Method and apparatus for treating fluoride ion- and cation-containing water

Abstract

This method and apparatus for treating fluoride ion- and cation-containing water conveys water containing fluoride ions and cations, such as ammonium ions, through a treatment water chamber of an electric regeneration type ion exchange device to separate the fluoride ions and the cations.

Description

Method and apparatus for treating water containing fluoride ions and cations

[0001] The present invention relates to a method and apparatus for treating water containing fluoride ions and cations, such as ammonium ions, and more particularly to a method and apparatus for separating fluoride ions and cations, such as ammonium ions, from water in which fluoride ions and cations, such as ammonium ions, coexist using an electrically regenerated ion exchange device.

[0002] In the electronics industry, ammonium fluoride solution or buffered hydrofluoric acid solution is used for etching semiconductors and other electronic devices. Because fluorine and ammonia are both valuable resources, their recovery from ammonium fluoride-containing wastewater is anticipated. A common recovery method involves adding sodium hydroxide in an amount equal to or greater than the mole of ammonium ions to transfer the ammonia into the gas phase, followed by the addition of calcium hydroxide or calcium chloride to precipitate the fluoride ions as calcium fluoride. This method requires the addition of a large amount of sodium hydroxide, and the pH of the wastewater becomes high after calcium fluoride precipitation, necessitating the addition of a large amount of acid for neutralization. This method has the drawbacks of being complex and requiring significant chemical and energy costs.

[0003] Electrodialysis is a method that uses an ion exchange membrane as a partition to separate and recover anions in the waste liquid as acids and cations as alkalis.

[0004] Electrodialysis can separate and recover fluoride ions as hydrofluoric acid and cations, such as ammonium ions, as ammonia without using excessive chemicals. However, as the separation progresses, the flow of electric current becomes more difficult, and the concentrations of fluoride ions and ammonia remaining in the desalinated water are not sufficiently reduced.

[0005] Patent Document 1 describes a method for recovering fluoride ions as hydrofluoric acid from hydrofluoric acid wastewater using an electrodialysis device having an anion exchange membrane and a bipolar membrane. In this method, after fluoride ions permeate the anion exchange membrane from the treated liquid chamber and move to the recovered water chamber, hydroxide ions are supplied to the treated liquid chamber, and alkaline water containing cation components and hydroxide ions is recovered from the outlet of the treated liquid chamber.

[0006] Patent Document 2 describes an apparatus for desalination of wastewater containing ammonium salts using an anion exchange membrane, a cation exchange membrane, and a bipolar membrane.

[0007] 3 is a diagram showing an example of an electrodialysis device equipped with bipolar membranes. As shown in the figure, a bipolar membrane 3, an anion exchange membrane 4, a cation exchange membrane 5, and a bipolar membrane 6 are arranged in this order between an anode (positive electrode) 1 and a cathode (negative electrode) 2. From the anode 1 toward the cathode 2, an anode chamber 11, an acidic water outlet chamber 12, a water chamber (demineralization chamber) 13, an alkaline water outlet chamber 14, and a cathode chamber 15 are formed in this order.

[0008] The water to be treated (water containing fluoride ions and cations) is passed through the water to be treated chamber 13. Pure water is passed through the acidic water outlet chamber 12 and the alkaline water outlet chamber 14 in a countercurrent direction to the water to be treated chamber 13.

[0009] The anode chamber 11 and the cathode chamber 15 are supplied with electrode water such as sodium sulfate water.

[0010] When a voltage is applied between the anode 1 and the cathode 2 and the water to be treated, pure water, and electrode water are passed through as described above, fluoride ions contained in the water to be treated in the water chamber 13 move to the anode 1 side, permeate the anion exchange membrane 4, and move to the acidic water outlet chamber 12. Then, hydrogen ions generated by dissociation of the water in contact with the bipolar membrane 3 are generated, and acidic water containing these fluoride ions is recovered from the acidic water outlet chamber 12.

[0011] Cations in the water to be treated in the water chamber 13 move to the cathode 2 side and permeate the cation exchange membrane 5. Then, hydroxide ions generated by dissociation of the water in contact with the bipolar membrane 6 are generated, and alkaline water containing these cations is recovered from the alkaline water outlet chamber 14.

[0012] When fluoride ions and cations in the water to be treated migrate to the acidic water outlet chamber 12 and alkaline water outlet chamber 14, the electrical conductivity of the water in the water to be treated chamber 13 decreases, making it difficult for current to flow. This requires a higher voltage to reduce these ions in the water to be treated, resulting in increased energy consumption. It is also necessary to ensure safety against high voltages and the durability of components. Furthermore, applying high voltages can cause problems, such as hydrogen ions breaking through the electrostatic barrier of the anion exchange membrane and passing through.

[0013] JP 2007-222779 A JP 2011-224445 A

[0014] In the method of separating fluoride ions and cations, such as ammonium ions, from water containing fluoride ions and cations, adding sodium hydroxide or calcium hydroxide (or calcium chloride) increases chemical and energy costs. While electrodialysis can reduce chemical and energy costs, there is a limit to the separation of fluoride ions and cations, such as ammonium ions, and the greater the separation efficiency, the higher the energy costs become.

[0015] An object of the present invention is to solve the problems inherent in the prior art of Patent Documents 1 and 2, that is, to provide a method and apparatus for separating fluoride ions and cations, such as ammonium ions, from water containing fluoride ions and cations, such as ammonium ions, using an electrodialysis apparatus, by suppressing a voltage rise in the electrodialysis apparatus and enabling sufficient separation of fluoride ions and cations, such as ammonium ions.

[0016] The method for treating water containing fluoride ions and cations according to the present invention is as follows: In the present invention, an electric regenerative ion exchange device, which combines an ion exchange resin and an ion exchange membrane, is used instead of an electrodialysis device to suppress the rise in voltage.

[0017] [1] A method for treating water containing fluoride ions and cations, comprising the step of passing water containing fluoride ions and cations through a water-to-be-treated chamber of an electrical regeneration type ion exchange device to separate the fluoride ions from the cations.

[0018] [2] The method for treating water containing fluoride ions and cations according to [1], further comprising a step of treating the water containing fluoride ions and cations with an electrodialysis device, in which the treated water from the electrodialysis device is passed through the treated water chamber of the electric regeneration type ion exchange device.

[0019] [3] The method for treating water containing fluoride ions and cations according to [1] or [2], wherein the cations are ammonium ions.

[0020] [4] The method for treating water containing fluoride ions and cations according to [1], wherein the fluoride salt concentration of the water containing fluoride ions and cations is 5 mg / L or more and 5000 mg / L or less, or the concentration of the fluoride ions is 3 mg / L or more and 3000 mg / L or less.

[0021] [5] The method for treating water containing fluoride ions and cations according to [4], wherein the cations are ammonium ions, and the fluoride salt concentration is an ammonium fluoride concentration.

[0022] [6] The method for treating water containing fluoride ions and cations according to [1], wherein the electrically regenerated ion exchange device has cation exchange membranes and anion exchange membranes alternately arranged between an anode and a cathode to form an anode chamber, an acidic water outlet chamber, a water-to-be-treated chamber, an alkaline water outlet chamber, and a cathode chamber, the water-to-be-treated chamber being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or the cation exchange resin.

[0023] [7] The method for treating water containing fluoride ions and cations according to [1], wherein the electrically regenerated ion exchange device has a cation exchange membrane, an anion exchange membrane, and a bipolar membrane disposed between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more sets of an acidic water outlet chamber, a water chamber to be treated, and an alkaline water outlet chamber are formed between the anode chamber and the cathode chamber, the water chamber to be treated being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or the cation exchange resin.

[0024] [8] The method for treating water containing fluoride ions and cations according to [1], wherein the electrically regenerated ion exchange device comprises an anode chamber adjacent to the anode and a cathode chamber adjacent to the cathode, the anode chamber being selected from a cation exchange membrane, an anion exchange membrane, and a bipolar membrane, and at least an anion exchange membrane and a bipolar membrane being disposed between the anode and the cathode, the anode chamber being adjacent to the cathode, and one or more pairs of an acidic water outlet chamber and an alkaline water outlet chamber being formed between the anode chamber and the cathode chamber, the alkaline water outlet chamber being filled with a mixed resin of a cation exchange resin and an anion exchange resin.

[0025] [9] A treatment device for water containing fluoride ions and cations, comprising an electric regeneration type ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electric regeneration type ion exchange device has cation exchange membranes and anion exchange membranes alternately arranged between an anode and a cathode to form an anode chamber, an acidic water outlet chamber, a water chamber to be treated, an alkaline water outlet chamber, and a cathode chamber, the water chamber to be treated being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or the cation exchange resin.

[0026]

[10] A treatment device for water containing fluoride ions and cations, comprising an electric regeneration type ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electric regeneration type ion exchange device has a cation exchange membrane, an anion exchange membrane, and a bipolar membrane disposed between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and also forms one or more sets of an acidic water outlet chamber, a water to be treated chamber, and an alkaline water outlet chamber between the anode chamber and the cathode chamber, wherein the water to be treated chamber is filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber is filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber is filled with the mixed resin or the cation exchange resin.

[0027]

[11] A treatment device for water containing fluoride ions and cations, comprising an electrically regenerated ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electrically regenerated ion exchange device is configured by disposing at least an anion exchange membrane and a bipolar membrane selected from a cation exchange membrane, an anion exchange membrane, and a bipolar membrane between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and by forming one or more pairs of an acidic water outlet chamber and an alkaline water outlet chamber between the anode chamber and the cathode chamber, and filling the alkaline water outlet chamber with a mixed resin of a cation exchange resin and an anion exchange resin.

[0028]

[12] The treatment device for water containing fluoride ions and cations according to any one of [9] to

[11] , wherein the cations are ammonium ions.

[0029]

[13] The apparatus for treating water containing fluoride ions and cations according to [6] or [7], further comprising an electrodialysis device for electrodialyzing the water containing fluoride ions and cations, wherein the electrodialysis-treated water of the electrodialysis device is supplied to the water chamber of the electroregeneration-type ion exchange device.

[0030] In the method and apparatus for treating water containing fluoride ions and cations, for example, ammonium ions, of the present invention, water containing fluoride ions and cations, for example, ammonium ions, is treated using an electrically regenerated ion exchange device in which a mixed resin of a cation exchange resin and an anion exchange resin is filled in the treatment water chamber. In this electrically regenerated ion exchange device, when the ion concentration in the treatment water decreases, water dissociates at the contact point between the cation exchange resin and the anion exchange resin, and H ＋ and OH － This reduces the electrical resistance in the treated water chamber, allowing a sufficient current to flow without causing a substantial increase in voltage, making it possible to sufficiently separate and recover fluoride ions and cations, such as ammonium ions.

[0031] In one aspect of the present invention, the electrically regenerated ion exchange device includes 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. Cations in the water to be treated permeate through the cation exchange membrane and are recovered as cation hydroxide water from the alkaline water permeation chamber.

[0032] In another aspect of the present invention, an electrically regenerated ion exchange device comprises an anion exchange membrane, a cation exchange membrane, and a bipolar membrane.

[0033] In this embodiment, fluoride ions in the water to be treated permeate the anion exchange membrane and are recovered as hydrofluoric acid, and cations in the water to be treated, such as ammonium ions, permeate the cation exchange membrane and mix with hydroxide ions supplied from the bipolar membrane or the like to be recovered as cation hydroxide water, such as ammonia water. In this embodiment, it is possible to separate and recover hydrofluoric acid and cation hydroxide water from fluoride ion and cation-containing water, and also recover treated water from which each ion has been sufficiently removed, and it is possible to make the fluoride ion concentration and cation concentration in the treated water sufficiently low (for example, 1 mg / L or less).

[0034] Generally, in the concentration compartments (acidic water extraction compartment, alkaline water extraction compartment), the ion concentration increases downstream, making it easier for current to flow. On the other hand, the ion concentration is low upstream, making it difficult for current to flow.

[0035] In one aspect of the present invention, by filling the concentration compartment with an ion exchange resin, electrolysis is appropriately caused in the concentration compartment, which has the effect of maintaining the flow of electric current. In addition, since it is known that ions move faster between functional groups on the ion exchange resin than in water, the effect of increasing the flow of electric current is also obtained.

[0036] Furthermore, the ion exchange resin contains protons (H ＋ ) than the protons (H ＋ ions) are hydroxide ions (OH － Therefore, by filling the concentration compartment with resin, ions that have migrated from the water compartment (demineralization compartment) are quickly transferred from the aqueous phase to the resin phase, preventing them from remaining in the aqueous phase and causing discharge delays, resulting in the effect of stably discharging the separated ions outside the device. If ions were to remain in the aqueous phase, they would ＋ , OH ― Ammonium ions and fluoride ions, which are less likely to generate an electric current than ions, may have a locally increased concentration, and the ions to be separated may return to the ion exchange membrane that they passed through due to concentration diffusion.

[0037] Since ions can be retained at a higher concentration by being adsorbed onto the resin than by remaining in the aqueous phase, the effect of improving the separation of ions can be obtained by filling the concentration compartments with ion exchange resin.

[0038] 1 is a configuration diagram of an electrically regenerated ion exchange device. 2 is a configuration diagram of an electrically regenerated ion exchange device. 3 is a configuration diagram of an electrodialysis device. 4 is a configuration diagram of an electrically regenerated ion exchange device. 5 is a configuration diagram of an electrically regenerated ion exchange device.

[0039] Hereinafter, an embodiment will be described with reference to the drawings.

[0040] FIG. 1 is a diagram showing the configuration of an electrically regenerated ion exchange device according to a first embodiment.

[0041] A cation exchange membrane 23, an anion exchange membrane 24, a cation exchange membrane 25, and an anion exchange membrane 26 are arranged in this order between an anode (positive electrode) 21 and a cathode (negative electrode) 22. From the anode 21 toward the cathode 22, an anode chamber 31, an acidic water outlet chamber 32, a water chamber (demineralization chamber) 33, an alkaline water outlet chamber 34, and a cathode chamber 35 are formed in this order. Each chamber 31 to 35 is filled with a resin (mixed resin) that is a mixture of anion exchange resin and cation exchange resin. The ratio of anion exchange resin in the mixed resin is preferably approximately 40 to 80 volume %. The anode chamber 31 and the alkaline water outlet chamber 34 may be filled with only cation exchange resin, and the acidic water outlet chamber 32 may be filled with only anion exchange resin.

[0042] The water to be treated (water containing fluoride ions and cations, for example, ammonium ions) is passed through the water chamber 33. Pure water is passed through the acidic water outlet chamber 32 and alkaline water outlet chamber 34 in a countercurrent direction to the water chamber 13. Pure water or an aqueous solution of sodium sulfate is passed through the anode chamber 31 and cathode chamber 35 as electrode water. Other cations include NH ４ , Na, K, Li, Mg, Ca, etc. are examples.

[0043] When a voltage is applied between the anode 21 and the cathode 22 and the water to be treated, pure water, and electrode water are passed through as described above, fluoride ions contained in the water to be treated in the water to be treated chamber 33 move toward the anode 21, permeate the anion exchange membrane 24, and move to the acidic water outlet chamber 32. Then, the acidic water containing these fluoride ions is recovered from the acidic water outlet chamber 32.

[0044] The cations in the water to be treated in the water to be treated chamber 33 (where H ＋ The cations (excluding ions; the same applies to cations below) move to the cathode 22 side and permeate the cation exchange membrane 25. Then, alkaline water containing these cations is recovered from the alkaline water outlet chamber 34.

[0045] Even if fluoride ions and cations in the water to be treated migrate to the acidic water outlet chamber 32 and the alkaline water outlet chamber 34, sufficient current flows through the water to be treated chamber 33 because the mixed resin is filled in the water to be treated chamber 33. Therefore, the applied voltage between the anode 21 and the cathode 22 hardly increases. That is, when fluoride ions and cations in the water to be treated migrate to the acidic water outlet chamber and the alkaline water outlet chamber, the conductivity of the water in the water to be treated decreases, making it difficult for current to flow. However, the action of the mixed resin in the water to be treated chamber causes water dissociation. Therefore, the reduced conductivity can be compensated for by the generated hydrogen ions and hydroxide ions. In this way, it is possible to sufficiently reduce the concentrations of fluoride ions and cations in the water to be treated without significantly increasing the applied voltage.

[0046] FIG. 2 is a diagram showing the configuration of an electrically regenerated ion exchange device according to another embodiment.

[0047] A cation exchange membrane 43, an anion exchange membrane 44, a cation exchange membrane 45, a bipolar membrane 46, an anion exchange membrane 47, a cation exchange membrane 48, and an anion exchange membrane 49 are arranged in this order between an anode (positive electrode) 41 and a cathode (negative electrode) 42. From the anode 41 toward the cathode 42, an anode chamber 51, an acidic water outlet chamber 52, a water chamber (demineralization chamber) 53, an alkaline water outlet chamber 54, an acidic water outlet chamber 55, a water chamber 56, an alkaline water outlet chamber 57, and a cathode chamber 58 are formed in this order. Each of the chambers 51 to 58 is filled with a resin (mixed resin) that is a mixture of anion exchange resin and cation exchange resin. The anode chamber 51 and the alkaline water outlet chambers 54 and 57 may be filled with only cation exchange resin, and the acidic water outlet chambers 52 and 55 may be filled with only anion exchange resin.

[0048] Water to be treated (water containing fluoride ions and cations, for example, ammonium ions) is passed through the water chambers 53 and 56. Pure water is passed through the acidic water outlet chambers 52 and 55 and the alkaline water outlet chambers 54 and 57 in a countercurrent direction to the water chambers 53 and 56. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 51 and the cathode chamber 58 as electrode water.

[0049] When a voltage is applied between the anode 41 and the cathode 42 and the water to be treated, pure water, and electrode water are passed through as described above, fluoride ions contained in the water to be treated in the water chambers 53 and 56 move toward the anode 41, permeate the anion exchange membranes 44 and 47, respectively, and move to the acidic water outlet chambers 53 and 55. Then, the acidic water containing these fluoride ions is recovered from the acidic water outlet chambers 52 and 55.

[0050] Cations in the water to be treated in the water to be treated chambers 53, 56 move toward the cathode 42 and permeate through the cation exchange membranes 45, 48. Then, alkaline water containing these cations is recovered from the alkaline water outlet chambers 54, 57.

[0051] Even if the fluoride ions and cations in the water to be treated move to the acidic water outlet chambers 53, 55 and the alkaline water outlet chambers 54, 57 in this way, the mixed resin filled in the water to be treated chambers 53, 56 allows a sufficient current to flow in the water to be treated chambers 53, 56. Therefore, the voltage applied between the anode 41 and the cathode 42 hardly increases, making it possible to reduce the concentration of fluoride ions and cations in the water to a sufficiently low level.

[0052] Although two treated water chambers 53 and 56 are installed in Figure 2, three or more combinations of acidic water extraction chamber, treated water chamber, and alkaline water extraction chamber may be provided, and three or more treated water chambers may be installed.

[0053] FIG. 4 is a diagram showing the configuration of an electrically regenerated ion exchange device according to another embodiment.

[0054] A bipolar membrane 63, an anion exchange membrane 64, a bipolar membrane 65, an anion exchange membrane 66, and a bipolar membrane 67 are arranged in this order between an anode (positive electrode) 61 and a cathode (negative electrode) 62. An anode chamber 71, an acidic water outlet chamber 72, a water-to-be-treated chamber 73, an acidic water outlet chamber 74, a water-to-be-treated chamber 75, and a cathode chamber 76 are formed in this order from the anode 61 to the cathode 62. Each chamber 71 to 76 is filled with a resin (mixed resin) that is a mixture of anion exchange resin and cation exchange resin. Note that the anode chamber 71 may be filled with only a cation exchange resin, and the acidic water outlet chambers 72 and 74 may be filled with only anion exchange resin.

[0055] Water to be treated (water containing fluoride ions and cations, e.g., ammonium ions) is passed through the water chambers 73 and 75. Pure water is passed through the acidic water outlet chambers 72 and 74 in a countercurrent direction to the water chambers 73 and 75. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 71 and the cathode chamber 76 as electrode water.

[0056] When a voltage is applied between the anode 61 and the cathode 62 and the water to be treated, pure water, and electrode water are passed through as described above, fluoride ions contained in the water to be treated in the water chambers 73 and 75 move toward the anode 61, permeate the anion exchange membranes 64 and 66, respectively, and move to the acidic water outlet chambers 72 and 74. Then, the acidic water containing these fluoride ions is recovered from the acidic water outlet chambers 72 and 74.

[0057] Cations in the water to be treated in the water chambers 73, 75 attempt to migrate toward the cathode 62, but are prevented from doing so by the bipolar membranes 65, 67. As a result, alkaline water containing these cations is recovered from the water chambers 73, 75.

[0058] Even if fluoride ions in the water to be treated move to the acidic water outlet chambers 72, 74 in this way, the mixed resin filled in the water to be treated chambers 73, 75 allows sufficient current to flow through the water to be treated chambers 73, 75. Therefore, the voltage applied between the anode 61 and the cathode 62 hardly increases, making it possible to reduce the concentration of fluoride ions in the water to a sufficiently low level.

[0059] Although two treated water chambers 73 and 75 are provided in FIG. 4, three or more combinations of acidic water extraction chambers and treated water chambers may be provided, and three or more treated water chambers may be provided.

[0060] FIG. 5 is a diagram showing the configuration of an electrically regenerated ion exchange device according to another embodiment.

[0061] A cation exchange membrane 83, an anion exchange membrane 84, a bipolar membrane 85, an anion exchange membrane 86, and a bipolar membrane 87 are arranged in this order between an anode (positive electrode) 81 and a cathode (negative electrode) 82. An anode chamber 91, an acidic water outlet chamber 92, a water-to-be-treated chamber 93, an acidic water outlet chamber 94, a water-to-be-treated chamber 95, and a cathode chamber 96 are formed in this order from the anode 81 to the cathode 82. Each chamber 91 to 96 is filled with a resin (mixed resin) that is a mixture of anion exchange resin and cation exchange resin. Note that the anode chamber 91 may be filled with only a cation exchange resin, and the acidic water outlet chambers 92 and 94 may be filled with only anion exchange resin.

[0062] Water to be treated (water containing fluoride ions and cations, e.g., ammonium ions) is passed through the water chambers 93 and 95. Pure water is passed through the acidic water outlet chambers 92 and 94 in a countercurrent direction to the water chambers 93 and 95. Pure water or an aqueous sodium sulfate solution is passed through the anode chamber 91 and the cathode chamber 96 as electrode water.

[0063] When a voltage is applied between the anode 81 and the cathode 82 and the water to be treated, pure water, and electrode water are passed through as described above, fluoride ions contained in the water to be treated in the water chambers 93 and 95 move toward the anode 81, permeate the anion exchange membranes 84 and 86, respectively, and move to the acidic water outlet chambers 92 and 94. Then, the acidic water containing these fluoride ions is recovered from the acidic water outlet chambers 92 and 94.

[0064] Cations in the water to be treated in the water chambers 93, 95 attempt to migrate toward the cathode 82, but are prevented from doing so by the bipolar membranes 85, 87. As a result, alkaline water containing these cations is recovered from the water chambers 93, 95.

[0065] Even if fluoride ions in the water to be treated move to the acidic water outlet chambers 92, 94 in this way, the mixed resin filled in the water to be treated chambers 93, 95 allows sufficient current to flow through the water to be treated chambers 93, 95. Therefore, the voltage applied between the anode 81 and the cathode 82 hardly increases, making it possible to reduce the concentration of fluoride ions in the water to a sufficiently low level.

[0066] Although two treated water chambers 93 and 95 are provided in FIG. 5, three or more combinations of acidic water extraction chambers and treated water chambers may be provided, and three or more treated water chambers may be provided.

[0067] In the present invention, water containing fluoride ions and ammonium ions may be subjected to electrodialysis treatment in an electrodialysis device, and the electrodialyzed water may be passed through the deionization compartment of an electroregeneration type ion exchange device.

[0068] The fluoride ion- and cation-containing water of the present invention has a fluoride salt concentration of 5 mg / L or more and a fluoride ion concentration of 3 mg / L or more. Furthermore, it is desirable that the fluoride salt concentration be 5000 mg / L or less, or that the fluoride ion concentration be 3000 mg / L or less. Furthermore, it is more desirable that the fluoride salt concentration be 500 mg / L or less, or that the fluoride ion concentration be 300 mg / L or less.

[0069] Example 1 (treatment of an aqueous ammonium fluoride solution) and Experimental Examples 1 to 7 (treatment of an aqueous sodium chloride solution) will be described below.

[0070] Example 1 The electrically regenerated ion exchange device shown in Figure 2 was configured as follows: Each chamber was filled with the following mixed resin.

[0071] <Configuration of Electrically Regenerated Ion Exchange Device> Anion exchange membrane: Astom anion exchange membrane (AHA) Cation exchange membrane: Astom cation exchange membrane (CMB) Mixed resin: Kurita ion exchange resin (KR-UM1) Membrane area: 100 cm ２ Distance between anode and cathode: 3.5 cm

[0072] The water to be treated was a 5 mg / L aqueous solution of ammonium fluoride (pH 5.91) at a flow rate of 70 mL / min, pure water was passed through each extraction chamber at a flow rate of 60 mL / min, and pure water was passed through the electrode at a flow rate of 440 mL / min. A set current of 0.015 A was applied. The initial voltage at the start of operation was 2.72 V.

[0073] <Results> After 3 hours of operation, the voltage was 2.92 V, the current was 0.015 A, the fluoride ions in the treated water were 0.01 mg / L, the ammonium ions in the treated water were 0.00 mg / L, and the pH was 8.57.

[0074] [Experimental Example 1] (Treatment of aqueous sodium chloride solution) A 5 mg / L aqueous sodium chloride solution (pH 5.65) was passed through an electrically regenerated ion exchange device having the same configuration as in Example 1 at a rate of 70 mL / min. The water flow conditions for each extraction chamber and electrode chamber were the same as in Example 1. A set current of 0.015 A was also applied. The voltage at the start of operation was 2.90 V.

[0075] <Results> After 3 hours of operation, the voltage was 3.15 V, the current was 0.015 A, the chloride ions in the treated water were 0.00 mg / L, the sodium ions in the treated water were 0.01 mg / L, and the pH was 7.26.

[0076] [Experimental Example 2] The electrodialysis device shown in Fig. 3 was configured as follows: <Configuration of electrodialysis device> Anion exchange membrane: Astom anion exchange membrane (AHA) Cation exchange membrane: Astom cation exchange membrane (CMB) Bipolar membrane: Astom bipolar membrane Membrane area: 50 cm ２ Distance between anode and cathode: 0.4 cm

[0077] A 5 mg / L aqueous solution of sodium chloride (pH 5.63) was passed through the treatment water at 70 mL / min, pure water was passed through each extraction chamber at 15 mL / min, and a 15 g / L aqueous solution of sodium sulfate was passed through the electrode water at 18 mL / min. A maximum voltage of 15 V was applied. The initial voltage at the start of operation was 15 V.

[0078] <Results> After 3 hours of operation, the voltage was 15 V, the current was 0.012 A, the chloride ions in the treated water were 1.74 mg / L, the sodium ions in the treated water were 0.68 mg / L, and the pH was 4.61.

[0079] <Discussion of Example 1, Experimental Example 1, and Experimental Example 2> In Example 1, by using an electrically regenerated ion exchange device, the ammonium fluoride concentration in the supply water, which was 5 mg / L, was reduced to 0.01 mg / L of fluoride ions and 0.00 mg / L of ammonium ions in the treated water.

[0080] Comparing Experimental Example 1 and Experimental Example 2, which used sodium chloride, Experimental Example 2, which used an electrodialysis device, was only able to reduce chloride ions to about 1.74 mg / L and sodium ions to about 0.68 mg / L, while Experimental Example 1, which used an electrical regeneration ion exchange device, reduced chloride ions to 0.00 mg / L and sodium ions to 0.01 mg / L.

[0081] Furthermore, after 3 hours, the voltage was 15 V and the current was 0.012 A in Experimental Example 2 (electrodialysis), while the voltage was 3.15 V and the current was 0.015 A in Experimental Example 1 (electrical regeneration ion exchange device), making it difficult for current to flow in Experimental Example 2. The power consumption was 0.18 W in Experimental Example 2 (electrodialysis), while it was 0.05 W in Experimental Example 1 (electrical regeneration ion exchange device). The membrane area of ​​the electrodialysis device in Experimental Example 2 was half that of the electrolytic regeneration ion exchange device in Experimental Example 1, but the power consumption was 3.8 times higher. It is believed that even if the membrane area was increased to reduce the ion concentration in the treated water, the power consumption would still increase.

[0082] From the above, it has been confirmed that an electroregenerative ion exchange device is effective for separating fluoride ions and cations, such as ammonium ions, from water to be treated containing fluoride salts, such as ammonium fluoride ions, at a concentration of 5 mg / L or less (fluoride ion concentration of 3 mg / L or less). It is also effective to use an electrodialysis device upstream of the electroregenerative ion exchange device to reduce the concentrations of fluoride ions and cations in the aqueous fluoride salt solution to a certain extent before using the electroregenerative ion exchange device.

[0083] [Experimental Examples 3-1, 3-2, 3-3, Experimental Example 4] (Treatment of 50 mg / L aqueous sodium chloride solution using an electroregenerative ion exchange device or an electrodialysis device) Experimental Example 3-1 used the electroregenerative ion exchange device of Experimental Example 1, and Experimental Example 4 used the electrodialysis device of Experimental Example 2. Tests were conducted in the same manner as Experimental Examples 1 and 2, except that an aqueous sodium chloride solution of approximately 50 mg / L was passed through as the water to be treated. In addition, Experimental Examples 3-2 and 3-3 were conducted in which the maximum current value was lowered and the applied voltage was lowered as shown in Table 1. The results are shown in Table 1.

[0084]

[0085] As shown in Table 1, in Experimental Example 4 using an electrodialysis device, even when a voltage of 15 V was applied, the current flowed no more than 0.046 A, and the chloride concentration in the treated water decreased by only 22.33%. On the other hand, in Experimental Example 3-1 using an electrically regenerated ion exchange device, the chloride ion concentration decreased by 100% when a voltage of 15 V was applied.

[0086] The power consumption was 0.69 W in Experimental Example 4 (electrodialysis device), while it was 37.96 W in Experimental Example 3-1 (electric regeneration type ion exchange device), and it can be said that most of the power was used for electrolysis of water.

[0087] When the applied voltage was lowered as in Experimental Examples 3-2 and 3-3, the power consumption in Experimental Example 3-3 (current 0.1 A) was 0.38 W, which was lower than the 0.69 W in Experimental Example 4 (electrodialysis device). The reduction rate of chloride ions was also 99.85%.

[0088] Experimental Examples 3-1, 3-2, 3-3, and 4 demonstrate that an electroregenerative ion exchanger has higher ion separation capability with lower power consumption than an electrodialysis device when used in an aqueous solution with a salt concentration of about 50 mg / L (an anion concentration of about 30 mg / L). Therefore, the method of subjecting fluoride salt-containing water with a fluoride salt concentration of about 50 mg / L (fluoride ion concentration of about 30 mg / L) to ion separation treatment using an electroregenerative ion exchanger is considered to be more advantageous in terms of treated water quality and power consumption than the use of an electrodialysis device.

[0089] [Experimental Examples 5-1, 5-2, and 6] (Treatment of 500 mg / L aqueous sodium chloride solution using an electroregenerative ion exchange device or an electrodialysis device) Experimental Examples 5-1 and 5-2 used the electroregenerative ion exchange device of Experimental Example 1, and Experimental Example 6 used the electrodialysis device of Experimental Example 2. Tests were conducted in the same manner as above, except that a 500 mg / L aqueous sodium chloride solution was passed through as the treated water and the applied voltage was as shown in Table 2. The results are shown in Table 2.

[0090]

[0091] As shown in Table 2, in Experimental Example 6 using an electrodialysis device, a current of 0.601 A or more did not flow even when a voltage of 15 V was applied, and the chloride ion concentration in the treated water decreased by only 43.39%. On the other hand, in Experimental Example 5-2 using an electrically regenerated ion exchange device, the chloride ion concentration decreased by 50.53% when a voltage of 5.31 V was applied.

[0092] The power consumption was 9.02 W in Experimental Example 6 (electrodialysis device), whereas it was 2.66 W in Experimental Example 5-2 (electrically regenerated ion exchange device applied with 5.31 V). In addition, in the case of Experimental Example 5-1 in which 8.90 V was applied, the chloride ion concentration decreased by 91.77% with a power consumption of 8.90 W.

[0093] Experimental Examples 5-1, 5-2, and 6 demonstrated that an electroregenerative ion exchanger has higher ion separation capability with lower power consumption than an electrodialysis device, even for aqueous solutions with a salt concentration of about 500 mg / L (anion concentration of about 300 mg / L). Therefore, a method of roughly separating ions from cations with a fluoride salt concentration of more than 500 mg / L (fluoride ion concentration of 300 mg / L or more), such as ammonium fluoride-containing water, using an electrodialysis device, and then subjecting the resulting fluoride salt-containing water to an ion separation treatment with an electroregenerative ion exchanger to a fluoride salt concentration of 500 mg / L or less (fluoride ion concentration of 300 mg / L or less) is considered advantageous in terms of treated water quality and power consumption.

[0094] [Experimental Example 7] (Treatment of 5000 mg / L sodium chloride aqueous solution using an electrical regeneration type ion exchange device) In Experimental Example 7, the electrical regeneration type ion exchange device of Experimental Example 1 was used. As the water to be treated, a 5000 mg / L sodium chloride aqueous solution was passed through at 4.3 mL / min. Pure water was passed through the acidic water extraction chamber at 3.9 mL / min, pure water was passed through the alkaline water extraction chamber at 2.8 mL / min, and pure water was passed through the electrode water at 400 mL / min. A set current of 2.0 A was also applied. The initial voltage at the start of operation was 13.3 V.

[0095] <Results> After 5.5 hours of operation, the voltage was 11.2 V, the current was 2.0 A, the chloride ion concentration in the treated water was 0.25 mg / L, the sodium ion concentration in the treated water was 0.1 mg / L, and the pH was 7.7. By using the electrically regenerated ion exchange device, the chloride ion concentration was reduced by approximately 100%.

[0096] As can be seen from Experimental Example 2, in electrodialysis, even at a voltage of 15 V, current stops flowing when the chloride ion concentration in the treated water becomes low, so the value cannot be reduced to 1 mg / L or less.

[0097] Experimental Example 7 demonstrated that the electroregenerative ion exchange device had higher ion separation ability with lower power consumption than the electrodialysis device, even for an aqueous solution with a salt concentration of about 5000 mg / L (anion concentration of about 3000 mg / L).

[0098] Therefore, a method in which fluoride ion-containing water having a fluoride salt concentration of 500 mg / L or more than 5000 mg / L (fluoride ion concentration of 300 mg / L or more than 3000 mg / L) is roughly subjected to ion separation using an electrodialysis device, and the ammonium fluoride-containing water having a fluoride salt concentration of 5000 mg / L or less than 500 mg / L (fluoride ion concentration of 3000 mg / L or less) is then subjected to ion separation treatment using an electrical regeneration ion exchange device is considered to be advantageous in terms of treated water quality and power consumption.

[0099] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the invention.

[0100] This application is based on Japanese Patent Application No. 2024-082007, filed on May 20, 2024, the entire contents of which are incorporated by reference.

[0101] 1, 21, 41, 61, 81 Anode 2, 22, 42, 62, 82 Cathode 3, 6, 46, 65, 67, 85, 87 Bipolar membrane 4, 24, 26, 44, 47, 49, 64, 66, 84, 86 Anion exchange membrane 5, 23, 25, 43, 45, 48, 83 Cation exchange membrane

Claims

1. A method for treating water containing fluoride ions and cations, comprising the step of passing water containing fluoride ions and cations through a water chamber of an electrically regenerated ion exchange device to separate the fluoride ions from the cations.

2. A method for treating water containing fluoride ions and cations according to claim 1, further comprising a step of treating the water containing fluoride ions and cations with an electrodialysis device, and passing the treated water from the electrodialysis device through the treated water chamber of the electrical regeneration type ion exchange device.

3. A method for treating water containing fluoride ions and cations according to claim 1 or 2, wherein the cations are ammonium ions.

4. A method for treating water containing fluoride ions and cations according to claim 1, wherein the fluoride salt concentration of the water containing fluoride ions and cations is 5 mg / L or more and 5000 mg / L or less, or the fluoride ion concentration is 3 mg / L or more and 3000 mg / L or less.

5. The method for treating water containing fluoride ions and cations according to claim 4, wherein the cations are ammonium ions, and the fluoride salt concentration is an ammonium fluoride concentration.

6. The method for treating water containing fluoride ions and cations according to claim 1, wherein the electrically regenerated ion exchange device has cation exchange membranes and anion exchange membranes alternately arranged between an anode and a cathode to form an anode chamber, an acidic water outlet chamber, a treated water chamber, an alkaline water outlet chamber, and a cathode chamber, the treated water chamber being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or an anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or a cation exchange resin.

7. The method for treating water containing fluoride ions and cations according to claim 1, wherein the electrically regenerated ion exchange device has a cation exchange membrane, an anion exchange membrane, and a bipolar membrane disposed between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more sets of an acidic water outlet chamber, a water chamber to be treated, and an alkaline water outlet chamber are formed between the anode chamber and the cathode chamber, the water chamber to be treated being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or an anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or a cation exchange resin.

8. The method for treating water containing fluoride ions and cations according to claim 1, wherein the electrically regenerated ion exchange device comprises a cation exchange membrane, an anion exchange membrane, and a bipolar membrane, at least an anion exchange membrane and a bipolar membrane, disposed between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more pairs of acidic water outlet chambers and alkaline water outlet chambers are formed between the anode chamber and the cathode chamber, and the alkaline water outlet chambers are filled with a mixed resin of a cation exchange resin and an anion exchange resin.

9. A treatment device for water containing fluoride ions and cations, comprising an electric regeneration type ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electric regeneration type ion exchange device has cation exchange membranes and anion exchange membranes alternately arranged between an anode and a cathode to form an anode chamber, an acidic water outlet chamber, a water chamber to be treated, an alkaline water outlet chamber, and a cathode chamber, the water chamber to be treated being filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber being filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber being filled with the mixed resin or the cation exchange resin.

10. A treatment device for water containing fluoride ions and cations, comprising an electric regenerative ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electric regenerative ion exchange device has a cation exchange membrane, an anion exchange membrane, and a bipolar membrane arranged between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and also forms one or more sets of an acidic water outlet chamber, a water chamber to be treated, and an alkaline water outlet chamber between the anode chamber and the cathode chamber, wherein the water chamber to be treated is filled with a mixed resin of a cation exchange resin and an anion exchange resin, the acidic water outlet chamber is filled with the mixed resin or the anion exchange resin, and the alkaline water outlet chamber is filled with the mixed resin or the cation exchange resin.

11. A treatment device for water containing fluoride ions and cations, comprising an electrically regenerated ion exchange device for treating water containing fluoride ions and cations to separate the fluoride ions from the cations, wherein the electrically regenerated ion exchange device is provided with at least an anion exchange membrane and a bipolar membrane selected from a cation exchange membrane, an anion exchange membrane, and a bipolar membrane, between an anode and a cathode to form an anode chamber along the anode and a cathode chamber along the cathode, and one or more pairs of an acidic water outlet chamber and an alkaline water outlet chamber are formed between the anode chamber and the cathode chamber, and the alkaline water outlet chamber is filled with a mixed resin of a cation exchange resin and an anion exchange resin.

12. The apparatus for treating water containing fluoride ions and cations according to any one of claims 9 to 11, wherein the cations are ammonium ions.

13. A treatment device for water containing fluoride ions and cations according to claim 6 or 7, further comprising an electrodialysis device for electrodialyzing the water containing fluoride ions and cations, and the electrodialysis-treated water from the electrodialysis device is supplied to the water chamber of the electroregeneration-type ion exchange device.

Images