KR20010087434A - Treatement process for fluorine-containing waters - Google Patents

Abstract

The present invention is a method for treating fluorine-containing water in which fluorine-containing water is brought into contact with calcium salts in a reaction tank to react fluorine in fluorine-containing water with calcium salts, fixed with calcium fluoride, and then solid / liquid separated to discharge treated water. Liquid separation is carried out by a method selected from filtration, centrifugation, steam condensation, and flotation separation, and a part of the sludge concentrated by solid / liquid separation is returned to the reaction tank.

Description

Fluorine-containing water treatment method {TREATEMENT PROCESS FOR FLUORINE-CONTAINING WATERS}

The present invention relates to a method for treating fluorine-containing water. In particular, the present invention relates to a treatment method for removing fluorine from fluorine-containing wastewater discharged during the manufacture of electrical appliances.

Industrial sectors such as semiconductor manufacturing, chemical fertilizer manufacturing, ceramics, and aluminum industry include processes for using or generating hydrogen fluoride, and the wastewater contains fluorine. The present invention seeks to establish an effective technique for treating fluorine-containing water in terms of strengthening environmentally friendly treatment, which is being discussed recently, and utilizing resources efficiently.

Recently, the domestic law and the local law enforcing the concentration of pollutants below the standard for water quality, especially for the environment such as the water pollution prevention law, have established the emission standards of various chemicals, and therefore, total wastewater treatment is required.

Since fluorine is known to break the ecological balance in the presence of high concentrations in the discharged wastewater, wastewater treatment facilities for fluorine removal are very important from an industrial point of view.

In conventional wastewater treatment for fluorine removal, as disclosed in Japanese Patent Laid-Open No. 5-253576, fluorine-containing water is directly contacted with a column filled with calcium carbonate to fix fluorine as calcium fluoride. In particular, as shown in FIG. 1, the fluorine-containing water is transferred from the water tank 1 to the column 19 filled with calcium carbonate using the transfer pump 2 to be converted into calcium fluoride in the column. However, due to the solidification of the calcium compound in the packed column and the phenomenon that the flow of the water passes through, as shown in FIG. Treatment imperfections that often did not react and breakthrough before the equivalents reacted often occurred. In addition, fine calcium compound particles are introduced into the treated water, which adversely affects the meter or the post-stage treatment apparatus.

Hydrogen fluoride is also used or generated in manufacturing processes in semiconductor manufacturing, chemical fertilizer manufacturing, ceramics, aluminum industry and other industries, which also emits fluorine-containing wastewater.

In general, the fluorine-containing wastewater is reacted with calcium salts such as calcium hydroxide (Ca (OH) ₂ ) to produce insoluble calcium fluoride (CaF ₂ ) by coagulation sedimentation, and the solid phase and liquid phase are separated by gravity. .

3 shows such a conventional example (for example, Japanese Patent Laid-Open No. 8-197070). The fluorine-containing wastewater is stored in the water tank 51. Calcium fluoride such as calcium hydroxide 60 is added to the primary reactor 52 to produce calcium fluoride at pH 6-10. Excess calcium salt is added to reduce the amount of fluorine in the wastewater, and in the secondary reactor 53, an inorganic flocculant 61 made of aluminum, iron or another compound is added to promote the production of insoluble calcium fluoride. Acid or alkali is added to the pH adjusting tank 54 to promote the production of calcium fluoride at pH 6-8, and then an organic coagulant 62 made of polyacrylamide partially hydrolyzate is added to the flocculating tank 55 to precipitate the product. Increased. Thereafter, the treated water was transferred to the settling tank 56 and solid-liquid separated from this tank by gravity.

In order to promote crystallization in the primary reactor 52 and the secondary reactor 53, a method of returning the sludge 75 to the primary reactor 52 via the conduit 64 and using it as a crystallization nucleus is generally used. Was adopted. A part of the sludge separated in the settling tank 56 is conveyed, while the rest is transferred to the sludge storage tank 57, dewatered by the dehydrator 58, and the dehydrated cake 59 is treated as industrial waste.

Insoluble calcium fluoride produced in the early stage is contained in the symbolic water and is thus transferred to the post treatment unit. Insoluble calcium fluoride which has not precipitated in the settling tank 56 is removed from the storage tank 67 by a filtration column 68 filled with sand or the like.

In addition, in order to remove residual fluorine in the wastewater, treatment is carried out in an adsorption column 70 filled with a resin in which metal ions such as fluoride ions and zirconium forming a chelate compound are dispersed or an adsorbent such as activated alumina. The wastewater is discharged after adjusting the pH in the pH adjusting tank 71 to meet the discharge standard. In Figure 3, 69 is a filtration water tank used for the buffer and water quality monitoring of the filtered water, 72 is a storage tank used for the buffer and water quality monitoring of the pH adjusted water.

Therefore, treating the fluorine-containing water by the conventional flocculation sedimentation method requires an excessive amount of calcium salt and a large amount of flocculant, thereby increasing the treatment cost. In the method of returning part of the sludge precipitated in the settling tank to the first reaction tank and using it as the crystallization nucleus in order to improve the cohesiveness, the coagulant is a factor for inhibiting the crystallization. This is because the calcium fluoride transported from the primary reaction tank reacts with aluminum and other compounds added to the secondary reaction tank as an inorganic coagulant, and gelates to prevent crystallization from progressing. As a result, treatment with a calcium fluoride carrier containing no coagulant is more effective, but addition of a coagulant is necessary because calcium fluoride does not precipitate in the precipitation tank.

In a system in which the solid insoluble calcium fluoride product is separated from the liquid by gravity precipitation, it is impossible to avoid the phenomenon of mixing insoluble calcium fluoride in the supernatant (usually 20 to 50 mg / L), so a post-stage filtration device is required. Sand filtration is used in post-stage filtration, but this method requires periodic cleaning.

In addition, in the treatment in which calcium salt and flocculant are added to the fluorine-containing waste water and the insoluble calcium fluoride salt is separated by gravity, a large amount of residual fluorine is contained in the waste water, so that the treatment in the adsorption column is necessary.

In addition, the sludge discharged from the conventional treatment apparatus is poor in dehydration properties due to the addition of the flocculant, and more expensive to treat the dehydrated cake. If the sludge has a high purity of calcium fluoride, it can be effectively used for high value-added applications such as, for example, a raw material for producing hydrogen fluoride, but since the sludge contains impurities such as SiO _{2 in} wastewater, Since it is impossible to achieve a high purity of about%, even if it is effective to use it, it was only available because of low added value such as cement extender.

When sedimentation is carried out by gravity in the sedimentation step, it is precipitated by gravity, so a large capacity is required when sedimenting, and consequently a large space is required.

Therefore, the object of the present invention is to solve the first problem of the prior art, does not cause the solidification of the calcium compound or the drift of the passing water, the fine particles of the calcium compound does not mix in the treated water and the treatment of fluorine-containing water very efficiently To provide a way to do it.

In order to achieve the above object, the present invention is a method for treating fluorine-containing water by contacting fluorine-containing water with calcium carbonate in order to react fluorine in the fluorine-containing water with calcium carbonate to fix the calcium fluoride. A method of adding fluorine-containing water to a circulation system in which water is added to the mixture and drawn out through the fluorine removal treatment rule separator device while circulating through the separator device and converting calcium carbonate into calcium fluoride is provided.

The present invention, in order to solve the second problem of the prior art, the solid-liquid separation of calcium fluoride produced by the reaction of fluorine and calcium salt in the conventional bloso-containing water, filtration, centrifugation, steam condensation, Provided is a method of reducing the fluorine concentration in the fluorine-containing water by carrying out a flotation method and returning a part of the concentrated sludge to the reaction tank to use as a nucleus for crystallization.

In addition, another object of the present invention is to reduce the water content of the calcium fluoride cake produced as well as the method of treating fluorine-containing water, which can be treated at low operating cost without using inorganic or organic flocculant, and to make it highly effective. Its purpose is to provide a treatment method that can expand the usage of the system and reduce the required space.

In order to achieve this object, the present invention is to contact the fluorine-containing water with the calcium salt in the reaction tank in order to react the fluorine in the fluorine-containing water with calcium salt and to remove the treated water by solid / liquid separation. As a method of performing solid-liquid separation, solid-liquid separation is carried out by a method selected from filtration, centrifugal separation, steam condensation, and flotation separation, and a part of the sludge concentrated by solid-liquid separation is returned to the reaction tank.

According to the present invention, there is no need to use an inorganic or organic flocculant for treating fluorine-containing water.

1 is a system diagram of a conventional fluorine-containing water treatment method corresponding to the first invention.

Fig. 2 is a schematic diagram of the drift phenomenon of the passing water in the conventional fluorine-containing water treatment method shown in Fig. 1;

3 is a schematic system diagram of a conventional fluorine-containing water treatment method corresponding to the second invention.

4 is a system diagram showing an example of a fluorine-containing water treatment method according to the first invention.

5A, 5B and 5C show an example of a separator used in the fluorine-containing water treatment method according to the first invention.

Figure 6 is a system diagram showing another example of the fluorine-containing water treatment method according to the first invention.

Fig. 7 is a system diagram showing still another example of the method for treating fluorine-containing water according to the first invention.

8 is a flow diagram showing still another example of the method for treating fluorine-containing water according to the first invention.

9 is a schematic system diagram of a fluorine-containing water treatment method according to the second invention.

10 is a graph showing the results of Reference Example 1. FIG.

11 is a graph showing the results of Reference Example 2. FIG.

12A, 12B, 12C are schematic views of the filtration apparatus used in Example 2. FIGS.

13 is a graph showing the results of Example 2. FIG.

14 is a schematic view of a filtration device used in Example 3. FIG.

15 is a partially enlarged view of FIG. 14;

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

Figure 4 is a system diagram showing an embodiment of the fluorine-containing water treatment method according to the first invention. Calcium carbonate particles are added to the fluorine-containing water, which is starting water, and circulate in the circulation tank 3, the membrane device 5, and the circulation conduit 13. The raw water is transferred from the raw water tank 1 to the circulation tank 3 by the transfer pump 2, and the circulation system consisting of the circulation tank 3, the membrane device 5, and the circulation conduit 13 is circulated in the pump 4 Reacts with the calcium carbonate circulating in the circulation system, and the treated purified water is transferred from the separation membrane device 5 to the treatment water tank 9 and discharged as treatment water by the transfer pump 10. Here, the transfer of raw water and discharge of treated water are continued until breakthrough by the progress of the reaction between fluorine and calcium carbonate. The membrane device 5, for example, as shown in Figs. 5A to 5C, is made of a polyester woven fabric into a cylinder 42 having a diameter of about 12 mm (Fig. 5A), and three cylinders of PVC having an internal diameter of about 35 mm. The transverse flow type device 44 (FIG. 5C) loaded in the pipe 43 can be used (FIG. 5B).

According to this method of the present invention, the reaction between calcium carbonate and fluorine is made in a circulation system composed of the circulation tank 3, the membrane device 5, and the circulation conduit 13 as described above, and the calcium compound is separated from the membrane device. It is circulated with the water to be treated immediately after passing through, and only the treated water is passed through the separation membrane and transferred to the treated water tank; As a result, there is no problem of incomplete treatment due to the solidification of calcium compounds or the drift of water, and the phenomenon of mixing of calcium compound fine particles into the treated water is considerably reduced. In addition, since the method of the present invention does not use a flocculant, high-purity calcium fluoride is produced during the treatment, so that the high-purity calcium fluoride may be used as a fluorine source such as hydrofluoric acid production.

When the fluorine-containing water treatment is continuously performed in the apparatus having the structure of FIG. 4 without causing breakage of the system, as shown in FIG. 6, the raw water is transferred from the raw water tank 1 to the circulation tank 3. (2) was continuously supplied, and fluorine and calcium carbonate were reacted in a circulation system consisting of a circulation tank 3, a membrane device 5, and a circulation conduit 13, and the treated purified water was treated from the membrane device 5. The calcium carbonate is transferred by the calcium carbonate supply pump 20 from the calcium carbonate storage tank 21 to the purified tank 3 while being discharged to the water tank 9 and the treated water is continuously discharged as treated water by the transfer pump 10. Calcium fluoride is supplied continuously, and it is performed by the method of taking out continuously with the calcium fluoride extraction pump 22 from the circulation tank 3 to the calcium fluoride storage tank 23. As shown in FIG.

In the case of carrying out the method of the present invention, two or three or more such circulation systems may be connected and performed simultaneously. For example, as shown in FIG. 7, calcium carbonate particles are added to the fluorine-containing raw water, and the circulation tank 3, the membrane device 5, the circulation conduit 13, the circulation tank 6, and the membrane device 8 are separated. And circulate within the conduit 14. In this state, the raw water is transferred from the raw water tank 1 to the circulation tank 3 by the transfer pump 2, and the circulation system composed of the circulation tank 3, the membrane device 5, and the circulation conduit 13 is circulated by the pump. Reacted with the calcium carbonate circulating in the circulation system during circulation by (4), the treated purified water is transferred from the membrane device (5) to the circulation tank (6); In addition, while being circulated by the circulation pump 7 in the circulation system composed of the circulation tank 6, the membrane device 8 and the circulation conduit 14, the reaction water is again reacted with calcium carbonate circulating in the circulation system, and the treated purified water is separated from the membrane device. It is transferred from (8) to the treatment water tank 9, and is discharged as treatment water by the transfer pump 10. The separator device 8 may have the same configuration as the separator device 5 described above.

In the embodiment shown in FIG. 8, the circulation tank 6 is also located behind the membrane device 8, followed by another circulation system consisting of the circulation pump 7, the membrane device 8 and the circulation conduit 24. It is connected.

Even in an apparatus in which two or three or more circulation systems are connected, the calcium carbonate feed system and the calcium fluoride extraction system are properly positioned by the method shown in Fig. 6, so that the continuous treatment can be performed while maintaining the constant water quality. It becomes possible.

7 and 8 can optionally be used for continuous processing in a merry-go round. For example, in the treatment with the apparatus shown in FIG. 7, the merigo round conversion conduit 16 is monitored before the breakthrough is reached by monitoring the change in the fluorine concentration of the treated water from the membrane device 8. ), The calcium compound in the first stage circulation system consisting of the circulation tank (3), the circulation pump (4), the membrane device (5) and the circulation conduit (13) was replaced with freshly prepared calcium carbonate, The conversion conduit 18 is converted into a merigo round conversion conduit 12, and the flow sequence of the raw water is composed of a circulation tank 6, a circulation pump 7, a membrane device 8 and a circulation conduit 14. Switch from the second stage circulatory system to the first stage circulatory system. By continuously changing the flow order in this manner, it is possible to continuously process the fluorine concentration of the treated water without increasing it. Similarly in the apparatus shown in Fig. 8, it is obvious that the operation can be carried out in a round and round manner by switching the flow sequence continuously.

Hereinafter, a preferred embodiment of the second invention will be described in detail.

The following description relates to an example of treating fluorine-containing wastewater as fluorine-containing water.

9 is a schematic system diagram showing a method according to the second invention. The fluorine-containing wastewater is stored in the raw water tank 76. In the reactor 77, calcium salts 86 such as calcium hydroxide salts are added to adjust the pH of the fluorine-containing wastewater to 4 to 10 to produce calcium fluoride. The pH is adjusted by adding acid (87) or alkali (88) in the pH control tank (78) to promote crystallization of calcium fluoride, and then the wastewater is subjected to solid-liquid separation in a concentrator (79), and the concentrated sludge is Transfer to the sludge storage tank 81 to dehydrate in the dehydrator (82). A portion of the concentrated sludge is returned to the reaction tank 77 via the conduit 84 and used as a nucleus for crystallization of calcium fluoride in the reaction tank 77. The sludge 85 and the fluorine-containing wastewater 92 conveyed here are stored in the storage tank 90, calcium salt 91 is added, and calcium fluoride crystals are grown as crystallization nuclei, and the crystals are transferred to the reaction tank 77. Conveying can effectively promote crystallization; It is particularly effective when the fluorine ion concentration of the fluorine-containing wastewater 89 is low. The amount of calcium salt 91 added is preferably slightly more than the equivalent of the amount of fluorine ions in the fluorine-containing wastewater 92, for example, 1.2 equivalents, and the fluorine-containing wastewater 92 introduced into the storage tank 90 is fluorine. About 10 to 20% of the total amount of the wastewater containing 89 is preferable. In addition, the conveyed sludge amount is preferably about 10 to 40% of the total amount of sludge generated.

When the returned sludge has low fluorine ion concentration or sludge concentration, the fluorine-containing wastewater 89 may be added to the storage tank 90.

The concentrating device 79 used is a device capable of solid / liquid separation of wastewater containing calcium fluoride discharged from the reaction tank 77. Concentration can be performed by filtration, centrifugation, steam condensation or flotation. have. When the solid / liquid separation is performed by gravity sedimentation, calcium fluoride crystals must have a large specific gravity, so a flocculant must be added, but the separation means can be performed without growing the crystals by filtration, centrifugation, steam condensation or flocculation. No addition of flocculant is necessary.

Examples of the solid / liquid separation means by filtration include a membrane separation method. Membranes used are ultrafiltration (UF) membranes, microfiltration (MF) membranes, strainers and the like.

The invention is further illustrated by the following examples.

Example 1

A fluorine-containing wastewater having a fluorine concentration of 1000 mg / L and a pH of 4.0 was treated as raw water using a treatment system as shown in Fig. 7, and the treatment conditions were as follows.

1) Raw water tank (1) and treated water tank (9): 200L, polyethylene material

2) Transfer pump (2) and treated water pump (10): 30L / H, magnetic pump

3) Circulation tank (3) and circulation tank (6): 50 L, polyethylene material

4) Circulating pump (4) and circulating pump (7): 4m ³ / H, magnetic pump

5) Separation membrane device 5 and membrane device 8: Horizontal flow membrane device (Figs. 5 (a) to 5 (c)), polyester film, filtration pressure 0.5 to 1.5 kg / cm ² , filtration flow rate 1 m / sec, circulation volume 3.4m ³ / H

6) Calcium carbonate: particle distribution 0.3-0.5mm (31.6%), 0.2-0.3mm (35.8%), <0.2mm (32.6%).

The calcium carbonate is circulated (3), circulating pump (4), membrane device (5), circulating conduit 13 and circulating tank (6), circulating pump (7), membrane device (8) and circulating conduit (14). Cycles through). First, when raw water is passed through the first stage circulation system, gas is generated, and a reaction in which the fluorine in the raw water is fixed to calcium fluoride occurs and is treated, which satisfies SS≤2 mg / L in which fine particles are not contained in the treated water from the separation membrane device 5. Lovely water quality was obtained. Next, when passing through the second stage circulation system for further removal of fluorine from the treated water, the treated water from the membrane device 8 also shows satisfactory water quality of SS ≦ 2 mg / L, and the fluorine concentration is 5 mg / L. Very low. The recovered calcium fluoride was also of high purity.

For continuous treatment of raw water in the present embodiment, the circulating tank 3, the circulating pump 4, and the membrane device 5 in accordance with the change in the concentration of fluorine in the treated water from the membrane device 8 using the merigo round method. Calcium compound of the first stage circulatory system composed of the circulating conduit 13 and the circulating conduit 13 is replaced with newly prepared calcium carbonate, and the flow order of the raw water is circulated in the circulating tank 6, the circulating pump 7, the membrane device 8, and the circulating conduit By switching from the second stage circulatory system of (14) to the first stage circulatory system, continuous processing was possible without increasing the fluorine concentration of the treated water. In other words, the mercury round treatment was carried out in a circulation system composed of two systems connected in series to continuously and stably remove fluorine in raw water.

5A to 5C, by quantitatively extracting the circulating calcium compound, new calcium carbonate can be continuously supplied, and fluorine in the raw water can be continuously and stably removed even when the merigo round system is not used. .

The calcium carbonate used for the treatment here may be any particle size and particle distribution. The separator used is a common separator or a microfiltration (MF) or ultrafiltration (UF) membrane.

Reference Example 1

Reference Example 1 was carried out in the following manner to confirm the effect of the present invention.

A wastewater model containing 200 mg / L, 100 mg / L, 50 mg / L and 20 mg / L of fluoride ions was prepared, and calcium hydroxide (Ca (OH) ₂ ) was added and the residual concentration of fluorine ions in the wastewater was measured. The pH at this time was adjusted to 6-8 range with sodium hydroxide (NaOH). This result is shown in FIG.

According to Fig. 10, the wastewater having a high fluorine ion concentration (200 mg / L, 100 mg / L) shows that the fluorine ion concentration immediately decreases even when a small amount of calcium salt is added, and the fluorine ion is formed between the calcium ion generated from the calcium salt. It reacted efficiently to and insoluble calcium fluoride (CaF ₂ ) precipitated. On the other hand, wastewater with a low fluorine concentration (50 mg / L, 20 mg / L) did not decrease the concentration of fluorine ion in the wastewater without adding an excess calcium salt.

The specific mechanism is not fully understood, but is assumed to be as follows. In other words, when the concentration of fluorine ions is high, insoluble calcium fluoride is precipitated even with a small amount of calcium ions, and the precipitated calcium fluoride becomes a crystallization nucleus for crystallization until crystallization until the residual fluorine ion concentration is low. On the contrary, when the concentration of fluorine ions is low, even if an excess calcium salt is added, initial crystallization is delayed, so that fluorine ions remain in the wastewater.

Reference Example 2

In order to confirm the above observation, the inventors performed Reference Example 2.

A calcium fluoride-containing solution prepared at a fluorine concentration of 500 mg / L and a calcium concentration of 580 mg / L was slowly added to a wastewater model having a fluorine ion concentration of 20 mg / L and a calcium ion concentration of 320 mg / L. The pH at this time was adjusted to 6-8 range with sodium hydroxide (NaOH). This result is shown in FIG.

According to Fig. 11, when the concentration of fluorine ion is 20 mg / L, the concentration of fluorine ion in the wastewater did not decrease under the conditions of Reference Example 1, but when a small amount of calcium fluoride was added as the crystallization nucleus, the fluorine ion became insoluble calcium fluoride. As a result, residual fluorine ions in the wastewater were reduced.

In comparison with FIG. 10 and FIG. 11, although the fluorine ion concentration is reduced to 5 mg / L, according to the prior art (FIG. 10), a residual calcium ion concentration of 100 mg / L is required. According to the present invention, it can be seen that even a small amount of calcium salt can be used.

Reference Examples 1 and 2 described above merely confirm the principles of the present invention and do not limit the design or operating conditions of the apparatus used in the present invention.

Example 2

An apparatus as shown in Fig. 9 was used. This embodiment relates to the method for treating fluorine-containing water according to the present invention, and the present invention is not limited to the illustrated method.

In this example, solid / liquid separation was performed by filtration with a strainer. As the strainer, polyester fiber, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile and the like having chemical resistance, heat resistance to operating temperature, and mechanical strength to withstand use are used. As a strainer, a woven fabric (twisted fabric cloth) is used, and the weight and fiber diameter of the woven fabric are selected according to the fluorine ion concentration and other ion concentrations of the wastewater and the physical properties of other substances.

In the case of using this type of strainer, when insoluble calcium fluoride having a predetermined particle size passes, coarse fine particles are mainly caused by inertial collision, and fine fine particles are mainly attached to the fibers by diffusion and screening to form particle crosslinks between the fibers. The primary adhesion layer formed in this way has a myriad of bent holes and therefore has a higher porosity than the new strainer. The fine particles are collected by this primary adhesion layer. In addition, the porosity was improved by filtering particles larger than the particle size of insoluble calcium fluoride normally produced in the step of forming the primary adhesion layer, thereby confirming that the flux passing through the strainer was large. The large particles mentioned here are calcium carbonate or silicon oxide (SiO ₂ ) particles that do not adversely affect the next cleaning process.

In this way, the removal of calcium fluoride can be achieved very effectively by the present invention, thereby eliminating the need for the post-stage filtration device of FIG. According to the method of the present invention, since no flocculant is used, high-purity calcium fluoride can be obtained as treated sludge, and the sludge can be reused for applications requiring high-purity calcium fluoride, such as hydrofluoric acid raw materials. Cylindrical or flat strainers may be used in the concentrator 79 as the structure of the filtration column.

In order to confirm the filtration performance, as shown in Figs. 12A to 12C by the concentrator 79, a polyester woven fabric was used as a cylinder 93 having a diameter of about 12 mm (Fig. 12A), and these three cylinders had an internal diameter of about 35 mm. The filtration apparatus 95 (FIG. 12C) loaded in the PVC pipe 43 (FIG. 12B) was used.

For this treatment, fluorine-containing wastewater containing 400 mg / L of fluorine ions was supplied. The circulation operation was started while adding 100 g of calcium hydroxide to 60 L of wastewater.

Fig. 13 is a view showing the flux recovery by changing the flux and cleaning. As shown in Fig. 13, the circulation operation tends to reduce the flux. This is because insoluble calcium fluoride accumulates on the surface of the strainer and the pressure loss rises. Calcium fluoride accumulated on the strainer surface was removed by washing to confirm the recovery of the flux. Although hydrochloric acid was used to wash in this example, the removal of calcium fluoride is not limited to hydrochloric acid washing.

Example 3

Example 3 was performed using the apparatus shown in FIG. 14 and FIG. 15 as a filtration apparatus of the concentration apparatus 79. As shown in FIG. In this example, an MF membrane having a pore diameter of 0.1 µm to 100 µm was used for the filtration apparatus. Plates 98 made of support 97 for supporting the MF film 96 are arranged at equal intervals, and bubbling occurs at the bottom when the treated wastewater passes, and excess calcium fluoride is accumulated on the film surface. To prevent them. If the flux is reduced, the flux can be recovered by removing deposits by chemical cleaning or physical removal.

The same result can be obtained even when a known centrifuge, steam condenser and flotation device having various structures as the concentrator 79 are used.

As described above, the fluorine-containing water treatment method according to the first invention can stably remove fluorine without including fine particles in the treated water. Therefore, it makes a major contribution to the industry that uses hydrofluoric acid and discharges fluorine-containing water and protects the natural environment.

The method for treating fluorine-containing water according to the second invention can reduce the use of the treatment agent, reduce the sludge, realize the simplification of the apparatus, reduce the required space, and efficiently use fluorine by recovering calcium fluoride of good quality.

Claims (5)

In order to fix the fluorine in the fluorine-containing water with calcium salt and fix it with calcium fluoride, the fluorine-containing water is contacted with the calcium salt in the reaction tank, and the solid / liquid separation is used to remove the treated water. , Centrifugal separation, steam condensation, flotation separation method, and a part of the sludge concentrated by solid / liquid separation is returned to the reaction tank. The method of claim 1, A method for treating fluorine-containing water, comprising contacting fluorine-containing water with calcium salt in a reaction tank without the presence of an inorganic or organic flocculant. The method of claim 1, A method of treating fluorine-containing water, characterized in that the pH is adjusted after the reaction and before the solid / liquid separation. The method of claim 1, A method for treating fluorine-containing water, characterized in that calcium salt is added to the sludge conveyed to the reaction tank during conveyance. The method of claim 1, The amount of sludge to be returned is a fluorine-containing water treatment method, characterized in that 10 to 40% by weight of the total amount of sludge generated.