JP4525601B2 - Treatment method for fluorine-containing wastewater - Google Patents

Description

  The present invention relates to a method for stably and efficiently treating fluorine-containing wastewater in which aluminum coexists with a calcium fluoride method.

  Fluorine-containing wastewater discharged from the silicon wafer manufacturing process in semiconductor parts manufacturing, pickling wastewater discharged from the stainless steel plate manufacturing process, aluminum building material processing factory wastewater, aluminum surface treatment wastewater, hydrofluoric acid manufacturing wastewater, fertilizer manufacturing wastewater, waste incineration Fluorine-containing wastewater such as wastewater needs to be discharged after fluorine removal treatment is performed to satisfy the wastewater standards. Regarding fluorine-containing wastewater, the development of treatment technology that can further reduce the fluorine concentration of treated water is expected as the wastewater standard was strengthened from 15 mg / L to 8 mg / L in 2001. It is rare.

  Conventionally, calcium fluoride method and hydroxide coprecipitation method as advanced treatment are known as treatment methods for fluorine-containing wastewater. After treatment with calcium fluoride method in the first stage, the second stage In addition, a two-stage treatment method in which advanced treatment is performed by a hydroxide coprecipitation method is also known (Non Patent Literature 1). That is, in the calcium fluoride method, the fluorine concentration of the treated water cannot be reduced below the solubility of calcium fluoride, and the waste water standard cannot be satisfied, so such a two-stage treatment is adopted.

In the calcium fluoride method, after adding a calcium compound to raw water (fluorine-containing wastewater), a neutralizing agent is added to adjust the pH to near neutral, and an insoluble salt of calcium fluoride is generated by the reaction between fluorine and calcium. In this method, a polymer flocculant is added and agglomeration treatment is performed, followed by solid-liquid separation. In this method, slaked lime (Ca (OH) ₂ ) is generally used as the calcium compound, but calcium chloride (CaCl ₂ ) and alkali (sodium hydroxide (NaOH)) may be used in combination. As the neutralizing agent, inexpensive sulfuric acid is usually used, but hydrochloric acid may be used or both may be used in combination. Further, the treatment pH is usually around pH 8 to neutrality from the viewpoint of discharge standard or secondary treatment.

The hydroxide coprecipitation method uses a coprecipitation action when aluminum is precipitated as aluminum hydroxide, and is generally used for advanced treatment. In this method, polyaluminum chloride (PAC) or aluminum sulfate (sulfuric acid band) is added to raw water, then neutralized with a neutralizing agent, a polymer flocculant is added for aggregation treatment, and then solid-liquid separation is performed.
“Pollution Prevention Technology and Regulations” pp. 288-289

  When adopting the above-mentioned two-stage treatment method, if the amount of aluminum salt such as sulfuric acid band added in the second-stage hydroxide coprecipitation method is large, the sludge treatment is caused not only by the chemical cost but also by the amount of generated sludge. Since the cost is high, it is desirable to sufficiently reduce the concentration of treated water fluorine in the first-stage calcium fluoride method and to reduce the amount of aluminum salt added in the second-stage hydroxide coprecipitation method.

  However, since the fluorine concentration in the first-stage treated water is unstable in the conventional two-stage treatment method, the treatment by the second-stage hydroxide coprecipitation method is an aluminum that can cope with the maximum fluctuation value. Since the addition amount of the salt was set, the addition amount of the aluminum salt could not be reduced.

  As a result of examining the cause of the variation in the fluorine concentration of the first-stage treated water, the present inventors have found that the main cause is the aluminum salt in the raw water.

  That is, in the treatment process after the two-stage treatment of fluorine-containing wastewater, a filtration process is usually provided after the precipitation process, but wastewater discharged by backwashing of the filtration process is sent to the raw water tank. And treated with raw water. The sludge dehydrated filtrate generated here is also fed to the raw water tank and treated together with the raw water. These backwash wastewater and sludge dehydrated filtrate naturally contain an aluminum salt derived from the sulfate band added in this step. And by supplying these to a raw | natural water tank, about several to several dozen mg / L of aluminum salt will coexist in the raw | natural water used for the process by a calcium fluoride method.

  The aluminum salt has an ability to adsorb fluorine, but an aluminum salt mixed at a low concentration of several to several tens mg / L in raw water deteriorates the treatment efficiency in the fluorine treatment by the calcium fluoride method. In particular, the treatment characteristics deteriorated rapidly at pH 6 to 8, and as a result, the fluorine concentration of the treated water obtained by the treatment by the first-stage calcium fluoride method was high.

  In order to confirm the influence of the aluminum salt, the present inventors conducted verification of Experimental Example 1 described later. From Table 2 below showing the results of Experimental Example 1, it is apparent that the treatment characteristics are greatly deteriorated when aluminum is mixed into the raw water.

Therefore, in order to further confirm the influence of aluminum, the present inventors performed Experimental Example 2 described later for examining the fluorine concentration and aluminum concentration of treated water when the aluminum concentration in the fluorine-containing wastewater was changed. From Table 3 below showing the results of Experimental Example 2, both the fluorine concentration and the aluminum concentration of the treated water increase with the increase of the aluminum concentration of the raw water. It was speculated that calcium fluoride would be solubilized. That is, when a calcium compound is added to raw water in which fluorine and aluminum coexist, an aluminum fluoride complex (AlF _x- ^(3-x) (where x> 3 ^{) is} caused by the reaction between aluminum and fluorine under acidic conditions of pH 3 or lower. )) Is known (reaction formula (1) below), but under pH neutral conditions, precipitation of calcium fluoride (CaF ₂ ) and this aluminum fluoride complex react to form CaF ₂ . It is presumed that when a part is colloided and dispersed, fluorine cannot be sufficiently removed as CaF ₂ (the following reaction formula (2)).
[Acid]
Al ³⁺ + xF ⁻ → AlF _x ^{− (3-x)} (1)
[neutral]
nCaF ₂ (precipitation) + AlF _x- ^(3-x) → (CaF ₂ ) _n · AlF _x- ^(3-x) (dispersion to dissolution)
... (2)

Therefore, the present invention solves the problem of solubilization of CaF ₂ when treating fluorine-containing wastewater in which aluminum coexists by the calcium fluoride method, and stably treats such fluorine-containing wastewater stably. It aims at providing the method of obtaining the treated water from which the fluorine was fully removed.

  In the present invention, as a source of aluminum salt coexisting in fluorine-containing wastewater, in the two-stage treatment method, as described above, the backwash wastewater generated in the filtration step after the two-stage treatment or the generated sludge Examples include dehydrated filtrate. Also in the case of the one-stage calcium fluoride method, wastewater containing aluminum salt generated in other systems (backwash water for filters in water treatment using aluminum salt, dewatered filtrate of the coagulated sludge, aluminum salt As a result of the supply of the ion exchange resin regeneration wastewater containing etc.) to the raw water tank according to the present invention, it becomes a fluorine-containing wastewater in which the aluminum salt coexists, and is the subject of the present invention.

  The method for treating fluorine-containing wastewater according to the present invention (Claim 1) is the method of treating aluminum-containing fluorine by adding calcium ions to fluorine-containing wastewater in which aluminum coexists, and solid-liquid separation of the fluorine in the wastewater as calcium fluoride insolubles. In the wastewater treatment method, calcium ions are added to the wastewater, and phosphate ions are added so that P / Al (molar ratio) is 1 or more with respect to the coexisting aluminum, and the pH is 3.5 to 5.5. Below, it is characterized by solid-liquid separation of the insolubilized product produced.

  The method for treating fluorine-containing wastewater according to claim 2 is characterized in that, in claim 1, phosphate ions are added so that P / Al (molar ratio) is 1 to 3 with respect to the coexisting aluminum.

  The method for treating fluorine-containing wastewater according to claim 3 is characterized in that a part of the solid-liquid separated insolubilized material is added to the aluminum coexisting fluorine-containing wastewater according to claim 1 or 2.

  The method for treating fluorine-containing wastewater according to claim 4 is characterized in that, in claim 3, a part of the solid-liquid separated insolubilized material and the calcium ions are mixed and added to the aluminum coexisting fluorine-containing wastewater. To do.

  According to the present invention, fluorine-containing wastewater in which aluminum coexists can be treated stably and efficiently by adding a predetermined amount of phosphate ions to raw water.

  In other words, the inventors of the present invention have a poor treatment characteristic when treating fluorine-containing wastewater in which aluminum coexists with the calcium fluoride method because the aluminum fluoride complex produced by the reaction of fluorine and aluminum in raw water is fluorinated. Since it is presumed to be due to the solubilization by reacting with calcium, it was presumed that the solubilization of calcium fluoride does not occur if the aluminum fluoride complex which is an inhibitory factor is decomposed.

  Therefore, as a result of earnestly examining the means for decomposing the aluminum fluoride complex and the treatment pH in a wide range of pH 2 to 12 including pH conditions that are not adopted in general wastewater treatment, the addition of phosphoric acid is effective. In addition, the present inventors have found that the proper pH is in a narrow range of 3.5 to 5.5 as is apparent from the results of Experimental Example 3 described later, and completed the present invention.

That is, according to the present invention, the phosphate ion added to the raw water reacts with the aluminum fluoride complex by the following reaction to decompose it, and generates an insolubilized product of calcium fluoride and aluminum phosphate. The fluoride ions released from the aluminum fluoride complex further react with the coexisting calcium and are removed as calcium fluoride.
(CaF ₂ ) _n · AlF _x- ^(3-x) + PO ₄ ^3- → nCaF ₂ (precipitation) + AlPO ₄ (precipitation) + xF ⁻
... (3)

  In the present invention, the amount of phosphate ion added is preferably an amount such that P / Al (molar ratio) in water is in the range of 1 to 3, as is apparent from the results of Experimental Example 3 described later. If phosphate ions already exist in the water, the deficiency may be added. As phosphate ions, normal phosphoric acid or water-soluble phosphates such as sodium salts and potassium salts thereof can be used. However, if phosphate ions are included, alkaline degreasing waste liquid, plating waste liquid, pickling A waste liquid such as a waste liquid may be used.

  In the present invention, it is preferable that the calcium fluoride-containing sludge separated into solid and liquid is returned to the reaction step and added to the raw water, and in particular, the calcium compound added to the raw water is mixed with the returned sludge in advance. (Hereinafter, the sludge mixed with the calcium compound may be referred to as “modified sludge”), and it is preferable to add this modified sludge to the raw water. As a result, the quality of the treated water can be further improved by the crystallization effect of the modified sludge, the amount of sludge generated can be reduced, and the dewaterability of the generated sludge can be improved.

  Embodiments of a method for treating fluorine-containing wastewater according to the present invention will be described below in detail with reference to the drawings.

  FIGS. 1A and 1B are system diagrams showing an embodiment of a method for treating fluorine-containing wastewater according to the present invention.

  In FIG. 1 (a), after adding a predetermined amount of phosphate ions and acid to the raw water from the raw water tank 1 (fluorine-containing wastewater in which aluminum salt coexists), it is introduced into the reaction tank 2, and this reaction tank After adding a calcium compound in 2 and adjusting the pH to 3.5 to 5.5, an insoluble salt of calcium fluoride is generated by the reaction of fluorine and calcium, and then introduced into the pH adjusting tank 3 to adjust the pH. (Acid or alkali) is added to adjust the pH finely. The effluent from the pH adjusting tank 3 is introduced into a coagulating tank 4 and a polymer coagulant is added for coagulation treatment, followed by solid-liquid separation in a precipitation tank 5. When calcium chloride is used as the calcium compound, an alkaline agent is simultaneously added to the reaction tank 2 as a pH adjuster to adjust the pH to 3.5 to 5.5.

  Phosphate ions are added so that P / Al (molar ratio) is 1 or more, preferably 1 to 3 with respect to aluminum in the raw water. If the amount of phosphate ion added is less than this lower limit, the aluminum fluoride complex will not be sufficiently decomposed, resulting in solubilization of calcium fluoride due to the aluminum fluoride complex remaining, resulting in an increase in the fluorine concentration in the treated water . Since an effect commensurate with the addition amount cannot be obtained even if the addition amount of phosphate ion is excessively large, the amount is preferably such that P / Al (molar ratio) is 3 or less.

The acid added at the inlet side of the reaction tank 2 is for securing calcium necessary for the production of calcium fluoride to completely precipitate calcium fluoride, and it varies depending on the pH of the raw water and the fluorine concentration. When sulfuric acid (H ₂ SO ₄ ) is added in an amount of about 200 to 500 mg / L and the necessary calcium cannot be secured with this amount, hydrochloric acid or nitric acid may be used in combination.

Although there is no restriction | limiting in particular as a calcium compound added to raw | natural water in the reaction tank 2, Usually, slaked lime (Ca (OH) ₂ ) is used. However, it is not limited to slaked lime at all, and calcium chloride may be used. However, when calcium chloride is used, an alkali for pH adjustment is additionally used. These calcium compounds may be used individually by 1 type, and may use 2 or more types together.

  If the adjusted pH value in the reaction tank 2 is outside the above range, sufficient fluorine insolubilization treatment cannot be performed, and the treatment characteristics deteriorate.

  As the pH adjuster, mineral acids such as sulfuric acid and hydrochloric acid, preferably sulfuric acid or alkali such as sodium hydroxide (NaOH) are used. The adjusted pH value in the pH adjusting tank 3 is set to pH 3.5 to 5.5 as described above.

  As the polymer flocculant to be adjusted in the flocculation tank 4, one or more of polyacrylamide partial hydrolyzate, sodium polyacrylate, polyvinylamidine and the like can be used. Although it varies depending on the water quality and the polymer flocculant used, it is usually about 0.1 to 5 mg / L.

  For the solid-liquid separation of the aggregating treatment liquid, a membrane separation device or the like can be used in addition to the precipitation tank 5.

  In FIG. 1B, a sludge reforming tank 6 is further provided in the apparatus of FIG. 1A, and a part of the sludge separated into solid and liquid in the sedimentation tank 5 is introduced into the sludge reforming tank 6 as a return sludge. In this sludge reforming tank 6, the calcium compound to be added to the raw water is added to and mixed with the returned sludge to reform the sludge, and this modified sludge is added to the reaction tank 2 to adjust the raw water to pH 3.5-5. The other processing is performed in the same manner.

  In this way, by returning a part of the separated sludge to the raw water side, the seed crystal effect of the returned sludge can improve the sludge crystallinity, lower the water content, and improve the sedimentation. As shown in FIG. 1B, the return sludge is mixed with a calcium compound such as slaked lime, and the mixture is added to the raw water, so that the quality of treated water can be further improved and the amount of sludge generated can be reduced.

In addition, if the amount of returned sludge in this case is too small, the above-mentioned effect by performing sludge return cannot be sufficiently obtained, and if it is too large, the load on the settling tank increases, so that the amount of returned sludge is newly generated. It is preferable to be about 20 to 60 times the amount of sludge. Here, the newly generated sludge is the amount of sludge generated in the reaction tank 2. For example, if the amount of CaF ₂ generated in the reaction tank 2 is 100 mg / L, the SS of the reaction tank 2 is about 2000 to 6000 mg. It is preferable to perform sludge return so that the sludge return ratio R described later is preferably 30 to 50 so as to be / L.

  FIG. 1 shows an example of an embodiment of a method for treating fluorine-containing wastewater of the present invention, and the present invention is not limited to the illustrated method as long as the gist thereof is not exceeded.

  For example, a treatment tank for adding phosphate ions may be provided separately, and when the treatment pH of the reaction tank is stable, the pH adjustment tank may be omitted.

In FIG. 1, phosphate ions are added on the inlet side of the reaction vessel for decomposition of the aluminum fluoride complex as shown in the above formula (3), but the addition order of phosphate ions and calcium compounds. When Ca (OH) ₂ is used as a calcium compound, adding phosphate ion simultaneously adds phosphate ion as shown in FIG. 1 because it becomes Ca ₃ (PO ₄ ) ₂ and is inactivated. After that, it is preferable to add Ca (OH) ₂ . However, when calcium chloride is used as the calcium compound, it can be added simultaneously with phosphate ions.

  The treated water obtained by the treatment by the calcium fluoride method using such phosphate ions is preferably further subjected to the treatment by the hydroxide coprecipitation method and discharged after the fluorine concentration is further reduced.

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

[Experimental example]
Experimental example 1
The presence or absence of coexisting aluminum salts and the effect of pH in the treatment of fluorine-containing wastewater were investigated.
After adding Ca (OH) ₂ to water quality synthetic wastewaters I and II shown in Table 1 below and adjusting the pH to each pH value shown in Table 2 and reacting for 30 minutes, filter paper no. The fluorine concentration of the filtrate (treated water) filtered in 5 was examined, and the results are shown in Table 2.

  From Table 2, it can be seen that when the aluminum salt coexists in the fluorine-containing wastewater, the treatment characteristics are greatly deteriorated at pH 5-8.

Experimental example 2
The effect of the amount of coexisting aluminum salt on the treatment of fluorine-containing wastewater on the quality of treated water was investigated.
The water obtained by adding a sulfuric acid band as an aluminum salt to the synthetic waste water I in Experimental Example 1 so as to have various aluminum concentrations is used as raw water, and the calcium fluoride method optimum pH value of 6.1 to 6.3 which is a conventional experience value is used. After adding Ca (OH) ₂ and reacting for 30 minutes, the filter paper no. The filtrate (treated water) filtered in 5 was examined for fluorine concentration and aluminum concentration, and the results are shown in Table 3.

  From Table 3, it is estimated that calcium fluoride is solubilized by the coexistence of aluminum because the fluorine concentration and the aluminum concentration of the treated water increase as the amount of coexisting aluminum in the fluorine-containing wastewater increases.

Experimental example 3
The effects of the amount of normal phosphoric acid added and the treatment pH in the treatment of fluorine-containing wastewater containing aluminum were investigated.
To synthetic waste water I in Experimental Example 1, a sulfuric acid band as aluminum is added so as to have an Al concentration of 4 mg / L, and normal phosphoric acid is added so as to have each concentration shown in Table 4, and P / Al of raw water is added. Using water having a value shown in Table 4 as the molar ratio as raw water, Ca (OH) ₂ was added so as to have the pH shown in Table 4 and reacted for 30 minutes. The filtrate (treated water) filtered in 5 was examined for fluorine concentration, aluminum concentration and phosphorus concentration, and the results are shown in Table 4.

  From Table 4, the amount of regular phosphoric acid added is such that P / Al (molar ratio) of raw water is 1 or more, that is, the theoretical amount or more, and P / Al (molar ratio) 1 to 3 has no significant difference in treatment effect. From this, it is understood that the preferred range is 1 to 3, and the treatment pH is preferably in the range of 3.5 to 5.5.

  In addition, when the state of the insolubilized material produced in this Experimental Example 3 was observed, white gel-like flocs, such as aluminum hydroxide flocs, were produced under the condition of pH 6 or higher. It was a translucent particulate matter and judged to be crystalline. Therefore, it was estimated that acceleration of precipitation of crystalline salt by the sludge return method was effective.

[Examples and Comparative Examples]
In the following examples and comparative examples, the apparatus shown in FIGS. 1A and 1B was used. The capacity of each tank of this apparatus was as follows, and the raw water treatment amount was 2 L / hr.
Raw water tank: 100L
Reaction tank: 0.8L
pH adjustment tank: 0.8L
Coagulation tank: 0.8L
Settling tank: 10L
Sludge reforming tank: 0.1L

Examples 1-3
The semiconductor drainage with pH: 2.7, fluorine: 180 mg / L, aluminum: 7.5 mg / L, ammoniacal nitrogen: 27 mg / L, sulfate ion: 10 mg / L, nitrate nitrogen: 58 mg / L is used as raw water. The treatment was performed according to the method shown in 1 (a). First, after adding 300 mg / L of H ₂ SO ₄ and 12 mg / L of normal phosphoric acid as PO ₄ -P into the baffle plate at the inlet of the reaction tank 2 to the raw water, Ca (OH) ₂ is added in the reaction tank 2 Then, the pH shown in Table 5 is adjusted, and then the pH adjusting agent is added in the pH adjusting tank 3 to finely adjust the pH. Thereafter, the anionic polymer flocculant (Kurita Industry Co., Ltd.) After adding 2 mg / L of “PA331” manufactured by the manufacturer, solid-liquid separation was performed in the precipitation tank 5.

The pH adjustment in the pH adjustment tank 3 is a fine adjustment of the pH, and an acid (H ₂ SO ₄ ) or an alkali (NaOH) was added as necessary to achieve the pH shown in Table 5.
The fluorine concentration of the obtained treated water (separated water in the precipitation tank 5) was examined, and the results are shown in Table 5.

Examples 4 and 5
In Example 1, as shown in FIG. 1B, the sludge (sludge concentration 80 g / L) in the sedimentation tank 5 is 0.4 L / hr in the sludge reforming tank 6 so that the sludge return ratio (R) is 40. In the same way, except that the modified sludge mixed with Ca (OH) ₂ is added to the reaction tank 2 so that the pH of the reaction tank 2 becomes the value shown in Table 5, The fluorine concentration of each treated water was examined, and the results are shown in Table 5.

  In any case, the generated SS amount in the reaction tank 2 is 400 mg / L, and the sludge return ratio indicates the ratio of the returned sludge amount to the generated SS 400 mg / L. The return ratio (R) is expressed as follows. In this embodiment, the sludge return amount of the sedimentation tank 5 is set to 0. 0 so that the return ratio (R) becomes (80 g / L × 0.4 L / hr) / (0.4 g / L × 2 L / hr) = 40. 4 L / hr was set.

Example 6
In Example 4, the treatment was performed in the same manner except that the sludge in the sedimentation tank 5 was fed directly to the reaction tank 2 instead of the sludge reforming tank 6, and the fluorine concentration of the treated water was similarly examined. It was shown to.

Comparative Examples 1 and 2
In Example 1, the treatment was conducted in the same manner except that the adjusted pH value in the reaction tank 2 was changed to the value shown in Table 5, and the fluorine concentration of the treated water was examined. The results are shown in Table 5.

Comparative Examples 3 and 4
In Example 1, normal phosphoric acid was not added, and the treatment was conducted in the same manner except that the adjusted pH value in the reaction tank 2 was changed to the value shown in Table 5, and the fluorine concentration of the treated water was examined. Indicated.

Comparative Example 5
In Comparative Example 1, the same treatment as in Example 4 was performed except that sludge was fed to the sludge reforming tank 6 and the modified sludge was added to the reaction tank 2, and the fluorine of each treated water was similarly treated. The concentration was examined and the results are shown in Table 5.

From Table 5, the following is clear.
That is, in the fluorine-containing wastewater in which aluminum coexists, the treatment by the conventional calcium fluoride method cannot sufficiently remove fluorine, but by adding normal phosphoric acid and carrying out the treatment at a predetermined pH, Can be removed to a high degree.

  In particular, in this case, a better treatment result can be obtained by returning the separated sludge and adding it to the raw water. In this case, it is preferable to mix the calcium compound with the returned sludge and add it as a modified sludge, but a sufficient effect is recognized by simply circulating the sludge.

  Thus, the sludge density | concentration in the case of returning sludge was 80 g / L, and the sludge density | concentration in the case of not performing sludge return was 30-40 g / L. When these sludges were dehydrated, the moisture content of the dehydrated cake when the sludge was returned was 48%, and the moisture content of the dehydrated cake when the sludge was not returned was 69%. It was confirmed that the generation amount was significantly reduced (about 40%).

  Such a fluorine-containing wastewater treatment method of the present invention includes fluorine-containing wastewater discharged from a silicon wafer manufacturing process in semiconductor component manufacturing, pickling wastewater discharged from a stainless steel plate manufacturing process, aluminum building material processing factory wastewater, aluminum surface It is effective for treating various fluorine-containing wastewater such as treated wastewater, hydrofluoric acid production wastewater, fertilizer production wastewater, and waste incineration wastewater. In particular, in the treatment by the two-stage treatment method in which the treatment by the hydroxide co-precipitation method as the advanced treatment is performed after the calcium fluoride method, use of an aluminum salt required for the treatment by the latter-stage hydroxide co-precipitation method The drastic reduction of the amount can reduce the processing cost and the amount of sludge generation, which is extremely advantageous industrially.

It is a systematic diagram which shows embodiment of the processing method of the fluorine-containing waste_water | drain of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Reaction tank 3 pH adjustment tank 4 Coagulation tank 5 Precipitation tank 6 Sludge reforming tank

Claims (4)

In the method of treating aluminum coexisting fluorine-containing wastewater in which calcium ions are added to fluorine-containing wastewater in which aluminum coexists and the fluorine in the wastewater is solid-liquid separated as calcium fluoride insoluble matter,
While adding calcium ions to the waste water, phosphate ions are added so that P / Al (molar ratio) is 1 or more with respect to the coexisting aluminum,
A method for treating fluorine-containing wastewater, comprising solid-liquid separating an insolubilized product produced under conditions of pH 3.5 to 5.5.   2. The method for treating fluorine-containing wastewater according to claim 1, wherein phosphate ions are added so as to have a P / Al (molar ratio) of 1 to 3 with respect to the coexisting aluminum.   3. The method for treating fluorine-containing wastewater according to claim 1 or 2, wherein a part of the insolubilized material separated by solid-liquid separation is added to the aluminum coexisting fluorine-containing wastewater.   4. The method for treating fluorine-containing wastewater according to claim 3, wherein a part of the solid-liquid separated insolubilized material and the calcium ions are mixed and added to the aluminum coexisting fluorine-containing wastewater.

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