JP2997265B1 - Electrolytic reduction device - Google Patents

Abstract

A relatively inexpensive and large-capacity electrolytic reduction device that can reliably insulate a cathode portion electrically from an electrolytic cell, improve the cathode current density and increase the recovery rate of molten metal, Can be provided. An electrolytic reduction device is configured to store a molten salt (18) and form a concave part (11) in a part of a bottom part, and to provide a predetermined gap between the concave part and the concave part in the concave part and to electrically insulate the electrolytic tank. A conductive container 13 provided, an inert gas introduction passage 12a communicating with the gap, gas supply means for pressure-feeding the inert gas into the introduction passage so as to blow out into the electrolytic bath, The apparatus includes a heater 17 provided outside to make a molten salt 18 into a molten state to be used as an electrolytic solution in an electrolytic cell, and an anode 19 held in the molten salt in the electrolytic cell. The periphery of the recess and the periphery of the upper end of the container are covered with a lid 16, and a conductive projection 13a serving as a cathode is provided at the bottom of the conductive container so as to protrude from the recess.

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 a metal having a plurality of valences in a molten state in a molten salt such as uranium 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 a device as shown in FIG. 4 is known. That is, the electrolytic cell 1 is heated by using heat generated when an electrolytic current flows through the molten salt 2, and the fluorinated salt portion 2 a of the side surface 1 a of the electrolytic cell 1 is controlled by strict temperature control of the electrolytic cell. By making the side portion 1a of the electrolytic cell in a non-molten state and insulated, the cathode area is substantially reduced.
Electrolysis is performed only on the bottom portion of the substrate, and a required cathode current density can be obtained. Further, as shown in FIG. 5, a molten salt bath 5 is generated in an Al electrolytic cell 4 having an insulating layer 3 on the inner surface, an anode 6 is suspended from above in the molten salt bath 5, and a cathode 7 is solid or The cathode 7 is provided at the bottom of the electrolytic cell 4 so as to protrude from a bath surface of a molten Al pad 8 formed at the bottom of the electrolytic cell 4. The gap between the lower surface of the anode 33 and the upper surface of the cathode 30 is specified. A method of electrolytically producing a metal is known in which the distance between the electrodes is reduced by reducing the distance between the electrodes by reducing the distance between the electrodes.
1,420).

[0003]

However, in the former molten salt electrolysis method shown in FIG. 4, since only the salt portion 2a on the side surface of the electrolytic cell is in a non-molten state, an insulating portion is formed on the side surface of the electrolytic cell. Temperature control around the melting point of the molten salt is required,
There is a problem that strict temperature control of the entire electrolytic cell is required during operation of the apparatus. Also, in aluminum electrolysis, since the melting point of aluminum is lower than the melting point of the supporting salt, aluminum is produced as a melt even when the supporting salt temperature is a temperature at which the supporting salt is partially frozen. Since the melting point of uranium is higher than the melting point of the supporting salt, uranium is in a solid state at a temperature at which a part of the temperature of the supporting salt is frozen, so that there is a problem that it is difficult to handle the generated metal thereafter. Further, it is difficult to make the cathode area smaller than the anode area by controlling the cathode area while keeping the side surface portion 1a of the electrolytic cell 1 in an insulated state, and the electrolysis at a high cathode current density such as uranium having a plurality of ion species is difficult. In the case of metals that require, the electrolysis may be difficult. In such a case, it is conceivable to increase the electrolysis current, but increasing the electrolysis current is accompanied by an increase in the anode current density, and the possibility that the so-called anodic effect in which the anode is covered with bubbles increases, which is not preferable. .

In the latter electrolytic manufacturing method shown in FIG.
Since the electrolytic cell 4 and the protruding cathode 7 are electrically connected to each other, when the insulating property of the insulating layer 3 is deteriorated, there is a problem that metal is easily deposited also in the electrolytic cell 4 in that portion.

SUMMARY OF THE INVENTION It is an object of the present invention to reliably insulate the cathode portion from the electrolytic cell, improve the cathode current density and increase the recovery rate of molten metal, and provide a relatively inexpensive and large-capacity battery. An electrolytic reduction device is provided.

[0006]

The invention according to claim 1 is
As shown in FIG. 1, an electrolytic cell 12 in which a molten salt 18 is stored and a concave portion 11 is formed in a part of a bottom portion, and a concave portion 11 is formed in the concave portion 11.
And a conductive container 13 provided with a predetermined gap and electrically insulated from the electrolytic cell 12, an inert gas introduction flow path 12 a communicating with the gap, and blown into the electrolytic cell 12. A gas supply means for pumping an inert gas into the introduction channel 12a, a heater 17 provided outside the electrolytic cell 12 to make the molten salt 18 into a molten state and serve as an electrolytic solution for the electrolytic cell 12, and a molten salt for the electrolytic cell 12 An electrolytic reduction device comprising an anode 19 held in an electrocatalyst 18, wherein a lid 16 is provided to cover the periphery of the concave portion 11 of the electrolytic cell 12 and the periphery of the upper end of the conductive container 13. An electrolytic reduction apparatus characterized in that one or more conductive projections 13a serving as cathodes are provided so as to protrude from the recesses 11. By providing a gap between the recess 11 and the conductive container 13, the conductive container 1
3 and the electrolytic cell 12 are electrically insulated. The recess 11 and the conductive container 1 are introduced by the gas supply means through the introduction channel 12a.
By pumping the inert gas into the gap between the molten salt 18 and the molten salt 3, the molten salt 18 is prevented from entering the gap. In this state, when electricity is supplied to the anode 19 and the conductive projection 13a serving as a cathode to perform electrolytic reduction, current concentrates on the projection 13a projecting from the concave portion 11, and metal cations in the molten salt 18 are deposited on the projection 13a by molten metal. The molten metal 21 flows down along the protrusion 13 a and is stored in the conductive container 13.

[0007] Further, the lid 16 is placed on the periphery of the concave portion 11 and the conductive container 1.
3 is provided between the periphery of the concave portion 11 and the conductive container 13 so as to cover the periphery of the upper end of the cathode 3 to prevent the molten salt from entering the gap even if the amount of the inert gas to be pumped is reduced. Since the distance between the conductive projection 13a and the anode 19 can be reduced, the current density of the cathode can be improved and the recovery rate of the molten metal can be increased.

The invention according to a second aspect is the invention according to the first aspect, wherein the plurality of conductive protrusions 13 a
Is an electrolytic reduction device provided symmetrically with respect to the center of the bottom. By using the plurality of conductive protrusions 13a, the surface area of the cathode facing the anode increases, and the recovery rate of the molten metal increases. The invention according to claim 3 is the invention according to claim 1, which is an electrolytic reduction device in which the lid 16 is an insulating member. By forming the lid 16 with an insulating member, even if the molten salt enters the gap, the area of the conductive container 13 serving as a cathode is prevented from being enlarged.

The invention according to claim 4 is the invention according to claims 1 to 3
An invention according to any one of the above, wherein the conductive container 13 is an electrolytic reduction device provided at the bottom of the electrolytic cell 12 via an insulating material 14. By installing the conductive container 13 with the insulating material 14 interposed therebetween, the conductive container 13 can be easily provided at the bottom of the electrolytic cell 12 with a certain gap from the concave portion 11.

[0010] The invention according to claim 5 is the invention according to claims 1 to 4.
An invention according to any one of the above, wherein the electrolytic cell 12, the conductive container 13, and the conductive protrusion 13a are each made of graphite, and the lid 16 is made of boron nitride. By using graphite and boron nitride as materials, the amount of relatively expensive boron nitride bulk material used can be reduced, and the device can be manufactured at low cost.

[0011]

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 uses uranium oxide (UO ₂ , U ₃₎ , which is a metal having multiple valences.
O ₈ ) is suitable for electrolytic reduction. As shown in FIG. 1, an electrolytic cell 12 made of graphite is a cylindrical body having a through hole 10 at the bottom, and a circular recess 11 is formed at the center of the bottom. A circular graphite conductive container 13 is provided in the recess 11 so as to have a predetermined gap with the recess 11. A single conductive protrusion 13 serving as a cathode is provided on the bottom of the conductive container 13.
a is provided so as to protrude from the concave portion 11. The conductive container 13 is provided at the bottom of the recess 11 via an insulating material 14 made of boron nitride. The insulating material 14 separates the electrolytic cell 12 and the conductive container 13 at an appropriate distance and electrically insulates the electrolytic cell 12 from the conductive container 13.
Between the periphery of the concave portion 11 of the electrolytic cell 12 and the periphery of the tip of the conductive container 13, a circular boron nitride lid 16 which is an insulating member is provided.
Is provided. The upper surface of the lid 16 is formed so as to be flush with the bottom surface of the electrolytic cell 12, and the lid 16 has an insertion tube portion 16a having an outer shape whose lower end can be inserted into the conductive container 13 with a predetermined gap. Is done. Introducing channel 12 for an inert gas communicating with a gap between conductive vessel 13 and electrolytic vessel 12
a is formed, and a gas cylinder (not shown) serving as a gas supply means for feeding an inert gas under pressure is provided in the introduction flow path 12a (not shown). Molten salt 18 of electrolytic cell 12
Inside, an anode 19 is held and provided. In addition, electrolytic cell 12
A heater 17 is provided outside of the heater 17 so that the molten salt 18 is turned into a molten state by heating and used as an electrolytic solution in the electrolytic cell 12.

In the electrolytic reduction apparatus configured as described above,
Since a gap is provided between the concave portion 11 and the conductive container 13,
The conductive container 13 and the electrolytic cell 12 are electrically insulated. A supporting salt is put into an electrolytic cell 12 of this electrolytic reduction device to be in a molten state.
The molten salt 18 is prevented from intruding into the gap by feeding an inert gas through the introduction flow path 12a as shown by the solid line arrow in FIG. It should be noted that, besides heating by a heater 17 provided outside the electrolytic cell 12 to bring the supporting salt into a molten state, the supporting salt may be melted using heat generated when an electrolytic current flows.

After the supporting salt is melted, when current is supplied to the anode 19 and the conductive projection 13a serving as a cathode, a current is concentrated on the projection 13a, and an effective current flows between them. When a metal oxide such as UO ₂ or U ₃ O _{8 as a} raw material is supplied to the electrolytic cell 12 in this state, the metal oxide is electrolytically reduced, and the metal cations in the molten salt 18 as an electrolytic solution are projected. 1
Molten metal is deposited on the surface of 3a. The molten metal 21 flows down along the protrusion 13 a due to a specific gravity difference from the molten salt and is stored in the conductive container 13. The metal 21 stored in the conductive container 13 is recovered by a vacuum suction device or a siphon device (not shown) or through an outlet 13b provided in the device as shown in FIG. In addition,
In the electrolytic reduction apparatus according to the embodiment shown in FIG. 1, a single conductive projection 13a is provided at the bottom of the conductive container 13 so as to project from the recess 11, but the number of the projections is two or three. ,
The number may be four or more. For example, as shown in FIGS. 3A and 3B, four conductive protrusions 13a may be provided symmetrically with respect to the center of the bottom of the conductive container 13.

[0014]

Next, embodiments of the present invention will be described. <Example 1> As shown in FIG.
An electrolytic cell 12 of cm ³ was prepared. That is, the graphite electrolytic cell 12 is a cylindrical body having the through hole 10 at the bottom, and the circular concave portion 11 is formed at the center of the bottom. Electrolysis tank 12
The lower end of the partition wall 12 is spaced apart from the bottom by a predetermined distance.
b, a supply port 12 c for supplying uranium oxide as a raw material into the molten salt 18 was formed by the partition wall 12 b and the side wall of the electrolytic cell 12. A heater 17 was provided outside the electrolytic cell 12 so that the salt was melted by heating to be used as an electrolytic solution in the electrolytic cell. The concave portion 11 is a circular hole formed at the bottom of the electrolytic cell 12 and has an inner diameter of 126.
A circular graphite conductive container 13 having a depth of 70 mm and a depth of 70 mm was placed at the bottom with a predetermined gap from the recess 11 via an insulating material 14 made of boron nitride. Conductive container 13
Between the recess 11 and the insertion cylinder 1 having an outer diameter of 116 mm.
6a, a circular lid 16 made of boron nitride is fitted therein, and the gap between the conductive container 13 and the insertion cylinder 16a is 5 mm.
Was sealed at the bottom of the electrolytic cell 12. A conductive projection 13a serving as a cathode is formed on the bottom of the conductive
It was provided so as to protrude more.

The conductive container 13 is formed with a crank-shaped outlet 13b capable of discharging the molten metal 21 generated by electrolysis, and a vertical hole 12d is formed so as to communicate with the middle of the outlet 13b. A blocking rod 24 formed on the side wall of the tank 12 and having a ceramic sealing plug 24a at the end was inserted into the vertical hole 12d. The shut-off rod 24 is configured to open the outlet 13b when raised as shown by a solid arrow in the drawing, and to shut off the outlet 13b when lowered as shown by a broken arrow. Next, a fluoride for forming the fluoride molten salt 18 was prepared. This fluoride contains 74% by weight of BaF ₂ , 11% by weight of LiF,
5 is a mixture of about 180kg consisting wt% of UF ₄ Prefecture. This fluoride mixture was supplied to the electrolytic cell 12, and the high-frequency induction heating coil of the heater 17 was energized to heat the electrolytic cell 12, and the temperature was gradually raised to 1200 ° C., which was higher than the melting point of uranium. At the same time, an inert gas, argon, was pumped into the gap between the recess 11 and the conductive container 13 from the gas cylinder, which is a gas supply means, through the introduction channel 12a, and the supplied fluoride mixture became a molten salt. Sometimes, the molten salt was prevented from entering the gap.

Next, the anode 19 is inserted into the fluoride molten salt 18 from above the electrolytic cell 12, and the current is applied to the conductive projection 13a as a cathode at a cathode current density of 0.7 to 1.6 A / cm ^2. After that, UO ₂ as a raw material was supplied from a supply port 12c to perform molten salt electrolysis. By this molten salt electrolysis, uranium ions (U ⁴⁺ ) in the molten salt 18 which is an electrolytic solution are deposited as uranium metal on the projections 13a, and this uranium ion
1 flows down along the protrusion 13 a and is stored in the conductive container 13. By raising the blocking rod 24 in this state and opening the discharge port 13b, the molten metal uranium 2
1 could be discharged through the outlet 13b, and the electrolysis work could be restarted again by lowering the shut-off rod 24 again to shut off the outlet 13b. Therefore, in the electrolytic reduction apparatus in Example 1, the raw material uranium oxide was newly supplied from the supply port 12c by the amount discharged from the molten metal uranium 21, so that the electrolytic reduction could be continuously performed.

Comparative Example 1 An electrolytic cell having the same structure as the electrolytic cell 1 shown in FIG. 4 and having a capacity of about 400 liters was prepared, and a fluoride having the same composition as in Example 1 was supplied to the electrolytic cell.
The temperature was raised to 1200 ° C. by an electric furnace to be melted. Thereafter, the raw material uranium oxide was placed in an electrolytic cell and electrolysis was performed.
At this time, although the cathode area is not particularly limited, electrolysis was performed with a cathode current density of about 0.4 A / cm ² barely maintained by increasing the volume of the cell and performing scale-up.

<Comparative Example 2> Although not shown, electrolysis was performed under the same conditions and procedures as in Example 1 except that the graphite electrolytic cell of Example 1 and the cathode were short-circuited. At this time, the cathode current density was 0.1 A / cm ² or less.

<Comparative Test and Evaluation> Example 1, Comparative Example 1
After the electrolysis in Comparative Example 2 was completed, each electrolytic cell was disassembled. As a result of visually observing the gap between the concave portion 11 of the electrolytic cell 12 of Example 1 and the conductive container 13, no intrusion of the molten salt was observed, and a space was secured. Further, metal uranium, which is an electrolysis product obtained by dismantling the electrolytic cells of Example 1, Comparative Examples 1 and 2, was taken out, and the current efficiency in molten salt electrolysis was measured from the amount of each metal uranium. As a result, the current efficiency in Example 1 was 55% or more, while that in Comparative Example 1 was about 30%. In Comparative Example 2, almost no metal uranium was precipitated, and thus the current efficiency was almost 0%. This is probably because the cathode current density in Comparative Example 1 was slightly insufficient.
Further, the reason why almost no metal uranium was precipitated in Comparative Example 2 is considered to be because the cathode current density was absolutely insufficient. Moreover, since electrolysis was effectively performed in Example 1 and metal uranium was not obtained in Comparative Example 2, it was found that the conductive container 13 was reliably insulated from the electrolytic tank 12.

[0020]

As described above, according to the present invention, a predetermined gap is formed in the recess formed in a part of the bottom of the electrolytic cell, and the conductive part is electrically insulated from the electrolytic cell. Provide an inert container, the introduction flow path of an inert gas communicating with the gap,
A gas supply means for pumping an inert gas into the introduction flow path, and an anode held in a molten salt in an electrolytic cell; and a conductive projection serving as one or more cathodes at the bottom of the conductive container is provided in the recess. Since the electrodes are provided so as to protrude, when the electrolysis is performed, the current concentrates and flows effectively between the conductive projections serving as the cathode and the anode. As a result, the cathode part can be reliably electrically insulated from the electrolytic cell, and the cathode current density can be improved to increase the recovery rate of the molten metal.

Further, if the lid is provided between the periphery of the concave portion and the periphery of the upper end of the conductive container, it is possible to prevent the molten salt from entering the gap even if the amount of the inert gas to be fed is reduced. Furthermore, if the electrolytic cell, the conductive container, and the conductive protrusions are each made of graphite, and the lid is made of boron nitride, the amount of expensive boron nitride bulk material can be reduced, and a relatively inexpensive and large-capacity battery can be used. An electrolytic reduction device can be obtained.

[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 central longitudinal sectional view of another electrolytic reduction device of the present invention.

FIG. 3A shows another conductive container of the present invention.
FIG. 2B is a sectional view taken along line AA.

FIG. 3 (b) is a plan view of FIG. 3 (a).

FIG. 4 is a sectional view corresponding to FIG. 1, showing a conventional electrolytic reduction device.

FIG. 5 is a partial sectional perspective view corresponding to FIG. 1 showing another conventional electrolytic reduction apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Concave part 12 Electrolysis tank 12a Introducing channel 13 Conductive container 13a Conductive protrusion 14 Insulating material 16 Cover 17 Heater 18 Molten salt 19 Anode

Continued on front page (72) Inventor Yasushi Hoshino 14-headed character, Mukaiyama, Naka-machi, Naka-machi, Naka-gun, Ibaraki Prefecture 1002 14 Mitsubishi Materials Corporation General Research Institute Environmental and Energy Research Laboratory (72) Inventor Hiroshi Takazawa Naka, Ibaraki Prefecture Mitsubishi Materials Co., Ltd.Environmental and Energy Research Laboratories, 1002, 1002, Mukaiyama-shi, 6-head, Naka-machi, Gunma (72) Inventor Takeshi Takeshi, Okayama, Naka-machi, Naka-gun, Naka-gun, Ibaraki Pref. Materials Co., Ltd. Research Laboratory Environment and Energy Research Laboratory (56) References JP-A-11-229173 (JP, A) JP-A-8-67998 (JP, A) JP-A-3-271389 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C25C 7/00, 3/34

Claims (5)

(57) [Claims] 1. A recess (11) for storing a molten salt (18) in a part of a bottom portion.
Formed in the electrolytic cell (12), a conductive container provided in the concave part (11) with a predetermined gap between the concave part (11) and electrically insulated from the electrolytic cell (12) ( 13), an introduction path (12a) of an inert gas communicating with the gap, and a gas supply means for pressure-feeding the inert gas to the introduction path (12a) so as to blow out into the electrolytic cell (12). A heater (17) provided outside of the electrolytic cell (12) to bring the molten salt (18) into a molten state and use the electrolytic solution of the electrolytic cell (12) as an electrolytic solution.
And an anode (19) held in a molten salt (18) of the electrolytic cell (12), wherein the electrolytic cell (12) has a periphery of a concave portion (11) and the conductive material. A lid (16) is provided to cover the periphery of the upper end of the container (13), and a conductive projection (13a) serving as one or more cathodes protrudes from the recess (11) at the bottom of the conductive container (13). An electrolytic reduction device, characterized in that it is provided to perform 2. A method according to claim 1, wherein the plurality of conductive protrusions are provided in a conductive container.
3. The electrolytic reduction device according to claim 1, wherein the device is provided symmetrically with respect to the center of the bottom of (3). 3. The electrolytic reduction device according to claim 1, wherein the lid is an insulating member. 4. The electrolytic reduction apparatus according to claim 1, wherein the conductive container (13) is provided at the bottom of the electrolytic cell (12) via an insulating material (14). 5. The electrolytic reduction according to claim 1, wherein the electrolytic cell (12), the conductive container (13) and the conductive protrusion (13a) are each made of graphite, and the lid (16) is made of boron nitride. apparatus.