JPH06280081A - Production of rare-earth metal by electrolytic reduction - Google Patents

Abstract

PURPOSE:To obtain a producing method for a rare-earth metal by electrolytic reduction capable of stable operation over a long period by using a rare-earth oxide specified in average particle diameter as a raw material in producing a rare-earth metal material by electrolytic reduction method. CONSTITUTION:In producing the rare-earth metal or a rare-earth alloy by electrolytic reduction, the rare-earth oxide <=8mu (preferably 2-6mu) in particle diameter is used as the raw material. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu including Y are used as the rare-earth element. As a result, the producing method for the rare-earth element or alloy by electrolytic reduction high in productivity and capable of stable operation over a long period is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to adjustment of the particle size of a rare earth oxide as a raw material when a rare earth metal is produced by an electrolytic reduction method.

[0002]

2. Description of the Related Art Conventionally, the method for electrolytic reduction of rare earth metals is
It was general to carry out electrolytic reduction in the rare earth fluoride molten salt using a rare earth oxide as a raw material.

[0003]

However, it is difficult to balance the supply rate of the rare earth oxide as a raw material with an appropriate amount of current, and there has been no definitive solution.
The present invention intends to provide an improved method for electrolytic reduction production of rare earth metals with high productivity, which enables stable operation for a long period of time by a method which solves the above problems.

[0004]

In order to solve the above problems, the present inventors have focused on the particle size of a rare earth oxide as a raw material, found that a specific particle size range is effective, and completed the present invention. The main point is that the average particle size is 8 as a raw material.
A method for electrolytic reduction production of rare earth metals or rare earth alloys is characterized by using a rare earth oxide having a size of not more than μm.

The present invention will be described in detail below. A method for electrolytic reduction production of a rare earth metal or alloy using a rare earth oxide as a raw material is a mixed molten salt of the rare earth fluoride and stable Li, Ba or the like fluoride with respect to the rare earth metal or alloy as an electrolytic bath, Rare earth metals or alloys (hereinafter referred to as metals) that have been electrolyzed using Mo as a cathode and graphite as an anode and have been accumulated on the furnace bottom due to the difference in specific gravity are taken out of the system by a siphon and made into ingots. In this reaction, when the feed rate of the raw material oxide is higher than a certain limit, if the operation is continued for a long time, slag mainly composed of rare earth acid fluoride accumulates on the bottom of the furnace and the bottom of the furnace rises to make it impossible to continue the operation. Therefore, the metal production rate decreases corresponding to the raw material supply rate. On the other hand, below a certain limit, the anode effect phenomenon occurs, and stable energization becomes difficult. That is, the fluctuation of the voltage and current starts, and then the current sharply decreases. Therefore, in order to maintain a stable operation, it is necessary to prevent the accumulation of slag and stabilize the energization by maintaining an appropriate amount of current and a raw material supply rate.

The greatest feature of the present invention is that the influence of the particle size of the raw material rare earth oxide on the limit of the feed rate of the raw material oxide is found to be the most remarkable, and the average particle size is 8 μm or less, preferably Is preferably 2 to 6 μm. 8μ from the state of using the raw material of 8μm or less and continuing stable operation
When switching to a raw material of m or more, the operation becomes unstable within a few hours, and the slag accumulates on the bottom of the furnace, making it impossible to operate. On the other hand, it became clear that the operation became stable as the particle size became finer and could be continued for 7 days or more. At the same time, productivity increased. However, if it is less than 1 μm, when it falls from the raw material supply port to the surface of the electrolytic bath, a part of it falls on the electrolytically generated gas and is discharged to the outside of the furnace together with the gas, which is accompanied by recovery and recycling, which reduces the economic efficiency. .

The molten salt electrolytic reduction method using the rare earth metal oxide of the present invention as a raw material may be a conventionally known method, and the outline thereof is as follows. For example, the electrolytic cell is 1,000 mmφ x 1,20
It is an iron cylinder of 0 mmH, consisting of 6 graphite rods as an anode and 1 Mo rod as a cathode. The electrolytic bath is a mixture of rare earth fluoride corresponding to the raw material rare earth oxide with lithium fluoride and barium fluoride. , Keep the bath temperature at about 1,000 ℃ by energizing. If the raw material rare earth oxides are supplied little by little to this molten salt bath for electrolysis, the rare earth metal will accumulate at the bottom of the furnace.Therefore, insert a tapping tube, apply a vacuum, and suck it into the mold to cool it to form a rare earth metal ingot. Good.

The applicable range of the present invention is one selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y as a rare earth element. Rare earth metals and two or more kinds of rare earth alloys.

[0009]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Example 1) Electrolysis conditions: Electrolytic cell: 1,000 mmφ x 1,200 mmH, made of iron. Anode: 150mmφ × 6 pieces, made of graphite, immersion length: about 600mm. Cathode: 100 mmφ x 1, made of Mo, immersion length: about 500 mm. Tapping tube: 50mmφ, made of iron. Electrolysis bath: Composition; NdF ₃ -LiF-BaF ₂ (70, 20, 10% by weight each),
Bath melting point; about 900 ° C. Electrolysis temperature: 1,075 ± 10 ° C, current amount: 8.0KA constant current, raw material rare earth oxide; neodymium oxide, raw material supply rate: 10Kg
/ Hr, raw material average particle size; 15 μm, 8 μm, 6 μm, 4 μm,
Adjust 5 types of 1μm.

After a stable operation of neodymium oxide having an average particle size of 6 μm as a raw material under the above electrolysis conditions for 4 hours or more,
Switched to another particle size powder. In the case of 15 μm, the anode effect occurred 2 hours after switching, and the voltage fluctuated and became unstable. At this point, when the voltage value was changed and the corresponding amount of current was measured, 7 KA and 11 V were the limits. The raw material supply was increased to 12Kg / Hr until the current of 8.0KA could be maintained, and the metal yield was 8.7Kg / Hr.
However, after 72 hours, the rise of the bottom of the furnace became large and the operation was stopped. For the other four raw materials, the voltage was changed 4 hours after switching to determine a stable current amount, and a constant current of 8.0KA
, The raw material supply rate was 10.0 Kg / Hr, and it shifted to long-term operation. When it was 8 μm, it was unstable, and it recovered normally when spot-added 1 to 2 kg of raw material was added, but after 7 days, the rise of the furnace bottom became large and the operation was stopped. 6 μm and 4 μm had no abnormality even after 7 days or more, stable operation was possible, and the metal yield was 8.3 to 8.6 Kg / Hr. The above is summarized in Table 1.

[0011]

[Table 1] ────────────────────────────── Particle size Constant current Raw material supply rate Stable operation time Metal yield (μm) (KA ) (Kg / Hr) (Sun) (Kg / Hr) ────────────────────────────── 15 8 12 3 in 3 days Stop 8.7 8 8 10 Stop in 7 days 8.3 to 8.6 6 8 10 7 days or more Continue 8.3 to 8.6 4 8 10 7 days or more 8.3 to 8.6 1 8 10 7 days or more 8.3 to 8.6 ───────── ──────────────────────

Example 2 Electrolysis conditions: The electrolytic bath and electrolytic bath are the same as in Example 1. Electrolysis temperature: 1,075 ± 10 ° C, current amount: (8.0 + i) KA, raw material rare earth oxide; neodymium oxide, raw material supply rate: (10.0 + w) Kg / Hr, where w = 1.25 (= 1
0/8) × i (raw material supply speed / current amount) ratio is constant (1.
25). For the raw materials 6 μm, 4 μm, and 1 μm, the stable operation of Example 1 for 7 days or longer was continued, and then the operation was continued for 4 hours or longer under the condition that i and w were sequentially increased, and the maximum current amount in which the current fluctuation was not found was obtained. The operation was continued for 7 days or more without any abnormality at the raw material supply rate corresponding to the amount. Table 2 shows the current amount, the raw material supply rate, and the metal yield for each raw material in the latter seven days. As is clear from Table 2, 4
The productivity of μm was improved and the result was the best.

[0013]

[Table 2] ────────────────────────────── Particle size Current amount Raw material supply rate Stable operation time Metal yield (μm) (KA ) (Kg / Hr) (Sun) (Kg / Hr) ────────────────────────────── 6 8 10.0 7. Continued for more than a day 8.4 4 9 11.3 Continued for more than 7 days 9.5 1 9 12.0 Continued for more than 7 days 9.8 ────────────────────── ──────────

[0014]

Example 3 The raw material oxides were neodymium oxide to dysprosium oxide 10% by weight and neodymium oxide 90% by weight,
Operation was carried out under the same conditions as in Example 1 except that the composition of the electrolytic bath was changed to NdF ₃ -DyF ₃ -LiF-BaF ₂ (58, 12, 20, 10 wt% each).
The composition of the obtained metal was Dy10 and Nd90, respectively.

[0015]

According to the present invention, it is possible to provide a method for electrolytic reduction production of a rare earth metal or alloy which has high productivity and can be stably operated for a long period of time by specifying the particle size of the raw material rare earth oxide.

Claims (1)

[Claims] 1. A method for electrolytically reducing rare earth metal, which comprises using a rare earth oxide having an average particle size of 8 μm or less as a raw material when producing a rare earth metal or a rare earth alloy by an electrolytic reduction method.