JP4489200B2 - Method for using caustic aqueous solution containing silicic acid and method for producing silicic acid sol - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recycling a caustic aqueous solution containing silicic acid, and in particular, recycles a caustic aqueous solution containing silicic acid that is by-produced when producing a silicic acid sol from an aqueous silicic acid solution by electrodialysis, and efficiently, The present invention relates to a method for producing a silicate sol without fear of environmental pollution.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
As a method for producing a silicic acid sol, also referred to as an active silicic acid aqueous solution, a method is known in which alkali silicate is dealkalized by electrodialysis using an anion exchange membrane and a cation exchange membrane (JP-A-7-802, JP-A-7-802, (See Sho 60-106985).
[0003]
However, the electrodialysis method using an ion exchange membrane has a problem that the ionized silicic acid of the aqueous alkali silicate solution passes through the ion exchange membrane and moves to the concentration chamber side.
[0004]
That is, as a result of the monosilicic acid moving to the concentration chamber, the silicic acid is mixed into the caustic aqueous solution obtained from the concentration chamber. The composition of the aqueous caustic solution obtained varies depending on the conditions of electrodialysis. Generally, when caustic soda is used as the caustic alkali, it is 2.0 to 4.0% by weight in terms of Na ₂ O. And 0.3 to 1.0% by weight of silicic acid in terms of SiO ₂ . Of course, caustic alkalis containing a large amount of silicic acid and having a low alkali concentration have very limited applications that can be used as industrial alkali raw materials.
[0005]
Therefore, the caustic alkali produced as a by-product contains silicic acid and the alkali is dilute, so it must be discarded as surplus alkali, but for that purpose, neutralization with acid is necessary. At that time, silicic acid is precipitated in the form of silica gel as a solid content, so that it is difficult to separate it and the cost is very high. In addition, effective use of silicic acid has not been achieved.
[0006]
The inventors of the present invention have made extensive studies to solve the above problems. As a result, it came to mind that the caustic aqueous solution containing silicic acid discharged from the concentrating chamber was separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using an electrodialyzer. The resulting caustic alkali concentrate can be adjusted to an appropriate concentration, for example, as an alkali source for No. 1 and No. 2 sodium silicate, and the diluted aqueous alkali silicate solution can be used as it is or after adjusting the appropriate concentration. In this manufacturing process, water and raw materials can be effectively used as a solvent, and the amount of waste can be reduced, so that the disposal cost and the risk of environmental pollution can be reduced.
[0007]
OBJECT OF THE INVENTION
An object of the present invention is to reduce the amount of waste and reduce the cost and the risk of environmental pollution by effectively recycling a caustic aqueous solution containing silicic acid discharged from the concentration chamber in the production of silicic acid sol by electrodialysis. It is said.
[0008]
SUMMARY OF THE INVENTION
The method of using the aqueous caustic solution containing silicic acid according to the present invention (in the present specification , also referred to as “ recycling method of aqueous caustic solution containing silicic acid ” for the sake of convenience ).
A method of using a caustic aqueous solution containing silicic acid, which is by-produced when producing a silicic acid sol by electrodialysis,
The caustic aqueous solution containing by-produced silicic acid is separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using an electrodialyzer ,
The dilute alkaline silicate aqueous solution is dealkalized and used for the production of a silicate sol .
Other usage methods of the aqueous caustic solution containing silicic acid according to the present invention are as follows:
A method of using a caustic aqueous solution containing silicic acid, which is by-produced when producing a silicic acid sol by electrodialysis,
The caustic aqueous solution containing by-produced silicic acid is separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using an electrodialyzer,
The caustic concentrate is used as an alkali source for preparing an alkali silicate aqueous solution which is a starting material in the production of silicate sol, or used for the production of JIS No. 1 silicate or JIS No. 2 silicate alkali.
It is characterized by that.
[0009]
In the method for producing a silicate sol according to the present invention, an alkaline silicate aqueous solution is electrodialyzed using a first electrodialysis apparatus in which a cation exchange membrane and an anion exchange membrane are alternately arranged between an anode and a cathode. When manufacturing the silicate sol,
The caustic aqueous solution containing a small amount of silicic acid by-produced from the concentrating chamber is separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using the second electrodialysis apparatus, and the dilute alkaline silicate aqueous solution is silicic acid. It is characterized by being supplied to the first electrodialysis apparatus as an alkaline aqueous solution.
[0010]
In the method for producing a silicate sol of the present invention, the alkali silicate supplied to the first electrodialysis apparatus is at least one selected from the group consisting of lithium silicate, sodium silicate, potassium silicate and ammonium silicate. Is preferred.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described more specifically.
[0012]
FIG. 1 shows a flowchart of a recycling method according to the present invention.
[0013]
Caustic aqueous solution containing silicic acid (hereinafter referred to as “silicic acid-containing caustic aqueous solution”), which is one of the starting materials, is a waste liquid discharged from the concentration chamber side in the production of silicic acid sol by electrodialysis, for example. Not done.
[0014]
In the silicic acid-containing caustic alkali aqueous solution, silicic acid and alkali (hereinafter sometimes abbreviated as “A”) have an SiO ₂ / A ₂ O (molar ratio), preferably 0.01 to 0.8, in terms of oxides. More preferably, it is 0.05 to 0.5, particularly preferably about 0.2 to 0.4.
[0015]
The concentration of silicate-containing aqueous caustic is an alkali metal oxide A ₂ O in terms of the order of 1 to 20% by weight.
[0016]
As shown in FIG. 2, the electrodialysis apparatus has a cation exchange membrane 1 and an anion exchange membrane 2 arranged alternately between an anode and a cathode, and a desalting chamber 3 and a concentration chamber 4 are alternately arranged. Is formed. As such an electrodialysis apparatus, a conventionally known apparatus can be used without any particular limitation. That is, known electrodes are used without particular limitation for the electrodes, ion exchange membranes, and other necessary members constituting such an electrodialysis apparatus. For example, as an ion exchange membrane, generally, a cation exchange group is a sulfonic acid group, an anion exchange group is a quaternary ammonium group, and a hydrocarbon made of a styrene-divinylbenzene copolymer material using a reinforcing substrate. System cation exchange membranes and anion exchange membranes are also used industrially. Further, a fluorinated ion exchange membrane in which the material of the ion exchange membrane is a fluoropolymer can also be used. In the electrodialysis apparatus of the present invention, it is desirable to use an alkali-resistant ion exchange membrane in order to concentrate (generate) caustic alkali while the alkali silicate aqueous solution used for electrodialysis is alkaline.
[0017]
In the recycling method of the present invention, electrodialysis is performed by supplying a silicic acid-containing caustic aqueous solution to the desalting chamber 3 of the electrodialysis apparatus and supplying water or a dilute caustic aqueous solution to the concentration chamber 4. In the desalting chamber 3, alkali metal ions (for example, Na ⁺ ) are transferred to the concentration chamber 4 side through the cation exchange membrane 1, and hydroxide ions (OH ⁻ ) are transferred to the concentration chamber side 4 through the anion exchange membrane 2. Transition to desalination. On the other hand, in the concentration chamber 4, the alkali metal ions and hydroxide ions that have migrated from the desalting chamber 3 are concentrated to obtain a caustic aqueous solution.
[0018]
The operating conditions of the electrodialysis apparatus vary depending on the size of the apparatus, the concentration of the alkali silicate aqueous solution, and the like. A feeding rate of about 3.1 liters / minute is appropriate. Note that water or a dilute caustic aqueous solution is supplied to the concentration chamber at a rate of about 3.1 liters / minute.
[0019]
From the desalting chamber 3, a dilute alkali silicate solution having a reduced alkali concentration is obtained by dealkalization. The composition of the obtained diluted alkali silicate depends on the concentration of the starting silicic acid-containing caustic aqueous solution and the dialysis conditions, and is appropriately selected according to the intended use of the obtained diluted alkali silicate.
[0020]
When the dilute alkali silicate obtained from the desalting chamber 3 is used as a starting material in the production of a silicate sol described later, the SiO ₂ / A ₂ O (molar ratio) is 0.5 to 4.0, preferably It is desirable to carry out dealkalization until about 2.8 to 3.5. In this case, the alkali is preferably sodium. The SiO ₂ / A ₂ O ratio as described above is substantially equal to JIS No. 3 sodium silicate manufactured by Tosoh Sangyo Co., Ltd., and can be directly recycled to the manufacturing process of silicate sol without adjusting the composition and concentration. The above-mentioned SiO ₂ / A ₂ O ratio can be achieved by performing electrodialysis under conditions where the electric conductivity is about 4 mΩ / cm. In this case, the concentration of the diluted alkali silicate is about 0.1 to 1.0% by weight in terms of SiO ₂ .
[0021]
The molar balance SiO ₂ / A ₂ O of the diluted alkali silicate can be adjusted by appropriately selecting the electrodialysis conditions, particularly the electric conductivity. In general, when the electrical conductivity is high, SiO ₂ / A ₂ O tends to be low, and when the electrical conductivity is low, SiO ₂ / A ₂ O tends to be high.
[0022]
A caustic aqueous solution is obtained from the concentration chamber 4. In this caustic aqueous solution, silicic acid migrates through the ion exchange membrane in the dialysis process, and a small amount of about 0.1 to 1% by weight of silicic acid may be mixed, but the mixing of a small amount of silicic acid is not a problem. When it is used as an alkali source for adjusting the use, for example, an alkali silicate aqueous solution which is a starting material in the production of silicate sol, it can be recycled as it is. It can also be used for the production of JIS No. 1 and No. 2 alkali silicates having a low SiO ₂ / A ₂ O ratio.
[0023]
Further, the alkali concentration can be improved by retaining the solution in the concentration chamber 4 during electrodialysis.
[0024]
Next, the manufacturing method of the silicic acid sol including the above recycling steps will be described with reference to FIG.
[0025]
In the method for producing a silicate sol according to the present invention, an alkaline silicate aqueous solution 11 is formed using a first electrodialysis apparatus 10 in which a cation exchange membrane and an anion exchange membrane are alternately arranged between an anode and a cathode. When producing silicate sol 13 by electrodialysis,
A caustic aqueous solution 14 containing a small amount of silicic acid by-produced from the concentrating chamber is separated into a caustic concentrated solution 23 and a dilute alkaline silicate aqueous solution 24 using the second electrodialysis apparatus 20, and the dilute silicic acid is used. The alkaline aqueous solution 24 is supplied to the first electrodialysis apparatus 10 as the alkaline silicate aqueous solution 11.
[0026]
For example, lithium silicate, sodium silicate, potassium silicate, or ammonium silicate is used as the alkali silicate 11 that is a raw material supplied to the desalting chamber of the electrodialyzer 10. The ratio of silicic acid to alkali in the alkali silicate is, for example, about 0.5 to 3 for SiO ₂ / Li ₂ O (molar ratio) for lithium silicate, and generally SiO ₂ / Na ₂ O (molar ratio) for sodium silicate. Is about 0.5 to 4, SiO ₂ / K ₂ O (molar ratio) is about 0.5 to 3 for potassium silicate, and SiO ₂ / (NH ₄ ) ₂ O (molar ratio) is about ammonium silicate. It is about 0.5-3. Further, water or dilute caustic aqueous solution 12 is supplied to the desalting chamber.
[0027]
Industrially, JIS No. 1 to No. 3 sodium silicate is preferably used as the alkali silicate, and generally an alkali silicate aqueous solution whose concentration is diluted to 5 to 15% by weight in terms of SiO ₂ is used. It is done. When an alkali silicate aqueous solution diluted to such a concentration is used, desalting and concentration thereof are performed smoothly.
[0028]
As the first electrodialysis apparatus 10 and the second electrodialysis apparatus 20, a commercially available apparatus is usually used as described above.
[0029]
The operating conditions of the electrodialysis apparatus 10 vary depending on the size of the apparatus, the concentration of the alkali silicate aqueous solution, and the like. In general, the cell voltage is 10 V, the stack voltage is 5 to 7 V, and the alkali silicate aqueous solution is supplied to the desalting chamber. A supply rate of about 3.1 liters / minute is appropriate. Note that water or a dilute caustic aqueous solution is supplied to the concentration chamber at a rate of about 3.1 liters / minute.
[0030]
When electrodialysis is performed under such operating conditions, the desired silicic acid sol 13 is obtained from the desalting chamber, and the silicic acid-containing caustic aqueous solution 14 as a by-product is discharged from the concentration chamber. The composition and concentration of the silicic acid-containing caustic aqueous solution 14 are the same as those described in the recycling method.
[0031]
This by-product silicic acid-containing caustic aqueous solution 14 is supplied to the desalting chamber of the second electrodialysis apparatus 20. That is, the silicic acid-containing caustic aqueous solution 21 in FIG. 3 is the same as the silicic acid-containing caustic aqueous solution 14. In addition, water or a dilute caustic aqueous solution 22 is supplied to the desalting chamber of the second electrodialysis apparatus 20.
[0032]
The dialysis conditions and the like in the second electrodialysis apparatus 20 are as described in the recycling method.
[0033]
As a result, a dilute alkali silicate solution 24 having a reduced alkali concentration is obtained from the desalting chamber of the second electrodialyzer 20 by dealkalization. As described above, by appropriately setting the dialysis conditions, a dilute alkali silicate solution 24 having a composition suitable as a starting material for the production of silicate sol can be obtained. By utilizing the desalination chamber of the dialyzer 10, silicic acid can be effectively used. A caustic aqueous solution 24 is obtained from the concentration chamber of the second electrodialyzer 20. This may contain a small amount of silicic acid as described above, but it can be preferably used for the preparation of starting materials in the production of silicate sols or the production of JIS No. 1 and No. 2 alkali silicates. Effective use is planned.
[0034]
The alkali concentration of the silicate sol obtained by the present invention is reduced to 0.4% or less, but if necessary, the alkali concentration can be further lowered by contact treatment with a cation exchange resin, and the alkali is substantially reduced. Silica sol that does not contain can be produced. That is, after producing a silicic acid sol by reducing / removing most of the alkali by an electrodialysis method using an ion exchange membrane, the ion exchanging method using a cation exchange resin for the silicic acid sol in which a small amount of alkali remains is a conventional method. Since the alkali ion adsorption ability of the ion exchange resin does not decrease in a short time as in the method, a silicic acid sol substantially free of alkali can be efficiently produced without requiring frequent regeneration treatment. As the ion exchange resin, R—SO ₃ H type, R—COOH type, and R—OH type cation exchange resins are used without particular limitation.
[0035]
The silicic acid sol obtained by the production method of the present invention as described above is widely used for various applications. In particular, a silicic acid sol containing no alkali is useful as a ground injection chemical. For example, when performing construction work on soft ground, the ground injecting drug is injected into the ground in order to give the ground strength and durability. If the ground injection contains alkali, the soil and groundwater may be contaminated. However, according to the present invention, the alkali content of the silicic acid sol can be extremely reduced, so that it can be used without the risk of contamination.
[0036]
Further, the resulting silicic acid sol can be used in various fields where silica fine particles have been conventionally used. For example, heat-resistant binder, catalyst, wrapping paper anti-slip, anti-slip matt, various coating agents, abrasives for wafer polishing, It can also be used as a reinforcing agent, a flocculant, an inkjet fixing agent, and the like.
[0037]
【The invention's effect】
According to the present invention as described above, water and raw materials can be used effectively as a solvent used particularly in the production of silicate sol, and the amount of waste can be reduced, thereby reducing the cost of disposal and environmental pollution. it can.
[0038]
【Example】
Examples of the present invention will be described below, but the present invention is not limited to these examples.
[0039]
As shown in FIG. 3, two electrodialyzers were connected.
[0040]
The specifications of the electrodialyzer used are as follows.
[0041]
Electrodialyzer Anion exchange membrane (10 sheets): AHA-2 (trade name), Tokuyama Co., Ltd. cation exchange membrane (12 sheets): CMB (trade name), Tokuyama Co., Ltd. electrode Material: Distance between Ni plate electrodes: 26.2 mm
Distance between anion exchange membrane and cation exchange membrane: 0.7mm
Area of ion exchange membrane: ² dm ² / sheet [0042]
[Example 1]
The specific gravity and composition of the alkali silicate aqueous solution used as a raw material were as follows.
[0043]
Specific gravity (15 ° C): 41.5 Be '
SiO ₂ (%): 28.12
Na ₂ O (%): 9.21
SiO ₂ / Na ₂ O (molar ratio): 3.15
This was further diluted with water to obtain an aqueous alkali silicate solution having a silicic acid concentration (SiO ₂ equivalent) of 6% by weight.
[0044]
The alkali silicate aqueous solution thus obtained was supplied to the desalting chamber of the first electrodialysis apparatus having the above specifications, and a dilute caustic soda solution was supplied to the concentration chamber.
[0045]
When electrodialysis was started at a cell voltage of 10 V, the initial conductivity was 24 mΩ / cm. After electrodialysis was started, the operation was continued until the electrical conductivity dropped below 4.5 mΩ / cm. The average dialysis time until the conductivity dropped below 4.5 mΩ / cm was 80 minutes. The silica sol obtained from the desalting chamber had a silica content (SiO ₂ ) of 6.4% by weight and an alkali content (Na ₂ O) of 0.35% by weight. The aqueous sodium hydroxide solution from the concentration chamber had a silica concentration (SiO ₂ ) of 0.6% by weight and a sodium concentration (Na ₂ O) of 3.13% by weight.
[0046]
The obtained sodium hydroxide aqueous solution containing silicic acid obtained from the concentration chamber was supplied to the desalting chamber of the second electrodialysis apparatus, and a dilute caustic soda solution was supplied to the concentration chamber.
[0047]
When electrodialysis was started at a cell voltage of 10 V, the initial conductivity was 160 mΩ / cm. After electrodialysis was started, the operation was continued until the electrical conductivity dropped below 4 mΩ / cm. The average dialysis time until the conductivity dropped below 4 mΩ / cm was 60 minutes. The SiO ₂ / Na ₂ O (molar ratio) of the dilute alkali silicate solution obtained from the desalting chamber is almost 3, which is almost equal to the SiO ₂ / Na ₂ O of the alkali silicate aqueous solution used as the starting material. This was supplied to the desalting chamber of the first electrodialyzer together with the alkali silicate aqueous solution to be newly replenished, and the silicic acid was recycled.
[0048]
Further, the solution in the concentration chamber of the second electrodialysis apparatus was retained, and only the sodium hydroxide-containing sodium hydroxide aqueous solution was supplied to the desalting chamber, and the operation was repeated until the conductivity decreased to less than 4 mΩ / cm. Seven batches were carried out, with one feed of the silicic acid-containing sodium hydroxide solution as one batch. The caustic concentrate finally obtained from the concentration chamber has a sodium concentration (Na ₂ O) of 11.14% by weight, a silica concentration (SiO ₂ ) of 0.67% by weight, an electric conductivity of 700 mΩ / cm, and a viscosity. (Cps, 25 ° C.) was 9.5.
[Brief description of the drawings]
FIG. 1 is a flowchart of a recycling method according to the present invention.
FIG. 2 is a schematic view of an electrodialysis apparatus used in the present invention.
FIG. 3 is a flowchart of a method for producing a silicate sol according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cation exchange membrane 2 ... Anion exchange membrane 3 ... Desalination chamber 4 ... Concentration chamber 10 ... Electrodialyzer 11 ... Alkaline silicate aqueous solution 12 ... Water or dilute caustic alkali solution 13 ... Silicate sol 14 ... Silica-containing caustic alkali aqueous solution DESCRIPTION OF SYMBOLS 20 ... Electrodialysis apparatus 21 ... Silica-containing caustic aqueous solution 22 ... Water or dilute caustic alkali solution 23 ... Caustic concentrate 24 ... Dilute alkali silicate aqueous solution

Claims (4)

A method of using a caustic aqueous solution containing silicic acid, which is by-produced when producing a silicic acid sol by electrodialysis,
The caustic aqueous solution containing by-produced silicic acid is separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using an electrodialyzer ,
A method of using a caustic alkaline aqueous solution containing silicic acid, wherein the diluted alkaline silicate aqueous solution is dealkalized and used for production of a silicic acid sol . A method of using a caustic aqueous solution containing silicic acid, which is by-produced when producing a silicic acid sol by electrodialysis,
  The caustic aqueous solution containing by-produced silicic acid is separated into a caustic alkali concentrate and a dilute alkaline silicate aqueous solution using an electrodialyzer,
  The caustic concentrate is used as an alkali source for preparing an alkali silicate aqueous solution which is a starting material in the production of silicate sol, or used for the production of JIS No. 1 silicate or JIS No. 2 silicate alkali.
A method of using a caustic aqueous solution containing silicic acid, characterized in that When producing a silicate sol by electrodialyzing an aqueous alkali silicate solution using a first electrodialysis apparatus constituted by alternately arranging a cation exchange membrane and an anion exchange membrane between an anode and a cathode,
The caustic aqueous solution containing a small amount of silicic acid by-produced from the concentrating chamber is separated into a caustic concentrated solution and a dilute alkaline silicate aqueous solution using the second electrodialysis apparatus, and the dilute alkaline silicate aqueous solution is silicic acid. A method for producing a silicic acid sol, comprising supplying an alkaline aqueous solution to the first electrodialysis apparatus. The silicic acid according to claim 3 , wherein the alkali silicate supplied to the first electrodialyzer is at least one selected from the group consisting of lithium silicate, sodium silicate, potassium silicate and ammonium silicate. A method for producing a sol.

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