Metal manufacturing system and metal manufacturing method

Abstract

Provided is a metal manufacturing system and a metal manufacturing method that suppress release of carbon dioxide gas into the atmosphere during operation, or that allow for efficient metal manufacture. The metal manufacturing system comprises: a chlorination furnace for generating anhydrous metal chloride by chlorinating a metal oxide; a molten salt electrolytic bath for generating metal by electrolyzing the anhydrous metal chloride; a supply path for supplying the anhydrous metal chloride from the chlorination furnace to the molten salt electrolytic bath; and a supply path for supplying chlorine gas generated by the electrolysis from the molten salt electrolytic bath to the chlorination furnace.

Description

Metal manufacturing system and metal manufacturing method

[0001] The present disclosure relates to a metal manufacturing system and method.

[0002] For example, when magnesium is produced by molten salt electrolysis, magnesium chloride is used as the material. If the magnesium chloride contains moisture, it can cause deterioration of the electrodes used in the molten salt electrolysis.

[0003] For this reason, anhydrous magnesium chloride is used in molten salt electrolysis, and Patent Document 1 discloses a method for producing anhydrous magnesium chloride, in which solid magnesium carbonate is reacted with chlorine gas at a temperature of 1200°C or less in the presence of carbon monoxide gas, and anhydrous magnesium chloride is extracted in a molten state to produce anhydrous magnesium chloride.

[0004] However, the method of Patent Document 1 has a problem in that carbon dioxide gas, a greenhouse gas, is generated as a by-product, and a disposal method such as atmospheric release is required.

[0005] Japanese Patent Application Laid-Open No. 55-20296 International Publication No. 2018 / 221698 Japanese Patent Application Laid-Open No. 2022-42280

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a metal production system and a metal production method that can suppress the release of carbon dioxide gas into the atmosphere during operation or that can efficiently produce metal.

[0007] To achieve the above object, the present disclosure is realized by the following configuration: (1) A metal production system according to an embodiment of the present disclosure includes a chlorination furnace that chlorinates a metal oxide to produce an anhydrous metal chloride, a molten salt electrolytic cell that electrolyzes the anhydrous metal chloride to produce a metal, a supply path that supplies the anhydrous metal chloride from the chlorination furnace to the molten salt electrolytic cell, and a supply path that supplies chlorine gas produced by the electrolysis from the molten salt electrolytic cell to the chlorination furnace.

[0008] (2) In the configuration of (1) above, the system may further include a gas reduction device that reduces carbon dioxide gas discharged from the chlorination furnace to produce carbon monoxide gas, a heating furnace that dehydrates metal hydroxides to produce the metal oxides to be supplied to the chlorination furnace, a supply path that supplies the carbon monoxide gas from the gas reduction device to the chlorination furnace, and a supply path that supplies the metal oxides from the heating furnace to the chlorination furnace.

[0009] (3) According to an embodiment of the present disclosure, a method for producing a metal using the production system described in (1) above includes chlorinating a metal oxide with a mixed gas of carbon monoxide gas and chlorine gas in the chlorination furnace to produce an anhydrous metal chloride, supplying the produced anhydrous metal chloride to the molten salt electrolytic cell, electrolyzing the anhydrous metal chloride in the molten salt electrolytic cell to produce a metal and chlorine gas, and supplying the produced chlorine gas to the chlorination furnace.

[0010] According to the present disclosure, it is possible to provide a metal production system and a metal production method that can suppress the release of carbon dioxide gas into the atmosphere during operation or that can efficiently produce metal.

[0011] 1 is a diagram illustrating the configuration of an apparatus for carrying out a chlorination step of a first embodiment according to the present invention. FIG. 2 is a diagram illustrating the configuration of an apparatus for carrying out a chlorination step of a second embodiment according to the present invention.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same elements are designated by the same reference numerals throughout the description of the embodiments.

[0013] The metal production system according to this embodiment includes a chlorination furnace that chlorinates a metal oxide to produce an anhydrous metal chloride, a molten salt electrolytic cell that electrolyzes the anhydrous metal chloride to produce a metal, a supply path that supplies the anhydrous metal chloride from the chlorination furnace to the molten salt electrolytic cell, and a supply path that supplies chlorine gas generated by electrolysis from the molten salt electrolytic cell to the chlorination furnace. By using this system, for example, chlorine generated at the anode of the molten salt electrolytic cell can be utilized in the chlorination furnace. Because chlorine gas is highly corrosive, it is preferable to utilize the chlorine gas generated in the molten salt electrolytic cell in the chlorination furnace, since this shortens the storage time of the chlorine gas. From the viewpoint of shortening the storage time of the chlorine gas, a chlorine gas storage chamber may be omitted from the chlorine gas supply path.

[0014] The chlorination furnace may be a batch type or a flow type. In the batch type reaction, after detecting the completion of the chlorination reaction in the chlorination furnace, the anhydrous metal chloride is transferred from the chlorination furnace to the molten salt electrolytic cell. In the flow type reaction, the anhydrous metal chloride is continuously transferred from the chlorination furnace to the molten salt electrolytic cell.

[0015] Hereinafter, an example will be described in which magnesium oxide, carbon monoxide gas, and chlorine gas are added in a chlorination furnace to produce magnesium chloride, and chlorine and magnesium are produced from the magnesium chloride in a molten salt electrolytic cell.

[0016] In the chlorination furnace, magnesium oxide, carbon monoxide gas, and chlorine gas are introduced to chlorinate the magnesium oxide. This reaction is preferably carried out in a molten salt of an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.). Because the solubility of magnesium oxide is low and the solubility of magnesium chloride is high in the molten salt, magnesium oxide exists as a solid, while magnesium chloride exists in the liquid phase. Furthermore, carbon dioxide is generated during the chlorination reaction of magnesium oxide. Therefore, when the chlorination furnace is a batch-type furnace, the solid components in the liquid phase may be monitored, and the contents of the chlorination furnace may be transported to a molten salt electrolytic cell when the decrease in the solid components falls below a certain level. Alternatively, the carbon dioxide concentration in the chlorination furnace may be measured, and the contents of the chlorination furnace may be transported to a molten salt electrolytic cell when the carbon dioxide concentration reaches or exceeds a predetermined value.

[0017] Therefore, the chlorination furnace may be equipped with a measuring device for measuring the concentration of solid components in the liquid phase and / or a measuring device for measuring the carbon dioxide concentration in the gas phase. Measuring devices for measuring the concentration of solid components in the liquid phase include absorption meters for measuring the absorbance or light transmittance of the suspension. Measuring devices for measuring the carbon dioxide concentration in the gas phase include known carbon dioxide meters.

[0018] Furthermore, when the chlorination furnace is of a flow type, it is preferable to provide a filter at the outlet of the chlorination furnace to trap solid magnesium oxide so that unreacted magnesium oxide is not discharged from the chlorination furnace.

[0019] Incidentally, impurities may be removed from the liquid phase of the content of the chlorination furnace before being transported to the molten salt electrolytic cell. Furthermore, when a filter for trapping magnesium oxide is provided at the outlet of the chlorination furnace, the pore size of the filter may be set to a size that allows particulate impurities to pass through. Furthermore, particulate impurities may be separately recovered using a filter with an even smaller pore size.

[0020] The anhydrous metal chloride produced in the chlorination furnace is transferred from the chlorination furnace to the molten salt electrolytic cell via a supply path. The anhydrous metal chloride may be supplied to the molten salt electrolytic cell together with a molten salt of an alkali metal or alkaline earth metal chloride without being separated from the anhydrous metal chloride along the supply path. For example, when a molten salt of sodium chloride is used as the molten salt of an alkali metal or alkaline earth metal, a molten salt of sodium chloride having magnesium chloride dissolved therein may be supplied to the molten salt electrolytic cell.

[0021] The temperature of the anhydrous metal chloride supplied from the chlorination furnace in this manner may differ from the operating temperature of the molten salt electrolytic cell. Therefore, the temperature of the liquid phase supplied to the molten salt electrolytic cell and the temperature of the molten salt electrolytic cell may be measured, and the temperature of the liquid phase supplied to the molten salt electrolytic cell may be adjusted depending on these temperatures. Therefore, the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the molten salt, and the supply path from the chlorination furnace to the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the supply (liquid phase), and a cooler and / or heater that controls the temperature of the supply.

[0022] As an example of temperature control, when the temperature of the molten salt electrolytic cell is higher than the desired reaction temperature, the temperature of the molten salt electrolytic cell may be lowered by supplying a liquid phase from a chlorination furnace that has a temperature lower than that of the molten salt in the molten salt electrolytic cell; when the temperature of the molten salt electrolytic cell is within the desired reaction temperature, the temperature change caused by supplying the liquid phase may be suppressed by adjusting the temperature of the liquid phase supplied from the chlorination furnace to the desired reaction temperature.

[0023] In a molten salt electrolytic cell, inorganic chlorides are electrolyzed in molten salt to produce chlorine and magnesium. The chlorine produced at the anode is recovered and supplied to the chlorination furnace for reuse. Magnesium may also liquefy in the molten salt and remain on the surface of the molten salt. In such cases, the liquefied magnesium can be recovered and cooled to obtain solid magnesium.

[0024] The chlorination process using the chlorination furnace and the preceding process will be described below.

[0025] (First embodiment) A method for producing a metal according to a first embodiment of the present invention includes a chlorination step in which anhydrous metal chloride is produced from a metal oxide using a mixed gas of carbon monoxide gas and chlorine gas. ２ ) to generate carbon monoxide gas (CO). In the following, specifically, the metal oxide is magnesium oxide (MgO), and the anhydrous metal chloride is anhydrous magnesium chloride (MgCl ２ ) will be used as an example.

[0026] (Chlorination step) Fig. 1 is a diagram for explaining the configuration of an apparatus (chlorination furnace) for carrying out the chlorination step of this embodiment. As shown in Fig. 1, the apparatus (chlorination furnace) for carrying out the chlorination step has a reactor, and the reactor is provided with a reaction section 1 (e.g., a reaction vessel) and a heating section H (e.g., a heater) for heating the reaction section 1.

[0027] The reaction unit 1 comprises a cylindrical main body 11 , an upper lid 12 that closes the upper opening of the main body 11 , and a lower lid 13 that closes the lower opening of the main body 11 .

[0028] For example, when magnesium oxide is to be placed in the reaction unit 1, the top lid 12 is opened, the magnesium oxide is placed in, and the top lid 12 is closed.

[0029] Conversely, when the anhydrous magnesium chloride produced after the treatment is to be taken out, the lower lid 13 is opened, the anhydrous magnesium chloride is taken out, and the lower lid 13 is closed.

[0030] The main body 11 of the reaction section 1 is connected to a gas supply pipe IN for supplying gas to the lower side and a gas exhaust pipe OUT for discharging gas to the upper side.

[0031] The gas supply pipe IN is connected to a line for a mixed gas (process gas) supplied from a gas mixer M that mixes carbon monoxide gas and chlorine gas, and a line for a general gas (an inert gas such as nitrogen gas or argon gas), and the line supplied to the gas supply pipe IN can be switched by controlling the valve B1. For example, the general gas may be used when replacing the gas in the reaction chamber 1 before opening the upper cover 12 and the lower cover 13.

[0032] The gas exhaust pipe OUT is branched into two lines, one of which may be connected to a vacuum pump (not shown) and the other of which may be connected to a gas treatment facility (not shown) for recovering the gas. The exhaust from the vacuum pump (not shown) may be sent to a detoxification device (e.g., a scrubber, not shown) that detoxifies chlorine gas and the like.

[0033] The gas treatment facility may mainly include a chlorine gas recovery section (chlorine gas recovery device) that recovers chlorine gas from the exhaust gas, and a carbon dioxide gas recovery section (carbon dioxide gas recovery device) that recovers carbon dioxide gas from the exhaust gas.

[0034] In addition, in the gas exhaust pipe OUT, it may be possible to select whether to send the exhaust to one line side (vacuum pump side) or the other line side (gas processing equipment side) by controlling the valve B2.

[0035] Prior to the chlorination step, a treatment for drying the magnesium oxide may be carried out. The drying treatment may be carried out, for example, by putting magnesium oxide into the reaction unit 1, closing the upper lid 12 to seal the reaction unit 1, and then, without supplying gas from the gas supply pipe IN, connecting the gas exhaust pipe OUT to the line on the vacuum pump side, driving the heating unit H while drawing a vacuum inside the reaction unit 1, and heating the reaction unit 1 to a temperature of 400° C. or higher.

[0036] In this way, by vacuum heating the magnesium oxide as a pretreatment before supplying the mixed gas (treatment gas) of carbon monoxide gas and chlorine gas in the chlorination process, it is possible to remove adsorbed water adsorbed on the surface of the magnesium oxide.

[0037] Alternatively, the magnesium oxide may be heat-treated and dried in a heating furnace connected to the chlorination furnace in a similar process.

[0038] The temperature of the subsequent chlorination treatment is set to a temperature below the melting point of anhydrous magnesium chloride (714°C) if anhydrous magnesium chloride is to be produced in a solid state, and is preferably set to a temperature range of, for example, about 500°C to 700°C.

[0039] Alternatively, magnesium oxide may be chlorinated in a molten salt of an alkali metal or alkaline earth metal (e.g., sodium chloride, potassium chloride, calcium chloride, etc.) by adding the magnesium oxide to the reactor. In such a case, the reactor is preferably heated to a temperature equal to or higher than the melting point of the added metal chloride salt.

[0040] The temperature for the chlorination treatment is preferably 300°C or higher, and in consideration of the reaction rate, it is more preferable to set the temperature in the range of about 500°C to 700°C.

[0041] Therefore, if the temperature during vacuum heating of this magnesium oxide is set to a range of 500°C to 700°C, chlorination can be initiated simply by starting the supply of the treatment gas, and therefore the temperature during vacuum heating may be set to a range of 500°C to 700°C.

[0042] After vacuum heating for a predetermined time, valve B2 on the vacuum side line is closed to seal the reaction section 1, and then the supply of treatment gas (a mixture of carbon monoxide gas and chlorine gas) is started from the gas supply pipe IN.

[0043] After that, when the pressure inside the reaction section 1 reaches atmospheric pressure, the valve B2 is controlled so that exhaust gas can be supplied from the gas exhaust pipe OUT to the gas treatment equipment side, and the exhaust gas flows to the other line side (gas treatment equipment side).

[0044] That is, a flow of the treatment gas is created from the gas supply pipe IN toward the gas exhaust pipe OUT inside the reaction unit 1. Note that performing treatment while keeping the gas flowing in this manner is sometimes called windsock treatment.

[0045] When magnesium oxide (metal oxide) is heated in a mixed gas of carbon monoxide gas and chlorine gas, the reaction shown in formula (1) below occurs, producing anhydrous magnesium chloride (anhydrous metal oxide): MgO + CO + Cl ２ → MgCl ２ +CO ２ ..... (1)

[0046] Then, carbon monoxide gas and chlorine gas that did not contribute to the reaction, and carbon dioxide gas produced by the reaction are discharged from the gas exhaust pipe OUT. The exhaust gas may be sent to the gas treatment facility (not shown) described above.

[0047] In the gas treatment facility (not shown), chlorine gas is recovered in a chlorine gas recovery section, and the recovered chlorine gas may be used again as chlorine gas to be sent to the gas mixer M.

[0048] Furthermore, carbon dioxide gas may be recovered in the carbon dioxide gas recovery section, and the recovered carbon dioxide gas may be sent to a gas reduction step, which will be described later.

[0049] Furthermore, the remaining carbon monoxide gas is also used again as carbon monoxide gas to be sent to the gas mixer M.

[0050] Then, when the production of anhydrous magnesium chloride is completed, the supply of the treatment gas to the reaction unit 1 is stopped, and valve B2 is controlled to stop the exhaust to the gas treatment equipment (not shown), the reaction unit 1 is sealed, the heating of the heating unit H is stopped, and then valve B2 is controlled to connect the gas exhaust pipe OUT to the line on the vacuum pump side, and the reaction unit 1 is evacuated. Before evacuating, it is preferable to wait until the temperature in the reaction unit 1 has dropped to at least 600°C or less. The reason for evacuating after waiting for the temperature in the reaction unit 1 to drop to 600°C or less is to prevent the produced anhydrous magnesium chloride from being discharged outside the reaction unit 1 by evacuating, since anhydrous magnesium chloride vaporizes at a temperature of about 650°C under vacuum.

[0051] After the reaction unit 1 has been evacuated, the valve B2 is again controlled to seal the reaction unit 1, and then a general gas (e.g., nitrogen gas) is supplied to the reaction unit 1 from the gas supply pipe IN. Once atmospheric pressure is reached, the lower cover 13 is opened and the anhydrous magnesium chloride is removed, thereby completing the chlorination process.

[0052] The above is an example of a process when the chlorination furnace is operated in a batch mode. When the chlorination furnace is operated in a flow mode, it is preferable to charge an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.) together with magnesium oxide into the reactor and chlorinate the magnesium oxide in a molten salt of the chloride. In this case, as described above, magnesium oxide exists as a solid in the molten salt, and magnesium chloride exists in a liquid phase. Therefore, magnesium chloride can be supplied in a liquid phase by transferring the molten salt from the chlorination furnace to the molten salt electrolytic cell. It is preferable to install a filter immediately before the supply path from the chlorination furnace to the molten salt electrolytic cell to prevent the transport of solid magnesium oxide. In addition, in a flow mode operation, the reaction gas may be supplied by a streamer or the like.

[0053] The metal production system according to this embodiment may further include a gas reduction device that reduces carbon dioxide gas discharged from a chlorination furnace to produce carbon monoxide gas, a heating furnace that dehydrates metal hydroxides to produce the metal oxides to be supplied to the chlorination furnace, a supply path that supplies the carbon monoxide gas from the gas reduction device to the chlorination furnace, and a supply path that supplies the metal oxides from the heating furnace to the chlorination furnace. By using such a system, carbon monoxide gas can be produced from carbon dioxide gas discharged from the chlorination furnace and reused in the chlorination process. Furthermore, metal oxides can be produced from metal hydroxides. Details of the heating furnace will be described later in a third embodiment.

[0054] (Gas Reduction Step) Next, the gas reduction step performed by the gas reduction device will be described. The gas reduction step is a step of reducing the carbon dioxide gas discharged in the chlorination step (i.e., the carbon dioxide gas recovered in the carbon dioxide gas recovery section of the chlorination furnace) to produce carbon monoxide gas.

[0055] Since various methods are known for reducing carbon dioxide gas to carbon monoxide gas, only a method suitable for this embodiment will be briefly described here.

[0056] For example, as disclosed in Patent Document 2, there is a gas reduction step according to the reaction formula (2) below (so-called reverse shift reaction), that is, a gas reduction step in which carbon dioxide gas is reduced using hydrogen gas as a reducing agent to produce carbon monoxide gas. ２ +H ２ → CO + H ２ O・・・・・・・・・・・・・・・・・・(2)

[0057] As shown in the formula (1) shown above, in the chlorination step, carbon dioxide gas is generated in an amount equivalent to the carbon monoxide gas that contributed to the reaction. Therefore, by generating carbon monoxide gas in an amount equivalent to the generated carbon dioxide gas in the gas reduction step, a gas circulation loop with just the right amount of gas between the chlorination step and the gas reduction step can be realized.

[0058] Therefore, all of the carbon dioxide gas generated in the chlorination step can be converted into carbon monoxide gas in the gas reduction step and reused in the chlorination step, so there is no need for a disposal means such as releasing carbon dioxide gas into the atmosphere in the production operation of anhydrous metal chlorides.

[0059] Another method is disclosed in Patent Document 3, in which carbon dioxide gas is electrolyzed to produce carbon monoxide gas.

[0060] In this way, even in the case of a method in which carbon dioxide gas is directly reduced by electrolysis, the amount of carbon dioxide gas input and the amount of carbon monoxide gas generated are approximately the same, so a gas circulation loop with just the right amount of excess or deficiency between the chlorination step and the gas reduction step can be realized.

[0061] On the other hand, as shown in Patent Document 1, when magnesium carbonate ore is chlorinated with carbon monoxide gas and chlorine gas, the amount of carbon dioxide gas produced is twice the amount of carbon monoxide gas used, as shown in the following formula (3): MgCO ３ +CO + Cl ２ → MgCl ２ +2CO ２ .....(3)

[0062] For this reason, even if carbon dioxide gas were converted into carbon monoxide gas and reused, only half of the produced carbon dioxide gas could be used, and the remaining half would have to be disposed of by means of atmospheric release or other methods.

[0063] Therefore, when magnesium oxide, which is a metal oxide, is treated with a mixed gas of carbon monoxide gas and chlorine gas as in this embodiment, the amount of carbon monoxide gas used in the chlorination step and the amount of carbon monoxide gas generated in the gas reduction step are approximately the same, making it possible to create a gas circulation loop with just the right amount of carbon monoxide gas and carbon dioxide gas, and eliminating the need for a disposal method such as releasing carbon dioxide gas into the atmosphere.

[0064] Furthermore, in the present embodiment, when magnesium oxide is converted into anhydrous magnesium chloride, only carbon monoxide gas is used as a reducing agent containing a carbon component. This has the advantage that impurities resulting from the carbon-based solid reducing agent (e.g., carbon powder, impurities contained in coke) are prevented from being mixed into the produced anhydrous magnesium chloride, as occurs when a carbon-based solid reducing agent such as coke is used.

[0065] (Molten Salt Electrolysis Process) Next, the molten salt electrolysis process in the molten salt electrolytic cell will be described. The molten salt electrolysis process is a process for producing metals using the anhydrous metal chloride produced in the chlorination process as a material. Hereinafter, an example will be described in which magnesium is produced by electrolysis using the anhydrous magnesium chloride produced in the chlorination process as a material.

[0066] The molten salt electrolysis process may be, for example, one method used to produce magnesium. Briefly, in the molten salt electrolysis process, for example, magnesium chloride is heated to a temperature of around 700°C in a molten salt electrolysis bath (e.g., a brick furnace) to melt the magnesium chloride.

[0067] At least one pair of electrodes is provided in the molten salt electrolytic cell. When a power source is connected between the electrodes and a voltage of 2.5 V or more is applied, chlorine gas is generated at the anode and magnesium is produced at the cathode.

[0068] The chlorine gas generated in the molten salt electrolysis step may be used in the chlorination step.

[0069] Second Embodiment In the second embodiment, a method suitable for the case where the treatment temperature in the chlorination step is equal to or higher than the melting point of anhydrous magnesium chloride or for the case where the chlorination step is carried out in molten salt will be described.

[0070] Fig. 2 is a diagram illustrating the configuration of an apparatus for carrying out the chlorination step of the second embodiment. Note that the configuration of the apparatus shown in Fig. 2 is similar in many respects to the configuration of the apparatus including the reactor described in the first embodiment, and therefore, a description of the same points as in the first embodiment may be omitted.

[0071] As shown in Figure 2, the reactor differs from the first embodiment in that the lower cover 13 (see Figure 1) is omitted and the main body 11 has a bottom, and that the main body 11 is provided slightly above the middle in the vertical direction and is connected to a recovery section 2 that recovers anhydrous magnesium chloride via a pipe having a valve B3.

[0072] The recovery section 2 for recovering anhydrous magnesium chloride comprises a cylindrical main body 21 having a ceiling and an opening on the lower side, and a lower lid 22 for closing the opening on the lower side.

[0073] As mentioned above, the main body 21 of the recovery unit 2 is connected to the main body 11 of the reactor by a pipe having a valve B3, and is also connected to a vacuum pump (not shown) by a pipe having a valve B4. Although not shown, a gas pipe that is controlled to open and close by a valve may be connected to the recovery unit 2 so that general gas can be supplied.

[0074] The procedure of the chlorination treatment is the same as that of the first embodiment except that the procedure is carried out in a state where the valve B3 is closed to isolate the reaction section 1 from the recovery section 2, and the treatment temperature in the chlorination step is set to the melting point of anhydrous magnesium chloride or higher, or the chlorination step is carried out in a molten salt.

[0075] Specifically, after magnesium oxide is introduced into the reaction section 1, it is heated in a vacuum to remove adsorbed water on the surface of the magnesium oxide, or it is heated in a separately provided heating furnace to remove adsorbed water on the surface of the magnesium oxide, and then a mixed gas of carbon monoxide gas and chlorine gas (treatment gas) is supplied to the reaction section 1 to produce anhydrous magnesium chloride.

[0076] It is preferable that the amount of magnesium oxide introduced is such that it does not reach the position of the pipe having the valve B3, which is connected to the recovery section 2.

[0077] In this case, for example, the temperature from the start of vacuum heating until the completion of the reaction for producing anhydrous magnesium chloride is preferably set to a temperature equal to or higher than the melting point of anhydrous magnesium chloride or the melting point of the added alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.), and is preferably set to a temperature of 1200°C or lower (e.g., around 1000°C).

[0078] In this case, the reaction formula itself is the same as that shown in Formula 1, but since the chlorination furnace is maintained under conditions where anhydrous magnesium chloride melts, when anhydrous magnesium chloride is produced, the anhydrous magnesium chloride becomes liquid. Note that, since the boiling point of anhydrous magnesium chloride is 1412°C, it is preferable to maintain the temperature of the chlorination furnace at, for example, 1400°C or less, or 1200°C or less so that the anhydrous magnesium chloride does not boil. Note that the melting point of magnesium oxide is 2852°C.

[0079] Therefore, even if the treatment gas is supplied by a streamer as in the first embodiment, there is no need to worry about the anhydrous magnesium chloride being discharged as vapor.

[0080] In this way, the treatment gas is supplied so as to bubble through the liquid of anhydrous magnesium chloride or the molten salt of the added alkali metal or alkaline earth metal chloride, which increases the probability of contact between the treatment gas and the unreacted magnesium oxide contained in the liquid, allowing the reaction to proceed efficiently.

[0081] After the chlorination treatment is carried out for a predetermined time, the supply of the treatment gas is stopped, the heating by the heating unit H is stopped, the reaction unit 1 is left sealed, and it is waited until the temperature inside the reaction unit 1 drops to a temperature preferably below 600°C.

[0082] While waiting for the temperature to drop, the recovery unit 2 is evacuated by a vacuum pump with the valve B4 open, until the internal pressure reaches, for example, 10 Pa or less. After the evacuation is complete, the valve B4 is closed, and the recovery unit 2 is put into a vacuum-sealed state.

[0083] On the other hand, when the temperature inside the reaction section 1 drops below 600°C, the reaction section 1 is also evacuated, for example, until the pressure reaches 10 Pa or less, and the reaction section 1 is again sealed (vacuum sealed).

[0084] Thereafter, valve B3 is opened to connect reaction section 1 and recovery section 2, and anhydrous magnesium chloride is supplied from reaction section 1 to recovery section 2. When no alkali metal or alkaline earth metal chloride has been added to reaction section 1, anhydrous magnesium chloride may be supplied to recovery section 2, for example, by driving heating section H to raise the temperature in reaction section 1 to a temperature at which the anhydrous magnesium chloride vaporizes. Note that when the anhydrous magnesium chloride is in a vacuum state, heating it to a temperature above 650°C, for example, about 700°C, will vaporize the anhydrous magnesium chloride.

[0085] In this case, the vaporized anhydrous magnesium chloride flows into recovery section 2 and returns to a liquid or solid in recovery section 2, which is at a temperature lower than the vaporization temperature. As a result, the anhydrous magnesium chloride is no longer in a gaseous state, the pressure in recovery section 2 decreases, and gaseous anhydrous magnesium chloride gradually flows in from reaction section 1, and anhydrous magnesium chloride is recovered in recovery section 2.

[0086] Although not shown, the pipe having the valve B3 is equipped with a heating mechanism for keeping the temperature (heating) so that the anhydrous magnesium chloride does not solidify inside.

[0087] Then, when the recovery of anhydrous magnesium chloride is completed, valve B3 is closed, the operation of heating section H is stopped, and ordinary gas (e.g., nitrogen gas) is supplied into recovery section 2 to make the pressure inside recovery section 2 atmospheric. Then, lower cover section 22 is opened and anhydrous magnesium chloride is taken out from recovery section 2, thereby completing the chlorination process.

[0088] In this embodiment, carbon dioxide gas is also generated during the chlorination treatment, but the generated carbon dioxide gas is recovered and converted back into carbon monoxide gas in the gas reduction step, and the carbon monoxide gas is used again in the chlorination step, which is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0089] Furthermore, as described above, when the produced anhydrous magnesium chloride is recovered as vapor, even if there is magnesium oxide that has not reacted, magnesium oxide has a high boiling point and does not vaporize, so there is an advantage in that it can be recovered as anhydrous magnesium chloride with almost no magnesium oxide contamination.

[0090] Although the above describes an example of a process for recovering anhydrous magnesium chloride as vapor, recovery of the anhydrous magnesium chloride from the reaction section 1 to the recovery section 2 may be carried out in the form of a liquid. That is, a molten salt of anhydrous magnesium chloride, or a mixture of a molten salt and an alkali metal or alkaline earth metal chloride, may be supplied in the liquid phase to the recovery section 2. By supplying the molten salt to the recovery section 2 in this liquid phase, it is also possible to perform a flow-type operation.

[0091] (Third embodiment) Although Japan is said to be poor in resources, magnesium resources are abundant in seawater. For example, when bittern water concentrated by an ion exchange membrane permeation method is treated with alkali, magnesium hydroxide (Mg(OH) ２ ) is obtained, and when magnesium hydroxide is heated to several hundred degrees Celsius, a dehydration reaction occurs, turning it into magnesium oxide, a metal oxide.

[0092] The alkali treatment is a process in which, for example, calcium oxide (CaO), sodium hydroxide (NaOH), or the like is added to bittern water to convert the magnesium chloride in the bittern water into magnesium hydroxide, which has low solubility, and precipitates it, which is then filtered and collected.

[0093] Therefore, by using magnesium oxide produced in this way, it is possible to secure a stable supply of raw materials that are not affected by world situations, etc.

[0094] Therefore, the magnesium oxide (metal oxide) used in the chlorination step of the previously described embodiment may be produced by a dehydration treatment in which magnesium hydroxide (metal hydroxide) is heated to dehydrate it. A case in which this dehydration treatment is included will be briefly described as a third embodiment. In the third embodiment, the metal production system according to this embodiment further includes a heating furnace that dehydrates the metal hydroxide and produces the metal oxide to be supplied to the chlorination furnace. By using such a system, metal oxide can be produced from the metal hydroxide.

[0095] Below, we will explain the case where the metal manufacturing method of this embodiment includes a dehydration process in which a metal hydroxide is dehydrated to produce a metal oxide, and the metal oxide produced in the dehydration process is used in the chlorination process.

[0096] As explained above, magnesium oxide is not a material that forms hydrates, but water may adsorb onto the surface.

[0097] For this reason, in the first embodiment, vacuum heating is performed as a pretreatment for the chlorination step before supplying a mixed gas (process gas) of carbon monoxide gas and chlorine gas. In this embodiment, metal oxide is produced from metal hydroxide, and the metal oxide is dehydrated by this pretreatment in order to be used in the chlorination step.

[0098] In other words, if the dehydration step is carried out as a pretreatment before supplying the mixed gas (treatment gas) for the chlorination step in a reactor (for example, in the reaction section 1) in which the chlorination step is performed or in a heating furnace connected to the reaction furnace, an efficient production method can be achieved in which the dehydration step, the chlorination step, and molten salt electrolysis are carried out in a continuous manner. Note that the reaction furnace may have a dehydration treatment section provided so that the material after the dehydration treatment can be supplied to the reaction section 1.

[0099] Therefore, the dehydration step of this embodiment can be carried out in the same manner as the vacuum heating step for removing adsorbed water from magnesium oxide in the first embodiment, and the subsequent chlorination step, gas reduction step, and molten salt electrolysis step can be carried out in the same manner as described in the first and second embodiments.

[0100] (Fourth embodiment) In the third embodiment, a method was described in which magnesium hydroxide was obtained by alkaline treatment of bittern water and then magnesium oxide was obtained by dehydrating the magnesium hydroxide. However, in the fourth embodiment, another method for obtaining magnesium hydroxide from seawater or bittern water will be described.

[0101] If seawater or bittern water is placed in an electrolysis furnace equipped with an anode and a cathode connected to a power source, and electricity is passed through it to carry out the electrolysis process, chlorine gas is generated from the anode and hydrogen gas is generated from the cathode. This reaction generates hydrogen ions (H ＋ ), and chloride ions (Cl － ) decreases. Note that a similar reaction occurs with a mixture of seawater and bittern water, so a mixture of seawater and bittern water is also acceptable.

[0102] As the hydrogen ions decrease, hydroxide ions (OH － ) increases, the aqueous solution becomes alkaline, but the decrease in chloride ions causes the magnesium ions (Mg ２＋ ) also increases, so they react to produce magnesium hydroxide. In other words, the hydroxyl groups react to compensate for the decrease in chlorine in magnesium chloride, producing magnesium hydroxide.

[0103] However, magnesium hydroxide has low solubility in water and will precipitate in seawater or bittern water, so that the magnesium hydroxide can be easily recovered by filtration.

[0104] In this case, as described above, chlorine gas is also generated from the anode, and if this chlorine gas is recovered by a chlorine gas recovery device, there is an advantage that the recovered chlorine gas can be used as chlorine gas in the chlorination step.

[0105] Therefore, the method for producing anhydrous metal chloride comprises an electrolysis step in which seawater, bittern water, or a mixture of seawater and bittern water is electrolyzed to produce magnesium hydroxide (metal hydroxide) and chlorine gas, the magnesium hydroxide produced in the electrolysis step is used in the dehydration step described in the third embodiment, and the chlorine gas produced in the electrolysis step is recovered in a chlorine gas recovery device and the recovered chlorine gas is used in the chlorination step.

[0106] (Other embodiments) As described in the fourth embodiment, in the electrolysis step of electrolyzing seawater, bittern water, or a mixture of seawater and bittern water, magnesium hydroxide, chlorine gas (Cl ２ ), as well as hydrogen gas (H ２ ) is also produced, and hydrogen chloride gas (HCl) can be produced by reacting this chlorine gas with hydrogen gas (see formula (4)). ２ +H ２ → 2HCl・・・・・・・・・・・・・・・・・・・・・(4)

[0107] If the temperature in the chlorination step is 300°C or higher and 1200°C or lower, hydrogen chloride gas reacts quickly with magnesium oxide to produce magnesium chloride (see formula (5)). MgO + 2HCl → MgCl ２ +H ２ O・・・・・・・・・・・・・・・(5)

[0108] Therefore, if hydrogen gas is recovered in a hydrogen gas recovery device in addition to the chlorine gas generated in the electrolysis step, and a gas generation step is provided in which the chlorine gas and hydrogen gas are reacted to generate hydrogen chloride gas, magnesium chloride can be generated even if hydrogen chloride gas is used instead of the embodiment in which a mixed gas of carbon monoxide gas and chlorine gas is used in the chlorination step described above.

[0109] As shown in formula (5), water (H ２ However, as explained above, if the chlorination step is carried out by a gas blow-off treatment, that is, if the chlorination step is carried out by a hydrogen chloride gas blow-off treatment, the generated water continues to be exhausted from the reaction section 1, and anhydrous magnesium chloride can be obtained by continuing the treatment until the water is gone.

[0110] Furthermore, since hydrogen chloride gas does not contain any carbon components, no carbon dioxide is generated by this process.

[0111] For this reason, even if a method for producing anhydrous metal chloride includes an electrolysis step in which seawater, bittern water, or a mixture of seawater and bittern water is electrolyzed to produce magnesium hydroxide (metal hydroxide), chlorine gas, and hydrogen gas, a gas production step in which chlorine gas and hydrogen gas are reacted to produce hydrogen chloride gas, a dehydration step in which magnesium hydroxide (metal hydroxide) is dehydrated to produce magnesium oxide (metal oxide), and a chlorination step in which magnesium oxide (metal oxide) is heated to 300°C or higher and 1200°C or lower in hydrogen chloride gas to produce anhydrous magnesium chloride (anhydrous metal chloride), it is still possible to achieve a method for producing anhydrous magnesium chloride (anhydrous metal chloride) that does not require the release of carbon dioxide into the atmosphere.

[0112] In the above specific embodiments, the metal oxide is magnesium oxide and the anhydrous metal chloride is anhydrous magnesium chloride. However, the present invention is not limited to the specific embodiments. For example, the metal oxide may be titanium oxide (TiO) and the anhydrous metal chloride may be titanium tetrachloride (TiCl). ４ ) may also be used.

[0113] In the embodiment, carbon monoxide gas and chlorine gas are mixed in the gas mixer M and supplied to the reaction section 1 in a uniformly dispersed state.

[0114] In this way, mixed gases that have been homogeneously dispersed and mixed by the gas mixer M do not separate due to differences in specific gravity. For example, oxygen gas and nitrogen gas are mainly present in air, but because these gases are homogeneously dispersed and mixed in air, gas separation due to specific gravity does not occur, and as a result, just as people do not suffocate, the gas mixer M performs mixing that does not cause gas separation. Note that the gas mixer itself is a device that is generally used to prevent gas separation in the cylinder when producing mixed gas cylinders.

[0115] Therefore, when carbon monoxide gas and chlorine gas are sent to the gas mixer M in a one-to-one ratio and the resulting homogeneously dispersed and mixed gas is supplied to the reaction section 1, the mixed gas comes into contact with the magnesium oxide uniformly in a reaction equivalence ratio (one-to-one ratio), thereby improving the reaction efficiency.

[0116] However, since the chlorination treatment itself can be carried out by joining carbon monoxide gas and chlorine gas and supplying the gas to the reaction section 1 without passing through the gas mixer M, it is not essential to prepare a mixed gas using the gas mixer M.

[0117] Furthermore, in the first embodiment, the anhydrous magnesium chloride is handled so as not to evaporate until it is extracted. However, the treatment temperature until the anhydrous magnesium chloride is produced may be set to a temperature below the melting point of the anhydrous magnesium chloride, and after the anhydrous magnesium chloride is produced, the anhydrous magnesium chloride may be recovered as vapor in the chlorination step as in the second embodiment (sent in a gaseous state from the reaction section 1 to the recovery section 2, solidified in the recovery section 2, and recovered).

[0118] In this way, as explained above, even if unreacted magnesium oxide is present, anhydrous magnesium chloride can be obtained with reduced contamination by the magnesium oxide.

[0119] In this way, appropriate modifications and improvements to the specific embodiments are also included within the technical scope of the present invention, and this will be clear to those skilled in the art from the description of the claims.

[0120] 1...reaction section, 11...main body section, 12...upper lid section, 13...lower lid section, 2...recovery section, 21...main body section, 22...lower lid section, B1, B2, B3, B4...valves, H...heating section, M...gas mixer, IN...gas supply pipe, OUT...gas exhaust pipe.

Claims

1. A metal production system comprising a chlorination furnace for chlorinating a metal oxide to produce an anhydrous metal chloride, a molten salt electrolysis cell for electrolyzing the anhydrous metal chloride to produce a metal, a supply path for supplying the anhydrous metal chloride from the chlorination furnace to the molten salt electrolysis cell, and a supply path for supplying the chlorine gas generated by the electrolysis from the molten salt electrolysis cell to the chlorination furnace.

2. The production system according to claim 1, further comprising a gas reduction device for reducing carbon dioxide gas discharged from the chlorination furnace to produce carbon monoxide gas, a heating furnace for dehydrating a metal hydroxide to produce the metal oxide supplied to the chlorination furnace, a supply path for supplying the carbon monoxide gas from the gas reduction device to the chlorination furnace, and a supply path for supplying the metal oxide from the heating furnace to the chlorination furnace.

3. A method for producing a metal using the production system according to claim 1, comprising chlorinating a metal oxide with a mixed gas of carbon monoxide gas and chlorine gas in the chlorination furnace to produce an anhydrous metal chloride, supplying the produced anhydrous metal chloride to the molten salt electrolysis cell, electrolyzing the anhydrous metal chloride in the molten salt electrolysis cell to produce a metal and chlorine gas, and supplying the produced chlorine gas to the chlorination furnace.

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