JPWO2007034605A1 - Reducing metal molten salt electrolysis apparatus, electrolysis method thereof, and method for producing refractory metal using reducing metal - Google Patents

Abstract

A molten salt electrolysis apparatus for efficiently producing a reducing metal by molten salt electrolysis, and a reducing metal electrolysis method using the molten salt electrolysis apparatus are provided. A reducing metal molten salt electrolyzer comprising an electrolytic cell filled with a molten salt containing a reducing metal chloride and having an anode and a cathode immersed therein, the anode side partition surrounding the periphery of the anode and the periphery of the cathode A molten metal electrolysis apparatus for reducing metal, characterized in that a surrounding cathode-side partition wall is disposed, and a method for producing the reducing metal using this apparatus.

Description

  The present invention relates to an electrolysis apparatus for obtaining a reducing metal from a metal chloride by molten salt electrolysis and an electrolysis method thereof.

  Titanium metal has been widely used for aircraft materials and parts in the past, and in recent years, application development has progressed and it is widely used for building materials, roads, sports equipment, and the like. Conventionally, single metal titanium has been produced by a crawl method in which titanium tetrachloride is reduced with molten magnesium to obtain sponge titanium, and production costs have been reduced by accumulating various improvements. However, since the crawl method is a batch process that repeats a series of operations discontinuously, there is a limit to the efficiency.

  For the above situation, a method of directly producing titanium metal by reducing titanium oxide with metallic calcium in molten salt (for example, see Patent Documents 1 and 2), or a reduction including a metal or alloy such as calcium An EMR method (see, for example, Patent Document 3) is disclosed in which an agent is produced and a titanium compound is reduced by electrons emitted from the reducing agent to obtain titanium metal.

  In these methods, after recovering titanium metal from the reaction system after the electrolytic reaction, calcium oxide by-produced in the electrolytic reaction is dissolved in calcium chloride, and the metal calcium is recovered by molten salt electrolysis. It is reused in the manufacturing process.

  Since the temperature of the electrolytic bath in the above process is maintained above the melting point of metallic calcium, metallic calcium produced by the electrolytic reaction exists in a liquid state. However, since molten calcium has high solubility in calcium chloride, it has a problem that it is easily dissolved and dissipated in calcium chloride and the yield of metallic calcium is reduced.

  On the other hand, an attempt to deposit metallic calcium on the cathode in a solid state using a composite molten salt having a melting point lower than that of metallic calcium has been disclosed (for example, see Patent Document 4). However, this method requires special preparation of the composite molten salt, and the problem of increased cost has not been solved.

  In addition, when calcium calcium produced by molten salt electrolysis is contacted with the chlorine gas produced as a by-product in the electrolytic reaction, the reverse reaction occurs and returns to calcium chloride. Therefore, the reverse reaction described above causes a decrease in current efficiency. .

  As described above, the conventional method has a problem that it is difficult to efficiently recover active metals such as metallic calcium, and the cost is high even if possible.

WO99 / 064638 JP 2003-129268 A JP 2003-306725 A US3226311

  The present invention has been made in view of the above circumstances, and is an apparatus and method for producing a reducing metal used for reducing, for example, oxides or chlorides of metallic titanium, and in particular, molten salt electrolysis It is an object of the present invention to provide a molten salt electrolysis apparatus that efficiently produces a reducing metal, a method for electrolyzing a reducing metal using the same, and a method for producing a refractory metal using the reducing metal.

  As a result of extensive studies in view of such circumstances, reduction is achieved while maintaining high current efficiency by arranging partition walls that surround each of the anode and cathode constituting the reducible metal melting electrolyzer. The present inventors have found that a conductive metal can be produced, and have completed the present invention.

  That is, the present invention relates to a reducible metal molten salt electrolyzer comprising an electrolytic cell filled with a reductive metal chloride-containing molten salt and having an anode and a cathode immersed therein, the anode side surrounding the anode. A cathode-side partition wall surrounding the partition wall and the cathode is arranged.

  According to the above configuration, since the periphery of the anode and the cathode is surrounded by the partition walls, it is possible to suppress the reverse reaction caused by diffusion of the generated chlorine gas and the reducing metal into the electrolytic bath. Furthermore, since the reducing metal is accumulated in the inside of the cathode-side partition wall with a high yield, it can be efficiently recovered, and as a result, highly efficient molten salt electrolysis can be performed.

  Moreover, this invention makes it a preferable form to have an opening part which can distribute | circulate molten salt to an anode side partition and a cathode side partition. According to such a form, since the molten salt can be circulated through the opening while suppressing the diffusion of the chlorine gas and the reducing metal by the partition wall, the decrease in the efficiency of the molten salt electrolysis reaction is suppressed. be able to.

  The anode side partition wall extends to the bottom of the electrolytic cell, and the anode side partition wall is preferably made of a porous body. According to such a form, the generated chlorine gas becomes bubbles, so that it floats on the surface of the electrolytic bath without passing through the porous body, while the electrolytic bath can pass through the porous body, so that chloride ions and The reaction can proceed by contacting the anode.

  In addition, it is preferable that the anode side partition is made of metal oxide, metal nitride or metal carbide, and the cathode side partition is made of metal, metal nitride or metal carbide. According to such a configuration, corrosion due to chlorine gas can be suppressed in the anode-side partition, and corrosion due to the reducing metal produced can be effectively avoided in the cathode-side partition.

  In addition, the method for producing a reducing metal according to the present invention uses the above-described molten salt electrolysis apparatus. By using the molten salt electrolysis apparatus of the present invention, it is possible to efficiently produce a highly pure reducing metal while maintaining high current efficiency.

  Further, the present invention is characterized in that a chloride of a refractory metal selected from titanium, zirconium, tantalum and niobium is reduced by the reducing metal produced by the above method.

It is a schematic cross section which shows the 1st and 2nd embodiment of the molten salt electrolysis apparatus of this invention. It is a schematic cross section which shows the 3rd embodiment of the molten salt electrolysis apparatus of this invention. It is a schematic cross section which shows the 4th embodiment of the molten salt electrolysis apparatus of this invention. It is a schematic cross section which shows the 5th embodiment of the molten salt electrolysis apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten salt electrolysis apparatus 11 Electrolysis tank 12 Electrolytic bath 21 Anode 22 Cathode 31 Anode side partition 32 Cathode side partition 33 Cathode side partition opening 34 Tank partition 35 Tank partition opening 36 Anode side partition opening 37 Partition 37a Ceramics layer 37b Metal Layer 41 Chlorine gas 42 Metal calcium concentration layer 51 Electrolytic bath supply pipe 52 Chlorine gas extraction pipe 53 Calcium concentration layer extraction pipe 54 Electrolysis bath extraction pipe

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of a preferred molten salt electrolysis apparatus for carrying out the present invention. Any combination of the electrolytic bath and the reducing metal to be produced can be used in this embodiment, but the electrolytic bath is calcium chloride, the reducing metal to be produced is metallic calcium, and the temperature of the electrolytic bath. A case where the metal calcium is recovered in a solid state with the melting point of the metal calcium being equal to or lower than the melting point (first embodiment) will be described as an example.

  In FIG. 1, the molten salt electrolysis apparatus 1 a is configured by filling an electrolytic bath 12 made of molten calcium chloride in an electrolytic bath 11, and an anode 21 and a cathode 22 are immersed in the electrolytic bath 12. An anode side partition wall 31 is disposed so as to surround the periphery of the anode 21, and a cathode side partition wall 32 is disposed so as to surround the periphery of the cathode 22. The anode-side partition wall 31 is made of a porous material, and the electrolytic bath 12 can move by permeating and diffusing the anode 21 side and the outside surrounded by the anode-side partition wall 31. On the other hand, the cathode-side partition wall 32 is made of a dense material, and the electrolytic bath 12 cannot permeate and diffuse. However, the cathode-side partition wall opening communicated with the cathode 22 side surrounded by the cathode-side partition wall 32 and the outside in the vicinity of the cathode 22 below. A portion 33 is provided.

  Next, the operation of this apparatus will be described. First, the molten salt electrolyzer 1 is heated to a melting point or higher of calcium chloride by a heating means (not shown) to bring the electrolytic bath 12 into a molten state. Next, a predetermined DC voltage is applied between the anode 21 and the cathode 22 to start molten salt electrolysis of the electrolytic bath 12. Chloride ions contained in the electrolytic bath 12 pass through the anode-side partition wall 31 and are attracted to the anode 21, and give electrons to the electrode to generate chlorine gas 41. The generated chlorine gas 41 is collected, transferred to another process (not shown) such as a chlorination process, and reused separately. On the other hand, calcium ions in the electrolytic bath 12 pass through the cathode side partition opening 33 and are attracted to the cathode 22 to receive electrons and generate metallic calcium. Since the electrolytic bath 12 is kept below the melting point of the metallic calcium, the metallic calcium precipitates in a solid state and floats on the electrolytic bath liquid surface, which is recovered and transferred to a titanium reduction step (not shown). It is done.

  According to the molten salt electrolyzer 1a having the above-described configuration, the bubbles of the chlorine gas 41 generated in the anode 21 are prevented from diffusing in the direction of the cathode 22 by being blocked by the anode-side partition wall 31, and most of them are in the electrolytic bath liquid surface direction. To surface. A part of the solid metallic calcium produced in the cathode 22 is dissolved in the electrolytic bath 12, but is prevented from diffusing in the direction of the anode 21 by being blocked by the cathode side partition wall 32. As described above, since the generated chlorine gas and metallic calcium are diffused and come into contact with each other and cause a reverse reaction by the partition wall surrounding the electrode, the efficiency of molten salt electrolysis is improved.

  Moreover, in the apparatus of FIG. 1, as a 2nd embodiment, it is also possible to collect | recover metallic calcium in a molten state by making the temperature of an electrolytic bath into more than melting | fusing point of metallic calcium. In that case, the metallic calcium produced by electrolysis is immediately dissolved in the electrolytic bath existing inside the cathode side partition wall 32 after the production to form a metallic calcium concentrated layer 42 containing calcium chloride. The metallic calcium concentrated layer 42 is appropriately extracted and transferred to a titanium reduction process (not shown) for use.

  Also in the molten salt electrolysis apparatus 1 of the second embodiment having the above configuration, the bubbles of the chlorine gas 41 generated in the anode 21 are blocked by the anode-side partition wall 31 and diffused in the direction of the cathode 22 as in the first embodiment. Is suppressed, and most of them float in the direction of the electrolytic bath liquid surface. Further, the calcium metal produced at the cathode 22 is prevented from diffusing in the direction of the anode 21 by being blocked by the cathode-side partition wall 32. As a result, since chlorine gas and metallic calcium are prevented from causing a reverse reaction, the efficiency of molten salt electrolysis is improved.

Next, the components of the molten salt electrolysis apparatus of the present invention will be described in more detail.
The electrolytic cell 11 is preferably made of a material that can withstand high temperatures during operation and hardly reacts with molten calcium chloride or molten metal calcium. Specifically, titanium, tantalum, or niobium is used. It is preferable to comprise.

Electrolytic bath The temperature of the electrolytic bath 12 differs depending on whether metallic calcium is recovered in a molten state or when it is recovered as a solid. When recovering metallic calcium in a molten state, it is preferable to perform molten salt electrolysis in a temperature range higher than the melting point of metallic calcium, specifically, a temperature range higher by 5 ° C. to 50 ° C. than the melting point of metallic calcium. Is preferably selected. Since the melting point of metallic calcium is 845 ° C, the temperature of the electrolytic bath is 850 ° C to 895 ° C. Further, considering the cost required for heating and the evaporation of calcium chloride, the range of 5 ° C. to 20 ° C. is more preferable. Since the melting point of calcium chloride is 780 ° C., which is lower than the melting point of metallic calcium, as long as metallic calcium is kept in a molten state, calcium chloride is also kept in a molten state.

  On the other hand, when recovering metallic calcium as a solid, it is preferable to maintain the temperature of the electrolytic bath in a temperature range not lower than the melting point of calcium chloride and not higher than the melting point of metallic calcium. The melting point is 845 ° C. or lower, which is a temperature range higher than the melting point of calcium chloride. However, since the calcium metal produced at the cathode dissolves in calcium chloride and easily diffuses, it is preferable to perform electrolysis at a temperature just above the melting point of calcium chloride if possible. Specifically, electrolysis is preferably performed at 785 ° C to 800 ° C.

  The electrolytic bath can reduce the melting point of the electrolytic bath by using not only a single bath of calcium chloride but also a mixed salt with potassium chloride or calcium fluoride. As a result, the electrolysis temperature can be lowered as compared with the case of a single calcium chloride bath, and precipitation of solid metallic calcium can be facilitated. For example, potassium chloride or calcium fluoride with respect to calcium chloride can exert a sufficient effect only by adding about 5 to 20 mol%.

The anode and the anode are immersed in the electrolytic bath, and chlorine gas is generated by the electrolysis of calcium chloride constituting the electrolytic bath. Since the temperature of the electrolytic bath is at a high temperature around 800 ° C., the anode is exposed to high-temperature chlorine gas or calcium chloride. Therefore, it is preferable to use a material that can withstand high-temperature chlorine gas and molten salt, and industrially, graphite is preferable. Graphite is relatively inexpensive and easy to process, and has excellent corrosion resistance against high-temperature molten salt and chlorine gas, and is suitable for the anode of the present invention.

The cathode is immersed in an electrolytic bath, and calcium metal is deposited by electrolysis of calcium chloride. Since metallic calcium exhibits reducibility, there is no particular limitation as long as it is a material that can withstand molten calcium chloride and has excellent electrical conductivity, and can be composed of, for example, carbon steel or stainless steel. The tip of the cathode is preferably processed in advance so as to exhibit as rough a surface state as possible. Specifically, it is preferable to perform sandblasting. It is also preferable to cut a screw on the surface in advance. By performing such a surface treatment, it becomes possible to facilitate the deposition of metallic calcium on the cathode.

Anode-side partition The anode-side partition is provided to suppress a reverse reaction in which chlorine gas generated at the anode reacts with metallic calcium generated at the cathode and returns to calcium chloride, and is arranged so as to surround the periphery of the anode. It is preferable. However, the electrolytic reaction cannot be continued unless the external electrolytic bath partitioned by the anode-side partition wall can move into the anode-side partition wall. For this reason, when the anode side partition wall having no opening as shown in FIG. 1 is mounted, chlorine gas does not diffuse in the anode side partition wall, but the electrolytic bath is made of a porous body that can move. It is preferable to keep it.

  The material of the porous body is preferably selected from metal oxides, metal nitrides or metal carbides that are corrosion resistant to chlorine gas or molten salt. The metal oxide is alumina, silica, zirconia, magnesia, or a composite made of these ceramics, and the metal nitride is selected from silicon nitride, boron nitride, titanium nitride, zirconium nitride, or tantalum nitride. It is preferable to do. Furthermore, the metal carbide is preferably selected from silicon carbide, boron carbide, titanium carbide, zirconium carbide, and tantalum carbide. Further, the porosity of the porous body is preferably in the range of 5 to 30%. By using a porous body having such a porosity, it is possible to facilitate the movement of the electrolytic bath while suppressing the diffusion of chlorine gas generated at the anode.

The cathode side barrier rib is also preferably arranged so as to surround the periphery of the cathode, and by disposing such a barrier wall, diffusion of metallic calcium generated at the cathode can be effectively suppressed. The cathode-side partition can be composed of a porous body like the anode-side partition, but the chlorine gas floats into the atmosphere and is removed from the system, whereas the metal calcium is an electrolytic bath. Since it stays floating inside, there is a possibility that it may permeate and diffuse toward the anode. Therefore, it is preferable that the material is made as dense as possible. In addition, when the cathode-side partition is made of ceramic, it is often reduced and corroded by molten calcium. Therefore, the cathode-side partition wall is preferably made of metal, metal nitride, or metal carbide. The metal is preferably selected from stainless steel, titanium, niobium or tantalum having corrosion resistance, and the metal nitride is selected from silicon nitride, boron nitride, titanium nitride, zirconium nitride or tantalum nitride. Further, the metal carbide is preferably composed of silicon carbide, boron carbide, titanium carbide, zirconium carbide, and tantalum carbide.

  The cathode side barrier rib is preferably as dense as possible in order to suppress diffusion of metallic calcium generated at the cathode. However, it is preferable to provide an opening in the cathode side partition in order to facilitate the movement of the electrolytic bath. The cathode-side partition opening is preferably disposed at a distance of 10 mm or more below the lower end of the cathode. This is because if the cathode side partition opening is disposed within 10 mm below the tip of the electrode, metallic calcium diffused downward from the bath surface is dissipated from the opening to the outside of the cathode side partition, which is not preferable. Moreover, when the cathode side partition is a cylinder, it is more preferable to provide a plurality of openings.

  In the electrolytic bath surrounded by the cathode side barrier rib, a concentrated layer of metallic calcium in which metallic calcium generated by the electrolytic reaction is dissolved alone or in calcium chloride is formed. The said metal calcium concentration layer can be used as a direct reducing agent of a titanium oxide or a titanium chloride, for example by rapidly extracting from an electrolytic cell to another container.

  FIG. 2 shows an electrolyzer 1b in another preferred embodiment (third embodiment) according to the present invention. In this embodiment, a tank partition 34 is provided between the anode side partition 31 and the cathode side partition 32. By immersing the tank partition wall 34 in the electrolytic bath 12, it is possible to effectively suppress the phenomenon in which the metallic calcium flowing out from the cathode side partition wall 32 diffuses and moves to the anode side. Moreover, the phenomenon that the chlorine gas flowing out from the anode-side partition wall 31 diffuses toward the cathode can be more effectively suppressed.

  Moreover, it is preferable to provide a tank partition opening 35 through which the electrolytic bath 12 can move in the tank partition 34 immersed in the electrolytic bath 12. By providing such an opening, it is possible to smoothly move the bath to the anode and the cathode.

  FIG. 3 shows an electrolyzer 1c in a preferred embodiment (fourth embodiment) when the present invention is applied to an actual machine. In this embodiment, various supply pipes and extraction pipes are additionally arranged in the third embodiment. Specifically, an electrolytic bath supply pipe 51 for supplying the electrolytic bath 12, a metallic calcium concentrated layer extraction pipe 53 that extracts the metallic calcium concentrated layer 42 and sends it to the next process, and an electrolytic bath extraction pipe 54 are added. It is arranged. Further, the anode side partition wall 31 in the first and second embodiments is changed to a shape that covers the entire anode 21, and the chlorine gas extraction pipe that can extract the chlorine gas 41 generated at the anode 31 out of the system without leakage. 52 is arranged.

  Further, an anode side partition opening 36 is provided at the lower end of the anode side partition 31 (52) so that the electrolytic bath 12 can move. In the present embodiment assuming an actual machine, in order to avoid permeation and diffusion of the electrolytic bath 12, the anode-side partition wall 31 is preferably composed of a dense metal oxide, metal nitride, or metal carbide. It is more preferable to configure.

  The heights of the electrolytic bath circulation openings 36, 35, and 33 provided in each of the anode-side partition wall 31, the tank partition wall 34, and the cathode-side partition wall 32 are not the same, but are arranged to be stepped. Is preferred. With this arrangement of openings, the flow of the electrolytic bath 12 to the anode 21 meanders up and down even when the metal calcium or metal calcium concentrated layer 42 generated at the cathode 22 reaches the opening. The reverse reaction with the chlorine gas generated in can be effectively avoided.

  FIG. 4 shows an electrolyzer 1d in another preferred embodiment (fifth embodiment) according to the present invention. This embodiment is composed of an electrolytic cell 11, an anode 21, a cathode 22, a partition wall 37 and an electrolytic bath 12, and the basic specifications are the same as those of the first to fourth embodiments. However, in this embodiment, the anode-side partition wall 31 and the cathode-side partition wall 32 in the first to fourth embodiments are joined together to form a single partition wall 37. The partition wall 37 is a ceramic layer on the anode side. It differs from the said 1st-4th embodiment that it is comprised with the clad material which consists of 37a and the metal layer 37b by the side of a cathode.

  The ceramic layer 37a and the metal layer 37b constituting the partition wall 37 are preferably made of the same material as that of the anode side partition wall 31 and the cathode side partition wall 32 described above. Furthermore, the ceramic layer 37a is more preferably formed of a metal oxide. When the ceramic layer 37a is made of a metal nitride, the metal layer 37b is not always necessary and can be made of the ceramic layer 37a alone.

  In this embodiment, since only one partition wall 37 is immersed in the electrolytic bath, the electrical resistance between the anode 21 and the cathode 22 is smaller than that in the above embodiment in which a plurality of partition walls are immersed. . As a result, less power is required for electrolysis of the molten salt, and the power consumption of metallic calcium can be reduced.

  By using each embodiment of the present invention described above, it is possible to efficiently produce calcium metal by molten salt electrolysis of calcium chloride, which has been difficult in the prior art.

  Moreover, metal titanium can be manufactured by using the metal calcium manufactured by the said method as a reducing agent of titanium tetrachloride. By using it as a reducing agent for the chloride of zirconium, tantalum or niobium instead of titanium tetrachloride, metal zirconium, metal tantalum or metal niobium can also be produced efficiently.

The following examples illustrate the invention in more detail.
[Example 1]
Using the electrolytic apparatus shown in FIG. 1 having the following apparatus configuration, calcium chloride (100%) was added as an electrolytic bath, and the temperature of the electrolytic bath was maintained at 880 ° C.
Equipment configuration Electrolyzer: Titanium crucible Anode: Graphite Cathode: Carbon steel Anode-side partition: Silicon nitride tube Cathode-side partition: Metal titanium tube
Results When molten salt electrolysis of calcium chloride was performed under the above conditions, a black solution that appeared to be metallic calcium was formed in the vicinity of the bath surface of the cathode. The current efficiency obtained by comparing with the calcium metal recovered by molten salt electrolysis and the theoretical amount of precipitated metal calculated from the amount of energization was 75%. When the recovered metal calcium was analyzed, the purity was 80%.

[Example 2]
Molten salt electrolysis was performed under the same conditions as in Example 1 except that the temperature of the electrolytic bath was 800 ° C., under the temperature conditions where solid metallic calcium was deposited on the cathode. As a result, solid metallic calcium was deposited on the surface of the cathode. The current efficiency obtained by comparing with the theoretical deposited metal amount calculated from the energization amount was 85%. When the deposited metal calcium was analyzed, the purity was 90%.

[Example 3]
Using the apparatus shown in FIG. 3, the temperature of the electrolytic bath was set to 800 ° C., and the other conditions were the same as in Example 1. The molten salt electrolysis of calcium chloride was performed for 5 hours. The current efficiency obtained by comparing with the calcium metal recovered by molten salt electrolysis and the theoretical amount of precipitated metal calculated from the amount of energization was 80%. Moreover, when the collect | recovered metallic calcium was analyzed, purity was 90%.

[Comparative Example 1]
In Example 1, when the molten salt electrolysis of calcium chloride was performed under the same conditions except that only the cathode-side partition wall 32 was not used, the theoretical amount of precipitated metal calculated from the metal calcium recovered by the molten salt electrolysis and the amount of electricity supplied The current efficiency obtained by comparing with the above was 25%.

[Comparative Example 2]
In Example 1, when the molten salt electrolysis of calcium chloride was performed under the same conditions except that only the anode-side partition wall 31 was not used, the theoretical amount of precipitated metal calculated from the metal calcium recovered by the molten salt electrolysis and the amount of electricity supplied The current efficiency obtained by comparing with the above was 40%.

  According to the examples and comparative examples described above, by implementing the present invention, there is an effect that metal calcium can be efficiently produced and recovered by molten salt electrolysis of metal chloride, especially calcium chloride. Further, the high-melting point metal chloride can be reduced using the produced metallic calcium.

Claims (17)

  A reducible metal molten salt electrolyzer comprising an electrolytic cell filled with a reductive metal chloride-containing molten salt and having an anode and a cathode immersed therein, the anode-side partition surrounding the anode and the cathode A reducing metal molten salt electrolysis apparatus comprising a cathode-side partition wall surrounding the periphery.   2. The molten metal electrolysis apparatus for reducing metal according to claim 1, wherein the anode side partition wall and the cathode side partition wall have openings through which the molten salt can flow.   2. The reducing metal molten salt electrolysis apparatus according to claim 1, wherein the anode-side partition wall extends to the bottom of the electrolytic cell, and the anode-side partition wall is formed of a porous body.   The said anode is comprised with the graphite, The molten salt electrolysis apparatus of the reducing metal in any one of Claims 1-3 characterized by the above-mentioned.   The molten metal electrolysis apparatus for reducing metal according to claim 1, wherein the cathode is made of carbon steel or stainless steel.   The said anode side partition is comprised with the metal oxide, the metal nitride, or the metal carbide, The molten salt electrolysis apparatus of the reducing metal in any one of Claims 1-3 characterized by the above-mentioned.   The molten metal electrolysis apparatus for reducing metal according to any one of claims 1 to 3, wherein the cathode-side partition wall is made of metal, metal nitride, or metal carbide.   The molten metal electrolyzer for reducing metal according to claim 6, wherein the metal oxide is composed of at least one selected from alumina, silica, zirconia, or magnesia.   8. The reducing metal molten salt electrolysis apparatus according to claim 6, wherein the metal nitride is silicon nitride, boron nitride, titanium nitride, zirconium nitride, or tantalum nitride.   The reducing metal molten salt electrolysis apparatus according to claim 6 or 7, wherein the metal carbide is silicon carbide, boron carbide, titanium carbide, zirconium carbide, or tantalum carbide.   The molten metal electrolysis apparatus for reducing metal according to claim 7, wherein the metal is any one of titanium, niobium, tantalum, and stainless steel.   The molten metal electrolysis apparatus for reducing metal according to any one of claims 1 to 11, wherein the reducing metal is metallic calcium, metallic sodium, or metallic magnesium.   The molten salt is calcium chloride, sodium chloride, magnesium chloride, a mixed salt of calcium chloride and potassium chloride, or a mixed salt of calcium chloride and calcium fluoride. A molten salt electrolyzer for reducing metal according to 1.   A method for producing a reducing metal by molten salt electrolysis, which is performed using the reducing metal molten salt electrolysis apparatus according to claim 1.   The method for producing a reducing metal by molten salt electrolysis according to claim 14, wherein the temperature of the molten salt is maintained in a temperature range 5 to 50 ° C higher than the melting point of the molten salt.   The method for producing a reducing metal by molten salt electrolysis according to claim 14 or 15, wherein the reducing metal is metallic calcium, metallic sodium, or metallic magnesium. A refractory metal produced by the method according to any one of claims 14 to 16, wherein a refractory metal chloride selected from titanium, zirconium, tantalum and niobium is reduced. Method.

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