High-purity sodium silicate aqueous solution and method for producing the same

Abstract

A manufacturing method is provided that enables the production of a high-purity sodium silicate aqueous solution with nickel reduced to an extremely low concentration from a nickel-containing sodium silicate aqueous solution using a simple method. The method for producing the nickel-reduced sodium silicate aqueous solution includes: a capture step that captures nickel from the nickel-containing sodium silicate aqueous solution using layered sodium silicate; and a separation step that removes the nickel-captured layered sodium silicate from the sodium silicate aqueous solution.

Description

Technical Field

[0001] This invention relates to a novel method for manufacturing a high-purity sodium silicate aqueous solution. Specifically, it provides a method for manufacturing a high-purity sodium silicate aqueous solution with reduced nickel concentration, making it highly suitable as a raw material for silica sol used in semiconductor polishing. Background Technology

[0002] Sodium silicate aqueous solution is widely used in various fields such as civil engineering and construction, paper and pulp, detergents and soaps, and ceramics, as a foundation conditioner, an additive in pulp bleaching agents, a binder for refractory materials and castings, and a flocculant in water purification. In addition, sodium silicate aqueous solution can be used to manufacture various silica products such as precipitated silica, silica gel, and silica sol (colloidal silica dispersion), as well as detergent additives and silicate products such as zeolite.

[0003] Silica sol is used in various applications, including coatings to impart hardness and scratch resistance to optical materials, anti-blocking agents for thin film materials, inorganic adhesives for ceramics, and precision grinding of various substrate surfaces. Particularly in the grinding of semiconductor wafers and semiconductor device surfaces, the demand for reducing metal impurities is increasing with advancements in semiconductor technology. Furthermore, these demands on silica sol have extended to its raw material, sodium silicate aqueous solution, leading to a growing need for high-purity sodium silicate aqueous solutions with reduced metal impurities.

[0004] Generally, sodium silicate aqueous solution is produced by mixing silica sand with alkaline sources such as soda ash or sodium hydroxide and melting it at high temperature to obtain anhydrous sodium silicate (also known as "crushed glass" because it is a glassy solid). Water is added to the mixture, and it is heated and dissolved in an autoclave. The dissolved aqueous solution is then passed through a filter press or similar device to remove insoluble substances.

[0005] Alternatively, sodium silicate aqueous solution can also be produced by heating and dissolving silicon dioxide in an alkaline aqueous solution.

[0006] Furthermore, silica sol is generally manufactured in the following manner: the sodium silicate aqueous solution produced in the above manner is diluted as needed, and then it is contacted with H-type strong acid cation exchange resin. The pH of the resulting active silicic acid is further adjusted, and impurities or foreign matter are removed by ion exchange, ultrafiltration and other methods. Then it is heated to adjust the particle size of silica particles, and the pH is adjusted by adding ammonia and other substances to stabilize it.

[0007] In the past, various explorations have been conducted on achieving high purity in the manufacturing process of silica sol. However, to achieve further high purity, it is necessary to suppress the impurities contained in the sodium silicate aqueous solution, which is used as a raw material for manufacturing silica sol, to a certain level. Especially for semiconductor applications, there is a strong demand to reduce metallic impurities, particularly the concentration of nickel (Ni), which is easily mixed into the sodium silicate aqueous solution during manufacturing processes.

[0008] As a method for manufacturing sodium silicate aqueous solution for the purpose of reducing metallic impurities, a method has been disclosed in which a high-purity silica source is dissolved in an alkaline aqueous solution such as sodium hydroxide. For example, methods include: dissolving high-purity glass byproducts in the manufacturing process of semiconductors and optical fibers in an alkaline aqueous solution (see Patent Document 1); neutralizing commercially available sodium silicate aqueous solution to prepare high-purity hydrated silica, and then dissolving it in an alkaline aqueous solution (see Patent Document 2); contacting sodium silicate aqueous solution with an ion exchange resin to generate high-purity silica sol or silica gel, and then dissolving it in an alkaline aqueous solution (see Patent Document 3), etc.

[0009] However, even when using high-purity raw materials as the silicon source, it is inevitable that nickel from the manufacturing equipment will contaminate the alkaline aqueous solution when using it. Regardless of the method used, the resulting sodium silicate aqueous solution will contain nickel at the ppm level. Moreover, as a manufacturing method, there are also problems such as limited procurement of high-purity silica sources or the need for numerous purification processes.

[0010] In addition, as another method for manufacturing high-purity sodium silicate aqueous solution, the following method is known (see Patent Document 4): after diluting a commercially available sodium silicate aqueous solution obtained by dissolving anhydrous sodium silicate in water, pressure filtration is performed using a membrane filter with specific micropores.

[0011] However, even after removing the solids present in the sodium silicate aqueous solution obtained by dissolving broken glass in water under normal conditions, the reduction in nickel concentration was insufficient, and the resulting sodium silicate aqueous solution contained a large amount of nickel that had not been completely removed.

[0012] Furthermore, as a method for removing impurities during the manufacturing process of silica sol, the following manufacturing method has been disclosed (see Patent Document 5): when dissolving chopped glass in water, a chelating agent is added in advance to generate a metal chelate with the metal impurities in the sodium silicate aqueous solution, silica sol is manufactured in this state, and the metal chelate is removed from the resulting silica sol.

[0013] However, in the above manufacturing method, the nickel captured by the chelating agent remains in the sodium silicate aqueous solution as a metal chelate, therefore a sodium silicate aqueous solution with reduced nickel content is not disclosed. Furthermore, there are concerns that the use of chelating agents increases manufacturing costs as a manufacturing method.

[0014] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2003-238143 Patent Document 2: Japanese Patent Application Publication No. 2003-183018 Patent Document 3: Japanese Patent Application Publication No. 61-101414 Patent Document 4: Japanese Patent Publication No. 2002-511379 Patent Document 5: International Publication No. WO2020-262406 Summary of the Invention The problem that the invention aims to solve Therefore, the object of the present invention is to provide a manufacturing method that can obtain a high-purity sodium silicate aqueous solution with nickel reduced to an extremely low concentration from a nickel-containing sodium silicate aqueous solution (hereinafter also referred to as crude sodium silicate aqueous solution) by a simple method.

[0015] Methods for solving problems One aspect of the present invention is a method for manufacturing a high-purity sodium silicate aqueous solution, characterized in that it includes: a capture step, which uses layered sodium silicate to capture nickel from a nickel-containing sodium silicate aqueous solution; and a separation step, which removes the layered sodium silicate containing the captured nickel from the sodium silicate aqueous solution.

[0016] In addition, one aspect of the present invention is a high-purity sodium silicate aqueous solution, characterized in that the nickel content is less than 100 ppb relative to the SiO2 content in the sodium silicate.

[0017] The effects of the invention According to one aspect of the present invention, a method for manufacturing a high-purity sodium silicate aqueous solution capable of reducing nickel concentration to extremely low levels can be provided. Attached Figure Description

[0018] Figure 1 This is an X-ray diffraction pattern showing the residue separated in the separation process in Example 1. Detailed Implementation

[0019] One embodiment of the present invention relates to a method for manufacturing a high-purity sodium silicate aqueous solution, characterized in that it includes: a capture step, which uses layered sodium silicate to capture nickel from a nickel-containing sodium silicate aqueous solution; and a separation step, which removes the layered sodium silicate containing the captured nickel from the sodium silicate aqueous solution.

[0020] According to one embodiment of the present invention, the manufacturing method can, by simple means, produce a high-purity sodium silicate aqueous solution with a nickel content of less than 100 ppb relative to the SiO2 content in the sodium silicate, from a crude sodium silicate aqueous solution made using nickel-contaminated raw materials.

[0021] Although the mechanism by which these effects are achieved is not yet clear, the inventors speculate that it is because the interlayer structure of layered sodium silicate is suitable for capturing nickel as nickel ions in crude sodium silicate aqueous solution.

[0022] Furthermore, according to one embodiment of the present invention, an aqueous sodium silicate solution with a nickel content of less than 100 ppb relative to the SiO2 content in sodium silicate, which is not achievable by the prior art, can also be provided. This aqueous sodium silicate solution can be well used as a silica sol raw material for semiconductor polishing.

[0023] The crude sodium silicate aqueous solution addressed in one embodiment of the present invention can be obtained by a known method for manufacturing sodium silicate aqueous solutions. Examples of specific manufacturing methods include: dissolving chopped glass in water, and dissolving silicon sources such as silica or glass in an aqueous sodium hydroxide solution. In these methods, dissolution is generally carried out at a temperature corresponding to the silicon source; for example, if it is chopped glass, it is carried out in an autoclave at a temperature of approximately 140°C, and the dissolution is completed in about 1 to 2 hours. On the other hand, sometimes a "partially dissolved product" obtained by dissolving a portion of chopped glass (e.g., half the amount of chopped glass) is used as the product. In one embodiment of the present invention, the crude sodium silicate aqueous solution obtained by any method can be used.

[0024] Alternatively, water glass, which is commonly circulated as industrial group standard No. 1, No. 2, and No. 3 as formulated by the Sodium Silicate Branch of the Japan Inorganic Pharmaceuticals Association, can also be used as a crude sodium silicate aqueous solution.

[0025] Furthermore, in one embodiment of the present invention, the concentration of sodium silicate in the crude sodium silicate aqueous solution is not particularly limited, but considering the ease of generating layered sodium silicate in the capture process and the ease of operation in the separation process, the concentration converted to SiO2 is preferably greater than 10% by mass and less than 35% by mass, and particularly preferably 12 to 30% by mass. In addition, the molar ratio (SiO2 / Na2O) of the crude sodium silicate aqueous solution is not particularly limited, and is usually 2.0 to 4.0.

[0026] Regarding the contamination of sodium silicate aqueous solution, it can be assumed that when using quartz glass, the contamination mainly originates from the raw materials and manufacturing equipment of the quartz glass; while when using sodium hydroxide aqueous solution, the contamination mainly originates from its manufacturing equipment. Furthermore, the amount of nickel contamination varies depending on the source of contamination, but it is generally 200 ppb or more relative to the SiO2 content in the sodium silicate aqueous solution, and depending on the situation, may even reach 500 ppb or more. One embodiment of the present invention is applicable to crude sodium silicate aqueous solution containing nickel at this concentration.

[0027] The most significant feature of the method for manufacturing a high-purity sodium silicate aqueous solution according to one embodiment of the present invention is that it includes a capture step, which utilizes layered sodium silicate to capture nickel in a nickel-containing sodium silicate aqueous solution.

[0028] By employing this capture process, nickel in the crude sodium silicate aqueous solution is captured by layered sodium silicate. By separating the nickel-captured layered sodium silicate from the crude sodium silicate aqueous solution, a high-purity sodium silicate aqueous solution with a significantly reduced nickel concentration can be obtained.

[0029] This method of removing nickel from crude sodium silicate aqueous solution using layered sodium silicate is unprecedented and is the first such discovery by the inventors.

[0030] Furthermore, the inventors have confirmed that, according to the method for manufacturing crude sodium silicate aqueous solution, particularly the method of manufacturing by heating in an autoclave, extremely fine layered sodium silicate may sometimes be present, or trace amounts of layered sodium silicate particles grown due to localized heating may be present. However, the presence of such extremely fine layered sodium silicate has not been confirmed to date, and it cannot be separated by foreign matter removal methods such as filtration commonly used in industry, and will remain unchanged in the purified sodium silicate aqueous solution. Therefore, it is speculated that the effect of reducing nickel concentration by using layered sodium silicate has not been confirmed. In addition, the amount of layered sodium silicate generated by localized heating is extremely small, and even if it is removed as a foreign matter, the effect of reducing nickel concentration in the purified sodium silicate aqueous solution cannot be confirmed.

[0031] In one embodiment of the method of the present invention, the capture step also includes capturing nickel by generating the aforementioned layered sodium silicate particles, and, if necessary, adding an insufficient amount of layered sodium silicate to capture nickel. Then, the nickel-captured layered sodium silicate is removed by the separation step described below, thereby effectively reducing the nickel content in the crude sodium silicate aqueous solution.

[0032] Therefore, the capture process involved in one embodiment of the present invention is applicable to either a crude sodium silicate aqueous solution containing layered sodium silicate generated in the sodium silicate aqueous solution manufacturing process as described above, or a crude sodium silicate aqueous solution without layered sodium silicate.

[0033] In one embodiment of the present invention, the layered sodium silicate is not particularly limited as long as it is a SiO2-Na2O-H2O layered crystal. Specifically, depending on the SiO2 content, examples include makatite, illite, magadiite, and kenyaite.

[0034] In one embodiment of the invention, the form of the capture process is not particularly limited as long as an aqueous solution of crude sodium silicate containing captured nickel-laden layered sodium silicate can be obtained, and the layered sodium silicate has an amount and size that can be separated in the separation process described below with sufficient removal rate and amount.

[0035] If we take specific methods as examples, we can give examples of: Form (1): forming layered sodium silicate from part of the sodium silicate in the crude sodium silicate aqueous solution; Form (2): bringing the layered sodium silicate into contact with the sodium silicate aqueous solution, etc.

[0036] Regarding the aforementioned form (1), by generating layered sodium silicate from a portion of the sodium silicate in the crude sodium silicate aqueous solution, the crude sodium silicate aqueous solution containing the fine layered sodium silicate has the following functions: increasing the amount of fine layered sodium silicate required for nickel capture, and growing the fine layered sodium silicate to a size that can be separated in subsequent separation processes. Furthermore, the crude sodium silicate aqueous solution containing trace amounts of layered sodium silicate has the following functions: increasing the amount of layered sodium silicate required for nickel capture, and growing the generated layered sodium silicate to a size that can be separated in subsequent separation processes. Of course, the ordinary crude sodium silicate aqueous solution without layered sodium silicate has the following functions: generating the amount of layered sodium silicate required for nickel capture, and growing it to a size that can be separated in subsequent separation processes. That is, "generating layered sodium silicate" in the capture process means generating layered sodium silicate with a size that can be separated in the separation process.

[0037] Regarding form (1), a preferred method can be exemplified by holding an aqueous solution of crude sodium silicate at a temperature of 140°C to 190°C under pressure. The holding time at this temperature is simply set to the time required to generate layered sodium silicate with sufficient removal rate and amount in the separation process described below. Specifically, a method can be exemplified by holding the solution at a temperature (°C) × holding time (hr) of 500 to 5000, particularly 1000 to 4000. Under these conditions, layered sodium silicate can be grown to a suitable size that is easily removed in the separation process described below, and a sufficient amount of layered sodium silicate to capture nickel can be generated.

[0038] That is, if the temperature is below 140°C, even with extended holding time, the formation and growth of layered sodium silicate will become extremely slow, making industrial implementation difficult. The lower limit of the temperature is preferably 145°C. Furthermore, if the temperature is above 190°C, some of the layered sodium silicate will further transform into quartz or cristobalite, resulting in a reduction in the amount of layered sodium silicate formed, thus raising concerns about a decrease in nickel capture capacity. The upper limit of the temperature is preferably 180°C.

[0039] Furthermore, if the "temperature (°C) × holding time (hr)" is less than the specified range, there is a tendency for insufficient generation of layered sodium silicate. This can lead to an absolute deficiency in the amount of layered sodium silicate, or difficulty in obtaining layered sodium silicate particles of a suitable size that is easily removed during the separation process. Regarding the suitable size of the layered sodium silicate, while it also depends on the capacity of the separation process, industrially, a particle size of 0.5 μm or more, preferably 1 μm or more, is preferred.

[0040] As a means of generating the layered sodium silicate, it can be carried out in or after the manufacturing process of the crude sodium silicate aqueous solution, or it can be carried out for a separately manufactured crude sodium silicate aqueous solution. In the form of generating layered sodium silicate in the manufacturing process of the crude sodium silicate aqueous solution, the temperature at which the glass shards or the like are dissolved is within the suitable temperature range of the form (1) in the capture process, and the time after the silica concentration of the crude sodium silicate aqueous solution reaches 10% by mass is included in the holding time required to generate layered sodium silicate.

[0041] Regarding the aforementioned form (2), more specifically, as a step of contacting the crude sodium silicate aqueous solution with layered sodium silicate, it is preferable to include a step of adding layered sodium silicate to the crude sodium silicate aqueous solution.

[0042] Regarding the layered sodium silicate, commercially available products can be used without particular restriction, but products manufactured using known methods can also be used. Regarding the size of the added layered sodium silicate, considering ease of removal during the separation process, a particle size of 0.5 μm or more is preferred, preferably 1 μm or more. There is no particular upper limit to the average particle size, but it can be around 10 μm. Furthermore, regarding the appropriate amount of the added layered sodium silicate, it is sufficient to achieve the removal rate and amount of nickel-captured layered sodium silicate removed in the separation process described below.

[0043] In the addition process, it is preferable to add layered sodium silicate to the crude sodium silicate aqueous solution and then stir thoroughly. Furthermore, there is no particular limitation on the contact time after addition, as long as it is at least 30 seconds.

[0044] The added layered sodium silicate is contacted with an aqueous solution of crude sodium silicate to capture nickel, which is then removed by the separation process described below.

[0045] The form (2) is particularly effective for crude sodium silicate aqueous solutions that do not contain layered sodium silicate or contain only trace amounts of layered sodium silicate particles. The content of layered sodium silicate particles is considered to be trace, for example, the content when the crude sodium silicate aqueous solution is dissolved in a manner outside the suitable range of "temperature (°C) × holding time (hr)" in the form (1) during the manufacturing process.

[0046] In one embodiment of the invention, the separation step is a step of removing the layered sodium silicate containing nickel captured in the capture step from the crude sodium silicate aqueous solution, and the means by which this operation can be performed can be used without particular limitation. In industrial implementation, filtration is preferred as an example of a specific method.

[0047] Regarding the filter material used in the above-mentioned filtration, it is preferably determined based on the removal rate and filtration speed of the layered sodium silicate present in the crude sodium silicate aqueous solution. Furthermore, considering the prevention of secondary pollution caused by filtration, materials composed of polymers such as polypropylene, fluoropolymers, nylon, polysulfonic acid, polyethersulfone, and cellulose are preferred as the filter material. Additionally, the pore size of the filter material is preferably set to a size that allows for the removal of as much nickel-captured layered sodium silicate as possible during the separation process. Regarding the pore size of the filter material, it is appropriate to determine a size that achieves the removal rate described below and is industrially advantageous, based on the particle size of the layered sodium silicate. For example, it can be 1.0 μm or less, or 0.5 μm or less. Furthermore, this pore size can be 0.05 μm or more, 0.1 μm or more, or 0.25 μm or more.

[0048] In addition, considering the filtration efficiency in industrial applications, an air permeability of approximately 10 (cm²) can be used. 3 / (cm) 2 The filter cloth used is conforming to JIS L 1096 ("Test Methods for Fabrics and Fabrics") and can be used with filter aids such as diatomaceous earth and perlite. Using filter aids allows for effective removal of the generated layered sodium silicate through filter aid pores smaller than the pore size of the filter material. Furthermore, as a filtration method using the aforementioned filter material, there are no particular limitations on methods such as atmospheric pressure filtration, pressure filtration, reduced pressure filtration, and centrifugation.

[0049] In one embodiment of the invention, the nickel removal efficiency depends on the removal rate and amount of layered sodium silicate that has captured nickel and removed from the crude sodium silicate aqueous solution through the combination of the capture and separation steps. That is, in order to sufficiently remove nickel from the crude sodium silicate aqueous solution, it is preferable to separate at least 90%, more preferably at least 95%, of the layered sodium silicate that has captured nickel from the crude sodium silicate aqueous solution.

[0050] Furthermore, the amount of layered sodium silicate removed from the crude sodium silicate aqueous solution is at least 100 times, preferably at least 1000 times, by mass ratio relative to the nickel content in the crude sodium silicate aqueous solution. However, if the amount of layered sodium silicate removed is too large, not only will the nickel reduction effect reach its upper limit, but there is also a concern that the molar ratio of the obtained high-purity sodium silicate will decrease, leading to problems in the formation of layered sodium silicate from the crude sodium silicate aqueous solution. Therefore, the upper limit for the amount of layered sodium silicate removed is preferably 50,000 times, by mass ratio, relative to the nickel content in the crude sodium silicate aqueous solution.

[0051] Here, the removal rate (%) of layered sodium silicate refers to the value calculated by ((W1-W2) / W1)×100, where W1 is the amount of layered sodium silicate in the crude sodium silicate aqueous solution containing layered sodium silicate obtained from the capture process, and W2 is the amount of layered sodium silicate in the high-purity sodium silicate aqueous solution obtained from the separation process. Furthermore, the amount of layered sodium silicate in each sodium silicate aqueous solution is obtained by filtering the sampled sodium silicate aqueous solution through a 0.1 μm filter, measuring the weight of the layered sodium silicate in the filter residue, and converting this weight into the weight in the sodium silicate aqueous solution.

[0052] In addition, the amount removed is determined by mass (W) S ) and quality (W N The mass ratio (W) obtained S / W N ) indicates that the mass (W) S The mass of layered sodium silicate removed during the separation process is calculated using W1-W2. NThe value is the mass of nickel in the crude sodium silicate aqueous solution, calculated based on the nickel concentration in the crude sodium silicate aqueous solution.

[0053] In one embodiment of the present invention, the capture step and the separation step may be performed simultaneously. That is, the following method can be used: in the form (2), a crude sodium silicate aqueous solution is passed through a filling layer containing layered sodium silicate.

[0054] More specifically, regarding this configuration, the following method is preferred: a packing layer containing layered sodium silicate is placed in the flow path of the crude sodium silicate aqueous solution, allowing the crude sodium silicate aqueous solution to pass through the packing layer and come into contact with the layered sodium silicate. Alternatively, the following method can be used: a cage filled with layered sodium silicate is housed in a container and immersed in the crude sodium silicate aqueous solution, and the crude sodium silicate aqueous solution is circulated or stirred as needed.

[0055] Regarding the layered sodium silicate filled in the filling layer, it is preferably set to a size in which the layered sodium silicate will not flow out, or made into a form of a filler loaded with layered sodium silicate.

[0056] Furthermore, regarding the filling amount, it is unrelated to the nickel content in the crude sodium silicate aqueous solution; even if an excess is present, there will be no problem. On the contrary, by using a filling layer filled with excess layered sodium silicate, there is the advantage of being able to continuously process the crude sodium silicate aqueous solution.

[0057] In one embodiment of the present invention, including the capture process and the separation process, the inner surfaces of containers, pipes, etc. in the process are preferably made of a material that does not leach nickel as much as possible.

[0058] In one embodiment of the present invention, nickel, which is considered particularly problematic due to contamination from raw materials and equipment, is present in extremely low concentrations in the high-purity sodium silicate aqueous solution obtained after the separation process, reaching less than 100 ppb relative to the SiO2 content in sodium silicate. In other words, the high-purity sodium silicate aqueous solution obtained by the manufacturing method according to one embodiment of the present invention has a nickel content of less than 100 ppb relative to the SiO2 content in sodium silicate. Furthermore, in the high-purity sodium silicate aqueous solution according to one embodiment of the present invention, the content of other metallic impurities is not particularly limited, but the concentration of metallic impurities such as Cr, Cu, and Zn is preferably less than 1 ppm. This concentration can be achieved by known methods.

[0059] One embodiment of the present invention relates to a high-purity sodium silicate aqueous solution, which, due to its extremely low nickel content, is useful in applications requiring high-purity sodium silicate aqueous solutions, such as silica sol raw materials for semiconductor polishing agents.

[0060] 〔Summarize〕 As described above, the inventors conducted in-depth research and obtained the following insights: In the purification of crude sodium silicate aqueous solution, layered sodium silicate has excellent performance in capturing nickel present in sodium silicate aqueous solution. Furthermore, it was discovered that by capturing nickel with layered sodium silicate and removing the layered sodium silicate containing the captured nickel from the aqueous solution using methods such as filtration, a sodium silicate aqueous solution with extremely high purity and a nickel concentration of less than 100 ppb can be obtained, thus completing the present invention.

[0061] That is, the first aspect of the present invention relates to a method for manufacturing a high-purity sodium silicate aqueous solution, characterized in that it includes: a capture step, which uses layered sodium silicate to capture nickel from a nickel-containing sodium silicate aqueous solution; and a separation step, which removes the layered sodium silicate containing the captured nickel from the sodium silicate aqueous solution.

[0062] Furthermore, according to the first aspect above, in the method for manufacturing a high-purity sodium silicate aqueous solution according to the second aspect of the present invention, in the separation step, the removal rate of the layered sodium silicate is 90% or more, and the amount of layered sodium silicate removed is 100 times or more by mass relative to the nickel content in the sodium silicate aqueous solution in the capture step, which is preferred as it can remove nickel to a high degree.

[0063] Furthermore, according to the first or second aspect described above, in the method for manufacturing a high-purity sodium silicate aqueous solution according to the third aspect of the present invention, preferably, the capture step is performed by generating the layered sodium silicate from a portion of the sodium silicate in the sodium silicate aqueous solution.

[0064] Furthermore, according to the third aspect above, in the method for manufacturing high-purity sodium silicate aqueous solution according to the fourth aspect of the present invention, layered sodium silicate is preferably generated by holding the sodium silicate aqueous solution at a temperature of 140°C to 190°C so that the "temperature (°C) × holding time (hr)" reaches a range of 500 to 5000.

[0065] Furthermore, according to the first or second aspect described above, in the method for manufacturing a high-purity sodium silicate aqueous solution according to the fifth aspect of the present invention, preferably, the capture step is performed by contacting the layered sodium silicate with the sodium silicate aqueous solution.

[0066] Furthermore, according to any one of the first to fifth aspects described above, in the method for manufacturing a high-purity sodium silicate aqueous solution according to the sixth aspect of the present invention, preferably, the operation of removing the layered sodium silicate in the separation step is filtration.

[0067] Furthermore, according to any one of the first to sixth aspects above, in the method for manufacturing a high-purity sodium silicate aqueous solution according to the seventh aspect of the present invention, preferably, the sodium silicate concentration of the sodium silicate aqueous solution, converted to SiO2, is greater than 10% by mass and less than 35% by mass.

[0068] The eighth aspect of the present invention also provides a high-purity sodium silicate aqueous solution, characterized in that it can be obtained by any one of the manufacturing methods of the first to seventh aspects, and the nickel content is less than 100 ppb relative to the SiO2 content in the sodium silicate.

[0069] Furthermore, as a ninth aspect of the present invention, the high-purity sodium silicate aqueous solution involved in the eighth aspect is useful as a raw material for silica sol for semiconductor polishing agents.

[0070] Example To illustrate the invention in more detail, embodiments will be shown, but the invention is not limited to these embodiments.

[0071] Furthermore, in the examples and comparative examples, the determination of various physical properties was carried out according to the following methods.

[0072] (i) Identification of layered sodium silicate removed during the separation process The layered sodium silicate removed during the separation process was identified using an X-ray diffraction apparatus (Rigaku Corporation SmartLab).

[0073] (ii) Particle size of layered sodium silicate removed during the separation process The particle size of the layered sodium silicate removed during the separation process was confirmed using images obtained by scanning electron microscopy (SU3500, Hitachi High Technology Co., Ltd.).

[0074] (iii) The concentration of nickel and other metals in the sodium silicate aqueous solution. Hydrofluoric acid was added to an aqueous sodium silicate solution, and the silicate component was removed by heating. The metal composition was then analyzed by inductively coupled plasma mass spectrometry (Agilent 7900). The ratio of the metal composition to the SiO2 composition in the aqueous sodium silicate solution was expressed as "ppb".

[0075] (iv) Removal rate and amount of layered sodium silicate in the separation process Regarding the removal rate, 100 ml of crude sodium silicate aqueous solution after the capture process was collected, filtered through a filter with a pore size of 0.1 μm, and the residue on the filter material was washed with water and dried. Then, the weight of the layered sodium silicate was measured and converted into the amount of layered sodium silicate in the total crude sodium silicate aqueous solution (W1). On the other hand, 100 ml of high-purity sodium silicate aqueous solution after the separation process was collected, filtered through a filter with a pore size of 0.1 μm, and the residue on the filter material was washed with water and dried. Then, the weight of the layered sodium silicate was measured and converted into the amount of layered sodium silicate in the total crude sodium silicate aqueous solution (W2). The removal rate is calculated based on the respective masses using the following formula.

[0076] ((W1-W2) / W1)×100 In addition, the amount removed is determined by mass (W) S ) and quality (W N The mass ratio (W) obtained S / W N ) indicates that the mass (W) S The mass of layered sodium silicate removed during the separation process is calculated using W1-W2. N The value is the mass of nickel in the crude sodium silicate aqueous solution, calculated based on the nickel concentration in the crude sodium silicate aqueous solution.

[0077] Furthermore, if the viscosity of the collected sodium silicate aqueous solution is high, it should be diluted to a suitable concentration for filtration before implementing the method. Specifically, in the filtration of the sodium silicate aqueous solution, if the viscosity does not meet the condition of below 50 mPa·s, dilution should be performed to meet this condition.

[0078] Examples 1-5, Comparative Example 1 Prepare a crude sodium silicate aqueous solution with the concentrations (SiO2 concentration, Na2O concentration) and nickel content shown in Table 1.

[0079] [Capture Process] The crude sodium silicate aqueous solution was treated in an autoclave according to the temperature and holding time shown in Table 1.

[0080] [Separation Process] The crude sodium silicate aqueous solution after the capture process was filtered through a fluoropolymer membrane filter with a pore size of 1 μm.

[0081] Table 1 shows the removal rate and amount of layered sodium silicate in the separation process, the particle size of the removed layered sodium silicate, and the nickel concentration of the resulting high-purity sodium silicate aqueous solution.

[0082] In addition, during the separation process, the residue can be confirmed by the analysis described in (i). In the X-ray diffraction pattern, only the peak of sodium hydrosilicate was detected, and the broad so-called halo pattern commonly found in amorphous materials was not observed, thus confirming that it is almost 100% sodium hydrosilicate. Figure 1 The X-ray diffraction pattern of the residue obtained in Example 1 is shown below for reference only.

[0083] Table 1

[0084] ※: Mass ratio of removed layered sodium silicate to nickel content in crude sodium silicate aqueous solution Example 6 In Example 2, 0.7 g of separately prepared layered sodium silicate (water-hydroxysodium silicate) powder was added relative to 1 kg of crude sodium silicate aqueous solution, and the mixture was stirred thoroughly at 40°C to carry out the capture process, thereby obtaining a high-purity sodium silicate aqueous solution.

[0085] The removal rate of layered sodium silicate in the separation process is 100%, the removal amount is 26,000, and the nickel concentration of the resulting high-purity sodium silicate aqueous solution is below 30 ppb.

[0086] Example 7 Next, a capture process was implemented in the step of dissolving the chopped glass in water to prepare a crude sodium silicate aqueous solution. Specifically, 15 g of chopped glass (SiO2: 75.5%, Na2O: 24.5%) and 60 g of ultrapure water were added to a PTFE crucible, which was then inserted into a stainless steel jacket and heated in an electric furnace at a temperature set at 160°C for 12 hours. The crucible was then removed from the furnace and cooled.

[0087] In addition, in order to confirm the time of the capture process in the above operation, the time for the SiO2 concentration of the crude sodium silicate aqueous solution to reach 10% by mass was confirmed under the same feeding conditions. The result was 2 hours. Therefore, the time obtained by subtracting 2 hours from the 12 hours (10 hours) was taken as the heating time of the capture process.

[0088] The crude sodium silicate aqueous solution after the above-mentioned capture process has a SiO2 equivalent concentration of 14.99% by mass, a Na2O equivalent concentration of 4.91% by mass, a nickel content of 360 ppb, and contains layered sodium silicate.

[0089] The crude sodium silicate aqueous solution obtained after the capture process was used to carry out the separation process in the same manner as in Example 1. The removal rate of layered sodium silicate in the separation process was 100%, the removal amount was 1800, and the nickel concentration of the resulting high-purity sodium silicate aqueous solution was 80 ppb.

Claims

1. A method for manufacturing a high-purity sodium silicate aqueous solution, characterized in that, include: The capture process utilizes layered sodium silicate to capture nickel from an aqueous solution of nickel-containing sodium silicate; as well as A separation process is performed to remove the layered sodium silicate containing the nickel from the aqueous sodium silicate solution.

2. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 1, wherein, In the separation process, the removal rate of the layered sodium silicate is over 90%, and the amount of layered sodium silicate removed is over 100 times by mass relative to the nickel content in the sodium silicate aqueous solution in the capture process.

3. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 1, wherein, The capture process is carried out by generating the layered sodium silicate from a portion of the sodium silicate in the aqueous sodium silicate solution.

4. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 3, wherein, The layered sodium silicate is generated by holding the sodium silicate aqueous solution at a temperature of 140°C to 190°C so that the temperature (°C) × holding time (hr) reaches a range of 500 to 5000.

5. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 1, wherein, The capture process is carried out by contacting the layered sodium silicate with the aqueous sodium silicate solution.

6. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 1, wherein, The process of removing the layered sodium silicate is filtration.

7. The method for manufacturing a high-purity sodium silicate aqueous solution according to claim 1, wherein, The sodium silicate concentration in the sodium silicate aqueous solution, after being converted to SiO2, is greater than 10% by mass and less than 35% by mass.

8. A high-purity sodium silicate aqueous solution, characterized in that, The nickel content is less than 100 ppb relative to the SiO2 content in sodium silicate.

9. A silica sol raw material for semiconductor polishing agents, comprising the high-purity sodium silicate aqueous solution as described in claim 8.

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