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: The method for recovering rare earth elements includes a step (S11) of disintegrating a mixture containing oxides of rare earth elements and metals of iron family elements by water treatment. For example, a rare earth element-containing composition is subjected to a treatment (heat treatment) of applying activation energy to the rare earth element-containing composition under an inert gas atmosphere or a vacuum atmosphere to obtain a mixture containing oxides of rare earth elements and metals of iron family elements (S10), the mixture is disintegrated by water treatment (S11), the mixture is separated into hydroxides of rare earth elements and metals of iron family elements by magnetic separation (S12), and rare earth elements are recovered from the hydroxides of rare earth elements by purification of non-magnetic substances after the magnetic separation (S13).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 rare earth elements according to the present invention includes a step of crushing a mixture containing oxides of rare earth elements and metals of iron group elements by water treatment. [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] 10 is a diagram showing the results of XRD measurement of a sintered body of an oxide of a rare earth element and a metal of an iron group element before and after water treatment in Example 2. FIG. 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, and is, for example, 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 alloys. The rare earth element-containing composition is, for example, a powder or granular material, 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 contains oxygen in its 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 crushing step S11 using water treatment, a magnetic separation step S12, and a rare earth element recovery step S13 by purifying non-magnetic materials after magnetic separation. 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 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 an iron group element. For example, a mixture of an oxide of the rare earth element and a metal of an iron group element can be obtained by heat treatment. The mixture of an oxide of the rare earth element and a metal of an iron group element may be, for example, a sintered body. Alternatively, the mixture may be a compact of an oxide of the rare earth element and a metal of an iron group element.

[0019] For example, rare earth elements may be represented by Re, iron group elements may be represented by Fe, and rare earth-containing compositions may be 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 NdFeB, 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] 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.

[0022] 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. Then, a second heat treatment at a second temperature higher than the first temperature grows metal particles of the iron group element.

[0023] The inert gas atmosphere in which the heat treatment is performed can be, for example, nitrogen, helium, neon, argon, or the like. The vacuum atmosphere in which the heat treatment is performed is, 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 process by refining the non-magnetic material after separation, as described below.

[0024] The heat treatment atmosphere is an inert gas atmosphere or a vacuum atmosphere as described above, and the oxygen concentration is controlled, preferably 1000 ppm or less. Specifically, the oxygen concentration of the heat treatment atmosphere is 300 ppm or more and 400 ppm or less. By controlling the oxygen concentration during the heat treatment, the rare earth element of the rare earth element-containing composition can react with oxygen contained in the rare earth element-containing composition to produce an oxide of the rare earth element and a metal of an iron group element, without the need for additional Nd.

[0025] [Disintegration process using water treatment] In the water treatment crushing step S11, the mixture obtained in the heat treatment step S10 is immersed in water to crush the mixture to a size that can be separated. In the water treatment crushing, the rare earth element oxides in the mixture of rare earth element oxides and iron group metals are reacted with water to become rare earth element hydroxides, which soften and pulverize the mixture. In the water treatment, the rare earth element oxides are converted into the Re hydroxides, which are the products of the above reaction formula (1), x O y In this case, the reaction shown in the following reaction formula (3) is considered to occur. Re x O y +yH2O→xRe(OH) 2y / x ···(3)

[0026] Specifically, in water treatment, when the oxide of a rare earth element is Nd2O3, which is the product of the above reaction formula (2), the reaction shown in the following reaction formula (4) is thought to occur. Nd2O3+3H2O →2Nd(OH)3···(4)

[0027] In water treatment, the oxides of rare earth elements react with water to become hydroxides of rare earth elements, which soften and easily disintegrate into powder in water, allowing them to be separated from the iron group metals.

[0028] The temperature of water in the water treatment is preferably 0°C or higher and 100°C or lower, and more preferably 30°C or higher and 60°C or lower. If the temperature is lower than 30°C, the reaction will be slow, and if the temperature exceeds 60°C, it is not preferable from the viewpoint of energy conservation. The water used in the water treatment may be water vapor at a temperature of 0°C or higher and 100°C or lower, preferably water vapor at a temperature of 30°C or higher and 100°C or lower, or superheated water vapor above 100°C.

[0029] The treatment time for the water treatment is not particularly limited, but is preferably 10 minutes to 48 hours. If it is less than 10 minutes, the crushing may be insufficient, and if it exceeds 48 hours, the crushing may be sufficient, which is not preferable.

[0030] In water treatment, for example, 3 A tank made of stainless steel, polyethylene resin, or Dilite (registered trademark) is used, and an amount of water is used that allows all or part of the mixture of rare earth element oxide and iron group element metal to be immersed. When water vapor or superheated steam is used as the water for water treatment, a gas such as air containing water vapor or superheated steam is used in an amount that allows the water vapor or superheated steam to come into contact with all or part of the surface of the mixture of rare earth element oxide and iron group element metal.

[0031] [Magnetic selection process] In the magnetic separation step S12, the crushed mixture obtained in the water treatment crushing step S11 is magnetically separated to separate it into non-magnetized materials containing rare earth element hydroxides and iron group element metals. Magnetic separation can be performed, for example, by bringing a magnet close to the crushed mixture to recover the magnetized materials and then filtering and separating the non-magnetized materials, repeatedly. The rare earth element hydroxides and iron group element metals naturally separate, and can be separated by methods other than magnetic separation, such as classification separation and gravity separation. After the rare earth element hydroxides and iron group element metals are separated, the iron group element metals are recovered. If the rare earth element-containing composition contains boron, the boron is recovered as a compound with the iron group element.

[0032] [Recovery process of rare earth elements by refining non-magnetic materials after magnetic separation] In the rare earth element recovery step S13, the non-magnetically separated material containing hydroxides of rare earth elements is purified. The rare earth element metal is isolated and recovered through purification. The non-magnetically separated material is purified as follows: For example, the non-magnetically separated material 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 convert it into an oxide of the rare earth element. The rare earth element metal is obtained from the obtained oxide of the rare earth element by, for example, molten salt electrolysis. In this way, the isolated rare earth element is recovered.

[0033] 2. Action and Effects According to the rare earth element recovery method of this embodiment, iron group elements are removed by magnetic separation, so large amounts of acid are not required, as in wet rare earth element recovery methods, resulting in low cost and 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 if the rare earth element-containing composition contains boron, 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. In this way, rare earth elements can be recovered inexpensively and without increasing environmental impact by reducing costs. Furthermore, by performing water treatment to crush the mixture after obtaining it, crushing can be performed at low cost without using mechanical crushing equipment such as a rod mill. Furthermore, since there is no need to heat the material to be treated to a high temperature that would melt the entire material, treatment costs can be reduced.

[0034] 3. Working Example The following describes experiments conducted to confirm the effects of the present invention.

[0035] 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. 14The crushed powder of B has oxidized particle surfaces and contains needle-shaped NdFeO3 particles. The shape and composition of the crushed powder and needle-shaped particles were confirmed by energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD).

[0036] In Experiment No. 1, the neodymium magnet sludge (2088 g) was placed in a reactor (a 70 L batch rotary kiln). After nitrogen replacement at 15 L / min for 1 hour, a first heat treatment was performed while flowing nitrogen at 5 L / min. The oxygen concentration in the furnace before heating was approximately 350 ppm. As the first heat treatment, heating was performed at 100°C for 37 minutes, followed by heating at 300°C for 30 minutes. A 500.6 g sample of the resulting rare earth element-containing composition after the first heat treatment was placed in a vacuum atmosphere heat treatment furnace, which was evacuated to 0.1 Pa, filled with nitrogen, and then nitrogen was flowed in at 1 L / min. As the second heat treatment, the temperature was increased at 300°C for 1 hour and maintained at 1500°C for 3 hours.

[0037] The first heat treatment was performed to induce a reaction in which rare earth elements were oxidized and iron-group elements were reduced. This first heat treatment removed gaseous components from the sludge. The generation of flammable white smoke was visually confirmed during the heat treatment. The second heat treatment was performed to grow and enlarge the particles of the iron-group element metal obtained in the first heat treatment. 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, there was almost no change in the weight of the sample before and after the second heat treatment, confirming that there was almost no adhesion or residue of the composition inside the furnace. The resulting sintered body of rare-earth element oxide and iron-group element metal is a solid body in which the rare-earth element oxide and iron-group element metal are tightly interlocked.

[0038] The obtained sintered body of rare earth element oxide and iron group metal (plate-shaped, approximately 5 cm on a side, 500.2 g) was crushed by water treatment by immersing it in 0.5 L of water at approximately 50°C for approximately 10 hours. No stirring was performed during the immersion. As a comparative example, the above sintered body of rare earth element oxide and iron group metal was crushed manually and then mechanically crushed using a rod mill. It was visually confirmed that the crushing by water treatment achieved crushing equal to or better than mechanical crushing. By immersing it in water without using a rod mill, crushing was possible at low cost.

[0039] The water after water treatment of the sintered body of rare earth element oxides and iron group metals was alkaline. It is believed that the disintegration by the water treatment described above caused the reaction shown in the following chemical formula (5). In formula (5), Nd2O3 / Fe represents the sintered body of Nd2O3 and Fe. Nd2O3 / Fe+3H2O→2Nd(OH)3+Fe ···(5)

[0040] Example 2 In Experiment No. 2, neodymium magnet sludge (2102 g) was used, and the heating temperature and time for the first heat treatment were 300°C for 1 hour, followed by 600°C for 1 hour. A 500.4 g sample of the resulting rare earth element-containing composition after the first heat treatment was used to obtain a sintered body of rare earth element oxide and iron-group element metal in the same manner as Experiment No. 1. The resulting sintered body of rare earth element oxide and iron-group element metal (plate-shaped, approximately 5 cm on a side, 497.3 g) was immersed in approximately 0.75 L of water at approximately 50°C for approximately 8 hours for crushing. After crushing, the sintered body was separated by magnetic separation into a non-magnetized material containing rare earth element hydroxide and a magnetized iron-group element metal, and an X-ray diffraction (XRD) test was performed. Figure 2 shows the XRD results for the magnetized iron-group metal (C) and the non-magnetized rare earth hydroxide (D). As a comparative example, Figure 2 also shows the results of XRD analysis for the rare earth-containing composition (A) after the first heat treatment obtained in Experiment No. 2 and the mechanically crushed sintered body (B) obtained by a rod mill using the rare earth-containing composition (499.4 g) after the first heat treatment obtained in Experiment No. 2, except that the temperature maintained for 3 hours in the second heat treatment was 1400°C. For the mechanically crushed rod milled product (B), XRD analysis was performed on the remaining powder after removing the clumps from the rod milled product through a 1 mm mesh sieve. Figure 2 shows the diffraction angles corresponding to Fe, Nd2O3, Nd(OH)3, and NdAlO3. In the sample without water treatment, peaks for Fe and Nd2O3 were confirmed, as shown in (A) and (B). After water treatment, as shown in (C), a peak of Fe was confirmed in the iron group metals that were magnetized, and as shown in (D), a peak of Nd(OH)3 was confirmed in the non-magnetized material.

[0041] 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.

[0042] In the method for recovering rare earth elements of the present invention, the mixture containing a rare earth oxide and an iron-group metal is not limited to a heat-treated rare earth-containing composition, but may also be a rare earth-containing composition containing a rare earth oxide, such as a mixture containing lanthanum oxide formed by the partial oxidation of the hydrogen storage alloy LaNi5 and metallic nickel. [Explanation of symbols]

[0043] S10 Heat treatment process S11 Crushing process by water treatment S12 Magnetic separation process S13 Recovery process of rare earth elements by refining non-magnetic materials after magnetic separation

Claims

1. The method includes a step of crushing a mixture containing an oxide of a rare earth element and a metal of an iron group element by water treatment. Methods for recovering rare earth elements.

2. a step of subjecting a rare earth element-containing composition containing the rare earth element, the iron group element, and oxygen to a treatment of applying activation energy in an inert gas atmosphere or a vacuum atmosphere to react the rare earth element with the oxygen, thereby obtaining the mixture. The method for recovering rare earth elements according to claim 1.

3. and separating the mixture disintegrated by the water treatment into non-magnetic materials and the iron group metals by magnetic separation. The method for recovering rare earth elements according to claim 1.

4. The mixture is a sintered body. The method for recovering rare earth elements according to claim 1.

5. The temperature of the water used in the water treatment is 0°C or higher and 100°C or lower. The method for recovering rare earth elements according to any one of claims 1 to 4.

6. The treatment time of the water treatment is 10 minutes or more and 48 hours or less. The method for recovering rare earth elements according to any one of claims 1 to 4.

7. The water treatment involves reacting water with the oxide of the rare earth element to produce the hydroxide of the rare earth element. The method for recovering rare earth elements according to any one of claims 1 to 4.

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