JP2019011207A - Method for washing amorphous silica - Google Patents

Abstract

To provide a method capable of washing an amorphous silica with efficiency in a short period of time by curtailing the amount of water used for washing.SOLUTION: There is provided a method for washing an amorphous silica with the use of a pressure adjustment container 1. The method comprises a water-absorption step (A) of supplying an amorphous silica 12 with water to give the amorphous silica 12 having absorbed water and (B) a step of subjecting the amorphous silica 12 having absorbed water simultaneously to pressurization in a pressurization chamber 2a and to depressurization in a depressurization chamber 2b to give a dehydrated amorphous silica. The pressure adjustment container 1 comprises amorphous silica-placing water permeation means (a perforated plate 10 and a filter cloth 11) that is capable of placing the amorphous silica 12 having absorbed water and that allows for the permeation of water contents; the pressurization chamber 2a arranged above the water-permeation means; and the depressurization chamber 2b arranged under the water-permeation means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for cleaning amorphous silica.

Silica includes natural silica and synthetic silica. Natural silica and synthetic silica are crystalline and amorphous, respectively. Therefore, there are many types of silica and they are used in various fields.
For example, amorphous synthetic silica (hereinafter referred to as “amorphous silica”) can control the size of silica particles, has a stable chemical component, and is excellent in reactivity. Therefore, it is used as a filler material in pharmaceuticals, cosmetics, toners in copying machines, printing paints and the like.
Further, high-purity amorphous silica of 99.99% by mass or more is used as a raw material in the semiconductor field, a chemical mechanical polishing (CMP) material, or the like.

As an example of the method for producing amorphous silica, there is a wet method for producing by a neutralization reaction between an aqueous alkali silicate solution and a mineral acid. The wet method includes a gel method and a sedimentation method. The sedimentation method is a method in which amorphous silica is precipitated and settled as particles by controlling the reaction temperature and the pH of the reaction solution so that silica gel is not generated during the neutralization reaction. In the sedimentation method, operations such as filtration are easier than the gel method, and the production cost is excellent.
The amorphous silica obtained by the precipitation method becomes a porous form due to the influence of the silicic acid concentration and the addition rate of the alkali silicate aqueous solution, the mineral acid concentration, the reaction temperature, and the like.
Porous amorphous silica has a problem that filtration, washing, and the like are difficult because a liquid containing impurities is retained inside silica particles.
As a method for cleaning porous amorphous silica (a method for removing a liquid containing impurities contained in silica particles), for example, porous amorphous silica is used in water (which contains almost no impurities). There is a method of immersing and replacing the liquid containing impurities contained in the silica particles with water. In this method, since the diffusion rate of impurities from the inside of the silica particles is slow, the productivity may be significantly lowered or the substitution may be insufficient.
As a method for efficiently washing amorphous silica, Patent Document 1 discloses a method for washing amorphous silica using a centrifuge, wherein the centrifugal force of the centrifuge is 1.0-2. A cleaning method for amorphous silica is described, which includes a cleaning step of performing water injection and cleaning of amorphous silica while maintaining 0.0 G.

JP 2013-234103 A

In the cleaning method described in Patent Document 1, there is a problem that replacement of the liquid containing impurities contained in the silica becomes insufficient or the amount of water used for cleaning becomes large.
An object of the present invention is to provide a method capable of reducing the amount of water used for cleaning and cleaning amorphous silica efficiently in a short time.

As a result of intensive studies to solve the above-mentioned problems, the present inventor supplied water to amorphous silica to obtain water-absorbed amorphous silica, and then, for the water-absorbed amorphous silica, The present invention has been completed by finding that the above object can be achieved by a cleaning method in which dehydration is performed by simultaneously applying pressure and pressure reduction using a specific pressure regulating container.
That is, the present invention provides the following [1] to [6].
[1] A method for washing amorphous silica using a pressure regulating container, wherein the pressure regulating container is a water permeable means for placing amorphous silica for placing the absorbed amorphous silica. The amorphous silica mounting water-permeable means configured to allow moisture contained in the absorbed amorphous silica to pass therethrough, and the amorphous silica mounting water-permeable means. A pressurized chamber for pressurizing the water-absorbed amorphous silica with a pressurized gas; and the water-absorbed amorphous silica provided below the water-permeable means for placing the amorphous silica. A decompression chamber is provided for recovering moisture contained in the absorbed amorphous silica by reducing the pressure with a reduced pressure gas, and (A) supplying amorphous water to the amorphous silica to absorb the amorphous Water absorption step for obtaining porous silica, and (B) the above absorbed amorphous silica A dehydration step of simultaneously depressurizing the pressure chamber and depressurizing the decompression chamber to obtain dehydrated amorphous silica using the pressure regulating container. Cleaning method.
[2] In the step (A), after placing the amorphous silica on the water-permeable means for placing the amorphous silica, water is supplied to the inside of the pressure chamber, and the amorphous The method for washing amorphous silica according to the above [1], which is performed by immersing the porous silica in water.
[3] The amorphous material according to [1] or [2], wherein the step (A) and the step (B) are repeated until the electric conductivity of water recovered in the decompression chamber becomes 10 mS / m or less. Silica cleaning method.
[4] The amorphous silica mounting water-permeable means has a plate that allows moisture to pass therethrough for mounting the amorphous silica that has absorbed water, and a ventilation rate that is mounted on the plate ( [1] to [3] above including a filter cloth having a value measured by the method defined in “JIS L 1096: 2010 Fabric and knitted fabric test method” of 0.3 to 10 cc / cm ² · s. Any one of the washing | cleaning methods of the amorphous silica in any one.
[5] In the step (B), the degree of pressurization in the pressurizing chamber is 2 MPa or more, and the degree of depressurization in the decompression chamber is 0.03 MPa or more. [1] to [4] The method for cleaning amorphous silica according to any one of the above.
[6] The method for cleaning amorphous silica according to any one of [1] to [5], wherein the amorphous silica is porous precipitated silica.

  According to the method for washing amorphous silica of the present invention, the amount of water used for one washing and the number of washings are reduced, the amount of water used for washing is reduced, and the amount of water used for washing is reduced efficiently in a short time. Crystalline silica can be washed.

It is sectional drawing which shows the state which cut | disconnected the example of the pressure regulation container (thing which accommodated the amorphous silica) used by this invention in the vertical direction in the approximate center part of this container. When the pressure regulating container shown in FIG. 1 (which does not contain amorphous silica) is cut in the horizontal direction at the position of line XX in FIG. 1 without laying the filter cloth. FIG. 3 is a cross-sectional view showing a state where a portion below the cut surface is viewed from above.

  The method for washing amorphous silica according to the present invention is a method for washing amorphous silica using a pressure regulating container, wherein the pressure regulating container is used to mount amorphous silica that has absorbed water. Water-permeable means for placing silica, which is configured to allow moisture contained in the absorbed amorphous silica to pass therethrough (for example, a plurality of members) A pressurizing chamber for pressurizing the absorbed amorphous silica with a pressurized gas, and a water permeation means for placing amorphous silica. (A) Amorphous silica provided with a decompression chamber for recovering water contained in the absorbed amorphous silica by depressurizing the absorbed amorphous silica with a decompressed gas. A water-absorbing step of supplying amorphous water to obtain absorbed amorphous silica; Against water and amorphous silica using the pressure adjusting container, a pressurization by the pressurizing chamber, performs decompression chamber by vacuum at the same time, is intended to include dehydration step, to obtain the amorphous silica dehydrated.

[1. Pressure regulating container]
Hereinafter, an example of the pressure regulating container used in the present invention will be described with reference to FIGS.
The pressure regulating container 1 used in the present invention includes a container body 2, water-permeable means for placing amorphous silica (a perforated plate 10 and a filter cloth 11), a lid 3, a stirring blade 4, and a vibration imparting member ( Knocker) 7,8.
In addition, the stirring blade 4 and the vibration imparting members (knockers) 7 and 8 are not essential members in the present invention, but are members arbitrarily installed for the purpose of performing a defoaming method or a bubble generation suppression method described later. Either one or both of the stirring blade 4 and the vibration imparting members (knockers) 7 and 8 may be installed. Further, either one or both of the vibration imparting members (knockers) 7 and 8 may be installed.
Amorphous silica 12 is accommodated inside the pressure regulating container 1. The internal space of the pressure regulating container 1 is divided into a pressurizing chamber 2 a and a decompressing chamber 2 b by a perforated plate 10. The pressurizing chamber 2a is formed by the lid 3 and a part of the container body 2 (a portion above the perforated plate 10). The decompression chamber 2b is formed by the remaining part of the container body 2 (the part below the perforated plate 10).
The container body 2 has a decompressed gas discharge port 6 and a drain port 13. The lid 3 is provided so as to be rotatable with respect to the container body 2 with the hinge portion 9 as an axis. The lid 3 has a pressurized gas inlet 5 for feeding pressurized gas. In addition, the stirring blade 4 is attached to the lid 3 in a state in which the rotation shaft is inserted into the through hole of the lid 3.
Although the shape of the pressure regulation container 1 is not specifically limited, Since pressurization and pressure reduction are performed, it is preferable from a durable viewpoint that a substantially cylindrical part is included.
In the present invention, the water-permeable means for placing amorphous silica (perforated plate 10 and filter cloth 11) is for placing amorphous silica that has absorbed water, and is included in the amorphous silica that has absorbed water. It is configured to allow moisture to pass therethrough. Moreover, from the viewpoint of further improving the yield of amorphous silica, it is preferable that the water-permeable means for placing amorphous silica allows only moisture to pass through without passing the placed amorphous silica.
As an example of the water permeable means for placing amorphous silica, as shown in FIG. 1, on the perforated plate 10 through which moisture can be passed for placing the absorbed amorphous silica, and on the perforated plate 10 The air permeability (value measured by the method defined in “Japanese Industrial Standard (referred to as“ JIS ”in this specification) L 1096: 2010 Fabric testing method for woven fabrics and knitted fabrics”) is 0. The thing containing the filter cloth 11 which is 3-10cc / cm < ² > s etc. is mentioned.
The perforated plate 10 may be any material that can support the filter cloth 11 and can pass moisture.

The perforated plate 10 has a plurality of holes 10a. The diameter of the hole 10a is preferably 1 to 20 mm, more preferably 5 to 15 mm. If the diameter is 1 mm or more, the time required for dehydration can be further shortened. When the diameter exceeds 20 mm, the support of the filter cloth 11 becomes insufficient, and amorphous silica may flow out from the gap around the curved filter cloth. The number of holes 10a varies depending on the size of the hole 10a, but is preferably 10 or more, more preferably 20 or more, still more preferably 30 or more, particularly preferably from the viewpoint of shortening the time required for dehydration. 50 or more.
The perforated plate 10 may be fixed to the container body 2 and may be detachable from the container body 2.

The air permeability of the filter cloth 11 is preferably 0.3 to 10 cc / cm ² · s, more preferably 0.4 to 8 cc / cm ² · s, still more preferably 0.8 to 6 cc / cm ² · s, particularly Preferably, it is 1 to 4 cc / cm ² · s. When the air permeability is 0.3 cc / cm ² · s or more, the dehydrating property is further improved, and the cleaning time can be further shortened. When the air permeability is 10 cc / cm ² · s or less, the amorphous silica 12 becomes more difficult to pass through the filter cloth 11, and the yield of amorphous silica can be further improved.
Examples of the air-permeable filter cloth 11 include cellulose fibers, polyamide fibers, vinylon fibers, polyester fibers, polyolefin fibers (for example, polypropylene fibers and polyethylene fibers), rayon fibers, aramid fibers, and other organic fibers, and glass fibers. , Woven fabric or non-woven fabric using fibers such as ceramic fibers, silica fibers, alumina fibers, rock wool, slag wool and other inorganic fibers.
The shape of the filter cloth 11 may be a sheet shape or a bag shape (for example, a flexible container bag). When a bag-shaped filter cloth (not shown) is used, after storing amorphous silica in the bag-shaped filter cloth, the bag-shaped filter cloth is placed on the upper surface of the perforated plate 10.

The pressurizing chamber 2a is provided above the water-permeable means for placing amorphous silica (the perforated plate 10 and the filter cloth 11). In the pressurizing chamber 2 a, the absorbed amorphous silica 12 is pressurized by the pressurized gas fed from the pressurized gas inlet 5.
The pressurized gas is not particularly limited as long as it does not react with silica, and examples thereof include air, nitrogen gas, and argon gas. Among these, air is preferable from the viewpoint of cost. In FIG. 1, symbol A indicates the direction in which the pressurized gas is fed.
The decompression chamber 2b is provided below the water-permeable means for placing amorphous silica (the perforated plate 10 and the filter cloth 11). In the decompression chamber 2b, the water-absorbed amorphous silica 12 is decompressed with a decompressed gas, whereby the water contained in the absorbed amorphous silica 12 is recovered from the drain port 13 provided at the lower portion of the decompression chamber 2b. can do.
Here, decompression is performed by discharging the gas in the decompression chamber 2b from the decompression gas discharge port 6 using a vacuum pump or the like. In FIG. 1, the symbol B indicates the direction in which the decompressed gas is discharged.

[2. Amorphous silica]
Next, the amorphous silica which is a treatment target of the present invention will be described.
In the present invention, the amorphous silica to be cleaned is not particularly limited, and may be porous silica or non-porous silica. Among these, porous silica is preferable in that the effect of the present invention is exerted more than non-porous silica.
The BET specific surface area of the amorphous silica is preferably 400 cm ² / g or more, more preferably 450 cm ² / g or more from the viewpoint of sufficiently obtaining the effect of reducing the amount of water used for the cleaning of the present invention. .
As the porous silica, for example, when mixing an alkali silicate aqueous solution and a mineral acid, particulate amorphous silica (hereinafter referred to as “precipitating property”) obtained by controlling so that gel silica is not generated. Also referred to as “silica”).
Hereinafter, a method for obtaining precipitated silica by mixing an alkali silicate aqueous solution and a mineral acid will be described.

Alkaline silicate aqueous solution refers to an alkaline aqueous solution containing a substance containing silicic acid (SiO ₂ ) in the chemical formula. Examples thereof include an alkali silicate aqueous solution prepared from a silica-containing mineral as a raw material, water glass, and the like. Is mentioned.
For the alkali silicate aqueous solution prepared using silica-containing mineral as a raw material, for example, silica-containing mineral powder and alkaline aqueous solution are mixed to prepare an alkaline slurry having a pH of 11.5 or more, and then this pH is maintained. By dissolving Si in the silica-containing mineral powder in the liquid so that the Si concentration in the liquid is preferably 6.0% by mass or more, the alkaline slurry is subjected to solid-liquid separation. Can be obtained.
Examples of the silica-containing mineral include diatomaceous earth and siliceous shale. The silica-containing mineral is desirably highly soluble in alkali.
The silica-containing mineral powder can be produced, for example, by pulverizing a silica-containing mineral such as siliceous shale with a pulverizer.
Examples of the pulverizer include a jaw crusher, a top grinder mill, a ball mill, and a jet mill. These devices may be used in combination.
In addition, the silica-containing mineral (powdered or before pulverization) is subjected to at least one of water washing and firing in advance, so that the clay content and the organic matter contained in the silica-containing mineral are organic. Minutes may be removed.

Examples of the alkaline aqueous solution used for the preparation of the alkaline slurry include a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution.
The pH of the alkaline slurry is 11.5 or higher, preferably 12.5 or higher, more preferably 13.0 or higher. When the pH is less than 11.5, the silica cannot be sufficiently dissolved, and the silica remains in the solid content, so that the yield of the resulting silica is reduced.
The Si concentration of the alkali silicate aqueous solution prepared using silica-containing mineral as a raw material is preferably 6.0% by mass or more, more preferably 8.0% by mass or more, and particularly preferably 10.0% by mass or more. When the concentration is 6.0% by mass or more, when the alkali silicate aqueous solution and the mineral acid are mixed, the silica is difficult to precipitate in a gel state, so that the time required for solid-liquid separation can be shortened. At the same time, the amount of silica obtained can be increased.

As the water glass, commercially available ones can be used, and in addition to Nos. 1, 2, and 3 defined by the JIS standard, products other than the JIS standard manufactured and sold by each water glass manufacturer are also used. be able to.
The Si concentration of the water glass is preferably 11.0% by mass or more, more preferably 12.0% by mass or more, and particularly preferably 13.0% by mass or more. When the concentration is 11.0% by mass or more, when water glass and mineral acid are mixed, silica is difficult to precipitate in a gel state, so that the time required for solid-liquid separation can be shortened, The amount of silica obtained can be increased. Although the upper limit of Si concentration of water glass is not specifically limited, Preferably it is 20 mass%.
In addition, when Si concentration of water glass exceeds 20 mass%, handling property will worsen. In this case, the Si concentration may be adjusted to 20% by mass or less by adding water to water glass.
The above-mentioned alkali silicate aqueous solution (prepared from silica-containing mineral or water glass) and mineral acid are mixed and neutralized to convert Si in the liquid into amorphous silica (non-silica). Gel-like precipitated silica).
A method for mixing the alkali silicate aqueous solution and the mineral acid is not particularly limited, but a method of adding the alkali silicate aqueous solution to the mineral acid is preferable. In this case, it is preferable to keep the pH of the mixed solution at 1.0 or less.

Examples of the mineral acid mixed with the alkali silicate aqueous solution include hydrochloric acid, sulfuric acid, nitric acid and the like. Among these, sulfuric acid is preferable from the viewpoint of reducing the cost of the material.
The concentration of the mineral acid may be such that non-gelled precipitated silica is precipitated by a neutralization reaction with an aqueous alkali silicate solution, preferably 20% by volume or more, more preferably 22% by volume or more, particularly preferably 25% by volume. % Or more. If this density | concentration is 20 mass% or more, the production | generation of gel-like silica can be prevented. The upper limit of the concentration of the mineral acid is not particularly limited, but is, for example, 50% by volume from the viewpoint of handleability and the like.
The temperature (precipitation temperature) when precipitating the precipitated silica is not particularly limited, but is, for example, 5 to 30 ° C.
The amorphous silica (precipitating silica) obtained by the neutralization reaction is porous. The macropore diameter of the amorphous silica is usually 50 to 100 μm. The nanopore diameter of the amorphous silica is usually 0.1 to 5 nm.

The particle size of the amorphous silica is not particularly limited, but is preferably 10 μm or more and 2 mm or less, more preferably 25 μm or more and 1 mm or less, and particularly preferably 50 μm or more and 750 μm or less. If the particle size is 10 μm or more, clogging of the filter cloth during dehydration is less likely to occur, and the efficiency of dehydration and the decrease in the yield of silica can be prevented. If the particle size is 2 mm or less, the time for water to penetrate into the silica particles can be shortened, and the cleaning efficiency of the present invention can be further improved.
The particle size of the amorphous silica can be adjusted by changing the production conditions of the amorphous silica or by pulverizing the amorphous silica. The pulverization method is not particularly limited, but in consideration of washing the obtained amorphous silica by the method of the present invention, the amorphous silica may be pulverized in an undried state. Examples of the pulverization method in this case include press pulverization and wet pulverization.

[3. Method for cleaning amorphous silica]
Hereinafter, the method for washing amorphous silica using the pressure regulating container described above will be described in detail for each step.
[Step (A): Water absorption step]
In this step, water is supplied to the amorphous silica 12 to obtain absorbed amorphous silica 12.
As a method of obtaining amorphous silica 12 that has absorbed water by supplying water, the amorphous silica 12 is placed on the permeable means for placing the amorphous silica (the perforated plate 10 and the filter cloth 11). After that, a method of supplying water into the pressurizing chamber 2a and immersing the amorphous silica in water is preferable.
The supply amount of water may be an amount that allows the amorphous silica 12 to be sufficiently immersed, but from the viewpoint of sufficiently replacing the liquid containing impurities contained in the silica particles and the water, The depth from the surface to the upper surface of the layer made of amorphous silica 12 (the thickness of the water layer) is preferably 6 mm or more, more preferably 8 mm or more, and particularly preferably 10 mm or more. Further, the amount of water supplied is preferably 30 mm or less, more preferably 25 mm or less, and particularly preferably 20 mm or less from the viewpoint of reducing the amount of water used for cleaning.

  The time for immersing the amorphous silica 12 in water is not particularly limited, but is preferably 2 to 15 minutes from the viewpoint of reducing the amount of water used for washing and improving the washing efficiency of the present invention. More preferably, it is 3 to 10 minutes, and particularly preferably 4 to 8 minutes. If the immersion time is 2 minutes or more, the number of washings can be reduced. When the immersion time exceeds 15 minutes, the amount of impurities eluted from the amorphous silica into the water reaches a peak, and the efficiency of the entire cleaning method of the present invention may be reduced.

The type of water to be supplied may be appropriately selected in consideration of the purity of the amorphous silica after washing and economic efficiency, and examples thereof include industrial water, ion-exchanged water, and distilled water. In this invention, when repeating a water absorption process and a dehydration process in multiple times, you may change the kind of water to be used according to the frequency | count of repetition from an economical viewpoint. Specifically, the water absorption step and the dehydration step are repeated a plurality of times (for example, four times) using industrial water, and then the water absorption step and the dehydration step are performed a plurality of times using ion-exchanged water instead of the industrial water ( For example, it may be repeated twice.
In addition, after the dehydration step, the electrical conductivity (described later) of the collected water may be measured, and the type of water used may be changed according to the obtained measurement result. Specifically, when the electrical conductivity of the water recovered from the decompression chamber 2b is less than a specific value (for example, 100 mS / m or less), the type of water used is changed from industrial water to ion-exchanged water. May be.

Further, when bubbles are involved in the layer made of amorphous silica 12, the contact between the silica particles and water is reduced by the bubbles attached to the surface of the silica particles, and impurities contained in the silica particles Replacement of the liquid containing water with water becomes insufficient. As a result, the number of cleanings increases and the amount of water used increases.
As a method for preventing bubbles from being entrained in the layer made of amorphous silica 12 (method for defoaming or suppressing bubble generation), a method for controlling the water supply rate to be reduced, or water was supplied. Thereafter, a method of performing stirring using the stirring blade 4, a method of placing vibration imparting bodies (knockers) 7 and 8 outside the container body 2, and tapping (giving vibration) the container body 2, an ultrasonic wave A method of performing a vibration treatment, a method of performing a pressure reduction treatment, and the like can be mentioned.
Further, from the viewpoint of shortening the washing time, before immersing amorphous silica in water, solid-liquid separation (for example, dehydration under reduced pressure) is performed, and a liquid containing impurities contained in amorphous silica is obtained. It may be removed to some extent.

[Step (B): Dehydration step]
In this step, the water-absorbed amorphous silica obtained in the step (A) was dehydrated by simultaneously applying pressure in the pressurizing chamber 2a and depressurizing in the depressurizing chamber 2b using the pressure regulating container 1. This is a step of obtaining amorphous silica.
Pressurization is performed by sending pressurized gas from the pressurized gas inlet 5. The degree of pressurization (a value obtained by subtracting the pressure before pressurization from the pressure after pressurization) is preferably 2 MPa or more, more preferably 2.5 to 8 MPa, still more preferably 3 to 7 MPa, and particularly preferably 3.5. ~ 6 MPa. If the degree of pressurization is 2 MPa or more, the cleaning time can be shortened and the number of cleanings can be reduced.
The decompression is performed by sucking the gas in the decompression chamber 2 b through the decompression gas discharge port 6. The degree of pressure reduction (a value obtained by subtracting the pressure after pressure reduction from the pressure before pressure reduction) is preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and particularly preferably 0.08 MPa or more. If the degree of depressurization is 0.03 MPa or more, the cleaning time can be shortened and the number of cleanings can be reduced.
In the present invention, by performing pressurization and pressure reduction simultaneously, the cleaning time can be shortened, and the number of times of cleaning can be reduced to reduce the amount of water used for cleaning.
The difference between the pressure in the pressurizing chamber 2a and the pressure in the decompression chamber 2b (the sum of the value of the degree of pressurization and the value of the degree of depressurization) is preferably 1 MPa or more, more preferably 2 MPa or more, and particularly preferably 3 MPa or more. . If the difference is 1 MPa or more, the cleaning time can be shortened and the number of cleanings can be reduced.
Further, from the viewpoint of preventing air bubbles from being entrained in the layer made of amorphous silica 12 due to the amorphous silica 12 deposited in the water soaring in the water or the water surface rippling, pressurization and depressurization are performed. Before performing simultaneously, only decompression may be performed in advance, preferably for 10 to 60 seconds, more preferably for 20 to 40 seconds.

  The above step (A) and step (B) may be repeated until the electrical conductivity of the water recovered in the decompression chamber becomes a specific numerical value or less. By repeating step (A) and step (B) in this manner, sufficiently washed amorphous silica can be obtained. The specific numerical value is preferably 100 mS / m or less, more preferably 50 mS / m or less, and particularly preferably 20 mS / m or less from the viewpoint of obtaining high-purity amorphous silica.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[Production of amorphous silica]
Water glass (water glass No. 3, manufactured by Tosoh Sangyo Co., Ltd., JIS standard product) having a Si concentration of 13.5% by mass was dropped onto sulfuric acid (industrial sulfuric acid, manufactured by Goyo Trading Company) having a concentration of 25% by volume. While maintaining the precipitation temperature at 20 ° C., porous amorphous silica (precipitated silica) was precipitated. The pH of the mixture of water glass and sulfuric acid was kept at 1.0 or less until the end of dropping. The obtained amorphous silica was a wet amorphous silica having a Blaine specific surface area of 480 cm ² / g and containing a liquid component containing impurities at a ratio of 70% by mass.

[Example 1]
A pressure regulating container 1 (φ1,500 mm × height 500 mm; see FIGS. 1 and 2) in which a filter cloth (air permeability: 1.3 cc / cm ² · s) 11 is placed on the entire upper surface of the perforated plate 10. 80 kg of the wet amorphous silica was added. Next, using a vacuum pump, vacuum dehydration was performed for 30 seconds while reducing the pressure in the vacuum chamber 2b so that the pressure was reduced to 0.1 MPa.
After dehydration under reduced pressure, 65 kg of industrial water (not shown) was added so that the height from the surface of the layer made of amorphous silica 12 to the water surface was 10 mm. Next, the tapping operation (applying an impact to the container body 2) is performed using the vibration imparting members (knockers) 7 and 8 to perform defoaming treatment, and then, in a state of standing, amorphous in industrial water. Silica 12 was immersed for 5 minutes.
After the immersion, dehydration was performed for 30 seconds while reducing the pressure in the vacuum chamber 2b to 0.1 MPa using a vacuum pump (shown as “pre-depressurization” in Table 1), and further. While maintaining the reduced pressure, pressurized air is fed from the pressurized gas inlet 5, and the degree of pressurization (the difference between the pressure after pressurization and the pressure before pressurization) is increased in the pressurization chamber 2a. The amorphous silica 12 was dehydrated by pressurizing to 4 MPa.
The time required for dehydration was 10 minutes (see “Decompression and pressurization” in “Dehydration time after immersion (minute)” in (a) in Table 1). After the completion of the dehydration, the electrical conductivity of the water recovered by the dehydration is measured, and the operation from the above-described immersion to the end of the dehydration using industrial water until the electrical conductivity becomes 100 mS / m or less (in Table 1 In the water collected after the fourth repetition, the electrical conductivity was 100 mS / m or less.
Thereafter, using ion-exchanged water instead of industrial water, the operation from the above-described immersion to the end of the dehydration was repeated twice until the electrical conductivity of the water recovered by dehydration became 10 mS / m or less (in Table 1). , Indicated as “b”), and 77.4 kg of wet silica was obtained. The total amount of water used for washing was 5.04 kg per kg wet silica.

[Example 2]
Dehydration in the same manner as in Example 1 except that a filter cloth having an air permeability of 0.5 cc / cm ² · s is used and the inside of the pressurizing chamber 2a is pressurized so that the degree of pressurization becomes 5 MPa. The same operation as in Example 1 was repeated using industrial water until the electrical conductivity of the water recovered by the above was 100 mS / m or less. As a result, the time required for dehydration was 15 minutes, and the number of repetitions of the above operation was 4.
Thereafter, using ion-exchanged water instead of industrial water, the same operation was repeated twice until the electric conductivity of the water recovered by dehydration became 10 mS / m or less, to obtain 76.5 kg of wet silica. . The total amount of water used for washing was 5.10 kg per kg of wet silica.

[Example 3]
Other than using a filter cloth having an air permeability of 5 cc / cm ² · s, setting the immersion time of amorphous silica to 7 minutes, and pressurizing the inside of the pressurizing chamber 2a to a degree of pressurization of 3 MPa. In the same manner as in Example 1, the same operation as in Example 1 was repeated using industrial water until the electrical conductivity of the water recovered by dehydration was 100 mS / m or less. The time required for dehydration was 7 minutes, and the above operation was repeated four times.
Thereafter, ion exchange water was used instead of industrial water, and the same operation was repeated twice until the electric conductivity recovered by dehydration became 10 mS / m or less, to obtain 74.3 kg of wet silica. The total amount of water used for washing was 5.25 kg / kg wet silica.

[Comparative Example 1]
80 kg of the wet amorphous silica is put into a centrifuge (trade name “CO-42 type” manufactured by Tanabe Wiltech Co., Ltd.), and the rotation speed of the centrifuge is kept at 45 rpm and the centrifugal force is kept at 1.5 G. However, 110 kg of industrial water was supplied by a water injection nozzle to perform cleaning. The time required for washing was 480 seconds.
After washing, the rotation speed of the centrifuge was increased to 950 rpm, and dehydration was performed for 560 seconds using a centrifugal force of 500G. The total time required for washing and dehydration was 17.3 minutes. After completion of dehydration, the electrical conductivity of the water recovered by dehydration was measured, and the above washing and dehydration was repeated using industrial water until the electrical conductivity reached 100 mS / m or less. The electrical conductivity of the water recovered by dehydration became 100 mS / m or less.
Then, using ion-exchanged water instead of industrial water, the same operation was repeated twice until the electric conductivity of the water recovered by dehydration became 10 mS / m or less, to obtain 75.4 kg of wet silica. . The total amount of water used for washing was 14.59 kg per kg wet silica.

[Comparative Example 2]
After immersing the amorphous silica 12, no pressure reduction is performed, and the inside of the pressurizing chamber 2a is pressurized so that the degree of pressurization is 4.1 MPa (shown as “pressurization only” in Table 1). In the same manner as in Example 1, the same operation as in Example 1 was repeated using industrial water until the electrical conductivity of the water recovered by dehydration was 100 mS / m or less. The time required for dehydration was 20 minutes, and the above operation was repeated 5 times.
Thereafter, using ion-exchanged water instead of industrial water, the same operation was repeated twice until the electric conductivity of the water recovered by dehydration became 10 mS / m or less, to obtain 76.5 kg of wet silica. . The total amount of water used for washing was 5.95 kg / kg wet silica.

[Comparative Example 3]
After the amorphous silica 12 is immersed, the amorphous silica 12 is dehydrated while reducing the pressure in the vacuum chamber 2b so that the degree of pressure reduction is 0.1 MPa (indicated as “depressurized only” in Table 1). Except for the above, the same operation as in Example 1 was repeated using industrial water until the electrical conductivity of the water recovered by dehydration was 100 mS / m or less in the same manner as in Example 1. The time required for dehydration was 33 minutes, and the above operation was repeated six times.
Thereafter, using ion-exchanged water instead of industrial water, the same operation was repeated twice until the electric conductivity of the water recovered by dehydration became 10 mS / m or less, to obtain 77.8 kg of wet silica. . The total amount of water used for washing was 6.68 kg per kg of wet silica.
Table 1 shows the total time required for washing, the total amount of water, and the yield of amorphous silica.

From Table 1, according to the washing | cleaning method (Examples 1-3) of the amorphous silica of this invention, when wash | cleaning using a centrifuge (comparative example 1), performing only a pressurization and performing washing | cleaning It can be seen that the cleaning time can be shortened and the total amount of water used for cleaning can be reduced as compared with the case where the pressure is reduced (Comparative Example 2) and the case where only decompression is performed (Comparative Example 3).
In particular, when Example 1 and Comparative Example 2 are compared, even when the numerical value of the pressure difference is the same (4.1 MPa), when pressure and pressure reduction are performed simultaneously (Example 1), only the pressure is It can be seen that the number of times of washing and the total amount of water used for washing (“total amount of water” in Table 1) can be reduced as compared with the case of performing (Comparative Example 2).

DESCRIPTION OF SYMBOLS 1 Pressure regulation container 2 Container body 2a Pressurization chamber 2b Decompression chamber 3 Cover body 4 Stirring blade 5 Pressurization gas inflow port 6 Decompression gas discharge port 7, 8 Vibration imparting member (knocker)
9 Hinge part 10 Perforated plate 10a Hole 11 Filter cloth 12 Amorphous silica 13 Drain port

Claims (6)

A method of washing amorphous silica using a pressure regulating container,
The pressure regulating container is a water-permeable means for placing amorphous silica for placing the absorbed amorphous silica, and allows moisture contained in the absorbed amorphous silica to pass therethrough. The amorphous silica placing water-permeable means configured as described above, and a pressure for pressurizing the water-absorbed amorphous silica, which is provided above the amorphous silica placing water-permeable means, with a pressurized gas. The water-absorbed amorphous silica is recovered by depressurizing the water-absorbed amorphous silica provided under the pressure chamber and the water-permeable means for placing the amorphous silica with a reduced-pressure gas. Equipped with a decompression chamber for
(A) a water absorption step of supplying water to amorphous silica to obtain absorbed amorphous silica;
(B) A dehydration step of obtaining dehydrated amorphous silica by simultaneously applying pressure in the pressurizing chamber and depressurizing in the decompression chamber to the absorbed amorphous silica using the pressure regulating container. ,
A method for cleaning amorphous silica, comprising:   In step (A), after placing the amorphous silica on the water-permeable means for placing the amorphous silica, water is supplied to the inside of the pressurizing chamber to The method for washing amorphous silica according to claim 1, wherein the method is performed by immersing in water.   The method for cleaning amorphous silica according to claim 1 or 2, wherein the step (A) and the step (B) are repeated until the electric conductivity of water recovered in the decompression chamber becomes 10 mS / m or less. The water permeation means for placing the amorphous silica is a plate that allows moisture to pass through to place the absorbed amorphous silica, and the air permeability (“JIS L”) placed on the plate. 1096: 2010 The value measured by the method prescribed in "Fabric and knitted fabric test method" is 0.3 to 10 cc / cm ² · s. A method for cleaning an amorphous silica.   5. The process according to claim 1, wherein in the step (B), the degree of pressurization in the pressurization chamber is 2 MPa or more, and the degree of decompression in the decompression chamber is 0.03 MPa or more. A method for cleaning an amorphous silica as described.   The method for cleaning amorphous silica according to any one of claims 1 to 5, wherein the amorphous silica is porous precipitated silica.

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