WO2006115027A1 - Molten salt electrolytic cell and process for producing metal using the same - Google Patents

Abstract

This invention provides a molten salt electrolytic cell for withdrawing calcium chloride containing calcium used for reducing an oxide or chloride of titanium, especially a molten salt electrolytic cell which can recover calcium chloride by molten salt electrolysis with high efficiency. The molten salt electrolytic cell comprises a vessel, which holds a molten salt bath and has a lid on its upper part, an anode and a cathode, which are extended through the lid from above the vessel and are immersed and disposed in the molten salt bath, a pressure reducing device connected to the cathode, a gas introduction nozzle for introducing gas from the outside of the vessel into the vessel, a gas discharge nozzle for discharging gas from the inside of the vessel to the outside of the vessel, and a molten salt feed nozzle for feeding a molten salt from the outside of the vessel into the vessel. The cathode is hollow. A fin member is joined to the outer surface of the cathode. Just above the joined part between the cathode and the fin member, a throughhole is provided in the cathode.

Description

 Specification

 Molten salt electrolytic cell and method for producing metal using the same

 Technical field

 The present invention relates to a molten salt electrolytic cell and a method for producing a metal using the same, and more particularly, for extracting calcium containing calcium used as a reducing agent in producing titanium from a titanium compound. The present invention relates to molten salt electrolysis technology.

 Background art

 [0002] Sponge titanium is conventionally manufactured by the Kroll method, and manufacturing costs have been reduced by stacking various improvements. At the same time, since the crawling method is a batch process, its efficiency is being seen as limited.

 [0003] As a technology pursued for the efficiency of titanium production by the Kroll method, there is known a technology for directly producing titanium by reducing titanium oxide with calcium in a molten salt (see, for example, Patent Document 1) . Further, as a technique similar to Patent Document 1, a step of preparing a molten salt by housing a mixed sample of calcium chloride and calcium oxide in a reduction container, heating the mixed sample, and preparing the molten salt, And forming a strongly reducible molten salt in which calcium ions and electrons are generated in the molten calcium chloride, and supplying the titanium oxide to the inside of the strongly reducible molten salt to form titanium oxide. A method for purifying titanium is disclosed which includes the steps of: reducing and deoxidizing with calcium ions and electrons to form titanium (see, for example, Patent Document 2). The technology described in Patent Document 2 generates titanium by reducing titanium oxide with calcium in a molten salt, dissolves by-produced calcium oxide in calcium chloride, and dissolves the calcium oxide in calcium chloride. Is electrolyzed to produce calcium, which is reused as a reducing agent.

Further, it is a method of producing titanium using a titanium compound containing halogen titanium or titanium oxide as a raw material and reducing these titanium compounds to produce titanium, which is an electrolytic bath containing a molten salt of an active metal. In the above, the molten salt is electrolyzed to produce a reducing agent comprising an active metal or an active metal alloy, and the titanium compound impregnated in the electrolytic bath by electrons emitted from the produced reducing agent is A method of producing reducing titanium is disclosed (e.g. Reference 3).

 [0005] A technology has been disclosed that deposits calcium on the cathode in the solid state using a molten complex salt having a melting point lower than that of calcium, as disclosed in, for example, Patent Document 4. This technique requires a step of exfoliating calcium deposited in the solid state.

 [0006] In each of the techniques described in Patent Documents 1 to 4 described above, calcium is used as a reducing agent used to generate titanium, and it is industrially possible to regenerate calcium oxide by-product in reduction reaction into calcium. Is required. At the same time, since calcium dissolved in molten salt electrolysis dissolves in calcium chloride, it is difficult to separate calcium alone.

 [0007] In order to solve such problems, a technology has been disclosed that, by adding calcium carbide to a molten salt, re-dissolution of the formed calcium into the molten salt can be effectively suppressed (for example, patent documents) 5). However, this technology is not always suitable for producing high-purity titanium because carbon in calcium carbide contaminates calcium.

 However, in the above-mentioned technology for directly producing titanium by reducing titanium oxide with calcium in a molten salt as described above, calcium does not have to be necessarily a single substance and is partially dissolved in calcium chloride. Even calcium can be used as a reducing agent.

 [0009] As described above, calcium chloride mixed with calcium or dissolved calcium (hereinafter simply referred to as "calcium containing calcium chloride") is prepared by subjecting calcium chloride to molten salt electrolysis. It is desirable to develop a technology that can efficiently generate

 Patent Document 1: WO 99 Z 064 638

 Patent Document 2: Japanese Patent Application Laid-Open No. 2003-129268

 Patent Document 3: Japanese Patent Application Laid-Open No. 2003-306725

 Patent document 4: US 3226311 gazette

 Patent Document 5: JP-A-49-70808

 Disclosure of the invention

 Problem that invention tries to solve

[0011] The present invention has been made in view of the above circumstances, and an acid product of titanium or An electrolytic cell for extracting calcium chloride-containing calcium used for reducing chlorides, particularly intended to provide a molten salt electrolytic cell that can efficiently recover calcium chloride by molten salt electrolysis. As you scold!

 Means to solve the problem

 The inventors of the present invention have intensively studied the molten salt electrolytic cell in view of the above situation. As a result, it was found that by making the cathode hollow, calcium chloride can be extracted efficiently. In addition, the anode and the hollow cathode are immersed and disposed in the molten salt bath, and the fin member is joined and disposed on the cathode surface, so that calcium chloride containing calcium generated at the cathode has a difference in specific gravity from the bath flow and the surroundings. It has been found that calcium chloride can be extracted and recovered more efficiently through this hollow portion by means of a pressure reducing device which is efficiently introduced into the hollow portion and externally installed, with the influence of In order to complete the invention of

 That is, the first molten salt electrolytic cell of the present invention comprises a container in which a molten salt bath is held, the anode and the cathode are immersed in the bath, and the cathode is hollow. Yes. Further, in the second molten salt electrolytic cell of the present invention, in the first molten electrolytic cell, a container with a lid in which the molten salt bath is held, and the lid which penetrates the lid from above the container. An anode and a cathode disposed in a molten salt bath, a pressure reducing device connected to the cathode, a gas introduction nozzle for introducing a gas from the outside to the inside of the vessel, and a gas inside the vessel Gas discharge nozzle, and a molten salt supply nozzle for supplying molten salt to the inside from the outside of the container, and a fin member is provided on the outer surface of the cathode, and the cathode is directly above the junction with the fin member. It is desirable that a through hole be provided in the

) o

 The inventors further focused on the calcium generation efficiency at the cathode and conducted intensive studies. As a result, by immersing all the cathodes in the molten salt bath, chloride calcium produced at the cathode is efficiently extracted and recovered with the influence of the bath flow and the difference in specific gravity from the surrounding being minimized. It has been found that it is possible to complete the following invention.

[0015] That is, in the first molten electrolytic cell, a container with a lid in which the molten salt bath is held, an anode which penetrates the lid from above the container and is immersed in the molten salt bath. A cathode which is disposed in the molten salt bath below the anode and which is expanded upward, a bath withdrawal pipe connected to the cathode and extending to the outside of the vessel, and a bath withdrawal pipe outside the vessel The pressure reducing device, the gas introduction nozzle for introducing the gas from the outside of the container to the inside, the gas discharge nozzle for discharging the gas to the outside of the inside of the container, and the molten salt for supplying molten salt from the outside to the inside of the container. It is desirable to have a feed nozzle (third molten salt electrolytic tank).

 [0016] Next, the method for producing a metal of the present invention is characterized by using the above-mentioned first to third molten salt electrolytic cells, and according to such a production method, molten calcium or molten magnesium is used. You can get it.

 Effect of the invention

 According to the present invention, the cathode is hollow, or the cathode is attached to the cathode and the fin member is joined to the cathode, and the cathode is deposited on the cathode surface by providing a through hole in the cathode immediately above the junction. Before calcium dissolves or diffuses in the entire sodium chloride calcium bath, the calcium or calcium chloride has the effect of being able to efficiently recover the sodium chloride calcium in which the calcium is partially dissolved and to be extracted to the outside. Further, according to the present invention, by immersing the entire cathode below the anode, in addition to the above-mentioned effects, it is possible to avoid the recombination of chlorine gas generated at the anode and calcium generated at the cathode. As a result, if the current efficiency can be increased, the effect will also be achieved.

 Brief description of the drawings

FIG. 1 is a side sectional view showing a preferred molten salt electrolytic cell of the present invention.

 FIG. 2 is a side sectional view showing another preferred molten salt electrolytic cell of the present invention.

 FIG. 3 is a side sectional view showing another preferred molten salt electrolytic cell of the present invention.

 FIG. 4 is a side cross-sectional view showing a cathode obtained by modifying the cathode used in the electrolytic cell shown in FIGS. 2 and 3;

 FIG. 5 is a schematic view of a longitudinal groove of an anode according to an embodiment of the present invention.

 Explanation of sign

B: Molten salt bath

10 ... container 10a-'Lid

 11 · "Anode

 12 · · · cathode

 13 · · · Decompression device

 14 · "Gas introduction nozzle

 15 · "Gas discharge nozzle

 16 · · · Molten salt supply nozzle

 17 · · · Fin members

 18 · · · Through holes

 28 · "Rectification

 51 · "Vertical groove

 BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the preferred embodiments of the molten salt electrolytic cell of the present invention and a method of producing a metal using the same will be described with reference to the drawings.

 FIG. 1 is a side sectional view showing a preferred molten salt electrolytic cell of the present invention. As shown in the figure, in the electrolytic cell, the molten salt bath B is held, and a container 10 provided with a lid 10a at the top and a lid 10a from above the container 10 penetrate the lid 10a and are immersed in the molten salt bath B And a decompression device 13 connected to the cathode 12. In addition, the lid 10a of the electrolytic cell includes a gas introduction nozzle 14 for introducing a gas from the outside of the container 10, a gas discharge nozzle 15 for discharging the gas to the outside from the outside of the container 10, and the outside of the container 10 A molten salt supply nozzle 16 for supplying molten salt to the inside is provided.

 In the molten salt electrolytic cell, the cathode 12 has a hollow shape, and a fin member 17 is joined to the outer surface of the cathode 12. Further, a through hole 18 is provided in the cathode 12 immediately above the junction between the cathode 12 and the fin member 17.

 By providing through holes 18 in the cathode 12 described above, the melting force generated on the surface of the cathode 12 is efficiently recovered in the hollow portion of the cathode 12 prior to dissolution or diffusion in the molten salt bath B. be able to.

When the molten salt electrolytic cell shown in FIG. 1 is used, the molten salt bath B held in the container 10 is Immerse the anode 11 and the cathode 12 and seal the container 10 with the lid 10 a. Next, it is preferable to introduce an inert gas such as a gas introduction nozzle 14 connected to the lid 10a into the space of the container 10 and to discharge it from the gas discharge nozzle 15 to the outside for circulation.

By thus circulating the inert gas in the space of the container 10, it is possible to effectively suppress the entry of air into the space of the container 10, and the chlorine gas generated at the anode 11 can be efficiently produced. It can be discharged outside. When air enters the space of the container 10, the calcium chloride constituting the molten salt bath B is oxidized, which may delay the electrolytic reaction of the molten salt.

 The material of the anode 11 described above is preferably made of a material such as carbon. By using such materials, stable electrolytic operation can be continued without being corroded by chlorine gas generated by the surface force of the cathode 11. On the other hand, it is preferable that the anode 12 formed of calcium is made of stainless steel or titanium material which is not easily corroded by the calcium formed on the surface of the electrolytic bath B or the cathode 12.

 As described above, the cathode 12 used in the electrolytic cell shown in FIG. 1 is hollow inside, and the fin member 17 is disposed on the surface of the portion to be immersed in the molten salt of the cathode 12 and joined. It is preferable to keep it. Further, it is preferable that the fin member 17 be disposed in a state of being expanded upward, and a through hole 18 communicating with the inside be provided at the bonding site of the fin member 17 to the cathode 12. The expansion angle of the fins constituting the fin member 17 is preferably selected from the range of 30 ° to 45 °.

 It is practical to set the number of fin members 17 to about 2 to 5 for the electrolytic cell shown in FIG. 1 according to the present invention. In addition, it is preferable that the size of the through holes 18 in which the through holes 18 be formed at equal intervals on the surface of the cathode 12 be in the range of 10 to 30% of the inner diameter of the cathode 12. By perforating the through-hole 18 of such a size, calcium chloride containing force flux generated on the surface of the cathode 12 can be extracted efficiently to the outside.

The inventors attempted various experiments in the process of completing the molten salt electrolytic cell shown in FIG. 1 and the like. As a result, when molten salt electrolysis is performed by immersing the cathode and anode, which do not have the fin member on the outer surface, in a calcium chloride bath, a molten salt bath of calcium (hereinafter simply referred to as "metal mist") around the cathode. May spread throughout the molten salt bath B in a short time). It was observed that the

 This metal mist tends to diffuse throughout the bath in a short time under the influence of the convection of the bath due to chlorine gas generation at the anode and the difference in specific gravity from the surroundings. It is also confirmed that, at the beginning of the formation of calcium on the surface of the cathode 12, a portion of the aforementioned calcium tends to settle in the molten salt bath B and accumulate at the bottom of the container 10. For this reason, in the present invention, it is preferable that the fin member 17 not only be joined to the cathode 12 in a state of being spread upward, but also be disposed as close as possible to the lower end of the cathode 12. By arranging in this manner, calcium generated on the entire surface of the cathode 12 immersed in the molten salt bath B can be efficiently recovered.

 The calcium produced on the surface of the cathode 12 passes through the through holes 18 formed on the surface of the cathode 12 along the fin members 17 arranged in the upper opening from the specific gravity difference with the surroundings, It is efficiently led to the hollow space. As described above, by efficiently introducing calcium generated on the surface of the cathode 12 into the hollow portion, a contact reaction between calcium generated in the cathode 12 and chlorine gas generated in the anode 11 can be suppressed. As a result, the decrease in current efficiency can be effectively prevented.

 The calcium-containing calcium-containing calcium introduced into the hollow portion of the cathode 12 can be extracted relatively easily to the outside by engaging the other end of the cathode 12 with the decompression device 13. The calcium produced on the surface of the cathode 12 is dissolved in the molten salt bath B and is led to the hollow portion of the cathode 12 via the through hole 18 provided on the surface of the cathode 12 and drawn upward by the pressure reducing device 13. Can be discharged into a tank (not shown) provided in the middle of the pressure reducing piping.

 When the above operation is performed, the level of the molten salt bath decreases according to the amount of molten salt bath B discharged from the container 10 to the outside, but the corresponding amount of the new molten salt calcium is The level of the molten salt bath B can be maintained constant by supplying the molten salt supply nozzle 16 installed in the lid 1 Oa to the inside of the container 10. With this type of operation, continuous operation of salt and calcium will be possible.

As the calcium chloride to be supplied to the container 10, a novel calcium chloride bath may be used, but as described in the prior art, the acid calcium by-produced by the calcium reduction of titanium oxide is used. It is also possible to use calcium chloride-containing calcium which has been chlorinated and converted into total sodium chloride. Yes.

 The calcium-containing calcium chloride extracted through the hollow portion of the cathode 12 can be used, for example, in the reduction of titanium directly by the titanium oxide, as cited in the prior art. It can be used as an agent. At this time, by cooling the calcium salt containing calcium sulfate extracted through the hollow portion of the cathode 12 to a temperature close to the melting point of calcium, it is dissolved in calcium chloride, You may deposit part!

 [0035] The temperature of the molten salt bath B is preferably maintained above the melting point of calcium chloride. In addition, this temperature is preferably maintained in a range not exceeding 100 ° C. above the melting point of calcium. If the temperature of the molten salt bath B is higher than the melting point of calcium by more than 100 ° C., the evaporation of the molten salt bath B is promoted, the yield is lowered, and this is not preferable.

 The melting point of the molten salt bath B can be lowered by adding potassium chloride to the calcium chloride constituting the molten salt bath B. By lowering the melting point of the molten salt bath B in this way, it is possible to have freedom in the electrolytic operation temperature. The amount of potassium chloride added to calcium chloride is preferably in the range of 18 wt% to 67 wt%. By adding potassium chloride in such a range, the melting point of the molten salt bath B can be lowered to 600 ° C. to 760 ° C., and the operating temperature of the molten salt bath B can be stably lowered. it can. As a result, it is possible to suppress the amount of generated calcium dissolved in calcium chloride.

 [0037] FIG. 2 is a side sectional view showing another preferred molten salt electrolytic cell of the present invention. As shown in the figure, the electrolytic cell is disposed in the molten salt bath B so as to penetrate the lid 20a from above the container 20 so as to hold the molten salt bath B and to which the lid 20a is provided at the upper part. An anode 21, a cathode 22 immersed in the molten salt bath B below the anode 21 and expanded upward, and a bath outlet 23 connected to the cathode 22 and extending to the outside of the container 20. , And a decompression device 24 connected to the bath outlet pipe 23 outside the container 20. The lid 20a of the electrolytic cell also includes a gas introduction nozzle 25 for introducing a gas from the outside of the container 20, a gas discharge nozzle 26 for discharging the gas to the outside from the outside of the container 20, and the outside of the container 20. A molten salt supply nozzle 27 for supplying molten salt to the inside is provided.

As described above, among the components of the electrolytic cell shown in FIG. 2, the container 20, the anode 21, the gas introduction nozzle 25, the gas discharge nozzle 26, and the molten salt supply nozzle 27 are the electrolysis shown in FIG. The same as the corresponding components of the tank. On the other hand, among the constituent elements of the electrolytic cell shown in FIG. 2, the cathode 22 completely immersed in the molten salt bath B and the bath outlet pipe 23 disposed between the cathode 22 and the pressure reducing device 24 This is the difference in configuration from the electrolytic cell shown in FIG.

 As shown in FIG. 2, by immersing the cathode 22 completely in the molten salt bath B and further disposing it under the anode 21, chlorine gas generated on the surface of the anode 21 and the surface of the cathode 22 are obtained. Contact with the generated force can be effectively suppressed immediately after the formation of calcium. For this reason, most of the produced calcium can be introduced to the bath outlet pipe 23 with the influence of the surrounding specific gravity being minimized, so the molten salt bath B can be efficiently withdrawn to the outside through the outlet pipe 23. be able to.

 In addition, as shown in FIG. 2, the cathode 22 may be arranged with high accuracy in the downward extension of the anode 21. The centers of the anode 21 and the cathode 22 may be offset from each other. Furthermore, in the state shown in FIG. 2, the cathode 22 is expanded upward, and the expansion angle can be selected in the range of 30 to 45 ° upward with respect to the horizontal plane. Such an expanded cathode 22 exerts the same effect as the fin member 17 which is a component in the electrolytic cell shown in FIG. 1, that is, the influence of the specific gravity difference from the surrounding is minimized. Function to efficiently extract the produced calcium to the outside.

 The back face of cathode 22 (the face of cathode 22 not facing anode 21 in FIG. 2) and the surface of bath outlet tube 23 are coated with ceramic such as highly insulating silica or alumina by means such as thermal spraying. It is preferable to keep it. By performing such an insulation treatment, not only the formation site of calcium can be limited to the inner surface of the cathode 22, but also the inner surface of the bath outlet tube 23 can be efficiently used as a precipitation surface of calcium. it can.

The end of the bath extraction pipe 23 opposite to the cathode 22 is engaged with the pressure reducing device 24, and the end is engaged with the pressure reducing device 24 in a tank (not shown). Is preferred. With such a device configuration, calcium can be extracted to the outside more efficiently. In addition, as shown in FIG. 2, the bath extraction pipe 23 is of a configuration in which the molten salt bath B is sucked upward to extend through the lid 20 a to the outside of the container 20, and the bottom of the container 20 is Alternatively, a through hole may be provided on the side to extend to the outside through the bottom and the side. You can also. With such an arrangement, the contact between chlorine gas generated at the anode 21 and calcium generated at the cathode 22 can be effectively suppressed.

[0043] FIG. 3 is a side sectional view showing another preferred molten salt electrolytic cell of the present invention. The electrolytic cell shown in the figure is a modification of the electrolytic cell shown in FIG. 2, and therefore the description of the same components as the electrolytic cell shown in FIG. 2 will be omitted. The electrolytic cell shown in FIG. 3 differs from the electrolytic cell shown in FIG. 2 in that a flow straightening plate 28 extending between the anode 21 and the cathode 22 from the inner wall of the container 20 is provided.

 It is preferable that the straightening vanes 28 be arranged to be inclined upward with respect to the horizontal plane, as shown in FIG. The inclination of the straightening vane 28 with respect to the horizontal plane is preferably selected in the range of 10 ° to 45 °. By selecting in such a range, the upward flow of the molten salt bath B generated near the cathode 22 can be efficiently suppressed.

 Further, it is preferable to provide a bent portion directed downward at the tip end of the straightening vane 28. By providing such a bend, the rising flow of the calcium-containing molten salt bath B can be directed toward the center of the cathode 22.

 When chlorine gas is generated on the surface of the anode 21, the chlorine gas ascends in the molten salt bath B. Therefore, in the molten salt bath B below the anode 21, a bath flow from the bottom to the top of FIG. 3 is generated, and chlorine gas generated at the anode 21 and calcium generated at the surface of the cathode 22 contact each other. It is because there is a possibility that it may react again.

 On the other hand, as shown in FIG. 3, when the baffle plate 28 is provided, when the bath flow containing a part of the calcium formed at the cathode 22 reaches the baffle plate 28, the bath flow is the container 20. The flow from each direction influences each other to form the downward flow of the bath shown by the arrow in FIG. As a result, the molten salt bath B containing calcium can be introduced toward the center of the cathode 22 and can be efficiently withdrawn from the system via the bath withdrawal pipe 23.

FIG. 4 is a side cross-sectional view showing a cathode 30 obtained by modifying the cathode 22 used in the electrolytic cell shown in FIGS. 2 and 3. The cathode 30 is formed in two stages of upwardly expanding portions 31 and 32, and a through hole 33 is provided between the expanded portions 31 and 32. By adopting such a configuration of the cathode 30, it is possible to further add to the cathode in which the fin member (corresponding to reference numeral 17 in FIG. 1) and the through hole (corresponding to reference numeral 18 in FIG. 1) shown in FIG. Of calcium It is possible to bring out the recovery effect. As a result, the productivity of calcium can be further improved as compared with the electrolytic cell shown in FIGS.

 In the electrolyzers shown in FIGS. 1 to 3 shown above, chlorine gas is generated in the anodes 11 and 21. Therefore, it is preferable to use a graphite in view of corrosion resistance. Further, in the example shown in FIG. 1, it is preferable to cover the lower end of the anode 11 in a hemispherical or tapered pencil shape. By forming the lower ends of the anodes 11 and 21 in such a shape, it is possible to suppress the growth of air bubbles due to the retention of chlorine gas, and as a result, the anodes 11 and 21 and the cathode 12 The convection of the molten salt bath B can be minimized. Further, as shown in FIG. 5, it is preferable to form longitudinal grooves 51 in the longitudinal direction at the lower end portions of the positive electrodes 11 and 21. By providing such a vertical groove, the rise of chlorine gas generated on the surfaces of the anodes 11 and 21 can be promoted more smoothly.

 The number of longitudinal grooves 51 provided at the lower end portion of the anodes 11 and 21 is preferably arranged at intervals obtained by equally dividing the circumferential direction of the anodes 11 and 21 into 4 to 10. Further, it is preferable to select a medium force in the range of 5% to 20% of the diameter of the anodes 11 and 21 as the width and depth of the grooves. For example, when the diameter of the anode 12 is 15 mm, the width and depth of the flutes are lmn! It is preferable to select from the range of ~ 3 mm. By selecting the width and depth of such a vertical groove, it can be set larger than the bubble diameter of the chlorine gas generated on the surfaces of the anodes 11 and 21, and as a result, the tip portions of the anodes 11 and 21 are generated. The effect of being able to smoothly advance the rising behavior of chlorine gas is achieved.

 The fin member 17 shown in FIG. 1 and the cathodes 22 and 30 shown in FIGS. 2 to 4 can be made of carbon steel or stainless steel because the calcium to be produced exhibits reducibility. However, due to the presence of chlorine gas generated at the anodes 11 and 21 in the space of the containers 10 and 20, the cathode 12 in FIG. 1 and the bath outlet pipe 23 in FIG. It is preferable to coat etc.

The calcium produced in the present invention can be used in the process of directly producing titanium by calcium reduction of titanium oxide using a molten salt. In addition, when manufacturing high purity titanium, it is preferable to use carbon steel with few nickel and a chromium content rate for cathode 12, 22, 30 shown to FIGS. The metals mentioned dissolve in calcium and molten salt baths This is because there is a risk that the titanium metal formed by the above-described calcium reduction of titanium oxide will be contaminated.

 The present invention can also be applied to the case where molten salt electrolysis of magnesium chloride is performed by converting the molten salt bath B into calcium chloride as described above. Also in this case, the force by which molten magnesium is formed at the cathode Unlike the case of calcium chloride as described above, magnesium has almost no solubility in magnesium sulfate. For this reason, the magnesium alone can be recovered by standing and separating the magnesium accompanied by sodium chloride magnesium extracted from the bath outlet pipe 23 outside the system. As a result, if the reduction reaction of titanium tetrachloride can be efficiently proceeded, the effect is produced.

 As described above, by using the molten salt electrolytic cell according to the present invention, calcium-containing calcium chloride can be efficiently extracted to the outside, and as a result, high current efficiency can be achieved. Can.

 Example 1

 Hereinafter, the present invention will be described in detail by way of examples.

 Using the electrolytic cell shown in FIG. 1, an electrolytic test of calcium chloride was performed under the following conditions.

1) Molten salt bath

 Molten salt: anhydrous calcium chloride

 Weight: 1 kg

 2) Anode

 Material: Graphite

 Dimensions: Diameter 15 (mm) X length 600 (mm)

 3) Cathode

 Material: Stainless steel

 Dimensions: Inner diameter 6 (mm) X Outer diameter 9 (mm) X length 600 (mm)

 Fin member: Conical shape, 3-stage arrangement

 Through hole: just above each connection point of the conical fin member to the cathode

 Six 3 mm φ through holes are formed on the cathode

4) Container Material: Transparent quartz

 Dimensions: Diameter 70 (mm) X Length 500 (mm)

 5) Extraction pipe

 Material: Transparent quartz

 Dimensions: Diameter 6 x Length 200 (mm)

 6) Heating furnace

 Output: lkW (rated)

 Heater: Nichrome wire

 [0056] Anhydrous calcium sulfate is supplied to the container 10 shown in FIG. 1, and the anode 11 and the cathode 12 are immersed in the anhydrous calcium chloride solution, and then the entire container 10 is sealed with the lid 10a. A small amount of argon gas is also supplied to the gas introduction nozzle 14 connected to a small amount, while exhausting from the gas discharge nozzle 15 connected to the lid 10a, the space above the supplied anhydrous calcium chloride is slightly pressurized The heater was heated to raise the temperature and kept at 800 ° C. ± 5 ° C. by energizing the heater.

Subsequently, a direct current voltage was applied between the anode 11 and the cathode 12 to start the electrolysis of anhydrous calcium chloride. Applied voltage, the current density at the cathode 12 was adjusted 0. 2AZcm ² ~0. 5AZcm ² to become so. Chlorine gas by-produced in the electrolytic reaction was discharged to the outside from the gas discharge nozzle 15 connected to the lid 10a.

 Since coloring due to the formation of calcium was confirmed in the vicinity of the surface of the cathode 12 after the start of energization, the pressure reducing device 13 was operated to lower the force of the lower end portion of the cathode 12 to calcium chloride in which calcium was dissolved. I pulled it out. During this time, it was impossible for the light flux generated by the force cathode 12 when the inside of the container 10 was visually observed to diffuse to the anode 11. Further, it was also possible that the formed calcium could stay at the bottom of the cathode 12.

 The above-described test was carried out seven times in total, and after the test, the amount of calcium in calcium sulfate extracted from container 10 was analyzed, and the current efficiency was calculated based on the amount of current flow. . The current efficiency achieved in the present invention was confirmed to be at a high level as shown in Table 1.

 [0060] [Table 1]

 (Unit:%)

 1 time 2 times 3 times 4 times 5 times average

Current efficiency 7 5 8 0 7 0 7 3 7 7 7 5 Example 2

 [0061] A molten salt of calcium chloride was electrolyzed under the same conditions as in Example 1 except that the cathode 12 was changed to the cathode 22 expanded upward as shown in FIG. Calculated. As a result, high current efficiency as shown in Table 2 could be achieved.

 [Table 2]

 (Unit:%)

 Example 3

 In Example 2, molten salt electrolysis of calcium chloride was performed under the same conditions as in Example 2 except that the cathode 12 sprayed with silica was changed to the outer surface, and the current efficiency was calculated. As a result, high current efficiency as shown in Table 3 could be achieved.

 [Table 3]

 (Unit:%)

産業上の利用可能性

Industrial applicability

 As described above, according to the present invention, calcium is deposited on the surface of the cathode by making the cathode hollow or additionally bonding the fin member to the cathode and providing a through hole immediately above it. Calcium chloride can be extracted to the outside efficiently. Thus, the present invention is particularly promising in that it can be applied to the extraction of calcium-containing calcium, which is a reducing agent used in producing titanium compound titanium.

Claims

The scope of the claims  [1] A molten salt electrolytic cell comprising: a vessel in which a molten salt bath is held, wherein an anode and a cathode are immersed and disposed, and the cathode is hollow.  [2] A container with a lid in which the molten salt bath is held, an anode and a cathode disposed in the molten salt bath penetrating the lid from above the container, and a pressure reducing device connected to the cathode A gas introduction nozzle for introducing gas from the outside of the container to the inside, a gas discharge nozzle for discharging gas to the outside of the container inside, and a molten salt supply nozzle for supplying molten salt to the inside of the container outside. A melting point according to claim 1, further comprising: a fin member provided on the outer surface of the cathode, and a through hole is provided in the cathode immediately above the junction with the fin member. Salt electrolyzer.  [3] The molten salt electrolysis according to claim 2, wherein the end on the molten salt bath immersion side of the cathode is closed, and the end on the molten salt bath non-immersion side is engaged with the pressure reducing device. Tank.  [4] A container with a lid in which the molten salt bath is held, an anode which is disposed to be immersed in the molten salt bath from the upper side of the container and penetrates the lid, and melting is performed under the anode. A cathode disposed in a salt bath and expanded upward, a bath withdrawal pipe connected to the cathode and extending to the outside of the vessel, and a pressure reducing device connected to the bath withdrawal pipe outside the vessel; A gas introduction nozzle for introducing gas from the outside of the container to the inside, a gas discharge nozzle for discharging gas to the outside of the container inside, and a molten salt supply nozzle for supplying molten salt from the outside of the container to the inside The molten salt electrolytic cell according to claim 1.  [5] The molten salt electrolytic cell according to [4], wherein an insulating layer is provided on the surface of the cathode not facing the anode and the outer surface of the bath outlet pipe.  [6] The inner wall force of the vessel [Claim 6] The molten salt electrolytic cell according to claim 4 or 5, wherein a straightening vane extending obliquely upward with respect to a horizontal plane is disposed between the cathode and the anode.  [7] The molten salt electrolytic cell according to any one of claims 4 to 6, wherein the bath outlet pipe extends through the lid of the container to the outside of the container.  [8] The molten salt electrolytic cell according to any one of claims 4 to 6, wherein the bath outlet pipe extends through the bottom or the side of the container to the outside of the container. [9] The anode is made of graphite and the cathode is made of carbon steel or stainless steel The molten salt electrolytic cell according to any one of claims 1 to 8, which is configured. [10] The molten salt electrolytic cell according to claim 9, wherein a longitudinal groove having a width larger than a bubble diameter of chlorine gas generated by the anode is formed on the surface of the anode. 11. The molten salt according to any one of claims 1 to 10, wherein the molten salt is also composed of calcium chloride, magnesium chloride, or a mixture of calcium chloride and potassium chloride. Electrolyzer. [12] A method for producing a metal, comprising using the molten electrolytic cell according to claim 1. [13] A method for producing a metal comprising using the molten electrolytic cell according to claim 2. [14] A method for producing a metal comprising using the molten electrolytic cell according to claim 4. [15] The method for producing a metal according to any one of claims 11 to 14, wherein the metal is molten calcium or molten magnesium.