A method for reducing the ph of sodium silicate and milk of lime to produce calcium silicate

Abstract

The application 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. The method comprises the following steps: reacting sodium silicate aqueous solution with lime milk to generate calcium silicate slurry, adding ammonium molybdate into the slurry, adjusting the pH value to 9.5-10.5 by introducing carbon dioxide, adding a compound acid modifier, performing ultrasonic treatment, and finally obtaining calcium silicate by treating the slurry. The method can effectively reduce the pH value of calcium silicate by reasonable step design and raw material selection, and avoids the problem of large pH value fluctuation in the traditional method. Meanwhile, the method can also optimize the particle size distribution of calcium silicate, so that the particles are finer and more uniform, thereby improving the specific surface area and reaction activity. In addition, the method is simple in operation, low in cost, good in economy and environmental protection, and suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical technology, and specifically relates to a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk. BACKGROUND

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

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

[0005] In addition, traditional pH value adjustment methods are often tedious to operate, requiring more time and steps. Especially in large-scale production, frequent pH value monitoring and adjustment will increase the difficulty of operation and labor cost. In addition, these methods rely on manual adjustment, which is prone to operation errors, resulting in unstable quality of the final product.

[0006] Therefore, there is an urgent need for a more efficient, economical and simple method for reducing the pH value of calcium silicate. SUMMARY

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

[0008] To achieve the above object, the present application provides the following technical solutions:

[0009] A method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, comprising the following steps:

[0010] (1) reacting the aqueous sodium silicate solution with the lime milk to generate calcium silicate slurry, filtering and washing the calcium silicate slurry to obtain calcium silicate filter cake;

[0011] (2) mixing the calcium silicate filter cake with water to obtain slurry;

[0012] (3) adding ammonium molybdate to the slurry of step (2) and simultaneously introducing carbon dioxide for carbon separation treatment;

[0013] (4) when the pH value of the slurry is reduced to 9.5-10.5, adding a compounded acidic modifier and performing ultrasonic treatment;

[0014] (5) after the ultrasonic treatment is completed, separating, washing and drying the slurry to obtain calcium silicate.

[0015] Further, the mass concentration of the aqueous sodium silicate solution in step (1) is 5-20%; the mass concentration of calcium hydroxide in the lime milk is 10-30%; the mass ratio of the aqueous sodium silicate solution to the lime milk is 1:0.8-1.5; and the reaction temperature is 30-100℃ and the reaction time is 15-90min.

[0016] Further, the mass ratio of the calcium silicate filter cake to water in step (2) is 1:5-15.

[0017] Further, the mass of the ammonium molybdate in step (3) is 0.1-0.3% of the slurry; and the aeration rate of the carbon dioxide is 0.5-2.0L / min.

[0018] In step (3), the ammonium molybdate and the carbon dioxide jointly refine the calcium silicate crystals and adjust the acidity. The ammonium molybdate promotes the refinement of the calcium silicate crystals through the interaction between its molybdenum ions and calcium ions, prevents the crystals from growing too fast, and thus avoids the particles from being too large or aggregated. At the same time, the addition of the carbon dioxide further adjusts the pH value of the slurry to 9.5-10.5. This process has an adjusting effect on the crystal structure and particle morphology of the 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 of the carbon dioxide can reduce the pH value of the slurry, reduce the solubility of silicate ions, and thus create a more suitable precipitation environment, indirectly promoting the formation and crystallization process of the calcium silicate.

[0019] Further, the mass of the compounded acidic modifier in step (4) is 2-20% of the calcium silicate.

[0020] Further, the complex acid modifier in step (4) is a combination of aluminum sulfate octadecahydrate, sodium citrate and magnesium chloride, with a mass ratio of 1:0.5-1:0.2-0.6.

[0021] Further, the power of the ultrasonic treatment in step (4) is 200-500 W, and the time is 5-15 minutes.

[0022] In step (4), the addition of the complex acid modifier can further finely adjust the pH value and optimize the uniformity of the calcium silicate particles. The aluminum ions provided by the aluminum sulfate octadecahydrate can promote the stability and precipitation of the crystals, the sodium citrate can enhance the stability of the solution through its chelating effect, avoid excessive crystallization, and improve the particle dispersibility, and the magnesium ions provided by the magnesium chloride can promote the directional precipitation of the calcium silicate, and can control the size and uniformity of the particles. The synergistic effect of the three substances in the complex acid modifier effectively promotes the optimization of the particle size, and ensures the uniformity of the precipitate and the miniaturization of the particles.

[0023] The ultrasonic treatment further improves the dispersibility of the calcium silicate particles in the slurry and optimizes the morphology of the crystals. After ultrasonic treatment, the calcium silicate particles are more fine and uniform, which helps the subsequent separation and drying process to proceed smoothly, and ultimately obtains a higher quality calcium silicate product.

[0024] In addition, it is worth noting that the pH value of the calcium silicate in the range of 9-10 generally has the best performance. When the pH value of the calcium silicate is higher than 10, the excessively high pH value may affect the dispersibility of the calcium silicate and the compatibility and adhesion with other ingredients, and when the pH value is too low, the stability of the calcium silicate may be affected and the reactivity of the calcium silicate may be reduced. The prior art often causes the pH value to be too low when using strong acidic substances to reduce the pH value of the calcium silicate. Therefore, the present application uses carbon dioxide in the process of reducing the pH value, but carbon dioxide adjusting the pH value is prone to cause unstable pH value, and using single carbon dioxide to adjust the pH value is extremely likely to cause the pH value of the final product to deviate from the expected control range. The present application introduces ammonium molybdate while introducing carbon dioxide, which can further stabilize and refine the pH value with the help of carbon dioxide, avoiding the fluctuation caused by relying only on carbon dioxide. The addition of ammonium molybdate can make the pH value of the system stable in the range of 9.5-10.5 after step (3) is completed. The addition of the complex acid modifier helps to further reduce the pH value within the controllable range, and also further optimizes the reaction environment by slowly releasing acidic components, ensuring the uniformity and stability of the calcium silicate particles.

[0025] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0026] The application provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which can effectively reduce the pH value of calcium silicate and control the pH value in the range of 9-10 by reasonable step design and raw material selection, thereby avoiding the problem of large pH value fluctuation in the traditional method. Meanwhile, the method can also optimize the particle size distribution of calcium silicate, so that the particles are finer and more uniform, thereby improving the specific surface area and reactivity. In addition, the method is simple in operation, low in cost, good in economy and environmental protection, and suitable for large-scale production. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0028] The raw materials used in the embodiments are all ordinary commercially available products unless otherwise specified.

[0029] Embodiment 1

[0030] The embodiment provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which comprises the following steps:

[0031] (1) Prepare a 10% sodium silicate aqueous solution and a 25% lime milk respectively, mix the sodium silicate aqueous solution and the lime milk according to a mass ratio of 1:1, and perform reaction in a water bath at 80℃, the reaction time is 30 min, and the reaction is continuously stirred to ensure that the reaction is fully carried out, so as to generate a calcium silicate slurry; after the reaction is completed, the calcium silicate slurry is filtered by using a vacuum filter device, the filter cake is collected, and the filter cake is washed with deionized water for 4 times to reduce the content of sodium oxide in the filter cake, so as to obtain a calcium silicate filter cake;

[0032] (2) Mix the obtained calcium silicate filter cake and deionized water according to a mass ratio of 1:10, and use a stirrer to stir at a speed of 80 r / min for 10 min to fully mix them, so as to obtain a slurry;

[0033] (3) Accurately weigh the ammonium molybdate solid, the mass of the ammonium molybdate is 0.2% of the slurry, slowly add the ammonium molybdate into the slurry in a stirring state, the stirring speed is 80 r / min, so that the ammonium molybdate is fully dissolved and dispersed in the slurry, and carbon dioxide is introduced for carbon separation treatment at the same time, the aeration rate of the carbon dioxide is 1.0 L / min, during the aeration process, the carbon dioxide reacts with alkaline substances such as sodium hydroxide in the slurry to gradually reduce the pH value of the slurry, and when the pH value of the slurry is reduced to 10, the aeration is stopped;

[0034] (4) According to the mass ratio 1:0.8:0.4, accurately take aluminum sulfate octadecahydrate, sodium citrate and magnesium chloride respectively, mix to obtain a compound acid modifier, and add the compound acid modifier to the slurry under stirring at a stirring speed of 80 r / min for 3 min, the mass of the compound acid modifier being 10% of the calcium silicate dry basis, and then place the slurry in an ultrasonic device for ultrasonic treatment at a power of 300 W for 10 min;

[0035] (5) After ultrasonic treatment, centrifugal separation is performed on the slurry at a centrifugal speed of 3000 r / min for 10 min to obtain a solid precipitate, which is then washed with deionized water for 2 times to remove residual acid modifier and other impurities, and the washed solid is placed in an oven for drying at 60°C for 12 h to obtain a calcium silicate product.

[0036] Example 2

[0037] The present embodiment provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, comprising the following steps:

[0038] (1) Prepare a 15% sodium silicate aqueous solution and a 23% lime milk respectively, mix the sodium silicate aqueous solution and the lime milk according to a mass ratio of 1:1.1, and perform reaction in a water bath at 40°C for 60 min, constantly stirring during the reaction to ensure full reaction, to generate a calcium silicate slurry; after the reaction, filter the calcium silicate slurry using a vacuum filter device, collect the filter cake, and wash the filter cake with deionized water for 3 times to reduce the sodium oxide content in the filter cake, to obtain a calcium silicate filter cake;

[0039] (2) Mix the obtained calcium silicate filter cake with deionized water according to a mass ratio of 1:10, and use a stirrer to stir at a speed of 300 r / min for 10 min to fully mix, to obtain a slurry;

[0040] (3) Accurately take ammonium molybdate solid, the mass of ammonium molybdate being 0.1% of the slurry, slowly add the ammonium molybdate to the slurry under 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, carbon dioxide is introduced for carbon separation treatment, the aeration rate of carbon dioxide being 1.0 L / min, during the aeration process, the carbon dioxide reacts with alkaline substances such as sodium hydroxide in the slurry to gradually reduce the pH value of the slurry, and when the pH value of the slurry is reduced to 10, stop aeration;

[0041] (4) Accurately take aluminum sulfate octadecahydrate, sodium citrate, and magnesium chloride in a mass ratio of 1:0.5:0.5, mix to obtain a compound acidic modifier, and add the compound acidic modifier to the slurry under stirring at a stirring speed of 500 r / min for 3 min, the mass of the compound acidic modifier being 10% of the calcium silicate, and then perform ultrasonic treatment on the slurry in an ultrasonic device, the power being set to 500 W and the time being 8 min;

[0042] (5) After the ultrasonic treatment is completed, perform centrifugal separation on the slurry at a centrifugal speed of 3000 r / min for 10 min, separate to obtain a solid precipitate, wash the solid precipitate with deionized water for 2 times to remove residual acidic modifier and other impurities, and place the washed solid in an oven for drying at 60°C for 12 hours to obtain a calcium silicate product.

[0043] Comparative Example 1

[0044] This comparative example provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which is different from Example 1 in that step (3) does not add ammonium molybdate.

[0045] Comparative Example 2

[0046] This comparative example provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which is different from Example 1 in that step (3) replaces ammonium molybdate with ammonium nitrate.

[0047] Comparative Example 3

[0048] This comparative example provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which is different from Example 1 in that step (3) is replaced by adding 98% concentrated sulfuric acid to the slurry of step (2) until the pH value is reduced to 10.

[0049] Comparative Example 4

[0050] This comparative example provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which is different from Example 1 in that the compound acidic modifier in step (4) is replaced by aluminum sulfate octadecahydrate.

[0051] Comparative Example 5

[0052] This comparative example provides a method for reducing the pH value of calcium silicate prepared from sodium silicate and lime milk, which is different from Example 1 in that the compound acidic modifier in step (4) is replaced by a mixture of aluminum sulfate octadecahydrate and 98% sulfuric acid in a mass ratio of 1:0.8.

[0053] Comparative Example 6

[0054] The comparative example provides a method for reducing the pH value of sodium silicate and lime milk to prepare calcium silicate, which is different from example 1 in that step (4) is: the mass ratio of the octadecahydrate aluminum sulfate, sodium citrate, and magnesium chloride is 0.5:1:1.

[0055] Performance test

[0056] The calcium silicate prepared in examples 1-2 and comparative examples 1-6 was tested for pH value, specific surface area, and particle size, and the results are shown in Table 1.

[0057] Table 1 Performance test results

[0058]

[0059] From the above performance test results, it can be seen that the calcium silicate prepared in examples 1-2 has an ideal pH value, a larger specific surface area of the particles, a finer particle size, and a narrower distribution, which helps to enhance the reactivity of the calcium silicate. Comparative example 1 has a poor pH value control effect due to the absence of ammonium molybdate, resulting in a higher pH value of the reaction solution. In addition, the absence of ammonium molybdate results in poor dispersion of the particles in the slurry and larger particle aggregation, thereby reducing the specific surface area and uneven particle size distribution. In comparative example 2, ammonium nitrate replaces ammonium molybdate, and ammonium nitrate is less effective than ammonium molybdate in reducing pH. In addition, ammonium nitrate fails to significantly reduce particle aggregation and improve particle size distribution as effectively 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 may also generate calcium sulfate impurities, which adhere to the surface of the calcium silicate particles, hindering the dispersion of the particles, thereby reducing the specific surface area, resulting in a larger particle size, and uneven distribution. In comparative example 4, a single octadecahydrate aluminum sulfate is used to replace the complex acid modifier. The acidity of octadecahydrate aluminum sulfate is weak, which cannot effectively reduce the pH value. When octadecahydrate aluminum sulfate is used alone, the dispersion effect on the particles is weak, and the particle distribution is not effectively improved, resulting in a relatively low specific surface area, a large particle size, and a wide distribution range. In comparative example 5, octadecahydrate aluminum sulfate and sulfuric acid are used, which have poor pH value control ability, resulting in a pH value that is too low. In addition, the complex of octadecahydrate aluminum sulfate and sulfuric acid fails to significantly improve the dispersion of the particles, resulting in a large particle size and a wide distribution. In comparative example 6, the mass ratio of the complex acid modifier is not ideal, which fails to fully exert the effect of the acid modifier, resulting in an ineffective control of the pH value, which is still high. In addition, although the complex acid modifier slightly improves the specific surface area, the dispersion of the particles is still limited due to the suboptimal control of the pH value, and the specific surface area and particle size distribution do not achieve the best effect.

[0060] The above is the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles described in the present application, can also make several improvements and refinements, these improvements and refinements should also be considered as the scope of protection of the present application.

Claims

1. A method for lowering the pH value of sodium silicate and lime milk in the preparation of calcium silicate, comprising the following steps: (1) React sodium silicate aqueous solution with lime milk to generate calcium silicate slurry. Filter and wash the calcium silicate slurry to obtain calcium silicate filter cake. (2) Mix the calcium silicate filter cake with water to obtain a slurry; (3) Add ammonium molybdate to the slurry from step (2) and simultaneously pass carbon dioxide through for treatment; the mass of ammonium molybdate is 0.1-0.3% of the slurry. (4) When the pH value of the slurry drops to 9.5-10.5, add the compound acid modifier and perform ultrasonic treatment; the mass of the compound acid modifier is 2-20% of the dry basis of calcium silicate, and the compound acid modifier is a combination of aluminum sulfate octadecyl hydrate, sodium citrate and magnesium chloride, with a mass ratio of 1:0.5-1:0.2-0.6; (5) After ultrasonic treatment, the slurry is separated, washed and dried to obtain calcium silicate.

2. The method according to claim 1, characterized in that, The sodium silicate aqueous solution in step (1) has a mass concentration of 5-20%, and the calcium hydroxide in the lime milk has a mass concentration of 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 in step (1) is carried out at a temperature of 30-100℃ for 15-90 min.

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

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

7. The method according to claim 1, characterized in that, The ultrasonic treatment in step (4) has a power of 200-500W and a duration of 5-15 minutes.

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