JP2007204797A - Molten-salt electrolysis apparatus for metal, and method for producing metal with the use of the apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molten-salt electrolysis apparatus for efficiently and directly producing a metal ingot from a metallic oxide of a raw material, and to provide a method for producing the metal ingot with the use of the apparatus. <P>SOLUTION: The molten-salt electrolysis apparatus is directed at electrolyzing a molten salt bath in which the metallic oxide has been melted to produce the metal; and has a molten-salt electrolysis tank 10 comprising an anode chamber 11 and a cathode chamber 12 which are separated from each other, and a molten salt bridge 13 arranged in between the anode chamber 11 and the cathode chamber 12. The method for producing the metal includes using the molten-salt electrolysis apparatus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molten salt electrolysis apparatus for a metal from a metal oxide by molten salt electrolysis and a method for producing a metal using the same.

  Titanium metal has been widely used for aircraft materials and parts in the past, and in recent years, application development has progressed and it is widely used for building materials, roads, sports equipment, and the like. Conventionally, single metal titanium has been produced by a crawl method in which titanium tetrachloride is reduced with molten magnesium to obtain sponge titanium, and production costs have been reduced by accumulating various improvements. However, since the crawl method is a batch process that repeats a series of operations discontinuously, there is a limit to the efficiency.

  For the above situation, the FFC method (for example, refer to Patent Document 1) in which titanium oxide is directly reduced to metal titanium by reducing titanium oxide in molten salt, or metal calcium in molten salt. A technique is disclosed in which metal titanium is recovered by reduction, and the by-produced calcium oxide is chlorinated to calcium chloride, and this is subjected to molten salt electrolysis to recover metal calcium (see, for example, Patent Document 2). Both of these techniques are attracting attention as methods for producing titanium metal using titanium oxide as a starting material.

  However, in any method, since the titanium produced is a solid titanium having a low purity containing a salt bath, in order to obtain a titanium ingot, the salt bath is separated and removed from the electrolytically produced solid titanium and further dissolved. A process is required.

  In order to solve the above problems, a molten salt in which titanium oxide is dissolved is heated to a temperature higher than the melting point of titanium, the molten salt is electrolyzed to form molten titanium, and this is settled and immersed in the bottom of the electrolytic layer to form a titanium ingot. A technique for directly manufacturing is disclosed (for example, see Patent Document 3).

WO99 / 064638 JP 2003-129268 A Japanese Patent Application Laid-Open No. 06-146049

  However, in this method, although a titanium ingot with high purity can be obtained, the current efficiency of molten salt electrolysis is low, and improvement has been demanded. Thus, a technique for efficiently producing a metal titanium ingot using titanium oxide as a raw material is desired.

  The object of the present invention is to provide an apparatus for directly producing a metal ingot using a metal oxide as a raw material, and to provide a method for producing a metal ingot efficiently by molten salt electrolysis using this apparatus.

  As a result of intensive studies in view of such circumstances, an anode chamber and a cathode chamber constituting a molten electrolytic cell in which a metal oxide is dissolved are provided independently, and a molten salt bridge is provided between the electrodes. The inventors have found that the metal ingot can be efficiently produced while maintaining high current efficiency, and have completed the present invention.

  That is, the present invention is a molten salt electrolysis apparatus for a metal that performs electrolysis by dissolving a metal oxide in a molten salt bath, and the molten salt electrolyzer comprises an independent anode chamber and a cathode chamber, and the anode chamber And a molten salt bridge between the cathode chamber and the cathode chamber.

  According to the present invention, since the anode chamber and the cathode chamber are provided independently, the reaction at the anode and the reaction at the cathode proceed independently, and the reverse reaction can be effectively suppressed.

  In the present invention, the oxygen ion conductor is preferably disposed in the molten salt bridge. According to such a form, it can prevent that oxygen ion flows backward from an anode chamber to a cathode chamber, and falls reaction efficiency.

In addition, a cathode made of molten metal generated by an electrolytic reaction is arranged at the bottom of the cathode chamber, an anode made of graphite is arranged at the top of the anode chamber, and the anode is immersed in the molten salt. It is a preferable form. According to such a form, since the cathode itself at the bottom of the cathode chamber is the target metal, the ingot can be produced integrally with the produced metal, and the ingot can be continuously produced as the reaction proceeds. . Further, since the anode is immersed in the upper part of the molten salt bath, the generated CO and CO ₂ are difficult to diffuse in the molten salt bath and immediately rise out of the system.

  Moreover, it is preferable that the electrolytic cell constituting the present invention and the molten salt bridge cage separating the anode chamber and the cathode chamber are made of water-cooled copper. According to such a form, molten salt precipitates on the surface of an electrolytic cell as a solid, and plays the role which protects an electrolytic cell from a hot molten salt bath.

  Furthermore, the method for electrolyzing a metal ingot according to the present invention is characterized by using the above-described molten salt electrolytic cell.

  By using the molten salt electrolysis apparatus according to the present invention, a high melting point metal ingot such as metal titanium can be efficiently produced using a high melting point metal oxide such as titanium oxide as a raw material.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a side view of a preferred apparatus configuration example for carrying out the present invention. FIG. 2 is a plan view (sectional view taken along line AA) of the apparatus configuration shown in FIG. 1 as viewed from above.

  In this embodiment, the case where the metal oxide as a raw material is titanium oxide and the molten salt bath is calcium fluoride will be described as an example. However, the present invention is not limited to this combination, and other metal oxides are used. The present invention can be similarly applied to a combination of a product and a molten salt bath.

  The electrolytic cell body 10 constituting the molten salt electrolysis apparatus F of FIG. 1 is provided with an anode chamber 11 and a cathode chamber 12 independently of each other, and is connected to each other by a molten salt bridge 13. A lid 14 is provided at the opening above the electrolytic cell main body 10, and the electrolytic cell main body 10 is filled with a molten salt bath 3 that is melted by a heating means (not shown). 3 can circulate the anode chamber 11 and the cathode chamber 12 by the molten salt bridge 13.

  An anode 20 is provided in the upper part of the anode chamber 11 and is immersed in the molten salt bath surface. A heating electrode 23 is provided in the upper part of the cathode chamber 12 and is immersed in the molten salt bath surface. A cathode 21 composed of a titanium ingot 24 and a molten titanium pool 25 is disposed at the bottom of the cathode chamber 12, and a base plate 22 is disposed at the bottom of the anode chamber 11. Furthermore, a heat supply plasma torch 4 that also serves as a titanium oxide raw material supply means (not shown) is attached to the upper part of the molten salt bridge 13. An inert gas supply nozzle 50 and an inert gas exhaust nozzle 51 are provided in the upper part of the electrolytic cell main body 10 so as to penetrate the lid 14. The nozzle 50 is an inert gas for adjusting the atmosphere in the electrolytic cell 10. It is an inlet for introduction, and the nozzle 51 is an inert gas outlet.

The basic configuration of the preferred embodiment of the present invention has been described above. Next, the function and effect of the above embodiment will be described.
<Preheating>
In FIG. 1, the molten salt electrolytic cell 10 is filled with the molten salt bath 3, and the anode chamber 11 is energized between the anode 20 and the base plate 22. In the cathode chamber 12, the heating electrode 23 and the cathode 21 (titanium ingot 24) During this period, the molten salt bath 3 is heated to the melting point of titanium or higher. At the same time, the molten salt bath 3 can be heated to the melting point of titanium or higher by using the plasma torch 4 together. When the temperature of the molten salt bath 3 held in the molten salt electrolysis tank 10 reaches the melting point of titanium or more and the temperature is stabilized, the molten salt electrolysis process is started.

<Molten salt electrolysis process>
In the molten salt electrolysis step, supply of titanium oxide from outside the system is started by a raw material supply means (not shown) in the plasma torch 4 arranged at the top of the molten salt bridge in FIG. The molten salt bath is supplied while heating and melting. At the same time, a current is passed between the anode 20 in the anode chamber 11 and the cathode 21 in the cathode chamber 12 to start molten salt electrolysis.

Since the titanium oxide supplied to the molten salt bath 3 is already heated by the plasma torch 4, it quickly dissolves in the molten salt bath 3 and at the same time, the molten salt is applied by the voltage applied between the anode 20 and the cathode 21. Electrolyzed. At this time, on the surface of the anode 20, oxygen ions O ²⁻ react with the graphite of the anode 20 by an electrolytic reaction as shown in the following formula (1) or (2) to generate CO or CO ₂ gas, Removed.
C + O ²⁻ = CO + 2e ⁻ (1)
C + 2O ²⁻ = CO ₂ + 4e ⁻ (2)
On the other hand, at the top of the titanium ingot 24 constituting the cathode 21, molten metal titanium is generated by the reaction of the following formula (3). Molten metal titanium is integrated with the cathode 21 to form a molten titanium pool 25 at the top of the ingot 24.
Ti ⁴⁺ + 4e ⁻ = Ti (3)

  As the molten salt electrolysis reaction proceeds, metallic titanium is generated at the cathode and the liquid level of the molten metal titanium pool 25 rises. Accordingly, the titanium ingot 24 is moved below the molten salt electrolyzer F by a drawing means (not shown). The liquid level of the molten titanium pool 25 is always kept constant, and the lower part of the molten titanium pool 25 is cooled and solidified by drawing downward, so that the titanium ingot 24 can be continuously generated.

Next, each component of the molten salt electrolysis apparatus of this invention is demonstrated in detail.
The electrolytic cell main body 10 is preferably composed of water-cooled copper so as to withstand the high-temperature molten salt bath 3. By constituting the electrolytic cell main body 10 with water-cooled copper, the surface of the water-cooled copper wall in contact with the molten salt bath 3 is called a solid phase (hereinafter referred to as “molten salt self-coat layer”) of the molten salt bath 3 (not shown). May precipitate). The molten salt self-coat layer exhibits a preferable effect that the water-cooled copper wall constituting the electrolytic cell main body 10 can be effectively protected from the molten salt bath 3 at a high temperature.

  The thickness of the molten salt self-coat layer is determined from the balance between heat input to the water-cooled copper wall and heat removal, but in the present invention, the thickness of the molten salt self-coat layer can be controlled to about 2 to 5 mm. preferable. As the molten salt self-coat layer is thicker, the protective function is increased, but it is necessary to increase the amount of heat removed from the water-cooled copper wall. As a result, the temperature of the molten salt bath 3 is lowered, which is not preferable. On the other hand, if the molten salt self-coating layer is thin, the function as a protective layer is deteriorated such that the high-temperature molten salt bath 3 damages the water-cooled copper wall. Therefore, the molten salt self-coat layer is preferably controlled to have a thickness within the above range.

The molten salt electrolytic cell 10 is configured to be shut off from the atmosphere by the lid 14, and further, an inert gas supply nozzle 50 and an exhaust nozzle 51 for adjusting the atmosphere may be provided at the top of the electrolytic cell 10. preferable. By providing such a nozzle, not only can the inside of the molten salt electrolytic cell F be maintained in an inert gas atmosphere, but also the argon gas injected from the plasma torch 4 is efficiently discharged out of the system. can do. Furthermore, the CO or CO ₂ gas generated with the electrolytic reaction can be discharged out of the system.

Electrode (Anode / Cathode / Heating electrode / Base plate)
The anode 20 provided in the anode chamber 11 is preferably made of graphite, and is preferably inserted from the top of the lid 14 and immersed in the molten salt bath 3. Further, it is preferable that a conductive base plate 22 is disposed at the bottom so as to face the anode 20. The base plate 22 can efficiently heat the molten salt bath 3 held in the anode chamber 11 by passing a direct current between the anode 20 and the anode 20 in the above-described preheating step to the molten salt electrolysis temperature. In this sense, the base plate 22 is preferably made of a highly corrosion-resistant titanium material or stainless steel.

  The cathode 21 constituting the cathode chamber 12 is preferably composed of a titanium ingot 24 disposed at the bottom of the cathode chamber and a molten titanium pool 25 formed thereon. The molten titanium pool 25 is heated by applying a direct current between the heating electrode 23 provided at the top of the cathode chamber 12 and the cathode 21 disposed at the bottom of the cathode chamber 12.

  Furthermore, as the direct current is applied, metallic titanium produced by the electrolytic reaction in the molten salt bath 3 is produced in the molten titanium pool portion 25 of the cathode 21, and this is deposited in the molten titanium pool 25 and combined. Thus, the titanium ingot 24 can be efficiently formed by pulling it downward.

  From such a viewpoint, it is preferable that the heating electrode 23 provided in the upper part of the cathode chamber is made of a titanium material. This is because the titanium material is excellent in corrosion resistance against high-temperature molten salt and has a specific resistance sufficient to be subjected to current heating.

Molten salt bridge The molten salt bridge 13 according to the molten salt electrolysis apparatus F of the present invention is configured to couple the anode chamber 11 and the cathode chamber 12 as shown in the plan view of FIG. It is preferable to use water-cooled copper that can withstand the molten salt.

  Further, a ceramic that can conduct oxygen ions such as zirconium oxide may be disposed in the molten salt bridge 13. By taking such an arrangement, it is possible to prevent oxygen ions from flowing back from the anode chamber 11 to the cathode chamber 12, and as a result, it is possible to suppress a decrease in current efficiency of molten salt electrolysis.

  Furthermore, it is preferable to arrange the plasma torch 4 at the top of the molten salt bridge 13. By using the plasma torch 4, in addition to the purpose of melting the titanium oxide raw material as described above, the temperature of the molten salt 3 held in the molten salt electrolysis tank 10 is heated and maintained to a temperature suitable for molten electrolysis. be able to.

  Further, it is preferable that a raw material supply means (feeder) (not shown) for supplying a titanium oxide raw material to communicate with a gas flow path constituting the plasma torch 4 is arranged outside the plasma torch 4. By configuring the plasma torch and the raw material supply means (feeder) in this way, it is possible to efficiently supply the titanium oxide raw material while heating or heating and melting it during molten salt electrolysis.

Molten salt bath / raw material titanium oxide The molten salt bath 3 used in the present invention uses calcium fluoride, calcium oxide, or a mixed salt thereof having a relatively low vapor pressure even when heated to a high temperature range higher than the melting point of titanium. preferable. Further, since titanium oxide has solubility in calcium fluoride, it can be used for the electrolytic reaction throughout the molten salt bath. Further, the melting point and vapor pressure of the molten salt bath can be appropriately adjusted by mixing calcium fluoride with another fluoride such as barium fluoride.

  In the present invention, the temperature of the molten salt bath 3 is preferably kept at a temperature equal to or higher than the melting point of titanium, and specifically, it is preferably heated by 100 to 200 ° C. above the melting point of titanium. If the heating temperature is low, the titanium metal produced in the molten salt bath 3 is deposited on the cathode in a solid state, and the structure of the produced ingot is not preferable. On the other hand, if the heating temperature is too high, the power required for heating increases, which is not economical.

  The molten salt bath 3 can be heated by using Joule heat generated by energizing between the anode 20 and the cathode 21. In addition, plasma disposed on the bath surface of the molten salt bath 3 can be used. By using the torch 4 together, it can be heated more efficiently.

  A high-frequency coil (not shown) may be disposed outside the side wall corresponding to the top of the ingot used as the cathode 21 disposed at the bottom of the cathode chamber 12. By disposing such a high frequency coil, the molten titanium pool 25 can be formed on the top of the titanium ingot 24. As a result, the titanium metal produced in the molten salt bath 3 can be efficiently precipitated in the molten titanium pool 25, and as a result, a uniform ingot can be melted.

  In this way, it is possible to adopt an apparatus configuration in which the heating high-frequency coil can supply a sufficient amount of heat to melt the solid titanium metal to the outer peripheral portion of the molten titanium pool 25. By adopting such an apparatus configuration, it is not always necessary to heat the temperature of the molten salt bath 3 over the melting point of titanium metal, and only the vicinity of the cathode 21 on which titanium is deposited should be heated to the melting point of titanium. It ’s fine.

  What is necessary is just to determine suitably the purity of the titanium oxide supplied to the molten salt bath 3 according to the quality characteristic requested | required of the titanium ingot 24 to produce | generate. However, if the purity is too low, the stable operation of the molten salt electrolysis process is hindered, so it is preferable to use titanium oxide having a purity of 99% or more.

  It is preferable to use a raw material titanium oxide that is sized or granulated in the range of 0.1 to 1.00 mm. The finer the raw material titanium oxide is, the faster the dissolution in the molten salt bath 3 is, so that it is preferable to promote the molten salt electrolysis reaction. However, the finer the raw material titanium oxide, the lower the dissolution yield in the molten salt bath 3. Therefore, it is preferable to use titanium oxide sized or granulated to the above particle size.

  The titanium oxide may be melted in advance and the molten titanium oxide may be supplied to the molten salt bath 3. By supplying the molten titanium oxide to the molten salt bath 3, the temperature of the molten salt bath 3 can be stably maintained above the melting point of titanium. The dissolution of the titanium oxide can be achieved, for example, by using a plasma spraying apparatus.

  By using the molten salt electrolysis apparatus F according to the present embodiment described above or the present invention and the use thereof, the raw metal oxide can be reduced and the corresponding metal ingot can be efficiently manufactured.

[Examples 1 to 3]
Using the apparatus configuration shown in FIG. 1, molten salt electrolysis of titanium oxide was performed under the following conditions.
1) Device configuration Side wall: Cylindrical water-cooled copper wall (outer diameter 180mm)
Molten salt bridge: Cylindrical water-cooled copper wall (outer diameter 150mm)
Anode: Graphite (outer diameter 60mm)
Cathode: Pure titanium ingot (outer diameter 110 mm)
Electrode: Pure titanium (outer diameter 60mm)
Plasma torch: Argon plasma torch (outer diameter 40mm)
2) Amount of energization and heating energy Anode to cathode: 10 to 20KA
Plasma torch: 25KW
3) Molten salt bath Composition: CaF ₂ : CaO = 70 to 90:10 to 30 (weight ratio)
Bath temperature: 1700-2000 ° C
4) Titanium oxide Purity: 99%
Particle size: 0.1-1.0mm

Under the above conditions, molten salt electrolysis of titanium oxide was carried out three times to produce 0.5 to 1.5 kg titanium ingots of Examples 1 to 3. When the produced titanium ingot was analyzed, as shown in Table 1, it was confirmed that the titanium ingot was pure titanium with very few impurities. In addition, the current efficiency was 60 to 85%, which was confirmed to be higher than the conventional efficiency.
[Comparative Example 1]

  Under the same conditions 2) to 4) as in the examples, except that the electrolytic apparatus having the structure shown in FIG. 3 which does not have the molten salt bridge of the present invention and does not have independent anode chamber and cathode chamber is used. Then, a molten salt electrolysis of titanium oxide was performed twice to produce a 0.2 kg metallic titanium ingot of Comparative Examples 1 and 2. When the produced titanium ingot was analyzed, the oxygen and carbon contents were high, and the quality characteristics of the pure titanium ingot could not be satisfied. Also, the current efficiency was in the range of 15-60%, which was not a satisfactory result.

  A metal ingot having a high melting point such as titanium metal can be efficiently produced using titanium oxide as a raw material.

It is a side view which shows one Embodiment of the molten salt electrolysis apparatus of this invention. It is the sectional view on the AA line in the side view of FIG. It is a side view which shows the conventional molten salt electrolysis apparatus.

Explanation of symbols

F Molten salt electrolysis apparatus 10 Electrolyzer main body 11 Anode chamber 12 Cathode chamber 13 Molten salt bridge 14 Lid 20 Anode 21 Cathode 22 Base plate 23 Heating electrode 24 Titanium ingot 25 Molten titanium pool 3 Molten salt bath 4 Plasma torch 50 Supply of inert gas Nozzle 51 Inert gas exhaust nozzle

Claims (10)

  A metal molten salt electrolysis apparatus that performs electrolysis by dissolving a metal oxide in a molten salt bath, wherein the molten salt electrolysis cell comprises an independent anode chamber and a cathode chamber, and the anode chamber and the cathode chamber A molten salt electrolysis apparatus for metals, wherein a molten salt bridge is provided therebetween.   The molten salt bridge is a communication pipe that connects the anode chamber and the cathode chamber and distributes the molten salt held in the anode chamber and the cathode chamber, and the molten salt bridge includes the molten salt inside. The metal molten salt electrolysis apparatus according to claim 1, wherein:   2. The molten salt electrolysis apparatus for metal according to claim 1, wherein the cathode in the cathode chamber is a molten metal pool itself that is electrolytically generated at the bottom of the cathode chamber.   2. The molten salt electrolysis apparatus for metal according to claim 1, wherein the anode in the anode chamber is made of graphite, and is immersed in the molten salt from the top of the anode chamber.   The metal molten salt electrolysis apparatus according to claim 2, wherein an oxygen ion conductor is disposed in the molten salt bridge.   2. The molten salt electrolyzer for metal according to claim 1, wherein an electrolytic cell wall constituting the electrolyzer is made of water-cooled copper.   The molten salt electrolysis apparatus according to any one of claims 1 to 6, wherein the molten salt is composed of calcium fluoride, calcium oxide, or a mixed salt thereof.   The molten metal electrolysis apparatus according to claim 1, wherein the metal oxide is titanium oxide, niobium oxide, or tantalum oxide.   The metal molten salt electrolysis apparatus according to any one of claims 1 to 8, wherein the metal is titanium, niobium or tantalum. A method for producing a metal, wherein the molten salt electrolysis apparatus according to claim 1 is used.

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