KR101723919B1 - Electrolytic reduction apparatus for metal oxide using conductive oxide ceramic anode and method thereof - Google Patents

Abstract

The present invention relates to an electrolytic reduction apparatus and an electrolytic reduction method of a metal oxide using a conductive oxide ceramic anode, comprising: a crucible (10) comprising a molten salt (60); A cathode basket (30) immersed in the molten salt (60) and filled with a metal oxide (35); A conductive oxide ceramic anode (40) immersed in the molten salt (60); And a reference electrode (50) immersed in the molten salt (60). The electrolytic reduction apparatus of the metal oxide using the conductive oxide ceramic anode is provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic reduction apparatus and an electrolytic reduction method of a metal oxide using a conductive oxide ceramic anode,

The present invention relates to an electrolytic reduction device for a metal oxide using a conductive oxide ceramic anode and an electrolytic reduction method.

Electrolytic reduction techniques using molten salt have been applied to metal conversion processes of various metal oxides (TiO ₂ , Ta ₂ O ₅ , UO _2, etc.). Particularly, in the field of nuclear energy, the electrolytic reduction process is an essential technology for pyroprocessing, which is a recycling process of spent fuel. It plays a role of replacing the oxide fuel used in the light water reactor with the metal fuel type that can be used in the sodium cooling high speed furnace do.

At present, pyrolytic oxide fuel firing electrolytic reduction process is carried out using a LiCl molten salt with a small amount of Li ₂ O, a metal cathode basket containing oxide fuel particles, and a Pt anode. In the molten salt, Li ₂ O exists in the form of Li ⁺ and O ^2- ions. When an electrical signal is applied between the two electrodes, Li ⁺ ions in the cathode are reduced to metal Li, ^2- ions emit electrons and produce oxygen (O ₂ ) gas.

At this time, the a metallic Li generated by the anode oxide nuclear fuel contained in the basket (usually UO ₂₎ at the same time as the reduction Sikkim in metallic form again a Li ₂ O consumed by the electrochemical reaction at the electrodes to produce a Li ₂ O (MO _x + 2xLi = xLi ₂ O + M). Therefore, the Li ₂ O concentration can be kept constant during the reaction and the electrochemical reaction can proceed stably. The metal reductant obtained through the electrolytic reduction process of the oxide fuel is recovered through a subsequent process and processed into a metal fuel form.

The electrolytic reduction process using the hot molten salt must maintain the reactor at a temperature higher than the melting point of the salt since the salt must be maintained in a liquid state. The above-mentioned LiCl-Li ₂ O molten salt requires a temperature of about 650 ° C. As described above, oxygen (O ₂ ) gas is generated at the anode. Since the temperature of the molten salt is very high during the process, a strong oxidizing atmosphere is formed around the anode.

Therefore, the anode material should be made of a material which can withstand high temperature oxygen atmosphere and has excellent electric conductivity, and currently widely used material is Pt. Pt, a noble metal, has high electrical conductivity and can not be reacted singly with oxygen gas even at a high temperature, so that it can be maintained relatively stable during the process. However, the cost of Pt is very high, which increases the overall process cost. Depending on the process conditions, a composite oxide such as Li ₂ PtO ₃ is formed or anodic dissolution reaction occurs. Accordingly, There is a growing need for new anode materials.

Korean Patent Publication (A) Publication No. 2002-0091046

A problem to be solved by the present invention is to provide a conductive oxide ceramic material as a new anode material which can be applied instead of the conventional Pt in a metal oxide electrolytic reduction process using a hot molten salt.

That is, even when the conductive oxide ceramic anode is used by using the present invention, the metal oxide can be effectively reduced to the metal form by using the electrochemical reaction, and the possibility of applying the electrolytic reduction process is confirmed in the future.

In order to solve the above-described problems, one aspect of the present invention provides a crucible comprising: a crucible (10) comprising a molten salt (60); A cathode basket (30) immersed in the molten salt (60) and filled with a metal oxide (35); A conductive oxide ceramic anode (40) immersed in the molten salt (60); And a reference electrode (50) immersed in the molten salt (60). The electrolytic reduction apparatus of the metal oxide using the conductive oxide ceramic anode is provided.

Further, another aspect of the present invention is a method of manufacturing a crucible, comprising: (S10) filling a crucible 10 with a molten salt 60; Immersing the anode basket 30 filled with the metal oxide 35 in the molten salt 60 (S30); Immersing the conductive oxide ceramic anode 40 in the molten salt 60 (S40); And a step (S50) of immersing the reference electrode (50) in the molten salt (60). The electrolytic reduction method of the metal oxide using the conductive oxide ceramic anode is also provided.

As described above, according to the present invention, it is expected that a Pt anode having a very high unit cost in the metal oxide electrolytic reduction process using a hot molten salt can be replaced by a conductive oxide ceramic anode material having a relatively low cost. This means that the price competitiveness of the electrolytic reduction process can be greatly enhanced as compared to other metal oxide reduction processes.

Particularly, when the conductive oxide ceramic anode according to the present invention is applied to pyro-processing, which is a spent fuel recycling process, it is possible to convert a spent nuclear fuel into a metallic form and recycle it in a sodium fast cooling furnace, It is thought that it will play a very important role in securing the castle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode according to an embodiment of the present invention; FIG.
2 is a flow chart showing a method for electrolytic reduction of a metal oxide using a conductive oxide ceramic anode according to an embodiment of the present invention.
3 is a graph showing measured values of a cathode potential and a cell current according to a cell voltage change in a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode and a SUS rod anode according to an embodiment of the present invention.
4 is a photograph showing Li metal formed in a cathode of a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode and an SUS rod anode according to an embodiment of the present invention.
5 is a graph showing measured values of cell currents according to anode potentials in a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode and a SUS rod anode according to an embodiment of the present invention.
FIG. 6 is a graph showing the results of measurement of the anode potential and the cell current according to the cell voltage change during the electrolytic reduction process in the metal oxide electrolytic reducing apparatus using the conductive oxide ceramic anode and the cathode basket filled with UO ₂ according to the embodiment of the present invention Showing graph.
7 is a photograph showing UO2 before and after an electrolytic reduction reaction in a metal oxide electrolytic reduction apparatus using a conductive oxide ceramic anode and a cathode basket filled with UO ₂ according to an embodiment of the present invention.
8 is a photograph showing La _0.33 Sr _0.67 MnO ₃ before and after an electrolytic reduction reaction in a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode and a cathode basket filled with UO ₂ according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a metal oxide electrolytic reduction apparatus and an electrolytic reduction method using a conductive oxide ceramic anode according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of a metal oxide electrolytic reducing apparatus using a conductive oxide ceramic anode according to an embodiment of the present invention. FIG.

1, the apparatus for electrolytic reduction of a metal oxide using the conductive oxide ceramic anode according to the present invention comprises a crucible 10, a flange 20, a cathode bus bar 30, a conductive oxide ceramic anode 40, A shroud 41, and a reference electrode 50. Hereinafter, the above-described configuration will be described in detail.

The crucible 10 receives the molten salt 60 in a liquid state and the cathode basket 30, the conductive oxide ceramic anode 40 and the reference electrode 50 are immersed in the molten salt 60. As the material of the crucible 10, a metal such as SUS or a ceramic such as magnesium oxide (MgO) can be used. The molten salt 60 may be a LiCl molten salt to which a small amount of Li ₂ O is added.

The flange 20 is provided on the upper portion of the crucible 10, and has a plurality of through holes and an insulating plate. The cathode bus bar 30, the conductive oxide ceramic anode 40, the anode shroud 41 and the reference electrode 50 are immersed in the molten salt 60 of the crucible 10 through the through holes.

The cathode basket 30 is immersed in the molten salt 60 in a state that the metal oxide 35 to be subjected to electrolytic reduction is filled. As the metal oxide (35), UO ₂ used in pyro processing can be applied, but the present invention can be applied not only to a single oxide of UO ₂ but also to various metal oxides such as Ta ₂ O ₅ , TiO ₂ and U ₃ O ₈ Do. The cathode bus bar 30 is made of a mesh or a porous metal film so that the metal oxide 35 and the molten salt 60 come into contact with each other to allow the dissolved substance from the metal oxide 35 to escape to the outside. .

The conductive oxide ceramic anode 40 is immersed in the molten salt 60 of the crucible 10. At this time, the conductive oxide ceramic anode (40) is surrounded by the anode shroud (41) and bonded to each other. An oxide including lanthanum (La), strontium (Sr), and manganese (Mn) can be used as the conductive oxide ceramic anode 40. More preferably, an oxide of La _x Sr _y MnO ₃ , y = 1 - x).

The anode shroud 41 has a gas injection pipe 42 and a gas discharge pipe 43 at the top of the crucible 10. The gas injection pipe 42 supplies an inert gas, preferably argon (Ar) gas. The gas injection pipe 42 maintains a positive pressure with respect to the gas discharge pipe 43, so that the oxygen ions are oxidized, (For example, argon gas) supplied through the gas injection pipe 42 is discharged to the outside of the crucible 10 through the gas discharge pipe 43 do. With the above-described configuration, the anode shroud 41 can prevent the crucible 10 from being attacked by removing the gas (for example, oxygen gas) at a high temperature generated in the anode 40.

The reference electrode 50 is immersed in the molten metal 60 of the crucible 10. The reference electrode 50 means an electrode for measuring the potential of the reducing electrode (cathode and anode). The description of the reference electrode 50 is disclosed in Korean Patent Application No. 10-2009-0105955, and thus a detailed description thereof will be omitted.

2 is a flow chart showing a method of electrolytic reduction of a metal oxide using a conductive oxide ceramic anode according to an embodiment of the present invention.

As shown in FIG. 2, the electrolytic reduction method of the metal oxide using the conductive oxide ceramic anode according to the present invention comprises the steps of filling the molten salt (S10), immersing the oxide having the common cation (S20), immersing the anode basket (S30), an immersion step (S40) of a conductive oxide ceramic anode, an immersion step (S50) of a reference electrode, and a voltage application step (S60). Hereinafter, each of the above-described steps will be described in detail with reference to FIG.

First, the crucible 10 is filled with a molten salt in a solid state, and then the crucible 10 is heated by an external heater (not shown) to prepare a molten salt 60 (S10). The LiCl salt used in the embodiment of the present invention is a strong electrolyte and when heated above 650 캜, a molten salt 60 is formed.

Next, the oxide having the salt 60 and the common cation is immersed in the molten salt 60 (S20). In an embodiment of the present invention, lithium oxide (LiO ₂ ) having a LiCl salt and Li ⁺ as a common ion is added to the molten salt 60. The amount of lithium oxide added is preferably less than 8.7 wt.%, Which is the solubility of lithium oxide in the lithium chloride molten salt at 650 ° C.

Next, the anode basket 30 filled with the metal oxide 35 is immersed in the molten salt 60 (S30). In an embodiment of the present invention, a metal basket containing UO ₂ is used as the cathode basket 30. The cathode basket 30 is made of SUS material.

Next, the conductive oxide ceramic anode 40 is bonded to the anode shroud 41 and then immersed in the molten salt 60 (S40). In an embodiment of the present invention, La ₀ .5 has an electrical conductivity as high as 0.1-0.2 ohm / cm _{. 33} Sr _{0 . 67} MnO ₃ is used as the conductive oxide ceramic anode (40).

Next, the reference electrode 50 is immersed in the molten salt 60 (S50). In the embodiment of the present invention, Li-Pb is used as the reference electrode 50.

Finally, a voltage is applied to the cathode and anode electrodes 30 and 40 to start the electrolytic reduction process (S60). At this time, a negative voltage is applied to the cathode bus bar 30 rather than the reduction potential of the molten salt cation (S60A). In addition, a positive voltage is applied to the conductive oxide ceramic anode 40 rather than the oxidation potential of the molten salt anion, rather than the oxidation potential of the oxygen ion (S60B). A detailed description thereof will be given later with reference to Figs. 3 to 5.

FIG. 3 is a graph showing measured values of a cathode potential and a cell current according to a cell voltage change in a metal oxide electrolytic reduction apparatus using a conductive oxide ceramic anode and a SUS load anode according to an embodiment of the present invention. FIG. 5 is a photograph showing Li metal formed in a cathode of a metal oxide electrolytic reduction apparatus using a conductive oxide ceramic anode according to an embodiment of the present invention and a SUS rod anode. FIG. 5 is a cross- FIG. 3 is a graph showing a measured value of a cell current according to an anode potential in an electrolytic reduction apparatus of a metal oxide using a cathode. FIG. Here, in order to measure the electrochemical characteristics of the conductive oxide ceramic anode, a cathode was used instead of a negative electrode basket in which UO ₂ was immersed.

Referring to FIG. 3, a step (S60A, FIG. 2) of applying a negative voltage to the negative electrode bus bar 30 with respect to the reducing potential of the molten salt cation will be described below. That is, when the cell voltage is 3.0 V or higher, the cathode potential falls to -0.6 V, which is the Li formation potential, to -0.7 V. At the same time, the cell current abruptly increases from 0.2 A to 1.1 A. As a result, in the open circuit state, the cathode potential maintains the redox reaction value of Li (about -0.56 V compared to the Li-Pb reference electrode). As can be seen from FIG. 4, ), It is observed that Li is formed.

Referring to FIG. 5, a step S60B of applying a positive voltage to the conductive oxide ceramic anode 40, which is more negative than the oxidation potential of the molten salt anion and positive than the oxidation potential of the oxygen ions, will be described. That is, when the anode potential of the Li-Pb reference electrode is higher than 2.2 V, the oxygen ion (O ^2- ) is oxidized to oxygen gas (O ₂ ), and the current increases greatly. Referring to FIG. 3, when the cell voltage formed between the cathode electrode and the anode electrode is 3.0 V, the anode potential is about -0.7 V as compared with the reference electrode, so that the anode potential becomes 2.3 V and Li begins to be formed. Therefore, it can be confirmed that the increase of the cell current is caused by the electrolysis of Li ₂ O.

The chemical reaction as described in FIG. 3 and FIG. 5 will be described according to the stoichiometric ratio as follows. That is, 2O ^{2 -} > O ₂ (g) + 4e ^- for the anode and 4Li ⁺ + 4e ^- -> 4Li for the cathode. Through this, oxygen gas is generated in the anode, lithium metal is formed in the cathode, and U is generated through chemical reaction with UO ₂ , that is, 4Li + UO ₂ → 2Li ₂ O + U.

FIG. 6 is a graph showing the results of measurement of the anode potential and the cell current according to the cell voltage change during the electrolytic reduction process in the metal oxide electrolytic reducing apparatus using the conductive oxide ceramic anode and the cathode basket filled with UO ₂ according to the embodiment of the present invention FIG. 7 is a photograph showing UO ₂ before and after an electrolytic reduction reaction in a metal oxide electrolytic reduction apparatus using a conductive oxide ceramic anode and a cathode basket filled with UO ₂ according to an embodiment of the present invention, and FIG. In the electrolytic reduction apparatus of a metal oxide using a conductive oxide ceramic anode and a cathode basket filled with UO ₂ according to an embodiment of the present invention, La _{0 . 33} Sr _{0 . 67} is a photograph showing MnO ₃ . Here, in order to evaluate the electrolytic reducing ability of the conductive oxide ceramic anode, a cathode basket filled with UO ₂ was used as the cathode.

As can be seen from FIG. 6, when 3.25 V was applied across the electrodes, a relatively constant cell current value was obtained regardless of the reaction time. Through this, La _{0 . 33} Sr _{0 . 67} It can be seen that the electrolytic reduction process of UO ₂ is steadily progressing in the embodiment of the present invention using MnO ₃ .

Referring to FIG. 7, UO ₂ before the electrolytic reduction reaction is brown (FIG. 7 (a)), while La _{0 . 33} Sr _{0 . It} can be seen that the UO ₂ reduced material using MnO ₃ as anode is silver-colored (FIG. 7 (b)), indicating that UO ₂ was successfully converted to U through electrolytic reduction.

Referring to FIG. 9, La _{0 . 33} Sr _{0 . 67} MnO ₃ shows no significant change in morphology except for a slight impurity adsorption on the surface before and after the electrolytic reduction (FIG. 9 (a)) and after (FIG. 9 (b)). This is because La _{0 . 33} Sr _{0 . 67} MnO ₃ can be stably maintained. Therefore, in the electrolytic reduction process using a high-temperature molten salt, the conductive oxide ceramic material can be considered to be highly applicable as a cathode material that can replace Pt.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

10: Crucible 20: Flange
30: cathode basket 35: metal oxide
40: conductive ceramic anode 41: anode shroud
50: reference electrode 60: molten salt

Claims (7)

delete A crucible formed by heating to a melting temperature of LiCl and LiO ₂ and containing a LiCl molten salt added with Li ₂ O;
A negative electrode basket immersed in the molten salt and filled with a metal oxide;
A conductive oxide ceramic anode immersed in the molten salt; And
A reference electrode immersed in the molten salt,
Wherein the metal oxide comprises UO ₂ or U ₃ O ₈ ,
The conductive oxide ceramic anode is used as an electrode for generating oxygen,
Wherein the conductive oxide ceramic anode comprises La _x Sr _y MnO ₃ , wherein x and y satisfy 0 < x < 1 and y = 1 - x,
Wherein the conductive oxide ceramic anode is surrounded by the anode shroud and is coupled to each other and the anode shroud is provided with a gas inlet tube and a gas outlet tube at the top of the crucible and is applied to pyro processing using an anode of a conductive oxide ceramic The electrolytic reduction device of the metal oxide. 3. The method of claim 2,
wherein x = 0.33 and y = 0.67. A device for electrolytic reduction of a metal oxide for application to pyro-processing using an anode of a conductive oxide ceramic. delete A method for electrolytically reducing a metal oxide using the electrolytic reduction apparatus according to claim 2 or 3,
It is formed in the crucible and heated to the melting temperature of LiCl and LiO _2, further comprising: filling an LiCl molten salt is Li ₂ O was added (S10);
Immersing the anode basket filled with the metal oxide in the molten salt (S30);
Immersing the conductive oxide ceramic anode in the molten salt (S40); And
(S50) immersing the reference electrode in the molten salt,
Wherein the metal oxide is UO ₂ or U ₃ O ₈ ,
Wherein the conductive oxide ceramic anode comprises La _x Sr _y MnO ₃ , wherein x and y satisfy 0 < x < 1 and y = 1 - x,
Wherein the conductive oxide ceramic anode is surrounded by the anode shroud and is coupled to each other and the anode shroud is provided with a gas inlet tube and a gas outlet tube at the top of the crucible and is applied to pyro processing using an anode of a conductive oxide ceramic A method for electrolytically reducing a metal oxide is provided. 6. The method of claim 5,
wherein x = 0.33 and y = 0.67. 2. The method of claim 1, wherein the metal oxide is an oxide. 6. The method of claim 5,
Applying (S60A) a negative voltage to the negative electrode basket above the reduction potential of the molten salt cation; And
(S60B) is applied to the conductive oxide ceramic anode (S60B), which is more negative than the oxidation potential of the molten salt anion and lower than the oxidation potential of the oxygen ion. The conductive oxide ceramic anode / RTI &gt; the method of electrolytic reduction of metal oxides for application to processing.

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