JP4502617B2 - Metal oxide reduction method and metal oxide reduction apparatus - Google Patents

Description

  The present invention relates to a method for reducing a metal oxide by electrolyzing it in an electrolytic bath made of an inorganic molten salt, and a method for reducing a metal oxide by electrolyzing in an electrolytic bath made of an inorganic molten salt. The present invention relates to a reduction device for a metal oxide to be reduced.

  Since many metals have a very strong affinity with oxygen, many of them exist as oxides in ores used for metal smelting. These metal oxides can be refined as higher-purity metal oxides by appropriate wet or dry treatment, or they can be treated to change their form to chlorides or fluorides mainly containing the target metal. Subsequently, the metal oxide or metal chloride is further reduced by an appropriate method to obtain the target metal.

For example, a large amount of titanium is produced as ilmenite ore in which iron oxide and titanium oxide are combined, and various methods for refining titanium oxide have already been reported. As a typical example, after reducing iron oxide in ilmenite ore to iron by carbon reduction, iron is dissolved and separated by wet treatment using an aqueous ammonium chloride solution (NH ₄ Cl) to form titanium oxide as a residual solid. And a method of obtaining titanium oxide by wet treatment using sulfuric acid after partial reduction of iron oxide in ilmenite ore with carbon.

  The titanium oxide obtained above is mixed with chlorine and carbon and reacted at a high temperature to convert the titanium oxide into titanium tetrachloride. Then, the titanium tetrachloride is reduced with magnesium, so that metal titanium is formed by a so-called crawl method. Can be obtained.

  However, in the smelting of titanium metal by this crawl method, titanium oxide obtained from ore is used as an intermediate raw material, and this titanium oxide is reduced to titanium tetrachloride having a low boiling point and then reduced. However, there is a large loss in terms of energy. In addition, as a characteristic of the crawl method, vacuum separation under high temperature and reduced pressure is indispensable in the production process, and further, crushing / pulverization processing and separation processing of sponge metal titanium, which is a product metal, are necessary. There is a problem that the manufacturing cost increases.

  Therefore, conventionally, several metal titanium smelting methods have been proposed in place of the crawl method, reflecting the growing demand for titanium metal. Generally, in these methods, an electrolytic bath made of an inorganic molten salt is formed in a reaction tank, and titanium oxide is reduced to titanium metal by utilizing electrolysis performed in the electrolytic bath.

For example, Sakae Takeuchi and Osamu Watanabe, The Japan Institute of Metals Vol. 28 (1964) No. 9, pp. 549 to 554, use a graphite crucible, and use this graphite crucible as an anode, A molybdenum electrode is placed as the cathode, and a mixed molten salt of 900 to 1100 ° C consisting of calcium chloride (CaCl ₂ ), calcium oxide (CaO) and titanium oxide (TiO ₂ ) is placed in the crucible as an electrolytic bath. Describes a method for producing metallic titanium by electrolyzing titanium oxide in an electrolytic bath under an atmosphere of argon (Ar) as an inert gas, and depositing the generated titanium ions (Ti ⁴⁺ ) on the surface of a molybdenum electrode. (See Non-Patent Document 1).

In this method, a graphite crucible is also used as a reaction vessel and an anode, and oxygen ions (O ²⁻ ) are generated when titanium oxide is electrolyzed in an electrolytic bath. Ltd. crucible becomes carbon dioxide attacked by oxygen ions (CO ₂ · CO), generated carbon dioxide while flying in the electrolytic bath, in contact with metallic titanium was deposited on the cathode (Ti), titanium metal Inevitably causes carbon pollution. Therefore, the authors teach the use of partition walls made of CaTiO ₃ to avoid carbon contamination of titanium metal due to physical contact between deposited titanium metal and CO gas generated from the anode (non-patent literature). 1 See page 552, left column).

In the electrolysis using a graphite crucible serving both as a reaction vessel and an anode, the cathode on which the titanium metal is deposited is located above the anode. Therefore, in order to completely shield it from carbon dioxide, at least the lower surface is desirable. It is necessary to completely block the periphery of the cathode with a partition wall.
However, since the carbon dioxide gas generated on the surface of the graphite crucible floats over almost the entire area of the electrolytic bath, the entire electrolytic bath in the graphite crucible tends to become a saturated solution of carbon dioxide gas. Therefore, when only the bottom surface is blocked, carbon contamination of titanium metal is unavoidable due to the electrolytic bath saturated with the anode reaction gas flowing in from other places, while when it is completely blocked by the partition wall, it can be energized. In order to achieve this, it is necessary to form the partition walls in a porous shape, and this makes it impossible to prevent the intrusion of carbon dioxide dissolved in the electrolytic bath. Therefore, in any case, carbon contamination of titanium metal cannot be prevented. In addition, in this method, the partition wall itself made of CaTiO ₃ is not only reduced to Ca, which is a strong reducing substance generated at the cathode, but also cracks occur in the partition wall in the air, so there is also a problem in terms of durability. There is.

On the other hand, the present inventors are a smelting method of metallic titanium that produces metallic titanium (Ti) by thermally reducing titanium oxide (TiO ₂ ), and includes calcium chloride (CaCl ₂ ), calcium oxide (CaO) and An electrolytic bath is composed of a mixed molten salt made of calcium (Ca), and this electrolytic bath is divided into an electrolytic zone for electrolyzing calcium oxide and / or calcium chloride in the mixed molten salt and a reducing zone for reducing titanium oxide. In the electrolysis zone, calcium oxide and / or calcium chloride in the mixed molten salt is electrolyzed and reduced to calcium (Ca) and monovalent calcium ions, and titanium oxide is reduced by these to form sponge metal titanium. A titanium metal smelting method for obtaining (Ti) is proposed (see Patent Document 1).

According to this method, it is possible to produce titanium metal directly and continuously from titanium oxide in a single reaction tank, and the concentration of solid solution oxygen in the metal titanium can be controlled. There is a special advantage that titanium can be produced industrially advantageously.
However, even in this method, the carbon dioxide gas generated by the anodic reaction at the anode dissolves as carbonate ions in the inorganic molten salt that is the electrolytic bath, so it moves with diffusion due to the convection and concentration gradient of the electrolytic bath, reducing titanium oxide. It reaches the area or near the cathode. The carbon dioxide gas thus reached reacts rapidly with the metal titanium due to the high reaction activity of the metal titanium at a high temperature to become titanium carbide or solute carbon, causing carbon contamination of the product metal titanium. Furthermore, the anode reaction gas that has reached the vicinity of the cathode also reacts with calcium (Ca), which was originally produced to thermally reduce titanium oxide, causing a reverse reaction to produce calcium oxide (CaO) and carbon (C). As a result, the reduction efficiency from titanium oxide to titanium metal also becomes a factor.

As described above, PDFerro et al., Waste Management, Vol. 7 (1997), in order to prevent contamination of metallic titanium and reduction in reduction efficiency to metallic titanium caused by the anode reaction gas generated by the anode reaction such as carbon dioxide gas. In No.7, P451-461, a carbon anode at the center of the magnetic crucible, a stainless cathode at the outer periphery, and a porous magnesia partition that partitions both electrodes between the anode and cathode are placed in an argon atmosphere. Has proposed a method of electrolyzing a mixed molten salt of calcium chloride (CaCl ₂ ) and calcium oxide (CaO) (see Non-Patent Document 2). According to this method, oxygen ions (O ²⁻ ) generated in the mixed molten salt move to the anode through the porous magnesia partition, and are released as the anode reaction gas. Also, the anode reaction gas released in the form of bubbles in the electrolytic bath cannot physically pass through the micropores of the porous magnesia partition wall, but floats and is discharged to the anode surface. In addition, the falling carbon inevitably generated due to uneven oxidation of the carbon anode floats on the surface of the electrolytic bath due to the difference in specific gravity, but the fine solid carbon may also physically pass through the pores of the porous magnesia partition. Therefore, the effect of preventing carbon contamination of the obtained metal titanium is exhibited.

  However, in the method according to Non-Patent Document 2, carbon dioxide gas generated as the anode reaction gas in the porous magnesia partition is partly dissolved in the electrolytic bath to become carbonate ions and the like. It is not only completely prevented from contamination of the resulting titanium metal through the porous magnesia partition due to the convection and concentration gradient of the electrolytic bath, but also produced to reduce titanium oxide. It also reacts with calcium (Ca), which causes a reduction in reduction efficiency from titanium oxide to titanium metal. In addition, calcium produced at the cathode also reduces magnesia, which is a partition wall, so that it gradually becomes metallic magnesium and the partition wall may be destroyed. As a method for avoiding this problem, a means for protecting the porous diaphragm with a solidified layer of an inorganic molten salt constituting the electrolytic bath is conceivable. In that case, the partition wall is not porous but is a completely closed wall. Therefore, it becomes impossible to flow electricity and the means cannot be applied. Furthermore, the calcium generation rate depends on the oxygen ion migration rate passing through the porous ceramic partition wall, and the migration rate depends on the thickness, porosity, shape, etc. of the porous ceramic partition wall. ~ 2.5mm thick porous magnesia partition is used, but considering the shape, size, strength, life, and cost of the porous ceramic, the electrolytic method using the porous ceramic partition is It must be said that application on an industrial scale is difficult.

On the other hand, for metals other than titanium, for example, niobium is produced as columbite ore [(Fe, Mn) (Ta, Nb) ₂ O ₆ ], etc., so these are complex fluorides using a mixed acid of hydrofluoric acid and sulfuric acid. Niobium fluoride (H ₂ NbF) remaining in the aqueous phase is separated from iron and manganese by dissolution as a compound, and further separated by selective extraction with an organic solvent to separate niobium (Nb) and tantalum (Ta). ₇ ) Treat niobium oxide (Nb ₂ O ₅ ) by reacting with ammonia (NH ₄ OH). Then, the obtained niobium oxide is reduced with an appropriate reducing agent such as aluminum, carbon, niobium carbide (NbC), and finally, niobium metal is obtained.

  In the above case, aluminum used as a reducing agent in the stage of forming metallic niobium after obtaining niobium oxide is inevitably mixed, resulting in a limited use of the product niobium, and 1900-2500K in carbon reduction. Because there is a need for a high-temperature vacuum reaction, there is a potential problem such that a large amount of energy is required. For this reason, attention has been focused on metal oxide reduction methods using molten salt electrolysis in metals other than titanium, and an immediate solution to the above-described problems in the production of metal titanium is desired.

As described above, to form an electrolytic bath of the inorganic molten salt in the reaction vessel, in particular a method of using electrolysis to reduce the metal oxide M _x O _y with carbon anodes, typically metal oxides Oxygen ions generated when the oxygen is reduced pass electrons through the anode and release an anode reaction gas such as oxygen (O ₂ ), carbon dioxide (CO ₂ ), and carbon monoxide (CO). At this time, the anode reaction gas rises as bubbles in the electrolytic bath due to the difference in specific gravity, and most of the bubbles are discharged to the surface of the electrolytic bath, but some bubbles move in the electrolytic bath by riding on the liquid flow. . Furthermore, since the inorganic molten salt forming the electrolytic bath dissolves part or all of the anode reaction gas, the anode reaction gas dissolved by convection of the inorganic molten salt moves in the reaction vessel.

The bubbled anode reaction gas that moves as bubbles along with the flow of the inorganic molten salt that is the electrolytic bath and the soluble anode reaction gas that dissolves in the electrolytic bath are immediately expressed by the following formula when they come into contact with the cathode reaction product generated at the cathode ( Causes the reaction represented by 1).
M + O ₂ / CO ₂ / CO → M _x O _y C _z + C (1)
(Here, M is the metal constituting the product metal or inorganic molten salt, and x, y, and z are the number of M, O, and C binding elements.)
That is, when the bubbling anode reaction gas and the soluble anode reaction gas are brought into contact with a metal that is reduced by electrolysis and becomes a product, such product metal reoxidation or carbon contamination is caused, and an inorganic molten salt is formed. If contact is made with a strong reducing metal such as calcium produced on the cathode by electrolysis, the strong reducing property of the metal is lost by the oxidation reaction, resulting in a reduction in reduction efficiency. Furthermore, when a carbon anode is used as the anode, the fine carbon produced simultaneously with the anodic reaction is suspended in the molten salt to cause secondary carbon contamination of the product metal. Fine carbon floats on the liquid surface of the electrolytic bath and stays between the anode and cathode for electrolysis, causing the electrodes to be short-circuited.

The saturation solubility of the anode reaction gas in the inorganic molten salt depends on the anode reaction gas partial pressure in the atmosphere, the inorganic molten salt temperature, the concentration of the mixture in the inorganic molten salt, and the like. For example, according to Masafumi Maeda et al., In a mixed molten salt of calcium chloride (CaCl ₂ ) and calcium oxide (CaO), the higher the carbon dioxide partial pressure (PCO ₂ ), the lower the molten salt temperature, and the higher the CaO concentration, It has been reported that the equilibrium solubility of carbon dioxide gas in the molten salt is increased (see Non-Patent Document 3). Here, carbon dioxide gas is a typical gas as an anode reaction gas in a method of smelting metal M using electrolysis using a carbon anode in an inorganic molten salt.

Specification and drawings of Japanese Patent Application No. 2002-210,537 Sakae Takeuchi and Osamu Watanabe, The Japan Institute of Metals Vol. 28 (1964) No. 9, pp. 549-554 P.D.Ferro, B.Mishra, D.L.Olson and W.A.Averill, Waste Management, Vol.17 (1997), No.7, P451-461 Masafumi Maeda, Alexander McLean, ISS TRANSACTIONS, Vol. 8 (1987), P23-27

  Therefore, the present inventors reduced the metal oxide by electrolysis performed in an electrolytic bath made of an inorganic molten salt, and inevitably caused various problems that occur when reducing the metal oxide for producing the metal, that is, from the anode. This is a problem of metal reoxidation or contamination caused by the generated anode reaction gas, reduction of reduction efficiency due to reverse reaction in an inorganic molten salt, and electrolysis using a carbon anode. The fine carbon produced by the decomposition suspends in the molten salt, causing secondary carbon contamination of the metal, or the fine carbon floats on the surface of the molten salt and stays between the anode and cathode used for electrolysis. The inventors have intensively studied a method for reducing metal oxides that solves the problem of short-circuiting the electrodes and that is industrially feasible and that is simple and inexpensive to produce metals.

  As a result, the anode reaction gas is discharged from the electrolytic bath as quickly as possible in the form of bubbles, and the above problem is solved by preventing movement and diffusion of the anode reaction gas dissolved in the electrolytic bath in the electrolytic bath. Reached the knowledge that it can. A partition that forms an anode reaction region, all or part of which is made of an oxygen ion conductor material, is disposed around the anode, and the anode reaction gas generated in the anode reaction region moves to the cathode side. It has been found that all the above problems can be solved by preventing the occurrence of the problem, and that the increase in electrolysis power inevitably generated by providing the partition walls can be suppressed, and the present invention has been completed.

Accordingly, the object of the present invention is to prevent the contamination of the metal obtained by reducing the metal oxide as much as possible and to have a good reduction efficiency, and can be carried out simply and inexpensively. It is an object to provide a method for reducing a metal oxide that can be carried out at the same time.
Another object of the present invention is to prevent the contamination of the metal obtained by reducing the metal oxide as much as possible, to improve the reduction efficiency, to be simple and inexpensive, The object is to propose a metal oxide reduction device that can be operated on a global scale.

That is, the present invention is a method for reducing a metal oxide (M _x O _y ) that reduces a metal oxide in an electrolytic bath made of an inorganic molten salt contained in a reaction vessel and releases an anode reaction gas from the anode. A partition that forms an anode reaction region is disposed around the anode to prevent the anode reaction gas generated in the anode reaction region from moving to the cathode side, and the cathode below the anode reaction region. It is possible to move ions in the electrolytic bath to and from the side, and part or all of the partition walls are formed of an oxygen ion conductive material, and oxygen ions in the electrolytic bath move through part or all of the partition walls. This is a method for reducing a metal oxide.

The present invention is also a metal oxide (M _x O _y ) reduction device that reduces metal oxide in an electrolytic bath made of an inorganic molten salt contained in a reaction vessel and releases an anode reaction gas from the anode. A partition that forms an anode reaction region is disposed around the anode to prevent the anode reaction gas generated in the anode reaction region from moving to the cathode side, and on the cathode side below the anode reaction region. The ions in the electrolytic bath can move, and part or all of the partition walls are formed of an oxygen ion conductive material, and oxygen ions in the electrolytic bath move through part or all of the partition walls. This is a metal oxide reduction device.

  The method for reducing metal oxide in the present invention is to reduce metal oxide by electrolysis in an electrolytic bath made of an inorganic molten salt formed in a reaction vessel, and from the anode, an anode reaction gas generated by an anode reaction. As long as it is a method for reducing a metal oxide that releases hydrogen, it can be used in all methods without any particular limitation.

In the metal oxide reduction method of the present invention, the metal oxide has the general formula M _x O _y (where M is a metal element, O is an oxygen element, and x and y are the numbers of M and O bonding elements, respectively). As for the metal element M, for example, titanium (Ti), silicon (Si), iron (Fe), germanium (Ge), zirconium (Zr), hafnium (Hf), uranium (U), neodymium (Nd), niobium (Nb), and one or more metals selected from tantalum (Ta) can be mentioned, preferably titanium (Ti), zirconium (Zr), uranium (U), niobium (Nb), and tantalum (Ta). Since these metals have a strong affinity for oxygen, a reduction method performed by electrolysis in an electrolytic bath made of an inorganic molten salt is advantageous. In addition, the metal oxide may be obtained by any method, and the shape is not particularly limited in terms of crystal type, particle diameter, shape, surface state, and the like.

In the present invention, an inorganic molten salt is used as an electrolytic bath formed in the reaction vessel. The inorganic molten salt are not specifically limited, for example, a calcium chloride (CaCl _2), mixed molten salt consisting of calcium (Ca) and calcium oxide (CaO), calcium chloride (CaCl ₂₎ and calcium oxide (CaO) Mixed molten salt, mixed molten salt consisting of calcium chloride (CaCl ₂ ), sodium chloride (NaCl) and calcium oxide (CaO), mixed molten salt consisting of calcium chloride (CaCl ₂ ) and magnesium chloride (MgCl ₂ ), etc. Preferably, it is a molten salt containing calcium chloride. If the inorganic molten salt is a molten salt containing calcium chloride, calcium, which is a strong reducing metal, can be generated at the cathode, and the reducing ability of the metal oxide is high. Moreover, since it has the solubility of the calcium oxide produced | generated by reduction | restoration of a metal oxide, it is advantageous at the point that the calcium oxide generated by reduction | dissolution melt | dissolves in an electrolytic bath, and reduction | restoration advances rapidly.
Further, for this inorganic molten salt, a single molten salt may be used, or a mixed molten salt in which a plurality of molten salts are mixed may be used, and when an electrolytic bath is formed and electrolysis is started. Is a single molten salt, and may be a mixed molten salt by electrolysis.

In the present invention, the anode used for electrolysis is not particularly limited, and an anode generally used in electrolysis of metal oxides can be used. For example, a carbon anode can be used. it can. Carbon anode is a mixture of all or part of carbon dioxide (CO ₂ ), carbon monoxide gas (CO), and oxygen gas (O ₂ ) with oxygen ions (O ²⁻ ) generated by electrolysis of the anode carbon itself. It is an anode released as a gas, and it has the effect of lowering the electrolysis voltage during metal oxide reduction, that is, the effect of saving electrical energy used for electrolysis, and the anode manufacturing cost including material costs is relatively low. Generally used in terms. However, as explained in the description of the prior art, the fine carbon produced by the consumption of the carbon anode may be suspended in the molten salt to contaminate the metal secondarily. May float and short-circuit the anode and the cathode. Therefore, according to the present invention, the problem caused by the fine carbon produced when the carbon anode is used can be solved for the reason described later, and therefore the effect of the present invention becomes more remarkable. .

  Further, in the metal oxide reduction method according to the present invention, a partition wall forming an anode reaction region is provided around the anode to be electrolyzed in an electrolytic bath, and the anode reaction gas generated in the anode reaction region is Prevents movement to the cathode side, enables movement of ions in the electrolytic bath with the cathode side below the anode reaction region, and forms part or all of the partition walls from an oxygen ion conductive material Thus, oxygen ions in the electrolytic bath can be moved through part or all of the partition walls.

In the present invention, it is necessary to form part or all of the partition walls from an oxygen ion conductive material so that oxygen ions in the electrolytic bath can be moved through part or all of the partition walls.
In the present invention, the oxygen ion conductive substance means a substance exhibiting oxygen ion conductivity by oxygen ions (O ²⁻ ) easily moving through oxygen vacancies existing in the structure of the substance. When there is a difference in oxygen concentration in each region separated by a partition wall that is partially or entirely formed by such an oxygen ion conductive material, the partition wall formed by the oxygen ion conductive material has oxygen in the partition wall. Ions move, and an electromotive force is generated according to the concentration difference of the oxygen ions. In addition, when a potential is applied to the front and back of the diaphragm, only oxygen ions are moved from the cathode toward the anode in accordance with the potential.

The oxygen ion conductive material in the present invention is preferably a zirconia solid electrolyte containing zirconia (ZrO ₂ ) as a main component. A zirconia solid electrolyte is advantageous in that it is stable with respect to an inorganic molten salt and exhibits performance excellent in oxygen ion conductivity. On the other hand, even when the main component is zirconia and has the same oxygen vacancy concentration, when another metal species is added and substituted with zirconia, its conductivity varies greatly depending on the metal species, so in recent years yttrium. A zirconia-based solid electrolyte to which (Y), calcium (Ca), scandium (Sc), or the like is added has been developed, but in the present invention, any substance that has oxygen ion conductivity mainly composed of zirconia may be used. The additive metal species is not limited.

In addition, when a part of the partition wall in the present invention is formed of an oxygen ion conductive material, materials other than the oxygen ion conductive material do not have a large solubility in the inorganic molten salt forming the electrolytic bath. For example, when the inorganic molten salt is composed of calcium chloride (CaCl ₂ ) and calcium oxide (CaO), a commonly used refractory material such as bricks and castables such as alumina and magnesia are used. Can be formed. For parts other than such oxygen ion conductive substances, functionality such as the passage of specific ions is not required, so partition walls can be formed without being affected by the selection of specific materials, thickness, porosity, etc. it can.
In the partition wall in the present invention, the proportion of the portion formed by the oxygen ion conductive material and the material forming the other portion is the size of the current required for the reduction of the metal oxide and the size of the reaction vessel, It can be designed appropriately in consideration of the shape of the partition wall.

  The operation of the partition wall in the present invention will be specifically described below. In addition, although the case where electrolysis is performed using a carbon anode will be described as an example, the same applies to an anode other than the carbon anode.

In the present invention, the anode reaction region formed by the partition wall arranged around the anode means that oxygen ions (O ²⁻ ) generated by electrolysis performed in the electrolytic bath react with the anode, and oxygen (O ₂ ) This is a region where an anodic reaction for generating gases such as carbon dioxide (CO ₂ ) and carbon monoxide (CO) is performed.
In addition, the anode reaction gas generated by the anode reaction is released into the electrolytic bath as bubbles in the anode reaction region, and most of the bubbles float toward the liquid level of the electrolytic bath due to the specific gravity difference in the electrolytic bath, It is released from the liquid surface of the electrolytic bath as a gas. The anode reaction gas that moves as bubbles in the electrolytic bath is referred to as a bubble anode reaction gas. Also, part or all of the anode reaction gas released as bubbles in the electrolytic bath dissolves in the electrolytic bath in the process of rising in the electrolytic bath. The anode reaction gas that dissolves in the electrolytic bath in this way is called a soluble anode reaction gas.

  Since the cellular anode reaction gas generated in the anode reaction region is physically prevented from moving to the cathode side by the partition wall, the cell anode reaction gas does not contact the electrolytic bath on the cathode side. Released from the surface of the electrolytic bath. In addition, since a part of the anode reaction gas generated in the anode reaction region is dissolved in the electrolytic bath, the concentration of the soluble anode reaction gas gradually increases in the electrolytic bath in the anode reaction region. The anode reaction gas (dissolvable anode reaction gas) is dissolved in a saturated state in the electrolytic bath in the anode reaction region. The solubility of the anode reaction gas in the electrolytic bath made of an inorganic molten salt varies depending on the type of the inorganic molten salt, the anode reactive gas partial pressure of the atmosphere at the liquid surface of the inorganic molten salt, the temperature of the inorganic molten salt, etc. In consideration of the above, the anode reaction region can be designed to provide a partition wall. Note that the partition formed by a part or all of the oxygen ion conductive material does not pass the above-described soluble anode reaction gas.

  Since no more anode reaction gas can be dissolved in the electrolytic bath in the anode reaction region where the anode reaction gas is dissolved in a saturated state, the anode reaction gas generated at the anode by electrolysis after saturation with the anode reaction gas. Does not dissolve in the electrolytic bath, floats toward the liquid surface of the electrolytic bath in a bubble state, and is released from this liquid surface. That is, after the electrolytic bath in the anode reaction region is saturated with the anode reaction gas, almost all the anode reaction gas generated by electrolysis can be discharged out of the system without moving to the cathode side.

  Further, in the present invention, the ions in the electrolytic bath can be moved to the cathode side below the anode reaction region, and electrolysis is performed through a partition formed partly or entirely by an oxygen ion conductive material. Allows movement of oxygen ions in the bath. That is, a metal produced by dissolving a strong reducible metal ion derived from an inorganic molten salt produced in an electrolytic bath by electrolysis, an oxygen ion produced by reduction of a metal oxide, or a target metal oxide directly in the molten salt Ions can be exchanged between the anode side and the cathode side through the region below the anode reaction region, and some of the above ions are oxygen ion conductive due to the potential applied by electrolysis. It moves from the cathode side toward the anode side through the partition formed of the material.

On the other hand, a soluble anode reaction gas that is generated on the surface of the anode by the anode reaction and dissolved in the electrolytic bath as carbonate ions (CO ₃ ^2- ), oxygen ions (O ^2- ), etc. in the anode reaction region Although it is possible to move to the cathode side through the region below the anode reaction region, these soluble anode gases are attracted to the anode side by the potential given by electrolysis, so these soluble anode reaction gases are Diffusion from the anode reaction region can be prevented. Since part or all of the partition walls are formed of an oxygen ion conductive material, these soluble anode reaction gases do not diffuse from the anode reaction region.

Furthermore, since the inorganic molten salt in which the anode reaction gas is dissolved becomes a mixed molten salt to which a soluble anode reaction gas is locally added, there is no difference between the electrolytic bath in the anode reaction region and the electrolytic bath outside the anode reaction region. Properties such as specific gravity change. For example, calcium chloride in the case of a mixed molten salt consisting of (CaCl ₂₎ and calcium oxide (CaO), is added with carbon dioxide gas dissolved in the molten salt, calcium chloride (CaCl ₂₎ and calcium oxide (CaO) And a mixed molten salt composed of calcium carbonate (CaCO ₃ ), the specific gravity is smaller than that of the mixed molten salt composed of the initial calcium chloride and calcium oxide. As a result, even if the entire electrolytic bath in the reaction vessel is a mixed molten salt composed of calcium chloride and calcium oxide, the anode reaction gas is saturated and becomes a mixed molten salt containing calcium carbonate. The electrolytic bath rises due to the difference in specific gravity and tries to stay in the anode reaction region. Therefore, it is possible to prevent the electrolytic bath in which the anode reaction gas is dissolved from being mixed into the electrolytic bath outside the anode reaction region.

  In addition, fine carbon produced from the carbon anode during the anodic reaction generally has a lower specific gravity than the electrolytic bath used for electrolysis, so it floats immediately on the surface of the electrolytic bath after dropping off the carbon anode, It is physically prevented from moving and does not move to the cathode side.

  In the method for reducing a metal oxide according to the present invention, it is preferable to supply a metal oxide as a raw material of the obtained metal into an electrolytic bath other than the anode reaction region. By supplying the metal oxide into the electrolytic bath other than the anode reaction region, carbon contamination and reoxidation of the obtained metal can be prevented. Further, it is preferable to increase the reduction efficiency by preferably supplying the region close to the cathode. Furthermore, the metal oxide may be disposed directly on the cathode so that the metal oxide is in contact with the cathode, and the metal oxide is utilized using a liquid-permeable container such as a metal net that is not in direct contact with the cathode. An object may be held in this, and may be pulled up after reduction, or a metal oxide may be previously formed in a solid form and suspended around or on the cathode.

In the metal oxide reduction method of the present invention, an anode reaction gas space region for containing the anode reaction gas released from the liquid surface of the electrolytic bath in the anode reaction region is preferably formed. By forming the anode reaction gas space region that contains the anode reaction gas, the anode reaction gas released from the liquid level of the electrolytic bath in the anode reaction region is dissolved in the electrolyte bath other than the anode reaction region, or the anode reaction The anode reaction gas once released outside the electrolytic bath is prevented from being dissolved again into the electrolytic bath through the surface of the electrolytic bath outside the anode reaction region. It is also possible to prevent the strong reducing metal produced at the cathode from being oxidized. More preferably, the anode reaction gas in the anode reaction gas space region is discharged from the reaction vessel. By discharging the anode reaction gas in the anode reaction gas space area out of the reaction tank, it is possible to prevent the anode reaction gas from leaking beyond the anode reaction gas space area even if a crack in the partition wall unexpectedly occurs. can do.
The means for forming such an anode reaction gas space region is not particularly limited, and for example, the liquid surface of the electrolytic bath in the anode reaction region may be surrounded by the partition wall forming the anode reaction region. And a side wall of the reaction vessel, a lid may be formed on the upper surface of the electrolytic bath in the anode reaction region.

  In the metal oxide reduction method of the present invention, the electrolytic bath in the anode reaction region is preferably sucked at a constant rate and discharged out of the reaction vessel. As described above, the anode reaction gas is dissolved in a saturated state in the electrolytic bath in the anode reaction region, but the electrolytic bath in the anode reaction region is sucked at a constant rate and discharged out of the reaction vessel. The electrolytic bath in which the anode reaction gas is saturated causes the flow of the electrolytic bath opposite to the flow to be mixed into the electrolytic bath outside the anode reaction region, and the electrolytic bath in which the anode reaction gas is dissolved is outside the anode reaction region. Can be prevented from moving to the electrolytic bath.

In the method for reducing a metal oxide in the present invention, the atmosphere on the liquid surface of the electrolytic bath other than the anode reaction region is preferably shut off from the outside. For example, in the electrolysis of an inorganic molten salt containing calcium chloride (CaCl ₂ ) and calcium oxide (CaO), calcium (Ca) is deposited on the cathode, and the target metal oxide is obtained using the strong reducibility of the calcium. In the case of a metal smelting method for reduction, since the specific gravity of calcium deposited at the cathode is smaller than the specific gravity of the inorganic molten salt, this calcium floats after precipitation. If this calcium cannot contact the metal oxide at a sufficient concentration or for a sufficient time during the ascent process, it will surface on the surface of the inorganic molten salt without reducing the target metal oxide. It reacts with oxygen in the atmosphere of the liquid level and burns immediately. Therefore, by shutting off the atmosphere at the liquid surface of the electrolytic bath other than the anode reaction region from the outside, after the oxygen originally mixed in this atmosphere has been consumed, calcium will no longer burn, and the inorganic molten salt The calcium floating on the surface of the metal moves again to the supply position of the metal oxide due to the convection of the inorganic molten salt, the concentration gradient of calcium, and the like, and the metal oxide is reduced to improve the reduction efficiency.

  In the present invention, more preferably, the atmosphere on the liquid surface of the electrolytic bath, which is shut off from the outside, is an inert gas atmosphere. When the atmosphere other than the anode reaction gas space area is opened to the outside for the purpose of recovering the target metal obtained by reducing the metal oxide, oxygen in the new atmosphere is prevented from being mixed and further reduced. Efficiency can be improved.

The arrangement of the partition walls in the present invention can be appropriately designed depending on the arrangement of anodes and cathodes used for electrolysis.
For example, when the anode and the cathode are positioned in the left-right direction in the electrolytic bath, the partition wall in the present invention is disposed between the anode and the cathode, and the lower end of the partition wall is provided at a position lower than the lower end of the anode. It is preferable that the partition wall and the side wall of the reaction tank surround the anode and that the anode reaction region be formed above the lower end of the partition wall. By providing the partition wall in this way, the above-described function of the partition wall in the present invention can be achieved.
In this case, the operation of the partition wall, part or all of which is formed of an oxygen ion conductive material, will be described below.

In the method of reducing a metal oxide in an electrolytic bath made of an inorganic molten salt, it is negative ions such as oxygen ions (O ²⁻ ) that are responsible for the movement of electrons in the electrolytic bath, for example, calcium chloride ( In a reduction method in which electrolysis is performed using a mixed molten salt of CaCl ₂ ) and calcium oxide (CaO), oxygen ions (O ²⁻ ) and chlorine ions (Cl ⁻ ) serve as electron media. The positive ions corresponding to the negative ions are, for example, calcium ions (Ca ⁺ ) in the case of the above mixed molten salt, and a metal oxide (MxOy) having solubility in the mixed molten salt as a raw material. In some cases, in addition to this, ions of metal M (M ^{2Y / X +} ) are present.

On the other hand, the pre-melting compound that generates these ions (for example, CaO for oxygen ions (O ²⁻ ) and CaCl _{2 for} chlorine ions (Cl ⁻ )) has a standard free energy change (ΔG) of the compound. And the theoretical decomposition voltage (E ^o ) calculated from the valence (n) and the reaction temperature (T), and the activity (a) and overvoltage (η) of the compound in the mixed molten salt are taken into account. There is an actual decomposition voltage (E). In actual electrolysis, the deposition starts from the ions of the substance having the smallest decomposition voltage (E). For example, in a reduction method in which a mixed molten salt of calcium chloride (CaCl ₂ ) and calcium oxide (CaO) is electrolyzed, oxygen ions (O ²⁻ ) migrate to the anode and carbon dioxide gas (CO ₂ / CO CO) first deposits on the anode surface, then oxygen (O ₂ ) and finally chlorine (Cl ₂ ). When the anode is not a carbon anode, oxygen (O ₂ ) starts to precipitate first, and then chlorine (Cl ₂ ) precipitates.

On the other hand, from the viewpoint of electrical energy, it is preferable that the substance deposited at the anode is a substance having a lower decomposition voltage. Therefore, it is desirable to generate carbon dioxide and / or oxygen having a lower decomposition voltage than chlorine. Furthermore, in the reduction of metal oxide, there is a problem that the oxygen cannot be continuously maintained unless oxygen is discharged out of the system in the same amount as the oxygen contained in the metal oxide to be charged. For example, deposition of an anodic reactive gas that does not contain oxygen such as chlorine (Cl ₂ ) must be avoided.

For example, the anode and the cathode are positioned in the left-right direction in the electrolytic bath, and a partition made of an electrical insulator is provided between these electrodes, and only a part on the lower end side of the partition is provided between the electrodes in the electrolytic bath. If the current density of the current flowing through this region exceeds ^{2 A} / cm ² or more, for example, the oxygen ion migration rate becomes rate-limiting. An anode reaction gas containing oxygen can no longer be generated, and an anode reaction gas not containing oxygen such as chlorine (Cl ₂ ) is deposited from the anode. And since the current bypasses the partition, the distance of ion movement in the electrolytic bath increases and the electrical resistance increases, and the electrical energy required for the entire electrolysis increases compared to when the partition is not inserted. .

  Therefore, in the case where the anode and the cathode are positioned in the left-right direction in the electrolytic bath, a potential is generated on the front and back of the partition by forming part or all of the partition using the oxygen ion conductive material as in the partition of the present invention. , Since oxygen ions corresponding to this potential pass from the cathode to the anode through the portion formed of the oxygen ion conductive material, current concentration does not occur, and for example, oxygen such as chlorine is not included. The deposition of the anode reaction gas can be reduced as much as possible. Furthermore, regarding the increase in electrical resistance inevitably caused by the partition provided between the anode and the cathode, this electrical resistance can be reduced by forming part or all of the partition with an oxygen ion conductive material. The increase can be reduced, and the increase in electrical energy can be reduced as much as possible compared with the case where no partition is provided.

If the partition wall between the anode and the cathode passes a soluble anode reaction gas such as carbonate ion (CO ₃ ^2- ), the metal oxide reduced on the cathode side is contaminated with carbon. In the present invention, the material that forms part or all of the partition wall is an oxygen ion conductive substance because a problem occurs that causes a reverse reaction with the strong reducing metal (calcium) and reduces the reduction efficiency. There must be.

In the case of the positional relationship of the electrodes, it is preferable to provide the partition so that the lower end of the partition wall is lower than the lower end of the cathode. For example, electrolysis of an inorganic molten salt containing calcium chloride (CaCl ₂ ) and calcium oxide (CaO), in which calcium (Ca) is deposited on the cathode and the target metal oxide is utilized by utilizing the strong reducibility of this calcium. In the case of metal smelting to reduce the amount of calcium, the specific gravity of calcium deposited at the cathode is smaller than the specific gravity of the inorganic molten salt, so that it floats after the precipitation. Therefore, the problem that the lower reducibility of the cathode due to the lower end of the cathode being higher than the lower end of the partition wall and the strongly reducing substance (calcium) at the cathode moving to the anode reaction region through the bottom end of the partition wall is prevented. Can do.

In the case of the positional relationship of the electrodes, the metal oxide is preferably supplied into a region where the partition wall and the side wall of the reaction vessel surround the cathode. For example, electrolysis of an inorganic molten salt containing calcium chloride (CaCl ₂ ) and calcium oxide (CaO), where calcium is precipitated at the cathode and the strong metal reductivity is used to oxidize the target metal. In the case of metal smelting to reduce materials, the strong reducing substance (calcium) at the cathode diffuses due to the concentration gradient and convection of the electrolytic bath in the process of rising, but the raw metal oxide reacts with the partition walls. Since the target metal oxide can be reduced before moving to the anode reaction region by diffusion by supplying it into the region where the side wall of the tank surrounds the cathode, it is advantageous in terms of reduction efficiency. .

  On the other hand, when the anode and the cathode are positioned in the left-right direction in the electrolytic bath, the partition wall in the present invention is disposed so as to surround the anode, and an opening is provided at a position lower than the lower end of the anode. It is preferable that an anode reaction region be formed above the opening and the region surrounding the substrate. By providing the partition wall in this way, the function of the partition wall in the present invention as described above can be achieved.

When the anode and the cathode are positioned in the left-right direction in the electrolytic bath, a shielding plate is preferably provided to block the atmosphere on the liquid surface of the electrolytic bath other than the anode reaction region from the outside, and a part of the shielding plate is disposed. Extending to surround the periphery of the cathode in the electrolytic bath, and providing an opening at a position lower than the lower end of the cathode, the shield plate is an area surrounding the cathode, and a metal oxide above the opening It is good to supply. When the shielding plate is arranged in this way, for example, in the electrolysis of an inorganic molten salt containing calcium chloride (CaCl ₂ ) and calcium oxide (CaO), calcium (Ca) is deposited on the cathode, and the strong reducing property of the calcium In the case of a metal smelting method for reducing the target metal oxide, the calcium precipitated at the cathode is prevented from diffusing by the convection of the inorganic molten salt, and the specific gravity of the calcium is the specific gravity of the inorganic molten salt. Since it is smaller, it can prevent moving to a cathode side through the opening of the lower end of a shielding board, and can reduce a target metal oxide efficiently. Further, in the work of reducing the metal oxide to the target metal and recovering it as a product, the cathode and the shielding plate can be used as a storage container for the target metal. It is possible to prevent reoxidation to oxygen in the atmosphere and improve recovery efficiency.

  Further, as another example when the anode and the cathode are positioned in the left-right direction in the electrolytic bath, preferably, a shielding plate is provided to block the atmosphere on the liquid surface of the electrolytic bath other than the anode reaction region from the outside, The lower end of the shielding plate is extended to a position lower than the lower end of the cathode, and the shielding plate and the side wall of the reaction vessel surround the cathode, and the metal oxide is supplied above the lower end of the shielding plate. It is preferable that the ions in the electrolytic bath can move with the anode side below the shielding plate. When the shielding plate is arranged in this way, the calcium precipitated at the cathode is prevented from diffusing due to the convection of the inorganic molten salt, and the specific gravity of calcium is smaller than the specific gravity of the inorganic molten salt, so that it exceeds the lower end of the shielding plate. The migration to the cathode side can be prevented, and the target metal oxide can be reduced efficiently.

  Further, when the cathode is located below the anode in the electrolytic bath, the partition wall in the present invention is disposed so as to surround the anode, and an opening is provided at a position lower than the lower end of the anode, so that the partition wall surrounds the anode. It is preferable that the anode reaction region is formed in the region and above the opening. By providing the partition wall in this way, the above-described function of the partition wall in the present invention can be achieved.

In the case of such an electrode positional relationship, it is preferable to supply the metal oxide below the opening. For example, in metal smelting to reduce the target metal oxide by electrolyzing a mixed molten salt of calcium chloride (CaCl ₂ ) and calcium oxide (CaO) to precipitate calcium (Ca), which is a strong reducing substance, The strongly reducing substance deposited at the cathode floats with a lower specific gravity than the entire electrolytic bath, so by supplying the metal oxide as the raw material below the opening, the target metal oxidation is performed before the reverse reaction occurs. Since it comes into contact with an object, the target metal oxide can be efficiently smelted.

  In the present invention, a metal oxide reduction apparatus can be obtained by using the above-described metal oxide reduction method, but preferably a plurality of anodes are provided in the reaction vessel. When producing metal by reducing metal oxide industrially, even when replacing an anode for reasons such as exhaustion of the anode, the presence of another anode does not stop the entire current in the reaction vessel. It becomes possible to exchange, and productivity as the whole reaction tank improves. In this case, each anode may be surrounded by an individual partition wall to form an anode reaction region, and a plurality of anodes may be arranged in the anode reaction region formed by the partition wall and the reaction vessel side wall. It may be.

  In the present invention, a plurality of cathodes are preferably provided in the reaction vessel. In this case, if the shielding plate is extended to surround the periphery of the cathode as described above and the metal oxide is supplied into the surrounded region, the metal oxide is reduced industrially. When the reduced metal and the cathode are collected together when producing the metal, the presence of another cathode makes it possible to replace the entire current in the reaction tank without stopping, and the reaction tank Overall productivity is improved. In the above case, the arrangement of the plurality of cathodes in the reaction vessel is not particularly limited and can be freely arranged. In addition, when a plurality of anodes are provided as described above, a cathode may be arranged so that the anode is sandwiched around the anode, and a plurality of combinations of such anodes and cathodes are provided in the reaction vessel. You may make it prepare.

  According to the present invention, the anode reaction gas inevitably generated in the anode can be discharged from the liquid surface of the electrolytic bath as quickly as possible in the form of bubbles, and the anode reaction gas dissolved in the electrolytic bath Since movement to the electrolytic bath outside the reaction region can be prevented, the contamination of the metal obtained in the reduction of the metal oxide can be reduced as much as possible, and the reduction efficiency is not lowered. It is simple, inexpensive and can reduce metal oxides industrially advantageously. In addition, the increase in electrolytic power inevitably generated by providing the partition walls can be reduced as much as possible, and can be made more industrially advantageous. In particular, in the case of utilizing electrolysis using a carbon anode, in addition to the above effects, problems such as metal contamination caused by fine carbon generated from the carbon anode and short-circuiting of the electrodes can be solved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

FIG. 1 shows a metal oxide reduction device X according to a reference embodiment . A reaction tank 1 formed of alumina brick, which is a refractory, contains a mixed molten salt 2 composed of calcium chloride (CaCl ₂ ), calcium (Ca) and calcium oxide (CaO). The carbon anode 3 and the stainless steel cathode 4 are immersed and arranged respectively. Further, the lower ends of these electrodes are inclined. A partition wall 5 is disposed between the carbon anode 3 and the stainless cathode 4, and a lower end portion of the partition wall 5 is formed of a stabilized zirconia (ZrO ₂ ) solid electrolyte 5 d which is an oxygen ion conductive material. The other parts are made of alumina brick. A shielding plate 6 is provided above the liquid surface of the mixed molten salt 2 in a region surrounding the carbon anode 3 by the partition wall 5 and the side wall of the reaction tank 1. A shielding plate 7 is provided above the liquid surface of the mixed molten salt 2 in the region surrounding the stainless steel cathode 4 by the partition wall 5 and the side wall 1a of the reaction tank 1 to block the external atmosphere. The shielding plate 6 and the shielding plate 7 can be opened and closed independently, and the shielding plate 6 provided on the carbon anode 3 side has carbon dioxide (CO ₂ ) generated from the carbon anode 3 by electrolysis. And an anode reaction gas discharge pipe 8 that sucks and discharges an anode reaction gas such as carbon monoxide (CO) to the outside of the reaction tank 1 so that the carbon anode 3 consumed by electrolysis can be replaced. It has become. On the other hand, the shielding plate 7 provided on the stainless steel cathode 4 side is provided with a raw material inlet 9 for introducing titanium oxide (TiO ₂ ) as a raw material into the mixed molten salt 2, and titanium oxide. Titanium metal produced by reducing the carbon can be recovered.

In addition, the reaction tank 1 in the metal oxide reduction apparatus X is covered with a solidified layer 10 made of the mixed molten salt 2 on the side wall 1a and the bottom 1b, which are portions where the mixed molten salt 2 accommodated directly touches. . Further, the lower end of the partition wall 5 is disposed so as to be lower than the lower end of the carbon anode 5, and the partition wall 5 and the side wall of the reaction tank 1 provided with the solidified layer 10 are regions surrounding the carbon anode 3. And the anode reaction area | region 11 is formed above the lower end of the partition 5 (area | region shown with the oblique line in the figure). In the reaction tank 1, the movement of ions such as calcium ions (Ca ⁺ ) and oxygen ions (O ²⁻ ) existing in the mixed molten salt 2 between the carbon anode 3 side and the cathode 4 side is caused by this anode. The oxygen ion (O ²⁻ ) can be moved through the portion of the stabilized zirconia (ZrO ₂ ) solid electrolyte 5 d forming the partition wall 5.

When electrolysis was performed by connecting a DC power source (not shown) to the carbon anode 3 and the cathode 4 of the metal oxide reduction device X, the carbon anode 3 and the stainless cathode 4 were below the anode reaction region 11. Conduction is performed, and an anode reaction gas containing carbon dioxide (CO ₂ ), carbon monoxide (CO), and oxygen (O ₂ ) is generated from the carbon anode 3, and the inclined portion 3 a formed on the carbon anode 3. And then floated in the mixed molten salt 2. The mixed molten salt 2 in the anode reaction region 11 in which the partition wall 5 and the side wall 1a of the reaction tank 1 covered with the solidified layer 10 surround the carbon anode 3 and above the lower end of the partition wall 5 is As the decomposition progressed, the carbon root (CO ₃ ) concentration increased, and finally the mixed molten salt 2 dissolved in a state in which carbon dioxide gas was saturated.

FIG. 2 shows another metal oxide reduction apparatus X according to the embodiment of the present invention.
The bottom portion of the reaction vessel 1 made of alumina brick corresponds to the cathode 4, and three carbon anodes 3 are arranged in parallel above the cathode 4. These carbon anodes 3 are moved up and down. Since the distance between the electrodes with the cathode 4 can be changed, the current value flowing through each carbon anode 3 can be controlled by the variation in the distance between the electrodes. In addition, partition walls 5 are disposed around the carbon anodes 3 so as to surround the respective carbon anodes 3, and a portion on the lower end side of the partition walls 5 is stabilized zirconia (oxygen ion conductive material). ZrO ₂ ) is formed of a solid electrolyte 5d, and other portions are formed of an alumina fireproof tube. The partition wall 5 is provided with an opening 5 a at a position lower than the lower end of the carbon anode 3. The partition wall 5 is a region surrounding the carbon anode 3, and an anode reaction region 11 is formed above the opening 5a of the partition wall 5 (a region indicated by diagonal lines in the figure). In the reaction tank 1, the movement of ions such as calcium ions (Ca ⁺ ) and oxygen ions (O ²⁻ ) existing in the mixed molten salt 2 between the carbon anode 3 side and the cathode 4 side is an opening. 5a, and oxygen ions (O ²⁻ ) can also move through the portion of the stabilized zirconia (ZrO ₂ ) solid electrolyte 5d forming the partition walls 5.

The reaction tank 1 contains a mixed molten salt 2 composed of calcium chloride (CaCl ₂ ), calcium (Ca) and calcium oxide (CaO). The upper part of the liquid level is shielded from the external atmosphere. Further, each partition wall 5 disposed in each carbon anode 3 is connected to an anode reaction gas discharge pipe 8, and carbon dioxide (CO ₂ ), carbon monoxide (CO), And the anode reaction gas containing oxygen (O ₂ ) is sucked and discharged to the outside of the reaction vessel 1.
Then, when powdered titanium oxide was placed on the upper surface of the cathode 4 and electrolysis was performed using a DC power supply (not shown) connected between the carbon anode 3 and the cathode 4, the opening 5a and the partition walls The carbon anode 3 and the iron cathode 4 were electrically connected to each other through the 5 stabilized zirconia (ZrO ₂ ) solid electrolyte 5d portion, and the anode reaction gas was generated from the carbon anode 3. When electrolysis is some time proceeds, the mixed molten salt 2 in the anode reaction region 11 to rise carbonates (CO ₃₎ concentration, eventually become a mixed molten salt 2 dissolved in a state in which carbon dioxide gas is saturated It was.

  Hereinafter, based on an Example and a comparative example, this invention is demonstrated more concretely.

[Example 1]
FIG. 3 shows a metal oxide reduction device X according to Example 1 of the present invention.
A reaction vessel 1 made of a stainless steel plate having a width of 840 mm, a depth of 150 mm, and a height of 400 mm was placed inside a closed electric furnace 12 having an internal space of 1000 mm in width, 280 mm in depth, and 900 mm in height. The reactor 1 is lined with a 150 mm × 150 mm × 2.5 mm alumina square plate 1c.

The carbon anode 3 is made of artificial graphite having a width of 30 mm, a depth of 30 mm and a height of 140 mm. Around the carbon anode 3 is an upper alumina container 5Xb having an inner diameter of 100 mmφ × height of 100 mm and an inner diameter of 100 mmφ × height of 100 mm. A partition wall 5X was formed so as to surround the lower alumina container 5Xc. The upper alumina container 5Xb was drilled 30mm x 30mm at two locations, and a square plate 5Xd made of 32mm x 32mm x 1mm thick zirconia (ZrO ₂ ) solid electrolyte was bonded with alumina ceramic bond. did. Further, holes having diameters of 8.5 mm and 17.5 mm are drilled, and these holes are fixed through a SUS round bar 13 having a diameter of 8 mm and an alumina tube 8 having an inner diameter of 13 mm. This SUS round bar 13 is for fixing the carbon anode 3 inside the upper alumina container 5Xb, and the other end of the SUS round bar 13 is taken out of the sealed electric furnace 12 to provide a DC power supply. 14 also serves as a conductive bar. The other end of the alumina tube 8 is taken out of the closed electric furnace 12 so that the inside of the partition wall 5X comprising the upper alumina container 5Xb, the stabilized zirconia (ZrO ₂ ) solid electrolyte (square plate) 5Xd, and the lower alumina container 5Xc. In this structure, the anode reaction gas generated in this step is discharged to the outside of the closed electric furnace 12 through the alumina tube 8. Further, an opening 5Xa of 20 mm × 20 mm is drilled in the lower alumina container 5Xc.

An electrolytic bath 2 in which calcium chloride (CaCl ₂ ) is dissolved is accommodated in the reaction vessel 1, and the cathode 4 is made of a SUS cathode round bar 4 a having a diameter of 8 mmφ and a width of 30 mm × height of 60 mm × thickness. SUS cathode square plate 4b having a thickness of 3 mm. During electrolysis, since the lower alumina container 5Xc is arranged in the lower direction and the upper alumina container 5Xb is arranged in the upper direction, two stabilized zirconia (forming the partition wall 5X when calcium chloride (CaCl ₂ ) is dissolved) ZrO ₂ ) The solid electrolyte 5Xd is immersed in the electrolytic bath 2 to allow oxygen ions (O ²⁻ ) contained in the electrolytic bath 2 to pass through, and is further provided in the lower alumina container 5Xc. The opening 5Xa is a place where ions such as calcium ions (Ca ⁺ ) and oxygen ions (O ²⁻ ) contained in the electrolytic bath 2 can move between the anode side and the cathode side. The carbon anode 3 is immersed in the electrolytic bath, and its lower end is located 20 mm above the upper end of the 20 mm × 20 mm opening 5Xa processed into the lower alumina container 5Xc. The partition wall 5X surrounds the carbon anode 3, and the anode reaction region 11 is formed above the opening 5Xa.

In Example 1 , start-up and electrolysis were performed as follows.
First, after the partition wall 5X was disposed in the reaction vessel 1, the cathode 4 was disposed so that the distance between the electrode and the carbon anode 3 was 130 mm. Next, about 40 kg of 95% pure calcium chloride is charged into the reaction vessel 1, and then the sealed electric furnace 12 is completely sealed, and the internal air is once evacuated by a vacuum pump (not shown), followed by argon gas (Ar). Sent in. After that, while flowing argon gas at a flow rate of 3 L / min, the electric furnace 12 was heated for about 2 days so that the inside of the closed electric furnace 1 became a positive pressure. After the temperature increase, the electric furnace 12 was controlled and held so that the temperature of the electrolytic bath 2 became 900 ° C.

The cathode round bar 4a of the cathode 4 and the SUS round bar 13 attached to the carbon anode 3 are connected to a DC power supply 14 with a maximum output of 750 W. Between the cathode round bar 4a and the SUS round bar 13 Pre-electrolysis was performed by applying a constant voltage of 1.5V. Preliminary electrolysis was mainly intended to remove impurities such as moisture and iron mixed in calcium chloride (CaCl ₂ ), and the voltage was continuously applied for about 20 hours until no current flowed. Meanwhile, impurities such as iron deposited on the cathode 4 were appropriately extracted from the electric furnace 12 and removed from the system. In the operation of extracting from the closed electric furnace 12, the flow rate of argon gas fed into the furnace was increased so that the pressure in the electric furnace 12 became positive.

After the preliminary electrolysis, the new cathode 4 having the same shape was replaced, and electrolysis was started with a constant current of 40A. During electrolysis, titanium oxide (TiO ₂ ) was charged from the raw material charging port (cum metal recovery port) 9 to the vicinity of the cathode 4 at a rate of 15 g per hour. Since titanium oxide settles in the electrolytic bath due to the difference in specific gravity, it was collected by a 100 mesh SUS net 15 every few hours. The recovery method is as follows. A SUS piping pipe (not shown) in which argon gas is flowed is connected to the closed electric furnace 12, and the SUS net 15 is covered with the piping pipe while being pulled up, and the accompanying calcium chloride is added together with argon. It was cooled and recovered as it was in gas. The recovered titanium oxide sample was cooled, washed with water and filtered to remove calcium chloride adhering to the surroundings, and dried in a vacuum thermostat not shown. Furthermore, the dried sample was analyzed by X-ray diffraction analysis, oxygen analysis and the like.

Further, during the electrolysis, the anode reaction gas was recovered appropriately using natural discharge due to an increase in internal pressure inside the partition wall 5X. The anode reaction gas discharged from the alumina tube 8 was collected without excess or deficiency in a bag made of vinyl fluoride resin (not shown), the amount of anode reaction gas generated per arbitrary time was measured, and the discharge rate was investigated. Further, the carbon dioxide concentration (CO ₂ ), oxygen concentration (O ₂ ), and carbon monoxide concentration (CO) in the discharged anode reaction gas were measured by Orsat analysis. During the measurement of these anode reaction gases, the current was temporarily increased or decreased, and the discharge rate and composition change due to the current value were also investigated.

Further, during the electrolysis, the electrolytic baths 2 around the cathode 4 and inside and outside the anode reaction region 11 are appropriately collected, and the concentration of calcium (Ca), calcium oxide (CaO), fixed carbon (C), and carbonate radical (CO ₃ ). Was measured. The electrolytic bath sample to be measured was collected by connecting one end of an unillustrated quartz glass tube with an inner diameter of 5.5 mmφ × length of 1000 mm to an unillustrated glass syringe and replacing the inside of the quartz glass tube with argon gas. Was immersed in a predetermined depth in the electrolytic bath 2, and a method of collecting the electrolytic bath sample to be measured by sucking a glass syringe and solidifying it in a quartz glass tube was used.
The electrolytic bath sample thus obtained is put into a container (not shown) filled with an aqueous nitric acid solution, and the volume of hydrogen when calcium (Ca) reacts with water to generate hydrogen (H ₂ ). By measuring the calcium concentration, and by further titrating the aqueous nitric acid solution, calcium (Ca) and calcium oxide (CaO) react with water to form calcium hydroxide [Ca (OH) ₂ ]. Then, calcium hydroxide was quantified, and the concentration of calcium oxide was calculated by subtracting the previously obtained amount of calcium. Furthermore, solid carbon (C) in the electrolytic bath was measured by filtering the residue in the nitric acid aqueous solution and performing combustion weight measurement. Furthermore, another electrolytic bath sample is dissolved in an aqueous nitric acid solution and boiled, and the discharged carbon dioxide gas is absorbed into a mixed aqueous solution of sodium hydroxide (NaOH) and barium chloride (BaCl ₂ ), and the carbon dioxide gas is precipitated as barium carbonate (BaCO ₃ ). The carbonate radical in the electrolytic bath was quantified by quantifying caustic soda consumed at that time by titration.

As a result, in Example 1 , the recovered titanium oxide sample was reduced to the entire amount of titanium metal (Ti). Further, no carbon compound was detected from the recovered titanium oxide sample. Furthermore, as a result of oxygen analysis, the oxygen concentration in the obtained titanium metal was 2100 ppm. On the other hand, the bath composition in the region surrounding the carbon anode 3 by the partition wall 5X composed of the upper alumina container 5Xb, the stabilized zirconia (ZrO ₂ ) solid electrolyte (square plate) 5Xd and the lower alumina container 5Xc is 20 mm × 20 mm opening 5Xa. In the bath composition 20 hours after the start of electrolysis, as shown in Table 1, the calcium oxide concentration is 0.39 near the bottom of the reaction vessel 1 (outside the anode reaction region). Whereas mol% and carbonate radical concentration are 0.05wt%, calcium oxide concentration is 0.05mol% and carbonate radical concentration is 1.12wt near the electrolytic bath surface above the opening 5Xa (in the anode reaction region). The concentration was considerably different between the electrolytic baths in both regions. In the analysis of the electrolytic bath in the region outside the partition walls 4, the calcium oxide concentration was 0.52 mol% and the carbonate radical concentration was 0.06 wt%. Therefore, the anode reaction product gas generated by the anodic reaction of the carbon anode 3 is dissolved in the electrolytic bath, and the electrolytic bath in which the anode reaction gas is dissolved is retained in the anode reaction region, and from the opening 5Xa of the partition wall 5X. It is considered that the electrolytic bath composition has changed above.

In addition, the anode reaction gas was appropriately collected and measured as an actual value of the discharge rate, and further, an Orsat analysis was performed. As a result, the composition of the anode reaction gas was changed by changing the current. For example, carbon dioxide and carbon monoxide accounted for a lot below 15A, a large proportion of oxygen was observed from 15A to 30A, and a gas considered to be chlorine was dominant above 30A. Furthermore, taking into account the composition of carbon dioxide concentration (CO ₂ ), oxygen concentration (O ₂ ), and carbon monoxide concentration (CO) measured by Orsat analysis, the anode reaction gas generation rate at the current value is calculated, As a result of investigating the ratio of the unrecovered amount and the calculated value of the anode reaction gas generation rate as the unrecovered rate, the difference from the measured value of the above discharge rate was the unrecovered amount of the anode reaction gas. Although the unrecovered rate was 40% immediately after the start of electrolysis, the unrecovered rate gradually decreased, and the unrecovered rate became 5% or less 8 hours after the start of electrolysis. Further, even at a current value of 15 A or more, the same result was obtained that the unrecovered rate was high at the beginning of electrolysis and gradually decreased thereafter. From this, it is considered that the saturation of the anode reaction gas in the anode reaction region 11 progressed with the electrolysis time.

Further, at the time of measurement 8 hours after the start of electrolysis, the current for electrolysis was temporarily reduced to 0 A, and then the current was increased at a constant rate, and the voltage between the electrodes corresponding to the current from 0 A to 50 A was measured. The result is shown in FIG. When the current is increased slightly from 0A, the voltage suddenly rises, then the current and voltage show a constant linear relationship up to 15A, and the voltage rises while maintaining a linear relationship with a slightly smaller slope from 15A to 30A. However, even at 30 A and above, the voltage increased while maintaining the constant relationship between current and voltage, although the slope was further reduced. This tendency is closely related to the decomposition voltage of the anode reaction gas generated on the anode surface. In Example 1 , the voltage expected from the decomposition voltage, the bath resistance of the electrolytic bath 2, the distance between the electrodes, and the like. The value was close to.

  On the other hand, in the electrolytic bath sample around the cathode 4, calcium (Ca) is as high as 1.0 to 1.3 mol%, calcium oxide (CaO) is as low as 0.8 to 1.0 mol%, and solid carbon (C) is as low as 0.03 wt%. Met. These results are shown in Table 1.

[Example 2]
FIG. 4 shows a part of a metal oxide reduction apparatus according to Example 2 of the present invention.
In Example 2 , the conditions relating to the carbon anode 3 and the partition wall 5X surrounding the carbon anode 3 were the same as in Example 1 . The cathode 4 was as follows.
Using an alumina tube having an inner diameter of 120 mmφ and a height of 600 mm, a shielding plate 16 having an opening 16 a having a width of 60 mm and a height of 30 mm is formed at one end thereof. The shielding plate 16 surrounds the cathode 4 and is opened. The port 16a was erected so as to be positioned on the bottom side of the reaction tank 1. The cathode 4 is formed by welding an 8 mmφ SUS cathode round bar 4a to a cathode disk 4c having a thickness of 6 mm × outer diameter 90 mmφ so that the SUS cathode round bar 4a has an inner diameter 9 mmφ not shown. It is covered with an alumina protective tube. For this cathode 4, an 8 mmφ SUS cathode round bar is placed at the top of the reaction tank 1 so that the cathode disk 4 c is horizontal at a position 10 mm above the upper end of the opening 16 a formed at the lower end of the shielding plate 16. Hang and fixed. The upper end of the shielding plate 16 is connected to the upper lid of the reaction tank 1, and the electrolytic bath in the region surrounded by the shielding plate 16 is shielded from the external atmosphere.

After the preliminary electrolysis, electrolysis was performed with a constant current of 40 A, and titanium oxide was charged and recovered under the same conditions as in Example 1, and an electrolytic bath sample was collected and analyzed.
As a result, the recovered titanium oxide sample was reduced to the total amount of titanium metal (Ti), and the oxygen concentration was 1600 ppm. No carbon compound was detected. Furthermore, the electrolytic bath sample collected around the cathode 4 has a high calcium (Ca) of 1.3 to 2.0 mol%, and calcium oxide (CaO) and solid carbon (C) of 0.3 to 0.6 mol% and 0.02 wt%, respectively. It was a thing. The results are shown in Table 1.

[Example 3]
FIG. 5 shows a part of a metal oxide reduction apparatus according to Example 3 of the present invention.
A reaction tank 1 made of a stainless steel plate having a width of 840 mm, a depth of 150 mm, and a height of 400 mm was placed in a closed electric furnace having an internal space of 1000 mm width × 280 mm depth × 900 mm height. The reaction tank 1 is lined with a 150 mm × 150 mm × 2.5 mm alumina square plate 1c.
The carbon anode 3 was made of artificial graphite having a diameter of 50 mm and a length of 80 mm, and one end thereof was threaded with M8 and connected to a SUS round bar 13 with a diameter of 8 mmφ. In addition, the partition wall 5Y disposed around the carbon anode 3 was formed using an alumina tube having an inner diameter of 60 mmφ and a length of 1000 mm. The side surface on the lower end side of the partition wall 5Y is formed with four holes of 10 mm width × 50 mm height, and a square plate 5Yd made of a stabilized zirconia solid electrolyte each having a width of 12 mm × height of 52 mm × thickness of 1 mm is made of alumina. Bonded with ceramic bond. An opening 5Ya is formed on the lower end side of the partition wall 5Y, the partition wall 5Y is immersed in the electrolytic bath 2 on the opening 5Ya side, and a square plate made of the above-mentioned stabilized zirconia solid electrolyte. A total of 4 pieces of 5Yd are all immersed in the electrolytic bath 2. On the other hand, the other end side of the partition wall 5Y is not shown in the figure, but goes out of the sealed electric furnace and is fixed to the upper lid of the sealed electric furnace.

The height of the carbon anode 3 in the partition wall 5Y was adjusted so as to be immersed in the electrolytic bath 2 by about 30 mm, and the carbon anode 3 was fixed to the partition wall 5Y made of an alumina tube by a silicon plug 17. The silicon plug 17 is further drilled with a diameter of 15 mmφ, and a glass tube 18 with an inner diameter of 12 mmφ is fixed so that the entire amount of the anode reaction gas is discharged out of the system. For the cathode 4, a SUS cathode square plate 4 b having a width of 400 mm, a depth of 120 mm and a thickness of 6 mm is laid on the bottom of the reaction vessel 1, and a SUS cathode round bar 4 a having a diameter of 8 mm as a conducting wire on the cathode square plate 4 b. Was connected to the outside of the closed electric furnace.
In this way, the anode reaction region 11 is formed above the opening 5Ya, and ions such as calcium ions (Ca ⁺ ) and oxygen ions (O ²⁻ ) move below the anode reaction tank region 11. This is possible through the opening 5Ya on the side, and oxygen ions (O ²⁻ ) can also move through the square plate 5Yd made of a stabilized zirconia solid electrolyte forming the partition wall 5Y.

About 40 kg of calcium chloride was put into the reaction tank 1 and dissolved in the same manner as in Example 1 . At that time, pre-electrolysis was performed in the same manner as in Example 1 . After preliminary electrolysis, electrolysis was performed at a constant current of 20A. During electrolysis, titanium oxide (TiO ₂ ) was added to the outer periphery of the partition wall 5Y at a rate of 7.5 g per hour. Since titanium oxide settles in the electrolytic bath due to the difference in specific gravity, it was collected on the cathode square plate 4b of the cathode 4 using a 100 mesh SUS net and collected every several hours. The recovery method and the analysis method of the recovered sample are the same as in Example 1 . In addition, an electrolytic bath around the cathode square plate 4b was appropriately collected, and the concentrations of calcium (Ca) and calcium oxide (CaO) were measured. The methods and analytical methods taking of samples, the same as in Example 1.

  As a result, the recovered titanium oxide sample was reduced to the total amount of titanium metal (Ti), and the oxygen concentration was 2200 ppm. No carbon compound was detected. Further, the electrolytic bath sample had a high calcium (Ca) of 1.0 to 1.2 mol%, a low calcium oxide (CaO) of 0.5 to 0.8 mol%, and a low solid carbon (C) of 0.03 wt%. The results are shown in Table 1.

[Example 4]
FIG. 6 shows a part of a metal oxide reduction apparatus according to Example 4 of the present invention.
Two sets of the same carbon anode 3 as in Example 3 and partition walls 5Y arranged so as to surround the carbon anode 3 were prepared, each having a width of 400 mm, a depth of 120 mm, and a thickness of 6 mm. The SUS cathode square plates 4b were arranged side by side. The anode reaction regions 11 formed in the respective carbon anodes 3 and the square plate 5Yd made of the stabilized zirconia solid electrolyte forming the partition walls 5Y and the movement of ions through the openings 5Ya below the anode reaction regions 11 pass. The relationship regarding the movement of oxygen ions was the same as in Example 3.

  Further, the two SUS round bars 13 in the carbon anode 3 are connected to the anode of one DC power supply, and the SUS cathode round bar 4a in each cathode 4 is connected to the cathode of the DC power supply. Parallel configuration. Preliminary electrolysis was performed by applying a constant voltage of 1.5 V between the SUS cathode round bar 4a of the cathode 4 and the SUS round bar 13 of the anode 3, and then the 40A constant was combined with the two sets of carbon anodes 3. Current electrolysis was performed. During electrolysis, in the conductor connecting the carbon anode 3 and the DC power supply, the voltage drop at both ends of the conductor is measured and converted into the current flowing through the conductor, so that the current flowing through the two sets of carbon anodes 3 becomes substantially equal. The current was adjusted by moving one of the carbon anodes 3 up and down to change the resistance between the cathode 4 and the cathode square plate 4b.

During the electrolysis, titanium oxide (TiO ₂ ) was charged around the outside of the partition wall 5Y at a rate of 15 g per hour. At this time, titanium oxide was divided into about 7.5 g per anode, and was put around the outside of the partition wall 5Y. Since titanium oxide settles in the electrolytic bath due to the difference in specific gravity, titanium oxide charged on the cathode square plate 4b of the cathode 4 was received and collected every several hours using a 100 mesh SUS net. The recovery method and the analysis method of the recovered sample are the same as in Example 1 . In addition, an electrolytic bath around the cathode square plate 4b was appropriately collected, and the concentrations of calcium (Ca) and calcium oxide (CaO) were measured. The sample collection method and analysis method are the same as in Example 1 .

  As a result, in Example 4 using the two carbon anodes 3, the recovered titanium oxide sample was reduced to the total amount of metallic titanium (Ti), and the oxygen concentration was 2400 ppm. No carbon compound was detected. Furthermore, the electrolytic bath sample had a high calcium (Ca) of 1.0 to 1.2 mol%, a low calcium oxide (CaO) of 0.4 to 0.9 mol%, and a low solid carbon (C) of 0.03 wt%. The results are shown in Table 1.

[Comparative Example 1]
FIG. 7 shows a part of the reduction device according to Comparative Example 1.
The lower alumina container 5Xc was removed while leaving the upper alumina container 5Xb and the square plate 5Xd made of the stabilized zirconia solid electrolyte shown in Example 1 . The distance between the lower end of the upper alumina container 5Xb and the liquid level of the electrolytic bath 2 was about 5 mm. Other conditions such as the apparatus, material, temperature increase / electrolysis method, and the like were the same as in Example 1 . Note that the upper end of the alumina tube 8 fixed to the upper alumina container 5Xb was normally sealed with a silicon stopper (not shown). Therefore, during electrolysis at a constant current, the anode reaction gas generated from the carbon anode 3 rises in the electrolytic bath and is discharged into the reaction vessel atmosphere at the liquid surface of the electrolytic bath 2 and below the upper alumina container 5Xb. However, since the upper end of the alumina tube 8 is closed and there is a gap of about 5 mm between the lower end of the upper alumina container 5Xb and the liquid level of the electrolytic bath 2, the anode reaction gas diffuses into the reaction tank atmosphere. It began to. That is, the anode reaction gas does not stay inside the upper alumina container 5Xb, and the argon gas fed into the closed electric furnace without dividing the anode reaction gas inside the upper alumina container 5Xb. (Ar) was discharged out of the system little by little.

On position, input amount of the titanium oxide, and recovery methods were the same as in Example 1. The anode reaction gas discharge rate was measured and the composition was analyzed by pushing down the whole anode downward, so that the lower end of the upper alumina container 5Xb was immersed in the electrolytic bath 2, and by natural discharge due to an increase in internal pressure inside the upper alumina container 5Xb. The anode reaction gas was recovered from the upper end of the alumina tube 8. The analysis of the exhaust gas non-recovery rate and gas composition was performed in the same manner as in Example 1 . Further, collection and analysis of the electrolytic bath 2 were performed in the same manner as in Example 1 .

As a result, in Comparative Example 1 in which the anode reaction region 11 was not formed around the carbon anode 3 as described above and the anode reaction gas was not quickly discharged, most of the recovered titanium oxide samples were It was a lower oxide (Ti ₆ O, Ti ₃ O, TiO). Also, some titanium carbide (TiC) was confirmed. The composition of the anode reaction gas was changed by changing the current, and the composition was almost the same as in Example 1 . The exhaust gas non-recovery rate was 40% at the stage immediately after the start of electrolysis at a current of 15 A or less, as in Example 1. However, there was almost no decrease thereafter, and no recovery was made even 20 hours after the start of electrolysis. The rate was 30%. Similarly, the unrecovered rate was rarely reduced even at a current value of 15 A or more. Thus, when the anode reaction region 11 is not formed, the molten salt in which the anode reaction gas is dissolved can be freely moved by convection and the like, and is consumed by reacting with calcium generated at the cathode. It is considered that the dissolution of the anode reaction gas did not converge even after elapse. On the other hand, the electrolytic bath had almost no calcium from 0.2 to 0.3 mol%, and conversely, calcium oxide was as high as 2.5 mol% and solid carbon was as high as 1.4 wt% to 2.3 wt%.

FIG. 8 shows a reduction apparatus according to Comparative Example 2.
In Comparative Example 2, the upper alumina container 5Xb shown in Example 1 was drilled with 20 mm × 20 mm without using the stabilized zirconia (ZrO ₂ ) solid electrolyte, which is an oxygen ion conductive material, in the formation of the partition wall 5X. A partition wall 5 was formed from the lower alumina container 5Xc. Other hermetic electric furnace 12, reaction vessel 1, the cathode 4 and the raw material feeding side method or the like were the same as in Example 1. Therefore, when about 40 kg of calcium chloride is dissolved in the reaction tank 1, the 20 mm × 20 mm opening 5 Xa provided in the partition wall 5 X is the only place where ions existing in the electrolytic bath 2 can move. became.

Preliminary electrolysis was performed and electrolysis was performed at a constant current of 40 A. As a result, it was confirmed that the voltage rapidly increased 6 hours after electrolysis was started. Therefore, once the current value was reduced, the voltage decreased to the normal value, so electrolysis was continued. As in Example 1 , the current was increased from 0 A at a constant rate 8 hours after the start of electrolysis, and between the corresponding electrodes. The voltage was measured. The results are shown in FIG.

As a result, the voltage increased when the current was slightly increased from 0A, and then the current and voltage showed a constant linear relationship up to 10A, but immediately after that, the voltage increased rapidly to 12V. This discontinuous rapid increase in voltage indicates that an anode reaction gas (chlorine) other than oxygen has been generated on the anode surface, and the partition walls 5 are all formed of an electrically insulating material. It is considered that this phenomenon occurred because the current was concentrated in the opening 5a and oxygen ions did not move toward the anode reaction region 11. Further, even at a current of 10 A or less, the voltage is higher than that of Example 1 due to the insertion of the partition wall of the electrical insulator. The analysis result of the recovered titanium oxide sample was almost the same as in Example 1 .

  According to the metal oxide reduction method and metal oxide reduction apparatus of the present invention, a metal smelting process that produces metal by reducing metal oxide by electrolysis in an electrolytic bath made of an inorganic molten salt, As much as possible of metal contamination, especially carbon contamination, in the alloy manufacturing field where metal oxides are produced by reducing metal oxides simultaneously or in the recycling field where the oxide film formed on the metal surface is reduced and removed. In addition, since the reduction efficiency is not lowered and the increase in electrolytic power can be reduced, the metal can be produced industrially advantageously. In particular, since the problem derived from fine carbon generated from the carbon anode in electrolysis can be solved, the effect in the present invention can be used more remarkably when electrolysis using a carbon anode is used. .

FIG. 1 is a conceptual cross-sectional view illustrating a metal oxide reduction apparatus according to a reference embodiment . FIG. 2 is a conceptual cross-sectional view illustrating a metal oxide reduction device according to an embodiment of the present invention. FIG. 3 is a conceptual cross-sectional view illustrating the metal oxide reduction apparatus according to Example 1 of the present invention. FIG. 4 is a conceptual cross-sectional view illustrating a part of a metal oxide reduction apparatus according to Embodiment 2 of the present invention. FIG. 5 is a conceptual cross-sectional view illustrating a part of a metal oxide reduction apparatus according to Embodiment 3 of the present invention. FIG. 6 is a conceptual cross-sectional view illustrating a part of a metal oxide reduction apparatus according to Embodiment 4 of the present invention. FIG. 7 is a conceptual cross-sectional view illustrating a part of the metal oxide reduction apparatus according to Comparative Example 1 of the present invention. FIG. 8 is a conceptual cross-sectional view illustrating a metal oxide reduction device according to Comparative Example 2 of the present invention. FIG. 9 shows measured values of current and voltage measured in Example 1 and Comparative Example 2 of the present invention.

Explanation of symbols

  1: reaction vessel, 1a: reaction vessel side wall, 1b: reaction vessel bottom, 1c: alumina square plate, 2: electrolytic bath (molten salt), 3: carbon anode, 3a: inclined portion, 4: cathode, 4a: SUS Cathode round bar, 4b: cathode square plate, 4c: cathode disk, 5: partition, 5d: stabilized zirconia solid electrolyte, 5X, 5Y: partition, 5Xa, 5Ya: opening, 5Xb: upper alumina container, 5Xc: lower Alumina container, 5Xd, 5Yd: Square plate (stabilized zirconia solid electrolyte), 6, 7: Shield plate, 8: Anode reaction gas discharge pipe (alumina tube), 9: Raw material inlet, 10: Solidified layer, 11: Anode Reaction region, 12: closed electric furnace, 13: SUS round bar, 14: DC power supply, 15: SUS net, 16: shield plate, 16a: open port, 17: silicon stopper, 18: glass tube, X : Metal oxide reduction device.

Claims (29)

In the electrolytic bath consisting of inorganic molten salt contained in the reaction vessel was reduced metal oxide, a method for reducing metal oxides which release anodic reaction gas from the anode (M _x O _y), so as to surround the anode An anode reaction region is formed by disposing a partition wall, an opening is provided at a position lower than the lower end of the anode, and a cathode is disposed below the anode, so that the anode reaction gas generated in the anode reaction region is on the cathode side. It is prevented from moving, to allow transfer of ions of the electrolytic bath between the anode and the cathode through the opening, and further, forms a part or the whole of the partition of an oxygen ion conductive material it into in the reduction method of the metal oxide, characterized in that to allow the transfer of oxygen ions in the electrolytic bath through at least part of the partition wall. The method for reducing a metal oxide according to claim 1, wherein the oxygen ion conductive material is a solid electrolyte containing zirconia as a main component.   The method for reducing a metal oxide according to claim 1 or 2, wherein the anode reaction gas includes a cellular anode reaction gas released as bubbles in the electrolytic bath and a soluble anode reaction gas dissolved in the electrolytic bath.   The method for reducing a metal oxide according to claim 1, wherein the anode reaction gas is dissolved in a saturated state in the electrolytic bath in the anode reaction region.   The method for reducing a metal oxide according to any one of claims 1 to 4, wherein the metal oxide is supplied into an electrolytic bath other than the anode reaction region.   The method for reducing a metal oxide according to any one of claims 1 to 5, wherein an anode reaction gas space region for containing an anode reaction gas released from the liquid surface of the electrolytic bath in the anode reaction region is formed.   The method for reducing a metal oxide according to claim 1, wherein the anode reaction gas in the anode reaction gas space region is discharged out of the reaction vessel.   The method for reducing a metal oxide according to claim 1, wherein the electrolytic bath in the anode reaction region is sucked at a constant rate and discharged out of the reaction vessel.   The method for reducing a metal oxide according to claim 1, wherein the atmosphere on the liquid surface of the electrolytic bath other than the anode reaction region is blocked from the outside.   The method for reducing a metal oxide according to claim 9, wherein the atmosphere on the liquid surface of the electrolytic bath blocked from the outside is an inert gas atmosphere.   The method for reducing a metal oxide according to claim 1, wherein the anode is a consumable carbon anode.   The method for reducing a metal oxide according to claim 1, wherein the inorganic molten salt is a molten salt containing calcium chloride. Metal (M) of metal oxide (M _x O _y ) is titanium (Ti), silicon (Si), iron (Fe), germanium (Ge), zirconium (Zr), hafnium (Hf), uranium (U) The method for reducing a metal oxide according to any one of claims 1 to 12, wherein the metal oxide is one or two or more metals selected from Nd, Niobium (Nd), and Tantalum (Ta). The method for reducing a metal oxide according to claim 1, wherein the metal oxide is supplied below the opening . The method for reducing a metal oxide according to claim 1, comprising a plurality of anodes in the reaction vessel . The method for reducing a metal oxide according to claim 1, comprising a plurality of cathodes in the reaction vessel . Metal oxide that reduces metal oxide in an electrolytic bath made of an inorganic molten salt contained in a reaction vessel and releases anode reaction gas from the anode (M _x O _y ) In which a partition wall is disposed so as to surround the anode to form an anode reaction region, an opening is provided at a position lower than the lower end of the anode, and a cathode is disposed below the anode, It is possible to prevent the anode reaction gas generated in the anode reaction region from moving to the cathode side, and to move ions in the electrolytic bath between the anode and the cathode through the opening, and a part of the partition walls. Alternatively, the metal oxide reduction device is formed entirely of an oxygen ion conductive material, and oxygen ions in the electrolytic bath can be transferred through at least a part of the partition wall. Oxygen ion conductivity material, reducing device of a metal oxide according to claim 17 which is a solid electrolyte containing zirconia as a main component. The metal oxide reduction device according to claim 17 or 18, wherein the anode reaction gas includes a cellular anode reaction gas released as bubbles in the electrolytic bath and a soluble anode reaction gas dissolved in the electrolytic bath. The metal oxide reducing device according to any one of claims 17 to 19, wherein the anode reaction gas dissolves in a saturated state in the electrolytic bath in the anode reaction region. 21. The apparatus for reducing a metal oxide according to claim 17, wherein the metal oxide is supplied into an electrolytic bath other than the anode reaction region. The metal oxide reduction device according to any one of claims 17 to 21, wherein an anode reaction gas space region for containing an anode reaction gas released from the liquid surface of the electrolytic bath in the anode reaction region is formed. The metal oxide reduction device according to any one of claims 17 to 22, further comprising means for discharging the anode reaction gas in the anode reaction gas space region to the outside of the reaction vessel. The apparatus for reducing a metal oxide according to any one of claims 17 to 23, further comprising means for sucking the electrolytic bath in the anode reaction region at a constant speed and discharging it outside the reaction tank . The apparatus for reducing a metal oxide according to any one of claims 17 to 24, wherein the atmosphere on the liquid surface of the electrolytic bath other than the anode reaction region is blocked from the outside . The metal oxide reduction device according to any one of claims 17 to 25, wherein the anode is a consumable carbon anode . Reduction apparatus of a metal oxide according to any one of claims 17 to 26 in which the metal oxide below the opening is provided. The apparatus for reducing a metal oxide according to any one of claims 17 to 27, comprising a plurality of anodes in the reaction vessel . The metal oxide reduction device according to any one of claims 17 to 28, comprising a plurality of cathodes in the reaction vessel .

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