JP3473472B2 - Treatment method for fluorine-containing water - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating fluorine-containing water with an electric desalination apparatus, and in particular, in a pure water producing apparatus in the field of electronics industry, raw water mixed with recovered water containing fluorine ions Calcium fluoride (CaF ₂ ) in the concentrating chamber of the electric desalination equipment when processing with the desalination equipment
The present invention relates to a method of preventing scale formation and performing stable treatment over a long period of time.

[0002]

2. Description of the Related Art Conventionally, in the production of demineralized water used for washing water for semiconductors, lenses, liquid crystals, etc., medical water, etc., a plurality of anion exchange membranes and cation exchange membranes are alternately arranged between electrodes and concentrated. An electric desalination apparatus in which chambers and desalting chambers are alternately formed is often used. The electric desalination equipment is capable of efficient desalination treatment, does not require regeneration like ion exchange resin, allows complete continuous water sampling, and has the excellent effect of obtaining extremely high-purity water. Play. In the electric desalination apparatus, there are a desalting chamber filled with a mixture of anion exchange resin and a cation exchange resin, and a desalting chamber not filled with an ion exchange resin. In terms of improving the quality of treated water, it is more effective to use a desalting chamber filled with an ion exchange resin.

In the electric desalination apparatus, the ions in the raw water flowing into the desalination chamber move in the direction of the electrode (a direction perpendicular to the flow of the water to be treated) to which an electric potential is applied based on the affinity, the concentration and the mobility. In addition, it moves across the cation exchange membrane or the anion exchange membrane that separates the desalting chamber and the concentration chamber, and the charge neutralization is maintained in all the chambers. Then, due to the semi-permeation property and potential of the ion exchange membrane, the ions of the raw water are reduced in the desalting chamber and concentrated in the adjacent concentration chamber. Therefore, demineralized water is recovered from the desalination chamber.

It is known that there is a hardness component as a factor of scale generation in such an electric desalination apparatus. However, in general, as raw water for an electric desalination device,
Since tap water, industrial water, etc. are supplied, the supplied water that flows into the electric desalination apparatus rarely contains fluoride ions. Therefore, in the conventional case, the electric desalination apparatus used CaF ₂
The scale of was never a problem.

[0005]

However, in recent years, while the application of an electric desalination apparatus to a pure water producing apparatus in the field of electronics industry has been progressing, the recovered water of a factory is used as raw water for the purpose of effective use of water. There are many cases of mixing and processing. In such a case, when the fluoride ions contained in the recovered water are concentrated by the electric desalting apparatus, CaF ₂ scale is generated, which causes scale failure.

The present invention solves the above-mentioned conventional problems and prevents the formation of CaF ₂ scale in the concentrating chamber of the electric desalination apparatus when treating the fluorine-containing water with the electric desalination apparatus, and stabilizes it for a long time. An object of the present invention is to provide a method for treating fluorine-containing water that can perform various treatments.

[0007]

A method for treating fluorine-containing water according to the present invention is a method for treating fluorine-containing water by supplying it to an electric desalination apparatus. Water recovery such that the relationship between Ca] (mg / L) and fluorine concentration [F] (mg / L) and the water recovery rate (production water amount / supply water amount) [R] of the electric desalination device satisfies the following formula: Calcium ion in feed water that reduces the rate
Reduce the concentration, reduce the fluorine ion concentration of the feed water
, At least one of which is treated with water
The recovery rate [R] is maintained at 0.8 or more .

[Ca] × [F] ² / {1- [R]} <50 That is, the present inventor has investigated CaF in various cases in which feed water containing fluoride ions is treated in an electric desalination apparatus.
₂ As a result of a comparative examination of the presence or absence of scale disturbance and the conditions of supply water and operating conditions, these have a certain relationship, and if treatment is performed so as to satisfy the above formula, scale failure of CaF ₂ can be prevented. Then, the present invention has been completed.

When it is difficult to satisfy the above equation under the condition of water supply, the simplest means to satisfy the above equation is to reduce the water recovery rate [R]. In this case, However, since the amount of produced water is small and the amount of concentrated water is large and the productivity is reduced, it is not desirable in terms of effective use of water.

Therefore, in this case, the fluorine-containing water is treated with an ion exchange resin to previously remove the fluorine ion or calcium ion of the scale component so as to satisfy the above formula without reducing [R]. It is preferable.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

According to the method of the present invention, in treating fluorine-containing water with an electric desalination apparatus, the calcium concentration (mg / L) of the water supplied to the electric desalination apparatus is set to [Ca], and the fluorine concentration (mg / L) When L) is [F] and the water recovery rate (production water amount / supply water amount) of the electric desalination apparatus is [R] , the water recovery rate is made small so that these relationships satisfy the following formula .
Supply water that reduces the calcium ion concentration of the supply water
Reduce the fluorine ion concentration of at least one of
Water recovery rate [R] is 0.8 or more with one treatment
To maintain .

[Ca] × [F] ² / {1- [R]} <50 When the value of [Ca] × [F] ² / {1- [R]} in the above relational expression is 50 or more, C in the concentration chamber of the electric desalination equipment
The aF ₂ scale is generated and scale failure occurs. It is preferable to adjust the conditions of the supply water and the operating conditions so that this value is 40 or less, particularly 30 or less.

In order to satisfy the above relational expression, the water recovery rate of the electric desalination device (ratio of the amount of produced water to the amount of supplied water)
Although it is the easiest method to reduce [R], it is necessary to reduce the water recovery rate [R] excessively as described above.
It is not preferable in terms of productivity. Accordingly, in the present invention, preferred
Specifically, the following method (1) or (2) is adopted to reduce the fluorine ion concentration or calcium ion concentration of the feed water, and the water recovery rate [R] is 0.8 or more, preferably 0.9 to
Keep the above relational expression while maintaining 0.95
It

(1) In order to reduce the concentration of fluorine ions in the feed water, pretreatment is performed with a non-regeneration type ion exchange device filled with an anion exchange resin. However, the removal of fluorine ions by the anion exchange resin requires periodic replacement of the resin. In order to reduce such regular maintenance, it is desirable to use a weakly basic anion exchange resin as the anion exchange resin. Weakly basic anion exchange resins are slightly inferior in ion exchange performance to strongly basic anion exchange resins, but the fluorine ions contained in the recovered water of semiconductor factories are mainly in the form of HF, and neutral salts (such as NaF) are used. ) Is small, it is possible to sufficiently remove even a weakly basic anion exchange resin.

In this case, the weakly basic anion exchange resin is
Although it may be used alone, it may be used as a mixture with a strongly basic anion exchange resin depending on the F form of the raw water.

(2) In order to reduce the calcium ion concentration in the feed water, pretreatment is performed with a non-regeneration type ion exchange device filled with a cation exchange resin. Even in this case,
Since removal of calcium ions by cation exchange resin requires periodic replacement of the resin, it is necessary to use a weakly acidic cation exchange resin as the cation exchange resin in order to reduce such regular maintenance. desirable. The weakly acidic cation exchange resin is slightly inferior in ion exchange performance to the strongly acidic cation exchange resin, but the calcium ions contained in the feed water are Ca (HCO ₃ )
_Since the form ₂ is mainly used and the amount of neutral salts (CaCl etc.) is small, the weakly acidic cation exchange resin can be sufficiently removed.

In this case, the weakly acidic cation exchange resin may be used alone, or may be mixed with the strongly acidic cation exchange resin depending on the Ca form of the raw water.

Although it is possible to adopt both of the above (1) and (2) , it is sufficient in the present invention that the above relational expression is satisfied, and in general, either (1) or (2) is used. It is enough to adopt only one, and from the aspect of facility simplification,
It is economical and advantageous to adopt either one of (1) and (2) .

The means for reducing the fluorine ion concentration or the calcium ion concentration is not limited to the above (1) and (2) , and a reverse osmosis (RO) membrane separation device, a chemical regeneration type ion exchange resin tower, etc. May be adopted. Generally, since an RO membrane separator is provided as a pretreatment means for the electric desalination apparatus, in such a case, in order to reduce the fluorine ion concentration or the calcium ion concentration in the RO membrane separator, two or more machines are used. The RO membrane separators of 1 are arranged in series to perform multi-stage RO treatment. However, it is advantageous to adopt the above-mentioned means (1) or (2) from the viewpoint of facility and ease of operation.

The electric desalination apparatus used in the present invention is a general one in which a plurality of anion exchange membranes and cation exchange membranes are alternately arranged to alternately form a concentration chamber and a desalination chamber. May be filled with a mixed resin of an anion exchange resin and a cation exchange resin, or may not be filled with it, but from the viewpoint of improving the quality of treated water (production water), It is preferable that the salt chamber is filled with a mixed resin of an anion exchange resin and a cation exchange resin.

The method for treating fluorine-containing water of the present invention as described above is extremely effective for treating raw water mixed with recovered water containing fluorine ions in a pure water producing apparatus in the field of electronics industry and the like.

[0023]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

The electric desalination apparatus used in the examples and comparative examples is (Pure Ace manufactured by Kurita Water Industries Ltd.) (treated water amount 1000 L / hr).
A strongly basic anion-exchange resins in the desalting compartment and a strongly acidic cation exchange resins are those filled with 35:65 (volume ratio).

Example 1 Raw water obtained by mixing recovered water of a semiconductor factory and city water was sequentially treated with an activated carbon tower 1 and an RO membrane separator 2 according to the flow shown in FIG. After the treatment with the filled non-regeneration type anion exchange device 3, it was treated with the water recovery rate [R] = 0.95 as the feed water of the electric desalination device 4.

At this time, the Ca concentration of the feed water of the electric desalination apparatus 4 is 0.3 mg / L, the F concentration is 0.1 mg / L or less,
[Ca] × [F] ² /{1-[R]}=0.3×(0.
1) ² /(1-0.95)=0.06.

After the electric desalination apparatus 4 was continuously operated for 3 months, the electric desalination apparatus 4 was disassembled to remove CaF ₂ in the concentration chamber.
When the presence or absence of scale was examined, no CaF ₂ scale was formed.

Example 2 Raw water obtained by mixing recovered water of a semiconductor factory and city water was sequentially treated with an activated carbon tower 1 and an RO membrane separation device 2 according to the flow shown in FIG. The treated water was treated with the non-regeneration type cation exchange device 5 and treated with water recovery rate [R] = 0.95 as the feed water of the electric desalination device 4.

At this time, the Ca concentration of the feed water of the electric desalination apparatus 4 is 0.1 mg / L or less, the F concentration is 3 mg / L, and [C
a] × [F] ² /{1-[R]}=0.1×(3) ² /
(1-0.95) = 18.

After the electric desalination apparatus 4 was continuously operated for 3 months, the electric desalination apparatus 4 was disassembled and CaF ₂ in the concentration chamber was removed.
When the presence or absence of scale was examined, no CaF ₂ scale was formed.

Comparative Example 1 Raw water obtained by mixing recovered water of a semiconductor factory and city water was sequentially treated with an activated carbon tower 1 and an RO membrane separator 2 according to the flow shown in FIG. Was treated with a water recovery rate [R] = 0.95.

At this time, the Ca concentration of the feed water of the electric desalination apparatus 4 was 0.3 mg / L, the F concentration was 3 mg / L, and [Ca]
× [F] ² /{1-[R]}=0.3×(3) ² / (1-
0.95) = 54.

After the electric desalination apparatus 4 was continuously operated for 3 months, the electric desalination apparatus 4 was disassembled and CaF ₂ in the concentration chamber was removed.
When the presence or absence of scale was examined, formation of CaF ₂ scale was confirmed.

Comparative Example 2 The same treatment as in Example 2 was carried out except that the water recovery rate [R] of the electric desalination apparatus 4 was increased to 0.99. The operating condition at this time is [Ca] × [F] ² / {1-
[R]} = 0.1 × (3) ² /(1-0.99)=90
Met.

After the electric desalination apparatus 4 was continuously operated for 3 months, the electric desalination apparatus 4 was disassembled to remove CaF ₂ in the concentration chamber.
When the presence or absence of scale was examined, formation of CaF ₂ scale was confirmed.

Example 3 The same treatment as in Comparative Example 1 was carried out except that the water recovery rate [R] of the electric desalination apparatus 4 was lowered to 0.90. The operating condition at this time is [Ca] × [F] ² / {1-
[R]} = 0.3 × (3) ² /(1−0.90)=27
Met.

After the electric desalination apparatus 4 was continuously operated for 3 months, the electric desalination apparatus 4 was disassembled and CaF ₂ in the concentration chamber was removed.
When the presence or absence of scale was examined, no CaF ₂ scale was formed.

The above Examples 1 to 3 and Comparative Examples 1 and 2
In all cases, the specific resistance of the treated water (produced water) obtained was 16 to 18 MΩ · cm, and there was no difference in the water quality of the treated water.

[0039]

As described above in detail, according to the method for treating fluorine-containing water of the present invention, in a pure water production apparatus in the field of electronics, etc., fluorine such as raw water mixed with recovered water containing fluorine ions is mixed. When the contained water is treated with the electric desalination apparatus, it is possible to prevent the generation of calcium fluoride scale in the concentration chamber of the electric desalination apparatus and perform the treatment stably for a long period of time.

According to the method of claim 2, it is possible to effectively prevent the scale failure of calcium fluoride without lowering the productivity of demineralized water.

[Brief description of drawings]

FIG. 1 is a system diagram showing a processing method according to a first embodiment.

FIG. 2 is a system diagram showing a processing method according to a second embodiment.

FIG. 3 is a system diagram showing a processing method in Comparative Example 1.

[Explanation of symbols]

1 activated carbon tower 2 RO membrane separator 3 Non-regenerative anion exchanger 4 Electric desalination equipment 5 Non-regenerative cation exchanger

Continuation of the front page (56) References JP 2000-176457 (JP, A) JP 9-262588 (JP, A) JP 9-10557 (JP, A) JP 7-171574 (JP, A) JP 7-265864 (JP, A) JP 7-214068 (JP, A) JP 7-195071 (JP, A) JP 1-130783 (JP, A) JP 52 -8987 (JP, A) JP-A-1-130782 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/46 B01D 61/44 C02F 1/42 C02F 1/58

Claims (2)

(57) [Claims] 1. A method of supplying fluorine-containing water to an electric desalination apparatus for treatment, wherein the water supplied to the electric desalination apparatus has a calcium concentration [Ca] (mg / L) and a fluorine concentration [F] (mg). / L) and the water recovery rate (production water amount / supply water amount) [R] of the electric desalination device , the water recovery ratio is made small so that the following formula is satisfied.
Reduce the concentration, reduce the fluorine ion concentration of the feed water
, At least one of which is treated with water
A method for treating fluorine-containing water, characterized in that the recovery rate [R] is maintained at 0.8 or more . [Ca] × [F] ² / {1- [R]} <50 2. The method according to claim 1, wherein the fluorine-containing water is preliminarily charged with calcium ions or fluorine ions with an ion exchange resin.
A method for treating fluorine-containing water, characterized in that the water is supplied to an electric desalination apparatus after being removed .