KR101651520B1 - Treatment method of low-concentration fluoride wastewater - Google Patents

Abstract

 The present invention relates to a method for treating hydrofluoric acid wastewater which is a mixture for treating hydrofluoric acid wastewater, which is capable of replacing calcium hydroxide used in conventional hydrofluoric acid wastewater treatment by mixing calcium carbonate, which is lower in unit cost than calcium hydroxide, Lt; / RTI >

Description

[0001] The present invention relates to a low-concentration fluoride wastewater treatment method,

The present invention relates to a low-concentration hydrofluoric acid wastewater treatment, and more particularly, to a mixture containing calcium hydroxide and calcium carbonate as a medium of a precipitation process and a method for treating hydrofluoric acid wastewater using the same.

Recently, Foshan wastewater is generated in the electronics manufacturing plant, LCD manufacturing process, and semiconductor industry, which are major industries in Korea. This is because raw materials such as wafers and glass are cleaned and particles, metal impurities, organic contaminants, and unnecessary oxidized surface films adhered to the surface of the substrate after the deposition, development, etching process and the like are cleaned, FOSHAN will be used for clean removal without any influence, and a large amount of FOSHAN WAX WATER will be discharged.

Hydrofluoric acid refers to a liquid in which hydrogen fluoride (F) is combined with hydrogen fluoride (HF), which is a colorless, irritating, volatile liquid. Particularly because of its high reactivity, it is used as a catalyst material in factories or as a dehydrating agent, and it is considered to be an essential chemical substance in the semiconductor industry due to its excellent efficacy in dissolving unnecessary parts of semiconductor silicon wafers.

The increase in the amount of waste water containing fluorine has been caused by the diversification of domestic industries and the generation of environmental pollutants in each workplace. Since the 1990s, Korea has been concentrating on the electronic product manufacturing industry, and as a result, the amount of hydrofluoric acid wastewater generated in the semiconductor factory, the panel manufacturing process, and the electronic product manufacturing factory has rapidly increased, and the treatment of the high concentration of hydrofluoric acid wastewater has become an urgent problem.

Treatment of fluorine in wastewater is carried out by adsorption using rare earth metals, ion exchange resins, agglomeration with alum (SO (SO ₄ ) ₃ , alum), Ca (OH) ₂ precipitation It has an inefficient structure due to high cost in processing. In particular, Ca (OH) ₂ precipitation has a disadvantage in that the solubility of Ca (OH) ₂ is low and the reactivity is lowered and the pH is increased. This treatment results in a low solubility of lime and a large amount of lime. As a result, a large amount of sludge is generated, thereby increasing the cost of scaling and processing.

In case of treatment of small amount of wastewater at a high concentration, most of the methods have been selected so far that calcium is added to precipitate filtration treatment with CaF ₂ . This method is an inexpensive treatment agent of calcium as an additive, and can be effectively removed when the concentration of fluorine at a high concentration is high. In this process, the reaction time is long, and the solubility of CaF ₂ in water is about 10 to 15 mg / L, which makes it difficult to lower the fluoride ion concentration to 10 mg / L or less. In addition, this method has a problem of efficiency when the treatment amount is large because the treatment time is longer and the reaction efficiency is lowered as the fluorine ion concentration is lowered and it is necessary to inject more than 5 times as much as the theoretical equivalent.

Disclosure of Invention Technical Problem [8] In view of the problems of the prior art, the present invention is directed to a mixture for treating hydrofluoric acid wastewater which is inexpensive and can be substituted for calcium hydroxide (Ca (OH) ₂ ) used in the existing lime precipitation method, .

An embodiment of the present invention provides a mixture for treating hydrofluoric acid wastewater comprising a first calcium salt having a strong basicity and a second calcium salt having a weak basicity and satisfying the following Formulas 1 and 2:

[Formula 1]

0.5? A1 + a2 / b1? 1.0 and 0 <b1? 0.5

(A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, and b1 is the molar concentration (M) of fluorine in the hydrofluoric acid wastewater.

[Formula 2]

pHA - pHB ≥ 3

(Where pHA is the pH of the hydrofluoric acid wastewater at the beginning of the reaction and pHB is the pH of the hydrofluoric acid wastewater after 6 hours of reaction).

The solubility of the third calcium salt is higher than the solubility of the first calcium salt and the second calcium salt, and the solubility of the third calcium salt in the following formula Thereby providing a satisfactory mixture for treating hydrofluoric acid wastewater.

[Formula 1-1]

0.5? A1 + a2 + a3 / b1? 1.0 and 0 <b1? 0.5

A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, a3 is the molar concentration (M) of the third calcium salt, b1 is the molar concentration of fluorine )to be.)

Further, an embodiment of the present invention provides a mixture for treating hydrofluoric acid wastewater satisfying the following formula (3).

[Formula 3]

0.15? A2 / (a1 + a2)? 0.96

(A1 is the molar concentration (M) of the first calcium salt, and a2 is the molar concentration (M) of the second calcium salt.)

Further, an embodiment of the present invention provides a mixture for treating hydrofluoric acid wastewater satisfying the following formula (3-1).

[Formula 3-1]

0.005? A3 / (a1 + a2 + a3)? 0.05

In one embodiment of the present invention, the pHB of the above-mentioned [formula 2] is 7.5 to 8.0, and provides a mixture for treating hydrofluoric acid wastewater.

According to another aspect of the present invention, there is provided a method for measuring a fluorine concentration in a hydrofluoric acid wastewater, Mixing a calcium hydroxide aqueous solution having a molar concentration of a1 and an aqueous calcium carbonate solution having a molar concentration a2 to prepare a hydrofluoric acid wastewater treatment mixture having (a1 + a2) / b1 of 0.5 to 1.0; And a precipitation step of adding the mixture for treating hydrofluoric acid wastewater to hydrofluoric acid wastewater and stirring the hydrofluoric acid wastewater under pH lower than the initial pH by 3 or more to precipitate fluorine in the form of CaF _{2 in} the hydrofluoric acid wastewater.

It is possible to provide a mixture for treating hydrofluoric acid wastewater containing calcium salts of various qualities which can replace calcium hydroxide (Ca (OH) ₂ ) used in the conventional lime precipitation method at a certain ratio. That is, when the hydrofluoric acid wastewater is treated using the mixture of the present invention, the fluorine removal efficiency is slightly lower than that of the conventional method in which hydrofluoric acid wastewater is treated using only calcium hydroxide, so that calcium hydroxide used in the conventional lime precipitation method can be replaced have.

In addition, when hydrofluoric acid wastewater is treated only with calcium hydroxide, basic pH is indicated and basic treatment is required. Further, when the hydrofluoric acid wastewater is treated with the mixture of the present invention, the pH is close to neutrality and additional treatment is required The cost of disposal of the wastewater can be cut by half.

Before describing the present invention in detail, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention, which is defined solely by the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise stated.

Throughout this specification and claims, the word "comprise", "comprises", "comprising" means including a stated article, step or group of articles, and steps, , Step, or group of objects, or a group of steps.

On the contrary, the various embodiments of the present invention can be combined with any other embodiments as long as there is no clear counterpoint. Any feature that is specifically or advantageously indicated as being advantageous may be combined with any other feature or feature that is indicated as being preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

The mixture for treating hydrofluoric acid wastewater according to an embodiment of the present invention is a mixture for treating hydrofluoric acid wastewater comprising a first calcium salt having strong basicity and a second calcium salt having weak basicity. Hydrofluoric acid mixture for waste water treatment according to the present invention comprises hydrofluoric acid in the hydrofluoric acid wastewater CaF ₂ (HF) concentration in the hydrofluoric acid wastewater is 0.005 M to 0.25 M, it is possible to obtain the optimum removal efficiency.

The first calcium salt having a strong basicity is a calcium salt having a calcium content of 50% or more, and the pH change sharply increases upon addition.

The second basic calcium salt having a weak basicity is a calcium salt having a calcium content of 30 to 40%, a sharp change in pH upon addition, a low unit price, and calcium carbonate (CaCO ₃ ) is preferably used. Since the calcium carbonate has low solubility but reacts with fluorine and precipitates, it gives enough time to give a calcium content suitable for use in the stirring reaction. Accordingly, the present invention is to supply a part of the calcium ions necessary for removing fluorine contained in the hydrofluoric acid wastewater by a weakly basic calcium salt.

In addition, in the treatment of hydrofluoric acid wastewater, the solubility of CaF ₂ is increased and the removal rate of F ^- is lowered. On the contrary, when pH is increased, Ca ^{2 +} is present in the form of calcium salt and the reactivity of F ^- 7, the highest removal rate can be obtained.

When a mixture containing a strongly basic calcium salt and a weakly basic second calcium salt is put into the hydrofluoric acid wastewater, the initial pH is about 11 as compared with the case where the mixture containing calcium hydroxide is put into the hydrofluoric acid wastewater, The pH after stirring is pH 9 or higher in the case of a mixture containing calcium hydroxide, while in the case of a mixture comprising a first calcium salt having a strong basicity and a second calcium salt having a weak basicity, even when a small amount of a second calcium salt is contained and exhibits a neutral state at a pH of about 7.5 to 8. This can be seen from the following experimental examples.

When calcium carbonate is contained as a second calcium salt having a weak basicity, calcium carbonate reacts in the hydrofluoric acid wastewater and forms carbonic acid ions (HCO ₃ ^- ) and carbonic acid (H ₂ CO ₃ ) is generated to cause a buffering action.

In addition, when hydrofluoric acid wastewater is treated only with calcium hydroxide, basic pH is indicated and basic treatment is required. Further, when the hydrofluoric acid wastewater is treated with the mixture of the present invention, the pH is close to neutrality and additional treatment is required The cost of disposal of the wastewater can be cut by half.

Further, the inventor of the present invention has found that the hydrofluoric acid wastewater of the hydrofluoric acid wastewater treatment mixture according to an embodiment of the present invention has a high hydrofluoric acid removal efficiency when the following formula 1 is satisfied.

[Formula 1]

0.5? A1 + a2 / b1? 1.0 and 0 <b1? 0.5

(A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, and b1 is the molar concentration (M) of the hydrofluoric acid in the hydrofluoric acid wastewater.

When (a1 + a2) / b1 is less than 0.5, there is a problem that the amount of calcium ions to be supplied is absolutely insufficient, and when it exceeds 1.0, excess calcium compounds are supplied to cause excessive waste generation. (A1 + a2) / b1 in the formula 1 is preferably 0.55 to 0.7. More preferably 0.625.

Further, a mixture for treating hydrofluoric acid wastewater comprising a first calcium salt having a strong basicity and a second calcium salt having a weak basicity satisfies the following formula 2 when it is added to a hydrofluoric acid wastewater and reacted. This will be explained by an experimental example to be described later.

[Formula 2]

pHA - pHB ≥ 3

(Where pHA is the pH of the hydrofluoric acid wastewater at the beginning of the reaction and pHB is the pH of the hydrofluoric acid wastewater after 6 hours of reaction).

It has also been found that a mixture for treating hydrofluoric acid wastewater comprising a first calcium salt having a strong basicity and a second calcium salt having a weak basicity has a high hydrofluoric acid removal efficiency when the following formula 3 is satisfied.

[Formula 3]

0.15? A2 / (a1 + a2)? 0.96

(A1 is the molar concentration (M) of the first calcium salt, and a2 is the molar concentration (M) of the second calcium salt.)

When the ratio of a2 / (a1 + a2) is less than 0.15, the effect on the pH is insignificant and the reaction with the hydrofluoric acid wastewater has a problem in that the pH is basic. When it exceeds 0.96, the solubility is low, There is a problem that the processing time is increased.

The mixture for treating hydrofluoric acid wastewater according to an embodiment of the present invention may further include a third calcium salt having neutrality.

The neutral third calcium salt has a calcium content of 20% or less and has a solubility greater than that of the first calcium salt and the second calcium salt. When the third calcium salt is further contained, it exhibits a high hydrofluoric acid removal efficiency when the following formula [1-1] is satisfied.

[Formula 1-1]

0.5? A1 + a2 + a3 / b1? 1.0 and 0 <b1? 0.5

A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, a3 is the molar concentration (M) of the third calcium salt, b1 is the molar concentration of fluorine )to be.)

If the third calcium salt is further included so as to satisfy the formula [1-1], the solubility of the third calcium salt is higher than that of the first calcium salt and the second calcium salt so that the initial reaction rate can be increased, When a calcium salt is contained, gelation occurs. Therefore, it is preferable to further include a third calcium salt so as to satisfy [Expression 1-1]. It is preferable to use calcium nitrate (Ca (NO ₃ ) ₂ ) as the third calcium salt.

Further, it has been found that the hydrofluoric acid wastewater treatment mixture further including the third calcium salt having neutrality has a high hydrofluoric acid removal efficiency when the following formula 3-1 is satisfied.

[Formula 3-1]

0.005? A3 / (a1 + a2 + a3)? 0.05

A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, a3 is the molar concentration (M) of the third calcium salt, b1 is the molar concentration of fluorine )to be.)

When the ratio of a3 / (a1 + a2 + a3) is less than 0.005, there is a problem that the settling time is prolonged during the treatment, and when it exceeds 0.05, the filtration time after the treatment becomes long.

The method for treating hydrofluoric acid wastewater using a hydrofluoric acid wastewater treatment mixture comprising a first calcium salt having a strong basicity and a second calcium salt having a weak basicity according to an embodiment of the present invention measures a molar concentration b1 of fluorine in a hydrofluoric acid wastewater ; Mixing a calcium hydroxide aqueous solution having a molar concentration of a1 and an aqueous calcium carbonate solution having a molar concentration a2 to prepare a hydrofluoric acid wastewater treatment mixture having (a1 + a2) / b1 of 0.5 to 1.0; And a precipitation step in which the mixture for treating hydrofluoric acid wastewater is introduced into hydrofluoric acid wastewater and stirred under pH lower than the initial pH by 3 or more to precipitate and remove fluorine in the form of CaF _{2 in} the hydrofluoric acid wastewater.

The mixing step may be a step of mixing (a1 + a2) / b1 so that the ratio (a1 + a2) / b1 is 0.55 to 0.7. The mixing step may further comprise mixing the aqueous solution of calcium carbonate and the aqueous solution of calcium hydroxide so that a2 / (a1 + a2) ranges from 0.15 to 0.96. The calcium salt may be mixed in powder form.

In the mixing step, the calcium hydroxide aqueous solution having a molar concentration of a1 and the calcium carbonate aqueous solution having a molar concentration a2 are further mixed with an aqueous calcium nitrate solution having a molar concentration of a3 to prepare a hydrofluoric acid wastewater treatment (a1 + a2 + a3) / b1 of 0.5 to 1.0 Lt; / RTI &gt;

In the mixing step of further mixing the calcium nitrate aqueous solution, the mixture may be prepared by further mixing an aqueous solution of calcium nitrate so that a3 / (a1 + a2 + a3) is 0.005 to 0.05.

The precipitation step was carried out by using CaF ₂ , The mixture for treating hydrofluoric acid wastewater according to the present invention is put into hydrofluoric acid wastewater and stirred until the reaction is completed to precipitate fluorine in the hydrofluoric acid wastewater in the form of CaF ₂ to be removed. More specifically, the mixture for treating hydrofluoric acid wastewater is put into hydrofluoric acid wastewater and stirred for at least 2 hours under pH 7.5 to 8 to remove fluorine in the form of CaF _{2 in} the hydrofluoric acid wastewater.

In order to increase the hydrofluoric acid removal rate of wastewater in the treatment of hydrofluoric acid wastewater, it may further include a two-stage treatment of flocculation precipitation process using alumina sulfate (Al (SO ₄ ) ₃ , alum) or a three-stage treatment of precipitation stage using rare- have.

Alumina (Al (SO ₄ ) ₃ , alum) used in the two-stage treatment forms an insoluble Al (OH) ₃ together with an alkaline action when added to water and adsorbs fluorine ions to Al (OH) ₃ The rare earth ions of rare earth metals used in the three-stage treatment are reacted with fluoride more rapidly than the calcium ions, and at the same time, the reaction efficiency is very high, To precipitate it.

Example

Examples 1 to 6

Industrial calcium hydroxide having a purity of not less than 95.0% and not more than 150 탆 is used as the first calcium salt having strong basicity and a pseudo second alkaline calcium salt having a purity of not less than 99.0% and not more than 150 탆 Of industrial calcium carbonate was used.

A sample of hydrofluoric acid to be used as a hydrofluoric acid wastewater was prepared by mixing 1 g of hydrofluoric acid (HF 50%) in a 500 ml round-bottomed flask and mixing distilled water.

The F contained in the hydrofluoric acid sample ^- the number of moles to the number of moles of Ca ^{2 +} for by Ca (OH) ₂ of the insert the Ca (OH) ₂ to 0.02625, 0.02125, 0.01625, 0.01125, 0.00625, 0.00125, CaCO 3 is similarly hydrofluoric acid sample the F included ^in-the embodiment was mixed so that the molar amount of Ca ^{2 +} by the _{CaCO 3 0.005, 0.01, 0.015,} 0.02, 0.025, 0.03 with respect to the mole number (a1 + a2) / b1 molar ratio is 0.625 in example 1 to conduct A mixture for treating hydrofluoric acid wastewater of Example 6 was prepared.

Examples 7 and 8

Examples 1 to 6 against a low-concentration hydrofluoric acid sample of the prepared 0.05 M is the number of moles of Ca ^{2 +} by Ca (OH) ₂ into the Ca (OH) ₂ to 0.011, 0.02075, CaCO ₃ similarly to the hydrofluoric acid sample for the number of moles of Ca ^{2 +} by the CaCO ₃ placed so that the _{0.02, 0.01, Ca (NO 3} ) to the number of moles of Ca ^{2 +} by ₂ 0.00025, 0.0005 mixture (a1 + a2 + a3) / b1 molar ratio of 0.625 A mixture for treating hydrofluoric acid wastewater in Examples 7 and 8 was prepared.

Comparative Example 1

(A1 + a2) / b1 molar ratio of 0.625, that is, a molar ratio of a1 / b1 of 0.625 was prepared with Ca (OH) ₂ only.

* Table 1 shows the content of each component according to Examples and Comparative Examples.

HF
(M) Calcium salt (M) Calcium salt (%) (a1 + a2 + a3) / b1 1st Second Third Second Third Example 1 0.05 0.02625 0.005 - 16.0 - 0.625 Example 2 0.05 0.02125 0.010 - 32.0 - 0.625 Example 3 0.05 0.01625 0.015 - 48.0 - 0.625 Example 4 0.05 0.01125 0.020 - 64.0 - 0.625 Example 5 0.05 0.00625 0.025 - 80.0 - 0.625 Example 6 0.05 0.00125 0.030 - 96.0 - 0.625 Example 7 0.05 0.0110 0.020 0.00025 64.5 0.8 0.625 Example 8 0.05 0.02075 0.010 0.00050 32.5 1.6 0.625 Comparative Example 1 0.05 0.03125 - - - - 0.625

Experimental Example

(1) Measurement of fluorine removal rate

The fluorine-containing wastewater treatment mixtures of Examples 1 to 8 and Comparative Example 1 were reacted with a 0.05 M fluoric acid sample, and the concentration of F ^- was analyzed to measure the fluorine removal rate. The fluorine removal rate was measured by absorbance spectrophotometry using a water analyzer after the sample was filtered through a glass fiber filter paper. Table 2 shows the F ^- concentration and fluorine removal rate.

Calcium salt (%) Initial fire quantity
(mg / L) Residual residual amount
(mg / L) Fluorine Removal Rate (%) Second Third Example 1 16.0 - 950 14.0 98.53 Example 2 32.0 - 950 12.9 98.64 Example 3 48.0 - 950 13.9 98.54 Example 4 64.0 - 950 12.7 98.66 Example 5 80.0 - 950 14.1 98.52 Example 6 96.0 - 950 13.0 98.63 Example 7 64.5 0.8 950 13.1 98.62 Example 8 32.5 1.6 950 13.9 98.54 Comparative Example 1 - - 950 15 98.42

As a result of the experiment, in Comparative Example 1 in which only the first calcium salt was incorporated and the second calcium salt was 0%, the residual F ^- concentration was 15 mg / L and the fluorine removal rate was 98.42% , The residual F ^- concentration was 12.7 mg / L and the fluorine removal rate was 98.66%. The difference between the lowest fluorine removal rate and the highest residual F ^- concentration of 2 mg / L and the fluorine removal rate of 0.18% shows that the removal efficiency of Examples 1 to 8 is slightly higher than that of Comparative Example 1, It is a substance.

(2) Measurement of pH over time

The hydrofluoric acid wastewater treatment mixtures of Examples 1 to 8 and Comparative Example 1 were reacted with 0.05 M of hydrofluoric acid to measure the pH change with time. A 0.05 M sample of hydrofluoric acid was injected into a 1 L beaker made of polyethylene which did not dissolve in hydrofluoric acid, and a mixed solution for treating hydrofluoric acid wastewater of Examples 1 to 8 and Comparative Example 1 was injected and subjected to a Jar test. The pH was measured with a pH meter every 2 hours with constant stirring at 180 rpm with a Jar tester. The pH was measured for 6 hours after the reaction was completed and the pH change was no longer present.

Table 3 shows the pH measurement results.

First pH After 2hr pH After 4hr pH After 6hr pH pH difference Example 1 11.02 8.47 7.81 7.78 3.24 Example 2 11.08 8.40 7.74 7.74 3.34 Example 3 11.07 8.21 7.73 7.73 3.34 Example 4 11.23 9.90 8.26 7.63 3.6 Example 5 11.07 9.50 8.13 7.66 3.41 Example 6 10.99 8.84 7.95 7.61 3.38 Example 7 10.23 8.35 7.62 7.52 2.71 Example 8 10.02 8.21 7.51 7.35 2.67 Comparative Example 1 11.88 11.07 10.40 9.65 2.23

The initial pH was close to pH 11, and the pH of Comparative Example 1 was slightly higher than that of the Example. In the case of Comparative Example 1, the pH value was 2.23, showing the lowest pH value difference. In Example 5, the pH value was 3.41, which is the highest pH value difference appear. In all cases of Examples 1 to 6, the pH value was close to neutrality with a difference of 3 or more.

Even at similar initial pH, higher pH values of medium with higher calcium salt loading were found. Also in the case of Example 1 in which a small amount of the second calcium salt was contained, the pH was close to neutrality, and it was found that the final pH was neutral by mixing a small amount of the second calcium salt.

The features, structures, effects, and the like illustrated in the above-described embodiments can be combined and modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

Claims (10)

A first calcium salt having strong basicity, a second calcium salt having weak basicity and a third calcium salt including calcium nitrate (Ca (NO ₃ ) ₂ ,
A mixture for treating hydrofluoric acid wastewater satisfying the following [formula 1-1] to [formula 3-1].
[Formula 1-1]
0.55? A1 + a2 + a3 / b1? 0.7 and 0 <b1? 0.5
A1 is the molar concentration (M) of the first calcium salt, a2 is the molar concentration (M) of the second calcium salt, a3 is the molar concentration (M) of the third calcium salt, b1 is the molar concentration of fluorine )to be.)
[Formula 2-1]
pHA - pHB ≥ 2.67 and 7.5 ≤ pHB ≤ 8.0
(Where pHA is the pH of the hydrofluoric acid wastewater at the beginning of the reaction and pHB is the pH of the hydrofluoric acid wastewater after 6 hours of reaction).
[Formula 3]
0.15? A2 / (a1 + a2)? 0.96
[Formula 3-1]
0.005? A3 / (a1 + a2 + a3)? 0.05 delete delete delete delete A measurement step of measuring a molar concentration b1 of fluorine in the hydrofluoric acid wastewater;
An aqueous solution of calcium hydroxide having a molar concentration of a1, an aqueous solution of calcium carbonate having a molar concentration of a2 and an aqueous solution of calcium nitrate having a molar concentration of a3 are mixed to satisfy the following [Expression 1-1], [Expression 3] and [Expression 3-1] A mixing step of producing a mixture for treating hydrofluoric acid wastewater; And
Wherein the hydrofluoric acid wastewater treatment mixture is introduced into hydrofluoric acid wastewater and stirred at a pH of from 7.5 to 8.0 which is lower than the initial pH by 2.67 or more to precipitate and remove fluorine in the form of CaF _{2 in} the hydrofluoric acid wastewater.
[Formula 1-1]
0.55? A1 + a2 + a3 / b1? 0.7 and 0 <b1? 0.5
[Formula 3]
0.15? A2 / (a1 + a2)? 0.96
(A1 is the molar concentration (M) of the first calcium salt, and a2 is the molar concentration (M) of the second calcium salt.)
[Formula 3-1]
0.005? A3 / (a1 + a2 + a3)? 0.05
delete delete delete The method according to claim 6,
Further comprising a two-stage treatment of a flocculation and sedimentation step using alumina sulfate (Al (SO ₄ ) ₃ , alum) after the hydrofluoric acid wastewater treatment, or a three-stage treatment of a precipitation step using a rare earth metal after the two- Wherein the wastewater is treated with a hydrofluoric acid.