JP2014040629A - Electrode for electrolysis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for electrolysis that enables effective, efficient electrolytic treatment by preventing a metal component of the electrode from dissolving in a solution, for example, in a process of electrochemically reducing oxide-form nitrogen in water to be treated, such as waste water, for removal.SOLUTION: The electrode for electrolysis is formed by coating a surface of a conductor with an alloy in an amorphous state. The electrode for electrolysis can be used as a cathode to electrolyze, for example, oxide-form nitrogen components in water to be treated.

Description

  The present invention relates to an electrode for electrolysis, and more particularly to an electrode for electrolysis that can be suitably used as a cathode in, for example, a treatment for removing oxidized nitrogen components in water to be treated by electrolysis.

  Treatment methods for nitrate nitrogen contained in wastewater include biological treatment methods that utilize the denitrification ability of microorganisms, physicochemical treatment methods such as ion exchange, reverse osmosis, and electrodialysis, and electrolysis There are electrochemical treatment methods using

  The biological treatment method is the most popular method because of its low running cost. However, since the reaction rate is low, a large treatment device is required to treat a large amount of waste water. In addition, this biological treatment method is difficult to apply to wastewater containing nitrate nitrogen at a high concentration of about 1 g / L or more, and fluctuations in the load on the treatment equipment such as changes in nitrate nitrogen concentration in the wastewater. Therefore, the processing performance tends to become unstable.

  The physicochemical processing method is a method in which a processing apparatus can be downsized and reliable processing can be expected. However, since this method is a method for separating and concentrating nitrogen in water, it is necessary to separately treat a liquid finally enriched with nitrogen, and the nitrogen is not fundamentally treated.

  The electrochemical treatment method using electrolysis is a method of fundamentally treating nitrogen components, which has a relatively large treatment capacity relative to the size of the device and is applicable to wastewater containing high concentrations of nitrogen. It is possible to expect stable processing against fluctuations in the load on the processing apparatus such as changes in nitrogen concentration.

  However, among the conventional electrochemical nitrogen removal methods, particularly with regard to the treatment method of oxidized nitrogen such as nitrate and nitrite, the durability (corrosion resistance) of the cathode for reducing nitrate and nitrite nitrogen and There is a problem in that a diaphragm for partitioning the anode and the cathode is required.

  For example, Patent Document 1 proposes to use a conductor containing 1B group or 2B group of the periodic table as a cathode material, or a material in which the same family is coated with a conductor. Specific examples include zinc, copper, silver, brass, which is an alloy of zinc and copper, copper and nickel, and an alloy of copper and aluminum, which show that the reduction characteristics of oxidized nitrogen are high. ing.

  However, particularly for brass, it is described that zinc having a large ionization tendency acts as a sacrificial electrode as a mechanism for improving the reduction characteristics. Therefore, when brass is used as the cathode, it is premised on the dissolution of zinc constituting the electrode, and there is a problem in durability of the electrode.

  Further, in Patent Document 2, it is pointed out that when an alloy containing copper is used for the cathode, the dissolution of copper is a problem from the viewpoint of toxicity. It has been proposed to use a conductor containing a group or a conductor coated with the same family. Specifically, iron is exemplified, and the reduction characteristics are described as being similar to brass.

  However, as will be described in a comparative example described later, when iron is used as the cathode, the dissolution of iron is remarkable. From the viewpoint of toxicity, even if iron is dissolved, it may not be a big problem, but not only the durability of the electrode is problematic, but a process for separately processing the dissolved iron is required.

  Further, in Patent Document 2 and Patent Document 3 described above, it is proposed to partition the anode and the cathode with a cation exchange membrane. Further, in the above-mentioned Patent Document 1, a shielding member that prevents the passage of oxygen bubbles and prevents the anode side from being affected by flowing water and allows the passage of ions may be disposed between the anode and the cathode. Proposed.

  According to the explanation of these technologies, partitioning between the anode and the cathode prevents nitrate ions from being reduced at the cathode and producing nitrite ions, which are then oxidized at the anode and again generate nitrate ions. In addition, the reduction of nitrate ions with high current efficiency is realized.

  Furthermore, on the cathode side, hypochlorite ions generated at the anode undergo a reaction that is reduced again to chloride ions, and it is estimated that the efficiency of the oxidized nitrogen reduction reaction is reduced. It is considered that there is an intention to prevent a reduction in reduction efficiency on the cathode side by partitioning.

  However, it is assumed that various components other than oxidized nitrogen are included in the water to be treated, and there are many cases where hardness components and suspended substances are included. Therefore, when the space between the anode and the cathode is partitioned, it is easily estimated that the ion exchange membrane and the shielding member used for the partition are clogged with hardness components and suspended substances.

  An example of electrolysis using such a diaphragm is the production of caustic soda. In the electrolytic production of caustic soda, the hardness component concentration in the raw water used for electrolysis is strictly controlled to a very low concentration in order to prevent clogging of the ion exchange membrane as a diaphragm. However, it is extremely difficult to apply such management to general water treatment.

  In addition, when the anode and the cathode are partitioned, ammonia generated at the cathode and hypochlorous acid generated at the anode do not react in situ. From this, for example, in the technique described in Patent Document 3 described above, after electrolysis is performed and ammonia is generated at the cathode, the liquid in the cathode chamber is fed to the anode chamber to react ammonia with hypochlorous acid. There is a problem that the operation becomes complicated.

  On the other hand, Patent Document 4 proposes a nitrate nitrogen treatment method using a diaphragm membrane electrolytic cell. However, in Patent Document 4, aluminum or an alloy containing the same as the main component is used for the cathode, and the reaction opposite to the purpose is performed (the oxidation reaction of the nitrogen compound at the anode and the reduction reaction of hypochlorous acid at the cathode). It is explained that the amount of electricity that is wasted is compensated apparently by dissolution of the cathode material. In this method, means for suppressing or preventing the reaction opposite to the purpose is not taken, and the method is based on the premise of dissolution of the cathode material as in the technique described in Patent Document 1 described above. In addition to the problem of the durability of the cathode, it is necessary to separately process the dissolved aluminum.

  Patent Document 4 describes that aluminum used as a cathode hardly dissolves only by being immersed in water to be treated, and rapidly dissolves when a voltage is applied. . Although the explanation for this reason is not described, it is presumed that when the cathode is energized, the environment becomes more corrosive than usual.

  In the electrolytic reaction, it is generally not assumed that the cathode side is in a corrosive environment, as is the case with metal electrowinning. However, since the dissolution of the cathode material is described or exemplified in all of Patent Documents 1 to 4 described above, the cathode used in the electrochemical decomposition reaction of oxidized nitrogen is placed in a severe corrosive environment. It is guessed.

Japanese Patent No. 3738186 Japanese Patent No. 3668234 Japanese Patent No. 3530511 JP 2007-61681 A

  Therefore, the present invention has been proposed in view of such a situation, and for example, the electrode is configured in a process of electrochemically reducing and removing oxidized nitrogen in water to be treated such as waste water. An object of the present invention is to provide an electrode for electrolysis capable of preventing an elution of a metal component into a solution and performing an effective and efficient electrolytic treatment.

  That is, the electrode for electrolysis according to the present invention is characterized in that the surface of a conductor is coated with an alloy in an amorphous state.

  Here, the electrode for electrolytic decomposition can be suitably used as a cathode in order to electrolyze oxidized nitrogen components in the water to be treated.

  According to the electrode for electrolysis according to the present invention, by coating the surface of the conductor with an alloy in an amorphous state, it is possible to prevent the metal component from eluting with electrolysis and to have high durability. Effective and efficient electrolysis can be performed.

It is a block diagram which shows an example of the electrolytic processing apparatus used for the removal process of oxidized nitrogen. It is a block diagram of the electrolytic vessel in an electrolytic treatment apparatus. It is a figure which shows the electrolytic treatment result of the oxidized nitrogen in Example 1. It is a figure which shows the electrolytic treatment result of the oxidized nitrogen in Example 2. It is a figure which shows the electrolytic treatment result with respect to the to-be-processed water containing oxidized nitrogen in high concentration. It is a figure which shows the electrolytic treatment result of oxidized nitrogen in the case of using a Pt electrode.

Hereinafter, specific embodiments of the electrode for electrolysis according to the present invention (hereinafter referred to as “this embodiment”) will be described in detail in the following order.
1. Electrolysis electrode 2. 2. Application example for electrolytic removal treatment of oxidized nitrogen components in water to be treated Example

<< 1. Electrode for electrolysis≫
The electrode for electrolysis according to the present embodiment is characterized in that the surface of the conductor is coated with an alloy in an amorphous state. More specifically, as an application example, this electrode can be suitably used as a cathode for reducing and removing oxidized nitrogen components in water to be treated containing chloride ions by electrolysis. An alloy having a reducing performance against oxidized nitrogen is coated in an amorphous state.

  Here, taking the electrolytic removal treatment of oxidized nitrogen as an example, the performance required for the electrode used for reducing the oxidized nitrogen is to effectively reduce the oxidized nitrogen to be treated. It has the reduction performance which can be carried out, it is excellent in durability (corrosion resistance), and also it is excellent in economical efficiency.

  Examples of the component having a reducing performance with respect to oxidized nitrogen include Group 8, Group 1B, Group 2B metals and alloys thereof in the periodic table.

  Conventionally, in the treatment for removing oxidized nitrogen in water to be treated by electrolysis as described above, a metal having a reducing performance with respect to the oxidized nitrogen and its alloy, or the metal and alloy thereof are used as a conductor. A coated electrode was used. However, when such a conventional electrode is energized with a voltage applied, the applied electricity becomes a catalyst and rapidly dissolves. Therefore, with the conventional electrodes, the electrolysis of the water to be treated causes the cathode to corrode after a predetermined time and the metal component elutes in the solution. Oxidized nitrogen could not be reduced. Further, the cathode cannot be used continuously due to dissolution of the cathode, which means that, for example, the amount of oxidized nitrogen is sufficiently low for water to be treated having a high content of oxidized nitrogen to be treated. It was impossible to process until the concentration was reached, and it was forced to replace with a new cathode for complete processing.

  On the other hand, for example, an electrode having an amorphous state coated with an alloy having a reducing ability with respect to oxidized nitrogen (hereinafter also referred to as “amorphous electrode”) is used as a cathode, thereby providing corrosion resistance and wear resistance. Can be improved extremely effectively. That is, even when a current is passed through the cathode, dissolution of the cathode can be prevented and the metal component can be prevented from being eluted into the solution. Moreover, even if it is a case where it uses in the environment where an electric current supplies with electricity and it corrodes excessively, the melt | dissolution can be prevented effectively. As a result, the electrode has both high reduction performance against oxidized nitrogen and excellent durability (corrosion resistance, wear resistance), and maintains its performance by preventing the reduction ability of oxidized nitrogen from decreasing. Even for water to be treated having a high nitrogen content, extremely efficient treatment can be performed without frequently replacing the cathode.

  As an alloy component to be coated on the surface of the conductor in an amorphous state, for example, when an electrode for electrolytic removal of oxidized nitrogen in the water to be treated is used, particularly if it has a reducing performance with respect to the oxidized nitrogen It is not limited. For example, an alloy containing a metal element of Group 8, Group 1B, Group 2B of the periodic table as a main component can be given as the first component. Specifically, an iron-based alloy containing iron (Fe) as a main component, a nickel-based alloy containing nickel (Ni) as a main component, and the like can be given.

  More specifically, examples of the iron-based alloy include an iron-chromium alloy, an iron-neodymium (Ne) alloy, an iron-silicon (Si) alloy, an iron-nickel alloy, and an iron-tellurium (Te) alloy. An alloy etc. are mentioned. Examples of the nickel-based alloy include a nickel-chromium alloy, a nickel-molybdenum (Mo) alloy, and a nickel-tungsten (W) alloy. Thus, as a 2nd component, the alloy containing metal elements, such as 4A group, 5A group, and 6A group other than the 8th group and 1B group of a periodic table, is mentioned. Among them, it is preferable to use an alloy based on iron or nickel in consideration of the amorphous manufacturing technique and the cost of the component concerned, in particular, using an iron-chromium alloy or a nickel-chromium alloy. More preferred.

  In addition, the “system alloy” in this specification means an alloy containing at least the presented metal element as a main component, and is only a binary alloy composed of only the metal element. It doesn't mean. That is, for example, in the case of an iron-chromium alloy, it may be an alloy having at least iron as the first component and chromium as the second component, and may be an alloy having one or more other metal elements in the balance. .

  Specifically, examples of the iron-chromium alloy include an iron-chromium alloy, an iron-chromium-phosphorus (P) -carbon (C) alloy, and an iron-chromium-nickel-tantalum (Ta) alloy. Examples of the iron-neodymium alloy include iron-neodymium alloys and iron-neodymium-boron (B) alloys. Examples of the iron-nickel alloy include an iron-nickel alloy, an iron-nickel-chromium alloy, an iron-nickel-boron-chromium alloy, and an iron-nickel-aluminum alloy. As described above, examples of the elements after the third component include alloys containing metal elements such as 3B group, 4B group, and 5B group in addition to 4A group, 5A group, and 6A group in the periodic table.

The electrode for electrolysis according to the present invention is characterized in that the above-described alloy is coated on a conductor in an amorphous state, and the composition of the alloy is not particularly limited. In addition, if an example of a composition of an alloy is given, as an iron-chromium-based alloy, for example, in a composition formula represented by Fe _80-ab Cr _a Mo _b P _c C _20-c (at%), 10 ≦ An alloy satisfying a ≦ 40 at%, 0 ≦ b ≦ 7 at%, and 5 ≦ c ≦ 15 at% can be used. Also, nickel - as a chromium-based alloy, for example, in _{Ni 80-d-e Cr d} P e B 20-e represented by the composition formula in (at%), 10 ≦ d ≦ 20at%, 0 ≦ e ≦ 20at% An alloy that satisfies the above can be used.

  Further, in the present embodiment, the electrolysis electrode is specifically described as an embodiment used as a cathode for electrolytic removal of oxidized nitrogen in the water to be treated, but is not limited thereto. That is, by appropriately setting the type of alloy to be coated on the surface of the conductor in an amorphous state according to the object to be treated, it can be widely used as an electrode for electrolysis.

  The method for amorphizing the alloy is not particularly limited as long as the alloy can be amorphized, and a known method can be used.

  The conductor for coating the amorphous alloy is not particularly limited, and examples thereof include titanium, carbon, and platinum.

≪2. Application example for electrolytic removal of oxidized nitrogen components in water to be treated >>
Next, the case where the electrode for electrolysis according to the present embodiment is applied as a cathode in the removal treatment by electrolytic decomposition of oxidized nitrogen in the water to be treated will be described in detail.

<2-1. About Electrolytic Processing Equipment>
FIG. 1 is a configuration diagram showing an outline of an example of an electrolytic treatment apparatus used for electrolytic removal treatment of oxidized nitrogen. As shown in FIG. 1, an electrolytic treatment apparatus 10 includes an electrolytic tank 11 that contains water to be treated containing oxidized nitrogen and performs electrolysis, an adjustment tank 12 that takes in and adjusts the water to be treated, and an electrolytic tank. 11 and the adjustment tank 12 are comprised from the circulation piping 13 which circulates to-be-processed water.

  The electrolytic cell 11 is composed of one or more sets of anode 11a and cathode 11b as a pair. FIG. 2 is a schematic view ((A) front view, (B) side view) of the electrolytic cell 11. As shown in FIG. 2, in the electrolytic cell 11, the to-be-processed water 20 containing oxidized nitrogen is accommodated, for example, the thin plate-shaped anode 11a and so on so that at least one part may be immersed in the to-be-processed water 20. A cathode 11b is disposed. In addition, a DC power supply device 14 is connected to each of the electrodes 11a and 11b, and water to be treated in the electrolytic cell 11 is supplied by passing a direct current applied from the DC power supply device 14 to the anode 11a and the cathode 11b. The oxidized nitrogen in 20 is electrolytically removed.

  Further, the electrolytic cell 11 is a diaphragm electrolytic cell in which the anode 11a and the cathode 11b are partitioned by using a diaphragm or the like, but the diaphragm 11 is not partitioned by the diaphragm. Any electrolytic cell can be effectively applied.

  Here, in the case of a diaphragm electrolytic cell, since the anode 11a and the cathode 11b are partitioned, hypochlorous acid generated at the anode 11a does not reach the cathode 11b. The acid does not inhibit the reduction reaction of oxidized nitrogen at the cathode 11b.

  On the other hand, in the case of a non-diaphragm electrolytic cell, hypochlorous acid produced at the anode 11a and ammonia produced at the cathode 11b react directly in the electrolytic cell 11 and are reacted separately in another reaction vessel. There is no need for processing, and efficient processing is possible. Further, since the anode 11a and the cathode 11b are not partitioned by a diaphragm, the problem that the hardness component contained in the water to be treated 20 is clogged in the diaphragm does not occur, and there is no load such as raw water management.

  The electrode for electrolysis according to the present embodiment can be suitably applied regardless of which electrolytic cell is used, there is no elution of metal components from the cathode 11b, and reduction in reduction efficiency is prevented. Thus, the oxidized nitrogen can be effectively removed. In addition, the block diagram shown as an example in FIG.1 and FIG.2 is a block diagram at the time of using a diaphragm membrane electrolytic cell as the electrolytic cell 11, and demonstrates below based on this.

  As the anode 11a, a commonly used insoluble electrode can be used. In the anode 11a, in order to generate hypochlorous acid from chloride ions, it is desirable to employ an electrode having high chlorine generation efficiency among insoluble electrodes. High chlorine generation efficiency means that the oxidation reaction from chloride ions to hypochlorite ions takes place over other reactions at the anode. This leads to preventing the oxidized nitrogen reduced at the cathode 11b from being oxidized again.

  On the other hand, as described above, the cathode 11b is a cathode used to remove oxidized nitrogen in the water to be treated by electrolysis, and has a reduction performance with respect to the oxidized nitrogen on the surface of the conductor. An amorphous electrode formed by coating an alloy in an amorphous state is used. In the present embodiment, by using the amorphous electrode as described above as a cathode, even if a direct current is supplied from the DC power supply device 14, the metal component constituting the cathode 11b does not elute into the solution. Electrolytic treatment can be performed while maintaining the reduction performance. Further, even when hypochlorous acid generated at the anode 11a is present in the vicinity of the cathode 11b and the corrosive environment is increased, the metal component constituting the cathode does not elute into the solution and electrolysis is performed with high durability. Processing can be performed.

  The adjustment tank 12 periodically takes in the treated water 20 to be subjected to the electrolytic treatment in the electrolytic tank 11 through the circulation pipe 13, adjusts the pH of the treated water 20, decomposes excess hypochlorous acid, and the like. I do. The treated water 20 adjusted in the adjustment tank 12 is circulated again to the electrolytic cell 11 through the circulation pipe 13.

  The adjustment tank 12 has a pH measuring device for measuring the pH of the water to be treated 20 taken from the electrolytic cell 11 and a hypochlorous acid concentration for measuring the concentration of hypochlorous acid generated at the anode 11 a of the electrolytic cell 11. A measuring unit 15 including a measuring device is provided. Further, in the adjustment tank 12, each of the pH adjuster supply unit 16 and the hypochlorous acid scavenger supply unit 17 is based on the pH and hypochlorous acid concentration of the water to be treated 20 measured by the measurement unit 15. A control unit 18 for controlling the supply of the medicine is provided.

  In the adjustment tank 12, when the treated water 20 from the electrolytic cell 11 is taken in through the circulation pipe 13, the measurement unit 15 measures the pH and hypochlorous acid concentration of the treated water 20, and controls the measurement results. Transmit to unit 18. Based on the received measurement results, the control unit 18 controls the pH adjuster supply unit 16 and the hypochlorous acid scavenger supply unit 17 so as to be within a predetermined pH range and a predetermined hypochlorous acid concentration. , Supplying pH adjusters and hypochlorous acid scavengers.

  As for the pH of the water 20 to be treated, chlorine gas is generated from hypochlorous acid generated at the anode 11a in the electrolytic cell 11 when the pH is low, and ammonia is volatilized when the pH is high. During the electrolytic treatment, the pH of the water to be treated 20 is approximately 4.0 to 10.0, preferably 5 because there is a problem that nitrate ions are easily generated when ammonia and hypochlorous acid react. It is preferable to maintain at 0.0-9.0. Therefore, in the adjustment tank 12, it is preferable to perform control to add a pH adjuster so as to maintain the pH of the water to be treated in the above range.

  The circulation pipe 13 mainly includes a pipe 13a for transferring the treated water 20 taken out from the electrolytic cell 11 to the adjustment tank 12, and a pipe 13b for returning the treated water 20 adjusted in the adjustment tank 12 to the electrolytic cell 11. It is made up of. In the circulation pipe 13, for example, the water to be treated 20 is circulated by a circulation pump 19.

  Further, the circulation pipe 13 may also be provided with a measurement unit that measures the pH of the treated water 20 and the concentration of hypochlorous acid. Similar to the measurement unit 15 provided in the adjustment tank 12, by providing a measurement unit in the circulation pipe 13, the pH of the water to be treated 20 and the hypochlorous acid concentration from the electrolytic tank 11 are circulated by the water to be treated 20. You may make it measure while passing in the piping 13, and may adjust pH and hypochlorous acid concentration in the adjustment tank 12 into which the to-be-processed water 20 was flowed in based on the measurement result. Such a measurement unit may be provided only in the circulation pipe 13 without being provided in the adjustment tank 12, and the above-described control may be performed.

<2-2. Electrolytic treatment reaction>
Next, the electrolytic treatment reaction of water to be treated that occurs in the electrolytic bath 11 in the above-described electrolytic treatment apparatus 10 will be specifically described.

  When energization of the electrodes 11a and 11b is started in the electrolytic cell 11, oxidation from chloride ions to hypochlorite ions is performed at the anode 11a as shown in the following reaction formula 1. On the other hand, at the cathode 11b, reduction from nitrate nitrogen to ammonia (ammonia nitrogen) is performed as shown in the following reaction formula 2. In addition, in the following reaction formula 1 and reaction formula 2, in order to compare the reaction equivalent per the same electric quantity, it represents with the reaction equivalent per 48 electron moles.

[Reaction Formula 1]
_{^{24Cl - + 24H 2 O → 24ClO}} - + 48H + + 48e
[Reaction Formula 2]
6NO ₃ ⁻ + 48e + 42H ₂ O → 6NH ₄ ⁺ + 60OH ⁻

  As shown in FIG. 1, when electrolysis is performed in a diaphragm membrane electrolytic cell that does not partition the anode 11a and the cathode 11b, a reduction reaction of hypochlorous acid produced at the anode 11a and oxidized nitrogen at the cathode 11b. The produced ammonia is uniformly mixed in the electrolytic cell 11 and reacted on the spot according to the following reaction formula 3 to be removed as nitrogen gas to complete the denitrification reaction. Even when a diaphragm electrolytic cell is used, nitrogen gas is generated by mixing the components produced in each compartment provided with the respective electrodes 11a and 11b in separate reaction vessels. Can do.

[Reaction Formula 3]
6NH ₄ ⁺ + 9ClO ⁻ → 3N ₂ + 9Cl ⁻ + 9H ₂ O + 6H ⁺

  The overall reaction formula from the electrode reaction to the denitrification reaction described above is as shown in the following reaction formula 4.

[Reaction Formula 4]
6NO ₃ ⁻ + 15Cl ⁻ + 3H ₂ O → 3N ₂ + 15ClO ⁻ + 6OH ⁻

  As shown in the above reaction formula 4, the hypochlorous acid generated at the anode 11a becomes excessive in the amount of the amount consumed for the denitrification reaction of the ammonia nitrogen generated at the cathode 11b, so that it becomes excessive in the electrolyte. . In the non-diaphragm electrolytic cell in which the space between the anode 11a and the cathode 11b is not partitioned, surplus hypochlorous acid is also present in the vicinity of the cathode 11b as it is.

  Here, in the removal treatment of oxidized nitrogen, an electrode made of a metal such as iron and an alloy thereof, or an electrode obtained by coating the metal and alloy with a conductor, which has a reduction performance with respect to oxidized nitrogen as in the prior art Is used, the metal component is eluted in the treatment liquid when the electrode is energized as described above. At this time, as shown in the above reaction formula 4, when the generated surplus hypochlorous acid is present in the vicinity of the cathode, the cathode becomes an environment where it is excessively corroded by hypochlorous acid, and deterioration due to energization occurs. Corrosion due to hypochlorous acid will proceed. As a result, the elution of the metal component into the water to be treated further proceeds, and the treatment efficiency is significantly reduced.

  Furthermore, the presence of hypochlorous acid in the vicinity of the cathode makes it easier for metal components such as iron eluted from the cathode to react with the hypochlorous acid and to form precipitates such as iron chloride. When precipitates are formed and accumulated in the electrolytic cell 11 in this way, the reaction efficiency at each electrode is remarkably lowered, and the work for removing the precipitates is required frequently, resulting in a reduction in processing efficiency. To do.

  On the other hand, in the present embodiment, since the cathode 11b formed by coating the surface of the conductor in an amorphous state with an alloy having a reducing performance against oxidized nitrogen is used, even if a current is applied. The elution of the metal component can be prevented, and even if excess hypochlorous acid generated in the electrolytic cell 11 is present near the cathode, corrosion by hypochlorous acid can be effectively prevented.

  In addition, by preventing deterioration due to energization and elution of metal components due to corrosion based on hypochlorous acid in this way, it is possible to suppress the formation of precipitates with hypochlorous acid present in the vicinity of the cathode, and high processing. The water to be treated containing oxidized nitrogen can be treated with efficiency.

  Moreover, in this removal process of oxidized nitrogen, the excess hypochlorous acid scavenger that captures and decomposes excess hypochlorous acid generated at the anode 11a by the electrolytic reaction becomes a predetermined concentration or more in the water to be treated. It is more preferable to perform the electrolytic treatment while maintaining the above.

  As described above, in the case of a diaphragm membrane electrolytic cell in which the anode 11a and the cathode 11b are not partitioned, hypochlorous acid is present in the vicinity of the cathode 11b that performs the reduction reaction. Since hypochlorous acid has a strong oxidizing action, if it exists in the vicinity of the cathode 11b, the reduction reaction for oxidized nitrogen at the cathode 11b may be inhibited.

  From this, in order to prevent the excessive hypochlorous acid from inhibiting the reduction reaction at the cathode 11b, the excess hypochlorous acid scavenger that consumes excess hypochlorous acid in the electrolytic reaction becomes a predetermined concentration or more. Thus, it is preferable to make it exist in the electrolytic cell 11. Thereby, before surplus hypochlorous acid reaches the vicinity of the cathode 11b, hypochlorous acid can be decomposed by the surplus hypochlorous acid scavenger, and the anode 11a and the cathode 11b are partitioned by a diaphragm. At least, high reduction efficiency with respect to oxidized nitrogen can be maintained.

  The surplus hypochlorous acid scavenger is not limited as long as it is a compound that reacts rapidly with hypochlorous acid. For example, ammonia, ammonium salt, sulfite and the like can be used. Among them, it is preferable to use ammonia or an ammonium salt in consideration of reactivity with hypochlorous acid, economy, and the like.

  Here, the surplus hypochlorous acid scavenger added to the treated water 20 varies in pH during electrolysis depending on the type. Accordingly, the pH control of the water to be treated 20 can be effectively performed by appropriately changing the type of the pH adjuster that adjusts the pH of the water to be treated 20 according to the type of surplus hypochlorous acid scavenger to be added. It is preferable to carry out.

  For example, when an ammonium salt is used as a hypochlorous acid scavenger, hypochlorous acid and ammonia react according to the following reaction formula 5, and the overall reaction is represented by the following reaction formula 6. As can be seen from the following reaction formula 6, when an ammonium salt is used as the surplus hypochlorous acid scavenger, the pH varies due to the electrolytic treatment, so an alkali, preferably caustic soda is used as the pH adjuster. It is preferable.

[Reaction Formula 5]
10NH ₄ ⁺ + 15ClO ⁻
→ 5N ₂ + 15Cl ⁻ + 15H ₂ O + 10H ⁺

[Reaction Formula 6]
6NO ₃ ⁻ + 10NH ₄ ⁺ → 8N ₂ + 18H ₂ O + 4H ⁺

  On the other hand, when sulfite is used as the surplus hypochlorous acid scavenger, hypochlorous acid and sulfurous acid react according to the following reaction formula 7, and the overall reaction becomes the following reaction formula 8. As can be seen from the following reaction formula 8, when sulfite is used as the surplus hypochlorous acid scavenger, the pH fluctuates due to the electrolytic treatment, so an acid, preferably hydrochloric acid or sulfuric acid is used as the pH adjuster. Use.

[Reaction Scheme 7]
15SO ₃ ²⁻ + 15ClO ⁻ → 15Cl ⁻ + 15SO ₄ ²⁻

[Reaction Formula 8]
6NO ₃ ⁻ + 15SO ₃ ²⁻ + 3H ₂ O
→ 3N ₂ + 15SO ₄ ²⁻ + 6OH ⁻

  A surplus hypochlorous acid scavenger may be added in advance to the water 20 to be treated before the start of the electrolytic treatment, or may be added to the measuring unit 15 provided in the adjustment tank 12 of the electrolytic treatment apparatus 10 during the electrolytic treatment. Then, the concentration of oxidized nitrogen or hypochlorous acid in the water to be treated 20 may be measured and added based on the result. As will be described later, the surplus hypochlorous acid scavenger concentration only needs to be maintained at a predetermined concentration or higher according to the amount of direct current applied to the electrodes 11a and 11b.

  The above reaction formula expresses the reaction equivalent relationship when the electrolytic reaction shown in the reaction formula 1 and the reaction formula 2 proceeds at a current efficiency of 100%. In the electrolytic treatment, there is an influence of coexisting substances in the water 20 to be treated, and the current efficiency is not necessarily 100% in the actual electrolytic treatment, and the above-described movement of pH and the necessary amount of surplus hypochlorous acid scavenger Is different from the amount described in the above reaction scheme. Therefore, in the electrolytic treatment, it is preferable to proceed with the treatment while constantly or intermittently monitoring important water quality items such as the pH of the treated water 20 and nitrate nitrogen.

  Specifically, the higher the surplus hypochlorous acid scavenger concentration, the higher the reaction rate with hypochlorous acid, and the higher the effect of promoting the reduction reaction of oxidized nitrogen. Therefore, it is preferable to continue the electrolysis while maintaining a surplus hypochlorous acid scavenger concentration that can maintain the required reaction rate. The required excess hypochlorous acid scavenger concentration also depends on the production rate of hypochlorous acid at the anode 11a. Therefore, it is necessary to increase the surplus hypochlorous acid scavenger concentration to be maintained as the production rate increases. In this regard, the rate of hypochlorous acid generation at the anode 11a is proportional to the amount of direct current applied to the electrodes 11a and 11b, so that the surplus hypochlorous acid scavenger concentration is maintained according to the amount of energization. It is preferable to perform electrolytic treatment.

  As described above, the electrode for electrolysis according to the present embodiment is characterized in that the surface of a conductor is coated with an alloy in an amorphous state. For example, when applied as a cathode for electrolytic removal treatment of oxidized nitrogen in the water to be treated, an alloy having a reducing performance for the oxidized nitrogen is coated in an amorphous state to perform electrolysis.

  According to such an electrode for electrolysis, it is possible to prevent the alloy component constituting the electrode from eluting into the solution even when an electric current is applied. For example, the alloy has a reduction performance of oxidized nitrogen, etc. While maintaining the performance, it is possible to perform an effective and efficient electrolytic removal of oxidized nitrogen with high durability.

  Moreover, not only in the melting catalysis due to the energization of current, but also in an environment where it is further corroded by components having a high oxidizing action such as hypochlorous acid generated with the removal treatment of oxidized nitrogen, for example. The constituent metal component can be prevented from eluting into the solution.

≪3. Examples >>
Hereinafter, specific examples of the present invention will be described. Note that the scope of the present invention is not limited to any of the following examples.

<Examination of electrolytic treatment ability of oxidized nitrogen and corrosion resistance of cathode>
[Example 1]
In Example 1, electrolytic treatment of oxidized nitrogen was performed using the electrolytic treatment apparatus 10 shown in FIG. 1 (the electrolytic cell 11 is the same as in FIG. 2).

In the electrolytic cell 11, a commercially available insoluble electrode for soda electrolysis is used as the anode 11a, and an iron-chromium alloy (Fe ₄₅ Cr ₃₅ P ₁₃ C ₇ (at%)) is amorphous on the surface of the titanium plate as the cathode 11b. The electrode coated with (amorphous electrode) was used. Then, water to be treated having a nitrate nitrogen concentration of 5000 mg / L is accommodated in the electrolytic cell 11, and a direct current is passed between the anode 11 a and the cathode 11 b from the DC power supply device 14 to the water to be treated containing oxidized nitrogen. On the other hand, the electrolytic treatment for 5 hours was performed. The test was carried out with the areas of the energized portions of the anode 11a and the cathode 11b being both 0.01 m ² and the amount of current to be energized being 12A.

  In addition, 600 ml of a solution in which 12,000 mg / L was added as an ammonia nitrogen concentration after addition of ammonium chloride as an excess hypochlorous acid scavenger was electrolyzed with respect to water to be treated having a nitrate nitrogen concentration of 5000 mg / L contained in the electrolytic cell 11 The electrolytic treatment was performed while decomposing surplus hypochlorous acid by putting it into the adjustment tank 12 in the treatment apparatus 10. In addition, during the electrolysis, the pH of the water to be treated fluctuates due to the electrolytic reaction, so that the pH of the water to be treated was adjusted by sequentially adding caustic soda as a pH adjusting agent to the adjustment tank 12 to cope with the fluctuation. .

[Example 2]
Example 2 was the same as Example 1 except that an electrode (amorphous electrode) coated with a nickel-chromium alloy (Ni ₆₅ Cr ₁₅ P ₁₆ B ₄ (at%)) in an amorphous state was used as the cathode. The test was conducted.

[Comparative Example 1]
In Comparative Example 1, the same test as in Example 1 was performed except that an Fe plate (carbon steel plate) was used as the cathode.

[Comparative Example 2]
In Comparative Example 2, the same test as in Example 1 was performed except that a Ni plate was used as the cathode.

[Comparative Example 3]
In Comparative Example 3, the same test as in Example 1 was performed except that a stainless steel (SUS304) plate was used as the cathode.

  Table 1 below shows the test results in Examples 1 to 2 and Comparative Examples 1 to 3 described above. Moreover, transition of nitrate nitrogen concentration with respect to the electrolysis time in the electrolytic treatment of Example 1 and Example 2 is shown in FIGS. 3 and 4, respectively. The analysis of the nitrate nitrogen concentration after the electrolytic treatment was performed using an ion chromatograph method. Further, the analysis of the metal components (Fe, Ni, Cr) eluted in the solution was performed using ICP spectroscopy or ICP mass spectrometry after dissolving the precipitate formed by elution.

  As shown in Table 1 and FIGS. 3 and 4, in Example 1 using an Fe—Cr alloy amorphous electrode and Example 2 using an Ni—Cr alloy amorphous electrode, the oxidized state was obtained by electrolysis. It was confirmed that nitrogen was effectively decomposed and the nitrate nitrogen concentration finally became less than 100 mg / L.

  Moreover, when the iron concentration of the solution after the test of Example 1 was analyzed, it was less than 0.5 mg / L, and the chromium concentration as another alloy component forming the cathode coating layer was also less than 0.5 mg / L. . Also in Example 2, the nickel concentration of the solution after the test was analyzed to be less than 0.5 mg / L, and chromium, which is another alloy component forming the cathode coating layer, was also less than 0.5 mg / L. there were. Thus, in Example 1 and Example 2, there was almost no elution of the metal component from a cathode, and it was shown that the corrosion resistance of an electrode is high.

  On the other hand, in Comparative Example 1 using Fe (carbon steel) and Comparative Example 2 using Ni plate, the final nitrate nitrogen concentration after 5 hours of electrolytic treatment remained at a rate of 500 to 1000 mg / L. Therefore, the oxidized nitrogen could not be sufficiently reduced and removed. Further, also in Comparative Example 3 using the stainless steel plate, the final nitrate nitrogen concentration remained at a rate of 1000 to 1500 mg / L, and the oxidized nitrogen could not be sufficiently reduced and removed. .

  Further, in Comparative Examples 1 to 3, when the metal components contained in the solution after the test were analyzed, in Comparative Example 1, Fe used as the cathode was included in 1800 to 2400 mg / L. It turns out that it has eluted. Similarly, in Comparative Example 2, Ni used as a cathode was also contained in the solution after the test in an amount of 1500 to 2000 mg / L, indicating that a large amount was eluted from the cathode. In these comparative examples 1 and 2, when the same test was performed next, it was necessary to use a new cathode.

  Similarly, in Comparative Example 3 using a stainless steel plate (SUS304), Fe derived from the stainless steel plate used as the cathode in the solution after the test was 1500 to 2000 mg / L, Ni was 150 to 200 mg / L, Cr 300-400 mg / L is also contained, and it can be seen that a large amount was eluted from the cathode. Also in this comparative example 3, when performing the same test next time, it was necessary to use a new cathode. As described above, even when an alloy such as a stainless steel plate is not in an amorphous state, the alloy component is eluted with electrolysis, and an effective and efficient removal of oxidized nitrogen is performed. I knew I couldn't do this.

<Oxidized nitrogen reducing ability and corrosion resistance for water to be treated containing oxidized nitrogen at high concentration>
[Example 3]
Next, as Example 3, water to be treated having a nitrate nitrogen concentration of 20000 mg / L was accommodated in the electrolytic cell 11, and the electrolytic treatment was performed for 20 hours. The other conditions were the same as in Example 1, and a cathode coated with an iron-chromium alloy in an amorphous state was used.

  FIG. 5 shows the result of the electrolytic treatment. As shown in FIG. 5, it was confirmed that the oxidized nitrogen was effectively decomposed with the lapse of the treatment time, and the nitrate nitrogen concentration finally became less than 100 mg / L. Moreover, when the iron concentration of the solution after the test was analyzed, it was less than 0.5 mg / L, and the chromium concentration as another alloy component forming the cathode coating layer was also less than 0.5 mg / L.

  Thus, even for water to be treated containing oxidized nitrogen at a high concentration, the oxidized nitrogen could be effectively reduced and removed without dissolving the cathode and eluting the metal component.

<About dissolution factors>
[Reference Example 1]
Next, as Reference Example 1, Fe (carbon steel plate) was used for the cathode, and the cathode was immersed in the same treated water for the same time as the energizing time of Comparative Example 1 without energizing.

  After the test, the iron concentration in the solution was analyzed and found to be 1 mg / L. Compared to Comparative Example 1, it was confirmed that the iron constituting the cathode was hardly eluted. From this, it was found that elution (cathode dissolution) of the cathode constituent metal in Comparative Examples 1 to 3 was caused by energization of the cathode.

  Based on this result, even in a corrosive environment caused by such energization, by using an amorphous electrode as a cathode as in Example 1 and Example 2, the metal component having high corrosion resistance and constituting the cathode It can be seen that the oxidized nitrogen can be treated while maintaining a high treatment capacity without eluting the.

<About the ability to reduce oxidized nitrogen and corrosion resistance using noble metal electrodes>
[Reference Example 2]
Next, as Reference Example 2, the same test as in Example 1 was performed using platinum (Pt) as the cathode.

  FIG. 6 shows the result of the electrolytic treatment. The solution after completion of the electrolysis showed almost no elution of platinum and high corrosion resistance. However, as shown in FIG. 6, the final nitrate nitrogen concentration after 5 hours of electrolysis remained about 2000 mg / L. Therefore, the oxidized nitrogen could not be sufficiently reduced and removed.

  DESCRIPTION OF SYMBOLS 10 Electrolytic processing apparatus, 11 Electrolysis tank, 11a Anode, 11b Cathode, 12 Adjustment tank, 13 Circulation piping, 14 DC power supply device, 15 Measurement part, 16 pH adjuster supply part, 17 Hypochlorous acid scavenger supply part, 18 Control , 19 Circulation pump, 20 Water to be treated

Claims (6)

  An electrode for electrolysis, wherein the surface of a conductor is coated with an alloy in an amorphous state.   The electrode for electrolysis according to claim 1, wherein the electrode for electrolysis is used as a cathode for electrolyzing an oxidized nitrogen component in water to be treated.   The electrode for electrolysis according to claim 2, wherein an iron-based alloy containing at least iron or a nickel-based alloy containing at least nickel is coated in an amorphous state.   Iron-chromium alloy, iron-neodymium alloy, iron-silicon alloy, iron-nickel alloy, iron-tellurium alloy, nickel-chromium alloy, nickel-molybdenum alloy, nickel-tungsten alloy The electrode for electrolysis according to claim 3, wherein the alloy is coated in an amorphous state.   The electrode for electrolysis according to claim 4, wherein an iron-chromium alloy or a nickel-chromium alloy is coated in an amorphous state.   The electrode for electrolysis according to any one of claims 2 to 5, wherein the electrode is used for electrolysis performed in a diaphragmless electrolytic cell.

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