WO2022130782A1

WO2022130782A1 - Electrodialysis device, and system and method for treating water

Info

Publication number: WO2022130782A1
Application number: PCT/JP2021/039051
Authority: WO
Inventors: 明広高田; 徹中野
Original assignee: オルガノ株式会社
Priority date: 2020-12-18
Filing date: 2021-10-22
Publication date: 2022-06-23
Also published as: JP2022097062A; TW202225103A

Abstract

An electrodialysis device is provided with: bipolar membranes and anion exchange membranes which are arranged alternatively between a positive electrode and a negative electrode; a positive electrode chamber which is defined by the positive electrode and the bipolar membrane; a negative electrode chamber which is defined by the negative electrode and the bipolar membrane; and at least one (acid chamber)-(alkali chamber) set which is arranged between the positive electrode chamber and the negative electrode chamber and in which an acid chamber and an alkali chamber are arranged adjacently to each other with the anion exchange membrane interposed therebetween. The acid chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the positive electrode chamber side and produces an acid solution by electrodialysis upon the supply of water, and the alkali chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the negative electrode chamber side and produces an alkali solution by electrodialysis upon the supply of a solution to be treated which contains an acid and an alkali.

Description

Electrodialysis equipment, water treatment systems and methods

The present invention relates to an electrodialysis apparatus, a water treatment system and a method.

It is an important task in various plants to develop a technique for reusing neutral salts, waste acids and waste alkalis discharged as by-products or wastes from various processes. For example, in the manufacturing process of a semiconductor device, a large amount of waste liquid in which hydrofluoric acid (HF) and buffered hydrofluoric acid ₍ HF + NH 4F: BHF) are mixed is discharged. Techniques for recovering acids (hydrofluoric acid) and alkalis (ammonia water: NH ₄ OH) from this waste liquid have been studied conventionally. This recovery also includes the recovery of fluorine (F) and ammonia gas (NH ₃ ).

As a method for recovering hydrofluoric acid (or fluorine) from such a waste liquid containing fluorine and ammonium (NH ₄₊ ⁾ (hereinafter, may be referred to as a liquid to be treated), calcium hydroxide (Ca (OH)) has been conventionally used. ) A coagulation sedimentation method using ₂ ) is known. However, the coagulation precipitation method has a problem that a large amount of sludge (sludge) requiring further treatment is generated, which contains unreacted calcium hydroxide and a fluorine compound not separated by precipitation.

On the other hand, as a method for recovering ammonia gas from the liquid to be treated, a stripping method using steam is known. However, the stripping method has a problem that the TDS (Total Dissolved Solid) value of wastewater increases as well as the cost of chemicals increases because it is necessary to add an alkali to adjust the pH.

In order to solve these problems, for example, Patent Document 1 proposes a method of recovering hydrofluoric acid and ammonia water (or ammonia gas) from the liquid to be treated by using well-known electrodialysis.

In the water treatment system described in Patent Document 1, an acid solution, an alkaline solution and a desalting solution are generated from the liquid to be treated by using an electrodialysis apparatus. However, the desalting solution is not always necessary in the water treatment system in the manufacturing process of the semiconductor device whose main purpose is to recover the acid and the alkali from the waste liquid. It may also require equipment to further process the desalted solution produced. Therefore, in a water treatment system containing such a desalting solution as a product, the cost of the entire system may increase.

Japanese Patent No. 3519112

The present invention has been made to solve the problems of the background techniques as described above, and to provide an electrodialysis apparatus, a water treatment system and a method capable of recovering an acid and an alkali from a liquid to be treated at low cost. The purpose.

In order to achieve the above object, the electrodialysis apparatus of the present invention is an electrodialysis apparatus used for treating a liquid to be treated containing an acid and an alkali.
Bipolar membranes and anion exchange membranes are alternately arranged between the anode and the cathode,
The anode, the anode chamber defined by the bipolar membrane, and
The cathode, the cathode chamber defined by the bipolar membrane, and the
At least one set of acid chamber and alkaline chamber arranged adjacent to each other with the anion exchange membrane interposed therebetween between the anode chamber and the cathode chamber.
Equipped with
The acid chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the anode chamber side, and water is supplied to generate an acid solution by electrodialysis.
The alkaline chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the cathode chamber side, and the liquid to be treated is supplied to generate an alkaline liquid by electrodialysis.

The water treatment system of the present invention includes the above electrodialysis apparatus and
A pure water tank for storing the water supplied to the acid chamber, and
A liquid tank to be treated that stores the liquid to be treated to be supplied to the alkaline chamber, and a liquid tank to be treated.
An acid circulation path in which an acid mixture discharged from the acid chamber and containing the acid solution produced by the electrodialysis and the water remaining without being involved in the formation of the acid solution is returned to the pure water tank and circulated. When,
The alkaline mixture discharged from the alkaline chamber and containing the alkaline solution generated by the electrodialysis and the solution to be treated that remains without being involved in the formation of the alkaline solution is returned to the liquid tank to be treated and circulated. Alkaline circulation path to make
A current measuring device that measures the current value flowing through the electrodialysis device during the electrodialysis, and a current measuring device.
A control device that controls the operation of the pure water tank and the liquid tank to be treated, and the acid circulation path and the alkali circulation path, and receives the current value measured by the current measuring device.
Have,
The control device circulates the acid mixed solution using the acid circulation path and circulates the alkaline mixed solution using the alkaline circulation path at the time of executing the electrodialysis, and the current value is within a predetermined range. When the electrodialysis is continued for a predetermined time, the acid mixed solution in the pure water tank is discharged as the acid solution, and the alkaline mixed solution in the treated liquid tank is discharged as the alkaline solution. It is a configuration to make it.

The water treatment method of the present invention is a water treatment method used for treating a liquid to be treated containing an acid and an alkali.
Bipolar films and anion exchange films are alternately arranged between the anode and the cathode, and the anode chamber defined by the anode and the bipolar film, the cathode chamber defined by the cathode and the bipolar film, and the anode. An electrodialysis apparatus including at least one set of acid chamber and alkaline chamber, which are arranged adjacent to each other with the anion exchange membrane sandwiched between the chamber and the cathode chamber, is prepared.
Water is supplied to the acid chamber defined by the anion exchange membrane and the bipolar membrane arranged on the anode chamber side, and an acid solution is generated by electrodialysis.
This is a method in which the liquid to be treated is supplied to the alkaline chamber defined by the anion exchange membrane and the bipolar membrane arranged on the cathode chamber side, and the alkaline liquid is generated by the electrodialysis.

FIG. 1 is a block diagram showing a configuration example of a water treatment system according to the first embodiment. FIG. 2 is a schematic diagram showing a schematic configuration of the electrodialysis apparatus shown in FIG. FIG. 3 is a block diagram showing a configuration example of the water treatment system according to the second embodiment. FIG. 4 is a block diagram showing a connection example of a current measuring device included in the water treatment system of the second embodiment. FIG. 5 is a block diagram showing a configuration example of the water treatment system according to the third embodiment. FIG. 6 is a block diagram showing a configuration example of the water treatment system according to the fourth embodiment. FIG. 7 is a graph showing a change in the abundance ratio (molar ratio) of fluorine ions and ammonium in the acid mixture and the alkali mixture of the examples. FIG. 8 is a graph showing changes in the conductivity of the acid mixture and the alkali mixture of the examples. FIG. 9 is a graph showing changes in the current value and the integrated current amount flowing through the electrodialysis apparatus of the embodiment.

Next, the present invention will be described with reference to the drawings.
(First Embodiment)
In the first embodiment, an example of a water treatment system including the electrodialysis apparatus of the present invention will be described.

FIG. 1 is a block diagram showing a configuration example of a water treatment system according to the first embodiment, and FIG. 2 is a schematic diagram showing a schematic configuration of the electrodialysis apparatus of the present invention shown in FIG.

As shown in FIG. 1, the water treatment system of the first embodiment includes a liquid treatment tank 11 for storing a liquid to be treated, a pure water tank 12 for storing water (pure water: _H2O ), and a water treatment tank 12. An electrodialysis device 13 to which a treatment liquid and water are supplied to generate an acid solution and an alkaline liquid from the liquid to be treated and water by electrodialysis, and a power source for supplying a predetermined DC voltage required for electrodialysis to the electrodialysis device 13. The device 14, the acid solution tank 15 for storing the acid solution generated by the electrodialysis device 13, the alkali solution tank 16 for storing the alkali solution generated by the electrodialysis device 13, and the entire water treatment system shown in FIG. It has a control device 17 for controlling the operation of the above.

The liquid tank 11, the pure water tank 12, the acid liquid tank 15, and the alkaline liquid tank 16 are each connected to the electrodialysis apparatus 13 via a flow path 18 provided with a pump and a valve (not shown). The control device 17 is connected to the power supply device 14 and the pumps and valves included in each flow path 18 via a well-known wired communication means or wireless communication means, and the power supply device 14 and the pumps and valves included in each flow path 18 are connected. Operation can be controlled. The control device 17 controls the on / off of the power supply device 14, and also uses the pumps and valves provided in each flow path 18 to supply and stop the liquid to be treated from the liquid tank 11 to the electrodialyzer 13 and purely. Controls the supply and stop of water from the water tank 12 to the electrodialysis device 13, the supply and stop of the acid solution from the electrodialysis device 13 to the acid solution tank 15, and the supply and stop of the alkaline solution from the electrodialysis device 13 to the alkaline solution tank 16. do.

In the water treatment system shown in FIG. 1, the control device 17 supplies a required amount of the liquid to be treated and pure water from the liquid tank 11 and the pure water tank 12 to the electrodialysis device 13, and the power supply device 14 supplies the electrodialysis device 13. A DC voltage is applied to the device, and electrodialysis is performed, for example, for a predetermined time set in advance. Then, when the electrodialysis is completed, the acid solution produced by the electrodialysis apparatus 13 is collected in the acid solution tank 15, and the alkaline solution produced by the electrodialysis apparatus 13 is collected in the alkaline solution tank 16. The control device 17 stores a CPU (Central Processing Unit) that executes processing according to a predetermined program, a main storage device that temporarily holds information and data necessary for the processing of the CPU, a program, and the above information and data. Realized by an auxiliary storage device (auxiliary storage device), a communication device for transmitting and receiving information to and from the outside, various input devices such as touch panels and keyboards, and an information processing device (computer) including various output devices such as display devices and printers. can. The control device 17 does not need to be constantly connected to the water treatment system of the present invention, and is subject to the change only when, for example, the settings of the power supply device 14 and the pumps and valves included in each flow path 18 are changed. It may be connected to the device.

The liquid to be treated stored in the liquid tank 11 to be treated is, for example, a waste liquid in which hydrofluoric acid (HF) and buffered hydrofluoric acid (BHF) are mixed, which is discharged from the manufacturing process of a semiconductor device. In that case, the acid solution produced by the electrodialysis apparatus 13 is hydrofluoric acid, and the alkaline solution is ammonia water.

As shown in FIG. 2, the electrodialysis apparatus 13 of the present invention has a bipolar membrane (BP membrane) 133 and an anion exchange membrane (A membrane) which are ion exchange membranes between the anode (+) 131 and the cathode (−) 132. ) 134 is alternately arranged to form a plurality of chambers. The electrodialysis apparatus 13 is arranged between the anode chamber 135 defined by the anode 131 and the BP membrane 133, the cathode chamber 136 defined by the cathode 132 and the BP membrane 133, and the anode chamber 135 and the cathode chamber 136. , At least one set of acid chambers 137 and alkali chambers 138. FIG. 2 shows a configuration example in which three sets of acid chambers 137 and alkaline chambers 138 are arranged between the anode chamber 135 and the cathode chamber 136.

For the anode 131 and the cathode 132, for example, a nickel (Ni) electrode, a titanium (Ti) platinum (Pt) plated electrode, or the like is used. The anode chamber 135 and the cathode chamber 136 are each filled with an electrode solution composed of, for example, a sodium hydroxide (NaOH) solution or a sodium sulfide (Na ₂ SO ₄ ) solution. A set of the acid chamber 137 and the alkali chamber 138 are adjacent to each other with the A film 134 interposed therebetween, and the acid chamber 137 is arranged on the anode 131 side and the alkali chamber 138 is arranged on the cathode 132 side. The acid chamber 137 is defined by the A film 134 and the BP film 133 arranged on the anode 131 side, and water (pure water: _H2O ) is supplied from the pure water tank 12. The alkaline chamber 138 is defined by the A film 134 and the BP film 133 arranged on the cathode 132 side, and the liquid to be treated is supplied from the liquid tank 11 to be treated.

The A film 134 is an ion exchange membrane that allows anions to pass through and blocks the passage of cations. The BP film 133 is a composite film in which a cation exchange membrane and an A film are laminated. The cation exchange membrane is an ion exchange membrane that allows cations to pass through and blocks the passage of anions.

In the BP film 133, a current flows when a positive potential difference (forward voltage) is applied to the cation exchange film side and a negative potential difference (forward voltage) is applied to the A film side, and a potential difference (reverse voltage) in the direction opposite to the forward voltage is applied. When it is done, it has a rectifying effect in which only a small amount of current flows. However, in the BP film 133, when the reverse voltage exceeds a predetermined critical value, water ( _H2O ) is ionized in the film, hydrogen ions and hydroxide ions are generated, and a large current flows. It will be like. The plurality of BP films 133 are arranged between the anode 131 and the cathode 132 so that a reverse voltage is applied to each of them.

In the electrodialysis apparatus 13 of the present embodiment shown in FIG. 2, a predetermined DC voltage is applied from the power supply device 14 between the anode 131 and the cathode 132 so that the anode 131 side is positive and the cathode 132 side is negative. Then electrodialysis is started.

When electrodialysis is started, the water in the membrane of each BP membrane 133 is ionized into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ), and the hydrogen ions move to the acid chamber 137 (or cathode chamber 136). It moves and the hydroxide ion moves to the alkali chamber 138 (or the anode chamber 135). In the alkali chamber 138, the liquid to be treated (HF, NH ₄ F) is ionized into hydrogen ions (H ⁺ ), fluorine ions (F ⁻ ), and ammonium (NH ₄ ⁺ ), and fluorine ions, which are anions, are generated. It passes through the A film 134 and moves to the adjacent acid chamber 137 on the anode 131 side.

As a result, in the acid chamber 137, hydrogen ions ionized in the BP film 133 and fluorine ions transferred from the alkali chamber 138 are combined to generate hydrofluoric acid (HF), which is discharged to the outside and discharged in the acid solution tank 15. Will be recovered. On the other hand, in the alkaline chamber 138, ammonium and the hydroxide ion ionized by the BP film 133 on the cathode 132 side are combined to generate ammonia water (NH ₄ OH), which is discharged to the outside and recovered in the alkaline liquid tank 16. Will be done.

As shown in FIG. 2, during the electrodialysis, the hydroxide ion ionized by the BP membrane 133 moves to the anode chamber 135, and the hydrogen ion ionized by the BP membrane 133 moves to the cathode chamber 136. do. Therefore, when the same electrode solution is used in the anode chamber 135 and the cathode chamber 136, for example, the electrode solution is circulated between the anode chamber 135 and the cathode chamber 136 to obtain hydrogen ions and hydroxide ions, respectively. It should be balanced.

According to the water treatment system of the first embodiment, the bipolar film (BP film) 133 and the anion exchange film (A film) 134 are alternately arranged between the anode 131 and the cathode 132, and the acid chamber 137 is provided. By performing electrodialysis using the electrodialysis apparatus 13 in which the alkali chamber 138 is formed, an acid solution (fluoric acid) and an alkaline solution (ammonia water) can be generated from the liquid to be treated and pure water.

Therefore, unlike the water treatment system described in Patent Document 1, the acid and alkali can be recovered from the liquid to be treated without containing the desalting liquid as a product, which may lead to an increase in cost. Therefore, the acid and alkali can be recovered from the liquid to be treated at low cost.
(Second embodiment)
FIG. 3 is a block diagram showing a configuration example of the water treatment system according to the second embodiment.

As shown in FIG. 3, the water treatment system of the second embodiment has an acid circulation path 21 for returning the solution discharged from the acid chamber 137 of the electrodialysis device 13 to the pure water tank 12 and circulating the solution, and the electrodialysis device. It has a configuration different from that of the water treatment system of the first embodiment in that it has an alkaline circulation path 22 for returning the solution discharged from the alkaline chamber 138 of 13 to the liquid tank 11 to be treated and circulating the solution.

In the water treatment system of the first embodiment shown in FIG. 1, hydrofluoric acid (HF) generated by electrodialysis from the acid chamber 137 of the electrodialysis apparatus 13 and pure water not ionized by the BP membrane 133. There is a possibility that the acid mixture consisting of and will be discharged to the outside of the room. Similarly, the alkaline chamber 138 of the electrodialysis apparatus 13 did not move to the ammonium water generated by the electrodialysis and the ammonium and the acid chamber 137 which were not bound to the hydroxide ion, or returned from the acid chamber 137. An alkaline mixture consisting of a liquid to be treated containing fluorine ions may be discharged to the outside of the room. That is, an acid solution containing an acid solution generated by electrodialysis and water (pure water) remaining without being involved in the formation of the acid solution is discharged from the acid chamber 137, and electricity is discharged from the alkali chamber 138. There is a possibility that the alkaline liquid produced by dialysis and the alkaline mixed liquid containing the liquid to be treated that remains without being involved in the formation of the alkaline liquid will be discharged.

Therefore, in the water treatment system of the second embodiment, the acid mixed solution discharged from the acid chamber 137 of the electrodialysis apparatus 13 is returned to the pure water tank 12 using the acid circulation passage 21 when the electrodialysis is performed. It is supplied again from the pure water tank 12 to the acid chamber 137. By circulating the acid mixed solution using the acid circulation path 21 during the execution of electrodialysis in this way, the acid solution (hydrofluoric acid) in the acid mixed solution is concentrated. When the concentration of the acid solution (hydrofluoric acid) reaches a predetermined value (or a predetermined range), the acid mixture is discharged (or extracted) from the pure water tank 12 and recovered as an acid solution (hydrofluoric acid). Just do it. The acid solution recovered from the pure water tank 12 may be stored in the acid solution tank 15 as shown in FIG. Pure water is newly supplied to the pure water tank 12 from which the acid mixture is discharged from an external tank (not shown).

Similarly, in the water treatment system of the second embodiment, the alkaline mixture discharged from the alkaline chamber 138 is returned to the liquid tank 11 to be treated by using the alkaline circulation path 22 at the time of performing electrodialysis, and the subject is said to be treated. It is supplied again from the treatment liquid tank 11 to the alkaline chamber 138. By circulating the alkaline mixed solution using the alkaline circulation path 22 during the execution of electrodialysis in this way, the concentration of the alkaline solution (ammonia water) in the alkaline mixed solution is concentrated. When the concentration of the alkaline solution (ammonia water) reaches a predetermined value (or a predetermined range), the alkaline mixture is discharged (or extracted) from the liquid tank 11 to be treated as an alkaline solution (ammonia water). You can collect it. The alkaline liquid recovered from the liquid tank 11 to be treated may be stored in the alkaline liquid tank 16 as shown in FIG. The liquid to be treated is newly supplied to the liquid tank 11 to be treated from which the alkaline mixed liquid is discharged from an external tank (not shown).

The acid mixture in the pure water tank 12 and the alkaline mixture in the liquid tank 11 may be discharged at the same timing. For example, the concentration of the acid solution in the acid mixture and the concentration of the alkaline solution in the alkali mixture may be adjusted. Depending on the situation, it may be discharged at different timings.

Pumps and valves (not shown) that can be controlled by the control device 17 are arranged in the acid circulation path 21 and the alkaline circulation path 22, respectively. The control device 17 can control the circulation and stop of the acid mixture in the acid circulation path 21 and the circulation and stop of the alkaline mixture in the alkaline circulation path 22 by using these pumps and valves. Further, a valve (not shown) that can be controlled by the control device 17 is arranged in the liquid tank 11 and the pure water tank 12 to be treated. The control device 17 can control the discharge and stop of the alkaline mixed liquid from the liquid tank 11 to be treated and the discharge and stop of the acid mixed liquid from the pure water tank 12 by using the valve.

In the water treatment system of the second embodiment, when the control device 17 supplies the required amount of the liquid to be treated and water from the liquid tank 11 to be treated and the pure water tank 12 to the electric dialysis apparatus 13, the electric dialysis is started. The acid mixed solution discharged from the acid chamber 137 is circulated using the acid circulation path 21, and the alkaline mixed solution discharged from the alkaline chamber 138 is circulated using the alkaline circulation path 22. On the other hand, when the electrodialysis is completed, the control device 17 stops the circulation of the acid mixed solution using the acid circulation path 21 and the circulation of the alkaline mixed solution using the alkaline circulation path 22, respectively, and the acid mixing in the pure water tank 12 The liquid is discharged and stored in the acid liquid tank 15, and the alkaline mixed liquid in the liquid tank 11 to be treated is discharged and stored in the alkaline liquid tank 16. Since other configurations are the same as those of the water treatment system of the first embodiment shown in FIG. 1, the description thereof will be omitted.

In such a configuration, the electrodialysis using the electrodialysis apparatus 13 can be performed for a predetermined predetermined time as illustrated in the first embodiment. However, in the water treatment system of the second embodiment, the timing to end the electrodialysis is determined by observing the change in the current value flowing between the anode 131 and the cathode 132 of the electrodialysis apparatus 13.

Although shown in Examples described later, the timing of ending electrodialysis can also be determined by observing changes in the conductivity of the acid mixture and the alkali mixture. However, in order to measure the conductivity using a general conductivity meter, it is necessary to insert the electrode portion made of metal provided in the conductivity meter into the acid mixed solution and the alkaline mixed solution. In that case, the electrode portion may be corroded by hydrofluoric acid or the like contained in the acid mixed solution. Therefore, for example, it is necessary to protect the electrode portion from corrosion by taking measures such as fluorine coating.

On the other hand, the current value flowing between the anode 131 and the cathode 132 of the electrodialysis apparatus 13 can be measured without inserting a part (electrode portion) of the current sensor or ammeter into the acid mixture or the alkali mixture. Therefore, no measures are required to protect it from corrosion. Further, in electrodialysis, since the current value flowing between the anode 131 and the cathode 132 of the electrodialysis apparatus 13 is generally monitored by using a current sensor or an ammeter, electrodialysis is performed based on the change in the current value. If the timing of termination is determined, there is no need to install a new instrument such as a conductivity meter. Therefore, it is preferable to determine the timing at which the electrodialysis is terminated by observing the change in the current value flowing between the anode 131 and the cathode 132 of the electrodialysis apparatus 13.

As shown in FIG. 4, the water treatment system of the second embodiment includes a current measuring device 30 connected in series with the power supply device 14 and the electrodialysis device 13. The current measuring device 30 includes a well-known current sensor or current meter that measures the current value flowing between the power supply device 14 and the electrodialysis device 13, and the current value measured by the current sensor or the current meter is well-known. It is transmitted to the control device 17 at all times or at predetermined intervals (for example, about several seconds to several minutes) by using a wired communication means or a wireless communication means. FIG. 4 shows a configuration example in which the water treatment system independently includes the current measuring device 30, but the current measuring device 30 may be provided in the power supply device 14 or in the control device 17. It may be.

As shown in Examples described later, when electrodialysis is started, the fluorine ion concentration in the alkaline mixed solution decreases, and the hydroxide ion concentration ionized by the BP film increases, so that the pH becomes alkaline and the alkaline mixture is used. Since ammonium in the liquid becomes free ammonia that does not contribute to conductivity, the conductivity gradually decreases and stabilizes at a low value after a certain period of time. On the other hand, in the acid mixed solution, pure water having low conductivity decreases and hydrogen ions and fluorine ions contributing to high conductivity increase, so that the conductivity gradually increases and relatively after a certain period of time elapses. Stable at high values.

Therefore, when electrodialysis is started, the current value flowing through the electrodialysis device 13 gradually rises, then starts to fall from a certain point, and then stabilizes at a relatively low value. Electrodialysis is terminated when the current value is relatively low and stable, that is, when the current value continues within a predetermined range for a predetermined time. Whether or not the current value continues within a predetermined range for a predetermined time may be determined, for example, by whether or not the slope of the change in the current value is within the predetermined range. As a result, the concentration of hydrofluoric acid and ammonia water by electrodialysis can be completed in the minimum required time. Therefore, the acid solution and the alkaline solution can be efficiently recovered from the liquid to be treated.

The control device 17 of the present embodiment observes the change while storing the current value received from the current measuring device 30, and as described above, at the timing when the slope of the change of the current value falls within a predetermined range. All you have to do is finish the electrodialysis.

According to the water treatment system of the second embodiment, in addition to the same effect as the water treatment system of the first embodiment, the acid solution and the alkaline solution can be efficiently recovered from the liquid to be treated.
(Third embodiment)
FIG. 5 is a block diagram showing a configuration example of the water treatment system according to the third embodiment.

As shown in FIG. 5, in the water treatment system of the third embodiment, the concentrated liquid concentrated by the reverse osmosis membrane device 40 is used as the liquid to be treated via the liquid tank 11 to be treated, and the alkali of the electrodialysis device 13 is used. It has a different configuration from the water treatment system of the first and second embodiments in that it supplies to the chamber 138. FIG. 5 shows a configuration example in which the water treatment system of the first embodiment shown in FIG. 1 is provided with the reverse osmosis membrane device 40, and the reverse osmosis membrane device 40 is the second embodiment shown in FIG. The configuration may be provided in the water treatment system of the embodiment.

In the flow path 41 connecting the reverse osmosis membrane device 40 and the liquid tank 11 to be treated, the control device 17 enables control of supply and stop of the concentrated liquid from the reverse osmosis membrane device 40 to the liquid tank 11 to be treated. The pump and valve shown are provided. The control device 17 and the pumps and valves included in the

flow paths

53 and 54 are connected via a well-known wired communication means or wireless communication means. The control device 17 of the present embodiment controls the supply and stop of the concentrated liquid to the liquid tank 11 to be processed by controlling the pump and the valve included in the flow path 41.

The reverse osmosis membrane device 40 uses a well-known reverse osmosis (RO) membrane to remove solutes from the supplied solution of permeated water (usually pure water), and a concentrated solution in which the solutes are concentrated. It is a device that produces two solutions of. The reverse osmosis membrane device 40 is supplied with, for example, a waste liquid in which the above-mentioned hydrofluoric acid (HF) and buffered hydrofluoric acid (BHF) are mixed. In that case, the reverse osmosis membrane device 40 outputs a concentrated solution in which hydrofluoric acid (HF) and ammonium fluoride (NH _4F ) are concentrated. Since other configurations are the same as those of the water treatment system of the first embodiment shown in FIG. 1 or the second embodiment shown in FIG. 3, the description thereof will be omitted.

According to the water treatment system of the third embodiment, the concentrated liquid concentrated by the reverse osmosis membrane device 40 is supplied to the electrodialysis device 13 as the liquid to be treated, so that the liquid to be treated is supplied to the electrodialysis device 13. Can be reduced in volume. Therefore, in addition to the same effects as those of the first embodiment or the second embodiment, the electrodialysis apparatus 13 can be miniaturized. Therefore, further cost reduction of the entire water treatment system can be expected. The larger the concentration of fluorine ions and the concentration of ammonium contained in the liquid to be treated after concentration, the more preferable it is because it contributes to the miniaturization of the electrodialysis apparatus 13. For example, the concentrations of fluorine ions and ammonium contained in the liquid to be treated are preferably 1000 mg / L or more, and more preferably 5000 mg / L or more.
(Fourth Embodiment)
FIG. 6 is a block diagram showing a configuration example of the water treatment system according to the fourth embodiment.

As shown in FIG. 6, in the water treatment system of the fourth embodiment, the fluorine recovery device 51 for recovering fluorine from the acid solution (fluoric acid) stored in the acid solution tank 15 and the alkaline solution tank 16 store the water. It has a configuration different from that of the water treatment system of the first to third embodiments in that it further includes an ammonia recovery device 52 that recovers ammonia gas from the alkaline liquid (ammonia water).

For example, the fluorine recovery device 51 may be configured to react fluorine obtained from the acid solution tank 15 with a calcium compound (for example, calcium hydroxide) to recover fluorine as solid calcium fluoride (CaF ₂ ). good. Further, the ammonia recovery device 52 may be configured to recover the ammonia gas by distilling the ammonia water obtained from the alkaline liquid tank 16.

In FIG. 6, the fluorine recovery device 51 recovers fluorine from the acid solution (fluoric acid) stored in the acid solution tank 15, and the ammonia recovery device 52 recovers ammonia from the alkaline solution (ammonia water) stored in the alkaline solution tank 16. A configuration example for recovering gas is shown. The fluorine recovery device 51 may recover fluorine from the acid solution discharged from the acid chamber 137 of the electrodialysis device 13, and the ammonia recovery device 52 may recover fluorine from the alkaline solution discharged from the alkali chamber 138 of the electrodialysis device 13. Ammonia gas may be recovered.

Further, FIG. 6 shows a configuration example in which the water treatment system of the first embodiment shown in FIG. 1 is provided with the fluorine recovery device 51 and the ammonia recovery device 52. The fluorine recovery device 51 and the ammonia recovery device 52 shown in FIG. 6 may have a configuration included in the water treatment system of the second embodiment shown in FIG. In that case, the fluorine recovery device 51 may recover fluorine from the acid mixture (acid solution) discharged from the pure water tank 12, and the ammonia recovery device 52 may recover the alkali mixture (ammonia) discharged from the liquid tank 11 to be treated. Ammonia gas may be recovered from water). Further, the fluorine recovery device 51 and the ammonia recovery device 52 shown in FIG. 6 may be configured to be provided in the water treatment system of the third embodiment shown in FIG.

In the flow path 53 connecting the acid liquid tank 15 and the fluorine recovery device 51, a pump (not shown) that enables control of supply and stop of the acid liquid from the acid liquid tank 15 to the fluorine recovery device 51 by the control device 17 Equipped with a valve. Similarly, in the flow path 54 connecting the alkaline liquid tank 16 and the ammonia recovery device 52, the control device 17 enables control of supply and stop of the alkaline liquid from the alkaline liquid tank 16 to the ammonia recovery device 52 (not shown). Equipped with pumps and valves. The control device 17 and the pumps and valves included in the

flow paths

53 and 54 are connected via a well-known wired communication means or wireless communication means. The control device 17 of the present embodiment controls, for example, the pumps and valves included in the

flow paths

53 and 54 to supply and stop the acid solution to the fluorine recovery device 51, and supply and stop the alkaline solution to the ammonia recovery device 52. To control.

According to the water treatment system of the fourth embodiment, by providing the fluorine recovery device 51 and the ammonia recovery device 52, not only the acid solution (fluoric acid) and the alkaline solution (ammonia water) but also fluorine and ammonia gas can be obtained. Can be recovered. Therefore, in addition to the same effects as those of the first to third embodiments, fluorine and ammonia gas can also be recovered from the liquid to be treated.

Next, examples of the present invention will be described with reference to the drawings.

In this example, electrodialysis was performed under the conditions shown in Table 1 below using the water treatment system of the second embodiment shown in FIG.

As shown in Table 1, in this embodiment, 1 mol of sodium hydroxide (1N-NaOH) solution is used as the electrode solution, and pure water ( _H2O ) is supplied to the acid chamber 137 of the electrodialysis apparatus 13 to circulate. Then, a BHF waste liquid (buffered hydrofluoric acid waste liquid) in which hydrofluoric acid and buffered hydrofluoric acid were mixed was supplied to the alkaline chamber 138 and circulated. The pure water and the BHF waste liquid are kept at room temperature (20 to 25 ° C.), respectively. Then, at the time of performing electrodialysis, the concentration of fluorine ions in the acid mixture, the concentration of ammonium in the alkali mixture, the conductivity of the acid mixture and the alkali mixture, the current value flowing through the electrodialysis apparatus 13, and the integrated current thereof. The amounts were measured respectively.

FIG. 7 is a graph showing a change in the abundance ratio (molar ratio) of fluorine ions and ammonium in the acid mixture and the alkali mixture of the examples, and FIG. 8 is the acid mixture and the alkali mixture of the examples. It is a graph which shows the state of the change of the conductivity of. FIG. 9 is a graph showing changes in the current value and the integrated current amount flowing through the electrodialysis apparatus of the embodiment. 7 to 9 show an example of the experimental results in this example.

The movement of ions through the ion exchange membrane is basically controlled by the above-mentioned electrodialysis. However, when there is a concentration difference between the solutions in two adjacent chambers sandwiching the ion exchange membrane, ions gradually move through the ion exchange membrane due to a well-known diffusion phenomenon caused by the concentration difference. That is, in the configuration in which water (pure water: H ₂ O) is supplied to the acid chamber 137 shown in FIG. 2 and the liquid to be treated (HF, NH ₄ F) is supplied to the alkali chamber 138, the alkaline chamber has a high concentration. Fluorine ions (F ⁻ ) and ammonium (NH ₄₊ ⁾ migrate from 138 to a low-concentration acid chamber by diffusion, respectively. The movement of ions due to the diffusion phenomenon occurs regardless of whether electrodialysis is performed or not. FIG. 7 shows an example in which the acid mixture contains fluorine ions and ammonium transferred from the alkaline chamber 138 due to the diffusion phenomenon before starting electrodialysis.

As shown in FIG. 7, when electrodialysis is started, as described above, fluorine ions (F ⁻ ) move from the alkaline mixed solution to the acid mixed solution, so that the ratio of fluorine ions in the acid mixed solution changes over time. Increases with. Then, when the amount of fluorine ions (F ⁻ ) transferred from the alkaline mixed solution decreases after a certain period of time, the increase of fluorine ions in the acid mixed solution stops. In addition, since ammonium (NH ₄₊ ⁾ does not move in electrodialysis, fluorine ions (F ⁻ ) move from the alkaline mixed solution to the acid mixed solution, so that the proportion of ammonium in the alkaline mixed solution increases. In FIG. 7, the proportion of ammonium in the acid mixture is once decreased and then gradually increased with the passage of time. This is because the proportion of ammonium in the acid mixture is increased due to the diffusion phenomenon. Is shown.

As described above, when electrodialysis is started, in the alkaline mixture, fluorine ions decrease and ammonium increases, so that the conductivity gradually decreases as shown in FIG. 8, and it is low after a certain period of time. Stable with value. On the other hand, in the acid mixed solution, hydrogen ions and fluorine ions increase, so that the conductivity of the acid mixed solution gradually increases as shown in FIG. 8 and stabilizes at a relatively high value after a certain period of time.

Therefore, as shown in FIG. 9, the current value flowing through the electrodialysis apparatus 13 gradually increases when electrodialysis is started, then starts to decrease from a certain point, and then stabilizes at a relatively low value. As shown in FIGS. 8 and 9, in this embodiment, the conductivitys of the alkaline mixed solution and the acid mixed solution become stable about 40 minutes after the start of electrodialysis, and the electrodialysis apparatus 13 is used. The current value that flows is also stable at a relatively low value.

As shown in FIG. 9, when a current is passed through the electrodialysis apparatus 13 even after the current value stabilizes at a relatively low value, the integrated current amount increases. However, after the current value stabilizes at a relatively low value, electrodialysis does not contribute to the concentration of hydrofluoric acid and ammonia water, so it is not necessary to continue the electrodialysis. Further, as shown in FIG. 7, in the acid mixture, the proportion of ammonium gradually increases due to the diffusion phenomenon with the passage of time. Therefore, when the increase in the ratio of fluorine ions in the acid mixture stops, it is desirable to stop the electrodialysis at that point and discharge the acid mixture and the alkali mixture from the electrodialysis apparatus 13, respectively. That is, it is desirable that the electrodialysis ends in a stable state where the current value flowing through the electrodialysis apparatus 13 is relatively low, for example, when the slope of the change in the current value falls within a predetermined range.

According to this embodiment, even if the electrodialysis apparatus 13 is provided with only one set of acid chambers 137 and alkaline chambers 138, the inventors can obtain an acid solution having a sufficient fluorine ion concentration and sufficient ammonium from the liquid to be treated and pure water. It was confirmed that an alkaline solution having a high concentration could be obtained.

Although the invention of the present application has been described above with reference to the embodiments and examples, the invention of the present application is not limited to the above-described embodiment. Various changes that can be understood by those skilled in the art are possible within the scope of the present invention in terms of the configuration and details of the present invention.

Claims

An electrodialysis machine used for treating a liquid to be treated containing an acid and an alkali.
Bipolar membranes and anion exchange membranes are alternately arranged between the anode and the cathode,
The anode, the anode chamber defined by the bipolar membrane, and
The cathode, the cathode chamber defined by the bipolar membrane, and the
At least one set of acid chamber and alkaline chamber arranged adjacent to each other with the anion exchange membrane interposed therebetween between the anode chamber and the cathode chamber.
Equipped with
The acid chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the anode chamber side, and water is supplied to generate an acid solution by electrodialysis.
The alkaline chamber is defined by the anion exchange membrane and the bipolar membrane arranged on the cathode chamber side, and the liquid to be treated is supplied to generate an alkaline liquid by the electrodialysis.
The electrodialysis apparatus according to claim 1 and
A pure water tank for storing the water supplied to the acid chamber, and
A liquid tank to be treated that stores the liquid to be treated to be supplied to the alkaline chamber, and a liquid tank to be treated.
An acid circulation path in which an acid mixture discharged from the acid chamber and containing the acid solution produced by the electrodialysis and the water remaining without being involved in the formation of the acid solution is returned to the pure water tank and circulated. When,
The alkaline mixture discharged from the alkaline chamber and containing the alkaline solution generated by the electrodialysis and the solution to be treated that remains without being involved in the formation of the alkaline solution is returned to the liquid tank to be treated and circulated. Alkaline circulation path to make
A current measuring device that measures the current value flowing through the electrodialysis device during the electrodialysis, and a current measuring device.
A control device that controls the operation of the pure water tank and the liquid tank to be treated, and the acid circulation path and the alkali circulation path, and receives the current value measured by the current measuring device.
Have,
The control device circulates the acid mixed solution using the acid circulation path and circulates the alkaline mixed solution using the alkaline circulation path at the time of executing the electrodialysis, and the current value is within a predetermined range. When the electrodialysis is continued for a predetermined time, the acid mixed solution in the pure water tank is discharged as the acid solution, and the alkaline mixed solution in the treated liquid tank is discharged as the alkaline solution. Let the water treatment system.
The water treatment system according to claim 2, wherein the control device ends the electrodialysis when the slope of the change in the current value falls within a predetermined range.
The water treatment system according to claim 2 or 3, further comprising a reverse osmosis membrane device that supplies a concentrated solution in which a solute is concentrated using a reverse osmosis membrane to the alkaline chamber as the liquid to be treated.
The water treatment system according to any one of claims 2 to 4, wherein the liquid to be treated contains fluorine and ammonium.
The water treatment system according to claim 5, wherein the liquid to be treated is a waste liquid discharged in a manufacturing process of a semiconductor device.
A fluorine recovery device that recovers fluorine by reacting hydrofluoric acid, which is the acid solution recovered by the electrodialysis device, with a calcium compound.
An ammonia recovery device that distills ammonia water, which is the alkaline solution recovered by the electrodialysis device, and recovers ammonia gas.
The water treatment system according to claim 5 or 6, further comprising.
The water treatment system according to any one of claims 5 to 7, wherein the concentration of fluorine ions and the concentration of ammonium contained in the liquid to be treated are 1000 mg / L or more, respectively.
The water treatment system according to claim 8, wherein the concentration of the fluorine ion and the concentration of the ammonium contained in the liquid to be treated are 5000 mg / L or more, respectively.
A water treatment method used for treating a liquid to be treated containing an acid and an alkali.
Bipolar films and anion exchange films are alternately arranged between the anode and the cathode, and the anode chamber defined by the anode and the bipolar film, the cathode chamber defined by the cathode and the bipolar film, and the anode. An electrodialysis apparatus including at least one set of acid chamber and alkaline chamber, which are arranged adjacent to each other with the anion exchange membrane sandwiched between the chamber and the cathode chamber, is prepared.
Water is supplied to the acid chamber defined by the anion exchange membrane and the bipolar membrane arranged on the anode chamber side, and an acid solution is generated by electrodialysis.
A water treatment method in which the liquid to be treated is supplied to the alkaline chamber defined by the anion exchange membrane and the bipolar membrane arranged on the cathode chamber side, and the alkaline liquid is generated by the electrodialysis.