JP2761002B2 - Method for producing Nd-Fe alloy or Nd metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rare earth metal or a rare earth alloy by a molten salt electrolysis method, and more particularly, to a method for producing Nd- which has recently attracted attention as a high-performance magnet. The present invention relates to a method for producing an Nd metal or an Nd-Fe alloy suitable for a material for an Fe-B magnet.

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

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

(2) A method of producing an 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 with the iron used for the cathode (E. Morrice et al. Author, Bureau of Mines, “Report of Investigations” N
o.7146, 1968).

A method for producing Nd metal using tungsten for the cathode and graphite for the anode (E. Morrice et al., Bureau of Mines, “Rep.
ort of Investigations "No. 6957, 1967).

(3) A method of producing an 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 with the iron used for the cathode (Japanese Patent Publication No. 63-63) 12947
issue).

(Problems to be Solved by the Invention) However, all of the above-mentioned methods (1) to (3) are reduced in an inert gas atmosphere, so that equipment costs are increased and handling is complicated. In particular, in the case of molten salt electrolysis, since continuous operation is assumed industrially,
The economic loss is large.

In addition, comparing the above-mentioned methods (1) to (3), the first method (1) uses an expensive metal such as Ca as a reducing agent and is a batch production, so that it is economical. Is poor and productivity is poor.

In the second method (2), since the solubility of the oxide (Nd oxide) in the molten salt is small, if there is a mixture of the oxides supplied at the solubility or higher, the lower part of the molten salt, that is,
Oxide is mixed into the deposited metal, and becomes a mixture of the metal, the molten salt and the oxide, and it becomes difficult to recover a high-quality metal.

Further, in the third method (3), the dissolution of fluoride (Nd fluoride) and the molten salt LiF forms an eutectic state, and a wide dissolution range causes troubles such as oxide electrolysis. Although it is said that this is an excellent method of recovering metal without any problem, it has a drawback that Nd-Fe alloy can be recovered but Nd metal cannot be recovered.

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

(Means for Solving the Problems) In order to achieve the above object, the present inventor has studied especially the method disclosed in the above-mentioned Japanese Patent Publication No. 63-12947, and found that the Nd-Fe alloy is more efficient and economical. And intensive research to find methods for producing Nd and Nd metals.

As a result, according to the study of the present inventors,
Even if the method disclosed in No. 7 is limited to a method of industrially producing a Nd—Fe alloy, it has been found that it has the following problems and is not economical.

That is, the method disclosed in Japanese Patent Publication No.
It is reported that the electrolytic bath mainly composed of iF is maintained so that the Nd fluoride is 35 to 76 wt%, and the electrolytic temperature is maintained at 770 to 950 ° C. to precipitate the Nd—Fe alloy.

Maintaining Nd fluoride as a raw material compound at 35 to 76 wt% is a eutectic state according to the phase diagram of LiF-NdF ₃ (FIG. 6), in which the melting point of LiF is about 850 ° C. and the eutectic point is NdF ₃ is about 66 wt% of the cases at about 730 ° C., from 3-point melting point above 1300 ° C. of NdF _3, considered a melting point of LiF-NdF ₃ composition which is the goal of the following composition to about 840 ℃ (REThoma , Progress in Science and
Technology of the Rare Earths Vol.2, p.110, Perga
mon Press, New York, 1966).

Generally, to obtain a metal by the molten salt electrolysis method, it is preferable that the electrolysis temperature is low, and it is considered that it is desirable to operate the molten salt composition at a low melting point for the following reasons. It is considered that it was selected from the points.

Operating at lower temperatures results in less damage to the electrolytic cell material and less volatilization loss of the electrolytic bath.

Operating at lower temperatures is more energy efficient.

In the case of molten salt electrolysis, once deposited metal becomes a metal mist and reacts with components in the bath, and the reaction returning to the raw material increases as the temperature increases. It is considered that the smaller the ratio of the recovered amount, that is, the higher the current efficiency, the lower the efficiency.

However, according to various studies made by the present inventors, the fluoride electrolysis is different from the oxide and chloride electrolysis known up to now, and the reaction proceeds by a complicated mechanism. It has been found that the composition in JP 63-12947 is not an economically desirable composition.

In other words, when metal is produced economically by molten salt electrolysis, two major factors have a particularly large effect for the following reasons.

1. High critical current density In molten salt electrolysis, when the current per unit area of the electrode is increased, a specific phenomenon occurs as an anode effect, and normal electrolysis cannot be performed. Therefore, in order to perform normal stable electrolysis, it is necessary to operate at or below this critical current density.

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

Then, the furnace becomes large, the equipment cost increases, and a large amount of expensive molten salt is required, which is not economical.

Therefore, in order to economically produce metal, it is desirable to operate at a point where the critical current density is large, but since the critical current density is determined by various factors, technically conducting various studies and conducting experiments, Although it is necessary to determine the optimal conditions, the method described in JP-B-63-12947 mentioned above is at most 0.6.
Operation is possible only at 0 A / cm ² or less.

2. High current efficiency As described above, the amount of metal that can be produced by electrolysis is a value obtained by multiplying the theoretical value calculated by Faraday's law by the current efficiency.

If the current efficiency is small, the amount of metal produced is small no matter how much current is applied. Since this current efficiency is determined by various factors similarly to the critical current density described above, technically conducting various studies and conducting experiments,
Optimal conditions need to be determined.

From the viewpoints of the above 1 and 2, the present inventor has studied various methods for producing metal economically, and as a result of repeating the research, the present inventors have invented a method that can produce Nd metal and Nd-Fe alloy extremely economically. That is what led to it.

That is, the production method of the Nd-Fe alloy according to the present invention is, when producing an Nd-Fe alloy by a molten salt electrolysis method, using a carbon electrode as an anode, an iron cathode as a cathode, and NdF ₃ as a raw material compound.
And adjusting such that the fluoride-containing molten salt electrolytic bath is substantially composed of 5-34 wt% of NdF ₃ and 95-66 wt% of LiF, and placing the resulting rare earth alloy below the molten salt. It is characterized by being deposited.

Further, the method for producing Nd metal according to the present invention, when producing Nd metal by a molten salt electrolysis method, a carbon electrode on the anode, a carbon electrode on the cathode, or an electrode made of a material that does not form an alloy with Nd such as a carbon electrode or Ta, Pt. NdF ₃ is used as a raw material compound, and a molten salt electrolytic bath containing such a fluoride is substantially 5-34 wt%.
Adjusted as constituted by NdF ₃ and 95～66Wt% of LiF, it is characterized in that to deposit a rare earth metal obtained in the molten salt below.

 Hereinafter, the present invention will be described in more detail.

(Function) Production of Nd-Fe Alloy The present inventor has previously proposed a method of producing a rare earth metal or a rare earth alloy by a molten salt electrolysis method in which an electrolysis is performed in an oxidizing atmosphere (Japanese Patent Application No. 62-204879). In addition, a method for efficiently producing metal in a small electrolytic cell using a plate-shaped cathode and anode was proposed (Japanese Patent Application No. 62-220893).

Using Such method was conducted an experiment to produce a Nd-Fe alloy NdF ₃ as a raw material, an electrolysis bath composition that is not intended by JP-B-63-12947, i.e., NdF ₃ is 5-34
In the electrolytic bath composition LiF is LiF-NdF ₃ system 95～66Wt% by wt%, in which was found to be able to significantly improve both the current efficiency and the critical current density as shown in the examples below.

This tendency is based on the method described in the above-mentioned Bureau of Mines report and Japanese Patent Publication No. 63-12947, that is, using a rod-shaped electrode in an inert gas atmosphere, using NdF ₃ as a raw material, LiF
When an experiment was performed method for manufacturing the Nd-Fe alloy using -NdF ₃ based electrolytic bath also, efficiency is lowered, in which the results of the same tendency.

According to the method of the present invention, the current efficiency is 60 to 90%, the critical current density is 1.0 to 2.7 A / cm ² , and the electrolysis temperature is 800 to 1000
C. is desirable.

Incidentally, the electrolytic bath composition of the present invention has a base of LiF-NdF ₃ system, not to mention it in an appropriate amount of CaF _2, BaF ₂ and CeF ₃ that may be added timely.

1 (a) (cross-sectional view) and (b) (plan view) show an example of an apparatus suitable for producing an 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 provided with a heating element 2, during which a part of the gasified electrolytic bath invades the heating element 2 for insulation and for insulation. Sealed by an insulator 5 which has a function of preventing the occurrence of the heat.

In the electrolytic bath, two graphite plate-shaped anodes 7 are arranged opposite to each other with an iron plate-shaped cathode 6 as a center.
The electrode can be adjusted to the optimum position during electrolysis by the electrode elevator 9 and the inter-electrode distance adjuster 10.

The generated Nd reacts with the iron of the cathode, and the Nd-Fe alloy droplet 11
And an alloy receiver with a lining 12 of Ta etc. inside
It goes into 13 and precipitates.

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

Further, it is desirable that the lower end of the cathode is tapered so that the produced alloy drops as a droplet 11 from the bottom point of the cathode. When the electrolysis is continuously performed, it is natural that the 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 by the interval until the next electrode replacement, and it is generally effective to pump out metal at the time of electrode replacement.

Production of Nd Metal Next, a method for producing Nd metal using NdF ₃ as a raw material will be described.

This method is used in the following cases (1) and (2).
It is more desirable and suitable to recover as Nd metal without recovering as Nd-Fe alloy.

(1) When used as a magnetic material, it may be used as an alloy with another rare earth metal, for example, an Sm-based material.
In this case, it is not always the case that only the composition containing Fe is used, so that the use range is more widened by recovering only the rare earth metal containing no Fe.

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

Therefore, it is necessary to establish a technology for producing Nd metal that is not an Fe alloy by a molten salt electrolysis method.

Generally, when a rare earth metal is produced by a molten salt electrolysis method, an oxide is used as a raw material, graphite is used for an anode, W is used for a cathode,
Mo is used and electrolyzed in an inert gas atmosphere to prevent oxidation of the cathode at high temperatures and to prevent oxidation of the formed metal (E. Morrice et al., Bureau of Mi
nes, “Report of Investigations” No. 6957, 1967
Year).

The present inventor has proposed electrolysis in an oxidizing atmosphere as described above.To produce a rare earth metal by this method, a 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, as the cathode material, in addition to carbon, an oxide is not used in the electrolytic bath, so that an oxidation reaction does not occur.Therefore, a metal which does not form an alloy with Nd such as Ta or Pt on the cathode surface can be used. .

When electrolysis is performed using carbon as the anode and carbon as the cathode in an oxidizing atmosphere, the following is different from the case of manufacturing the above-described Nd-Fe alloy.

Carbon Nd-Fe alloy anode, the reaction in the case of producing using the iron ^{_{cathode, NdF 3 → Nd 3+ + 3F}} - The ^{anode, nC + mF - → CnFm +} me - at the ^{cathode, Fe + Nd 3+ + 3e -} → Nd-Fe Alloy. Therefore, both the cathode and the anode become consumable electrodes.

On the other hand, the reaction in the case of producing using a carbon-carbon, a cathode of Nd metal ^{anode, NdF 3 → Nd 3+ + 3F} - The ^{anode, nC + mF - → CnFm +} me - at the cathode, Nd ³⁺ + 3e ^- → in Nd metal is there. Thus, the anode is a consumable electrode while the cathode is a non-consumable electrode.

When carbon is used as an electrode in an oxidizing atmosphere, the electrode portion covered with the oxidizing atmosphere above the electrolytic bath is oxidized and consumed, but this part may be coated with an antioxidant, and carbon is inexpensive. It may be discarded because it is a suitable material. When a high melting point material such as Mo or W is used for the cathode, an alloy with Nd is formed, and the cathode material is mixed with several hundred to several thousand ppm. Because there is nothing, you can use it with confidence.

To prevent oxidation of the cathode using Ta, the reaction surface of the graphite electrode in the electrolytic bath can be coated with Ta or Nd-
As in the case of producing an Fe alloy, an iron cathode may be made and only the reaction surface thereof may be coated with Ta, or only the exhausted anode may be replaced.

Since the melting point of Nd is about 1020 ° C., the electrolysis temperature may be such that Nd is deposited as a melt at a temperature equal to or higher than the melting point of Nd. Is also good.

In the latter case, when electrolysis is performed at an electrolysis temperature lower than the melting point of Nd metal, the Nd metal precipitates in the form of needles on the cathode. When the deposited needle-like Nd metal grows to reach the anode, it temporarily becomes positive. A large current flows between the cathodes, and the Nd metal melts and precipitates downward.

Using Such method was conducted an experiment to produce a Nd metal by molten salt electrolysis method NdF ₃ as a raw material, NdF ₃ 5
The electrolytic bath composition LiF is mainly composed of LiF-NdF ₃ of 95～66Wt% in ～34Wt%, preferably in the current efficiency and the critical current density both as shown in the examples below, in which it was found that can be economically produced is there.

Although this tendency is lower in efficiency when an experiment for producing Nd metal using a round bar-shaped graphite electrode in an inert gas atmosphere is performed, the same tendency is obtained, but the method of the present invention is more economical. It will be readily understood that this is a manufacturing method.

According to the method of the present invention, the current efficiency is 60 to 80%, the critical current density is 1.5 to 2.6 A / cm ² , and the electrolysis temperature is 800 to 1100.
C. is desirable.

The electrolytic bath composition uses a LiF—NdF ₃ system, but it goes without saying that an appropriate amount of CaF ₂ , BaF _2, and CeF ₃ may be added as needed.

Apparatus suitable for producing Nd metal by the above method,
It is almost the same as the apparatus shown in FIGS. 1 (a) and 1 (b), except that it is basically made of a high melting point material which does not form an alloy with Nd such as carbon or Ta or Pd as a cathode material.

In addition, the generated Nd precipitates on graphite of the cathode, but when the electrolytic bath temperature is higher than the melting point of Nd, it precipitates as droplets, and when the electrolytic bath temperature is lower than the melting point of Nd, it becomes needle-like crystals. To deposit on the cathode. In the latter case, when the needle-like crystal grows and reaches the cathode, a large current temporarily flows between the cathode and the anode, and the needle-like crystal may melt and precipitate downward.

The metal receiver 13 is effective as it is when operating at an electrolytic bath temperature higher than the melting point of Nd, but is not necessarily required when operating at a temperature lower than the melting point of Nd. In the case of continuous operation, the cathode may be pulled up periodically to recover Nd when electrolysis is performed at a temperature lower than the melting point, and the molten metal (Nd) may be vacuum-vacuated when electrolysis is performed at a temperature higher than the melting point.

(Example) The following example of the present invention is shown.

It was investigated in Example 1 LiF-NdF mixture composition by changing the electrolytic temperature relationship between the composition ratio on the critical current density of _3. The manufactured metal is an Nd-Fe alloy. The equipment used was the first
This is the device shown in FIGS. (A) and (b), and this experiment was performed in the atmosphere.

FIG. 2 shows the relationship between the critical current density and the composition of the electrolytic bath at various electrolysis temperatures when an Nd-Fe alloy was manufactured using the apparatus having the above configuration. FIG. 3 shows that the electrolytic bath temperature was 90 °.
The relationship between the electrolytic bath composition and the current efficiency when the temperature is kept constant at 0 ° C. is shown.

2 and 3, the composition of the electrolytic bath having a large critical current density, a large current efficiency and a good production efficiency is NdF ₃ : 5 to 34 wt.
%.

By changing the composition of the mixture of Example 2 LiF-NdF _3, it was investigated relationship between the composition ratio and the temperature on the critical current density. The manufactured metal is Nd metal.

The used apparatus is almost the same as that of Example 1, but the following points are slightly different.

That is, when the Fe alloy is manufactured, the electrode disposed in the electrolytic bath 3 is provided with the carbon plate anode 7 centered on the iron plate cathode 6.
Were arranged opposite to each other, but a carbon plate cathode 6 was arranged instead of the iron plate cathode.

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

4 and 5, the composition of the electrolytic bath having a high critical current density and a high current efficiency and a high production efficiency is NdF ₃ : 5 to 80 wt.
%.

Example 3 An Nd-Fe alloy was manufactured using the apparatus shown in FIGS. 1 (a) and 1 (b). As the electrodes, two graphite cathodes were arranged around an iron plate cathode. Molten salt NdF _3: 20wt% -LiF: and 80 wt%, and supplies the amount that NdF ₃ is consumed by electrolysis in the electrolytic cell,
The composition of the electrolytic bath was kept constant. Other electrolysis conditions are shown in Table 1.

The results of the electrolysis are as shown in Table 1, and it can be seen that the Nd-Fe alloy was recovered extremely efficiently, and that oxygen and carbon as impurities in the alloy were also small. In particular, it is understood that the current density is large and the current efficiency is high.

Example 4 The same experiment as in Example 3 was performed to produce an Nd—Fe alloy. However, the molten salt composition NdF _3: 30wt% -LiF: an experiment by changing the 70 wt%.

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

Example 5 Nd metal was produced using the apparatus shown in FIG. As for the electrodes, two graphite cathodes were opposed to each other with a graphite plate electrode as the center. Molten salt NdF _3: 30wt% -LiF: at 70 wt%, and electrolyzed at 900 ° C.. At that time, the consumed amount of NdF ₃ was supplied to the electrolytic cell, and the composition of the electrolytic bath was kept constant. The metal was deposited on the cathode surface. Other electrolysis conditions are the conditions shown in Table 1.

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

Comparative Example Nd metal was produced in the same manner as in Example 5. However, the electrolysis temperature is set to 1050 ° C. and the melting point of Nd or higher, and the molten salt composition is set to Nd
The electrolysis was changed to F ₃ : 50 wt% -LiF: 50 wt%. The metal was deposited below the molten salt in a molten state. Other electrolysis conditions are the conditions shown in Table 1.

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

(Effects of the Invention) As described in detail above, according to the present invention, an Nd-Fe alloy and a Nd metal can be produced by a molten salt electrolysis method, and the following excellent effects can be obtained.

1. Since the current density is large and the current efficiency is large, a large amount of metal can be efficiently and economically manufactured with small equipment.

2. Nd-Fe alloy and Nd metal can be easily produced simply by changing the cathode material.

3. It is possible to manufacture metal with low oxygen and carbon, which deteriorates performance as a magnetic material.

4. Since a protective gas sealing device is not required, the construction and maintenance costs of the equipment can be reduced, and the supply and removal of raw materials, auxiliary raw materials, and products can be facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are views for explaining an example of an apparatus used for carrying out the present invention, where (a) is a sectional view and (b) is a plan view. FIGS. 2 and 3 are diagrams showing the relationship between the electrolytic bath composition, the critical current density, and the current efficiency at various electrolysis temperatures when the Nd-Fe alloy was electrolyzed by the molten salt electrolysis method of the present invention. 4 and 5 are diagrams showing the relationship between the electrolytic bath composition and the critical current density efficiency and current efficiency when Nd metal is electrolyzed by the molten salt electrolysis method of the present invention. FIG. 6 is a diagram showing LiF-NdF ₃ It is a system phase diagram (wt% display). DESCRIPTION OF SYMBOLS 1 ... External heating furnace, 2 ... Heating element, 3 ... Electrolysis bath, 4 ... Electrolysis tank, 5
... Insulator, 6 ... Cathode, 7 ... Anode, 8 ... Electrode mount, 9 ...
Electrode lifting / lowering machine, 10: inter-electrode distance adjuster, 11: droplet, 12: lining of receiver, 13: Nd metal or Nd alloy receiver, 14: thermocouple, 15 ...
atmosphere.

Claims (3)

(57) [Claims] When producing a Nd-Fe alloy by a 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 a molten salt electrolytic bath containing such a fluoride is used. substantially 5~34wt% of NdF ₃ and 95~66wt%
A method for producing an Nd-Fe alloy, characterized in that the alloy is adjusted to be constituted by LiF, and the obtained rare earth alloy is precipitated below a molten salt. 2. When producing Nd metal by a molten salt electrolysis method, a carbon electrode is used as an anode, and a carbon electrode or Nd such as Ta or Pt is used as a cathode.
Using an electrode made of a material that does not form an alloy with
NdF ₃ is used and the fluoride-containing molten salt electrolytic bath is adjusted to be substantially composed of 5-34 wt% of NdF ₃ and 95-66 wt% of LiF. A method for producing Nd metal, which is deposited downward. 3. The method according to claim 1, wherein the electrodes are plate-shaped, and the electrodes are electrolyzed in an oxidizing atmosphere including the air.