter cake, thereby obtaining a calcium silicate filter cake; (2) mixing the obtained calcium silicate filter cake with deionized water in a mass ratio of 1:10, and stirring with a stirrer at a speed of 80 r / min for 10 min to fully mix the mixture to obtain a slurry; (3) Accurately weigh ammonium molybdate solid, the mass of which is 0.2% of the slurry, and slowly add it into the slurry while stirring at a stirring speed of 80 r / min, so that the ammonium molybdate is fully dissolved and dispersed in the slurry. At the same time, introduce carbon dioxide for carbon separation treatment at a carbon dioxide aeration rate of 1.0 L / min. During the aeration process, carbon dioxide reacts with alkaline substances such as sodium hydroxide in the slurry to gradually reduce the pH value of the slurry. When the pH value of the slurry is reduced to 10, stop aeration; (4) Aluminum sulfate 18hydrate, sodium citrate, and magnesium chloride were accurately weighed in a mass ratio of 1:0.8:0.4, and mixed to obtain a composite acid modifier, which was added to the slurry under stirring at a speed of 80 r / min for 3 minutes. The mass of the composite acid modifier was 10% of the dry calcium silicate. The slurry was then placed in an ultrasonic device for ultrasonic treatment at a power of 300 W for 10 minutes. (5) After the ultrasonic treatment is completed, the slurry is centrifuged at a centrifugal speed of 3000 r / min for 10 min to separate a solid precipitate, which is then washed twice with deionized water to remove residual acid modifiers and other impurities. The washed solid is placed in an oven and dried at 60° C. for 12 hours to obtain a calcium silicate product.

[0023] Example 2 This embodiment provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, comprising the following steps: (1) respectively preparing a sodium silicate aqueous solution with a mass concentration of 15% and a lime milk with a mass concentration of 23%, mixing the sodium silicate aqueous solution and the lime milk in a mass ratio of 1:1.1, reacting in a water bath at 40° C. for 60 minutes, stirring continuously during the reaction to ensure that the reaction proceeds fully, and generating a calcium silicate slurry; after the reaction, filtering the calcium silicate slurry with a vacuum filtration device, collecting a filter cake, and washing the filter cake with deionized water for 3 times to reduce the sodium oxide content in the filter cake, thereby obtaining a calcium silicate filter cake; (2) mixing the obtained calcium silicate filter cake with deionized water in a mass ratio of 1:10, and stirring the mixture at a speed of 300 r / min for 10 min to fully mix the mixture to obtain a slurry; (3) Accurately weigh ammonium molybdate solid, the mass of which is 0.1% of the slurry, and slowly add it into the slurry while stirring at a stirring speed of 400 r / min, so that the ammonium molybdate is fully dissolved and dispersed in the slurry, and at the same time, introduce carbon dioxide for carbon separation treatment at a carbon dioxide aeration rate of 1.0 L / min. During the aeration process, carbon dioxide reacts with alkaline substances such as sodium hydroxide in the slurry to gradually reduce the pH value of the slurry. When the pH value of the slurry is reduced to 10, stop aeration; (4) Aluminum sulfate 18hydrate, sodium citrate, and magnesium chloride were accurately weighed in a mass ratio of 1:0.5:0.5, and mixed to obtain a compound acid modifier, which was added to the slurry under stirring at a stirring speed of 500 r / min for 3 minutes. The mass of the compound acid modifier was 10% of the calcium silicate. The slurry was then placed in an ultrasonic device for ultrasonic treatment at a power of 500 W for 8 minutes. (5) After the ultrasonic treatment is completed, the slurry is centrifuged at a centrifugal speed of 3000 r / min for 10 min to separate a solid precipitate, which is then washed twice with deionized water to remove residual acid modifiers and other impurities. The washed solid is placed in an oven and dried at 60° C. for 12 hours to obtain a calcium silicate product.

[0024] Comparative Example 1 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, which differs from Example 1 in that ammonium molybdate is not added in step (3).

[0025] Comparative Example 2 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, which differs from Example 1 in that ammonium molybdate is replaced by ammonium nitrate in step (3).

[0026] Comparative Example 3 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk. The difference from Example 1 is that step (3) is replaced by adding 98% concentrated sulfuric acid to the slurry of step (2) until the pH value drops to 10.

[0027] Comparative Example 4 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, which differs from Example 1 in that the compound acid modifier in step (4) is replaced by aluminum sulfate 18hydrate.

[0028] Comparative Example 5 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, which differs from Example 1 in that the compound acid modifier in step (4) is replaced by a mixture of aluminum sulfate 18hydrate and 98% sulfuric acid in a mass ratio of 1:0.8.

[0029] Comparative Example 6 This comparative example provides a method for reducing the pH value of preparing calcium silicate from sodium silicate and lime milk, which differs from Example 1 in that: step (4) is: the mass ratio of aluminum sulfate 18hydrate, sodium citrate and magnesium chloride is 0.5:1:1.

[0030] Performance Testing The pH value, specific surface area and particle size of the calcium silicate prepared in Examples 1-2 and Comparative Examples 1-6 were tested. The results are shown in Table 1.

[0031] Table 1 Performance test results

[0032] It can be seen from the above performance test results that the calcium silicate prepared in Examples 1-2 has an ideal pH value, and the particles have a large specific surface area, a fine particle size, and a narrow distribution, which helps to enhance the reactivity of calcium silicate. In Comparative Example 1, due to the absence of ammonium molybdate, the pH control effect is poor, resulting in a high pH value of the reaction solution. At the same time, the lack of the effect of ammonium molybdate leads to poor particle dispersibility in the slurry, large particle aggregation, thereby reducing the specific surface area and uneven particle size distribution. In Comparative Example 2, ammonium nitrate replaces ammonium molybdate. The effect of ammonium nitrate in reducing pH is not as significant as ammonium molybdate, and ammonium nitrate fails to achieve the effect of significantly reducing particle aggregation and improving particle size distribution as ammonium molybdate. In Comparative Example 3, 98% concentrated sulfuric acid is used to reduce the pH value, which can quickly reduce the pH value, but it may also cause the generation of impurities of calcium sulfate. The impurities adhere to the surface of the calcium silicate particles, hindering the dispersion of the particles, thereby reducing the specific surface area, resulting in a large particle size and uneven distribution. In Comparative Example 4, a single aluminum sulfate 18hydrate is used to replace the compound acidic modifier. The acidity of aluminum sulfate 18hydrate is weak, and the pH value cannot be effectively reduced. When aluminum sulfate 18hydrate is used alone, the dispersion effect on the particles is weak, and the distribution of the particles cannot be effectively improved, resulting in a relatively low specific surface area, a large particle size and a wide distribution range. In Comparative Example 5, aluminum sulfate 18hydrate and sulfuric acid are used, and their control ability to the pH value is poor, resulting in the pH value falling too low, and the compounding of aluminum sulfate 18hydrate and sulfuric acid fails to significantly improve the dispersibility of the particles, resulting in a large particle size and a wide distribution. The mass ratio of the compound acidic modifier in Comparative Example 6 is not ideal, and the effect of the acidic modifier cannot be fully exerted, resulting in the pH value failing to be effectively controlled, and still on the high side. In addition, although the compound acidic modifier slightly improves the specific surface area, the particle dispersibility is still limited due to the failure to obtain the best control of the pH value, and the specific surface area and particle size distribution do not reach the best effect.

[0033] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, comprising the following steps: (1) reacting a sodium silicate aqueous solution with lime milk to generate a calcium silicate slurry, filtering and washing the calcium silicate slurry to obtain a calcium silicate filter cake; (2) mixing the calcium silicate filter cake with water to obtain a slurry; (3) adding ammonium molybdate to the slurry of step (2) and simultaneously introducing carbon dioxide for treatment; (4) When the pH value of the slurry drops to 9.5-10.5, add a compound acid modifier and perform ultrasonic treatment; (5) After the ultrasonic treatment is completed, the slurry is separated, washed, and dried to obtain calcium silicate.

2. The method according to claim 1, characterized in that The mass concentration of the sodium silicate aqueous solution in step (1) is 5-20%, and the mass concentration of calcium hydroxide in the lime milk is 10-30%.

3. The method according to claim 1, characterized in that The mass ratio of the sodium silicate aqueous solution to lime milk in step (1) is 1:0.8-1.

5.

4. The method according to claim 1, characterized in that: The reaction temperature in step (1) is 30-100°C and the reaction time is 15-90 minutes.

5. The method according to claim 1, characterized in that The mass ratio of the calcium silicate filter cake to water in step (2) is 1:5-15.

6. The method according to claim 1, characterized in that The mass of the ammonium molybdate in step (3) is 0.1-0.3% of the slurry.

7. The method according to claim 1, characterized in that The ventilation rate of carbon dioxide in step (3) is 0.5-2.0 L / min.

8. The method according to claim 1, characterized in that The mass of the compound acid modifier in step (4) is 2-20% of the dry calcium silicate.

9. The method according to claim 1, characterized in that: The compound acid modifier in step (4) is a composition of aluminum sulfate 18hydrate, sodium citrate and magnesium chloride, with a mass ratio of 1:0.5-1:0.2-0.

6.

10. The method according to claim 1, characterized in that The power of the ultrasonic treatment in step (4) is 200-500W, and the time is 5-15 minutes.

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