JP2002079257A - Method for manufacturing alkali removed water glass aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a water glass aqueous solution to a desalting chamber of an electrodialysis apparatus to perform a dealkalization treatment, and to produce a dealkalized water glass aqueous solution that can be suitably used as a ground improvement material. And a method for continuously producing an object. An electrodialysis tank, a storage tank disposed outside the electrodialysis tank, the storage tank having a raw material supply line for supplying a raw water glass aqueous solution to the storage tank, and water glass from the storage tank to the desalination chamber Using an electrodialysis apparatus having a salt chamber supply line for supplying an aqueous solution, and a return line for returning the alkali glass solution to the storage tank from the desalting chamber to the storage tank, the water glass solution is supplied to the desalting chamber. Is circulated and supplied, and a part of the dealkalized water glass aqueous solution is withdrawn, and the same amount of the raw material water glass aqueous solution as the extracted dealkalized water glass aqueous solution is supplied to the storage tank via the material supply run. And producing the aqueous solution of dealkalized water glass, wherein the aqueous solution of raw water glass to be supplied to the storage tank has a SiO ₂ concentration of 1 to 25 wt.
% Aqueous glass solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aqueous alkali-free water glass solution useful as a material for ground injection.

[0002]

2. Description of the Related Art In civil engineering work, a chemical solution injection method for improving a ground by injecting a ground improvement material from the outside into a ground which may be collapsed due to excavation or a ground which is difficult to excavate due to spring water or the like is used. It is widely used.

[0003] Various types of soil improvement materials currently used are known, but a ground injection material mainly composed of water glass is inexpensive and the gel time can be easily adjusted.

Recently, the solidified material obtained by injection has a high strength and is excellent in durability, the injection solution is a single solution, the gel time can be easily adjusted, and the handling is easy. The main material is that water glass is treated with an acid to make it acidic and hardens, with the characteristic that the type of foreign matter eluted from the solidified material after ground improvement is limited and the effect on the environment is small. Non-alkali silica sol ground improvement injection materials are often used.

However, the water glass used for the non-alkaline ground improvement material contains a large amount of alkali or salt, and the strength of the consolidated body obtained using the non-alkaline ground improvement material decreases. There is a problem that the alkali or salt is released or deviates from the compact within a long period of time, and the compact shrinks and its durability is reduced.

In order to improve such disadvantages, a method of removing alkali from water glass by an ion exchange resin method has been adopted (JP-A-11-279552).

However dealkalization treatment by ion exchange resin method is prolonged dealkalization requires a regeneration of the resin is impossible, even higher water glass with or SiO ₂ concentrations that play effluent is discharged Since gelation occurs near the resin, the conditions used are restricted.

Therefore, recently, a method has been adopted in which water glass is dealkalized by an ion exchange membrane electrodialysis apparatus. According to this method, an anode and a cathode are arranged at each end of the electrodialysis tank, and a cation exchange membrane and an anion exchange membrane are alternately positioned therebetween, thereby forming a concentration chamber and a desalination chamber alternately. A direct current is applied to each electrode and water glass is circulated in the desalting chamber, and an aqueous sodium hydroxide solution or potassium hydroxide solution is circulated in the other concentrating chamber to dealkalize the aqueous solution of water glass in the desalting chamber. It is characterized in that a dealkalized water glass aqueous solution can be efficiently obtained, and the obtained dealkalized water glass aqueous solution can be used as a ground improvement material.

[0009]

Further, in the above method, a water glass solution storage tank is provided outside the electrodialysis tank, and the water glass solution is circulated from the storage tank to the desalting chamber. Is supplied. In such a method, the degree of desalination can be ascertained by monitoring the electric conductivity of the circulating fluid, and a solution desalinated to a desired property (produced desalted solution) is used as a product. It is also possible to carry out continuous operation by supplying a raw water glass solution in an amount commensurate with the amount withdrawn at the same time to the storage tank.

However, when the present inventors tried the above-mentioned continuous operation, the high SiO ₂ concentration water glass aqueous solution and water, which are industrially easily available as a raw water glass solution, were separately separated from the water. When replenished, there is a problem that turbidity, that is, precipitation of solid content occurs in the storage tank, and in extreme cases, deposits on the membrane surface of the electrodialysis tank, and there is a problem that stable continuous operation cannot be performed. found.

Accordingly, an object of the present invention is to provide a method capable of stably and continuously producing an alkali-free water glass aqueous solution by subjecting the aqueous water glass solution to a dealkalization treatment using an electrodialysis apparatus.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, when the concentration of the aqueous solution of raw water glass to be replenished during the production operation is within a specific range, The present inventors have found that continuous operation can be stably performed without clouding, and the present invention has been completed.

That is, according to the present invention, the cation exchange membrane and the anion exchange membrane are alternately arranged between the anode and the cathode, and are separated by the cation exchange membrane on the anode side and the anion exchange membrane on the cathode side. An electrodialysis tank in which a concentration chamber and a desalination chamber partitioned by an anion exchange membrane on the anode side and a cation exchange membrane on the cathode side are alternately formed, and a storage tank arranged outside the electrodialysis tank. A storage tank having a raw material supply line for supplying a raw water glass aqueous solution to the storage tank, a desalination chamber supply line for supplying a water glass aqueous solution from the storage tank to the desalination chamber, and a desalination chamber from the desalination chamber to the storage tank. Using an electrodialysis apparatus having a return line for returning the alkalized water glass aqueous solution, electrodialysis is performed while circulating and supplying the water glass solution to the desalting chamber, and the SiO ₂ concentration from the return line is 1 wt% or more. in SiO ₂ / X ₂ O However, X represents an alkali metal atom.) A part of the aqueous alkali glass solution having a molar ratio of 6 or more and a pH of 7 to 12 is extracted, and the same as the extracted aqueous alkali glass solution. A method for producing the aqueous alkali-free water glass solution by supplying an amount of a raw water glass aqueous solution to the storage tank via the raw material supply line, wherein the raw water glass aqueous solution to be supplied to the storage tank has a SiO ₂ concentration of 1 to 1. The method for producing an alkali-free water glass aqueous solution, comprising using a 25 wt% aqueous glass solution.

According to the manufacturing method of the present invention, when the SiO ₂ concentration which can be used as a ground improvement material is 1 wt% or more,
A stable and continuous production of an aqueous alkali-free water glass solution having a molar ratio of O ₂ / X ₂ O (where X represents an alkali metal atom) of 6 or more and having a pH of 7 to 12. Can be.

In general, the SiO ₂ concentration of an aqueous alkali-free water glass solution obtained by electrodialysis is not sufficient to be suitably used as a material for ground injection.
_{(2) It} is desirable to increase the concentration, but the dealkalized water glass aqueous solution obtained by the production method of the present invention can be easily concentrated by ultrafiltration, and is suitable for a soil injection material. Can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, a cation exchange membrane and an anion exchange membrane are alternately arranged between an anode and a cathode, and the cation exchange membranes on the anode side and the cathode side are opposed to each other. An electrodialysis tank in which a concentration chamber partitioned by a membrane and an anion exchange membrane, and a desalination chamber partitioned by an anion exchange membrane and a cation exchange membrane on the anode side and the cathode side, respectively, are alternately formed; A storage tank disposed outside the tank, the storage tank having a raw material supply run for supplying the raw water glass aqueous solution to the storage tank, a salt chamber supply line for supplying a water glass aqueous solution from the storage tank to the desalination chamber, And an electrodialysis apparatus having a return line for returning the dealkalized aqueous solution of water glass from the desalting chamber to the storage tank.

As the electrodialysis tank in the electrodialysis apparatus, for example, a cation exchange membrane and an anion exchange membrane are alternately provided between an anode and a cathode as disclosed in JP-A-11-61124. An enrichment chamber that is arranged and partitioned by a cation exchange membrane located on the anode side and an opposing anion exchange membrane located on the cathode side, and an anion exchange membrane located on the anode side and a counterpart located on the cathode side A known electrodialysis tank having a plurality of alternately formed desalting chambers separated by a cation exchange membrane can be used without any limitation.

The electrodes, ion exchange membranes, and other necessary members constituting the tank can be used without any particular limitation. For example, for the ion exchange membranes, the aqueous solution of water glass is alkaline and It is desirable to use an alkali-resistant ion exchange membrane for passing sodium oxide or potassium hydroxide. Generally, the exchange group of the cation exchange membrane is a sulfonic acid group, the anion exchange membrane is a quaternary ammonium base, and a styrene-divinylbenzene copolymer hydrocarbon-based cation exchange membrane and an anion are used by using a reinforcing substrate. An exchange membrane is preferably used. Further, a fluorine-containing ion exchange membrane in which the material of the ion exchange membrane is made of a fluoropolymer can also be used.

The electrodialysis apparatus of the present invention is a storage tank disposed outside the electrodialysis tank for continuous operation, and a water supply line for diluting the raw water glass aqueous solution line with the storage tank in the storage tank. A desalting solution storage tank and an electrodialysis tank supply line for circulating and supplying the aqueous solution of water glass from the conditioning tank to the desalting chamber, and sending the aqueous solution of alkali glass removed from the desalting chamber. And a desalinated solution feed line for the production.

By having such a configuration, for example, by monitoring the electric conductivity of the circulating fluid during the electrodialysis operation, the degree of desalination can be grasped, and the desalination has been performed in the desired properties. The continuous operation can be stably performed by extracting the solution (produced desalted solution) as a product and simultaneously supplying the raw water glass solution in an amount corresponding to the extracted amount to the desalted liquid storage tank.

That is, while the aqueous sodium hydroxide solution and the aqueous potassium hydroxide solution are passed through the anode chamber, the cathode chamber, and the concentration chamber for alkali concentration of the water glass aqueous solution, the water glass aqueous solution in the desalting chamber is continuously or intermittently supplied. When supplied to the reactor, sodium ions pass through the cation membrane and decrease, while hydroxide ions pass through the anion exchange membrane and sodium hydroxide is concentrated in the concentration chamber. The circulating fluid in the return line has a lower alkali concentration than the inlet side.

By continuously or intermittently supplying a constant amount of the circulating liquid during the repetition of the circulation, a steady state having a certain width is obtained, and continuous operation becomes possible.

In the production method of the present invention, the aqueous dialysis solution is electrodialyzed using the above electrodialysis apparatus,
"Aqueous alkali water glass aqueous solution having a SiO ₂ concentration of 1 wt% or more, a molar ratio of SiO ₂ / X ₂ O (X represents an alkali metal atom) of 6 or more, and a pH of 7 to 12” (Also referred to as a product desalination solution), and the product desalination solution has particularly high utility value as a ground improvement injection agent.

The water glass solution used in the production method of the present invention comprises silicon dioxide and an alkali (generally, sodium hydroxide,
Alternatively, potassium hydroxide is used. ) Is not limited in particular as long as an aqueous solution of alkali silicate salt obtained by melting, SiO ₂ concentration of 1 to 10 wt%, SiO ₂ / X ₂ O molar ratio 1.5 to 5, the PH12 more aqueous solutions It is generally used. Here, X means an alkali metal atom. From the viewpoint of industrial availability, an aqueous solution prepared by diluting an aqueous solution of JIS standard No. 3 water glass or the like with water and having the above properties is preferably used.

Here, the raw material at the time of preparation means a water glass solution supplied to the storage tank at the start of electrodialysis, unlike the raw material supplied during continuous operation.

In the production method of the present invention, the method of the continuous operation and the various conditions are not particularly limited, except that the concentration of the aqueous glass solution to be supplied is within a specific range.

For example, the circulation of the liquid can be carried out, for example, by installing a liquid feed pump in the supply line of the salt room. The circulating flow rate cannot be specified unequivocally because it differs depending on the apparatus. However, it is usually expressed as a linear velocity in the membrane interval between the anion exchange membrane and the cation exchange membrane, and generally 1 to 10 cm /
sec.

The most characteristic feature of the production method of the present invention is to control the SiO ₂ concentration of the raw water glass aqueous solution (also referred to as a replenishing solution) to be supplied (replenished) during operation to 1 to 25% by weight. . When the SiO ₂ concentration of the replenishing solution is out of the above range, solid deposition occurs in the storage tank, and stable continuous operation cannot be performed. For example, the above-mentioned water glass aqueous solution of JIS standard No. 3 (SiO ₂ concentration of about 30% by weight) is easily available industrially. Therefore, it is necessary to supply it to a storage tank as it is and add water separately. Although it is the simplest, the above problem occurs when such a method is adopted. From the viewpoint of operation stability, the replenishment solution preferably has a SiO ₂ concentration of 5 to 20% by weight, particularly 5 to 15% by weight.

The method of controlling the SiO ₂ concentration of the replenishing solution is not particularly limited. For example, a concentration adjusting tank is provided upstream of the raw material supply run, and a concentrated aqueous solution such as JIS standard No. 3 water glass aqueous solution is mixed with water. Then, the concentration of the solution is adjusted, and the solution whose concentration has been adjusted may be supplied (supplied) to the storage tank via the raw material supply line.

The amount of the replenishing solution to be supplied (supplied) needs to be an amount corresponding to the amount of the extracted desalted solution. However, even if there is a fluctuation, the quality of the produced desalted solution is not adversely affected. The difference between the two can be as long as the amount is appropriate for a long span.

Incidentally, including the production method of the present invention, the concentration of SiO ₂ in the aqueous solution of de-alkaline water glass obtained by desalting using an electrodialyzer is often about 3 to 10% by weight. In order to obtain a high improvement effect when used as a material, it is desirable to perform concentration and increase the SiO ₂ concentration. The aqueous alkali-free water glass solution obtained by the production method of the present invention can be easily concentrated by ultrafiltration, and has an SiO ₂ concentration of, for example, 6 to 40.
An aqueous solution of alkali-free water glass as high as wt% can be easily obtained.

The ultrafiltration method at this time is not particularly limited.
For example, an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 50,000 is used, and the filtration pressure is 0 to 0.4 MPa, preferably 0 to 0.4 MPa.
What is necessary is just to filter at 2 MPa.

When the aqueous solution of dealkalized water glass having a high SiO ₂ concentration obtained by such a method is used as a ground improving material, a ground having high strength can be obtained.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

In the following Examples and Comparative Examples, desalting treatment was performed using an electrodialyzer as shown in FIG. The apparatus comprises a cation exchange membrane 3 and an anion exchange membrane 4 alternately arranged between an anode 1 and a cathode 2,
The concentrating chamber 5 in which the anode side and the cathode side are partitioned by a cation exchange membrane and an anion exchange membrane, respectively, and the desalting chamber 6 in which the anode side and the cathode side are partitioned by an anion exchange membrane and a cation exchange membrane, respectively, alternately. An electrodialysis tank 7 formed, a storage tank 12 provided outside the electrodialysis tank and having a raw material supply line 8 for supplying a raw water glass aqueous solution to the storage tank by a liquid circulation pump 13; A desalination chamber supply line 16 for supplying an aqueous solution of water glass from the desalination chamber 6 to the desalination chamber 6, and a return line 20 for returning the aqueous solution of de-alkalized water glass from the desalination chamber 6 to the storage tank,
A concentration adjusting tank 11 is provided upstream of the raw material supply line. The concentration adjusting tank 11 is connected to a line 9 for supplying an aqueous solution of high silica concentration such as an aqueous solution of JIS No. 3 water glass and a line 10 for supplying dilution water. The aqueous solution of water glass whose concentration has been adjusted here can be supplied to the storage tank by the pump 19. Further, the aqueous solution of sodium hydroxide stored in the concentrated liquid storage tank 14 can be supplied to the concentrated chamber through the concentrated chamber supply line 17 by the pump 15.

The electrodialysis tank in FIG. 1 is an electrodialysis tank manufactured by Tokuyama (TS2-10) having the specifications shown in Table 1 below.
Type).

[0037]

[Table 1]

Example 1 A 2 L aqueous solution of JIS No. 3 water glass diluted to a concentration of 5% of SiO2 was circulated and circulated into a concentration chamber / anode chamber.
0.5 mol / l NaOH was circulated through the cathode compartments. De-alkali at a current density of 2 A / dm ² and the electric conductivity of the liquid is 6 mS / cm
, And 1 L of a dealkalized solution was withdrawn. Subsequently, 1 L of a 5% SiO ₂ solution was replenished to the circulation tank to remove alkali, and the operation was repeated until the electric conductivity of the solution reached 6 mS / cm. Repeat this for 30
This was repeated to produce a total of 30 L of a dealkalized solution. In addition, the silica concentration of the obtained dealkalized solution was 6.5% by weight.
The Na ₂ O concentration was 0.33% by weight, the silica / Na ₂ O molar ratio was 20, and the pH was 11.

Further, the obtained aqueous solution was treated with a cut-off molecular weight of 1
Filtration pressure 0.2MP using 000 ultrafiltration membrane
Ultrafiltration was performed under the condition a. When the SiO ₂ concentration of the obtained filtrate was measured, it was 20% by weight.

The SiO ₂ concentration of 5 similarly JIS3 water glass solution as in Comparative Example 1 Example 1
%, And circulates 2 L of the dealkalized solution.
0.5 mol / l NaOH was circulated in each of the concentration room, the anode room, and the cathode room. The alkali was removed at a current density of 2 A / dm2 until the electrical conductivity of the solution became 6 mS / cm, and 1 L of the dealkalized solution was taken out. Subsequently, when 1 L of a solution having a SiO2 concentration of 27% was replenished to the circulation tank, the liquid in the tank became cloudy and the liquid circulation was stopped at the same time. The operation was stopped because the current density was lowered and the dealkalization could not be continued.

[0041]

According to the present invention, a water glass aqueous solution can be stably and continuously produced using an electrodialysis apparatus. Therefore, there is a great advantage in applying the production method of the present invention to a method of using the desalted water glass aqueous solution as a ground improvement material as it is, particularly when the method has a long term.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electrodialysis apparatus used in Example 1.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Anode 2 ... Cathode 3 ... Cation exchange membrane 4 ... Anion exchange membrane 5 ... Concentration room 6 ... Demineralization room 7 ... Electrodialysis tank 8 ... Raw material supply line 9 ... high concentration water glass supply line 10 ... dilution water supply line 11 ... concentration adjustment tank 12 ... storage tank 13 ... liquid circulation pump 14 ... concentrated liquid storage tank 15 ...・ Liquid circulation pump 16 ・ ・ ・ Salt supply line 17 ・ ・ ・ Concentration room supply line 18 ・ ・ ・ Salt liquid extraction line 19 ・ ・ ・ Material water glass aqueous solution supply pump 20 ・ ・ ・ Return line

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2D040 AA04 AB01 CA02 4D006 GA06 GA17 KA11 KA22 KA63 KE02R KE13R KE15R KE19P MA13 MA14 MB05 MC24 MC28 MC74 MC78 PB12 PB26 PC80 4D061 DA10 DB18 EA09 EB01 EB04 EB19 EB04 EB04 CB09 FD10 UB45

Claims (2)

[Claims] 1. A cation exchange membrane and an anode between an anode and a cathode.
On-exchange membranes are alternately arranged, and the cation exchange membrane on the anode side
And a concentration chamber separated by an anion exchange membrane on the cathode side and the anode
Separated by an anion exchange membrane on the cathode side and a cation exchange membrane on the cathode side
Electrodialysis tank having alternately formed deionized chambers,
A storage tank disposed outside the tank, wherein raw water
Storage tank having a raw material supply line for supplying an aqueous solution,
To supply a water glass aqueous solution from the storage tank to the desalination chamber
The desalination chamber supply line and the desalination chamber to the storage tank.
Return line for returning alkalized water glass solution
Water glass in the desalting chamber using an electrodialysis device having
Perform electrodialysis while circulating and supplying the solution.
In to SiO_TwoWhen the concentration is 1 wt% or more, SiO_Two/ X _TwoO
(Provided that X represents an alkali metal atom).
And the pH of the alkali-free water is 7 to 12.
Part of the glass solution and withdraw
Use the same amount of raw water glass solution as the alkali water glass solution.
By supplying to the storage tank via the raw material supply line,
A method for producing an aqueous alkali water glass solution,
SiO2 as the raw water glass solution to be supplied to the storage tank_Twoconcentration
Is characterized by using a water glass aqueous solution of 1 to 25 wt%.
The method for producing an aqueous alkali-free water glass solution described above. 2. A dealkalization method comprising the steps of: concentrating an aqueous alkali glass solution obtained by the production method according to claim 1 by ultrafiltration to produce an aqueous alkali glass solution having a high SiO ₂ concentration. A method for producing a water glass solution.