JP6743629B2 - Method for separating both Dy and Tb from a processing object - Google Patents

Description

The present invention relates to a method of separating a heavy rare earth element Dy and a Tb from a processing target containing Tb.

It is well known that R-Fe-B permanent magnets (R is a rare earth element) are used in various fields today because of their high magnetic properties. Under such a background, a large amount of magnets are produced every day at the R-Fe-B system permanent magnet production plant. The amount of magnet scraps discharged as, and the amount of magnet processing scraps discharged as cutting scraps, grinding scraps, and the like is also increasing. In particular, since the magnets used therefor have been downsized due to the weight reduction and downsizing of information devices, the processing yield ratio has increased, and the manufacturing yield tends to decrease year by year. Therefore, how to recover and reuse metal elements, especially rare earth elements, contained in the magnet scraps and magnet processing wastes discharged during the manufacturing process will be an important technical issue in the future. There is. The same applies to how to recover and reuse the rare earth element as a circulating resource from an electric appliance or the like that uses an R-Fe-B based permanent magnet. Therefore, as a method for recovering a rare earth element from a processing object containing a rare earth element and an iron group element such as an R—Fe—B permanent magnet, after oxidizing the processing object, the processing environment is changed to carbon. Patent Document 1 proposes a method of separating a rare earth element as an oxide from an iron group element and recovering it by moving it to the presence and performing a heat treatment at a temperature of 1150° C. or higher.

The above method proposed in Patent Document 1 is excellent as a recycling system that requires low cost and simplicity, but the object to be treated is derived from, for example, an R-Fe-B based permanent magnet having a different composition. When a mixture of magnet scraps and magnet processing scraps containing light rare earth elements and heavy rare earth elements as rare earth elements, the rare earth element oxides separated and recovered from the iron group element are usually mixed with light rare earth elements and heavy rare earth elements. It is a complex oxide or mixture of oxides of rare earth elements. A complex oxide or a mixture of light rare earth elements and heavy rare earth elements can be separated into light rare earth element ions and heavy rare earth element ions by subjecting to a solvent extraction method proposed in Patent Document 2, for example. However, when the object to be treated contains Dy and Tb as heavy rare earth elements, the heavy rare earth element ions separated from the light rare earth element ions are a mixture of Dy ions and Tb ions. Separation of both can also be performed by using a solvent extraction method, but in order to separate both adjacent atomic numbers by the solvent extraction method, large-scale equipment and a large amount of extractant or organic solvent are required. Need.

International Publication No. 2013/018710 Japanese Unexamined Patent Publication No. 2-80530

Therefore, an object of the present invention is to provide a method for separating Dy and Tb without using a solvent extraction method.

The inventors of the present invention have conducted extensive studies in view of the above points, and as a result, by utilizing the difference in the ease of reduction of oxidized Tb by molten salt electrolysis based on the difference in the degree of oxidation, Dy and Tb It has been found that can be effectively separated.

A method for separating Dy and Tb from a treatment target containing Dy and Tb without using the solvent extraction method of the present invention made based on the above findings is a treatment including Dy and Tb as described in claim 1. A mixture of Dy ion and Tb ion prepared from an object is reacted with at least one precipitating agent selected from metal salts of oxalic acid, acetic acid, and carbonic acid to convert into a respective salt, A step of calcining the mixture in the presence of oxygen, and subjecting the obtained mixed oxide of Dy and Tb or a mixture of oxides ( including Tb ₄ O ₇ ) to molten salt electrolysis to reduce oxidized Dy It is characterized by comprising at least.
The method according to claim 2 is characterized in that, in the method according to claim 1, Dy and Tb are respectively derived from an R—Fe—B based permanent magnet.

According to the present invention, Dy and Tb can be separated by using the molten salt electrolysis method without using the solvent extraction method.

The method of separating both of the Dy and Tb-containing processing objects of the present invention is a method of preparing a mixture of Dy ions and Tb ions prepared from Dy and Tb-containing processing objects from metal salts of oxalic acid, acetic acid, and carbonic acid. After reacting with at least one selected precipitating agent to convert to each salt, the mixture of each salt is calcined in the presence of oxygen, and the obtained composite oxide or mixture of both oxides is It is characterized by comprising at least a step of reducing only oxidized Dy by electrolyzing molten salt.

The object to be treated containing Dy and Tb to which the method of the present invention can be applied is not particularly limited as long as it contains Dy and Tb as heavy rare earth elements, and light rare earth elements such as Nd and Pr, Fe, It may contain an iron group element such as Co or Ni, or boron. Specifically, for example, it is a mixture of magnet scraps and magnet processing scraps derived from R-Fe-B based permanent magnets having different compositions, and in addition to light rare earth elements such as Nd and Pr as rare earth elements, Dy and Tb are added. Examples include those that include.

In the method of the present invention, first, a mixture of Dy ions and Tb ions is prepared from an object to be treated containing Dy and Tb, and the obtained mixture of Dy ions and Tb ions is treated with a metal salt of oxalic acid, acetic acid, or carbonic acid. It is converted into the respective salt by reacting with at least one precipitating agent selected from As a method for preparing a mixture of Dy ions and Tb ions from an object to be treated containing Dy and Tb, the object to be treated containing Dy and Tb may be magnet scraps derived from R-Fe-B based permanent magnets having different compositions or In the case of a mixture of magnet processing scraps, which contains Dy and Tb in addition to light rare earth elements such as Nd and Pr as rare earth elements, for example, by the method described in Patent Document 1, a magnet scrap or a magnet processing object to be processed After oxidizing the mixture of scraps, the treatment environment is moved to the presence of carbon, and heat treatment is performed at a temperature of 1150° C. or higher to separate oxides of rare earth elements from iron group elements, A method of separating the mixture of Dy ions and Tb ions from the light rare earth element ions by subjecting the oxide of the rare earth element separated from the above to the solvent extraction method, for example, by the method described in Patent Document 2. The mixture of Dy ions and Tb ions separated from the light rare earth element ions in this way is reacted with at least one precipitating agent selected from metal salts of oxalic acid, acetic acid, and carbonic acid to be converted into respective salts. The metal salt of oxalic acid, acetic acid or carbonic acid (for example, sodium salt) can be used in such an amount that a precipitate composed of oxalate salt of Dy and Tb, acetate salt or carbonate salt can be obtained. Considering the standard amount of Dy and Tb contained in the R-Fe-B system permanent magnet, the metal salt of oxalic acid, acetic acid, and carbonic acid is 1 g of a mixture of the magnet scrap and the magnet processing waste to be treated (usually Of these, about 1 mass% to 5 mass% may be used in a ratio of, for example, 6 mg to 80 mg with respect to the total amount of Dy and Tb. The precipitation temperature may be, for example, 20°C to 85°C. The precipitation time may be, for example, 1 hour to 6 hours.

Next, the mixture of Dy and Tb salts obtained by the above method is calcined in the presence of oxygen to obtain a complex oxide or a mixture of Dy and Tb. What is important in the method of the present invention is that the complex oxide or the mixture of oxides of Dy and Tb needs to be obtained by firing the mixture of the salt of Dy and Tb in the presence of oxygen. It is known that oxidized Tb includes an oxide (Tb ₂ O ₃ ) having a low degree of oxidation and an oxide (Tb ₄ O ₇ ) having a high degree of oxidation. The difference in the degree causes the difference in the easiness of reduction of the oxidized Tb by the molten salt electrolysis, and the oxide with a low degree of oxidation is reduced by the molten salt electrolysis, but the oxide with a high degree of oxidation is melted. The present inventors have confirmed that they are not reduced by salt electrolysis. The method of the present invention takes advantage of this property of oxidized Tb to obtain a composite oxide of Dy and Tb or a mixture of oxides by firing in the presence of oxygen, so that Tb is sufficiently contained. Oxidation prevents oxidized Tb from being reduced by molten salt electrolysis, and only oxidized Dy is reduced by molten salt electrolysis, thereby separating Dy and Tb. The calcination of a mixture of Dy and Tb salt in the presence of oxygen to prepare a complex oxide or mixture of Dy and Tb in which Tb is sufficiently oxidized is performed in the presence of oxygen, for example, in the atmosphere. It is convenient to carry out the treatment at 500° C. to 1000° C. in an atmosphere. The firing temperature is preferably 600°C to 950°C, more preferably 700°C to 900°C. The firing time may be, for example, 1 hour to 6 hours.

The total content of Dy and Tb in the mixture of Dy and Tb complex oxides or oxides in which Tb is sufficiently oxidized is preferably 70 mass% or more, more preferably 75 mass% or more, and further 80 mass% or more. desirable. The complex oxide or the mixture of oxides of Dy and Tb may contain light rare earth elements, iron group elements, boron and the like as other elements in addition to oxygen, but the content of each of the other elements is 5. It is preferably 0 mass% or less, more preferably 3.0 mass% or less, and further preferably 1.0 mass% or less.

Molten salt electrolysis of the thus obtained complex oxide or mixture of oxides of Dy and Tb in which Tb is sufficiently oxidized is carried out by a molten salt electrolysis apparatus known per se, for example, in an electrolytic cell for holding molten salt. Inside, a columnar cathode made of tungsten, molybdenum, iron, etc., and a plurality of columnar or arcuate anodes made of graphite, etc., arranged facing the cathode, and a cylindrical shape surrounding the cathode. Can be carried out using an apparatus having the above anode (see, for example, JP-A-62-222095 if necessary). As the molten salt, for example, one composed of LiF, DyF _3, and TbF ₃ can be used, and BaF ₂ or the like may be added if necessary. When using one made of LiF, DyF ₃ and TbF ₃ as a molten salt, as is the composition, for example, LiF is 70mol% ~90mol%, DyF ₃ is 5mol% ~15mol%, TbF ₃ there is 5 mol% 15 mol% Can be mentioned. The electrolytic treatment may be performed, for example, at a temperature of 800° C. to 1200° C. by applying a voltage of 3V to 10V. The processing time is usually about 1 to 6 hours, although it depends on the processing amount and processing conditions. By performing the electrolytic treatment in this manner, only oxidized Dy is reduced at the cathode and deposited on the surface of the cathode as metal Dy or an alloy of Dy and Fe. On the other hand, fully oxidized Tb is not reduced at the cathode and remains in the molten salt, so that Dy and Tb can be separated. The metal Dy or the alloy of Dy and Fe deposited on the surface of the cathode can be reused as a raw material for the R—Fe—B system permanent magnet.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention should not be construed as being limited to the following description.

Test Example 1:
Brown powder Tb ₄ O ₇ purchased as a reagent was calcined in an inert gas (argon gas) atmosphere at 800° C. for 3 hours to obtain a milky white powder. This milky white powder was confirmed to be Tb ₂ O ₃ by X-ray diffraction analysis (apparatus used: D8 ADVANCE manufactured by Bruker AXS, the same applies hereinafter). The following experiment was conducted using these Tb ₄ O ₇ and Tb ₂ O ₃ .

7.5 g of each of Tb ₄ O ₇ and Dy ₂ O ₃ purchased as a reagent was added to a molten salt (total amount: 500 g) composed of 80 mol% of LiF, 10 mol% of DyF _{3 and} 10 mol% of TbF ₃ , and 900 At a temperature of °C, a voltage of 4 V was applied to carry out a molten salt electrolysis treatment for 3 hours. A graphite rod having a diameter of 8 mm was used as the anode, and an iron rod having a diameter of 8 mm was used as the cathode. After the completion of the treatment, the apparatus was cooled to room temperature and the contents of the electrolytic cell were taken out. As a result, the contents contained metal balls having a diameter of about 5 mm. Table 1 shows the results of SEM/EDX analysis of this metal ball A (apparatus used: S800 manufactured by Hitachi High-Technologies Corporation, the same applies hereinafter).

Next, molten salt electrolysis was performed in the same manner as above except that 7.5 g of Tb ₂ O ₃ was used instead of 7.5 g of Tb ₄ O ₇ , and after the treatment was completed, the apparatus was put into operation. After cooling to room temperature and taking out the contents of the electrolytic cell, the contents also contained metal balls having a diameter of about 5 mm. The results of SEM/EDX analysis of this metal ball B are shown in Table 2.

As is clear from Table 1, when Tb ₄ O ₇ having a high degree of Tb oxidation was subjected to electrolytic treatment with molten salt together with Dy ₂ O ₃ , the obtained metal spheres A were mainly composed of an alloy of Dy and Fe. Yes, Tb was not included. On the other hand, as is clear from Table 2, when Tb ₂ O ₃ having a low degree of Tb oxidation is subjected to molten salt electrolytic treatment together with Dy ₂ O ₃ , the obtained metal balls B are alloys of Dy, Tb and Fe. Was the main subject. The above results indicate that oxidized Tb has a difference in easiness of reduction by molten salt electrolysis based on a difference in the degree of oxidation, and by utilizing this property, the composite oxidation of Dy and Tb is performed. It has been found that by fully oxidizing Tb contained in the mixture of the substance or the oxide, only the oxidized Dy is reduced by the molten salt electrolysis, whereby Dy and Tb can be separated.

Example 1:
From a mixture of magnet scraps and magnet processing wastes derived from R-Fe-B-based permanent magnets having different compositions, which contains Dy and Tb in addition to light rare earth elements such as Nd and Pr as rare earth elements, Patent Document 1 An oxide of a rare earth element (a complex oxide or a mixture of oxides of Nd, Pr, Dy and Tb) was obtained according to the method described in 1. Next, the obtained oxide of a rare earth element was subjected to a solvent extraction method by the method described in Patent Document 2 to separate a mixture of Dy ions and Tb ions from a mixture of Nd ions and Pr ions. Oxalic acid dihydrate as a precipitating agent was added to a mixture of Dy and Tb ions (hydrochloric acid solution) separated from a mixture of Nd and Pr ions, and 1 g of a mixture of magnet scraps and magnet processing scraps to be treated. A mixture of Dy and Tb oxalate was obtained by adding 50 mg to the mixture and stirring at room temperature for 2 hours. The obtained mixture of Dy and Tb oxalate is calcined in an air atmosphere at 800° C. for 3 hours by using a commercially available calciner (KBF-624N1 manufactured by Koyo Thermo Systems Co., Ltd.) to obtain Dy and Tb. A complex oxide or a mixture of oxides was obtained (total of Dy content and Tb content by SEM/EDX analysis is about 85.8 mass %). In Test Example 1, except that instead of 7.5 g of Tb ₄ O ₇ and 7.5 g of Dy ₂ O ₃ in Test Example 1, 15 g of a mixture of Dy and Tb complex oxides or oxides was used. Molten salt electrolysis was performed in the same manner as in step 1, and after the treatment was completed, the equipment was cooled to room temperature and the contents of the electrolytic cell were taken out. As a result, the contents contained metal balls with a diameter of about 5 mm. Was there. Since the metal spheres were mainly composed of an alloy of Dy and Fe and did not contain Tb (by SEM/EDX analysis), it was found that Dy and Tb could be separated.

Comparative Example 1:
An experiment similar to that in Example 1 was performed, except that the mixture of Dy and Tb oxalate was calcined in an inert gas (argon gas) atmosphere at 800° C. for 3 hours. Although metal spheres having a diameter of about 5 mm were obtained, since these metal spheres were mainly composed of an alloy of Dy, Tb, and Fe (by SEM/EDX analysis), the oxalate of Dy and Tb was It was found that Dy and Tb could not be separated even if a molten salt electrolytic treatment was performed on the fired product obtained by firing the mixture in an inert gas (argon gas) atmosphere.

Example 2:
A metal sphere having a diameter of about 5 mm was obtained in the same manner as in Example 1 except that sodium carbonate was used as the precipitant instead of oxalic acid dihydrate. Since the metal spheres were mainly composed of an alloy of Dy and Fe and did not contain Tb (by SEM/EDX analysis), it was found that Dy and Tb could be separated.

INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that a method for separating Dy and Tb can be provided by using a molten salt electrolysis method without using a solvent extraction method.

Claims (2)

A method for separating Dy and Tb from a processing target containing Dy and Tb without using a solvent extraction method, wherein a mixture of Dy ions and Tb ions prepared from the processing target containing Dy and Tb is After reacting with at least one precipitating agent selected from metal salts of acids, acetic acid and carbonic acid to convert into respective salts, the mixture of the respective salts is calcined in the presence of oxygen to obtain Dy and Tb. A mixed oxide or a mixture of oxides ( including Tb ₄ O ₇ ) is subjected to molten salt electrolysis to reduce oxidized Dy. The method according to claim 1, wherein Dy and Tb are derived from an R-Fe-B based permanent magnet, respectively.