Method for recovering rare earth element

Abstract

To provide a method for recovering rare earth elements by which the rare earth elements can be recovered at a low cost by reducing the cost without increasing the environmental load.SOLUTION: Performing a treatment (heat treatment) of applying activation energy to a rare earth element-containing composition containing a rare earth element, an iron group element, and oxygen under an inert gas atmosphere or a vacuum atmosphere; A mixture containing oxides of rare earth elements and metals of iron group elements is obtained (S10), the mixture is separated into the metals of the iron group elements and the remainder excluding the metals of the iron group elements by pulverization and separation (S11), the oxides of the rare earth elements are recovered by purification of the remainder excluding the metals of the iron group elements after the separation, and the rare earth elements are recovered from the oxides of the rare earth elements (S12).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering rare earth elements. [Background technology]

[0002] Rare earth elements are widely used in rare earth magnets, hydrogen storage alloys, magnetic recording materials, giant magnetostrictive materials, and the like. For example, neodymium is used in neodymium magnets, which are one type of rare earth magnet. When materials containing rare earth elements are used for the above-mentioned applications, scrap or sludge containing rare earth elements is generated. There is a need for a method for recovering rare earth elements from rare earth element-containing compositions such as the above-mentioned scrap or sludge.

[0003] A wet process using an acid is known as a method for recovering rare earth elements from rare earth-containing compositions. In this wet process, rare earth elements can be separated into single elements by repeating acid treatment and solvent extraction.

[0004] Patent Document 1 discloses a method for separating and recovering rare earth element compounds and alloys composed of elements other than rare earth elements by blending rare earth metal scraps containing rare earth elements with sludge containing rare earth elements in a predetermined weight ratio and melting the mixture in a heating section of a melting furnace.

[0005] Patent Document 2 discloses a method for recovering rare earth elements, in which a material to be treated containing rare earth elements and iron-group elements is subjected to an oxidation treatment, the treatment environment is then changed to one in the presence of carbon black, and heat treatment is carried out at a temperature of 1000°C or higher in an inert atmosphere or in a vacuum, thereby separating the rare earth elements as oxides from the iron-group elements. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3716908 [Patent Document 2] International Publication No. 2014 / 104205 Summary of the Invention [Problem to be solved by the invention]

[0007] The wet method for recovering rare earth elements described above has the problem of high processing costs and a heavy environmental impact because it uses a large amount of acid that dissolves all elements.

[0008] In the method described in Patent Document 1, rare earth metal scraps containing rare earth elements are mixed with sludge containing rare earth elements, which requires the rare earth metal scraps to be prepared separately from the sludge to be treated, resulting in a problem of higher treatment costs due to the increased amount of rare earth elements. In addition, in the method described in Patent Document 1, the material to be treated is melted for treatment, which requires the addition of a large amount of energy, resulting in a problem of higher costs.

[0009] In the method described in Patent Document 2, when the material to be treated contains boron, if rare earth elements are separated as oxides from iron group elements by heat treatment in the presence of carbon black, the boron concentration in the wastewater increases, which poses a problem of high wastewater treatment costs.

[0010] Therefore, an object of the present invention is to provide a method for recovering rare earth elements that can reduce costs, recover rare earth elements inexpensively, and without increasing the environmental load. [Means for solving the problem]

[0011] The method for recovering a rare earth element according to the present invention includes the steps of: treating a rare earth element-containing composition containing a rare earth element, an iron group element, and oxygen with activation energy in an inert gas atmosphere or a vacuum atmosphere to react the rare earth element with the oxygen, thereby obtaining a mixture containing an oxide of the rare earth element and a metal of the iron group element; and recovering the oxide of the rare earth element by separating the mixture into the oxide of the rare earth element and the metal of the iron group element. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for recovering rare earth elements that can reduce costs, recover rare earth elements inexpensively, and without increasing the environmental load. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a flowchart illustrating a method for recovering rare earth elements according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the results of XRD measurement of the rare earth element-containing composition after heat treatment according to Example 1. [Figure 3] 10 is a scanning electron microscope photograph of the residue after acid treatment obtained in the purification of the non-magnetic material after separation in Example 3. [Figure 4] FIG. 10 is a diagram showing the results of XRD measurement of oxides of rare earth elements and residues after purification treatment in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1. Embodiment Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] The method for recovering rare earth elements according to this embodiment is a method for recovering rare earth elements from a composition containing rare earth elements.

[0016] (Rare earth element-containing composition) The rare earth element-containing composition to be processed for rare earth element recovery is a composition containing rare earth elements, iron-group elements, and oxygen. For example, it is a rare earth element-containing composition used in rare earth magnets such as NdFeB-based and SmCoFe-based, hydrogen storage alloys such as LaNi5-based, magnetic recording materials such as GdFe-based, TbFe-based, and GdCo-based, and giant magnetostrictive materials such as TbDyFe-based alloys. The rare earth element-containing composition is, for example, a powder, and scrap or sludge of the above-mentioned composition can be preferably used. In particular, sludge generated in the cutting process during the production of neodymium magnets can be preferably used. For example, the rare earth element-containing composition is obtained by drying magnet sludge stored underwater or the like in a low-oxygen atmosphere to obtain a powder, and contains oxygen in the composition due to the oxide film formed on the surface. When the rare earth element is represented by Re and the iron-group element is represented by Fe, Re α Fe β is the main component and Re δ Fe ε O ζ When the rare earth element-containing composition is NdFeB-based, Nd2Fe 14 The main component is B, and NdFeO3 is included on the surface.

[0017] (Method for recovering rare earth elements) 1, the method for recovering rare earth elements according to this embodiment includes a heat treatment step S10, a pulverization and separation step S11, and a rare earth element recovery step S12, which involves purifying the remaining portion after removing iron-group metals from the separated material. Each step will be described in detail below.

[0018] [Heat treatment process] In the heat treatment step S10, activation energy is applied to the rare earth element-containing composition in an inert gas atmosphere or a vacuum atmosphere. Examples of the activation energy application include heat treatment, discharge sintering, and plasma treatment. The activation energy causes the rare earth element of the rare earth element-containing composition to react with oxygen contained in the rare earth element-containing composition, resulting in the production of an oxide of the rare earth element and a metal of the iron group element. For example, a mixture of an oxide of the rare earth element and a metal of the iron group element is obtained by heat treatment. Preferably, a sintered body in which the oxide of the rare earth element and the metal of the iron group element are integrated is obtained. Alternatively, the mixture may be a compact of an oxide of the rare earth element and a metal of the iron group element.

[0019] The rare earth element is represented by Re, the iron group element is represented by Fe, and the rare earth element-containing composition is represented by Re. α Fe β +Re δ Fe ε O ζ When the reaction temperature is as shown in the formula (1), the reaction shown in the following formula (1) is thought to occur during the above heat treatment. As shown in formula (1), the rare earth elements are oxidized and the iron group elements are reduced. Re α Fe β +γRe δ Fe ε O ζ +E(activation energy) →ηRe x O y +θFe (1) (α, β, γ, δ, ε, ζ, η, θ, x, and y are constants determined when the rare earth element Re is identified.)

[0020] Specifically, when the rare earth element-containing composition is a NdFeB rare earth magnet, the reaction shown in the following reaction formula (2) is thought to occur during the heat treatment. As shown in reaction formula (2), Nd is oxidized and Fe is reduced. NdFe 14 B + 2NdFeO3 + E (activation energy) → 2Nd2O3 + FeB + 15Fe (2)

[0021] From the above reaction formula (1), when the content of the rare earth element (Re) in the rare earth element-containing composition is A mol, the rare earth element (Re) is oxidized to form the rare earth element oxide (Re x O y The amount of oxygen required to convert the rare earth element to Re2O3 is A·(y / x) mol. The oxygen content of the rare earth element-containing composition is preferably A·(y / x)·1.5 mol or less. If A·(y / x)·1.5 mol or more, the purity of the recovered rare earth element decreases. In particular, A·(y / x)·1.0 mol or less is preferable. An oxygen content of A·(y / x)·1.0 mol or less can prevent the iron-group element from being oxidized during heat treatment. For example, when the rare earth element-containing composition is an NdFeB-based rare earth magnet, when the rare earth element Re is oxidized to produce a rare earth element oxide represented by Re2O3, the amount of oxygen required to convert Re to Re2O3 is preferably A·(3 / 2) mol or less. Considering the recovery rate of the rare earth element, the lower limit of the oxygen content of the rare earth element-containing composition is preferably A·(y / x)·0.6 mol or more. The oxygen content within this range can be adjusted by drying the sludge of the rare earth-containing composition in an atmosphere with an appropriate oxygen concentration before the heat treatment process. For example, in the case of a NdFeB-based rare earth-containing composition, a rare earth-containing composition with an oxygen content within the above range can be obtained by drying magnet sludge stored in water in a low-oxygen atmosphere.

[0022] The heat treatment temperature is 100°C or higher. By setting the heat treatment temperature to 100°C or higher, a reaction can occur in which the rare earth element is oxidized and the iron group element is reduced. The heat treatment temperature is preferably 600°C or higher. Furthermore, the heat treatment temperature is 2200°C or lower, more preferably 1800°C or lower. By setting the heat treatment temperature to this value or lower, the above reaction can occur without melting the rare earth element-containing composition. Furthermore, from the viewpoint of energy conservation, the heat treatment temperature is particularly preferably 1600°C or lower. The heat treatment time is 1 hour or longer, more preferably 3 hours or longer. By setting the heat treatment time to this value or longer, the above reaction can occur. There is no particular upper limit to the heat treatment time, but from the viewpoint of energy conservation, it is preferable to set it to 6 hours or shorter.

[0023] The heat treatment is preferably carried out in two stages at different temperatures. For example, a first heat treatment at a first temperature causes a reaction in which the rare earth element is oxidized and the iron group element is reduced. Next, a second heat treatment at a second temperature higher than the first temperature grows metal particles of the iron group element. The first heat treatment may be carried out in two stages, heating at a low temperature followed by heating at a high temperature, or in one stage.

[0024] The inert gas atmosphere in which the heat treatment is performed may be, for example, nitrogen, helium, neon, argon, or the like. The vacuum atmosphere in which the heat treatment is performed may be, for example, 0.1 Pa or less. When the heat treatment is performed in a nitrogen atmosphere, some of the boron contained in the rare earth element-containing composition becomes boron nitride. Because boron nitride is insoluble in acid, it can be separated and recovered as a residue in a treatment with hydrochloric acid in the rare earth element recovery step, which is described below, in which the residue after separation is purified from the iron group element metals is removed.

[0025] The heat treatment is performed in an inert gas atmosphere or a vacuum atmosphere, as described above, with the oxygen concentration controlled, and the oxygen concentration may be 1000 ppm or less, or may be 300 ppm to 400 ppm. By controlling the oxygen concentration during the heat treatment, the rare earth element of the rare earth element-containing composition can be reacted with the oxygen contained in the rare earth element-containing composition to obtain an oxide of the rare earth element and a metal of an iron group element, without requiring additional Re such as rare earth metal scrap.

[0026] [Crushing and separation process] In the pulverization and separation step S11, the mixture is pulverized to a size that allows separation, and after pulverization, it is separated into iron-group element metals and the remainder excluding the iron-group element metals. The remainder excluding the iron-group element metals contains oxides of rare earth elements. The pulverization of the mixture can be performed, for example, mechanically. The crushing of the mixture may also be performed by a non-mechanical method. After separation of the iron-group element metals and the remainder excluding the iron-group element metals, the iron-group element metals are recovered. When the rare-earth element-containing composition contains boron, at least 50% or more of the boron is recovered as a compound with the iron-group element. Methods for separating the iron-group element metals from the rare-earth element-containing composition include, for example, magnetic separation, and other methods such as classification separation and gravity separation.

[0027] [Recovery process of rare earth elements by purifying the residue after removing iron group metals after separation] In the rare earth element recovery step S12, the separated residue excluding iron-group element metals is purified, containing rare earth element oxides. Rare earth element oxides are obtained by purification, and rare earth element metals are isolated and recovered from the obtained rare earth element oxides. The separated residue excluding iron-group element metals is purified as follows: For example, the separated residue excluding iron-group element metals is reacted with hydrochloric acid and filtered to separate it into a rare earth element solution and a residue. Next, the rare earth element solution is reacted with oxalic acid to produce a precipitate of rare earth element oxalate, which is then filtered and separated. The obtained rare earth element oxalate is calcined to obtain rare earth element oxides. Rare earth element metals are obtained from the obtained rare earth element oxides, for example, by molten salt electrolysis. In this way, the isolated rare earth elements are recovered.

[0028] When the rare earth element-containing composition contains boron and the heat treatment in the heat treatment step is carried out in a nitrogen atmosphere, part of the boron is converted into boron nitride during the heat treatment, and the obtained boron nitride is separated and recovered as a residue in the reaction between the remainder after excluding the iron group element metals after the above separation and hydrochloric acid.

[0029] 2. Action and Effects According to the method for recovering rare earth elements of this embodiment, iron-group elements are separated and removed by magnetic separation or the like, eliminating the need for large amounts of acid, as in wet rare earth element recovery methods, resulting in low cost and a low environmental impact. Furthermore, since no rare earth metal is required in addition to the rare earth element-containing composition to be treated, treatment costs can be reduced. Furthermore, even when boron is contained in the rare earth element-containing composition, boron is recovered as a compound with an iron-group element. Furthermore, if the heat treatment is performed under a nitrogen atmosphere, it is also recovered as boron nitride, thereby reducing the boron concentration in the wastewater and reducing wastewater treatment costs. Furthermore, since high temperatures that would melt the entire material to be treated are not required, treatment costs can be reduced. In this way, rare earth elements can be isolated and recovered inexpensively, reducing costs, and without increasing the environmental impact.

[0030] 3. Working Example The following describes experiments conducted to confirm the effects of the present invention.

[0031] Example 1 Neodymium magnet sludge was prepared as a rare earth element-containing composition. The neodymium magnet sludge was NdFe with a particle size of about 8 μm. 14 The crushed powder is composed of a composition with B as the main phase, and the particle surfaces are oxidized, resulting in needle-shaped NdFeO3 particles. The shape and composition of the crushed powder and needle-shaped particles were confirmed using energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The neodymium magnet sludge used was low-oxidation sludge, which was stored underwater and then dried in a low-oxygen atmosphere to produce a powder. The oxygen concentration of this low-oxidation sludge was 4.2-4.3 wt% (A·(y / x)·1.01).

[0032] The low-oxidation sludge of the neodymium magnet was subjected to the first heat treatment described below.

[0033] In Experiment No. 1, low-oxidation neodymium magnet sludge (2102 g) was placed in a reactor (a 70 L batch rotary kiln) and purged with nitrogen at 15 L / min for one hour. After that, the first heat treatment was carried out while nitrogen was flowing at 5 L / min. The oxygen concentration in the furnace before heating was approximately 350 ppm. For the first heat treatment, the sludge was heated at 300°C for one hour, followed by heating at 600°C for one hour.

[0034] In Experiment No. 2, low-oxidation sludge (2088 g) of neodymium magnet was used, and the same procedure as Experiment No. 1 was repeated except that the first heat treatment was performed at 100°C for 37 minutes, followed by 300°C for 30 minutes.

[0035] In the above Experiments No. 1 and No. 2, the temperature of the first heat treatment was set to two stages. The first heat treatment was performed to cause a reaction in which rare earth elements were oxidized and iron group elements were reduced. In the first heat treatment, gas components were removed from the low-oxidation sludge. In Experiments No. 1 and No. 2, the generation of flammable white smoke during the heat treatment was visually confirmed, confirming that the gas components had been removed from the low-oxidation sludge.

[0036] After the above heat treatment, a mixture containing oxides of rare earth elements and metals of iron group elements was recovered in Experiments No. 1 and No. 2. 1903 g was recovered in Experiment No. 1, for a recovery rate of 90.5%. 1983 g was recovered in Experiment No. 2, for a recovery rate of 92.8%. The decrease in recovery rate from 100% in Experiments No. 1 and No. 2 is thought to be due to the adhesion and residue of the composition inside the furnace. The recovery rate is expressed as a weight percentage of the amount recovered when the total mass of the low-oxidation sludge charged is taken as 100%.

[0037] X-ray diffraction (XRD) tests were performed on the mixtures containing rare earth element oxides and iron group metals in Experiments No. 1 and 2. Figure 2 shows the XRD measurement results, showing the rare earth element-containing composition before heat treatment (A), the mixture containing rare earth element oxides and iron group metals after heat treatment in Experiment No. 1 (B), and the mixture containing rare earth element oxides and iron group metals after heat treatment in Experiment No. 2 (C). Figure 2 shows the diffraction angles corresponding to Fe and Nd2O3.

[0038] In both Experiment No. 1 and Experiment No. 2, it was confirmed that oxides of rare earth elements (Nd2O3) and metals of iron group elements (Fe) were produced by the heat treatment.

[0039] From the above results, it is believed that in Experiments No. 1 and No. 2, the heat treatments caused a self-reaction represented by the following chemical formula (2). NdFe 14 B + 2NdFeO3 + E (activation energy) → 2Nd2O3 + FeB + 15Fe (2)

[0040] Example 2 In Experiment No. 3, the rare earth element-containing composition (499.0 g) obtained in Experiment No. 1 after the first heat treatment was placed in a vacuum atmosphere heat treatment furnace, which was then evacuated to 0.1 Pa and filled with nitrogen, after which nitrogen was introduced at a rate of 1 L / min. As the second heat treatment, the furnace was heated to 300°C / hour and maintained at 1600°C for 3 hours.

[0041] Experiment No. 4 was carried out in the same manner as Experiment No. 3, except that the rare earth element-containing composition (500.3 g) obtained in Experiment No. 2 after the first heat treatment was used.

[0042] Experiment No. 5 was carried out in the same manner as Experiment No. 3, except that the rare earth element-containing composition (499.4 g) obtained in Experiment No. 1 after the first heat treatment was used and the temperature maintained for 3 hours in the second heat treatment was 1400°C.

[0043] Experiment No. 6 was carried out in the same manner as Experiment No. 5, except that the rare earth element-containing composition (500.4 g) obtained in Experiment No. 2 after the first heat treatment was used.

[0044] Experiment No. 7 was carried out in the same manner as Experiment No. 3, except that the rare earth element-containing composition (500.4 g) obtained in Experiment No. 1 after the first heat treatment was used and the temperature maintained for 3 hours in the second heat treatment was 1500°C.

[0045] Experiment No. 8 was carried out in the same manner as Experiment No. 7, except that the rare earth element-containing composition (500.6 g) obtained in Experiment No. 2 after the first heat treatment was used.

[0046] The second heat treatment was carried out to grow and enlarge the particles of the iron-group element metal obtained in the first heat treatment. In Experiments 3 to 8, the second heat treatment caused particle growth of the iron-group element metal, resulting in a sintered body of rare earth element oxide and iron-group element metal. Furthermore, in Experiments 3 to 8, there was almost no change in the weight of the sample before and after the second heat treatment, and it was confirmed that there was almost no adhesion or residue of the composition inside the furnace.

[0047] Example 3 The sintered body of rare earth element oxides and iron group element metals obtained in Experiment No. 7 after the second heat treatment was pulverized and subjected to magnetic separation to separate the non-magnetic material containing rare earth element oxides from the iron group element metals, and the iron group element metals were recovered after magnetic separation. Boron contained in the low-oxidation sludge of the neodymium magnet was recovered as a compound with the iron group element.

[0048] Next, the non-magnetic material after magnetic separation, which contained rare earth element oxides, was purified. First, the non-magnetic material after magnetic separation was reacted with hydrochloric acid and filtered to separate it into a rare earth element solution and a residue. The resulting residue was analyzed by energy dispersive X-ray spectroscopy (SEM-EDS). Figure 3 shows an SEM image of the residue after acid treatment. The SEM image in Figure 3 was taken using a JEOL SEM (JMC-7000) under the following conditions: magnification: 2000x, signal: BED-C, input voltage: 15.0 kV, WD: 12.0 mm, probe current mode: High-PC, vacuum mode: Low Vac. SEM-EDS measurements were performed at two measurement points P1 and P2, indicated by white crosses on the black particles in Figure 3. The SEM-EDS results indicated the presence of particles with an atomic ratio of B to N of approximately 1:1 at both of these locations, confirming the presence of boron nitride in the residue. Next, the rare earth element solution was reacted with oxalic acid to produce a precipitate of rare earth element oxalate, which was then separated by filtration. The obtained rare earth element oxalate was calcined to obtain the rare earth element oxide. In this way, the rare earth element oxide was recovered.

[0049] X-ray diffraction (XRD) tests were performed on the rare earth element oxides finally obtained by calcining the oxalate salt obtained as described above, and on the residue obtained after treatment with hydrochloric acid during the purification process. Figure 4 shows the XRD measurement results after heat treatment, showing the final rare earth element oxide (D) and the residue obtained during the purification process (E). Figure 4 shows the rare earth element oxides (Fe, Nd2O3, Nd 0.7 Pr 0.3 The diffraction angles corresponding to AlO3 are shown.

[0050] Nd2O3 was detected in the final rare earth oxides. 0.7 Pr 0.3 AlO3 was detected.

[0051] Inductively coupled plasma (ICP) emission spectroscopy was performed on the low-oxidation sludge, the raw material for the sintered compact of rare earth oxides and iron-group metals obtained in Experiment No. 7, and on the magnetized and non-magnetized fractions after crushing and magnetic separation of the sintered compact. The boron concentrations were 0.79 wt% in the raw material for the sintered compact, 1.07 wt% in the magnetized fraction after magnetic separation, and 0.01 wt% in the non-magnetized fraction after magnetic separation. ICP emission spectroscopy was also performed on the filtrate generated during the filtration and separation of the oxalate precipitate in the rare earth element purification process. The boron concentration was 4 ppm. This value was below the wastewater standard value of 10 ppm, confirming that this example successfully reduced the boron concentration in wastewater.

[0052] Assuming that all of the boron had migrated from the magnetized material to the non-magnetized material after magnetic separation in the sintered body obtained in Experiment No. 7 above as Comparative Example 1, the boron concentration in the non-magnetized material after magnetic separation was calculated to be 1.79% by weight. When this non-magnetized material containing a high concentration of boron was purified as described above, the boron concentration in the filtrate obtained when the oxalate precipitate was filtered and separated was calculated to be 1600 ppm, which was higher than the wastewater standard value of 10 ppm.

[0053] The concentration of rare earth elements in the non-magnetized material obtained in Experiment No. 7 after pulverization and magnetic separation was determined by ICP optical emission spectroscopy to be 69.3% by weight. Calculations based on the concentration of rare earth elements in the non-magnetized material determined that the weight of non-magnetized material required to obtain 100 g of rare earth elements was 144.5 g, and the amount of hydrochloric acid required to purify the rare earth elements to obtain 100 g of rare earth elements was 335 g.

[0054] In Comparative Example 2, assuming that low-oxidation sludge that had not been heat-treated was treated with hydrochloric acid instead of the sintered body obtained in Experiment No. 7 to purify rare earth elements, the concentration of rare earth elements in the low-oxidation sludge was calculated to be 27.7 wt %. Based on this concentration, the weight of low-oxidation sludge required to obtain 100 g of rare earth elements was calculated to be 360.5 g, and the amount of hydrochloric acid required to obtain 100 g of rare earth elements was calculated to be 2090 g. In this example, by performing heat treatment before the pulverization and separation process, the amount of hydrochloric acid used was reduced to about one-sixth of the amount used when heat treatment was not performed.

[0055] 4. Variations The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention.

[0056] The method for recovering rare earth elements of the present invention is not limited to a method for recovering neodymium from scrap or sludge of neodymium magnets, but can also be applied to a method for recovering rare earth elements from scrap or sludge of other rare earth element-containing compositions containing rare earth elements, iron group elements, and oxygen. [Explanation of symbols]

[0057] S10 Heat treatment process S11 Crushing and separation process S12 A process for recovering rare earth elements by purifying the remainder after removing iron group metals after separation.

Claims

1. a step of providing activation energy to a rare earth element-containing composition containing a rare earth element, an iron group element, and oxygen in an inert gas atmosphere or a vacuum atmosphere to react the rare earth element with the oxygen, thereby obtaining a mixture containing an oxide of the rare earth element and a metal of the iron group element; and recovering the rare earth oxide by separating the mixture into the rare earth oxide and the iron group metal. Methods for recovering rare earth elements.

2. The rare earth element is represented by Re, and the oxide of the rare earth element produced by oxidizing the rare earth element is Re. ｘ O ｙ When the content of the rare earth element in the rare earth element-containing composition is A mol, the oxygen content of the rare earth element-containing composition is A·(y / x)·1.5 mol or less. The method for recovering rare earth elements according to claim 1.

3. The oxygen concentration in the atmosphere in the treatment for applying activation energy is 1000 ppm or less. The method for recovering rare earth elements according to claim 1.

4. The treatment for providing the activation energy to the rare earth element-containing composition is a heat treatment. The method for recovering rare earth elements according to any one of claims 1 to 3.

5. The temperature of the heat treatment is 100°C or higher and 2200°C or lower. The method for recovering rare earth elements according to claim 4.

6. The rare earth element-containing composition is scrap or sludge of a composition containing the rare earth element and the iron group element. The method for recovering rare earth elements according to any one of claims 1 to 3.

7. The rare earth element-containing composition contains boron, and the boron is recovered as a compound with the iron group element. The method for recovering rare earth elements according to any one of claims 1 to 3.

8. The inert gas atmosphere is a nitrogen atmosphere. The method for recovering rare earth elements according to any one of claims 1 to 3.

9. the rare earth-containing composition contains boron; in the step of obtaining a mixture containing an oxide of a rare earth element and a metal of an iron group element, the boron reacts with nitrogen in the nitrogen atmosphere to produce boron nitride, In the step of recovering the oxide of the rare earth element, the boron nitride is recovered. The method for recovering rare earth elements according to claim 8.

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