JPH02101186A - Production of nd-fe alloy or metallic nd - Google Patents

Abstract

PURPOSE:To efficiently obtain the title high-grade Nd-Fe alloy and metallic Nd by specifying the ratio of LiF to NdF3 at the time of producing the materials from NdF3 in an LiF-NdF3 based electrolytic bath by molten-salt electrolysis. CONSTITUTION:A carbon anode 7 and an iron cathode 6 are used, NdF3 is used as the raw material, and the molten-salt electrolytic bath 3 contg. a fluoride and consisting of, by weight, 5-34% Nd and 95-66% LiF is prepared. The bath 3 in an electrolytic cell 4 is heated by the heating element 2 of an externally-heated furnace 1, the bath temp. is detected by a thermocouple 14 and controlled to an optimum temp., and electrolysis is carried out in an oxidizing atmosphere. The formed Nd-Fe alloy is dripped from the bottom point of the cathode 6 as droplets 11, charged into an alloy receiver 13 lined 12 with Ta, etc., and deposited. By this method, the current density and efficiency can be increased, and a product contg. small amts. of the O and C deteriorating the performance as the magnetic material is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing rare earth metals or rare earth alloys by molten salt electrolysis, and more particularly relates to a method for producing rare earth metals or rare earth alloys by molten salt electrolysis. The present invention relates to a method for manufacturing Nd metal or Nd-Fe alloy suitable for Fe-B magnet materials.

(Prior Art) The following methods are mainly known as methods for producing Nd metal or Nd-Fe alloys.

(1) A method of recovering Nd metal or Nd-Fe alloy by reducing a Nd compound in an inert gas atmosphere with an active metal such as metal Ca.

(2) A method of manufacturing Nd-Fe alloy by subjecting Nd oxide to molten salt electrolysis in an inert gas atmosphere, using iron for the cathode and graphite for the anode, and alloying it with the iron used for the cathode (E, M
Author: Bureau of Mines
.

“Report of Investigati
ons” Ha 7146.1968).

■Method of manufacturing Nd metal using tungsten for the cathode and graphite for the anode (E, Morrjce et al., Bure
au of Mjnes, ”Report of
Investigat-jons” Na 6 9
5 7, 1967).

(3) A method of manufacturing Nd-Fe alloy by subjecting Nd fluoride to molten salt electrolysis in an inert gas atmosphere, using iron for the cathode and graphite for the anode, and alloying it with the iron used for the cathode (Tokyo Publications No. 6).
3-1.2947).

(Problem to be solved by the invention) However, all of the above methods (1) to (3)
Reduction is carried out in an inert gas atmosphere, which has the disadvantage of requiring equipment costs and being complicated to handle.In particular, in the case of molten salt electrolysis, continuous operation is assumed for industrial use, which can result in large economic losses. Become.

In addition, when comparing the methods (1) to (3) above, the first method (]) uses expensive metals such as Ca as a reducing agent and is an old batch manufacturing method, so it is economical. poor performance and poor productivity.

In addition, in the second method (2), since the solubility of the oxide (Nd oxide) in the molten salt is low, if there is a mixture of oxides supplied below the solubility, the oxide is deposited below the molten salt, that is, the precipitation occurs. Oxides get mixed into the metal, forming a mixture of metal, molten salt, and oxide, making it difficult to recover high-grade metal.

Furthermore, in the third method (3), the dissolution of fluoride (Nd fluoride) and LiF, which is a molten salt, creates a eutectic state and the dissolution range is wide. Although this method can be said to be an excellent method for recovering metal without generation, it has the disadvantage that it can recover Nd-Fe alloy but cannot recover Nd metal.

An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a method for efficiently and economically producing Nd-Fe alloys and Nd metal by molten salt electrolysis.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have developed a more efficient and economical Nd-Fe alloy by specifically reviewing the method disclosed in Japanese Patent Publication No. 63-12947. and conducted extensive research to find a method for producing Nd metal.

As a result, according to the research of the present inventor,
Even if the method disclosed in No. 94.7 is limited to a method for industrially producing Nd-Fe alloys, it has been found that it has the following problems and cannot be called an economical method for producing it.

That is, in the method disclosed in Japanese Patent Publication No. 12947/1983, an electrolytic bath mainly composed of LiF is mixed with 35% of Nd fluoride.
~7'6wt% and the electrolysis temperature was 770%.
This can be said to be a method of maintaining the temperature at -950°C to precipitate the Nd-Fe alloy.

The reason why Nd fluoride, which is a raw material compound, is maintained at 35 to 76 tgt% is in a eutectic state according to the LiF-NdF phase diagram (Figure 6), and the melting point of LiF is about 850°C and the eutectic point is When Nd F3 is about 66wt%, about 730℃, Nd
F3 (71) From the three points with a melting point of 1300'C or higher, it is thought that the LiF=4-NdF3 composition is aimed at a composition with a melting point of about 840°C or lower (R, E, T
homa, Progress in 5science
and Technology of theRare
Earths, Vo Q, 2, p, 110, P
ergal IIon Press, New Year
K., 1966).

In general, in order to obtain metals by molten salt electrolysis, it is desirable to have a low electrolysis temperature, and therefore it is considered desirable to operate in a place where the molten salt composition has a low melting point for the following reasons. It is believed that the composition range was selected based on this point.

■Operation at low temperatures causes less damage to the electrolytic cell materials and reduces volatilization loss of the electrolytic bath.

■It is more energy efficient to operate at low temperatures.

■In the case of molten salt electrolysis, there is a phenomenon in which the precipitated metal becomes a metal layer again and reacts with the components in the bath, and the reaction that returns to the raw material increases as the temperature increases, and the theoretical value calculated from this balance increases. It is thought that the ratio of the actual metal recovery amount, that is, the current efficiency, is the smaller the diameter where the temperature is.

However, as a result of various research conducted by the present inventor, fluoride electrolysis, unlike the oxide and chloride electrolysis known up to now, proceeds through a complex mechanism, and is particularly It has been found that the composition in Publication No. 6312947 is not an economically desirable composition.

In other words, when producing metal economically by molten salt electrolysis,
Two major factors have a particularly large influence for the following reasons.

1. Large electric current In molten salt electrolysis, as the electric current per unit area of the electrode is increased, a peculiar phenomenon occurs as an anode effect, and normal electrolysis is no longer possible. Therefore, in order to perform normal and stable electrolysis, it is necessary to operate below this critical current density.

However, if the critical current density is small, the electrode area must be increased in order to pass a constant current.

In this case, the furnace becomes large, equipment costs increase, and a large amount of expensive molten salt is required, making it uneconomical.

Therefore, in order to economically produce metal, it is desirable to operate at a point where the critical current density is high, but since the critical current density is determined by various factors, we conducted various technical studies and experiments. Although it is necessary to determine the optimum conditions, the method disclosed in Japanese Patent Publication No. 63-12947 can only operate at 0.60 A/cIn2 at most.

2. Large electric current As mentioned above, the amount of metal that can be produced by electrolysis is the value calculated by multiplying the theoretical value calculated by Faraday's law by the current efficiency.

If the current efficiency is low, the amount of metal produced will be small no matter how much current is applied, so the higher the current efficiency is, the more desirable it is.

Since this current efficiency is determined by various factors like the critical current density mentioned above, it is necessary to perform various technical studies and experiments to determine the optimum conditions.

From the above points 1 and 2, the inventor has considered various ways to economically produce metal, and as a result of repeated research,
This led to the invention of a method for producing Nd metal and NdFe alloy very economically.

That is, the method for manufacturing an Nd-Fe alloy according to the present invention is as follows:
When producing Nd-Fe alloy by molten salt electrolysis method,
A carbon electrode is used as an anode, an iron cathode is used as a cathode, NdF3 is used as a raw material compound, and the molten salt electrolytic bath containing the fluoride contains substantially 5 to 34 wt% NdF3 and 95-6
It is characterized in that it is composed of 6w1:% LiF and is precipitated below the obtained rare earth alloy molten salt.

Further, in the method for producing Nd metal according to the present invention, when producing Nd metal by molten salt electrolysis, a carbon electrode is used as an anode,
A carbon electrode or an electrode made of a material that does not form an alloy with Nd, such as Ta or Pt, is used as the cathode, and NdF3 is used as the raw material compound, and the molten salt electrolytic bath containing such fluoride contains substantially 5 to 8 Qwt% of NdF3. 95-20t% LiF
It is characterized by adjusting the molten salt so that it is composed of the following: and precipitating the obtained rare earth metal below the molten salt.

The present invention will be explained in more detail below.

(Function) The present inventor previously proposed a method of electrolyzing in an oxidizing atmosphere (Japanese Patent Application No. 62-204879) as a method for producing rare earth metals or rare earth alloys by molten salt electrolysis. He also proposed a method for efficiently producing metal in a small electrolytic cell using a plate-shaped cathode and S pole (Japanese Patent Application No. 1982-220893).

When we conducted an experiment to manufacture Nd-Fe alloy using NdF3 as a raw material using the S method, we found that
Electrolytic bath composition in the range not covered by No. 47, that is,
NdF3 is 5-34wt% and LiF is 95-66wt%
In the LiF-NdF3-based electrolytic bath composition, it has been found that both current efficiency and critical current density can be significantly improved as shown in Examples below.

This trend is reflected in the Bureau of Mjnes mentioned above.
report and Japanese Patent Publication No. 63-12947, that is, N
When we conducted an experiment on a method for manufacturing Nd-Fe alloy using dF3 as a raw material and a LiF-NdF system electrolytic bath, we obtained results with the same tendency, although the efficiency was lower. be.

Incidentally, according to the method of the present invention, the current efficiency is 60 to 90%, and the critical current density is 1. , O-2,7A/c+n2, and the electrolysis temperature is preferably in the range of 800 to 950°C.

In addition, the electrolytic bath composition in the present invention is I,jF-NdF3
system, but it also contains appropriate amounts of CaF2 and BaF.
, and CeF3 may be added at appropriate times.

FIGS. 1(a) (cross-sectional view) and (b) (plan view) show an example of an apparatus suitable for producing a Nd--Fe alloy by the above method. This device has the following configuration.

An electrolytic bath 4 for holding an electrolytic bath 3 is attached to an external heating furnace 1 equipped with a heating element 2, and during that time, a part of the gasified electrolytic bath enters and damages the heating element 2. It is sealed with an insulator 5 which has the role of preventing this.

In the electrolytic bath, there is an iron plate cathode 6 and a graphite plate anode 7.
Two electrodes are arranged facing each other, and these electrodes are held by an electrode mounting base 8, and the electrodes can be adjusted to the optimum position even during electrolysis using an electrode elevator 9 and an interelectrode distance adjuster 10.

The generated Nd reacts with the iron of the cathode, becomes Nd-Fe alloy droplets 11, enters an alloy receiver 13 having a lining 12 made of Ta, etc., and precipitates therein.

The temperature of the electrolytic bath 3 is detected by a thermocouple 14 set in the electrolytic bath, and the external furnace heater 2 is adjusted to the optimum temperature.
controlled by This electrolysis improves workability, equipment cost, product purity, current efficiency, and critical current density.
It is carried out in an oxidizing atmosphere.

Further, it is desirable that the lower end of the cathode be tapered so that the produced alloy drips as droplets 11 from the bottom point of the cathode. When electrolysis is carried out continuously, it is natural that this apparatus is equipped with a continuous raw material supply device, a metal pumping device, and other accessory devices.

Further, the thickness of the plate electrode may be determined based on the interval until the next electrode replacement; - For boat fishing, it is effective to pump out the metal when replacing the electrode.

Nd:&iyu4 Shoji Toko, a method for producing Nd metal using NdF3 as a raw material will be explained.

This method is applicable to cases such as (]) to (2) below.
It is more desirable and suitable to recover the Nd metal instead of the d-Fe alloy.

(1) When used as a magnetic material, it may be alloyed with other rare earth metals, such as Sm.
In this case, since it is not necessarily the case that only those with a composition containing Fe are used, the range of use is greater if only rare earth metals that do not contain Fe are recovered.

(2) The use of Nd metal as a magneto-optical material is being studied, and in this case, it is often used in a composition that does not contain Fe.

Therefore, it is necessary to establish a technology for producing Nd metal other than Fe alloy by molten salt electrolysis.

Generally, when producing rare earth metals by molten salt electrolysis,
The raw material is oxide, graphite is used for the anode, and W and Mo are used for the cathode.
etc. are used to prevent oxidation of the cathode at high temperatures,
In order to prevent oxidation of the resulting metal, it is electrolyzed in an inert gas atmosphere.
of Investigations” Nn 6
957.1967).

The present inventor has proposed electrolysis in an oxidizing atmosphere as described above, and in order to produce rare earth metals by this method, fluoride is used as a raw material, a carbon electrode is used as an anode, and a carbon electrode is also used as a cathode. It was invented to use. In addition to carbon, this cathode material does not involve oxidation reactions because no oxides are used in the electrolytic bath, so Ta and Pt are used on the cathode surface.
Metals that do not form alloys with Nd, such as Nd, can also be used.

When electrolyzing is performed in an oxidizing atmosphere using carbon as an anode and carbon as a cathode, the difference from the case of manufacturing the Nd-Fe alloy described above is as follows.

When producing a Nd-Fe alloy using carbon for the anode and iron for the cathode, the reaction is as follows: NdF3→Nd''+3F At the anode, nC+mF −+CnFm+me At the cathode, Fe+Nd''+3e-→Nd-Fe alloy. Therefore, both the cathode and the anode become consumable electrodes.

On the other hand, when manufacturing Nd metal using carbon for the anode and carbon for the cathode, the reaction is NdF3→Nd"+3F at the anode, nC+mF-+CnFm+me, and Nd"+3e-+Nd metal at the cathode. Therefore, the anode becomes a consumable electrode, while the cathode becomes a non-consumable electrode.

When carbon is used as an electrode in an oxidizing atmosphere, the part of the electrode covered in the oxidizing atmosphere at the top of the electrolytic bath will be oxidized and consumed, but this part may be coated with a fermentation inhibitor, and carbon Since it is an inexpensive material, it can be disposable. Furthermore, when high melting point materials such as Mo and W are used for the cathode, they form an alloy with Nd, resulting in several hundred to several thousand ppm of cathode material being mixed in, but when Ta, Pd, etc. are used, these There are no problems, so you can use it with confidence.

Measures to prevent oxidation of cathodes using Ta include coating the reaction surface of graphite electrodes with Ta in the electrolytic bath, and coating them with N.
An iron cathode may be made in the same way as when producing a d-Fe alloy, and only the reaction surface thereof may be coated with Ta.

Since the melting point of Nd is about 1020°C, the electrolytic temperature may be set at a temperature higher than the melting point to precipitate Nd as a melt,
Alternatively, the electrolytic temperature may be set to below the melting point, and the solid may be deposited on the cathode.

In the latter case, if electrolysis is performed at a temperature below the melting point of Nd metal, it will precipitate in the form of needles on the cathode, but when the precipitated needle-shaped Nd metal grows until it reaches the anode, -
At times, a large current flows between the anode and the cathode, causing the Nd metal to melt and precipitate downward.

When we conducted an experiment to produce Nd metal using the molten salt electrolysis method using NdF3 as a raw material, we found that Nd
L with F3 from 5 to 80 wt% and LiF from 95 to 2 Qwt%
It has been found that an electrolytic bath composition mainly composed of iF-NdF3 has desirable current efficiency and critical current density, and can be produced economically, as shown in Examples below.

This tendency was also observed in an experiment in which Nd metal was manufactured using a round rod-shaped graphite electrode in an inert gas atmosphere. Although the efficiency decreased, the same tendency was obtained, but the method of the present invention was more economical. It is easy to understand that this is a manufacturing method.

According to the method of the present invention, the current efficiency is 50 to 80%, the critical current density is 1.5 to 2.6 A/cm2, and the electrolysis temperature is preferably in the range of 800 to 1050°C.

Although the electrolytic bath composition uses a LiF-NdF3 system, it goes without saying that appropriate amounts of CaF2, BaF2 and CeF3 may be added thereto at any time.

-16= Apparatus suitable for producing Nd metal by the above method is:
It is almost the same as the device shown in Fig. 1 (a) and (b), but basically the cathode material is carbon, Ta, Pd, etc.
The difference is that it is a high melting point material that does not form an alloy.

In addition, the generated Nd precipitates on the graphite of the cathode, but when the electrolytic bath temperature is higher than the melting point of Nd, it precipitates in the form of droplets.
When the electrolytic bath temperature is lower than the melting point of Nd, it forms needle-shaped crystals and deposits on the cathode. In the latter case, when the needle-like crystals grow larger and reach the cathode, a large current may temporarily flow between the cathode and the anode, causing them to dissolve and precipitate downward.

In addition, the metal receiver 13 is effective as is when operating at an electrolytic bath temperature higher than the melting point of Nd, but
This is not necessary when operating at temperatures below the melting point of In the case of continuous operation, the cathode may be periodically pulled up to recover Nd when electrolysis is carried out below the melting point, and the molten metal (Nd) may be vacuum-suctioned when electrolysis is carried out above the melting point.

(Example) Next, examples of the present invention will be shown.

The relationship between the composition ratio and electrolysis temperature on the critical current density was investigated by changing the composition of the LiF-NdF3 mixture. The metal produced is a Nd-Fe alloy.

The apparatus used was the apparatus shown in FIGS. 1(a) and 1(b), and this experiment was conducted in the atmosphere.

FIG. 2 shows the relationship between critical current density and electrolytic bath composition at various electrolysis temperatures when Nd--Fe alloys were produced using the apparatus configured as described above. Further, FIG. 3 shows the relationship between the electrolytic bath composition and current efficiency when the electrolytic bath temperature was kept constant at 900°C.

From Figures 2 and 3, the electrolytic bath composition with high critical current density, high current efficiency, and good production efficiency is NdF3:5 ~
34 wt%.

The relationship between the composition ratio and temperature on the critical current density was investigated by changing the composition of the mixture of LiF-NdFl]. The manufactured metal is Nd metal.

The apparatus used was almost the same as in Example 1, but the following points were slightly different.

In other words, when producing an Fe alloy, the electrodes arranged in the electrolytic bath 3 include a plate-shaped iron cathode 6 and a carbon plate-shaped anode 7.
Two sheets of the carbon cathode 6 were arranged facing each other, but a carbon plate cathode 6 was arranged instead of the iron plate cathode.

FIG. 4 shows the relationship between critical current density, electrolytic bath composition, and electrolysis temperature when Nd metal is manufactured using the apparatus having the above configuration. Further, FIG. 5 shows the relationship between electrolytic bath composition and current efficiency at various electrolysis temperatures.

From Figures 4 and 5, the electrolytic bath composition with high critical current density, high current efficiency, and good production efficiency is NdF3:5 ~
It turns out that it is 80wt%.

A Nd-Fe alloy was produced using the apparatus shown in FIGS. 1(a) and 1(b). The electrodes consisted of two graphite cathodes arranged around an iron plate cathode. Molten salt is NdF: 20wt%-L
iF: 80%, and the amount of NdF3 consumed by electrolysis was supplied to the electrolytic bath to maintain the electrolytic bath composition constant.

Other electrolysis conditions are shown in Table 1.

The results of electrolysis are shown in Table 1.

It can be seen that the Nd-Fe alloy was recovered extremely efficiently and that the impurities in the alloy, such as oxygen and carbon, were also small.

In particular, it can be seen that the current density is high and the current efficiency is high.

An experiment similar to that in Example 3 was conducted using the missing wild goose to produce a Nd-Fe alloy. However, the experiment was conducted by changing the molten salt composition to NdF3:30wt%LiFnear 0vt%.

As shown in Table 1, good results were obtained from the experiment.

Sennodou 1 Nd metal was manufactured using the apparatus shown in FIG. The electrodes were a graphite plate electrode with two graphite cathodes facing each other. The molten salt is NdF3:30wt%-LiFNia0
wt% and electrolyzed at 900°C. At that time, the consumed amount of NdF3 was supplied to the electrolytic bath to maintain the electrolytic bath composition constant. Metal was deposited on the cathode surface. Other electrolysis conditions are shown in Table 1.

As shown in Table 1, good results were obtained from the experiment.

Example 6 Nd metal was produced in the same manner as in Example 5.

However, the electrolysis temperature was set to 1050°C, which was higher than the melting point of Nd, and the molten salt composition was changed to NdFa: 50 wt%-LiF:
The concentration was changed to 50% and electrolyzed. The metal precipitated under the molten salt in a molten state. Other electrolysis conditions are shown in Table 1.

As shown in Table 1, good results were obtained from the experiment.

[Blank 1 (Effects of the Invention) As detailed above, according to the present invention, Nd-Fe alloys and Nd metals can be produced by molten salt electrolysis, and the following excellent effects can be obtained. It will be done.

1. Since the current density and current efficiency are high, a large amount of metal can be produced efficiently and economically using small equipment.

2. Nd-Fe alloy and Nd by simply replacing the cathode material
Metals can be manufactured easily.

3. It is possible to produce metals that are low in oxygen and carbon, which degrade performance as magnetic materials.

4. Since a protective gas sealing device is not required, construction costs and maintenance costs for the equipment can be reduced, and raw materials, auxiliary raw materials, and products can be easily supplied and taken out.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams for explaining an example of an apparatus used for carrying out the present invention, in which (a) is a cross-sectional view, and (b) is a plan view. Figure 3 is a diagram showing the relationship between electrolytic bath composition, critical current density, and current efficiency at various electrolysis temperatures when Nd-Fe alloy is electrolyzed by the molten salt electrolysis method of the present invention. is a diagram showing the relationship between electrolytic bath composition, critical current density efficiency, and current efficiency when Nd metal is electrolyzed by the molten salt electrolysis method of the present invention, and Figure 6 is a LiF-NdF3 system phase diagram (wt% display). It is. 1... External heat furnace, 2... Heating element, 3... Electrolytic bath, 4
・Electrolytic cell, 5... Insulator, 6... Cathode, 7... Anode, 8... Electrode mounting base, 9... Electrode elevator, 10.
... Distance adjustment device between poles, 11... Droplet, 12... Receiver lining, 13... Nd metal or Nd alloy receiver, 14.
・・Thermocouple, 15...Atmosphere・ Patent applicant Hisashi Nakamura, patent attorney representing Showa Denko K.K. Figure (b) NdF3 (wt%) Figure NdF3 (wt%) Figure NdF3 (wt%) Procedure amendment

Claims (3)

[Claims] (1) When producing a Nd-Fe alloy by the molten salt electrolysis method, a carbon electrode is used as an anode, an iron cathode is used as a cathode, NdF_3 is used as a raw material compound, and the molten salt electrolytic bath containing such fluoride is 5-34wt% NdF_3
and 95 to 66 wt% of LiF, and the resulting rare earth alloy is precipitated below the molten salt. (2) When producing Nd metal by molten salt electrolysis method,
Carbon electrode for the anode, carbon electrode for the cathode, or N such as Ta, Pt, etc.
Using an electrode made of a material that does not form an alloy with d, NdF_3 is used as a raw material compound, and a molten salt electrolytic bath containing such a fluoride contains substantially 5 to 80 wt% of NdF_3 and 95%.
Adjusted to be composed of ~20wt% LiF,
A method for producing Nd metal, characterized in that the obtained rare earth metal is precipitated below a molten salt. (3) The method according to claim 1 or 2, wherein the electrode is plate-shaped and the electrolysis is carried out in the atmosphere.