JP7043275B2 - Molten salt electrolysis method, molten metal manufacturing method, and molten salt electrolysis tank - Google Patents

Description

In the present invention, the inside of the electrolytic cell is used as a molten salt bath, the molten salt is flowed from the storage chamber to the electrolytic cell, and the molten metal produced by electrolyzing the molten salt in the electrolytic cell is flowed into the storage chamber to convection. The present invention relates to a molten salt electrolysis method for circulating a molten salt bath, a method for producing a molten metal using the same, and a molten salt electrolytic cell, and particularly proposes a technique that contributes to improvement of current efficiency.

For example, magnesium chloride secondary to the production of metallic titanium by the Kroll process is decomposed into metallic magnesium and chlorine gas by electrolysis using a molten salt electrolytic tank, and the reduction of titanium tetrachloride and chlorine tetrachloride, respectively. It may be used for chlorination of titanium ore and reused.

In this type of electrolysis, generally, a molten salt such as magnesium chloride is stored inside an electrolytic cell divided into a storage chamber and an electrolytic cell by a partition wall to form a molten salt bath, and the molten salt inside the electrolytic cell is stored. It flows from the chamber to the electrolytic cell, where it is decomposed into molten metal such as magnesium metal and gas such as chlorine based on the energization of the electrode. The molten metal generated in the electrolytic cell is further circulated inside the electrolytic cell to the storage chamber, floats on the liquid surface of the molten salt bath due to the density difference with the molten salt, and then recovered, and the gas is recovered in the electrolytic cell. It is discharged to the outside of the electrolytic cell through the gas discharge passage provided in. As such a technique, there are conventionally those described in Patent Documents 1 to 4.

Japanese Unexamined Patent Publication No. 2005-08901 Japanese Unexamined Patent Publication No. 2005-171357 Japanese Unexamined Patent Publication No. 2007-231388 JP-A-2015-140459

By the way, in the above-mentioned electrolysis of molten salt, when the amount of electricity supplied to the electrode decreases, the vicinity of the electrode, particularly the rear of the electrolytic cell located away from the storage chamber on the opposite side of the partition wall across the electrode. There is a problem that the flow of the molten salt bath stays in the vicinity of the wall surface or the corner of the electrode on the corner side, which causes a decrease in the production yield of the molten metal and a decrease in the current efficiency. In this case, not only the bath flow stays, but also the molten metal may solidify between the electrodes.

An object of the present invention is to solve such a problem of the prior art, and an object of the present invention is to effectively suppress the retention of the flow of the molten salt bath in the electrolytic cell of the electrolytic cell and to obtain a current. It is an object of the present invention to provide a molten salt electrolysis method that can contribute to the improvement of efficiency, a method for producing a molten metal using the same, and a molten salt electrolytic cell.

In the molten salt electrolysis method of the present invention, the inside of the electrolytic tank is used as a molten salt bath, and in the electrolytic chamber inside the electrolytic tank having a storage chamber and an electrolytic chamber, melting is performed based on energization of electrodes arranged in the electrolytic chamber. When the salt is electrolyzed, the molten salt flows from the storage chamber to the electrolytic chamber through the bottom side of the electrolytic tank and is electrolyzed in the electrolytic chamber, and the molten metal obtained thereby is on the bath surface side of the molten salt bath. It is a molten salt electrolysis method accompanied by convection of a molten salt bath flowing into a storage chamber from the electrolysis chamber, in which a bubble flow of an inert gas is generated from the bottom side of an electrolytic tank toward an electrode in the electrolytic chamber.

In the molten salt electrolysis method of the present invention, the electrodes have an anode and a cathode, and the anode and the cathode extend in a direction orthogonal to the partition wall separating the storage chamber and the electrolytic cell in a plan view of the electrolytic cell. , An electrolytic cell comprising alternating anode and cathode portions can be used.
In this case, the electrolytic cell further comprises a bipolar electrode, wherein the bipolar electrode includes a bipolar electrode portion located between an anode portion and a cathode portion alternately arranged between the anode and the cathode. Can be used.

Here, in the molten salt electrolysis method of the present invention, the bubble flow is applied from the bottom side of the electrolytic cell to at least the corners of the electrodes having a rectangular shape in a plan view of the electrolytic cell, which are located away from the storage chamber. It is preferable to flow toward the vicinity. When having a plurality of anodes or the like, and even bipolar electrodes, it is more preferable to flow the bubble flow toward each vicinity of the respective corners thereof.

Here, in the molten salt electrolysis method of the present invention, the flow rate of the inert gas sent to the bottom side of the electrolytic cell in order to generate the bubble flow is set to the maximum gas generation amount of 5. It is set to 0vоl% to 50vоl%, and the maximum gas generation amount is the amount of inert gas generated by the electrolysis of the molten salt with the energization amount distributed to each unit electrolytic cell, according to Faraday's law. It is calculated based on this.

Further, in the molten salt electrolysis method of the present invention, it is preferable that the diameter of each bubble constituting the bubble flow is 0.5 mm to 30 mm.

In the molten salt electrolysis method of the present invention, the bubble flow causes electrolysis from the surface portion adjacent to the partition wall separating the storage chamber and the electrolytic chamber with respect to the horizontal plane in a cross-sectional view along the depth direction of the molten salt bath. It is preferable to incline the bath surface of the molten salt bath in the electrolytic chamber so that the bath surface height is high at the surface portion adjacent to the rear wall surface located on the opposite side of the partition wall across the electrode of the chamber.
In this case, the bath surface is set so that the average bath surface height of the surface portion adjacent to the rear wall surface is 1.01 to 1.30 times the average bath surface height of the surface portion adjacent to the partition wall. It is preferable to incline.

The above-mentioned inert gas is preferably argon gas.

The method for producing a molten metal of the present invention is to produce a molten metal from a molten salt by using any of the above-mentioned molten salt electrolysis methods.

The molten salt electrolysis tank of the present invention is divided into an electrolytic tank having a molten salt bath inside, an electrolytic chamber for electrolyzing the molten salt, and a storage chamber into which the molten metal obtained by the electrolysis flows. A partition wall and an electrode arranged in the electrolytic chamber are provided, and the molten salt flows from the storage chamber to the electrolytic chamber through the bottom side of the electrolytic tank and is electrolyzed in the electrolytic chamber, whereby the molten metal obtained is obtained. A molten salt electrolysis tank that electrolyzes molten salt with convection of the molten salt bath flowing into the storage chamber from the bath surface side of the molten salt bath. It has an arranged gas discharge end and is provided with a gas feed pipe to which an inert gas is supplied.

In the molten salt electrolytic cell of the present invention, the electrodes have an anode and a cathode, and the anode and the cathode extend in a direction orthogonal to the partition wall separating the storage chamber and the electrolytic cell in the plan view of the electrolytic cell. , Can include alternating anode and cathode portions.
In this case, the electrode may further have a bipolar electrode, and the bipolar electrode may include a bipolar electrode portion located between an anode portion and a cathode portion alternately arranged between the anode and the cathode.

Here, in the molten salt electrolytic cell of the present invention, the gas discharge end of the gas feed pipe is at least separated from the storage chamber of the electrode having a rectangular shape in a plan view of the electrolytic cell on the bottom side of the electrolytic cell. It is preferably placed directly below the vicinity of each corner where it is located. When having a plurality of anodes or the like, and even bipolar electrodes, it is more preferable to arrange the outgassing end portion directly under each of the respective corner portions thereof.

Further, in the molten salt electrolytic cell of the present invention, it is preferable that the gas feed pipe extends from the storage chamber to the electrolytic cell through the bottom side of the electrolytic cell.

According to the molten salt electrolysis method of the present invention, the flow of the molten salt bath in the vicinity of the electrode is promoted by generating a bubble flow of inert gas from the bottom side of the electrolytic cell toward the electrode in the electrolytic cell. Therefore, it is possible to effectively prevent the flow of the molten salt bath from staying there. Moreover, since the bubble flow is generated from the bottom side of the electrolytic cell toward the electrode, the flow direction of the bubble flow is substantially the same as the flow direction of the molten salt bath in the electrolytic cell. The flow does not obstruct the flow of the molten salt bath. Thereby, during the electrolysis of the molten salt when the electrode is energized, the flow of the molten salt bath can be promoted by the bubble flow.

Further, according to the molten salt electrolytic cell of the present invention, the electrolytic cell is provided with a gas feed tube for an inert gas having a gas discharge end arranged deeper than the electrode on the bottom side of the electrolytic cell. The inert gas can be discharged from the gas discharge end of the gas feed pipe to effectively generate a bubble flow of the inert gas from the bottom side of the electrolytic cell toward the electrode.

It is a vertical sectional view which shows an example of the molten salt electrolysis tank which can carry out the molten salt electrolysis method of one Embodiment of this invention. It is a top view of the molten salt electrolytic cell of FIG. It is the same figure as FIG. 2 which shows the deformation example of an electrode. It is a top view of the molten salt electrolytic cell which shows the installation position of the end part of the gas feed pipe of each Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to those shown in the drawings.
The molten salt electrolytic cell 1 illustrated in FIG. 1 has a container shape mainly made of fire-resistant bricks such as Al ₂ O ₃ and other suitable materials, and is a molten salt bath made of molten salt supplied therein. The depth of the molten salt bath in the electrolytic cell 2 in which the molten salt is electrolyzed and the molten metal is generated by the electrolysis, and as shown in the cross-sectional view of FIG. 1 and the plan view of FIG. It is provided with an electrode 3 including an anode 3a and a cathode 3b having portions arranged side by side in parallel with the direction, and a temperature adjusting tube 4 as a heat exchanger for adjusting the temperature in the electrolytic cell 2. In the present invention, the temperature control tube 4 can be omitted.

Here, a case where the molten salt is molten magnesium chloride (MgCl ₂ ) will be described as an example. In this case, as shown in FIG. 1, metallic magnesium (Mg) is produced as the molten metal by electrolysis of the molten magnesium chloride. At the same time as being generated, chlorine gas (Cl ₂ ) is generated as a gas. Metallic magnesium can be used for the reduction of titanium tetrachloride in the Kroll process for producing metallic titanium, and chlorine gas can be used for the chlorination of titanium ore in the same method. As the magnesium chloride used as a raw material for this electrolysis, those produced as a by-product by the Kroll process can be used. However, the molten salt electrolysis method of the present invention can also be used for electrolysis of other molten salts such as molten calcium chloride (CaCl ₂ ), molten aluminum chloride (AlCl ₃ ), and molten zinc chloride (ZnCl ₂ ).

Here, the illustrated molten salt electrolytic cell 1 is further provided with a partition wall 5 arranged slightly to the left from the center of the figure as shown in FIG. 1 inside the electrolytic cell 2, and the partition wall 5 is used for electrolysis. The inside of the tank 2 is located on the right side in FIG. 1 and is located on the left side of the electrolytic cell 3 and is located on the left side in FIG. 1, and the molten metal obtained by electrolysis in the electrolytic cell 2a flows into the tank 2. The molten metal is partitioned into a storage chamber 2b that collects on the upper side due to a density difference with the molten salt. Specifically, the partition wall 5 is arranged close to a lid member for covering the upper opening of the electrolytic cell 2 (not shown here) so as to be between the partition wall 5 and the lower bottom portion of the electrolytic cell 2. , A molten salt circulation path 5a that enables the movement of the molten salt from the storage chamber 2b to the electrolytic cell 2a is formed. Further, the molten metal flow path 5b provided so as to penetrate the partition wall 5 itself enables the molten metal to flow from the electrolytic chamber 2a into the storage chamber 2b.

Further, here, the electrode 3 arranged in the electrolytic chamber 2a has at least an anode 3a and a cathode 3b connected to a rectifier or the like, and is based on a predetermined reaction such as MgCl ₂ → Mg + Cl ₂ or the like, and the surface of the anode 3a. Gas such as chlorine is generated by the oxidation reaction, and molten metal such as metallic magnesium is generated by the reduction reaction on the surface of the cathode 3b.

If the electrode 3 has at least an anode 3a and a cathode 3b, the molten salt can be electrolyzed. However, from the viewpoint of improving the efficiency of electrolysis generation, as shown in FIG. 2, the electrode 3 is combined with the anode 3a. It is preferable to further have one or more, here two bipolar electrodes 3c and 3d, which are polarized by the application of a voltage between the anode 3a and the cathode 3b between the cathode 3b and the cathode 3b. However, such bipolar electrodes 3c and 3d are not always necessary.

When the electrode 3 shown in FIG. 2 is described in detail, the anode 3a thereof is composed of a substantially rectangular parallelepiped plate-shaped anode portion extending in a direction orthogonal to the partition wall 5 in a plan view of the electrolytic cell 2. A plurality of anode portions are arranged at intervals from each other in a direction parallel to the extending direction of the partition wall 5. Further, the cathode 3b extends from the plurality of anodes 3a on both sides of each of the anodes 3a in a direction orthogonal to the partition wall 5 in a plan view and extends in parallel with the partition wall 5. It consists of a portion connecting the ends of the adjacent cathode portions on the partition wall 5 side, and is a rear wall surface 2c located on the opposite side of the partition wall 5 across the electrode 3 of the electrolytic cell 2 and the anode 3a. Surround each anode portion from its surroundings. The anode portion and the cathode portion are arranged side by side alternately when viewed in a direction orthogonal to the partition wall 5.

The bipolar electrodes 3c and 3d each extend in a rectangular shape in a plan view so as to surround the periphery of each anode portion of the anode 3a inside the cathode 3b, and the anode portion extends in a direction orthogonal to the partition wall 5. It is located between the cathode portion and the cathode portion, and has a bipolar electrode portion extending in a direction orthogonal to the partition wall 5.
It should be noted that not only the bipolar electrodes 3c and 3d and the cathode 3b surround the anode portion as shown in FIG. 2, but also the anode 3a, the cathode 3b and the bipolar electrodes 3c and 3d, respectively, as in the modified example shown in FIG. However, it is also possible that all of them are composed of only an anode portion, a cathode portion and a bipolar electrode portion extending in a direction orthogonal to the partition wall 5 in a plan view.

In the molten salt electrolysis method using the molten salt electrolysis tank 1 as described above, the molten salt that has flowed from the storage chamber 2b through the molten salt circulation path 5a on the bottom side to the electrolytic chamber 2a is electrolyzed by the convection of the molten salt bath. Then, a molten metal is generated in the electrolytic chamber 2a, and the molten metal flows into the storage chamber 2b through the molten metal flow path 5b on the bath surface side of the partition wall 5, and then melts with a small specific gravity to the molten salt. The metal floats to a shallow portion of the storage chamber 2b and accumulates there, and this can be recovered by a pump or the like (not shown). Therefore, here, the molten metal can be produced from the molten salt.

By the way, when such molten salt is electrolyzed, the amount of electricity supplied to the electrode 3 is reduced for reasons such as maintaining the heat balance of the electrolytic cell, adjusting the production amount, and effectively utilizing the low unit price of nighttime electricity. However, in this case, the flow of the molten salt bath stays in the vicinity of the electrode 3 of the electrolytic cell 2a, which may cause a problem that the yield of molten metal formation is lowered and the current efficiency is lowered. .. This retention of the bath flow is particularly remarkable in the rear wall surface 2c of the electrolytic chamber 2a located away from the storage chamber 2b and the partition wall 5, and the corner portion 2d shown by the broken line in FIGS.

In order to deal with such a problem, in this embodiment, as schematically shown in FIG. 1, in the electrolytic cell 2a, from the lower side, which is the bottom side of the electrolytic cell 2, toward the upper side where the electrode 3 is arranged, A bubble flow consisting of bubbles GB of the inert gas is generated.
According to this, the circulation of the molten salt bath which flows from the storage chamber 2b to the electrolytic chamber 2a via the molten salt circulation passage 5a and further flows from there to the storage chamber 2b through the molten metal flow path 5b is electrolyzed. Since the bubble flow in the direction substantially coincide with the flow in the chamber 2a is promoted, the retention of the bath flow in the vicinity of the electrode 3 in the electrolytic chamber 2a can be effectively prevented. As a result, the yield and the current efficiency can be improved.

Further, in the electrolysis of the molten salt, the molten metal such as metallic magnesium solidifies between the electrodes 3 due to a temperature drop or the like, which may cause a short circuit. By generating a bubble flow, such a solidified molten metal can be removed. Moreover, it is possible to prevent such solidification of the molten metal by performing electrolysis while generating a bubble flow of the inert gas.
In this embodiment, since the bubble flow of the inert gas is generated in substantially the same direction as the convection of the molten salt bath in the electrolytic chamber 2a, the bubble flow of the inert gas does not interfere with the circulation of the molten salt bath. It is possible to effectively remove the solidified metal from the molten metal and prevent the occurrence of solidification. Therefore, it is not necessary here to temporarily stop the energization of the electrode 3.

In the illustrated embodiment, a gas feed pipe 6 extending from the storage chamber 2b through the molten salt circulation path 5a on the bottom side of the electrolytic cell 2 to the electrolytic cell 2a is provided, and an inert gas is supplied to the gas feed pipe 6. By discharging the inert gas from the gas discharge end 6a located in the deep part of the molten salt bath on the lower side of the electrode 3, a bubble flow is generated toward the electrode 3. Since the storage chamber 2b is easier to secure a space for arranging the gas feed pipe 6 than the electrolytic chamber 2a in which a large number of anodes 3a, cathodes 3b, bipolar electrodes 3c, 3d, etc. are arranged, such a gas feed pipe It is preferable to use 6 to send the inert gas from the bath surface side of the storage chamber 2b. However, it is also possible to send the inert gas to the bottom side of the electrolytic cell 2a by other aspects. For example, although not shown, a through hole is provided in the wall portion such as the rear wall surface 2c of the electrolytic cell 2. It is conceivable to send an inert gas from.

As described above, the retention of the bath flow and the solidification of the molten metal occur at a position away from the partition wall 5 such as the rear wall surface 2c and the corner 2d facing the partition wall 5 via the electrode 3 of the electrolytic chamber 2a. It often occurs.
Therefore, the bubble flow of the inert gas is located at least away from the storage chamber 2b from the bottom side of the electrolytic cell 2 among the four corners of the electrode 3 having a rectangular shape in a plan view of the electrolytic cell 2. It is preferable to flow toward the vicinity of each corner. For example, in FIG. 2, the gas discharge end of the gas feed pipe 6 is located at a position substantially directly below the corner of the anode 3a and the bipolar electrodes 3c and 3d on the side away from the partition wall 5 (on the right side in the figure). 6a can be arranged. Further, in the one shown in FIG. 3, the gas discharge end portion 6a of the gas feed pipe 6 may be arranged at a position substantially directly below the corner portion on the side away from the partition wall 5 (on the right side in the figure) such as the anode 3a. can. Although not shown, by branching the gas feed pipe 6 in the middle in the extending direction of the partition wall 5, or by arranging the plurality of gas feed pipes 6 side by side, each of the plurality of corner portions of the electrode 3 is provided. It is preferable to arrange a plurality of gas emission end portions 6a corresponding to them directly under the above.

The inert gas sent to the bottom side of the electrolytic cell 2 in order to generate a bubble flow is preferably supplied to and supplied to at least one unit electrolytic cell of the electrolytic cell having N unit electrolytic cells connected in parallel. The flow rate of the inert gas to be generated is 5.0 vol% to 50 vol%, more preferably 15 vol% to 45 vol%, which is the maximum amount of gas that can be generated based on Faraday's law by the amount of electricity distributed per unit electrolytic cell. That is, if the flow rate of the inert gas is too small, the effect of supplying the inert gas is slight but weak, and there is a concern that the retention of the flow in the molten salt bath and the solidification of the molten metal cannot be sufficiently suppressed. On the other hand, if the flow rate of the inert gas is too large, the flow of the molten salt bath may become turbulent and the current efficiency may deteriorate. Therefore, it can be said that it is preferable to supply the inert gas at a flow rate at which the flow of the molten salt bath does not become turbulent. The flow rate of the inert gas can be measured by a gas flow meter attached to the gas feed pipe 6 or the like. The unit electrolytic cell is composed of an electrode portion existing in the energization path of the electrolytic current flowing through one anode with respect to the electrolytic current flowing through at least one anode existing in the electrolytic cell. In the embodiment shown in the figure (FIG. 3), the two cathodes 3b are arranged on the left and right sides of the anode 3a, and the bipolar electrodes 3c and 3d are arranged between the anode 3a and the two cathodes 3b. The flow rate of the above-mentioned inert gas means the flow rate supplied per unit electrolytic cell.

Further, it is preferable that the diameter of any of the bubble GBs discharged from the gas discharge end portion 6a and constituting the bubble flow of the inert gas is within the range of 0.5 mm to 30 mm. In particular, it is even more preferable that the diameter of the bubble GB is in the range of 0.5 mm to 15 mm. In the bubble GB whose diameter is too small, the buoyancy of the bubble GB is small, so that the bubble floating speed may become slow and the retention of the flow of the molten salt bath may not be sufficiently suppressed. If the diameter is too large, the space between the electrodes may be reduced. There is a concern that the resistance received by the bubble GB when ascending will increase, hindering the flow of the molten salt bath.

As described above, when a bubble flow is generated from the bottom side of the electrolytic cell 2 at a position away from the partition wall 5, the bath surface height of the molten salt bath in the electrolytic cell 2a is caused by the bubble GB floating upward from the bubble flow. Is adjacent to the rear wall surface 2c located on the opposite side of the partition wall 5 across the electrode 3 from the surface portion closer to the storage chamber 2b (that is, the surface portion adjacent to the partition wall 5) and away from the storage chamber 2b (that is, the surface portion adjacent to the partition wall 5). The bath surface of the molten salt bath of the electrolytic cell 2a may be inclined so as to be higher at the surface portion away from the storage chamber 2b with respect to the horizontal plane. As a result, the bath flow in the vicinity of the rear wall surface 2c and the corner 2d of the electrolytic chamber 2a is more effectively promoted.

More specifically, by generating a bubble flow from the bottom side of the electrolytic cell 2 at a position away from the partition wall 5, the average bath surface height of the surface portion adjacent to the rear wall surface 2c is the surface adjacent to the partition wall 5. It is preferable to incline the bath surface so that the average bath surface height of the portion is 1.01 to 1.30 times. When the average bath surface height of the surface portion adjacent to the rear wall surface 2c is less than 1.01 times the average bath surface height of the surface portion adjacent to the partition wall 5, the bath flow is promoted at a predetermined location as described above. There is concern that the effect will not be sufficient. On the other hand, if the average bath surface height of the surface portion adjacent to the rear wall surface 2c is made higher than 1.30 times the average bath surface height of the surface portion adjacent to the partition wall 5, the electrolytic bath can be placed outside the electrolytic cell. There is a risk of leakage.
The average bath surface height is obtained by measuring the bath surface heights at a plurality of locations and by arithmetically averaging the measured values of the bath surface heights at the plurality of locations. Here, for the measurement of the bath surface height at one place, a long insulating thin plate (made of quartz or the like) that can be inserted between the electrodes 3 from the inspection hole provided in the lid member of the electrolytic cell 2 is used in the electrolytic cell 2. Insert it vertically until it hits the hearth of the plate, and visually read the scale provided on the surface of the thin plate.

As described above, an argon gas, a helium gas or the like can be used as the inert gas of the bubble flow, but among them, the argon gas is preferable in terms of cost.

Next, since the molten salt electrolysis method of the present invention was carried out on a trial basis, it will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limited thereto.

Electrolysis of the molten salt was started in the molten salt electrolytic cell under the conditions shown below, and the electrolysis was continued for 2 weeks after the start of the electrolysis.
In Comparative Examples and Examples, the molten salt electrolytic cell was evaluated after 2 weeks from the start of electrolysis. During the evaluation period, the current efficiency was compared under the condition that the presence / absence of the supply of the inert gas from the bottom side of the electrolytic cell to the electrode, the amount of the supplied gas, and the installation position of the gas feed tube were changed. In the comparative example, the inert gas was not supplied from the bottom side of the electrolytic cell, whereas in the example, the inert gas (argon gas) was supplied from the bottom side of the electrolytic cell.
For each condition, the case of 8.2 kA (current density equivalent to 0.4 A / cm ² ), which is a low energization amount, and the case of 14.3 kA (current density 0.7 A / cm ² ), which is a high energization amount, are used. evaluated.

(Conditions for molten salt electrolytic cell)
-Bath composition of molten salt: MgCl ₂ , CaCl ₂ , NaCl, and MgF ₂ are 20%, 30%, 49%, and 1% by mass ratio, respectively (while the electrolysis of the molten salt is continued, the metal magnesium In order to replenish magnesium chloride corresponding to the amount produced, magnesium chloride, which is a by-product of the crawl method, is supplied to the electrolytic tank as a replenished molten salt, and the content of magnesium chloride in the molten salt becomes 15 to 20% by mass. Adjusted to.)
-Amount of molten salt: 2800 kg
-Average molten salt temperature: 660 ° C
・ Electrolysis chamber volume: 2m ³
・ Storage room volume: 1m ³
・ Number of unit electrolytic cells: 2
-Number of bipolar electrodes between anode and cathode: 2
・ Arrangement of anode and cathode: Place one cathode parallel to both sides of the anode electrolytic surface ・ Arrangement of bipolar electrodes: Arrange two pieces parallel to both sides of the anode electrolytic surface ・Effective electrolysis area of each electrode: 5100 cm ²
-Distance between initial anode-bipolar electrode A, cathode-bipolar electrode B, bipolar electrode A-bipolar electrode B: 1 cm
-Current densities: 0.4 A / cm ² and 0.7 A / cm ² (In the molten salt electrolytic cell shown in this example, the current density is 8.2 kA at a current density of 0.4 A / cm ² . The energization amount in one unit electrolytic cell under the condition of 0.4 A / cm ² is 4.1 kA. Since the energization amount in the current density 0.7 A / cm ² is 14.3 kA, the current density is 0. The amount of current in one unit electrolytic cell under the condition of .7 A / cm ² is 7.15 kA.)

(Comparative Example 1 and Comparative Example 2)
From 2 weeks after the start of electrolysis of the molten salt electrolytic cell under the above conditions, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle.

The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency under each condition was calculated by the following formula.
Current efficiency = Mass of magnesium recovered from the electrolytic cell / Mass of theoretically produced magnesium The theoretically produced magnesium mass is the theoretically produced amount of metal obtained from Faraday's law.
It is calculated by the following formula.
Theoretical generated magnesium mass = ((current (A) x energization time (seconds)) / (magnesium ion charge number n x Faraday constant F)) x (electrolysis frequency N) x (magnesium atomic weight)

In Comparative Example 1, electrolysis was carried out at an energization amount of 8.2 kA without supplying the inert gas to the electrolytic chamber.
In Comparative Example 2, electrolysis was carried out at an energization amount of 14.3 kA without supplying the inert gas to the electrolytic chamber.

(Example 1 and Example 7)
As shown in FIG. 4, the positions of the gas feed pipe end (gas discharge end) were set to the side surfaces (two places in total) near the rear wall surface in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 1, 0.05 Nm ³ / hr (1 of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. (Equivalent to 0.0 vol%). In Example 7, each unit electrolytic cell was set to 0.09 Nm ³ / hr (corresponding to 1.0 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA). ..

The evaluation period of Example 1 and Example 7 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

(Example 2 and Example 8)
As shown in FIG. 4, the positions of the gas feed pipe ends were set to the side surfaces (two places in total) near the rear wall surface in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 2, 0.26 Nm ³ / hr (5 of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. (Equivalent to 0.0 vol%). In Example 8, each unit electrolytic cell was set to 0.45 Nm ³ / hr (corresponding to 5.0 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA). ..

The evaluation period of Example 2 and Example 8 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

(Example 3 and Example 9)
As shown in FIG. 4, the positions of the gas feed pipe ends were set to the side surfaces (two places in total) near the rear wall surface in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 3, 0.77 Nm ³ / hr (15 vol of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. Equivalent to%). In Example 9, 1.3 Nm ³ / hr (corresponding to 15 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA) for each unit electrolytic cell.

The evaluation period of Example 3 and Example 9 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

(Example 4 and Example 10)
As shown in FIG. 4, the positions of the gas feed pipe ends were set to the side surfaces (two places in total) near the rear wall surface in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 4, 2.3 Nm ³ / hr (45 vol of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. Equivalent to%). In Example 10, 4.0 Nm ³ / hr (corresponding to 45 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA) was set for each unit electrolytic cell.

The evaluation period of Example 4 and Example 10 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

(Example 5 and Example 11)
As shown in FIG. 4, the positions of the gas feed pipe ends were set to the side surfaces (two places in total) near the rear wall surface in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 5, 2.8 Nm ³ / hr (55 vol of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. Equivalent to%). In Example 11, each unit electrolytic cell was set to 4.9 Nm ³ / hr (corresponding to 55 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA).

The evaluation period of Example 5 and Example 11 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

(Example 6 and Example 12)
As shown in FIG. 4, the positions of the gas feed pipe ends were set to the side surfaces (two places in total) near the partition wall in each of the two unit electrolytic cells.
Regarding the supply amount of the inert gas, in Example 6, 0.77 Nm ³ / hr (15 vol of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 8.2 kA) for each unit electrolytic cell. Equivalent to%). In Example 12, 1.3 Nm ³ / hr (corresponding to 15 vol% of the maximum gas generation amount that can be generated in one unit electrolytic cell at an energization amount of 14.3 kA) was set for each unit electrolytic cell.

The evaluation period of Example 6 and Example 12 was 5 days. Here, as in the comparative example, the electrolysis of the molten salt was continued for 5 days while switching the energization amount between 8.2 kA and 14.3 kA in a 12-hour cycle. The mass of magnesium generated and recovered during operation under each energization amount condition was totaled, and the current efficiency at the time of supplying the inert gas was calculated.

The supply conditions of the inert gas at the time of each electrolysis of Comparative Examples 1 and 2 and Examples 1 to 12 described above are summarized in Table 1, and the results of the current efficiency under the supply conditions are also shown in Table 1. .. The current efficiency in Table 1 is a relative value when the current efficiency of Comparative Example 1 is 100.

From the results shown in Table 1, Examples 1 to 12 in which the inert gas was supplied from the bottom side of the electrolytic cell toward the electrode at any current density equivalent (8.2 kA, 14.3 kA) were shown in Examples 1 to 12. It can be seen that the current efficiency was improved as compared with Comparative Example 1 and Comparative Example 2 in which the inert gas was not supplied.

1 Molten salt electrolytic cell 2 Electrolytic cell 2a Electrolytic cell 2b Storage chamber 2c Rear wall surface 2d Corner 3 Electrode 3a Anode 3b Cathode 3c 3d Bipolar electrode 4 Temperature control tube 5 Partition 5a Molten salt circulation path 5b Molten metal flow path 6 Gas feed Tube 6
6a Outgassing end GB bubble

Claims (13)

The inside of the electrolytic tank is used as a molten salt bath, and in the electrolytic chamber inside the electrolytic tank having a storage chamber and an electrolytic chamber, the molten salt is electrolyzed based on the energization of the electrodes arranged in the electrolytic chamber. Flows from the storage chamber through the bottom side of the electrolytic tank to the electrolytic chamber and is electrolyzed in the electrolytic chamber, and the molten metal obtained thereby flows into the storage chamber from the bath surface side of the molten salt bath. It is a molten salt electrolysis method that involves convection.
In the electrolytic cell, a bubble flow of the inert gas is generated from the bottom side of the electrolytic cell toward the electrode .
A method for electrolyzing a molten salt in which the inert gas contains argon gas or helium gas . The electrodes have an anode and a cathode, and the anode and the cathode extend in a direction orthogonal to the partition wall separating the storage chamber and the electrolytic cell in a plan view of the electrolytic cell, and the anode portions and the anode portions arranged alternately. The molten salt electrolysis method according to claim 1, wherein an electrolytic cell including a cathode portion is used. The second aspect of the present invention uses an electrolytic cell in which the electrode further has a bipolar electrode, and the bipolar electrode includes a bipolar electrode portion located between an anode portion and a cathode portion alternately arranged between the anode and the cathode. The molten salt electrolysis method according to the above. 13. The molten salt electrolysis method according to any one of the above. The flow rate of the inert gas sent to the bottom side of the electrolytic cell to generate the bubble flow per unit electrolytic cell is set to 5.0vоl% to 50vоl% of the maximum gas generation amount, and the maximum gas generation amount is , The amount of inert gas generated by the electrolysis of the molten salt, which is the amount of electricity distributed per unit electrolytic cell, and is any of claims 1 to 4 calculated based on Faraday's law. The molten salt electrolysis method according to item 1. Due to the bubble flow, in a cross-sectional view along the depth direction of the molten salt bath, the partition wall is separated from the partition wall of the electrolytic chamber from the surface portion adjacent to the partition wall separating the storage chamber and the electrolytic chamber with respect to the horizontal plane. The molten salt electrolysis according to any one of claims 1 to 5, wherein the bath surface of the molten salt bath in the electrolytic chamber is inclined so that the bath surface height is high at the surface portion adjacent to the rear wall surface located on the opposite side. Method. Claims to incline the bath surface so that the average bath surface height of the surface portion adjacent to the rear wall surface is 1.01 to 1.30 times the average bath surface height of the surface portion adjacent to the partition wall. Item 6. The molten salt electrolysis method according to Item 6. A method for producing a molten metal, wherein the molten metal is produced from the molten salt by using the molten salt electrolysis method according to any one of claims 1 to 7 . An electrolytic tank having a molten salt bath inside, a partition partition that divides the inside of the electrolytic tank into an electrolytic chamber for electrolyzing molten salt and a storage chamber into which molten metal obtained by the electrolysis flows, and an electrolytic chamber. The molten salt flows from the storage chamber through the bottom side of the electrolytic tank to the electrolytic chamber and is electrolyzed in the electrolytic chamber, and the molten metal obtained thereby is stored from the bath surface side of the molten salt bath. A molten salt electrolysis tank that electrolyzes molten salt with convection of the molten salt bath flowing into the chamber.
The electrolytic cell has a gas discharge end located deeper than the electrode on the bottom side of the electrolytic cell, and is provided with a gas feed pipe to which an inert gas containing argon gas or helium gas is supplied. Salt electrolytic cell. The electrodes have an anode and a cathode, and the anode and the cathode extend in a direction orthogonal to the partition wall separating the storage chamber and the electrolytic cell in a plan view of the electrolytic cell, and the anode portions and the anode portions arranged alternately. The molten salt electrolytic cell according to claim 9 , which comprises a cathode portion. The molten salt according to claim 10 , wherein the electrode further comprises a bipolar electrode, wherein the bipolar electrode includes a bipolar electrode portion located between an anode portion and a cathode portion alternately arranged between the anode and the cathode. Electrolytic cell. The gas discharge end of the gas feed pipe is arranged on the bottom side of the electrolytic cell, at least in the vicinity of each corner located away from the storage chamber, of the electrodes having a rectangular shape in a plan view of the electrolytic cell. The molten salt electrolytic cell according to any one of claims 9 to 11 . The molten salt electrolytic cell according to any one of claims 9 to 12 , wherein the gas feed pipe extends from the storage chamber to the electrolytic cell through the bottom side of the electrolytic cell.

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