JPH04214824A - Manufacture of low oxygen-containing rare earth metal - Google Patents

Abstract

PURPOSE:To offer an industrial manufacturing method for rare earth metal having low content of oxygen and calcium as impurity and useful as the material for a permanent magnet and magneto-optical recording. CONSTITUTION:In the method for manufacturing rare earth metal obtd. by reducing rare earth metal fluoride with metal calcium, as for the method for manufacturing low oxygen-contg. rare earth metal to be brought into a heating reaction with metal calcium by the theoretical amt. required for reducing the relevant fluoride or below, particularly, at the time of executing this heating reaction in the atmosphere of an inert gas or in a vacuum condition, rare earth metal with high purity can more effectively be obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low-oxygen rare earth metals, and more particularly to an effective method for producing low-oxygen rare earth metals useful as permanent magnets and magneto-optical recording materials.

0002

2. Description of the Related Art Rare earth metals are generally silvery white to gray highly active metals that are gradually oxidized by oxygen in the air. Oxygen combined by this oxidation deteriorates the quality of derived products in various applications, so rare earth metals as materials are required to have as low an oxygen content as possible.

Conventionally, typical methods for producing such high-purity rare earth metals include, for example, a molten salt electrolysis method and a thermal reduction method using metallic calcium (Ca). The former molten salt electrolysis method has excellent productivity because it can be operated continuously, but it has a fatal flaw in that it can be applied to rare earth metals with relatively low melting points, but cannot be applied to heavy rare earth metals with high melting points. Therefore, heavy rare earth metals are only manufactured in the form of alloys by using iron or the like as a consumable cathode.

On the other hand, the latter thermal reduction method is a batch method and has the advantage of being able to produce high-purity rare earth metals with relatively few impurities. It is an industrially desirable method because it is necessary to purify metallic calcium as a reducing agent by distillation, etc., and it is also required to perform preliminary treatment such as refining and deoxidizing the raw material rare earth metal fluoride. I can't say that.

[0005] These impurities contained in rare earth metals are considered to be impurities such as oxygen and calcium contained in the raw materials, considering their typical uses as permanent magnets and magneto-optical recording materials. Both amounts are 1000
It is extremely important that the content of rare earth metals be below ppm, and no method for industrially advantageous production of such highly purified rare earth metals has been known so far.

[0006]

OBJECTS OF THE INVENTION Therefore, it is an object of the present invention to provide an effective method for producing such low oxygen and low calcium rare earth metals that can be applied to all rare earth metals. There is a particular thing. Another object of the present invention is to provide an industrial method capable of obtaining high-yield rare earth metals of high purity with a low content of impurities such as calcium and fluorine.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted extensive research on methods for reducing rare earth metal fluorides, and as a result, they have found that metallic calcium can be reduced in a limited and extremely narrow range. When acting as a reducing agent,
It has been found that the above-mentioned problems can be effectively achieved and an industrially desirable low-oxygen-containing rare earth metal can be obtained.

That is, the present invention provides a method for producing rare earth metals in which a rare earth metal fluoride is reduced with metallic calcium, in which a rare earth metal fluoride is reduced by heating and reacting with metallic calcium in an amount less than the theoretical amount necessary to reduce the fluoride. The gist of this paper is a method for producing oxygen-containing rare earth metals.

The technical feature of the present invention is that, particularly in the reduction of rare earth metal fluorides, the rare earth metal fluorides are reduced with a relatively small amount of metallic calcium, which is less than the theoretical amount required for the reduction reaction. Use of metallic calcium in an amount greater than the stoichiometric amount increases the yield of the rare earth metal produced, but is not preferred because it significantly increases the amount of impurities in the produced metal. Also, if we consider industrial productivity, the theoretical amount is 0.9
More than twice as much is preferable.

The theoretical amount of calcium metal that reduces fluorine is the theoretical molar ratio expressed by the following reaction formula 1, where R represents the rare earth metal. RF3 +1.5 Ca →R+1.5 Ca F2

The rare earth metals targeted in the method of the present invention are yttrium Y and elements with atomic numbers 57-71. Examples of rare earth metals in this atomic number group include lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd, and samarium Sm.
, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, ytterbium Yb
and lutetium Lu.

In addition, in the method of the present invention, these fluorides are reduced by heating and melting with metallic calcium, and the heating reduction reaction varies depending on the type of rare earth metal, but is usually heated at, for example, 1300°C. or 1600
It is carried out in a high temperature range of around ℃. If the temperature is too low, the yield will decrease, and if the temperature is too high, it will not only be economically disadvantageous but also increase the amount of impurities from the reaction vessel, which is not preferred. The defluorination reduction reaction in such a high temperature region is
It is important to carry out the reaction in a reaction zone substantially free of oxygen, and it is particularly preferred in practice to carry out the reaction in an atmosphere of an inert gas such as argon, helium, neon, etc., or under vacuum conditions.

Furthermore, in such a reduction reaction, it is extremely important to use metallic calcium in an extremely narrow range of less than the above-mentioned theoretical amount, preferably 0.9 to 1.0 times the amount of rare earth metal fluoride. be. If it is less than 0.9 times, the amount of calcium impurities contained in the obtained rare earth metal is small and the oxygen content is also relatively small;
Since the yield of the target rare earth metal is low, it is difficult to employ it industrially. Furthermore, if the amount exceeds 1.0 times, the yield of rare earth metals improves, but the amount of calcium and oxygen as impurities increases rapidly, which is extremely inconvenient as a material for permanent magnets and magneto-optical recording materials. It is. It is more preferable that the metallic calcium used in this reduction reaction be purified by distillation or the like, but commercially available common calcium can also be suitably used.

[0014]

[Operation] The smelting reduction reaction method of the present invention has excellent practicality because it can be applied to all rare earth metals.
Furthermore, rare earth metals with a low content of impurities that are undesirable as raw materials can be effectively produced. Furthermore, since such highly purified rare earth metals can be obtained in high yield, it is extremely advantageous industrially.

[0015]

EXAMPLES Next, the method of the present invention will be explained in more detail using specific examples.

Example 1 500 g of neodymium fluoride and 142 g of metallic calcium (0.95 times the theoretical amount for neodymium fluoride) were placed in a tantalum crucible, heated and maintained at a temperature of 1400°C in an argon atmosphere, and reacted for 30 minutes. I let it happen.

The two-layer product of neodymium metal and calcium fluoride was taken out of the crucible, and the neodymium metal layer was examined. The results were as follows, and neodymium metal was obtained that was satisfactory as a material for various uses. Amount of neodymium metal obtained: 333g (yield 93%) Amount of oxygen contained: 430ppm Amount of calcium: 520ppm

[0018]
Example 2 Dysprosium fluoride 500g and metallic calcium 137
g (1.0 times the theoretical amount) and the heating reaction temperature was 14
Metallic dysprosium was produced in the same manner as in Example 1 except that the temperature was 50°C. The metallic dysprosium layer and the calcium fluoride layer were separated and the metallic dysprosium layer was investigated, and the results were as follows. Neodymium metal was obtained that could be used as a material for various purposes. Amount of neodymium metal obtained: 352 g (yield 95%) Amount of oxygen contained: 910 ppm Amount of calcium: 860 ppm The amount of oxygen and calcium contained are both practically required 10
00 ppm or less.

Example 3 500 g of terbium fluoride was mixed with various amounts of metallic calcium (
(0.7 to 1.2 times the theoretical amount) in an argon atmosphere at a temperature of 1400° C. for about 30 minutes to produce metallic terbium. The yield of each produced metal terbium and the amount of oxygen and calcium impurities contained therein are summarized in Table 1 below, together with the theoretical amount of calcium magnification.

[0020]

[Table 1]

As is clear from the above table, the amount of metal calcium added is 0.9 of the theoretical amount that reacts with all fluorine atoms.
If it is less than 1 times, the yield of the target rare earth metal will be poor;
．． If it exceeds 0 times, the amount of oxygen and calcium contained in the obtained metal will increase significantly, so it cannot be used practically.

Comparative Example 1 In Example 1, neodymium fluoride was thermally reduced using 165 g of metallic calcium (1.1 times the theoretical amount) to produce metallic neodymium. The obtained metallic neodymium was 34
Oxygen and calcium contained in the produced metal at 7g (97% yield) are 1050ppm and 3500ppm, respectively.
It was pm.

Comparative Example 2 In Example 2, 116 g of metallic calcium (0.85 times the theoretical amount) was heated and melted with dysprosium fluoride and reduced to produce metallic dysprosium. The oxygen and calcium contained in the obtained metal dysprosium were both 750 ppm and 510 ppm,
The yield is as low as 76% (281 g), and it cannot be used industrially.

[0024]

Effects of the Invention According to the method of the present invention, high-purity rare earth metals with reduced oxygen and calcium content can be produced in high yield and effectively, and can be used as raw materials for permanent magnets and magneto-optical recording materials. Rare earth metals desirable as such are industrially advantageously provided.

Claims (2)

[Claims] Claim 1: A method for producing a rare earth metal by reducing a rare earth metal fluoride with metallic calcium, characterized in that the fluoride is heated and reacted with less than the theoretical amount of metallic calcium necessary to reduce the fluoride. A method for producing rare earth metals. 2. The method according to claim 1, wherein the heating reaction is carried out under an inert gas atmosphere or under vacuum conditions.