JPH024994A - Manufacture of neodymium or neodynium alloy - Google Patents

Abstract

PURPOSE:To manufacture high-purity Nd or Nd alloy reduced in carbon content and suitable for permanent magnet material by incorporating oxygen gas into the atmosphere above an electrolytic bath. CONSTITUTION:A plate-like carbon electrode as an anode and a plate-like metal or carbon electrode as a cathode are oppositely disposed in a molten-salt electrolytic bath. The part above the electrolytic bath is covered with an atmosphere containing oxygen gas in a concentration sufficient to consume, by oxidation, the powdery carbon generated from the carbon electrodes in the course of electrolysis and floating. Electrolysis is carried out in the above state to deposit Nd or Nd alloy on the cathode, which is dropped into the part below the cathode and collected in the bottom of the electrolytic bath. It is preferable that the atmosphere above the electrolytic bath contains 10-40vol.% oxygen gas. As the electrolytic bath, those of NdF3, LiF, Nd2O3, etc., are used. When Fe is used as the cathode, an Nd-Fe alloy can be prepared. By this method, Nd or Nd alloy for permanent magnet material can be obtained with high productivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing neodymium or neodymium alloy,
In particular, Nd-Fe-, which has recently attracted attention as a high-performance magnet,
The present invention provides a method for inexpensively producing high-purity neodymium or neodymium-iron alloy suitable as a raw material for B-series magnets.

[Conventional technology]

Recently, Nd-Fe-
B-based or Nd-Fe-Co-B-based permanent magnets were proposed (Japanese Patent Application Publication No. 1983-413008).
No. and the same Publication No. 59-64739). It is known that Nd used in the production of these permanent magnets can be produced by a calcium thermal reduction method or a molten salt electrolysis method (
For example, Japanese Patent Application Publication No. 13B42 (1982). Although the calcium thermal reduction method can obtain highly pure Nd, it has the problem of high manufacturing cost. The present invention is directed to the production of Nd by molten salt electrolysis.

Molten salt electrolysis methods are broadly divided into methods using a chloride electrolytic bath and methods using a fluoride electrolytic bath. The molten salt electrolysis method using a fluoride electrolytic bath is, for example, a method for obtaining a Nd-Fe alloy, in which iron is used as a cathode and carbon is used as an anode, the electrode shape is a round rod shape or a concentric circle, and the process is carried out in an appropriate molten salt electrolytic bath. Nd2O3
The method of electrolytically reducing neodymium to precipitate metal neodymium on an iron cathode and alloying it with iron is known as the consumable electrode method (
E. Maurice et al. Ru, S. Bur, Min.
Rep.

InvestJ No. 714B, 19fi8),
The possibility of using fluoride as a raw material neodymium compound is also described (E, Morris et al.
S, Bur.

Min, Rap, Invest J No. 89
57.1967).

In addition, Japanese Patent Application Publication No. 1983-159593,
Showa No. 81-87888 and Showa No. 81-1278
The molten salt electrolysis method of Nd is also taught in Japanese Patent No. 84 and the like.

] 0 However, generally speaking, the molten salt electrolysis method of Nd has only just reached the beginning of research and development, and the research to date has been limited to studies at the academic level, and there is no research on the electrolysis method of Nd at the industrial production level. It seems that no study has been conducted yet, and the present inventor is not aware of any such reports.

Therefore, the present inventor has developed an approach for Nd-Fe-B system or Nd
With the aim of industrially producing and supplying Nd, which is expected to be in large demand as a raw material for -Fe -Co -B permanent magnets, we are conducting intensive research on the production of Nd using molten salt electrolysis on an industrial scale. , has completed the present invention.

[Problem to be solved by the invention]

Therefore, the object of the present invention is to
N as a raw material for d -Fc -Co -B permanent magnets
In order to meet the demand for d, it is an object of the present invention to provide a molten salt electrolysis method for Nd or Nd alloy, which can produce high-purity Nd or Nd alloy at low cost on an industrial scale.

The above object is achieved by the present invention, in which a plate-shaped carbon electrode is used as an anode and a plate-shaped metal or carbon electrode is used as a cathode in a molten salt electrolytic bath, and these plate-shaped electrodes are arranged facing each other in the electrolytic bath. Then, the electrolytic bath is covered with an atmosphere containing oxygen gas at a concentration sufficient to oxidize and consume the powdered carbon generated from the carbon electrode during electrolysis and floating on the electrolytic bath surface. This is achieved by a method for producing neodymium or neodymium alloy, which comprises depositing neodymium or neodymium alloy thereon, dropping the neodymium or neodymium alloy under the cathode, and collecting it at the bottom of the electrolytic bath.

The first feature of the method of the invention is that the atmosphere above the electrolytic bath contains oxygen gas. In the conventional Nd molten salt electrolysis method using the consumable electrode method as taught by E. Morris et al., neodymium is active and easily reacts with oxygen in the atmosphere, so the reaction of neodymium is prevented and used. C.Mo.
Electrolysis is performed in a protective gas atmosphere, based on the idea that it is necessary to perform electrolysis in a protective gas atmosphere such as an inert gas in order to prevent oxidation of electrodes such as W.

1] Therefore, during electrolysis, it is necessary to seal the protective gas, which leads to high equipment costs, and it is difficult to supply raw materials and repair the equipment, leading to high manufacturing costs.

In addition, since carbon is used for the electrodes, this reacts with the electrolytic reaction gas, which is mainly composed of fluorine, and the carbon electrodes are consumed. However, because the atmosphere is a protective gas such as an inert gas, some of the carbon electrodes become powder. This has the disadvantage that the powdered carbon changes to cover the surface of the electrolytic bath, forms a current short circuit between the two electrodes, and discharge occurs through the powdered carbon, reducing current efficiency and changing the anode current density. Furthermore, some of the powdered carbon on the surface of the electrolytic bath may become mixed in and float in the electrolytic bath, changing the conductivity and making the electrolytic bath conditions unstable, making it difficult to maintain normal electrolytic operation, or There was a drawback that the mixed carbon was mixed into the manufactured alloy and degraded its quality.

In particular, the incorporation of carbon into manufactured alloys is a serious problem in terms of product quality. Since the above method has a carbon concentration of several thousand ppm, it is necessary to take into account that the permissible carbon concentration of raw materials for magnets, especially Nd and Nd-Fe alloys for Nd magnets, which have recently been attracting attention, is 400 ppm or less. This means that it cannot be used as a raw material for magnets as it is.

[Means and effects for solving the problem] Therefore, in the present invention, a neodymium salt having a low melting temperature and a specific gravity lower than that of Nd or Nd alloy (for example, lithium fluoride is added to neodymium fluoride) is added to the electrolytic bath. Nd
Alternatively, the Nd or Nd alloy obtained was isolated from the atmosphere above the electrolytic bath by collecting the Nd alloy below the electrolytic bath and covering the upper part with the electrolytic bath. In this way, by containing oxygen gas in the atmosphere above the electrolytic bath, the powdered carbon generated from the carbon electrode is actively oxidized with the oxygen gas in the atmosphere to form carbon compounds (C'O, Co
It was possible to prevent the Nd or Nd alloy that was removed into the atmosphere as 2'I and precipitated from being consumed by oxygen gas in the atmosphere. Powdered carbon is lighter than the electrolytic bath and floats on the surface of the electrolytic bath, so it is easily oxidized and consumed by the oxygen gas in the atmosphere above the electrolytic bath. Because it is light, when it floats to the surface of the electrolytic bath due to the convection of the electrolytic bath, it comes into contact with oxygen and is easily oxidized and consumed.

Thus, according to the present invention, in particular, Nd or Nd alloys (especially Nd-Fe alloys) with significantly reduced carbon content by containing oxygen gas in the atmosphere above the electrolytic bath.
is obtained, which is a high-purity Nd or Nd-Fe alloy that can be used as it is as a permanent magnet raw material.

The oxygen gas concentration in the atmosphere above the electrolytic bath may be sufficient to oxidize and consume the powdery carbon generated from the carbon electrodes and floating on the surface of the electrolytic bath.
40% by volume, preferably in the range of 15-30% by volume. Powdered carbon increased when the oxygen concentration decreased to 15% by volume or less, and rapidly increased when the concentration decreased to less than 10% by volume.
This is because normal operation becomes difficult and the carbon concentration in the deposited metal increases rapidly. Furthermore, when the oxygen concentration exceeds 30% by volume, the oxidative consumption of the exposed part of the graphite electrode above the bath surface increases, and 40% by volume increases.
Exceeding this will result in rapid wear and tear, leading to trouble.

Therefore, since the oxygen concentration in the atmosphere is included within the control range of the present invention, electrolysis in the atmosphere is also possible as the simplest method. Furthermore, an atmosphere in which air is enriched with oxygen or an atmosphere in which the necessary amount of oxygen is added to an inert gas can be used.

As a permanent magnet raw material of Nd-Fc-B system or Nd-Fe-Co-B system, it is necessary that the carbon content is 400 ppm or less.
d or Nd-Fe alloy meets this requirement as well as 200p
It is also easy to set the carbon content to pm or less, or even 1100 pp or less.

The second feature of the method of the present invention lies in the electrode shape and electrode arrangement. As mentioned above, a round rod-shaped consumable electrode is used in the known molten salt electrolysis method for Nd or Nd-Fe alloys. However, when a round bar-shaped consumable electrode is used, the electrolytic reaction mainly proceeds in the shortest distance between the cathode and the anode, so as the electrolytic reaction progresses and the electrode is consumed, the following problems occur.

1) It is difficult to maintain an optimal current density because the current density changes as the electrode wears out. Furthermore, since the current density changes, the electrolytic current and electrolytic voltage change, making it difficult to maintain the electrolytic current, electrolytic voltage, etc. at optimum values.

2) Current efficiency also changes with changes in pole spacing, making it difficult to maintain optimal current efficiency.

3) The amount of metal deposited in molten salt electrolysis is determined by the amount of current according to Faraday's law, but in molten salt electrolysis, if the current is passed above a certain anode current density, an anode effect will occur and normal electrolysis will not occur. Therefore, it is necessary to operate at a current density below the critical current density at which this anodic effect occurs. However, with round rod-shaped electrodes, the current density is locally high, and the current density changes as the electrode wears out, so it is necessary to operate at a low level of current, which is directly related to production volume.

Due to the above-mentioned problems, it is difficult to maintain constant operation at the optimal value.

As a result of various experiments conducted to solve the above problems, the present invention has changed the shape of the electrode from the conventional round bar shape.
This problem was solved by changing the shape to a plate-like shape in which the electrolytic reaction area does not substantially change. In other words, when using round rod-shaped electrodes, the electrolytic reaction mainly proceeds in the shortest distance between the electrodes, so if the critical anode current density is reached only in the shortest distance, an anode effect occurs, and the operation is performed below the critical anode density. However, as the electrodes wear out, the distance between the electrodes increases and the electrode surface area decreases moment by moment. However, the wear of the electrode does not proceed uniformly on the surface of the round bar electrode, and the shorter the distance between the two electrodes, the faster the wear occurs. Therefore, the rate of electrode surface area that decreases per unit time also differs depending on the thickness of the electrode. It is not constant, and it is difficult to accurately determine the distance between poles. The first problem is that the current density changes as the electrode wears out, and the second problem is that the amount of change in the distance between the electrodes per unit time due to the next electrode wear changes over time.
This is a problem.

When a round bar electrode is used in this manner, it becomes difficult to accurately grasp the state of the electrode as electrolysis progresses, and the operating conditions change in a complicated manner, making it difficult to maintain optimal electrolysis conditions.

Therefore, the first problem can be solved by creating a shape in which the electrolytic reaction area does not change even when the electrodes are worn out.Secondly, the distance between the electrodes changes as the electrodes wear out, and the amount of change in the distance between the electrodes is the unit. If the shape is constant over time, a constant inter-electrode distance can be easily maintained by moving the electrodes at a constant rate according to the amount of change.

Based on the above idea, the electrode shape that solves the above-mentioned problems is basically a plate shape that has a constant electrolytic reaction area, that is, the area of the opposing parts of the cathode and anode, and has a large electrolytic reaction area. The problem was solved by adopting a shaped electrode.

In the case of molten salt electrolysis, as mentioned above, it is important to suppress the occurrence of the anode effect during electrolysis, so it is extremely important to keep the electrolytic reaction area on the anode surface constant and properly manage the anode current density. It is. Therefore, even if only the anode is a plate-shaped electrode, a certain effect can be exerted, and the object of the present invention can be achieved. Examples of electrode arrangement in this case are shown in FIGS. 1A and 18.

In addition, 1A, IB, 2A, 26, 3A, 3B.

In figures 4.5A and 5B, 1 is an electrolytic cell, 2 is an electrolytic bath, 3 is an anode, 4 is a cathode, 5 is a droplet of Nd or Nd alloy,
6 indicates deposited Nd or Nd alloy, and 7 indicates a power source.

However, when a round rod is used as the cathode and a plate electrode is used as the anode, the distance between the electrodes is not constant at each part of the anode surface.
It is thought that the entire surface of the anode does not have the optimum current density.

Therefore, it is most effective to use plate-shaped electrodes for both the cathode and anode.

Examples of electrode arrangement in this case are shown in FIGS. 2A and 26.

In this case, it can be assumed that the current density is the same over the entire surface of the anode.

Next, the present inventor investigated various methods that would allow a large amount of current to flow and continue electrolysis stably without increasing the size of the electrolytic furnace, that is, by increasing the substantial reaction area of the anode. As a result, when comparing the solid line portions of FIGS. 5A and 5B, in which round rod-shaped electrodes are arranged with the same electrode surface area in the bath, and in FIGS. 2A and 26, in which plate-shaped electrodes are used, it is clear that FIGS. It can be seen that there is more room to make the electrode larger. Therefore, by enlarging the electrodes to the size indicated by the broken lines in Figures 2A and 3B, the surface area of the electrodes in the bath could be greatly increased, making it possible to flow a large amount of current. Therefore, by adopting the present invention, it is possible to increase production by about five times compared to the conventional arrangement shown in FIGS. 5A and 5B.

Next, the inventor found that the ability to improve the shape and size of the anode to allow a large amount of current to flow is limited by expanding the anode to the position indicated by the broken line in FIGS. Although it is not possible to flow current, after various studies, we found that rather than passing current through a pair of plate-shaped cathodes and anodes, the amount of current for electrolysis is determined by the anode current density rather than the cathode current density. By arranging two plate-shaped anodes on both sides of a cathode, he invented a method that doubled the anode reaction area and approximately doubled the production volume in an electrolytic furnace of the same size.

This method is effective in molten salt electrolysis of neodymium and neodymium alloys, including neodymium-iron alloys, where the cathode current density is less limited and the anode current density is more limited. The current density is twice that of the anode, and the current is 1/2 the current output from the rectifier.
All you have to do is wire it so that it separates into two anodes, merges at the central cathode, and enters the rectifier. An example of wiring is shown in FIG. 4.

In the present invention, as described above, the cathode can be placed in the center, and the plate-like anode can be placed opposite to it, and the shape of the cathode does not pose any particular problem since the cathode current density can be large. A further effect can be obtained by making it into a plate shape. Examples of electrode arrangement are shown in Figures 3A and 3B.

Next, in molten salt electrolysis, as described above, it is extremely important to maintain the distance between the electrodes at an appropriate value. However, even in the known literature to date, there is no disclosure of the optimum distance between poles. Therefore, as a result of repeated experiments to find the appropriate distance between the poles, the present inventor found that the distance between the poles greatly contributed to the current efficiency, and the distance was set to 10 to 1.
It has been discovered that high current efficiency can be maintained by maintaining the thickness at 5 mm.

In order to investigate the effect of the distance between the electrodes on the current efficiency, we used graphite plate electrodes for the anode and iron plate electrodes for the cathode, and used L as the electrolytic bath.
FIG. 6 shows the results of an electrolytic experiment using the iF-N d F 3 bath.

From the results shown in FIG. 6, it was found that the distance between the poles is preferably 10 to 50 mm, and more preferably 20 to 40 mm. If the distance between the electrodes is closer than 10 + + + m, anions such as F- (oxide N
When dO is decomposed, 02-) and the neodymium metal generated on the cathode react and return to a neodymium compound.If it is too far away than 50 mm, neodymium metal will precipitate due to the diffusion effect of the electrolytic bath in the furnace, etc. This is because it is hindered.

Adjustment of the distance between the electrodes is performed by moving one or both of the electrodes as electrolysis progresses, but with round bar electrodes, the distance between the electrodes cannot be accurately determined and the distance between the electrodes cannot be adjusted accurately. be. On the other hand, when using plate-shaped electrodes for both the anode and cathode, the electrode surface changes only in a plane, so by moving one or both electrodes at a constant speed, it is easy to find the optimal electrode. It is possible to maintain distance between people.

As mentioned above, the main feature of the method of the present invention is that molten salt electrolysis is carried out in an oxygen-containing atmosphere, and the electrolytic bath used for this purpose is a molten salt having a specific gravity lighter than that of the precipitated metal, such as LiF. Preferably, a salt containing a neodymium metal source is used. By using LiF, the melting point of the electrolytic bath can be lowered, and the specific gravity is lighter than the precipitated metal produced, so the target metal can be deposited below the electrolytic bath and shielded from an atmosphere containing oxygen. . Furthermore, since the electrolytic bath has a higher specific gravity than the free carbon, the free carbon can be actively pushed up to the top of the electrolytic bath and oxidized and consumed.

As a molten salt, LiF and NdF as a neodymium metal source are used.
3. with Nd2O3, i.e. LiF-Nd
F system or L mixed with inexpensive Nd2O3
iF-NdF3-Nd203 system is used, but B
a F , Ca F 2 , etc. may be added as appropriate. Also,
NdCjl13 may be used instead of NdF.

Note that LiF lowers the melting point of the NdF3 bath (for example,
When mixed at 80 mo1%, it is also effective in improving electrical conductivity (1420'C-720°C).

In the case of LiF-NdFa system, 96-Eib, preferably 95-75 mo1% LiF and 4-35 mo
A composition consisting of 1%, more preferably 5 to 25 mo1% of NdF3 is preferred. LiF from Figure 7 to Figure 1O
Figure 3 shows the changes in critical anode current density and current efficiency when the composition and electrolysis temperature are changed in the -N d Fa system. 7th
Figures 1 to 10 show data for the production of neodymium-iron alloy, but almost similar data are obtained for the production of neodymium metal.

These figures show that the composition within the above range is excellent in both critical anode current density and current efficiency.

In the case of LiF-NdF-Nd203 system, Nd2O is added to the LzF-NdFa system with the above preferred composition.
A composition in which several wt% of 3 is added and mixed is preferable.

As the raw material for the electrolytic bath, the components consumed in the above bath composition may be supplied or replenished according to the consumption amount, but LiF-NdFa system, LiF-NdF
-In the Nd203 system, NdF3 is the main raw material, and Nd2O
3 and LiF only need to be replenished from time to time depending on the amount consumed.

If Nd2O3 is used, the content of Nd2O3 should be 3 wt% or less so that it is within the solubility in the LtF-Nd2F3 bath.

It is important to maintain the depth of the electrolytic bath covering the deposited metal at an appropriate depth in order to efficiently electrolytically deposit the metal. In addition, in the present invention, LiP which is lighter than the precipitated metal
An electrolytic bath mainly composed of is effective in blocking the deposited metal from oxygen in the atmosphere, but if the depth of the electrolytic bath is small, this blocking effect is small, and the anode gas generated during electrolysis is This causes the bath surface to move up and down,
It is necessary to maintain a sufficient depth of the electrolytic bath in consideration of this vertical movement of the bath surface. Experiments conducted by the present inventors have revealed that the appropriate depth of the electrolytic bath must be at least 5 cm, and preferably maintained at 10 cm or more. If the depth of the electrolytic bath is smaller than this, the blocking effect will not improve and the electrolytic region will become narrower, resulting in a significant drop in the yield of deposited metal. However, in the method of the present invention, as the plate electrodes are arranged vertically in parallel as described above, the depth of the electrolytic bath inevitably exceeds 10 mm in order to ensure the effective area of the electrodes. Bath depth is not a problem with the present invention.

When manufacturing neodymium metal, carbon electrodes are used for both the cathode and the anode, and neodymium alloys, such as neodymium-
When manufacturing iron alloys, a carbon electrode is used for the anode and iron is used for the cathode. When manufacturing neodymium metal, only the anode is a consumable electrode, and when manufacturing neodymium alloy, both electrodes are consumable electrodes. Furthermore, when producing an alloy of neodymium and other metals, that metal may be used as the cathode.

Graphite electrodes are commonly used as carbon electrodes and are preferred in terms of oxidation resistance, but those with a low graphitization rate can also be used. As the iron electrode, it is preferable to use one with high purity such as electrolytic iron, but the method of the present invention has the advantage that a high purity Nd-Fe alloy can be obtained even if mild steel with a relatively low carbon content is used. .

Taking the case of producing an Nd-Fc alloy as an example, the following reaction occurs at the cathode to produce a Nd-Fe alloy.

Fe 10Nd'+3e -Nd-Fe alloy On the other hand,
At the anode, carbon is consumed by the following reaction, although this differs between oxide electrolysis and fluoride electrolysis.

In the case of oxide electrolysis, C+02-C0+2e In the case of fluoride electrolysis, nC0mF -CnFm+me (In the formula, CnFm is CF4.C2F6.C3F8, etc.) If there is moisture in the atmospheric gas, the above fluorine will be rehydrated. It may react with HF to form HF.

F + HO → 2 HF + L/202 On the other hand, taking the case of Nd metal as an example, the following reaction occurs at the cathode and Nd
Metal is produced, and at the anode the same reactions occur at the anode as in the fluoride electrolysis described above, depleting the carbon.

Nd+3+3e--Nd↓ To suppress the oxidative wear and tear of the electrode exposed in the atmosphere above the bath, in addition to using a graphite electrode with a high graphitization rate, a metallic or ceramic coating material should be applied to the electrode surface. Known anti-oxidation measures such as coating or covering with a sleeve are effective.

In addition, in the production of neodymium-iron alloys, since graphite in the anode is a consumable electrode, it is possible to use it as is by selecting conditions such that the rate of consumption due to electrolytic reactions in the bath is greater than the rate of oxidation consumption in the upper part of the bath. You can also do that. In the case of Nd metal production, Nd precipitates in the graphite of the cathode, increasing the carbon concentration in the produced metal. To prevent this, the reaction surface is coated with a metal (Ta, Pt) that does not form an alloy with neodymium. This can prevent an increase in carbon concentration.

A third feature of the method of the invention is that it allows electrolytic operation at high anodic current densities and current efficiencies. According to the method of the invention, at least 0.5 A/c, preferably 0
．． 7A/c or more or 1. It is possible to stably perform electrolytic operation at a high anode current density of OA/c+ff or higher. Further, according to the method of the present invention, it is possible to carry out electrolytic operation with a high current efficiency of 70% or more, more preferably 80% or more, and furthermore 85% or more. The reason for being able to operate at such high anodic current densities and current efficiencies lies primarily in the improvements in the shape and arrangement of the electrodes, the removal of airborne or suspended powdery carbon by the oxygen-containing atmosphere, but also in , bath composition, and bath temperature optimization. In this specification, the anode current density is a value obtained by dividing the average current of the anode by the anode area, and the anode area is the area of the part of the anode that faces the cathode. Further, current efficiency is a value obtained by dividing the amount of metal produced by the amount of supplied current by the theoretical amount of electrolysis determined by Faraday's equation.

When producing Nd metal, the electrolytic bath temperature can be lower or higher than the melting point of the Nd metal, or a temperature between the melting point of the molten salt and the melting point of the Nd metal.

For example, when electrolysis is performed at an electrolytic bath temperature lower than the melting point of Nd, Nd precipitates in the form of needles on the graphite surface, but since it is heavier than the molten salt, it precipitates in the molten salt below the electrode. In addition, if the crystals precipitate in a needle shape and extend to the anode, it will short-circuit with the anode, and a large current will flow in the boat, causing the crystals to dissolve and precipitate below the electrode. Nd
A temperature higher than the melting point of Nd or a temperature between the melting point of the molten salt and that of Nd is also possible.

When manufacturing a Nd-Fe alloy, the melting point of the Nd-Fe alloy is 64 at 75 mo1% Nd, according to the phase diagram of Nd-Fe.
0°C, which is lower than the eutectic point of 720°C in the phase diagram of L IF -N d Fa, so by making the electrolytic bath temperature higher than the melting point of the electrolytic bath, the precipitated NdFe alloy becomes liquid at the cathode and melts. Since it is heavier than salt, it precipitates in the molten salt below the electrode. In addition, by controlling the electrolysis temperature, N
It is also possible to control the composition ratio of d-Fe.

Therefore, the electrolytic bath temperature may be higher than the melting point of the electrolytic bath, and may be 750°C or higher, which is slightly higher than 720°C, and a range of 750°C to 1100°C is suitable. However, increasing the electrolytic bath temperature increases oxidation consumption of the electrodes,
Damage to the bathtub material is also promoted.

Furthermore, from the relationship between electrolytic bath temperature, critical anode current density, current efficiency, and bath composition shown in Figures 7 to 10, it is clear that if the bath temperature becomes too low or too high, the current efficiency deteriorates and the anode Since the critical current density changes greatly, it is economical to maintain the temperature at about 825° C. to 1000° C., which is determined comprehensively based on the above relationship.

Furthermore, the temperature of the electrolytic bath can be controlled solely by the heat generated by the current between the electrodes.In fact, this internal heating method is often adopted in conventional molten salt electrolysis methods, but the method of the present invention It is preferable to use an external heating type in which the electrolytic bath is heated from outside with a heating means to control the bath temperature. Since the method of the present invention has high current efficiency and high electrical conductivity, in order to supply sufficient heat generation only with the interelectrode current to keep the bath temperature constant, the distance between the electrodes must be increased. This is because there is a possibility that operation under optimum electrolysis conditions may not be possible. In addition, even when the electrodes are taken out of the bath for replacement or repair, the bath can be kept in a molten state if the external heating type is used, making it easy to restart operations and make production adjustments easier. Therefore, it is preferable.

The electrolytic cell may be made of austenitic stainless steel (Japanese Industrial Standard (JIS) standard (7) 5US-30) as long as it has corrosion resistance depending on the bath composition and bath conditions used.
4, SO3-316, 5US-310S, etc.) is preferable because it is inexpensive and has high durability against molten salt.

In relation to the corrosion resistance of electrolytic cells, Nd metal or Nd-F
Since Nd alloys such as C easily form alloys with iron and other metals, the container (receiver) for receiving Nd or Nd alloys must be made of tantalum, tungsten, molybdenum, etc., which are difficult to form alloys with. Research shows that tantalum is the best.

These metals such as tantalum are expensive, so Nd
Alternatively, only the portion that contacts the Nd alloy may be lined with tantalum or the like. However, even if the surface of the receiver is simply lined, as the dimensions of the electrode, particularly the width, increase, the required dimensions of the receiver will increase, and the amount of tantalum or the like used will inevitably increase. Therefore, when manufacturing Nd alloys such as Nd-Fe, the bottom of the plate-shaped cathode is sloped and the tip of the cathode is made to protrude, so that droplets of Nd alloy are collected at one point on the protruding end. If the produced alloy is dropped from the container, the size of the required receiver can be reduced. The shape of the lower end of the cathode may be a tapered shape in which droplets are dispersed at the lower end or droplets are collected at one point without remaining, and may be a simple linear taper or a taper with a slight bulge. , preferably with a taper of 10 to 30°.

In addition, the tip of the taper, that is, the position of the point where the droplet falls, may be at the center of the electrode, at the edge, or at a position in between. If the position is desirable for the recovery method, it can be changed as appropriate.

The Nd or Nd alloy collected at the receiver or bottom of the electrolyzer is
It is possible to collect the metal directly from the receiver or electrolytic cell through the metal outlet provided through the wall of the electrolytic cell, but it is also possible to introduce a pipe from above the electrolytic bath into the electrolytic bath or into the receiver and suck it up using a vacuum. It's easy and good.

Preferred embodiments will be described below.

11A and 11B show an electrolysis apparatus for carrying out the method of the present invention, FIG. 11A is a schematic vertical cross-sectional view, and FIG.
Figure B is a schematic plan view. The anode 13 and cathode 14 immersed in the electrolytic bath 12 are plate-shaped electrodes, and the cathode 14
Anodes 13 are arranged facing each other on both sides of the center. When the cathode 14 is made of iron, the bottom side 15 of the cathode 14 is, for example, tapered and has a protrusion in the center in order to allow the Nd-Fe alloy to drip in one place. The upper part of the electrolytic bath 12 is open to the atmosphere 16, and the inner wall surface 17 of the bathtub is made of austenitic stainless steel. Around the bathtub is an external heat furnace 1
8 and has a heating element 19. 20 is an insulating plate. The temperature of the electrolytic bath 12 is detected by a thermocouple 21, and adjusted by controlling the heating element 19 by an external heating furnace control device (not shown). The plate electrodes 13 and 14 are suspended from above and supported by an electrode mounting base 24 via an inter-electrode distance adjuster 22 and an electrode elevator 23. The inter-electrode distance adjuster 22 and the electrode elevator 23 are of a worm gear type, and their rotation allows the electrodes 13 and 14 to be moved left and right and up and down. Further, within the electrolytic cell there is a receiver 25 for recovering Nd or Nd alloy, the inner surface of which is lined with tantalum. In this device, the upper part of the electrolytic bath is opened to the atmosphere, but the upper part of the electrolytic bath may be surrounded to utilize an atmosphere with a specific oxygen concentration.

In such an electrolyzer, NdF3 is used as a raw material and electrolyzed under predetermined bath composition, bath temperature, current and voltage conditions, etc., and NdF3 is used as a raw material.
d or Nd alloy is dropped from the cathode 14 into the receiver 25 and collected. During electrolysis, the electrodes are worn out and the distance between the electrodes changes. Therefore, by using the distance adjustment device 22 to move the electrodes and keeping the distance between the electrodes constant, the electrolytic conditions can be kept constant. can be maintained.

This will be explained below based on an example.

In these examples, electrolytic experiments were conducted in an electrolytic cell as shown in FIG. In the figure, molten salt 3 is placed in a lower iron tank 32.
1 is accommodated, and an anode 33 and a cathode 34 are arranged facing each other. The distance between the electrodes was kept at 30 mm, and the depth of the electrolytic bath was 2.
It was set to 0cm. The upper part of the electrolytic cell 32 was covered with a lid 35, and a predetermined atmosphere 38 was maintained by introducing atmospheric gas from a gas inlet 36 and exhausting it from a gas outlet 37 as necessary.

However, in the experiment in the atmosphere, the lid 35 was removed. In the figure, 39 is the raw material input port, 40 is the receiver body, 41
is the inner lining of the receiver (made of tantalum). In these electrolysis, Nd becomes needle-shaped crystals, and the Nd alloy reacts with the cathode to form droplets, and due to the difference in specific gravity and the current flowing through the needle-shaped crystals, the Nd becomes acicular crystals.
(In the figure, 42 is a droplet of Nd or Nd alloy, and 43 is a droplet of Nd or Nd alloy).

Example 1 (Conventional Example) For comparison, L i F 80IIlo was used as a molten salt.
1% (34,1wt%) -N d F320mo, 1
% ([i5.9 wt%), and the upper part of the electrolytic bath was filled with argon gas, and a round bar-shaped graphite electrode (graphitization rate 98%) was used as an anode, and a round bar-shaped electrolytic iron electrode (carbon content 0) was used as a cathode. , 02%) to produce a Nd-Fc alloy. Table 1 shows other electrolytic conditions and their changes as well as the analysis results of the obtained Nd-Fc alloy product.

Example 2 (Comparative Example) Although not a conventional example, for comparison, electrolysis was carried out under exactly the same conditions as in Example 1 except that both electrodes were plate-shaped electrodes. The results are also shown in Table 1.

By making the electrode plate-shaped, the critical current value is improved,
It is also seen that the carbon content in the Nd-Fc alloy is slightly reduced. However, the current-voltage transition of the electrolytic bath is still unstable, and the bath surface is filled with powdered carbon, and the carbon content in the Nd-Fe alloy (1500pp
It is recognized that m) is not suitable for use as it is as a raw material for permanent magnets (400 ppm or less).

〔Example〕

Examples 3 to 7 (Examples of the present invention) In order to examine the effect of the oxygen gas concentration in the atmosphere, experiments were carried out under the same conditions as in Example 2, except that the atmosphere gas was a mixture of nitrogen and oxygen, and the oxygen concentration was varied. Electrolysis was performed.

The results are shown in Table 1.

As is clear from Table 1, as the oxygen gas concentration in the atmosphere increases, the powdery carbon on the bath surface decreases significantly.
At oxygen concentrations of 20%, 40%, and 50%, powdered carbon completely disappeared from the bath surface.

Correspondingly, the carbon content in the obtained Nd-Fc alloy also decreases as the oxygen gas concentration in the atmosphere increases. 4 for %, 40%, 50%
The raw material for permanent magnets (400ppm) decreased significantly to 0ppm.
m or less), which can be used as is.

In addition, if we take the case where the oxygen gas concentration in the atmosphere is 20% as an example, compared to the conventional example, the critical current value (7 times) and current efficiency (2.7 times) increase significantly, and during electrolysis The current and voltage trends and critical current values of N
It is recognized that the amount of recovered d-Fe alloy has increased by as much as 21 times.

When the oxygen gas concentration in the atmosphere is low, the above effect is small, but on the other hand, as the oxygen gas concentration increases beyond 30%, it is observed that the carbon electrode wears out more rapidly and the anode falls off faster. It will be done.

Examples 8 to 10 (Examples of the Present Invention) Electrolysis experiments were conducted with the atmosphere set to an oxygen gas concentration of 20% and the shape and arrangement of the electrodes changed. In Example 8, both electrodes were shaped like round rods, in Example 9, both electrodes were shaped like a pair of plates, and in Example 10, a plate-shaped cathode was arranged in the center, and plate-shaped anodes were arranged in parallel on both sides thereof.

The results are shown in Table 1.

By changing the electrolytic shape from a round rod shape (Example 8) to a plate shape (Example 9), the critical current value (4.7 times) and current efficiency (1.3 times) are improved, and as a result, the Nd-Fe It is recognized that the amount of alloy recovery also increases synergistically (7.2 times). Furthermore, by arranging the plate anodes on both sides of the plate cathode, the critical current value is doubled and the current efficiency is slightly improved compared to the case of a single plate anode. It is observed that the amount of -Fe alloy recovered has increased by more than twice. It is also observed that the carbon content in the Nd-Fe alloy is reduced by making the electrode shape plate-like. Furthermore, from Examples 8 to 10, it is recognized that if the oxygen gas concentration is set appropriately, the current-voltage transition during electrolysis can be stabilized regardless of the electrode shape.

In addition, when Example 10 is compared with the conventional example (Example 1), the critical current value is 14 times, the current efficiency is 2.8 times, and the total Nd-Fe recovery amount is 4 times.
The carbon content has been improved to 1/50th of that of the Nd-Fe alloy.

(Left below) Examples I↑ and 12 (Example of the present invention) The electrolytic bath composition was L i F 80mo1% (33.4wt
%) NdF320Ino1% ([i4.8wt%) −
Electrolysis was carried out under the same conditions as in Example 1 and Example 10 except that N d 20 a 2 vt%.

The results are shown in Table 2. The bath composition is LiF-NdF
It has been shown that there is no difference in the effect of the present invention between the a system and the LiF-NdF-Nd203 system.

Examples 13 and 14 (Examples of the Present Invention) Electrolysis was carried out under the same conditions as in Examples 1 and 10, except that a graphite electrode was used as the cathode.

The results are shown in Table 2. Also when manufacturing Nd, Nd-F
The same effect as in the case of manufacturing e-alloy is observed.

Examples 15 and 1B (Example of the present invention) The upper part of the electrolytic bath was opened to the atmosphere, and the cathode was replaced with a graphite electrode (Example 1
5) or using an iron electrode (Example 1G), electrolysis was carried out under the same conditions as in Example 10.

The results are shown in Table 2. The effects of the present invention can be observed even in the atmosphere.

Example 17 (Example of the present invention) Example 10 except that the cathode was a round rod-shaped electrode (5φXIO”)
Electrolysis was carried out under the same conditions.

The results are shown in Table 2. It is recognized that a certain effect can be achieved even when only the anode is a plate-shaped electrode.

Examples 18 and 19 (Examples of the present invention) Same conditions as Example 10, except that the width of the plate electrode was 70 mm.
A comparative experiment was conducted for the case of + (Example 18) and the case of 140 mm (Example 19).

The results are shown in Table 2. From Table 2, it is recognized that by increasing the effective area of the electrode, the amount of current and the production amount of Nd-Fe alloy increase proportionally. Therefore, according to the present invention, it is recognized that an improvement is achieved in that an electrode having a larger effective area can be used in the same electrolytic cell compared to the round rod-shaped electrode of the conventional example.

FIG. 13 shows current-voltage curves during electrolysis for Examples 181 and 19, and it is recognized from this figure that the voltage in Example 19 is lower than that in Example 18 if the current values are the same.

Example 20 (Example of the Present Invention) Corrosion tests were conducted on various bathtub materials for holding molten salt.

Figure 14 shows an apparatus using molten salt for corrosion testing of various materials (common steel, JIS standard 5O8-304, 5O8-316, 5O8-8108°SO8-430).
Figure 5 shows the results.

As shown in Fig. 14, various materials 53 are put into the molten salt 52, and the total amount of corrosion in the molten salt, the interface between the molten salt and the atmosphere, and the area spanning the upper part of the molten salt is investigated every day, and the results are reported in Fig. 15.
Shown in the figure.

The experimental conditions were a bathtub 5 made of SUS-304 in the atmosphere.
4 was used to maintain the bath temperature at 880'C without applying electricity.

Molten salt 52 is LiF 80M%-NdF 32
0M% LiF-NdFa system and LiF
Two types of LiF-NdF3-Nd203 systems in which 2 wt% of Nd2O3 was added to 80 M%-NdF32°M% were used, but the results showed the same tendency.

Figure 15 shows ordinary steel and ferritic stainless steel (
SO3-430) is austenitic stainless steel (S
It can be seen that the austenitic stainless steel is superior as the amount of corrosion is greater than that of the steels (US-904, 5O8-318, 5US-310S).

Also, among the austenitic stainless steels, SO! l(
-'310S (Composition: Cr 25vt%, Ni
It can be seen that 20vt%) is the most excellent.

Examples 21 and 22 (Example of the present invention) Based on the results of Example 18, an electrolytic cell shown in Fig. 16 was made and N
A continuous operation experiment was conducted to produce d-Fe.

In FIG. 16, an electrolytic bath 63 containing molten salt 62 was made of SO8-3103 (Example 21) based on the above-mentioned experimental results, and also made of ordinary steel (Example 22) for comparison. 16th
In the figure, the metal container 64 is made of 5O8-31O8 because Nd easily forms an alloy with other metals, and the inside of the container 64 is lined with TaB5.

When iron cathode 6B and graphite anode B7 are arranged and energized,
The electrolyzed Nd reacts with the cathode 6G and becomes NdFe alloy droplets B8, and the metal receiver is accommodated in the container 64 and Nd
It precipitates as d-Fe alloy 69.

Note that the electrolysis was performed in the atmosphere at 70°C.

Two types of electrolytic baths, namely L i F 80mo1%N
dF 320mo1% LiF-NdF
a system and LiF80mo1%-NdF320IIio
LiF-NdF with 2vt% Nd2O3 added to 1%
As a result of operating both 3-Nd203 systems at an electrolytic temperature of 880° C., there was no significant change due to the electrolytic bath composition.

The results are shown in Table 3. The number of days of continuous use was expressed as the number of days in which the risk of electrolytic bath leakage has diminished to some extent because the material used for the electrolytic bath becomes thinner as the number of operating days passes. The thickness of both materials used was 5.
It was set as III/I11.

(Left below) Table 3 From Table 3, 5US- which is austenitic stainless steel
It can be seen that by using the 3108, the number of ports that can be used continuously has increased significantly.

〔Effect of the invention〕

According to the method of the present invention, the neodymium or neodymium alloy obtained, especially the neodymium-iron alloy, has a low carbon content and high productivity, so it is possible to
This method is most suitable as an industrial method for producing raw materials for Co-B permanent magnets.

[Brief explanation of the drawing]

1A and 18, 2A and 26, and 3A and 3B are diagrams illustrating the electrode arrangement according to the present invention,
Figures 1A, 2A and 3A are plan views, Figures 1B, 26 and 3
Figure B is a sectional view, and Figure 4 is a cross-sectional view of Figures 3A and 3B of the present invention.
5A and 5B are a plan view and a cross-sectional view, respectively, for explaining the conventional electrode arrangement, and FIG. 6 shows the relationship between the distance between poles and current efficiency. Figure 7 is a diagram showing the relationship between electrolysis temperature and critical anode current density in LiF-NdF a bath, and Figure 8 is a diagram showing the relationship between electrolysis temperature and current efficiency in LiF-NdF 3 bath. FIG. 9 is a diagram showing the relationship between the bath composition, electrolysis temperature, and critical anode current density in the LiF-NdFs bath, and FIG. 10 is the diagram showing the relationship between the critical anode current density and the bath composition in the LiF-NdFs bath. Fig. 1LA and Fig. 11B are a schematic vertical cross-sectional view and a plan view of an electrolyzer for carrying out the method of the present invention, and Fig. 12 is a diagram showing the relationship between bath composition and current efficiency in an example. FIG. 13 is a diagram showing the relationship between voltage and current in Example 18 and Example 19, and FIG. 14 is a schematic cross-sectional view of the electrolyzer used. FIG. 14 is a diagram showing the relationship between voltage and current in Example 18 and Example 19. FIG. 15 is a graph showing the results of the corrosion test according to FIG. 14, and FIG. 16 is a schematic cross-sectional view of the electrolyzer used in the durability test of the electrolytic cell. 1... Electrolytic bath 2... Electrolytic bath 3...
・Anode 411. Cathode 5...droplet (
Nd or Nd alloy) 6...Nd or Nd alloy 7...Power source 12.
... Electrolytic bath 13 ... Anode 14 ...
Cathode 16... Atmosphere 18... External heat furnace 20... Insulator 22... Inter-electrode distance adjuster 24... Electrode mounting base 25... Nd or Nd alloy receiver 26... - Receiver lining 31... Electrolytic bath 33... Anode 35... Lid body 37... Gas outlet 39... Raw material supplier 41... Receiver lining 42... Nd or Nd alloy Droplet 43... Nd or Nd alloy 53... Test object 62... Electrolytic bath 64... Receiver body 66... Cathode 15... Bottom side of cathode 17... Inner wall of electrolytic tank 19... Heating element 21... Thermocouple 23... Electrode elevator 27... Liquid droplet 32... Electrolytic cell 34... Cathode 36... Gas inlet 38... Atmosphere 40...・Receiver body 52... Molten salt 54... Tank 63... Electrolytic tank 65... Receiver lining 67... Anode 68... Nd alloy droplet 70... Atmosphere 69.・・Nd alloy

Claims (1)

[Claims] 1. In a molten salt electrolytic bath, a plate-shaped carbon electrode is used as an anode, and a plate-shaped metal or carbon electrode is used as a cathode, and these plate-shaped electrodes are arranged to face each other in the electrolytic bath. Then, the electrolytic bath is covered with an atmosphere containing an oxidizing gas with a concentration sufficient to oxidize and consume the powdered carbon generated from the carbon electrode during electrolysis and floating on the electrolytic bath surface. 1. A method for producing neodymium or neodymium alloy, which comprises precipitating neodymium or neodymium alloy in water, dropping the neodymium or neodymium alloy under a cathode, and collecting the neodymium or neodymium alloy at the bottom of an electrolytic bath. 2. The method according to claim 1, wherein the atmosphere above the electrolytic bath contains oxygen gas in a range of 10 to 40% by volume. 3. The method according to claim 2, wherein the atmosphere above the electrolytic bath contains oxygen gas in a range of 15 to 30% by volume. 4. The method according to claim 3, wherein the atmosphere above the electrolytic bath is air. 5. The distance between the plate anode and plate cathode is 10 to 50 mm.
The method of claim 1 within the scope of. 6. The distance between the plate anode and plate cathode is 20 to 40 mm.
6. The method of claim 5 within the scope of. 7. The method according to claim 5, wherein the distance between the plate-shaped anode and the plate-shaped cathode is controlled to be constant in consideration of electrode wear. 8. The method according to claim 1, wherein one plate-shaped cathode is placed in the center, and a pair of plate-shaped anodes are placed on both sides of the plate-shaped cathode so as to face the plate-shaped cathode. 9. The method according to claim 1, wherein the electrolytic bath comprises neodymium fluoride and lithium fluoride. 10. The method according to claim 1, wherein the electrolytic bath comprises neodymium fluoride, lithium fluoride, and neodymium oxide. 11. The method according to claim 1, wherein the electrolytic bath replenishment raw material is neodymium fluoride. 12. The method according to claim 1, wherein the cathode is made of iron and a neodymium-iron alloy is produced. 13. The method according to claim 1, wherein the neodymium or neodymium alloy produced has a carbon content of less than 400 ppm. 14. In a molten salt electrolytic bath, a plate-shaped carbon electrode is used as an anode, and a plate-shaped metal or carbon electrode is used as a cathode, and these plate-shaped electrodes are arranged facing each other in the electrolytic bath, and above the electrolytic bath. is covered with an atmosphere containing an oxidizing gas with a concentration sufficient to oxidize and consume the powdered carbon generated from the carbon electrode during electrolysis and floating on the surface of the electrolytic bath, and the anode current density is 0.5 A/cm^2 or more. A method for producing neodymium or neodymium alloy, which comprises performing electrolysis to precipitate neodymium or neodymium alloy on a cathode, dropping the neodymium or neodymium alloy dropwise below the cathode, and collecting it at the bottom of an electrolytic bath. 15. The method according to claim 14, wherein the anode current density is 0.7 A/cm^2 or more. 16. The method according to claim 14, wherein the anode current density is 1.0 A/cm^2 or more. 17. The method according to claim 14, wherein the atmosphere above the electrolytic bath contains oxygen gas in a range of 10 to 40% by volume. 18. The method according to claim 17, wherein the atmosphere above the electrolytic bath contains oxygen gas in the range of 15 to 30% by volume. 19. Claim 11, wherein the atmosphere above the electrolytic bath is air.
The method described in section. 20. The distance between the plate anode and plate cathode is 10 to 50 m.
15. The method of claim 14, wherein m. 21. The distance between the plate anode and plate cathode is 20 to 40 m.
21. The method of claim 20, wherein m. 22. The method according to claim 14, wherein the distance between the plate-shaped anode and the plate-shaped cathode is controlled to be constant in consideration of electrode wear. 23. The method according to claim 14, wherein one plate-shaped cathode is placed in the center, and a pair of plate-shaped anodes are placed on both sides of the plate-shaped cathode to face the plate-shaped cathode. 24. The method according to claim 14, wherein the electrolytic bath temperature is within the range of 750 to 1100°C. 25, the electrolytic bath temperature is 8
25. The method according to claim 24, wherein the temperature is within the range of 25 to 1000C. 26. The method of claim 14, wherein the electrolytic bath comprises a mixture of 4 to 35 mole percent neodymium fluoride and 96 to 65 mole percent lithium fluoride. 27, the electrolytic bath contains 5 to 25 mol% neodymium fluoride and 95
27. The method of claim 26 comprising a mixture of ~75 mole % lithium fluoride. 28, the electrolytic bath contains 4 to 35 mol% neodymium fluoride and 96
15. The method of claim 14, comprising 100 parts by weight of a mixture of ~65 mole percent lithium fluoride to which up to 3 parts by weight neodymium oxide is added. 29. The method according to claim 14, wherein the cathode is made of iron and a neodymium-iron alloy is produced. 30. In a molten salt electrolytic bath, a plate-shaped carbon electrode is used as an anode, and a plate-shaped metal or carbon electrode is used as a cathode, and these plate-shaped electrodes are placed facing each other in the electrolytic bath. The temperature is controlled by a heating means provided outside the electrolytic bath, and an oxidizing gas with a concentration sufficient to oxidize and consume the powdery carbon generated from the carbon electrode and floating on the surface of the electrolytic bath during electrolysis is supplied to the electrolytic bath. Neodymium or neodymium alloy is deposited on the cathode by electrolyzing at an anode current density of 0.5 A/cm^2 or more, and the neodymium or neodymium alloy is dropped under the cathode to the bottom of the electrolytic bath. A method for producing neodymium or neodymium alloy, which comprises collecting neodymium or neodymium alloy. 31. The method according to claim 30, wherein the electrolytic bath temperature is within the range of 750 to 1100°C. 32, the electrolytic bath temperature is 8
32. The method according to claim 31, wherein the temperature is within the range of 25 to 1000C. 33. The method of claim 30, wherein the electrolytic bath comprises 4 to 35 mol% neodymium fluoride and 96 to 65 mol% lithium fluoride. 34, the electrolytic bath contains 5 to 25 mol% neodymium fluoride and 95
34. The method of claim 33 comprising a mixture of ~75 mole % lithium fluoride. 35, the electrolytic bath contains 4 to 35 mol% neodymium fluoride and 96
31. The method of claim 30, comprising 100 parts by weight of a mixture of ~65 mole percent lithium fluoride plus up to 3 parts by weight neodymium oxide. 36. The method according to claim 30, wherein the distance between the plate-shaped anode and the plate-shaped cathode is controlled to be constant in consideration of electrode wear. 37. The method according to claim 30, wherein one plate-shaped cathode is placed in the center, and a pair of plate-shaped anodes are placed on both sides of the plate-shaped cathode to face the plate-shaped cathode. 38. The plate-shaped cathode is shaped to have an inclined base and a downwardly convex apex formed at the end of the base, so that the neodymium or neodymium alloy that is precipitated at the cathode and drips down the cathode is placed below the apex. 31. The method of claim 30, wherein the collection is performed centrally. 39. The method according to claim 38, wherein a tantalum-lined receiver is disposed below the apex of the plate cathode, and the neodymium or neodymium alloy dripping is collected in the receiver. 40. The method according to claim 30, using an electrolytic bath made of austenitic stainless steel. 41. A molten salt electrolytic bath with a depth of 5 mm or more consisting of 4 to 35 mol% neodymium fluoride and 96 to 65 mol% lithium fluoride, with a plate-shaped carbon electrode as the anode and a plate-shaped iron or iron electrode as the cathode. Carbon electrodes are used, and these plate-shaped electrodes are placed facing each other in an electrolytic bath with a distance between the electrodes within a range of 10 to 50 mm. The electrolytic bath is covered with an atmosphere containing an oxidizing gas with a concentration sufficient to oxidize and consume the powdered carbon suspended in the electrolytic bath, and the bath temperature of the electrolytic bath is set to 750-1.
Neodymium or neodymium is deposited on the cathode by controlling the temperature within the range of 100°C, electrolyzing at an anode current density of 0.5 A/cm^2 or more, and controlling the distance between the electrodes to be constant in consideration of electrode wear. A method for producing neodymium or neodymium-iron alloy, which comprises precipitating an iron alloy, dropping the neodymium or neodymium-iron alloy under a cathode, and collecting it at the bottom of an electrolytic bath. 42. The method according to claim 41, wherein the inner wall of the electrolytic bath is made of austenitic stainless steel, and the inner wall of the receiver is made of tantalum. 43. The method according to claim 41, wherein the neodymium or neodymium-iron produced has a carbon content of less than 100 ppm. 44. The method according to claim 41, wherein the current efficiency is 70% or more. 45. The method according to claim 44, wherein the current efficiency is 80% or more. 46. Claim 1 in which the cathode has a shape other than a plate shape
The method described in section. 47. Claim 1 in which the cathode has a shape other than a plate shape
The method described in Section 4. 48. Claim 4 in which the cathode has a shape other than a plate shape
The method described in Section 1.