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

Abstract

Provided is a production method that makes it possible to obtain, by a simple manner, a high-purity aqueous sodium silicate solution in which nickel is reduced to an extremely low concentration from a nickel-containing aqueous sodium silicate solution. The method for producing an aqueous sodium silicate solution in which nickel is reduced comprises: a capture step in which nickel is captured from a nickel-containing aqueous sodium silicate solution using layered sodium silicate; and a separation step in which the layered sodium silicate having captured the nickel is removed from the aqueous sodium silicate solution.

Description

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

[0001] The present invention relates to a novel method for producing a high-purity aqueous sodium silicate solution, and more particularly to a method for producing a high-purity aqueous sodium silicate solution having a reduced nickel concentration, which is suitable as a raw material for silica sol for semiconductor polishing.

[0002] Sodium silicate aqueous solutions are widely used in various fields, such as civil engineering and construction, paper and pulp, detergents and soaps, and ceramics, as soil improvement agents, additives for pulp bleaching agents, binders for refractories and castings, and flocculants for water purification. Furthermore, sodium silicate aqueous solutions are used as a raw material to manufacture various silica products, such as precipitated silica, silica gel, and silica sol (colloidal silica dispersion), as well as detergent builders and silicate products such as zeolites.

[0003] Among these, silica sol is used for applications such as a coating agent that imparts hardness and scratch resistance to the surface of optical materials, imparting antiblocking properties to film materials, an inorganic binder for ceramics, and precision polishing of various substrate surfaces, but in particular, in applications such as polishing the surfaces of semiconductor wafers and semiconductor devices, the demand for reducing metal impurities has increased further with the progress of semiconductor technology.The demand for the above silica sol has also spread to the sodium silicate aqueous solution that is its raw material, and there is an increasing demand for a high-purity sodium silicate aqueous solution with reduced metal impurities.

[0004] In general, aqueous sodium silicate solutions are produced by mixing silica sand with an alkali source such as soda ash or sodium hydroxide, melting the mixture at high temperature to obtain anhydrous sodium silicate (also called "cullet" because it is a glass-like solid), adding water to the resulting solution, heating it in an autoclave to dissolve it, and passing the dissolved solution through a filter press or the like to remove insoluble matter.

[0005] Another method for producing an aqueous sodium silicate solution is to heat and dissolve silica in an alkaline aqueous solution.

[0006] Silica sol is generally produced by diluting the aqueous sodium silicate solution produced as described above as necessary, bringing it into contact with an H-type strongly acidic cation exchange resin, further adjusting the pH of the resulting activated silica, removing impurities or foreign matter using techniques such as ion exchange or ultrafiltration, heating to adjust the particle size of the silica particles, and stabilizing the solution by adjusting the pH by adding ammonia water or the like.

[0007] Conventionally, various attempts have been made to increase the purity of silica sol in the manufacturing process, but in order to achieve even higher purity, it is necessary to suppress the impurities contained in the aqueous sodium silicate solution used as a raw material for producing silica sol to a certain level or less. In particular, for semiconductor applications, there is a strong demand for reducing the concentration of metal impurities, particularly nickel (Ni), which is likely to be mixed into the aqueous sodium silicate solution during the manufacturing process.

[0008] Disclosed methods for producing aqueous sodium silicate solutions with the aim of reducing metal impurities include dissolving a high-purity silica source in an alkaline aqueous solution such as sodium hydroxide. Examples include a method of dissolving high-purity glass, a by-product of semiconductor or optical fiber production, in an alkaline aqueous solution (see Patent Document 1), a method of neutralizing a commercially available aqueous sodium silicate solution to produce high-purity hydrated silica, which is then dissolved in an alkaline aqueous solution (see Patent Document 2), and a method of contacting an aqueous sodium silicate solution with an ion exchange resin to produce high-purity silica sol or silica gel, which is then dissolved in an alkaline aqueous solution (see Patent Document 3).

[0009] However, even if a high-purity raw material is used as the silicon source, when an alkaline aqueous solution is used, it is inevitable that nickel will be mixed into the alkaline aqueous solution in the production equipment, and in either method, the resulting sodium silicate aqueous solution contains nickel on the order of ppm. Moreover, the production methods have also had problems such as limitations on the availability of high-purity silica sources and the need for a large number of purification steps.

[0010] Another known method for producing a high-purity aqueous sodium silicate solution is to dilute a commercially available aqueous sodium silicate solution obtained by dissolving anhydrous sodium silicate in water, and then filter the diluted solution under pressure using a membrane filter having specific micropores (see Patent Document 4).

[0011] However, even if the solids present in the aqueous sodium silicate solution obtained by dissolving cullet in water under normal conditions are removed, the effect of reducing the nickel concentration is not sufficient, and the resulting aqueous sodium silicate solution contains a large amount of nickel that has not been completely removed.

[0012] Furthermore, as a method for removing impurities in the process of producing silica sol, a production method has been disclosed in which a chelating agent is added in advance when dissolving cullet in water, thereby forming a metal chelate complex with the metal impurities in the aqueous sodium silicate solution, producing silica sol in this state, and then removing the metal chelate complex from the obtained silica sol (see Patent Document 5).

[0013] However, in the above-mentioned production method, the nickel captured by the chelating agent remains in the sodium silicate aqueous solution in the form of a metal chelate complex, and the method does not disclose an aqueous sodium silicate solution with reduced nickel. Furthermore, as a production method, there is a concern that the use of a chelating agent will increase production costs.

[0014] Japanese Patent Publication No. 2003-238143 Japanese Patent Publication No. 2003-183018 Japanese Patent Publication No. 61-101414 Japanese Patent Publication No. 2002-511379 International Publication No. WO2020-262406

[0015] Therefore, an object of the present invention is to provide a production method capable of obtaining a high-purity aqueous sodium silicate solution in which nickel is reduced to an extremely low concentration by a simple method from an aqueous sodium silicate solution containing nickel (hereinafter also referred to as a crude sodium silicate aqueous solution).

[0016] One aspect of the present invention is a method for producing a high-purity aqueous sodium silicate solution, comprising: a capture step of capturing nickel from a nickel-containing aqueous sodium silicate solution with layered sodium silicate; and a separation step of removing the layered sodium silicate that has captured nickel from the aqueous sodium silicate solution.

[0017] In addition, one aspect of the present invention is a sodium silicate having a nickel content of SiO ２ This is a high-purity aqueous sodium silicate solution characterized by having a sodium silicate content of 100 ppb or less relative to the total amount of the component.

[0018] According to one aspect of the present invention, a production method can be provided that can obtain a high-purity aqueous sodium silicate solution in which nickel is reduced to an extremely low concentration.

[0019] FIG. 2 is a diagram showing an X-ray diffraction chart of the residue separated in the separation step in Example 1.

[0020] A method for producing a high-purity aqueous sodium silicate solution according to one embodiment of the present invention is characterized by comprising: a capturing step of capturing nickel from a nickel-containing aqueous sodium silicate solution with layered sodium silicate; and a separation step of removing the layered sodium silicate that has captured nickel from the aqueous sodium silicate solution.

[0021] According to a manufacturing method according to one embodiment of the present invention, a crude sodium silicate aqueous solution produced using a raw material contaminated with nickel is used to obtain SiO of sodium silicate having a nickel content. ２ A highly pure aqueous sodium silicate solution with a concentration of 100 ppb or less of the components can be produced by simple means with good reproducibility.

[0022] Although the mechanism by which this effect is exerted is not clear, the inventors presume that this is because the interlayer structure of layered sodium silicate is suitable for capturing nickel present as nickel ions in the aqueous solution of crude sodium silicate.

[0023] Furthermore, according to one embodiment of the present invention, it is possible to obtain a nickel-containing sodium silicate SiO 2 , which has not been achieved in the prior art. ２It is also possible to provide an aqueous sodium silicate solution with a concentration of 100 ppb or less relative to the components, and such an aqueous sodium silicate solution can be suitably used as a silica sol raw material for semiconductor polishing.

[0024] The crude sodium silicate aqueous solution that is the subject of one embodiment of the present invention can be obtained by a known method for producing a sodium silicate aqueous solution. Specific examples of the production method include a method of dissolving cullet in water and a method of dissolving a silicon source such as silica or glass in a sodium hydroxide aqueous solution. In these methods, dissolution is carried out at a temperature depending on the silicon source; for example, in the case of cullet, dissolution is carried out in an autoclave at a temperature of about 140°C, and dissolution is generally completed within about 1 to 2 hours. On the other hand, a partially dissolved cullet (e.g., half of the cullet) may also be used as a product, and one embodiment of the present invention can be used to produce a crude sodium silicate aqueous solution obtained by either method.

[0025] Furthermore, as the aqueous solution of crude sodium silicate, water glass generally available as No. 1, No. 2 or No. 3 industrial group standard prepared by the Sodium Silicate Committee of the Japan Inorganic Chemicals Association may be used.

[0026] Furthermore, in one embodiment of the present invention, the sodium silicate concentration of the crude sodium silicate aqueous solution is not particularly limited, but considering the ease of producing layered sodium silicate in the capture step and the ease of handling in the separation step, it is preferably more than 10% by mass and not more than 35% by mass, particularly 12 to 30% by mass, calculated as SiO2. In addition, the molar ratio (SiO ２ / Na ２ O) is not particularly limited, but is generally in the range of 2.0 to 4.0.

[0027] The contamination of sodium silicate aqueous solution with nickel is thought to occur mainly from the raw material and manufacturing equipment of cullet when the cullet is used, and mainly from the manufacturing equipment when sodium hydroxide aqueous solution is used. The amount of nickel contamination varies depending on the contamination source, but it is thought that the amount of nickel contamination is mainly due to the SiO2 of the sodium silicate aqueous solution. ２The concentration of nickel in the aqueous solution of crude sodium silicate is 200 ppb or more, and in some cases, 500 ppb or more.

[0028] The most notable feature of the method for producing a high-purity sodium silicate aqueous solution according to one embodiment of the present invention is that it includes a capture step of capturing nickel in a nickel-containing sodium silicate aqueous solution with layered sodium silicate.

[0029] By employing this capture step, nickel in the crude sodium silicate aqueous solution is captured by the layered sodium silicate, and by separating the layered sodium silicate that has captured nickel from the crude sodium silicate aqueous solution, a high-purity sodium silicate aqueous solution with a significantly reduced nickel concentration can be obtained.

[0030] Such behavior regarding nickel removal by layered sodium silicate in a crude sodium silicate aqueous solution has not been reported before, and was discovered for the first time by the present inventors.

[0031] The present inventors have confirmed that, depending on the method for producing a crude sodium silicate aqueous solution, particularly the method for producing it by heating in an autoclave, extremely fine layered sodium silicate may be present, or a small amount of layered sodium silicate particles grown by localized heating may be present. However, the existence of the extremely fine layered sodium silicate has not been confirmed in the past, and it cannot be separated even by the usual industrially implemented means for removing foreign matter such as filtration, and it remains in the purified sodium silicate aqueous solution, so it is presumed that the effect of layered sodium silicate in reducing the nickel concentration has not been confirmed. Furthermore, the amount of layered sodium silicate produced by localized heating is extremely small, and even if it is removed as a foreign matter, the effect of reducing the nickel concentration in the purified sodium silicate aqueous solution has not been confirmed.

[0032] In a method according to one embodiment of the present invention, the capture step includes capturing nickel by producing the layered sodium silicate particles described above, and further, if necessary, nickel can be captured by adding layered sodium silicate to make up for the shortage. Then, by removing the layered sodium silicate that has captured nickel in a separation step described below, the nickel content in the crude sodium silicate aqueous solution can be effectively reduced.

[0033] Therefore, the capture step according to one embodiment of the present invention is applicable to both a crude aqueous sodium silicate solution containing layered sodium silicate produced in the production step of an aqueous sodium silicate solution as described above, and a crude aqueous sodium silicate solution not containing layered sodium silicate.

[0034] In one embodiment of the present invention, the layered sodium silicate is SiO ２ -Na ２ O-H ２ There are no particular limitations as long as the layered crystal is O-based. ２ Depending on the content, examples include makatites, iraites, magadiites, and kenyaites.

[0035] In one embodiment of the present invention, the capture step is not particularly limited in its mode, as long as it can provide a crude aqueous sodium silicate solution containing layered sodium silicate that has captured nickel in an amount and size that allows layered sodium silicate to be separated with a sufficient removal rate and amount in a separation step described below.

[0036] Specific examples of the method include (1) a method in which layered sodium silicate is produced from a portion of the sodium silicate in a crude sodium silicate aqueous solution, and (2) a method in which layered sodium silicate is brought into contact with a sodium silicate aqueous solution.

[0037] The above-mentioned embodiment (1) generates layered sodium silicate from a portion of the sodium silicate in a crude sodium silicate aqueous solution, thereby increasing the amount of fine layered sodium silicate necessary for capturing nickel in a crude sodium silicate aqueous solution containing the fine layered sodium silicate, and growing the fine layered sodium silicate to a size separable in the subsequent separation step. Furthermore, in a crude sodium silicate aqueous solution containing a trace amount of layered sodium silicate, the embodiment functions to increase the amount of layered sodium silicate necessary for capturing nickel, and to grow the layered sodium silicate generated to a size separable in the subsequent separation step. Of course, in a general crude sodium silicate aqueous solution not containing layered sodium silicate, the embodiment functions to generate the amount of layered sodium silicate necessary for capturing nickel, and to grow the layered sodium silicate to a size separable in the subsequent separation step. That is, "generating layered sodium silicate" in the capture step refers to generating layered sodium silicate of a size separable in the separation step.

[0038] For the embodiment (1), a suitable example of a method is to hold a crude sodium silicate aqueous solution under pressure at a temperature of 140 to 190°C. The holding time at this temperature should be a time that allows layered sodium silicate to be produced with a sufficient removal rate and amount in the separation step described below. Specifically, a method can be used in which the temperature (°C) x holding time (hr) is 500 to 5,000, particularly 1,000 to 4,000. Under such conditions, layered sodium silicate can be grown to an appropriate size that allows easy removal in the separation step described below, and layered sodium silicate can be produced in an amount sufficient to capture nickel.

[0039] That is, if the temperature is lower than 140°C, even if the holding time is extended, the production and growth of layered sodium silicate becomes extremely slow, making industrial implementation difficult. The lower limit of the temperature is preferably 145°C. On the other hand, if the temperature exceeds 190°C, a portion of the layered sodium silicate will further convert to cristobalite or quartz, reducing the amount of layered sodium silicate produced, which may result in a decrease in nickel capture ability. The upper limit of the temperature is preferably 180°C.

[0040] Furthermore, when the temperature (°C) x holding time (hr) is smaller than the above range, the amount of layered sodium silicate produced tends to be insufficient, the absolute amount of layered sodium silicate becomes insufficient, and it becomes difficult to obtain layered sodium silicate particles of an appropriate size, i.e., a size that can be easily removed in the separation step. Here, the suitable size of layered sodium silicate depends on the capacity of the separation step, but industrially, it is a particle diameter of 0.5 μm or more, preferably 1 μm or more.

[0041] The means for producing layered sodium silicate may be carried out during or subsequent to the production process of a crude sodium silicate aqueous solution, or may be carried out on a separately produced crude sodium silicate aqueous solution. In an embodiment in which layered sodium silicate is produced during the production process of a crude sodium silicate aqueous solution, the temperature at which cullet or the like is dissolved is within the temperature range suitable for the capture step (1) and the time after the silica concentration of the crude sodium silicate aqueous solution has reached 10 mass % is counted as the retention time for producing layered sodium silicate.

[0042] More specifically, in the embodiment (2) above, a method including an addition step of adding layered sodium silicate to the aqueous crude sodium silicate solution is suitable as the step of contacting the aqueous crude sodium silicate solution with layered sodium silicate.

[0043] The layered sodium silicate may be commercially available and is not particularly limited, but may be one produced by a known production method. The size of the layered sodium silicate to be added is preferably a particle diameter of 0.5 μm or more, preferably 1 μm or more, considering ease of removal in the separation step. The upper limit of the average particle size is not particularly limited, but may be about 10 μm. The appropriate amount of layered sodium silicate to be added may be an amount that can achieve the removal rate and amount of layered sodium silicate that has captured nickel and is removed in the separation step described below.

[0044] In the addition step, it is preferable to thoroughly stir the mixture after adding the layered sodium silicate to the aqueous solution of crude sodium silicate. The contact time after the addition is not particularly limited, but it is sufficient to ensure 30 seconds or more.

[0045] The added layered sodium silicate is brought into contact with an aqueous solution of crude sodium silicate to capture nickel, which is then removed by a separation step described below.

[0046] The above-mentioned embodiment (2) is particularly effective for a crude sodium silicate aqueous solution that does not contain layered sodium silicate or contains a trace amount of layered sodium silicate particles. The trace amount of layered sodium silicate particles refers to the content when, for example, dissolution in the production process of the crude sodium silicate aqueous solution is carried out outside the range of temperature (°C) x retention time (hr) that is suitable for the embodiment (1) above.

[0047] In one embodiment of the present invention, the separation step is a step of removing the layered sodium silicate that has captured nickel in the capture step from the aqueous solution of crude sodium silicate, and any means capable of performing such an operation may be employed without particular limitation. As a specific example of a method, removal by filtration is suitable for industrial implementation.

[0048] The filter material used for the filtration is preferably determined taking into consideration the removal rate and filtration speed of the layered sodium silicate present in the crude sodium silicate aqueous solution. In addition, considering the prevention of secondary contamination due to filtration, the material of the filter material is preferably made of a polymer material such as polypropylene, fluororesin, nylon, polysulfonic acid, polyethersulfone, cellulose, etc. In addition, it is desirable to set the pore size of the filter material to a size that can remove as much of the layered sodium silicate that has captured nickel as possible in the separation process. The pore size of the filter material may be appropriately determined to an industrially advantageous size that can achieve the removal rate described below depending on the particle size of the layered sodium silicate. For example, it may be 1.0 μm or less, or 0.5 μm or less. In addition, the pore size may be 0.05 μm or more, 0.1 μm or more, or 0.25 μm or more.

[0049] In addition, taking into consideration the filtration efficiency in industrial implementation, the air permeability is generally 10 ((cm ３ / (cm ２ Filter cloths conforming to JIS L 1096 (Testing Methods for Woven and Knit Fabrics) can be used, and can be used together with filter aids such as diatomaceous earth and perlite. The use of filter aids allows the pores in the filter aid, which are smaller than the pore size of the filter material, to efficiently remove the layered sodium silicate that has formed. Furthermore, filtration methods using the filter material include atmospheric pressure filtration, pressure filtration, reduced pressure filtration, and centrifugation, without any particular restrictions.

[0050] In one embodiment of the present invention, the nickel removal effect is determined by the removal rate and amount of layered sodium silicate that captures nickel and is removed from the crude sodium silicate aqueous solution through a combination of the capture step and the separation step. That is, in order to sufficiently remove nickel from the crude sodium silicate aqueous solution, it is preferable to separate 90% or more, preferably 95% or more, of the layered sodium silicate that has captured nickel from the crude sodium silicate aqueous solution.

[0051] The amount of layered sodium silicate removed from the aqueous crude sodium silicate solution is 100 times or more, preferably 1000 times or more, by mass ratio, relative to the nickel content in the aqueous crude sodium silicate solution. However, if the amount of layered sodium silicate removed is too large, not only will the nickel reduction effect plateau, but in an embodiment in which layered sodium silicate is produced from the aqueous crude sodium silicate solution, problems may arise due to a decrease in the molar ratio of the resulting high-purity sodium silicate. Therefore, the upper limit of the amount of layered sodium silicate removed is preferably 50,000 times, by mass ratio, relative to the nickel content in the aqueous crude sodium silicate solution.

[0052] Here, the removal rate (%) of layered sodium silicate is a value calculated by ((W1-W2) / W1) x 100, where W1 is the amount of layered sodium silicate in the crude sodium silicate aqueous solution containing layered sodium silicate obtained in the capture step, and W2 is the amount of layered sodium silicate in the high-purity sodium silicate aqueous solution obtained in the separation step. The amount of layered sodium silicate in each sodium silicate aqueous solution was determined by filtering a sampled sodium silicate aqueous solution through a filter with a pore size of 0.1 μm, measuring the weight of the layered sodium silicate remaining on the filtration, and converting the weight into the weight in the sodium silicate aqueous solution.

[0053] The amount of removal is the mass (W Ｓ ) and the mass of nickel in the crude sodium silicate aqueous solution (W Ｎ ) and the mass ratio (W Ｓ / W Ｎ )

[0054] In one embodiment of the present invention, the capture step and the separation step can be carried out simultaneously, i.e., in the embodiment (2), a method can be exemplified in which the crude aqueous sodium silicate solution is passed through a packed bed containing layered sodium silicate.

[0055] More specifically, a preferred embodiment of this method is to provide a packed bed containing layered sodium silicate in the middle of a flow path for the aqueous crude sodium silicate solution, and pass the aqueous crude sodium silicate solution through the packed bed to bring the aqueous crude sodium silicate solution into contact with the layered sodium silicate.Another example is to immerse a basket filled with layered sodium silicate in the aqueous crude sodium silicate solution contained in a container, and circulate or stir the aqueous crude sodium silicate solution as needed.

[0056] The layered sodium silicate packed in the packed bed is preferably of a size that prevents the layered sodium silicate from leaking out, or in the form of a packing that supports the layered sodium silicate.

[0057] Furthermore, regardless of the nickel content of the aqueous solution of crude sodium silicate, there is no problem even if an excess amount of layered sodium silicate is present. Rather, the use of a packed bed filled with an excess amount of layered sodium silicate has the advantage of enabling the process of continuously treating the aqueous solution of crude sodium silicate to be realized.

[0058] In one embodiment of the present invention, it is preferable that the inner surfaces of containers, pipes, etc. used in the process, including the capture process and separation process, be made of materials that do not leach nickel as much as possible.

[0059] In one embodiment of the present invention, the high-purity sodium silicate aqueous solution obtained through the separation step has an extremely low content of nickel, which has been a particular problem due to contamination from raw materials and equipment, and can achieve a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate. In other words, the high-purity sodium silicate aqueous solution obtained by the production method according to one embodiment of the present invention has a nickel content that is lower than the SiO2 content of sodium silicate. ２ The concentration of other metal impurities in the high-purity sodium silicate aqueous solution according to one embodiment of the present invention is not particularly limited, but it is preferable that the concentration of metal impurities such as Cr, Cu, and Zn is 1 ppm or less. Such concentrations can be achieved by known methods.

[0060] The high-purity sodium silicate aqueous solution according to one embodiment of the present invention has an extremely low nickel content and is therefore useful in applications requiring a high-purity sodium silicate aqueous solution, such as a raw material for silica sol for semiconductor abrasives.

[0061] [Summary] As described above, the present inventors have conducted extensive research and have found that, in the purification of a crude aqueous solution of sodium silicate, layered sodium silicate has an excellent ability to capture nickel present in the aqueous solution of sodium silicate. They have also found that by trapping nickel in the layered sodium silicate and then removing the layered sodium silicate that has trapped nickel from the aqueous solution by a method such as filtration, an extremely high-purity aqueous solution of sodium silicate with a nickel concentration of 100 ppb or less can be obtained, and have completed the present invention.

[0062] That is, the method for producing a high-purity aqueous sodium silicate solution according to Aspect 1 of the present invention is characterized by comprising: a capturing step of capturing nickel from a nickel-containing aqueous sodium silicate solution with layered sodium silicate; and a separation step of removing the layered sodium silicate that has captured nickel from the aqueous sodium silicate solution.

[0063] In addition, in the method for producing a high-purity aqueous sodium silicate solution according to Aspect 2 of the present invention, in Aspect 1, it is preferable that the removal rate of the layered sodium silicate in the separation step is 90% or more and the amount of the layered sodium silicate removed is 100 times or more, in mass ratio, the nickel content in the aqueous sodium silicate solution in the capture step, in order to remove nickel to a high degree.

[0064] A preferred embodiment of the method for producing a high-purity aqueous sodium silicate solution according to Aspect 3 of the present invention is the method for producing a high-purity aqueous sodium silicate solution according to Aspect 1 or 2, wherein the capturing step is carried out by producing the layered sodium silicate from a part of the sodium silicate in the aqueous sodium silicate solution.

[0065] In addition, in the method for producing a high-purity aqueous sodium silicate solution according to Aspect 4 of the present invention, in the method for producing a high-purity aqueous sodium silicate solution according to Aspect 3, it is preferable that the layered sodium silicate is produced by holding the aqueous sodium silicate solution at a temperature of 140 to 190°C so that the temperature (°C) x holding time (hr) is in the range of 500 to 5,000.

[0066] In addition, in the method for producing a high-purity aqueous sodium silicate solution according to Aspect 5 of the present invention, in Aspect 1 or 2, the capturing step is preferably carried out by contacting the layered sodium silicate with the aqueous sodium silicate solution.

[0067] In addition, in the method for producing a high-purity aqueous sodium silicate solution according to Aspect 6 of the present invention, in any one of Aspects 1 to 5, it is preferable that the operation of removing the layered sodium silicate in the separation step is filtration.

[0068] A seventh aspect of the present invention provides a method for producing a high-purity aqueous sodium silicate solution according to any one of the first to sixth aspects, wherein the sodium silicate concentration in the aqueous sodium silicate solution is SiO ２ It is preferable that the content of the cellulose ester compound is more than 10 mass % and 35 mass % or less in terms of the total mass of the cellulose ester compound.

[0069] Aspect 8 of the present invention is a method for producing a SiO2-containing sodium silicate having a nickel content, which can be obtained by the production method of any one of aspects 1 to 7. ２ The present invention also provides a high-purity aqueous sodium silicate solution characterized by having a sodium silicate content of 100 ppb or less relative to the total amount of the component.

[0070] In a ninth aspect of the present invention, the high-purity aqueous sodium silicate solution according to the eighth aspect is useful as a raw material for silica sol for semiconductor abrasives.

[0071] EXAMPLES In order to explain the present invention more specifically, examples are shown below, but the present invention is not limited to these examples.

[0072] In the examples and comparative examples, the measurements of various physical properties were carried out by the following methods.

[0073] (i) Identification of Layered Sodium Silicate Removed in the Separation Step The layered sodium silicate removed in the separation step was identified using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation).

[0074] (ii) Particle size of layered sodium silicate removed in the separation step The particle size of the layered sodium silicate removed in the separation step was confirmed from images obtained by a scanning electron microscope (SU3500 manufactured by Hitachi High-Technologies Corporation).

[0075] (iii) Nickel concentration and other metal concentrations in aqueous sodium silicate solution Hydrofluoric acid was added to the aqueous sodium silicate solution, and the silicic acid component was removed by heating. Then, the metal components were analyzed using an inductively coupled plasma mass spectrometer (Agilent 7900 manufactured by Agilent Technologies). ２ The proportion of each component is shown in ppb.

[0076] (iv) Removal rate and removal amount of layered sodium silicate in separation step The removal rate is measured by taking 100ml of the crude sodium silicate aqueous solution that has been through the capture step, filtering through a filter with a pore size of 0.1 μm, washing the residue on the filter material, drying, then measuring the weight of the layered sodium silicate, and converting this into the layered sodium silicate amount (W1) of the total amount of crude sodium silicate aqueous solution.On the other hand, taking 100ml of the high-purity sodium silicate aqueous solution that has been through the separation step, filtering through a filter with a pore size of 0.1 μm, washing the residue on the filter material, drying, then measuring the weight of the layered sodium silicate, and converting this into the layered sodium silicate amount (W2) of the total amount of crude sodium silicate aqueous solution, and the value calculated by the following formula from each mass is taken as the removal rate.

[0077] ((W1-W2) / W1) x 100. The amount of removal is calculated by subtracting W1 from W2, which is the mass (W Ｓ ) and the mass of nickel in the crude sodium silicate aqueous solution (W Ｎ ) and the mass ratio (W Ｓ / W Ｎ ) are shown.

[0078] In addition, when the viscosity of the collected sodium silicate aqueous solution was high, it was diluted to an appropriate concentration that allowed filtration, and then the above-mentioned method was carried out. Specifically, when the viscosity of the sodium silicate aqueous solution did not satisfy the condition of 50 mPa s or less in the filtration, it was diluted so as to satisfy this condition.

[0079] Examples 1 to 5 and Comparative Example 1 The concentrations (SiO ２ Concentration, Na ２ A crude sodium silicate aqueous solution having a 0 concentration, a nickel content, and a 100% aqueous solution of sodium silicate was prepared.

[0080] [Capturing Step] The crude aqueous sodium silicate solution was treated in an autoclave at the temperature and for the retention time shown in Table 1.

[0081] [Separation Step] The crude sodium silicate aqueous solution treated in the capture step was filtered through a fluororesin membrane filter having a pore size of 1 μm.

[0082] Table 1 also shows the removal rate and amount of layered sodium silicate removed in the separation step, the particle size of the removed layered sodium silicate, and the nickel concentration of the obtained high-purity aqueous sodium silicate solution.

[0083] In the separation step, the residue could be confirmed by the analysis (i) above, and in the X-ray diffraction chart, only the Kenyaite peak was detected, and the broad, so-called halo pattern seen in amorphous materials was not observed, so it was confirmed that it was almost 100% Kenyaite. For reference, the X-ray diffraction chart of the residue obtained in Example 1 is shown in Figure 1.

[0084]

[0085] Example 6 In Example 2, 0.7 g of separately prepared layered sodium silicate (Kenyaite) powder was added to 1 kg of the crude sodium silicate aqueous solution, and the mixture was thoroughly stirred at 40°C to carry out a capture step, thereby obtaining a high-purity sodium silicate aqueous solution.

[0086] The removal rate of layered sodium silicate in the separation step was 100%, the removal amount was 26,000, and the nickel concentration of the obtained high-purity aqueous sodium silicate solution was 30 ppb or less.

[0087] Example 7 A capturing step was carried out immediately after the step of dissolving cullet in water to produce a crude sodium silicate aqueous solution. ２ 75.5%, Na ２ A PTFE crucible was charged with 15 g of ammonium nitrate (24.5%) and 60 g of ultrapure water, which was then inserted into a stainless steel jacket and heated in an electric furnace set at 160° C. for 12 hours, then removed from the electric furnace and allowed to cool.

[0088] In order to confirm the time for the capture step in the above operation, the SiO ２ The time taken for the concentration to reach 10% by mass was checked and found to be 2 hours, so the heating time for the capture step was determined by subtracting 2 hours from the 12 hours (10 hours).

[0089] After the capture step, the crude sodium silicate aqueous solution contains SiO ２ Concentration is 14.99% by mass, Na ２ The O concentration was 4.91% by mass, the nickel content was 360 ppb, and the layered sodium silicate was contained.

[0090] The crude aqueous sodium silicate solution obtained through the capture step was used to carry out a separation step in the same manner as in Example 1. The removal rate of layered sodium silicate in the separation step was 100%, the removal amount was 1,800, and the nickel concentration of the obtained high-purity aqueous sodium silicate solution was 80 ppb.

Claims

1. A method for producing a high-purity sodium silicate aqueous solution, characterized by comprising a capture step of capturing nickel from a sodium silicate aqueous solution containing nickel using layered sodium silicate, and a separation step of removing the layered sodium silicate containing the captured nickel from the sodium silicate aqueous solution.

2. A method for producing a high-purity sodium silicate aqueous solution according to claim 1, wherein the removal rate of the layered sodium silicate in the separation step is 90% or more, and the amount of the layered sodium silicate removed is 100 times or more by mass ratio with respect to the nickel content in the sodium silicate aqueous solution in the capture step.

3. A method for producing a high-purity sodium silicate aqueous solution according to claim 1, wherein the capture step is performed by generating the layered sodium silicate from a portion of the sodium silicate in the sodium silicate aqueous solution.

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

5. A method for producing a high-purity sodium silicate aqueous solution according to claim 1, wherein the capture step is performed by bringing the layered sodium silicate and the aqueous sodium silicate aqueous solution into contact.

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

7. The sodium silicate concentration of the aforementioned sodium silicate aqueous solution is SiO ２ A method for producing a high-purity aqueous solution of sodium silicate according to claim 1, wherein the concentration, when converted to a fraction, exceeds 10% by mass and is 35% by mass or less.

8. Nickel content is SiO ２ A high-purity aqueous sodium silicate solution characterized by having a concentration of 100 ppb or less relative to the components, and a sodium silicate concentration exceeding 10% by mass and 35% by mass or less when converted to SiO2.

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