JP2007296444A - Method and system for treating waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste water, in which mineral acid ions are separated from waste water containing mineral acid ions and a fluorine ion at the least to reduce the content of mineral acid ions and obtain fluorine ion-concentrated water suitable for recovering recyclable calcium fluoride. <P>SOLUTION: A system for treating waste water is provided with a first electrodialyzer 1, a second electrodialyzer 2 and a fluorine recycling unit 3. The waste water MFW containing mineral acid ions and the fluorine ion at the least is supplied to the first electrodialyzer 1 to separate mineral acid ions from the waste water MFW and produce mineral acid ion-concentrated water M and fluorine-containing water FW. The fluorine-containing water FW is supplied to the second electrodialyzer 2 to separate the fluorine ion from the fluorine-containing water FW and produce fluorine ion-concentrated water F and treated water W. In the fluorine recycling unit 3, calcium fluoride is recovered from the fluorine ion-concentrated water F. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment method and a wastewater treatment system, and in particular, PFC (PerFluoro Compounds) gas removal wastewater and used chemicals discharged from semiconductor manufacturing plants, flat panel display (FPD) manufacturing plants, and electronic component manufacturing plants. The present invention relates to a wastewater treatment method and a wastewater treatment system for treating fluorine-containing wastewater such as rinse wastewater.

  In the process of manufacturing semiconductors, liquid crystals, and electronic components, a film forming process (such as a CVD process) for forming a thin film on the surface of a wafer or a glass substrate, the entire surface of the formed thin film, or a specific portion is required. There is a process (etching process) of scraping only. In these processes, PFC gas, hydrofluoric acid (HF), buffered hydrofluoric acid (BHF), and the like are used. Due to these, a large amount of fluorine-containing wastewater is generated from a factory that manufactures semiconductors and the like.

  These fluorine-containing wastewater may contain ions other than fluorine resulting from the decomposition treatment of PFC gas or ions other than fluorine contained in wastewater from other systems, especially fluorine-containing wastewater in which mineral acid ions coexist. In many cases.

  When discharging fluorine-containing wastewater outside the factory, there is an emission regulation value for the fluorine concentration (less than 15 ppm in Japan, less than 8 ppm in other areas), semiconductor manufacturing factories and flat panel displays (FPD) In manufacturing factories and electronic component manufacturing factories, wastewater is treated by the following treatment methods or a combination of these treatment methods.

[Coagulation precipitation method]
In the coagulation precipitation method, a calcium compound such as calcium hydroxide is added to fluorine-containing wastewater to react calcium ions with calcium ions in the wastewater to form calcium fluoride, and then polyaluminum chloride (PAC) or In this method, flocs are formed by adding a sulfuric acid band and a flocculant such as a polymer, and then they are precipitated (solid-liquid separation) to obtain treated water having a low fluorine concentration.

[Ion exchange resin method]
The ion exchange resin method is a method for obtaining treated water having a low fluorine concentration by adsorbing and removing fluorine ions by bringing fluorine-containing waste water into contact with an ion exchange resin that adsorbs fluorine ions. The adsorbed and removed fluorine ions become dense fluorine-containing wastewater by regenerating the ion exchange resin with alkali. Generally, this fluorine-containing wastewater is treated by a coagulation sedimentation method.

[Evaporation concentration method]
The evaporation concentration method is a method of condensing fluorine in fluorine-containing wastewater by evaporating water from the fluorine-containing wastewater in an evaporator, and condensing water vapor to obtain treated water having a low fluorine concentration (for example, patents). Reference 1).

[Electrodialysis]
In electrodialysis, fluorine ions are separated and concentrated by flowing fluorine-containing wastewater through an electrodialyzer configured by combining ion-exchange membranes, and the concentration of fluorine ions is increased and treatment with low fluorine concentrations is performed. This is a method for obtaining water (see, for example, Patent Documents 2 and 3).

[Crystallization method]
The crystallization method is a method of growing calcium fluoride particles generated by adding a calcium compound to fluorine-containing wastewater, and collecting calcium fluoride particles (fluorite) having a reusable particle size and purity. . According to this method, about 90% of the fluorine in the fluorine-containing wastewater can be recovered as fluorite and can be recycled as a raw material for hydrofluoric acid.

JP 2004-188411 A JP 2003-305475 A JP 2004-174439 A

  As described above, the crystallization method is a method of growing a seed crystal of calcium fluoride, and a higher fluorine concentration in the waste water is advantageous because the crystal growth rate is faster. Therefore, when the crystallization method is applied to dilute fluorine-containing wastewater, it is desirable to perform concentration work in advance to increase the fluorine concentration.

  Further, even when fluorine-containing wastewater with a high fluorine concentration is treated by crystallization, it is desirable that mineral acids such as sulfuric acid and nitric acid are not mixed in the fluorine-containing wastewater. In addition, the mineral acid here has the same meaning as an inorganic acid. Examples of the effects of mineral acids mixed in fluorine-containing wastewater are described below.

When a large amount of sulfuric acid is mixed in the fluorine-containing waste water, calcium sulfate hydrate (CaSO ₄ .2H ₂ O) is mixed in the fluorite recovered by the crystallization method. For this reason, when producing hydrofluoric acid,
CaSO ₄ · 2H ₂ O → CaSO ₄ + 2H ₂ O
Reaction occurs and water is generated. The generated water may react with the produced hydrofluoric acid to damage the hydrofluoric acid production apparatus. For this reason, it is preferable to remove sulfate ions before the treatment by the crystallization method.

  Further, if a large amount of nitric acid is mixed in the fluorine-containing wastewater, it is necessary to perform nitrogen treatment of nitric acid present in the treated wastewater after the fluorine is recovered by the crystallization method. Nitrogen compounds such as nitrate ions in the wastewater are generally decomposed into nitrogen gas by biological treatment, and this is an energy-saving method. However, if fluorine ions remain in the treated wastewater, biological activities are prevented. There is a problem that it is weakened and effective biological treatment cannot be performed. For this reason, when processing the fluorine-containing waste_water | drain containing a mineral acid ion by a crystallization method, it is desired to isolate | separate a mineral acid ion previously.

  Here, the effect of mineral acid ions mixed in fluorine-containing wastewater has been described with respect to the crystallization method. However, in the substitution method in which calcium carbonate is replaced with calcium fluoride as a seed, mineral acid ions are preliminarily used for the same reason. It is desired to be removed.

  On the other hand, the above-described coagulation sedimentation method has a disadvantage that it cannot be reused because it makes sludge containing a large amount of impurities other than fluorine ions. In addition, the ion exchange resin method is an expensive treatment method, and the recycled wastewater becomes alkaline. Therefore, in order to apply it to the crystallization method operated on the acidic side, it is necessary to adjust the pH by adding a large amount of aqueous HCl solution. There is. Furthermore, the evaporative concentration method concentrates both fluorine ions and mineral acid ions at the same time, so that only mineral acid ions cannot be separated.

  The present invention has been made in view of such problems of the prior art, and separates mineral acid ions from wastewater containing at least mineral acid ions (impurity ions) and fluorine ions, and determines the content of mineral acid ions. An object of the present invention is to provide a wastewater treatment method and a wastewater treatment system capable of obtaining fluoride ion-concentrated water suitable for reducing (recycling) recyclable calcium fluoride.

  By performing electrodialysis treatment tests on various types of fluorine-containing wastewater using an electrodialyzer filled with an ion exchanger, the present inventors have different behaviors of fluorine ions and mineral acid ions (impurity ions). As a result, the present invention has been completed.

  That is, according to the first aspect of the present invention, mineral acid ions are separated from waste water containing at least mineral acid ions (impurity ions) and fluorine ions, the content of the mineral acid ions is reduced, and the recyclable fluorine is recovered. Provided is a wastewater treatment method capable of obtaining fluorine-containing water (treated water) suitable for recovering (recycling) calcium fluoride. According to this waste water treatment method, waste water containing at least mineral acid ions and fluorine ions is treated by electrodialysis. By this electrodialysis method, fluorine-containing water in which the concentration of mineral acid ions is reduced and mineral acid ion-enriched water in which the concentration of mineral acid ions is increased are generated.

The second aspect of the present invention separates mineral acid ions from waste water containing at least mineral acid ions (impurity ions) and fluorine ions, reduces the content of mineral acid ions, and recovers recyclable calcium fluoride. Provided is a wastewater treatment system capable of obtaining fluorine ion concentrated water suitable for (recycling). This waste water treatment system includes a first electrodialysis apparatus, a second electrodialysis apparatus, and a fluorine recycling apparatus. The first electrodialysis apparatus supplies a waste water containing at least mineral acid ions and fluorine ions to a desalting chamber filled with an ion exchanger, and separates the mineral acid ions from the waste water, thereby the mineral acid. Mineral acid ion concentrated water with increased ion concentration and fluorine-containing water (treated water) with reduced mineral acid ion concentration are generated. The second electrodialysis apparatus supplies the fluorine-containing water (treated water) to a desalting chamber filled with an ion exchanger, separates the fluorine ions from the fluorine-containing water, and the concentration of the fluorine ions is reduced. An increased fluoride ion-concentrated water and treated water with a reduced concentration of the fluorine ions are generated. The fluorine recycling apparatus recovers calcium fluoride (CaF ₂ ) from the fluorine ion concentrated water.

In the third aspect of the present invention, mineral acid ions are separated from wastewater containing at least mineral acid ions (impurity ions) and fluorine ions, the content of mineral acid ions is reduced, and recyclable calcium fluoride is recovered. Provided is a wastewater treatment system capable of obtaining fluorine ion concentrated water suitable for (recycling). This waste water treatment system includes a first electrodialysis apparatus, a second electrodialysis apparatus, and a fluorine recycling apparatus. The first electrodialysis apparatus supplies waste water containing at least mineral acid ions and fluorine ions to a desalting chamber filled with an ion exchanger, and separates the mineral acid ions and fluorine ions from the waste water. Then, ion-concentrated water in which the concentrations of the mineral acid ions and the fluorine ions are increased, and treated water in which the concentrations of the mineral acid ions and the fluorine ions are reduced are generated. The second electrodialysis apparatus supplies the ion concentrated water to a desalting chamber filled with an ion exchanger, separates the mineral acid ions from the ion concentrated water, and increases the concentration of the mineral acid ions. The concentrated water thus produced and ion-concentrated water (treated water) in which the concentration of the mineral acid ions is reduced are generated. The fluorine recycling apparatus recovers calcium fluoride (CaF ₂ ) from the ion-enriched water (treated water).

  According to the present invention, from waste water containing at least mineral acid ions (impurity ions) and fluorine ions, treated water having very few mineral acid ions and fluorine ions and high-purity fluorine ion concentrated water having very few mineral acid ions are obtained. Can be generated. Moreover, it becomes possible to produce high-purity calcium fluoride from this high-purity fluoride ion-concentrated water, and to reuse this calcium fluoride as a raw material for producing hydrofluoric acid.

  Hereinafter, an embodiment of a wastewater treatment system according to the present invention will be described in detail with reference to FIGS. 1 to 7. 1 to 7, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic diagram showing an example of an electrodialysis apparatus that can be used in the wastewater treatment system according to the present invention. As shown in FIG. 1, this electrodialyzer has seven treatment chambers, that is, an anode chamber 11, a buffer chamber 12, a first concentration chamber (anode-side concentration chamber) 13, a desalting chamber 14, and a second concentration chamber. A chamber (cathode side concentrating chamber) 15, an acid supply chamber 16, and a cathode chamber 17. The space between the anode chamber 11 and the buffer chamber 12 is a cation exchange membrane C1, and the space between the buffer chamber 12 and the first concentration chamber 13 is a cation exchange membrane C2, and the first concentration chamber 13 and the desalting chamber 14 are separated from each other. Between the anion exchange membrane A1, between the desalting chamber 14 and the second concentration chamber 15 is a cation exchange membrane C3, and between the second concentration chamber 15 and the acid supply chamber 16 is an anion exchange membrane A2. The acid supply chamber 16 and the cathode chamber 17 are partitioned by an anion exchange membrane A3. Moreover, the inside of each processing chamber 11-17 is filled with the ion-exchange fiber material (ion-exchange nonwoven fabric) and the ion-exchange spacer which forms the flow path of water, and, thereby, ion separation and concentration efficiency are filled. Has been enhanced.

  An anode plate (plus electrode plate) 18 is accommodated in the anode chamber 11, and a cathode plate (minus electrode plate) 19 is accommodated in the cathode chamber 17. Fluorine-containing waste water is supplied to the desalting chamber 14, and ions (fluorine ions, mineral acid ions, calcium ions, etc.) in the waste water are separated in the desalting chamber 14 by electrodialysis. Pure water is circulated and supplied to the first concentrating chamber 13, and in the first concentrating chamber 13, anions (for example, fluorine ions and mineral acid ions) that have moved from the desalting chamber 14 are concentrated and the concentration of the anions is reduced. Concentrated water 21 in which the water content is increased is generated. Further, pure water is circulated and supplied to the second concentration chamber 15, and cations (for example, calcium ions) moved from the desalting chamber 14 are concentrated in the second concentration chamber 15 to increase the concentration of cations. The concentrated water 22 is produced. A part of pure water circulated in the concentrating chambers 13 and 15 is discharged.

  Further, in order to prevent the anion concentrated in the first concentration chamber 13 from moving to the anode chamber 11 and corroding the anode 18, there is a pure space between the anode chamber 11 and the first concentration chamber 13. A buffer chamber 12 in which water (buffer water) 23 is circulated and supplied is provided. Further, in order to prevent cations such as calcium ions moving from the desalting chamber 14 from becoming hydroxides and depositing, an acid such as hydrochloric acid is present between the second concentration chamber 15 and the cathode chamber 17. An acid supply chamber 16 to be circulated is provided. Thereby, anions such as chlorine ions are supplied to the second concentration chamber 15 and concentrated as a soluble salt, and the concentration in the second concentration chamber 15 is promoted.

  Anode water (pure water) 24 is supplied to the anode chamber 11, and the anode water 24 is mixed with the buffer water 23 supplied to the buffer chamber 12. Furthermore, a part of the buffer water 23 is mixed with the concentrated water 21, whereby the concentrations of the concentrated water 21, the anode water 24, and the buffer water 23 are adjusted. Cathode water (pure water) 25 is circulated and supplied to the cathode chamber 18.

  In the electrodialysis apparatus having such a configuration, when fluorine-containing wastewater is introduced into the desalting chamber 14, adsorption (adsorption characteristics) by the ion exchanger (ion exchange nonwoven fabric or ion exchange spacer) and electric field force (movement characteristics). The ions are separated by the above, moved to the concentration chambers 13 and 15, and concentrated. Anions such as fluorine ions move toward the anode 18 and are concentrated in the first concentration chamber 13, and cations such as calcium ions move toward the cathode 19 and are concentrated in the second concentration chamber 15. As described above, pure water is circulated in the concentration chambers 13 and 15, and ions are concentrated in the pure water to generate concentrated waters 21 and 22. By such a separation action, the fluorine concentration of the treated water discharged from the desalting chamber 14 can be reduced to a drainage standard value of less than 8 mg / L or an environmental standard value of less than 0.8 mg / L. .

  Here, the inventors of the present invention are completely different in the adsorption and transfer characteristics of ions between fluorine ions and other impurity ions (mineral acid ions). We have found that this phenomenon can be applied to the formation of calcium fluoride. That is, the present inventors performed the following experiment using the electrodialysis apparatus shown in FIG.

The dialysis area of the electrodialyzer is 0.06 m ^2, and dilute fluorine-containing wastewater (impurity content: 46.4) containing 92.3 ppm fluorine, 28.7 ppm nitric acid, 45.7 ppm sulfuric acid, and 5.7 ppm chlorine. %). At this time, when the value of the current applied between the anode and the cathode was changed, results as shown in FIGS. 2 and 3 were obtained. In FIGS. 2 and 3, the number (%) in parentheses represents the current load relative to the total mineral acid ion concentration load.

From the results shown in FIGS. 2 and 3, the following was found.
1) When a current value applied between the anode and the cathode is small, impurity ions are more easily separated than fluorine ions. That is, impurity ions are removed first, and fluorine ions are removed after the concentration of impurity ions is lowered.
2) Sufficient separation of fluorine ions can be achieved by making the current value applied between the anode and the cathode larger than the current value necessary for removing impurity ions.

  Moreover, although the current efficiency at the time of removing impurity ions was different depending on the composition ratio and concentration of each impurity ion, it was generally in the range of 70% to 90%. From this, it became clear that applying a current of 110% to 150% of the electrical equivalent of impurity ions is particularly suitable for obtaining treated water (fluorine-containing water) with very few impurity ions. Of course, when there is no problem as an application, it is possible to perform an operation in which a relatively large amount of impurity ions remains in the treated water with less than 110% of the electrical equivalent of impurity ions. Further, it is possible to operate in a region where the separation and movement of fluorine ions becomes a main phenomenon as a value exceeding 150% of the electrical equivalent of impurity ions.

  Thus, when the present inventors treat fluorine-containing wastewater with an electrodialyzer, the characteristics of ions to be separated differ depending on the current value applied between the anode and the cathode, and there is a difference between the anode and the cathode. It was found that the ions in the waste water can be selectively separated and concentrated by adjusting the current value applied to the. Based on this knowledge, the inventors have invented a wastewater treatment system described below.

FIG. 4 is a schematic diagram showing the wastewater treatment system in the first embodiment of the present invention. As shown in FIG. 4, the wastewater treatment system in the present embodiment includes a first electrodialysis apparatus 1 for separating mineral acid ions (impurity ions) and a second electrodialysis apparatus for separating fluorine ions. 2 and a fluorine recycling apparatus (CaF ₂ crystallizer) 3. As the electrodialyzers 1 and 2, for example, an electrodialyzer having a structure shown in FIG. 1 can be used.

  The first electrodialysis apparatus 1 is supplied with waste water (diluted hydrofluoric acid waste water) MFW containing at least mineral acid ions and fluorine ions. In the first electrodialysis apparatus 1, the diluted hydrofluoric acid waste water is obtained by adjusting the current value applied between the anode and the cathode as described above to obtain a current value necessary for removing only mineral acid ions. Mineral acid ions are selectively separated from the MFW, and the mineral acid ion concentrated water M having an increased mineral acid ion concentration is generated. Further, the diluted hydrofluoric acid waste water MFW introduced into the first electrodialysis apparatus 1 becomes fluorine-containing water FW with a reduced mineral acid ion concentration by removing mineral acid ions (impurity ions).

  The fluorine-containing water FW treated by the first electrodialysis apparatus 1 is supplied to the second electrodialysis apparatus 2. In the second electrodialysis apparatus 2, as described above, by adjusting the current value applied between the anode and the cathode, the fluorine ions are separated from the fluorine-containing water FW, the fluorine ions are concentrated, and the mineral acid ions Fluorine ion concentrated water F with very few (impurity ions) can be produced. Further, the fluorine-containing water FW introduced into the second electrodialysis apparatus 2 becomes treated water W with very few mineral acid ions and fluorine ions by removing fluorine ions.

  The fluorine ion concentrated water F whose fluorine ion concentration has been increased by the second electrodialysis apparatus 2 is supplied to the fluorine recycling apparatus 3. In the fluorine recycling apparatus 3, by adding a calcium compound to the fluorine ion concentrated water F, high-purity calcium fluoride (fluorite) with few impurities can be generated. This calcium fluoride can be reused as a raw material for hydrofluoric acid.

FIG. 5 is a schematic diagram showing a wastewater treatment system according to the second embodiment of the present invention. As shown in FIG. 5, the wastewater treatment system in this embodiment includes a first electrodialysis apparatus 101 for separating mineral acid ions (impurity ions) and fluorine ions, and a second electrodialysis apparatus 101 for separating mineral acid ions. Electrodialyzer 102 and a fluorine recycling apparatus (CaF ₂ crystallizer) 3. As the electrodialyzers 101 and 102, for example, an electrodialyzer having a structure shown in FIG. 1 can be used.

  The first electrodialysis apparatus 101 is supplied with waste water (diluted hydrofluoric acid waste water) MFW containing at least mineral acid ions and fluorine ions. In the first electrodialysis apparatus 101, as described above, the current value applied between the anode and the cathode is adjusted so that the current value is a current value necessary for removing mineral acid ions and fluorine ions. Then, mineral acid ions and fluorine ions are separated from the dilute hydrofluoric acid waste water MFW to reduce the volume of the dilute hydrofluoric acid waste water MFW and generate the ion-enriched water MF. As a result, the diluted hydrofluoric acid waste water MFW introduced into the first electrodialysis apparatus 101 becomes the treated water W with very few mineral acid ions and fluorine ions.

  The ion-enriched water MF concentrated in the first electrodialysis apparatus 1 is supplied to the second electrodialysis apparatus 102. In the second electrodialysis apparatus 102, as described above, the current value applied between the anode and the cathode is adjusted to a current value necessary for removing only the mineral acid ions, whereby the ion concentrated water MF is obtained. Mineral acid ions are selectively separated from the mineral acid ions, and mineral acid ion concentrated water M having a higher mineral acid ion concentration is produced. In addition, the ion concentrated water MF introduced into the second electrodialysis apparatus 102 becomes a fluorine ion concentrated water F with very little mineral acid ions (impurity ions) by removing mineral acid ions (impurity ions). .

  The fluorine ion concentrated water F discharged from the second electrodialysis apparatus 102 is supplied to the fluorine recycling apparatus 3. In the fluorine recycling apparatus 3, by adding a calcium compound to the fluorine ion concentrated water F, high-purity calcium fluoride (fluorite) with few impurities can be generated. This high-purity calcium fluoride can be reused as a raw material for hydrofluoric acid.

  A large amount of fluorine-containing wastewater is discharged from semiconductor manufacturing factories, liquid crystal manufacturing factories, and electronic component manufacturing factories, but fluorine content discharged from these semiconductor manufacturing factories, flat panel display (FPD) manufacturing factories, and electronic component manufacturing factories. Waste water can be treated by the waste water treatment system according to the present invention. In this case, in semiconductor manufacturing plants, flat panel display (FPD) manufacturing plants, and electronic component manufacturing plants, depending on the type of water used (engineering water, city water, pure water, etc.) and processes, Since the components change, it is preferable to change the configuration of the electrodialysis apparatus in each embodiment described above according to the components of the waste water. For example, in the case where cations such as calcium ions that easily precipitate in the concentrated water of fluorine-containing wastewater are not included, an electrodialyzer as shown in FIG. 6 can be used. Further, when the fluorine-containing waste water is dilute and it is not necessary to increase the fluorine concentration of the concentrated water, an electrodialyzer without a buffer chamber as shown in FIG. 7 can be used. In any electrodialysis apparatus, pure water of makeup water may be added to the pure water piping system circulating in the cathode chamber, and a part thereof may be transferred to drainage or another circulation system. Also in these electrodialysis apparatuses shown in FIGS. 6 and 7, it is confirmed that the ions in the waste water can be selectively separated and concentrated by adjusting the current value applied between the anode and the cathode. It was done.

Moreover, in the electrodialysis apparatus used in the wastewater treatment system according to the present invention, it is preferable to perform constant current operation or constant voltage operation, and the current density is preferably 3 A / dm ² or less. Moreover, in the example shown in FIG.1, FIG.6 and FIG.7, the thickness of the desalination chamber 14 and the concentration chambers 13 and 15 is 1-10 mm, Preferably it is 2-4 mm. Moreover, when ion exchangers, such as an ion exchange nonwoven fabric and an ion exchange spacer, are comprised with a sheet-like ion exchanger, the number and kind of ion exchangers filled in each processing chamber 11-17 should be set arbitrarily. Can do. The amount of pure water supplied to the anode chamber of the electrodialysis apparatus is preferably set so that the fluorine concentration in the anode chamber 11 is less than 1 mg / L and the fluorine concentration in the buffer chamber 12 is less than 10 mg / L.

  Moreover, as an ion exchanger with which the inside of each processing chamber 11-17 of an electrodialysis apparatus is filled, the existing ion exchanger, for example, ion exchange resin etc., can also be used. However, from the viewpoint of ease of handling, it is preferable to use a polymer fiber substrate in which an ion exchange group is introduced by a graft polymerization method. The polymer substrate may be a single polymer such as a polyolefin-based polymer, for example, polyethylene or polypropylene, or may be a composite fiber composed of a polymer having a different shaft core and sheath. . Examples of the composite fiber include a core-sheath composite fiber having a polyolefin-based polymer, for example, polyethylene as a sheath component and a polymer other than that used as the sheath component, for example, polypropylene as a core component. A material obtained by introducing an ion exchange group into a composite fiber material by using a radiation graft polymerization method is preferable as an ion exchange fiber material to be used because it has excellent ion exchange ability and can be produced in a uniform thickness. Examples of the form of the ion exchange fiber material include a woven fabric and a non-woven fabric.

  In addition, as an ion exchanger in a form used as a spacer member such as an oblique mesh, a polyolefin polymer resin, for example, an oblique mesh (net) made of polyethylene widely used in conventional electrodialysis tanks is used. As the base material, a material obtained by imparting an ion exchange function using a radiation graft polymerization method is preferable because of its excellent ion exchange capability and excellent dispersibility of water to be treated.

  The radiation graft polymerization method is a technique in which a monomer is introduced into a substrate by irradiating a polymer substrate with radiation to form radicals and reacting the monomer with this. Examples of radiation that can be used in the radiation graft polymerization method include α rays, β rays, γ rays, electron beams, ultraviolet rays, and the like, and it is preferable to use gamma rays and electron beams. The radiation graft polymerization method includes pre-irradiation graft polymerization method in which a graft substrate is irradiated with radiation in advance and then brought into contact with the graft monomer and reacted, and simultaneous irradiation graft polymerization method in which radiation is irradiated in the presence of the substrate and the monomer. Any method can be used.

  In addition, by the contact method of the monomer and the base material, a liquid phase graft polymerization method for performing polymerization while the base material is immersed in the monomer solution, a vapor phase graft polymerization method for performing the polymerization by bringing the base material into contact with the vapor of the monomer, Examples of the method include an impregnation gas phase graft polymerization method in which the substrate is immersed in the monomer solution and then taken out from the monomer solution and reacted in the gas phase, and any method can be used.

  The ion exchange group introduced into the fiber base material such as a nonwoven fabric or the spacer base material is not particularly limited, and various cation exchange groups or anion exchange groups can be used. For example, as the cation exchange group, a strong acid cation exchange group such as a sulfone group, a neutral acid cation exchange group such as a phosphate group, a weak acid cation exchange group such as a carboxyl group, and an anion exchange group include primary to first-order cation exchange groups. Weakly basic anion exchange groups such as tertiary amino groups and strong basic anion exchange groups such as quaternary ammonium groups can be used. Or the ion exchanger which has both the said cation exchange group and anion exchange group can also be used.

  In addition, as a functional group, a functional group derived from iminodiacetic acid and its sodium salt, various amino acids such as phenylalanine, lysine, leucine, valine and proline and a functional group derived from its sodium salt, derived from iminodiethanol An ion exchanger having a functional group or the like may be used.

  Examples of the monomer having an ion exchange group that can be used for the above-described purpose include acrylic acid (AAc), methacrylic acid, sodium styrenesulfonate (SSS), sodium methallylsulfonate, sodium allylsulfonate, sodium vinylsulfonate, Examples thereof include vinylbenzyltrimethylammonium chloride (VBTAC), diethylaminoethyl methacrylate, dimethylaminopropylacrylamide and the like.

  For example, by conducting radiation graft polymerization using sodium styrenesulfonate as a monomer, a sulfone group that is a strongly acidic cation exchange group can be introduced directly into the substrate, and vinylbenzyltrimethylammonium chloride is used as a monomer. By using the radiation graft polymerization, a quaternary ammonium group which is a strongly basic anion exchange group can be directly introduced into the substrate.

  Examples of the monomer having a group that can be converted into an ion exchange group include acrylonitrile, acrolein, vinylpyridine, styrene, chloromethylstyrene, and glycidyl methacrylate (GMA). For example, glycidyl methacrylate is introduced into the substrate by radiation graft polymerization, and then a sulfone group, which is a strongly acidic cation exchange group, is introduced into the substrate by reacting with a sulfonating agent such as sodium sulfite, or chloromethyl After graft polymerization of styrene, a quaternary ammonium group that is a strongly basic anion exchange group can be introduced into the substrate by immersing the substrate in an aqueous trimethylamine solution to perform quaternary ammonium formation.

  Among the various types of ion exchangers described above, an ion exchange fiber material in the form of a nonwoven fabric or a woven fabric is particularly preferable. Fiber materials such as woven fabric and non-woven fabric have a very large surface area compared to materials in the form of resin beads and diagonal meshes, so the amount of ion-exchange groups introduced is large, and micropores inside the beads like resin beads. Or, there are no ion exchange groups in the macropores, and all ion exchange groups are arranged on the surface of the fiber, so that ions in the treated water are easily diffused in the vicinity of the ion exchange groups, Adsorbed. Therefore, if ion exchange fiber material is used, the removal and collection | recovery efficiency of ion can be improved more.

  Further, platinum, tantalum, niobium, diamond, SUS, or the like can be used as a material for the electrodes (anode 18 and cathode 19). In addition, a material obtained by plating platinum, gold, iridium oxide, or the like on a base material such as titanium, nickel, monel, hastelloy, or inconel can be used as an electrode. The shape may be a flat plate shape or a lath net shape having water permeability and gas permeability.

  In the wastewater treatment system shown in FIG. 4, dilute fluorine-containing wastewater (impurity content: 46.4 wt%) of 92.3 ppm fluorine, 28.7 ppm nitric acid, 45.7 ppm sulfuric acid, and 5.7 ppm chlorine is first electrodialyzed. The apparatus 1 was supplied. In the first electrodialysis apparatus 1, a current of 0.8 A, which is 66% of the electrical equivalent of mineral acid ions that are impurity ions, was applied. At this time, it was found that dilute fluorine-containing water FW having an impurity content of 13.2% of fluorine 85.0 ppm, nitric acid 6.02 ppm, sulfuric acid 4.21 ppm and chlorine 2.65 ppm was obtained, and impurity ions were removed. It was. Here, the impurity content is calculated by (total value of concentration of impurity ions such as sulfuric acid and nitric acid in fluorine-containing wastewater) / (total concentration of ions in fluorine-containing wastewater).

  Furthermore, when this diluted fluorine-containing water FW was supplied to the second electrodialysis apparatus 2 and a current of 0.4 A was applied, fluorine ion concentrated water F having 1030 ppm of fluorine was obtained. Moreover, the water quality of the treated water W at this time was less than 1.0 ppm of fluorine, and satisfied the drainage standard. In addition, in the 1st electrodialysis apparatus 1, it confirmed that the same tendency was acquired with the electric current value to 150% of the electric equivalent of mineral acid ion.

(Comparative Example 1)
Similarly, in the wastewater treatment system shown in FIG. 4, dilute fluorine-containing wastewater (impurity content: 46.4 wt%) of 92.3 ppm fluorine, 28.7 ppm nitric acid, 45.7 ppm sulfuric acid, and 5.7 ppm chlorine is used as the first electric The dialysis machine 1 was supplied. In the first electrodialysis apparatus 1, a current of 4.2 A, which is 350% of the electric equivalent of mineral acid ions that are impurity ions, was applied. At this time, it was 26.9 ppm of fluorine, 0.85 ppm of nitric acid, 0.68 ppm of sulfuric acid, and 0.11 ppm of chlorine, and not only impurity ions but also fluorine ions were removed.

(Comparative Example 2)
The same dilute fluorine-containing wastewater as above (fluorine 92.3ppm, nitric acid 28.7ppm, sulfuric acid 45.7ppm, chlorine 5.7ppm) with a single electrodialyzer, the fluorine concentration of the treated water reaches 5.0 ppm or less. When treated with such a current value, the concentrated water contained 55.0% impurities.

  In the wastewater treatment system shown in FIG. 5, dilute fluorine-containing wastewater (impurity content: 46.4 wt%) of 92.3 ppm fluorine, 28.7 ppm nitric acid, 45.7 ppm sulfuric acid, and 5.7 ppm chlorine is the first electrodialyzer. 101. In the first electrodialysis apparatus 101, a current of 5.4 A is applied, and in the second electrodialysis apparatus 102, the electric equivalent of mineral acid ions that are impurity ions of the inflow water to the second electrodialysis apparatus 102 is obtained. A current of 1.6 A, which is 130%, was applied. As a result, fluorine ion concentrated water F having 1070 ppm fluorine, 32.0 ppm nitric acid, 43.7 ppm sulfuric acid, 15.2 ppm chlorine and 7.7% impurity content could be obtained. Moreover, the water quality of the treated water W at this time was 6.5 ppm of fluorine, which satisfied the drainage standard.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and it goes without saying that the present invention may be implemented in various forms within the scope of the technical idea.

It is a schematic diagram which shows an example of the electrodialysis apparatus which can be used for the waste water treatment system which concerns on this invention. It is a graph which shows the relationship between the applied electric current value and residual rate when experimenting using the electrodialyzer shown in FIG. It is a graph which shows the relationship between the applied electric current value and ion concentration when experimenting using the electrodialyzer shown in FIG. It is a schematic diagram which shows the waste water treatment system in the 1st Embodiment of this invention. It is a schematic diagram which shows the waste water treatment system in the 2nd Embodiment of this invention. It is a schematic diagram which shows the other example of the electrodialysis apparatus which can be used for the waste water treatment system which concerns on this invention. It is a schematic diagram which shows the other example of the electrodialysis apparatus which can be used for the waste water treatment system which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 1st electrodialysis apparatus 2,102 2nd electrodialysis apparatus 3 Fluorine recycling apparatus 11 Anode chamber 12 Buffer chamber 13 1st concentration chamber 14 Desalination chamber 15 2nd concentration chamber 16 Acid supply chamber 17 Cathode chamber 18 Anode 19 Cathode 21, 22 Concentrated water 23 Buffer water (pure water)
24 Anode water (pure water)
25 Cathode water (pure water)
C1, C2, C3 Cation exchange membrane A1, A2, A3 Anion exchange membrane F Fluorine ion concentrated water FW Fluorine-containing water M Mineral acid ion concentrated water MFW Fluorine-containing wastewater W Treated water

Claims (8)

  Wastewater containing at least mineral acid ions and fluorine ions is treated by electrodialysis, fluorine-containing water in which the concentration of mineral acid ions is reduced, and mineral acid ion-enriched water in which the concentration of mineral acid ions is increased A wastewater treatment method characterized by producing   2. The wastewater treatment method according to claim 1, wherein a value of an electric current applied in the electrodialysis method is 110% or more and 150% or less of an electrical equivalent of mineral acid ions in the wastewater. The mineral acid ions are separated from the waste water by electrodialysis to produce mineral acid ion concentrated water having a higher concentration of mineral acid ions and fluorine-containing water having a reduced concentration of mineral acid ions. ,
Separating the fluorine ions from the fluorine-containing water by electrodialysis, a fluorine ion concentrated water in which the concentration of the fluorine ions is increased, and treated water in which the concentrations of the mineral acid ions and the fluorine ions are reduced It produces | generates, The waste water treatment method of Claim 1 or 2 characterized by the above-mentioned. The mineral acid ions and the fluorine ions are separated from the waste water by electrodialysis, and the ion-concentrated water in which the concentrations of the mineral acid ions and the fluorine ions are increased, and the concentrations of the mineral acid ions and the fluorine ions are Producing reduced treated water,
The mineral acid ions are separated from the ion-enriched water by electrodialysis to produce mineral acid ion-enriched water in which the mineral acid ions are increased and fluorine-containing water in which the concentration of the mineral acid ions is reduced The waste water treatment method according to claim 1 or 2. The wastewater treatment method according to any one of claims 1 to 4, wherein the fluorine-containing water is sent to a fluorine recycling apparatus, and calcium fluoride (CaF ₂ ) is recovered from the fluoride ion concentrated water.   The wastewater treatment method according to any one of claims 1 to 5, wherein the wastewater is wastewater discharged from a semiconductor manufacturing factory, a flat panel display (FPD) manufacturing factory, or an electronic component manufacturing factory. . Mineral acid having a concentration of mineral acid ions increased by supplying wastewater containing at least mineral acid ions and fluorine ions to a desalting chamber filled with an ion exchanger and separating the mineral acid ions from the wastewater. A first electrodialyzer that generates ion-concentrated water and fluorine-containing water in which the concentration of mineral acid ions is reduced;
Supplying the fluorine-containing water to a desalting chamber filled with an ion exchanger, separating the fluorine ions from the fluorine-containing water, and increasing the concentration of the fluorine ions; and the fluorine ions A second electrodialyzer that produces treated water having a reduced concentration of
A fluorine recycling apparatus for recovering calcium fluoride (CaF ₂ ) from the fluoride ion concentrated water;
A wastewater treatment system characterized by comprising: Supplying waste water containing at least mineral acid ions and fluorine ions to a desalting chamber filled with an ion exchanger, separating the mineral acid ions and fluorine ions from the waste water, and separating the mineral acid ions and fluorine ions A first electrodialyzer that produces ion-enriched water having an increased concentration of and treated water having reduced concentrations of the mineral acid ions and the fluorine ions;
Supplying the ion-concentrated water to a desalting chamber filled with an ion exchanger, separating the mineral acid ions from the ion-concentrated water, and a mineral acid ion-concentrated water in which the concentration of the mineral acid ions is increased; A second electrodialyzer for producing fluorine ion-concentrated water in which the concentration of mineral acid ions is reduced;
A fluorine recycling apparatus for recovering calcium fluoride (CaF ₂ ) from the fluoride ion concentrated water;
A wastewater treatment system characterized by comprising:

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