JP7264758B2 - Electrode, molten salt electrolysis device, molten salt electrolysis method, and metal production method - Google Patents

Description

The present invention relates to an electrode provided in a molten salt electrolysis device, a molten salt electrolysis device, a molten salt electrolysis method, and a metal production method.

For example, in the production of metallic titanium by the Kroll method, magnesium chloride, which is secondarily produced, may be decomposed into metallic magnesium and chlorine gas by electrolysis using a molten salt electrolyzer. In this case, metallic magnesium and chlorine gas are respectively used for the reduction of titanium tetrachloride and the chlorination reaction of titanium ore and reused.

In this type of electrolysis, in general, for example, a molten salt containing a metal chloride such as magnesium chloride is stored and melted in an electrolytic cell that is partitioned into a recovery chamber and an electrolytic chamber by a partition wall of a molten salt electrolysis device. Take a salt bath. In this molten salt bath, the molten salt inside the electrolytic cell flows from the recovery chamber to the electrolytic chamber, where the metal chloride is mixed with the molten metal such as metallic magnesium and the gas such as chlorine based on the energization of the electrodes. decomposed. Gases generated in the electrolysis chamber provide a bath stream that circulates the molten salt bath, whereby the molten metal produced in the electrolysis chamber is sent to the recovery chamber. In the recovery chamber, the molten metal floats on the surface of the molten salt bath due to the difference in density from the molten salt, and then recovered. Also, the gas is discharged to the outside through a gas discharge passage provided in the molten salt electrolysis apparatus.

Techniques related to molten salt electrolysis include those described in Patent Document 1 and the like. In Patent Document 1, the purpose is "an electrolytic cell for extracting calcium chloride containing calcium used for reducing oxides or chlorides of titanium, and particularly for efficiently recovering calcium chloride by molten salt electrolysis", A molten salt electrolytic cell has been proposed, comprising a container holding a molten salt bath, an anode and a cathode being immersed in the bath, and the cathode being hollow. According to this document, "calcium or calcium chloride in which calcium is partially dissolved can be efficiently recovered and extracted to the outside".

WO2006/115027

By the way, in the electrolysis of molten salt as described above, when the amount of electricity supplied to the electrodes decreases, the molten metal solidified between the electrodes may aggregate in the vicinity of the electrodes. There is a problem that a short circuit is caused by In addition, even if the short circuit does not occur, the amount of gas generated in the electrolysis decreases due to the decrease in the amount of energization, and the flow of the bath deteriorates. Concerned.

Patent Document 1 describes that "the cathode is hollow". It is for "extracting calcium chloride efficiently" (see FIG. 1), and cannot deal with the problem that occurs when the amount of current is reduced as described above. Further, in Patent Document 1, no consideration is given to the problem of short circuit and deterioration of bath flow.

An object of the present invention is to provide an electrode capable of suppressing the occurrence of a short circuit between electrodes due to agglomeration of molten metal and promoting bath flow, a molten salt electrolysis device, a molten salt electrolysis method, and a metal production method. is to provide

As a result of intensive studies, the inventors have found that gas bubbles are generated from the immersion end side of the electrode located on the bottom side of the electrolytic cell through the gas supply passage including the hole extending inside the electrode. I came up with the idea. The inventors have also found that this can effectively remove agglomeration of the molten metal in the vicinity of the electrode and promote the flow of the bath.

The electrode of the present invention has an immersion end that is arranged to be immersed in a molten salt bath inside a molten salt electrolysis device, and is connected to a gas supply source outside the molten salt electrolysis device. It has a gas supply passage including a supply port and a gas discharge port located on the immersion end side, and the gas supply passage has at least an immersion side opening that extends into the electrode and opens to the immersion end. It is configured including one hole.

Here, the electrode includes a plurality of rod-shaped electrode members extending in the depth direction of the molten salt bath, and the rod-shaped electrode members are arranged side by side in the width direction of the molten salt electrolysis device, It is preferable that each of the plurality of rod-shaped electrode members includes at least one hole.

It is preferable that the hole has an exposed side opening that opens to the exposed end of the electrode arranged to be exposed to the outside of the molten salt electrolysis device.
In this case, the hole preferably has a shape extending linearly between the exposed end and the immersed end inside the electrode.

In the above electrode, the gas supply passage may further include a tubular passage extension member attached to the immersion end and communicating with the hole at the immersion end.

A molten salt electrolysis apparatus of the present invention performs electrolysis of molten salt, and includes an electrolytic cell containing a molten salt bath and at least one of the electrodes described above.

When the molten salt electrolysis apparatus has at least a pair of an anode and a cathode, it is preferable that only the anode out of the anode and the cathode is the electrode.

The above molten salt electrolysis apparatus may further include a bipolar electrode arranged between the anode and the cathode. In this case, the immersion end portion of the electrode serving as the anode may be located closer to the bath surface than the end portion of the bipolar electrode on the bottom surface side of the electrolytic cell in the depth direction of the molten salt bath. preferable.

In this case, the gas supply passage of the electrode further includes a tubular passage extension member attached to the immersion end and communicating with the hole at the immersion end, and the passage extension member allows the gas It is preferable that the supply passage extends to a position deeper than the end portion of the bipolar electrode in the depth direction of the molten salt bath.

A molten salt electrolysis method of the present invention is a method of electrolyzing a molten salt using any one of the molten salt electrolysis apparatuses described above, wherein the gas supply passage of the electrode is connected to the molten salt electrolysis apparatus. It includes a step of supplying gas to the inside.

A method for producing a metal according to the present invention comprises producing a metal by electrolyzing a molten salt using any one of the molten salt electrolysis apparatuses described above.

According to the present invention, it is possible to suppress the occurrence of a short circuit between electrodes due to aggregation of molten metal, and to promote bath flow.

1 is a longitudinal sectional view showing an example of a molten salt electrolysis apparatus provided with electrodes according to one embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1; FIG. 3 is a cross-sectional view similar to FIG. 2 showing another embodiment of an electrode; 4(a) and 4(b) are vertical cross-sectional views showing other examples of the passage extension member that constitutes the gas supply passage. FIG. 6 is a vertical cross-sectional view showing a molten salt electrolysis apparatus provided with electrodes according to still another embodiment. 3 is a cross-sectional view similar to FIG. 2 showing yet another embodiment of an electrode; FIG.

Embodiments of the present invention will be described in detail below with reference to the drawings.
A molten salt electrolysis _{apparatus 1} exemplified in a longitudinal sectional view in FIG. and The molten salt electrolysis apparatus 1 further includes a lid member 4 for covering the upper opening of the electrolytic cell 2, and a recovery chamber 2b (not shown) inside the electrolytic cell 2, etc., which are arranged to cool the molten salt bath. A temperature control tube or the like may be provided as a heat exchanger for temperature control.

Here, the molten salt electrolyzer 1 further comprises a partition wall 5 arranged substantially along the depth direction (vertical direction in FIG. 1) inside the electrolytic cell 2 as shown in FIG. be. The inside of the electrolytic cell 2 is separated by the partition wall 5 into an electrolytic chamber 2a located on the right side of FIG. and a collection chamber 2b in which the molten metal accumulates on the upper side due to the difference in density from the molten salt. The partition wall 5 is arranged close to the lid member 4 on the upper side of the electrolytic cell 2 . Thus, a molten salt circulation path 5a is formed between the bottom surface of the electrolytic cell 2 and the lower bottom surface of the electrolytic cell 2 to allow the molten salt to move from the recovery chamber 2b to the electrolytic chamber 2a. Further, the molten metal channel 5b provided in the partition wall 5 allows the molten metal to flow from the electrolysis chamber 2a to the recovery chamber 2b.

Also here, the electrodes 3 arranged in the electrolysis chamber 2a have at least an anode 3a and a cathode 3b connected to a power supply. At the anode 3a and the cathode 3b, based on a predetermined reaction such as MgCl ₂ →Mg+Cl ₂ , gas such as chlorine is generated by an oxidation reaction on the surface of the anode 3a, and metallic magnesium is generated by a reduction reaction on the surface of the cathode 3b. Molten metal such as

If the electrode 3 has at least an anode 3a and a cathode 3b, it can electrolyze the metal chloride in the molten salt. On the other hand, the electrode 3 is polarized between the anode 3a and the cathode 3b by applying a voltage between the anode 3a and the cathode 3b, as can be seen from FIG. It is preferable to further have at least one bipolar electrode 3c. In this example, two double poles 3c are used. However, such a double pole 3c is not necessarily required.
The anode 3a may be made of graphite, the cathode 3b may be made of graphite or carbon steel, and the bipolar electrode 3c may be made of graphite.

In the molten salt electrolysis that can be performed using the molten salt electrolysis apparatus 1, for example, by electrolysis of magnesium chloride, as shown in FIG. 1, metallic magnesium (Mg) is produced as molten metal and chlorine ( Cl ₂ ) is generated. The metallic magnesium produced by the molten salt electrolysis can be used for reducing titanium tetrachloride in the Kroll process for producing metallic titanium, and the chlorine gas can be used for the chlorination reaction of titanium ore. Magnesium chloride used as a raw material for this electrolysis may be those produced secondarily by the Kroll process.

To explain this molten salt electrolysis in detail, as shown in FIG. 1, due to the convection of the molten salt bath, the molten salt flows from the recovery chamber 2b to the electrolytic chamber 2a through the molten salt circulation path 5a on the bottom side of the electrolytic cell 2. . In the electrolytic chamber 2a, the magnesium chloride in the molten salt is electrolyzed to produce metallic magnesium in the electrolytic chamber 2a. Then, this metal magnesium flows through the molten metal channel 5b on the bath surface Sb side of the partition wall 5 into the recovery chamber 2b. Thereafter, magnesium metal, which has a low specific gravity relative to the molten salt, floats to a shallow portion of the recovery chamber 2b and accumulates there. The magnesium metal floating in the recovery chamber 2b can be recovered by a pump (not shown) or the like. Therefore, according to this, it is possible to produce metallic magnesium as a molten metal from a molten salt.

The molten salt bath generally contains a supporting salt in addition to the above magnesium chloride. This supporting salt constitutes a molten salt bath together with magnesium chloride, and is an electrolyte that lowers the crystallization temperature, viscosity and electrical resistivity when mixed with magnesium chloride. Specifically, the supporting salt is at least selected from the group consisting of sodium chloride (NaCl), calcium chloride ( _CaCl2 ), potassium chloride (KCl), magnesium fluoride ( _MgF2 ) and calcium fluoride ( _CaF2 ). can be of one type.

In the molten salt electrolysis as described above, when the molten salt electrolysis device 1 is started to be used or stopped for a long period of time, the heat balance of the electrolytic cell 2 is maintained, the production volume is adjusted, and nighttime power with a low unit price is effectively used. For the purpose, the amount of electricity supplied to the electrode 3 may be reduced. In this case, due to a decrease in the temperature of the molten salt bath and a decrease in the amount of chlorine gas generated that causes bath flow, the molten metal solidifies and aggregates between the electrodes 3 such as the lower part of the electrode 3, and this may cause a short circuit. There is In addition, the decrease in the amount of energization causes the molten salt bath to stagnate in the vicinity of the electrode 3 in the electrolysis chamber 2a, which may lead to a decrease in the yield of molten metal production and a decrease in current efficiency.

In contrast, in this embodiment, an anode 3a having gas supply passages 6 is used. More specifically, the anode 3a is exposed to the outside of the molten salt electrolysis device 1 outside the lid member 4 of the molten salt electrolysis device 1 and the immersion end portion 7a arranged so as to be immersed in the molten salt bath. and an exposed end portion 7b arranged in the same direction. The anode 3a is formed with a hole 6a extending into the anode 3a and having an immersion-side opening opening at the immersion end 7a. The gas supply passage 6 includes a gas supply port 6c connected to a gas supply source (not shown) outside the molten salt electrolysis apparatus 1, a gas discharge port 6d located on the immersion end portion 7a side, and the above-described hole portion 6a. composed of In the embodiment shown in FIG. 1, the immersion side opening of the hole portion 6a and the gas discharge port 6d are aligned.

By supplying an inert gas such as argon or helium or other gas from the outside of the molten salt electrolysis apparatus 1 to the gas supply passage 6 of the anode 3a, the gas is supplied from the immersion end 7a side of the anode 3a to the molten salt bath. to generate bubbles Bg in the molten salt bath. Since the immersion end 7a is located at a certain depth on the bottom side of the electrolytic bath 2, the bubbles Bg generated at the immersion end 7a side float and come into contact with the agglomeration of the molten metal generated between the electrodes 3. , functions to remove the agglomeration. Thereby, occurrence of a short circuit can be suppressed.

In addition, the bubbles Bg generated at the immersion end 7a float upward in the electrolytic chamber 2a in a direction substantially matching the flow of the molten salt bath, thereby promoting the bath flow. As a result, the stagnation of the bath flow near the electrode 3 in the electrolysis chamber 2a can be effectively prevented, and the yield and current efficiency can be improved.

Although not shown, an operator inserts a long gas blowing pipe into the molten salt bath to generate air bubbles in the molten salt bath, remove agglomeration of the molten metal between the electrodes 3, and promote bath flow. can also be considered. However, since the electrolysis chamber 2a is usually sealed with a lid member 4 from the viewpoint of preventing leakage of chlorine gas, the pipe for gas injection is introduced into the electrolysis chamber from the recovery chamber 2b side, for example, through the molten salt circulation path 5a. It is necessary to insert up to the lower side of 2a. Therefore, in this method, it is not easy to insert and arrange the gas injection pipe, and it is difficult to generate bubbles at the desired position. Also, in this case, the sludge deposited on the bottom surface of the electrolytic cell 2 may be stirred up by the insertion of the gas injection pipe and mixed into the molten metal.
On the other hand, in the above-described embodiment, the anode 3a itself is formed with the hole 6a opening to the immersion end 7a, and the gas supply passage 6 including the hole 6a is provided. Air bubbles Bg are easily generated at the position, and sludge is less likely to be rolled up. In addition, there is no need to insert a gas injection pipe.

When the gas supply passage 6 of the anode 3a is not used for agglomeration removal of molten metal or promotion of bath flow, it is preferable to keep the internal pressure of the gas supply passage 6 somewhat high by the gas supplied therein. As a result, it is possible to suppress the inflow of the molten salt into the gas supply passage 6 and blockage due to the solidification of the molten salt in the gas supply passage 6 .

For example, the diameter of the gas supply passage 6, which has a circular cross section or the like, can be, for example, 5 mm to 50 mm. If the diameter of the gas supply passage 6 is set to 5 mm or more, it is easy to process, and good bubble generation makes it difficult for clogging between electrodes to occur. By setting the diameter of the gas supply passage 6 to 50 mm or less, it becomes easier to ensure the required strength of the anode 3a. The anode 3a preferably has a thickness of 100 mm or more, from the viewpoint of the workability of drilling the gas supply passage 6 and electrical resistance. Although the upper limit of the thickness of the anode is not particularly limited, it can be 400 mm or less to give an example. The thickness of anode 3a can be, for example, 50 mm to 400 mm, preferably 100 mm to 400 mm. The width of the anode 3a may be determined as appropriate, but as an example, it can be set within the range of 1000 mm to 2500 mm.

In the molten salt electrolysis method carried out in the molten salt electrolysis apparatus 1 provided with such an anode 3a, argon gas or A step of supplying a gas such as helium gas into the electrolytic cell 2 is included.
In the step of supplying the gas to the gas supply passage 6, the gas supply flow rate of the gas supply passage 6 can be set to 10 L/min to 1000 L/min, for example, in order to favorably generate bubbles Bg in the molten salt bath. On the other hand, during the period during which only a small amount of bubbles Bg are generated in the molten salt bath or during which no bubbles Bg are generated (during standby), for example, the internal pressure of the gas supply passage 6 is at least positive (for example, 0.01 MPa or more), and the gas supply flow rate is reduced. It can be from 0.5 L/min to 5.0 L/min. If the molten salt bath enters the gas supply passage 6, it may solidify in the passage and clog the immersion side opening. Therefore, it is preferable to generate a small amount of air bubbles Bg even in the standby state.

By the way, the anode 3a includes a portion immersed in the molten salt bath in the electrolytic bath 2 and a portion located above the bath surface Sb of the molten salt bath. The portion of the anode 3a on the bath surface Sb passes through the lid member 4, and the exposed end portion 7b is at the tip of the portion exposed to the outside of the molten salt electrolysis apparatus 1. As described above, the other end of the hole 6a, one end of which is open to the immersion end 7a, preferably opens to a portion of the anode 3a outside the molten salt electrolysis apparatus 1, typically the exposed end 7b. is. In this case, it becomes easy to connect a gas conduit with a valve (not shown) for supplying gas to the gas supply passage 6 to the other end of the hole 6a. Thus, in this example, the hole 6a has a dipped side opening and an exposed side opening at the dipped end 7a and the exposed end 7b of the anode 3a, respectively.

The shape of the hole 6a forming the gas supply passage 6 can be appropriately determined in consideration of various conditions. As in the illustrated embodiment, the hole portion 6a extends linearly substantially parallel to the depth direction of the molten salt bath and penetrates between the exposed end portion 7b and the immersed end portion 7a inside the anode 3a. When it has a shape, the molten salt forming the molten salt bath flows through the hole 6a when the gas cannot be supplied through the gas supply passage 6 due to a malfunction of the gas supply source device or the like. There is an advantage that it is difficult to leak to the outside of the electrolytic device 1 . In addition, such a hole 6a can be easily formed by processing the anode 3a, and the straight hole 6a has the advantage of being less resistant to gas. Alternatively, although illustration is omitted, it is also possible to form a hole that bends, curves and/or branches in the middle of the interior of the anode. In the case of a hole branching in the middle, the immersion end 7a may be opened at a plurality of locations.

Along with or instead of the anode 3a, the cathode 3b and/or the bipolar electrode 3c may be provided with gas supply passages similar to the gas supply passages 6 of the anode 3a described in this specification.
However, since the anode 3a is generally thicker than the cathode 3b, the drilling work for forming the hole 6a is relatively easy. For this reason, of the anode 3a and the cathode 3b, it is preferable to provide the gas supply passage 6 only to the anode 3a as in this embodiment. When the molten salt electrolysis device 1 has a double electrode 3c arranged between the anode and the cathode, the gas supply passage 6 can be provided only in the anode 3a among the anode 3a, the cathode 3b and the double electrode 3c. preferred. This is because the anode 3a, which is often exposed to the outside of the molten salt electrolysis device 1, is easy to supply gas. Further, in the gas supply passage 6 provided in the anode 3a, leakage of molten salt to the outside is less likely to occur. Further, when the gas supply passage 6 is provided in the anode 3a, even if the gas supply passage 6 is clogged with molten salt, the anode 3a can be pulled out upward, and replacement is easy.

As shown in FIG. 2, the immersion end 7a of the anode 3a is positioned in the depth direction of the molten salt bath from the end 8a of the bipolar electrode 3c on the bottom side of the electrolytic cell 2 so as not to generate a bypass current. may be arranged so as to be positioned on the bath surface Sb side.
In this case, as shown in FIG. 3, a tube-like passage extension member 16b such as a circular tube may be provided at the immersion end 17a of the anode 13a so as to communicate with the hole 16a at the immersion end 17a. can. According to this, the passage extension member 16b can extend the gas supply passage 16 to a position deeper than the end portion 8a of the bipolar electrode 3c in the depth direction of the molten salt bath, and the air bubbles can be generated from the deep position. It becomes possible to generate Bg. As a result, as shown in the figure, the air bubbles Bg spread over a wide area between the anode 13a and the cathode 3b, enhancing the effect of removing aggregation and promoting bath flow. In the example of FIG. 3, the immersion-side opening of the hole 16a provided in the anode 13a does not coincide with the gas discharge port 16d, and the gas discharge port 16d is positioned at the end of the passage extension member 16b on the bottom BS side. do.

The passage extension member 16b can be made of, for example, ceramics, preferably silicon nitride (Si ₃ N ₄ ) from the viewpoint of corrosion resistance and insulation. The passage extension member 16b can be attached to the immersion end 17a by press-fitting or screwing it into the hole 16a of the anode 13a from the immersion end 17a side. The mounting location may be reinforced with graphite cement or the like, if necessary.
A passage extension member 16b extends the gas supply passage 16 in the depth direction of the molten salt bath to a position between the end 8a of the bipolar electrode 3c and a position 500 mm away from the bottom surface BS toward the bath surface Sb. It is preferable to As a result, it is possible to spread the bubbles Bg over a wide range while suppressing the sediment from being rolled up near the bottom surface BS.

In FIG. 3, the path extension member 16b is a simple circular tube, but it may be a path extension member 26b or 36b shaped as shown in FIGS. 4(a) or 4(b).
The passage extension member 26b in FIG. 4(a) has a tapered portion in the vicinity of the end located on the bottom side of the electrolytic cell 2, the inner diameter of which gradually increases toward the tip side, and the passage in FIG. It has the same shape as the extension member 16b. In the passage extension member 26b, the tapered portion diffuses the gas bubbles Bg into the molten salt bath, so that the bubbles Bg can be sent over a wider range.

The passage extension member 36b shown in FIG. 4B has the same configuration as the passage extension member 16b shown in FIG. It has the same shape as This flange portion functions to better diffuse the gas. The shape of the flange portion is particularly suitable to be substantially the same as the shape of the end surface of the immersion end 17a of the anode 13a. For example, the flange portion may be rectangular in plan view.

As shown in FIG. 5, the anode 43a includes a plurality of rod-shaped electrode members 49 having a rectangular cross section or the like, and extending in the depth direction of the molten salt bath. 5) are arranged next to each other. The cross-section of the rod-shaped electrode member 49 here means a cross-section along a plane perpendicular to the longitudinal direction of the rod, which substantially coincides with the depth direction of the molten salt bath (the direction perpendicular to the bath surface Sb). A plurality of rod-shaped electrode members 49 are arranged in close contact with each other, and may be connected as necessary. For example, the width of each rod-shaped electrode member 49 (the length along the width direction) can be 500 mm to 2000 mm. The thickness of each rod-shaped electrode member 49 (the length in the direction orthogonal to both the width direction and the longitudinal direction) can be, for example, 50 mm to 400 mm, preferably 100 mm to 400 mm.

In the case of the anode 43a including such a plurality of rod-shaped electrode members 49, it is sufficient that at least one hole 46a is formed in the plurality of rod-shaped electrode members 49 as a whole. In this case, it is preferable that at least one hole 46a is formed in each of the plurality of rod-shaped electrode members 49, and each rod-shaped electrode member 49 includes the hole 46a. As a result, the bubbles Bg can be generated in a wide range in the width direction and the thickness direction of the anode 43a, so that the effect of removing the aggregation of the molten metal and promoting the flow of the bath can be further enhanced. The number of rod-shaped electrode members 49 constituting the anode 43a is not limited to four as shown in the figure, and may be one to three or five or more.

FIG. 6 shows an electrode including an anode 53a of yet another embodiment.
In FIG. 6, the electrodes are a cylindrical anode 53a, a bottomed cylindrical cathode 53b spaced from the anode 53a around the anode 53a, and a predetermined distance between the anode 53a and the cathode 53b. and one or more bottomed cylindrical bipolar electrodes 53c spaced apart from each other. A through hole is provided in the center of each bottom wall of the cathode 53b and the bipolar electrode 53c.

The anode 53a has a longitudinal direction (vertical direction in FIG. 6) substantially in the central region of its cross section (a plane perpendicular to the longitudinal direction of the anode 53a which substantially coincides with the depth direction of the molten salt bath). A hole portion 56a extending along and penetrating therethrough is formed. In addition, the anode 53a is provided with a passage extension member 56b that communicates with the hole portion 56a at the immersion end portion 57a. extends to the bottom side of the The hole portion 56a and the passage extension member 56b constitute a gas supply passage 56 for discharging the gas supplied from the outside of the molten salt electrolysis apparatus from the immersion end portion 57a side.

Even in the anode 53a shown in FIG. 6, generation of air bubbles Bg in the molten salt bath using the gas supply passage 56 makes it possible to favorably remove agglomeration of the molten metal and promote the bath flow.
It should be noted that the passage extension member 56b can be omitted as in the above-described embodiment, and the shape of the hole portion 56a can be appropriately changed. Also, the double pole 53c may be omitted.

Next, the present invention was carried out on a trial basis, which will be described below. However, the description herein is for illustrative purposes only and is not intended to be limiting.

(Test example 1)
The operation of the molten salt electrolysis was temporarily stopped, and after performing prescribed maintenance, the operation was restarted. When restarting operation, the time required to reach a predetermined target voltage was compared in Examples 1 to 3 and Comparative Examples 1 and 2, which will be described below.

In Example 1, the molten salt electrolysis apparatus as shown in FIGS. 1 and 2 was used, and argon gas was supplied to the molten salt bath through the gas supply passage of the anode at the restart of operation to generate bubbles. The condition for supplying argon gas was 100 L/min per anode. The gas supply passage had a circular cross section and a diameter of φ20 mm. The dimensions of the anode were 200 mm thick and 1600 mm wide.
Example 2 was the same as Example 1, except that a molten salt electrolysis apparatus as shown in FIG. 5 was used. Each of the rod-shaped electrode members had a thickness of 200 mm and a width of 400 mm, and four rod-shaped electrode members were placed adjacent to each other to form an anode having a width of 1600 mm. A hole having the same size and shape as in Example 1 was provided as a gas supply passage in each of the rod-shaped electrode members.
Example 3 was similar to Example 1 except that a cylindrical passage extension member as shown in FIG. 3 was used. The inner diameter of the passage extension member was the same as the inner diameter of the gas supply passage. The gas outlet was arranged at a position 500 mm away from the bottom toward the bath surface, and the gas outlet was located closer to the bottom of the electrolytic cell than the bottom end of the bipolar electrode.

In Comparative Example 1, the same molten salt electrolyzer as in Example 1 was used except that the anode did not have a gas supply passage, and the operation was restarted without supplying argon gas.
In Comparative Example 2, the same molten salt electrolysis apparatus as in Example 1 was used except that the anode did not have a gas supply passage. , thereby supplying argon gas. As a gas injection pipe, one pipe having an inner diameter of 20 mm was used. The conditions for supplying argon gas were the same as in Example 1, with a blow rate of 100 L/min.

In any of Examples 1 to 3 and Comparative Examples 1 and 2, the composition of the molten salt bath when restarting operation was MgCl ₂ : 20%, NaCl: 50%, CaCl ₂ : 30%, and the average molten salt temperature was 655. °C, and the current density was 0.65 A/cm ² .

The time required to reach the target voltage after the completion of energization was 0.3 hours in Example 1, 0 hours (immediately after) in Example 2, and 0 hours (immediately after) in Example 3, whereas the comparative example 1 was 1.5 hours, and Comparative Example 2 was 1.0 hours.
In Examples 1 to 3, the solidification or agglomeration of metallic magnesium that had occurred between the electrodes due to the stoppage of operation was successfully removed by bubbles of argon gas supplied from the gas supply passage of the anode. is assumed to have been reached. On the other hand, in Comparative Example 1, since argon gas was not supplied, it is considered that the aggregation of metallic magnesium between the electrodes inhibited the voltage increase, and it took a long time to reach the target voltage. In Comparative Example 2, it is considered that the agglomeration of metallic magnesium was not smoothly removed by supplying argon gas through the gas blowing pipe, and as a result, it took a certain amount of time.

(Test example 2)
In each of the molten salt electrolyzers of Examples 1 to 3 and Comparative Examples 1 and 2, the current efficiency at this time was determined by reducing the amount of electricity supplied to the electrodes when adjusting the production amount.

The conditions for supplying argon gas in Examples 1 to 3 and Comparative Example 2 were the same as in Test Example 1. The electrolysis conditions were the same as in Test Example 1, except that the current density was 0.40 A/cm ² when the current flow was reduced, and the current density was 0.65 A/cm ² before adjusting the production volume and after recovery. .

The operation was performed for 6 hours before adjustment of the production volume (before reducing the amount of electricity supplied), and the operation was also performed for 6 hours during the adjustment of the production volume, and the current efficiency was obtained using the amount of metallic magnesium recovered in each operation. When determining the current efficiency, the amount of metallic magnesium before adjustment of the production amount was used as a reference (mass reference), and the decrease in the amount of recovered magnesium during the adjustment of production was evaluated as the decrease in current efficiency. The results are as follows.
Example 1: -9%
Example 2: -8%
Example 3: -8%
Comparative Example 1: -10%
Comparative Example 2: -10%

(Discussion)
From the results of Test Examples 1 and 2 above, in Examples 1 to 3, the bath flow was favorably promoted by supplying argon gas through the gas supply passage provided in the anode. It is believed that he returned soon after. In addition, the production amount of metallic magnesium was relatively large even during the adjustment of the production amount.

On the other hand, in Comparative Example 1, it is presumed that the fact that no argon gas was supplied and that the amount of chlorine gas generated due to the decrease in the amount of energization greatly affected the bath flow, and that it took a long time to recover. be. In Comparative Example 2, the manual supply of argon gas using the gas blowing pipe did not contribute very effectively to the promotion of the bath flow, and therefore it took a certain amount of time to recover. In addition, Comparative Examples 1 and 2 were affected by the bath flow, and the amount of decrease in the production amount of metallic magnesium during the adjustment of the production amount was relatively large.

REFERENCE SIGNS LIST 1 molten salt electrolyzer 2 electrolytic cell 2a electrolytic chamber 2b recovery chamber 3 electrodes 3a, 13a, 43a, 53a anodes 3b, 53b cathodes 3c, 53c bipolar electrodes 4 lid member 5 partition walls 6, 16, 46, 56 gas supply passage 6a, 16a, 46a, 56a holes 16b, 26b, 36b, 56b passage extension members 6c, 16c, 46c, 56c gas supply ports 6d, 16d, 46d, 56d gas discharge ports 7a, 17a, 47a, 57a immersion ends 7b, 17b , 47b, 57b exposed end portion 8a bipolar end portion 49 rod-shaped electrode member Sb bath surface of molten salt bath Bg bubble BS bottom surface

Claims (8)

A molten salt electrolysis device for electrolyzing molten salt,
An electrolytic cell having a molten salt bath inside is provided, and at least one electrode having an immersed end portion is arranged so as to be immersed in the molten salt bath inside the molten salt electrolysis device,
The electrode has a gas supply passage including a gas supply port connected to a gas supply source outside the molten salt electrolysis device and a gas discharge port located on the immersion end side , and the gas supply passage comprises at least one hole extending into the electrode and having a dip-side opening opening into the dip end ;
comprising at least one pair of an anode and a cathode, and a double electrode positioned between the anode and the cathode;
only the anode of the anode and the cathode is the electrode;
A molten salt electrolysis apparatus in which the immersion end of the electrode serving as the anode is located closer to the bath surface than the end of the bipolar electrode on the bottom surface side of the electrolytic cell in the depth direction of the molten salt bath. The electrode includes a plurality of rod-shaped electrode members extending in the depth direction of the molten salt bath, and the rod-shaped electrode members are arranged side by side in the width direction of the molten salt electrolysis device,
The molten salt electrolysis apparatus according to claim 1, wherein each of the plurality of rod-shaped electrode members includes at least one hole. The molten salt electrolysis device according to claim 1 or 2, wherein the hole has an exposed side opening that opens to an exposed end portion of the electrode arranged to be exposed to the outside of the molten salt electrolysis device . 4. The molten salt electrolysis apparatus according to claim 3, wherein the hole has a shape extending linearly between the exposed end and the immersed end inside the electrode. The molten salt electrolysis apparatus according to any one of claims 1 to 4, wherein the gas supply passage further includes a tubular passage extension member attached to the immersion end and communicating with the hole at the immersion end. . 6. The molten salt electrolysis apparatus according to claim 5 , wherein the passage extension member extends the gas supply passage to a position deeper than the end of the bipolar electrode in the depth direction of the molten salt bath. A molten salt electrolysis method for electrolyzing a molten salt using the molten salt electrolysis apparatus according to any one of claims 1 to 6 ,
A molten salt electrolysis method, comprising the step of supplying a gas to the inside of a molten salt electrolysis device from the gas supply passage of the electrode. A method for producing a metal, comprising producing a metal by electrolysis of a molten salt using the molten salt electrolysis apparatus according to any one of claims 1 to 6 .

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