JP2001219177A - Method and apparatus for treating fluorine-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain treated water of high quality low in the concentration of fluorine ions while reducing the volume of generated sludge, when together adding Ca(OH)2 and CaCl2 to fluorine-containing water to form CaF2 and removing this CaF2 by solid-liquid separation. SOLUTION: At first, Ca(OH)2 is added to a Ca(OH)2 reaction tank to be reacted with fluorine-containing water and, subsequently, CaCl2 is added to a CaCl2 reaction/pH adjusting tank 2 to perform the reaction with fluorine- containing water and the pH adjustment thereof before removing the formed CaF2 by solid-liquid separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Calcium hydroxide (Ca (O)
H)₂) And calcium chloride (CaCl₂) And add
Calcium fluoride (CaF)₂)
In particular, the invention relates to Ca (OH) ₂And CaC
l₂High-quality treated water can be obtained and
Method and apparatus for treating fluorine-containing water to reduce raw sludge capacity
About.

[0002]

2. Description of the Related Art Fluorine-containing wastewater discharged from a silicon wafer manufacturing process in semiconductor component manufacturing, pickling wastewater discharged from a stainless steel plate manufacturing process, hydrofluoric acid manufacturing wastewater,
As a method for treating fluorine-containing water such as fertilizer production wastewater and garbage incineration wastewater, CaF ₂ is added to a fluorine-containing water by adding a Ca salt.
Is widely used because of the low drug cost. In this method, since these fluorine-containing wastewaters are generally acidic, alkaline Ca (OH) ₂ is used as a Ca salt, and CaF ₂ is generated by neutralization with Ca (OH) ₂ .

In such a processing method, Ca Shioryou necessary for the fluorine in the waste water by sufficiently react to produce CaF ₂ is are more equivalents of fluorine ions in the waste water, in fact, , In wastewater, other than fluorine ions, anions that form a sparingly soluble precipitate by reaction with Ca,
For example, SO ₄ ²⁻ ions and PO ₄ ³⁻ ions are contained. Therefore, it is necessary to add the amount of Ca salt consumed in the reaction with these anions.

However, if the fluorine ions contained in the waste water as NH ₄ F, or _SO ^{4 2-ions} N
When a ₂ SO ₄ is contained in the wastewater, if the necessary amount of Ca salt is entirely supplied by Ca (OH) ₂ , the pH becomes too high, and it becomes necessary to neutralize the treated water with an acid. Therefore, in such a case, Ca (OH) is used as a Ca salt.
₂ and neutral CaCl ₂ are used in combination to obtain neutral treated water.

[0005]

In such treatment of fluorine-containing water, in many cases, the concentration of fluorine ions in the treated water is not stable and varies between 10 and 30 mg / L.
This instability of the treated water quality is considered to be affected by the raw water quality, that is, the coexistence in the wastewater to be treated.
In the case where Ca (OH) ₂ and CaCl ₂ are used in combination as the salt a, the present situation is that stable high-quality treated water has not been obtained.

The present invention solves the above-mentioned conventional problems, and adds Ca (OH) ₂ and CaCl ₂ as a Ca salt to fluorine-containing water to produce CaF ₂ , which is subjected to solid-liquid separation. It is an object of the present invention to provide a method and an apparatus for treating fluorine-containing water capable of stably obtaining high-quality treated water having a low fluorine ion concentration and reducing the amount of generated sludge.

[0007]

According to the present invention, there is provided a method for treating fluorine-containing water, comprising adding calcium hydroxide and calcium chloride to fluorine-containing water to separate fluorine into calcium fluoride by solid-liquid separation. The method is characterized in that calcium hydroxide is added to the contained water and reacted after adding calcium hydroxide.

The apparatus for treating fluorine-containing water according to the present invention is characterized in that calcium hydroxide is added to fluorine-containing water for reaction.
A second reaction means for adding calcium chloride to the treated water of the first reaction means to cause a reaction, and a solid-liquid separation means for solid-liquid separation of the treated water of the second reaction means. It is characterized by comprising.

The present inventors have proposed Ca (OH) ₂ and CaCl
₂ and a result of intensive studies on the cause of the instability of the treated water quality when used together, Ca in the _{(OH) 2} and the CaCl _2, there is a difference in structure of the product CaF ₂ in the initial reaction, the product CaF ₂ It was found that the difference in structure affected the quality of treated water and the amount of generated sludge.

[0010] That is, the addition of Ca _{(OH) 2} prior to the waste water, Ca _{(OH) 2} and F ^- and two colloidal compounds such as the following in the reaction of (1), (2) Is generated. Simultaneously with the generation of the compounds (1) and (2),
The compound (1) reacts with SO ₄ ^2- coexisting in the wastewater to produce the following compound (3).

[0011]

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[0012]

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The compound (1) has an OH group at the terminal, and the compound (2) is saturated with F. These are all colloidal, and are hard to aggregate and precipitate as they are.

On the other hand, the compound (3) which is a high polymer produced at the same time incorporates the colloidal compounds (1) and (2) by chain adsorption or charge neutralization to form a precipitate.

As described above, it is important to generate the above-mentioned highly polymerized compound (3) which is the core of coagulation and precipitation in order to reduce the fluorine concentration in the treated water and the amount of generated sludge.
_When compound ₂ is added first, compound (3) is produced smoothly.

On the other hand, when CaCl ₂ is added first, only the compound (2) is formed, and the compound (3) does not exist in the initial stage. Therefore, it is impossible to reduce the fluorine concentration of the treated water and the amount of generated sludge.

When Ca (OH) ₂ and CaCl ₂ are added simultaneously, CaCl ₂ having high solubility becomes CaCl _2.
The compound (2) is dissolved prior to (OH) ₂ to produce the compound (2) preferentially, and the compound (1) is produced with a delay, so that the compound (3) is also produced with a delay. It is not possible to reduce the amount of generated sludge.

From the above, Ca (OH) ₂ and C
In the combined treatment with aCl ₂ , Ca according to the present invention
By adding (OH) ₂ first and reacting, and then adding CaCl ₂ , it is possible to stably obtain high-quality treated water having a low fluorine concentration and reduce the volume of generated sludge. .

In the present invention, it is preferable to adjust the pH to neutral with an acid and / or alkali in the step of adding CaCl ₂ .

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method and apparatus for treating fluorine-containing water 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 and apparatus for treating fluorine-containing water of the present invention.

Fluorine-containing wastewater discharged from a silicon wafer manufacturing process in the production of semiconductor parts, which is raw water, pickling wastewater discharged from a stainless steel plate manufacturing process, hydrofluoric acid manufacturing wastewater, fertilizer manufacturing wastewater, waste incineration wastewater, etc. Water is first introduced into the Ca (OH) ₂ reaction tank 1 so that Ca (O)
H) Add ₂ and react. The amount of Ca (OH) ₂ added depends on the amount of hydrofluoric acid (HF) and sulfuric acid (H ₂ SO ₄ ) in the raw water.
Or an amount corresponding to phosphoric acid (H ₃ PO ₄ ), that is, an equivalent amount to HF in raw water or a slightly excessive amount. In the actual treatment, Ca (OH) ₂ may be added until neutrality.

The reaction time with Ca (OH) ₂ may be a time sufficient to produce the above-mentioned polymerizable compound (3), and generally 5 to 30 minutes is sufficient.

[0024] Ca _{(OH) 2} the reaction solution in the reaction vessel 1 is then introduced into CaCl ₂ reaction · pH adjustment tank 2, CaCl ₂
And an acid and / or alkali to add p
The pH is adjusted to H neutral (pH 5 to 8, preferably 6 to 7). The amount of CaCl ₂ added depends on the amount of fluorine ions other than HF in the raw water, such as NH ₄ F and C
SO ₄ ^2- and PO ₄ ^3- which form a salt and a sparingly soluble precipitate
An amount sufficient to precipitate a sparingly soluble Ca salt from ions may be sufficient. The reaction time of the CaCl ₂ reaction / pH adjustment tank 2 is a time sufficient for CaCl ₂ to react with these ions and to be further incorporated into the polymerizable compound (3) to form a precipitate having excellent cohesiveness. And generally for about 5 to 30 minutes.

The acid and alkali used for pH adjustment are not particularly limited, and acids such as HCl, NaOH, KOH
Or the like, but H ₂ S may be used as the acid.
When O ₄ is added, it is necessary to consider the amount of CaCl ₂ consumed in the reaction with H ₂ SO ₄ .

The reaction solution in the CaCl ₂ reaction / pH adjustment tank 2 is then introduced into a coagulation tank 3, where an organic polymer coagulant (polymer) is added and coagulation treatment is performed. You. As the solid-liquid separation means, besides precipitation separation, membrane separation, centrifugation and the like can also be used.

[0027]

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

Example 1 HF: 4000 mg / L, NH ₄ -F: 1000 mg / L
L (asHF), NaNO ₃ : 3150 mg / L, Na
₂ SO ₄ : Using synthetic wastewater containing 1000 mg / L (asH ₂ SO ₄ ) as raw water, first, 7400 mg / L of Ca (OH) ₂ was added to convert HF to CaF ₂ and reacted for 5 minutes. In order to convert NH ₄ F and Na ₂ SO ₄ into Ca salts, 1500 mg / L of CaCl ₂ (asCa, NH ₄
F and Na ₂ SO ₄ , a CaCl ₂ amount required for the reaction of about 100 mg / L was added), and NaOH for fine pH adjustment was added to adjust the pH to 6.5, followed by a reaction for 20 minutes. After the reaction, the reaction mixture was The solution was filtered with a 5A filter paper, and the fluorine concentration of the filtrate (treated water) was measured.
It was shown to.

Separately, the reaction solution was allowed to stand for 24 hours, and the sludge volume was measured. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1 In Example 1, the raw water composition and the chemical injection amount were the same, and Ca
(OH)₂And CaCl ₂And the order of addition
₂And reacted for 5 minutes, then Ca (OH)₂With
And adjusted to pH 6.5 with NaOH for fine pH adjustment
And treated for 20 minutes in the same manner,
The fluorine concentration and sludge volume of the treated water were examined, and the results are shown in Table 1.
Posted.

Comparative Example 2 In Example 1, the raw water composition and the chemical injection amount were the same, and Ca
(OH)₂And CaCl ₂And Ca (O)
H)₂And CaCl₂After adding and reacting for 5 minutes,
The pH was adjusted to 6.5 with NaOH and reacted for 20 minutes.
Except for the above, the same treatment is performed.
The volume was determined and the results are shown in Table 1.

[0032]

[Table 1]

From Table 1, it can be seen that according to the present invention, it is possible to reduce the fluorine concentration of the treated water and to reduce the generated sludge capacity.

[0034]

As described in detail above, according to the method and apparatus for treating fluorine-containing water of the present invention, the fluorine-containing water is treated with C.
In addition, Ca (OH) ₂ and CaCl ₂ are added in combination as a salt to produce CaF ₂ , which is subjected to solid-liquid separation.
It is possible to stably obtain high-quality treated water having a low fluorine ion concentration and reduce the generated sludge capacity.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method and an apparatus for treating fluorine-containing water of the present invention.

[Explanation of symbols]

Reference Signs List 1 Ca (OH) ₂ reaction tank 2 CaCl ₂ reaction / pH adjustment tank 3 flocculation tank 4 sedimentation tank

Claims (4)

[Claims] 1. A method of adding calcium hydroxide and calcium chloride to fluorine-containing water to solid-liquid separate fluorine as calcium fluoride, wherein calcium fluoride is added to the fluorine-containing water and reacted. A method for treating fluorine-containing water, comprising adding calcium chloride. 2. The method for treating fluorine-containing water according to claim 1, wherein the pH is adjusted by adding an acid and / or an alkali while adding calcium chloride. 3. A first reaction means for adding and reacting calcium hydroxide to fluorine-containing water, and a second reaction means for adding and reacting calcium chloride to treated water of the first reaction means; An apparatus for treating fluorine-containing water, comprising: solid-liquid separating means for solid-liquid separating the treated water of the second reaction means. 4. The apparatus for treating fluorine-containing water according to claim 3, wherein the second reaction means is provided with a pH adjusting means for adjusting the pH by adding an acid and / or an alkali.