JPS62146291A - Method for refining rare earth metal - Google Patents

Abstract

PURPOSE:To refine high purity alloy of rare earth and iron with a low cost, without using vessel made of precious Ta, etc., by using high Cr ferritic stainless steel as reaction vessel, at refining alloy of rare earth metal iron by fused salt electrolysis or metal thermal reduction method. CONSTITUTION:At manufacturing R-Fe alloy composed of 80-99.9% R (rare earth metal such as La, Ce, Pr, Nd, Sm), 0.02-20.0% Fe, raw material is fed into a retort and cathode 2 and fused salt electrolytic refining is carried out at 850-1200 deg.C using a graphite anode 1 while heating and melting by an electric furnace 4. In this case, at adding Nd2O3 into molten salt bath, since melting temp. of Nd is as high as 10204 deg.C, Nd-Fe alloy having low m.p. is prepd. by previously feeding high purity electrolytic iron powder in the retort 2 and high purity rare earth - iron alloy alloy is manufactured. By using high Cr ferritic stainless steel contg. >26% Cr as material of the retort 2, high purity rare earth - iron alloy is manufactured with a low cost without errosion of retort by rare earth - iron alloy.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to the smelting of rare earth metals or alloys (hereinafter referred to as rare earth metals) having the composition represented by R-M.
The present invention relates to a method for producing rare earth metals with high purity and at low cost.

(Prior Art and Problems to be Solved) As methods for smelting rare earth metals, a molten salt electrolysis method and a metal thermal reduction method are employed.

The former molten salt electrolysis method further includes a method using a halide (chloride) as an electrolytic bath, and a method using an oxide as an electrolytic bath, that is, a method in which an oxide is dissolved in a fluoride-based electrolytic bath. The main target is the smelting of light rare earth metals with low melting points.

On the other hand, the latter metal thermal reduction method includes a halide method in which fluoride or chloride is reduced with an alkali or alkaline earth metal, and a method in which oxides with high vapor pressure such as Sm, Eu, Yb, and Tm are reduced with La, Ce, etc. Alternatively, there is an oxide method in which it is reduced with Mitshu metal and deposited on the capacitor.

However, in the case of the above-mentioned molten salt electrolysis method, in order to prevent the cathode and electrolytic cell materials from being eroded by the deposited metal, it is necessary to use special and expensive materials such as Ta, W, and Mo. In addition, in the metal thermal reduction method, the retort and condenser of the reaction vessel are attacked by the metal produced by the reduction, resulting in contamination of the produced metal or extremely shortening the life of the material. There were disadvantages such as high cost.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, construct a reaction vessel with a cheaper material that is corrosion resistant to rare earth metals, and enable the production of rare earth metals with high purity and at low cost. Our goal is to provide the following.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have investigated various materials for forming the reaction vessel. We focused on steel materials that are cheaper than Ta, W, Mo, etc., and furthermore, we conducted a more detailed study of stainless steel, which is generally considered to have excellent corrosion resistance among steel materials, and found that ferritic stainless steel Generally, stainless steel has inferior corrosion resistance compared to austenitic stainless steel, so it is not very suitable as a material for chemical industrial equipment. However, surprisingly, it can be used in practical applications even under harsh conditions at high temperatures, such as when working with molten salts of halides, such as in the smelting of rare earth metals. We have discovered the fact that it exhibits excellent corrosion resistance without any problems, and based on this fact, we have confirmed through experiments that ferritic stainless steel can be used as a material for reaction vessels for producing rare earth metals of various compositions, and based on this we have developed the present invention.

That is, the gist of the present invention is that the composition represented by RM (where R: La, Ce, Pr, Nd, Sm
One or a combination of two or more rare earth metals such as, M: Fe
, weight percentage 80.0%≦R≦99.9%, 0.02
%≦M≦20.0%), the method is characterized in that ferritic stainless steel is used as a material for a reaction vessel.

The present invention will be explained in detail below based on examples.

The reaction vessel material used in the method of the present invention is ferritic stainless steel, but typical so-called 13cr steel,
Not only 18Crt[ and 25Crli but also various compositions with a higher or lower Cr content or other alloying elements may be used, and there are no particular limitations.

However, depending on which of the various methods listed above is adopted as the rare earth metal smelting method and the chemical composition of the rare earth metal to be smelted, in general, high Cr containing high Cr content is used.
It is more desirable to have an r-based composition, especially Cr26-30.
% is preferred.

For example, when y1 refining rare earth metals containing Fe,
Among ferritic stainless steels, one with a composition that is slightly less corrosion resistant than other stainless steels may be selected as the material for the reaction vessel, and the eluted Fe should be taken into account in the target composition of the rare earth metal (alloy). It is possible.

Such ferritic stainless steel may be used to constitute the entire reaction vessel, or may be used for a part thereof.

The target rare earth metal composition is Sm.

When one or more rare earth metals such as Nd, Ce, Pr, etc. are represented by R and Feti-M, R''-M is 80.0%≦R≦99.9%, 0.02% ≦M≦20
．． It is a rare earth metal with a composition of 0%.

In other words, the target is the smelting of alloys containing some M from pure rare earth metals, and in particular, R with M>20.0%.
In the case of producing rare earth metals with a -M composition, the present invention method not only results in an impractical composition but also alleviates the corrosive environment and dilutes the need to maintain high purity. It is not effective.

Note that other conditions in the smelting of rare earth metals are not particularly limited, but the reaction temperature may vary depending on the mode of the smelting method.
The temperature is preferably within the range of 50 to 1200°C,
The effects of the method of the present invention can be particularly expected.

(Example) Harmful.

In the external heat type electric furnace 4 shown in Fig. 1, JIS-8US4
47J1 ferritic stainless steel crucible and cathode 2
is inserted through the insulation material 3, and NdF, : LiF
10 kg of electrolytic bath 5 having a composition of: BaF, = 70: 20: 10 (wt%) was added and dissolved, 4 wt% of Nd, 03 was added and added, and the bath temperature was raised to 95%.
The graphite anode 1 was immersed in the temperature of 0°C, and 3~
Molten salt electrolysis was carried out for 35 hours at a voltage of 5 V and an anode current density of 0.5 to 1.2 A/aJ.

Note that the produced Nd has a melting point of 1024° C. and is precipitated in a solid state at the electrolysis temperature. Therefore, the produced Nd is replaced by Nd with a lower melting point.
In order to obtain a d-Fe alloy in a liquid phase at the electrolysis temperature, a predetermined amount of electrolytic iron powder is placed in a crucible at the beginning of electrolysis, and additional electrolytic iron powder is added over time according to the amount of electrolytic current. I entered.

As a result, 2.8 kg of metal having the quality shown in Table 1 could be obtained. Note that wear and tear on the crucible-cum-cathode was slight, and the lifespan of the crucible was extended 5 to 10 times compared to conventional iron crucibles.

Table 1 (wt%) When manufacturing metal Sm by the vision method in the retort furnace shown in Figure 2, the retort 7 is heat-resistant &H9 (JIS-G-!
5122-8CHI 8 equivalent), but J
In order to protect the raw material receiving tray 9 made of ferritic stainless steel of IS-3US447J 1 and the inner periphery of the retort 7, a thin plate 8 made of the same material is set as shown in the figure. Of course, samarium oxide (purity 96
%) and Mitsushmetal (commercially available).

Furthermore, the capacitor 6, which corresponds to the samarium metal precipitation part, was made of the same ferritic stainless steel.

Next, the pressure was reduced to a high vacuum of I x 10-' Torr or less, and the temperature was raised to 1180°C and maintained for 6 hours. As a result, from 22 kg of raw material, Sm metal 8.
1g was obtained.

This operation was repeated and used 50 times, but the damage to the retort was slight.

In addition, in FIG. 2, 10 indicates an exhaust port, 11 indicates an electric furnace, and 12 indicates a deposited Sm metal.

Table 2 (wt%) (Effects of the Invention) As detailed above, according to the present invention, ferritic stainless steel is used as a reaction vessel material in the production of rare earth metals with RM composition, so that the purity is high. Rare earth metals can be obtained by any smelting method at low cost. Furthermore, the discovery of new corrosion resistance properties of ferritic stainless steel is expected to expand its range of applications.

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic sectional views showing an example of a smelting apparatus used in an embodiment of the present invention. 1... Graphite electrode, 2... Container/cathode, 3... Heat insulating material, 4... Externally heated electric furnace, 5... Electrolytic bath,
6... Condenser, 7... Retort, 8...
・Thin plate. 9... Raw material saucer, 10... Exhaust port, 11... Electric furnace 12... Precipitated Sm metal.

Claims (1)

[Claims] 1 R-Fe (R: La, Ce, Pr, Nd, S
One or a combination of two or more rare earth metals such as m, weight percentage: 80.0%≦R≦99.9%, 0.02%
A method for smelting rare earth metals, the method comprising using ferritic stainless steel for a reaction vessel in the smelting of rare earth metals having a composition expressed by ≦Fe≦20.0%). 2. The method according to claim 1, wherein the refining reaction temperature is in the range of 850 to 1200°C. 3. The method according to claim 1, wherein the ferritic stainless steel is a high chromium ferritic stainless steel with a Cr content of 26% or more.