JP2001314868A - Method for preparing deionized water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing deionized water stably over a long term, preventing the specific resistance of the deionized water and the removal ratio of silica from decreasing and also preventing the generation of scale. SOLUTION: In a method for preparing deionized water by an electric regeneration type deionizing method, an S value, which is a parameter comprising hydrogen ion concentration and electric conductance, of concentrated water at the outlet is adjusted to 7 or higher by adding a monovalent cation type electrolyte to water to be treated or supply water to a concentration chamber or by selectively removing Mg ions in the water to be treated.

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 deionized water by an electric regeneration type deionization method (hereinafter referred to as EDI method). For more details, it is possible to efficiently use highly deionized deionized water called pure water or ultrapure water used in various manufacturing industries such as the pharmaceutical manufacturing industry, semiconductor manufacturing industry, foodstuff industry, or boiler water or research facilities. To a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing deionized water, generally, a method of obtaining deionized water by flowing treated water through a packed bed of ion exchange resin and adsorbing and removing impurity ions on the ion exchange resin is generally used. It is a target. However, in this method, it is necessary to regenerate the ion-exchange resin having a reduced exchange / adsorption ability, and the regeneration is usually performed using an acid or an alkali. As a result, in this method, there is a problem that a waste liquid caused by the acid or alkali is discharged together with a troublesome regeneration operation.

[0003] Therefore, a method of producing deionized water that does not require regeneration is desired. In recent years, an EDI method that does not require a regeneration operation using a chemical solution has been developed and put into practical use. In this method, a mixture of an anion exchange resin and a cation exchange resin is placed in a desalting chamber of an electrodialysis tank in which an anion exchange membrane and a cation exchange membrane are alternately arranged, and the water to be treated is placed in the desalting chamber. This is to perform electrodialysis by applying a voltage while flowing concentrated water into the concentrated room, which is formed and arranged alternately with the demineralization room while flowing, thereby producing deionized water and regenerating the ion exchange resin. This is a method which does not need to separately regenerate the ion exchange resin.

That is, in the conventional EDI method, a cation exchange membrane and an anion exchange membrane are alternately arranged between an anode chamber provided with an anode and a cathode chamber provided with a cathode, and the anode side is partitioned by an anion exchange membrane and the cathode is separated. An anion exchange resin and a positive electrode are placed in a desalination chamber of an electrodialysis tank in which a desalination chamber defined by a cation exchange membrane on the side and a concentration chamber defined on the anode side by a cation exchange membrane and the cathode side defined by an anion exchange membrane. Using a deionized water production apparatus containing an ion exchange resin, the treated water flows into the desalination chamber while applying a voltage, and the treated water or a part of the treated water is used as concentrated water in the concentration chamber. By flowing the impurities, impurity ions in the water to be treated are removed.

According to this method, since the ion-exchange resin is continuously and simultaneously regenerated as described above, there is no need for a regeneration step using a chemical such as an acid or an alkali and a waste liquid treatment used for the regeneration. However, at this time, the EDI device causes an increase in electrical resistance due to hardness components such as calcium ions and magnesium ions in the water to be treated, causing an increase in applied voltage or a decrease in current, and further a decrease in desalination performance. There is a problem that the specific resistance of the treated water produced by the process decreases.

Therefore, a method for overcoming such a problem is as follows.
There have already been many proposals, for example, a method in which water to be supplied to an EDI device is subjected to reverse osmosis membrane treatment in two stages in advance to remove as much hardness as possible, and then supplied as water to be treated by the EDI method ( JP-A-2-40220) or a method in which water is electrolyzed in a separately prepared acidic water-producing electrolytic cell and acidic water generated in the anode chamber is passed through a EDI-type concentrating chamber (Japanese Patent Laid-Open No.
0-128338). By adopting such a method, the long-term performance of the EDI method can be stabilized, but the investment cost is increased, and as a result, there is another problem that the advantage of the EDI system is reduced as compared with other deionization methods. Will be.

Further, an aqueous solution of an alkali metal hydrochloride or sulfate is added to supply a liquid having an electric conductivity of 100 to 800 μS / cm to a concentration chamber of an EDI apparatus, thereby stabilizing a flowing current to stabilize high-purity treated water. (Japanese Patent Laid-Open No. 9-24374) has also been proposed, but the long-term stability of its performance has not been clarified.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a conventional ED.
The present invention relates to a method for long-term stabilization of a deionized water production system by the method I, and a method for solving the above-mentioned problems of the proposed improved deionized water production method and the like.
SUMMARY OF THE INVENTION An object of the present invention is to provide a simple and inexpensive method for preventing and eliminating performance deterioration due to impurities such as hardness components of water to be treated supplied in the method.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a method for producing deionized water for solving the above-mentioned problems, comprising a cation exchange membrane and a cathode between an anode chamber having an anode and a cathode chamber having a cathode. An ion exchange membrane is arranged alternately, a desalting chamber where the anode side is partitioned by an anion exchange membrane and the cathode side is partitioned by a cation exchange membrane, and a concentration chamber where the anode side is partitioned by a cation exchange membrane and the cathode side is partitioned by an anion exchange membrane. Using a deionized water producing apparatus in which an ion exchanger is accommodated in the desalting chamber of the electrodialysis tank in which the water has been formed, the water to be treated is supplied to the desalting chamber while applying a voltage, and the electrolyte is supplied to the concentrating chamber. In the electric regeneration type deionized water production method of supplying a concentrated solution composed of a solution and removing impurity ions in the water to be treated by moving the concentrated water to the concentrated water, the concentrated water at the outlet of the concentrated chamber is defined by the following formula 1 Value is 7 or more And those which can be achieved by pH of the retentate is 2.5 or more. That is, in the present invention, by setting the S value of the concentrated water at the outlet of the concentration chamber to 7 or more, hardness components such as Mg ions are combined with OH ions and carbonate ions near the anion exchange membrane on the concentration chamber side. The formation of a hardly soluble salt can be suppressed.

[0010]

Embedded image

In the present invention, there are roughly two methods for setting the S value to 7 or more in the concentrated water at the outlet of the concentration chamber (hereinafter referred to as "outlet concentrated water"). The first method is a method of supplying the water to be treated with the above-mentioned S value of 7 or more, preferably 10 or more, to the desalting chamber of the deionized water producing apparatus. Further, the second method is a method of directly supplying the deionized water to the deionized water production apparatus without performing pretreatment when the S value of the water to be treated is less than 7, and in this case,
The water to be treated is supplied as it is, and a monovalent cation-type electrolyte is added to the concentrated liquid, or the S value at the outlet concentrated water is 7 or more, preferably 10 The above is the description.

Further, in the present invention, by adopting or using one of the above two methods, the performance of the electric regeneration type deionized water producing apparatus can be reduced without removing the hardness component of the water to be treated as much as possible in advance. Can be stabilized for a long time. In particular, even in the case of water to be treated containing impurities which are difficult to ionize, such as silica and carbon dioxide, the production apparatus can be operated with an increased current density, so that the impurities can be efficiently removed. In addition, since the operation can be performed with a low applied voltage due to the high concentration chamber conductivity, the power consumption can be reduced.

[0013] To explain the first method more specifically, the S value of river water, lake water, groundwater, tap water, or the like, which is the raw material water of deionized water, is usually 1 or less. Then, after the S value is set to 7 or more, the water to be treated is to be supplied to the deionized water producing apparatus. For this purpose, a method of adding an electrolyte other than Mg ions to increase the electric conductivity, There is a method of selectively removing Mg ions in water or performing ion exchange with ions other than Mg ions.

In the former method, the concentration of the electrolyte in the water to be treated is increased, resulting in an increase in the amount of ions that must be removed by the EDI device, and a problem such as a reduction in the treatment speed. On the other hand, the latter method uses Mg
There is a method in which a so-called softener that selectively removes ions or exchanges ions other than Mg ions, particularly, monovalent cations, is used for pretreatment of an EDI apparatus. These methods are one of preferred embodiments of the present invention. However, since the high concentration of Mg ions leaks abruptly after passing through the point of ion exchange, maintenance tends to be complicated.

As a result of intensive studies on the above problems, the present inventor has found that a reverse osmosis membrane having specific characteristics is preferable as a pretreatment device for an EDI device. That is, as a pretreatment device of a deionized water production device, a reverse osmosis in which the T value defined by the following equation 2 using the NaCl removal rate and the MgCl ₂ removal rate, which are the basic physical property values of the reverse osmosis membrane, is 10 or more. It has been found that the above problem can also be achieved by employing a reverse osmosis device having a membrane and supplying the water to be treated pretreated with the reverse osmosis device to the deionized water production device. [Equation 2] T value = (100-NaCl removal rate) / (100-MgCl ₂ removal rate) [Here, the NaCl removal rate and the MgCl ₂ removal rate are each determined by using an aqueous solution having a concentration of 0.1% by mass. 0.8M
It is a value measured at Pa and a temperature of 25 ° C. ]

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the following, an embodiment of the method for producing deionized water of the present invention using the electric regeneration type deionized water producing apparatus shown in FIG. 1 will be described.
It is needless to say that the present invention is not limited to this embodiment and is specified by the description of the claims.

In the apparatus for producing deionized water used in the method for producing deionized water of the present invention, the anion exchange membrane A and the cation exchange membrane K are provided in the electrodialysis tank 1 in the desalination chamber frames D1, D2, D
3... Dn and the enrichment chamber frames C1, C2, C3... Cn are arranged at predetermined intervals, whereby the anode chamber 2, the enrichment chambers S1, S2. R2 ... Rn and the cathode chamber 3 are constituted. In addition, desalination chambers R1, R2,.
An anion exchanger and a cation exchanger are accommodated and filled in n, and a structure such as a mesh, that is, spacers N1, N2,...

An anode 4 and a cathode 5 are provided in the anode chamber 2 and the cathode chamber 3, respectively, and a voltage is applied between both electrodes during the production of deionized water. Thereby, the anion component in the water to be treated, which is introduced from the conduit 6 into the desalting chambers R1, R2,... Rn, permeates and transfers to the concentration chamber on the anode side through the anion exchange membrane A, and the cation component in the water to be treated is The permeation shifts to the concentration chamber on the cathode side through the cation exchange membrane K. As a result, the water to be treated itself is deionized and taken out through the conduit 7 after passing through the desalting chamber.

On the other hand, the concentrated water to be supplied to the concentration chamber is introduced by adding a monovalent cation-type electrolyte and controlling the S value of the above [Equation 1] at the outlet concentrated water to be 7 or more. Are introduced into each of the concentration chambers S1, S2,.
Here, the anions and cations permeated and transferred as described above are collected and discharged from the conduit 9 as concentrated water. Although FIG. 1 shows a case where the direction of the water stream to be treated and the direction of the concentrated water stream are opposite (countercurrent), it is a matter of course that both may be co-current.

In the electrodialysis tank 1, each desalting chamber R
1. The cations in the water to be treated captured by the cation exchanger in R2... Rn are given a driving force by an electric field, and are adjacent to the cation exchanger in contact with the captured cation exchanger. , Sequentially reach the cation exchange membrane, pass through the membrane, and move to each of the concentration chambers S1, S2,... Sn. Similarly, the anions in the water to be treated captured by the anion exchanger sequentially pass through adjacent anion exchangers, reach the anion exchange membrane, and further permeate through the membrane to each of the concentration chambers S1, S2,.
・ Move to Sn.

The electric regeneration type deionized water producing apparatus shown in FIG. 1 used in the present invention exemplifies a case where the S value of the water to be treated is 7 or less. Concentrated water supplied to the concentrating chamber is supplied to a pump P between the tank and the separately installed tank 10.
1, P2 and the concentrated water circulating conduit 11 are circulated and reused, and a part of the water to be treated or the treated water is added to the tank 10 of the circulation system to be replenished.

The replenishment is effected by branching pipes 15 and 1 with valves 15a and 16a, respectively, branching off from conduits 6 and 7, respectively.
6 is performed. Further, the amount of the water to be treated or the replenishment amount of the treated water at that time is not particularly limited, but is practically preferably 0.00
The range is preferably from 1 to 10% (hereinafter, it means mass% unless otherwise specified).

Then, a monovalent cation-type electrolyte is added to the concentrated water in the tank 10 of the circulation system in order to maintain the S value defined by the equation 1 at 7 or more. Is an aspect of the most significant feature of the present invention. S at that time
The value is adjusted by measuring with a conductivity meter 14 installed between the conduit 9 and the tank 10 which are discharged as a concentrate,
When the S value of the concentrated water at the outlet is similar to the S value supplied to the concentration chamber, the conductivity can be adjusted by measuring the conductivity of the concentrated water in the tank 10 with the conductivity meter 14. In the adjustment of the apparatus shown in FIG. 1, the electric conductivity is measured and the monovalent cation type electrolyte adding apparatus 1 is controlled so as to maintain the electric conductivity at a predetermined value.
The adjustment is performed by adjusting the addition amount from 3.

That is, the monovalent cation-type electrolyte adding device 13 is maintained so that the pH is 7 and the Mg ion concentration of the concentrated water is maintained at 1400 μS / cm at 200 ppb and 14000 μS / cm at 2000 ppb.
The amount is adjusted by adjusting the amount added.
The electrolyte added at this time is preferably used in the form of an aqueous solution because the amount of addition is very small. The concentration is preferably 5 to 36%, and more preferably 10 to 20%.

In the apparatus of the present invention shown in FIG.
In the production of deionized water using water to be treated having a value of less than 7, a monovalent cation-type electrolyte is added to the concentrated water to maintain its S value within a predetermined range. Although water is recycled, which is a preferred embodiment, the present invention is not limited thereto.

Therefore, the concentrated water does not need to be circulated, and in this case, the monovalent cation-type electrolyte may be added directly to the concentrated water supplied to the concentration chamber. In addition, the amount of the monovalent cation-type electrolyte to be added is small, and it is difficult to finely adjust the electrolyte. Therefore, it is necessary to use an aqueous solution as described above, and the concentration thereof is 5 to 5. 36% is good, preferably 10-20%.

In the present invention, the S value of the concentrating chamber to which the monovalent cation-type electrolyte has been added is set to 7 or more at the outlet of the concentrating chamber. Although it depends on the impurity composition of the treated water and the current density flowing through the ion exchange membrane of the electrodialysis tank, it is 30 or less, preferably 13 to 15. The reason is that when the S value increases and the conductivity of the supply water to the concentration chamber becomes excessively high, the conductivity component diffuses and leaks from the concentration chamber to the desalination chamber through the ion exchange membrane separating the concentration chamber and the desalination chamber. Inconveniences such as a decrease in the quality of the treated water, an increase in the current flowing through the electrodialysis tank as a countermeasure, and the necessity of an ion exchange membrane having a better separation performance become apparent. In addition, the reason why the lower limit is set to 7 is that if it is less than 7, the stability is inferior.

Then, the S value is adjusted by measuring the conductivity of the concentrated water with a conductivity meter 14 and adding the same from a monovalent cation type electrolyte adding device 13 so as to maintain a predetermined value. This is mainly performed by adjusting the amount of water, but when the concentrated water is circulated, the amount of circulating water or the amount of water to be treated or the amount of replenished water to be added to the circulating water is adjusted. It can be done next. When circulating concentrated water, it is preferable to interpose a tank, but it is not essential to intervene, and it is possible to circulate without a tank. The addition of the monovalent cation-type electrolyte and the replenishment of the water to be treated or the treated water may be performed halfway.

The monovalent cation-type electrolyte to be added to the concentrated water is an electrolyte in which a monovalent cation and a monovalent or polyvalent anion are combined, and dissolves to provide the monovalent cation quickly. Any monovalent cation can be used without particular limitation as long as it can be used. As the monovalent cation at that time, a hydrogen ion, a lithium ion, a sodium ion, a potassium ion, an ammonium ion, a quaternary alkylammonium ion and the like are preferable. .

The anion is preferably a monovalent ion such as a fluorine ion, a chloride ion or a nitrate ion, or a polyvalent ion such as a sulfate ion or a carbonate ion. The above-mentioned electrolyte is preferably a compound in which an anion and a cation selected from these ions are bonded, and among them, hydrochloric acid, sodium chloride, and potassium chloride are particularly preferable in terms of effect and availability.

These monovalent cation-type electrolytes can be used alone or in combination of two or more.
Combine Cl or KCl with hydrochloric acid, and adjust the pH of the concentrated water at the outlet of the concentration chamber to 2.5 to 6, preferably 2.6 to 2.6.
By setting it to 5, the S value can be achieved even when the amount of addition of NaCl or KCl is suppressed to a small amount, which is preferable. The reason is that, in this way, in particular, the decarbonation of the water to be treated supplied to the desalination chamber, that is, even if the separation and removal of the contained carbon dioxide gas is insufficient, the calcium carbonate which may be generated therewith may be generated. This is because there is an advantage that precipitation can be prevented.

In the EDI method of the present invention, the S value of the water to be supplied to the desalination chamber is desirably 7 or more, and various raw waters such as tap water, groundwater, and river water can be obtained by the following formula 2 of the present invention. T value is 10 or more, preferably 25 or more, especially 5
Pretreatment with a reverse osmosis device having a reverse osmosis membrane having characteristics of 0 or more, S value is 7 or more, and electric conductivity is 200 μS /
cm or less.

As described above, the water to be treated S
If the value is less than 7, it can be dealt with by setting the S value of the outlet concentrated water to 7 or more. In this case, in view of the objects and effects of the present invention, the water to be treated has an electric conductivity of 1 to 20.
Those having 0 μS / cm and Mg ion concentration of 1 to 200 ppb can be preferably used. When such water to be treated is used, long-term performance stability is achieved in the present invention, as described in Examples below.

In the present invention, deionized water is produced using such water to be treated, that is, in the desalting chamber, the conductivity is 1 to 200 μS / cm and the Mg ion concentration is 1 to 200 ppb. The water to be treated is supplied, and 1
While adding a cation-type electrolyte and supplying concentrated water so that the S value of the concentrated water at the outlet becomes 7 or more, a voltage is applied to the electrodialysis tank to cause deionization. The amount, that is, the amount of current per membrane area through which ions permeate, is preferably increased in a timely manner with an increase in the amount of ions in the water to be treated, that is, the conductivity and the supply amount of the water to be treated,
0.1~2A / dm ^2, in particular a current density of 0.2~1A / dm ² is used.

In this case, if the water to be treated contains silica or carbon dioxide gas, the present invention increases the amount of current,
It is possible to deionize the water to be treated by ionizing silica or carbon dioxide gas with the generated OH ions, but when the present invention is not used, scale is generated on the anion exchange membrane surface with the passage of time, Since the permselectivity decreases, the specific resistance of the treated water decreases. The present invention has an advantage that long-term stability of performance is achieved.

A cation exchange membrane used in the present invention,
As for the anion exchange membrane, the conductivity meter, the tank, the pump, etc., various known ones can be used without particular limitation, and the known structure of the electrodialysis tank can be used without particular limitation. it can. As for the ion exchanger, various shapes such as a granular shape, a fibrous shape, and a plate shape can be used. As for the type of functional group and the exchange performance of the ion exchanger, it is preferable to use a mixture of an ion exchanger having an anion exchange group and a cation exchange group, that is, an anion exchange resin and a cation exchange resin. The exchange capacity may be either strong or weak, but preferably strong acidity and strong basicity.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it should be understood that the present invention is not limited to these Examples and is specified by the appended claims. As the apparatus used, an electric regeneration type deionized water producing apparatus as shown in FIG. 1 was used. However, unlike the apparatus shown in the drawing, the water to be treated and the concentrated water were used in the upward cocurrent flow.

The specific structure of the electrodialysis tank in the deionized water producing apparatus used in this embodiment is as follows. Strongly acidic cation exchange membrane (thickness 600 μm, ion exchange capacity 2.7 meq / g dry membrane) and strong basic anion exchange membrane (thickness 600 μm, ion exchange capacity 2.1)
Milli-equivalents / gram dry membrane) are arranged via a desalting chamber frame (made of polypropylene) and a concentrating chamber frame (made of polypropylene) and tightened, and a filter press type dialysis tank (a polypropylene net is inserted in the concentrating chamber) is effective. Area 507c
m ² [horizontal (= room frame width) 13cm, vertical (= desalting length) 39c
m] × 3 pairs of electrodialysis tanks.

The desalting chamber is filled with a mixture formed by mixing a cation exchange resin, an anion exchange resin and a binder into a plate shape in a dry state. A spacer made of a synthetic resin was filled.
At this time, the particle size of both ion exchange resins is 400 to 60.
A sulfonic acid type (H type) cation exchange resin (manufactured by Mitsubishi Chemical Corporation, trade name: Diaion SK-1B) having a dry resin of 0 μm and an ion exchange capacity of 4.5 meq / g and a particle size of 4
00 to 600 μm, ion exchange capacity is 3.5 meq /
g An ion exchange capacity ratio of 50/50 was used using a quaternary ammonium salt type (OH type) anion exchange resin (manufactured by Mitsubishi Chemical Corporation, trade name: DIAION SA-10A).

[Examples 1 and 2 and Comparative Examples 1 and 2] T value at which the removal rate of NaCl and the removal rate of MgCl ₂ were 99% and 99%, respectively, after sand filtration of industrial water using the EDI apparatus described above. The water to be treated shown in Table 1 which had been treated in one stage with a reverse osmosis membrane device having a reverse osmosis membrane having a value of 1 was supplied to the desalination chamber of the deionized water production apparatus, and Examples 1 and 2 and Comparative Example 1 were obtained. 2 were tested.

[0041]

[Table 1]

In this case, in Examples 1 and 2 and Comparative Example 1, sodium chloride was added to the water to be treated, and the S value and the conductivity of the outlet concentrated water were as shown in Table 2 in Examples 1 and 2 and Comparative Example 1. The adjusted product was supplied and recycled. Comparative Example 2
Has a 90% utilization rate without adding electrolyte to the water supplied to the enrichment chamber.
%, And the S value and conductivity at that time are as shown in Table 2.

[0043]

[Table 2]

At that time, the amount of water supplied to the desalting chamber and the concentrating chamber,
Table 2 shows the electrical conductivity, hardness and Mg concentration of the concentrated water, and the current density of the EDI device. In Examples 1 and 2 and Comparative Examples 1 and 2, operation was performed continuously for 1000 hours under the conditions shown in Table 2, and the voltage, the specific resistance of the treated water, and the stability of the silica removal rate were examined. After the operation was completed, the used electrodialysis tank was disassembled, and the scale generation status on the enrichment room side was confirmed.
Table 3 shows these results.

[0045]

[Table 3] From the results in Table 3, in the example, there was no difference between the initial operation and after 1000 hours in both the specific resistance and the silica removal rate, and there was no scale on the enrichment chamber side even in the dismantling inspection.
It turns out that it is stable for a long time. On the other hand, in the comparative example, both the specific resistance and the silica removal rate were significantly lower than the initial operation after 1000 hours, and the specific resistance was 1/100.
It is extremely reduced to about 5１ ／. In the dismantling survey, it can be seen that scale is generated on the enrichment room side.

From these results, it was proved that the monovalent cation-type electrolyte was added to the concentrated water to be supplied to the concentration chamber and the S value was adjusted to a predetermined value so that the water was stable for a long period of time. Further, it can be seen that the higher the current density, the higher the silica removal rate, and the addition of the monovalent cation-type electrolyte can prevent a decrease in the silica removal performance.

Embodiment 3 In this embodiment 3, the desalting chamber has an electric conductivity of 13 μS / cm, silica of 600 ppb, and a hardness component of
300 ppb (as CaCO ₃ ), Mg ₃₀ ppb, CO ₂ 1
Supply the water to be treated having a pH of 6.0 containing ppm and adding sodium chloride and hydrochloric acid to a concentration water circulating tank into the concentration chamber, and supply the concentrated water so that the conductivity of the concentrated water at the outlet becomes 1800 μS / cm 2 and pH 3.5. The test was performed under the same conditions as in Example 1 except that the test was performed. The outlet concentrated water had an S value of 7.4, a Mg ion concentration of 290 ppb, and a treated water specific resistance after 1000 hours of 16 MΩ · cm or more. Inspection after dismantling showed no scale development in the enrichment room.

[Embodiment 4] In this embodiment 4, the desalting chamber is
600 ppb silica, 500 ppb hardness component (as CaC
O ₃ ), Mg 50 ppb, conductivity 2 containing ₂ ppm of CO ₂
5 μS / cm, water to be treated having a pH of 6.0 is supplied, hydrochloric acid and sodium chloride are added to a concentrated water circulation tank in the concentration chamber, and the conductivity of the concentrated water at the outlet is 2500 μS / cm 2, p
The test was performed under the same conditions as in Example 1 except that concentrated water adjusted to H3 was supplied. The results show that the outlet concentrated water has an S value of 9.9, a Mg ion concentration of 500 ppb,
The treated water specific resistance after 00 hours was 16 MΩ · cm or more. In the investigation after dismantling, no scale was generated in the enrichment room.

Example 5 Instead of the reverse osmosis device of Example 1, the NaCl removal rate was 65% and the MgCl ₂ removal rate was 99.4%.
And a reverse osmosis membrane having a T value of 58.8 (manufactured by Toray, SU2
00S), electric conductivity of 70 μS / cm, Mg ion concentration of 7 ppb, pH pretreated by a reverse osmosis membrane device equipped with
The treated water of 6.0 was treated with a treated water recovery rate of 90% and a current density of 0.
Tested at 8 A / dm ² . The pH of the outlet concentrated water is 6.0,
S value is 10, Mg ion concentration is 70 ppb, conductivity is 7
00 μS / cm, the initial specific resistance is 12 MΩ · cm,
The specific resistance after 1000 hours was 12 MΩ · cm, which was not changed. In the inspection after dismantling, no scale was generated.

[Embodiment 6] In this embodiment 6, the desalting chamber is
Silica 1000ppb, hardness component 1000ppb (as
CaCO ₃ ), Mg ion concentration 100ppb, CO ₂ 2p
pm, water to be treated having a conductivity of 20 μS / cm and a pH of 6.0 is supplied, sodium chloride is added to the concentrated water circulation tank in the concentration chamber, and the conductivity of the concentrated water at the outlet is 12000 μS / c.
m, except that concentrated water was supplied so as to have a pH of 6.0.
The test was performed under the same conditions as in Example 1. As a result, the S value of the outlet concentrated water was 12, the Mg ion concentration was 1000 ppb,
The treated water resistivity after 1000 hours was 16 MΩ · cm or more. Investigation after dismantling of the electrolytic cell showed no scale generation in the enrichment room.

[0051]

According to the present invention, the hardness of the water to be treated is removed as much as possible in advance by adding a monovalent cation-type electrolyte to the water supplied to the concentration chamber and controlling the conductivity to a specific range. Even without this, the performance of the electric regeneration type deionized water production apparatus could be stabilized for a long period of time. In particular, since water to be treated containing impurities that are difficult to ionize, such as silica and carbon dioxide, can be operated with an increased current density, the impurities could be removed efficiently. In addition, since the operation can be performed at a low applied voltage due to the high concentration chamber conductivity, the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing one example of an electric regeneration type deionization production apparatus that can be used in the deionized water production method of the present invention.

[Explanation of symbols]

 A Anion exchange membrane K Cation exchange membrane 1 Electrodialysis tank 2 Anode chamber 3 Cathode chamber 4 Anode 5 Cathode 6 Inlet pipe for treated water 7 Deionized water conduit 8 Concentrated water inlet pipe 9 Concentrated water outlet pipe S1, ... Sn concentration Room R1, ... Rn Deionization room D1, ... Dn Deionization room frame C1, ... Cn Concentration room frame 10 Tank 11 Concentrated water circulation conduit 13 Monovalent cation-type electrolyte addition device 14 Conductivity meter P1 , P2 pump

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C02F 1/44 C02F 1/46 103 (72) Inventor Hiroshi Toda 10 Goi Kaigan, Ichihara-shi, Chiba Prefecture Asahi Glass Company F-term (Reference) 4D006 GA03 GA17 HA42 HA47 JA30C KA33 KA57 KD12 KD30 KE13R KE15P KE15R KE18R KE19P KE19Q KE19R MA03 MA13 MA14 MB07 PA01 PB04 PB05 PB06 PB23 PB27 PB64 PC02 PC11 BA31 BA04 ABA BA23 BA14 ABA ABA ABA23 DA06 4D061 DA02 DA03 DB18 EA09 EB01 EB04 EB13 EB19 EB37 EB39 ED12 ED13 FA08 FA09 GA21 GA22 GC05 GC12 GC18

Claims (6)

[Claims] 1. A cation exchange membrane and an anion exchange membrane are alternately arranged between an anode chamber having an anode and a cathode chamber having a cathode, and the anode side is defined by an anion exchange membrane and the cathode side is defined by a cation exchange membrane. A deionized water production apparatus comprising an ion exchanger in a desalination chamber of an electrodialysis tank having a desalination chamber and a concentration chamber partitioned on the anode side by a cation exchange membrane and a cathode side partitioned by an anion exchange membrane. In this method, water to be treated is supplied to a desalting chamber while voltage is applied, and a concentrated liquid comprising an electrolyte solution is supplied to a concentrating chamber to remove impurity ions in the water to be treated by moving the concentrated water to the concentrated water. In the method for producing regenerated deionized water, the S value defined by the following formula 1 at the outlet of the concentration chamber is 7 or more, and the pH of the concentrated water is 2.5 or more. Deionization by regenerative deionization Ion water production method. Embedded image 2. The deionization by the electric regeneration type deionization method according to claim 1, wherein the water to be treated having the S value of 7 or more is supplied to a deionization chamber of the deionized water production apparatus. Water production method. 3. A reverse osmosis apparatus provided with a reverse osmosis membrane having a T value defined by the following equation 2, which is 10 or more, using a NaCl removal rate and a MgCl ₂ removal rate, which are basic physical property values of the reverse osmosis membrane. The method for producing deionized water according to claim 1 or 2, wherein the treated water to be treated is supplied to a deionization chamber of the deionized water producing apparatus. [Equation 2] T value = (100-NaCl removal rate) / (100-MgCl ₂ removal rate) 4. The water to be treated having an S value of less than 7 is supplied to a desalting chamber of the deionized water producing apparatus, and a monovalent cation-type electrolyte is added to the concentrated solution. 4. The method according to claim 1, wherein the S value of the liquid is 7 or more. 5. The deionization method according to claim 4, wherein the monovalent cation-type electrolyte added to the concentrate is selected from the group consisting of hydrochloric acid, sodium chloride and potassium chloride. Ion water production method. 6. A method for applying a voltage to a deionized water producing apparatus to apply a current of 0.1 to 2 A / effective area per effective area of the ion exchange membrane.
The method for producing deionized water by the electric regeneration type deionization method according to any one of claims 1 to 5, wherein dm ² is used.