Molten salt electrolysis apparatus and production method for magnesium metal

Abstract

To provide a molten salt electrolysis apparatus that can effectively cool a molten bath using a heat exchanger of a collection chamber and a production method for a magnesium metal.SOLUTION: A molten salt electrolysis apparatus 11 of the present invention comprises: an electrolysis tank 1 in which a collection chamber 2b and an electrolytic chamber 2a are installed; and a heat exchanger 6 having a tubular member and disposed in the collection chamber 2b. The electrolysis tank 1 includes a partition wall 4 that partitions the collection chamber 2b and the electrolytic chamber 2a, and a rear wall 2c positioned behind the heat exchanger 6 with respect to the partition wall 4 in the collection chamber 2b. The heat exchanger 6 is provided with a bath flow adjustment plate 7 that raises at least part of the flow of a molten bath Bm, which flows diagonally downward from the electrolytic chamber 2a into the collection chamber 2b, and directs it toward the rear wall 2c located behind the heat exchanger 6.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a molten salt electrolysis apparatus including an electrolytic cell having a recovery chamber and an electrolysis chamber therein, and a heat exchanger disposed in the recovery chamber and having a tubular member, and a method for producing metallic magnesium using the same. [Background technology]

[0002] In industrial production of metallic titanium, magnesium chloride, which is a by-product of the reduction of titanium tetrachloride by the Kroll process, is decomposed into metallic magnesium and chlorine gas by molten salt electrolysis. The metallic magnesium obtained by molten salt electrolysis is used in the reduction of the titanium tetrachloride. In this way, magnesium is recycled. The chlorine gas obtained together with metallic magnesium by molten salt electrolysis can be used for the chlorination of titanium ore, which is a process prior to the reduction of titanium tetrachloride.

[0003] In molten salt electrolysis, molten salt containing magnesium chloride is stored in an electrolytic cell to form a molten bath, and magnesium chloride is decomposed into metallic magnesium and chlorine in the molten bath in the electrolysis chamber by applying a voltage between the anode and cathode of the electrodes. The metallic magnesium flows from the electrolysis chamber into the recovery chamber following the flow of the molten bath, and is recovered after floating to the bath surface of the molten bath due to the density difference with the molten salt in the recovery chamber.

[0004] As a technology related to molten salt electrolysis, Patent Document 1 proposes, with the objective of "providing a magnesium electrolytic production apparatus capable of increasing the magnesium capture rate in the collection chamber", a magnesium electrolytic production apparatus characterized in that it is equipped with: "an electrolytic chamber equipped with an anode and a cathode, and a collection chamber adjacent thereto via a partition wall, in which MgCl2 in the molten bath salt is electrolyzed in the electrolytic chamber to precipitate metallic magnesium, an electrolytic cell in which bath salt flow ports are provided in two levels, upper and lower, in the partition wall so that the molten bath salt in the electrolytic chamber is circulated to the collection chamber, and a bath salt collision member provided in the collection chamber opposite the upper level bath salt flow port so that at least a part of the molten bath salt flowing from the electrolytic chamber of the electrolytic cell through the upper level bath salt flow port collides with the collection chamber". [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-226683 A Summary of the Invention [Problem to be solved by the invention]

[0006] During molten salt electrolysis, if the temperature of the molten bath rises, metallic magnesium once produced in the molten salt electrolysis may react with chlorine gas, resulting in a re-reaction back to magnesium chloride. This leads to a decrease in current efficiency. To prevent this, it is necessary to maintain the temperature of the molten bath at a certain level using a heat exchanger placed in the recovery chamber of the electrolytic cell.

[0007] However, under the operating conditions of a typical heat exchanger arranged in the recovery chamber, the temperature of the molten bath may not be lowered as much as expected. For example, when further cooling is attempted by changing the operating conditions of the heat exchanger in order to lower the temperature of the molten bath, metallic magnesium remaining near the bath surface above the heat exchanger in the recovery chamber may be excessively cooled and solidify, which may force the operation to be stopped. Patent Document 1 does not pay any attention to the problems associated with cooling the molten bath using such a heat exchanger in the recovery chamber.

[0008] An object of the present invention is to provide a molten salt electrolysis apparatus and a method for producing metallic magnesium, which are capable of effectively cooling a molten bath by a heat exchanger in a recovery chamber. [Means for solving the problem]

[0009] As a result of extensive research using simulations, the inventors found that the molten salt does not flow smoothly near the rear wall behind the heat exchanger, and that this area is overcooled by the heat exchanger, while the temperature of the entire molten bath is difficult to lower. Based on this knowledge, the inventors have made the following invention.

[0010] The molten salt electrolysis apparatus of the present invention comprises an electrolytic cell having a recovery chamber and an electrolysis chamber therein, and a heat exchanger disposed in the recovery chamber and having a tubular member, wherein the electrolytic cell has a partition wall separating the recovery chamber from the electrolysis chamber, and a rear wall located in the recovery chamber rearward of the heat exchanger relative to the partition wall, and the heat exchanger is provided with a bath flow adjustment plate that raises at least a portion of the flow of molten bath flowing obliquely downward from the electrolysis chamber into the recovery chamber, and directs it toward the rear wall rearward of the heat exchanger.

[0011] The heat exchanger may have a plurality of main pipes spaced apart from one another and extending in the depth direction of the electrolytic cell, and one or more branch pipes connecting the main pipes to one another.

[0012] In this case, the bath flow adjusting plate can be attached to the branch pipe.

[0013] Furthermore, in this case, it is preferable that the bath flow adjusting plate protrudes from the branch pipe toward the partition wall and is provided in a direction inclined or perpendicular to the depth direction.

[0014] In addition, the branch pipe may include a straight pipe section extending from one of the two main pipes connected by the branch pipe to the other in a direction perpendicular to the depth direction, and in this case, it is preferable that the bath flow adjustment plate is provided along the straight pipe section.

[0015] The partition wall is provided with a partition flow passage that opens into the electrolysis chamber and the recovery chamber, respectively, and communicates the electrolysis chamber with the recovery chamber, and the recovery chamber side opening of the partition flow passage may be located deeper than the electrolysis chamber side opening in a cross section along the depth direction of the electrolytic cell. In this case, it is preferable that the bath flow adjustment plate is provided at a position deeper than the center point of the depth of the recovery chamber side opening.

[0016] Furthermore, it is even more preferable that, in a cross section along the depth direction, the bath flow adjustment plate is provided at the same depth position as the deep end point of the recovery chamber side opening or at a position deeper than said end point.

[0017] The bath flow adjusting plate can be detachably provided on the heat exchanger.

[0018] The method for producing metallic magnesium of the present invention involves electrolyzing magnesium chloride in a molten bath inside the electrolytic cell using any one of the molten salt electrolysis apparatuses described above. Effect of the Invention

[0019] According to the molten salt electrolysis apparatus of the present invention, the molten bath can be cooled effectively by the heat exchanger in the recovery chamber. [Brief description of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view taken along the depth direction of an electrolytic cell, showing a molten salt electrolysis apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] 3 is a cross-sectional view similar to FIG. 2, showing an electrolysis chamber of a molten salt electrolysis apparatus according to another embodiment. FIG. [Figure 4] FIG. 2 is an enlarged cross-sectional view showing a main part of the molten salt electrolysis apparatus of FIG. [Diagram 5] FIG. 13 is a diagram showing the results of a simulation with and without a bath flow adjustment plate. [Figure 6] FIG. 2 is a perspective view showing a heat exchanger provided in the molten salt electrolysis apparatus of FIG. [Figure 7] FIG. 11 is a perspective view showing another example of a heat exchanger. [Figure 8] FIG. 8 is a side view of the heat exchanger of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The drawings may show an example of an embodiment in a schematic manner to facilitate understanding, and the dimensions, shapes, numbers of members, and other aspects of each part in the drawings may be changed as appropriate.

[0022] A molten salt electrolysis apparatus 11 according to one embodiment of the present invention, as exemplified in FIG. 1, includes an electrolytic cell 1 having a molten bath Bm therein and provided with a recovery chamber 2b and an electrolysis chamber 2a.

[0023] The electrolytic cell 1 shown in the figure is made of firebrick and has a container shape, and is provided with a lid 5 that covers its upper opening. Note that the lid 5 may be divided into a portion that covers the opening on the electrolytic chamber 2a side of the electrolytic cell 1 and a portion that covers the opening on the recovery chamber 2b side, for example, as shown in Fig. 1.

[0024] This electrolytic cell 1 is provided with a partition wall 4 disposed substantially along the depth direction (the vertical direction in Fig. 1) inside. The partition wall 4 divides the inside of the electrolytic cell 1 into an electrolysis chamber 2a located on the right side of Fig. 1, where molten salt electrolysis is performed, and a recovery chamber 2b located on the left side of Fig. 1, into which metallic magnesium obtained by molten salt electrolysis in the electrolysis chamber 2a flows and into which the metallic magnesium accumulates on the upper side due to the density difference with the molten salt.

[0025] In the illustrated example, the partition wall 4 is disposed on the upper side in close proximity to the lid body 5. As a result, a bottom side flow path 4a that allows the movement of the molten salt from the recovery chamber 2b to the electrolysis chamber 2a is formed between the partition wall 4 and the bottom surface inside the electrolysis cell 1. In addition, the partition wall 4 is provided with a partition wall flow path 4b that opens into each of the electrolysis chamber 2a and the recovery chamber 2b and communicates the electrolysis chamber 2a with the recovery chamber 2b, thereby allowing the flow of metallic magnesium and the molten salt from the electrolysis chamber 2a to the recovery chamber 2b. Although the partition wall 4 is installed in two separate locations, left and right, in FIG. 1, the configuration, such as the shape and number, can be appropriately changed as long as the bottom side flow path 4a and the partition wall flow path 4b can be provided.

[0026] The electrolysis chamber 2a is provided with electrodes 3, which include an anode 3a and a cathode 3b that are partially immersed in the molten bath Bm and arranged side by side in a direction parallel to the depth direction. The anode 3a and the cathode 3b are connected to a power source or the like (not shown) when in use.

[0027] As long as the electrodes 3 include at least an anode 3a and a cathode 3b, the magnesium chloride in the molten bath Bm can be electrolyzed. On the other hand, from the viewpoint of improving the efficiency of producing metallic magnesium by electrolysis, it is preferable to dispose one or more, for example two, bipolar electrodes 3c, which are not connected to a power source and are polarized by applying a voltage between the anode 3a and the cathode 3b, in parallel with the anode 3a and the cathode 3b, between the anode 3a and the cathode 3b as shown in Figures 1 and 2. However, the bipolar electrode 3c is not necessarily required.

[0028] In addition, the electrolytic cell 1 in FIG. 1 and FIG. 2 has a substantially flat anode 3a, a cathode 3b, and a bipolar electrode 3c arranged side by side, but the electrolytic cell 21 may have an anode 23a, a cathode 23b, and a bipolar electrode 23c with the shape and arrangement shown in FIG. 3. The electrolytic cell 21 has a columnar or plate-like anode 23a such as a square column extending inside and outside the electrolytic cell 21 along the depth direction of the molten bath Bm in an electrolytic chamber 22a partitioned from a recovery chamber by a partition wall 24, a rectangular cylindrical cathode 23b such as a square cylindrical cathode arranged at a distance from the anode 23a to surround the periphery of the anode 23a, and a rectangular cylindrical bipolar electrode 23c arranged between the anode 23a and the cathode 23b. Although not shown, the electrodes may have a cylindrical anode and a cylindrical cathode and bipolar electrode. The rectangular cylindrical bipolar electrode 23c and the cylindrical bipolar electrode may be omitted. The electrolytic cell 21 in FIG. 3 can be substantially similar to the electrolytic cell 1 in FIG. 1 and FIG. 2 in terms of configuration other than the anode 23a, the cathode 23b, and the bipolar electrode 23c, and therefore detailed description thereof will be omitted.

[0029] In electrolysis performed using the molten salt electrolysis apparatus 11, molten salt electrolysis of magnesium chloride in the electrolysis chamber 2a produces metallic magnesium (Mg) as a molten metal on the surface of the cathode 3b through a reduction reaction based on the reaction MgCl2→Mg+Cl2, and generates chlorine (Cl2) gas on the surface of the anode 3a through an oxidation reaction.

[0030] More specifically, as shown in FIG. 1, the flow of the molten bath Bm (hereinafter also referred to as "bath flow") causes the molten salt to flow from the recovery chamber 2b through the bottom side flow passage 4a on the bottom side to the electrolysis chamber 2a. In the electrolysis chamber 2a, magnesium chloride in the molten salt is electrolyzed to generate metallic magnesium. Then, this metallic magnesium flows into the recovery chamber 2b together with the molten salt through the partition wall flow passage 4b ​​on the bath surface Sb side of the partition wall 4. Thereafter, the metallic magnesium, which has a smaller specific gravity than the molten salt, floats to a shallow portion of the recovery chamber 2b and accumulates there. The metallic magnesium that floats in the recovery chamber 2b can be recovered by a pump or the like (not shown). Therefore, metallic magnesium can be produced by such molten salt electrolysis. Chlorine gas generated together with metallic magnesium in the molten salt electrolysis is discharged to the outside, for example, through a pipe (not shown) provided on the cover 5 on the electrolysis chamber 2a side.

[0031] The metallic magnesium obtained by molten salt electrolysis 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. Magnesium chloride, which is a by-product of the Kroll process, can be used as the raw material for molten salt electrolysis.

[0032] In the above-mentioned molten salt electrolysis apparatus 11, not only metallic magnesium but also metallic aluminum and metallic zinc can be produced. In addition, the metal produced by the molten salt electrolysis can be used for the reduction of metallic chlorides, not limited to titanium tetrachloride, and can be used for the production of metallic zirconium, metallic hafnium, or metallic silicon in addition to metallic titanium.

[0033] Meanwhile, a heat exchanger 6 having a tubular member is disposed in the recovery chamber 2b. The heat exchanger 6 is a tubular member through which a gas or other fluid flows, and exchanges thermal energy between the fluid and the molten bath Bm. The molten bath Bm can be adjusted to a desired temperature by heating or cooling it using the heat exchanger 6. The heat exchanger 6, which may be made of steel, is disposed in the recovery chamber 2b to suppress corrosion caused by chlorine gas generated in the electrolysis chamber 2a.

[0034] 1, when viewed from the heat exchanger 6 of the recovery chamber 2b, the direction in which the partition wall 4 is located is defined as the front, and behind the heat exchanger 6 is located the rear wall 2c which constitutes part of the peripheral wall of the electrolytic cell 1. In other words, the heat exchanger 6 is disposed between the front partition wall 4 and the rear rear wall 2c.

[0035] In this embodiment, the heat exchanger 6 is provided with a bath flow adjusting plate 7 made of steel or the like. The inventors believe that this causes the bath flow described below. That is, when the flow of the molten bath Bm in the electrolytic cell 1 flows obliquely downward from the electrolysis chamber 2a through the partition wall 4 into the recovery chamber 2b, at least a part of the flow is raised by the bath flow adjusting plate 7 provided in the heat exchanger 6 as shown by the solid arrow in Fig. 4 compared to the case where the bath flow adjusting plate 7 is not provided, and is directed toward the rear wall 2c behind the heat exchanger 6.

[0036] According to this, the molten salt that tends to remain in the upper region between the heat exchanger 6 and the rear wall 2c is drawn into the flow of the molten bath Bm. As a result, the heat exchanger 6 can effectively cool almost the entire molten bath Bm, and solidification of metallic magnesium due to excessive cooling of the above region is suppressed. In particular, cooling by the heat exchanger 6 of this embodiment is effective when the temperature of the molten bath Bm rises due to Joule heat caused by the passage of electricity through the electrode 3. If the heat exchanger 6 can be effectively used to cool the molten bath Bm in this way, it is possible to suppress the re-reaction of metallic magnesium to magnesium chloride caused by the rise in temperature of the molten bath Bm and the associated decrease in current efficiency.

[0037] On the other hand, when the bath flow control plate 7 is not provided, the flow of the molten bath Bm flowing obliquely downward from the electrolysis chamber 2a to the recovery chamber 2b remains obliquely downward in the recovery chamber 2b as shown by the dashed arrow in FIG. 4, and passes through the bottom side flow path 4a from the recovery chamber 2b to the electrolysis chamber 2a. Therefore, the molten salt is likely to remain in the upper region between the heat exchanger 6 and the rear wall 2c, and the molten salt in that region tends to be excessively cooled by the heat exchanger 6. If the operating conditions of the heat exchanger 6 are changed to further lower the temperature of the molten bath Bm, the molten salt in the above region is further cooled, inducing the solidification of metallic magnesium. In this case, the solidification of metallic magnesium may force the operation to be stopped, and in order to avoid this, the operating conditions of the heat exchanger 6 must be returned to the original conditions, which makes it difficult to suppress the temperature rise of the molten bath Bm, which leads to a decrease in the current efficiency.

[0038] The results of a simulation to explain this are shown in FIG. 5. Fluent, manufactured by Ansys, was used for this simulation. In FIG. 5(a), since there is no bath flow adjustment plate, the flow of the molten bath in the recovery chamber is obliquely downward, and the temperature of the upper region between the heat exchanger and the rear wall is significantly reduced. In contrast, in FIG. 5(b), since the bath flow adjustment plate is provided, at least a part of the obliquely downward flow of the molten bath is directed more upward than in FIG. 5(a) toward the rear wall behind the heat exchanger. This suppresses the temperature reduction in the upper region between the heat exchanger and the rear wall.

[0039] As an example, as shown in Fig. 6, the heat exchanger 6 may have two or more main pipes 6a that are spaced apart from each other and extend in the depth direction of the molten bath Bm, and one or more branch pipes 6b that are located inside the molten bath Bm during molten salt electrolysis and communicate with the main pipes 6a. The main pipes 6a and the branch pipes 6b correspond to tubular members. In the heat exchanger 6 in Fig. 6, three branch pipes 6b consisting of straight pipe portions are aligned in the depth direction, extend in a direction perpendicular to the depth direction, and are connected to the opposing portions of the two main pipes 6a.

[0040] 7 and 8, the branch pipes 16b may include curved pipe portions extending from the sides of the main pipes 16a, and straight pipe portions extending linearly between the curved pipe portions in a direction perpendicular to the depth direction. In this case, as shown in the figures, the pair of branch pipes 16b located on both sides of the main pipe 16a may be arranged in multiple pairs, for example, three pairs, in the depth direction. However, although not shown, the main pipe may be a single pipe, and there are also heat exchangers that do not have branch pipes.

[0041] In the case of the heat exchanger 6, 16 having the main pipe 6a, 16a and the branch pipe 6b, 16b as exemplified in Figs. 6 to 8, the bath flow adjusting plate 7 can be attached to the branch pipe 6b, 16b. More specifically, as shown in Figs. 1, 4 and 6 to 8, the bath flow adjusting plate 7 is preferably oriented in a direction inclined or perpendicular to the depth direction so as to protrude from the branch pipe 6b, 16b toward the partition wall 4. In the figures, the bath flow adjusting plate 7 is oriented almost perpendicular to the depth direction. In this way, the bath flow that is diagonally downward is changed in direction by the bath flow adjusting plate 7, so that it becomes easier to rise, and it is considered that the retention of the molten salt behind the heat exchanger 6 is more easily eliminated.

[0042] In addition, it is considered that the bath flow adjusting plate 7 attached to the branch pipes 6b, 16b as described above allows most of the molten salt in the bath flow to come into contact with the branch pipes 6b, 16b, and therefore the molten bath Bm can be cooled more effectively. In particular, in the heat exchanger 16 shown in Figures 7 and 8, the bath flow adjusting plate 7 is attached to the branch pipe 16b located on the partition wall 4 side of the pair of branch pipes 16b separated by the main pipe 16a, in a direction protruding toward the partition wall 4 side. Therefore, it is considered that the bath flow is guided between or inside the pair of branch pipes 16b, and the molten salt is cooled more effectively between them.

[0043] In the heat exchangers 6, 16 in which the branch pipes 6b, 16b include straight pipe portions as shown in Figs. 6 to 8, the bath flow adjusting plate 7 is preferably provided along the straight pipe portions. In this way, the bath flow change effect of the bath flow adjusting plate 7 can be obtained in the direction parallel to the straight pipe portions of the branch pipes 6b, 16b (depth direction in Figs. 1 and 4). In particular, it is more preferable to provide the bath flow adjusting plate 7 along almost the entire extension direction of the straight pipe portions. In addition, when the main pipes 6a, 16a are arranged side by side along the extension direction of the partition wall 4 and the rear wall 2c in a cross section perpendicular to the depth direction as shown in Fig. 2, the straight pipe portions of the branch pipes 6b, 16b often follow the extension direction of the partition wall 4 and the rear wall 2c.

[0044] Incidentally, the partition wall flow passage 4b ​​formed in the partition wall 4 opens to each of the electrolysis chamber 2a and the recovery chamber 2b, and therefore has a recovery chamber side opening 4c and an electrolysis chamber side opening 4d, as shown in Fig. 4. In this case, the recovery chamber side opening 4c may be provided at a deeper position than the electrolysis chamber side opening 4d in the depth direction. Even if the recovery chamber side opening 4c and the electrolysis chamber side opening 4d are partially overlapped in the depth direction, the deeper end point Pe2 of the recovery chamber side opening 4c may be located below the deeper end point of the electrolysis chamber side opening 4d.

[0045] Here, the bath flow adjusting plate 7 is preferably provided at a position deeper than the center point Pc of the depth of the collection chamber side opening 4c (the midpoint in the depth direction between the shallow end point Pe1 and the deep end point Pe2) in the cross section in the depth direction. Furthermore, it is even more preferable that the bath flow adjusting plate 7 is provided at the same depth position as the deep end point Pe2 of the collection chamber side opening 4c or at a position deeper than the end point Pe2 in the same cross section. This makes it easier for the molten salt that flows obliquely downward from the collection chamber side opening 4c and enters the collection chamber 2b to hit the bath flow adjusting plate 7, and the flow is more effectively directed toward the rear wall 2c. It is sufficient that the bath flow adjusting plate 7 is provided at the above position in at least a part of the cross section in the direction in which the straight pipe part of the branch pipe 6b extends.

[0046] In the illustrated example, the bath flow adjusting plate 7 is flat. Although not illustrated, the bath flow adjusting plate may have a bent or curved portion. The bath flow adjusting plate 7 may be a single plate or multiple plates, and multiple plates may be arranged intermittently in the direction in which the straight pipe portion of the branch pipe extends, or may be arranged side by side in the depth direction. Although not illustrated, one or more through or non-through holes and / or one or more grooves may be formed in a portion of the bath flow adjusting plate.

[0047] The bath flow adjusting plate 7 may be fixed to the heat exchangers 6, 16, such as the branch pipes 6b, 16b, by welding or the like, but is preferably detachably attached to the heat exchangers 6, 16. If the bath flow adjusting plate 7 is detachable from the heat exchangers 6, 16, when the heat exchangers 6, 16 are replaced due to aging or other reasons, the same bath flow adjusting plate 7 can be attached to the new heat exchangers 6, 16 and used. Also, if the bath flow adjusting plate 7 needs to be replaced for some reason, it can be replaced with a new bath flow adjusting plate 7, and the same heat exchangers 6, 16 can be used.

[0048] There is no particular limitation on the manner in which the bath flow adjusting plate 7 can be detachably attached, but for example, in Figures 6 to 8, the bath flow adjusting plate 7 is provided with two engagement members 7a that can be hooked onto the branch pipes 6b, 16b. The engagement members 7a can be hooked onto any of the branch pipes 6b, 16b that are lined up in the depth direction so that the bath flow adjusting plate 7 is at an appropriate position in the depth direction, but here, they are hooked onto the branch pipes 6b, 16b located at the shallowest side (upper side). EXAMPLES

[0049] Next, a prototype of the molten salt electrolysis apparatus of the present invention was produced and its effects were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0050] Magnesium chloride was electrolyzed using a molten salt electrolysis device having the configuration shown in Figures 1 and 2, except for the heat exchanger. The electrolysis cell had an inner wall made of bricks with an Al2O3 content of 95% or more and a 2m 3 of electrolysis chamber and 1m 3 The electrolysis chamber had a graphite anode and a carbon steel cathode, and two graphite bipolar plates were placed between the anode and the cathode. As a result, the number of anodes and cathodes in the cross-sectional view shown in Figure 2 was three, that is, the number of electrolysis times N was three. The composition of the molten salt in the molten bath was 20%, 30%, 49%, and 1% by mass of MgCl2, CaCl2, NaCl, and MgF2, respectively. The operation was started under these conditions, and the period from the 25th month after the start of operation to one month was the operation period to be evaluated. During the operation period to be evaluated, the temperature of the molten bath was measured using a thermocouple placed between the opening of the partition wall on the recovery chamber side and the heat exchanger.

[0051] The heat exchanger was a pair of branch pipes, each having a straight portion and a curved portion, connected to two main pipes, as shown in Figures 7 and 8. In the comparative example, the heat exchanger was not provided with a bath flow control plate, whereas in the example, the bath flow control plate was provided by hanging it from the uppermost branch pipe on the partition wall side by hooking two engaging members on the branch pipe, as shown in Figures 7 and 8. In addition, the bath flow control plate was provided at a position deeper than the deepest end point of the opening of the partition wall on the recovery chamber side, as shown in Figure 4.

[0052] In the comparative example, the temperature of the molten bath was relatively high at 657°C. Therefore, just before the end of the operation period to be evaluated, an attempt was made to further cool the molten bath by changing the operating conditions of the heat exchanger, but the metallic magnesium on the upper side of the recovery chamber solidified. Since the metallic magnesium had solidified, it was difficult to operate at a lower temperature of the molten bath. The current efficiency for one month was 84.8%. The current efficiency is a value calculated by the following formula, and the same applies to the examples described below. Current efficiency (%) = 100 × mass of metallic magnesium recovered from electrolytic cell / theoretical metallic magnesium production The theoretical production amount of metallic magnesium is the theoretical production amount of metal obtained from Faraday's law and is calculated by the following formula. Theoretical metallic magnesium production volume = ((current (A) x current flow time (sec)) / (number of charges on magnesium ions n x Faraday constant F)) x number of electrolysis times N x atomic weight of magnesium

[0053] In the embodiment, the temperature of the molten bath was maintained at 654°C. In the embodiment, the temperature of the molten bath was lower than that in the comparative example, but the metallic magnesium did not solidify. The current efficiency for one month was 86.6%. This result indicates that the current efficiency was improved by 1.8% compared to the comparative example, and that electricity saving of about 200 kWh is expected when producing one ton of metallic magnesium.

[0054] From the above, it is suggested that the molten salt electrolysis apparatus of the present invention can effectively cool the molten bath by the heat exchanger in the recovery chamber. [Explanation of symbols]

[0055] 1, 21 Electrolytic cell 2a, 22a Electrolysis room 2b Recovery Room 2c back wall 3 electrodes 3a, 23a anode 3b, 23b cathode 3c, 23c bipolar 4, 24 Bulkhead 4a Bottom side channel 4b Partition channel 4c Recovery room side opening 4d Electrolytic chamber side opening 5 Lid 6, 16 Heat exchanger 6a, 16a master 6b, 16b branch pipe 7 Adjustment plate 7a Engagement member 11 Molten salt electrolysis equipment Bm molten bath Pc Depth center point of the opening on the recovery chamber side Pe1 Shallow end of the opening on the recovery chamber side Pe2 Deep end point of the opening on the recovery chamber side Sb bath surface

Claims

1. A molten salt electrolysis apparatus comprising: an electrolytic cell having a recovery chamber and an electrolysis chamber therein; and a heat exchanger disposed in the recovery chamber and having a tubular member, the electrolytic cell has a partition wall that separates the recovery chamber from the electrolysis chamber, and a rear wall that is located rearward of the heat exchanger with respect to the partition wall in the recovery chamber, A molten salt electrolysis apparatus in which the heat exchanger is provided with a bath flow adjustment plate that raises at least a portion of the molten bath flow flowing obliquely downward from the electrolysis chamber into the recovery chamber and directs it toward the rear wall side behind the heat exchanger.

2. 2. The molten salt electrolysis apparatus according to claim 1, wherein the heat exchanger has a plurality of main pipes spaced apart from each other and extending in the depth direction of the electrolytic cell, and one or more branch pipes connecting the main pipes to each other.

3. 3. The molten salt electrolysis apparatus according to claim 2, wherein the bath flow adjusting plate is attached to the branch pipe.

4. 4. The molten salt electrolysis apparatus according to claim 3, wherein the bath flow adjusting plate protrudes from the branch pipe toward the partition wall and is provided in a direction inclined or perpendicular to the depth direction.

5. the branch pipe includes a straight pipe portion extending in a direction perpendicular to the depth direction from one of the two main pipes communicated by the branch pipe to the other of the two main pipes, 3. The molten salt electrolysis apparatus according to claim 2, wherein the bath flow adjusting plate is provided along the straight pipe portion.

6. a partition wall having a partition wall flow passage that opens to each of the electrolysis chamber and the recovery chamber and communicates between the electrolysis chamber and the recovery chamber; 2. The molten salt electrolysis apparatus according to claim 1, wherein, in a cross section along the depth direction of the electrolytic cell, a recovery chamber side opening of the partition flow path is located at a deeper position than an electrolysis chamber side opening, and the bath flow adjustment plate is provided at a deeper position than a center point of a depth of the recovery chamber side opening.

7. The molten salt electrolysis apparatus according to claim 6, wherein, in a cross section along the depth direction, the bath flow adjustment plate is provided at the same depth position as the deep end point of the recovery chamber side opening or at a position deeper than the deep end point.

8. 2. The molten salt electrolysis apparatus according to claim 1, wherein the bath flow adjusting plate is detachably provided on the heat exchanger.

9. A method for producing metallic magnesium, comprising electrolyzing magnesium chloride in a molten bath inside the electrolytic cell using the molten salt electrolysis apparatus according to any one of claims 1 to 8.

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