JP2001104955A - Pure water making method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently make pure water by RO membrane separation treatment from raw water consisting of Ca ion-containing water such as industrial water and F ion-containing water such as waste water from an electronic part producing process without requiring complicated pretreatment while preventing the formation of CaF2 scale. SOLUTION: Ca ion-containing water and F ion-containing water are mixed and the mixed water is adjusted to pH 6 or less to be passed through an RO membrane separator 1.

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 pure water, and more particularly to a method for purifying water containing calcium (Ca) ions such as industrial water and water containing fluorine (F) ions such as waste water for producing electronic parts as raw water. It relates to a method for producing water.

[0002]

2. Description of the Related Art Ultrapure water used in the production process of electronic parts such as semiconductors and liquid crystal display panels generally comprises a primary pure water production process consisting of membrane separation and ion exchange, ultraviolet oxidation, mixed-bed ion exchange, and the like. It is manufactured through a secondary pure water manufacturing process (also called a subsystem) consisting of ultrafiltration. In such ultrapure water production process, electronic component production wastewater, that is, used ultrapure water discharged from the electronic component production process is collected and supplied as raw water, in order to compensate for the shortage of raw water,
Industrial water, such as tap water (city water), groundwater (well water), and river water, is supplied as makeup water.

In this case, when industrial water and wastewater for producing electronic parts are mixed, Ca ions in the industrial water and F ions in the wastewater for producing electronic parts react to form calcium fluoride (Ca).
A colloid of F ₂ ) is produced and scaled by concentration in a membrane separator. That is, CaF ₂ has a remarkably small solubility product K _SP = [Ca ²⁺ ] [F ⁻ ] = 10 ^−10, and when concentrated by membrane separation treatment, CaF ₂ precipitates and is scaled. When the CaF ₂ scale adheres to the separation membrane, the performance does not easily recover even with chemical cleaning, and the amount of treated water decreases, and the quality of treated water decreases due to an increase in membrane surface concentration. For this reason, conventionally, industrial water and electronic component production wastewater are not mixed, but are treated in separate primary pure water production processes and then sent to a secondary pure water production process for treatment. However, there is a disadvantage that the processing apparatus and the processing operation are complicated.

[0004] As a pure water production technology for solving this problem and mixing and treating the electronic component production wastewater and industrial water, the electronic component production wastewater is treated with an anion exchange resin to remove F ions, and the industrial water is removed. A method has been proposed in which a Ca ion is removed by treating with a cation exchange resin, and then both treated waters are mixed and then deionized with a reverse osmosis (RO) membrane separator (Japanese Patent Laid-Open No. 7-39871, 10-272
465).

[0005] By mixing after removing the F ions and Ca ions in the raw water in advance, generation of CaF ₂ scale in the RO membrane separation apparatus is prevented, and stable treatment can be performed for a long period of time.

[0006]

However, even in the method of treating raw water with each ion exchange resin, it is necessary to provide respective treatment systems, and there is a problem of regeneration of the ion exchange resin. It is desired to develop a pure water production method capable of performing a stable RO membrane separation treatment by suppressing the generation of CaF ₂ scale by a simpler method without performing an ion exchange treatment.

Although the addition of a chelating agent or a dispersing agent can prevent the formation of CaF ₂ scale to some extent, in order to obtain a sufficient effect with the chelating agent, it is necessary to add a large amount. In this case, the effect is unstable, and the generation of scale cannot be reliably prevented.

The present invention has been made in view of the above-mentioned conventional circumstances, and requires a complicated pretreatment using water containing Ca ions such as industrial water and water containing F ions such as wastewater for manufacturing electronic components as raw water. An object of the present invention is to provide a method for easily and efficiently producing pure water by RO membrane separation treatment while preventing the generation of CaF ₂ scale without reducing the water content.

[0009]

The method for producing pure water according to the present invention is directed to a method for producing pure water using water containing calcium ions and water containing fluorine ions as raw water. And adjusting the pH to 6 or less, and then passing the water through a reverse osmosis membrane separation device.

[0010] The removal rate of F ions by the RO membrane depends on the pH.
If it is 5.5 or less, it becomes 90% or less.

In the present invention, when mixing RO water containing Ca ions and water containing F ions and performing RO membrane separation treatment, pH
By setting the ratio to 6 or less, the removal rate of F ions in the RO membrane is suppressed low, only Ca ions are removed, and F ions are transmitted to the permeated water side to prevent F ions from being concentrated. This allows
On the concentrated water side, Ca ions are concentrated, but F ions are hardly concentrated, so that the generation of CaF ₂ scale is prevented.

This RO membrane separation apparatus is intended to remove Ca ions and does not require removal of other salts. Therefore, the RO membrane separation apparatus can be operated at a low pressure and has a small decrease in membrane flux. ) Ion removal rate is 98
%, It is preferable to use an RO membrane having a low desalination ratio of not more than 10%. By using the RO membrane having such a low desalting rate, the removal rate of F ions is further reduced and the concentration of F ions is further prevented, so that the generation of CaF ₂ scale can be surely prevented. .

The permeated water from which Ca ions have been removed by the RO membrane separator is adjusted to pH 6 to 10, and then passed through an RO membrane separator and / or an electric regeneration type deionizer to be deionized. High-purity pure water can be obtained.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the method for producing pure water of the present invention.

In the present invention, the Ca ion-containing water used as raw water is industrial water such as tap water (city water), ground water (well water), river water and the like. Further, the F ion-containing water is electronic component production wastewater such as semiconductor production wastewater and liquid crystal production wastewater.

In the present invention, the Ca ion-containing water and the F ion-containing water are pretreated, if necessary, by a turbidizer or an organic matter decomposer, and then mixed, followed by pH adjustment and RO membrane separation treatment. This turbidity and organic matter decomposition treatment is C
It may be performed after mixing the a-ion-containing water and the F-ion-containing water. The mixing ratio of the Ca ion-containing water and the F ion-containing water is not particularly limited.

The mixed water of Ca ion-containing water and F ion-containing water is adjusted to pH 6 or less and passed through the RO membrane separation device 1. When the pH of the mixed water exceeds 6, F ions do not permeate the RO membrane, and both Ca ions and F ions are concentrated to form CaF ₂ scale. If the pH of the mixed water is excessively low, the removal rate of Ca, Na ions, and the like decreases, and a problem of corrosion of constituent materials of the apparatus occurs.
H is preferably adjusted to 3 to 6, particularly 4 to 5. For the pH adjustment of the mixed water, it is preferable to use a mineral acid such as hydrochloric acid or sulfuric acid, but it is not limited to these.

The RO membrane of the RO membrane separation apparatus 1 can be operated at a low pressure, has a low problem of membrane flux reduction, and has a high Na removal rate because it allows F ions to permeate and prevent its concentration. It is preferable to use an RO film having a low desalination rate of 98% or less, and such an RO film is a so-called loose RO film having a Na removal rate of 50 to 98%, specifically, Nitto Denko Corporation NTR-7250, 729H
F, SU-500 manufactured by Toray Industries, Inc. or the like can be used.

The RO membrane separation treatment in the RO membrane separation apparatus 1 is preferably performed at a water recovery rate of about 70 to 90% by circulating a part of the concentrated water as necessary.

In order to more reliably prevent the formation of scale in the RO membrane separation device 1, a dispersant or a chelating agent may be added to the feed water of the RO membrane separation device 1 if necessary. The dispersant is not particularly limited as long as it has a dispersing effect of Ca salt, but phosphonic acid, acrylic acid, polymerized phosphoric acid-based dispersant and the like are preferable, and usually about 1 to 5 ppm is added. . The chelating agent is not particularly limited as long as it has a chelating effect with Ca or F, and sodium ethylenediaminetetraacetate or the like is suitably used, and usually 10 to 30 ppm
To some extent.

A decarbonation device may be provided before or after the RO membrane separation device 1 to perform a decarbonation treatment. Examples of the decarbonation device include a decarbonation tower in which water to be treated and air are brought into countercurrent contact with each other through a packing, a membrane deaerator, a vacuum deaerator, a nitrogen deaerator, a heated deaerator, and the like. What is usually used for the production of pure water can be used. It is preferable to adjust the pH of the feed water of this decarbonation device to 4 to 5.5.

The permeated water of the RO membrane separation apparatus 1 has Ca ions removed therefrom, but contains F ions and other ions, so that it can be further added to an RO membrane separation apparatus or an electric regeneration type deionization apparatus. Is deionized by the deionization apparatus 2 described above. When an RO membrane separator is used as the deionizer 2, the RO membrane of the RO membrane separator has a Na removal rate of 9%.
It is preferable to use a RO membrane having a high desalination rate of 8% or more, particularly 99% or more. Specifically, ES-20 manufactured by Nitto Denko Corporation,
NTR-759, SU-700 manufactured by Toray, SUL-
10 or the like can be used. If the pH of the feed water of the RO membrane separation device is too low, F ions cannot be removed, and if the pH is too high, problems such as a decrease in desalination performance and scale formation such as calcium carbonate may occur. The pH is preferably adjusted to 6 to 10, particularly 7 to 8, by adding an alkali agent such as potassium.

When an electric regeneration type deionization apparatus is used as the deionization apparatus 2, a commercially available general electric regeneration type deionization apparatus can be used.
The H condition is also the same as in the case where the above RO membrane separation apparatus is used. However, in the electric regeneration type deionization apparatus, there is a problem of electrode corrosion due to generation of hydrofluoric acid.
It is more advantageous to use a RO membrane separation device than an electric regeneration type deionization device.

[0025]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Water (Ca: 16p) in which city water was turbidized by an ultrafiltration membrane separator
pm, pH: 7.4, conductivity: 130 μS / cm)
Simulated wastewater containing hydrofluoric acid and sodium hydroxide added to pure water (F: 10 ppm, pH: 5.0,
Conductivity: 25 μS / cm) was used as F ion-containing water, and water (Ca: 4 ppm, F: 7.5 ppm, pH: 6.4) mixed with city water 100 L / hr and simulated wastewater 300 L / hr.
(Conductivity: 61 μS / cm) by adding HCl to pH5.
It was adjusted to 0 and the RO membrane separation treatment was performed.

As the RO membrane of the RO membrane separation apparatus, NTR-729HR (2.5%, manufactured by Nitto Denko Corporation) having a Na removal rate of 97% was used.
Inch) and a pressure of 12 kg / cm ² (= 1.2MP)
Water was passed in a), and a part of the concentrated water was circulated so that the water recovery rate was 80%.

At this time, the F concentration of the permeated water was examined to determine the F removal rate, and the results are shown in Table 1. Further, the film flux maintenance rate after the operation was continued for 30 days (film flux after 30 days / film flux at the start of operation) was determined.
It was also described in.

Example 2 NTR-produced by Nitto Denko with a Na removal rate of 99% was used as the RO film.
759HF (2.5 inch), pressure 15kg / c
Example 1 except that water was passed at m ² (≒ 1.5 MPa).
, And the F removal rate and the film flux retention rate were examined. The results are shown in Table 1.

Comparative Example 1 A mixture of pH 6.4 and RO
The same treatment as in Example 1 was performed except that water was passed through the membrane separator, and the F removal rate and the membrane flux retention rate were examined. The results are shown in Table 1.

Comparative Example 2 The pH-adjusted mixed water of pH 6.4 was directly used for RO
The same treatment as in Example 2 was performed except that water was passed through the membrane separator, and the F removal rate and the membrane flux retention rate were examined. The results are shown in Table 1.

[0032]

[Table 1]

From Table 1, it can be seen that by setting the pH of the feed water of the RO membrane separation device to 6 or less, the F removal rate is reduced, and the concentration of F ions and the formation of CaF ₂ scale are prevented.
It can be seen that the film flux can be kept high for a long time. Comparing Examples 1 and 2, it can be seen that more favorable results can be obtained by using an RO film having a Na removal rate of 98% or less.

In Comparative Example 2, after the operation was continued for 30 days, the RO membrane separation device was disassembled and the RO membrane surface was subjected to ED.
As a result of X analysis, Ca and F were detected, and it was confirmed that CaF ₂ scale was generated.

Examples 3 and 4 NaOH was added to the permeated water of the RO membrane separation apparatus obtained in Examples 1 and 2 to adjust the pH to 8, and NTR-759HR (2.5 Nitto Denko Corporation) was used as the RO membrane. 15 kgf / cm ^{2 at} the second stage RO membrane separation device using
(= 15MPa), treated by passing water at a water recovery rate of 90%,
The F concentration and conductivity of the permeated water of each RO membrane separation device were examined, and the results are shown in Table 2.

Comparative Example 3 The pH of the feed water of the second stage RO membrane separation device was not adjusted, and p
The same treatment as in Example 4 was performed except that the permeated water of the first-stage RO membrane separation device of H5.3 was passed as it was, and each R was separated.
The F concentration and conductivity of the permeated water of the O membrane separator were examined, and the results are shown in Table 2.

[0037]

[Table 2]

As is clear from Table 2, high-purity pure water can be obtained by adjusting the pH of the permeated water of the first-stage RO membrane separation apparatus and further subjecting the permeated water to RO membrane separation treatment.

[0039]

As described in detail above, according to the method for producing pure water of the present invention, water containing Ca ions such as industrial water and water containing F ions such as waste water for producing electronic parts are used as raw water, which is a complicated process. The generation of CaF ₂ scale can be prevented without the need for treatment, and pure water can be easily and efficiently produced by RO membrane separation treatment.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for producing pure water of the present invention.

[Explanation of symbols]

 1 RO membrane separation device 2 Deionization device

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[Procedure amendment]

[Submission date] October 26, 1999 (1999.10.
26)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

As the RO membrane of the RO membrane separation apparatus, NTR-729H F (2.5%, manufactured by Nitto Denko Corporation) having a Na removal rate of 97% was used.
Inch) and a pressure of 12 kg / cm ² (= 1.2MP)
Water was passed in a), and a part of the concentrated water was circulated so that the water recovery rate was 80%.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

Example 2 NTR-produced by Nitto Denko with a Na removal rate of 99% was used as the RO film.
759H R (2.5 inch), pressure 15kg / c
Example 1 except that water was passed at m ² (≒ 1.5 MPa).
, And the F removal rate and the film flux retention rate were examined. The results are shown in Table 1.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 GA04 GA05 KA02 KA03 KA52 KA55 KA57 KA63 KB14 KB30 KD03 KD27 KD30 KE02P KE05P KE07P KE12P KE13P KE15R KE19P KE30P MB06 PA01 PB04 PB05P06

Claims (3)

[Claims] 1. A method for producing pure water using calcium ion-containing water and fluorine ion-containing water as raw water, wherein the calcium ion-containing water and the fluorine ion-containing water are mixed and the pH is adjusted to 6 or less. A method for producing pure water, comprising passing water through a reverse osmosis membrane separation device. 2. The method according to claim 1, wherein said reverse osmosis membrane separation device is a reverse osmosis membrane separation device using a reverse osmosis membrane having a sodium ion removal rate of 98% or less. 3. The method according to claim 1, wherein the permeated water of the reverse osmosis membrane separator is adjusted to pH 6 to 10 and then passed through a reverse osmosis membrane separator and / or an electric regeneration type deionizer. Characteristic pure water production method.