JP2001049480A - Electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic cell having a function for lowering the silver concentration in an electrolyte by electrolytically reducibly depositing Ag as metal silver in the electrolytic cell for electrolytically oxidatively depositing Ag. SOLUTION: Second main electrodes 6 and auxiliary electrodes 7 are placed in a nitric acid solution containing Ag. Ag is efficiently formed by both as positive electrodes in an electrolytic oxidation stage and silver is deposited as metal by the other as a negative electrode while Ag is formed by either thereof as a positive electrode in an electrolytic reduction stage. Since the presence of nitrous acid to hinder the deposition of silver is suppressed, the silver concentration in the solution may be drastically lowered. The end point of the electrolytic reduction stage is determined by detecting the high potential at which the Ag concentration lowers and finally Ag deposits directly as metal silver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a divalent valent silver species (AgN) formed electrolytically in a nitric acid solution containing silver nitrate (hereinafter abbreviated as "Ag (I)").
The complex having the chemical formula of O ₃ ⁺ is referred to as “Ag (I
I) ") as a medium to carry out an oxidation reaction (hereinafter abbreviated as" electrolytic oxidation step "), and thereafter, silver in the nitric acid solution is electrolytically precipitated and recovered (hereinafter referred to as" electrolytic reduction step "). In particular, the present invention relates to a suitable electrolytic cell, which can easily generate Ag (II) in the electrolytic oxidation step, reduce the amount of by-products, and reduce the concentration of silver remaining in the nitric acid solution in the electrolytic reduction step. It relates to an electrolytic cell.

[0002]

2. Description of the Related Art Ag produced by dissolving AgO in nitric acid
The oxidation reaction using (II) as a medium has been known for a long time, but Fleischmann et al.
The electrooxidative formation of I) and the oxidation reaction using Ag (II) as a medium have been reported (Fleischman).
n, et al, "The Kinetics o
fsilver (I) / silver (II) cou
ple at a platinum electro
de in perchloric and nitr
ic acid solution, "J. of A
Applied Electrochemistry,
Vol. 1 (1971) p. 1-7). A method of oxidizing and dissolving poorly soluble PuO ₂ or the like in a nitric acid solution containing silver using Ag (II) as a medium in a nitric acid solution containing silver in an electrolytic cell having an anode and a cathode respectively. JP-A-58-176133, JP-A-60-6100
No. 9 and JP-A-60-61010. Further, Japanese Patent Application Laid-Open No. Hei 8-233994 discloses a method in which silver contained in a solution is precipitated and recovered on an electrode surface or an electrolytic vessel obtained by changing the polarity of an electrode in an electrolytic cell.

[0003]

Since the conventional electrolytic cell is constructed as described above, the electrolytic reduction deposition of metallic silver takes precedence while the silver concentration is high, but the silver deposition potential and the reduction of nitric acid are reduced. Since the potentials are close to each other, when the silver concentration decreases, the generation of nitrous acid starts as a side reaction. When this nitrous acid accumulates, not only does the precipitation of metallic silver stop, but as the nitrous acid concentration increases, the metallic silver once deposited begins to dissolve, and further dissolution of this silver produces nitrous acid. Even if electrolytic reduction is continued, there is a problem that all silver is finally redissolved.

[0004] It is an object of the present invention to electrolytically oxidize Ag (I
It is an object of the present invention to provide an electrolytic cell having a function of reducing silver concentration in an electrolytic solution by electrolytically precipitating it as metallic silver in an electrolytic cell for producing I).

Another object of the present invention is to provide an electrolytic cell having a high current efficiency for producing Ag (II) by electrolytic oxidation in the electrolytic cell.

It is another object of the present invention to easily provide an electrolytic cell in a geometric shape with a limited diameter that allows for critical shape control in the handling of fissile material.

[0007]

According to the present invention, there is provided an electrolytic cell comprising a pair of main electrodes serving as a negative electrode and a positive electrode opposed to each other with a diaphragm in the same electrolytic solution as the main electrode serving as a positive electrode. A single sub-electrode whose polarity can be switched is installed, and Ag (II) is generated on the main electrode serving as the positive electrode, and silver is electrolytically reduced on the surface of the sub-electrode by setting the polarity of the sub-electrode to the negative electrode. Is deposited.

In the electrolytic cell according to the present invention, since one sub-electrode is made of the same electrochemical catalytic substance as the main electrode serving as a positive electrode, the surface of the sub-electrode is used when the polarity of the sub-electrode is positive. In the same manner as the main electrode serving as the positive electrode
(II).

An electrolytic cell according to the present invention comprises a pair of main electrodes which are opposed to each other with a diaphragm therebetween and whose polarity can be mutually converted, and which is in the same electrolytic solution as one of the main electrodes and has the same electrochemical catalyst as the main electrode. It is composed of a substance and consists of one sub-electrode that is always a positive electrode, which converts polarity and deposits silver as a metal on the surface of a main electrode that has become a negative electrode, and at the same time, has a sub-electrode that is a positive electrode Ag (II) is generated on the surface of

An electrolytic cell according to the present invention has the features of the first or second aspect, and the diaphragm is a cylindrical container, which is located at the center of the cylindrical electrolytic container and serves as a negative electrode. The main electrode is provided inside the diaphragm, the main electrode serving as the positive electrode is provided outside the diaphragm, and one sub-electrode whose polarity can be switched is between the main electrode serving as the positive electrode and the inner surface of the electrolytic cell container, The electrolytic cell is configured in a cylindrical geometric shape with a limited diameter.

[0011] The electrolytic cell according to the present invention has the features of the first or second aspect of the present invention, and the diaphragm is a cylindrical container, which is located at the center of the cylindrical electrolytic cell container and serves as a negative electrode. The main electrode is provided inside the diaphragm, the main electrode serving as the positive electrode is provided outside the diaphragm, and one sub-electrode whose polarity can be switched is constituted by the inner surface of the electrolytic cell container, so that the cylindrical shape is limited in diameter. In this case, the electrolytic cell can be easily configured in the above geometrical shape.

An electrolytic cell according to the present invention has the features of the third aspect of the present invention, and further comprises a cylindrical container having a cylindrical membrane, and a main electrode located at the center of the cylindrical electrolytic cell container and outside the diaphragm. One sub-electrode, which is in the same electrolytic solution and is always a positive electrode, is between the main electrode and the inner surface of the electrolytic cell container.

The electrolytic cell according to the present invention has the features of the third aspect of the present invention, and further comprises a cylindrical container having a diaphragm, which is located at the center of the cylindrical electrolytic container and which is located outside the diaphragm. One sub-electrode, which is always in the same electrolyte as the positive electrode and is always the positive electrode, is formed on the inner surface of the electrolytic cell container, making it easy to configure the electrolytic cell in a cylindrical geometry with a limited diameter It is to let.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 The electrolytic cell according to Embodiment 1 of the present invention will be described below with reference to FIG. The electrolytic cell according to the first embodiment includes an electrolytic cell container 1 made of glass and 1L of a first electrolytic solution 3 and a second electrolytic solution 4 separated by a diaphragm 2 which is a porous sintered ceramic cylindrical container. 1L
Having. Although not shown, the electrolytic solutions 3 and 4 are circulated from the external electrolytic solution circulating tank to the electrolytic cell container 1 via a pump. The first electrolyte 3 has a circulation volume of 5 L and a concentration of 6
M nitric acid solution. The second electrolytic solution 4 is a nitric acid solution having a circulation volume of 5 L and a concentration of 6 M containing silver nitrate having a concentration of 0.1 M in the electrolytic oxidation step. A nitric acid solution containing 3M concentration.

First main electrode 5 installed in first electrolytic solution 3
Is manufactured in a cylindrical shape with a titanium expanded mesh and has an effective surface area of 450 cm ² . The second main electrode 6 installed in the second electrolytic solution 4 is made of a titanium expanded mesh in a cylindrical shape, and has an effective surface area of 750 cm ² . The sub-electrode 7 is made of a titanium expanded mesh in a cylindrical shape, has an effective surface area of 950 cm ² , and is plated with platinum according to the purpose. The sub-electrode 7 is connected to the first main electrode 5 or the second main electrode 6. The electrical resistance between the main electrodes 5 and 6 via the diaphragm 2 is 0.07Ω, and the second main electrode 6 and the sub-electrode 7
Is 0.03Ω.

Specific Example 1-1 In this specific example, the second main electrode 6 is plated with platinum, but the sub-electrode 7 is not plated with platinum. The first main electrode 5 does not necessarily need to be plated with platinum. In the electrolytic oxidation step, the first main electrode 5 is used as a negative electrode, the second main electrode 6 is used as a positive electrode, the sub-electrode 7 is connected to the second main electrode 6, and a DC current of 13.4 A flows between the positive and negative electrodes as a positive electrode. And the voltage between the electrode terminals is 1.9V. As a result, nitrogen oxide was generated from the first electrolytic solution 3, and black-brown Ag (II) was generated on the surface of the second main electrode 6 serving as a positive electrode. At this time, no electrolytic reaction occurred on the surface of the sub-electrode 7. Also,
The current efficiency in the electrolytic oxidation until reaching the Ag (II) saturation concentration was 70%.

In the electrolytic reduction step, the polarity of the main electrode is maintained, and the sub-electrode 7 is connected to the first main electrode 5 to make the polarity negative. When the voltage between the electrode terminals becomes 2.6 V, the second electrolyte 4 Ag (II) remained therein, and brown silver remained on the sub-electrode 7 to precipitate metallic silver crystals. At this time, the amount of black-brown Ag (II) generated on the surface of the second main electrode 6 decreases with time, and the total silver concentration of the second electrolytic solution 4 becomes 10%.
And when the coloring became weak, the electrode terminal voltage rapidly increased to 3.2 V. Along with this, black amorphous metal silver was deposited on the sub-electrode 7, and the total silver concentration of the second electrolytic solution 4 was reduced to 1% or less.

When the electrolysis is further continued, nitrous acid starts to be generated in the second electrolytic solution 3, and as the concentration of nitrous acid increases, silver re-dissolution proceeds, so that the silver concentration in the second electrolytic solution 4 decreases. At this point, the circulation of the second electrolytic solution was stopped, and the electrolysis was stopped. Then, the metallic silver deposited on the electrode begins to fall off and dissolve, and completely falls off and dissolves in about 15 minutes. Since the liquid amount of the second electrolytic solution 4 is 10% of the total circulation amount, the silver concentration of the second electrolytic solution 4 finally reaches 0.5 M and the nitric acid concentration decreases to about 2.5 M. The second electrolytic solution 4 having the increased silver concentration is mixed with nitric acid of an appropriate concentration to prepare a second electrolytic solution 4 for the next electrolytic oxidation step batch. In this specific example, the amount of electricity required to deposit silver contained in the second electrolytic solution 4 as a metal on the sub-electrode 7 was 1.7 times the theoretical amount of electricity.

According to this embodiment, the following effects can be obtained. By placing a sub-electrode that becomes a positive electrode in the electrolytic oxidation step and a negative electrode in the electrolytic reduction step,
The silver concentration in the electrolytic solution can be reduced in the electrolytic reduction step without inhibiting the electrolytic oxidation step. The optimal end point can be determined from the change in the electrode voltage at the end of the electrolytic reduction step.

Specific Example 1-2 In this specific example, the sub-electrode 7 is plated with platinum in the same manner as the second main electrode 6. The first main electrode 5 does not necessarily need to be plated with platinum. In the electrolytic oxidation step, the first main electrode 5 is used as a negative electrode, the second main electrode 6 is used as a positive electrode,
Is connected to the second main electrode 6 so as to serve as a positive electrode,
When a DC current of 3.4 A flows, the voltage between the electrode terminals is 1.9 V
It became. At this time, nitric oxide is generated from the first electrolytic solution 3, and black-brown Ag is formed on the surface of the second main electrode 6 serving as a positive electrode.
(II) was produced. In addition, a relatively small amount of black-brown Ag (II) was also formed on the surface of the sub-electrode 7. Ag
(II) The current efficiency in the electrolytic oxidation until reaching the saturation concentration was higher than that of the specific example 1-1 and was 80%.

In the electrolytic reduction step, when the polarity of the main electrode is maintained and the sub-electrode 7 is connected to the first main electrode 5 to make the polarity negative, the voltage between the electrode terminals becomes 2.4 V and the second electrolyte 4 Ag (II) remained therein, and brown silver remained on the sub-electrode 7 to precipitate metallic silver crystals. The amount of black-brown Ag (II) generated on the surface of the second main electrode 6 decreases with the passage of time, and when the total silver concentration of the second electrolytic solution 4 becomes 10% and the coloring becomes weak, the electrode terminal voltage is reduced. Rapidly increases to 3.0V. Along with this, black amorphous metal silver was deposited on the sub-electrode 7, and the total silver concentration of the second electrolytic solution 4 was reduced to 1% or less.

When the electrolysis is further continued, nitrous acid starts to be generated in the second electrolytic solution 4, and as the nitrite concentration increases, silver re-dissolution proceeds, so that the silver concentration in the second electrolytic solution 4 decreases. At this point, the circulation of the second electrolytic solution is stopped, and when the electrolysis is stopped, the metallic silver deposited on the electrodes starts to fall off and dissolve,
It completely falls off and dissolves in about 15 minutes. Since the amount of the second electrolytic solution 4 is 10% of the total circulation amount, the silver concentration of the second electrolytic solution finally reaches 0.5 M and the nitric acid concentration decreases to about 2.5 M. The second electrolytic solution 4 having a higher silver concentration is mixed with nitric acid at an appropriate concentration to prepare a second electrolytic solution 4 for the next electrolytic oxidation step batch. In this specific example, the amount of electricity required to deposit silver contained in the second electrolytic solution 4 as a metal on the sub-electrode 7 was 1.7 times the theoretical amount of electricity.

According to this embodiment, the following effects can be obtained in addition to the effects of the embodiment 1-1. The sub-electrode 7 contributes to the electrolytic oxidation step, and can improve the current efficiency of Ag (II) generation. The deposition potential of silver in the electrolytic reduction step decreases, and the power consumption decreases.

Embodiment 1-3 In this embodiment, all the electrodes are plated with platinum. In the electrolytic oxidation step, the first main electrode 5 is used as a negative electrode,
When the second main electrode 6 was used as a positive electrode and the sub-electrode 7 was connected to the second main electrode 6 and a DC current of 13.4 A was passed between the positive and negative electrodes as a positive electrode, the voltage between the electrode terminals became 1.9 V. At this time,
Nitrogen oxide is generated from the first electrolytic solution 3, and the second
Black-brown Ag (II) was formed on the surface of the main electrode 6. In addition, a relatively small amount of black-brown Ag (II) was also formed on the surface of the sub-electrode 7. The current efficiency in the electrolytic oxidation until reaching the saturated concentration of Ag (II) was as high as that of Example 1-2 and was 80%.

In the electrolytic reduction step, when the polarity of the main electrode is changed to make the first main electrode 5 a positive electrode and the second main electrode 6 and the sub-electrode 7 a negative electrode, the voltage between the electrode terminals becomes 2.4 V. (2) Ag (II) remained in the electrolytic solution 3 and the second main electrode 6 and the sub-electrode 7 precipitated metal silver crystals with the brown color remaining. However, the Ag (I) concentration in the second electrolyte 3 is 30
% Nitrite was formed at the same time as the brown color of Ag (II) was lost. As the nitrite concentration increases, the decrease in the Ag (I) concentration stops, and thereafter, the second electrolyte 3
The Ag (I) concentration in the solution increased, and finally reached the initial concentration, whereby nitric oxide was generated from the second electrolytic solution 3.
The polarity of the main electrode is converted again to make the first main electrode 5 a negative electrode,
When the second main electrode 6 and the sub-electrode 7 were used as positive electrodes, the voltage between the electrode terminals returned to 1.9 V after a transient change, and when the nitrous acid in the second electrolytic solution 4 disappeared, Ag ( II)
The brown color has returned.

The polarity of the main electrode is converted again and the first main electrode 5
When the secondary electrode 7 was used as a positive electrode and the second main electrode 6 was used as a negative electrode, the voltage between the electrode terminals was 2.4 V, and Ag (II) remained in the second electrolyte 3 and the second electrolyte remained brown. Crystals of metallic silver were deposited on the main electrode 6. The amount of black-brown Ag (II) generated on the surface of the sub-electrode 7 decreases with time, and the electrode terminal voltage sharply increases when the total silver concentration of the second electrolytic solution 4 becomes 10% and the color becomes thin. To 3.0V. Accompanying this, black amorphous metal silver was deposited on the surface of the second main electrode 6, and the total silver concentration of the second electrolytic solution 4 was reduced to 1% or less.

When the electrolysis is further continued, nitrous acid starts to be generated in the second electrolytic solution 4, and as the nitrous acid concentration increases, silver re-dissolution proceeds, so that the silver concentration in the second electrolytic solution 4 decreases. At this point, the circulation of the second electrolytic solution 4 is stopped, and when the electrolysis is stopped, the metallic silver deposited on the electrode starts falling off and dissolving, and completely falls off and dissolves in about 15 minutes. Second electrolyte 4
Is 10% of the total circulation volume, so that the silver concentration of the second electrolyte eventually reaches 0.5 M and the nitric acid concentration is about 2.5 M
To decline.

The second electrolytic solution 4 having an increased silver concentration is mixed with nitric acid of an appropriate concentration and mixed with the second electrolytic solution in the second electrolytic oxidation step batch.
An electrolyte 4 is prepared. In this specific example, the second electrolyte 4
The amount of electricity required to deposit the silver contained in the sub-electrode 7 as a metal was 1.2 times the theoretical amount of electricity.

According to this embodiment, the following effects can be obtained. Through the electrolytic oxidation step and the electrolytic reduction step in which the polarity of the main electrode is reversed, the cathode always becomes a positive electrode, and by placing a sub-electrode that contributes to the electrochemical reaction, the efficiency of the electrolytic oxidation step is increased. In the electrolytic reduction step, Ag ( In the presence of II), the generation of nitrous acid which hinders the precipitation of silver can be suppressed, and the silver concentration in the electrolytic solution can be reduced. The optimal end point can be determined from the change in the electrode voltage at the end of the electrolytic reduction step.

The current efficiency in the electrolytic reduction step can be improved by 1.4 times as compared with the specific examples 1-1 and 1-2.

Embodiment 2 An electrolytic cell according to Embodiment 2 of the present invention will be described below with reference to FIG. The electrolytic cell according to the second embodiment is composed of 1 L of the first electrolytic solution 3 and 2 L of the second electrolytic solution 4 separated by a diaphragm 2 which is a porous sintered ceramic cylindrical container in an electrolytic cell container 1 made of titanium. Has 1L. Although not shown, the electrolytic solution is circulated from the external electrolytic solution circulating tank to the electrolytic cell container 1 via a pump.
The first electrolyte 3 is a nitric acid solution having a circulation volume of 5 L and a concentration of 6 M, and the second electrolyte 4 is a nitric acid solution having a circulation volume of 5 L and a concentration of 6 M containing silver nitrate having a concentration of 0.1 M in the electrolytic oxidation step. And the circulation volume is 10 in the electrolytic reduction step.
L, a 3M nitric acid solution containing 0.05M silver nitrate.

First main electrode 5 installed in first electrolytic solution 3
Is manufactured in a cylindrical shape with a titanium expanded mesh and has an effective surface area of 450 cm ² . The second main electrode 6 installed in the second electrolyte 4 is made of a titanium expanded mesh in a cylindrical shape, has an effective surface area of 750 cm ² , and is plated with platinum according to the purpose. The sub-electrode 7 is constituted by the inner surface of the electrolytic cell container 1, has an effective inner surface area of 950 cm ² , is platinum-plated according to the purpose, and has the first main electrode 5 or the second main electrode 6.
Connected to The electric resistance across the diaphragm between the main electrodes 5 and 6 was 0.07Ω, and the electric resistance between the second main electrode 6 and the sub-electrode 7 was 0.03Ω.

Specific Example 2-1 In this specific example, the sub-electrode 7 formed on the inner surface of the electrolytic cell container 1 is plated with platinum in the same manner as the second main electrode 6. The first main electrode 5 does not necessarily require platinum plating. In the electrolytic oxidation step, the first main electrode 5 is used as a negative electrode,
When the second main electrode 6 was used as a positive electrode and the sub-electrode 7 was connected to the second main electrode 6 and a DC current of 13.4 A was passed between the positive and negative electrodes as a positive electrode, the voltage between the electrode terminals became 1.9 V. At this time,
Nitrogen oxide was generated from the first electrolytic solution 3, Ag (II) was generated in the second electrolytic solution 4, and the current efficiency in electrolytic oxidation until the saturated concentration of Ag (II) reached 80%. .

In the electrolytic reduction step, when the polarity of the main electrode is maintained and the electrolytic cell vessel 8 is connected to the first main electrode 5 to make the polarity negative, the voltage between the electrode terminals becomes 2.4 V and the second
Ag (I) with Ag (II) remaining in electrolyte 3
The concentration has dropped. The Ag (II) concentration in the second electrolytic solution 4 decreases with time, and the total silver concentration of the second electrolytic solution 4 becomes 1
At 0%, the total silver concentration was reduced to 1% or less as the electrode terminal voltage rapidly increased to 3.0V.

When the electrolysis is further continued, nitrous acid starts to be generated in the second electrolytic solution 4, and as the nitrite concentration increases, silver re-dissolution proceeds, so that the silver concentration in the second electrolytic solution 4 decreases. At this point, the circulation of the second electrolytic solution 4 is stopped, and when the electrolysis is stopped, the metallic silver deposited on the electrode starts falling off and dissolving, and completely falls off and dissolves in about 15 minutes. Second electrolyte 4
Is 10% of the total circulation amount, so that the silver concentration of the second electrolytic solution 4 finally reaches 0.5 M and the nitric acid concentration is about 2.5
M.

The second electrolytic solution 4 having an increased silver concentration is mixed with nitric acid of an appropriate concentration and mixed with the second electrolytic solution in the second electrolytic oxidation step batch.
An electrolyte 4 is prepared. In this specific example, the second electrolyte 4
The amount of electricity required for depositing and removing silver contained in the sub-electrode 7 as a metal was 1.7 times the theoretical amount of electricity.

According to this example, the following effects can be obtained in addition to the effects of the examples 1-1 and 1-2. The electrolytic cell can be easily configured in a cylindrical geometry with a limited diameter, which allows for critical shape management in relation to the handling of fissile material.

Specific Example 2-2 In this specific example, the first main electrode 5, the second main electrode 6, and the sub-electrode 7 formed on the inner surface of the electrolytic cell container 1 are all plated with platinum. In the electrolytic oxidation step, the first main electrode 5
Is a negative electrode, the second main electrode 6 is a positive electrode, and the sub-electrode 7 is a second
13.4 A between positive and negative electrodes as positive electrode connected to main electrode 6
When a DC current of? Is applied, the voltage between the electrode terminals becomes 1.9 V,
Nitrogen oxide was generated from the first electrolytic solution 3, and Ag (II) was generated in the second electrolytic solution 4. The current efficiency in electrolytic oxidation until the Ag (II) saturation concentration was reached was 80%. In the electrolytic reduction step, the polarity of the main electrode is changed to make the first main electrode 5 a positive electrode, and the second main electrode 6 and the sub-electrode 7 are connected to form a negative electrode. Ag (I) concentration decreased while Ag (II) remained in second electrolytic solution 4.

The Ag (II) concentration in the second electrolytic solution 4 decreases with time, and the total silver concentration of the second electrolytic solution 4 becomes 10%.
At this point, the total silver concentration decreased to 1% or less as the electrode terminal voltage rapidly increased to 3.0 V. When the electrolysis is further continued, nitrous acid starts to be generated in the second electrolytic solution 4, and as the nitrite concentration increases, the silver re-dissolution proceeds, so that when the silver concentration in the second electrolytic solution 4 decreases, Second
When the circulation of the electrolytic solution 4 is stopped and the electrolysis is stopped, the metallic silver deposited on the electrode begins to fall off and dissolve, and completely falls off and dissolves in about 15 minutes. The amount of the second electrolyte 4 is 1 of the total circulation amount.
Since it is 0%, the silver concentration of the second electrolyte finally becomes 0.5%.
M and the nitric acid concentration drops to about 2.5M. The second electrolytic solution 4 having an increased silver concentration is mixed with nitric acid of an appropriate concentration to prepare a second electrolytic solution 4 for the next electrolytic oxidation step batch.
In this specific example, the amount of electricity required to precipitate and remove silver contained in the second electrolytic solution 4 as a metal on the sub-electrode 7 was 1.2 times the theoretical amount of electricity.

According to this embodiment, the following effects can be obtained in addition to the effects of the embodiments 1-3. The electrolytic cell can be easily configured in a cylindrical geometry with a limited diameter, which allows for critical shape management in relation to the handling of fissile material. The current efficiency in the electrolytic reduction step can be improved by a factor of 1.4 as compared with the specific example 2-1.

[0041]

As described above, according to the present invention, in an electrolytic cell comprising a pair of main electrodes serving as a negative electrode and a positive electrode facing each other across a diaphragm, the same electrolytic solution as the main electrode serving as a positive electrode is used. Install one sub-electrode that can switch polarity,
Since Ag (II) is generated on the main electrode serving as the positive electrode, silver is electrolytically reduced and silver is deposited on the surface of the sub-electrode by setting the polarity of the sub-electrode to the negative electrode. By doing so, silver can be deposited as a metal by using a negative electrode in the electrolytic reduction step without hindering the electrolytic oxidation step. More specifically, in the electrolytic oxidation step, it is particularly effective that the main electrode serving as the positive electrode holds platinum as an electrochemical catalyst material in order to electrolytically oxidize Ag (I) to Ag (II). . If the sub-electrode is a valve metal that does not hold an electrochemical catalytic substance, when it becomes a positive electrode in the normal potential range, it becomes passivated and contributes not only to oxidation of Ag (I) but also to generation of oxygen However, when a negative electrode is formed in a nitric acid electrolyte, it contributes to a nitrate reduction reaction and a silver precipitation reaction under an overvoltage slightly higher than that of platinum. Therefore, claim 1
In the invention of the present invention, the polarity of the sub-electrode is set to a negative electrode, and silver is electrolytically reduced to deposit silver as a metal on the surface of the sub-electrode.
As long as (I) is present, Ag (I) is oxidized electrolytically to produce Ag (II).

Further, since the main electrode serving as a positive electrode is present in the electrolytic solution, Ag (I) is used as long as silver is present in the electrolytic solution.
The presence of I) prevents the presence of nitrous acid, which inhibits the deposition of metallic silver, and consequently makes it possible to significantly reduce the silver concentration in the electrolytic solution. That is, the production rate of Ag (II) is proportional to the concentration of Ag (I), and Ag (II) is converted to Ag (I).
I) reacts with water at a rate proportional to the square of the concentration and inversely proportional to the Ag (I) concentration to generate oxygen, and returns to Ag (I); therefore, the ratio of the Ag (II) saturated concentration to the Ag (I) concentration is Should not exceed 50%. As the Ag (I) concentration decreases, the Ag (II) concentration also decreases, and the total Ag concentration decreases. The presence of Ag (II) does not hinder the electrolytic reduction reaction of depositing Ag (I) as metallic silver on the sub-electrode serving as the negative electrode, but rather reacts with nitrous acid generated as a side reaction at the sub-electrode serving as the negative electrode, Preventing the accumulation of nitrous acid and continuing the deposition and removal of silver until the silver concentration of the electrolytic solution is extremely reduced.

Further, there is the effect that the potential is fluctuated in the final stage of the electrolytic reduction step, and the optimal end time can be determined. Ag (II) is known to be an AgNO ₃ ⁺ complex, but when the Ag (I) concentration eventually decreases, Ag (II) is
The NO ₃ ⁺ complex is directly reduced to metallic silver at a deposition potential slightly more noble than Ag (I) and is deposited on the sub-electrode. When Ag (II) is no longer present in the electrolyte, a reduction reaction of nitric acid occurs on the sub-electrode, nitrous acid is generated, and the once precipitated metallic silver starts to dissolve. Therefore, the AgNO ₃ ⁺ complex is directly reduced to metallic silver and deposited on the sub-electrode, and the electrolytic reduction is stopped at the time when the noble-side deposition potential appears as a guide to reduce the silver concentration in the electrolytic solution to the lowest. can do. Between the pair of main electrodes, there is a diaphragm having an ohmic resistance about twice as high as the electrolyte between the main electrode and the sub-electrode, which is a positive electrode, and the amount of electricity flowing to the sub-electrode and contributing to electrolytic reduction becomes a positive electrode This is about 2/3 of the amount of electricity flowing to the main electrode and contributing to electrolytic oxidation.

According to the present invention, since one sub-electrode is made of the same electrochemical catalytic substance as the main electrode serving as the positive electrode, when the polarity of the sub-electrode is the positive electrode, A is the same as the main electrode serving as the positive electrode.
Since g (II) is produced, the effect obtained by the invention of claim 1 is produced, and since the sub-electrode is made of the same electrochemical catalyst material as the main electrode serving as the positive electrode, Ag (II) is used in the electrolytic oxidation step. ), And consequently has the effect of increasing the current efficiency associated with the generation of Ag (II). That is, since the sub-electrode is made of the same electrochemical catalyst substance as the main electrode in the same electrolytic solution, when the main electrode and the sub-electrode simultaneously become the positive electrode, Ag ( Oxidation reaction of I) to Ag (II) occurs and current flows, so that the current density at the main electrode decreases and A
The current efficiency related to g (II) generation increases. As a result, the amount of electricity consumed to generate the required amount of Ag (II) in the electrolytic oxidation step is reduced, and the amount of Ag (II) is reduced.
An electrochemical catalytic substance such as platinum, which is effective for electrolytic oxidation of (I) to Ag (II), reduces the overvoltage of the electrolytic reduction reaction and reduces power consumption.

According to the present invention, opposing each other across the diaphragm,
By having a pair of main electrodes whose polarity can be mutually converted and one sub-electrode that is in the same electrolytic solution as one of the main electrodes, is composed of the same electrochemical catalyst substance as the main electrode, and is always a positive electrode In a nitric acid solution containing silver nitrate, the polarity is converted and silver is electrolytically reduced and silver is deposited as a metal on the surface of the main electrode which has become the negative electrode. At the same time, Ag (I) is electrolytically oxidized on the surface of the sub-electrode which is the positive electrode. Is oxidized to produce Ag (II), so that the polarities of the pair of main electrodes are mutually converted, but the sub-electrode made of the same electrochemical catalyst material as the main electrode is always kept at the positive electrode. In addition to the effects obtained by the first and second aspects of the present invention through the electrolytic reduction step, the present invention has the effect of increasing the current efficiency relating to the deposition of metallic silver on the main electrode serving as the negative electrode. In this case, all the electrodes need to be made of an electrochemical catalyst material (such as platinum) effective for oxidizing Ag (I) to produce Ag (II). In the electrolyte in which Ag (I) and Ag (II) coexist, the deposition of metallic silver on the negative electrode surface is described in paragraph 00.
It is the same as the invention of the above. Between the pair of main electrodes, there is a diaphragm having an ohmic resistance that is about twice higher than the electrolyte between the main electrode and the sub-electrode, which is the negative electrode. About 2/3 of the amount of electricity that contributes to electrolytic reduction.

According to the present invention, the diaphragm is a cylindrical container, and is located at the center of the cylindrical electrolytic cell container. The main electrode serving as the negative electrode is inside the diaphragm and the main electrode serving as the positive electrode is outside the diaphragm. Each of the sub-electrodes, each of which can be switched in polarity, is located between the main electrode serving as a positive electrode and the inner surface of the electrolytic cell vessel, so that the electrolytic solution can be formed in a cylindrical geometric shape having a limited diameter. Since the tank is constituted, the effects obtained by the inventions of claim 1 and claim 2 are produced through the electrolytic oxidation step and the electrolytic reduction step, and the diameter is limited to enable the critical shape control related to the handling of fissile material. There is an effect that the electrolytic cell can be configured in a cylindrical geometric shape. Also, there is an effect that the surface area of the sub-electrode for depositing silver in the concentric electrolytic cell can be maximized.

According to the present invention, the diaphragm is a cylindrical container, and the diaphragm is located at the center of the cylindrical electrolytic cell container. The main electrode serving as the negative electrode is inside the diaphragm and the main electrode serving as the positive electrode is outside the diaphragm. Each of the sub-electrodes, each of which is provided with a switchable polarity, is formed on the inner surface of the electrolytic cell container, so that the electrolytic cell can be easily configured in a cylindrical geometric shape having a limited diameter. Cylindrical geometry with a limited diameter that produces the effects obtained by the inventions of claims 1 and 2 through an electrolytic oxidation step and an electrolytic reduction step, and enables critical shape control related to the handling of fissile material. There is an effect that the electrolytic cell can be easily configured in the target shape. Further, the arrangement of the sub-electrode in a limited space is not required. In this case, the material of the container of the electrolytic cell is made of a valve metal (Ti, Zr, Nb,
Ta or the like, and such a valve metal contributes to the electrolytic reduction reaction as a negative electrode, but becomes passive as a positive electrode at a normal potential and does not contribute to the electrolytic oxidation reaction.
Only when the same electrochemical catalytic substance as the positive electrode is attached to the surface of the valve metal, it can contribute to the same electrolytic oxidation reaction as the positive electrode.

According to the present invention, the diaphragm is a cylindrical container, is located at the center of the cylindrical electrolytic cell container, is in the same electrolytic solution as the main electrode outside the diaphragm, and is always the positive electrode. Since the two sub-electrodes are located between the main electrode and the inner surface of the electrolytic cell vessel, the effects obtained by the inventions of claims 1, 2 and 3 can be obtained through the electrolytic oxidation step and the electrolytic reduction step, and the fissile There is an effect that the electrolytic cell can be configured in a cylindrical geometric shape having a limited diameter, which enables critical shape management in relation to handling of a substance.

According to the present invention, the diaphragm is a cylindrical container, which is located at the center of the cylindrical electrolytic cell container, is in the same electrolytic solution as the main electrode outside the diaphragm, and is always the positive electrode. The two sub-electrodes are formed on the inner surface of the electrolytic cell container, so that the main electrode, the diaphragm, and the main electrode, which are mutually cylindrical and can exchange polarities, are always kept at the positive electrode from the center of the cylindrical electrolytic cell. Since the surface of the electrolytic cell container serving as the sub-electrode is arranged concentrically, the effects obtained by the inventions of claims 1, 2 and 3 are produced through the electrolytic oxidation step and the electrolytic reduction step, and the fissile substance is removed. There is an effect that the electrolytic cell can be easily configured in a cylindrical geometric shape with a limited diameter, which enables critical shape management related to handling. Further, the arrangement of the sub-electrode in a limited space is not required. In this case, the material of the container of the electrolytic cell is made of a corrosion-resistant valve metal (Ti,
Zr, Nb, Ta, etc.). These valve metals passivate as a positive electrode at normal potential and do not contribute to the electro-oxidative reaction, but only when the same electrochemical catalytic substance as the main electrode is attached to the surface of the valve metal, the electro-oxidative It can contribute to the reaction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus including an electrolytic cell according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram of an apparatus including an electrolytic cell according to Embodiment 2 of the present invention.

[Explanation of symbols]

1 electrolytic cell container, 2 diaphragm, 3 first electrolytic solution, 4 second
Electrolyte, 5 first main electrode, 6 second main electrode, 7 sub-electrode.

Claims (7)

[Claims] 1. An electrolytic cell comprising a pair of main electrodes, which become a positive electrode and a negative electrode facing each other across a diaphragm, has one sub-electrode whose polarity can be switched in the same electrolytic solution as the main electrode which becomes a positive electrode. Characteristic electrolytic cell. 2. The electrolytic cell according to claim 1, wherein one sub-electrode is made of the same electrochemical catalytic substance as the main electrode in the same electrolytic solution. 3. A pair of main electrodes which are opposed to each other across a diaphragm and whose polarities can be mutually converted, and one sub-electrode which is in the same electrolytic solution as one of the main electrodes and is always a positive electrode. Wherein the main electrode and the one sub-electrode are made of the same electrochemical catalyst material. 4. The diaphragm is a cylindrical container, and is located at the center of the cylindrical electrolytic cell container. The main electrode serving as a negative electrode is inside the diaphragm and the main electrode serving as a positive electrode is outside the diaphragm. 3. The electrolytic cell according to claim 1, wherein the one sub-electrode provided and whose polarity can be switched is located between the main electrode serving as the positive electrode and the inner surface of the electrolytic cell container. 4. 5. The diaphragm is a cylindrical container, and is located at the center of the cylindrical electrolytic cell container. A main electrode serving as a negative electrode is provided inside the diaphragm, and a main electrode serving as a positive electrode is provided outside the diaphragm. The one sub-electrode provided and switchable in polarity is constituted by an inner surface of the electrolytic cell container.
Or the electrolytic cell according to claim 2. 6. The diaphragm is a cylindrical container, which is located at the center of the cylindrical electrolytic cell container, is in the same electrolytic solution as the main electrode outside the diaphragm, and always has one sub-electrode which is a positive electrode. The electrolytic cell according to claim 3, wherein an electrode is provided between the main electrode and the inner surface of the electrolytic cell container. 7. A diaphragm, wherein the diaphragm is a cylindrical container, which is located at the center of the cylindrical electrolytic cell container, is in the same electrolyte as the main electrode outside the diaphragm, and is always a positive electrode. The electrolytic cell according to claim 3, wherein an electrode is constituted by an inner surface of the electrolytic cell container.