Silica manufacturing method

Abstract

To provide a method for producing silica that can reduce the amounts of sodium and calcium contained in the produced silica. [Solution] In a method for producing silica, a sodium silicate aqueous solution is added dropwise to an aqueous solution containing sulfuric acid, silica produced in the aqueous solution containing sulfuric acid is separated from the aqueous solution containing sulfuric acid, and the separated silica is washed with a washing solution having a pH of 0.1 to 4. The washing solution is, for example, an acid solution or cation-exchanged water. The acid contained in the acid solution is, for example, hydrochloric acid, nitric acid, acetic acid, or citric acid.

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, it is difficult to reduce the amounts of sodium and calcium contained in the manufactured silica. In one aspect of the present disclosure, it is preferable to provide a manufacturing method for silica that can reduce the amounts of sodium and calcium contained in the manufactured silica. [Means for solving the problem]

[0005] One aspect of the present disclosure is a method for producing silica, comprising: adding dropwise an aqueous solution of sodium silicate to an aqueous solution containing sulfuric acid; separating silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid; and washing the separated silica with a washing liquid having a pH of 0.1 or more and 4 or less.

[0006] According to the method for producing silica that is one aspect of the present disclosure, the amounts of sodium and calcium contained in the produced silica can be reduced. [Brief explanation of the drawings]

[0007] [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

[0008] 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 is added dropwise to an aqueous solution containing sulfuric acid. The silica produced in the aqueous solution containing sulfuric acid is then separated from the aqueous solution containing sulfuric acid. The separated silica is washed with a washing solution having a pH of 0.1 or more and 4 or less.

[0009] 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.

[0010] When the aqueous sodium silicate solution is dropped, it is preferable to stir the aqueous solution containing sulfuric acid. By stirring, impurities in the produced silica can be further reduced. As a method for separating the silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid, for example, filtration can be mentioned. For example, a centrifuge can be used for filtration. In this case, impurities in the produced silica can be further reduced.

[0011] Furthermore, by using a centrifuge, even if the silica before separation is in the form of, for example, a shell-like mass, it can be converted into a powder (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. Examples of filter media used for filtration include filter cloth, filter paper, mesh, etc. High-purity silica produced by the production method of the present disclosure can be used, for example, to produce high-purity sodium silicate.

[0012] (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 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.

[0013] 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).

[0014] 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, impurities in the produced silica can be further reduced. Furthermore, 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, impurities in the produced silica can be further reduced.

[0015] 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 impurities in the produced silica can be further reduced.

[0016] 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, impurities in the produced silica can be further reduced.

[0017] 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.

[0018] The temperature of the aqueous solution containing sulfuric acid is preferably 60° C. or higher. When the temperature of the aqueous solution containing sulfuric acid is 60° C. or higher, impurities in the produced silica can be further reduced.

[0019] (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, for example, 20 wt% or more and 39 wt% or less. The silica concentration in the aqueous sodium silicate solution is, for example, 24 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 (for example, clumps of about 5 mm in size), improving water washability and filterability, thereby further reducing impurities in the produced silica.

[0020] The molar ratio of sodium silicate in the aqueous sodium silicate solution is preferably 3 to 4. When the molar ratio of sodium silicate in the aqueous sodium silicate solution is within this range, impurities 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.

[0021] 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.

[0022] When the neutralization rate R of sulfuric acid is 40% or less, the impurities 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 impurities in the produced silica can be further reduced.

[0023] 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%.

[0024] 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.

[0025] (4) Cleaning with cleaning fluid Washing with a washing solution is performed on silica separated from an aqueous solution containing sulfuric acid. The pH of the washing solution is 0.1 or more and 4 or less. Examples of the washing solution include an acid solution and cation-exchanged water. The acid solution is a solution containing an acid. Examples of the acid include hydrochloric acid, nitric acid, acetic acid, and citric acid.

[0026] As a method for washing silica with a washing liquid, for example, there is a method in which the washing liquid is supplied to the silica on the filter medium. In this case, the supplied washing liquid comes into contact with the silica on the filter medium, and then passes through the filter medium and flows down. Examples of the filter medium include filter cloth, filter paper, mesh, etc. The filter medium is, for example, the one used when separating silica from an aqueous solution containing sulfuric acid.

[0027] Washing with the washing liquid can be repeated, for example, multiple times. The number of times washing with the washing liquid can be, for example, 1 to 10 times. The amount of washing liquid used in one washing can be, for example, 1 L to 20 L per 1 kg of silica.

[0028] (5) Pre-cleaning Pre-washing is performed on the silica separated from the aqueous solution containing sulfuric acid before washing with a washing liquid. In pre-washing, a pre-washing liquid with a pH of 6 to 8 is supplied to the silica on the filter medium. The supplied pre-washing liquid comes into contact with the silica on the filter medium and then flows down through the filter medium. Pre-washing is performed until the pH of the liquid that has passed through the filter medium becomes 2 or higher. Examples of filter medium include filter cloth, filter paper, mesh, etc. Filter medium is, for example, the same as that used when separating silica from the aqueous solution containing sulfuric acid. Examples of pre-washing liquid include pure water, soft water, tap water, etc.

[0029] Pre-washing can be repeated, for example, multiple times. The number of pre-washings can be, for example, from 1 to 10 times. The amount of pre-washing solution used in one pre-washing can be, for example, from 1 L to 20 L per kg of silica. Pre-washing may or may not be performed. When pre-washing is performed, the amount of sodium and calcium contained in the produced silica can be further reduced.

[0030] (6) Post-cleaning Post-washing is performed on the silica separated from the aqueous solution containing sulfuric acid after washing with a washing liquid. In post-washing, pure water is supplied to the silica on the filter media. After contacting the silica on the filter media, the supplied pure water passes through the filter media and flows down. Post-washing is performed, for example, until the pH of the liquid that has passed through the filter media reaches 3 or higher.

[0031] Examples of the filter material include filter cloth, filter paper, mesh, etc. The filter material is, for example, the same as that used when separating silica from an aqueous solution containing sulfuric acid. Examples of the pure water include ion-exchanged water, RO water, etc.

[0032] The post-washing can be repeated, for example, multiple times. The number of post-washing times can be, for example, from 1 to 10 times. The amount of pure water used in one post-washing can be, for example, from 1 L to 20 L per 1 kg of silica. The post-washing may or may not be performed. When the post-washing is performed, the amount of sodium and calcium contained in the produced silica can be further reduced.

[0033] (7) 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 the aqueous sodium silicate 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 aqueous sodium silicate solution being dropped is higher, the silica concentration is lower, the neutralization rate R is lower, and the impurity content is lower.

[0034] The content of sodium, magnesium, aluminum, calcium, titanium, iron, and zirconium in the produced silica is preferably 10 ppm or less, respectively. For example, by adding a chelating agent or hydrogen peroxide to an aqueous solution containing sulfuric acid, the content of sodium, magnesium, aluminum, calcium, titanium, iron, and zirconium in the produced silica can be reduced.

[0035] 2. Benefits of silica manufacturing method According to the method for producing silica of the present disclosure, the amounts of sodium and calcium contained in the produced silica can be reduced. The reason for this is presumed to be as follows.

[0036] In the method for producing silica described in Patent Document 1, the neutralization rate R is 40% or less. Therefore, when the dropwise addition of the aqueous sodium silicate solution is completed, the pH of the reaction solution is 2 or less. The reaction solution is a solution obtained by adding an aqueous sodium silicate solution to an aqueous solution containing sulfuric acid. When the pH of the reaction solution is 2 or less, the surface of the silica is positively charged. A large amount of sodium ions derived from the sodium silicate are present in the reaction solution, but the positively charged sodium ions are electrically repelled by the positively charged surface of the silica.

[0037] If the silica is separated from the reaction solution and then washed with a neutral solution, the pH of the silica surface will gradually increase. When the pH of the silica surface exceeds 2, the silica surface will begin to take on a negative charge. Positively charged sodium ions are attracted to and adsorbed onto the negatively charged silica surface. In addition to sodium ions, positively charged calcium ions and other ions will also adsorb onto the silica surface.

[0038] In the method for producing silica according to the present disclosure, after the silica is separated from the reaction solution, it is washed with a washing solution having a pH of 0.1 to 4, which makes it difficult for the pH of the silica surface to increase, and prevents the silica surface from becoming negatively charged. As a result, it is possible to prevent cations such as sodium and calcium from being adsorbed onto the silica surface.

[0039] <Example> 1. Silica manufacturing method Silica was produced by each of the production methods S1 to S9. The production methods S1 to S7 had the following in common.

[0040] (i) Commonalities between S1 and S7 355 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 the above process, an aqueous solution containing sulfuric acid was obtained.

[0041] 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.

[0042] The molar ratio of sodium silicate in the sodium silicate aqueous solution was 3.4. The SiO2 concentration in the sodium silicate aqueous solution was 26 wt%. The amount of sodium silicate aqueous solution added was 335 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%.

[0043] 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 (H-110A manufactured by Kokusan) equipped with a filter cloth, and solid-liquid separation was carried out at a rotation speed of 2000 rpm for 2 minutes.

[0044] After that, the first washing was performed eight times. In each first washing, 0.4 L of the first washing liquid was supplied to the silica on the filter cloth with the rotation of the small centrifuge stopped, followed by washing and dehydration for 2 minutes at a rotation speed of 2000 rpm. In each first washing, the supplied first washing liquid contacted the silica on the filter cloth, then passed through the filter cloth and flowed down. In S1 to S5, the first washing corresponds to washing with the washing liquid.

[0045] After that, the second washing was performed four times. In each second washing, 0.4 L of the second washing solution was supplied to the silica on the filter cloth with the rotation of the small centrifuge stopped, and then the small centrifuge was operated to perform washing and dehydration. In the first to third second washings, the rotation speed during washing and dehydration was 2000 rpm, and the washing and dehydration time was 2 minutes.

[0046] In the fourth second washing, the rotation speed during washing and dehydration was 3000 rpm, and the washing and dehydration time was 10 minutes. After the fourth second washing, the pH of the second washing liquid that passed through the filter cloth was 3 or higher. The second washing corresponds to a post-washing.

[0047] (ii) Composition and pH of the first and second cleaning solutions in S1 to S7 The compositions and pH values ​​of the first and second cleaning solutions used in S1 to S7 are shown in Table 1.

[0048] [Table 1]

[0049] The first cleaning solution in S1 was a solution in which sulfuric acid was added to pure water so that the sulfuric acid concentration was 0.05 wt%. The first cleaning solution in S2 was cation-exchanged water. The first cleaning solution in S3 was a solution in which sulfuric acid was added to cation-exchanged water so that the sulfuric acid concentration was 0.05 wt%.

[0050] The first cleaning solution in S4 was a solution in which sulfuric acid was added to tap water so that the sulfuric acid concentration was 0.05 wt%, and the first cleaning solution in S5 was a solution in which citric acid was added to pure water so that the citric acid concentration was 1.0 wt%.

[0051] The first cleaning liquid in S6 was pure water, the first cleaning liquid in S7 was tap water, and the second cleaning liquid in S1 to S7 was all pure water.

[0052] Pure water was produced from tap water by reverse osmosis using a water purification system (Millipore Elix Essential 3 UV). The conductivity of the pure water was 0.1 mS / m. The pH of the pure water was 6.9. Cation-exchanged water was prepared by passing tap water from Nakatsugawa City through a column packed with cation-exchange resin (Amberlite IRC-120(H)).

[0053] The conductivity of the cation-exchanged water was 11-12 mS / m. The pH of the cation-exchanged water was 3.6. Note that the cations contained in tap water are exchanged for hydrogen ions, making the cation-exchanged water weakly acidic. The more cations there are in the tap water (i.e., the higher the hardness), the lower the pH of the cation-exchanged water.

[0054] The tap water was municipal water from Nakatsugawa City. The conductivity of the tap water was 5.7 mS / m. The pH of the tap water was 7.1. A pH meter F-52 manufactured by Horiba, Ltd. was used to measure the pH. The pH values ​​in this specification are values ​​converted to 20°C. (iii) Manufacturing methods of S8 to S9 The manufacturing method of S8 to S9 was as follows. The silica produced in S6 was subjected to the third washing eight times. In each third washing, with the rotation of the small centrifuge stopped, 0.4 L of the third washing liquid was supplied to the silica on the filter cloth, followed by washing and dehydration for 2 minutes at a rotation speed of 2000 rpm. In each third washing, the supplied third washing liquid came into contact with the silica on the filter cloth, then passed through the filter cloth and flowed down. The third washing corresponds to washing with a washing liquid.

[0055] The fourth wash was then carried out four times. During each fourth wash, 0.4 L of the fourth wash solution was supplied to the silica on the filter cloth with the small centrifuge stopped, and then the small centrifuge was operated to perform washing and dehydration. In the first to third fourth washes, the rotation speed during washing and dehydration was 2000 rpm, and the washing and dehydration time was 2 minutes.

[0056] In the fourth washing, the rotation speed during washing and dehydration was 3000 rpm, and the washing and dehydration time was 10 minutes. After the fourth washing, the pH of the fourth washing liquid that passed through the filter cloth was 3 or higher. The fourth washing corresponds to a post-washing. The compositions and pH of the third and fourth washing liquids used in S8 and S9 were as shown in Table 2.

[0057] [Table 2]

[0058] The third cleaning liquid in S8 was a liquid in which sulfuric acid was added to pure water so that the sulfuric acid concentration was 0.05 wt%. The third cleaning liquid in S9 was a liquid in which sulfuric acid was added to pure water so that the sulfuric acid concentration was 0.5 wt%. The fourth cleaning liquid in S8 to S9 was all pure water.

[0059] 2. Measurement of impurity content in silica The impurity contents in the silica produced by the production methods S1 to S9 were measured. The impurities whose contents were measured were sodium (Na), magnesium (Mg), aluminum (Al), calcium (Ca), titanium (Ti), iron (Fe), and zirconium (Zr).

[0060] The impurity content was measured 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.

[0061] 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 method. The impurity content was converted to the content in silica dried at 120°C. The measurement results of the impurity content are shown in Tables 1 and 2.

[0062] As shown in Tables 1 and 2, S1 to S5, which used a first cleaning solution with a pH of 0.1 or more and 4 or less, and S8 to S9, which used a third cleaning solution with a pH of 0.1 or more and 4 or less, were able to reduce the sodium and calcium contents in the silica compared to S6 to S7. In S1 to S5 and S8 to S9, the contents of all impurities were less than 10 ppm.

[0063] <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.

[0064] (1) Pure water may be produced by methods such as ion exchange and distillation. (2) 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.

[0065] (3) 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, a method for washing silica, an apparatus for producing silica, and a filtering apparatus.

[0066] [Technical idea disclosed in this specification] [Item 1] Droplet-wise addition of an aqueous solution of sodium silicate to an aqueous solution containing sulfuric acid; Separating the silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid; The separated silica is washed with a washing solution having a pH of 0.1 or more and 4 or less. Method for producing silica. [Item 2] Item 1, a method for producing silica, The cleaning solution is an acid solution or cation-exchanged water. Method for producing silica. [Item 3] Item 2. A method for producing silica according to item 2, The acid contained in the acid solution is hydrochloric acid, nitric acid, acetic acid, or citric acid. Method for producing silica. [Item 4] A method for producing silica according to any one of items 1 to 3, Before cleaning with the cleaning liquid, a pre-cleaning liquid having a pH of 6 or more and 8 or less is supplied to the silica on the filter medium to perform pre-cleaning; The pre-washing is carried out until the pH of the liquid that has passed through the filter medium becomes 2 or higher. Method for producing silica. [Item 5] A method for producing silica according to any one of items 1 to 4, After washing with the cleaning solution, pure water is supplied to the silica on the filter medium to perform post-cleaning. The post-cleaning is carried out until the pH of the liquid that has passed through the filter medium becomes 3 or more. Method for producing silica. [Item 6] 6. A method for producing silica according to any one of items 1 to 5, the molar ratio of sodium silicate in the aqueous sodium silicate solution is 3 or more and 4 or less, The silica concentration in the sodium silicate aqueous solution is 20 wt% or more and 39 wt% or less, The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt% or more and 60 wt% or less, The temperature of the aqueous solution containing sulfuric acid is 60°C or higher, The amount of the sodium silicate aqueous solution dropped is an amount that results in a neutralization rate of 40% or less. Method for producing silica. [Item 7] A method for producing silica according to any one of items 1 to 6, The content of sodium, magnesium, aluminum, calcium, titanium, iron, and zirconium in the produced silica is each less than 10 ppm. Method for producing silica. [Item 8] A method for producing silica according to any one of claims 1 to 7, 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. [Explanation of symbols]

[0067] 1. Aqueous solution containing sulfuric acid, 3. Aqueous solution of sodium silicate

Claims

1. Droplet-wise addition of an aqueous solution of sodium silicate to an aqueous solution containing sulfuric acid; Separating the silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid; The separated silica is washed with a washing solution having a pH of 0.1 or more and 4 or less. Before cleaning with the cleaning liquid, a pre-cleaning liquid having a pH of 6 or more and 8 or less is supplied to the silica on the filter medium to perform pre-cleaning; The pre-washing is carried out until the pH of the liquid that has passed through the filter medium becomes 2 or more. Method for producing silica.

2. A method of adding a sodium silicate aqueous solution dropwise to an aqueous solution containing sulfuric acid, Separating the silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid; The separated silica is washed with a washing solution having a pH of 0.1 or more and 4 or less. After washing with the cleaning solution, pure water is supplied to the silica on the filter medium to perform post-cleaning. The post-cleaning is performed until the pH of the liquid that has passed through the filter medium becomes 3 or more. Method for producing silica.

3. A method of adding a sodium silicate aqueous solution in the form of drops to an aqueous solution containing sulfuric acid, Separating the silica produced in the aqueous solution containing sulfuric acid from the aqueous solution containing sulfuric acid; The separated silica is washed with a washing solution having a pH of 0.1 or more and 4 or less. the molar ratio of sodium silicate in the aqueous sodium silicate solution is 3 or more and 4 or less, the silica concentration in the sodium silicate aqueous solution is 20 wt % or more and 39 wt % or less, The concentration of sulfuric acid in the aqueous solution containing sulfuric acid is 31 wt % or more and 60 wt % or less, The temperature of the aqueous solution containing sulfuric acid is 60°C or higher, The amount of the sodium silicate aqueous solution dropped is an amount that results in a neutralization rate of 40% or less. Method for producing silica.

4. The method for producing silica according to any one of claims 1 to 3, The cleaning solution is an acid solution or cation-exchanged water. Method for producing silica.

5. 5. The method for producing silica according to claim 4, The acid contained in the acid solution is sulfuric acid, hydrochloric acid, nitric acid, acetic acid, or citric acid. Method for producing silica.

6. The method for producing silica according to any one of claims 1 to 3, The content of sodium, magnesium, aluminum, calcium, titanium, iron, and zirconium in the produced silica is each less than 10 ppm. Method for producing silica.

7. The method for producing silica according to any one of claims 1 to 3, 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.

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