JP2023037458A - Electrolytic reduction apparatus and electrolytic reduction method - Google Patents

Abstract

To provide an electrolytic reduction apparatus and an electrolytic reduction method that have improved the reduction efficiency compared to the traditional one.SOLUTION: An electrolytic reduction apparatus 1 has a cathode 2, an anode 3, a salt bath 4, a DC power supply 8, and an insulative ion permeation member 6 covering a metal oxide 5 arranged to cover the cathode 2. The energization between the cathode 2 and the anode 3 by the DC power supply 8 reduces the metal oxide 5.SELECTED DRAWING: Figure 1

Description

The present invention provides an electrolytic reduction apparatus for reducing a metal oxide by immersing a cathode and an anode in contact with a metal oxide to be reduced in a salt bath and passing an electric current between the cathode and the anode, and an electrolytic reduction. Regarding the method.

As an example of a technology that can lower the operating temperature and reduce the amount of waste generated between the subsequent electrorefining process when reducing the spent oxide fuel, Patent Document 1 discloses an oxide to be reduced , an anode, a molten salt in which the oxide and the anode are immersed, a container containing the molten salt, and a DC power supply for reducing the oxide by applying current to the cathode and the anode. It is described that the apparatus uses a lithium chloride-potassium chloride eutectic salt as the molten salt.

JP 2003-166094 A

Spent fuel generated from nuclear power plants contains not only uranium and transuranic elements, but also alkali metals, alkaline earth metals, rare earths, etc., which are nuclear fission products. Of these, uranium and plutonium can be reused as fuel through a reprocessing process that separates and removes transuranic elements other than plutonium and fission products.

When used oxide fuels and mixed oxide fuels (MOX fuels) are to be reused as metal fuels, it is necessary to reduce oxides to metals, and an electrolytic reduction method is known as a reduction method.

Conventional electrolytic reduction methods use an electrolytic cell containing a cathode, an anode, and a salt bath to retain a metal oxide on the cathode side and receive electrons from the cathode to reduce the metal oxide to a metal, or Alternatively, the salt bath contains cations of metals that can chemically reduce metal oxides (hereinafter referred to as reducing metals), and the cations receive electrons from the cathode and are reduced to form metals. By operating the electrolytic cell at a potential higher than that which can be deposited on the cathode, the metal oxide is chemically reduced by the reducing metal deposited on the cathode.

In Patent Document 1, a basket-shaped cathode is used as a cathode for holding a metal oxide to be reduced.

In the electrolytic reduction method, the rate at which the current supplied to the cathode is used to reduce the target metal oxide is called "reduction efficiency". I can say

In the method of reducing a metal oxide by holding it in a basket-shaped cathode described in Patent Document 1, the metal oxide is held inside the basket-shaped cathode. When performing electrolytic reduction, the entire basket-shaped cathode is energized, so the electrode inside the basket holding the metal oxide can contribute to the reaction with the metal oxide, but the electrode outside the basket can contribute to the reaction with the metal oxide. The problem is that the moieties cannot participate in the reaction with the metal oxide.

In addition, when the positive ions contained in the salt bath are deposited on the cathode as a reducing metal and chemically reduce the metal oxide, both the inside and the outside of the basket are in contact with the salt bath. Therefore, cations are deposited as reducing metals both inside and outside the basket. Among these, there is a problem that the reducing metal deposited on the outside of the basket cannot contribute to the reduction of the metal oxide because it is not in contact with the metal oxide.

As described above, when a basket-shaped cathode is used, current consumption outside the basket results in a loss, so it has been clarified that there is room for further improvement in reduction efficiency.

An object of the present invention is to provide an electrolytic reduction apparatus and an electrolytic reduction method with improved reduction efficiency compared to conventional methods.

The present invention includes a plurality of means for solving the above problems. One example is a cathode, an anode, a salt bath, a DC power supply, and a metal oxide disposed so as to cover the cathode. and an insulating ion-permeable material covering the metal oxide, wherein the metal oxide is reduced by energizing between the cathode and the anode from the DC power supply.

According to the present invention, it is possible to improve the reduction efficiency as compared with the conventional art. Problems, configurations and effects other than those described above will be clarified by the following description of the embodiments.

1 is a diagram showing the configuration of an electrolytic reduction apparatus according to Example 1 of the present invention; FIG. The figure which shows the structure of the electrolytic reduction apparatus of Example 2 of this invention. The figure which shows the structure of the electrolytic reduction apparatus of Example 3 of this invention.

Embodiments of the electrolytic reduction apparatus and the electrolytic reduction method of the present invention are described below with reference to the drawings. In the drawings used in this specification, the same or corresponding components are denoted by the same or similar reference numerals, and repeated descriptions of these components may be omitted.

<Example 1>
Embodiment 1 of the electrolytic reduction apparatus and the electrolytic reduction method of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing the configuration of the electrolytic reduction apparatus of the first embodiment.

Electrolytic reduction apparatus 1 shown in FIG. 7, a DC power source 8, a reference electrode 9, a temperature control mechanism 10, an inert gas supply pipe 11, a control device 14, and the like.

This electrolytic reduction apparatus 1 reduces a metal oxide 5 by energizing between a cathode 2 and an anode 3 from a DC power source 8 . More specifically, a reducing metal supply source 12 is added to and dissolved in the salt bath 4 to form cations of the reducing metal, and a potential difference is applied between the cathode 2 and the anode 3 to generate the reducing metal at the cathode 2 . It reduces the cation of the metal to produce the reducing metal. By bringing the generated reducing metal and the metal oxide 5 into contact with each other, the metal oxide 5 is reduced in a solid state. Further, by giving electrons to the metal oxide 5 brought into contact with the cathode 2, the metal oxide 5 is reduced in a solid state.

In this embodiment, the metal oxide 5 is UO ₂ , which is the spent oxide fuel of a nuclear power plant, but it is not limited to this and can be, for example, a mixed oxide fuel or a mineral.

The salt bath 4 is, for example, LiCl, but is not limited thereto, and may consist of an alkali metal halide, an alkaline earth metal halide, or an ionic liquid.

The salt bath 4 may be added with an inorganic salt or an ionic liquid containing one or more of Li, K, Ca, and Mg as a source of a reducing metal. A source of reducing metal is dissolved in the salt bath 4 and reduced at the cathode to a zero valent reducing metal, which can reduce the metal oxide 5 to metal.

In this embodiment, the reducing metal supply source 12 is lithium oxide, but is not limited to this, and a salt containing any one or more of Li, K, Ca, and Mg can be used.

The reaction vessel 7 is a vessel containing the salt bath 4, and is, for example, a glass vessel. Note that the reaction vessel 7 is not limited to a glass vessel, and a vessel made of stainless steel, ceramic, or the like can be used.

The cathode 2 is made of Ti and the anode 3 is made of platinum. Although the anode 3 is made of platinum, it is not limited to this, and may be made of a material containing any one of Ni, carbon, La, Zr, Bi, and Ti. Among them, carbon dioxide is generated from the anode 3 when it is made of carbon. Moreover, as the material constituting the anode 3, an electrode made of a material containing at least one of Pt, Ni, carbon, La, Zr, Bi, and Fe can be used.

At the cathode 2 the metal oxide is reduced to metal and at the anode 3 oxygen or carbon dioxide is generated.

In the electrolytic reduction apparatus 1 of the present embodiment, a cage-shaped insulating ion-permeable material 6 is filled with UO ₂ as a metal oxide 5 , and the cathode 2 is placed in the center of the filled UO ₂ . Thereby, the metal oxide 5 shall cover the cathode 2 in the circumferential direction.

The insulating ion permeable material 6 is made of ceramics, more specifically LiAlO ₂ . As the insulating ion permeable material 6 covering the metal oxide 5 in the circumferential direction, an ion permeable material made of a material containing one or more of Li, carbon, Al, Mg and Ca is used. Alternatively, an ion-permeable material made of a fluororesin material can be used in a temperature range where an organic material can be used.

The mesh size of the insulating ion permeable material 6 is desirably smaller than the particle size of the metal oxide. In the prior art, a pellet-shaped metal oxide is used, but by making the mesh size of the insulating ion permeable material 6 finer, it is possible to handle a fine metal oxide 5 . The micronized metal oxide 5 can improve the reduction rate more than when using a pellet-shaped metal oxide, and for treating the same amount as the pellet-shaped metal oxide used in the prior art. The required time can be shortened compared to the conventional method.

The arrangement of the cathode 2, the metal oxide 5, and the insulating ion-permeable material 6 is not particularly limited because the same effect can be obtained even in the axial direction centered on the cathode 2.

The DC power supply 8 is a power supply for applying current to the cathode 2 and the anode 3 when reducing the metal oxide 5 .

The reference electrode 9 is an electrode for measuring the potential of the salt bath 4 and is made of platinum, for example.

In the electrolytic reduction apparatus 1 of the present embodiment, instead of applying a large current without monitoring as in the conventional case, the target is aimed at between the reduction potential of U and the reduction potential of Li, or the potential at which Li is deposited. be able to. For this purpose, a new reference electrode 9 can be added.

Also, a control device 14 can be provided for controlling the output of the DC power supply 8 based on the potential of the salt bath 4 measured by the reference electrode 9 .

When the total amount of the metal oxide 5 is limited, for example, when Pu or the like is contained, a potentiostat can be used in the DC power supply 8 for the purpose of finely controlling the current value to be applied.

The temperature control mechanism 10 is a heater or the like that adjusts the temperature of the salt bath 4 to a melting point or higher.

The inert gas supply pipe 11 supplies an inert gas for preventing oxidation of the produced metal.

Next, the electrolytic reduction method of the metal oxide 5 according to this embodiment, which is preferably carried out by the electrolytic reduction apparatus 1 described above, will be described below.

LiCl in a salt bath 4 containing 1 wt % or more of lithium oxide added and dissolved as a reducing metal supply source is placed in a reaction vessel 7 , and the salt bath 4 is heated to 650° C. by a temperature control mechanism 10 .

The lithium oxide of the reducing metal supply source 12 added to the salt bath 4 dissolves in the salt bath 4 as lithium ions, which are cations of the reducing metal. An anode 3 , UO ₂ filled in an insulating ion permeable material 6 and a cathode 2 placed in the center of the UO ₂ are immersed in a salt bath 4 .

A DC power source 8 is connected to the anode 3 and the cathode 2 to apply a voltage of 3.1 volts. By applying a voltage, lithium ions dissolved from lithium oxide are reduced to metallic lithium, which is a reducing metal, on the surface of the cathode 2 . This reducing metal, metallic lithium, reduces UO ₂ in contact with the surface of the cathode 2 to U.

Used oxide fuels and mixed oxide fuel products from nuclear power plants are used as metal oxides 5 to be reduced. That is, uranium oxide and plutonium oxide contained in spent oxide fuel and mixed oxide fuel products are targeted for reduction. This allows oxide fuel from the light water reactor fuel cycle to be converted to metal fuel.

Next, the effects of this embodiment will be described.

In the conventional method, the reduction reaction starts from the basket-shaped cathode covering the outside of the metal oxide, so the reduction reaction progresses from the outside to the inside of the metal oxide. Since the contact area between the cathode surface and the metal oxide decreases as the reaction progresses, so does the reduction rate. At this time, since the reducing metal is deposited over the entire metal layer after reduction, it is deposited at locations where it cannot contribute to the reaction with the metal oxide, resulting in a decrease in reduction rate and reduction efficiency.

On the other hand, the electrolytic reduction apparatus 1 of Example 1 of the present invention described above includes a cathode 2, an anode 3, a salt bath 4, a DC power supply 8, and a metal oxide 5 arranged so as to cover the cathode 2. and an insulating ion permeable material 6 covering the metal oxide 5 by energizing between the cathode 2 and the anode 3 from a DC power supply 8 .

In this way, by using an insulating material, generation of the reducing metal that does not contribute to the reduction reaction on the holding mechanism of the metal oxide 5 is suppressed, and the electric current supplied to the electrode is reduced to electrolysis of the metal oxide 5. It can be used efficiently for reduction.

Further, by using the ion permeable material, cations contained in the salt bath 4 can pass through the holding mechanism and reach the cathode 2 placed inside the metal oxide 5 .

Furthermore, oxygen ions are generated by the reduction reaction, but since the oxygen ions can pass through the ion permeable material, they can move from the cathode 2 to the anode 3 side in the salt bath 4, and are discharged outside the system as oxygen gas at the anode 3. be done. Since the reduction reaction progresses concentrically from the surface of the cathode 2 in a direction away from the cathode 2 , the oxygen ions generated by the reduction reaction reach the bulk salt bath 4 through the metal oxide 5 layer.

Moreover, when the metal oxide 5 is reduced to metal, the metal acts as a new cathode 2 surface, so the contact area between the cathode 2 surface and the metal oxide 5 increases as the reaction progresses. The reduction rate of the metal oxide 5 depends on the contact area between the surface of the cathode 2 and the metal oxide 5, and the reduction rate increases as the contact area increases. Therefore, the reduction rate increases as the reduction reaction progresses from the start of the reduction reaction.

That is, the reduction efficiency can be improved as compared with the conventional method. In particular, the electrolytic reduction apparatus and the electrolytic reduction method are suitable for reducing oxide fuels, mixed oxide fuels, and minerals to metals in nuclear power plants.

In addition, since the metal oxide 5 covers the cathode 2 in its circumferential direction, contacting most of the surface of the cathode 2 with the metal oxide 5 can increase the contact area, further improving the reduction efficiency. can be made

Furthermore, the insulating ion permeable material 6 is made of a material containing one or more of Li, carbon, Al, Mg, and Ca, or a fluorine resin material, so that ions contributing to thermal reduction of the metal oxide 5 can be absorbed. Supply or decomposition thereof can be strongly suppressed, and more efficient reduction can be realized.

Further, by further providing the reference electrode 9 for measuring the potential of the salt bath 4, fine current control can be realized according to the purpose of electrolytic reduction.

Furthermore, by further providing the control device 14 for controlling the output of the DC power source 8 based on the potential of the salt bath 4 measured by the reference electrode 9, fine current control can be performed more easily.

In addition, the salt bath 4 is made of an alkali metal halide, an alkaline earth metal halide, or an ionic liquid. can be realized.

Furthermore, the salt bath 4 is added with an inorganic salt or an ionic liquid containing one or more of Li, K, Ca, and Mg as a source of metal for reduction, so that a more efficient metal oxide Reduction of 5 can be realized.

Moreover, by making the cathode 2 and anode 3 from a material containing at least one of Pt, Ni, carbon, La, Zr, and Bi, stable reduction can be achieved.

<Example 2>
Embodiment 2 An electrolytic reduction apparatus and an electrolytic reduction method of Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the electrolytic reduction apparatus of the second embodiment.

The electrolytic reduction apparatus 1A of this embodiment shown in FIG. The ion permeable material 6 is immersed.

In the electrolytic reduction apparatus 1A of the second embodiment, the number of cathodes 2 and anodes 3 does not need to be the same, but the total area of anodes 3 is preferably larger than the total area of cathodes 2 .

Although the case where all of the anodes 3, the cathodes 2, and the insulating ion permeable materials 6 are provided in multiple numbers, it is assumed that one or more of the anodes 3, the cathodes 2, and the insulating ion permeable materials 6 are provided in multiple numbers. do it.

The potential applied to each cathode 2 is adjusted by the DC power source 8A to deposit the reducing metal on the cathode 2 from the reducing metal supply source 12 . Since the reduction rate of the metal oxide 5 depends on the size of the metal oxide 5, the thickness of the metal oxide 5 covering the cathode 2 in the circumferential direction should be smaller than the conventional pellet diameter (approximately 10 mmφ). Therefore, the reduction rate can be improved as compared with the conventional method.

Although the processing amount per cathode 2 becomes small, by preparing a plurality of cathodes 2 and anodes 3, the processing amount equivalent to that of the conventional method can be reduced.

Other configurations and operations are substantially the same as those of the electrolytic reduction apparatus and the electrolytic reduction method of the first embodiment described above, and the details are omitted.

In the electrolytic reduction apparatus and the electrolytic reduction method of the second embodiment of the present invention, substantially the same effects as those of the electrolytic reduction apparatus and the electrolytic reduction method of the first embodiment can be obtained.

In addition, a plurality of any one or more of the anodes 3, the cathodes 2, and the insulating ion permeable materials 6 are provided, and the plurality of the anodes 3, the cathodes 2, and the insulating ion permeable materials 6 are immersed in one salt bath 4. Since the salt baths 4 can be integrated and a large amount of the metal oxide 5 can be reduced at one time, more efficient reduction than in the first embodiment can be realized.

Furthermore, since the total area of the anode 3 is larger than the total area of the cathode 2, stable reduction can be achieved.

<Example 3>
Embodiment 3 An electrolytic reduction apparatus and an electrolytic reduction method of Embodiment 3 of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of the electrolytic reduction apparatus of the third embodiment.

The electrolytic reduction apparatus 1B of this embodiment shown in FIG. 3 further includes a rotation drive mechanism 13 for rotating the cathode 2 as a rotation mechanism for causing the salt bath 4 to flow.

The rotating mechanism is not limited to rotating the cathode 2 as shown in FIG.

In this embodiment, the metal oxide 5 circumferentially covering the cathode 2 , the insulating ion permeable material 6 circumferentially covering the metal oxide 5 , and the anode 3 are immersed in a salt bath 4 , and a direct current is applied to the cathode 2 and the anode 3 . A reduction reaction of the metal oxide 5 is caused by energizing the power supply 8 at a potential at which the metal for reduction is deposited.

In addition, along with the energization, the rotation drive mechanism 13 is operated. The rotation driving mechanism 13 may be operated before or during the energization, but it can be rotated at a predetermined timing during the energization or always during the energization. The rotation driving mechanism 13 improves the diffusion rate of oxygen ions generated by the reduction reaction of the metal oxide 5 in the cathode 2 . Oxygen ions whose diffusion rate has been improved by the rotary driving mechanism 13 reach the anode 3 from the cathode 2 and are released outside the system in a shorter time than in the conventional method. By improving the diffusion rate of oxygen ions, oxygen ions, which are reaction products, are rapidly consumed at the anode 3, so that a large amount of current can be applied in a short time, and the reduction rate is improved. .

Other configurations and operations are substantially the same as those of the electrolytic reduction apparatus and the electrolytic reduction method of the first embodiment described above, and the details are omitted.

In the electrolytic reduction apparatus and the electrolytic reduction method of Example 3 of the present invention, substantially the same effects as those of the electrolytic reduction apparatus and electrolytic reduction method of Example 1 described above can be obtained.

In addition, by further providing the rotation drive mechanism 13 for generating flow in the salt bath 4, it is possible to generate flow in the salt bath 4, thereby further promoting the movement of cations and oxygen ions, thereby improving the reduction efficiency. can be further improved.

Furthermore, since the rotation drive mechanism 13 rotates the cathode 2, it is possible to change the arrangement of the metal oxide 5 in contact with the cathode 2, further promoting the movement of cations and oxygen ions. At the same time, the reduction reaction of the metal oxide 5 can be further promoted, and the reduction efficiency can be further improved.

<Others>
It should be noted that the present invention is not limited to the above examples, and includes various modifications. The above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations.

It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

DESCRIPTION OF SYMBOLS 1, 1A, 1B... Electrolytic reduction apparatus 2... Cathode 3... Anode 4... Salt bath 5... Metal oxide 6... Insulating ion-permeable material 7... Reaction container 8, 8A... DC power supply 9... Reference electrode 10... Temperature control mechanism REFERENCE SIGNS LIST 11: Inert gas supply pipe 12: Reduction metal supply source 13: Rotation drive mechanism (rotation mechanism)
14... control device

Claims (13)

a cathode;
an anode;
salt bath and
a DC power supply;
an insulating ion permeable material covering a metal oxide arranged to cover the cathode;
An electrolytic reduction apparatus, wherein the metal oxide is reduced by energizing between the cathode and the anode from the DC power supply. In the electrolytic reduction device according to claim 1,
The electrolytic reduction apparatus, wherein the metal oxide covers the cathode in its circumferential direction. In the electrolytic reduction device according to claim 1,
The electrolytic reduction device, wherein the insulating ion-permeable material is made of a material containing one or more of Li, carbon, Al, Mg, and Ca, or a fluororesin material. In the electrolytic reduction device according to claim 1,
A plurality of any one or more of the anode, the cathode, and the insulating ion permeable material,
An electrolytic reduction apparatus, wherein a plurality of said anodes, said cathodes, and said insulating ion-permeable materials are immersed in one said salt bath. In the electrolytic reduction device according to claim 4,
The electrolytic reduction device, wherein the total area of the anode is larger than the total area of the cathode. In the electrolytic reduction device according to claim 1,
An electrolytic reduction apparatus, further comprising a rotating mechanism that causes the salt bath to flow. In the electrolytic reduction device according to claim 6,
The electrolytic reduction apparatus, wherein the rotating mechanism rotates the cathode. In the electrolytic reduction device according to claim 1,
An electrolytic reduction apparatus, further comprising a reference electrode for measuring the potential of the salt bath. In the electrolytic reduction device according to claim 8,
An electrolytic reduction apparatus, further comprising a controller for controlling the output of the DC power supply based on the potential of the salt bath measured by the reference electrode. In the electrolytic reduction device according to claim 1,
The electrolytic reduction apparatus, wherein the salt bath comprises an alkali metal halide, an alkaline earth metal halide, or an ionic liquid. In the electrolytic reduction device according to claim 1,
The electrolytic reduction apparatus, wherein the salt bath is added with an inorganic salt or an ionic liquid containing at least one of Li, K, Ca, and Mg as a supply source of the reducing metal. In the electrolytic reduction device according to claim 1,
The electrolytic reduction apparatus, wherein the cathode and the anode are made of a material containing at least one of Pt, Ni, carbon, La, Zr, and Bi. inserting the cathode into the metal oxide of the insulating ion-permeable material holding the metal oxide to be reduced inside;
immersing the insulating ion permeable material, the cathode, and the anode in a salt bath;
An electrolytic reduction method, wherein the metal oxide is reduced by energizing between the cathode and the anode from a DC power supply.

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