KR20100118139A - Wastewater treatment apparatus and method of wastewater treatment - Google Patents

Abstract

The wastewater treatment apparatus 10 of the present invention includes a chemical tank 15 in which calcium powder, which is added to the treated water 12 containing fluorine and generates calcium fluoride, is stored, and calcium fluoride is removed from the treated water 12. The filtration membrane 13 which isolate | separates, and the RO filtration apparatus 14 which removes fluorine ion from the to-be-processed water 12 from which calcium fluoride was isolate | separated, The calcium powder which did not react with fluorine is carried out by the RO filtration apparatus 14 The concentrated to-be-processed water 12 has a structure conveyed to the front end rather than the filtration film 13.

Description

Drainage and drainage methods {WASTEWATER TREATMENT APPARATUS AND METHOD OF WASTEWATER TREATMENT}

The present invention relates to a wastewater treatment apparatus and a wastewater treatment method for removing fluorine powder from wastewater.

At the present time, reducing industrial waste and reusing and recycling industrial waste is an important theme from an ecological point of view and an urgent corporate task. Among these industrial wastes are various fluids containing substances to be removed.

These are expressed by words such as sewage, waste liquid, and drainage. Hereinafter, a substance containing a substance to be removed in a fluid such as water or medicine will be described as drainage.

A large amount of drainage occurs during the process of manufacturing a semiconductor device. Most of the fluorine used in the semiconductor factory is discharged as wastewater which is difficult to reuse.

For example, in a dry (plasma) etching apparatus or a plasma CVD apparatus, carbon tetrafluoride (CF ₄ ), hexafluoroethane (C ₂ F ₆ ), perfluorocyclobutane (C) in wafer processing or cleaning in the apparatus. ₄ F ₈₎ or the like, in many cases of the fluorine-based gas is used. Most of these gases are discharged out of the chamber as CF ₄ , but because they are substances having a global warming promoting action (Perfluorocompounds (PFCs) gas), decontamination treatment is required. In this decontamination treatment, fluorine is absorbed by water, and lean hydrofluoric acid wastewater (waste liquid) is discharged. In addition, in a wet etching apparatus using a fluorine-based material (for example, hydrofluoric acid), a concentrated hydrofluoric acid drainage (waste solution) that is a waste liquid after wafer processing or a lean hydrofluoric acid drainage (waste solution) that is a drainage of pure rinse is discharged. . In addition, the hydrofluoric acid is hereinafter referred to as hydrofluoric acid.

If drainage with high concentrations of fluoride flows into nature, it is known to disrupt the balance of the ecosystem. Therefore, removing fluorine from wastewater is extremely important in industry. For example, the discharge value of the wastewater containing fluorine has a reference value determined by the Water Pollution Prevention Act, the Local Government Ordinance, or the like. Specifically, the concentration of fluorine contained in the drainage should be 8 mg / L or less. In addition, there is a possibility that regulation of the total amount of fluorine emitted is also performed.

On the other hand, the fluorine removed from the wastewater can be reused in the semiconductor processing apparatus using hydrofluoric acid or the like. As an example of the removal method, fluorine can be removed as calcium fluoride from the wastewater by reacting fluorine-containing wastewater (waste solution) with a calcium compound to produce calcium fluoride.

Moreover, after removing the fluorine content contained in waste water as calcium fluoride, it is also known to perform advanced wastewater treatment by performing a filtration process further.

In the following Patent Document 1, a method of treating water containing calcium powder and fluorine powder using a cation exchange column and a RO membrane separation device is disclosed. In particular, referring to FIG. 1 and the description of the publication, after adjusting the PH of Ca · F-containing water in the PH adjusting tank 1, Ca is removed by the cation exchange column 2, after which the RO membrane F is removed by the separating device (3). By doing in this way, since the Ca in water is previously removed by the cation exchange tower ₂ , clogging of the RO film by CaF2 is prevented.

In addition, Patent Literature 2 below discloses a method in which calcium carbonate or the like is added to water to be treated to produce poorly soluble fluorite apatite, and the ion treatment after membrane filtration of the fluorine apatite. Specifically, referring to FIG. 1 and its description, first, raw water in which calcium ion-containing water and fluorine ion-containing water are mixed is stored in the raw water tank 1. And fluorine apatite is produced by adding calcium carbonate and phosphoric acid to this raw water. In addition, the produced fluorine apatite is removed by the MF membrane filtration device 2, and the treated water is purified by the RO membrane filtration device 4.

Japanese Patent Laid-Open No. 10-244259 Japanese Patent Laid-Open No. 2001-149950

However, the above described problems have been encountered in the technology described in Patent Document 1 and Patent Document 2.

That is, in the technique of patent document 1, since the cation exchange column for removing a Ca component is used, there existed a problem that a processing installation enlarged and a process operation became complicated.

Moreover, in the technique of patent document 2, in order to produce a fluorine apatite, since it is necessary to adjust pH of a process water and add a special additive, this has a problem which raises processing cost.

The wastewater treatment apparatus of the present invention includes an addition means for adding calcium powder to fluorine-containing water to be treated to produce calcium fluoride, first separation means for separating the calcium fluoride from the water to be treated, and the calcium fluoride. A second separation means for removing fluorine ions from the separated water to be treated, wherein the treated water in which the calcium powder which has not reacted with the fluorine is concentrated by the second separation means is less than the first separation means. It is characterized by being conveyed to the front end.

The present invention also provides a method of treating wastewater comprising the steps of generating calcium fluoride by adding a calcium component to water to be treated containing fluorine components, separating the calcium fluoride from the for-treatment water by first separating means, And removing fluorine ions from the treated water from which the calcium fluoride is separated by a second separating means, wherein the calcium powder which has not reacted with the fluorine is concentrated in the treated water. It is characterized by conveying to the front end rather than the said 1st separating means.

According to the present invention, after separating the fluorine powder in the state of calcium fluoride by the first separating means, the calcium powder which has not reacted with the fluorine is concentrated by the second separating means and conveyed to the front end than the first separating means. . Therefore, since the calcium powder which did not contribute to the production of calcium fluoride can be reused, the total amount of calcium required for the removal of the fluorine powder is reduced, and the processing cost is reduced by that amount.

In addition, since the fluorine ions are removed by the second separation means after the calcium fluoride is removed by the first separation means, early blockage of the second separation means is suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the drainage apparatus of this invention.
It is a figure which shows the RO filtration apparatus with which the wastewater treatment apparatus of this invention is equipped.
3 is a flow chart showing the wastewater treatment method of the present invention.
4 is a view for explaining a filter device applied to the wastewater treatment apparatus of the present invention.
5 is a view for explaining the principle of operation of the filter device (A) applied to the wastewater treatment apparatus of the present invention, and (B) an enlarged view of the first filter.
6 is a characteristic diagram for explaining the characteristics of a filtration apparatus applied to the wastewater treatment apparatus of the present invention.

As one embodiment of the present invention, a wastewater treatment apparatus for treating wastewater containing hydrofluoric acid (aqueous solution of hydrogen fluoride (HF)) and a wastewater treatment method for hydrofluoric acid using the same will be described. In addition, hydrofluoric acid is hereafter called hydrofluoric acid.

With reference to FIG. 1, the structure of the wastewater treatment apparatus 10 is demonstrated. The wastewater treatment apparatus 10 of the present embodiment includes a first treatment tank 11A (addition means) in which calcium fluoride is produced by adding calcium powder to the water 12 to be treated containing fluorine powder, and the immersed filter membrane. (13) RO filtration device 14 for highly filtering second treatment tank 11B through which calcium fluoride is filtered by (first separating means) and untreated water 12 filtered by filtration membrane 13. (2nd separation means) and the 6th path | route P6 which conveys the to-be-processed water 12 concentrated by RO filtration apparatus 14 to the 1st process tank is comprised mainly.

The first treatment tank 11A is a tank in which treated water 12 that is wastewater containing fluorine components is stored and calcium fluoride is added to the treated water 12 to generate calcium fluoride.

In this embodiment, the to-be-processed water 12 is wastewater containing a fluorine powder. This wastewater is discharged from a semiconductor processing plant, and is discharged by, for example, an etching process of a semiconductor, glass, metal or the like, a wafer processing process such as formation of a CVD film, or cleaning of a semiconductor processing apparatus.

For example, in a dry (plasma) etching apparatus or a plasma CVD apparatus, fluorine-based gases such as CF ₄ , C ₂ F ₆ , and C ₄ F ₈ are often used. These gases are also used when cleaning the chamber after wafer processing. Most of these gases are discharged out of the chamber as CF ₄ , but since they are substances (perfluoro compound (PFCs) gas) having a global warming promoting action, decontamination treatment is required. In this decontamination treatment, fluorine burned and decomposed is absorbed into water, and lean hydrofluoric acid wastewater is discharged. In addition, in the wet etching apparatus, since hydrofluoric acid is used to improve the corrosiveness during etching, the concentrated hydrofluoric acid drainage, which is the waste liquid after wafer processing, and the lean hydrofluoric acid drainage, which is the drainage of pure water rinse, are discharged.

In 11 A of 1st processing tanks, hydrogen fluoride (HF) contained in the to-be-processed water 12 dissociates 99.9% or more to hydrogen ion (H ⁺ ) and fluorine ion (F <^-> ) (formula A below). In addition, in order to promote this dissociation, the water to be treated 12 may be stirred in the first treatment tank 11A by stirring means such as a propeller.

HF → H ^{+ +} F ^- (formula A)

The 1st path P1 is a path | route to which the to-be-processed water 12 discharged | emitted from the said environment is supplied to 11 A of 1st process tanks. Via the 1st path P1, the to-be-processed water 12 containing fluorine ion (F <^-> ), for example is introduce | transduced into 11 A of 1st process tanks. As an example, 10 t / day of untreated water with a fluorine ion concentration of 100 mg / L is supplied from the first path P1. Here, the pH of the water to be treated containing hydrogen fluoride is, for example, about PH 3 to 4, and is very strong acid. From this, PH of the to-be-processed water 12 may be set to 7-9 by adding NaOH as an alkali chemicals.

The chemical tank 15 is a tank in which an aqueous solution of calcium powder is stored in order to fix the fluorine powder contained in the water to be treated 12. As the calcium powder to be used, calcium chloride (CaCl ₂ ) or calcium hydroxide (Ca (OH) ₂ ) is employed. In view of low cost and high solubility product, calcium chloride is suitable as the calcium powder to be used. As an example, the chemical tank 15 stores an aqueous solution containing 35% by weight of calcium chloride.

The aqueous solution stored in the chemical | medical agent tank 15 is introduce | transduced into 11 A of 1st processing tanks via 2nd path P2 (addition means).

In the first treatment tank 11A, the fluorine ions contained in the for-treatment water 12 introduced from the first path P1 and the calcium ions introduced from the second path P2 are combined to form calcium fluoride . Specifically, by the reaction represented by the following formula (B), the fluorine component contained in the water to be treated 12 is fixed as calcium fluoride.

^{_{2F - + CaCl 2 → CaF 2}} + 2Cl - ( formula B)

Referring to the above formula (B), in order to make calcium fluoride the fluorine ions contained in the water to be treated 12, theoretically, half the number of moles of calcium of the fluorine ions is required. For example, in order to treat the water to be treated having a fluorine ion concentration of 100 mg / L as described above at a rate of 10 t / day, an aqueous solution of calcium chloride having a concentration of 35% by weight needs to be 5.5 L / day. However, the entire amount of the added calcium powder is not combined with fluorine ions, and some of the added calcium powder is not combined with fluorine ions. Therefore, in this embodiment, a large amount of calcium chloride is injected into the to-be-processed water 12 rather than the quantity theoretically required. Specifically, calcium chloride in an amount of twice or more of the amount theoretically required in order to fix the total amount of fluorine content contained in the water to be treated 12 is subjected to the first treatment tank (via the second path P2). 11A). By doing in this way, the density | concentration of the fluorine ion contained in the to-be-processed water 12 discharged from 11 A of 1st processing tanks can be 4 mg / L or less, for example. The concentration of this fluorine ion satisfies the general discharge standard.

In this embodiment, since a large amount of calcium fluoride is added to to-be-processed water in this way rather than a theoretical value, there exists a possibility that processing cost may increase. From this, in order to reduce processing cost, the to-be-processed water concentrated by RO filtration apparatus 14 is conveyed to 11 A of 1st treatment tanks, and calcium powder is recycled. This matter will be described later.

The water to be treated 12 in which fluorine ions are immobilized as calcium fluoride as described above is introduced into the second treatment tank 11B via the third path P3.

In the second treatment tank 11B, the calcium fluoride is separated from the treatment water 12 by filtering the treatment water 12 by the filtration membrane 13 (first separation means). Here, as the filtration membrane 13, the filtration mechanism which can perform filtration in a fluid can be employ | adopted generally. Furthermore, you may separate from a to-be-processed water by precipitating calcium fluoride. In this embodiment, solid-liquid separation of calcium fluoride and the water to be treated 12 is performed by filtration using a self-forming film formed on the surface of the filtration membrane 13. The detail of this self-forming film is mentioned later.

The treated water 12 filtered by the filtration membrane 13 immersed in the second treatment tank 11B is a state in which calcium fluoride is almost separated and removed, and fluorine ions (F ⁻ ) which do not react with calcium powder are exemplified. For example, it contains about 4mg / L. Further, the unreacted calcium fluoride Division ion (Ca ^{+ 2)} also, is included in the filtered water to be treated (12). Fluorine ions and calcium ions remaining in the water to be treated 12 are removed by the RO filter 14 in the next stage.

The self-forming film may be a self-forming film made of a substance to be removed containing calcium fluoride generated in the water to be treated 12. That is, the to-be-processed water 12 is filtered by the to-be-adsorbed thing adsorbed by the filtration surface of the filtration membrane 13. In addition, when recovering calcium fluoride, this self-forming film is also removed from the filtration film 13 and recovered.

The air diffuser 18 has an action of supplying bubbles to the filtration membrane 13 from below in the water 12 to be treated. Specifically, gas is supplied to the diffuser device 18 from a pump (not shown) provided outside to generate bubbles. Bubbles generated from the air diffuser 18 move upward along the filtration surface of the filtration membrane 13. In this way, by generating bubbles from the air diffuser 18, the thickness of the self-forming film formed on the surface of the filtration membrane 13 can be set to a predetermined value or less. From this, the blockage of the self-formed film can be suppressed and the water to be treated 12 can be filtered while securing some flux.

As the gas generated from the diffuser 18, an inert gas such as helium, neon, argon or nitrogen can be employed. When the air is supplied from the air diffuser 18 to the water to be treated 12, the carbon dioxide gas contained in the air and the fluoride ions contained in the for-treatment water 12 react with each other to lower the concentration of calcium fluoride There is. By employing an inert gas as the gas supplied from the diffuser 18, the concern can be eliminated.

The fourth path P4 is a path through which the filtered water filtered by the filtration membrane 13 passes. The storage tank 15C is provided in the branched path in the middle of the fourth path P4.

In the storage tank 15C, a part of the filtrate filtered by the filtration membrane 13 is stored. The position of the storage tank 15C is set above the liquid level of the to-be-processed water 12 stored in the separation tank 11C. The filtrate or tap water stored in the storage tank 15C is used to reverse flow of the fourth passage P4 when the self-forming film formed on the surface of the filtration membrane 13 is peeled off.

7th path | route P7 is a path | route which conveys the to-be-removed substance containing the precipitated calcium fluoride from the 2nd process tank 11B to the filter press 17. FIG. Specifically, the to-be-removed substance deposited on the surface of the filtration membrane 13 and the to-be-removed substance which precipitated under the 2nd process tank 11B are conveyed to the filter press 17. As shown in FIG. The treated water 12 to be transported contains calcium fluoride with high purity. In addition, when neutralization process of the to-be-processed water 12 is performed, neutralized salt is also contained in the to-be-processed water 12 conveyed.

The to-be-removed substance containing calcium fluoride is supplied to the filter press 17 by the 7th path P7, and the water content of a to-be-removed substance falls by performing a dehydration process. The moisture content of the to-be-removed object dewatered by the filter press 17 is about 50 weight%, for example. Further, when the substance to be removed is dried, a block (solid matter) having a purity of about 85% by weight of calcium fluoride is obtained. Calcium fluoride contained in high purity in the substance to be removed is reused as a fluorine source.

The eighth path P8 is a path for injecting water into the filter press 17 and washing the neutralized salt contained in the substance to be stored contained in the filter press 17. The to-be-removed thing in the pH-treated to-be-processed water contains about 15 weight% of neutralizing salt (NaCl), for example. By injecting water into the filter press 17 from the eighth path P8, most of the neutralized salt is discharged from the filter press 17 to the outside. In addition, calcium fluoride having a larger size than that of the neutralized salt is stored in the filter press 17. That is, by injecting water into the filter press 17, the purity of the calcium fluoride contained in the to-be-removed object accommodated in the filter press 17 can be improved.

The water injected into the filter press 17 is temporarily stored in the import tank 19. The to-be-processed water stored in the import tank 19 is conveyed to the 2nd process tank 11B via 9th path P9, and is filtered.

Here, the above-mentioned first processing tank 11A and the second processing tank 11B may be the same processing tank. As a result, the fixing of fluoride ions and the solid-liquid separation can be performed in the same tank, and the structure of the entire installation can be simplified and downsized. In addition, since the number of bathtubs is reduced, the initial cost and running cost are also reduced.

In the middle of the fourth path P4, the pump 20 is exchanged and mounted, and the filtration by the filtration membrane 13 is performed by the suction pressure generated by the pump 20, and the pump 20 generates the pump 20. Filtration of the to-be-processed water 12 by the RO filtration apparatus 14 (2nd separating means) is performed by the pressing force which becomes. By using the pump 20 together with the filtration of the filtration membrane 13 and the RO filtration apparatus 14 in this way, the number of pumps required will be reduced, and the cost required for installation will be reduced.

The RO filtration device 14 is a device for filtering a fluid by an RO membrane (Reverse Osmosis Membrane). In the present embodiment, the treated water 12 filtered by the filtration membrane 13 is further filtered and purified. Has the effect of Specifically, the RO filtration device 14 is composed of a filtration membrane having a hole having a diameter of several nanometers, and can separate impurities such as fluorine ions and calcium ions from the water to be treated 12. Specifically, by treating the treated water 12 containing 4 mg / L of fluorine ions with the RO filtration device 14, the concentration of the treated water 12 can be reduced to 1 mg / L. In addition, in the RO filtration device 14, calcium ions and chloride ions are removed from the water to be treated 12 in addition to the fluorine ions. In addition, instead of the RO filtration device 14, a filtration device having an NF membrane (nanofiltration membrane) may be employed.

The water to be treated 12 filtered by the RO filtration device 14 is discharged out of the system of the wastewater treatment device 10 via the fifth path P5. The water to be treated 12 discharged via the fifth path P5 is in a state where impurities such as fluorine ions are highly removed, and thus can be used as washing water in a semiconductor manufacturing process. Furthermore, since the concentration of fluorine ions to be contained is extremely low, it is also possible to discharge to natural systems such as rivers as it is.

On the other hand, the water to be treated 12 remaining in the RO filtration device 14 is in a state where impurities such as fluorine ions, calcium ions and chloride ions are concentrated. In this embodiment, this concentrated to-be-processed water 12 is conveyed to 11 A of 1st process tanks via the 6th path P6. As a result, the calcium ions that do not react with the fluorine ions can be reused as calcium powder for producing calcium fluoride. As a result, the concentration of calcium ions in the first treatment tank 11A can be increased while reducing the amount of calcium chloride consumed.

Here, in the sixth path P6, which is a path from which the treated water is returned to the first treatment tank 11A from the RO filtration device 14, a conductivity meter that measures the concentration of chloride ions by measuring the conductivity of the water to be treated ( 32) is interposed. As the means for measuring the concentration of chloride ions, a chloride ion concentration meter can be employed in addition to the conductivity meter 32, but the conductivity meter 32 which can be used inline is preferable as this means.

When the wastewater treatment apparatus 10 having the above configuration is continuously operated, the calcium ions contained in the added calcium chloride are combined with the fluorine ions in the water to be treated and consumed for the generation of calcium fluoride. On the other hand, chloride ions separated from calcium chloride remain in the water to be treated without contributing to the production of calcium fluoride. Therefore, with the progress of the wastewater treatment, the concentration of the chloride ions contained in the for-treatment water becomes extremely high, and there is a fear that the filtration treatment by the RO filtration apparatus 14 is hindered. Therefore, when the concentration of chloride ion measured by the measuring means provided in the path | route (for example, 6th path | route P6) to which the to-be-processed water circulates is fixed or more, you may make it replace the to-be-processed water to circulate.

Here, the means for measuring the concentration of chloride ions may be interposed in a place other than the sixth route P6 as long as the water to be treated is circulated, and may be provided, for example, in the middle of the third route P3. It may be. However, for example, when the conductivity meter 32 is mounted in the middle of the third path P3, the treated water passing through the third path P3 contains a large amount of suspended solids (SS), It is difficult to accurately determine the concentration of chloride ions by the conductivity meter 32. On the other hand, in the sixth path P6, since the treated water 12 in which SS and the like are highly removed by the RO filtration device 14 passes, it is possible to accurately determine the concentration of chloride ions. In addition, since the treated water passing through the sixth path P6 contains chloride ions at a high concentration, the value of the chloride ions to be detected is hardly influenced by the sensitivity of the sensor (the conductivity meter 32). The concentration can be obtained with high precision.

One end of the eleventh path P11 is connected to the middle of the fourth path P4, and the other end thereof is connected to the middle of the sixth path P6. The untreated water filtered by the filtration membrane 13 is returned to the first treatment tank 11A and is circulated without being supplied to the RO filtration apparatus 14 as the water to be treated passes through the eleventh path P11. Moreover, the eleventh path P11 is equipped with the turbidity meter 30 which measures the turbidity of the to-be-processed water which passed the filtration membrane 13. And if the turbidity of the to-be-processed water detected by the turbidimeter 30 is more than fixed (the amount of to-be-removed thing contained in the to-be-processed water), the to-be-processed water is not supplied to the RO filtration apparatus 14, and It is conveyed to 11 A of 1st process tanks via 11 path P11. On the other hand, when the turbidity of the to-be-processed water detected by the turbidimeter 30 is below fixed, the to-be-processed water is supplied to the RO filtration apparatus 14. By doing in this way, the to-be-processed water containing the to-be-removed substance, such as a large amount of calcium fluoride, enters the RO filtration apparatus 14, and the filtration membrane of the RO filtration apparatus 14 is prevented from clogging prematurely. Here, instead of the turbidimeter 30, an optical sensor, a conductivity meter, or the like capable of detecting the water quality of the water to be treated may be employed. However, there is SDI (Silt Density Index) as an index indicating turbidity of the water to be introduced into the RO filtration device 14, and the output of the turbidimeter 30 is easily correlated with SDI. Therefore, from this viewpoint, the turbidity meter 30 is suitable as a means of detecting the turbidity of the to-be-processed water.

One end of the twelfth path P12 is connected to the middle of the fifth path P5, and the other end is connected to the storage tank 15C. A part of the water to be filtered by the RO filtration device 14 is transferred to the storage tank 15C via this twelfth path P12 and is stored as the filtrate 16. This filtered water 16 is used to remove the self-forming film constituting the filtration membrane 13 by flowing back to the filtration membrane 13. Therefore, it is necessary to prepare clean water with low turbidity as the filtered water 16, and tap water is stored in the storage tank 15C for the first period in which the wastewater treatment apparatus 10 is operated. After the normal operation of filtration by the filtration membrane 13 and the RO filtration device 14 is started, a part of the water to be filtered by the RO filtration device 14 is stored in the storage tank 15C.

In addition, the head of the filtered water 16 stored in the storage tank 15C is higher than the head of the water to be treated 12 stored in the second treatment tank 11B. Therefore, when peeling the self-formed film formed on the surface of the filtration film 13, the filtration water 16 stored in the storage tank 15C is discharged using the water head difference of the fluid stored in both tanks, without using a driving force such as a pump. Counterflow to the filtration membrane 13 can be carried out. Therefore, power such as a pump is unnecessary for peeling off the self-forming film, and the maintenance cost of the processing apparatus is reduced.

One end portion of the tenth path P10 is connected to the fourth path P4 preceding the pump 20, and the other end thereof is connected to the fourth path P4 located later than the pump 20. That is, the tenth path P10 is a bypass path of the fourth path P4. The tenth path P10 is provided with the adjusting valve 36 and the adjusting valve 36 is adjusted in accordance with the output of the pressure gauge 34 which detects the pressure inside the fourth path P4. Thereby, the suction pressure provided to the filtration membrane 13 by the pump 20 and the pressing force provided to the RO filtration apparatus 14 are adjusted to predetermined value. In the present embodiment, the calcium powder introduced from the chemical tank 15 is mixed with fluorine ions to form calcium fluoride, except that the first treatment tank 11A → second treatment tank 11B → RO filter apparatus ( 14) → 1st treatment tank 11A is circulated in order. Therefore, almost all of the charged calcium powder can be used for the production of calcium fluoride.

In addition, in this embodiment, the to-be-processed water 12 from which calcium fluoride was removed by the filtration film 13 is further filtered by the RO filtration apparatus 14. Therefore, since the hole of the fine filtration membrane of the RO filtration device 14 is not likely to be blocked by calcium fluoride, the RO filtration device 14 can be used continuously for a long time.

With reference to FIG. 2, the detail of said RO filtration apparatus 14 is demonstrated. The RO filtration apparatus 14 is arranged in series with respect to the path | route to which the to-be-processed water 12 is processed, Specifically, the 1st RO filtration apparatus 14A, the 2nd RO filtration apparatus 14B, and the agent The RO filtration device 14 is configured by the 3 RO filtration device 14C. Each RO filtration device is configured to include an RO filtration membrane 28 therein. In addition, filtration by the 1st RO filtration apparatus 14A, the 2nd RO filtration apparatus 14B, and the 3rd RO filtration apparatus 14C is performed by apply | coating a pressurization force with the pump 20 here.

The 1st RO filtration apparatus 14A is provided in the front-end | tip, and the to-be-processed water 12 from which calcium fluoride was removed by filtering by the filtration membrane 13 (refer FIG. 1) is the 1st RO filtration apparatus 14A. Is introduced. In addition, inside the 1st RO filtration apparatus 14A, the filtration by the pressing force of the pump 20 is performed, and the process water which permeate | transmitted through the RO filtration membrane 28 is a state where impurities, such as a fluorine ion and calcium ion, were removed. Is emitted to the outside via the fifth path P5. On the other hand, the treated water that does not penetrate the RO filtration membrane 28 of the first RO filtration device 14A is transported to the second RO filtration device 14B in a state where impurities such as fluorine ions and calcium ions are concentrated. In this first RO filtration device 14A, for example, 55% of the treated water introduced is filtered by the RO filtration membrane 28, and the remaining 45% of the treated water is transported to the second RO filtration device 14B. do.

In the second RO filtration device 14B, similarly to the first RO filtration device 14A, the water to be treated by the RO filtration membrane is filtered. Here, the treated water which has permeated the RO filtration membrane is taken out from the fifth path P5 to the outside. On the other hand, the to-be-processed water concentrated without passing through the RO filtration membrane is transported to the third RO filtration device 14C in a state where fluorine ions and calcium ions are further concentrated. Here, the amount of treated water that has passed through the RO filtration membrane of the second RO filtration device 14B and is discharged to the outside is about 25% of the treated water flowing into the RO filtration device 14. Then, about 20% of the water to be treated is introduced into the third RO filtration device 14C in a more concentrated state without being filtered by the second RO filtration device 14B.

In the 3rd RO filtration apparatus 14C, similarly to the above-mentioned 1st RO filtration apparatus 14A etc., filtration of the to-be-processed water is performed further. Therefore, the treated water that has permeated through the RO filtration membrane of the third RO filtration device 14C is discharged to the outside, and the treated water that has not permeated through the RO filtration membrane is further concentrated, and then the first treatment via the sixth path P6. It is conveyed to tank 11A (refer FIG. 1). As an example, the amount of the water to be passed through the RO filtration membrane of the third RO filtration device 14C is about 11% of the total amount of the water to be introduced into the RO filtration device 14. And about 9% of the to-be-processed water does not permeate the RO filtration membrane of 3rd RO filtration apparatus 14C, and the 1st processing tank 11A (FIG. 1) in the state in which the concentration of calcium ion was concentrated about 10 times (FIG. 1). Reference).

In the present embodiment, by arranging the plurality of RO filtration devices 14 in series with respect to the path of the water to be treated as described above, the blockage of the individual RO filtration devices can be suppressed to perform a high filtration process. Specifically, for example, by increasing the permeate ratio, it is possible to filter a large amount of treated water using one RO filtration device. However, if it does in this way, sufficient filtration by RO membrane will not be performed and an electrical conductivity will rise and a removal rate will fall. Further, problems such as shortening of the life of the RO film and frequent cleaning of the RO film are required.

From this, in the present invention, as shown in FIG. 2, the RO filtration apparatus is arranged in three stages in series. Thereby, even if the permeated water ratio of an individual RO filtration apparatus is made into 55%, for example, since the filtered water is taken out from each RO filtration apparatus, the water recovery rate as a whole apparatus can be raised to about 90%. Moreover, since water recovery rate becomes high, the to-be-processed water in which the calcium ion contained is extremely high concentration is obtained from 14 C of 3rd RO filtration apparatuses. Therefore, since the quantity of the to-be-processed water conveyed for reuse is reduced, the efficiency of a 1st separation means (filtration membrane 13) raises, and the cost can be reduced by that much.

Further, in one RO filtration device, the proportion of fluorine ions to be replenished is about 80%. By arranging the RO filtration devices in three stages in this way, the proportion of fluorine ions to be replenished can be raised to about 99% in theory. have.

In addition, although the 1st RO filtration apparatus 14A etc. are provided in three steps in series with respect to the path | route of a process water, the number of RO filtration apparatuses provided may be two or four or more stages.

Here, the monitoring means which monitors the density | concentration of calcium ion contained in the to-be-processed water 12 stored in 11 A of 1st treatment tanks may be provided. That is, only when the concentration of calcium ion measured by this monitoring means is below a fixed level, the aqueous solution of calcium chloride is supplied from the chemical | medical agent tank 15 via the 2nd path P2. By doing in this way, the quantity of calcium chloride consumed can be reduced, making the density | concentration of the calcium powder contained in the to-be-processed water 12 stored in 11 A of 1st treatment tanks constant or more.

The above is the structure of the wastewater processing apparatus 10 which is this embodiment.

Next, with reference to FIG. 1 and FIG. 3, the wastewater processing method using the wastewater processing apparatus 10 of the said structure is demonstrated. As shown in the flowchart of FIG. 3, the wastewater treatment method of the present embodiment includes step S1 for generating calcium fluoride, step S2 for solid-liquid separation of calcium fluoride by filtration, and filtration by further performing filtration. Step S3 for removing ions, step S4 for conveying the calcium powder concentrated in step S3, and step S5 for recovering calcium fluoride are mainly provided.

Step S1: Step of Generating Calcium Fluoride

With reference to FIG. 1, first, the to-be-processed water 12 containing the fluorine powder discharged | emitted from the semiconductor manufacturing process etc. is introduce | transduced into the 1st process tank 11A via the 1st path P1. This to-be-processed water 12 contains fluorine ion in the density | concentration of about 100 mg / L, for example. The treated water 12 containing hydrofluoric acid exhibits extremely strong acidity, so that neutralization is performed in the first treatment tank 11A or earlier than the first treatment tank 11A, so that the treated water 12 You may control PH to the value of 7-9, for example.

Next, calcium powder is added from the chemical tank 15 to the first treatment tank 11A via the second path P2. Here, an aqueous solution of calcium chloride is added to the first treatment tank 11A from the chemical tank 15. Theoretically, the amount of calcium to be added requires a mole of 1/2 of the fluorine ions contained in the water to be treated 12. However, since a part of the added calcium powder does not bind with fluorine ions, a large amount (for example, two times or more, more preferably five times or more) of calcium chloride is added to the amount that is theoretically required in the present embodiment.

By introducing an aqueous solution of calcium chloride into the first treatment tank 11A, the fluorine ions and calcium ions contained in the water to be treated 12 are combined to be immobilized as calcium fluoride. The water to be treated 12 in which calcium fluoride is generated is transferred to the second treatment tank 11B via the third passage P3.

Step S2: separating calcium fluoride from the water to be treated by membrane filtration

In this step, the calcium fluoride generated in the previous step is separated from the water to be treated (12). As an apparatus for separating calcium fluoride from the water to be treated 12, a filter capable of filtration can be employed, and as an example, a flat membrane filter having a pore diameter of 0.2 mu m is employed as the filtration membrane 13. As the filtration membrane 13, a self-forming membrane made of deposited substances (calcium fluoride) is employed. The filtered water filtered by the filtration membrane 13 is transported to the RO filtration apparatus 14 via the 4th path P4. The filtration membrane 13 used in this step is a filtration membrane that prevents passage of calcium fluoride but allows fluorine ions of an atomic level to pass therethrough. Therefore, fluorine ions remain in the treated water 12 filtered by the filtration membrane 13 at a concentration of about 4 mg / L. This fluorine ion did not combine with calcium powder in the previous step S1.

In addition, a part of the water to be treated 12 filtered by the filtration membrane 13 is stored in the storage tank 15C. And the filtered water 16 stored in 15 C of storage tanks is used in order to peel the self-formed film adhering to the surface of the filtration film 13. Specifically, by performing filtration by the filtration membrane 13 continuously, the self-forming membrane attached to the surface of the filtration membrane 13 is blocked and the flux gradually decreases. And when the quantity of this flux becomes below fixed, filtration by the filtration membrane 13 is stopped. In addition, the filtrate 16 stored in the storage tank 15C is flowed back to the filtration membrane 13 to release the self-forming membrane attached to the surface of the filtration membrane 13. After that, the filtration by the filtration membrane 13 is resumed to circulate the water to be treated, whereby the self-forming membrane is formed again on the surface of the filtration membrane 13.

In the initial stage of operating the apparatus, tap water is stored in the storage tank 15C. In the normal operation, the water to be filtered by the RO filtration device 14 may be stored in the storage tank 15C via the twelfth path P12.

In addition, while filtration of the to-be-processed water 12 is performed by the filtration membrane 13, air bubbles are made to pass through the surface of the filtration membrane 13 by the diffuser device 18. Thereby, the film thickness of the self-formed film formed in the surface of the filtration film 13 can be controlled, and filtration ability can be maintained.

In addition, although the filtration of this step is performed by the suction force of the pump 20 interposed in the 4th path P4, this pump 20 is used also in a next step as a pressurizing means. As a control method of the filtration by the filtration membrane 13 by the pump 20, rotation of the pump 20 may be controlled so that suction pressure may become constant, and the flow volume of the to-be-processed water filtered by the filtration membrane 13 may be You may control so that it may become constant. Moreover, the 10th path | route P10 which bypasses the 4th path | route P4 before and behind the part in which the pump 20 was installed is provided, and this 10th path | route P10 is provided with the adjustment valve 36 interposed. have. In this step, by adjusting the adjustment valve 36 according to the value of the pressure measured by the pressure gauge 34, the suction pressure acting on the filtration membrane 13 and the pressing force acting on the RO filtration device 14 are appropriate values. Controlled.

Here, when the turbidity of the water to be detected by the turbidimeter 30 does not satisfy a predetermined value, the water to be filtered by the filtration membrane 13 is not introduced into the RO filtration device 14, It conveys to 11 A of 1st process tanks via 11th path P11 and 6th path P6. For example, since the self-forming film is not sufficiently formed on the surface of the filtration membrane 13 in the initial stage of operating the wastewater treatment apparatus 10, the turbidity of the water to be filtered by the filtration membrane 13 is not sufficient. not. In this case, the to-be-processed water filtered by the filtration film 13 is conveyed to 11 A of 1st process tanks via the 11th path P11. On the other hand, if the self-forming film is sufficiently formed on the surface of the filtration membrane 13, and the turbidity measured by the turbidimeter 30 satisfies a predetermined value, the treated water filtered by the filtration membrane 13 is subjected to the RO filtration device ( 14).

Step S3: further filtering the treated water from which calcium fluoride has been removed

In this step, the filtration by the RO filtration apparatus 14 is further performed using the pressing force of the pump 20, and the fluorine ion contained in the to-be-processed water is removed. As described above, the filtration membrane 13 subjected to the filtration in the previous step is supplemented with calcium fluoride having a relatively large particle size, but not with ions having an atomic level. Therefore, fluorine ions remain in the treated water that has passed through the filtration membrane 13 at about 4 mg / L. If the concentration of the remaining fluorine ions is about this level, it is possible to discharge to nature such as rivers as it is, but it is not suitable for use as washing water or the like in the semiconductor manufacturing process. From this, in this embodiment, the filtered water which permeate | transmitted the filtration membrane 13 is further purified using the RO filtration apparatus 14. The treated water filtered by the RO filtration device 14 is discharged to the outside via the fifth path P5. On the other hand, the to-be-processed water in which calcium ion etc. were concentrated without permeating the RO filtration membrane inside the RO filtration apparatus 14 is conveyed to 11 A of 1st treatment tanks via 6th path P6, and it is a calcium source. It is reused as.

The RO filtration device 14 filters the water to be treated by the pressing force provided by the pump 20. As described above, the pump 20 is shared by the filtration membrane 13 and the RO filtration device 14.

As shown in FIG. 2, the RO filtration apparatus 14 is comprised by the several RO filtration apparatus 14 arrange | positioned in series with respect to the process path of the to-be-processed water. Specifically, the first RO filtration device 14A, the second RO filtration device 14B, and the third RO filtration device 14C are disposed from an upstream side of the path where the water to be treated 12 is treated. The water to be treated is first introduced into the first RO filtration device 14A by the pressing force of the pump 20. The treated water that has passed through the RO filtration membrane 28 inside the first RO filtration device 14A is discharged to the outside via the fifth path P5. On the other hand, in the water to be treated that has not permeated the RO filtration membrane 28, calcium ions and fluorine ions are concentrated and transferred to the second RO filtration device 14B. Also in the 2nd RO filtration apparatus 14B, filtration by RO membrane is performed similarly to 1st RO filtration apparatus 14A, and the to-be-processed water is discharged | emitted outside through the 5th path P5, and is filtered Untreated water is transferred to the third RO filtration device 14C after the concentration is further performed. In the third RO filtration device 14C, the same filtration by the RO filtration membrane is performed, and the water to be treated that has passed through the RO filtration membrane is discharged to the outside via the fifth path P5, and does not penetrate the RO filtration membrane. The untreated water is recycled through the sixth path P6. That is, it is conveyed to 11 A of 1st processing tanks shown in FIG. Here, calcium ion and fluorine ion are concentrated about 10 times in the to-be-processed water concentrated by the RO filtration apparatus arrange | positioned in three stages, and passing through the 6th path | route P6.

Step S4: Step of Returning the Concentrated Calcium Powder

In this step, the to-be-processed water 12 which was not filtered by the RO filtration apparatus 14 is conveyed to 11 A of 1st treatment tanks via 6th path P6, and is recycled in order to produce calcium fluoride. do. As described above, in the present embodiment, in order to reduce the amount of fluorine ions remaining in the water to be treated 12, the amount of calcium powder (calcium chloride) added is in the range of 2 to 10 times the amount theoretically required. to be. From this, the to-be-processed water 12 via the 1st processing tank 11A, the 2nd processing tank 11B, and the RO filtration apparatus 14 contains a large amount of calcium ion which did not couple | bond with fluorine powder, By the RO filtration apparatus 14, the to-be-processed water 12 is concentrated about 10 times.

Calcium ion contained in the to-be-processed water conveyed to 11 A of 1st treatment tanks is used in order to fix fluorine content contained in the to-be-processed water introduce | transduced from the 1st path P1 as calcium fluoride.

Here, when the first treatment tank 11A is omitted and the fluorine powder is immobilized in the second treatment tank 11B, the water to be treated containing calcium powder at a high concentration passes through the sixth path P6. It is conveyed to the 2nd process tank 11B.

By performing the above-mentioned conveyance, the calcium powder added to the first treatment tank 11A from the chemical tank 15 is treated by the wastewater treatment apparatus 10 except for the one that combines with fluorine ions to produce calcium fluoride. It will cycle through the path. Therefore, most of the calcium powder supplied from the chemical tank 15 contributes to immobilization of fluorine ions, and there is almost no calcium powder released to the outside from the fifth path P5. As a result, the amount of calcium required for the immobilization of fluorine ions is reduced, and the processing cost is reduced.

In addition, the density | concentration of the ion (for example, chloride ion) contained in the to-be-processed water which passes through 6th path P6 is measured by the conductivity meter 32. As shown in FIG. And when the quantity of the measured ion is more than predetermined amount, the to-be-processed water to circulate is replaced.

By advancing the above-mentioned step S1 to step S4, the produced calcium fluoride precipitates in the lower part of the 2nd process tank 11B. In order to collect this precipitated calcium fluoride, the following step S5 is performed in this embodiment.

Step S5: recovering calcium fluoride precipitated in the second treatment tank 11B

In this step, first, the object to be removed containing calcium fluoride precipitated at the bottom of the second treatment tank 11B is transferred to the filter press 17 via the seventh path P7.

Next, by injecting water into the filter press 17, the neutralized salt (NaCl) contained in the to-be-processed water 12 is wash | cleaned and removed. Since pH-treated water 12 contains neutralized salts, the water to be removed from the water 12 contains neutralized salts and other calcium salts (for example, calcium carbonate) in addition to calcium fluoride. It is. In addition, in the case of drainage from a wet etching apparatus, silicon may be contained, for example. By injecting water into the filter press 17, the neutralized salt is dissolved in water and discharged to the outside. Since calcium fluoride has a large diameter, it is not discharged from the filter press 17 to the outside even if it is washed by water. In this way, the concentration of calcium fluoride contained in the substance to be removed is improved.

Next, after dewatering the object to be removed by the filter press 17, the object to be removed in the semi-solidified state is taken out. In this state, the water content of the substance to be removed is about 50% by weight. Next, by drying the object to be removed, a block of the object to be solidified is formed. In this embodiment, the to-be-removed substance containing 85 weight% of calcium fluoride is obtained.

In this embodiment, since solid-liquid separation process is performed without using a flocculant, such as a polymeric flocculant, immobilized calcium fluoride can be obtained with high purity from waste water containing a fluoride ion. The obtained calcium fluoride can be reused in a semiconductor manufacturing process as hydrofluoric acid by reacting with a strong acid (for example, sulfuric acid).

Furthermore, it is also possible to use the high purity calcium fluoride obtained here as a flux mixed with steel. Calcium chloride can also be obtained by adding hydrochloric acid to the obtained calcium fluoride. In addition, since sulfuric acid, hydrochloric acid, etc. which are added in order to recycle | reuse calcium fluoride are chemicals which are always standing in a semiconductor factory, calcium fluoride can be reused without adding a new facility in a factory.

Next, with reference to FIGS. 4-6, the detail of the filtration mechanism (filter apparatus 23) applicable as the above-mentioned filtration membrane 13 is demonstrated. In the following aspect, although the filtration mechanism using a self-forming film | membrane is demonstrated, it is also possible to apply another form of filtration apparatus to this invention. For example, as the filtration membrane 13, it is also possible to use the usual filtration membrane which consists of a high molecular compound.

With reference to FIG. 4, the filter apparatus 23 removes the to-be-processed water which the to-be-removed substance which was calcium fluoride mixed with the filter which consists of a self-formed film formed from the to-be-removed substance.

Specifically, the filter device 23 of the present embodiment includes the second filter 22 (self-forming film) formed on the surface of the first filter 21 of the organic polymer with a substance to be removed containing calcium fluoride. ) Is formed. The to-be-processed water which the to-be-removed thing mixed in is filtered using the 2nd filter 22 which is this self-forming film | membrane.

As long as the first filter 21 can attach a self-forming film, it can be considered in principle, either organic polymer type or inorganic type (ceramic type). Here, a polyolefin polymer membrane having an average pore diameter of 0.25 μm and a thickness of 0.1 mm was employed. The surface photograph of the filter membrane which consists of this polyolefin type is shown to FIG. 5 (B).

Further, the first filter 21 has a flat membrane structure provided on both sides of the frame 24 and is immersed to be perpendicular to the liquid level of the fluid. The filtrate 27 (water to be treated) can be taken out by sucking by the pump 26 from the hollow portion 25 of the frame 24.

Next, the second filter 22 is a self-forming film that is attached to the entire surface of the first filter 21 and solidified by sucking the particles having agglomerated substances removed. This self-forming film may be agglomerated in a gel or cake shape.

The filtration which forms the 2nd filter 22 which is a self-formed film of said to-be-removed object, and removes a to-be-removed object is demonstrated.

Referring to FIG. 5A, the first filter 21 has a plurality of filter holes 21A, and is formed in layers in the openings of the filter holes 21A and the surface of the first filter 21. The self-forming film of the object to be removed is the second filter 22. On the surface of the first filter 21, there are agglomerated particles of a to-be-removed object made of calcium fluoride, and the agglomerated particles are sucked through the first filter 21 by suction pressure from the pump, so that the water of the fluid is absorbed. After drying (dehydrating) and solidifying immediately, a second filter 22 is formed on the surface of the first filter 21.

Since the second filter 22 is formed of the agglomerated particles of the substance to be removed, it immediately becomes a predetermined film thickness, and filtration of the agglomerated particles of the substance to be removed is started by using the second filter 22. Therefore, if the filtration is continued while sucking with the pump 26 (see FIG. 4), the self-forming film of aggregated particles is laminated and thickened on the surface of the second filter 22, and the second filter 22 is subsequently blocked to continue filtration. It becomes impossible. During this period, the calcium fluoride of the substance to be removed solidifies and adheres to the surface of the second filter 22 so that the water to be treated passes through the first filter 21 and is taken out as filtered water.

In FIG. 5 (A), one side of the first filter 21 has a to-be-processed water in which to-be-removed substances, such as calcium fluoride, were mixed, and the 1st filter ( Filtrate water passed through 21) is produced. The water to be treated flows by being sucked in the direction of the arrow, and solidified as the agglomerated particles in the water to be treated 12 approach the first filter 21 by the suction. In addition, the self-forming film to which the aggregated particles are bonded to each other is adsorbed on the surface of the first filter 21 to form the second filter 22. By the action of the second filter 22, the object to be removed in the solution is solidified and the water to be treated is filtered.

By slowly sucking the water to be treated through the second filter 22 as described above, the water in the water to be treated can be taken out as the filtered water, and the object to be removed is dried and solidified, stacked on the surface of the second filter 22, and Aggregated particles of the removed product are captured as a self-forming film.

The first filter 21 is vertically immersed in the water to be treated, and the water to be treated is in a state where the substance to be removed is dispersed. When the water to be treated is sucked by the pump 26 through the first filter 21 at a weak suction pressure, the agglomerated particles of the substance to be removed are bonded to each other on the surface of the first filter 21, so that the first filter 21 Is adsorbed on the surface. The agglomerated particles S1 having a diameter smaller than that of the filter hole 21A pass through the first filter 21, but in the process of forming the second filter 22, the filtered water is circulated to the for-treatment water again.

Next, the above-described processing of filtration by the self-forming film will be described in order.

First, by treating the water to be treated with the first filter 21, a second filter is formed on the surface of the first filter. In this process of forming a film, the water to be treated is sucked at a very slight suction pressure, so that the agglomerated particles S1 are laminated while forming a gap having various shapes, thereby becoming the second filter 22 of the soft self-forming film having a very high swelling degree. . The water in the water to be treated penetrates through the highly formed swelling film and is sucked through the first filter 21 to be taken out as filtered water, and finally, the water to be treated is filtered.

In addition, by sending bubble A from the bottom surface (the air diffuser 18 shown in FIG. 1) of the to-be-processed water, parallel flow is formed in the to-be-processed water along the surface of the 1st filter 21. FIG. This is because the second filter 22 uniformly adheres to the entire surface of the first filter 21 and forms a gap in the second filter 22 so as to smoothly attach it. Specifically, the air flow rate is set to 1.8 liters / minute, but it is selected by the quality of the second filter 22.

When the 2nd filter 22 is fully formed by the said film-forming process, and the filtered to-be-processed water achieves predetermined | prescribed transparency, it will transfer to a filtration process. In this filtration process, the aggregate particle S1 which consists of calcium fluoride is adsorbed by the weak suction pressure on the surface of the 2nd filter 22, and is laminated gradually. At this time, purified water penetrates the 2nd filter 22 and the aggregated particle | grains S1 laminated further, and is taken out as filtered water from the 1st filter 21. FIG.

However, if the filtration is continued for a long time, since the self-forming film is thickly attached to the surface of the second filter 22, the above-described gap is immediately blocked, and the filtered water cannot be taken out. For this reason, in order to regenerate filtration capability, it is necessary to remove this laminated self-forming film.

An example of regeneration of filtration capacity is as follows.

For example, with reference to FIG. 4, since the hollow part 25 of the 1st filter 21 becomes negative pressure compared with the outer side by weak suction pressure, the 1st filter 21 becomes concave inward. It is shaped. Therefore, the 2nd filter 22 adsorb | sucked to the surface also has the shape which concave inwardly similarly.

In the regeneration process, the weak suction pressure is stopped to return to almost atmospheric pressure, whereby the first filter 21 is returned to its original state. As a result, the second filter 22 and the self-forming film adsorbed on the surface thereof are similarly returned to the original state. As a result, since the suction pressure which adsorb | sucked the self-formation film | membrane disappears first, the self-formation film | membrane loses the adsorption force to the 1st filter 21, and receives the force which swells outward. As a result, the adsorbed self-forming film starts to detach from its own weight.

In addition, when the filtered water flows back to the hollow part 25 in this regeneration process, it helps the 1st filter 21 return to an original state, and also the hydrostatic pressure of the filtered water is added, and the force which bulges outward is added. Further, the filtered water begins to penetrate the boundary between the first filter 21 and the second filter 22 through the filter hole 21A (see FIG. 5A) from the inside of the first filter 21. The separation of the self-forming film of the second filter 22 from the surface of the first filter 21 is promoted. The reverse flow can be performed by flowing the filtered water 16 temporarily stored in the storage tank 15C shown in FIG. 1 into the filtration membrane.

As described above, when the filtration is continued while the second filter 22 is being regenerated, the concentration of the substance to be treated in the for-treatment water 12 is increased, and the viscosity of the water to be treated 12 is increased soon. Therefore, if the concentration of the to-be-removed object of the to-be-processed water 12 exceeds predetermined | prescribed density | concentration, it will stand to stop a filtration operation and settle. Then, the concentrated slurry is stored at the bottom of the second treatment tank 11B (FIG. 1), and the cake-shaped concentrated slurry is recovered. The recovered concentrated slurry is dehydrated using a filter press 17 (see FIG. 1), and is further compressed and thermally dried to remove water contained therein to reduce the weight.

This slurry can be reused as a hydrofluoric acid source. That is, the concentration efficiency of the concentrated slurry used as the raw material of hydrofluoric acid can be improved by backflowing the filtrate 16 stored in the storage tank 15C and repeating peeling of the self-forming film.

With reference to FIG. 6, the experiment which filtered the to-be-processed water 12 using the filtration membrane 13 shown in FIG. 1 is demonstrated. 6 is a graph showing changes over time of the flux when the filtration treatment is performed. In this graph, the axis of abscissas represents the time of continuous treatment, and the axis of ordinates represents the magnitude of the flux.

First, the conditions of this experiment are explained. In this experiment, filtration was performed by providing a suction pressure of 7 kPa to a filtration membrane having an area of 0.1 m ² . In the water to be treated, calcium chloride is added to the wastewater containing 1000 mg / L of fluorine ions, and fluoride ions are fixed as calcium fluoride. The diameter of calcium fluoride is about 0.25 micrometer. And the experiment was performed by measuring the quantity and flux of the to-be-processed water regularly.

By this experiment, the average flux was 0.4 m / day, and it was proved that the filtration membrane 13 of this form can tolerate practically enough. In addition, the concentration of fluoride ions contained in the filtered water obtained by the filtration membrane is 3.5 mg / L, and this value satisfies the general discharge standard.

The experimental method will be described in detail. First, a self-forming film is formed on the surface of the filtration membrane by circulating an object to be removed such as calcium fluoride, and filtration is started when the filtered water having a certain transparency or higher is obtained.

The flux at the time of starting the filtration is about 0.7 m / day, and the flux gradually decreases when the filtration is continued. This is because blockage of the self-forming film proceeds with the passage of filtration. The flux at the time point 130 minutes after the start of filtration is about 0.2 m / day. At this point, the self-forming film is peeled off from the filtration film to recover the concentrated substances in the water to be treated.

When peeling of a self-formed film | membrane and collection | recovery of a to-be-removed object are complete | finished, a new self-formed film is formed in the surface of a filtration film, and a to-be-processed water is filtered again. By repeating the above steps, the object to be removed containing calcium fluoride can be separated from the water to be treated.

From the experiments described above, it has been found that sufficient flux can be secured by periodically peeling and regenerating the self-forming film.

Industrial Applicability

Cost reduction in the wastewater treatment technology for removing fluorine from the wastewater is possible.

10: drainage device
12: water to be treated
13: filtration membrane
14: RO filtration device
14A: first RO filtration device
14B: second RO filtration device
14C: 3rd RO filtration device
15: chemical bath
16: filtered water
17: filter press
18: diffuser device
19: Import tank
20: pump
21: first filter
22: second filter
23: filter device
24: frame
25: hollow part
26: pump
27: filtrate
28: RO filtration membrane
30: Turbidimeter
32: conductivity meter
34: pressure gauge
36: regulating valve
P1: first path
P2: second path
P3: Third Path
P4: fourth route
P5: fifth route
P6: sixth path
P7: seventh path
P8: Eighth Path
P9: Path 9
P10: Route 10
P11: Eleventh Path
P12: 12th path

Claims (10)

Addition means for adding calcium powder to the water to be treated containing fluorine to produce calcium fluoride;
First separating means for separating the calcium fluoride from the water to be treated,
A second separation means for removing fluorine ions from the treated water from which the calcium fluoride is separated;
The said to-be-processed water in which the said calcium powder which did not react with the said fluorine was concentrated by the said 2nd separating means is conveyed to the front end rather than the said 1st separating means, The wastewater processing apparatus characterized by the above-mentioned. The said 2nd separating means is arrange | positioned in multiple numbers with respect to the path | route by which the to-be-processed water is processed,
The to-be-processed water concentrated by the said 2nd separating means arrange | positioned at the rear end is conveyed to the front end rather than the said 1st separating means, The wastewater processing apparatus characterized by the above-mentioned. The wastewater treatment apparatus according to claim 1, wherein the second separation means is a filtration device having an RO membrane or an NF membrane. The wastewater treatment apparatus according to claim 1, wherein the first separation means is a self-forming film containing the calcium fluoride laminated on the filtration film. The storage tank according to claim 4, further comprising a storage tank in which a fluid flowing back to the first separating means is stored.
And said treated water filtered by said second separating means is stored in said storage tank. The method according to claim 1, wherein the first separation means is a suction type filtration device, and the second separation means is a pressure type filtration device,
A suction pressure is applied to the first separation means by a pump mounted between a path between the first separation means and the second separation means, and pressure is applied to the second separation means. Drainage device. The method of claim 6, further comprising a bypass path for bypassing the path of the portion where the pump is mounted,
And a regulating valve for adjusting the amount of the water to be treated passing through the bypass path. The wastewater treatment apparatus according to claim 1, further comprising ion concentration measuring means for measuring a concentration of ions contained in the water to be treated in a path through which the water to be treated is circulated. The method according to claim 1, further comprising turbidity detection means for detecting turbidity of the water to be treated which has passed through the first separation means,
And when the turbidity of the water to be detected detected by the turbidity detecting means is equal to or less than a predetermined value, the water to be treated is supplied to the second separating means. A step of producing calcium fluoride by adding calcium powder to the water to be treated containing fluorine powder,
Separating the calcium fluoride from the water to be treated by a first separating means,
And removing fluorine ions from the treated water from which the calcium fluoride is separated by a second separating means,
And said calcium powder which has not reacted with said fluorine returns said to-be-processed water concentrated by said second separating means to a front end than said first separating means.

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