Rare earth recovery device

Abstract

The objective is to provide a rare earth recovery device that can recycle the desired rare earth element from used rare earth magnets using lower energy. [Solution] The rare earth element recovery apparatus of the present invention comprises an evaporator in which a spent rare earth magnet containing a target rare earth element is placed inside, a recovery chamber communicating with the evaporator and in which a rare earth magnet precursor is placed inside, and an oxygen concentration reduction device. The evaporator heats the spent rare earth magnet to evaporate the target rare earth element from the spent rare earth magnet and separates it as vapor of the target rare earth element. The recovery chamber cools the vapor of the target rare earth element and supplies it to the surface of the rare earth magnet precursor, diffusing it into the interior of the rare earth magnet precursor to recover the target rare earth element. The oxygen concentration reduction device reduces the oxygen concentration of the atmosphere inside the evaporator and the recovery chamber to a concentration that prevents oxidation of the vapor of the target rare earth element.

Description

Technical Field

[0001] The present invention relates to a rare earth recovery device for recovering a target rare earth element from a used rare earth magnet containing the target rare earth element.

Background Art

[0002] In recent years, rare earth elements have been used in a wide range of fields as materials such as rare earth magnets used in motors of electric vehicles (EV, HV, PHV, etc.), and their demand is expected to increase in the future. On the other hand, rare earth elements are expensive and their production areas are concentrated in specific regions. Therefore, from the viewpoints of resource utilization and stable supply of rare earth elements, many recycling technologies for separating, recovering, and reusing rare earth elements from products such as rare earth magnets in which rare earth elements are used as materials have been developed. For example, a method for separating and recovering a rare earth element from a solid material containing at least one rare earth element and another substance, the method including a vacuum heating step of heating the solid material from one surface side in a vacuum atmosphere to form a solid-liquid coexistence product and selectively evaporating the rare earth element in the solid material, and a collection step of collecting the evaporated rare earth element in a solid state (Patent Document 1). Also, a recycling method is known that includes a melting step of melting the sludge (cutting powder during magnet production) of a sintered magnet, which is a rare earth magnet, with a melting furnace and cooling the molten metal to obtain a scrap alloy, a separation step of disposing the scrap alloy in a processing container and adjusting the temperature and water vapor pressure in the processing container to separate rare earth element oxides from the scrap alloy, and a recovery step of recovering rare earth element metals from the rare earth element oxides (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] Conventional rare earth element recycling technologies, particularly those that obtain rare earth elements as oxides, require the reduction of these oxides, resulting in high energy consumption during the reduction process. Furthermore, methods involving the dissolution of rare earth magnets require the magnets to be melted at high temperatures, such as 1200°C or higher, necessitating high energy consumption.

[0005] This invention has been made in view of these points, and its objective is to provide a rare earth recovery device that can recycle the desired rare earth element from used rare earth magnets with lower energy. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a rare earth element recovery apparatus comprising: an evaporator in which a spent rare earth magnet containing a target rare earth element is placed inside; a recovery chamber communicating with the evaporator and in which a rare earth magnet precursor is placed inside; and an oxygen concentration reduction device. The evaporator heats the spent rare earth magnet to evaporate the target rare earth element from the spent rare earth magnet and separates it as vapor. The recovery chamber cools the vapor of the target rare earth element and supplies it to the surface of the rare earth magnet precursor, diffusing it into the interior of the rare earth magnet precursor to recover the target rare earth element. The oxygen concentration reduction device reduces the oxygen concentration of the atmosphere inside the evaporator and the recovery chamber to a concentration that prevents oxidation of the vapor of the target rare earth element. [Effects of the Invention]

[0007] According to the present invention, the desired rare earth element can be recycled from used rare earth magnets with lower energy consumption. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of a rare earth recovery device according to the first embodiment. [Figure 2] (a) to (c) are schematic cross-sectional views illustrating the rare earth recovery method according to the first embodiment. [Figure 3] This is the vapor pressure curve of the elements contained in used rare-earth magnets. [Figure 4] This is a schematic cross-sectional view of a rare earth recovery device according to the second embodiment. [Figure 5] This graph shows the change in coercivity of rare earth magnets with respect to the heating temperature (temperature after heating) of the rare earth magnet precursor in Examples 1-3 and Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0009] The following describes embodiments of the rare earth recovery apparatus according to the present invention. First, the rare earth recovery apparatus according to the first embodiment and the rare earth recovery method according to the first embodiment using the apparatus will be described as examples. Figure 1 is a schematic cross-sectional view of the rare earth recovery apparatus according to the first embodiment. Figures 2(a) to 2(c) are schematic cross-sectional views showing the rare earth recovery method according to the first embodiment.

[0010] As shown in Figure 1, the rare earth recovery apparatus 1 according to the first embodiment comprises an evaporator 10, a recovery furnace 20 (recovery chamber), and an oxygen concentration reduction device 30. The evaporator 10 has a ceramic tube 10t, a spent magnet holder 10h arranged inside the ceramic tube 10t (inside the evaporator), and a high-frequency induction coil 10f surrounding the outer circumference of the ceramic tube 10t. An inlet 10c is provided on the side of the ceramic tube 10t of the evaporator 10 opposite to the recovery furnace 20, and the evaporator 10 further has a door 10d that can open, close, and seal the inlet 10c of the ceramic tube 10t. One or more spent rare earth magnets 10m are arranged on the upper surface of the spent magnet holder 10h inside the ceramic tube 10t of the evaporator 10. The recovery furnace 20 has a ceramic tube 20t, a precursor holder 20h arranged inside the ceramic tube 20t (inside the recovery furnace), and a high-frequency induction coil 20f surrounding the outer circumference of the ceramic tube 20t. The interior of the ceramic tube 20t of the recovery furnace 20 constitutes a recovery chamber (the interior of the recovery chamber). An inlet 20c is provided on the side of the ceramic tube 20t of the recovery furnace 20 opposite to the evaporator 10, and the recovery furnace 20 further has a door 20d that can open, close, and seal the inlet 20c of the ceramic tube 20t. One or more rare earth magnet precursors 20p are arranged on the upper surface of the precursor holder 20h inside the ceramic tube 20t of the recovery furnace 20. The ceramic tube 10t of the evaporator 10 and the ceramic tube 20t of the recovery furnace 20 are arranged so that their central axes coincide and are assembled so that their interiors communicate with each other via opposing communication ports 10ch and 20ch. The oxygen concentration reduction device 30 includes a vacuum pump 30p for evaporating the inside of the ceramic tubes 10t of the evaporator 10 and the ceramic tubes 20t of the recovery furnace 20, and an Ar gas supply device 30g for supplying Ar gas to the inside of the ceramic tubes 10t of the evaporator 10 and the ceramic tubes 20t of the recovery furnace 20.

[0011] A used 10m rare earth magnet contains the target rare earth element R T R2T contains Dy (dysprosium) together with Nd (neodymium) as the rare earth element R. 14This is a used RTB-type rare earth sintered magnet having crystal grains with a type B crystal structure and grain boundary phases surrounding the crystal grains. On the other hand, the rare earth magnet precursor 20p contains Nd and Pr (praseodymium) as the rare earth element R2T 14 This is an RTB-type rare-earth sintered magnet precursor having crystal grains with a type B crystal structure and grain boundary phases surrounding the crystal grains.

[0012] The rare earth recovery system 1 comprises a control device 2, a temperature sensor 3 for measuring the surface temperature of a spent rare earth magnet 10m, a temperature sensor 4 for measuring the surface temperature of a rare earth magnet precursor 20p, a pressure sensor 5 for measuring the atmospheric pressure inside the ceramic tubes 10t of the evaporator 10 and 20t of the recovery furnace 20 (inside the evaporator and recovery furnace), and an oxygen concentration meter 6 (for example, a zirconia oxygen concentration meter) for measuring the partial oxygen pressure inside the ceramic tubes 10t of the evaporator 10 and 20t of the recovery furnace 20. The measurement results from these temperature sensors, pressure sensors, and oxygen concentration meter are input to the control device.

[0013] Based on control by the control device 2, the evaporator 10 heats the spent rare earth magnet 10m to a temperature within the range of, for example, 1200°C to 1400°C using a high-frequency induction coil 10f, thereby bringing the spent rare earth magnet 10m into a molten or semi-molten state, evaporating Dy from the spent rare earth magnet 10m, and separating it as Dy vapor. Based on control by the control device 2, the recovery furnace 20 heats the rare earth magnet precursor 20p using a high-frequency induction coil 20f, adjusting the temperature of the rare earth magnet precursor 20p to a temperature within the range of, for example, 850°C to 950°C. In this way, Dy vapor is circulated from the inside of the ceramic tube 10t of the evaporator 10 to the inside of the ceramic tube 20t of the recovery furnace 20. The recovery furnace 20 adjusts the temperature inside the ceramic tube 20t (inside the recovery chamber) so that the Dy vapor cools down, and also adjusts the temperature of the rare earth magnet precursor 20p to a temperature at which grain boundary diffusion of Dy vapor occurs and grain coarsening is suppressed. This supplies Dy vapor to the surface of the rare earth magnet precursor 20p and diffuses it into the interior of the rare earth magnet precursor 20p by grain boundary diffusion. As a result, Dy is recovered by the rare earth magnet precursor 20p (rare earth magnet 20m). Based on the control by the control device 2, the oxygen concentration reduction device 30 reduces the pressure of the atmosphere inside the ceramic tube 10t of the evaporator 10 and the ceramic tube 20t of the recovery furnace 20 using a vacuum pump 30p and an Ar gas supply device 30g, and sets the oxygen partial pressure of the atmosphere to, for example, 10 -10 By reducing the temperature to below atm, the oxygen concentration in the atmosphere is lowered to a level where oxidation of Dy vapor can be avoided.

[0014] In the rare earth recovery method according to the first embodiment, first, as shown in Figure 2(a), in the rare earth recovery apparatus 1' before magnet placement, the door 10d of the evaporator 10 is opened, and one or more used rare earth magnets 10m are placed on the upper surface of the used magnet holder 10h inside the ceramic tube 10t from the inlet 10c. Furthermore, the door 20d of the recovery furnace 20 is opened, and one or more rare earth magnet precursors 20p are placed on the upper surface of the precursor holder 20h inside the ceramic tube 20t from the inlet 20c. Next, as shown in Figure 2(b), the doors 20d, 10d of the evaporator 10 and the recovery furnace 20 are closed, sealing the inlets 10c, 20c of the ceramic tubes 10t, 20t. This completes the fabrication of the rare earth recovery apparatus 1.

[0015] Next, as shown in Figure 2(b), the oxygen concentration reduction device 30 is used to evacuate the inside of the ceramic tubes 10t of the evaporator 10 and 20t of the recovery furnace 20 (the inside of the evaporator and recovery furnace) using a vacuum pump 30p. Then, Ar gas is supplied to the inside using an Ar gas supply device 30g, and the inside is evacuated again. This reduces the pressure of the atmosphere inside (Ar atmosphere), and the partial pressure of oxygen in the atmosphere is reduced to, for example, 10 -10 By reducing the temperature to below atm, the oxygen concentration in the atmosphere is lowered to a level where oxidation of Dy vapor can be avoided.

[0016] Next, as shown in Figure 2(b), in the evaporator 10, the spent rare earth magnet 10m is heated to a temperature within the range of, for example, 1200°C to 1400°C by the high-frequency induction coil 10f and held at that temperature for a predetermined time. Simultaneously, in the recovery furnace 20, the rare earth magnet precursor 20p is heated by the high-frequency induction coil 20f to adjust its temperature to a temperature within the range of, for example, 850°C to 950°C and held at that temperature for a predetermined time. In this way, the spent rare earth magnet 10m is brought to a molten or semi-molten state inside the ceramic tube 10t of the evaporator 10, Dy is evaporated from the spent rare earth magnet 10m, separated as Dy vapor, and the Dy vapor is circulated inside the ceramic tube 20t of the recovery furnace 20. Then, in the recovery furnace 20, the temperature inside the ceramic tube 20t (inside the recovery chamber) is adjusted so that the Dy vapor cools down, and the temperature of the rare earth magnet precursor 20p is adjusted to a temperature at which grain boundary diffusion of Dy vapor occurs and grain coarsening is suppressed. By cooling the Dy vapor, it is supplied to the surface of the rare earth magnet precursor 20p and diffused into the interior of the rare earth magnet precursor 20p by grain boundary diffusion. This is how the rare earth magnet 20m is manufactured.

[0017] Next, as shown in Figure 2(c), the door 20d of the recovery furnace 20 is opened, and the rare earth magnet 20m is removed from the entrance 20c of the ceramic tube 20t. By carrying out the rare earth recovery method as described above, the Dy from the spent rare earth magnet 10m is recovered using the rare earth magnet precursor 20p, and the rare earth magnet 20m is manufactured.

[0018] In the rare earth recovery apparatus according to the first embodiment, the oxygen concentration in the atmosphere inside the ceramic tubes of the evaporator and the recovery furnace is reduced to a concentration that prevents oxidation of Dy vapor. Then, Dy is evaporated from the spent rare earth magnet, separated as Dy vapor, and supplied to the surface of the rare earth magnet precursor. This allows Dy to be diffused into the rare earth magnet precursor without oxidation, thereby recovering Dy in the rare earth magnet precursor and manufacturing a rare earth magnet. Therefore, Dy separated as vapor from the spent rare earth magnet can be reused in the rare earth magnet by continuously diffusing it into the rare earth magnet precursor without going through the process of metallization to a solid phase. As a result, Dy can be recycled from spent rare earth magnets with lower energy consumption.

[0019] Furthermore, in the rare earth recovery apparatus according to the first embodiment, the temperature of the rare earth magnet precursor in the recovery furnace is adjusted to a temperature at which grain boundary diffusion of Dy vapor occurs and grain coarsening is suppressed, thereby diffusing Dy vapor into the interior of the rare earth magnet precursor by grain boundary diffusion. As a result, grain boundary diffusion occurs in which Dy vapor diffuses directly into the grain boundary phase of the rare earth magnet precursor as atoms without going through the process of deposition as a solid phase (deposited film). This makes it possible to preferentially induce grain boundary diffusion (diffusion into the grain boundary phase) over intra-grain diffusion (diffusion into the interior of the crystal grain) as the diffusion of Dy into the interior of the rare earth magnet precursor. In addition, diffusion of Dy from the grain boundary phase to the outer shell of the crystal grain can be promoted. Therefore, the supply of Dy to the grain boundary phase and the outer shell of the crystal grain, which contribute greatly to the improvement of coercivity when Dy is supplied, can be increased, and the supply of Dy to the central part of the crystal grain, which contributes little to the improvement of coercivity and causes a decrease in residual magnetization when Dy is supplied, can be suppressed. Furthermore, the coercivity of the rare-earth magnet precursor does not decrease due to grain coarsening. Therefore, when manufacturing rare-earth magnets by diffusing Dy into the rare-earth magnet precursor, it is possible to improve the coercivity of the rare-earth magnet while suppressing the decrease in residual magnetization. Next, the configuration of the rare-earth recovery apparatus according to the embodiment will be described in more detail.

[0020] The rare earth recovery device is not particularly limited as long as it includes an evaporation furnace, a recovery chamber communicating with the evaporation furnace, and an oxygen concentration reduction device. The evaporation furnace has the target rare earth element R T The used rare earth magnet containing is disposed therein, and by heating the used rare earth magnet, the target rare earth element R T is evaporated and separated as vapor of the target rare earth element R T and is not particularly limited as long as it can be separated as vapor.

[0021] The used rare earth magnet is not particularly limited as long as it is a used rare earth magnet containing the target rare earth element R T The target rare earth element R T is not particularly limited as long as it is a rare earth element that can improve magnetic properties such as coercive force by diffusing into the interior of the rare earth magnet precursor. For example, it is one or more elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among them, one or more elements selected from the group consisting of Dy, Tb (terbium), and Ho (holmium) are preferable, and Dy is particularly preferable. This is because the coercive force can be effectively improved by diffusing into the interior of the rare earth magnet precursor. In particular, in the case of Dy, since the vapor pressure is high, it is easy to evaporate preferentially by heating the magnet and recover it as vapor of Dy (a part of the vapor in which Dy is concentrated). Here, FIG. 3 is a vapor pressure curve of the elements contained in the used rare earth magnet. As shown in FIG. 3, the vapor pressure of Dy is significantly higher than that of Nd, Tb, and Fe.

[0022] The used rare earth magnet may be a used rare earth sintered magnet or a used hot-worked magnet. The used rare earth sintered magnet may be a magnet containing the target rare earth element R T by including it in the powder compact before sintering, or the target rare earth element R T may be diffused into the interior of the sintered body of the powder compact to contain R T and R TA magnet containing the same may also be used. Examples of used rare-earth sintered magnets include those containing rare-earth element R, transition metal element T, and boron B as basic components, and having R2T containing rare-earth element R 14 A used R-T-B-based rare-earth sintered magnet having crystal grains (main phase) with a 14 -type crystal structure and a grain boundary phase existing around the crystal grains, wherein at least one of the crystal grains and the grain boundary phase contains R T Examples of such magnets include those containing R. The used R-T-B-based rare-earth sintered magnet is not particularly limited, but a used R-T-B-M-based rare-earth sintered magnet further containing element M may also be used. The rare-earth element R may be one or more elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. For example, one or more elements selected from Nd and Pr, and one or more elements selected from R T which are Dy, Tb, and Ho are preferable. Among them, Nd and R T which is Dy is particularly preferable. The transition metal element T is preferably one or more elements selected from the group consisting of Fe and Co. The element M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as inevitable impurity elements.

[0023] As the temperature for heating the used rare-earth magnet, for example, as the used rare-earth magnet, the overall composition in molar ratio is represented by the formula (R 1 (1-d) Dy d ) a (Fe (1-e) Co e ) (100-a-b-c) B b M c (wherein R 1 is one or more elements selected from the group consisting of Nd, Pr, Ce, and La, and 12 ≤ a ≤ 20, 5 ≤ b ≤ 7, 0 ≤ c ≤ 2, 0 < d ≤ 0.5, and 0 ≤ e ≤ 0.3). Such as a used R-T-B-based rare-earth sintered magnet containing Nd and Dy as rare-earth elements R, etc., of R2T 14A used RTB-type rare earth sintered magnet having crystal grains and grain boundary phases with a type B crystal structure is used to obtain the target rare earth element R T If the material is Dy, a temperature range of, for example, 1200°C to 1400°C is preferable. This is because a temperature above the lower limit of this range allows for efficient evaporation of Dy, and because oxygen in the atmosphere inside the evaporator and recovery furnace is drawn into the molten metal produced by heating the used rare earth magnets, thereby reducing the oxygen concentration in the atmosphere. Furthermore, a temperature below the upper limit of this range ensures a sufficient proportion of Dy vapor in the vapor generated from the rare earth sintered magnets, while also suppressing the energy required for heating.

[0024] As the evaporator, for example, it may be a high-frequency induction furnace having a high-frequency induction coil for heating the spent rare-earth magnets, as in the first embodiment, but it may also be an electric furnace having a heater for heating the atmosphere inside the furnace.

[0025] The recovery chamber is connected to the evaporator, and a rare earth magnet precursor is placed inside it. The target rare earth element R flows from the inside of the evaporator to the inside of the recovery chamber. T By cooling the vapor and supplying it to the surface of the rare earth magnet precursor, and diffusing it into the interior of the rare earth magnet precursor, the target rare earth element R is supplied. T It is not limited to anything that recovers the material.

[0026] As a rare earth magnet precursor, the target rare earth element R T The precursor is not particularly limited as long as it can be used to manufacture rare earth magnets with improved magnetic properties such as coercivity by supplying vapor to the surface and diffusing it into the interior. The rare earth magnet precursor may be a rare earth sintered magnet precursor or a hot-worked magnet precursor. The rare earth sintered magnet precursor is not particularly limited, but is usually a sintered body of a powder molded body with the target rare earth element R inside. T This is a precursor that allows for the production of rare-earth sintered magnets with improved magnetic properties by diffusing the element. Examples of rare-earth sintered magnet precursors include R2T, which contains rare-earth element R, transition metal element T, and boron B as basic components, and also contains the rare-earth element R.14 Examples include RTB-type rare earth sintered magnet precursors having crystal grains (main phase) with a type B crystal structure and grain boundary phases surrounding the crystal grains. The RTB-type rare earth sintered magnet precursor is not particularly limited, but it may also be an RTB-type rare earth sintered magnet precursor containing element M. The rare earth element R may be one or more elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, but for example, one or more elements selected from Nd and Pr are preferred, and Nd and Pr are particularly preferred. The transition metal element T is preferably one or more elements selected from Fe and Co, for example. The element M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements.

[0027] The above-mentioned rare earth element recovery apparatus includes a recovery furnace, the interior of which constitutes the recovery chamber, and the recovery furnace recovers the target rare earth element R T By adjusting the temperature inside the recovery chamber so that the vapor cools down, the target rare earth element R T Preferably, the vapor is supplied to the surface of the rare earth magnet precursor and diffused into the interior of the rare earth magnet precursor. Among the recovery furnaces, the rare earth element R for the above purpose is preferred. T The temperature inside the recovery chamber is adjusted so that the vapor cools down, and the temperature of the rare earth magnet precursor is adjusted to the temperature of the target rare earth element R. T By adjusting the temperature to one in which vapor diffusion at grain boundaries occurs and grain coarsening is suppressed, the rare earth element R for the above purpose can be obtained. T It is preferable to diffuse the vapor into the interior of the rare earth magnet precursor by grain boundary diffusion. Here, "the target rare earth element R T The temperature at which grain boundary diffusion of vapor occurs and grain coarsening is suppressed is defined as the temperature at which R supplied to the surface of the rare earth magnet precursor. T This refers to a temperature at which grain boundary diffusion occurs, in which the vapor (gas phase) directly diffuses as atoms into the grain boundary phase of the rare earth magnet precursor without going through the process of deposition as a solid phase (deposited film), and at a temperature at which grain coarsening is suppressed so as not to cause a decrease in coercivity in the rare earth magnet precursor.

[0028] The target rare earth element R T As a temperature at which grain boundary diffusion of vapor occurs and grain coarsening is suppressed, for example, as a rare earth magnet precursor, the overall composition in molar ratio is given by the formula (Nd (1-x) Pr x ) u (Fe (1-y) Co y ) (100-u-v-w) B v M w R2T, such as RTB-type rare earth sintered magnet precursors, which contain one or more elements selected from Nd and Pr as the rare earth element R (where 12≦u≦20, 5≦v≦7, 0≦w≦2, 0≦x≦0.5, and 0≦y≦0.3). 14 When using an RTB-based rare earth sintered magnet precursor having crystal grains and grain boundary phases having a type B crystal structure, a temperature range of, for example, 850°C to 950°C is preferred. This temperature being above the lower limit of this range ensures that the target rare earth element R T This is because grain boundary diffusion easily occurs, in which the vapor (gas phase) directly diffuses as atoms into the grain boundary phase of the rare earth magnet precursor without going through the process of precipitation as a solid phase (deposited film). Furthermore, because the temperature is below the upper limit of this range, a decrease in the coercivity of the rare earth magnet precursor due to grain coarsening is less likely to occur.

[0029] As for recovery reactors, R T The recovery furnace is not particularly limited as long as it has a heating device that can adjust the temperature inside the recovery furnace (inside the recovery chamber) and the temperature of the rare earth magnet precursor so that the steam is cooled and supplied to the surface of the rare earth magnet precursor and diffused into the interior of the rare earth magnet precursor. For example, as in the first embodiment, it may be a high-frequency induction furnace having a high-frequency induction coil (heating device) that adjusts the temperature inside the recovery furnace by heating the rare earth magnet precursor and adjusting its temperature, or it may be an electric furnace having a heater (heating device) that adjusts the temperature of the rare earth magnet precursor by heating the inside of the recovery furnace and adjusting its temperature. Note that the recovery chamber does not have to be formed from the inside of the recovery furnace, R TBy cooling the vapor, it can be supplied to the surface of the rare earth magnet precursor and diffused into the interior of the rare earth magnet precursor, R T Alternatively, the steam may be used to dissipate heat into the atmosphere inside the recovery chamber and into the rare earth magnet precursor.

[0030] The above-mentioned oxygen concentration reduction device reduces the oxygen concentration of the atmosphere inside the evaporator and the recovery chamber to the target rare earth element R T The method is not particularly limited as long as it reduces the concentration of the vapor to a level where oxidation can be avoided, for example, the target rare earth element R T If the oxygen partial pressure is Dy, etc., the oxygen partial pressure of the atmosphere inside the evaporator and the recovery chamber should be set to 10 -10 By reducing the oxygen concentration in the atmosphere to below atm, the target rare earth element R T Preferably, the concentration of the vapor is reduced to a level where oxidation can be avoided, and in particular, the partial pressure of oxygen in the atmosphere is set to 10 -20 By reducing the oxygen concentration in the atmosphere to below atm, the R T It is preferable to reduce the concentration of the vapor to a level where oxidation can be avoided, because it can effectively suppress the oxidation of Dy. Furthermore, as an oxygen concentration reduction device, it is preferable to reduce the pressure of the atmosphere inside the evaporator and the recovery chamber to 8 Pa or less, and among these, it is preferable to reduce the pressure of the atmosphere to 4 Pa ​​or less. From used rare earth magnets R T This is because it can accelerate evaporation.

[0031] Examples of oxygen concentration reduction devices include, as in the first embodiment, a device having a vacuum pump for evaporating the inside of the evaporator and recovery chamber, and an inert gas supply device for supplying an inert gas such as Ar gas or N2 gas to the inside of the evaporator and recovery chamber.

[0032] Figure 4 is a schematic cross-sectional view of a rare earth recovery apparatus according to the second embodiment. The rare earth recovery apparatus 51 according to the second embodiment is further equipped with a valve 40 that can open and close the flow path between the inside of the ceramic tube 10t of the evaporator 10 (inside the evaporator) and the inside of the ceramic tube 20t of the recovery furnace 20 (inside the recovery furnace), in addition to the configuration of the rare earth recovery apparatus 1 according to the first embodiment, based on control by the control device 2. The rare earth recovery method according to the second embodiment using the rare earth recovery apparatus 51 is the same as the rare earth recovery method according to the first embodiment, except that in the recovery furnace 20, when adjusting the temperature inside the ceramic tube 20t so that the Dy vapor cools down, a process is performed to pressurize the atmosphere inside the ceramic tube 20t of the recovery furnace 20. In this process, with the flow path closed by the valve 40, the oxygen concentration reduction device 30 (pressurization device) supplies Ar gas to the inside of the ceramic tube 20t of the recovery furnace 20 by the Ar gas supply device 30g, thereby pressurizing the atmosphere inside the ceramic tube 20t of the recovery furnace 20. This facilitates the process of supplying Dy vapor to the surface of the rare earth magnet precursor 20p. The rare earth recovery apparatus may further include, as in the second embodiment, a valve capable of opening and closing the flow path between the inside of the evaporator and the inside of the recovery chamber (inside the recovery furnace), and a pressurizing device capable of pressurizing the inside of the recovery chamber. By pressurizing the inside of the recovery chamber, the target rare earth element R can be recovered. T The vapor can be supplied to the surface of the rare earth magnet precursor, or R T This is because it can accelerate the process of supplying the vapor to the surface of the rare earth magnet precursor.

[0033] The rare earth recovery method using the rare earth recovery apparatus, as in the first embodiment, uses the oxygen concentration reduction device to reduce the oxygen concentration of the atmosphere inside the evaporator and the recovery chamber to the target rare earth element R. T The process involves reducing the oxygen concentration to a level where oxidation of the vapor can be avoided, and heating the used rare earth magnet using the above-mentioned evaporator, thereby releasing the target rare earth element R from the used rare earth magnet. T Evaporate the above-mentioned rare earth element R T A separation process separates the element as vapor, and the recovery chamber recovers the target rare earth element R TBy cooling the vapor and supplying it to the surface of the rare earth magnet precursor, and diffusing it into the interior of the rare earth magnet precursor, the target rare earth element R is supplied. T The separation step and recovery step include a recovery step for recovering the oxygen concentration of the atmosphere by the oxygen concentration reduction step, and the oxygen concentration of the atmosphere is reduced by the oxygen concentration reduction step. T With the concentration of the vapor reduced to a level where oxidation can be avoided, R is extracted from the above-mentioned used rare earth magnet. T Evaporate R T It is separated as vapor, R T Alternatively, the vapor may be cooled and supplied to the surface of the rare earth magnet precursor, and then diffused into the interior of the rare earth magnet precursor. [Examples]

[0034] The rare earth recovery apparatus according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0035] [Example 1] The rare earth recovery method was carried out by fabricating and using an example of the rare earth recovery apparatus according to the first embodiment described above. In this case, first, a rare earth recovery apparatus before magnet placement was prepared, which included an evaporator before magnet placement, a recovery furnace (recovery chamber) before magnet placement, and an oxygen concentration reduction device. Next, the overall composition was Nd: 23.5% by weight, Dy (the target rare earth element R TThree spent rare earth magnets were prepared, each having a rectangular parallelepiped shape and a composition of 5% Nd, 5.7% Pr, 1% Fe, 2% Co, 0.16% Cu, 0.47% Al, and 0.97% B. In addition, one rare earth magnet precursor was prepared, also having a rectangular parallelepiped shape and a total composition of 24.8% Nd, 5.7% Pr, 1% Fe, 1% Co, 0.5% Cu, 0.1% Al, 0.4% Ga, and 0.97% B by weight. Next, in the rare earth recovery apparatus before magnet placement, the evaporator door was opened, and the prepared spent rare earth magnets were placed on the upper surface of the spent magnet holder inside the ceramic tube through the inlet. Furthermore, the recovery furnace door was opened, and the prepared rare earth magnet precursor was placed on the upper surface of the precursor holder inside the ceramic tube through the inlet. Next, the doors of the evaporator and recovery furnace were closed, sealing the inlets of the ceramic tubes. This allowed us to create a rare earth element recovery device.

[0036] Next, using an oxygen concentration reduction device, the insides of the ceramic tubes of the evaporator and the ceramic tubes of the recovery furnace (the insides of the evaporator and recovery furnace) were evacuated using a vacuum pump. Then, Ar gas was supplied to the inside using an Ar gas supply device, and the inside was evacuated again. As a result, the pressure of the internal atmosphere (Ar atmosphere) was reduced to 4 Pa, and the partial pressure of oxygen in the atmosphere was reduced to a concentration in which oxidation of Dy vapor could be avoided.

[0037] Next, in the evaporator, the spent rare earth magnets were heated to 1300°C using a high-frequency induction coil and held at 1300°C for 30 minutes. Simultaneously, in the recovery furnace, the rare earth magnet precursor was heated using a high-frequency induction coil, and its temperature was adjusted to 850°C and held at that temperature for 30 minutes. In this way, the spent rare earth magnets were brought into a molten state inside the ceramic tube of the evaporator, Dy was evaporated from the spent rare earth magnets, separated as Dy vapor, and the Dy vapor was circulated inside the ceramic tube of the recovery furnace. Then, in the recovery furnace, the temperature inside the ceramic tube (inside the recovery chamber) was adjusted to cool the Dy vapor, and the temperature of the rare earth magnet precursor was adjusted to a temperature at which grain boundary diffusion of Dy vapor occurred and grain coarsening was suppressed, thereby cooling the Dy vapor and supplying it to the surface of the rare earth magnet precursor. Furthermore, at the point when the used rare earth magnets are in a molten state, the oxygen partial pressure in the atmosphere inside the ceramic tubes of the evaporator and the ceramic tubes of the recovery furnace is 10 -20 The pressure was atm. This is thought to be the result of a decrease in oxygen partial pressure due to vacuuming, in addition to oxygen being drawn into the molten metal produced from the spent rare-earth magnets.

[0038] Next, the door of the recovery furnace was opened, and the rare earth magnet was removed from the ceramic tube entrance. By carrying out the rare earth recovery method described above, the Dy from the spent rare earth magnet was recovered using the rare earth magnet precursor, and a new rare earth magnet was manufactured.

[0039] [Examples 2 and 3 and Comparative Examples 1 and 2] In Examples 2 and 3 and Comparative Examples 1 and 2, the rare earth recovery apparatus was constructed and the rare earth recovery method was carried out in the same manner as in Example 1, except that when heating the rare earth magnet precursor in the recovery furnace to adjust the temperature of the rare earth magnet precursor, the temperature of the rare earth magnet precursor was adjusted to 900°C, 950°C, 500°C, and 1000°C, respectively, as shown in Table 1 below. As a result, the Dy from the used rare earth magnet was recovered using the rare earth magnet precursor, and a rare earth magnet was manufactured.

[0040] [evaluation] The coercivity [kA / m] and remanent magnetization [T] of rare earth magnet precursors and rare earth magnets produced by using a rare earth recovery apparatus and rare earth recovery method in each of the examples and comparative examples were measured at room temperature using a VSM (vibrating sample magnetometer). In this process, the magnets were pre-magnetized with a 10T pulsed magnetic field, and the maximum applied magnetic field in the VSM was set to 1900 kA / m. The results are shown in Table 1 below. Figure 5 is a graph showing the change in coercivity of rare earth magnets with respect to the heating temperature (temperature after heating adjustment) of the rare earth magnet precursors in Examples 1-3 and Comparative Examples 1 and 2.

[0041] [Table 1]

[0042] As shown in Table 1 and Figure 5 above, the coercivity of the rare earth magnet precursor was 816 kA / m. In Examples 1-3, the rare earth magnets produced by adjusting the temperature of the rare earth magnet precursor to 850-950°C showed improved coercivity compared to the rare earth magnet precursor. This improvement in coercivity is thought to be due to grain boundary diffusion, where Dy vapor directly diffuses as atoms into the grain boundary phase of the rare earth magnet precursor. On the other hand, in Comparative Example 1, the rare earth magnet produced by adjusting the temperature of the rare earth magnet precursor to 500°C showed almost no change in coercivity compared to the rare earth magnet precursor. Observation of this rare earth magnet revealed the presence of a vapor-deposited film, but it is thought that grain boundary diffusion like that in Examples 1-3 did not occur. Furthermore, in Comparative Example 2, the rare earth magnet produced by adjusting the temperature of the rare earth magnet precursor to 1000°C showed decreased coercivity compared to the rare earth magnet precursor. In Comparative Example 2, it is thought that grain boundary diffusion like that in Examples 1-3 occurred, but grain coarsening also occurred.

[0043] After carrying out the rare earth recovery method in Example 1, the composition of the vapor-deposited film formed on the inner surfaces of the ceramic tubes of the evaporator and the ceramic tubes of the recovery furnace was evaluated by ICP (inductively coupled plasma) emission spectroscopy. As a result, the composition of the vapor-deposited film was Nd: 35% by weight, Dy (target rare earth element R) TThe composition was estimated to be 30% (Dy), bal. (Fe), 0.2% (Co), and 3% (Cu), indicating a significantly higher concentration of Dy compared to spent rare-earth magnets. This is thought to be because Dy has a higher vapor pressure compared to other elements, causing it to preferentially evaporate during heating of spent rare-earth magnets, resulting in the generation of Dy-enriched vapor.

[0044] Although embodiments of the rare earth recovery apparatus according to the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0045] 1: Rare earth recovery device, 10: Evaporator, 10m: Used rare earth magnet, 20: Recovery furnace (recovery chamber), 20p: Rare earth magnet precursor, 20m: Rare earth magnet, 30: Oxygen concentration reduction device

Claims

1. The system comprises an evaporator in which used rare earth magnets containing the target rare earth element are placed, a recovery chamber communicating with the evaporator and in which rare earth magnet precursors are placed, and an oxygen concentration reduction device. The evaporator heats the spent rare earth magnet to evaporate the target rare earth element from the spent rare earth magnet, and separates it as vapor of the target rare earth element. The recovery chamber recovers the target rare earth element by supplying the vapor of the target rare earth element to the surface of the rare earth magnet precursor by cooling it and diffusing it into the interior of the rare earth magnet precursor. The rare earth recovery apparatus is characterized by reducing the oxygen concentration of the atmosphere inside the evaporator and the recovery chamber to a concentration that prevents oxidation of the vapor of the target rare earth element.

2. The rare earth recovery apparatus comprises a recovery furnace, and the interior of the recovery furnace constitutes the recovery chamber. The rare earth recovery apparatus according to claim 1, characterized in that the recovery furnace adjusts the temperature inside the recovery chamber so that the vapor of the target rare earth element cools down, and adjusts the temperature of the rare earth magnet precursor to a temperature at which grain boundary diffusion of the vapor of the target rare earth element occurs and grain coarsening is suppressed, thereby diffusing the vapor of the target rare earth element into the interior of the rare earth magnet precursor by grain boundary diffusion.

3. The rare earth element recovery apparatus according to claim 1 or 2, characterized in that the rare earth element for the purpose is Dy.

4. The oxygen concentration reduction device reduces the oxygen partial pressure of the atmosphere inside the evaporator and the recovery chamber to 10 －１０ The rare earth recovery apparatus according to claim 3, characterized in that the oxygen concentration of the atmosphere is reduced to a concentration such that oxidation of the vapor of the target rare earth element can be avoided by reducing it to below atm.

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