Metal manufacturing methods

Abstract

To provide a method for producing metals that can cope with a reduction of production of metals while keeping power consumption at a relatively low level.SOLUTION: A method for producing metals is to produce metals by molten salt electrolysis. In the method, an electrolysis device 1 is used that includes an electrolytic cell 2 to store molten salt bath inside and two or more sets of electrodes 3 including an anode 3a to be brought into contact with the molten salt bath and a cathode 3b; in at least one period from the start of use of the electrolysis device 1 to a lapse of 30 months, application of voltage to at least one pair of electrodes 3 out of the two or more sets of electrodes 3 is stopped; and the current density at the remainder of the electrode 3 is controlled to 0.5 A / cm2 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing metals by molten salt electrolysis, and in particular to a technique for enabling good production of metals during reduced production. [Background technology]

[0002] For example, to produce metallic magnesium, molten salt electrolysis may be performed using a molten salt bath containing magnesium chloride. In molten salt electrolysis, molten salt is stored in an electrolytic cell of an electrolytic device to form a molten salt bath, and magnesium chloride in the molten salt bath is decomposed into metallic magnesium and chlorine by electrodes including an anode and a cathode. Thus, metallic magnesium is obtained. An electrolytic device equipped with two or more pairs of electrodes including an anode and a cathode may be used.

[0003] The metallic magnesium thus produced can be used to reduce titanium tetrachloride to metallic titanium by the Kroll process. Note that the magnesium chloride produced as a by-product of the reduction of titanium tetrachloride can be used in the production of metallic magnesium by being added to the molten salt bath in the above-mentioned molten salt electrolysis.

[0004] As a related technique, Patent Document 1 describes "a method for producing a metal by molten salt electrolysis using a molten metal electrolysis apparatus having an electrolytic cell and an electrode pair, characterized in that electrolysis of the molten metal salt in the electrolytic cell and heating of the molten metal salt by Joule heat generated between the electrode pair performing the electrolysis are performed simultaneously, the molten metal electrolysis apparatus has at least two sets of electrode pairs, and at least one of the electrode pairs is open." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 002377 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, in the production of metals such as metallic magnesium by the above-mentioned molten salt electrolysis, it may be necessary to reduce the production amount of metals depending on the situation or time. For example, when producing metallic magnesium for use in the production of metallic titanium in the Kroll process described above, when the production amount of metallic titanium is reduced, the production amount of metallic magnesium may also be reduced accordingly. This is because if metallic magnesium is produced and stored as usual without reducing the production amount, there is a concern that metallic magnesium, which easily reacts with oxygen in the air, will oxidize during storage and that magnesium oxide impurities will be brought into the reduction reaction of titanium tetrachloride. For this reason, it is desirable to produce metallic magnesium in the required amount at the appropriate time.

[0007] One possible way to reduce metal production is to reduce the total amount of current flowing through the electrolysis device. However, even if the total amount of current is simply reduced in an electrolysis device equipped with two or more sets of electrodes, a problem remains in that a certain amount of power consumption is still required to achieve the desired amount of metal production through reduced production.

[0008] An object of the present invention is to provide a method for producing metal that can effectively deal with reduced metal production while keeping power consumption relatively low. [Means for solving the problem]

[0009] After much deliberation, the inventors came up with the idea of ​​stopping the application of voltage between some of the two or more pairs of electrodes during the reduced production period, while maintaining a relatively high current density at the remaining electrodes. This makes it possible to achieve the desired reduced production volume with relatively low power consumption. However, as the electrolysis device is used, the electrodes thin, and the electric resistance increases due to the increase in the distance between the electrodes, which increases power consumption. Therefore, it is desirable to set the reduced production period at least once during the 30th month after the start of use of the electrolysis device.

[0010] The method for producing metals of the present invention is a method for producing metals by molten salt electrolysis, which uses an electrolysis device having an electrolytic cell for storing a molten salt bath therein and two or more pairs of electrodes including an anode and a cathode that are in contact with the molten salt bath, and at least one period within 30 months from the start of use of the electrolysis device, stops the application of a voltage between at least one of the two or more pairs of electrodes, and keeps the current density at the remaining part of the electrodes at 0.5 A / cm 2 That is all.

[0011] In the method for producing metals of the present invention, an electrolytic device in which two or more pairs of electrodes, the anodes and cathodes, are arranged alternately side by side, can be used.

[0012] During the at least one period, at least one anode can be electrically disconnected from the power source to stop application of voltage between the electrodes including the anode.

[0013] At least one set of electrodes may further include a bipolar electrode disposed between the anode and the cathode.

[0014] During said at least one period, the current density at the remainder of said electrode is 0.5 A / cm 2 ~1.2A / cm 2 It is preferable to set the above.

[0015] During the at least one period, it is preferable to reduce the total amount of current flowing through the electrolysis device to 70% to 90% of the total amount of current during a normal period.

[0016] The electrolysis apparatus may include a temperature regulator capable of adjusting the temperature of the molten salt bath. In this case, it is preferable to adjust the temperature of the molten salt bath using the temperature regulator during the at least one period.

[0017] The metal may be magnesium metal, aluminum metal or zinc metal.

[0018] When the above metals are produced by molten salt electrolysis, chlorine gas may be produced.

[0019] The metal may be one used in the production of titanium metal, zirconium metal, hafnium metal or silicon metal. Effect of the Invention

[0020] According to the metal manufacturing method of the present invention, it is possible to effectively deal with reduced metal production while keeping power consumption relatively low. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view taken along the depth direction of a molten salt bath, showing an example of an electrolysis apparatus capable of carrying out a metal production method 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] 1 is a graph showing an example of an increase in interelectrode voltage over the course of use of an electrolysis device. [Figure 4] 3 is a cross-sectional view similar to FIG. 2, showing an electrolysis chamber of another example of the electrolysis device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail. A method for producing a metal according to one embodiment of the present invention involves, in producing a metal using an electrolysis apparatus 1 as exemplified in FIG. 1, stopping the application of a voltage between at least one pair of electrodes that is a part of two or more pairs of electrodes, and setting the current density between the remaining portions of the electrodes to 0.5 A / cm at least once during the period up to 30 months after the start of use of the electrolysis apparatus 1. 2 This method is particularly effective in dealing with production cuts that reduce the amount of metal produced.

[0023] (electrolyzer) The illustrated electrolysis device 1 includes an electrolysis cell 2 that stores a molten salt bath therein, and two or more pairs of electrodes 3 including an anode 3a and a cathode 3b that are brought into contact with the molten salt bath.

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

[0025] In the illustrated example, the partition wall 4 is disposed adjacent to a cover member 5 for covering an upper opening of the electrolytic cell 2. As a result, a molten salt circulation path 4a that allows the molten salt bath to move from the recovery chamber 2b to the electrolytic cell 2a is formed between the partition wall 4 and the bottom surface inside the electrolytic cell 2. In addition, a molten metal flow path 4b provided in a portion of the partition wall 4 above the molten salt circulation path 4a allows metallic magnesium to flow from the electrolytic cell 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 molten salt circulation path 4a and the molten metal flow path 4b can be provided.

[0026] The electrode 3 is disposed on the electrolysis chamber 2a side inside the electrolysis cell 2, and has a portion disposed side by side parallel to the depth direction of the molten salt bath. The electrode 3 includes an anode 3a and a cathode 3b connected to a power source or the like (not shown). As long as the electrode 3 has at least the anode 3a and the cathode 3b, it is possible to electrolyze magnesium chloride in the molten salt bath.

[0027] From the viewpoint of improving the efficiency of electrolysis to produce metallic magnesium, it is preferable to further provide one or more, for example two, bipolar electrodes 3c between the anode 3a and the cathode 3b that are not connected to a power source and are polarized by application of a voltage between the anode 3a and the cathode 3b, as can be seen from Fig. 2. Here, a set of electrodes 3 refers to one including at least one anode 3a and one cathode 3b. When a bipolar electrode 3c is provided, a set of electrodes 3 also refers to one including one or more bipolar electrodes 3c. It is also possible to omit the bipolar electrode 3c from at least one of the two or more sets of electrodes 3.

[0028] In this electrolysis device 1, as can be seen from Fig. 2, the anodes 3a and cathodes 3b of each electrode 3 are arranged alternately and parallel to each other in a direction (electrode alignment direction) perpendicular to the depth direction of the molten salt bath. The bipolar electrode 3c is arranged alternately between adjacent anodes 3a and cathodes 3b and parallel to the anodes 3a and cathodes 3b. In the illustrated example, the anodes 3a and cathodes 3b in the electrode 3 are shared with the adjacent electrode 3, and electrolysis is carried out on both sides of each anode 3a and cathode 3b.

[0029] The electrolysis device 1 may further include a temperature regulator 6, which is disposed in the recovery chamber 2b or the like and adjusts the temperature of the molten salt bath. In the illustrated example, the temperature regulator 6 is a tubular heat exchanger through which gas flows as a heating medium or a cooling medium, and has two main pipes extending in the depth direction of the molten salt bath and a branch pipe extending in a direction perpendicular to the depth direction and connecting the main pipes. However, the temperature regulator is not limited to the one illustrated, as long as it can adjust the temperature of the molten salt bath.

[0030] The molten salt constituting the molten salt bath may contain a supporting salt in addition to magnesium chloride (MgCl2). The supporting salt means an electrolyte that lowers the crystallization temperature and reduces the viscosity when mixed with magnesium chloride. Specifically, the supporting salt may be at least one selected from the group consisting of sodium chloride (NaCl), calcium chloride (CaCl2), potassium chloride (KCl), magnesium fluoride (MgF2) and calcium fluoride (CaF2). The crystallization temperature refers to the temperature at which a phenomenon called crystallization occurs, in which one electrolyte component begins to precipitate as a solid, when the temperature of a molten salt consisting of two or more electrolytes is lowered from a liquid state. If there is only one type of molten salt, the entire salt becomes solid at the freezing point when the temperature is lowered from a liquid state, so the crystallization temperature corresponds to the freezing point, i.e., the melting point. In addition, in order to preferentially decompose magnesium chloride by electrolysis, it is common to use an electrolyte with a higher decomposition voltage than magnesium chloride as the supporting salt.

[0031] In molten salt electrolysis performed using the electrolytic cell 2, magnesium chloride is electrolyzed in the electrolytic chamber 2a, and based on the reaction MgCl2 → Mg + Cl2, metallic magnesium (Mg) as a molten metal is produced by a reduction reaction on the surface of the cathode 3b, while chlorine (Cl2) gas is generated by an oxidation reaction on the surface of the anode 3a.

[0032] More specifically, due to convection in the molten salt bath, as shown in FIG. 1, the molten salt flows from the recovery chamber 2b through the molten salt circulation path 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. This metallic magnesium then flows into the recovery chamber 2b through the molten metal flow path 4b on the bath surface 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, this allows metallic magnesium to be produced from the molten salt. In addition, chlorine gas is obtained.

[0033] The metallic magnesium produced 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.

[0034] The electrolysis apparatus 1 described above can produce not only metallic magnesium but also metallic aluminum and metallic zinc. In addition, the metal produced in the molten salt bath using the electrolysis apparatus 1 can be used for the reduction of metal chlorides, not limited to titanium tetrachloride, and can be used to produce metallic zirconium, metallic hafnium, or metallic silicon in addition to metallic titanium.

[0035] (Production cutback period) When producing metals such as metallic magnesium using the electrolysis apparatus 1 as described above, it may be necessary to temporarily reduce the production amount of the metal. For example, when producing metallic magnesium to be used in the production of metallic titanium by the Kroll process, the production amount of metallic magnesium may be reduced in line with the reduction in the production amount of metallic titanium. This is because metallic magnesium is prone to react with oxygen in the air to form oxides, and it is desirable to produce an appropriate amount at a time to prevent contamination of metallic titanium caused by such oxides.

[0036] As the electrolysis device 1 is used to perform molten salt electrolysis, the inter-electrode voltage increases, and large power consumption is required, as shown in an example in Figure 3. This is thought to be because the electrodes 3 are thinned with use of the electrolysis device 1, the distance between the electrodes 3 increases, and the electrical resistance increases. Even if the voltage increases significantly, for example to about 15V, it is maintained below the decomposition voltage of the supporting salt, so the supporting salt does not usually decompose. Magnesium chloride decomposes at about 2.8V. In order to keep power consumption during the reduced production period low, the reduced production period is preferably set at least once during the period up to 30 months from the time the electrolysis device 1 is constructed and the use of the molten salt electrolysis is started. More preferably, the reduced production period is set at least once during the period up to 16 months from the time the use of the electrolysis device 1 is started.

[0037] In addition, when the interelectrode voltage increases and the electrical resistance becomes large, a larger proportion of the power supplied to the electrolysis device 1 is consumed as Joule heat. Maintenance of the temperature of the molten salt bath depends heavily on the temperature regulator 6 in the early stages of use when the interelectrode voltage is small, but as the period of use progresses, the molten salt bath becomes more likely to be heated by Joule heat of the electrodes 3, and so the dependency on the temperature regulator 6 may decrease.

[0038] During the production cutback period, the application of voltage between at least one pair of electrodes 3 that is a part of two or more pairs of electrodes 3 is stopped, and the current density between the remaining electrodes 3 where the voltage application is not stopped is set to 0.5 A / cm 2 This makes it possible to achieve the desired amount of metal production through reduced production while consuming less electricity than during periods when production is not reduced.

[0039] When the total amount of current flowing through the electrolysis apparatus 1 is reduced without stopping the application of voltage between some of the electrodes 3, the total amount of current required for production of a metal such as metallic magnesium becomes larger than when the application of voltage to some of the electrodes 3 is stopped.

[0040] Furthermore, by stopping the application of voltage between some of the electrodes 3 and maintaining the current density of the remaining electrodes 3 to which the voltage application is not stopped high as described above, a certain amount of metal required for reduced production can be produced with high current efficiency. If the current density of the remaining electrodes 3 is made too low, the required reduced production volume may not be achieved, and the current efficiency may decrease.

[0041] Stopping the application of voltage between some of the electrodes 3 can be achieved, for example, in the illustrated electrolysis device 1 by electrically disconnecting at least one anode 3a from a power source (not shown). When an anode 3a in which electrolysis is performed on both sides is electrically disconnected from the power source, electrolysis on both sides is no longer performed. Both the anode 3a and the cathode 3b included in at least one pair of electrodes 3 may be electrically disconnected from the power source.

[0042] During the production cut-off period, the current density of the remaining part of the electrode 3 to which the voltage application is not stopped is preferably 0.5 A / cm 2 ~1.2A / cm 2 , more preferably 0.5 A / cm 2 ~1.0A / cm 2 By lowering the current density in the remaining portion of the electrode 3 to a certain degree, it is possible to suppress power consumption caused by the generation of Joule heat.

[0043] Here, the "reduced production period" is an example in which, at least for a period of 30 months from the start of use of the electrolysis apparatus, the application of voltage between at least one pair of electrodes is stopped and the current density at the remaining part of the electrodes is reduced to 0.5 A / cm. 2 This invention includes any period during which the production volume of metals does not have to decrease.

[0044] When the application of voltage between some of the electrodes 3 is stopped during the reduced production period, the current density of the remaining electrodes 3 increases even if the total amount of current flowing through the electrolysis device 1 is not changed. An excessive increase in current density generates a lot of Joule heat and increases power consumption. To prevent this, it is preferable to reduce the total amount of current flowing through the electrolysis device 1 during the reduced production period to 70% to 90% of the total current amount during normal periods other than the reduced production period. By reducing the total amount of current, it is also possible to adjust the amount of metal produced during the reduced production period.

[0045] As described above, if the current density of the remaining part of the electrode 3 is maintained at a certain level or the total current to the electrolysis device 1 is reduced, the Joule heat of the electrode 3 is reduced. In this case, it is preferable to adjust the temperature of the molten salt bath using the temperature regulator 6. This allows the molten salt bath to be heated efficiently with less power compared to the case where a large amount of Joule heat is generated by increasing the current density or the total current. It is preferable to heat the molten salt bath using the temperature regulator 6 at least within 30 months after the start of use of the electrolysis device. This is because during that time, there is not much thinning of the electrode 3 and the amount of Joule heat generated is relatively small.

[0046] In this way, it is desirable to heat the molten salt bath by using an appropriate combination of the Joule heat of the electrode 3 and the temperature regulator 6. For example, when producing metallic magnesium, the temperature of the molten salt bath can be maintained within a range of preferably 655°C to 680°C, more preferably 655°C to 665°C. By increasing the temperature of the molten salt bath to a certain degree, it is possible to suppress the solidification of metallic magnesium. However, if the temperature of the molten salt bath is too high, there is no particular advantage and thermal energy is wasted.

[0047] In the above description, the electrolysis device 1 in which the plate-shaped electrodes 3 are arranged in parallel in the electrolysis chamber 2a has been described as an example, but an electrolysis device 11 as shown in FIG. 4 may also be used. In this electrolysis device 11, the electrodes provided in the electrolysis chamber 12a include a columnar or plate-shaped anode 13a such as a square column extending inside and outside the electrolysis cell 12, a rectangular cylindrical cathode 13b such as a square cylindrical cathode arranged at a distance from the anode 13a while surrounding the periphery of the anode 13a, and a rectangular cylindrical bipolar electrode 13c arranged between the anode 13a and the cathode 13b. Although the bipolar electrode 13c can be omitted, an electrolysis device having two or more sets of such electrodes may be used. Although not shown in the drawings, the electrodes may be changed to one having a cylindrical anode and a cylindrical cathode and bipolar electrode.

[0048] As described above, when using an electrode 13 having a shape in which the cathode 13b (and the cathode 13b and the bipolar electrode 13c when the electrode 13 further includes the bipolar electrode 13c) surrounds the anode 13a, the current density may differ between the anode 13a and the cathode 13b. In this case, when the application of a voltage between at least one of the two or more pairs of electrodes 13 included in the electrolysis device 11 is stopped, the current density of the cathode 13b among the current densities in the remaining part of the electrodes 13 may be 0.5 A / cm 2 If the voltage is equal to or greater than 0.5 A / cm2, the application of voltage to at least one of the two or more pairs of electrodes is stopped, and the current density in the remaining part of the electrodes is set to 0.5 A / cm2. 2 It is assumed that the above-mentioned condition is satisfied. Since the anode 13a is surrounded by the cathode 13b and the bipolar electrode 13c, the current density of the anode 13a is usually higher than that of the cathode 13b. EXAMPLES

[0049] Next, the method for producing metallic magnesium according to the present invention was experimentally carried out, and the effects thereof were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0050] (Test Example 1) An electrolytic device having the configuration shown in Figs. 1 and 2 was constructed, and metallic magnesium was produced during a one-month reduced production period when 10 months had passed since the start of use of the electrolytic device. In other words, the reduced production period was set to one month, which was the 11th month after the start of use of the electrolytic device. During the reduced production period, an attempt was made to reduce the production volume so that the target production volume of metallic magnesium would be 80% of the normal period before that, which was set to 100%. In addition, during the reduced production period, the total current flowing through the electrolytic device was reduced to 80% of the total current (A) during the normal period. Note that "the start of use of the electrolytic device" refers to the point in time when the temperature of the molten salt bath reaches the lower limit (here, 655°C) of the target temperature range (655°C to 665°C in the embodiment), as described later. The preparation period for the electrolytic device, such as the formation of the molten salt bath, corresponds to "before the start of use of the electrolytic device".

[0051] In both normal and reduced production periods, the temperature of the molten salt bath was maintained within the range of 655°C to 665°C by adjusting the flow rate of the combustion gas of the heating medium of the temperature regulator. If the heating by Joule heat of the electrodes is not sufficient, the gas consumption in the temperature regulator will increase in order to maintain the temperature of the molten salt bath.

[0052] The electrolytic cell of the electrolysis device has an inner wall made of bricks with an Al2O3 content of 95% or more, and the electrolysis chamber is 2 m 3 , the recovery room is 1m 3 Seven graphite anodes and eight steel cathodes were installed in the electrolysis chamber, and two graphite bipolar electrodes were placed between each anode and cathode. The composition of the molten salt bath was 20%, 30%, 49%, and 1% by mass of MgCl2, CaCl2, NaCl, and MgF2, respectively.

[0053] In Example 1, during the reduced production period, one of the seven anodes located in the center (fourth from the end) in the electrode alignment direction was electrically disconnected from the power source to produce metallic magnesium. During the reduced production period, the current density was continuously 0.5 A / cm from before the reduced production period. 2 maintained.

[0054] In Comparative Example 1, the application of voltage between the electrodes was not stopped during the reduced production period, and the current density of the electrodes was 0.4 A / cm due to the reduction in the total current amount. 2 Metallic magnesium was produced in substantially the same manner as in Example 1, except that the temperature was reduced to

[0055] In Example 1, 80% of the target production amount during the reduced production period was achieved. On the other hand, in Comparative Example 1, the production amount during the reduced production period was reduced by 2% compared to Example 1. Therefore, in Comparative Example 1, the target production amount could not be achieved. That is, it means that the necessary amount of metallic magnesium could not be secured at the desired time in the titanium tetrachloride reduction process. The total current amount flowing through the electrolysis device is the same in Example 1 and Comparative Example 1. From this result of Comparative Example 1, it can be seen that it is difficult to deal with a reduction in a predetermined production amount by simply reducing the total current amount. If the total current amount is increased to more than 80% during the reduced production period in Comparative Example 1, it is considered that the target production amount can be achieved without stopping the application of voltage between the electrodes, but in this case, the current consumption per unit amount of metallic magnesium increases.

[0056] When Comparative Example 1 is taken as the standard (100%), the flow rate of the gas used in the temperature regulator in Example 1 was reduced by 25% compared to Comparative Example 1. Example 1 has a smaller flow rate of the gas used in the temperature regulator, and can be said to be superior to Comparative Example 1 in terms of temperature regulation of the molten salt bath.

[0057] (Test Example 2) In Example 2, metallic magnesium was produced in a manner substantially similar to that of Example 1, except that a one-month production cutback period was provided when 14 months had passed since the start of use of the electrolytic apparatus. In other words, the production cutback period was set to one month, which was the 15th month after the start of use of the electrolytic apparatus.

[0058] As a result, even in Example 2, it was possible to achieve 80% of the above-mentioned target production volume during the reduced production period. The flow rate of the gas used in the temperature regulator in Example 2 was further reduced by 2% compared to Example 1. The total current was the same as in Example 1.

[0059] From the results of Example 2, it was found that even if a production reduction period is set when the electrolysis device has been in use for a certain period of time, the device can respond well to the production reduction. However, if the period of time elapsed since the start of use of the electrolysis device becomes too long, the power loss due to the generation of Joule heat increases. Therefore, as can be seen from FIG. 3, it is preferable to set a production reduction period within 30 months from the start of use. More preferably, the production reduction period is set within 16 months from the start of use. However, the electrolysis device can be used even after 30 months have passed.

[0060] [Table 1]

[0061] From the above, it has been found that the present invention can effectively deal with the reduction in metal production while keeping power consumption relatively low. [Explanation of symbols]

[0062] 1, 11 Electrolyzer 2, 12 Electrolytic cell 2a, 12a Electrolysis room 2b Recovery Room 3 electrodes 3a, 13a anode 3b, 13b cathode 3c, 13c bipolar 4, 14 Bulkhead 4a Molten salt circulation path 4b Molten metal flow path 5 Cover member 6 Temperature regulator

Claims

1. A method for producing metals by molten salt electrolysis, An electrolysis device is used that includes an electrolytic cell that stores a molten salt bath therein, and two or more pairs of electrodes including an anode and a cathode that are in contact with the molten salt bath, During at least a period of time within 30 months from the start of use of the electrolysis apparatus, application of a voltage between at least one pair of electrodes that is a part of two or more pairs of electrodes is stopped, and the current density between the remaining portions of the electrodes is set to 0.5 A / cm 2 A method for manufacturing metals, during which production reduction is to be longer than this.

2. The method for producing a metal according to claim 1, which uses an electrolytic device in which two or more pairs of electrodes, anodes and cathodes, are arranged alternately side by side.

3. 3. The method for producing a metal according to claim 1 or 2, wherein, during the at least one period, application of a voltage between the electrodes including at least one anode is stopped by electrically disconnecting the at least one anode from a power source.

4. The method for producing a metal according to any one of claims 1 to 3, wherein at least one set of electrodes further comprises a bipolar electrode disposed between an anode and a cathode.

5. During said at least one period, the current density at the remainder of said electrode is 0.5 A / cm 2 ~1.2 A / cm 2 The method for producing a metal according to any one of claims 1 to 4,

6. The method for producing a metal according to any one of claims 1 to 5, wherein the total amount of current flowing through the electrolysis device during the at least one period is reduced to 70% to 90% of the total current amount during a normal period.

7. the electrolysis apparatus is provided with a temperature regulator capable of adjusting the temperature of the molten salt bath; The method for producing a metal according to any one of claims 1 to 6, wherein the temperature of the molten salt bath is adjusted using the temperature regulator during at least the part of the period.

8. The method for producing a metal according to any one of claims 1 to 7, wherein the metal is metallic magnesium, metallic aluminum or metallic zinc.

9. The method for producing a metal according to any one of claims 1 to 8, wherein chlorine gas is produced when the metal is produced by molten salt electrolysis.

10. The method for producing a metal according to any one of claims 1 to 9, wherein the metal is used in the production of titanium metal, zirconium metal, hafnium metal or silicon metal.

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