Silica manufacturing method

Abstract

To provide a method for producing silica, which can reduce the time required for filtering silica. In the method for producing silica, a sodium silicate aqueous solution having a silica concentration of 24 wt% or more and 32 wt% or less is added dropwise to an aqueous solution containing sulfuric acid, and the silica produced in the aqueous solution containing sulfuric acid is mixed with a solution having an air permeability of 4100 cm 3 / cm 2 · min or more 7800cm 3 / cm 2 The aqueous solution containing sulfuric acid is extracted by filtration using a filter cloth with a flow rate of 1000 kJ / min or less. The temperature of the aqueous solution containing sulfuric acid is 60°C or higher. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt% or higher and 60 wt% or lower. The molar ratio of sodium silicate in the aqueous sodium silicate solution is 2 or higher and 4 or lower. The amount of the aqueous sodium silicate solution added is within a range such that the neutralization rate of sulfuric acid is 40% or lower.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing silica. [Background technology]

[0002] Recently, high-purity silica has been widely used in the fields of catalyst materials, optical materials, electronic materials, semiconductor materials, etc. A method for producing silica is known in which an aqueous solution of sodium silicate is added dropwise to an aqueous solution containing sulfuric acid (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6114955 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacturing method described in Patent Document 1, silica produced in an aqueous solution containing sulfuric acid is filtered and extracted using a centrifuge equipped with a filter cloth. The inventors found that when the manufacturing method described in Patent Document 1 is carried out using an aqueous sodium silicate solution with a silica concentration of 24 wt% to 32 wt%, filtration takes a long time.

[0005] In one aspect of the present disclosure, it is preferable to provide a method for producing silica that can reduce the time required for filtering silica. [Means for solving the problem]

[0006] One aspect of the present disclosure is a method for producing silica by adding a sodium silicate aqueous solution having a silica concentration of 24 wt % or more and 32 wt % or less dropwise to an aqueous solution containing sulfuric acid, and then subjecting the silica produced in the aqueous solution containing sulfuric acid to a process for producing silica by adding a sodium silicate aqueous solution having an air permeability of 4100 cm 3 / cm 2 · min or more 7800cm 3 / cm 2This method involves filtering silica using a filter cloth with a solvent content of 1.5-1.5 min or less.

[0007] In the method for producing silica, the temperature of the aqueous solution containing sulfuric acid is 60°C or higher, the concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt% or higher and 60 wt% or lower, the molar ratio of sodium silicate in the aqueous sodium silicate solution is 2 or higher and 4 or lower, and the amount of the aqueous sodium silicate solution added is within a range such that the neutralization rate of sulfuric acid is 40% or lower.

[0008] According to the method for producing silica of the present disclosure, the time required for filtering silica can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] Fig. 1A is a schematic diagram illustrating the dropwise addition of an aqueous solution of sodium silicate to an aqueous solution containing sulfuric acid, and Fig. 2B is a schematic diagram illustrating the continuous flow of the aqueous solution of sodium silicate to an aqueous solution containing sulfuric acid. DETAILED DESCRIPTION OF THE INVENTION

[0010] Exemplary embodiments of the present disclosure will now be described with reference to the drawings. First Embodiment 1. Silica manufacturing method (1) Basic structure of silica manufacturing method In the method for producing silica disclosed herein, a sodium silicate aqueous solution having a silica concentration of 24 wt% or more and 32 wt% or less is added dropwise to an aqueous solution containing sulfuric acid. Thereafter, the silica produced in the aqueous solution containing sulfuric acid is subjected to a filtration process using a solution having an air permeability of 4100 cm 3 / cm 2 · min or more 7800cm 3 / cm 2 The solution is extracted by filtration using a filter cloth with a speed of 1000 kJ / min or less.

[0011] The term "droplet-like addition" refers to the case where, when an aqueous solution of sodium silicate 3 is added to an aqueous solution containing sulfuric acid 1, each drop of the aqueous solution of sodium silicate 3 has a form independent from the other drops, as shown schematically in Fig. 1A. On the other hand, as an example of a case where the aqueous solution of sodium silicate 3 is added to an aqueous solution containing sulfuric acid 1, a continuous flow of the aqueous solution of sodium silicate 3 is generated, as shown schematically in Fig. 1B.

[0012] When the aqueous sodium silicate solution is dropped, it is preferable to stir the aqueous solution containing sulfuric acid. By stirring, the content of impurities in the produced silica can be further reduced. When the silica produced in the aqueous solution containing sulfuric acid is extracted, filtration can be performed using a centrifuge equipped with a filter cloth. In this case, the content of impurities in the produced silica can be further reduced.

[0013] Furthermore, when a centrifuge equipped with a filter cloth is used, even if the silica before extraction is in the form of, for example, a shell-like mass, it can be made into a powder form (for example, a powder state with a particle size of about 0.1 to 2 mm), which makes it easier to transport and use the silica afterwards.

[0014] Furthermore, when the silica produced in the aqueous solution containing sulfuric acid is extracted, suction filtration can be performed using a filter cloth. The high-purity silica produced by the production method of the present disclosure can be used, for example, to produce high-purity sodium silicate.

[0015] (2) Aqueous solutions containing sulfuric acid The aqueous solution containing sulfuric acid may consist of sulfuric acid and water, or may further contain other components. Examples of other components include a chelating agent and hydrogen peroxide. When the aqueous solution containing sulfuric acid contains a chelating agent or hydrogen peroxide, the content of impurities in the produced silica can be further reduced. Examples of impurities include Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Ti, Zn, and Zr.

[0016] Examples of chelating agents include organic acids with chelating properties, such as citric acid, fumaric acid, and malic acid. Other examples of chelating agents include DNA (deoxyribonucleic acid) and EDTA (ethylenediaminetetraacetic acid).

[0017] The concentration of the chelating agent in the aqueous solution containing sulfuric acid is preferably 1 wt % or more. When the concentration of the chelating agent is 1 wt % or more, the content of impurities in the produced silica can be further reduced.

[0018] The concentration of hydrogen peroxide in the aqueous solution containing sulfuric acid is preferably 1 wt % or more. When the concentration of hydrogen peroxide is 1 wt % or more, the content of impurities in the produced silica can be further reduced.

[0019] Furthermore, when the aqueous solution containing sulfuric acid contains both a chelating agent and hydrogen peroxide, the chelating effect of impurities in sodium silicate is further enhanced, and the content of impurities in the produced silica can be further reduced.

[0020] The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is preferably 31 wt% or more and 60 wt% or less. When the concentration of sulfuric acid in the aqueous solution containing sulfuric acid is within this concentration range, the content of impurities in the produced silica can be further reduced.

[0021] Furthermore, when the sulfuric acid concentration in the sulfuric acid-containing aqueous solution is 31 wt% or more, the produced silica tends to form lumps (for example, lumps of about 5 mm in size), making subsequent handling of the silica easier. Furthermore, when the sulfuric acid concentration in the sulfuric acid-containing aqueous solution is 60 wt% or less, the silica yield per reaction volume improves and corrosion of the production equipment can be reduced.

[0022] The temperature of the aqueous solution containing sulfuric acid is preferably 60° C. or higher, and more preferably 70° C. or higher. When the temperature of the aqueous solution containing sulfuric acid is 60° C. or higher, the content of impurities in the produced silica can be further reduced.

[0023] (3) Sodium silicate solution The aqueous sodium silicate solution may consist of sodium silicate and water, or may further contain other components. The silica concentration in the aqueous sodium silicate solution is 24 wt% or more and 32 wt% or less. The silica concentration in the aqueous sodium silicate solution is, for example, 25 wt% or more and 27 wt% or less, e.g., 25 wt% or more and 26 wt% or less. When the silica concentration in the aqueous sodium silicate solution is within this concentration range, the produced silica tends to form clumps (e.g., clumps about 5 mm in size), improving water washability and filterability, thereby further reducing the impurity content in the produced silica.

[0024] The molar ratio of sodium silicate in the aqueous sodium silicate solution is preferably 2 or more and 4 or less. When the molar ratio of sodium silicate in the aqueous sodium silicate solution is within this range, the impurity content in the produced silica can be further reduced. Here, the molar ratio of sodium silicate is n when sodium silicate is expressed as Na2O·nSiO2.

[0025] The amount of sodium silicate aqueous solution to be dropped is preferably in a range in which the neutralization rate R of sulfuric acid is 40% or less. Here, the neutralization rate R (unit: %) is expressed by the following formula (1). Formula (1) R=((PQ) / P)×100 In formula (1), P is the proton concentration (mol / L) in the aqueous solution containing sulfuric acid before the sodium silicate aqueous solution is added dropwise. In formula (1), Q is the proton concentration (mol / L) in the aqueous solution containing sulfuric acid after all the sodium silicate aqueous solution has been added dropwise.

[0026] When the neutralization rate R of sulfuric acid is 40% or less, the impurity content in the produced silica can be further reduced. It is more preferable that the neutralization rate R of sulfuric acid is 30% or less. When the neutralization rate R of sulfuric acid is 30% or less, the impurity content in the produced silica can be further reduced.

[0027] Industrial-grade sodium silicate solutions are available in grades 1 to 5. Nos. 1 to 5 are standardized by sodium (Na2O) concentration, silica (SiO2) concentration, and specific gravity. The higher the grade number, the higher the molar ratio of sodium silicate. No. 3 sodium silicate has a silica concentration of approximately 28 to 30 wt%. No. 4 sodium silicate has a silica concentration of approximately 24 to 26 wt%.

[0028] Since a high molar ratio of sodium silicate results in a low ratio of sodium, the amount of acid used can be reduced in the process of producing silica by the neutralization reaction of sodium silicate with acid. Therefore, using an aqueous solution of sodium silicate with a larger number is preferable from both an environmental and economic perspective.

[0029] (4) About the filter cloth The filter cloth is used to filter silica produced in an aqueous solution containing sulfuric acid. The air permeability of the filter cloth is 4100 cm 3 / cm 2 · min or more 7800cm 3 / cm 2 ·min or less. The method for measuring the air permeability is based on JIS L-1096. The material of the filter cloth is, for example, polypropylene or Tetron.

[0030] (5) About the produced silica The nitrogen specific surface area of ​​the dried silica is 600m 2 / g or more 850m 2 / g or less. After drying, the nitrogen specific surface area of ​​the silica is preferably 600 m 2 / g or more 850m 2 / g or less is a measure of the instantaneous production of silica when a sodium silicate aqueous solution is dropped into an aqueous solution containing sulfuric acid. The nitrogen specific surface area of ​​silica after drying tends to increase as the temperature of the aqueous solution containing sulfuric acid is higher during silica production, the molar ratio of sodium silicate in the sodium silicate aqueous solution being dropped is higher, the silica concentration is lower, and the neutralization rate R is lower.

[0031] The aluminum, titanium, iron, and zirconium contents of the produced silica are preferably 5 ppm or less, and more preferably 2.5 ppm or less, respectively. For example, the aluminum, titanium, iron, and zirconium contents can be reduced by adding a chelating agent or hydrogen peroxide to an aqueous solution containing sulfuric acid.

[0032] 2. Benefits of silica manufacturing method (1A) According to the method for producing silica of the present disclosure, the time required for filtering silica can be reduced. (1B) According to the method for producing silica of the present disclosure, the amount of silica passing through the filter cloth can be reduced, thereby increasing the yield of silica. (1C) According to the method for producing silica of the present disclosure, the content of impurities in the produced silica can be reduced. The impurities include any one or more of aluminum, titanium, iron, and zirconium.

[0033] Example 1 1. Silica manufacturing method Silica was produced by the production methods S1 to S5, respectively. The production methods for S1 to S5 were as follows.

[0034] (1) S1 226 g of sulfuric acid with a concentration of 78 wt% and 148 g of pure water were weighed into a 1 L separable flask. The pure water was produced from tap water by reverse osmosis using a water purification system (Millipore Elix Essential 3UV). The conductivity of the pure water was 0.1 mS / m. The pH of the pure water was 6.9.

[0035] Next, 9 g of anhydrous citric acid (Fuso Chemical Co., Ltd.) and 35 g of 30 wt% hydrogen peroxide solution (Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the separable flask. Through these steps, an aqueous solution containing sulfuric acid was obtained. The sulfuric acid concentration in the aqueous solution containing sulfuric acid was 42 wt%. The weight of the aqueous solution containing sulfuric acid was 418 g.

[0036] Next, the outer periphery of the separable flask was immersed in water heated to 80° C., and the aqueous solution containing sulfuric acid was stirred at 300 rpm to raise the temperature of the aqueous solution containing sulfuric acid to 80° C. In this state, the aqueous sodium silicate solution was added dropwise to the aqueous solution containing sulfuric acid.

[0037] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.18. The SiO2 concentration in the sodium silicate aqueous solution was 29.2 wt%. The amount of sodium silicate aqueous solution added was 300 g. The time required for the sodium silicate aqueous solution to be added dropwise was 60 minutes. A tube pump (Tokyo Rikakikai) was used for adding the sodium silicate aqueous solution. Stirring and heating of the reaction solution were maintained for 10 minutes after the addition was completed. The reaction solution was a solution obtained by adding the sodium silicate aqueous solution to an aqueous solution containing sulfuric acid. The neutralization rate R was 25%.

[0038] Next, the silica produced in the aqueous solution containing sulfuric acid was separated from the aqueous solution containing sulfuric acid by suction filtration. The suction filtration procedure was as follows: The cut filter cloth was fixed to a Buchner funnel with an inner diameter of 180 mm with double-sided tape. The air permeability of the filter cloth was 6400 cm 3 / cm 2 / min. The filter cloth was made of polypropylene.

[0039] Next, the Buchner funnel was set in a suction bottle. Next, a vacuum pump (MDA-015 manufactured by ULVAC Kiko) was connected to the suction bottle. While the inside of the suction bottle was suctioned at a vacuum of 0.02 MPa, the reaction liquid containing silica was supplied onto the filter cloth. The silica remained on the filter cloth, while the reaction liquid passed through the filter cloth. As a result, the silica was separated from the reaction liquid.

[0040] Next, the silica was washed by supplying pure water to the silica on the filter cloth. Washing was continued by adding pure water until the total amount of pure water supplied reached 4,400 g. Suction continued even after the supply of pure water was completed. Suction was stopped when the interval between drops of filtrate falling from the filter cloth became 10 seconds or more. The time from the start of suction filtration to the end of suction was measured and recorded as the filtration washing time.

[0041] Table 1 shows the aqueous solution containing sulfuric acid, the aqueous sodium silicate solution, the neutralization rate R, and the air permeability of the filter cloth for S1 to S5.

[0042] [Table 1]

[0043] (2)S2 Silica was produced in the same manner as in S1. However, the aqueous solution containing sulfuric acid was produced by mixing 355 g of sulfuric acid with a concentration of 47 wt%, 9 g of anhydrous citric acid, and 35 g of hydrogen peroxide solution with a concentration of 30 wt%. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid was 42 wt%. The weight of the aqueous solution containing sulfuric acid was 399 g.

[0044] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.35. The SiO2 concentration in the sodium silicate aqueous solution was 26.3 wt%. The amount of sodium silicate aqueous solution dropped was 333 g. The neutralization rate R was 25%.

[0045] (3) S3 Silica was produced in the same manner as in S1. However, the aqueous solution containing sulfuric acid was produced by mixing 226 g of sulfuric acid with a concentration of 78 wt%, 180 g of pure water, 9 g of anhydrous citric acid, and 30 g of hydrogen peroxide solution with a concentration of 30 wt%. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid was 40 wt%. The weight of the aqueous solution containing sulfuric acid was 445 g.

[0046] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.18. The SiO2 concentration in the sodium silicate aqueous solution was 29.2 wt%. The amount of sodium silicate aqueous solution dropped was 300 g. The neutralization rate R was 25%. The air permeability of the filter cloth was 1000 cm 3 / cm 2 / min.

[0047] (4)S4 Silica was produced in the same manner as in S1. However, the aqueous solution containing sulfuric acid was produced by mixing 226 g of sulfuric acid with a concentration of 78 wt%, 180 g of pure water, 9 g of anhydrous citric acid, and 35 g of hydrogen peroxide solution with a concentration of 30 wt%. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid was 39 wt%. The weight of the aqueous solution containing sulfuric acid was 398 g.

[0048] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.36. The SiO2 concentration in the sodium silicate aqueous solution was 25.9 wt%. The amount of sodium silicate aqueous solution dropped was 333 g. The neutralization rate R was 24%. The air permeability of the filter cloth was 1000 cm 3 / cm 2 / min.

[0049] (5)S5 Silica was produced in the same manner as in S1. However, the aqueous solution containing sulfuric acid was produced by mixing 354 g of sulfuric acid with a concentration of 47 wt%, 9 g of anhydrous citric acid, and 35 g of hydrogen peroxide solution with a concentration of 30 wt%. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid was 42 wt%. The weight of the aqueous solution containing sulfuric acid was 445 g.

[0050] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.35. The SiO2 concentration in the sodium silicate aqueous solution was 26.3 wt%. The amount of sodium silicate aqueous solution dropped was 338 g. The neutralization rate R was 26%. The air permeability of the filter cloth was 4000 cm 3 / cm 2 / min.

[0051] 2. Evaluation of silica production methods For each of S1 to S5, the filtration and washing time, the nitrogen specific surface area of ​​the silica, the silica yield, and the content of impurities in the silica were measured. The results are shown in Table 2.

[0052] [Table 2]

[0053] The nitrogen specific surface area of ​​silica was measured as follows. First, the produced silica was pretreated at 180°C for 90 minutes using a vacuum pretreatment device (Quantachrome FloVac Degasser). The final vacuum during pretreatment was 0.05 to 0.07 torr. Next, nitrogen adsorption measurements were performed using a gas adsorption device (Quantachrome Quadrasorb SI) to obtain an adsorption isotherm. The nitrogen specific surface area of ​​silica was calculated from the adsorption isotherm using the BET multipoint method.

[0054] The silica yield is the percentage of the weight of silica dried at 120°C to the amount of SiO2 in sodium silicate. Note that silica dried at 120°C contains adsorbed water and hydroxyl groups, but the amount of SiO2 in sodium silicate is an anhydrous value. Therefore, the yield is a relatively high value.

[0055] The impurities whose content was measured were sodium (Na), magnesium (Mg), aluminum (Al), calcium (Ca), titanium (Ti), iron (Fe), and zirconium (Zr). The method for measuring the content of impurities was as follows: First, undried silica was weighed. Next, hydrofluoric acid was added to the silica to convert SiO2 into hexafluorosilicic acid. Next, the hexafluorosilicic acid was vaporized and removed by heating.

[0056] The residue was then dissolved in nitric acid. The spectrum was measured using a high-resolution ICP-OES (Plasma Quant PQ9000 Elite, manufactured by Analytik Jena) and the impurity content was obtained using a calibration curve. The impurity content was then converted to the content in silica dried at 120°C.

[0057] In S1 and S2, the filtration and washing time was short and the impurity content was low, while in S3 to S5, the filtration and washing time was long.

[0058] <Example 2> 1. Silica manufacturing method Silica was produced by the production methods S11 to S26, respectively. The production methods for S11 to S26 were as follows.

[0059] (1)S11 473 g of sulfuric acid with a concentration of 47 wt% was weighed and placed in a 1 L separable flask. Next, 9 g of anhydrous citric acid (manufactured by Fuso Chemical Co., Ltd.) and 35 g of hydrogen peroxide solution with a concentration of 30 wt% (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the separable flask. Through these steps, an aqueous solution containing sulfuric acid was obtained. The concentration of sulfuric acid in the aqueous solution containing sulfuric acid was 43 wt%. The weight of the aqueous solution containing sulfuric acid was 517 g.

[0060] Next, the outer periphery of the separable flask was immersed in water heated to 80° C., and the aqueous solution containing sulfuric acid was stirred at 300 rpm to raise the temperature of the aqueous solution containing sulfuric acid to 80° C. In this state, the aqueous sodium silicate solution was added dropwise to the aqueous solution containing sulfuric acid.

[0061] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 2.51. The SiO2 concentration in the sodium silicate aqueous solution was 28.6 wt%. The amount of sodium silicate aqueous solution added was 306 g. The time required for the sodium silicate aqueous solution to be added dropwise was 60 minutes. A tube pump (Tokyo Rikakikai) was used for adding the sodium silicate aqueous solution dropwise. The reaction solution was kept stirred and heated for 10 minutes after the addition was completed. The neutralization rate R was 25%.

[0062] Next, the silica produced in the aqueous solution containing sulfuric acid was separated from the aqueous solution containing sulfuric acid by filtering using a centrifuge equipped with a filter cloth. Specifically, the reaction solution containing the obtained silica was poured into a small centrifuge (Kokusan H-110A type) equipped with a filter cloth, and solid-liquid separation was carried out at a rotation speed of 2000 rpm for 2 minutes. The air permeability of the filter cloth was 6400 cm 3 / cm 2 The filter cloth was made of polypropylene.

[0063] After that, the first washing was performed 10 times. In each first washing, 0.4 L of pure water was supplied to the silica on the filter cloth with the rotation of the small centrifuge stopped, and then washing and dehydration were performed for 2 minutes at a rotation speed of 2000 rpm. In each first washing, the supplied pure water came into contact with the silica on the filter cloth and then passed through the filter cloth and flowed down.

[0064] After that, a second washing was performed once. In the second washing, 0.4 L of pure water was supplied to the silica on the filter cloth with the rotation of the small centrifuge stopped, followed by washing and dehydration for 10 minutes at a rotation speed of 3000 rpm.

[0065] Table 3 shows the aqueous solution containing sulfuric acid, the aqueous sodium silicate solution, the neutralization rate R, and the air permeability of the filter cloth for S11 to S26.

[0066] [Table 3]

[0067] (2) S12~S26 In S12 to S26, silica was produced basically in the same manner as in S11. However, in S12 to S26, the sulfuric acid concentration in the aqueous solution containing sulfuric acid and the weight of the aqueous solution containing sulfuric acid were as shown in Table 3. In S12 to S26, the blending amounts of anhydrous citric acid and 30 wt% hydrogen peroxide solution were the same as in S11.

[0068] In S12 to S26, the molar ratio of sodium silicate in the aqueous sodium silicate solution, the SiO2 concentration in the aqueous sodium silicate solution, the amount of sodium silicate solution dropped, the neutralization rate R, and the SiO2 amount were as shown in Table 3. In S12 to S26, the air permeability of the filter cloth was as shown in Table 3.

[0069] 2. Evaluation of silica production methods For each of S11 to S26, the nitrogen specific surface area of ​​the silica, the silica yield, and the content of impurities in the silica were measured. The measurement methods were the same as in Example 1. The measurement results are shown in Table 4.

[0070] [Table 4]

[0071] In S11 to S20, the silica yield was high and the impurity content was low. In S21 to S22, the silica yield was high. In S21 to S22, the aluminum and titanium contents were higher than in S11 to S20. This is because the neutralization rate R was high.

[0072] S23 to S24 had low yields. This was due to the high air permeability of the filter cloth. S25 had a lower yield and a higher aluminum content than S11 to S20. This was due to the high neutralization rate R. S26 had a lower yield and a higher aluminum and iron content than S11 to S20. This was due to the high neutralization rate R. In all of S11 to S26, the filtration time was short.

[0073] <Other embodiments> Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0074] (1) The function of one component in each of the above embodiments may be shared among multiple components, or the functions of multiple components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Furthermore, at least part of the configuration of each of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0075] (2) In addition to the above-described method for producing silica, the present disclosure can also be realized in various forms, such as silica, a method for filtering silica, an apparatus for producing silica, and a filtering apparatus.

[0076] [Technical idea disclosed in this specification] [Item 1] A sodium silicate aqueous solution having a silica concentration of 24 wt% or more and 32 wt% or less is added dropwise to an aqueous solution containing sulfuric acid, The silica produced in the aqueous solution containing sulfuric acid was subjected to a process having an air permeability of 4100 cm 3 / cm 2 · min or more 7800cm 3 / cm 2 The material is extracted by filtration using a filter cloth with a speed of 1000 kJ / min or less. The temperature of the aqueous solution containing sulfuric acid is 60°C or higher, The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt% or more and 60 wt% or less, the molar ratio of sodium silicate in the aqueous sodium silicate solution is 2 or more and 4 or less, The amount of the sodium silicate aqueous solution dropped is within a range in which the neutralization rate of sulfuric acid is 40% or less. Method for producing silica. [Item 2] Item 1, a method for producing silica, The aqueous solution containing sulfuric acid further contains citric acid or hydrogen peroxide. Method for producing silica. [Item 3] Item 1 or 2, a method for producing silica, After drying, the nitrogen specific surface area of ​​the silica is 600m 2 / g or more 850m 2 / g or less, Method for producing silica. [Item 4] A method for producing silica according to any one of items 1 to 3, The silica contains aluminum, titanium, iron, and zirconium at a content of 2.5 ppm or less. Method for producing silica. [Explanation of symbols]

[0077] 1. Aqueous solution containing sulfuric acid, 3. Aqueous solution of sodium silicate

Claims

1. A sodium silicate aqueous solution having a silica concentration of 24 wt % or more and 32 wt % or less is added dropwise to an aqueous solution containing sulfuric acid, The silica produced in the aqueous solution containing sulfuric acid was subjected to a process having an air permeability of 4100 cm ３ / cm ２ ・Min or more 7800cm ３ / cm ２ - Remove by filtering using a filter cloth with a flow rate of 0.1 min or less, The temperature of the aqueous solution containing sulfuric acid is 60°C or higher, The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt % or more and 60 wt % or less, the molar ratio of sodium silicate in the aqueous sodium silicate solution is 2 or more and 4 or less, The amount of the sodium silicate aqueous solution dropped is within a range such that the neutralization rate of sulfuric acid is 40% or less. Method for producing silica.

2. 2. The method for producing silica according to claim 1, The aqueous solution containing sulfuric acid further contains citric acid or hydrogen peroxide. Method for producing silica.

3. 3. The method for producing silica according to claim 1 or 2, The nitrogen specific surface area of ​​the silica after drying is 600 m ２ / g or more 850m ２ / g or less, Method for producing silica.

4. 3. The method for producing silica according to claim 1 or 2, The silica has an aluminum, titanium, iron, and zirconium content of 2.5 ppm or less, respectively. Method for producing silica.

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