JPH06280077A - Production of rare-earth metal by electrolytic reduction - Google Patents

Abstract

PURPOSE:To economically produce rare-earth metals with high productivity by electrolytically reducing the fired material of an intermediate composition of the rare-earth carbonates and oxide obtained by firing rare-earth carbonates. CONSTITUTION:Rare-earth metals are produced by electrolytic reduction. In this case, the fired material of inexpensive and easy-to-obtain rare-earth carbonates consisting of Re2O2CO3 (Re is a rare-earth element) is used as the raw material. The fired material is obtained by firing rare-earth carbonates at about 500 deg.C, preferably at 500-700, for about 10min to 2hr. A molten salt bath mixed with rare-earth fluorides such as LiF and BaF2 is kept at about 1000 deg.C by applying current to electrolytically reduce the calcined rare-earth carbonates. The formed rare-earth metals accumulated on the furnace bottom is drawn off and cast into the ingot.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a raw material composition adjusting method for producing a rare earth metal 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, when the raw material rare earth oxide is supplied in a small amount, the anode effect is exerted, which makes it difficult to conduct electricity. Problems such as an increase in the number of phases are likely to occur, and improvement thereof has been desired. The solidified layer mainly consisting of oxyfluoride is not reactive with the generated rare earth metal, and functions as a reservoir for rare earth metal by forming a cell flying layer without the need for an expensive tantalum container. The increase leads to a decrease to disappearance of the rare earth metal accumulation portion, which is not preferable. The present invention is intended to provide a method for electrolytic reduction production of a rare earth metal which solves the above problems and which has a low raw material cost and high productivity.

[0004]

The present inventors have focused on rare earth carbonates in order to solve the above problems, found that an intermediate composition of carbonate and oxide is effective, and completed the present invention. The main point of this is to use a calcined product of a rare earth carbonate composed of the general formula Re ₂ O ₂ CO ₃ (where Re represents a rare earth element) as a raw material when producing a rare earth metal by the electrolytic reduction method. And a method for electrolytically reducing rare earth metals.

The present invention will be described in detail below. Rare earth carbonates, which are cheaper and easier to obtain than conventional rare earth oxide raw materials, can be obtained at 500 ° C or higher, preferably at 500-700 ° C for 10 minutes-
The greatest feature of the present invention is that a calcined product of the general formula Re ₂ O ₂ CO ₃ obtained by calcining for 2 hours is used as a raw material for the molten salt electrolytic reduction method. Below 500 ° C, carbonate Re ₂ (CO ₃ ) ₃
Is hardly decomposed, and when supplied as a raw material to a molten salt bath, CO ₂ is rapidly generated, and most of it is scattered, which is unsuitable. If the temperature exceeds 800 ° C, only the oxide Re ₂ O ₃ remains, which is no different from the conventional method using the conventional oxide as a raw material, and there is no merit. At 600 ± ℃, Re ₂ O ₂ CO ₃ is 100%, which is the optimum condition. In the molten salt electrolytic reduction method, Re ₂ O ₂ CO ₃ gives good results because one molecule of CO ₂ is combined with Re ₂ O ₃ .
It is presumed that ₂ O ₂ CO ₃ is supplied to the molten salt bath, and when heated rapidly to 1,000 ° C or higher, CO ₂ gas is appropriately generated, which promotes dissolution in the molten salt bath.

Here, Re represents a rare earth element, and the present invention is Y
It is applicable to one or more mixtures selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. , Especially suitable for Nd. The firing of the rare earth carbonate may be carried out in an electric furnace by putting the raw materials in a crucible if it is a batch system, and by using a rotary kiln if it is a continuous system. The rare earth carbonate is obtained, for example, by neutralizing a crude aqueous solution of rare earth chloride with ammonium carbonate and filtering and drying the precipitate.

The molten salt electrolytic reduction method using Re ₂ O ₂ CO ₃ as a raw material may be a conventionally known method, and the outline thereof is as follows. For example, the electrolytic cell is a 1,000 mmφ x 1,200 mmH iron cylinder, consisting of 6 graphite rods as the anode and 1 Mo rod as the cathode. It is a mixture of lithium and barium fluoride, and the bath temperature is kept at about 1,000 ° C by applying electricity. If the raw material rare earth carbonate is supplied little by little to this molten salt bath and electrolyzed,
Since the rare earth metal accumulates on the bottom of the furnace, a tapping tube is inserted, a vacuum is applied, suction is made, and it is poured into a mold and cooled to form a rare earth metal ingot.

[0008]

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) (Preparation of raw material for electrolysis) Nd carbonate was calcined at the following temperatures for an hour, and the crystal form of the calcined product was identified by X-ray. The results are as follows. A: 800 ° C ・ ・ ・ Nd ₂ O ₃ 100% B: 700 ° C ・ ・ ・ Nd ₂ O ₂ CO ₃ is mainly present, and a small amount of Nd ₂ O ₃ is observed. C: 600 ° C .... Nd ₂ O ₂ CO ₃ 100% D: 500 ° C .... Nd ₂ O ₂ CO ₃ is mainly present, and a small amount of NdCO ₃ .OH is observed.

(Electrolytic reduction) Molten salt electrolytic reduction was performed using the calcined product calcined at each of the above temperatures as a raw material. Electrolysis conditions Electrolyzer: 1,000mmφ x 1,200mmH, 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: NdF ₃ -LiF-BaF ₂ (70,20,10 wt% each), bath melting point: about 900 ° C. Raw material supply rate: 10.5 Kg / Hr in terms of Nd ₂ O ₃ . The results are shown in Table 1.

Comparative Example Commercially available Nd ₂ O ₃ (purity 95%)
Electrolytic reduction was performed under the same conditions as in Example 1 except that the above) was used. The results are also shown in Table 1.

[0011]

[Table 1]

[0012]

Industrial Applicability According to the present invention, it is possible to provide an economical and highly productive electrolytic reduction production method of rare earth metal by using Re ₂ O ₂ CO ₃ obtained by firing inexpensive rare earth carbonate as a raw material. it can.

Claims (1)

[Claims] 1. A method for producing a rare earth metal by an electrolytic reduction method, wherein a calcined product of a rare earth carbonate having a general formula Re ₂ O ₂ CO ₃ (wherein Re represents a rare earth element) is used as a raw material. A method for electrolytic reduction of rare earth metals.