JP4446760B2 - Method and apparatus for removing cyanide by electrolysis - Google Patents

Description

  In the present invention, an anode and a cathode, which are electrodes for electrolysis, are inserted into a liquid to be treated accommodated in an electrolytic bath, and an electric current is passed between the anode and the cathode, thereby electrolyzing a cyanide compound contained in the liquid to be treated. The present invention relates to a method for removing a cyanide compound by an electrolysis method that removes by treatment, and further, an apparatus that is directly used for carrying out the method, specifically, an electrolytic tank that contains a liquid to be treated, and an electrode for electrolysis with respect to the liquid to be treated It is related with the cyanide compound removal apparatus by the electrolytic method provided with the anode and cathode which are these.

Conventionally, as a method for removing a cyanide from a liquid to be treated such as waste water contaminated with a cyanide, oxidative decomposition mainly by an alkali chlorine method or an electrolytic oxidation method has been used.
However, in particular, when removing a cyanide compound from a liquid to be treated containing iron or the like and a stable cyanide complex compound, it is very difficult to decompose the cyanide complex compound by the electrolytic oxidation method as described above. Unusable.

Therefore, when removing a cyanide from a liquid to be treated containing iron or the like and a stable cyanide complex, a method of separating and removing by aggregation precipitation using a bitumen method, a zinc white method or the like has been generally used. . These methods are methods of adding a metal ion that reacts with a metal cyanide complex such as iron or zinc to produce a precipitate, and adjusting the pH conditions to precipitate a cyanide compound and separate it from the liquid to be treated as sludge. It is.
However, when the coagulation sedimentation method is used, there are problems that a large amount of chemicals are added and a chemical cost is high, a large amount of sludge is generated to add chemicals, and noise is generated because stirring is required.
Furthermore, since a large-scale facility is required, there is a problem that it is difficult to apply to a liquid to be processed generated in a narrow place or a liquid to be processed that is generated in a small amount in a short time.

In order to solve such problems caused by the coagulation sedimentation method, a method of removing cyanide by electrolyzing the liquid to be treated to float the deposit and removing the floating substance has been proposed (for example, patents). Reference 1).
According to the electrolytic flotation separation method described in this patent document, cyanide compounds, particularly cyanide compounds forming a complex with a metal such as iron, are generally stable with iron ions, zinc ions, copper ions, etc. In order to remove cyanide compounds in the liquid to be treated, the metal ions are added as described above to precipitate and separate as a salt, which elutes iron. It has been proposed to use the electrode as the anode.

JP-A-48-104346

The present inventors provide a cyanide removal technology with low chemical costs, low sludge generation, and low noise, and can be applied to liquids to be processed that are generated in narrow spaces and liquids that are generated in small amounts in a short period of time. In order to provide a possible cyanide removal technique, an investigation was made on a method for separating and removing cyanide compounds from the liquid to be treated by electrolytic flotation separation.
And, as described in the above patent document, when the treatment of the liquid to be treated containing the cyanide compound was attempted using the electrode eluting iron as an anode, the cyanide compound in the liquid to be treated could be removed, Since the generated precipitate does not float and settles at the lower part of the liquid to be treated, it has become clear that it is difficult to separate the precipitate.
Furthermore, an attempt was made to remove the cyanide compound in the liquid to be treated by using an electrode that elutes aluminum as the anode. As a result, precipitates floated up and the cyanide compound could be considerably removed. The problem became difficult to remove.

  The present invention has been completed through various experiments and studies including the above-described attempts. The purpose of the present invention is to remove cyanide compounds in the liquid to be treated to a very low concentration and to easily separate the precipitates. The present invention provides a method and apparatus for removing a cyanide compound by an electrolysis method.

According to the first characteristic configuration of the present invention, an anode and a cathode, which are electrodes for electrolysis, are inserted into a solution to be treated accommodated in an electrolytic cell, and an electric current is passed between the anode and the cathode, whereby a cyanide removal method by electrolytic method of removing cyanide-containing and electrolytic treatment, as the electrode, two electrodes with aluminum electrodes primarily eluted aluminum ions and iron electrode which mainly elute iron ions And can be switched between a first electrolysis state in which the iron electrode is an anode and the aluminum electrode is a cathode, and a second electrolysis state in which the iron electrode is a cathode and the aluminum electrode is an anode. A plurality of electrode pairs comprising at least one iron electrode and one aluminum electrode are provided, and each electrode pair can be switched between the first electrolysis state and the second electrolysis state. , When at least one electrode pair is in the first electrolysis conditions, there is to the other electrode pair to electrolytic treatment by switching to become the second electrolysis conditions.

According to the first characterizing feature of the present invention, as the electrodes for electrolysis, using two kinds of electrodes with aluminum electrodes primarily eluted aluminum ions and iron electrode which mainly elute iron ions, iron Since the electrolytic treatment is performed by switching between the first electrolysis state in which the electrode is an anode and the aluminum electrode is the cathode, and the second electrolysis state in which the iron electrode is the cathode and the aluminum electrode is the anode, the cyanide contained in the liquid to be treated Reacts with iron ions eluted from the iron electrode and precipitates as iron cyan complex, and the precipitated iron cyan complex adheres to the flocs and bubbles generated by the aluminum ions eluted from the aluminum electrode, Since the surface of the liquid to be treated floats reliably, the cyanide compound in the liquid to be treated can be removed until the concentration becomes very low.
In other words, simply using an aluminum electrode that elutes aluminum ions makes it difficult to remove cyanide to a low concentration because the salt produced by cyanide and aluminum ions is unstable. I expected it to be. Then, in order to obtain a stable precipitate, an iron ion that reacts with a cyanide compound to precipitate a stable iron-cyanide complex is added. As is apparent from the experimental results described later, the removal rate of the cyanide compound is improved. It was confirmed.
The deposited iron cyanide complex adheres to the flocs generated by aluminum ions and bubbles generated in the electrode and reliably floats on the water surface of the liquid to be treated, so that the cyanide compound is removed until the concentration becomes very low. And wastewater containing harmful cyanide can be efficiently treated.
Furthermore, since the iron electrode and the aluminum electrode can be switched between the anode and the cathode, impurities attached to the surface when used as the cathode are positively removed by switching to the anode. By switching appropriately, the surfaces of the iron electrode and the aluminum electrode can be maintained in the initial state as much as possible, and the desired electrolytic treatment can be performed for a long time.
In addition, a plurality of electrode pairs composed of at least one iron electrode and one aluminum electrode are provided, and each electrode pair is configured to be switchable between a first electrolysis state and a second electrolysis state. By appropriately switching to the second electrolysis state, while maintaining the surface of the iron electrode and the aluminum electrode as much as possible, the cyanide compound in the liquid to be treated can be removed to a very low concentration, When at least one electrode pair is in the first electrolysis state, the other electrode pair is switched so as to be in the second electrolysis state. Therefore, as described above, the surfaces of the iron electrode and the aluminum electrode are maintained in the initial state as much as possible. In addition to removing the cyanide compound from the liquid to be treated, the cyanide compound can be removed continuously.

A second characteristic configuration of the present invention is that in the above-described cyan compound removal method, an electrolytic treatment is performed by adding a cationic surfactant to the liquid to be treated.

According to the second characteristic configuration of the present invention, since a cationic surfactant is added to the liquid to be treated and electrolytically treated, a cyanide compound which is an anion can be bound to the cationic hydrophilic group, As described above, the bonded substance adheres to the flocs and bubbles generated by the aluminum ions, and also reliably floats to the water surface of the liquid to be treated along with the surfactant. It can be removed to a low concentration, and wastewater containing harmful cyanide can be treated efficiently.

A third characteristic configuration of the present invention resides in that in the above-described cyanide removal method, the electrolytic treatment is performed by controlling the pH of the liquid to be treated to 7 or less.

According to the third characteristic configuration of the present invention, since the electrolytic treatment is performed by controlling the pH of the liquid to be treated to 7 or less, the precipitation of the cyanide compound is promoted to efficiently remove the cyan compound from the liquid to be treated. In particular, when the pH of the liquid to be treated is controlled to 5.5 or lower, the cyanide compound can be removed more efficiently.

According to a fourth aspect of the present invention, there is provided a cyanide compound removing apparatus by an electrolysis method comprising an electrolytic tank for storing a liquid to be processed, and an anode and a cathode that are electrodes for electrolysis with respect to the liquid to be processed. The electrode comprises at least two types of electrodes, ie, an iron electrode that mainly elutes iron ions and an aluminum electrode that mainly elutes aluminum ions, and the first electrolysis using the iron electrode as an anode and the aluminum electrode as a cathode. Electrode switching means for switching between a state and a second electrolysis state in which the iron electrode is a cathode and the aluminum electrode is an anode, and a plurality of electrode pairs each including at least one iron electrode and one aluminum electrode are provided. Each electrode pair is configured to be switchable between the first electrolysis state and the second electrolysis state by the electrode switching means. Means, when at least one electrode pair is in the first electrolysis conditions, there is to be switched to the other electrode pair is the second electrolysis conditions.

According to the fourth characteristic configuration of the present invention, the electrode for electrolysis includes at least two types of electrodes, ie, an iron electrode that mainly elutes iron ions and an aluminum electrode that mainly elutes aluminum ions. Electrode switching means is provided for switching between a first electrolysis state using a metal electrode as an anode and an aluminum electrode as a cathode, and a second electrolysis state using an iron electrode as a cathode and an aluminum electrode as an anode. By performing the method described in the first characteristic configuration, the cyan compound in the liquid to be treated can be removed until the concentration becomes very low. In addition, the iron electrode and the aluminum electrode However, since it is switched between the anode and the cathode, impurities attached to the surface when used as the cathode are positively removed by switching to the anode. By changing, it is possible to maintain the surface of the iron electrode and aluminum electrode as much as possible the initial state can be carried out over a long period of time electrolytic treatment of as desired.

According to the fourth characterizing feature of the present invention, an electrode for electrolysis, an electrode pair consisting of at least one iron electrode and one aluminum electrode comprise a plurality of pairs, each of these electrode pairs, the electrode switching Since it is configured to be switchable between the first electrolysis state and the second electrolysis state by means, the surface of the iron electrode and the aluminum electrode can be switched to the initial state as much as possible by appropriately switching between the first electrolysis state and the second electrolysis state. The cyanide compound in the liquid to be treated can be removed until the concentration becomes very low.

Then, according to the fourth characterizing feature of the present invention, the electrode switching means, when the at least one electrode pair is in the first electrolysis conditions, other electrode pairs so switched so that the second electrolysis conditions, above As described above, the cyan compound in the liquid to be treated can be removed while maintaining the surfaces of the iron electrode and the aluminum electrode as much as possible in the initial state, and the cyan compound can be removed continuously. it can.

Embodiments of a method and apparatus for removing a cyanide compound by an electrolytic method according to the present invention will be described with reference to the drawings.
The cyanide compound removing method and apparatus to which the present invention is applied is a method for removing a cyanide compound from a liquid to be treated containing the cyanide by electrolytic treatment. When the batch type electrolytic treatment apparatus as shown in FIG. 1 is processed continuously, the continuous form electrolytic treatment apparatus as shown in FIG. 2 is used.

The batch type electrolytic treatment apparatus of FIG. 1 includes an electrolytic cell 2 for containing a treatment liquid 1 containing a cyanide, and an anode 3 and a cathode that are electrodes for electrolysis of the treatment liquid 1 in the electrolytic cell 2. 4 and a power source 5 for energizing between the anode 3 and the cathode 4, and further, a surfactant addition means 6 for adding a cationic surfactant to the liquid 1 to be treated. Is configured to remove.
The continuous electrolytic treatment apparatus shown in FIG. 2 is similar to the batch electrolytic treatment apparatus in that an electrolytic tank 2 that contains the liquid 1 to be treated, an anode 3 and a cathode 4 that are electrodes for electrolysis, a power source 5, and a cationic surfactant. Is provided with a surface active agent adding means 6 for adding the surface active agent, and is configured to remove the levitated material 7 that has been levitated.
However, in the continuous electrolytic treatment apparatus, the treatment liquid supply means 8 for continuously supplying the treatment liquid 1 is connected to the lower part of the electrolytic cell 2 and the surfactant addition means 6 is connected to the treatment tank 1 to be treated. A cationic surfactant is added and supplied to the liquid 1 to be processed flowing through the liquid supply means 8.

Further, in the continuous electrolytic treatment apparatus, the levitated substance discharge path 9 and the processing liquid discharge path 10 are connected in communication with each other above the electrolytic cell 2, and levitated substance removing means 11 is also provided. Is collected and discharged from the floated material discharge path 9, and the processing liquid after removing the floated object 7 is discharged from the process liquid discharge path 10, and if necessary, the floated material 7 is guided upward. A plurality of guide plates 12 are also provided.
As the levitated substance removing means 11, for example, a rake or the like that scrapes the levitated substance 7 can be applied. However, the levitated substance removing means 11 is naturally provided by overflow from the levitated substance discharge passage 9 without providing any special removing means. It can also be configured to be removed.

In the basic form described above , the anode 3 for electrolysis is composed of two types of electrodes F and A.
That is, in the batch type electrolytic treatment apparatus of FIG. 1 and also in the continuous type electrolytic treatment apparatus of FIG. 2, two anodes 3 and a cathode 4 are provided , and one of the two anodes 3 is It is mainly composed of an iron electrode F that elutes iron ions, and the other one is composed of an aluminum electrode A that mainly elutes aluminum ions.
The cathode 4 is not particularly limited, and may be composed of, for example, iron or aluminum, stainless steel, carbon, or the like, but in this basic form, both of the two cathodes 4 mainly elute aluminum ions. The electrode A is made of aluminum.

Next, the operation of the cyan compound removing apparatus according to this basic mode will be described, and a cyan compound removing method will be referred to.
When the anode 3 and the cathode 4 for electrolysis are inserted into the liquid 1 to be treated and the anode 3 and the cathode 4 are energized, for example, iron ions (Fe ²⁺ ) are ^generated from the anode 3 made of the iron electrode F. The iron ions are eluted and react with the cyanide compound in the liquid 1 to be treated, and as shown in the following chemical formula 1, an iron cyanide complex and an iron salt are generated and precipitated.

(Chemical formula 1)
[Fe (CN) ₆ ] ^4- + 2Fe ²⁺ → Fe ₂ [Fe (CN) ₆ ]

This iron cyanide complex and iron salt Fe ₂ [Fe (CN) ₆ ] floats by adhering to flocs and bubbles generated by aluminum ions (Al ³⁺ ) eluted from the anode 3 made of the aluminum electrode A. Then, it floats to the surface of the liquid 1 to be treated as the float 7. Therefore, by removing the levitated material 7, the cyanide compound contained in the liquid 1 can be reliably removed.

Such electrolytic treatment is performed by adding a cationic surfactant from the surfactant addition means 6 to the liquid 1 to be treated, so that the levitated substance 7 more reliably moves to the water surface of the liquid 1 to be treated. As a result, the cyanide can be efficiently removed.
In addition, as a cationic surfactant added to the liquid 1 to be treated, among the cationic surfactants, cetyltrimethylammonium bromide (CTAB) is particularly preferable, and the amount of the cationic surfactant added is determined by prior experiments. The optimum concentration should be determined. For example, it may be added so as to have a concentration of 10 to 100 mg / L.

Furthermore, in order to reduce the electrical resistance, it is preferable to perform an electrolytic treatment on the liquid 1 to be treated in the electrolytic cell 2, and to adjust the pH of the liquid 1 to be treated. Then, an acidic substance is added to the liquid 1 to be treated to adjust the pH to 7 or less, more preferably to pH 5.5 or less, and to perform electrolytic treatment.
The electrolyte or acidic substance may be added before or after the liquid 1 to be treated is supplied to the electrolytic cell 2, automatically supplied by a supply means such as a pump, or the pH is adjusted by an automatic pH adjusting device. Various addition times and addition methods can be selected as appropriate, such as supplying while automatically adjusting.
Moreover, the residence time of the liquid 1 to be treated in the electrolytic cell 2 should be determined to be an optimum residence time by a prior experiment, and is preferably 2 to 60 minutes, for example.

As the liquid 1 to be treated, various solutions containing cyanide compounds are applicable, for example, groundwater containing cyanide compounds, industrial wastewater, landfill leachate, and the like. As a suitable example, there is groundwater that is continuously discharged or pumped up, and the groundwater is continuously treated as the liquid 1 to be treated using a continuous electrolytic treatment apparatus.
Furthermore, the method and apparatus according to the present invention are suitable for use under conditions where the amount of the liquid 1 to be treated is small and not suitable for installation of a large-scale water treatment facility, for example, during a short construction period. It is very effective when it is used for the treatment of construction wastewater to be used or when it is used in a place where groundwater is pumped up by a small amount every day.

Examples of the cyanide compound contained in the liquid 1 to be treated include an iron cyanide complex, a cobalt cyanide complex, a gold cyanide complex, a nickel cyanide complex, and a silver cyanide complex. The gold-cyanide complex is effective because the oxidative decomposition method is very difficult to apply.
The treatment liquid after the electrolytic treatment can be discharged as it is, but the pH may increase due to the electrolytic treatment, and normally there is a restriction on the pH of the discharged liquid, so the pH of the treatment liquid is restricted. It is desirable to discharge after adjusting the pH to satisfy.
In addition, the levitated material 7 is likely to contain the above-mentioned cyanide, so after taking volume reduction measures such as dehydration, it is discarded as industrial waste or incinerated to harm the cyanide. It is desirable to break down into various forms.

In addition, since various experiments were conducted in order to confirm the effects of the present invention, some of them will be referred to below as experimental examples and comparative examples.
In this experimental example and comparative example, as the liquid to be treated, potassium ferrocyanide was added to tap water to be 12.74 mg-CN / L, and sodium chloride was added to be 500 mg / L as an electrolyte. Using. The initial pH at that time was 7.97.
In the experiment, an experimental apparatus having a volume of about 4L as shown in FIG. 2 was used, a total of 8 electrodes (4 anodes and 4 cathodes) were used, and the distance between the electrodes was set to 5 mm. Were arranged alternately. And the to-be-processed liquid was supplied to the experimental apparatus at a speed | rate of 200 mL / min, and it supplied with a voltage of 4V between the anode and the cathode, and measured the total cyan density | concentration in the discharged | emitted process liquid after that.
The total cyan concentration in the treatment liquid was distilled according to JIS-K0102 “Factory Wastewater Test Method” 38.1.2 Total Cyan (hydrogen cyanide generated at pH 2 or less), and a fully automatic cyan measuring device (T-manufactured by Anatech Yanako) CN501) was used and quantified according to the 38.4 ion electrode method.

(Experimental example)
Of the eight electrodes, an iron electrode was used for the second anode from the leftmost and rightmost, and the remaining six (two anodes, four cathodes) were aluminum electrodes.
When the treatment liquid was treated with 10 L and the total cyan density of the treatment liquid was measured, the average total cyan density was 1.07 mg-CN / L, that is, the removal rate of all cyan was 91.0%. All precipitates surfaced on the water surface.

(Comparative example)
The experiment was conducted using all eight electrodes as aluminum electrodes.
Similar to the above experimental example, the treatment liquid was treated for 10 L, and the total cyan density of the treatment liquid was measured. The average total cyan density was 2.75 mg-CN / L, that is, the removal rate of all cyan was It was 78.5%, and almost all precipitates floated on the water surface.

  From this experimental example and the comparative example, the total cyan removal rate can be greatly improved by making two anodes out of eight electrodes (four anodes, four cathodes) an iron electrode, and It was confirmed that the precipitates could be lifted reliably and recovered.

In addition, with respect to the addition of surfactants, the anionic and nonionic surfactants were slightly added and the cyanide removal rate was slightly reduced as compared with the case where no surfactant was added. It is clear that the addition of a surfactant increases the cyanide removal rate. In particular, in the case of cetyltrimethylammonium bromide (CTAB), it is clear that the cyan removal rate increases remarkably as the addition amount increases. It became.
Furthermore, with regard to the pH of the liquid to be treated, it has been clarified that the lower the pH, the higher the cyan removal rate.

As described above, in the basic mode, an example in which two anodes 3 and two cathodes 4 are provided is shown, and in the experimental example and the comparative example, an example in which four anodes 3 and four cathodes 4 are actually arranged is shown. The number or the number of the anodes 3 and the cathodes 4 can be appropriately changed according to the size of the device, and the anodes 3 and the cathodes 4 do not necessarily have to be the same number.
For example, as shown in FIG. 3, two anodes 3 and one cathode 4 are provided, one of the anodes 3 is an iron electrode F, the other is an aluminum electrode A, and the cathode 4 is an aluminum electrode A. You can also

(Embodiment of the present invention)
In the embodiment of the present invention , as shown in FIG. 4, two types of electrodes, an iron electrode F that mainly elutes iron ions and an aluminum electrode A that mainly elutes aluminum ions, are provided as electrodes for electrolysis. The electrodes F and A are alternately arranged to provide a total of four electrodes.
In other words, in FIG. 4, the two left electrodes, that is, the iron electrode F and the aluminum electrode A make one pair, and the two right electrodes, that is, the iron electrode F and the aluminum electrode A are separated from each other. It is arranged to make a pair.

Then, manual electrode switching means 13 is interposed between the total of four electrodes and the power source 5. For example, in the left electrode pair, as shown in FIG. As the anode 3 and the aluminum electrode A as the cathode 4, and as shown in FIG. 4B, the second electrolysis state as the iron electrode F as the cathode 4 and the aluminum electrode A as the anode 3. It is configured to be switchable between.
Furthermore, as shown in FIG. 4A, when the left electrode pair is in the first electrolysis state, the right electrode pair is in the second electrolysis state, and as shown in FIG. When the electrode pair is in the second electrolysis state, it is configured to be switchable so that the right electrode pair is in the first electrolysis state.

According to this embodiment of the present invention , the iron electrode F and the aluminum electrode A are switched between the anode 3 and the cathode 4, so that impurities attached to the surface when used as the cathode 4 are transferred to the anode 3. Therefore, the surface of the iron electrode F and the aluminum electrode A can be maintained in the initial state as much as possible, and the desired electrolytic treatment can be performed for a long time.
In the embodiment of the present invention, a manual type is shown as the electrode switching means 13, but, for example, in combination with a timer or the like, the first electrolysis state and the second electrolysis state are automatically set every predetermined time. It can also be configured to switch.

Conceptual diagram illustrating a basic form of batch-type electrolytic treatment apparatus Conceptual diagram illustrating a basic form of continuous expression electrolytic treatment apparatus Conceptual diagram of the main part of the electrolytic treatment apparatus showing a modification of the basic form The conceptual diagram of the principal part of the electrolytic treatment apparatus by embodiment of this invention .

DESCRIPTION OF SYMBOLS 1 Liquid to be processed 2 Electrolysis tank 3 Anode 4 Cathode 13 Electrode switching means A Aluminum electrode F Iron electrode

Claims (4)

The cyanide contained in the liquid to be treated is removed by electrolytic treatment by inserting an anode and a cathode, which are electrodes for electrolysis, into the liquid to be treated contained in the electrolytic bath and energizing between the anode and the cathode. A method of removing cyanide by an electrolytic method,
As the electrode , two types of electrodes, an iron electrode that mainly elutes iron ions and an aluminum electrode that mainly elutes aluminum ions, are used , and the first electrolysis state in which the iron electrode is an anode and the aluminum electrode is a cathode And a second electrolysis state in which the iron electrode is a cathode and the aluminum electrode is an anode, and a plurality of electrode pairs each including at least one iron electrode and one aluminum electrode are provided, and Each electrode pair is configured to be switchable between the first electrolysis state and the second electrolysis state, and when at least one electrode pair is in the first electrolysis state, the other electrode pair is in the second electrolysis state. Cyanide removal method by electrolysis method of switching to galvanic treatment. The method for removing a cyanide compound by electrolysis according to claim 1, wherein a cationic surfactant is added to the liquid to be treated for electrolysis. The method for removing a cyanide compound by an electrolytic method according to claim 1 or 2 , wherein the electrolytic treatment is performed by controlling the pH of the liquid to be treated to 7 or less. An apparatus for removing a cyanide compound by an electrolysis method including an electrolytic cell for storing a liquid to be processed, and an anode and a cathode that are electrodes for electrolysis of the liquid to be processed,
The electrode includes at least two types of electrodes, an iron electrode that mainly elutes iron ions and an aluminum electrode that mainly elutes aluminum ions, wherein the iron electrode is an anode and the aluminum electrode is a cathode. Electrode switching means for switching between an electrolytic state and a second electrolytic state in which the iron electrode is a cathode and the aluminum electrode is an anode is provided , and a plurality of electrode pairs each including at least one iron electrode and one aluminum electrode are provided . Each of the electrode pairs is configured to be switchable between the first electrolysis state and the second electrolysis state by the electrode switching means, and the electrode switching means includes at least one electrode pair in the first electrolysis state. A cyanide compound removing device using an electrolysis method that switches the other electrode pair to the second electrolysis state .

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