JPH06240475A - Treatment of iron chloride based etchant containing nickel - Google Patents

Abstract

(57) [Summary] [Purpose] Recovery and generation of metallic nickel and metallic iron from an etching solution containing excess nickel chloride and ferrous chloride generated in the etching process with simple operation and at low operating cost. Recycle the liquid by safely and effectively utilizing chlorine gas. [Structure] An iron chloride-based etching solution containing nickel is treated by a diaphragm electrolysis method to deposit and recover nickel and iron at the cathode, and chlorine gas generated in the anode chamber is led to an etching solution containing ferrous chloride. , Oxidize the liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an iron chloride-based etching solution containing nickel, in particular, electrolytically treating the etching solution with a diaphragm, and effectively regenerating the chlorine gas generated therein. It relates to a method used for processing.

[0002]

2. Description of the Related Art For example, a shadow mask, which is a component of a color picture tube, has a thin plate of 0.1 to 0.3 mm in thickness made of a material containing iron and nickel as main components, and is subjected to an etching treatment to produce a large number of electrons. It is formed by forming a beam opening.

In the etching step, when a material containing iron and nickel as the main components is perforated with ferric chloride, the nickel contained in the components is

[0004]

[Chemical 1]

By the reaction, and for iron,

[0006]

[Chemical 2]

By the above reaction, FeCl ₂ and NiCl ₂ having no etching ability are produced. As described above, it is desirable that the etching waste liquid containing divalent iron ions and nickel ions obtained by reducing the trivalent iron ions is regenerated from the viewpoint of preventing environmental pollution and economical requirements, and reused in the etching operation.

Several methods have conventionally been proposed for removing nickel from a nickel-containing waste liquid.

[0009] For example, in Japanese Patent Laid-Open No. 4-11989, for example, iron powder and a small amount of ferric chloride are mixed into an iron chloride waste liquid containing a heavy metal such as nickel to adjust the redox potential and pH. It is proposed that nickel be deposited and removed by carrying out the following reaction to cause the following reaction.

[0010]

[Chemical 3]

[0011]

[Chemical 4]

[0012] In this case, if a passive film is formed on the surface of the charged iron, the progress of the reaction is hindered, but by mixing a small amount of ferric chloride, the formation of the film is prevented and the iron powder is formed. By activating the surface, the reaction of iron powder proceeds and
The deposited nickel is adhered to the iron powder to generate a precipitate.

FeCl formed in the etching process
FeCl ₂ formed by the above reaction formula due to the mixture of ₂ and iron powder
Has no etching ability, and the etching efficiency decreases as the etching solution containing FeCl ₂ increases, but the etching ability of the etching solution is recovered from the above environmental pollution prevention and economical requirements. Is required. For that purpose, it is necessary to take measures to regenerate the FeCl ₂ into ferric chloride having etching ability.

Therefore, in Japanese Patent Laid-Open No. 4-11989, by blowing chlorine gas, FeCl ₂
Is said to be oxidized to FeCl ₃ to regenerate the waste liquid.

Further, in JP-A-59-190367, an oxime reagent is added to a composition containing NiCl ₂ or FeCl ₂ to modify the composition containing nickel into a precipitating complex salt. It has been proposed to dissolve chlorine gas in the separated composition containing divalent iron ions to regenerate FeCl ₃ .

[0016]

However, in the method of depositing and removing nickel by introducing the iron powder disclosed in Japanese Patent Laid-Open No. 4-11989, FeCl ₂ is mixed by mixing the iron powder in addition to the etching step. Since it is formed and is oxidized, a considerably large amount of excess FeCl ₃ is generated, and its treatment becomes a problem.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 59-190367, in which nickel is precipitated and removed by adding an oxime reagent, the nickel complex salt generated by the addition of the oxime reagent is discharged as a waste. That process becomes a problem. In addition, Fe generated in the etching process
By oxidizing Cl ₂ , excessive FeCl ₃ is generated due to the etching material, and its treatment also poses a problem.

In view of the above-mentioned problems in the conventional method, the present invention uses an etching solution containing surplus nickel chloride and ferrous chloride generated in the etching step, which enables simple operation and low operating cost. The challenge is to recover nickel and metallic iron, and safely and effectively utilize the chlorine gas generated to regenerate the liquid.

[0019]

According to the present invention, the above-mentioned problems are generated in an anode chamber while treating an iron chloride-based etching solution containing nickel by a diaphragm electrolysis method to deposit and recover nickel and iron at a cathode. This is solved by introducing the chlorine gas to the etching solution containing ferrous chloride and oxidizing the solution.

The basic concept of the present invention is to treat the etching solution by both the diaphragm electrolysis method and the chlorine gas method. In particular, all chlorine gas generated in the anode chamber of the diaphragm electrolysis cell is chlorine gas. Since it is used for the law, there is no waste.

The chlorine gas method is described in, for example, Japanese Patent Laid-Open No.
As pointed out in Japanese Patent Laid-Open No. 254188, conventionally, it was considered to be a reproduction method only theoretically, but the present inventor confirmed its effectiveness, and in particular, the closed-type regeneration method developed for this method. By using an electrolyzer to positively generate chlorine gas by high current density electrolysis and using an absorption tower together, "environmental hygiene problem" mentioned in the publication
Has been successfully avoided.

The detailed steps of the present invention will be described below.

A step of introducing an iron chloride-based etching solution containing nickel into the anode chamber of the diaphragm electrolyzer to oxidize the divalent iron ions contained therein to trivalent iron ions and generate chlorine gas, and through the diaphragm. To recover nickel and iron from the metal ions that have moved to the cathode chamber and to oxidize the ferrous chloride-containing etching liquid with the chlorine gas generated in the anode chamber. Is preferred.

Further, a step of introducing an iron chloride-based etching solution containing nickel into the cathode chamber of the diaphragm electrolytic cell to deposit and recover nickel and iron from the metal ions contained therein, and chlorine transferred to the anode chamber through the diaphragm. It is also preferable to regenerate the etching solution from the step of oxidizing the ions to generate chlorine gas and the step of oxidizing the solution in which the metal ion concentration is reduced by reduction electrodeposition with the chlorine gas. At that time, by providing a plurality of diaphragm electrolyzers, the solution in which the metal ion concentration was reduced by reduction electrodeposition was introduced to the next cathode chamber, and nickel and iron were electrodeposited and recovered, and chlorine gas was discharged in the anode chamber. You may make it add the repeating process to generate.

Further, a step of introducing an iron chloride-based etching solution containing nickel into the first cathode chamber of the two-stage diaphragm electrolysis cell to reduce trivalent iron ions to divalent iron ions, and a step after the reduction treatment. A step of cooling the liquid to separate ferrous chloride as crystals, a step of introducing the liquid from which ferrous chloride has been separated into a second cathode chamber to deposit and recover nickel and iron, and a metal by reduction electrodeposition A step of re-dissolving the ferrous chloride crystal in a liquid having a reduced ion concentration; a step of oxidizing chlorine ions transferred to each anode chamber through a diaphragm to generate chlorine gas;
It is also possible to regenerate the etching solution from the step of oxidizing the solution in which the ferrous chloride crystals are redissolved with the chlorine gas.
More preferable. This is because the concentration of iron becomes low at the stage of electrodepositing and recovering the metal, so that the ratio of nickel to iron in the recovered metal can be increased.

The electrolytic diaphragm used in the present invention includes:
Limiting the migration of the trivalent to divalent reduced iron chloride complex present in the cathode to the anode side, and even if the liquid level fluctuates slightly, mixing of the catholyte and anolyte does not occur. It is airtight, has the lowest possible electrical resistance, does not increase the electrical resistance between the electrodes as much as possible, has excellent chemical resistance, especially chlorination resistance, and the membrane itself is a bipolar electrode. It is required to have properties such as not forming, electrically neutral, that is, having no polarity, for example, modacrylic, vinyl acetate,
Examples thereof include polyester, PTFE, Saran and the like.

The anode in the electrolytic cell is required to have a function of lowering the overvoltage when chlorine gas is generated.
Platinum and dimentional y stable anod
e, abbreviated as DSA) (Ru-Sn) O ₂
/ Ti, (Pt-Ir) O ₂ / Ti is preferably used. It is preferable to use iron, iron-nickel alloy, nickel, titanium, carbon or the like for the cathode. With these electrode specifications, it is possible to obtain a metal crystal that is easy to peel from the electrode plate without elution of impurities in the liquid.

The electrolytic solution is preferably maintained at 50 to 90 ° C. in order to reduce the electric resistance of the solution and maintain a practical current density.

[0029]

For example, when the nickel concentration is as low as about 2.5 to 15 g / l, the etching solution containing divalent iron ions and nickel ions is first introduced into the anode chamber of the diaphragm electrolyzer. The divalent iron ions are oxidized and regenerated into trivalent iron ions, and a part of the divalent iron ions moves to the cathode chamber together with the divalent iron ions and nickel ions and undergoes reduction electrodeposition as an alloy.

In the anode chamber, chlorine ions lose electrons and chlorine gas is generated. The chlorine gas is introduced into the absorption tower. The liquid in which chlorine concentration is reduced by the generation of chlorine gas and a part of divalent iron ions is electrolytically oxidized into trivalent iron ions is returned from the anode chamber to the etching tank. The generated chlorine gas oxidizes another ferric chloride-containing etching solution and returns it to the etching tank as a regenerating etchant.

When the nickel concentration is relatively high, an etching solution containing divalent iron ions and nickel ions is first introduced into the cathode chamber of the diaphragm electrolyzer, contrary to the above. The metal ions contained in the etching solution are subjected to reduction electrodeposition to recover an alloy containing nickel or iron.

On the other hand, in the anode chamber, chlorine ions are oxidized to generate chlorine gas. The chlorine gas is collected in the absorption tower. The liquid whose chlorine concentration has been reduced by generation of chlorine gas and whose metal ion concentration has been reduced by reduction electrodeposition is extracted from the cathode chamber, oxidized and regenerated by chlorine gas, and returned to the etching tank.

Taking advantage of the fact that the solubility of ferrous chloride is smaller than that of ferric chloride, the catholyte is cooled to obtain ferric chloride.
By once crystallizing iron, nickel can be efficiently recovered by changing the electrolysis conditions.

In the present invention, chlorine gas, which has been considered to suppress the generation as much as possible in the usual electrolysis method, is positively utilized for regeneration of the etching solution in a completely sealed system.

[0035]

EXAMPLES The present invention will be described in more detail below with reference to examples. The optimum method is selected according to the composition of the etching solution. The electrolysis method is a batch method in which the entire amount of liquid is extracted for each electrolysis, and an electrolytic cell in which the electrolytic solution whose concentration is adjusted circulates,
It suffices to select one of continuous methods in which a fixed amount of the stock solution is supplied so as to keep the concentration of the electrolytic solution in an integrated manner, and a fixed amount of the solution is withdrawn and recovered.

Example 1 In the apparatus conceptually shown in FIG. 1, the etching stock solution used in the etching process was used as an etching waste solution from the etching tank 1 at a flow rate of 7 ml / min and had a modacrylic membrane. It is guided to; anode chamber 3 of the diaphragm electrolytic cell 2 of the electrolytic voltage 4V ((Ru-Sn) O 2 / Ti electrode). A part of the stock solution for etching drawn out from the etching tank 1 is introduced into the absorption tower 5. In the anode chamber 3, divalent iron ions are oxidized into trivalent iron ions, and a part of the trivalent iron ions together with the divalent iron ions and nickel ions are intercalated into the cathode chamber 4 (electrode; Ti).

At the anode, chlorine ions are deprived of electrons,
Generates chlorine gas. This chlorine gas is guided to the absorption tower 5. Due to this introduced chlorine gas, ferrous chloride is converted to ferric chloride in a part of the stock solution for etching, which is extracted from the etching tank 1 and guided to the absorption tower 5. The liquid containing ferric chloride oxidized and regenerated in this manner is returned to the etching tank 1 as a regenerating etchant. In addition, the anolyte whose chlorine concentration is reduced by the generation of chlorine gas is also returned to the etching tank 1 as a regenerating etchant.

Of the metal ions that have moved to the cathode chamber 4 through the diaphragm, the trivalent iron ions receive electrons and once
It becomes a valent iron ion. In the cathode chamber 4, the catholyte flows in and out and circulates. With electrolysis, the pH of the catholyte increases,
Since sludge is generated, it is preferable to circulate the catholyte while filtering the sludge. In this cathode chamber 4, metal ions are reduced and electrodeposited. When the composition of the metal recovered by precipitation was investigated, iron 88.6%, nickel 3.0%, copper 5.9%,
The results were 1.2% chromium and 0.3% cobalt. The amount of recovered metal was 2.0 g / h. The electrolysis power per 1 g of deposited metal was 4.2 Wh / g.

Table 1 shows the composition of the waste liquid, the composition of the circulating catholyte, and the composition of the regenerated etchant immediately before entering the diaphragm electrolyzer, which is adjusted to the range of 78 to 82 ° C.

[0040]

[Table 1]

Example 2 In the apparatus conceptually shown in FIG. 2, the undiluted etching solution used in the etching process has a modacrylic membrane as a waste etching solution from the etching tank 1 at a flow rate of 5 ml / min. It is introduced to the cathode chamber 4 (electrode; Ti) of the diaphragm electrolyzer 2 having an electrolysis voltage of 4.5V. In the cathode chamber 4,
Trivalent iron ions are reduced to divalent iron ions, and further metal ions are subjected to reduction electrodeposition. Chlorine ions that have moved to the anode chamber 3 (electrode; (Ru-Sn) O ₂ / Ti) via the diaphragm are oxidized at the anode to generate chlorine gas. The generated chlorine gas is guided to the absorption tower 5. The anolyte in the diaphragm electrolyzer 2 circulates in and out of the anode chamber 3.

The catholyte whose metal ion concentration has been reduced by reduction electrodeposition is introduced into the absorption tower 5, and the chlorine gas introduced into the absorption tower 5 turns ferrous chloride into ferric chloride. The liquid containing ferric chloride that has been oxidized and regenerated is returned to the etching tank 1 as a regenerating etchant.

When the composition of the metal deposited and recovered in the cathode chamber 4 was examined, the results were iron 35.0%, nickel 56.5%, copper 3.8% and chromium 0.9%. The amount of recovered metal was 8.5 g / h. The electrolysis power per 1 g of deposited metal was 15.0 Wh / g.

The composition of the waste liquid just before entering the diaphragm electrolyzer adjusted to 68 to 72 ° C., the composition of the catholyte before entering the absorption tower, the composition of the circulating anolyte, and the composition of the regenerated etchant leaving the absorption tower. The composition is as shown in Table 2, respectively.

[0045]

[Table 2]

Example 3 In the apparatus conceptually shown in FIG. 3, the stock solution for etching used in the etching step has a modacrylic membrane as a waste etching solution from the etching tank 1 at a flow rate of 5 ml / min. It is introduced into the cathode chamber 4 (electrode; Ti) of the first diaphragm electrolyzer 2 with an electrolysis voltage of 4V. In the cathode chamber 4, trivalent iron ions are reduced to divalent iron ions, and some metal ions are electro-deposited by reduction. Anode chamber 3 (electrode;
Chloride ions transferred to (Ru-Sn) O ₂ / Ti) are
It is oxidized at the anode to generate chlorine gas. The generated chlorine gas is guided to the absorption tower 5. The anolyte in the first diaphragm electrolyzer 2 circulates in and out of the anode chamber 3.

The catholyte of the first diaphragm electrolyzer 2 whose metal ion concentration has been reduced by reduction electrodeposition and whose chloride ion concentration has been reduced by transfer to the anode chamber 3 has the same modacrylic membrane and has an electrolysis voltage of 4.5V. The cathode chamber 7 of the second diaphragm electrolyzer 6 (electrode; T
i). In the cathode chamber 7, metal ions are reduced and electrodeposited. When the composition of the metal deposited and recovered from the first diaphragm electrolyzer 2 and the second diaphragm electrolyzer 6 was investigated, iron 7.0%,
Nickel 13.2%, Copper 78.0%, Chromium 0.25
%, Tin 1.9%. The amount of recovered metal is 9.
It was 1 g / h. The electrolysis power per 1 g of deposited metal is
It was 15 Wh / g.

Anode chamber 8 (electrode; (Ru-S
n) Chlorine ions transferred to O ₂ / Ti) are oxidized at the anode as in the first diaphragm electrolyzer to generate chlorine gas. The generated chlorine gas is guided to the absorption tower 5. The anolyte in the second diaphragm electrolyzer 6 also circulates in and out of the anode chamber 8.
The catholyte of the second diaphragm electrolyzer 6 whose metal ion concentration has been reduced and whose chlorine ion concentration has also been reduced by moving to the anode chamber 8 is introduced into the absorption tower 5 and contacts the introduced chlorine gas. As a result, ferrous chloride is converted to ferric chloride. The liquid containing ferric chloride that has been oxidized and regenerated is returned to the etching tank 1 as a regenerating etchant.

Composition of the waste liquid immediately before entering the first diaphragm electrolyzer,
Table 3 shows the compositions of the catholyte and the anolyte and the composition of the regenerating etchant in the first diaphragm electrolytic cell and the second diaphragm electrolytic cell, respectively, adjusted to 68 to 72 ° C.

[0050]

[Table 3]

Example 4 In the apparatus conceptually shown in FIG. 3, an etching stock solution having a composition different from that of Example 3 used in the etching process was discharged from the etching tank 1 as an etching waste solution and was used as in Example 3. Then, it is introduced into the cathode chamber 4 of the first diaphragm electrolyzer 2.

Electrolysis was carried out under the same conditions as in the example except for the composition, and the composition of the metal deposited and recovered from the first diaphragm electrolytic cell 2 and the second diaphragm electrolytic cell 6 was investigated. Iron 71.
0%, nickel 6.5%, copper 17.2%, chromium 0.2
%, Cobalt 0.04%, zinc 0.03%. The amount of recovered metal was 7.0 g / h. The electrolysis power per 1 g of deposited metal was 7.2 Wh / g.

Composition of waste liquid immediately before entering the first diaphragm electrolyzer,
Table 4 shows the compositions of the catholyte and anolyte and the composition of the regeneration etchant in the first and second diaphragm electrolyzers and the second diaphragm electrolyzers, respectively, adjusted to the range of 78 to 82 ° C.

[0054]

[Table 4]

Example 5 In the apparatus conceptually shown in FIG. 4, the etching stock solution used in the etching step has a modacrylic membrane as a waste etching solution from the etching tank 1 at a flow rate of 5 ml / min. It is introduced into the cathode chamber 4 (electrode; Ti) of the first diaphragm electrolyzer 2 with an electrolysis voltage of 4V. In the cathode chamber 4, trivalent iron ions are reduced to divalent iron ions. The catholyte containing the reduced divalent iron ions is introduced into one of the two cooling tanks 10 whose opening and closing is adjusted by the switching valve 9 and is cooled. Ferrous chloride has a smaller solubility than ferric chloride and can be separated as crystals.

In the cooling tank 10, the overflow liquid from which the precipitated crystals are separated is the cathode chamber 7 of the second diaphragm electrolytic tank 6 which also has a modacrylic diaphragm and has an electrolytic voltage of 4.5V.
(Electrode; Ti).

On the other hand, the anode chamber 3 (electrode; (R
_{u-Sn) O 2 / Ti} ) chlorine ions moved to generates chlorine gas is oxidized at the anode. The generated chlorine gas is guided to the first absorption tower 5. The anolyte in the first diaphragm electrolyzer 2 circulates in and out of the anode chamber 3.

In the cathode chamber 7 which has received the overflow liquid in which the concentration of the iron component has been reduced, metal ions are reduced and electrodeposited. When the composition of the metal deposited and recovered from the second diaphragm electrolyzer 6 was investigated, iron 15.5%, nickel 81.0
%, Copper 0.05% were obtained. The amount of recovered metal is 4.
It was 8 g / h. The electrolysis power per 1 g of deposited metal is
It was 13.5 Wh / g.

Anode chamber 8 (electrode; (Ru-S
n) Chlorine ions transferred to O ₂ / Ti) are oxidized at the anode as in the first diaphragm electrolyzer to generate chlorine gas. The generated chlorine gas is guided to the second absorption tower 11. The anolyte in the second diaphragm electrolyzer 6 also circulates in and out of the anode chamber 8. The catholyte in the second diaphragm electrolyzer 6 whose metal ion concentration has decreased and chlorine ion concentration has also decreased due to movement to the anode chamber 8 is the second
It is guided to the absorption tower 11 and comes into contact with the introduced chlorine gas,
It oxidizes divalent iron ions to trivalent iron ions.

The liquid containing the oxidized ferric chloride is introduced into any one of the cooling tanks 10 in which the introduction of the liquid from the first cathode chamber 4 is stopped by closing the switching valve 9, and the ferric chloride is introduced therein. 1 Melt iron crystals. Cooling tank 1 according to the amount of crystals deposited
0 is switched to perform cooling on the one hand and melting of crystals on the other hand. The recovered liquid in which the ferrous chloride crystals are dissolved is introduced into the first absorption tower 5 and brought into contact with the introduced chlorine gas to oxidize and regenerate almost all divalent iron ions into trivalent iron ions. It is returned to the etching tank 1.

Composition of the waste liquid immediately before entering the first diaphragm electrolyzer,
The composition of the circulating anolyte in the first and second diaphragm electrolyzers, the composition of the overflow liquor, the composition of the catholyte in the second diaphragm electrolyzer, and the first chloride Table 5 shows the composition of the recovered liquid that melted the iron crystals and exited the cooling tank, and the composition of the regenerated etchant.

[0062]

[Table 5]

Example 6 In the apparatus conceptually shown in FIG. 4, the etching solution was treated in the same manner as in Example 5.

When the composition of the metal deposited and recovered from the second diaphragm electrolyzer 6 was examined, iron 46.5%, nickel 48.
Results of 4% and copper 0.06% were obtained. The amount of recovered metal is 1
It was 2.6 g / h. The electrolysis power per 1 g of deposited metal was 10.5 Wh / g.

Composition of the waste liquid immediately before entering the first diaphragm electrolyzer,
The composition of the circulating anolyte in the first diaphragm electrolyzer and the second diaphragm electrolyzer, the composition of the overflow liquid, the composition of the catholyte in the second diaphragm electrolyzer, the ferrous chloride crystals were dissolved, and the cooling bath was discharged. The composition of the recovered liquid and the composition of the regeneration etchant are as shown in Table 6, respectively.

[0066]

[Table 6]

[0067]

As is apparent from the above description,
The present invention has the following effects.

In the present invention, since the etching solution is treated by both the diaphragm electrolysis method and the chlorine gas method, the solution can be regenerated without waste.

In the method according to the present invention, not only iron and nickel but also metals such as copper, tin, chromium and zinc can be separated as electrodeposition or sludge, so that the concentration of these impurities contained in the etching solution can be kept constant. It also has the advantage that it can be used in cycles without increasing above the value.

[Brief description of drawings]

FIG. 1 is a conceptual flow diagram according to an embodiment of the present invention.

FIG. 2 is a conceptual flow diagram according to another embodiment of the present invention.

FIG. 3 is a conceptual flow chart according to still another embodiment of the present invention.

FIG. 4 is a conceptual flow diagram according to another embodiment of the present invention including a cooling bath.

[Explanation of symbols]

 1 etching tank 2 diaphragm electrolysis tank 3 absorption tower

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Tanimura 8-10-16 Shimorenjaku, Mitaka City, Tokyo Nittetsu Mining Co., Ltd.

Claims (5)

[Claims] 1. An iron chloride-based etching solution containing nickel is treated by a diaphragm electrolysis method to deposit and recover nickel and iron at a cathode, and chlorine gas generated in an anode chamber is converted into chlorine chloride.
A method for treating an etching solution, which comprises introducing the etching solution containing iron and oxidizing the solution. 2. A step of introducing an iron chloride-based etching solution containing nickel into an anode chamber of a diaphragm electrolyzer to oxidize divalent iron ions contained therein to trivalent iron ions and generate chlorine gas, and a diaphragm. Method for treating an etching solution, which comprises a step of electrodepositing and recovering nickel and iron from metal ions transferred to the cathode chamber through a cathode, and a step of oxidizing the etching solution containing ferrous chloride with chlorine gas generated in the anode chamber . 3. A step of introducing an iron chloride-based etching solution containing nickel into a cathode chamber of a diaphragm electrolytic cell to deposit and recover nickel and iron from metal ions contained therein, and chlorine transferred to the anode chamber through the diaphragm. A method for treating an etching solution, comprising a step of oxidizing ions to generate chlorine gas, and a step of oxidizing a solution of which metal ion concentration is reduced by reduction electrodeposition with the chlorine gas. 4. A step of introducing an iron chloride-based etching solution containing nickel into the first cathode chamber of a multi-stage membrane electrolytic cell to deposit and recover nickel and iron, and chlorine transferred to the anode chamber through the membrane. A step of oxidizing chlorine ions to generate chlorine gas, and introducing a liquid whose metal ion concentration has been reduced by reduction electrodeposition to the next cathode chamber to deposit and recover nickel and iron, and also generate chlorine gas in the anode chamber. A method of treating an etching solution, which comprises at least one repeating step of performing the above step and a step of oxidizing the solution extracted from the cathode chamber at the final stage with the chlorine gas. 5. A step of introducing an iron chloride-based etching solution containing nickel into a first cathode chamber of a two-stage diaphragm electrolysis cell to reduce trivalent iron ions to divalent iron ions, and after the reduction treatment. A step of cooling the liquid to separate ferrous chloride as crystals, a step of introducing the liquid from which ferrous chloride has been separated into a second cathode chamber to deposit and recover nickel and iron, and a metal by reduction electrodeposition A step of re-dissolving the ferrous chloride crystals in a liquid having a reduced ion concentration, a step of oxidizing chlorine ions transferred to each anode chamber through a diaphragm to generate chlorine gas, and the chlorine gas. A method of treating an etching solution, which comprises a step of oxidizing a solution in which ferrous chloride crystals are redissolved.