A method for purifying rare earth metals

Abstract

This application provides a method for purifying rare earth metals. The purification method includes the following steps: smelting and cooling the rare earth metal, the smelting and cooling process including sequential vacuum electron beam regional melting and cooling to prepare a high-purity rare earth metal rod; the smelting and cooling process including sequential vacuum electron beam regional melting and cooling; removing impurity-rich regions from the high-purity rare earth metal rod; wherein, the vacuum electron beam regional melting includes the following steps: initial smelting of the rare earth metal, followed by stable smelting after a molten zone appears on the surface of the rare earth metal; the interval between the start time of stable smelting and the end time of initial smelting is 5s~15s; the filament current of initial smelting is 45A~80A, and the filament current of stable smelting is 25A~50A.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a method for purifying rare earth metals. Background Technology

[0002] Rare earth metals possess excellent comprehensive properties and serve as raw materials for the preparation of numerous high-tech materials. For example, scandium is widely used in novel optoelectronic materials, laser materials, alloy additives, and metal modifiers, and has become a key new material in fields such as integrated circuit memory chips, radio frequency filters, and OLED displays. Terbium can be used to prepare supermagnetostrictive alloys and magnetic functional materials, finding wide application in precision sensing and information storage technologies. Yttrium can be used to prepare high-purity yttrium targets, neutron moderators for mobile nuclear reactors, corrosion-resistant coatings for components in semiconductor manufacturing equipment, and CMOS dielectric materials.

[0003] The quality and purity of rare earth metals are closely related, and improving the purity of rare earth metals is of great significance for improving their quality. To address trace impurities that are difficult to remove using traditional methods, researchers have employed electron beam zone melting purification technology. This technology uses an electron gun to emit a high-speed electron beam to melt rare earth metals, causing impurities to migrate directionally at the boundary between the liquid and solid phases of the metal, thus removing key impurities. During zone melting, key impurities accumulate at both ends of the scandium rod; shortening the area of ​​impurity accumulation at these ends can yield high-yield, high-purity rare earth metals. However, the escape of metal vapor generated after the rare earth metal melts can cause a rapid discharge of the electron gun, leading to instability in the electron beam emission-rare earth metal melting process and collapse of the molten metal zone, resulting in poor purification effects. Summary of the Invention

[0004] Based on this, one or more embodiments of this application provide an efficient method for purifying rare earth metals.

[0005] According to an embodiment of this application, a method for purifying rare earth metals is provided, comprising the following steps:

[0006] High-purity rare earth metal rods are prepared by smelting and cooling rare earth metals; the smelting and cooling process includes sequential vacuum electron beam regional smelting and cooling.

[0007] The impurity enrichment region of the high-purity rare earth metal rod is removed;

[0008] The vacuum electron beam regional melting process includes the following steps: initial melting of the rare earth metal, followed by stable melting after a molten zone appears on the surface of the rare earth metal; the time interval between the start of the stable melting and the end of the initial melting is 5s to 15s.

[0009] The filament current for initial melting is 45A~80A, and the filament current for stable melting is 25A~50A.

[0010] In some embodiments, during the vacuum electron beam zone melting, the electron gun moves at a speed of 1 mm / min to 15 mm / min.

[0011] In some embodiments, during the vacuum electron beam zone melting, the rotation speed of the rare earth metal is 5 r / min to 20 r / min.

[0012] In some embodiments, the purification method satisfies at least one of the following characteristics:

[0013] (1) The emission current for the initial melting is 0.1A~0.4A;

[0014] (2) The emission current of the stable melting is 0.1A~0.5A.

[0015] In some embodiments, the purification method satisfies at least one of the following characteristics:

[0016] (1) The accelerating voltage for the vacuum electron beam region melting is 3kV~20kV;

[0017] (2) The vacuum degree of the vacuum electron beam region melting is less than or equal to 1×10⁻⁶. -3 Pa.

[0018] In some embodiments, the filament diameter of the electron gun in the vacuum electron beam regional melting is 0.6 mm to 1.2 mm.

[0019] In some embodiments, the purification method further includes the following step: vacuum electron beam regional melting of the rare earth metal using a preheated electron gun;

[0020] Optionally, the preheating step of the electron gun includes: at 7×10 -4 Pa ~ 1×10 -3 Under vacuum conditions of Pa, adjust the filament current of the electron gun to 60A~80A and preheat for 20min~30min.

[0021] In some embodiments, the cooling rate of the cooling process is 10°C / min to 20°C / min.

[0022] In some embodiments, the purification method satisfies at least one of the following characteristics:

[0023] (1) The rare earth metals include one or more of scandium, yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, holmium, erbium and lutetium;

[0024] (2) The rare earth metal is rod-shaped.

[0025] In some embodiments, the process further includes the step of repeatedly subjecting the rare earth metal to the smelting-cooling treatment.

[0026] Optionally, the total number of melting-cooling processes is 5 to 10.

[0027] Compared with traditional technologies, this application has the following advantages:

[0028] In this application, when using vacuum electron beam regional melting to melt rare earth metals, the solubility of impurity elements differs between the solid and molten states of the rare earth metals. Furthermore, under the influence of gravitational segregation, impurity elements accumulate at both ends. Therefore, purification of the rare earth metals can be achieved by removing the impurity-rich regions. Simultaneously, after a molten zone appears on the surface of the rare earth metal, promptly reducing the filament current during vacuum electron beam regional melting can decrease the increase in emission current and heat accumulation caused by metal vapor escape, thereby mitigating the phenomenon of molten zone collapse and ultimately improving the purification effect of the rare earth metals. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram showing the positions of rare earth metals and electron guns in an electron beam zone melting furnace in some embodiments of this application;

[0031] Figure 2 The diagram shows the external structure of the purified rare earth metal rods in Examples 2 and 4 of this application.

[0032] Explanation of reference numerals in the attached drawings: 1. Rare earth metal rod; 2. Rare earth metal suspension molten zone; 3. Upper fixing clamp; 4. Lower fixing clamp; 5. Electron gun tungsten filament; 6. Boron nitride insulating component; 7. Alumina ceramic tube. Detailed Implementation

[0033] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in this application are commercially available or can be prepared by existing methods.

[0035] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0036] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0037] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0038] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0039] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0040] Some embodiments of this application provide a method for purifying rare earth metals, including steps S10 and S20:

[0041] S10: High-purity rare earth metal rods are prepared by sequentially melting and cooling rare earth metals; the melting and cooling process includes sequential vacuum electron beam regional melting and cooling.

[0042] S20: Remove impurity-rich areas from high-purity rare earth metal rods;

[0043] The vacuum electron beam regional melting process includes the following steps: initial melting of rare earth metals, followed by stable melting after a molten zone appears on the surface of the rare earth metals; the interval between the start of stable melting and the end of initial melting is 5 to 15 seconds.

[0044] The filament current for initial melting is 45A~80A, and the filament current for stable melting is 25A~50A.

[0045] It should be noted that the filament current for initial melting and stable melting both refer to the filament current of the electron gun. The filament current for stable melting is the filament current when the high-purity rare earth metal rod is melted and purified in a stable operating state, and is not an absolute limitation on the value of the filament current.

[0046] As an example, the interval between the start time of stable smelting and the end time of initial smelting can be 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, 15s, or any value within the range formed by any two of the above points.

[0047] In the purification method described above, when rare earth metals are smelted using vacuum electron beam regional melting, the solubility of impurity elements differs between the solid and molten states of the rare earth metals. Furthermore, under the influence of gravitational segregation, impurity elements accumulate at both ends. Therefore, purification of the rare earth metals can be achieved by removing the impurity-rich regions. Simultaneously, after a molten zone appears on the surface of the rare earth metal, the melting current of the vacuum electron beam regional melting is promptly reduced from the initial melting stage to a stable melting stage. This reduces metal vapor escape and the resulting increase in emission current, heat accumulation, and power supply malfunctions, thereby mitigating the phenomenon of molten zone collapse.

[0048] It should be noted that after the rare earth metal surface is melted and a molten zone appears through the initial melting process, the escaping rare earth metal vapor will cause the electron gun to discharge rapidly, resulting in unstable emission current and abnormal power supply failure. Furthermore, excessive emission current will cause heat accumulation, leading to the collapse of the molten zone. After the molten zone collapses, impurity elements may not be able to fully volatilize, and element segregation may be aggravated, affecting the purification effect of rare earth elements. Therefore, timely adjustment of the melting current of the electron gun can maintain the stability of the electron beam and the power supply, thereby allowing the melting of the electron beam region to continue.

[0049] In some embodiments, the impurity enrichment region is located at the head and tail of the high-purity rare earth metal rod. It is understood that the solubility of impurities differs between the solid and molten states of the host metal, and the directional redistribution of impurities occurs during the alternation of solid and liquid states, thereby enriching the impurities at the head and tail of the high-purity rare earth metal rod.

[0050] In some embodiments, the rare earth metal rods are placed axially along the direction of gravity during purification.

[0051] In some of these examples, the rare earth metal rods have a diameter of 6 mm to 30 mm and a length of 100 mm to 500 mm.

[0052] As an example, the diameter of the rare earth metal rod can be 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, or 30mm, or any value within the range formed by any two of the above values. The length of the rare earth metal rod can be 100mm, 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, or 500mm, or any value within the range formed by any two of the above values.

[0053] In some embodiments, the rare earth metals include one or more of scandium, yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, holmium, erbium, and lutetium.

[0054] As an example, the filament current at the start of melting can be 45A, 46A, 47A, 48A, 49A, 50A, 51A, 52A, 53A, 54A, 55A, 56A, 57A, 58A, 59A, 60A, 61A, 62A, 63A, 64A, 65A, 66A, 67A, 68A, 69A, 70A, 71A, 72A, 73A, 74A, 75A, 76A, 77A, 78A, 79A, or 80A, or any value within the range formed by any two of the above points.

[0055] As an example, the filament current for stable melting can be 25A, 26A, 27A, 28A, 29A, 30A, 31A, 32A, 33A, 34A, 35A, 36A, 37A, 38A, 39A, 40A, 41A, 42A, 43A, 44A, 45A, 46A, 47A, 48A, 49A, or 50A.

[0056] In some embodiments, the initial melting emission current is 0.1A to 0.4A. As an example, the initial melting emission current can be 0.1A, 0.2A, 0.3A, 0.4A, or any value within the range formed by any two of the above values.

[0057] In this application, "emission current" refers to the current emitted from the cathode of the electron gun and ultimately forming an electron beam during the electron beam melting process.

[0058] In some embodiments, the emission current for stable melting is 0.1A to 0.5A. As an example, the emission current for stable melting can be 0.1A, 0.15A, 0.2A, 0.25A, 0.3A, 0.35A, 0.4A, 0.45A, or 0.5A, or any value within the range formed by any two of the above values. The emission current for stable melting refers to the emission current during the stable operation of high-purity rare earth metal rod melting and purification, and is not an absolute limitation on the value of the emission current.

[0059] In some embodiments, during vacuum electron beam regional melting, the electron gun moves at a speed of 1 mm / min to 15 mm / min.

[0060] Furthermore, the direction of movement of the electron gun is parallel to the axial direction of the rare-earth metal rod. Even further, the direction of movement of the electron gun is along the direction of gravity.

[0061] Understandably, as the electron gun moves, the molten zone on the rare earth metal surface also moves. In other words, the electron gun moves at the same speed as the molten zone.

[0062] As an example, the movement speed of the electron gun can be 1 mm / min, 2 mm / min, 3 mm / min, 4 mm / min, 5 mm / min, 6 mm / min, 7 mm / min, 8 mm / min, 9 mm / min, 10 mm / min, 11 mm / min, 12 mm / min, 13 mm / min, 14 mm / min, 15 mm / min, or any value within the range formed by any two of the above points.

[0063] By controlling the movement speed of the electron gun within the aforementioned specific range, it is possible to effectively separate impurity elements in rare earth metals, further improving the purification effect, while also preventing the smelting time from becoming too long.

[0064] Furthermore, in vacuum electron beam zone melting, the electron gun moves at a speed of 2 mm / min to 10 mm / min.

[0065] In some embodiments, during vacuum electron beam zone melting, the rotation speed of the rare earth metal is 5 r / min to 20 r / min. As an example, the rotation speed of the rare earth metal can be 5 r / min, 6 r / min, 7 r / min, 8 r / min, 9 r / min, 10 r / min, 11 r / min, 12 r / min, 13 r / min, 14 r / min, 15 r / min, 16 r / min, 17 r / min, 18 r / min, 19 r / min, 20 r / min, or any value within the range formed by any two of the above values.

[0066] In some of these examples, the top and bottom of the rare earth metal rotate clockwise or counterclockwise.

[0067] It is understandable that controlling the rotation speed of rare earth metals within the above range can enable the metal surface to attract electron beams uniformly, allowing the metal in the molten zone to be fully melted, thereby improving the diffusion efficiency of impurity elements and further enhancing the purification effect.

[0068] In some embodiments, the accelerating voltage for vacuum electron beam regional melting is 3kV to 20kV. As an example, the accelerating voltage for vacuum electron beam regional melting can be 3kV, 4kV, 5kV, 6kV, 7kV, 8kV, 9kV, 10kV, 11kV, 12kV, 13kV, 14kV, 15kV, 16kV, 17kV, 18kV, 19kV, or 20kV, or any value within the range formed by any two of the above values.

[0069] In some embodiments, the vacuum level of the vacuum electron beam region melting is less than or equal to 1 × 10⁻⁶. -3 Pa.

[0070] In some examples, mechanical pumps and molecular pumps are used for vacuuming.

[0071] In some embodiments, the filament of the electron gun in vacuum electron beam regional melting is a tungsten filament.

[0072] In some embodiments, the filament diameter of the electron gun is 0.6 mm to 1.2 mm. For example, the filament diameter can be 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, or 1.2 mm. Compared to conventional electron gun filaments, the electron gun filament of this application has a larger diameter, making it less prone to breakage during the melting process and enabling continuous and stable melting in the electron beam region.

[0073] Furthermore, the filament diameter of the electron gun is 0.8mm~1.2mm.

[0074] In some of these embodiments, such as Figure 1 As shown, the rare earth metal rod 1 is fixed between the upper fixing clamp 3 and the lower fixing clamp 4. The electron gun tungsten filament 5 and the edge of the electron gun are separated by a distance of 3mm to 8mm, and the two do not contact each other. The electron gun filaments are parallel and are isolated by a boron nitride insulating part 6 or an alumina ceramic tube 7. The annular electron gun surrounds the rare earth metal rod 1 and forms a rare earth metal suspension melting zone 2 after melting.

[0075] Furthermore, the dimensions of the boron nitride insulator 6 are 3mm~6mm×10mm~15mm×1mm~2mm.

[0076] Furthermore, the dimensions of the alumina ceramic tube 7 are φ1mm×φ2mm×20mm~φ2mm×φ3mm×50mm.

[0077] In some embodiments, transparent high-temperature resistant tape is used to adhere to the observation window and the inside of the furnace door in the vacuum electron beam regional melting process to prevent rare earth metals from volatilizing and condensing on the observation window glass and furnace door. After melting is completed, the volatilized metals can be effectively cleaned by peeling off the high-temperature resistant tape.

[0078] In some embodiments, the purification method further includes the following step: vacuum electron beam regional melting of rare earth metals using a preheated electron gun.

[0079] In some of these examples, the preheating steps for the electron gun include: at 7×10 -4 Pa ~ 1×10 -3 Under vacuum conditions of Pa, adjust the filament current of the electron gun to 60A~80A and preheat for 20min~30min.

[0080] In some embodiments, the cooling rate of the cooling process is 10°C / min to 20°C / min. As an example, the cooling rate of the cooling process can be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min, 20°C / min, or any value within the range formed by any two of the above points.

[0081] In some of these examples, the molten zone is cooled to a solid state by cooling water within the upper and lower fixed clamps of the smelting furnace.

[0082] In some examples, the upper fixing clamp is moved to a position 5mm to 15mm beyond the top of the rare earth metal rod, and the upper fixing clamp is slowly lowered at a speed of 5mm / min to 10mm / min, so that the rod is slowly and stably inserted into the upper and lower clamps, the position of the rare earth rod is fixed and the clamp is tightened.

[0083] In some embodiments, the following step is also included: repeatedly smelting and cooling the rare earth metal.

[0084] In some of these examples, the total number of melting-cooling processes is 5 to 10. As an example, the total number of melting-cooling processes can be 5, 6, 7, 8, 9, or 10, or any value within the range formed by any two of the above points.

[0085] The purification method of this application, through electron beam zone melting, utilizes the synergistic effect of melting condensation segregation and vertical gravity segregation to enrich and remove impurities of rare earth metals at both ends of the rod, thereby achieving deep purification of the rare earth metal rod.

[0086] The present application will be further described below with reference to specific embodiments and comparative examples, but these should not be construed as limiting the scope of protection of the present application. Unless otherwise specified, the raw materials involved in the following specific embodiments are all commercially available, the instruments used are all commercially available, and the processes involved are conventionally selected by those skilled in the art unless otherwise specified.

[0087] Example 1

[0088] (1) Providing rare earth metals: The raw material scandium metal is cast into scandium in an induction melting furnace to obtain scandium ingots, which are then processed by wire cutting and turning into scandium rods with a diameter of φ16mm and a length of 350mm; the purity is 99.95%.

[0089] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The tungsten filament of the electron gun has a diameter of 1.0 mm. A 5 mm distance is left between the electron gun filament and the edge of the electron gun to prevent contact. A boron nitride insulating part with dimensions of 5 mm × 10 mm × 1 mm is placed in the middle of the parallel electron gun filaments to isolate them. It is also prohibited to approach or contact them. The upper and lower clamping devices for the material rod are divided into upper and lower ends. The rare earth metal scandium rod is placed in the material rod fixing device of the electron beam zone melting furnace. The rare earth metal scandium rod is inserted into the lower fixing clamp. According to the length of the metal scandium rod, the upper fixing clamp is moved to a position 15 mm beyond the top of the material rod. The upper fixing clamp is controlled to slowly descend at a speed of 10 mm / min so that the material rod is slowly and stably inserted into the upper and lower clamps. The position of the scandium rod is fixed and the clamp is tightened. Transparent high-temperature resistant tape is used to stick to the observation window and the inside of the furnace door to prevent the rare earth metal from volatilizing and condensing on the observation window glass and the furnace door.

[0090] (3) Electron gun preheating: A mechanical pump and a molecular pump are equipped outside the vacuum electron beam zone melting furnace to simultaneously draw a vacuum. When the absolute pressure inside the vacuum electron beam zone melting furnace is 7.8 × 10 -4 At Pa, rotate the metal scandium rod clockwise at a speed of 10 r / min, and increase the filament current to 70 A to bake the filament for 25 minutes.

[0091] (4) Initial melting: When the vacuum degree of the furnace chamber reaches 7.3×10 -4 At Pa, the accelerating voltage was started and adjusted to 8.0kV, the filament current was adjusted to 45.0A, and the emission current was controlled to increase to 0.1A. Initially, the surface of the rare earth scandium rod showed a bright light. As the emission current and power increased, a 3mm wide suspended molten zone appeared on the rod.

[0092] (5) Stabilization and Cooling: After the scandium rod surface melts, a suspended molten zone appears, and the emission current increases sharply. The electron gun is started and moves automatically upward along the direction parallel to the scandium rod. The moving speed of the electron gun melting is 2 mm / min. As the melting area of ​​the rod expands, liquid fluctuations occur. The filament current is reduced, and the emission current is controlled within the range of 0.15A~0.25A during the adjustment of the filament current. Finally, the filament current is adjusted to be reduced to 25.0A and the emission current is stabilized at 0.22A. The melting power is controlled at 1.76kW, so that the suspended molten zone of metallic scandium can exist stably between the unmelted solids of the rod without collapsing. The molten zone moves with the upward movement of the electron gun and is cooled to solid by the rod under the action of cooling water from the upper and lower fixed clamps. The average cooling rate during and after the melting process is 15℃ / min, realizing the stable electron beam region melting and purification of rare earth metallic scandium rods.

[0093] The time interval between the start of stable smelting and the end of initial smelting is 5 seconds.

[0094] (6) The metal scandium melting area showed an inward shrinkage state, and a large amount of metal enrichment appeared in the observation windows on both sides and the inside of the furnace door. A total of 7 melting and purifications were carried out. After melting, the effective melting length was 302 mm. The amount of impurity enrichment areas removed at both ends was 13.71% of the total length of the rare earth scandium rod, and high-purity rare earth scandium was obtained. Its purity was tested to be >99.996%.

[0095] Example 2

[0096] (1) Providing rare earth metals: Yttrium raw material is cast into rare earth metal yttrium in an induction melting furnace, and then processed into yttrium rods with a diameter of φ30mm and a length of 300mm by wire cutting and turning machine; its purity is 99.95%.

[0097] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The tungsten filament of the electron gun has a diameter of 1.2 mm. A 3 mm distance is left between the electron gun filament and the edge of the electron gun to prevent contact. An alumina ceramic tube with dimensions of φ1.5 mm × φ3 mm × 30 mm is placed in the middle of the parallel electron gun filaments to isolate them. The filaments must not be close to each other. The upper and lower clamping devices for the material rod are divided into upper and lower ends. The rare earth metal yttrium rod is placed in the material rod fixing device of the electron beam zone melting furnace. The rare earth metal yttrium rod is inserted into the lower fixing clamp. According to the length of the metal yttrium rod, the upper fixing clamp is moved to a position 10 mm beyond the top of the material rod. The upper fixing clamp is controlled to slowly descend at a descent speed of 7 mm / min so that the material rod is slowly and stably inserted into the upper and lower clamps. The position of the yttrium rod is fixed and the clamp is tightened. Transparent high-temperature resistant tape is used to stick to the observation window and the inside of the furnace door to prevent the rare earth metal from volatilizing and condensing on the observation window glass and the furnace door.

[0098] (3) Electron gun preheating: A mechanical pump and a molecular pump are equipped outside the vacuum electron beam zone melting furnace and run simultaneously to draw a vacuum. When the absolute pressure inside the vacuum electron beam zone melting furnace is 8.3×10 -4 At Pa, rotate the metal yttrium rod counterclockwise at a speed of 5 r / min, and increase the filament current to 80 A to bake the filament for 20 minutes.

[0099] (4) Initial melting: When the vacuum degree of the furnace chamber reaches 7.7×10 -4 At Pa, the accelerating voltage was started and adjusted to 20.0kV, the filament current was adjusted to 80A, and the emission current was controlled to increase to 0.2A. Initially, the surface of the rare earth yttrium rod showed a bright light. As the emission current and power increased, a 2mm wide suspended molten zone appeared on the rod.

[0100] (5) Stabilization and Cooling: After the surface of the yttrium rod melts, a suspended molten zone appears, and the emission current increases sharply. The electron gun is started and moves automatically upward along the direction parallel to the scandium rod. The moving speed of the electron gun during melting is 5 mm / min. As the melting area of ​​the rod expands, liquid fluctuations occur. The filament current is reduced. During the adjustment of the filament current, the emission current is controlled within the range of 0.37A~0.5A. Finally, the filament current is adjusted to reduce to 50.0A and stabilized at 0.45A. The melting power is controlled at 9kW, so that the suspended molten zone of yttrium metal can exist stably between the unmelted solids of the rod without collapsing. The molten zone moves with the upward movement of the electron gun and is cooled to solid by the cooling water of the upper and lower fixed clamps. The average cooling rate during and after melting is 10℃ / min, realizing the stable electron beam region melting and purification of rare earth metal yttrium rod.

[0101] The time interval between the start of stable smelting and the end of initial smelting is 10 seconds.

[0102] (6) The yttrium smelting area showed an inward shrinkage state, and a large amount of metal enrichment appeared in the observation windows on both sides and the inside of the furnace door. A total of 10 smelting and purification processes were carried out. After smelting, the effective smelting length was 260 mm. The amount of impurity enrichment areas removed at both ends was 13.33% of the total length of the rare earth yttrium rod, and high-purity rare earth yttrium was obtained. Its purity was tested to be >99.996%.

[0103] Example 3

[0104] (1) Providing rare earth metals: The raw material terbium metal is cast into rare earth metal terbium in an induction melting furnace, and then processed into terbium rods with a diameter of φ6mm and a length of 500mm by wire cutting and turning machine; its purity is 99.96%.

[0105] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The tungsten filament of the electron gun has a diameter of 0.6 mm. An 8 mm distance is left between the electron gun filament and the edge of the electron gun to prevent contact. A boron nitride insulating piece with dimensions of 6 mm × 12 mm × 1.5 mm is placed in the middle of the parallel electron gun filaments to isolate them. It is also prohibited to approach or contact them. The upper and lower clamping devices for the metal rod are divided into upper and lower ends. The rare earth metal terbium rod is placed in the metal rod fixing device of the electron beam zone melting furnace. The rare earth metal terbium rod is inserted into the lower fixing clamp. According to the length of the metal terbium rod, the upper fixing clamp is moved to a position 5 mm beyond the top of the metal rod. The upper fixing clamp is controlled to descend slowly at a speed of 5 mm / min so that the metal rod is slowly and stably inserted into the upper and lower clamps. The position of the terbium rod is fixed and the clamp is tightened. Transparent high-temperature resistant tape is used to stick to the observation window and the inside of the furnace door to prevent the rare earth metal from volatilizing and condensing on the observation window glass and the furnace door.

[0106] (3) Electron gun preheating: A mechanical pump and a molecular pump are equipped outside the vacuum electron beam zone melting furnace to simultaneously draw a vacuum. When the absolute pressure inside the vacuum electron beam zone melting furnace is 9.6 × 10 -4 At Pa, rotate the metal terbium rod clockwise at a speed of 15 r / min, and increase the filament current to 60 A to bake the filament for 30 minutes.

[0107] (4) Initial melting: When the vacuum degree of the furnace chamber reaches 6.7×10 -4 At that time, the acceleration voltage was started and adjusted to 3.0kV, the filament current was adjusted to 50.0A, and the emission current was controlled to increase to 0.35A. Initially, the surface of the rare earth terbium rod showed a bright light, and as the emission current and power increased, a 4mm red area appeared on the rod.

[0108] (5) Stabilization and Cooling: After the terbium rod surface melts, a suspended molten zone appears, and the emission current increases sharply. The electron gun is started and moves automatically upward along the direction parallel to the scandium rod. The moving speed of the electron gun during melting is 7 mm / min. As the melting area of ​​the rod expands, liquid fluctuations occur. The filament current is reduced, and the emission current is controlled within the range of 0.26A~0.35A during the adjustment of the filament current. Finally, the filament current is adjusted to reduce to 35.0A and stabilized at 0.32A. The melting power is controlled at 0.96kW, so that the suspended molten zone of metallic terbium can exist stably between the unmelted solids of the rod without collapsing. The molten zone moves with the upward movement of the electron gun and is cooled to solid by the rod under the action of cooling water from the upper and lower fixed clamps. The average cooling rate during and after melting is 20℃ / min, realizing the stable electron beam region melting and purification of rare earth metallic terbium rods.

[0109] The time interval between the start of stable smelting and the end of initial smelting is 15 seconds.

[0110] (6) The terbium metal smelting area shows an inward shrinkage state, and a large amount of metal enrichment appears in the observation windows on both sides and the inside of the furnace door. A total of 5 smelting and purification processes were carried out. After smelting, the effective smelting length was 460 mm. The amount of impurity enrichment areas removed at both ends was 8% of the total length of the rare earth terbium rod, and high-purity rare earth terbium was obtained with a purity of >99.995%.

[0111] Example 4

[0112] The process is basically the same as in Example 2, except that the electron gun moves at a different speed. Specifically, in Example 4, the electron gun moves at a speed of 25 mm / min, and the remaining steps and parameters are the same as in Example 2.

[0113] In Example 4, the melting length of the yttrium rod after melting was 225 mm, and the amount of impurity enrichment at both ends was 25% of the total length of the rare earth yttrium rod. Due to the excessively fast movement speed of the melting zone, the impurities in the rare earth yttrium melting zone solidified rapidly before they could be effectively separated, resulting in a relatively poor purification effect on the yttrium rod, with a detection purity > 99.98%.

[0114] Figure 2 The figures show the appearance of the purified yttrium rods in Examples 2 and 4. As can be seen from the figures, the surface of the metal yttrium rod in Example 2 is smoother after being melted and purified in the stable electron beam region, while the spiral pattern of the metal yttrium rod in Example 4 is coarse. The reason may be that the cooling speed is fast and the molten metal is not effectively melted.

[0115] Example 5

[0116] The process is basically the same as in Example 2, except that the electron gun moves at a different speed. Specifically, in Example 5, the electron gun moves at a speed of 15 mm / min, and the remaining steps and parameters are the same as in Example 2.

[0117] In Example 5, during the stable melting of the yttrium rod, as the melting area of ​​the rod expanded, fluctuations in the liquid region occurred, leading to a reduction in the filament current. The emission current was controlled within the range of 0.31A to 0.45A during the filament current adjustment process. Ultimately, the filament current was reduced to 50.0A, and the emission current was stabilized at 0.41A. The melting power was controlled at 8.2kW, allowing the suspended terbium zone to remain stably within the unmelted solids of the rod without collapsing. The molten area moved with the rising electron gun, and the terbium melting area exhibited an inward contraction. A large amount of metal enrichment appeared in the observation windows on both sides and inside the furnace door. A total of 10 melting and purification cycles were performed. After melting, the effective melting length was 241mm. The amount of impurity-rich areas removed at both ends was 19.66% of the total length of the rare earth yttrium rod, yielding high-purity rare earth yttrium with a purity >99.995%.

[0118] Example 6

[0119] It is basically the same as Example 3, except that the rotation speed of the metal terbium rod is different; specifically, the rotation speed of the metal terbium rod in Example 6 is 2 r / min.

[0120] In Example 6, the melting zone of the terbium metal rod is an asymmetric suspended melting zone. The planar state exhibits a localized inward melting and shrinkage followed by localized solidification, and the molten metal in the melting zone tends to collapse downwards. After melting, the effective melting length is 400 mm. The amount of impurity-rich areas removed at both ends is 20% of the total length of the rare earth terbium rod. The metal rod rotates slowly, and the electron beam attracted by the rod plane is uneven. Only a portion of the metal in the melting zone is melted into molten metal, indicating insufficient melting. The purity is >99.993%.

[0121] Example 7

[0122] It is basically the same as Example 3, except that the rotation speed of the metal terbium rod is different; specifically, the rotation speed of the metal terbium rod in Example 7 is 25 r / min.

[0123] In Example 7, after the surface of the terbium metal rod melts, a suspended molten zone appears. As the melting area of ​​the rod expands, liquid fluctuations occur. Reducing the filament current causes the suspended molten zone of the terbium metal to increase, resulting in molten metal splashing. The emission current fluctuates within the range of 0.32~0.47A. The terbium metal melting area exhibits an inward contraction state. The molten zone exists between the unmelted solids of the rod, fluctuating and moving with the rising electron gun. After melting, the effective melting length is 370mm. The amount of impurity-rich areas removed at both ends is 26% of the total length of the rare earth terbium rod, and the purity is >99.991%.

[0124] Comparative Example 1

[0125] The process is basically the same as in Example 1, except that the filament current was not reduced after the melting zone appeared; specifically, the steps of Comparative Example 1 are as follows:

[0126] (1) Rare earth metal scandium ingots are obtained by casting raw scandium metal in an induction melting furnace, and scandium rods with a diameter of φ16mm and a length of 350mm are processed by wire cutting and turning machine; the purity is 99.95%.

[0127] (2) An electron gun is installed in the vacuum electron beam zone melting furnace. The diameter of the electron gun tungsten filament is 1.0 mm. A 5 mm distance is left between the electron gun filament and the edge of the electron gun. Contact is prohibited. A boron nitride insulating part with a size of 5 mm × 10 mm × 1 mm is placed in the middle of the parallel electron gun filaments. It is prohibited to approach or contact it.

[0128] (3) The bar clamping device is divided into upper and lower ends. Place the rare earth metal scandium rod in the bar fixing device of the electron beam melting furnace, insert the rare earth metal scandium rod into the lower fixing clamp, and control the upper fixing clamp to move to a position 15mm beyond the top of the bar according to the length of the scandium rod. Control the upper fixing clamp to slowly descend at a speed of 10mm / min, so that the bar is slowly and stably inserted into the upper and lower clamps, fix the position of the scandium rod and tighten the clamp. Use transparent high-temperature resistant tape to stick to the observation window and the inside of the furnace door to prevent rare earth metal from volatilizing and condensing on the observation window glass and furnace door.

[0129] (4) A mechanical pump and a molecular pump are installed outside the vacuum electron beam melting furnace to simultaneously pump vacuum. When the absolute pressure inside the vacuum electron beam melting furnace is 7.8 × 10⁻⁶, -4 At a pressure of Pa, rotate the metal scandium rod clockwise at a speed of 10 r / min, and increase the filament current to 70 A to bake the filament for 25 minutes. When the vacuum degree of the furnace chamber reaches 7.3 × 10⁻⁶, -4At Pa, the accelerating voltage was started and adjusted to 8.0kV, the filament current was adjusted to 45.0A, and the emission current was controlled to increase to 0.1A. Initially, the surface of the rare earth scandium rod showed a bright light. As the emission current and power increased, a 3mm wide suspended molten zone appeared on the rod.

[0130] (5) After the surface of the rare earth metal scandium rod melts, a suspended molten zone appears, the emission current increases sharply, and after the filament current stabilizes, the emission current increases to 1A~2A. Liquid fluctuations and continuous electron sparks appear in the melting area on the surface of the metal scandium. The emission current and melting power increase sharply, causing the high voltage power supply to be abnormal and unable to effectively perform electron beam melting on the metal scandium.

[0131] Comparative Example 2

[0132] The results are basically the same as in Example 1, except that the time interval between the end of the initial melting and the start of the stable melting is different; specifically, in Comparative Example 2, the interval between the end of the initial melting and the start of the stable melting is 30 seconds.

[0133] In Comparative Example 2, during the adjustment and reduction of the filament current, the molten fluctuation of the scandium metal rod increased, the shrinkage of the scandium metal suspension molten zone increased, the molten liquid at the top of the molten zone accumulated towards the bottom, and some molten liquid flowed down the rod wall. During the adjustment of the filament current, the emission current was controlled within the range of 0.23A~0.66A. Finally, the filament current was adjusted to reduce to 25.0A and stabilized at 0.25A. The melting power was controlled at 2.0 kW. The scandium metal suspension molten zone could stably exist between the unmelted solids of the rod without collapsing. The inward shrinkage of the scandium metal melting area increased. After melting, the effective melting length was 273mm. The amount of impurity enrichment at both ends was 22% of the total length of the rare earth scandium rod, resulting in high-purity rare earth scandium with a purity >99.993%.

[0134] Impurity content test: The main impurity elements and their contents in the purified rare earth metal rods of the above examples and comparative examples were tested by GDMS detection and analysis. The results are shown in Table 1.

[0135] Table 1

[0136]

[0137] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0138] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for purifying rare earth metals, characterized in that, Includes the following steps: High-purity rare earth metal rods are prepared by smelting and cooling rare earth metals; the smelting and cooling process includes sequential vacuum electron beam regional smelting and cooling. The impurity enrichment region of the high-purity rare earth metal rod is removed; The vacuum electron beam regional melting process includes the following steps: initial melting of the rare earth metal, followed by stable melting after a molten zone appears on the surface of the rare earth metal; the time interval between the start of the stable melting and the end of the initial melting is 5s to 15s. The filament current for initial melting is 45A~80A, and the filament current for stable melting is 25A~50A.

2. The method for purifying rare earth metals according to claim 1, characterized in that, In the vacuum electron beam regional melting process, the electron gun moves at a speed of 1 mm / min to 15 mm / min.

3. The method for purifying rare earth metals according to claim 1, characterized in that, In the vacuum electron beam region melting process, the rotation speed of the rare earth metal is 5 r / min to 20 r / min.

4. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, The purification method satisfies at least one of the following characteristics: (1) The emission current for the initial melting is 0.1A~0.4A; (2) The emission current of the stable melting is 0.1A~0.5A.

5. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, The purification method satisfies at least one of the following characteristics: (1) The accelerating voltage for the vacuum electron beam region melting is 3kV~20kV; (2) The vacuum electron beam zone melting is performed at a vacuum of less than or equal to 1 x 10 -3 Pa.

6. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, In the vacuum electron beam regional melting process, the filament diameter of the electron gun is 0.6 mm to 1.2 mm.

7. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, The purification method further includes the following steps: vacuum electron beam regional melting of the rare earth metal using a preheated electron gun; The step of preheating the electron gun includes: adjusting the filament current of the electron gun to 60A~80A under the vacuum condition of 7x10 -4 Pa~1x10 -3 Pa, and preheating for 20min~30min.

8. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, The cooling rate of the cooling process is 10℃ / min to 20℃ / min.

9. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, The rare earth metals include one or more of scandium, yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, holmium, erbium, and lutetium.

10. The method for purifying rare earth metals according to any one of claims 1 to 3, characterized in that, It also includes the following steps: repeatedly performing the smelting-cooling treatment on the rare earth metal; The total number of melting-cooling processes is 5 to 10.

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