JP2022183910A - Anode, molten salt electrolysis device and method for producing metal - Google Patents

Abstract

To provide an anode that can reduce the effects of oxidative burn-off of an anode for use in molten salt electrolysis.SOLUTION: An anode 130 has an anode body 132 used in an electrolytic cell 110 in which molten salt bath Bf is stored, a cover member 134 that covers part of the anode body 132, and a cavity 136 between the anode body 132 and the cover member 134. The distance between the outer surface 132a of the anode body 132 and the inner surface 134b of the cover member 134 is 0.5 to 20 mm.SELECTED DRAWING: Figure 1A

Description

The present invention relates to an anode, a molten salt electrolyzer, and a method for producing metal.

Metallic titanium ingots and the like are industrially manufactured using sponge titanium manufactured by the crawl method. The sponge titanium manufacturing process including the Kroll method can be roughly divided into four steps: a chlorination step, a reductive separation step, a crushing step, and an electrolysis step. In the electrolysis step, which is one of these steps, magnesium chloride, which is a by-product of the reductive separation step of reducing titanium tetrachloride with metallic magnesium to produce sponge titanium, is decomposed by molten salt electrolysis to produce metallic magnesium. is the process of obtaining

Regarding the molten salt electrolysis, for example, Patent Document 1 describes "a molten salt electrolytic cell comprising an electrolytic chamber for electrolyzing molten salt in a molten salt bath and a metal recovery chamber communicating with the electrolytic chamber, A molten salt electrolytic bath, wherein a molten metal storage part for storing metal in a metal recovery chamber has a first wall on at least a part thereof, and a molten salt solidified layer on at least a part of the inner surface of the first wall. .” is described. By using such a molten salt electrolytic bath, it is possible to effectively suppress contamination of the molten metal obtained by the electrolysis of metal chlorides with impurities.

JP 2021-021134 A

Molten salt electrolysis for producing metallic magnesium, for example, generally uses a molten salt bath at a high temperature of about 650 to 700° C. and is carried out under severe conditions such as the generation of chlorine gas as a reaction product. be. In addition, the inside of the molten salt electrolysis apparatus is maintained at a negative pressure with respect to the external environment so that chlorine generated in the molten salt electrolysis does not leak to the outside. Therefore, outside air may enter the electrolytic cell through a minute clearance between the anode and the upper lid, so the clearance is usually sealed. However, anodes are often large and made of graphite. The large graphite anode is sometimes manufactured through a high temperature heat treatment, which causes the anode to contain minute pores. Therefore, even if the clearance is properly sealed, the interior of the molten salt electrolysis apparatus is maintained at a negative pressure, so outside air cannot enter the interior of the molten salt electrolysis apparatus through the inside of the anode rather than through the sealing portion. There is
Here, in the space above the bath surface of the molten salt bath in the molten salt electrolysis apparatus, the temperature near the bath surface is high, the temperature is low near the upper lid, and there is a temperature gradient in the height direction. Oxygen and graphite in the air passing through the inside of the anode react more quickly at high temperatures, and the anode may be oxidized and consumed. An anode whose wall thickness has been reduced to some extent due to oxidative consumption may break due to its own weight.

Accordingly, in one embodiment, an object of the present invention is to provide an anode that can reduce the influence of oxidation consumption of the anode used for molten salt electrolysis.

That is, in one aspect of the present invention, an anode main body used in an electrolytic cell in which a molten salt bath is stored, a cover member covering a part of the anode main body, and a cover member existing between the anode main body and the cover member The anode includes a gap portion that fills the gap, and the distance between the outer surface of the anode main body and the inner surface of the cover member is within the range of 0.5 to 20 mm.

In one embodiment of the anode according to the present invention, the anode has an open end of the gap at a position lower than the bath surface of the molten salt bath.

In one embodiment of the anode according to the present invention, the anode body has at least one step, and the cover member covers at least part of the anode body at a position higher than the flat surface of the step.

In one embodiment of the anode according to the present invention, the cover member contains one or more selected from silicon nitride, silicon carbide, aluminum oxide, silicon oxide, magnesium oxide and calcium oxide.

In one embodiment of the anode according to the invention, the anode body is made of graphite.

In another aspect, the present invention is a molten salt electrolysis device comprising any one of the above anodes.

In another aspect of the present invention, there is provided a method for producing a metal using the above molten salt electrolysis apparatus, comprising: is a manufacturing method.

An embodiment of the metal manufacturing method according to the present invention further includes a solidified layer forming step of forming a molten salt solidified layer at a position higher than the bath surface of the molten salt bath in the gap.

In one embodiment of the metal production method according to the present invention, the metal chloride to be electrolyzed is magnesium chloride.

According to one embodiment of the present invention, it is possible to reduce the influence of oxidation consumption of the anode used for molten salt electrolysis.

1 is a schematic cross-sectional view for explaining the internal structure of an embodiment of a molten salt electrolysis apparatus according to the present invention; FIG. 1B is a schematic end view along line XX of FIG. 1A; FIG. 1B is a schematic end view along line YY of FIG. 1A; FIG. FIG. 2 is a schematic end view for explaining formation of a molten salt solidified layer in an electrolytic chamber of an embodiment of the molten salt electrolysis apparatus according to the present invention; 1B is a schematic perspective view showing a modification of the anode of FIG. 1B; FIG. FIG. 4 is a schematic cross-sectional view for explaining the internal structure of another embodiment of the molten salt electrolysis apparatus according to the present invention; 2B is a schematic end view along line ZZ of FIG. 2A; FIG. FIG. 5 is a schematic end view for explaining formation of a molten salt solidified layer in an electrolytic chamber of another embodiment of the molten salt electrolysis apparatus according to the present invention; 2B is a schematic end view showing a variation of the anode of FIG. 2A; FIG. 2B is a schematic end view showing a variation of the anode of FIG. 2A; FIG. FIG. 4 is a schematic cross-sectional view for explaining the internal structure of another embodiment of the molten salt electrolysis apparatus according to the present invention;

The present invention is not limited to the embodiments described below, and can be embodied by modifying the constituent elements without departing from the spirit of the present invention. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in each embodiment. For example, the invention may be formed by omitting some components from all the components shown in the embodiments. In addition, in the drawings, some members are shown schematically in order to facilitate understanding of the embodiments included in the invention, and the illustrated sizes, positional relationships, etc. may not necessarily be accurate.
Further, as used herein, "above" the electrolytic cell 110, e.g., as indicated by the arrows in FIGS. It means the direction from the bottom wall 112 side to the top cover 120 side, and "downward" means the direction from the top cover 120 side to the bottom wall 112 side of the electrolytic cell 110 . Further, in this specification, "molten metal" means a metal in a molten state obtained by electrolytically decomposing a metal chloride. In this specification, the term "solidified molten salt layer" means a layer in which molten salt is solidified. It is formed. As will be described later, the molten salt solidified layer may be formed using the molten salt bath in the electrolytic cell 110, or may be formed using molten salt separately supplied from the outside. The molten salt separately supplied from the outside can have the same composition as the molten salt bath.

[1. Molten salt electrolysis device]
Molten salt electrolysis apparatus 100 shown in FIG.

(Electrolyzer)
The electrolytic cell 110 is in the form of a container with an opening at the top and is made of, for example, refractory bricks, such as aluminum oxide, or other suitable material. The electrolytic cell 110 is composed of a bottom wall 112 and two pairs of side walls 114 connected to the bottom wall and extending upward. The electrolytic cell 110 stores a molten salt bath Bf made of a molten salt containing metal chloride supplied therein. In addition, in the electrolytic cell 110 , the presence of the first partition 116 and the second partition 117 partitions the electrolytic chamber 150 and the metal recovery chamber 160 . In order to send the metal produced by the electrolysis of the molten salt in the electrolysis chamber 150 to the metal recovery chamber 160 and send the molten salt from the metal recovery chamber 160 to the electrolysis chamber 150 to circulate the molten salt bath, the first partition wall 116 and a second partition 117 are arranged. That is, in the molten salt electrolysis apparatus 100, the flow of the molten salt bath indicated by the arrow A (metal recovery from the flow to chamber 160) can be ensured. A passage through which the molten salt bath can flow is also formed on the lower surface side of the second partition wall 117, and the flow of arrow B (flow from the metal recovery chamber 160 to the electrolytic chamber 150) can be ensured.

(Molten salt)
A case where the molten salt contains magnesium chloride (MgCl ₂ ) will be described below as an example. In this case, the electrolysis of magnesium chloride produces metal magnesium (Mg) as molten metal and chlorine (Cl ₂ ) gas as gas. The molten salt includes magnesium chloride (MgCl ₂ ) as described above, and supporting salts such as sodium chloride (NaCl), calcium chloride (CaCl ₂ ), potassium chloride (KCl) and/or calcium fluoride (CaF ₂ ). may be included. The component used as the supporting electrolyte preferably has a higher electrolyzed voltage than magnesium chloride. Metallic magnesium can be used for reducing titanium tetrachloride in the Kroll process for producing metallic titanium, and chlorine gas can be used for chlorinating titanium ore. Magnesium chloride used as a raw material for this electrolysis may be those produced secondarily by the Kroll method.

(top lid)
The upper lid 120 serves to insulate the outside of the electrolytic cell 110 from the high temperature of the molten salt bath Bf. In addition, the upper lid 120 is arranged to make the electrolytic cell 110 a closed space, and the pressure inside the electrolytic cell 110 is made negative with respect to the outside in order to prevent leakage of chlorine gas generated from the anode main body 132 during molten salt electrolysis.
The material of the upper lid 120 is not particularly limited, but from the viewpoint of preventing a short circuit between the upper lid 120 and the anode main body 132 during molten salt electrolysis, the lid rear surface of the upper lid 120 on the molten salt bath Bf side is A ceramic material may be placed on the lid back surface 121 side of the upper lid 120 on the molten salt bath Bf side, or a castable refractory may be applied. The method of providing this castable refractory may be any known method. For example, the castable refractory may be applied to the back surface 121 of the lid by dry spraying or wet spraying.

The upper lid 120 may be provided with a supply port 122 , a first gas recovery port 124 , a second gas recovery port 126 , and a supply/discharge port 128 . Each of these openings may be one or more.
Among these, the supply port 122 is for supplying the molten salt to the gap 136 between the anode main body 132 and the cover member 134 . The supply port 122 is provided in a region where the electrolytic chamber 150 is located and which is located between the anode main body 132 and the cover member 134 . From the viewpoint of forming the previously described closed space, the supply port 122 is usually filled with powders or granules of components constituting the molten salt bath. When the molten salt is supplied from the supply port 122, the filler may be removed once, and the powder or granules may be filled again into the supply port 122 after supplying the molten salt.
Also, the first gas recovery port 124 is used to recover chlorine gas produced by electrolysis in the electrolytic chamber 150 . The first gas recovery port 124 is provided in a region where the electrolytic chamber 150 is located.
Also, the gas produced by electrolysis in the electrolytic chamber 150 may be recovered at the second gas recovery port 126 . The second gas recovery port 126 is provided in the region where the metal recovery chamber 160 is located. The second gas recovery port 126 may be used to recover the remaining gas that has flowed into the metal recovery chamber 160 without being recovered by the first gas recovery port 124 among the gases generated by the electrolysis.
The supply/discharge port 128 is used for collecting molten metal generated by electrolysis in the electrolytic chamber 150 and for supplying molten salt into the electrolytic cell 110 . The supply/discharge port 128 is provided in a region where the metal recovery chamber 160 is located.

(Electrolysis room)
In the electrolytic chamber 150, the molten salt is electrolyzed to generate molten metal by the electrolysis. For example, electrolysis of magnesium chloride produces chlorine gas in addition to molten metal magnesium. Inside the electrolytic chamber 150, an anode body 132 and a cathode 140 having an electrolytic surface substantially parallel to the depth direction of the molten salt bath (vertical direction in FIG. 1A) are arranged.

The anode 130 has an anode body 132 that is placed in the electrolytic bath 110 in which the molten salt bath Bf is stored and is used for electrolysis, and a cover member 134 that partially covers the anode body 132 . As shown in FIGS. 1A and 1B, the anode body 132 is inserted through the upper lid 120 and extends downward, and is arranged so that a portion thereof is immersed in the molten salt bath Bf. The cover member 134 is also inserted through the upper lid 120 and extends downward, and is partly immersed in the molten salt bath Bf. However, the cover member 134 is provided so as not to block the space between the anode body 132 and the cathode 140 inserted through the side wall 114 of the electrolytic cell 110 and extending toward the first partition wall 116 and the second partition wall 117 . Moreover, it is preferable that the lower end surface 134a of the cover member 134 is positioned lower than the bath surface S of the molten salt bath Bf and higher than the upper end surface 140a of the cathode 140 .
If there is a slight clearance between the anode main body 132 and the upper lid 120 and between the cover member 134 and the upper lid 120, the negative pressure inside the electrolytic cell 110 during the molten salt electrolysis will cause outside air to enter the electrolytic cell 110. may enter. Therefore, from the viewpoint of forming a closed space in the electrolytic cell 110, a sealing member may be provided in the clearance. good.

As shown in FIG. 1C, a gap 136 exists between anode body 132 and cover member 134 . Since part of the anode main body 132 and part of the cover member 134 are both immersed in the molten salt bath Bf, one open end 136a of the gap 136 is positioned at the height of the bath surface S of the molten salt bath Bf. placed at a lower position than A distance D1 between the outer surface 132a of the anode main body 132 and the inner surface 134b of the cover member 134 is within the range of 0.5 to 20 mm. With such a configuration, in the gap 136, for example, the molten salt of the molten salt bath Bf can rise to a position higher than the bath surface S of the molten salt bath Bf in the electrolytic cell 110 by capillary action, and the capillary action can be If it is not available, the molten salt can be supplied from the supply port 122, and the molten salt bath can be supplied to a high position in the gap 136 by intentionally supplying excess magnesium chloride to the molten salt bath. can. The temperature of the molten salt in the gap 136 decreases as it approaches the back surface 121 of the lid. Then, the molten salt positioned above the gap 136 is cooled and solidified to form a solidified molten salt layer 138 in the gap 136 as shown in FIG. 1D. Since the solidified molten salt layer 138 plays a role of a plug, it is possible to suppress the mixing of oxygen from the outside even if the molten salt bath is not filled under the solidified molten salt layer 138 thereafter. As shown in the figure, the opening end 136b of the cavity 136 is preferably provided at a position higher than the bath surface S of the molten salt bath Bf. It is possible to suppress thinning of the anode main body 132 located in the gas phase portion of .
Here, typically during molten salt electrolysis, the inside of the electrolytic cell is divided into a liquid phase consisting of the molten salt bath and a gas phase containing gas such as chlorine generated from the anode body. As previously mentioned, the gas phase may be influxed by outside air. For this reason, conventionally, there has been a problem that the thickness of the anode is reduced by the influence of oxygen in the inflowing outside air, and the anode may break and fall during the operation of the molten salt electrolysis. This thinning of the anode often occurs at a position higher than the bath surface S, and furthermore, thinning of the anode often occurs near the rear surface 121 of the lid.
In contrast, in the present invention, in the gap 136 between the anode main body 132 and the cover member 134, the molten salt bath enters a position higher than the bath surface S of the molten salt bath Bf, and furthermore, the molten salt solidified layer The formation of 138 reduces the area of anode body 132 exposed to the gas phase in the electrolytic cell. In addition, even if anode main body 132 is made of graphite and has minute holes formed by high-temperature heat treatment or the like when manufacturing anode main body 132 , molten salt solidified layer 138 closes the minute holes, thereby preventing anode main body 132 from forming. Reduce the amount of outside air passing through the interior. Furthermore, since the molten salt solidified layer 138 is formed by cooling and solidifying the molten salt, even if the outside air passes through the inside of the anode main body, it will mainly pass through the low temperature side. reaction is inhibited. As a result, thinning of the anode main body 132 is suppressed, and the influence of oxidative consumption of the anode main body can be reduced. Furthermore, the following operations can reduce the influence of oxidation consumption of the anode main body. That is, when a thinned portion occurs in the anode main body 132, it is reduced by an appropriate method such as moving the bath surface S of the molten salt bath Bf up and down or supplying molten salt from the outside to the gap portion 136. A molten salt solidification layer 138 can be formed on the meat portion to reinforce the anode body. As a result, anode main body 132 is apparently thicker, and the thinned portion is protected by molten salt solidified layer 138 , and as a result, breakage of anode main body 132 can be suppressed.
Further, when the other open end 136b of the gap 136 is positioned higher than the bath surface S of the molten salt bath Bf, the supply port 122 of the upper lid 120 is used to open the molten salt. You may supply toward the space|gap part 136 from the edge 136b. As a result, the molten salt in the gap 136 becomes higher than the bath surface S of the molten salt bath Bf in the electrolytic bath 110, and the molten salt solidified layer 138 can be formed there.
In addition, the distance D1 is, for example, 0.5 mm or more as the lower limit side, and is, for example, 1.0 mm or more. Further, the distance D1 is, for example, 20 mm or less as an upper limit side, and is, for example, 5 mm or less.

The shape of the anode main body 132 is not particularly limited, and examples thereof include a plate shape, a columnar shape, a prismatic shape, and the like. The shape of the cover member 134 may be appropriately changed in accordance with the shape of the anode main body 132, and may be, for example, a plate shape, a rectangular tube shape, a cylindrical shape, or the like. An anode 130 shown in FIG. 1E, for example, has a plate-like cover member. The anode 130 includes an anode main body 132 and a plate-like cover member 135 on the outer surface 132a of the anode main body 132 . When each part of the anode main body 132 and the cover member 135 is immersed in the molten salt bath, the molten salt bath enters the gap between the anode main body 132 and the cover member 135, and the molten salt bath A molten salt solidified layer 138 is formed in the gap at a position higher than the bath surface. The molten salt bath enters the fine holes of the anode main body, forming a solidified molten salt layer 138 to close the fine holes. The method of arranging the cover member 135 is not particularly limited, and the upper end side thereof may be extended and connected to the upper lid 120 as in the embodiment shown in FIG. 1A. The cover member 135 may be connected to the anode body 132 using a connecting tool, or a part of the cover member 135 may be placed on a part of the anode body 132. .
From the viewpoint of production efficiency of molten metal, the molten salt electrolysis apparatus 100 may include a plurality of anodes, cathodes, and bipolar electrodes.

Another embodiment will now be described below using FIGS. 2A-E and 3. FIG. It should be noted that each configuration of the above-described embodiment can be appropriately applied, and redundant description will be omitted.

In another embodiment, the anode 230 of the molten salt electrolysis apparatus 200 shown in FIGS. 2A and 2B includes an anode body 232 having at least one downward step on the outer surface thereof, and a cover member 234 . In the step, an upper outer surface 232a of the anode body 232 and a lower outer surface 232b of the anode body 232 are connected by a flat surface 231, respectively. Although the anode main body 232 has one step in the illustrated example, it may have two or more steps.
The cover member 234 covers at least a portion of the anode body 232 at a position higher than the stepped flat surface 231 of the anode body 232 . A gap is provided between the anode main body 232 and the cover member 234, and the distance D1 between the outer surface 232a of the anode main body 232 and the inner surface 234b of the cover member 234 is within the range of 0.5 to 20 mm. Here, not only a gap is provided between the anode main body 232 and the cover member 234, but also a gap may be provided between the stepped flat surface 231 of the anode main body 232 and the cover member 234. is located below the bath surface S of the molten salt bath Bf, the molten salt flows from the anode main body 232 and the cover member 234 from the opening end 236a formed by the stepped flat surface 231 of the anode main body 232 and the lower end surface 234a of the cover member 234. 234 can be entered. As long as the entrance of the molten salt bath is ensured in this manner, the arrangement and shape of the open end are not particularly limited. For example, a plurality of through holes 237 may be arranged on the lower end surface side of the cover member 234 so that the molten salt bath can enter the gap. Although the embodiment shown in FIGS. 2A-2C includes the above-described open end 236a and through hole 237, only one of them may be provided. Further, although not shown, the anode 230 may be provided with a U-shaped or inverted recessed notch in the lower end surface 234a of the cover member 234, and a through hole may be formed by bringing the cover member 234 and the flat surface 231 into contact with each other. good. If the through-hole 237 is positioned lower than the height of the bath surface S, the opening end of the gap is positioned below the bath surface S of the molten salt bath Bf, so that the molten salt bath Bf can enter the gap. .
As described above, the distance D2 between the flat surface 231 of the anode main body 232 and the lower end surface 234a of the cover member 234 is not particularly limited as long as the molten salt can enter the gap. It is preferably within the range of 0.5 to 20 mm. When a through hole is provided from the opening end to the gap, the distance D2 means the longest line segment length that can be taken within the opening end. As described above, as the bath surface S of the molten salt bath Bf in the gap becomes higher, the temperature of the molten salt bath Bf at that portion becomes lower, and the part of the molten salt bath Bf on the side of the upper lid 120 is cooled. It solidifies to form a molten salt solidified layer 138 in the gap as shown in FIG. 2C. Further, when the other open end 236b of the gap is located at a position higher than the bath surface S of the molten salt bath Bf, the supply port 122 of the upper lid 120 is opened to supply the molten salt to the open end. The molten salt solidified layer 138 may be formed in the gap by supplying from 236b toward the gap.
As shown in FIG. 2D, a gap is provided between the anode main body 232 and the cover member 234, but the gap may not be provided between the stepped flat surface 231 of the anode main body 232 and the cover member 234. That is, the stepped flat surface 231 of the anode main body 232 is in contact with the lower end surface 234 a of the cover member 234 . In this case, the molten salt bath can enter the gap through the through hole 237 . Although the upper end of the cover member 234 is inserted through the upper lid 120, the upper end of the cover member may not be inserted through the upper lid 120 like the anode 230 shown in FIG. 2E.
Although illustration is omitted, as shown in FIG. 2D, no gap is provided between the flat surface 231 of the anode body 232 and the cover member 234, and the cover member 234 is not provided with the through hole 237. may be The upper open end 236b of the gap is positioned higher than the height of the bath surface S of the molten salt bath Bf. can be supplied As a result, the molten salt becomes higher than the bath surface S of the molten salt bath Bf in the electrolytic cell 110 in the gap, and a part of the molten salt bath Bf on the upper lid 120 side is cooled and solidified, and the molten salt solidifies in the gap. A layer 138 is formed.

The cover members 134, 234 can be made of brick or the like, and preferably include one or more selected from ceramics such as silicon nitride, silicon carbide, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, and steel, for example. From the viewpoint of insulation, it is more preferably any one of silicon nitride, silicon carbide, aluminum oxide, silicon oxide, magnesium oxide and calcium oxide. Silicon carbide is particularly preferred. When the cover members 134 and 234 are made of steel, the upper lid 120 is preferably provided with an insulator such as castable refractory material in order to ensure insulation between the cover members 134 and 234 and the upper lid 120 .

The anode bodies 132, 232 and the cathode 140 are connected to a power source via conductive wires. In the anode bodies 132 and 232 and the cathode 140, the electrolytic surface of the anode bodies 132 and 232 immersed in the molten salt bath Bf undergoes an oxidation reaction based on a predetermined reaction such as the following chemical formula (1). As gas is generated, a reduction reaction occurs on the electrolytic surface of the cathode 140 immersed in the molten salt bath Bf to produce a molten metal such as metallic magnesium.
_MgCl2 →Mg+ _Cl2 ...Chemical formula (1)
Although the material of the cathode 140 is not particularly limited, examples thereof include iron and graphite. Also, the shape of the cathode 140 can be appropriately changed in consideration of the shapes of the anode bodies 132 and 232 .

Electrolysis of the metal chloride in the molten salt bath can be performed if it has at least the anode bodies 132 and 232 and the cathode 140, and the electrolytic chamber 150 is provided from the viewpoint of improving the production efficiency of the electrolysis. , may have a plurality of pairs of electrodes. In addition, from the viewpoint of improving the production efficiency of electrolysis, the electrodes are arranged between the anode bodies 132, 232 and the cathode 140, It is preferred to further have one or more bipolar electrodes 142, 144 that are polarized by the application of a voltage to. In this example, two bipolar electrodes 142 and 144 are used, but the number of bipolar electrodes can be adjusted as appropriate. However, such bipolar electrodes 142 and 144 are not necessarily required. The distances between the anode bodies 132, 232 and the bipolar electrode 142, between the cathode 140 and the bipolar electrode 144, and between the bipolar electrodes 142 and 144 may be the same or different.

(metal recovery room)
The metal recovery chamber 160 recovers the molten metal produced by electrolysis in the electrolysis chamber 150 . Metal recovery chamber 160 communicates with electrolysis chamber 150 and may include a heat exchanger (not shown).

A heat exchanger can adjust the temperature of the molten salt bath Bf in the electrolytic cell 110 . The heat exchanger may include an inlet through which the fluid flows, an outlet through which the fluid is discharged, and a pipe connecting the inlet and the outlet. And the tube may be made of steel (carbon steel or stainless steel).

(Heat exchange chamber)
The molten salt electrolysis apparatus 300 shown in FIG. 3 includes an electrolytic cell 110, an upper lid 120, an anode 130, a cathode 140, an electrolytic chamber 150, a metal recovery chamber 160, and a heat exchanger (not shown). A chamber 370 is provided. In the molten salt electrolysis apparatus 300, the electrolysis chamber 150, the metal recovery chamber 160, and the heat exchange chamber 370 are arranged side by side in this order in the lateral direction of the drawing. The top cover 120 has a supply/discharge port 328 in the area of the heat exchange chamber 370 . As a result, the molten metal can be recovered using the supply/discharge port 128 and the molten salt such as molten magnesium chloride can be replenished using the supply/discharge port 328 . As a result, the molten metal can be stably stored in the metal recovery chamber 160 . In addition to these, the heat exchange chamber 370 may further have a stirrer (not shown) for stirring the molten salt bath Bf.

The electrolytic cell 110 is partitioned into an electrolytic chamber 150, a metal recovery chamber 160, and a heat exchange chamber 370 by a first partition 116, a second partition 317 and a third partition 318, respectively.

[2. Metal manufacturing method]
An embodiment of the method for producing a metal according to the present invention includes an electrolysis step of producing a metal using the molten salt electrolysis apparatuses 100, 200, and 300 described above. Furthermore, at an appropriate timing such as before the electrolysis step or during the electrolysis step, a solidified layer forming step may be further included. Preferred aspects of each step using the molten salt electrolysis apparatus 100 shown in FIGS. 1A to 1D will be described below.

<Fixed layer forming step>
In the solidified layer forming step, molten salt solidified layer 138 is formed at a position higher than bath surface S of molten salt bath Bf in gap 136 between anode main body 132 and cover member 134 by the method described above. Molten salt may be filled in the lower side of the solidified molten salt layer 138, but the molten salt may not be filled in the lower side of the solidified molten salt layer 138. When molten salt electrolysis is performed for a long period of time, the bath surface S may move up and down, but even in such a case, the molten salt solidified layer 138 functions effectively. The vertical movement of the bath surface S may cause outside air to enter the inside of the molten salt electrolysis apparatus 100 through the inside of the anode. As described above, the formation of the solidified molten salt layer 138 can suppress the outside air from entering the molten salt electrolysis device 100 through the inside of the anode body 132, thereby reducing the influence of oxidative consumption of the anode body 132. As a result, the life of the anode body 132 is extended in molten salt electrolysis.

<Electrolysis process>
In the electrolysis step, the metal chloride contained in the molten salt bath Bf is electrolyzed. As an example, molten magnesium chloride, which is a by-product obtained in the production of sponge titanium, is introduced into the molten salt bath Bf in the molten salt electrolysis apparatus 100, and the molten magnesium chloride is electrolyzed to produce metallic magnesium. . The solidified layer forming step can be performed at any timing, for example, it may be performed before the electrolysis step is started or after the electrolysis step is started.

Molten salt bath Bf flows from electrolytic chamber 150 through flow port 115 to metal recovery chamber 160 as indicated by arrow A in FIG. 1A, and flows from metal recovery chamber 160 as indicated by arrow B in FIG. It flows under the partition 117 into the electrolytic chamber 150 . In the electrolytic chamber 150, the metal chloride in the molten salt bath Bf is electrolyzed to produce molten metal. This molten metal then flows into the metal recovery chamber 160 due to the flow of the molten salt bath Bf. After that, the molten metal, which has a low specific gravity relative to the molten salt, floats to a shallow portion of the metal recovery chamber 160 and accumulates there. The molten metal floating in the metal recovery chamber 160 can be recovered by inserting a recovery pipe or the like into the supply/discharge port 128 .

Also, cracks or the like may occur in the molten salt solidified layer 138 formed in the solidified layer forming process during the electrolysis process. In this case, it is preferable to form the molten salt solidified layer 138 again. For example, the molten salt is introduced from the supply/discharge port 128 of the upper lid 120 to raise the height position of the bath surface S of the molten salt bath Bf to the vicinity of the lid rear surface 121 to once melt the solidified molten salt layer. After melting, a recovery pipe or the like is inserted through the supply/discharge port 128, and part of the molten salt bath Bf is slowly extracted from the pipe to form a molten salt solidified layer 138 while the bath surface S is lowered. Since the formed molten salt solidified layer 138 is maintained even without contact with the molten salt bath, the molten salt solidified layer 138 suppresses the entry of oxygen from the outside.

When performing molten salt electrolysis using the molten salt electrolysis apparatuses 100, 200, and 300, the clearance between the anode bodies 132 and 232 and the upper lid 120 is set so that outside air does not enter the molten salt electrolysis apparatuses 100, 200, and 300. In some cases, the sealing member is filled with powders of components constituting the molten salt bath Bf. During long-term molten salt electrolysis, the amount of the powder or the like that slides down into the electrolytic bath 110 may increase. Also, the electrical resistance between the electrodes may suddenly increase. Since thinning of the anode body 132 is suspected when these phenomena occur, it is preferable to form or re-form the molten salt solidified layer 138 .

The present invention will be specifically described based on examples and comparative examples. The descriptions of the following examples and comparative examples are merely experimental specific examples for facilitating the understanding of the technical content of the present invention, and the technical scope of the present invention is limited by these specific examples. is not.

[Example 1]
(Formation of molten salt solidified layer)
In Example 1, a molten salt electrolysis apparatus 100 having the configuration shown in FIGS. 1A to 1C was used. In the molten salt electrolysis apparatus 100, the electrolytic cell 110, the first partition 116, and the second partition 117 are each made of a standard refractory (refractory brick) containing aluminum oxide, and the upper lid 120 is made of carbon steel. A layer of insulating castable refractory material was applied to the lid back surface 121 of the top lid 120 . Anode body 132 , cathode 140 , and two bipolar electrodes 142 and 144 are all plate-shaped, and rectangular tube-shaped cover member 134 is arranged outside plate-shaped anode body 132 . The cover member 134 is made of refractory brick (mullite). The width (thickness) of the anode main body 132 was set to 200 mm, and the distance D1 between each outer surface 132a of the anode main body 132 and each inner surface 134b of the cover member 134 was adjusted to 3 mm. Next, the molten salt was charged into the molten salt electrolysis apparatus 100, and the temperature of the molten salt was adjusted to 650-700.degree. As a result, the distance from the lower end surface 134a of the cover member 134 to the bath surface S in the height direction was within the range of 30 mm to 150 mm. The composition of the molten salt was within the range of 5 to 25% by mass of magnesium chloride, 28 to 36% by mass of calcium chloride, and 47 to 59% by mass of sodium chloride. The material of the anode body 132 was graphite, and the material of the cathode 140 was carbon steel. The material of the bipolar electrodes 142 and 144 is graphite.

The temperature of the molten salt bath Bf was maintained within the range of 650-700°C. This maintenance allows the molten salt bath Bf to enter the gap 136 from the open end 136a, and the bath surface S of the molten salt bath Bf in the gap 136 rises due to capillary action, and is cooled by approaching the upper lid 120. A portion of the molten salt bath Bf on the upper lid 120 side in the gap 136 was solidified to form a solidified molten salt layer 138 as shown in FIG. 1D.

(Manufacturing of metallic magnesium)
The electrolysis process was carried out by supplying current between the anode body 132 and the cathode 140 from a power source through a conductive wire. The electrolysis process was started after formation of the molten salt solidified layer. After 30 months from the start of electrolysis, the current supply was stopped. After that, the anode main body 132 of the molten salt electrolysis apparatus 100 was taken out and checked, and the maximum thickness reduction depth in the width direction of the anode main body 132 was 20 mm. Table 1 shows the results.

[Example 2]
In Example 2, the molten salt electrolysis apparatus 100 was operated in the same manner as in Example 1, except that the cover member 134 was changed from silicon nitride as shown in Table 1. After 30 months from the start of electrolysis, the current supply was stopped. After that, the anode main body 132 of the molten salt electrolysis apparatus 100 was taken out and checked, and the maximum thickness reduction depth in the width direction of the anode main body 132 was 1 mm or less. Table 1 shows the results.

[Comparative Example 1]
In Comparative Example 1, the molten salt electrolysis apparatus was operated in the same manner as in Example 1, except that the cover member was not used as shown in Table 1. After 30 months from the start of electrolysis, the current supply was stopped. After that, when the anode main body of the molten salt electrolysis device was taken out and checked, the maximum thickness reduction depth was 50 mm in the width direction of the anode main body 132 inserted into the upper lid. Table 1 shows the results.

(Consideration by Example)
In Examples 1 and 2, the degree of thinning in the width direction of the anode body was smaller than that in Comparative Example 1, so that the influence of oxidative consumption of the anode body could be reduced. That is, in Examples 1 and 2, it is useful to cover a part of the anode main body with the cover member so that the distance between the outer surface of the anode main body and the inner surface of the cover member is within the range of 0.5 to 20 mm. It can be said that there is.
In addition, in Example 2, the degree of thinning in the width direction of the anode body was considerably smaller than in Example 1. The reason for this is thought to be that silicon nitride has better heat transfer than mullite and easily forms a molten salt solidified layer. Moreover, the silicon nitride cover member has a longer life than the mullite cover member, and the cover member is less likely to crack. Therefore, it is considered that the fact that cracks in the solidified salt layer are less likely to occur due to cracks in the cover member also contributes to the favorable results.

100, 200, 300 molten salt electrolyzer 110 electrolytic cell 112 bottom wall 114 side wall 115 flow port 116 first partition 117, 317 second partition 120 upper lid
121 lid back surface 122 supply port 124 first gas recovery port 126 second gas recovery port 128, 328 supply/discharge port 130, 230 anode 132, 232 anode main body 132a, 232a, 232b outer surface 134, 135, 234 cover member 134a , 234a lower end surfaces 134b, 234b inner surface 136 voids 136a, 136b, 236a, 236b open end 138 molten salt solidified layer 140 cathode 140a upper end surfaces 142, 144 bipolar electrode 150 electrolytic chamber 160 metal recovery chamber 231 flat surface 237 through hole 318 Partition wall 370 of 3 Heat exchange chambers A and B Arrow Bf Molten salt bath S Bath surface

Claims (9)

an anode body used in an electrolytic cell in which a molten salt bath is stored;
a cover member that covers a portion of the anode body;
a gap existing between the anode body and the cover member,
The anode, wherein the distance between the outer surface of the anode main body and the inner surface of the cover member is within the range of 0.5 to 20 mm. 2. The anode according to claim 1, wherein said anode has an open end of said gap portion at a position lower than a height position of said molten salt bath surface. the anode body has at least one step,
3. The anode according to claim 1, wherein said cover member covers at least part of said anode body at a position higher than the flat surface of said step. The anode according to any one of claims 1 to 3, wherein the cover member contains one or more selected from silicon nitride, silicon carbide, aluminum oxide, silicon oxide, magnesium oxide and calcium oxide. Anode according to any one of the preceding claims, wherein the anode body is made of graphite. A molten salt electrolysis device comprising the anode according to any one of claims 1 to 5. A metal production method using the molten salt electrolysis apparatus according to claim 6,
A method for producing a metal, comprising an electrolysis step of electrolyzing a metal chloride contained in the molten salt bath. 8. The method for manufacturing a metal according to claim 7, further comprising a solidified layer forming step of forming a molten salt solidified layer at a position higher than the bath surface of said molten salt bath in said gap. 9. A method for producing a metal according to claim 7 or 8, wherein the metal chloride to be electrolyzed is magnesium chloride.

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