JP2002143841A - Method for treating waste water containing fluorine and boron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy and efficient method for treating waste water containing fluorine and boron by efficiently decompose hardly decomposable borofluoride ion. SOLUTION: After borofluoride ion is decomposed by adding a polyvalent metal salt 4 and a pH controlling agent 5 to the waste water 1 and radiating the water with ultrasonic waves, a calcium salt 7 and a pH controlling agent 8 are added to the water to convert fluorine into calcium fluoride. After a flocculant 10 is added to settle and separate the product, the water is passed through a boron adsorbing resin 12 to obtain final treated water 13. By radiating the waste water 1 with ultrasonic waves, decomposition of the borofluoride ion into boric acid and hydrogen fluoride is promoted, and the efficiency of sedimentation and removal by the calcium salt 7 is improved.

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 wastewater containing fluorine and boron. And wastewater containing boron and a part of fluorine and boron forms borofluoride ions.

[0002]

2. Description of the Related Art Conventionally, as a method of treating wastewater containing fluorine, calcium fluoride (CaF) is added by adding a calcium salt.
_As the method ₂ ), there is known a method of performing solid-liquid separation, and a method of performing solid-liquid separation by adsorbing fluorine on gelled aluminum hydroxide formed by adding an aluminum salt.

However, when fluorine is combined with boron to form borofluoride ions, the addition of a calcium salt only produces soluble Ca (BF ₄ ) ₂ ,
Almost no precipitate can be removed.

[0004] Further, since borofluoride ions hardly adsorb to the gelled aluminum hydroxide, almost no treatment can be performed even if an aluminum salt is added.

[0005] That is, the treatment of fluorine with calcium or aluminum is applicable when fluorine is present alone, that is, when it is present as fluoride ion. There is a problem that the reactivity with calcium and aluminum is remarkably reduced when is formed.

In order to solve this problem, as a method for treating wastewater containing borofluoride ions, a method using an ion exchange resin (Japanese Patent Publication No. 53-43745), an aluminum salt is added, and heating is performed under acidic conditions. Treatment to decompose borofluoride ions, and fix and remove the generated fluorine with calcium (Japanese Patent Publication No. 54-18 / 1979)
No. 064), a method of adding an iron salt, heat-treating under acidic conditions to decompose borofluoride ions, and precipitating the generated fluoro complex of iron with a calcium or aluminum salt (Japanese Patent Application Laid-Open No. Hei 9-131592). And so on.

[0007]

However, in the above method, since anions other than borofluoride ions are also adsorbed at the same time, there is a problem that stable treatment is difficult when the amount of coexisting anions increases. However, there is a problem that the operation of regenerating the resin is complicated, and the cost of the apparatus, especially the cost of the resin, is high. Further, there is a problem that it is necessary to separately treat resin regenerated water containing a high concentration of borofluoride.

In the methods (1) and (2), since the reaction time is too long at a low temperature, it is necessary to heat the material to at least 60 ° C. in practical use, and there is a problem that much energy is required for heating. .

The present invention solves the above-mentioned problems of the prior art,
A method for easily and inexpensively treating fluorine and boron by efficiently decomposing borofluoride ions in treating wastewater containing fluorine and boron and a part of the fluorine and boron forms borofluoride ions The purpose is to provide.

[0010]

That is, the present invention relates to a method for treating a fluorine- and boron-containing wastewater containing fluorine and boron, wherein part of the fluorine and boron forms borofluoride ions. And irradiating the ultrasonic waves to decompose borofluoride ions.

Further, the present invention is characterized in that a polyvalent metal salt is added to the borofluoride ion decomposing step.

The present inventors have conducted intensive studies on the conditions for decomposing borofluoride ions.
It has been found that the irradiation efficiency of the above sound waves, that is, ultrasonic waves, is improved. The preferred frequency of the ultrasonic wave is 10 KHz to several MHz.

When ultrasonic waves are irradiated into water, strong sound pressure is generated. However, when the sound pressure is negative pressure, the liquid is mechanically broken, and bubbles are generated. When the sound pressure is positive pressure, the bubbles are crushed and collapsed. May be. This is a phenomenon called cavitation. When crushing occurs, a local ultra-high temperature / ultra-high pressure state is generated, and the extreme state can promote the decomposition reaction of borofluoride ions.

The decomposition reaction of borofluoride ions is represented by the following formula. HBF ₄ + 3H ₂ O → H ₃ BO ₃ + 4HF (1) In the above formula (1), if hydrogen fluoride (HF) on the right side is removed outside the system by any method, the equilibrium moves to the right side, and Can accelerate the decomposition reaction of a chloride ion.
This decomposition reaction can be accelerated as the temperature increases, and the temperature of the waste water subjected to ultrasonic treatment is desirably heated to 30 ° C. or higher.

The present invention makes use of such a chemical equilibrium relationship, and uses a polyvalent metal salt which reacts with HF in the borofluoride ion decomposition step, for example, calcium salts such as slaked lime, calcium carbonate, calcium chloride, and aluminum salts such as aluminum sulfate. Alternatively, a decomposition reaction is promoted by adding a ferric salt such as ferric sulfate or the like to generate CaF ₂ , an Al—F complex, or an Fe—F complex, respectively.

The present invention is characterized by a method for decomposing borofluoride ions, and is not limited at all by the operation of removing fluorine or boron located before or after the decomposition step.

That is, in the preceding stage of the borofluoride ion decomposing step, it is possible to remove in advance boron which does not form borofluoride using, for example, a boron-adsorbing resin. It is also possible to adopt a method in which fluorine or boron which does not form borofluoride ions is previously treated by coagulation precipitation using a salt, an aluminum salt such as aluminum sulfate, a magnesium sulfate such as magnesium sulfate, or the like.

Further, in the latter stage of the borofluoride ion decomposition step, coagulation precipitation treatment is carried out using the above-mentioned slaked lime, calcium salts such as calcium carbonate and calcium chloride, aluminum salts such as aluminum sulfate and magnesium sulfate salts such as magnesium sulfate. A known method such as a method of treating fluorine or boron with a fluorine-adsorbing resin or a boron-adsorbing resin can be employed.

[0019]

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

FIG. 1 is a process explanatory view of a wastewater treatment method according to a first embodiment of the present invention. First, the wastewater 1 containing borofluoride ions is introduced into the first reaction tank 2. The first reaction tank 2 is provided with an ultrasonic generator 3 so that ultrasonic waves propagate in the tank. As a method of attaching the ultrasonic generator 3, a method of fixing a piezoelectric element, which is an ultrasonic oscillator, to a lower portion of the tank, or a method of inserting a rod-shaped homogenizer into the liquid from above the liquid can be adopted. The frequency of the ultrasonic wave generated from the ultrasonic generator 3 is 10 KHz to several M
Hz (usually up to about 2 MHz) is used.

In the first reaction tank 2, a polyvalent metal salt 4 and a pH adjuster 5 are added. The polyvalent metal salt 4 is added to remove HF, which is a decomposition product of borofluoride ions, from the outside of the system and to promote the decomposition reaction. That is, as the polyvalent metal salt 4, a substance that reacts with HF, for example, calcium salt such as slaked lime or calcium chloride, aluminum salt such as aluminum sulfate, or ferric salt such as ferric chloride or ferric sulfate is used. Can be. When these polyvalent metal salts 4 are used, CaF ₂ and Al react with HF, respectively.
F ^{_{n 3-n,}} the decomposition reaction of the fluoroborate hydride ion is promoted by generating the FeF ^{_{n 3-n.}} As the pH adjuster 5, an acid or alkali agent such as sulfuric acid, hydrochloric acid, and caustic soda can be used. In order to efficiently decompose borofluoride ions, the pH is preferably 4 or less, particularly under acidic conditions.

Next, a calcium salt 7 such as slaked lime and a pH adjuster 8 are added in the second reaction tank 6. Here, the calcium salt 7 is added to convert fluorine into an insoluble substance. That is, when an aluminum salt or a ferric salt is used as the polyvalent metal salt 4, soluble AlF _n ^3-n
-To form FeF _n ^3-n complex, calcium salt is added to convert to CaF ₂ and insolubilize. When a calcium salt is used as the polyvalent metal salt 4 in the first reaction tank 2, it may not be added in the second reaction tank 6. P in the second reactor 6
H is preferably a pH at which a reaction product precipitates. For example, when the aluminum salt is used as the polyvalent metal salt 4 in the first reaction tank 2, the pH is 5 to 8, and when the ferric salt is used, the pH is pH.
Four or more are suitable.

Next, a coagulant 10 such as a polyacrylamide-based anionic polymer coagulant is added in the coagulation tank 9 to make the particles of the reaction product coarser, that is, floc. The floc having sedimentation properties is separated into solid and liquid in the sedimentation tank 11 to obtain clear supernatant water. Of the boron and fluorine, fluorine is sedimented and separated as CaF ₂ , so that fluorine in the supernatant water has been treated to a low concentration.

Next, the supernatant water from the sedimentation tank 11 is passed through the boron adsorption resin 12 to remove boron, and the final treated water 13 is obtained.

Hereinafter, the present invention will be described in more detail with reference to examples.

(Example 1) First, NaBF_FourTo distilled water
Artificial wastewater 5 dissolved to a fluorine concentration of 100 mg / L
L was prepared. Next, aluminum sulfate is used as Al
mg / L and adjusted to pH 3.0 with HCl
After that, a desktop ultrasonic cleaner (output 300W, frequency 38k)
(Hz) for 2 hours. Next, Ca (OH)
_TwoTo 400 mg / L as Ca, and HCl
After adjusting the pH to 7, the mixture was stirred for 30 minutes. Polyacrylamide
Produced by adding 2mg / L of anionic polymer flocculant in the system
The material was flocculated and allowed to stand to take out clear supernatant water
Later, as a boron adsorption resin,
SV = 2 hr using 100 mL of ion CRB-02
^-1Water was passed. The fluorine concentration of the obtained treated water is 11 mg
/ L and boron concentration were 0.7 mg / L. In addition, people
The temperature of the wastewater was controlled at 30 ° C.

(Comparative Example 1) In Example 1, after adjusting the pH by adding aluminum sulfate, the mixture was stirred for 2 hours without irradiating ultrasonic waves. All other conditions were the same as in Example 1, and the fluorine concentration of the treated water was 69 mg / L and the boron concentration was 9.5 mg / L.

(Embodiment 2) In the artificial drainage of Embodiment 1, Fe
Ferric chloride so as to be 300 mg / L.
The pH was adjusted to 2.0 with Cl. After that, ultrasonic waves were irradiated under the same conditions as in Example 1, and the treatment after ultrasonic irradiation was also performed under the same conditions as in Example 1.
mg / L, and boron concentration was 0.5 mg / L.

Comparative Example 2 In Example 2, after the pH was adjusted by adding ferric chloride, the mixture was stirred for 2 hours without irradiating ultrasonic waves. All other conditions were the same as in Example 2. When treated, the fluorine concentration of the treated water was 81 mg / L and the boron concentration was 11 mg / L.

(Embodiment 3) In the artificial drainage of Embodiment 1, Ca
Was added so that the concentration became 2000 mg / L, and the pH was adjusted to 3.0 with HCl. Thereafter, ultrasonic waves were irradiated for 5 hours in the same ultrasonic cleaner as in Example 1. Next, Na
After stirring at pH 7 with OH for 30 minutes, a polyacrylamide-based anionic polymer flocculant was added at 2 mg / L to flocculate the product, and the mixture was allowed to stand to take out clear supernatant water. Thereafter, when water was passed through the boron-adsorbing resin under the same conditions as in Example 1, the fluorine concentration of the treated water was 14 mg / L, and the boron concentration was 0.8 mg / L.

(Comparative Example 3) In Example 3, the pH was adjusted by adding calcium chloride, and the mixture was stirred for 5 hours without irradiating ultrasonic waves. The other conditions were all the same as in Example 3, and the fluorine concentration of the treated water was 84 mg / L and the boron concentration was 12 mg / L.

The above is summarized in Table 1.

[0033]

[Table 1]

By comparing the results of Examples 1 to 3 and Comparative Examples 1 to 3, it is clear that according to the present invention through the step of irradiating ultrasonic waves, fluorine and boron can be efficiently treated.

Next, a method for treating wastewater according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a process explanatory view of a wastewater treatment method according to a second embodiment of the present invention. In the present embodiment, the first embodiment of the first embodiment is described.
This is the case where the addition of the polyvalent metal salt 4 was omitted when irradiating the ultrasonic wave to the reaction tank 2.

First, waste water 1 containing borofluoride ions is introduced into a first reaction tank 2. The first reaction tank 2 is provided with an ultrasonic generator 3 similar to that of the above-described first embodiment so that ultrasonic waves propagate in the tank.

In the first reaction tank 2, a pH adjuster 5 is added. As the pH adjuster 5, an acid or alkali agent such as sulfuric acid, hydrochloric acid, and caustic soda can be used. In order to decompose borofluoride ions efficiently, the pH is preferably 4 or less, particularly under acidic conditions. The temperature of the waste water 1 in the tank of the first reaction tank 2 is set to 30
It is preferable to heat the mixture to a temperature of not less than ° C. to promote the decomposition of borofluoride ions by ultrasonic waves.

Next, a calcium salt 7 such as slaked lime and a pH adjuster 8 are added in the second reaction tank 6. Here, the calcium salt 7 is added to convert fluorine into an insoluble substance.

Next, a coagulant 10 such as a polyacrylamide-based anionic polymer coagulant is added in the coagulation tank 9 to make the particles of the reaction product coarse, that is, floc. The floc having sedimentation properties is separated into solid and liquid in the sedimentation tank 11 to obtain clear supernatant water. Of the boron and fluorine, fluorine is sedimented and separated as CaF ₂ , so that fluorine in the supernatant water has been treated to a low concentration.

Next, the supernatant water from the sedimentation tank 11 is passed through the boron-adsorbing resin 12 to remove boron, and the final treated water 13 is obtained. Also in the present embodiment, borofluoride ions in the wastewater can be removed in the same manner as in the first embodiment.

[0041]

According to the present invention, the decomposition of borofluoride ions in wastewater into boric acid and hydrogen fluoride can be promoted by irradiating ultrasonic waves to wastewater containing borofluoride ions. There is an effect that borofluoride ions in the inside can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of a wastewater treatment method according to a first embodiment of the present invention.

FIG. 2 is a process explanatory view of a wastewater treatment method according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drainage 2 First reaction tank 3 Ultrasonic generator 4 Polyvalent metal salt 5,8 pH adjuster 6 Second reaction tank 7 Calcium salt 9 Coagulation tank 10 Coagulant 11 Sedimentation tank 12 Boron adsorption resin 13 Treated water

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 9/00 502 C02F 9/00 502Q 502Z 502P 503 503G 504 504B 504E F-term (reference) 4D024 AA04 AB11 AB14 BA17 BB01 BC01 DB10 DB12 DB30 4D037 AA13 AA14 AB14 AB18 BA26 CA01 CA08 CA14 4D038 AA08 AB25 AB40 AB41 AB42 BA04 BB06 BB13 BB18 BB20

Claims (7)

[Claims] 1. A method for treating wastewater containing fluorine and boron, wherein part of fluorine and boron forms borofluoride ions, wherein the wastewater is irradiated with ultrasonic waves to decompose the borofluoride ions. Fluorine and boron-containing wastewater treatment method characterized by containing 2. The method for treating wastewater containing fluorine and boron according to claim 1, wherein a polyvalent metal salt is added to the wastewater in the borofluoride ion decomposition step. 3. The method for treating wastewater containing fluorine and boron according to claim 2, wherein a calcium salt, an aluminum salt or a ferric salt is used as the polyvalent metal salt. 4. A step of removing boron-containing ions other than the borofluoride ions in the wastewater using a boron adsorption resin before the step of irradiating the ultrasonic waves to the wastewater to decompose the boron fluoride ions. The method for treating wastewater containing fluorine and boron according to claim 1 or 2, wherein the wastewater contains fluorine and boron. 5. A calcium salt, an aluminum salt, or a magnesium salt is added to the wastewater prior to the step of irradiating the ultrasonic wave to the wastewater to decompose the borofluoride ion, and the wastewater is subjected to coagulation and sedimentation. 2. The method according to claim 1, further comprising the step of previously removing said fluorine or said boron that has not formed borofluoride ions therein.
The method for treating wastewater containing fluorine and boron according to any one of claims 1 to 3. 6. A method of irradiating the wastewater with the ultrasonic wave and adding a calcium salt, an aluminum salt or a magnesium salt to the wastewater after the borofluoride ion decomposition step, and subjecting the wastewater to coagulation and sedimentation. The method for treating wastewater containing fluorine and boron according to claim 1, wherein the wastewater contains fluorine and boron. 7. The step of irradiating the wastewater with the ultrasonic wave to decompose the borofluoride ions in the wastewater,
The method for treating wastewater containing fluorine and boron according to any one of claims 1 to 6, wherein the pH of the wastewater is controlled to 4 or less.