WO2017017833A1

WO2017017833A1 - Fluorine-containing wastewater treatment method and device therefor

Info

Publication number: WO2017017833A1
Application number: PCT/JP2015/071613
Authority: WO
Inventors: 祐司和田; 則子志村; 寛子河村; とみ子斎藤
Original assignee: Ｎｅｃファシリティーズ株式会社
Priority date: 2015-07-30
Filing date: 2015-07-30
Publication date: 2017-02-02
Also published as: JPWO2017017833A1; TWI651275B; TW201726558A; JP6508747B2

Abstract

In order to provide a method for treating fluorine-containing wastewater which makes it possible to treat fluorine-containing wastewater that contains a high concentration of various types of coexisting material, and as a result, obtain treated water of high water quality that sufficiently falls below the effluent standard of 8 mg/L by using a simple device equipped with only one solid-liquid separator, and also minimize the amount of an added phosphate compound which greatly affects running costs, the present invention provides a method for treating fluorine-containing wastewater that involves adding calcium to the fluorine-containing wastewater, and solid-liquid separating the fluorine in the wastewater as a calcium-fluoride insoluble material, wherein the calcium is added to the wastewater, a drug containing a phosphate compound is added thereto without separating the produced insoluble precipitate, and next, an aluminum salt having a basicity of 20-80% is added thereto.

Description

Fluorine-containing wastewater treatment method and apparatus

The present invention relates to a processing method and a processing apparatus which are widely used as a processing method for fluorine-containing wastewater and which separates solid and liquid by converting calcium into calcium fluoride by adding calcium.

Fluorine is a substance used in large quantities in the industry, and fluorine-containing wastewater is generated from, for example, semiconductor manufacturing plants, liquid crystal manufacturing plants, metal surface treatment plants, stainless steel manufacturing plants, ceramics manufacturing plants, and the like. It is a substance harmful to the human body, and the Water Pollution Control Law requires that it be treated to 8 mg / L or less, which is the drainage standard, when discharged into land water.

Conventionally, as a method for treating fluorine-containing wastewater, there is known a method (referred to as a calcium method) in which a calcium compound is added to fluorine-containing wastewater, and fluorine is converted into hardly soluble calcium fluoride fine particles and then solid-liquid separation is performed. However, in this calcium method, there is a problem that about 10 to 20 mg / L of fluorine that has not been completely converted to calcium fluoride remains dissolved and flows out into the treated water. Therefore, in order to comply with wastewater standards, it is necessary to install advanced treatment equipment after the calcium method. Examples of advanced treatment methods include the aluminum method in which an aluminum salt is added and then solid-liquid separation, or phosphoric acid. A fluoroapatite method in which a compound is added and then solid-liquid separated is known.

The aluminum method uses the property that dissolved fluorine is taken into the insoluble precipitates of aluminum hydroxide (Al (OH) ₃ ) produced by the reaction between aluminum ions and alkali by adsorption or coprecipitation. It is. As aluminum salts, sulfate bands (generic name for aluminum sulfate) and polyaluminum chloride (PAC) are widely used.

PAC has characteristics such as a greater turbidity effect, that is, a suspended substance (SS) trapping effect than a sulfate band, and excellent agglomeration performance even at low water temperatures. However, since there is almost no difference in the ability to capture dissolved fluorine, both are widely used for fluorine wastewater treatment.

The aluminum method is widely adopted as an advanced treatment method because the aluminum salt is inexpensive and the fluorine concentration is surely lowered as the amount of aluminum added is increased.

On the other hand, in the fluoroapatite method, calcium, phosphoric acid and fluorine react to produce fluoroapatite (Ca ₅ (PO ₄ ) ₃ F) having a lower solubility than calcium fluoride. Although it is necessary to add an expensive phosphoric acid compound, surplus calcium from the calcium method flows into the advanced treatment equipment, so that the calcium can be used effectively (see, for example, Patent Document 1).

The fluoroapatite method requires at least three times the amount of removed fluorine (about 5 times the mass) of phosphorus from its chemical formula, but in fact, calcium phosphate other than fluoroapatite is simultaneously produced, It is necessary to add much more phosphorus. The price of a phosphoric acid compound is about 10 times that of an aluminum salt, and the running cost is very high, so the fluoroapatite method is rarely used as an advanced treatment method.

In the above three treatment methods, solid-liquid separation is most often performed by precipitation separation. Precipitation separation requires a long residence time, and the sedimentation tank is a relatively large apparatus. For this reason, in a place where the space where installation is possible is narrow, the membrane separation method may be applied although the apparatus cost is high. In the case where the two-stage treatment in series of the aluminum method or the fluoroapatite method is performed after the calcium method, this means that two solid-liquid separation devices, that is, two-stage treatment is required for solid-liquid separation.

By the way, in the calcium method, it can be said that by adding an aluminum salt between the addition of the calcium compound and the solid-liquid separation, the same processability as in the series two-stage treatment can be obtained with one solid-liquid separator. ,It is not. The reason is that if aluminum is added under the condition where calcium fluoride is present, re-dissolution of calcium fluoride occurs due to the interaction between aluminum and calcium fluoride, and the treated water quality becomes unstable. In other words, in order to sufficiently develop the fluorine treatment performance with an aluminum salt, it is necessary to add the aluminum salt after solid-liquid separation of the calcium fluoride fine particles produced by the calcium method, so that a large area or high cost is required. There was a problem that two solid-liquid separation devices had to be installed. Although there are cases where aluminum salts are used in the calcium method, this is mainly aimed at improving the agglomeration performance of the generated precipitate rather than the fluorine treatment performance. Therefore, the aluminum salt used in the calcium method hardly contributes to insolubilization of dissolved fluorine, like the aluminum salt used in the aluminum method.

In addition, in the calcium method, by adding a phosphoric acid compound between the addition of a calcium compound and solid-liquid separation, whether the same processability as in a series two-stage treatment can be obtained with one solid-liquid separator. That's not the case. The reason is considered that when fluoroapatite is generated in the presence of calcium fluoride, the concentration of dissolved fluorine decreases, and the equilibrium shifts in a direction in which the generated calcium fluoride is redissolved. Therefore, in the same manner as in the aluminum method, if the calcium fluoride is separated and removed and the phosphoric acid compound is not added, the treatment effect will not be fully manifested. Many cases apply.

By the way, a method for obtaining a high quality of treated water by one-stage treatment has been studied. In the method described in Patent Document 2, an aluminum salt is neutralized in advance in order to express the fluorine treatment effect of aluminum in the calcium method. However, the concentration of fluorine in the treated water is only improved from about 20 mg / L to 10 to 15 mg / L, and it is impossible to obtain a performance that stably falls below 8 mg / L.

Also, as a method using a phosphoric acid compound, a method of adding a phosphoric acid compound after adding calcium and before solid-liquid separation is disclosed. The method described in Patent Document 3 has a feature that it can treat a relatively high concentration fluorine-containing wastewater to several mg / L or less in a single stage treatment. However, as described above, in the presence of calcium fluoride, the treatment effect by fluoroapatite is not sufficient, and it is necessary to add about several hundred mg / L of phosphoric acid compound as phosphorus, which increases the running cost. was there.

Also disclosed is a method of using a phosphate compound and an aluminum salt in combination. Although the method described in Patent Document 4 can treat semiconductor factory wastewater containing 400 mg / L of fluorine up to 2.9 mg / L, there is a problem that the effect is not sufficient if the type of wastewater is different, as will be described later. .

Japanese Patent Laid-Open No. Sho 62-125894 JP 2000-140863 A JP 2002-370093 A Japanese Patent Laid-Open No. 55-3802

The object of the present invention is to provide an advanced treatment sufficiently lower than the wastewater standard of 8 mg / L even with fluorine-containing wastewater containing a wide variety of coexisting substances at a high concentration by a simple device having only one solid-liquid separation device. It is an object of the present invention to provide a method for treating fluorine-containing wastewater, which can obtain water quality and can minimize the addition amount of a phosphoric acid compound that greatly affects running cost.

The inventors have earnestly studied the calcium method for fluorine-containing wastewater, and as a result, have obtained the following new knowledge. In other words, in a state where calcium compounds are added to fluorine-containing wastewater to produce calcium fluoride, a chemical containing a phosphate compound is added, and then an aluminum salt having a basicity of 20 to 80% is added. The present inventors have found that even a wastewater containing various coexisting substances can be treated to a fluorine concentration that is surely lower than the wastewater standard of 8 mg / L, and the present invention has been completed.

The present invention has been made on the basis of the above knowledge, and the fluorine-containing wastewater treatment method according to the present invention adds calcium to the fluorine-containing wastewater to solidify the fluorine in the wastewater as a calcium fluoride insolubilized product. In the method for treating fluorine-containing wastewater to be liquid-separated, calcium is added to the wastewater, a chemical containing a phosphoric acid compound is added without separating insoluble precipitates formed, and aluminum having a basicity of 20 to 80% is then added. It is characterized by adding salt.

In the method for treating fluorine-containing wastewater according to the present invention, the pH after addition of the phosphoric acid compound is preferably 4 to 9, and the pH after addition of the aluminum salt is preferably 5.5 to 8.
In addition, the phosphoric acid compound is preferably added in an amount of 1 to 5 times the amount of dissolved fluorine after adding calcium in the wastewater as phosphorus, and the aluminum salt is the phosphoric acid compound to be added On the other hand, it is preferably added in the range of 0.2 to 3.0 by mass ratio of P / Al.
Furthermore, it is preferable that the solid-liquid separated sludge does not have a crystalline fluoroapatite peak in X-ray diffraction.

In addition, the fluorine-containing wastewater treatment apparatus according to the present invention includes a reaction tank A that causes a calcium compound to act on fluorine-containing wastewater, a reaction tank B that causes a phosphoric acid compound to act on a treatment liquid from the reaction tank A, and the reaction. A reaction tank C in which an aluminum salt having a basicity of 20 to 80% is allowed to act on the treatment liquid from the tank B; and a mechanism for solid-liquid separation of the treatment liquid from the reaction tank C.

According to the method for treating fluorine-containing wastewater of the present invention, even a fluorine-containing wastewater containing a wide variety of coexisting substances at a high concentration, a simpler amount of phosphoric acid compound used and one solid-liquid separation device can be used. With such a processing apparatus, the fluorine concentration can be reliably processed to 8 mg / L or less.

It is the apparatus and process explanatory drawing which showed embodiment of the fluorine-containing waste_water | drain of this invention. It is an X-ray-diffraction measurement result of the insoluble precipitate obtained in Example 1 and Comparative Example 3. It is a measurement result of the treated water fluorine concentration of Examples 2 and 3. It is a measurement result of the treated water fluorine concentration of Comparative Examples 8 and 9. It is a graph which shows the relationship between the basicity of an aluminum salt, and a treated water fluorine concentration. It is a measurement result of the treated water fluorine concentration of Examples 5 and 6.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is an apparatus and process explanatory diagram showing an embodiment of the present invention. The fluorine-containing wastewater treatment apparatus in this embodiment includes a reaction tank A10, a reaction tank B20, a reaction tank C30, a coagulation tank 40, and a precipitation tank 50.

Fluorine-containing waste water 1 is introduced into the reaction tank A10, and calcium 2 and, if necessary, a pH adjusting agent 3 such as sulfuric acid, hydrochloric acid, caustic soda, slaked lime, and the like are added and mixed. In the reaction tank A10, fine particles of calcium fluoride are generated.

Next, the chemical 4 containing a phosphoric acid compound is added to the treated water from the reaction tank A10 in the reaction tank B20 and mixed with stirring. Here, of the calcium 2 added in the reaction tank A10, surplus calcium that did not react with fluorine reacts with fluorine and phosphoric acid to produce fluoroapatite. Here, the dissolved fluorine concentration does not decrease so much by the re-dissolution of calcium fluoride.

The phosphoric acid compound used here may be any compound that can react with calcium and fluorine in the liquid to form fluoroapatite, and examples thereof include phosphoric acid and phosphate. In addition to substances containing phosphate ions, phosphorous acid or hypophosphorous acid and its salts, such as low-oxidized phosphorus, are added, and an oxidizing agent is added to generate phosphate ions in the reaction vessel B20. You may let them.

The amount of the phosphoric acid compound to be added here depends greatly on the concentration of dissolved fluorine that did not react with calcium in the reaction tank A10. If the dissolved fluorine concentration is 10 to 20 mg / L, fluorine can be processed to about 4 mg / L, which is significantly lower than 8 mg / L, by adding 1 to 2 times the mass of phosphorus. If 2 to 5 times the mass of phosphorus is added, it can be processed to about 1 mg / L.

The pH in the reaction vessel B20 is desirably adjusted to a range suitable for the production of fluoroapatite, and specifically, it is desirably 4 to 9.

Next, in the reaction vessel C30, the aluminum salt 5 having a basicity of 20 to 80% is added. The basicity is a numerical value representing the alkali content of an aluminum salt. If PAC, that is, Al ₂ (OH) _n Cl _6-n is taken as an example, the basicity is calculated by n / 6 × 100 (%). The Commercial PAC basicity around 50%, i.e. OH ^- is but those contained 1.5 moles before and after Al is typically different basicity are also sold. The basicity of sulfuric acid band and aluminum chloride is 0%. For the aluminum salt 5 corresponding to the scope of the present invention other than PAC, a predetermined amount of alkali such as NaOH is added to an aluminum salt having a basicity of 0%, or an acid such as HCl is added to a PAC having a high basicity. Can be manufactured.

The addition amount of the aluminum salt 5 is determined by the required fluorine concentration and phosphorus concentration of the treated water, and is preferably 0.2 to 3.0 in terms of P / Al mass ratio (P / Al ratio), preferably 0.5 to 1. 0 is more preferable. When the P / Al ratio is small, the amount of phosphorus outflow to the treated water decreases, but the fluorine treatment performance decreases. On the other hand, when the P / Al ratio is increased, the fluorine treatment performance is improved, but the amount of phosphorus outflow to the treated water increases and the amount of expensive phosphorus used increases.

In the reaction vessel C30, once generated fluoroapatite disappears. Since aluminum reacts with phosphoric acid to produce amorphous aluminum phosphate (AlPO ₄ ), it is considered that the aluminum ion dissolves when the phosphate ions in the fluoroapatite are extracted. Further, if aluminum is added in an amount equivalent to or more than that for forming aluminum phosphate, almost all of the fluoroapatite disappears, and a part of the aluminum also forms aluminum hydroxide.

By the way, aluminum phosphate itself has little ability to capture fluorine. Also, the fluorine scavenging ability of aluminum hydroxide is almost the same regardless of the basicity and type. In view of conventional technical common sense, it is not at all predictable that the fluorine treatment ability will be manifested in the state where the fluoroapatite with fluorine treatment ability disappears and aluminum phosphate without fluorine treatment ability is produced.

As a result of detailed examination of the reaction of fluorine with calcium, a phosphoric acid compound, and an aluminum salt, including the range that the conventional technical common sense does not reach, the present inventors surprisingly processed fluorine in the reaction tank C30. The reaction was found to proceed rapidly. That is, aluminum phosphate that originally has no fluorine capturing ability, and aluminum hydroxide that should hardly contribute to insolubilization of fluorine by interaction with calcium fluoride, after passing through the steps of reaction tank A10 and reaction tank B20, It was found that the processing ability of fluorine was expressed specifically.

In addition, although the sulfuric acid band and PAC originally have almost no difference in the fluorine trapping ability of the aluminum hydroxide to be produced, the aluminum to be added is surprisingly provided after the steps of the reaction tank A10 and the reaction tank B20. The inventors have found that the basicity of the salt is greatly influenced, and that the higher basicity is not necessarily better, and that there is an effective range, and the present invention has been completed.

The pH in the reaction vessel C30 is desirably adjusted to a range suitable for the production of aluminum phosphate and aluminum hydroxide, and specifically, it is desirably pH 5.5 to 8.

Next, the polymer flocculant 6 is added in the agglomeration tank 40, and the insoluble precipitate is agglomerated and the particles become coarse.

Next, the liquid mixture from the flocculation tank 40 is allowed to stand in the precipitation tank 50, so that it is separated into the supernatant water 7 and the sludge 8, and the supernatant water 7 becomes the treated water 9. The sludge 8 is pulled out from the bottom of the sedimentation tank 50 and is reduced in volume by performing a dehydration process or the like as necessary. In addition, as a solid-liquid separation mechanism, a membrane treatment apparatus can be used instead of the aggregation tank 40 and the precipitation tank 50.

First, aluminum salts having different basicities used in the experiment were prepared.
・ Sulfuric acid band: Aluminum sulfate for waterworks manufactured by Daimei Chemical Co., Ltd. Basicity 0%
-PAC: Taimei Chemical Industry Co., Ltd. Thailand Pack 53% basicity
-High basicity PAC: Taimei Chemical Industry Co., Ltd. Thai Pack 6010
61% basicity
-Ultra high basicity PAC: Alphain 83 manufactured by Daimei Chemical Co., Ltd.
83% basicity
-Basicity 20% sulfuric acid band: To a dilute solution of aluminum sulfate for water supply manufactured by Daimei Chemical Industry Co., Ltd., 0.6 times moles of NaOH is added, and pure water is added to make the aluminum concentration 1,000 mg / Adjusted to L.
・ Basicity 20% PAC: To a dilute solution of Taipak Chemical Co., Ltd. Taipack, HCl 1.0 times the molar amount of aluminum was added, and pure water was added to adjust the aluminum concentration to 1,000 mg / L. thing.

In the experiments of Examples and Comparative Examples, wastewater having a fluorine concentration of 1,100 mg / L generated from the process of recycling precious metal from waste was used. Table 1 shows the results of water quality analysis. Waste-derived substances are dissolved, the conductivity is very high, and substances other than the measured items are also contained at a high concentration.

(Comparative Example 1)
A beaker experiment based on the flow diagram of FIG. 1 was conducted. Slaked lime was added as calcium to 1,400 mg / L to the waste water, adjusted to pH 6.5 ± 0.5 with sulfuric acid, and stirred for 30 minutes. It filtered with 5A filter paper, the insoluble deposit was removed, the treated water was obtained, and the fluorine concentration of the treated water was measured.

(Comparative Example 2)
Compared to Comparative Example 1, except that 50 mg / L of sulfate band or PAC as aluminum was added as aluminum salt and stirred for 30 minutes while maintaining pH 6.5 ± 0.5 with NaOH. The same operation as Example 1 was performed and the fluorine concentration of treated water was measured.

(Comparative Example 3)
The same operation as Comparative Example 1 except that 40 mg / L of phosphoric acid as phosphorus was added immediately before the filtration in Comparative Example 1 and the mixture was stirred for 30 minutes while maintaining the pH at 6.5 ± 0.5 with NaOH. And the treated water fluorine concentration was measured. Moreover, the X-ray-diffraction measurement of the insoluble precipitate obtained by filtration was performed.

(Comparative Example 4)
Comparative Example 3 except that 50 mg / L of an aluminum salt sulfate band as an aluminum salt was added at the stage immediately before filtration in Comparative Example 3 and stirring was performed for 30 minutes while maintaining the pH at 6.5 ± 0.5 with NaOH. The same operation was performed, and the fluorine concentration of the treated water was measured.

Example 1
In Comparative Example 4, the same operation as in Comparative Example 4 was carried out except that basic basin 53% PAC was used instead of the sulfuric acid band, and the treated water fluorine concentration was measured. Moreover, the X-ray-diffraction measurement of the insoluble precipitate obtained by filtration was performed. Furthermore, immediately before the addition of phosphoric acid, immediately before the addition of PAC, and after adding PAC and adjusting the pH with NaOH, the liquid after 30 minutes is filtered through 5A filter paper to remove insoluble precipitates and dissolved. The concentrations of fluorine, phosphorous phosphorus and aluminum were measured.

(Comparative Example 5)
In Example 1, phosphoric acid was added simultaneously with the addition of slaked lime, and the same operation as in Example 1 was performed except that the pH was adjusted to 6.5 ± 0.5 with sulfuric acid and stirred for 30 minutes. Was measured.

(Comparative Example 6)
In Example 1, the addition of PAC was performed simultaneously with the addition of phosphoric acid, and the same operation as in Example 1 was performed except that the pH was adjusted to 6.5 ± 0.5 with NaOH and stirred for 30 minutes. Was measured.

(Comparative Example 7)
In Example 1, the same operation as in Example 1 was performed except that the addition order of phosphoric acid and PAC was reversed, and the fluorine concentration of treated water was measured.

Table 2 shows the treatment conditions of Example 1 and Comparative Examples 1 to 7 and the measurement results of the treated water fluorine concentration. Moreover, the X-ray-diffraction measurement result of the deposit (sludge) of Example 1 and Comparative Example 3 is shown in FIG. Further, Table 3 shows the dissolved fluorine, phosphate phosphorus, and aluminum concentrations measured in each reaction stage in Example 1. According to Table 2, the order of addition of chemicals is important for improving the fluorine treatment performance, and it is effective to add in the order of calcium → phosphoric acid → aluminum, and chemicals are added in this order. Even in this case, it can be seen that it is more effective to use PAC than aluminum sulfate as the aluminum salt.

2 and Table 3, in Example 1, after the addition of phosphoric acid, dissolved fluorine and a part of phosphoric acid produce fluoroapatite. Then, by addition of PAC, the fluoroapatite disappears and dissolved fluorine. It can be seen that the phosphate ion concentration is greatly reduced. Moreover, since the dissolved Al concentration does not change, it can be said that the total amount of added aluminum is insoluble. Nevertheless, the X-ray diffraction measurement of Example 1 did not have the crystalline fluoroapatite peak as seen in Comparative Example 3, but only the calcium fluoride peak was detected. Further, in Example 1, aluminum is added in an amount equal to or greater than the equivalent of aluminum phosphate production, that is, 0.8 with a P / Al (mass ratio) of 0.87 or less. From the above, it can be seen that after the disappearance of fluoroapatite, a mixture of aluminum phosphate, which is an amorphous substance, and aluminum hydroxide is formed, and simultaneously dissolved fluorine is insolubilized.

(Example 2)
In Example 1, the same operation as in Example 1 was performed except that the addition ratio of phosphoric acid and PAC was fixed at P / Al = 0.8 (mass ratio), and the addition amount was increased or decreased. It was measured.

(Example 3)
In Example 2, the same operation as Example 2 was performed except that disodium hydrogen phosphate was used instead of phosphoric acid, and the treated water fluorine concentration was measured. Even when disodium hydrogenphosphate was added, the pH hardly changed and the pH was in the range of 6.5 ± 0.5 for 30 minutes, so NaOH was not added.

The measurement result of the treated water fluorine concentration of Examples 2 and 3 is shown in FIG. As in the aluminum method applied in advanced treatment, the treatment water fluorine concentration tends to decrease as the addition amount of phosphoric acid and PAC increases.

(Comparative Example 8)
An experiment for confirming whether there is a difference between the sulfuric acid band and the PAC regarding the ability of aluminum hydroxide to capture dissolved fluorine was performed. That is, a sodium fluoride reagent was dissolved in pure water, and 20-80 mg / L of sulfuric acid band or PAC as aluminum was added to simulated waste water adjusted to 14 mg / L, which was the same as the fluorine concentration of treated water in Comparative Example 1. The pH was adjusted to 6.5 ± 0.5 with NaOH and stirred for 30 minutes. It filtered with 5A filter paper, the insoluble deposit was removed, the treated water was obtained, and the fluorine concentration of the treated water was measured.

(Comparative Example 9)
An experiment was conducted to confirm the trapping ability of dissolved fluorine possessed by a mixture of aluminum phosphate and aluminum hydroxide. That is, using the simulated waste water of Comparative Example 8, the addition amount ratio of phosphoric acid and PAC was changed by fixing the addition amount ratio of phosphoric acid and PAC at P / Al = 0.8 (mass ratio). After adjusting the pH to 6.5 ± 0.5 with NaOH and stirring for 30 minutes, it was filtered with 5A filter paper to remove insoluble precipitates to obtain treated water, and the treated water fluorine concentration was measured.

The treated water fluorine concentration of Comparative Examples 8 and 9 is shown in FIG. From the results of Comparative Example 8, it can be seen that the fluorine treatment effect produced by the aluminum salt producing aluminum hydroxide has almost no difference between sulfate bands and PACs having different basicities. Further, from the results of Comparative Example 9, it can be recognized that aluminum phosphate itself has a very low ability to capture fluorine because the treatment effect of fluorine is greatly reduced when aluminum phosphate coexists.

Example 4
The same operation as in Example 1 was performed except that aluminum salts having various basicities were used as the aluminum salt, and the fluorine concentration of the treated water was measured. The results are shown in Table 4 together with the results of Example 1 and Comparative Example 4. FIG. 5 is a graph showing the relationship between basicity and treated water fluorine concentration.

According to Table 4, in the aluminum salt whose basicity is adjusted to 20%, there is no difference in the fluorine treatment property between the sulfuric acid band and the PAC. Therefore, the fluorine treatment performance is not influenced by the coexisting components other than aluminum but the basicity. It can be seen that it is greatly affected. Further, FIG. 5 shows that when the basicity is in the range of about 20% to 80%, it is possible to treat to a fluorine concentration of 5 mg / L or less, which is well below the drainage standard of 8 mg / L.

(Example 5)
In Example 1, the same operation as in Example 1 was performed except that the pH after addition of phosphoric acid was set to 3 to 9, and the fluorine concentration in the treated water was measured.

(Example 6)
In Example 1, the same operation as in Example 1 was performed except that the pH after addition of PAC was set to 4.5 to 9, and the treated water fluorine concentration was measured.

The results of Examples 5 and 6 are shown in FIG. It can be seen that it is effective to adjust the pH after addition of phosphoric acid to 4.5-8 and the pH after addition of PAC to 5.5-8.

1 Fluorine-containing wastewater 2 Calcium 3 pH adjuster 4 Drug containing phosphate compound 5 Aluminum salt with basicity 20% to 80% 6 Polymer flocculant 7 Supernatant water 8. 8. Sludge Treated water 10. Reaction tank A
20. Reaction tank B
30. Reaction tank C
40. Coagulation tank 50. Sedimentation tank

Claims

In the method for treating fluorine-containing wastewater, in which calcium is added to fluorine-containing wastewater and the liquid in the wastewater is solid-liquid separated as calcium fluoride insolubilized material
Fluorine-containing, characterized in that calcium is added to the waste water, a chemical containing a phosphoric acid compound is added without separating insoluble precipitates formed, and then an aluminum salt having a basicity of 20 to 80% is added Wastewater treatment method.
The method for treating fluorine-containing wastewater according to claim 1, wherein the pH after addition of the phosphoric acid compound is 4 to 9, and the pH after addition of the aluminum salt is 5.5 to 8.
The method for treating fluorine-containing wastewater according to claim 1 or 2, wherein the phosphoric acid compound is added in an amount of 1 to 5 times the amount of dissolved fluorine after adding calcium in the wastewater as phosphorus.
The method for treating fluorine-containing wastewater according to claim 3, wherein the aluminum salt is added in a P / Al mass ratio of 0.2 to 3.0 with respect to the added phosphate compound.
The method for treating fluorine-containing wastewater according to claim 4, wherein the aluminum salt is added in a P / Al mass ratio of 0.2 to 0.8 with respect to the added phosphate compound.
6. The method for treating fluorine-containing wastewater according to claim 5, wherein the solid-liquid separated sludge does not have a crystalline fluoroapatite peak in X-ray diffraction.
A reaction tank A in which a calcium compound is allowed to act on fluorine-containing wastewater;
A reaction vessel B in which a phosphate compound is allowed to act on the treatment liquid from the reaction vessel A;
A reaction vessel C in which an aluminum salt having a basicity of 20 to 80% is allowed to act on the treatment liquid from the reaction vessel B;
A mechanism for solid-liquid separation of the processing liquid from the reaction vessel C;
An apparatus for treating fluorine-containing wastewater.
The solid-liquid separation mechanism includes a coagulation tank that performs aggregation by adding a polymer flocculant to the processing liquid from the reaction tank C, and a solid-liquid separation tank that performs solid-liquid separation of the mixed liquid from the aggregation tank. The processing apparatus of the fluorine-containing waste water of Claim 7 containing this.