JP3022871B1 - Electrolytic reduction device - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To recover a molten metal having a low carbon concentration by suppressing corrosion of a bottom portion of an electrolytic cell in contact with the molten metal. SOLUTION: The electrolytic reduction apparatus 10 includes an electrolytic cell 11 which stores a molten salt 18 and has a cathode 13 at a bottom portion, and an anode 19 held in the molten salt 18 of the electrolytic cell 11. The molten metal 21 reduced by the electrolysis of the molten salt 18 by being energized can be stored in the bottom of the electrolytic cell 11. A ceramic tile 23 is provided on the inner surface of the bottom of the electrolytic cell 11 in which the molten metal 21 is stored. A plurality of intersecting ridges are formed on the inner surface of the electrolytic cell 11 with which the molten metal 21 contacts, and the ceramic tile 23 is embedded in a plurality of recesses defined by the plurality of ridges. It is preferable to lay a thin plate made of graphite or carbon material on the bottom of the electrolytic cell so as to cover the ceramic tile 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic reduction apparatus for producing an active metal such as uranium in a molten state by molten salt electrolysis.

[0002]

2. Description of the Related Art In molten salt electrolysis, a metal oxide or a metal salt is reduced and formed as a molten metal on a cathode. As a method for producing a metal such as aluminum, a molten salt electrolysis method using a fluoride molten salt as an electrolytic solution is known. Are known. In this molten salt electrolysis method, an electrolytic reduction apparatus having a structure in which an anode is provided above an electrolytic cell and the bottom of the electrolytic cell is used as a cathode is generally used.
Conventionally, such an apparatus as shown in FIG. 5 is known. The electrolytic reduction device shown in FIG. 5 includes an electrolytic cell 1 that stores a molten salt 2 and is connected to a cathode, and an anode 3 that is held in the molten salt 2 of the electrolytic cell 1. Since the electrolytic cell 1 stores molten salt, it is necessary to have corrosion resistance to the molten salt 2 and to be electrically conductive as a condition for forming a cathode. It is made by processing. In this electrolytic cell 1, the electrolytic current is
Is heated by utilizing the heat generated when flowing through the inside of the electrolytic cell, and the strict temperature control of the electrolytic cell causes the fluoride salt portion 2a of the side surface 1a of the electrolytic cell 1 to be in a non-molten state so as to be in a non-molten state.
Is in an insulated state, so that the cathode area is substantially limited to only the bottom of the electrolytic cell 1 to perform electrolysis. In this apparatus, the molten metal reduced by electrolyzing the molten salt by energizing the cathode and the anode is stored at the bottom of the electrolytic cell.

[0003]

However, although graphite or carbon materials are excellent in corrosion resistance to molten salts, they have the disadvantage that they are poor in corrosion resistance to active molten metals. That is, in the above-described electrolytic reduction apparatus, when the active molten metal reduced by electrolysis is stored in the bottom of the electrolytic cell, there is a problem that the bottom of the electrolytic cell in contact with the molten metal is corroded by the molten metal. Further, when the electrolytic cell made of graphite or carbon material is corroded by the molten metal, the carbon concentration of the molten metal generated by reduction increases, and the molten metal is contaminated with carbon. In order to solve this problem, it is conceivable to form the electrolytic cell with a ceramic such as an oxide having good corrosion resistance against molten metal, but there is a problem that the ceramic is significantly corroded by molten salt initially stored in the electrolytic cell. . It is an object of the present invention to provide an electrolytic reduction apparatus capable of suppressing corrosion of the bottom of an electrolytic cell in contact with a molten metal and recovering a molten metal having a low carbon concentration.

[0004]

The invention according to claim 1 is
As shown in FIGS. 1 and 2, a bottomed cylindrical portion stored the molten salt 18
Electrolyzer 11 having cathode 13 on which bottom 13a is formed
And an anode 19 held in the molten salt 18 of the electrolytic cell 11, and the molten metal 21 reduced by energizing the cathode 13 and the anode 19 to electrolyze the molten salt 18 has a bottomed cylindrical portion.
This is an improvement of the electrolytic reduction device configured to be able to store in the storage device 13a . The characteristic configuration is a bottomed bottom where molten metal 21 is stored.
A plurality of ridges 24 crossing each other are formed on the inner surface of the cylindrical portion 13a.
Formed by a plurality of ridges 24
The ceramic tiles 23 are embedded in the concave portions 26 in the number . In the invention according to the first aspect, the tile made of ceramic having good corrosion resistance to the molten metal is provided on the inner surface of the bottomed cylindrical portion 13a in which the molten metal 21 is stored, so that the electrolytic bath 11 is formed by the stored molten metal 21. Prevents corrosion. Insulation on inner surface of bottomed cylindrical part 13a
Is stored in the electrolytic cell 11 even if the ceramic tile 23 is provided.
Molten metal 21 contacts the tip of the ridge 24 to form a cathode.
To achieve. The ridges 24 that the molten metal 21 contacts are corroded.
However, between the ceramic tiles 23, the ridges 24 are reduced in corrosion.
After the pit is formed, the molten metal 21 in the pit becomes
It stays inside the depression. Because of this, it stays in the depression
The carbon concentration of the molten metal 21 rises and the ridges
4 is suppressed, and the carbon concentration of the molten metal 21 other than the depressions is reduced.
Prevent the degree from rising.

The invention according to claim 2 is the invention according to claim 1, wherein the thin plate 27 made of graphite or carbon material is made of ceramic.
Laid on the bottom of the electrolytic cell 11 so as to cover the
The is an electrolytic reduction apparatus. In the invention according to claim 2,
Means that molten salt 18 is graphite before molten metal 21 is stored.
Contacting the surface of a thin plate 27 made of
The tile 23 is prevented from coming into contact with the molten salt 18 and
Corrosion of ceramic tile 23 by molten salt 18
To prevent After the molten metal 21 is stored, the thin plate 27 becomes rotten.
The ceramic tiles 23 that disappear and disappear afterwards are black
Corrosion of the electrolytic cell 11 made of lead or the like is suppressed.

[0006] The invention according to claim 3 is the invention according to claim 1 or 2, ceramic tiles (23) from Y ₂ O ₃
It is composed of electrolytic reduction apparatus. In the invention according to claim 3, Y ₂ O ₃ has good corrosion resistance to molten metal.
Therefore, the electrolytic cell 11 may be corroded by the molten metal 21.
Can be effectively prevented.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electrolytic reduction apparatus according to the present invention will be described with reference to the drawings. This electrolytic reduction apparatus 10 is an active metal uranium oxide (UO ₂ , U ₃ O _8, etc.)
Is suitable for electrolytic reduction. As shown in FIG. 1, an electrolytic cell 11 of this apparatus 10 is constituted by a cell body 12 made of graphite and a conductive member 13 made of graphite. The tank main body 12 is a bottomed cylindrical body, and has a circular opening 12a at the center of the bottom. The conductive member 13 is provided in the opening 12a so as to have a predetermined gap with the opening 12a. Specifically, the conductive member 13 is provided with the opening 12 a via the insulating material 14.
The tank body 12 and the conductive member 13 are spaced apart from each other at an appropriate distance and insulated, and a cathode is connected to the conductive member 13.

The portion of the conductive member 13 facing the inside of the tank body 12 is formed in a bottomed cylindrical portion 13 a, and the upper edge of the cylindrical portion 13 a is formed lower than the inner bottom surface of the tank body 12. A coating member 16 made of boron nitride, which is an insulating member, is provided between the periphery of the opening 12a of the tank body 12 and the periphery of the distal end of the bottomed cylindrical portion 13a. The upper surface of the covering member 16 is formed so as to be flush with the bottom surface of the tank body 12, and the lower end of the covering member 16 has an outer shape capable of being inserted into the bottomed cylindrical portion 13a with a predetermined gap. 16a are formed. Introducing passage 1 for the inert gas communicating with the gap between conductive member 13 and tank body 12
2b, a gas cylinder (not shown) is provided outside the tank body 12 as gas supply means for feeding an inert gas under pressure to the introduction flow path 12b. An anode 19 is provided in the molten salt 18 of the tank body 12 while being held.

The tank body 12 is provided with a partition wall 12c with a lower end spaced from the bottom by a predetermined distance.
A supply port 12 d for supplying uranium oxide as a raw material into the molten salt 18 is formed by c and the side wall of the tank body 12. A heater 17 is provided outside the tank body 12 so that the salt is melted by heating to be used as an electrolytic solution of the electrolytic tank 11. On the other hand, the conductive member 13 is formed with a crank-shaped discharge port 13b which is connected to the bottomed cylindrical portion 13a so as to discharge the molten metal 21 generated by the electrolysis, and is vertically connected to the middle of the discharge port 13b. A hole 12 e is formed in the side wall of the tank body 12. A cut-off rod 22 having a ceramic sealing plug 22a at its tip is inserted into the vertical hole 12e. When the cut-off rod 22 rises as shown by a solid line arrow in the figure, the discharge port 13b is opened and a broken line is drawn. When descending as indicated by the arrow, the discharge port 13b is shut off.

In the electrolytic cell 11, a gap is provided between the opening 12a and the conductive member 13 so that the conductive member 13
The electrically conductive member 13 acts as a cathode at the bottom of the electrolytic cell 11 by electrically insulating between the cell and the cell body 12 and electrically connecting to the cathode. The tank body 12 of the electrolytic cell 11
A supporting salt is put into the molten state, and at the same time, an inert gas is introduced into a gap between the opening 12a and the conductive member 13 by a gas cylinder as a gas supply means through an introduction flow path 12b as indicated by a solid line arrow in the drawing. As shown in the drawing, the molten salt 18 is prevented from entering the gap by pressure feeding.

[0011] After melting supporting salt which is placed in the electrolytic bath 11 is heated by the heater 17 in the electrolytic reduction apparatus 10, by energizing the conductive member 13 made of an anode 19 and a cathode, UO ₂ of the raw material in this state When a metal oxide such as U ₃ O ₈ is supplied to the tank body 12, the metal oxide is electrolytically reduced, and the metal cations in the molten salt 18, which is an electrolytic solution, are contained in the conductive member 13 which is a cathode. Molten metal 2 is applied to the inner surface of
It becomes 1 and precipitates. The generated molten metal 21
Is stored in the bottomed cylindrical portion 13a due to the difference in specific gravity, and the metal 21 stored in the bottomed cylindrical portion 13a is raised via the discharge rod 13b provided in the conductive member 13 by raising the blocking rod 22. And can be collected.

The feature of the present invention is that the ceramic tile 2 is provided on the inner bottom surface of the conductive member 13 in which the molten metal 21 is stored.
3 is provided. As shown in FIG. 2, in this embodiment, a plurality of ridges 24 that intersect each other are formed on the inner surface of the conductive member 13 with which the molten metal contacts, and a plurality of ridges 24 formed by being partitioned by the plurality of ridges 24 are formed. Recess 26
The ceramic tile 23 is embedded. As shown in FIGS. 2 and 3, in this embodiment, a hole 26 a is further formed inside the concave portion 26 formed by the ridge 24, and the ceramic tile 23 has a thickness corresponding to the depth of the concave portion 26. And a flat plate portion 23a fitted into the concave portion 26 to form the inner surface of the electrolytic cell, and a hole 26a formed in the concave portion 26.
The ceramic tile 23 is embedded in the concave portion 26 with an adhesive.

More specifically, a pair of grooves 23c facing the inner surface of the hole 26a are formed on both sides of the projection 23b, and a square bar 25 having the same cross section as the cross section of the groove 23c is formed. 23c is inserted so as to fill it. The square bar 25 is made of graphite, which is the same material as the conductive member 13, and an adhesive containing carbon and firmly bonding graphite or the like is used. The adhesive is a square bar 25 inserted into the groove 23c.
In this state, the projection 23b is inserted into the hole 26a together with the square bar 25. The adhesive is applied to the side wall of the hole 26a facing the square bar 25 (the portion shown by hatching in FIG. 2).
May be applied. As a result, as shown in the enlarged view of FIG. 3, the square bar 25 is adhered to the side wall of the hole 26a to prevent the protrusion 23b from coming off from the hole 26a, and the flat plate in which the protrusion 23b is integrally formed. The portion 23a is buried in the concave portion 26. Thus, the surface of the ceramic tile 23 buried in the concave portion 26 is flush with the tip surface of the ridge 24 to form the inner surface of the electrolytic cell.

As shown in FIG.
A thin plate 27 made of graphite or a carbon material is laid on the bottom of the conductive member 13 which is an electrolytic cell embedded in the concave portion 26 so as to cover the ceramic tile 23. The thickness of the thin plate 27 is determined by the liquid depth of the molten salt 18 and is 0.1 mm to 3 mm.
It is preferred that Thin plate 2 in this embodiment
7 is a ceramic tile 23 made of an adhesive containing carbon.
Is adhered to the surface of the ridge and the front end face of the ridge 24, and is laid so as to be electrically connected to the cathode through the ridge 24. In the electrolytic reduction apparatus 10 configured as described above, when the supporting salt placed in the electrolytic cell 11 is melted by heating by the heater 17, the molten salt is applied to the electrolytic cell 11 made of graphite and the thin plate 27 made of graphite. Contact with surface. For this reason, the thin plate 27
Prevents the ceramic tile 23 from coming into contact with the molten salt 18 and prevents the ceramic tile 23 from being corroded by the molten salt 18.

Thereafter, when the anode 19 and the conductive member 13 serving as the cathode are energized to supply the metal oxide to the tank body 12,
The electrolytic reduction of the metal oxide is performed, and the molten metal 21 is deposited on the bottomed cylindrical portion 13a of the conductive member 13 serving as the cathode. The deposited molten metal 21 is separated from the bottomed cylindrical portion 1 by the difference in specific gravity.
Store in 3a. The molten metal 21 corrodes a thin plate 27 made of graphite laid so as to cover the ceramic tile 23. The ceramic tile 23 appearing after the thin plate 27 has been corroded and disappeared has corrosion resistance to the molten metal 21 and has a corrosion resistance. I will not do it. For this reason, the ceramic tile 23 prevents the conductive member 13 made of graphite from coming into contact with the molten metal and suppresses the electrolytic cell 11 from being corroded by the molten metal 21.

As shown in FIG. 4, after the thin plate 27 has been corroded and disappeared, the molten metal 21 comes into contact with the ridge 24, and the molten metal 21 corrodes the ridge 24.
The molten metal 21 in the depressed portion due to the reduced corrosion is interposed between the ceramic tiles 23 and stays. For this reason,
Molten metal 2 stagnating in depressions between ceramic tiles 23
The carbon concentration of No. 1 increases, and the corrosion of the ridges 24 of a predetermined amount or more is suppressed. Further, since the molten metal 21 having an increased carbon concentration stays in the depression, the increase in the carbon concentration of the molten metal 21 stored in the bottomed cylindrical portion 13 a other than the depression is suppressed, and the discharge port of the conductive member 13 is reduced. Prevents the molten metal 21 recovered via 13b from being contaminated by carbon.

[0017]

Next, embodiments of the present invention will be described. Example 1 An apparatus shown in FIG. 1 and a fluoride for producing a fluoride molten salt 18 were prepared. The ceramic tile 23 provided on the inner surface of the bottom of the electrolytic cell was made of Y ₂ O ₃ , and this ceramic tile 23 was covered with a thin plate 27 of 0.3 mm thick graphite. As the fluoride, a mixture consisting of 74% by weight of BaF ₂ , 11% by weight of LiF, and 15% by weight of UF ₄ was prepared. The fluoride mixture was supplied to the tank main body 12, and an electric current was supplied to the induction heating coil of the heater 17 to heat the electrolytic tank 11, and the temperature was gradually raised to 1200 ° C., which was equal to or higher than the melting point of uranium. At the same time, the opening 12
When the inert gas argon is pressure-fed from the gas cylinder as the gas supply means to the gap between the a and the conductive member 13 through the introduction flow path 12b, and the supplied fluoride mixture becomes the molten salt 18, The molten salt 18 was prevented from entering the gap.

Next, the anode 19 was inserted into the molten fluoride salt 18 from above the tank body 12, and the current was applied at a cathode current density of 0.7 to 1.6 A / cm ² using the conductive member 13 as a cathode. Thereafter, UO ₂ as a raw material was supplied from the supply port 12d to perform molten salt electrolysis. By this molten salt electrolysis, uranium ions (U ⁴⁺ ) in the molten salt 18 as the electrolytic solution are deposited as molten metal uranium 21 on the inner surface of the bottomed cylindrical portion 13a of the conductive member 13 as the cathode, and are deposited. It was stored in the bottom cylindrical portion 13a. When a predetermined amount of metal uranium 21 was deposited, the blocking rod 22 was raised to open the discharge port 13b, and the molten metal uranium 21 was discharged through the discharge port 13b by a predetermined amount. Thereafter, the shut-off rod 22 is lowered again to shut off the discharge port 13b, and the raw material uranium oxide is newly supplied from the supply port 12d by the amount discharged by the molten metal uranium 21, thereby continuously performing electrolytic reduction. went.

Comparative Example 1 An electrolytic reduction apparatus having the same structure as in Example 1 was prepared except that the ceramic tile 23 made of Y ₂ O ₃ and the thin plate 27 made of graphite were not provided.
Was supplied to the electrolytic cell, and the temperature was raised to 1200 ° C. by an electric furnace to be melted. Then, uranium oxide as a raw material was put into an electrolytic cell, and Example 1 was omitted except for electrolysis time.
Electrolysis was carried out under the same conditions and procedure as described above.

<Comparative Test and Evaluation> In Example 1, each of the metal uranium discharged through the discharge port 13b after 10 hours from the start of electrolysis and the metal uranium discharged after 50 hours from the start of electrolysis, The carbon concentration was measured. As a result, the carbon concentration of metallic uranium discharged after 10 hours was 200 ppm, but the carbon concentration of metallic uranium discharged after 50 hours was 150 ppm. It is considered that the carbon concentration of the metallic uranium discharged after 10 hours was 200 ppm because the thin plate 27 made of graphite was corroded, and the carbon concentration of the metallic uranium discharged after 50 hours was 150 ppm. It is considered that the thin plate 27 disappeared.

In Comparative Example 1, metal uranium discharged through the discharge port 13b 10 hours after the start of electrolysis,
The respective carbon concentrations of the metallic uranium discharged 20 hours after the start of electrolysis were measured. As a result, the carbon concentration of each metallic uranium discharged after the passage of 10 hours and 20 hours was 200 ppm. The carbon concentration is still 200 ppm even after 10 hours or more,
It is considered that in Comparative Example 1, the electrolytic cell made of graphite was always corroded by metallic uranium as a molten metal. Further, in Example 1, the electrolytic cell was disassembled 70 hours after the start of electrolysis, and in Comparative Example 1, the electrolytic cell was disassembled 20 hours after the start of electrolysis, and the electrolytic uranium of Example 1 and Comparative Example 1 was stored. The bottom of the tank was visually observed. As a result, although the thin plate 27 laid on the bottom surface of the electrolytic cell in Example 1 had almost disappeared, the ceramic tile 23 did not show any signs of damage. On the other hand, traces of corrosion were observed in the graphite on the bottom surface of the electrolytic cell of Comparative Example 1.

[0022]

As described above, according to the present invention, the ceramic tile having good corrosion resistance to the molten metal is provided on the inner surface at the bottom of the electrolytic cell in which the molten metal is stored. Can be suppressed from being corroded. In particular, if a plurality of intersecting ridges are formed on the inner surface of the electrolytic cell in contact with the molten metal, and the ceramic tiles are embedded in a plurality of concave portions formed by the plurality of ridges, the ridges are stored in the electrolytic cell. The molten metal that comes into contact with the tips of the ridges can form a cathode. in this case,
The ridges that the molten metal contacts are corroded, but after the ridges have been corroded and reduced, causing a depression between the ceramic tiles, the molten metal in that depression stays inside the depression, so it stays in the depression. As a result, the carbon concentration of the molten metal increases and the corrosion of the ridges of a predetermined amount or more is suppressed, and the carbon concentration of the molten metal other than the depressions can be prevented from increasing. In addition, if a thin plate made of graphite or carbon material is laid on the bottom of the electrolytic cell so as to cover the ceramic tile, the molten salt before the molten metal is stored is prevented from contacting the ceramic tile, and the ceramic tile is melted. Corrosion due to salt can be prevented. In this case, the thin plate is corroded and disappeared after the molten metal is stored, and the ceramic tile that appears thereafter suppresses the corrosion of the electrolytic cell made of graphite or the like.

[Brief description of the drawings]

FIG. 1 is a central longitudinal sectional view of an electrolytic reduction device of the present invention.

FIG. 2 is a perspective view showing a relationship between an inner bottom portion of the electrolytic cell in which a ridge is formed and a ceramic tile.

FIG. 3 is an enlarged sectional view of a portion A in FIG. 1;

FIG. 4 is an enlarged sectional view of a portion B in FIG. 3 after the thin plate has been corroded and disappeared.

FIG. 5 is a cross-sectional view corresponding to FIG. 1, showing a conventional electrolytic reduction device.

[Explanation of symbols]

 Reference Signs List 10 electrolytic reduction device 11 electrolytic bath 13 conductive member (cathode) 18 molten salt 19 anode 21 molten metal 23 ceramic tile 24 ridge 26 concave portion 27 thin plate

Continuing from the front page (72) Inventor Yasushi Hoshino 14-headed six-headed character, Mukaiyama, Naka-machi, Naka-gun, Naka-gun, Ibaraki Pref. 271389 (JP, A) JP-A-11-80987 (JP, A) JP 40-28441 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25C 7 / 00,3 / 34

Claims (3)

(57) [Claims] 1. A bottomed cylindrical portion (13a) for storing a molten salt (18).
An electrolytic cell (11) having a cathode (13) at the bottom, and an anode (19) held in a molten salt (18) of the electrolytic cell (11),
Energizing the cathode (13) and the anode (19), the molten salt (1
8) The molten metal (21) reduced by electrolysis is
In the electrolytic reduction device configured to be stored in the bottomed cylindrical portion (13a), an inner surface of the bottomed cylindrical portion (13a) in which the molten metal (21) is stored.
A plurality of ridges (24) crossing each other are formed, and a plurality of ridges formed by being partitioned by the plurality of ridges (24) are formed .
Note that the ceramic tile (23) was buried in the recess (26).
Electrolytic reduction apparatus according to symptoms. 2. A thin plate made of graphite or carbon material (27)
Laying at the bottom of the electrolytic cell (11) so as to cover the Mic tile (23)
The electrolytic reduction device according to claim 1 , wherein: 3. A ceramic tile (23) is electrolytically reduced device <br/> claim 1 or 2, wherein consists Y ₂ O _3.