JP2005193167A - Drainage purification method and purification method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drainage purification method by which treated water of very low fluorine concentration can be obtained by removing fluorine contained in fluorin-containing drainage to the utmost without necessitating a large quantity of a calcium compound such as calcium chloride and calcium hydroxide or a flocculant and discharging a large quantity of sludge. <P>SOLUTION: This drainage purification method comprises the steps of: adding the calcium compound to the fluorine-containing drainage to produce calcium fluoride; subjecting a calcium fluoride-containing reaction product to solid-liquid separation such as a flocculating/settling method to remove the calcium fluoride; adjusting the pH of the calcium fluoride-removed treated water; adding hydrotalcite to the pH-adjusted treated water to adsorb remaining fluorine on hydrotalcite (called a fluorine adsorption step); subjecting the treated water containing fluorine-adsorbed hydrotalcite to solid-liquid separation such as the flocculating/settling method to remove the fluorine-adsorbed hydrotalcite; desorbing fluorine from the fluorine-adsorbed hydrotalcite (called a fluorine desorption step); adding the fluorine-desorbed hydrotalcite again at the fluorine adsorption step and; mixing the fluorine-containing drainage before calcium fluoride is produced with the fluorine-containing water produced at the fluorine desorption step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wastewater purification method and a purification method for removing fluorine from fluorine-containing wastewater drained from, for example, a semiconductor factory or power plant.

  For example, as a technology for removing fluorine from fluorine-containing wastewater discharged from semiconductor factories, power plants, etc., there is a method in which calcium fluoride is reacted with fluorine to produce calcium fluoride, and agglomerates and precipitates. Yes. For example, the pH is adjusted by adding a pH adjusting agent to acidic wastewater containing fluorine, and the pH-adjusted wastewater is sent to the reaction tank, and calcium hydroxide or calcium chloride is added in the reaction tank to fluorinate. Produces calcium. After that, the reaction liquid having calcium fluoride is sent to the coagulation tank, the coagulant is added to coagulate the calcium fluoride, and the sludge containing calcium fluoride coagulated in the precipitation tank is precipitated and removed. It is.

  Moreover, there is Patent Document 1 as a known document related to a technique for removing fluorine from fluorine-containing wastewater. Patent Document 1 describes a treatment method for removing fluorine in waste water using calcium chloride. Before adding the calcium chloride solution to the waste water, the total amount or a partial pH of the calcium chloride solution is set to 11 in advance. It is disclosed that the amount is adjusted to 5 or more and the solution is reacted with waste water, so that the amount of calcium chloride used can be reduced or a large amount of flocculant can be avoided.

JP-A-7-214072

  By the way, when calcium fluoride is generated by reaction of the above calcium chloride and the like and fluorine and sludge containing calcium fluoride is removed, in order to remove fluorine so as to be treated water of a high level or less, Calcium compounds such as calcium chloride and calcium hydroxide are required in large quantities. In addition, a large amount of flocculant is required to collect by coagulation sedimentation, and the amount of sludge discharged is extremely large. It is practically difficult to remove fluorine so that it becomes treated water below a high level reference value. Therefore, there has been a strong demand for a technique that can remove fluorine from wastewater to a high level without having such problems.

  The present invention is proposed in view of the above-mentioned problems, and does not require a large amount of calcium compound such as calcium chloride or calcium hydroxide or a flocculant, and does not discharge a large amount of sludge. An object of the present invention is to provide a method for purifying wastewater that can remove the fluorine at a high level and make treated water with a very low fluorine concentration. Another object of the present invention is to provide a wastewater purification method and a purification method that can regenerate and efficiently use hydrotalcites and can perform advanced fluorine purification at low cost.

  The wastewater purification method of the present invention includes a step of adjusting pH to fluorine-containing wastewater as needed, adding a calcium compound to produce calcium fluoride, and solid-liquid separation of the reaction solution after the calcium fluoride is produced Removing calcium fluoride, adjusting the pH of the treated water after removing calcium fluoride, adding hydrotalcite to adsorb fluorine remaining in hydrotalcite, and the adsorption And a process of removing hydrotalcite after adsorption of fluorine by solid-liquid separation of the subsequent treated water.

  In the present invention, solid-liquid separation in the case where calcium fluoride and hydrotalcite after adsorption of fluorine are removed by solid-liquid separation, for example, a flocculant is added to coagulate and precipitate the solid phase, or It is appropriate to recover the solid phase by flotation separation by air bubbling, or recover the solid phase by membrane filtration using a filter or the like, and the calcium compound is preferably calcium chloride or calcium hydroxide, Any material can be used as long as it can react with fluorine to produce calcium fluoride, and may be calcium carbonate, for example. In addition, the pH of the treated water or the like when fluorine is adsorbed to hydrotalcites is preferably 4 to 10, more preferably 5 to 7.

  Furthermore, the waste water purification method of the present invention comprises a step of subjecting the removed hydrotalcite after fluorine adsorption to a fluorine desorption treatment, and the hydrotalcite after fluorine desorption treatment is again performed in the fluorine adsorption step. And a step of adding fluorine-containing water produced by the fluorine desorption treatment to the fluorine-containing wastewater before the calcium fluoride is produced.

  Furthermore, in the wastewater purification method of the present invention, the fluorine desorption treatment step performs the fluorine desorption treatment by stirring the hydrotalcite after fluorine adsorption in a solution having a pH of 9 <pH <11. Preferably, the pH of the solution to be subjected to the fluorine desorption treatment is preferably about 10.

  In addition, the wastewater purification method of the present invention includes a step of adjusting the pH of fluorine-containing wastewater as necessary, adding a calcium compound to produce calcium fluoride, and hydrolyzing the reaction liquid after the calcium fluoride is produced. A step of adding talcite to adsorb fluorine remaining in hydrotalcite; a step of solid-liquid separation of the reaction liquid after the adsorption to remove calcium fluoride and hydrotalcite after fluorine adsorption; It is characterized by having at least.

Furthermore, the waste water purification method of the present invention is characterized in that the hydrotalcite is hydrotalcite. Since hydrotalcites (layered double hydroxide mineral, LDH) exhibit good anion adsorption characteristics, the hydrotalcites that adsorb fluorine or fluorine ions of the present invention have the general formula: [M ²⁺ ₁₋ represented by _{^{x M 3+ x (OH) 2}} ] [a n- x / n · zH 2 O] (M 2+ is a divalent ^{metal, M 3+} is a trivalent ^{metal, a n-n-valent} anion) An appropriate hydrotalcite can be used, but for example, hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O is preferable.

  The purification method of the present invention is a purification method in which hydrotalcite is adsorbed by adding hydrotalcite to a purification target containing fluorine, and the hydrotalcite after fluorine adsorption is a solution of 9 <pH <11. The fluorine desorption treatment is performed by stirring in the solution, and the hydrotalcite after the fluorine desorption treatment is added again to the purification target to adsorb fluorine, and preferably the fluorine desorption treatment is performed. The pH of the solution is preferably about 10. In addition, the purification | cleaning object containing a fluorine can also be soil etc. besides drainage.

  The method for purifying wastewater of the present invention does not use a large amount of calcium compound such as calcium chloride or calcium hydroxide, a large amount of flocculant, and does not discharge a large amount of sludge. Can be removed to a high level. For example, fluorine-containing wastewater can be made into treated water with a very low fluorine concentration, such as 8 ppm or less, which is a public water discharge standard. Furthermore, it is not necessary to use a large amount of calcium chloride or a flocculant, and since a large amount of sludge is not discharged, the cost of chemical treatment and sludge treatment is reduced, and high-level fluorine removal is low cost. Is possible efficiently.

  Moreover, the wastewater purification method or purification method of the present invention comprises desorbing fluorine from hydrotalcite after fluorine adsorption, and adsorbing fluorine again with hydrotalcite after desorption treatment, It is possible to recycle and effectively use it, and it is possible to perform advanced fluorine purification at a very low cost. In particular, the hydrotalcite after adsorption of fluorine is stirred in a solution of 9 <solution pH <11, more preferably in a solution having a pH of about 10, so as to perform a desorption treatment, thereby achieving a very high regeneration efficiency. Can be realized.

  Below, although this invention is demonstrated concretely based on the waste water purification process and Example of 1st, 2nd embodiment, this invention is not limited to the embodiment and Example which concern.

  First, the drainage purification process of the first embodiment in which hydrotalcite is circulated and reused to remove and purify fluorine from fluorine-containing wastewater will be described. As shown in FIG. 1, the waste water purification treatment of the first embodiment introduces fluorine-containing waste water into the primary reaction coagulation sedimentation tank 1, adds a pH adjuster to the primary reaction coagulation sedimentation tank 1, The fluorine-containing waste water is adjusted to a predetermined pH, for example, about pH 8-10. As the pH adjuster to be added, an appropriate acid or alkali can be used. For example, when the fluorine-containing wastewater is acidic wastewater, an alkali such as sodium hydroxide (NaOH) is used as the pH adjuster. Added.

Then, by adding calcium chloride (CaCl ₂₎ in the fluorine-containing waste water to adjust the pH of the primary reaction coagulating sedimentation tank 1, the fluorine ion in the fluorine-containing waste water (F ^-) is reacted with calcium chloride, Ca ²⁺ Calcium fluoride (CaF ₂ ) is generated by the reaction of + 2F ⁻ → CaF ₂ . Further, a flocculant such as sulfuric acid band or PAC is added to the primary reaction coagulation sedimentation tank 1 to coagulate calcium fluoride and precipitate sludge containing calcium fluoride. The precipitated sludge is led out from the primary reaction coagulation sedimentation tank 1 to the dehydrator 4, where the sludge is dehydrated and discharged as a dehydrated cake.

  Moreover, the primary treated water obtained by removing sludge in the primary reaction coagulation sedimentation tank 1 is introduced into the secondary reaction coagulation sedimentation tank 2, and a pH adjuster is added to the secondary reaction coagulation sedimentation tank 2, The primary treated water is adjusted to a predetermined pH, for example, around pH 6 at which the hydrotalcite adsorption performance described below is most effective. As the pH adjuster to be added, an appropriate one can be used. For example, an acid such as hydrochloric acid (HCl) is added as a pH adjuster to the primary treated water.

Then, hydrotalcite is added to the primary treated water whose pH in the secondary reaction coagulation sedimentation tank 2 is adjusted, and fluorine ions (F ⁻ ) remaining in the primary treated water are adsorbed on the hydrotalcite. The hydrotalcite to be added is a layered double hydroxide mineral having a composition formula: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, has anion exchange properties, and various anions can be inserted between the layers. Is possible. Hydrotalcite: Most of Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O takes in and adsorbs the fluorine ions (F ⁻ ) between the layers, and hydrotalcite adsorbs the fluorine ions: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O is produced.

Further, a hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O in which a flocculant such as sulfuric acid band or PAC is added to the secondary reaction coagulation sedimentation tank 2 to adsorb fluorine ions. And hydrotalcite that could not adsorb fluorine ions: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O aggregates and precipitates. By the aggregation precipitation, treated water having a fluorine concentration further reduced by adsorption of fluorine ions by hydrotalcite is obtained, and the treated water is discharged out of the system, and hydrotalcite containing hydrotalcite that has adsorbed fluorine or The precipitate is sent to the fluorine desorption tank 3.

The fluorine desorption tank 3 or the delivery path to the fluorine desorption tank 3 contains hydrotalcite adsorbed with the fluorine ions: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O. The hydrotalcite or the precipitate is suspended in a solution, and a pH adjusting agent such as sodium hydroxide (NaOH) is added to the solution, and the pH of the solution is set to a predetermined pH, for example, pH 9 to 11, preferably around 10. And carbon dioxide (CO ₂ ) is added to facilitate the elimination of fluorine.

In the fluorine desorption tank 3, the solution is stirred and hydrotalcite adsorbed with fluorine ions: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O to fluorine ions (F ⁻ ). And hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, and most of the hydrotalcite from which fluorine was eliminated: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O , And hydrotalcite that could not completely desorb fluorine: a liquid phase containing Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ · 4H ₂ O and a fluorine ion (F ⁻¹ ) Is separated into solid and liquid.

The separated solid phase is sent out from the fluorine desorption tank 3 and introduced into the secondary reaction coagulation sedimentation tank 2 for circulation and used as needed in the secondary reaction coagulation sedimentation tank 2. : Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O is introduced. The liquid phase or solution containing the separated fluorine ions (F ⁻ ) is returned to the primary reaction coagulation sedimentation tank 1 and treated with the fluorine-containing wastewater newly introduced in the primary reaction coagulation sedimentation tank 1.

  The waste water purification treatment of the first embodiment is performed by removing fluorine from fluorine-containing waste water with the primary reaction coagulation sedimentation tank 1 and the secondary reaction coagulation sedimentation tank 2, the fluorine desorption tank 3, and the dehydrator 4. Since the hydrotalcite separated in step 3 is reused, it is only necessary to add additional hydrotalcite for the loss if necessary, and the hydrotalcite can be used effectively. Furthermore, the consumption of hydrotalcite can be reduced and the cost can be reduced. Furthermore, by adsorbing the fluorine ions remaining after the formation of calcium fluoride with hydrotalcite, it is possible to efficiently make treated water with a very low fluorine concentration and to use a large amount of calcium chloride or a flocculant. There is no need. Furthermore, it is possible to finally recover the fluorine adsorbed on the hydrotalcite as calcium fluoride by circulating the fluorine.

  In the waste water purification process of the first embodiment, the same primary reaction coagulation sedimentation tank 1 is used to perform pH adjustment process, calcium fluoride production process by calcium chloride reaction, coagulation process, and precipitation process. However, as a modification, for example, a configuration in which each treatment is performed in a pH adjustment tank, a reaction tank for generating calcium fluoride, a coagulation tank, a precipitation tank, or a combination of these appropriate treatments in the same tank, etc. It is possible. Similarly, in the same secondary reaction coagulation sedimentation tank 2, pH adjustment treatment, fluorine ion adsorption treatment with hydrotalcite, coagulation treatment, and precipitation treatment are performed. A configuration in which each treatment is performed in a reaction tank, an agglomeration tank, and a precipitation tank in which adsorption treatment is performed, or a combination in which these appropriate treatments are performed in the same tank can be employed.

  Next, the waste water purification process of the second embodiment in which hydrotalcite is used in one tank type equipment to remove and purify fluorine from fluorine-containing waste water will be described.

As shown in FIG. 2, the wastewater purification treatment of the second embodiment introduces fluorine-containing wastewater into the reaction coagulation sedimentation tank 5, adds an alkali or acid pH adjuster to the reaction coagulation sedimentation tank 5, The fluorine-containing waste water is adjusted to a predetermined pH, for example, about pH 6. Calcium chloride (CaCl ₂ ) is added to the fluorine-containing wastewater whose pH in the reaction coagulation sedimentation tank 5 is adjusted, and the fluorine ions (F ⁻ ) and calcium chloride in the fluorine-containing wastewater are reacted to produce Ca ²⁺ + 2F ⁻ → CaF _2. To produce calcium fluoride (CaF ₂ ).

Further, hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O is added to the reaction coagulation sedimentation tank 5 to leave the fluorine ions remaining in the waste water after the formation of calcium fluoride (CaF ₂ ) ( F ⁻ ) is adsorbed on hydrotalcite. Most of the added hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O is a hydrotalum in which the fluorine ions (F ⁻ ) are taken in and adsorbed between the layers, and the fluorine ions are adsorbed. Site: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O is generated.

Then, a hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) in which a flocculant such as a sulfate band or PAC is added to the reaction coagulation sedimentation tank 5 to adsorb calcium fluoride (CaF ₂ ) and fluorine. ) ₂ · _{4H 2} O, and hydrotalcite could not adsorb ^{_{fluorine: Mg 6 Al 2 (OH)}} 16 (F -1) agglomerating ₂ · 4H 2 O, precipitating the sludge containing them. The precipitated sludge is led out from the reaction coagulation sedimentation tank 5 to the dehydrator 6, and the sludge is dehydrated by the dehydrator 6 and discharged as a dehydrated cake, and the treated water obtained by removing the sludge is discharged out of the system.

  The wastewater purification treatment of the second embodiment is to remove fluorine from fluorine-containing wastewater with a single reaction coagulation sedimentation tank 5 and a single dehydrator 6, and to save fluorine with a small capital investment at low cost and in a space-saving manner. Can be removed. Furthermore, by adsorbing the fluorine ions remaining after the formation of calcium fluoride with hydrotalcite, it is possible to efficiently make treated water with a very low fluorine concentration and to use a large amount of calcium chloride or a flocculant. There is no need.

  In the wastewater purification treatment of the second embodiment, in the same reaction coagulation sedimentation tank 5, pH adjustment treatment, calcium fluoride production treatment by reaction with calcium chloride, fluoride ion adsorption treatment by hydrotalcite However, the modification of the first embodiment can be appropriately used in the second embodiment. For example, a pH adjustment tank, a reaction tank for generating calcium fluoride, fluorine A structure in which each treatment is performed in a reaction tank, an agglomeration tank, and a precipitation tank for performing ion adsorption treatment, or a structure in which these appropriate treatments are combined in the same tank, or agglomeration and precipitation are performed after the calcium fluoride production treatment It is possible to adopt a configuration in which a tank is added.

  Next, simulation tests and results of hydrotalcite fluorine adsorption, desorption, and resorption corresponding to the wastewater purification process of the first embodiment will be described.

First, in the hydrotalcite fluorine adsorption test, about 1 mol / L of potassium fluoride solution 1 L (measured fluorine content by ion chromatography: 1850.0 mg / L) was prepared, and hydrotalcite: 10 g of Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O was added, and the mixture was stirred for 1 hour while adjusting the pH of the solution to around 6 using HCl. After the stirring, the suspension was filtered, and the remaining solid phase K1 was dried at 50 ° C. in a constant temperature dryer.

When the fluorine content of the filtrate R1 obtained by the filtration was measured by ion chromatography, it was 231.0 mg / L, and 10 g of the added hydrotalcite contained 1850.0-231.0 = 1619.0 mg / L of fluorine ions. The amount of fluorine adsorbed per 1 g of hydrotalcite adsorbed and added was 161.9 mg / g (see Table 2, (1) below). The remaining solid phase K1 is composed of hydrotalcite adsorbed with fluorine: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O and normal hydrotalcite: Mg ₆ Al ₂ (OH) ₁₆ CO. consisting of ₃ · 4H ₂ O.

  Next, in the fluorine desorption test of hydrotalcite that adsorbed fluorine, first, NaOH was used and 500 mL each of NaOH solutions adjusted to pH 9, 10, and 11 were prepared in a beaker, and the solid-liquid ratio was 1 g / Add 500 mg each of solid phase K1 containing hydrotalcite adsorbing fluorine to each beaker, and stir while adjusting the pH to be maintained at 9, 10 and 11 with NaOH, respectively. Filtration was performed every 5 minutes, 10 minutes, 15 minutes, 30 minutes, and 60 minutes of stirring time.

  The relationship between the fluorine desorption amount obtained by measuring the fluorine content of the filtrate R2 by filtration and the stirring time is shown in the graph of FIG. The graph of FIG. 3 shows that the higher the pH as a whole and the longer the stirring time, the greater the amount of desorption of fluorine in each of the beakers of pH 9, 10, and 11. For example, in the case of stirring at pH 9 for 5 minutes, fluorine: 44.2 mg / g per 1 g of solid phase K was released, and in the case of stirring at pH 11 for 60 minutes, fluorine: 132.0 mg was released per 1 g of solid phase K. The amounts of F desorption when the stirring time is 60 minutes for each pH 9, 10, and 11 are shown in Table 2 (2) below, and the solid phase after desorption when the stirring time is 60 minutes is fixed. Let it be phase K2.

  Thereafter, in the hydrotalcite fluorine resorption test, a test method basically similar to that of the hydrotalcite fluorine adsorption test is performed. First, it is made to correspond to each of pH 9, 10 and 11, and about 0.1 mol / L. Of potassium fluoride solution 1L (actually measured fluorine content by ion chromatography: 1850.0 mg / L) of pH 9, 10, and 11 obtained by filtering with a stirring time of 60 minutes as a sample in a desorption test. Each solid phase K2 was added at a rate of 10 g / L (see Table 2, (2) below), and stirred for 1 hour while adjusting the pH of each solution to around 6 using HCl. Thereafter, solid-liquid separation was performed using a membrane filter (0.2 μm), followed by filtration to obtain a liquid-phase filtrate R3 and a solid-phase K3 for analysis.

The results are shown in Table 1 and FIG. Table 1 shows that the fluorine content per 1 L of potassium fluoride solution of about 0.1 mol / L before the addition of solid phase K2: The fluorine content (filtrate: F) of the filtrate R3 after adsorption, the fluorine adsorption amount of the solid phase K3 (solid phase: F), and the fluorine adsorption amount per gram of the solid phase K3 are shown in FIG. , 11 shows the amount of fluorine adsorbed per 1 g of the solid phase K3. The solid phase K3 is composed of hydrotalcite adsorbed with fluorine: Mg ₆ Al ₂ (OH) ₁₆ (F ⁻¹ ) ₂ .4H ₂ O or hydrotalcite adsorbed with fluorine: Mg ₆ Al ₂ (OH) ₁₆ ( F ^-1) ₂ · 4H ₂ O and normal _{hydrotalcite:} Mg ₆ Al _{2 (OH)} consists of 16 _CO 3 · 4H ₂ O.

  Table 2 shows the amount of fluorine adsorbed after the fluorine re-adsorption at each pH of 9, 10, and 11 by the above-described simulation test of fluorine adsorption, desorption, and re-adsorption. The amount of fluorine adsorbed after resorption in Table 2 is obtained by subtracting the amount of fluorine desorption from the fluorine desorption test in (2) from the amount of fluorine adsorption from the adsorption test in (1), and the amount of fluorine adsorption from the resorption test in (3). It is a numerical value obtained by adding.

As Table 2 shows, the higher the pH at fluorine desorption, the higher the amount of fluorine desorption, the greater the amount of fluorine desorption, but at the time of fluorine resorption, the pH at desorption is 9, 10, The amount of adsorption of fluorine decreases as the value increases to 11, and the cause thereof is, for example, that when the degree of alkali at the time of desorption is different, what enters between the layers of hydrotalcite is different from OH ⁻ and CO 3 ^2−. It can be considered something. In addition, at pH 11, the adsorption amount at the time of fluorine re-adsorption is lower than the desorption amount at the time of desorption, whereas at pH 9, 10, the adsorption amount at fluorine re-adsorption is less than the desorption amount at the time of desorption. This is thought to be due to the fact that there was room for fluorine adsorption between the hydrotalcite layers after the adsorption test of (1).

  Furthermore, when desorbing after re-adsorption, Table 3 shows the amount of fluorine desorption when the desorption ratio is assumed to be equivalent to the desorption ratio in the desorption test of (2).

  As shown in Tables 2 and 3, the amount of fluorine adsorbed and the amount of fluorine desorbed show that when pH is 9, the amount of adsorption during re-adsorption is large but the amount of desorption is small, so desorption and re-adsorption cause fluorine. Regeneration efficiency when hydrotalcite is repeatedly used for removal is low, and in the case of pH 11, since the amount of desorption is large but the amount of adsorption at the time of re-adsorption is small, similarly, the regeneration efficiency of hydrotalcite Becomes lower. On the other hand, in the case of pH 10, since both the adsorption amount and the desorption amount at the time of re-adsorption are large, the regeneration efficiency when using hydrotalcite repeatedly for fluorine removal by desorption and re-adsorption is the highest. Become. Moreover, since pH around 10 is the optimum pH for the synthesis of hydrotalcite, the solubility is low, and there is little loss of hydrotalcite when regenerated and used. From this point of view, desorption at around pH 10 contributes to improvement in regeneration efficiency.

In addition, when HCl is added for pH adjustment in the above resorption test, the amount of HCl added per 1 g of solid phase K2 is 766.7 μL for pH 9 resorption, and 384. In the case of 6 μL and pH 11 re-adsorption: 458.3 μL, and the required amount of HCl added was the smallest at pH 10 where hydrotalcite regeneration efficiency was high. This is thought to be because hydrotalcite or solid phase K2 after desorption at pH 10 has a large amount of weak acid CO 3 ²⁻ between the layers, indicating high regeneration efficiency at pH 10.

  By using the wastewater purification method or purification method of the present invention, fluorine is removed from fluorine-containing wastewater discharged from, for example, a semiconductor factory or power plant, and the fluorine-containing wastewater is efficiently treated with low fluorine concentration, for example, Treated water below the emission standard established in view of environmental protection.

Explanatory drawing which shows the flow of the waste water purification process of 1st Embodiment. Explanatory drawing which shows the flow of the waste water purification process of 2nd Embodiment. The graph which shows the relationship between stirring time and the amount of fluorine ion desorption from hydrotalcite. The graph which shows the amount of fluorine adsorption in the re-adsorption of each hydrotalcite from which fluorine was desorbed at pH 9, 10, and 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary reaction coagulation sedimentation tank 2 Secondary reaction coagulation sedimentation tank 3 Fluorine desorption tank 4, 6 Dehydrator 5 Reaction coagulation sedimentation tank

Claims (6)

A step of adding calcium compound to fluorine-containing wastewater to produce calcium fluoride, a step of removing the calcium fluoride by solid-liquid separation of the reaction solution after the production of calcium fluoride, and a step of removing the calcium fluoride Adjusting the pH of treated water, adding hydrotalcite to adsorb fluorine remaining in hydrotalcite, and hydrotalcite after fluorine adsorption by solid-liquid separation of the treated water after adsorption And a step of removing water at least. A step of subjecting the removed hydrotalcite after the adsorption of fluorine to a fluorine desorption treatment; a step of adding the hydrotalcite after the fluorine desorption treatment again in a fluorine adsorption step; The drainage purification method according to claim 1, further comprising a step of combining fluorine-containing water generated by the fluorine desorption treatment with fluorine-containing wastewater before calcium generation. 3. The fluorine desorption treatment step, wherein the hydrotalcite after fluorine adsorption is stirred in a solution having a pH of 9 <pH <11 to perform the fluorine desorption treatment. Wastewater purification method. Adding calcium compounds to fluorine-containing wastewater to generate calcium fluoride, adding hydrotalcite to the reaction solution after the calcium fluoride is generated, and adsorbing fluorine remaining in the hydrotalcite; And a step of solid-liquid separation of the reaction liquid after adsorption to remove calcium fluoride and hydrotalcite after fluorine adsorption. The drainage purification method according to claim 1, 2, 3, or 4, wherein the hydrotalcite is hydrotalcite. In a purification method in which hydrotalcite is added to a purification target containing fluorine to adsorb fluorine, the hydrotalcite after fluorine adsorption is stirred in a solution of 9 <pH <11 to remove fluorine. And a hydrotalcite after the fluorine desorption treatment is added again to the purification target to adsorb fluorine.

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