JP2016043290A - Electrodialyzer and electrodialysis method for cleaned waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodialyzer for cleaned waste water where the increase of the pH of a catholyte upon electrolysis can be suppressed, both of nitric ions and metallic ions are separated from cleaned water water, and water of high purity can be suitably obtained.SOLUTION: There is provided an electrodialyzer comprising: an intermediate chamber 10 for pouring cleaned waste water including nitric ions and metallic ions; an anode chamber 20 separated with an anion-exchange membrane 21 from the intermediate chamber 10 and storing an anolyte 23; and a cathode chamber 30 separated with a cation-exchange membrane 31 from the intermediate chamber 10 and storing a catholyte 33. The anolyte 23 is an aqueous solution including nitric acid, and the catholyte 33 is an aqueous solution added with organic acid in such a manner that its electric conductivity is controlled to the range of 0.1 to 1.0 mS/cm.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electrodialysis apparatus and an electrodialysis method for washing wastewater.

  Conventionally, in various vapor deposition apparatuses, nitric acid cleaning and subsequent water cleaning are performed in order to remove metal deposits attached and deposited on a substrate other than a substrate to be formed (such as an inner wall of a chamber or a deposition plate disposed in the chamber). Is performed regularly. However, the water used for washing with water contains metal ions in addition to nitrate ions, although in very small amounts. Such washing wastewater cannot be reused as it is for water washing to prevent contamination, and therefore, a high amount of high-purity water is required for each washing and a large amount of washing wastewater is disposed of. There are situations where improvement is strongly demanded from the viewpoint of cost reduction and environmental load reduction.

  Here, there is a method of separating metal ions in water by electrodialysis. In this type of method, electrolysis is performed using an electrodialysis apparatus in which the intermediate chamber and the anode chamber are separated by an anion exchange membrane and the intermediate chamber and the cathode chamber are separated by a cation exchange membrane. To the cathode chamber and electrodeposited on the cathode. On the other hand, in the apparatus in which the nitric acid cleaning and the water cleaning as described above are performed periodically, other ions (chlorine ions, sulfate ions, etc.) also cause contamination. There was recognition that it was not possible. In view of this recognition, it is conceivable to separate metal ions by electrolysis using ammonium nitrate composed of nitric acid and its hydrolyzate ammonia as the electrolyte of the catholyte.

  As a method for separating metal ions in water by electrodialysis itself, a method using a catholyte containing an inorganic salt and a pH buffer has also been proposed (for example, see Patent Document 1). In this Patent Document 1, various examples of pH buffering agents are described, and citric acid which is an organic acid is mentioned therein.

Japanese Patent Laid-Open No. 08-000966

  However, when the cathode solution made of ammonium nitrate is used, nitrate ions are reduced in the cathode chamber by electrolysis to generate ammonium ions, which raises the problem of increasing the pH of the cathode solution. In this case, the anion exchange membrane is deteriorated and the catholyte is deteriorated.

  Patent Document 1 also describes that it is essential that the catholyte contains an inorganic salt (for example, the same kind as the ionic species of the anolyte), and it is preferable that the concentration of the inorganic salt be higher. For this reason, it is impossible to exclude the possibility that metal ions derived from inorganic salts diffuse and permeate the cation exchange membrane and re-transfer to the intermediate chamber, and water that is so pure that it can be used for the above-described water washing can be used. It was difficult to get. In the first place, Patent Document 1 requires that the anolyte contains an acid other than nitric acid. For this reason, there is a possibility that contamination may occur due to ions derived from acids other than nitric acid (chlorine ions, sulfate ions, etc.), and it was not applicable to the apparatus in which nitric acid cleaning and water cleaning as described above are performed periodically. .

  In view of such circumstances, the present invention can suppress an increase in the pH of the catholyte during electrolysis, and can clean water waste water that can suitably obtain high-purity water by separating both nitrate ions and metal ions from the cleaning waste water. It is an object of the present invention to provide an electrodialysis apparatus and an electrodialysis method.

  An aspect of the present invention that solves the above problems includes an intermediate chamber for introducing cleaning waste water containing nitrate ions and metal ions, and an anode for accommodating an anolyte separated from the intermediate chamber by an anion exchange membrane. A cathodic chamber for containing a catholyte separated from the intermediate chamber by a cation exchange membrane, wherein the anolyte is an aqueous solution containing nitric acid, and the catholyte is electrically conductive The electrodialysis apparatus for washing wastewater is an aqueous solution containing an organic acid so that the rate is in the range of 0.1 to 1.0 mS / cm.

  According to such an embodiment, since the catholyte is an aqueous solution containing an organic acid, for example, generation of ammonium ions due to reduction of nitrate ions in the cathode chamber can be prevented even when compared with the case where the catholyte is made of ammonium nitrate. It is possible to prevent the pH of the catholyte from increasing. And since the electrical conductivity of said range is ensured with the catholyte, electrolysis can be advanced suitably. From the above, it is possible to suppress an increase in the pH of the catholyte during electrolysis, and it is possible to suitably obtain high-purity water by separating both nitrate ions and metal ions from the washing wastewater.

  Here, the concentration of the organic acid in the catholyte is preferably 5 to 20% by mass. According to this, it becomes easy to prevent an increase in the pH of the catholyte, and it becomes easy to ensure the electric conductivity in the above range with the catholyte during electrolysis.

  Moreover, it is preferable that the said organic acid is 90 mass% or more among the acids contained in the said catholyte. According to this, an increase in the pH of the catholyte can be sufficiently prevented.

  Further, it is preferable that the catholyte contains substantially no inorganic salt. According to this, since the inorganic salt is not included in the range excluding the inorganic salt that cannot be completely removed due to conditions and errors, metal ions derived from the inorganic salt permeate from the cathode chamber through the cation exchange membrane. The possibility of moving to the intermediate chamber can be eliminated. For this reason, the electrodialysis apparatus can be suitably applied to cleaning wastewater generated in various apparatuses in which nitric acid cleaning and water cleaning are performed periodically, and contamination can be reliably prevented.

  Another aspect of the present invention that solves the above-described problem is that an intermediate chamber for introducing cleaning wastewater containing nitrate ions and metal ions is separated from the intermediate chamber by an anion exchange membrane and contains an anolyte. Using an electrodialyzer having an anode chamber and a cathode chamber separated from the intermediate chamber by a cation exchange membrane and containing a catholyte, and using an aqueous solution containing nitric acid as the anolyte, In the electrodialysis method of wastewater, an aqueous solution containing an organic acid is used as the anolyte so that its electric conductivity is in the range of 0.1 to 1.0 mS / cm.

  According to this aspect, since an aqueous solution containing an organic acid is used as the catholyte, for example, generation of ammonium ions due to reduction of nitrate ions in the cathode chamber can be achieved as compared with the case where the cathode solution is made of ammonium nitrate. It is possible to prevent the pH of the catholyte from increasing. And since the electric conductivity of the predetermined range is ensured with the catholyte, electrolysis can be advanced suitably. From the above, it is possible to suppress an increase in the pH of the catholyte during electrolysis, and it is possible to suitably obtain high-purity water by separating both nitrate ions and metal ions from the washing wastewater.

  According to the electrodialysis apparatus and electrodialysis method of the cleaning wastewater of the present invention, the pH increase of the catholyte during electrolysis can be suppressed, and both high purity water is preferable by separating both nitrate ions and metal ions from the cleaning wastewater. Can get to.

The figure which shows the example of application of the electrodialysis apparatus of the washing waste water which concerns on Embodiment 1. FIG. FIG. 3 is a cross-sectional view illustrating a configuration example of an electrodialysis apparatus for washing wastewater according to the first embodiment. The figure which shows the test result by the electrodialysis apparatus of the washing waste water which concerns on Examples 1-3. The figure which shows the test result by the electrodialysis apparatus of the washing waste water which concerns on Example 4 and 5. FIG. The figure which shows the test result by the electrodialysis apparatus of the washing waste water which concerns on the comparative examples 1 and 2. FIG.

(Embodiment 1)
FIG. 1 is a diagram showing an application example of a washing wastewater electrodialysis apparatus (hereinafter, simply referred to as “electrodialysis apparatus”) according to Embodiment 1 of the present invention.

In various vapor deposition apparatuses such as PVD apparatus and CVD apparatus, in order to remove metal deposits that adhere to and deposit other than the substrate to be deposited, nitric acid dissolution cleaning (nitric acid cleaning) and subsequent ultrasonic cleaning with water and rinsing are easy. Cleaning (water cleaning) is performed periodically. The cleaning wastewater used for the water cleaning contains a very small amount of metal ions; M ⁺ in addition to nitrate ions; NO ₃ ^−, and such cleaning wastewater is electrodialyzed according to the present embodiment. The device 1 is charged.

  The electrodialysis apparatus 1 is separated from the intermediate chamber 10 by an anion exchange membrane 21 for introducing washing waste water, and the anode chamber 20 for containing the anolyte and the cation exchange from the intermediate chamber 10. A cathode chamber 30 which is separated by a membrane 31 and contains catholyte. By electrolysis, nitrate ions moved from the intermediate chamber 10 are concentrated in the anode chamber 20, and metal ions moved from the intermediate chamber 10 are electrodeposited in the cathode chamber 30. As a result, both nitrate ions and metal ions can be separated from the cleaning wastewater introduced into the intermediate chamber 10.

  The water after separation of both nitrate ions and metal ions by the electrodialyzer 1 is, for example, less than several hundred ppm of nitrate ions, and the level at which metal ions are hardly detected. Can be reused. Therefore, according to the electrodialysis apparatus 1, it is possible to realize cost reduction and environmental load reduction as compared with the conventional case where high-purity water is newly required for each washing and a large amount of washing wastewater is disposed.

  The washing waste water is not limited to the water after washing as long as it contains both nitrate ions and metal ions within the scope of the present invention. Water obtained by electrolysis of washing wastewater can be used for other purposes different from those for washing water. The concentration of nitrate ions and metal ions that may remain in the water obtained after electrolysis also varies depending on the intended use of the water.

  FIG. 2 is a cross-sectional view showing a configuration example of the electrodialysis apparatus.

  In the electrodialysis apparatus 1, the anode 22 is disposed in the anode chamber 20 separated from the intermediate chamber 10 by the anion exchange membrane 21, and the cathode 32 is disposed in the cathode chamber 30 separated from the intermediate chamber 10 by the cation exchange membrane 31. The anode 22 and the cathode 32 are electrically connected via the power source 11. The anode chamber 20 contains an anolyte 23 and the cathode chamber 30 contains a catholyte 33.

  Of these, commercially available anion exchange membranes 21 and cation exchange membranes 31 can be used. Many inexpensive ones are not sufficiently resistant to deterioration of the pH of the electrolytic solution. However, according to the electrodialysis apparatus 1, the pH increase of the catholyte 33 during electrolysis can be suppressed. Even an ion exchange resin can be suitably used. The anion exchange membrane 21 and the cation exchange membrane 31 may be provided with a reinforcing member for improving the strength.

  The anode 22 and the cathode 32 have conductivity, and have a certain degree of corrosion resistance and are not easily eluted into the electrolytic solution. As an example, titanium (Ti) plated with stainless steel as the anode 22 and platinum (Pt) as the cathode 32 can be used. The materials of the anode 22 and the cathode 32 are not limited to the above examples, and gold (Au), silver (Ag), or the like can be used as an electrode material or a plating material.

  The anolyte 23 is an aqueous solution containing nitric acid. This is because in various apparatuses in which nitric acid cleaning and subsequent water cleaning are performed periodically, ions derived from other acids (chlorine ions, sulfate ions, etc.) also cause contamination. The concentration of nitric acid in the anolyte 23 can be about several mass%, for example, 0.5 to 3 mass%. By adjusting the concentration of nitric acid in the anolyte 23 to be in the above range at the start of electrolysis, the electrolysis can be suitably advanced.

  By electrolysis, nitrate ions pass through the anion exchange membrane 21 from the intermediate chamber 10 and are concentrated in the anolyte 23. When the concentration of nitrate ions in the anolyte 23 is excessively high, the anion exchange membrane 21 is adversely affected, and nitrate ions are also difficult to move to the anode chamber 20. Therefore, it is preferable to replace or replenish part or all of the anolyte 23 every predetermined time so that the concentration of nitric acid is maintained within the above range even during electrolysis.

  Here, the catholyte 33 is an aqueous solution containing an organic acid. According to this, for example, compared with the case where the cathode solution 33 is made of ammonium nitrate, generation of ammonium ions due to reduction of nitrate ions in the cathode chamber 30 can be prevented, and the pH of the cathode solution 33 is increased. Can be prevented. As a result, deterioration of the cation exchange membrane 31 and alteration of the catholyte 33 can also be prevented.

  Such an organic acid generally shows weak acidity. For this reason, although it depends on the type of organic acid, the catholyte 33 containing the organic acid can exhibit a pH buffering function, which is one factor that can prevent the pH of the catholyte 33 from increasing. .

  In addition, the organic acid itself is relatively easy to prevent its dissociation and alteration, and even if a trace amount of the organic acid permeates the cation exchange membrane 31 and moves to the intermediate chamber 10, it can be converted into various inorganic acids. In comparison, its pollution level is low.

  The catholyte 33 contains such an organic acid so that the electric conductivity is in the range of 0.1 to 1.0 mS / cm. When the electrical conductivity is less than the above range, electrolysis does not proceed suitably. On the other hand, the higher electrical conductivity works favorably for electrolytic treatment, but the organic acid tends to increase in viscosity when the concentration is high, so the organic acid is contained so that the electrical conductivity is above the above range. In some cases, there is a risk of adversely affecting the mobility of metal ions and the permeability of the ion exchange membrane. In addition, the concentration of the organic acid further increases due to the evaporation of water due to the electrolysis of the water, and the solubility of the organic acid in water is exceeded, resulting in the formation of crystals. There is also a risk of clogging the exchange membrane. Also from the viewpoint of cost, it is not preferable that the organic acid is excessively contained so that the electric conductivity exceeds the above range. Based on these, since the organic acid is contained in the anolyte 23 so as to ensure the electric conductivity in the above range, the electrolysis is suitably advanced, and both the nitrate ion and the metal ion from the cleaning waste water are obtained. Can be separated.

  The concentration of the organic acid in the catholyte 33 is 5 to 20% by mass. When the concentration of the organic acid is less than the above range, it is difficult to obtain a function of preventing the pH of the catholyte 33 from increasing. On the other hand, when the concentration of the organic acid exceeds the above range, there is a high risk that the above various problems will occur, and it becomes difficult to ensure the electrical conductivity in the above range in the catholyte 33. By adjusting the concentration of the organic acid in the catholyte 33 to be in the above range at the start of electrolysis, it becomes easy to prevent the pH of the catholyte 33 from increasing, and the catholyte 33 at the start of electrolysis. It becomes easy to ensure the electrical conductivity of said range. It is preferable to replace or replenish part or all of the catholyte 33 every predetermined time so that the concentration of the organic acid in the catholyte 33 is maintained within the above range continuously during electrolysis.

Such an organic acid is an acid of an organic compound, and the organic compound here is synonymous with what is generally called an organic compound. As the organic acid, any of carboxylic acid (RCOOH), phenol (ArOH), enol (RCH = C (OH) R ′), oxime (RCH═NOH), nitro compound (RNO ₂ ) and the like can be used. As described above, a weak acid can exert a pH buffer function, so that it is preferable that the acidity as a whole does not become too strong. Examples of organic acids include formic acid, acetic acid, butyric acid, oxalic acid, citric acid, ascorbic acid, tartaric acid, benzoic acid, lactic acid, malic acid and the like. Moreover, as an organic acid, it is preferable to use the acid of the C2-C8 organic compound from viewpoints, such as availability and solubility.

Of these, acetic acid, citric acid, and ascorbic acid are relatively inexpensive and readily available, and are easily soluble in water, so the electrical conductivity of the aqueous solution is also in a good range. Therefore, it can be said that it is a more preferable additive. The electrical conductivity of acetic acid, citric acid, and ascorbic acid in the concentration range of 5% to 20% is as follows.
Acetic acid: 5% to 20%, electric conductivity: 0.1 to 0.5 mS / cm
Citric acid: 5% to 20%, electric conductivity: 0.5 to 1.0 mS / cm
Ascorbic acid: 5% to 20%, electric conductivity: 0.1 to 0.5 mS / cm

  The organic acid includes a hydrate of the organic acid. An organic acid may be used individually by 1 type, and may use 2 or more types together.

  Among the acids contained in the catholyte 33, the organic acid is 90% by mass or more, preferably 95% by mass or more. In other words, among the acids contained in the catholyte 33, the presence of an acid other than the above-mentioned organic acid can be allowed to be less than about 10% by mass although it depends on the type of the acid. According to this, an increase in the pH of the catholyte 33 can be sufficiently prevented.

  In addition, the catholyte 33 is substantially free of inorganic salts. According to this, since the catholyte 33 does not contain an inorganic salt in a range excluding an inorganic salt that cannot be completely removed due to conditions and errors, metal ions derived from the inorganic salt are transferred from the cathode chamber 30 to a cation. The possibility of passing through the exchange membrane 31 and moving to the intermediate chamber 10 can be eliminated. The inorganic salt in the catholyte 33 depends on the kind of the inorganic salt and the use of water after separation of the nitrate ion and the metal ion. When the water after the metal ions are separated is to be reused for the above water washing, 100 ppm or less is acceptable, and in this case, it can be said that it contains substantially no inorganic salt.

  The production timing of the catholyte 33 is not limited, and the catholyte 33 is produced by adding an organic acid to water in a stage before being accommodated in the cathode chamber 30, and is accommodated in the cathode chamber 30. Alternatively, the catholyte 33 may be produced by adding an organic acid to the water after the water is accommodated in the cathode chamber 30. These methods can be combined. Examples of the water used for the catholyte 33 include pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water, or ultrapure water, but are not limited to the above examples. Such water can of course also be used for the anolyte 23 described above.

  The electrodialysis method using the electrodialysis apparatus 1 described above is as follows. That is, an aqueous solution containing nitric acid is used as the anolyte 23, and an aqueous solution containing an organic acid is used as the catholyte 33 so that its electric conductivity is in the range of 0.1 to 1.0 mS / cm. Then, cleaning wastewater containing nitrate ions and metal ions is put into the intermediate chamber 10, and electrolysis is performed by applying a voltage to the anode 22 and the cathode 32.

  In the anode chamber 20, nitrate ions that have passed through the anion exchange membrane 21 from the intermediate chamber 10 are concentrated in the anode chamber 20. The anolyte 23 in which nitrate ions are concentrated may be reused as nitric acid for cleaning acetic acid or may be used for other purposes. Of course, you may dispose without using for a predetermined use.

  In addition, due to electrolysis, in the cathode chamber 30, metal ions pass through the cation exchange membrane 31 from the intermediate chamber 10 and are electrodeposited on the cathode 32 as metal M. The cathode 32 may be replaced and cleaned every predetermined time.

  According to such an electrodialysis method, since an aqueous solution containing an organic acid is used as the catholyte 33, an increase in pH of the catholyte 33 can be prevented. And since the electric conductivity of the predetermined range is ensured in the catholyte 33, electrolysis can be advanced suitably. From the above, it is possible to suppress an increase in pH of the catholyte 33 during electrolysis, and it is possible to suitably obtain high-purity water by separating both nitrate ions and metal ions from the washing waste water.

  Hereinafter, the present invention will be described in more detail based on examples. However, the scope of the present invention is not limited at all by the following examples.

(Example 1)
An electrodialysis apparatus 1 according to Embodiment 1 was configured. Of these, the anode 22 was made of titanium (Ti) plated with platinum (Pt), and the cathode 32 was made of stainless steel. As the anolyte 23, a 1% by mass nitric acid aqueous solution was used, and as the catholyte 33, an aqueous solution containing an organic acid was used so as to satisfy the electric conductivity range in the present invention. Citric acid was used as the organic acid. Here, when the organic acid was added so that the initial pH of the catholyte 33 was about 1.27, the initial concentration of citric acid was 20% by mass.

  Except for operational errors and detection errors, among the acids contained in the catholyte 33, the organic acid is 100% by mass, and the catholyte 33 does not substantially contain an inorganic acid (Example 2 below). The same applies to ~ 5).

  As cleaning wastewater to be introduced into the intermediate chamber 10, one containing 0.5 mass% nitric acid and 0.05 mass% zinc (Zr) is used, and electrolysis is performed by applying a voltage of about 24 V to the anode 22 and the cathode 32. went.

(Example 2) to (Example 3)
As a result of containing an organic acid so as to satisfy the electric conductivity range in the present invention, the concentration of the organic acid was as shown in Table 1. Further, in order to examine the influence of the initial pH of the catholyte 33, ammonia was contained and the initial pH of the catholyte 33 was adjusted as shown in Table 1 (indicated as “NH ₃ adjustment” in Table 1). Except for these, electrolysis was performed in the same manner as in Example 1. Ammonia does not necessarily affect the electrical conductivity and pH variation of the catholyte 33 and is not necessarily necessarily contained essentially.

Example 4
The type of organic acid was changed as shown in Table 1. In addition, as a result of containing an organic acid so that the initial pH of the catholyte 33 was about 2.22, while satisfying the electric conductivity range in the present invention, the concentration of the organic acid was 5% by mass. Except for these, electrolysis was performed in the same manner as in Example 1.

(Example 5)
As a result of adding an organic acid so that the initial pH of the catholyte 33 was about 2.05 while satisfying the electric conductivity range of the present invention, the concentration of the organic acid was 5% by mass. In addition, the types of metal ions contained in the washing wastewater were changed as shown in Table 1. Except for these, electrolysis was performed in the same manner as in Example 1.

(Comparative Example 1)
Unlike Examples 1 to 5, an aqueous solution containing an organic acid was not used as the catholyte 33. That is, ammonium nitrate was used as the catholyte, and ammonium nitrate was added so that the initial pH was about 4.58. As a result, the concentration of ammonium nitrate was 1% by mass. As the anolyte 23, an aqueous nitric acid solution of about 2 to 3% by mass was used. Then, as the cleaning wastewater to be put into the intermediate chamber 10, electrolysis was performed under the same conditions as in Example 1 using 0.2% by mass of nitric acid and 0.02% by mass of zinc (Zn).

(Comparative Example 2)
In order to investigate the influence of the initial pH of the catholyte, the initial pH of the catholyte was adjusted as shown in Table 1 by adding ammonia (indicated as “NH ₃ adjustment” in Table 1). Otherwise, electrolysis was performed in the same manner as in Comparative Example 1.

(Test Example 1)
While performing the electrolysis, the cleaning wastewater in the intermediate chamber 10 and the catholyte 33 in the cathode chamber 30 are collected at regular intervals, and the nitrate ion concentration of the cleaning wastewater and the metal ion concentration of the catholyte 33 are collected. And observed the transition. The results in Examples 1 to 3 are shown in FIGS. 3 (a) to 3 (c), the results in Examples 4 to 5 are shown in FIGS. 4 (a) to (b), and the results in Comparative Examples 1 and 2 are shown. Is shown in FIGS.

  In Comparative Examples 1 and 2 shown in FIGS. 5A and 5B, since a large pH increase of the catholyte was observed immediately after the start of electrolysis, the electrolysis had to be interrupted within a few hours. This is because nitrate ions derived from ammonium nitrate in the cathode chamber and trace amounts of nitrate ions diffused from the anode chamber to the cathode chamber 30 via the anion exchange membrane 21, the intermediate chamber 10 and the cation exchange membrane 31 are reduced. This is presumed to be due to the formation of hydroxide components together with ammonium ions. When such a hydroxide component is generated, it adheres to the ion exchange membrane to cause deterioration of the ion exchange membrane, and also leads to alteration of the catholyte itself.

  On the other hand, in Examples 1-5 shown in Drawing 3 (a)-(c) and Drawing 4 (a)-(b), in the middle room 10 within several hours after starting electrolysis. It was found that the nitric acid concentration in the washing wastewater was greatly reduced, and the nitric acid concentration could be reduced to 100 ppm or less after 24 hours by continuing the electrolysis. In particular, in Examples 1-2 and 5, it was found that the nitric acid concentration could be reduced to 60 ppm or less after 24 hours. Further, it was found that during electrolysis, the pH increase of the catholyte 33 in the cathode chamber 30 can be sufficiently prevented, and thus the deterioration of the cation exchange membrane 31 and the alteration of the catholyte 33 can be suitably prevented. It was also found that such a result can be obtained regardless of the type of organic acid, the initial pH of the catholyte 33, the type of metal ions contained in the washing waste water, and the like.

(Test Example 2)
After Test Example 1, the cathode 32 pulled up from the catholyte was visually observed. A case where metal electrodeposition was confirmed on the cathode 32 was evaluated as “◯”, and a case where metal electrodeposition was not confirmed was evaluated as “x”. The results are shown in Table 2.

  In Comparative Examples 1 and 2, metal electrodeposition was not confirmed. This is because, as described above, the electrolysis must be interrupted within a few hours from the start, and the electrolysis could not be continued to the extent that metal is electrodeposited on the cathode 32.

  On the other hand, in Examples 1 to 5, metal electrodeposition was confirmed on the cathode 32. It was also found that such a result can be obtained regardless of the type of organic acid, the initial pH of the catholyte 33, the type of metal ions contained in the washing waste water, and the like.

  As described above, according to Test Examples 1 and 2, by the electrodialysis apparatus 1 and the electrodialysis method of the washing wastewater of this embodiment exemplified in Examples 1 to 5, the pH increase of the catholyte during electrolysis can be suppressed. It was found that high purity water can be suitably obtained by separating both nitrate ions and metal ions from the washing waste water. If high-purity water obtained by electrolysis is reused for water washing, improvement can be achieved from the viewpoint of cost reduction and environmental load reduction.

(Other embodiments)
Although one embodiment of the present invention has been described above, the basic configuration of the present invention is not limited to the above. For example, a plurality of the above electrodialysis apparatuses 1 may be prepared and electrically connected. The shape and size of each component of the electrodialysis apparatus 1 are also merely shown as examples, and can be appropriately changed within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 Electrodialyzer, 10 Middle chamber, 11 Power supply, 20 Anode chamber, 21 Anion exchange membrane, 22 Anode, 23 Anolyte, 30 Cathode chamber, 31 Cation exchange membrane, 32 Cathode, 33 Catholyte

Claims (5)

An intermediate chamber for introducing cleaning waste water containing nitrate ions and metal ions, an anion chamber separated from the intermediate chamber by an anion exchange membrane and containing an anolyte, and a cation exchange membrane from the intermediate chamber A cathode chamber for containing the catholyte, separated by
The anolyte is an aqueous solution containing nitric acid;
An electrodialyzer for washing wastewater, wherein the catholyte is an aqueous solution containing an organic acid so that its electric conductivity is in the range of 0.1 to 1.0 mS / cm. The electrodialysis apparatus for washing wastewater according to claim 1, wherein the concentration of the organic acid in the catholyte is 5 to 20% by mass. The electrodialysis apparatus for washing wastewater according to claim 1 or 2, wherein the organic acid in the acid contained in the catholyte is 90% by mass or more. The electrodialyzer for washing wastewater according to claim 1 or 2, wherein the catholyte contains substantially no inorganic salt. An intermediate chamber for introducing cleaning waste water containing nitrate ions and metal ions, an anion chamber separated from the intermediate chamber by an anion exchange membrane and containing an anolyte, and a cation exchange membrane from the intermediate chamber An electrodialyzer having a cathode chamber for containing the catholyte, separated by
As the anolyte, an aqueous solution containing nitric acid is used,
An electrodialysis method for washing wastewater, wherein an aqueous solution containing an organic acid is used as the catholyte so that the electric conductivity is in the range of 0.1 to 1.0 mS / cm.

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