Method and apparatus for treating fluoride-containing water

Abstract

The present invention provides a method and apparatus for treating fluorine-containing water that allows for the recovery and reuse of the alkali used for fluorine separation, and moreover, enables the production of treated water with a sufficiently reduced fluorine concentration. [Solution] A method for treating fluorine-containing water, comprising: an alkali addition step of ionizing fluorine by adding alkali to fluorine-containing water; a reverse osmosis membrane separation step of separating the ionized fluorine and the added alkali from the water to be treated using a reverse osmosis membrane device to obtain concentrated water; a fluorine-alkali separation step of separating the fluorine and alkali contained in the concentrated water by electrolytic treatment of the concentrated water using an electroregenerative deionizer; and a step of recovering the alkali obtained in the fluorine-alkali separation step and adding this alkali in the alkali addition step.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for treating fluorine-containing water, and more particularly to a method and apparatus for treating fluorine-containing water suitable for treating fluorine-containing water from a semiconductor manufacturing process.

Background Art

[0002] In the electronics industry and the like, ammonium fluoride water or buffered hydrofluoric acid water is used for etching electronic devices such as semiconductors. Since fluorine and ammonia are both precious resources, recovery from ammonium fluoride-containing waste liquid is expected. As a general recovery method, sodium hydroxide equal to or more than the equivalent amount of ammonium ions is added to transfer ammonia into the gas phase, and then calcium hydroxide or calcium chloride is added to precipitate fluoride ions as calcium fluoride. This method has problems that a large amount of sodium hydroxide needs to be added, the pH of the waste liquid after precipitating calcium fluoride becomes high, and a large amount of acid needs to be added for neutralization, so the process is complicated and the chemical cost and energy cost become enormous.

[0003] Electrodialysis is a method of separating and recovering anions in waste liquid as an acid and cations as an alkali using an ion exchange membrane as a partition wall.

[0004] In electrodialysis, it is possible to separate and recover fluoride ions as hydrofluoric acid and cations such as ammonium ions as ammonia without using excessive chemicals. However, as the concentrations of anions and cations in the water chamber to be treated decrease, the current becomes difficult to flow, so the concentrations of fluoride ions and ammonia remaining in the desalted treated water do not become sufficiently low.

[0005] Patent Document 1 describes a method for treating fluorine-containing water, comprising the steps of: ionizing fluorine by adding alkali to water to be treated that contains fluorine; separating a mixture of the ionized fluorine and the added alkali from the water to be treated to obtain concentrated water of the mixture; separating the fluorine and alkali contained in the concentrated water from each other by electrolytically treating the concentrated water through an ion exchange membrane; and recovering the alkali obtained in the separation step and reusing at least a portion of the recovered alkali for ionizing fluorine in the water to be treated.

[0006] Furthermore, Patent Document 1 describes a device for treating fluorine-containing water, comprising: an alkali addition device for adding alkali to water to be treated that contains fluorine; a separation device having means for fractionating by molecular size to separate a mixture of fluorine and alkali from the water to be treated that contains fluorine; an electrolytic separation device having an electrolytic cell, an ion exchange membrane and a pair of electrodes disposed therein, for separating fluorine and alkali from the mixture by electrolytic treatment via the ion exchange membrane; and a recovery means for recovering the separated alkali into the alkali addition device.

[0007] According to the method and apparatus of Patent Document 1, the alkali used for separating fluorine can be recovered and used for separating fluorine from fluorine-containing water. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2004-358316 [Overview of the project] [Problems that the invention aims to solve]

[0009] The electrolytic separation apparatus used in the method and apparatus of Patent Document 1 is an electrodialysis apparatus.

[0010] As mentioned above, electrodialysis machines can separate and recover anions as acids and cations as alkalis in wastewater using an ion exchange membrane as a partition. However, in electrodialysis machines, the water to be treated flows through the water treatment chamber toward the outlet, and as the ion concentration decreases, it becomes more difficult for the current to flow. Therefore, the amount of fluoride ions remaining in the desalination treatment water does not decrease sufficiently.

[0011] The present invention aims to provide a method and apparatus for treating fluorine-containing water that allows for the recovery and reuse of alkali used for fluorine separation, and moreover, can produce treated water with a sufficiently reduced fluorine concentration. [Means for solving the problem]

[0012] The gist of this invention is as follows:

[0013] [1] An alkali addition step in which alkali is added to fluorine-containing water to ionize the fluorine, A reverse osmosis membrane separation step to obtain concentrated water by separating ionized fluorine and the added alkali from the water to be treated using a reverse osmosis membrane apparatus, A fluorine-alkali separation step is performed by electrolytically treating the concentrated water with an electro-regenerative deionizer to separate the fluorine and alkali contained in the concentrated water. The process includes recovering the alkali obtained in the fluorine-alkali separation step and adding this alkali in the alkali addition step. A method for treating fluoride-containing water.

[0014] [2] The fluorine-containing water treatment apparatus of [1], wherein the concentrated water from the reverse osmosis membrane apparatus is separated into fluorine-concentrated water, alkaline water, and desalinated water by the electro-regenerative deionizer.

[0015] [3] As the reverse osmosis membrane device, a first reverse osmosis membrane device and a second reverse osmosis membrane device to which the concentrated water of the first reverse osmosis membrane device is supplied as feed water are used, and the concentrated water from the second reverse osmosis membrane device is supplied to the electric regeneration type deionization device [1] A method for treating fluorine-containing water.

[0016] [4] Desalted water from the electric regeneration type deionization device is discharged out of the system without performing wastewater treatment (excluding pH adjustment) [1] or [2] A method for treating fluorine-containing water.

[0017] [5] Fluorine concentrated water from the electric regeneration type deionization device is treated by a fluorine resource recovery device to recover fluorine [1] or [2] A method for treating fluorine-containing water.

[0018] [6] The permeated water separated by the reverse osmosis membrane device is used as recovered water [1] or [2] A method for treating fluorine-containing water.

[0019] [7] An alkali addition device for adding alkali to fluorine-containing water, A reverse osmosis membrane device for subjecting the fluorine-containing water added with alkali to reverse osmosis treatment to separate it into concentrated water and permeated water, An electric regeneration type deionization device for separating the concentrated water of the reverse osmosis membrane device into at least fluorine concentrated water and alkali water, An alkali supply means for supplying at least a part of the alkali water from the electric regeneration type deionization device to the alkali addition device, A treatment device for fluorine-containing water having

[0020] [8] As the reverse osmosis membrane device, it has a first reverse osmosis membrane device and a second reverse osmosis membrane device to which the concentrated water of the first reverse osmosis membrane device is supplied as feed water, and the concentrated water from the second reverse osmosis membrane device is supplied to the electric regeneration type deionization device [7] A treatment device for fluorine-containing water.

[0021] [9] The electric regeneration type deionization device separates the concentrated water from the reverse osmosis membrane device into fluorine concentrated water, alkali water and desalted water [7] A treatment device for fluorine-containing water.

[0022]

[10] It is provided with distillation means for distilling alkaline water from the electric regeneration type deionizer to separate it into ammonia water and alkaline metal hydroxide water, By the alkali supply means, a treatment device for any one of [7] to [9] fluorine-containing waters that supplies the alkaline metal hydroxide water to the alkali addition device.

[0023]

[11] A treatment device for any one of [7] to [9] fluorine-containing waters having a fluorine resource recovery device for treating fluorine-concentrated water from the electric regeneration type deionizer to recover fluorine. [Advantages of the Invention]

[0024] In the present invention, in a method and device for adding an alkali to fluorine-containing water, then separating fluorine and the alkali with a reverse osmosis membrane device, and electrolytically treating the concentrated water, as this electrolytic treatment device, an electric regeneration type deionizer is used. This electric regeneration type deionizer has a structure in which at least a desalination chamber is filled with an ion exchange resin. By filling the ion exchange resin in this way, even with the same current value, the moving speed of ions in the drainage passing through the cell becomes larger compared to the case where the ion exchange resin is not filled.

[0025] This means that when the same water flow rate and the same cell length are set, at the timing when the treated water reaches the desalination chamber outlet, the probability that the moving speed of ions is slow and the ion load in the drainage remains in the desalination chamber is less in the electric regeneration type deionizer compared to electrodialysis.

[0026] <00\00111>Therefore, the quality of the treated water of the electric regeneration type deionizer is extremely good compared to an electrodialysis device, and direct discharge of the treated water becomes possible.

[0027]

[0028] In one aspect of the present invention, water dissociates at the contact point between the cation exchange resin and the anion exchange resin in the electroregenerative deionizer, and H + and OH - This generates a substance. As a result, the electrical resistance inside the treated water chamber decreases, allowing sufficient current to flow without significantly increasing the voltage, and enabling the complete separation and recovery of fluoride ions and alkali ions.

[0029] In one aspect of the present invention, the electroregenerative deionizer comprises an anion exchange membrane and a cation exchange membrane. In this aspect, fluoride ions in the water to be treated permeate through the anion exchange membrane and are recovered as hydrofluoric acid from the acidic water extraction chamber. Alkali in the water to be treated permeate through the cation exchange membrane and are recovered as alkaline hydroxide water from the alkaline water permeation chamber.

[0030] In another aspect of the present invention, the electroregenerative deionizer comprises an anion exchange membrane, a cation exchange membrane, and a bipolar membrane.

[0031] In this embodiment, fluoride ions in the treated water permeate through an anion exchange membrane and are recovered as hydrofluoric acid, and alkali ions in the treated water permeate through a cation exchange membrane and are mixed with hydroxide ions supplied from a bipolar membrane or the like to be recovered as alkaline hydroxide water. In this embodiment, hydrofluoric acid and alkaline hydroxide water can be separated and recovered from the fluoride ions and alkali-containing water, and treated water from which each ion has been sufficiently removed can be recovered, making it possible to sufficiently lower the fluoride ion concentration and alkali concentration in the treated water.

[0032] Generally, in concentration chambers (acidic water extraction chamber, alkaline water extraction chamber), the ion concentration increases downstream, making it easier for current to flow. Conversely, the ion concentration is lower upstream, making it more difficult for current to flow.

[0033] In one aspect of the present invention, by filling the concentration chamber with an ion exchange resin, the effect of maintaining the flow of electric current by causing appropriate electrolysis in the concentration chamber is obtained.

[0034] Furthermore, it is known that ion movement is faster between the functional groups of ion exchange resins than in water, which can also enhance the flow of electric current.

[0035] Furthermore, ion exchange resins contain protons (H + Alkaline ions are adsorbed more than hydroxide ions (OH) - Fluoride ions are selectively adsorbed rather than ions. Therefore, by filling the concentration chamber with ion exchange resin, ions that have moved from the treated water chamber (desalination chamber) are quickly transferred from the aqueous phase to the ion exchange resin, resulting in the stable discharge of separated ions outside the device. [Brief explanation of the drawing]

[0036] [Figure 1] This is a diagram showing the configuration of a fluorine-containing water treatment apparatus according to an embodiment. [Figure 2] This is a diagram showing the configuration of an electro-regenerative deionization device. [Figure 3] This is a diagram showing the configuration of an electro-regenerative deionization device. [Figure 4] This is a diagram showing the configuration of an electro-regenerative deionization device. [Figure 5] This is a diagram showing the configuration of an electro-regenerative deionization device. [Figure 6] This is a flow chart of a fluoride-containing water treatment system. [Modes for carrying out the invention]

[0037] The embodiments will be described below with reference to the drawings.

[0038] Figure 1 shows an example of a fluorine-containing water treatment apparatus according to an embodiment.

[0039] The raw water, which consists of fluorine-containing water, is introduced into the neutralization tank 1, and a concentrated alkaline aqueous solution from the electro-regenerative deionizer 4 is added to adjust the pH to 5-9, preferably 6-8.

[0040] Furthermore, if the amount of alkali added is insufficient with only the return alkali from the electro-regenerative deionizer, an alkaline agent from Newfeed, such as NaOH chemicals, may be added to the neutralization tank 1 by the alkali addition means 2.

[0041] The water in the neutralization tank 1 is supplied to the reverse osmosis membrane device (hereinafter sometimes referred to as the RO device) 3, where it is separated into permeate and concentrated water. The permeate is taken out as treated water and used as recovered water.

[0042] The concentrated water is supplied to the electro-regenerative deionizer 4, where it is separated into HF aqueous solution, alkaline water, and desalinated water. The alkaline water is sent to the neutralization tank 1 via piping 5.

[0043] In this way, by adding alkaline water to the raw water and ionizing the fluorine in the raw water, fluoride ions are sufficiently separated in the electro-regenerative deionizer 4. Furthermore, since the electro-regenerative deionizer 4 has an ion exchange resin (preferably a mixed resin of anion exchange resin and cation exchange resin) filled in the water to be treated chamber, sufficient current flows even when the ion concentration is lower compared to an electrodialysis device, and anions and cations can be sufficiently separated.

[0044] In this embodiment, the separation and recovery efficiency of alkali is high, resulting in a reduced amount of alkaline chemicals used for pH adjustment. Furthermore, the high fluorine recovery rate means less fluorine is wasted.

[0045] In this embodiment, the downstream equipment of the electro-regenerative deionizer 4 can be simplified.

[0046] As fluorine-containing water, wastewater from semiconductor manufacturing processes is preferred, but fluorine-containing wastewater discharged from pollution control equipment that decomposes toxic gases and PFCs (polymerized fuels) that cause global warming, such as those discharged from semiconductor manufacturing processes, may also be used. The fluorine concentration of the fluorine-containing water is F - A concentration of 50-5,000 mg / L is preferred, with a particularly favorable range of around 100-500 mg / L.

[0047] This fluorine-containing water is concentrated in the reverse osmosis membrane device 3 and then supplied to the electro-regenerative deionizer 4, but the fluorine concentration in the water supplied to the electro-regenerative deionizer 4 is F - Preferably, the concentration is 200 to 20,000 mg / L, and particularly 1,000 to 5,000 mg / L. If this range is not reached, it is preferable to increase the number of reverse osmosis membrane stages (the number of stages when concentrated water from the upstream reverse osmosis membrane device is supplied as feedwater).

[0048] Examples of alkalis include alkali metals such as sodium and potassium, amines such as TMAH (tetramethylammonium hydroxide) and ethylenediamine, and ammonia, but sodium is preferred.

[0049] [Electroregenerative deionization device] A preferred example of the electro-regenerative deionizer 4 described above is one in which a cation exchange membrane and an anion exchange membrane are alternately arranged between the anode and the cathode to form an anode chamber, an acidic water extraction chamber, a water to be treated chamber, an alkaline water extraction chamber, and a cathode chamber, and the water to be treated chamber is filled with a mixed resin of cation exchange resin and anion exchange resin, the acidic water extraction chamber is filled with the mixed resin or anion exchange resin, and the alkaline water extraction chamber is filled with the mixed resin or cation exchange resin.

[0050] Another preferred example of the above-mentioned electroregenerative deionizer is one in which a cation exchange membrane, anion exchange membrane, and bipolar membrane are arranged between the anode and the cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more sets of acidic water extraction chambers, treated water chambers, and alkaline water extraction chambers are formed between the anode chamber and the cathode chamber, the treated water chamber is filled with a mixed resin of cation exchange resin and anion exchange resin, the acidic water extraction chamber is filled with the mixed resin or anion exchange resin, and the alkaline water extraction chamber is filled with the mixed resin or cation exchange resin.

[0051] Furthermore, another preferred example of an electroregenerative deionizer is one in which at least an anion exchange membrane and a bipolar membrane are placed between the anode and the cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more sets of acidic water extraction chambers and alkaline water extraction chambers are formed between the anode chamber and the cathode chamber, and the alkaline water extraction chamber is filled with a mixed resin of cation exchange resin and anion exchange resin.

[0052] <An example of an electroregenerative deionization device> Figure 2 is a diagram showing an example of an electroregenerative deionizer used in the embodiment.

[0053] Between the anode (positive electrode) 11 and the cathode (negative electrode) 12, a bipolar membrane 13, an anion exchange membrane 14, a cation exchange membrane 15, and a bipolar membrane 16 are arranged in this order. From the anode 11 toward the cathode 12, the anode chamber 21, the acidic water extraction chamber 22, the treated water chamber (desalination chamber) 23, the alkaline water extraction chamber 24, and the cathode chamber 25 are formed in this order. Each chamber 21 to 25 is filled with a resin (mixed resin) which is a mixture of anion exchange resin and cation exchange resin. The ratio of anion exchange resin in the mixed resin is preferably about 40 to 80 volume percent. The alkaline water extraction chamber 24 may be filled with only cation exchange resin, and the acidic water extraction chamber 22 may be filled with only anion exchange resin.

[0054] The water to be treated, containing fluoride ions and sodium ions, is passed through the water to be treated chamber 23. Pure water is passed through the acidic water extraction chamber 22 and the alkaline water extraction chamber 24 in a parallel flow with the water to be treated chamber 13. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 21 and the cathode chamber 25 as electrode water. The water to be treated may also contain cations other than Na, such as NH4, K, and Li.

[0055] When a voltage is applied between the anode 11 and the cathode 12, and the water to be treated, pure water, and electrode water are passed through as described above, the fluoride ions contained in the water to be treated in the water to be treated chamber 13 move towards the anode 11, permeate the anion exchange membrane 14, and move to the acidic water extraction chamber 22. This acidic water containing fluoride ions is then recovered from the acidic water extraction chamber 22.

[0056] Cationic substances in the water to be treated in the water to be treated chamber 23 (where H + Ions are excluded. The same applies to the following cations.) These ions move to the cathode 12 side and permeate the cation exchange membrane 15. Then, alkaline water containing these cations is recovered from the alkaline water extraction chamber 24.

[0057] Even though fluoride ions and cations in the water to be treated move to the acidic water extraction chamber 22 and the alkaline water extraction chamber 24, the water to be treated chamber 23 is filled with a mixed resin, so a sufficient current flows through the water to be treated chamber 23. Therefore, the applied voltage between the anode 11 and the cathode 12 hardly increases. In other words, when fluoride ions and cations in the water to be treated move to the acidic water extraction chamber and the alkaline water extraction chamber, the conductivity of the water in the water to be treated chamber decreases, making it difficult for current to flow. However, the mixed resin in the water to be treated chamber causes dissociation of the water. As a result, the decreased conductivity can be compensated for by the generated hydrogen ions and hydroxide ions. In this way, it is possible to reduce the concentration of fluoride ions and cations in the water to be treated to a sufficiently low level without significantly increasing the applied voltage.

[0058] <Another example of an electro-regenerative deionization system> Figure 3 is a configuration diagram showing another example of an electro-regenerative deionizer used in the embodiment.

[0059] Between the anode (positive electrode) 31 and the cathode (negative electrode) 32, an anion exchange membrane 33, a cation exchange membrane 34, a bipolar membrane 35, an anion exchange membrane 36, and a cation exchange membrane 37 are arranged in this order. From the anode 31 toward the cathode 32, the anode chamber 41, the treated water chamber (desalination chamber) 42, the alkaline water extraction chamber 43, the acidic water extraction chamber 44, the treated water chamber 45, and the cathode chamber 36 are formed in this order. Each chamber 41 to 48 is filled with a resin (mixed resin) which is a mixture of anion exchange resin and cation exchange resin. The anode chamber 41 and the alkaline water extraction chamber 43 may be filled with cation exchange resin only, and the cathode chamber 46 and the acidic water extraction chamber 44 may be filled with anion exchange resin only.

[0060] The water to be treated, containing fluoride ions and sodium ions, is passed through the water to be treated chambers 42 and 45. Pure water is passed through the acidic water extraction chamber 44 and the alkaline water extraction chamber 43 in a parallel flow direction with the water to be treated chambers 53 and 56. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 41 and the cathode chamber 46 as electrode water.

[0061] When a voltage is applied between the anode 31 and the cathode 32, and the treated water, pure water, and electrode water are passed through as described above, the fluoride ions contained in the treated water in the treated water chambers 42 and 45 move towards the anode 41, permeate the anion exchange membranes 33 and 36 respectively, and move to the anode chamber 41 and the acidic water outlet chamber 44. Then, the acidic water containing these fluoride ions flows out from the anode chamber 41 and the acidic water outlet chamber 44.

[0062] The cations in the water to be treated in the water to be treated chambers 42 and 45 move towards the cathode 32 and permeate the cation exchange membranes 34 and 37. This alkaline water containing the cations then flows out from the alkaline water extraction chamber 43 and the cathode chamber 46.

[0063] Even if fluoride ions and cations in the treated water move from the treated water chambers 42 and 45 to the adjacent chamber and exit, the treated water chambers 42 and 45 are filled with mixed resin, so a sufficient current flows through them. Consequently, the applied voltage between the anode 31 and cathode 32 hardly rises, making it possible to sufficiently reduce the concentration of fluoride ions and cations in the treated water.

[0064] Although Figure 3 shows two water treatment chambers 42 and 45, it is also possible to provide three or more water treatment chambers by providing two or more combinations of an acidic water extraction chamber, a water treatment chamber, and an alkaline water extraction chamber.

[0065] <Another example of an electroregenerative deionization device> Figure 4 is a configuration diagram showing yet another example of the electroregenerative deionizer used in the embodiment.

[0066] A bipolar membrane 53, a cation exchange membrane 54, a bipolar membrane 55, a cation exchange membrane 56, and a bipolar membrane 57 are arranged in this order between the anode (positive electrode) 51 and the cathode (negative electrode) 52. An anode chamber 61, a water treatment chamber 62, an alkaline water extraction chamber 63, a water treatment chamber 64, an alkaline water extraction chamber 65, and a cathode chamber 66 are formed in this order from the anode 51 toward the cathode 52. Each chamber 61 to 66 is filled with a resin (mixed resin) which is a mixture of anion exchange resin and cation exchange resin. The water treatment chambers 62 and 64 may be filled with cation exchange resin only, and the alkaline water extraction chamber 63 may be filled with anion exchange resin only.

[0067] The water to be treated, containing fluoride ions and cations, is passed through the water to be treated chambers 62 and 64. Pure water is passed through the alkaline water extraction chambers 63 and 65 in a parallel flow direction with the water to be treated chambers 62 and 64. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 61 and cathode chamber 66 as electrode water.

[0068] When a voltage is applied between the anode 51 and the cathode 52, and the water to be treated, pure water, and electrode water are passed through as described above, the cations contained in the water to be treated in the water to be treated chambers 62 and 64 move to the cathode 52 side, permeate the cation exchange membranes 54 and 56 respectively, and move to the alkaline water extraction chambers 63 and 65. This alkaline water containing cations is then recovered from the alkaline water extraction chambers 63 and 65.

[0069] Anions in the water to be treated in the water to be treated chambers 62 and 64 attempt to move toward the anode 51, but this movement is prevented by the bipolar membranes 53 and 55. As a result, acidic water containing these anions is recovered from the water to be treated chambers 62 and 64.

[0070] Even though cations in the water to be treated move to the alkaline water extraction chambers 63 and 65, the water to be treated chambers 62 and 64 are filled with mixed resin, so a sufficient current flows through them. Consequently, the applied voltage between the anode 51 and cathode 52 hardly rises, and highly concentrated alkaline water (NaOH water in this embodiment) is extracted from the alkaline extraction chambers 63 and 65.

[0071] Although Figure 4 shows two water treatment chambers 62 and 65, it is also possible to provide three or more combinations of alkaline water extraction chambers and water treatment chambers, resulting in three or more water treatment chambers.

[0072] In the electro-regenerative deionizers shown in Figures 2-4 above, the treated water and pure water are in parallel flow, but they may also be in counter-flow.

[0073] The pure water mentioned above can include desalinated water from an electro-regenerative deionization system, permeate from an RO system, pure water from a separately installed pure water production system, or other types of water. Among these, desalinated water from an electro-regenerative deionization system and permeate from an RO system are preferred.

[0074] <Another form of electroregenerative deionization device> As an electro-regenerative deionizer, an electro-regenerative deionizer is also preferred, characterized in that a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between an anode and a cathode to alternately form concentration chambers and desalting chambers, the concentration chambers located between the desalting chambers are divided into an anode-side concentration chamber and a cathode-side concentration chamber by a buffer chamber, the buffer chamber and the anode-side concentration chamber are separated by an anion exchange membrane, the buffer chamber and the cathode-side concentration chamber are separated by a cation exchange membrane, and the buffer chamber is filled with an ion exchange material.

[0075] In one embodiment of this electroregenerative deionizer, the anode chamber, first concentration chamber, first desalination chamber, second concentration chamber, buffer chamber, third concentration chamber, second desalination chamber, fourth concentration chamber, and cathode chamber are arranged in this order from the anode to the cathode. Furthermore, an anion exchange resin and a cation exchange resin are mixed and filled into the buffer chamber.

[0076] Figure 5 is a diagram showing the configuration of such an electro-regenerative deionization apparatus.

[0077] Multiple cation exchange membranes (C membranes) and anion exchange membranes (A membranes) are arranged alternately between the anode (+) and cathode (-), forming an anode chamber, a first concentration chamber, a first desalination chamber, a second concentration chamber, a buffer chamber, a third concentration chamber, a second desalination chamber, a fourth concentration chamber, and a cathode chamber in that order from the anode (+) side to the cathode (-) side.

[0078] The first desalination chamber, the second desalination chamber, the anode chamber, the cathode chamber, and the buffer chamber are filled with a mixed resin of anion exchange resin and cation exchange resin. The first and third concentration chambers are filled with anion exchange resin, and the second and fourth concentration chambers are filled with cation exchange resin.

[0079] In this electro-regenerative deionizer, the water to be treated (raw water) is passed through each desalination chamber. Pure water is passed through each concentration chamber in the opposite direction to that of the desalination chamber. Pure water (for example, a portion of the effluent from the desalination chamber) is passed through the buffer chamber in the same direction as the water flow in the concentration chamber. Electrode water is passed through the anode chamber and cathode chamber. The direction of water flow in the anode chamber and cathode chamber is arbitrary.

[0080] By passing water through in this manner, acidic water with concentrated anions is recovered from the first and third concentration chambers, and alkaline water with concentrated cations is recovered from the second and fourth concentration chambers.

[0081] If the water flowing through the buffer chamber has an ion load, cationic components will be mixed into the second concentration chamber adjacent to the anode side of the buffer chamber, and anionic components will be mixed into the third concentration chamber adjacent to the cathode side of the buffer chamber. Therefore, it is necessary to flow pure water without an ion load through the buffer chamber.

[0082] Furthermore, the direction of water flow may be parallel rather than this opposing flow system.

[0083] Furthermore, a portion of the pure water flowing out of the desalination chamber may be passed not only through the buffer chamber but also through each concentration chamber, anode chamber, and cathode chamber as pure water.

[0084] [Fluoride-containing water treatment system] Figure 6 is a flow chart showing an example of a fluorine-containing water treatment system using an electro-regenerative deionizer.

[0085] The raw water is introduced into the neutralization tank 71, where it is neutralized by adding NaOH water from the electro-regenerative deionizer 81, as well as NaOH water from Newfeed's NaOH addition means as needed. After neutralization, it passes through the intermediate tank 72 and is pre-treated in the pre-treatment equipment 73. The pre-treatment equipment 73 includes a filter or SS remover such as a UF membrane, and is equipped with a flocculation / flotation device and a biological treatment device as needed.

[0086] The pre-treated water from the pre-treatment equipment 73 is sent via the relay tank 74 to the RO device (reverse osmosis membrane device) 75, where it is subjected to RO treatment.

[0087] The backwash wastewater from the pretreatment facility 73 is sent to the intermediate tank 72 via the intermediate tank 76 and SS removal equipment 77 such as the UF device.

[0088] The permeate from RO unit 75 is extracted as treated water and used as recovered water.

[0089] The concentrated brine from the RO unit 75 is supplied to the brine recovery RO unit 78, the permeate is sent to the intermediate tank 74, and the concentrated brine is sent to the intermediate tank 79. Alternatively, the brine recovery RO unit 78 may be omitted, and the concentrated brine from the RO unit 75 may be sent directly to the intermediate tank 79.

[0090] Water from the intermediate tank 79 is supplied to the electro-regenerative deionizer 81, where it is separated into alkaline water, acidic water, and treated water (deionized water).

[0091] Alkaline water is introduced into distillation column 82, where the ammonia component is removed from the top of the column and reused.

[0092] The bottom liquid is concentrated NaOH water, which is supplied to the neutralization tank 71 via the intermediate tank 83. A portion of the NaOH water in the intermediate tank 83 is added to the discharge neutralization tank 87 and softener 91, which will be described later. If the liquid does not contain ammonia or the ammonia concentration is low, the evaporation and concentration device can be omitted.

[0093] The acidic water from the electro-regenerative deionizer 81 is introduced into the fluorine resource recovery device 85, where fluorine is recovered. The fluorine resource recovery device 85 can be, but is not limited to, those that recover fluorine from HF concentrated water as CaF2 (fluorite), NaAlF6 (crylite), or AlF3 (aluminum fluoride). Furthermore, the acidic water from the electro-regenerative deionizer 81 can be reused as is, or after further concentration and, if necessary, after purification treatment.

[0094] The treated water from the fluorine resource recovery device 85 is introduced into the neutralization tank 87 via the intermediate tank 86. A portion of the NaOH water from the intermediate tank 83 is added to this neutralization tank 87 and neutralized.

[0095] The water neutralized in the neutralization tank 87 is filtered in the filter 88 (or UF device) and then introduced into the water softener 91 via the intermediate tank 89.

[0096] The softened water (ion exchange treatment) is sent to the relay tank 79. A portion of the softened water is stored in the regeneration tank 92 and used when regenerating the water softener 91.

[0097] During regeneration, a portion of the NaOH water from the intermediate tank 83 is added to the softener 91. The regeneration wastewater is evaporated and condensed in the evaporator 93, and the concentrated liquid is discharged as a fluorine concentrate. The condensed liquid is discharged after passing through the intermediate tank 94 and the neutralization tank 95. Treated water (desalinated water) from the electro-regenerative deionizer 81 is also introduced into the intermediate tank 94.

[0098] In this processing system, the amount of pH-adjusting chemicals used is reduced by recycling and reusing NaOH. Furthermore, no fluorine-based inorganic sludge is discharged from the fluorine resource recovery device 85.

[0099] By using RO devices 75 and 78, an electro-regenerative deionizer 81, and a fluorine resource recovery device 85, it becomes possible to reuse more than 98% of the fluorine in raw water as a resource.

[0100] Furthermore, when HF concentrated water is recovered using a CaF2 recovery facility, the CaF2 recovery rate is approximately 90%, meaning 10% leaks into the treated water. Therefore, after pretreatment such as SS removal, the treated water is returned to the intermediate tank 79 (raw water tank of the electro-regenerative deionization device) and circulated within the system to achieve a high resource reuse rate.

[0101] Regarding TOC in raw water, for example, in semiconductor factories, it mainly consists of uncharged substances such as IPA. In this case, it is not removed by the electro-regenerative deionizer and is discharged into the treated water, so there is no problem with the system. However, if the pretreatment equipment 73 includes a biological treatment device or biological activated carbon, the TOC in the treated water may be reformed to have a negative charge. In this case, TOC is concentrated along with the HF load on the anion-concentrated water side of the electro-regenerative deionizer 81.

[0102] When such HF concentrated water is recovered using a CaF2 recovery system, almost all of the TOC leaks into the CaF2 treated water side. If this is returned to the raw water tank of an electro-regenerative deionizer, the TOC becomes concentrated within the system, which increases the risk of slime failure in the electro-regenerative deionizer.

[0103] In such cases, the treated CaF2 water may be discharged via a dedicated fluorine wastewater treatment facility instead of being returned to the system.

[0104] [Example of operation of a fluorine-containing water treatment system (operation example)] An example of the operation (operation example) of this fluorine-containing water treatment system will be described below.

[0105] An example of raw water quality is as follows:

[0106] pH: 1~4 F concentration: 50~500mg / L NH4-N: 100mg / L or less TOC: 10mg / L or less

[0107] The concentration of NaOH added in neutralization tank 71 is 100-1000 mg / L.

[0108] The RO system 75 has a recovery rate of 80% and an F removal rate of 99.5% (F concentration 2 mg / L).

[0109] The concentration of F in the concentrated water from the RO system 78 used for brine recovery is 1,000 to 5,000 mg / L, and the concentration of NaOH is 2,000 to 10,000 mg / L.

[0110] The F concentration of acidic water (anion-concentrated water) from the electro-regenerative deionizer 81 is 3,000 to 15,000 mg / L, while the NaOH concentration of alkaline water (cation-concentrated water) is 6,000 to 30,000 mg / L, and the NH4-N concentration is 0 to 1,500 mg / L.

[0111] The F concentration in the desalinated water is 4 mg / L or less, and the NaOH concentration is 4 mg / L or less (removal rate of 99.5% or more).

[0112] The fluorine concentration in the water effluent from the fluorine resource recovery device 85 to the intermediate tank 86 is 500-1,500 mg / L (90% recovery rate). The amount of fluorine recovered by the fluorine resource recovery device 85 is approximately 99% or more of the amount of fluorine in the raw water.

[0113] The F concentration in the treated water from neutralization tank 95 is 4.0 mg / L or less.

[0114] Assuming that the amount of raw water flowing into the intermediate tank 72 is 100%, the amount of water introduced into the SS removal device 77 is 3%, and the amount of water supplied from the pretreatment equipment to the intermediate tank 74 is 100%.

[0115] The permeate volume of RO unit 75 is 80%, the concentrated water volume is 20%, the concentrated water volume of the brine recovery RO unit 78 is 5%, and the desalinated water (treated water) volume of the electro-regenerative deionizer 81 is 3.5%. The water supply volume to the fluorine resource recovery unit 85 is 1.5%, and the filtered water volume of the filter 88 is 1.45%. The outflow volume of the water softener 91 is 1.41%.

[0116] The above embodiment is just one example of the present invention, and the present invention may have configurations other than those described above. [Explanation of Symbols]

[0117] 1. Raw water tank 2. Means of adding alkali 3 RO device 4. Electroregenerative deionization device 11,31,51 Anode 12,32,52 cathode 15,34,37,54,56 Cation exchange membrane 14,33,36 Anion exchange membrane 13,16,35,53,55,57 Bipolar membrane 21,41,61 Anode chamber 22,44 Acidic water extraction chamber 23, 42, 45, 62, 64 Water treatment chambers 24,43,63,65 Alkaline water extraction room 25,46,66 Cathode chambers 71 Neutralization tank 73 Pre-treatment equipment 75,78 RO equipment 81. Electro-regenerative deionizer 82 Distillation Column 85 Fluorine resource recovery device 88 Filter

Claims

1. An alkali addition step in which alkali is added to fluorine-containing water to ionize the fluorine, A reverse osmosis membrane separation step to obtain concentrated water by separating ionized fluorine and the added alkali from the water to be treated using a reverse osmosis membrane apparatus, A fluorine-alkali separation step is performed by electrolytically treating the concentrated water with an electro-regenerative deionizer to separate the fluorine and alkali contained in the concentrated water. The process includes recovering the alkali obtained in the fluorine-alkali separation step and adding this alkali in the alkali addition step. A method for treating fluoride-containing water.

2. The apparatus for treating fluorine-containing water according to claim 1, wherein the electro-regenerative deionizer separates concentrated water from the reverse osmosis membrane apparatus into fluorine-concentrated water, alkaline water, and desalinated water.

3. The method for treating fluorine-containing water according to claim 1, wherein the reverse osmosis membrane apparatus includes a first reverse osmosis membrane apparatus and a second reverse osmosis membrane apparatus to which concentrated water from the first reverse osmosis membrane apparatus is supplied as feedwater, and the concentrated water from the second reverse osmosis membrane apparatus is supplied to the electro-regenerative deionization apparatus.

4. The method for treating fluorine-containing water according to claim 1 or 2, wherein the desalinated water from the electro-regenerative deionizer is discharged outside the system without wastewater treatment (excluding pH adjustment).

5. A method for treating fluorine-containing water according to claim 1 or 2, wherein fluorine is recovered by treating fluorine-concentrated water from the electro-regenerative deionization device with a fluorine resource recovery device.

6. The method for treating fluorine-containing water according to claim 1 or 2, wherein the permeate separated by the reverse osmosis membrane apparatus is used as recovered water.

7. An alkali addition device for adding alkali to fluoride-containing water, A reverse osmosis membrane apparatus that separates fluorine-containing water to which alkali has been added into concentrated water and permeate water by reverse osmosis treatment, An electro-regenerative deionizer that separates the concentrated water from the reverse osmosis membrane apparatus into at least fluorine-concentrated water and alkaline water, Alkali supply means for supplying at least a portion of the alkaline water from the electro-regenerative deionizer to the alkali addition device, A treatment device for fluorine-containing water.

8. The apparatus for treating fluorine-containing water according to claim 7, comprising a first reverse osmosis membrane apparatus and a second reverse osmosis membrane apparatus to which concentrated water from the first reverse osmosis membrane apparatus is supplied as feedwater, wherein concentrated water from the second reverse osmosis membrane apparatus is supplied to the electro-regenerative deionizer.

9. The apparatus for treating fluorine-containing water according to claim 7, wherein the electroregenerative deionizer separates concentrated water from the reverse osmosis membrane apparatus into fluorine-concentrated water, alkaline water, and desalinated water.

10. The system includes a distillation means for distilling alkaline water from the aforementioned electro-regenerative deionizer to separate it into ammonia water and alkali metal hydroxide water. A fluorine-containing water treatment apparatus according to any one of claims 7 to 9, wherein the alkali supply means supplies the alkali metal hydroxide water to the alkali addition device.

11. A fluorine-containing water treatment apparatus according to any one of claims 7 to 9, comprising a fluorine resource recovery apparatus for recovering fluorine by treating fluorine-concentrated water from the electro-regenerative deionizer.

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