JP5049987B2 - Fluorine ion immobilization and fluorine recycling method - Google Patents

Description

  The present invention relates to a fluorine immobilization treatment technique targeting soluble fluorine ions in an acidic region to a weakly alkaline region, and further, calcium fluoride recovered by the immobilization treatment is used as a raw material for producing hydrogen fluoride, or The present invention relates to a fluorine resource recycling method used for a steel refining flux.

  Usually, the fixation of fluorine from wastewater containing fluorine is made after reacting with calcium compounds such as quicklime, slaked lime, calcium carbonate, and calcium chloride to fix most of the fluorine as sparingly soluble calcium fluoride. Fluorine concentration in waste water by secondary treatment such as coagulation precipitation method using aluminum salt or iron salt, fluorapatite precipitation method, activated alumina adsorption method, adsorption method to basic ion exchange resin or chelate resin as required Is below the regulation value.

  Calcium fluoride obtained by immobilization using the calcium salt in the previous stage is fine in particle size and cannot be filtered as it is, so it is made into a floc with good sedimentation using a polymer flocculant etc. and precipitated with a thickener. Things are filtered with a filter press. The calcium fluoride thus obtained has a purity as low as 60 to 80% on a dry basis, and has a fine particle diameter and contains 50 to 70% of water, and thus is difficult to use as industrial calcium fluoride.

  A part of the generated calcium fluoride sludge is returned to its original state, and the role of seed crystal is increased to increase the particle size somewhat, and the volume of waste sludge is reduced by reducing the water content by 5 to 20%. (For example, refer nonpatent literature 1).

  For dilute fluorine-containing waste liquor of several hundred ppm, there is also a technology for growing calcium fluoride crystals to increase the particle size (for example, see Non-Patent Document 2), but the crystallization speed is very slow, so the equipment scale In addition to the small amount of processing, the technology for recycling the collected material has not been established yet, so far it is treated as industrial waste.

  Among them, an attempt to generate calcium fluoride while maintaining the skeleton of natural calcium carbonate by passing fluorine wastewater through natural calcium carbonate having a uniform particle size in order to increase the particle size (see, for example, Patent Document 1). Has been made. At this time, there are problems such as escape of generated carbon dioxide, generated calcium fluoride floc, and the central part of calcium carbonate remaining unreacted, but this report reports that the recovered calcium fluoride was mixed with fluorite and processed. (See, for example, Non-Patent Document 3).

  Attempts have also been made to use calcium fluoride (recovered calcium fluoride) obtained by fluorine fixation treatment with fluorite, which is a raw material for producing hydrogen fluoride, but the recovered calcium fluoride has an average particle size. Due to problems such as small (large but small aggregates are secondary agglomerated), low bulk density (about half of fluorite), and many impurities (especially chlorine) Since it is not well-suited with stone and impurities in the product hydrogen fluoride increase, the limit is to use 5 to 10% mixed with fluorite.

  There is a method in which the recovered calcium fluoride is mixed with gypsum and dried to increase the particle size and then mixed with fluorite (see, for example, Patent Document 2).

  Methods for immobilizing fluorine in wastewater using anhydrous gypsum and 2-water gypsum are already known, but it is necessary to use an excess amount to remove the fluorine concentration in the treated water to near the regulation value. (See, for example, Patent Document 3), the calcium fluoride content in the solid content to be recovered is as low as about 50% and cannot be used for industrial use.

  Further, for the purpose of reusing fluorine, one of the present inventors treated a neutral aqueous solution with a fluorine concentration of 1 to 2% to recover a solid content containing 80 to 90% of calcium fluoride. A system has been found in which gypsum used as a hydrogen fluoride production raw material and by-produced in hydrogen fluoride production is reused to fix fluorine (see Patent Document 4).

Japanese Patent Laid-Open No. 06-063561 (Applicant: Kurita Kogyo Co., Ltd., Hashimoto Kasei Co., Ltd., Title of Invention: Treatment device for fluorine-containing water)

JP 2002-534346 A (Applicant: Atowina, Title of Invention: Process for recycling calcium fluoride fine powder)

Japanese Patent Application Laid-Open No. 59-120286 (Applicant: Nippon Steel Pipe Co., Ltd., Title of Invention: Treatment method of waste water containing fluorine-based components)

JP 2005-200273 A (Applicant: Cabot Super Metal Co., Ltd., Morita Chemical Co., Ltd., Title of Invention: Method for producing hydrogen fluoride)

Kurita Industry Co., Ltd. Isao Kato, “Water and Wastewater” Vol. 42, No. 10, Industrial Water Research Committee, Inc., October 1, 2000, pp. 27-32.

Organo Co., Ltd. Takayuki Hashimoto, "Hydrofluoric acid recycling technology using crystallization method" Clean Technology, May issue, Nihon Kogyo Publishing Co., Ltd., May 2001, pp. 40-42

New Energy and Industrial Technology Development Organization 2001 Results Report 51101125 (Fiscal 2001 Technology Development Related to Global Warming Prevention “Development of HFC-23 Destruction Technology”) March 2002 Report Subcontractor: Industrial Environmental Management Association

  The purpose of the present invention is to recover the fluoride ion present in the waste water and calcium fluoride as calcium fluoride with a high calcium fluoride content and excellent filterability when immobilized as calcium fluoride. Furthermore, it is to reduce the remaining amount of fluorine in the treated water to 5 to 15 ppm only by this treatment. Then, the recovered calcium fluoride is used as a raw material for producing hydrogen fluoride or a flux for refining steel.

  As a result of intensive studies to achieve the above object, the present inventors have made a crystal containing calcium fluoride by reacting an effluent containing sulfate ions and fluoride ions with an aqueous solution of soluble calcium, particularly an aqueous solution of calcium chloride. It was found that dihydrate gypsum having a particle size of 30 to 100 μm with good properties was produced, and as a result, the concentration of fluorine ions could be reduced to 5 to 15 ppm below 2000 ppm sulfate ions in the waste water.

  Further, when the fluorine wastewater is treated using the dihydrate gypsum containing calcium fluoride obtained here, 80 to 95% of the fluorine content in the wastewater is fixed and the calcium fluoride content in the solid content is set to 90%. It was found that it can be more than%.

That is, in the treatment of fluorine-containing wastewater, an apparatus comprising a first reaction tank, a first solid-liquid separation tank, a second reaction tank, and a second solid-liquid separation tank is used, and is generated in the second reaction tank in the first reaction tank. Using dihydrate gypsum containing calcium fluoride to be squeezed, salt exchange of fluorine ion and sulfate ion in fluorine-containing wastewater is performed, and at least recycled as raw material for hydrogen fluoride production in the first solid-liquid separation tank Calcium fluoride having a purity and a particle size that can be recovered was recovered, and in the second reaction tank, sulfate ions that were dissolved in the liquid by the salt exchange reaction and were not removed by the treatment in the first reaction tank. By reacting fluoride ions with a soluble calcium salt, dihydrate gypsum containing calcium fluoride is precipitated, and the precipitated dihydrate gypsum containing calcium fluoride is precipitated. Serial subjected to the reaction of the first reaction vessel.
By doing in this way, while being able to fix the fluorine in fluorine-containing waste liquid as useful calcium fluoride with a large particle size, the fluorine concentration in a process liquid can be reduced to 5-15 ppm.

As described above, as the first stage treatment, salt exchange between fluoride ions and sulfate ions in the fluorine-containing waste water is performed using dihydrate gypsum containing calcium fluoride generated by the second stage treatment. In the first solid-liquid separation tank, at least calcium fluoride having a purity and particle size that can be recycled as a raw material for producing hydrogen fluoride is recovered. Further, as the second stage treatment, the sulfate ions dissolved in the liquid by the salt exchange reaction and the fluorine ions not removed by the first stage treatment are reacted with a soluble calcium salt. Then, crystals of dihydrate gypsum containing calcium fluoride are precipitated. Then, the precipitated dihydrate gypsum containing calcium fluoride is subjected to the first-stage reaction. Through this two-step reaction, the fluorine recycling system was completed.
By this two-stage reaction, 99% or more of the fluorine content can be recovered as beneficial calcium fluoride from the fluorine-containing waste liquid, and the fluorine concentration in the treatment liquid can be reduced to 5 to 15 ppm.

  In the above-described fixation of fluorine, the amount corresponding to the amount of sulfate ion dissolved in the waste liquid discharged from the second solid-liquid separation tank (calcium sulfate solubility) or more, more preferably 1 to 2 times the amount. It is desirable to add a sulfate solution, particularly a sodium sulfate aqueous solution, or a waste solution containing sodium sulfate, either in the waste water to be treated or until the second reaction tank. If it does in this way, the above-mentioned fixation process of fluorine can be carried out effectively.

  In the above-described fixation of fluorine, more than the amount corresponding to the amount lost and dissolved in the drainage discharged from the second solid-liquid separation tank, more preferably 1 to 2 times the amount of 2-hydrate gypsum is solid, or It is desirable to replenish as a two-water gypsum slurry. If it does in this way, the above-mentioned fixation process of fluorine can be carried out effectively.

  In the above case, if the calcium fluoride obtained in the first solid-liquid separation tank is filtered and dried, it can be used at least as a raw material for producing hydrogen fluoride and can be used as a refining flux for steel. Thus, the recovered calcium fluoride can be used industrially beneficially.

  It is desirable to use an aqueous calcium chloride solution or a wastewater containing calcium chloride as the soluble calcium in an amount equal to or more than that of sulfate ions to be treated in the second reaction tank, more preferably 1 to 2 times. If it does in this way, the above-mentioned fixation process of fluorine can be carried out effectively.

The present invention will be described more specifically.
Usually, to treat wastewater containing high concentrations of fluorine, the wastewater is reacted with water-soluble calcium compounds such as quicklime, slaked lime and calcium chloride to immobilize most of the fluorine as sparingly soluble calcium fluoride. ing.
Calcium fluoride obtained by such an immobilization treatment has a very fine particle size and cannot be filtered as it is. Therefore, the flocculant is used to form a floc, followed by sedimentation separation and filter press filtration. Therefore, the water content is as high as 50 to 70%, and not only cannot be reused for industrial purposes, but also its volume is large, so that disposal is a problem.

  In order to solve this problem, there is an attempt to produce calcium fluoride while maintaining the calcium carbonate skeleton substantially by reacting natural calcium carbonate with an appropriate particle size and hydrogen fluoride (formula (1)). Has been made. At that time, most of the calcium carbonate is recovered as calcium fluoride while maintaining the particle size. However, the generated carbon dioxide gas is difficult to escape, and further progress of the reaction is inhibited. There are problems such as generation of calcium flocs and unreacted calcium carbonate remaining in the center of calcium carbonate.

  Since the method using dihydrate gypsum in the present invention is simply salt exchange between the fluorine anion and the sulfate anion (formula (2)), there arises a problem that the crystals are broken and refined as when calcium carbonate is used. Therefore, it is possible to obtain calcium fluoride having a purity of 90% or more while maintaining the particle size of the dihydrate gypsum used.

  Unreacted dihydrate gypsum, when used as a raw material for hydrogen fluoride production, is pre-dried to become anhydrous gypsum, and the solid content produced as a by-product during hydrogen fluoride production is anhydrous gypsum, so it contains about 20% It does not matter at all.

  The most important point of the present invention is to precipitate crystals of dihydrate gypsum containing calcium fluoride having a particle size of 30 μm or more in the reaction of the second reaction tank. It is better to immobilize more fluorine, more preferably 90% or more.

  If the immobilization ratio of fluorine in the first reaction tank is too low, the fluorine concentration in the waste water used for the reaction in the second reaction tank will increase, and in this case, crystals of dihydrate gypsum containing precipitated calcium fluoride. Becomes finer.

  As an example, 1000 g each of 4.16% aqueous sodium sulfate solution containing 50 ppm, 250 ppm, 500 ppm, 1000 ppm, 2500 ppm, and 5000 ppm fluorine was prepared, and an aqueous solution containing 6.78% calcium chloride with stirring. 500 g was dropped and reacted to precipitate dihydrate gypsum crystals containing calcium fluoride. The reaction occurring here is a reaction represented by the formulas (3) and (4).

  After the reaction, it was filtered after confirming the sedimentation of the generated solid content. For the filtrate, the dissolved fluorine concentration and sulfate ion concentration were measured, the solid content was lightly washed with water, dried, weighed, and photographed with SEM (scanning electron microscope). Compared. The results are shown in Table 1 and FIGS.

  Regardless of the fluorine concentration in the stock solution, approximately 10 ppm of fluorine ions and 1500 ppm of sulfate ions remained in the filtrates of Runs 1 to 4. These concentrations were close to the solubility of calcium fluoride and dihydrate gypsum in water. The reason why the sulfate ion concentration increased in Runs 5 and 6 was that the amount of unreacted sodium sulfate increased due to the lack of calcium chloride. If there was a sufficient amount of calcium ions, the sulfate ion would be about 1500 ppm. Become.

  As can be seen by comparing FIG. 3 and FIG. 4, if Run 1 to 4, that is, the fluorine concentration before the treatment is 1000 ppm or less, clean crystal growth is observed, and the grain size is as large as 30 to 100 μm (FIG. 3 ( a), (b)). On the other hand, when the fluorine concentration is 2500 ppm or more, more fine calcium fluoride is generated, so that the generated particles are finer and the sedimentation property is also lowered (FIGS. 4A and 4B). According to the data shown in Table 1, if the fluorine content is reduced to 1000 ppm or less in the treatment of the first reaction tank, dihydrate gypsum containing calcium fluoride produced in the second reaction tank maintains a large particle size. it can.

  Assuming a reaction in the second reaction tank, 20.0 kg of a 4.16% sodium sulfate aqueous solution containing 1000 ppm of fluorine is placed in a 50 L polyethylene container equipped with a stirrer and stirred with a metering pump. Over about 1 hour, 10.0 kg of an aqueous solution containing 6.78% calcium chloride was dropped and reacted. Stirring was continued for 10 minutes after the completion of dropping, and solid-liquid separation was performed using a centrifugal dehydrator. 1008 g of a solid content containing 6.2% moisture, 1.8% calcium fluoride, and 92.0% dihydrate gypsum was recovered. The fluorine concentration in the filtrate was 10.8 ppm, and the sulfate ion concentration was 1650 ppm.

  Assuming a reaction in the first reaction tank, 2.21% of sodium fluoride is dissolved in water to prepare a 10000 ppm fluorine-containing waste water, and the reaction in the second reaction tank is performed on 1000 g of this prepared waste water. Prepared solid content containing 6.2% moisture, 1.8% calcium fluoride, and 92.0% dihydrate gypsum based on the formula (2). 1.0 equivalents, 1.1 times equivalents, 1.2 times equivalents, 1.3 times equivalents, 1.5 times equivalents were added and stirred, and the change in fluorine ion concentration in the liquid was measured. Table 2 shows the change with time, the initial pH value, and the pH value after 240 minutes.

  The pH of the liquid gradually shifts to the acidic side because sulfate ions dissolve out as the reaction of formula (2) proceeds. Therefore, when discharging as waste water, it is necessary to adjust pH. The pH adjustment is desirably performed in the second reaction tank.

  Similarly, in order to investigate the influence of pH of the effluent on the fixation of fluorine, 10000 ppm fluorine-containing wastewater (acid effluent) prepared to pH 3.06 using hydrochloric acid, pH 9.95 using sodium hydroxide. Table 3 shows the measurement results when the 10000 ppm fluorine-containing wastewater (alkaline wastewater) prepared in Example 1 was stirred after adding 1.0 equivalent of 2-hydrate gypsum. In order to compare with both wastewater, the value of 1.0 times equivalent in Table 2 is shown in Table 3 as neutral wastewater.

  As can be seen from Table 3, the difference in initial reactivity is small in any region, and 72 to 75% of fluorine is immobilized in the first 15 minutes. The difference in reactivity after that is large, and acidic wastewater hardly reacts after 30 minutes. In neutral and alkaline wastewater, the reaction proceeds with time.

  If 1.0 times equivalent of Table 2 is used and the reaction time of the first stage is 2 hours, 90.5% of fluorine is fixed, and considering calcium fluoride in dihydrate gypsum used for the reaction, A solid containing 90 wt% calcium fluoride can be recovered. If the fluorine content in the effluent increases, the fluorine immobilization rate in the first reaction tank increases, and in the effluent having a fluorine content of 30000 ppm, 1.0 eq. The calcium fluoride content of becomes as high as 92 to 94 wt%. Conversely, when it is as thin as 3000 ppm, it is as low as 82 to 86 wt%.

  As a conceptual flow chart of the present invention, FIG. 1 shows a case where a deficient sulfate ion is replenished as an aqueous sodium sulfate solution, and FIG.

  Sulfate ions corresponding to the solubility of 2-hydrate gypsum are dissolved in the waste water from the second solid-liquid separation tank, and the solid content recovered from the first solid-liquid separation tank in the first reaction tank Contains 5 to 13 wt% of dihydrate gypsum, and since sulfate ions for this amount are taken out of the system, it is necessary to supplement sulfate ions.

  As a replenishment method, wastewater containing a water-soluble sulfate, such as an aqueous solution of sodium sulfate or sodium sulfate, is used as raw water for drainage, a first reaction tank, a first solid-liquid separation tank, a second reaction tank, and a second solid-liquid. Although it may be replenished at any point in the middle of the separation tank and the main pipe, more preferably, it is carried out in a line flowing into the second reaction tank after the first solid-liquid separation tank as shown in FIG. good.

  When using gypsum, calcium sulfate may be used in the form of anhydrous gypsum, hemihydrate gypsum, or water hydrate gypsum, but use dihydrate gypsum with a faster reaction of formula (2) and no problem of solidification. It is desirable. Since the fluorine immobilization reaction shown in Formula (2) is a solid-liquid reaction and the reaction is carried out while maintaining the shape of calcium sulfate, when the calcium sulfate particle size is large, the reaction to the inside occurs. It becomes difficult.

  According to the first aspect of the invention, 99% or more of the fluorine content can be recovered from the fluorine-containing effluent as useful calcium fluoride, and the fluorine concentration in the treatment liquid can be reduced to 5 to 15 ppm.

  According to the invention described in claim 2, the fluorine immobilization treatment described in claim 1 can be effectively carried out.

  According to the invention described in claim 3, the fluorine immobilization treatment according to claim 1 can be effectively carried out.

  According to invention of Claim 4, the collect | recovered calcium fluoride can be utilized industrially beneficially.

  According to the fifth aspect of the invention, the fluorine immobilization treatment of the first aspect can be effectively carried out.

An example of the fluorine recovery processing system by this invention is shown, and it is a conceptual flowchart for implementing invention of Claim 1, 2, 5 especially. Another example of the fluorine collection | recovery processing system by this invention is shown, and it is a conceptual flowchart for implementing invention of Claim 1,3,5 especially. In the SEM photograph of the solid content generated from the fluorine-containing effluent having a fluorine concentration of 1000 ppm or less before treatment, in particular, (a) was generated from the 250 ppm fluorine-containing effluent, and (b) was generated from the 1000 ppm fluorine-containing effluent. Show the case. SEM photographs of solids generated from a fluorine-containing effluent having a fluorine concentration of 2500 ppm or more before treatment. In particular, (a) was generated from a 2500 ppm fluorine-containing effluent, and (b) was generated from a 5000 ppm fluorine-containing effluent. Show the case.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1

According to the flow chart of FIG. 1 using a pilot facility having an actual volume of 100 L in each tank, fluorine waste gas cleaning wastewater having a pH of 8.5 containing 21000 ppm of fluorine as wastewater was supplied to the first reaction tank at 20 kg / h and reacted. 5% sodium sulfate at 3.52 kg / h is supplied into the piping between the first solid-liquid separation tank and the second reaction tank, and 10% calcium chloride is supplied at 14.7 kg / h to the second reaction tank. Reacted. Since the pH of the second reaction tank was in the neutral range (6.4-6.6), no neutralizer was supplied. The slurry separated in the second solid-liquid separation tank was sent to the first reaction tank at 15 L / h with a tube pump. In a state in which the reaction was stable, this slurry had a solid content of 12.9 wt%, a solid content composition: 98.1 wt% of water gypsum, and 1.9 wt% of calcium fluoride. The slurry extracted in the first solid-liquid separation tank was subjected to centrifugal dehydration, and the dehydrated mother liquor was returned to the first solid-liquid separation tank. The average solid content recovered by dehydration was 938 g / h on a dry basis, and the composition was 92.6 wt% calcium fluoride and 7.4 wt% dihydrate gypsum. The recovered material was dried and used as a raw material for producing hydrogen fluoride.
The treated wastewater discharged from the second solid-liquid separation tank had an average pH of 6.5, fluorine of 9.2 ppm, sulfate ion of 1506 ppm, and calcium of 1755 ppm.
In this example, the immobilization rate of fluorine was 99.9%, the sodium sulfate aqueous solution used was 1.5 times equivalent to the amount of sulfate ions lost by dissolution in the drainage, and the calcium chloride aqueous solution was in the second reaction tank. It was 1.2 times equivalent to the sulfate ion to be treated. The average residence time of the liquid in each tank is 2.86 h in the first reaction tank, 2.86 h in the first solid-liquid separation tank, 1.9 h in the second reaction tank, and 1.9 h in the second solid-liquid separation tank. there were.
(Example 2)

Using the same apparatus as in Example 1, fluorine-containing wastewater having a pH of 6.5 containing 16000 ppm of fluorine as wastewater was supplied to the first reaction tank at 20 kg / h and reacted. 5% sodium sulfate is supplied at 3.0 kg / h into the pipes of the first solid-liquid separation tank and the second reaction tank, and 10% calcium chloride is supplied at 12.8 kg / h to the second reaction tank. Reacted. Since the pH of the first solid-liquid separation tank was 5.2, 1% sodium hydroxide aqueous solution was added dropwise as a neutralizing agent to the second reaction tank for neutralization. The slurry separated in the second solid-liquid separation tank was sent to the first reaction tank at 15 L / h with a tube pump. With the reaction stabilized, this slurry had a solid content of 9.9 wt%, a solid content composition: 97.9 wt% of gypsum, and 2.1 wt% of calcium fluoride. The slurry extracted in the first solid-liquid separation tank was subjected to centrifugal dehydration, and the dehydrated mother liquor was returned to the first solid-liquid separation tank. The average solid content recovered by dehydration was 721 g / h on a dry basis, and the composition was 91.2 wt% calcium fluoride and 8.8 wt% dihydrate gypsum. The recovered material was dried and used as a raw material for producing hydrogen fluoride.
The treated wastewater discharged from the second solid-liquid separation tank was, on average, pH 7.2, fluorine 8.3 ppm, sulfate ions 1317 ppm, and calcium 2070 ppm.
In this example, the immobilization ratio of fluorine was 99.9%, the used sodium sulfate aqueous solution was 1.54 times equivalent to the amount of sulfate ions lost by dissolution in the drainage, and the calcium chloride aqueous solution was in the second reaction tank. It was 1.37 times equivalent to the sulfate ion to be treated. The average residence time of the liquid in each tank is 2.86 h in the first reaction tank, 2.86 h in the first solid-liquid separation tank, 2.0 h in the second reaction tank, and 2.0 h in the second solid-liquid separation tank. there were.
(Example 3)

Using the same apparatus as in Example 1, fluorine-containing wastewater having a pH of 5.6 containing 7500 ppm of fluorine as wastewater was supplied to the first reaction tank at 20 kg / h and reacted. 5% sodium sulfate is supplied at 2.5 kg / h into the piping of the first solid-liquid separation tank and the second reaction tank, and 10% calcium chloride is supplied to the second reaction tank at 7.0 kg / h. Reacted. Since the pH of the first solid-liquid separation tank was 5.1, 1% -aqueous sodium hydroxide solution was added dropwise as a neutralizing agent to the second reaction tank for neutralization. The slurry separated in the second solid-liquid separation tank was sent to the first reaction tank at 10 L / h with a tube pump. In a state where the reaction was stable, this slurry had a solid content of 6.6 wt%, a solid content composition: 98.1 wt% of double gypsum, and 1.9 wt% of calcium fluoride. The slurry extracted in the first solid-liquid separation tank was subjected to centrifugal dehydration, and the dehydrated mother liquor was returned to the first solid-liquid separation tank. The average solid content recovered by dehydration was 334 g / h on a dry basis, and the composition was 86.2 wt% calcium fluoride and 13.8 wt% dihydrate gypsum. The recovered material was dried and used as a raw material for producing hydrogen fluoride.
The treated wastewater discharged from the second solid-liquid separation tank had an average pH of 6.9, fluorine of 11.2 ppm, sulfate ion of 1480 ppm, and calcium of 1890 ppm.
In this example, the immobilization rate of fluorine was 99.9%, the used sodium sulfate aqueous solution was 1.35 times equivalent to the amount of sulfate ions lost in the waste liquid, and the calcium chloride aqueous solution was in the second reaction tank. It was 1.71 times equivalent of the sulfate ion to be treated. The average residence time of the liquid in each tank is 3.33 h in the first reaction tank, 3.33 h in the first solid-liquid separation tank, 2.1 h in the second reaction tank, and 2.1 h in the second solid-liquid separation tank. there were.
Example 4

  According to the flow chart of FIG. 2 using a pilot facility having an actual volume of 100 L in each tank, pH 8.5 fluorine exhaust gas cleaning wastewater containing 21000 ppm of fluorine was supplied to the first reaction tank at 20 kg / h and reacted. 10% dihydrate gypsum slurry liquid is supplied into the piping of the first solid-liquid separation tank and the second reaction tank at 2.2 kg / h, and 10% calcium chloride is supplied to the second reaction tank at 14.7 kg / h. To be reacted. Since the pH of the second reaction tank was in the neutral range (6.4-6.6), no neutralizer was supplied. The slurry separated in the second solid-liquid separation tank was sent to the first reaction tank at 15 L / h with a tube pump. As a result, almost the same result as in Example 1 was obtained.

Claims (5)

  In the treatment of fluorine-containing wastewater, an apparatus comprising a first reaction tank, a first solid-liquid separation tank, a second reaction tank, and a second solid-liquid separation tank is used, and is generated in the second reaction tank in the first reaction tank. Purity that can be recycled as a raw material for producing at least hydrogen fluoride in the first solid-liquid separation tank by salt exchange of fluoride ion and sulfate ion in fluorine-containing wastewater using dihydrate gypsum containing calcium fluoride And calcium fluoride having a particle size are collected, and in the second reaction tank, sulfate ions dissolved in the liquid by the salt exchange reaction, and fluorine ions not removed by the treatment in the first reaction tank Is reacted with a soluble calcium salt to precipitate dihydrate gypsum containing calcium fluoride, and the precipitated dihydrate gypsum containing calcium fluoride is converted into the first anti-reactive gypsum. Fluorinated immobilization method characterized by subjecting the reaction vessel.   An amount equal to or greater than the amount of sulfate ions dissolved in the waste liquid discharged from the second solid-liquid separation tank (the solubility of calcium sulfate), more preferably 1 to 2 times the amount of sulfate solution, particularly sulfuric acid 2. The method for immobilizing fluorine according to claim 1, wherein an aqueous solution of sodium or wastewater containing sodium sulfate is added either in waste water to be treated or up to the second reaction tank. .   More than the amount corresponding to the amount lost in the waste liquid discharged from the second solid-liquid separation tank, more preferably 1 to 2 times the amount of dihydrate gypsum is replenished as a solid or dihydrate gypsum slurry The method for immobilizing fluorine according to claim 1.   2. The fluorine recycling method according to claim 1, wherein the calcium fluoride obtained in the first solid-liquid separation tank is filtered and dried to be used as a raw material for producing hydrogen fluoride and a flux for refining steel. .   The aqueous calcium chloride solution or the waste water containing calcium chloride as soluble calcium according to claim 1 is used in an amount equal to or more than the equivalent of sulfate ions treated in the second reaction tank, more preferably 1 to 2 times. Fluorine immobilization method.