JP2001246385A - Treatment process of water containing fluorine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine-containing water treatment process which comprises adding a Ca compound to fluorine-containing water to precipitate and separate flourine as CaF2 and removing residual Ca2+ ion in the resulting water by cation-exchange resin and enables reduction in concentration of the residual Ca2+ ion by optimizing the amount of addition of the Ca compound without increasing the F- ion concentration in treated water by this CaF2 formation treatment and also reduction in regeneration frequency of the cation- exchange resin. SOLUTION: In this treatment process, when the equivalent amount of a calcium compound to the amount of ions in fluorine-containing water, which ions can be combined with calcium to form their respective hardly soluble salts, is A mg/L (expressed in terms of Ca), the amount of addition of the Ca compound to the fluorine-containing water is adjusted to A to (A-200) mg/L (expressed in terms of Ca).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a calcium (Ca) compound added to water containing fluorine to precipitate and separate fluorine as calcium fluoride (CaF ₂ ).
^According to a method for removing ²⁺ ions with a cation exchange resin,
In particular, the present invention relates to a method for treating fluorine-containing water in which the required amount of a Ca compound is optimized and the frequency of regeneration of a cation exchange resin is reduced.

[0002]

2. Description of the Related Art As a method for treating fluorine-containing water such as fluorine-containing wastewater discharged from a silicon wafer manufacturing process in the manufacture of semiconductor parts, a Ca compound is added to fluorine-containing water to generate CaF ₂ and this is precipitated. Separation methods have become widespread due to the low drug cost. In particular, since semiconductor manufacturing wastewater contains inorganic salts such as SO ₄ ²⁻ , NO ₃ ⁻ , and NH ₄ ^{+ in} addition to fluorine, CaF ₂ is precipitated and separated,
₄ ^2-, _NO ³ -, and inorganic salts derived from wastewater _NH ^{4 +} or the like,
As shown in FIG. 1, a raw water tank 1, a neutralization tank 2 for adding a Ca compound to raw water, and a neutralization treatment liquid are subjected to a coagulation treatment in order to separate remaining Ca ²⁺ and F ⁻ and reuse as recovered water. Processed water obtained by generating and separating CaF ₂ through a flocculation tank 3, a settling tank 4 for generating a precipitate, and a filter 5 for solid-liquid separation of the generated precipitate (hereinafter, this water is referred to as “CaF ₂ treated water”). ) May be further passed through a softening tower (cation exchange resin tower) 6 and a reverse osmosis (RO) membrane separation device 7 for treatment. The backwash drainage from the filter 5, the reclaimed waste liquid from the softening tower 6, and the concentrated water from the RO membrane separation device 7 are sent to the raw water tank 1 and processed together with the raw water.

[0003] That is, from the semiconductor manufacturing wastewater, CaF₂Raw
CaF obtained by performing₂The treated water is CaF₂
And CaSO₄Scale-causing substances that produce precipitated salts such as
Since it is contained, it is passed through the RO membrane separation device 7 as it is.
And then desalination treatment, these scale-causing substances become RO
It is concentrated in the membrane separation device 7 and deposited as scale, and R
The O membrane is closed, and water cannot be passed. Therefore, this RO
In order to prevent clogging of the membrane, the pre-stage of the RO membrane separation device 7
To remove these scale-causing substances in advance.
It is needed. In this case, Ca²⁺, SO₄ ^2-, F⁻
It is not necessary to remove all scale-causing substances such as
CaF₂To prevent the formation of Ca²⁺And F ⁻Any of
Or one of them may be removed.₄To prevent the generation of
Also Ca²⁺And SO₄ ^2-If you remove one of
good. For this reason, as shown in FIG.
A softening tower 6 is provided in the preceding stage, and Ca is exchanged with a cation exchange resin.²⁺To
Removal is common.

By the way, in such a processing process,
If the recovered water temporarily becomes excessive, CaF₂place
The water, ie, the filtered water from the filter 5 is discharged out of the system
This CaF₂F of treated water⁻To the concentration
For wastewater, treat it to the wastewater standard of 15 mg / L or less.
There is a need to. Raw water by adding Ca compound
F in fluorine-containing water⁻In order to remove this highly
In general, Ca²⁺+ 2F⁻→ CaF₂  Based on the reaction formula, the Ca compound is converted to F⁻Against
It is added in excess of the equivalent amount.
Conventionally, CaF was added by excessive addition of Ca compound. ₂place
Ca remaining in the water²⁺Index of concentration is 100 to 300
mg / L.

[0005]

SUMMARY OF THE INVENTION However, 100
When CaF ₂ treated water containing ~ 300 mg / L Ca ²⁺ ion is passed through the softening tower 6 and treated with the cation exchange resin, the ion exchange capacity of the calcium compound reaches saturation early and 2 to 4 cycles / day It is necessary to frequently regenerate the cation exchange resin.

[0006] Frequent regeneration as described above requires maintenance and management of the apparatus, the cost of regenerating chemicals, the cost of treating waste liquid, and the like.
It is industrially very disadvantageous in terms of the operating efficiency of the softening tower. On the other hand, by reducing the Ca compound added amount as described above, F of CaF ₂ treated water ^- since there is a possibility to increase the concentration, Ca compound addition amount of optimization is required.

[0007] The present invention solves the above-mentioned conventional problems and solves the above problem.
F added to Ca-containing water by adding Ca compound₂As sunk
After the separation,²⁺Cation exchange of ions
Optimum amount of Ca compound added when removing with resin
And CaF₂F in treated water ⁻Without increasing the concentration
Residual Ca²⁺Reduces the concentration and reduces the frequency of regeneration of the cation exchange resin.
A method for treating fluorine-containing water that can reduce the
The purpose is to provide.

[0008]

According to the method for treating fluorine-containing water of the present invention, calcium fluoride formed by adding a calcium compound to fluorine-containing water is separated, and the remaining calcium ions are removed by a cation exchange resin. The amount of a calcium compound equivalent to the amount of ions that form a sparingly soluble salt with calcium in the fluorine-containing water is Amg (as Ca) / L, the calcium compound in the fluorine-containing water Amg (as C
a) / L to (A-200) mg (as Ca) / L.

As described above, conventionally, the Ca ²⁺ concentration in the CaF ₂ treated water is 100 to 300 mg / L, but if this concentration is 30 mg / L or less,
The frequency of regenerating the calcium compound is also reduced to about 1/5 of the conventional frequency, so that the maintenance and management of the apparatus is reduced, the cost of regenerating chemicals, the cost of treating waste liquid, and the operation efficiency of the softening tower can be improved.

As described above, when the CaF ₂ treated water is discharged, the F ^- concentration in the CaF ₂ treated water is 15%.
mg / L or less.

Accordingly, the present inventors have determined that the F ^- concentration is 15 mg.
/ L or less, ^{Ca 2+} concentration 30 mg / L or less of CaF ₂ treated water intensive studies to obtain reliably a result, the amount of ions generated a ^{Ca 2+} and sparingly soluble salt contained in the fluorine-containing water is raw water Ca equivalent of Ca compound
When the converted amount is Amg / L, the amount of the Ca compound added is C
The present inventors have found that, when the amount is in the range of Amg / L to (A-200) mg / L, the F ^- concentration and the Ca2 ⁺ concentration can be satisfied, and the present invention has been completed. (Note that, in the present invention, the fluorine-containing water as the raw water is water to which a Ca compound is added.
As shown in (2), in the processing process in which the regenerating solution or the like of the subsequent processing device is returned, it refers to water flowing into the neutralization tank 2. ).

That is, in order to effectively generate CaF ₂ from F ⁻ in raw water and to remove F ⁻ to a high degree, not only F ⁻ in raw water but also Ca ²⁺ other than F ⁻ and a hardly soluble salt can be used. It is also necessary to consider the coexisting ions that form the compound (hereinafter, these ions are referred to as “poorly soluble salt-forming ions”), and the Ca compound not only reacts with F ^{− in} the raw water, but also with respect to F ⁻ in the raw water. Is also required for the hardly soluble salt-forming ions.

[0013] The F ^- The other sparingly soluble salt-forming ion, phosphate ion _(PO ^{4 3-),} sulfate ion (SO ₄
^2), carbonate ions _(CO ^{3 2-)} and others as mentioned,
The mechanism by which such poorly soluble salt forming ions affect the fluorine concentration of the CaF ₂ treated water is presumed as follows.

That is, for example, in the case of SO ₄ ^2- ,
The solubility of ₄ was 2000 mg / L, and the solubility of CaF ₂ was 1
At 5 mg / L, the solubility of CaF ₂ is much lower than the solubility of CaSO _4. Therefore, if Ca salts equivalent to fluorine are present, the reaction of CaF ₂ formation is generally CaS _2.
It should occur in preference to the O ₄ formation reaction. But,
Actually, simultaneously with the precipitation of CaF ₂ , CaSO ₄ (aq.) Which does not cause precipitation, that is, so-called molecular CaSO ₄ is generated, and the Ca salt is fixed to SO ₄ ^2- ,
²⁺ + 2F ^- → reaction of CaF ₂ is inhibited. Therefore,
It is also necessary to add a Ca compound that reacts with such poorly soluble salt-forming ions.

Fluorine-containing water, such as semiconductor manufacturing wastewater, contains these sparingly soluble salt-forming ions and, as previously proposed by the present applicant, is treated by adding a Ca compound to fluorine-containing water. In order to improve the quality of treated water, Ca
For the purposes of the crystallization accelerating F _2, sulfuric acid and a fluorine-containing water /
Alternatively, a sulfate may be added (Japanese Patent Application No. 11-146).
No. 822, Japanese Patent Application No. 11-218990). In such a case, of course, the raw water F ^- and thus the presence of SO ₄ ^2-besides.

Such a sparingly soluble salt-forming ion, for example,
When SO ₄ ^2- is considered, the required amount of the Ca compound to be added to the raw water is determined by the amount of the Ca compound required to generate CaF ₂ by the reaction with F ^{− in} the raw water and the amount of the SO ₄ ^{2- in the} raw water. Is slightly smaller than the total amount of the Ca compound and the amount of the Ca compound necessary for generating CaSO ₄ by the reaction of the above-mentioned F ⁻ : 1.
5 mg / L or less, Ca ²⁺ : 30 mg / L or less of CaF
_{2 It is} an ideal addition amount for obtaining treated water.

Thus, Amg (as Ca) / L
This ideal addition amount can be realized within the range of (A-200) mg (as Ca) / L.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method for treating fluorine-containing water of the present invention will be described below in detail.

In the present invention, when to generate a CaF ₂ with the addition of Ca compound to the fluorine-containing water such as a semiconductor fabrication wastewater process as shown in FIG. 1, the addition of Ca
The amount of the compound is reduced to Ca equivalent amount of Ca compound, Amg / L or less, which is equivalent to the amount of the insoluble salt-forming ions in the raw water,
(A-200) mg / L or more.

When the amount of the Ca compound added is (A-200) m
If the amount is less than g (as Ca) / L, the Ca compound becomes insufficient.
And F in raw water⁻Cannot be removed to a high degree and the residual F⁻Increases
Then F ⁻: CaF of 15 mg / L or less₂Obtain treated water
I can't do that. Conversely, when the Ca compound addition amount is Amg (as
 If Ca) / L is exceeded, the Ca compound becomes excessive.
G, CaF₂F in treated water⁻Although the concentration decreases, Ca
²⁺Greatly increase the frequency of cation exchange resin regeneration
The Rukoto.

The poorly soluble salt forming ion is generally
Typically, Ca²⁺And the amount of dissolution based on the solubility product
It produces a poorly soluble salt of 700 mg / L or less.
And F in raw water⁻Other hardly soluble salt-forming ions
As mentioned earlier, PO₄ ^{3 −}, SO₄ ^2-, CO₃
^2-In the present invention, F in raw water
⁻Concentration, PO₄ ^3-Concentration, SO₄ ^2-Concentration, CO₃ ^2-
Based on the concentration, Amg (as C
a) The amount of the Ca compound added to the value of / L is A to (A-
200) mg (as Ca) / L.

A (mg / L) = (F ⁻ concentration × Ca / 2F) + (PO ₄ ^3- concentration × 3Ca / 2PO ₄ ) + (SO ₄ ^2- concentration × Ca / SO ₄ ) + (CO ₃ ² ) ^- concentration _{× Ca / CO 3) = (} F - concentration _{× 40/38) + (PO} 4 3- concentration _{× 120/190) + (SO} 4 2- concentration _{× 40/96) + (CO} 3 2- concentration × 40/60) As described above, when a sparingly soluble salt-forming ion is added to raw water, as in the case of adding sulfuric acid and / or a sulfate, the sparingly soluble salt-forming ion in the raw water is naturally converted to this. The added sparingly soluble salt-forming ions are also included.

When there are a plurality of types of sparingly soluble salt-forming ions in the raw water, the amounts of all the sparingly soluble salt-forming ions are measured and Ca
It is not necessary to use for calculating the amount of added salt, and the concentration of the main sparingly soluble salt-forming ion, ie, the concentration in raw water is high, for example, 100 pp.
One or more of m or more hardly soluble salt forming ions may be selected, and the amount of the hardly soluble salt forming ions may be measured to set the Ca salt addition amount.

As the Ca compound to be added to raw water, generally, inexpensive calcium hydroxide (slaked lime: Ca (O
H) ₂ ) is used, but the invention is not limited to this, and quick lime or the like may be used. Further, calcium chloride or calcium carbonate may be used in combination with sodium hydroxide.

The pH condition at which CaF ₂ is precipitated by the addition of such a Ca salt is 5 to 10, preferably 5.5 to 7.5.
Therefore, particularly when Ca (OH) ₂ is added as a Ca compound, the pH becomes too high, and when it is not possible to adjust to such a pH condition, an acid such as sulfuric acid, hydrochloric acid or the like is added and appropriately added. It is necessary to adjust the pH.

As described above, the quality of the treated water can be improved,
CaF₂Sulfuric acid and / or raw water for the purpose of promoting crystallization of
When adding sulfate, add sulfuric acid or sulfate
Can be used industrial sulfuric acid, sodium sulfate, etc.
The sulfuric acid source is SO ₄ ^2-Contains ions
Using other wastewater, for example, steel plate pickling wastewater, flue gas desulfurization wastewater
You can also.

According to the method of the present invention, CaF ₂ is produced by adding a Ca compound, and CaF ₂ obtained by separating CaF ₂ is obtained.
The method can be applied to any treatment process as long as the treated water is further treated with a cation exchange resin. Therefore, as shown in FIG. 1, not only the treated water of the softening tower 6 is further treated by the RO membrane separation device 7, but also the softened water obtained from the softening tower 6 is directly used as treated water, Further, a method in which deionized water is obtained by passing water through an anion exchange resin, or a treatment process in which demineralized water obtained by treating softened water by an electric regeneration type continuous desalination apparatus is used as treated water may be used.

[0028]

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

Examples 1 to 3 and Comparative Examples 1 and 2 F ⁻ : 2500 mg / L, SO ₄ ²⁻ : 500 mg / L
The artificial waste liquid of (as H ₂ SO ₄ ) is used as raw water, and Ca (O ₂ SO ₄ )
H) Ca compounds such as ₂ were added in the amounts shown in Table 1 to adjust the pH to 6.
It was adjusted to 5 to 7.0 and reacted for 30 minutes. F filtration to filtration treatment water in filter paper 5A ^- measuring the concentration and Ca ²⁺ concentration, and the results are shown in Table 1.

[0030] In Table 1, the equivalent of A, the Ca compound in the raw water F ^- and a case of adding an equivalent amount with respect to the sum of both the SO ₄ ^2-, in this case, as a Ca compound By adding only Ca (OH) ₂ , pH 6.5-
It was adjusted to 7.0.

When the Ca compound is insufficient with respect to this equivalent A, H ₂ SO ₄ as a SO ₄ ²⁻ source is added so that Ca (OH) ₂ corresponding to SO ₄ ²⁻ is not added.
Was replaced with Na ₂ SO ₄ and added.

When the Ca compound is excessive relative to the equivalent A, H ₂ SO ₄ is used as the SO ₄ ²⁻ source, and neutral CaCl ₂ is further added in addition to Ca (OH) _2. Ca
Added as compound.

[0033]

[Table 1]

Examples 4 to 6, Comparative Examples 3, 4 F ⁻ : 5000 mg / L, SO ₄ ²⁻ : 1000 mg / L
The treatment was performed in the same manner as in Examples 1 to 3 and Comparative Examples 1 and 2 except that the artificial waste liquid of L (as H ₂ SO ₄ ) was used as raw water, and the F ⁻ concentration and the Ca ²⁺ concentration of the treated water were measured. The results are shown in Table 2.

[0035]

[Table 2]

As shown in Tables 1 and 2, by setting the amount of the Ca compound to be equivalent A to (A-200) mg (as Ca) / L, high-quality treated water having both low F ⁻ and Ca ²⁺ concentrations. It can be seen that can be obtained.

[0037]

As described above in detail, according to the processing method of the fluorine-containing water of the present invention, by adding a Ca compound precipitates separated F as CaF ₂ to a fluorine-containing water, residual Ca
^In removing ²⁺ ions with a cation exchange resin, C
by optimizing the addition amount of a compound of CaF ₂ treated water F
^- it is possible to reduce residual Ca ²⁺ concentration without increasing the concentration. For this reason, the frequency of regeneration of the cation exchange resin can be reduced, and the maintenance and management of the apparatus can be reduced, the cost of regenerating chemicals, the processing cost of the regenerated waste liquid can be reduced, and the operating efficiency of the softening tower can be improved. The treatment of fluorine-containing water can be performed very advantageously.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a general treatment process of semiconductor manufacturing wastewater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Neutralization tank 3 Coagulation tank 4 Sedimentation tank 5 Filter 6 Softening tower 7 RO membrane separation apparatus

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D015 BA19 BB01 BB02 CA17 DA24 EA04 EA13 EA32 FA02 FA22 4D025 AA09 AB19 BA08 BB01 CA10 DA10 4D038 AA08 AB41 BB08 BB18 4D062 BA19 BB01 BB02 CA17 DA24 EA04 FA22 EA22

Claims (1)

[Claims] 1. A method for removing calcium fluoride generated by adding a calcium compound to fluorine-containing water and removing remaining calcium ions with a cation exchange resin, comprising the steps of: Assuming that the amount of the calcium compound equivalent to the amount of the ions forming the salt is Amg (as Ca) / L, the amount of the calcium compound added to the fluorine-containing water is Amg (as Ca).
/ L to (A-200) mg (as Ca) / L.