Method for purifying rare earth metal

Abstract

The invention provides a rare earth metal purification method. The purification method comprises the following steps that rare earth metal is subjected to smelting-cooling treatment, the smelting-cooling treatment comprises vacuum electron beam zone smelting and cooling treatment which are sequentially conducted, and a high-purity rare earth metal rod is prepared; the smelting-cooling treatment comprises vacuum electron beam zone smelting and cooling treatment which are performed in sequence; removing an impurity enrichment area of the high-purity rare earth metal rod; the vacuum electron beam zone melting comprises the following steps that rare earth metal is subjected to initial melting, and stable melting is carried out after a melting zone appears on the surface of the rare earth metal; the interval between the starting time node of the stable smelting and the ending time node of the initial smelting is 5-15 seconds; the current of the filament for initial smelting is 45A-80A, and the current of the filament for stable smelting is 25A-50A.

Description

Technical Field

[0001] The present application relates to the field of metallurgy technology, and in particular to a method for purifying rare earth metals. Background Art

[0002] Rare earth metals possess excellent comprehensive properties and are used as raw materials for the preparation of numerous high-tech materials. For example, scandium metal is widely used in new optoelectronic materials, laser materials, alloy additives, and metal modifiers, and has become a key new material in integrated circuit memory chips, radio frequency filters, and OLED displays. Terbium metal can be used to prepare giant magnetostrictive alloys and magnetic functional materials, and is widely used in precision sensing and information storage high-tech fields. Yttrium metal 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 of rare earth metals is closely related to their purity, and improving their purity is crucial for improving their quality. To address trace impurity elements that are difficult to remove using traditional processes, researchers have adopted electron beam zone melting (EBSM) purification technology. This technique 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, thereby removing key impurities. During zone melting, key impurities are concentrated at both ends of the scandium rod, and shortening the range of the impurity-enriched end can yield high-yield, high-purity rare earth metals. However, the escape of metal vapor produced after melting rare earth metals can cause a sharp discharge from the electron gun, making the electron beam emission-rare earth metal melting process unstable and causing the molten metal zone to collapse, resulting in poor rare earth metal purification results. Summary of the Invention

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

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

[0006] The rare earth metal is subjected to a smelting-cooling treatment to prepare a high-purity rare earth metal rod; the smelting-cooling treatment includes vacuum electron beam zone melting and cooling treatment performed sequentially;

[0007] removing the impurity-rich region of the high-purity rare earth metal rod;

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

[0009] The filament current of the initial smelting is 45A-80A, and the filament current of the stable smelting is 25A-50A.

[0010] In some embodiments, during the vacuum electron beam zone melting, the moving speed of the electron gun is 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 of the initial smelting is 0.1A~0.4A;

[0014] (2) The emission current for stable smelting is 0.1A~0.5A.

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

[0016] (1) The acceleration voltage of the vacuum electron beam zone melting is 3kV~20kV;

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

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

[0019] In some embodiments, the purification method further comprises the following steps: performing vacuum electron beam zone melting on the rare earth metal using a preheated electron gun;

[0020] Optionally, the step of preheating the electron gun includes: -4 Pa~1×10 -3 Under the vacuum condition of 1.5 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 treatment 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 metal includes one or more of scandium, yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, holmium, erbium and lutetium;

[0024] (2) The rare earth metal is in the shape of a rod.

[0025] In some embodiments, the following steps are further included: repeatedly performing the smelting-cooling process on the rare earth metal;

[0026] Optionally, the total number of smelting-cooling treatments is 5 to 10 times.

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

[0028] When this application uses vacuum electron beam zone melting to melt rare earth metals, the solubility of impurity elements in the solid and molten rare earth metals differs. Due to gravity segregation, the impurity elements are concentrated at both ends. Therefore, the rare earth metals can be purified by removing the impurity-rich areas. Furthermore, after a molten zone appears on the surface of the rare earth metal, promptly reducing the filament current during vacuum electron beam zone melting can reduce the increase in emission current and heat accumulation caused by metal vapor escape, thereby improving the phenomenon of molten zone collapse and enhancing the purification effect of the rare earth metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 Schematic diagram of the positions of rare earth metals and electron guns in an electron beam zone melting furnace in some embodiments of the present application;

[0031] Figure 2 This is a structural diagram of the appearance of the rare earth metal rods after purification in Examples 2 and 4 of the present application.

[0032] Explanation of the accompanying symbols: 1. rare earth metal rod; 2. rare earth metal suspended melting zone; 3. upper fixing fixture; 4. lower fixing fixture; 5. electron gun tungsten filament; 6. boron nitride insulation; 7. alumina ceramic tube. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotations of the present application. Therefore, the present 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 those generally understood by those skilled in the art in the technical field of this application. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or can be prepared by existing methods.

[0035] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0036] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

[0037] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0038] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the optional numerical distribution within the numerical interval is considered continuous and includes the two numerical endpoints of the numerical range (i.e., the minimum and maximum values), as well as every numerical value between these two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two numerical endpoints of the numerical range, as well as every integer between the two numerical endpoints. In this document, this is equivalent to directly listing each integer. For example, "t is an integer selected from 1-10" means that t is any integer selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. In addition, when multiple ranges are provided to describe a feature or characteristic, these ranges may be combined. In other words, unless otherwise specified, ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0039] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

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

[0041] S10: performing a smelting-cooling treatment on the rare earth metal in sequence to prepare a high-purity rare earth metal rod; the smelting-cooling treatment includes sequentially performing a vacuum electron beam zone melting and a cooling treatment;

[0042] S20: removing impurity-rich areas of the high-purity rare earth metal rod;

[0043] The vacuum electron beam zone melting includes the following steps: performing initial melting of the rare earth metal, and performing stable melting after a molten zone appears on the surface of the rare earth metal; the interval between the start time of the stable melting and the end time of the initial melting is 5s to 15s;

[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 currents for initial smelting and stable smelting refer to the filament currents of the electron gun. The filament current for stable smelting refers to the filament current during the stable operation of smelting and purification of high-purity rare earth metal rods, and is not an absolute limit on the filament current value.

[0046] As an example, the interval between the time node when stable smelting starts and the time node when initial smelting ends 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 point values.

[0047] In the purification method described above, when rare earth metals are smelted using vacuum electron beam zone melting (VEZM), the solubility of impurity elements in the solid and molten rare earth metals differs. Due to gravitational segregation, the impurity elements tend to concentrate at both ends. Therefore, the rare earth metals can be purified by removing the impurity-rich regions. Furthermore, after a molten zone appears on the surface of the rare earth metal, the smelting current during VZM is promptly reduced, transitioning from initial melting to stable melting. This reduces metal vapor escape and the resulting increase in emission current, heat accumulation, and power supply failures, thereby alleviating molten zone collapse.

[0048] It should be noted that after the rare earth metal surface is melted and a molten zone appears through initial smelting, the escaped rare earth metal vapor will cause the electron gun to discharge rapidly, resulting in unstable emission current and abnormal power supply failure. In addition, excessive emission current will cause heat energy accumulation, thereby leading to the collapse of the molten zone. After the molten zone collapses, it may be difficult for the impurity elements to fully volatilize and the element segregation will be aggravated, affecting the purification effect of the rare earth elements. Therefore, timely regulation of the electron gun's melting current can maintain the stability of the electron beam and power supply, so that the electron beam area melting can continue.

[0049] In some embodiments, impurity-rich regions are located at the head and tail of the high-purity rare earth metal rod. It is understood that the solubility of impurities in the solid and molten states of the host metal differs, and the alternating solid-liquid state results in a directional redistribution of impurities, resulting in impurity concentration at the head and tail of the high-purity rare earth metal rod.

[0050] In some embodiments, the rare earth metal rod is placed with its axis 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 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm, 26 mm, 27 mm, 28 mm, 29 mm, 30 mm, or any value within a range formed by any two of the above values. The length of the rare earth metal rod can be 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, or any value within a range formed by any two of the above values.

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

[0054] As an example, the filament current for initial 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, 80A, or any value within the range formed by any two of the above point values.

[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, 50A.

[0056] In some embodiments, the emission current of the initial smelting is 0.1 A to 0.4 A. As an example, the emission current of the initial smelting can be 0.1 A, 0.2 A, 0.3 A, 0.4 A, 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 the electron beam during the electron beam melting process.

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

[0059] In some embodiments, during vacuum electron beam zone melting, the moving speed of the electron gun is 1 mm / min to 15 mm / min.

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

[0061] It is understood that as the electron gun moves, the molten zone on the surface of the rare earth metal also moves. In other words, the moving speed of the electron gun is the same as the moving speed of the molten zone.

[0062] As an example, the moving 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 point values.

[0063] Controlling the moving speed of the electron gun within the above-mentioned specific range can not only effectively separate the impurity elements in the rare earth metal and further improve the purification effect, but also prevent the smelting time from being too long.

[0064] Furthermore, during vacuum electron beam zone melting, the moving speed of the electron gun is 2 mm / min to 10 mm / min.

[0065] In some embodiments, during vacuum electron beam zone melting, the rare earth metal has a rotation speed of 5 to 20 r / min. For example, the rare earth metal can have a rotation speed of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 r / min, or any value within a range between any two of the aforementioned values.

[0066] In some of these examples, the top and bottom portions of the rare earth metals are rotated in a clockwise or counterclockwise direction.

[0067] It can be understood that controlling the rotation speed of the rare earth metal within the above range can make the metal surface attract the electron beam uniformly, so that the metal in the molten zone can be fully melted, thereby improving the diffusion efficiency of impurity elements and further improving the purification effect.

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

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

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

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

[0072] In some embodiments, the filament diameter of the electron gun is 0.6 mm to 1.2 mm. As examples, the filament diameter of the electron gun 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 the present application has a larger diameter and is less likely to break during the melting process, enabling continuous and stable electron beam zone melting.

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

[0074] In some embodiments, such as Figure 1 As shown, a rare earth metal rod 1 is fixed between an upper fixing fixture 3 and a lower fixing fixture 4. A distance of 3 mm to 8 mm is left between the electron gun tungsten filament 5 and the edge of the electron gun so that the two do not touch each other. A boron nitride insulating member 6 or an alumina ceramic tube 7 is provided in the middle of the parallel electron gun filaments for isolation. An annular electron gun surrounds the outer periphery of the rare earth metal rod 1, and after smelting, a rare earth metal suspended melt zone 2 is formed.

[0075] Furthermore, the size of the boron nitride insulating member 6 is 3 mm to 6 mm×10 mm to 15 mm×1 mm to 2 mm.

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

[0077] In some embodiments, transparent, high-temperature-resistant tape is applied to the observation window and the inside of the furnace door of the vacuum electron beam zone melting furnace to prevent condensation of volatilized rare earth metals on the observation window glass and the furnace door. After the melting is completed, the volatilized metal can be effectively cleaned by removing the high-temperature-resistant tape.

[0078] In some embodiments, the purification method further comprises the following step: performing vacuum electron beam zone melting on the rare earth metal using a preheated electron gun.

[0079] In some examples, the steps for preheating the electron gun include: -4 Pa~1×10 -3 Under the vacuum condition of 1.5 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 a range formed by any two of the above values.

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

[0082] In some of these examples, the upper fixture is controlled to move to a position 5mm to 15mm beyond the top of the rare earth metal rod, and the upper fixture is controlled to slowly descend with a descending speed controlled at 5mm / min to 10mm / min, so that the material rod is slowly and steadily inserted into the upper and lower chucks, the position of the rare earth rod is fixed, and the fixture is tightened.

[0083] In some of the embodiments, the method further comprises the step of repeatedly subjecting the rare earth metal to a smelting-cooling process.

[0084] In some 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, 10, or any value within a range between any two of the above values.

[0085] The purification method of the present application, through electron beam zone melting, based on the synergistic effect of melting condensation segregation and vertical gravity segregation, enriches rare earth metal impurities at both ends of the material rod and cuts them off, thereby achieving deep purification of the rare earth metal rod.

[0086] The present application will be further described below in conjunction with specific examples and comparative examples, but they should not be construed as limiting the scope of protection of the present application. The raw materials involved in the following specific examples, unless otherwise specified, can all be sourced from commercial sources, the instruments used, unless otherwise specified, can all be sourced from commercial sources, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0087] Example 1

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

[0089] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The diameter of the electron gun tungsten filament is 1.0mm. There is a distance of 5mm between the electron gun filament and the edge of the electron gun. Contact is prohibited. Boron nitride insulation is placed in the middle of the parallel electron gun filaments. The size is 5mm×10mm×1mm. Close contact is prohibited. The upper and lower clamping devices of 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 fixture. According to the length of the metal scandium rod, the upper fixing fixture is controlled to move to a position 15mm beyond the top of the material rod. The upper fixing fixture is controlled to slowly descend at a speed of 10mm / min. The material rod is slowly and steadily inserted into the upper and lower clamps. The position of the scandium rod is fixed and the clamps are tightened. Use transparent high-temperature resistant tape to stick on the observation window and the inside of the furnace door to prevent rare earth metal volatilization and condensation on the observation window glass and the furnace door.

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

[0091] (4) Initial smelting: When the vacuum degree of the furnace chamber reaches 7.3×10 -4 Pa, start the acceleration voltage and adjust the value to 8.0kV, adjust the filament current to 45.0A, and control the emission current to increase to 0.1A. Initially, bright light appears on the surface of the rare earth scandium rod. As the emission current and power increase, a suspended melt zone with a width of 3mm appears on the rod.

[0092] (5) Stable melting and cooling treatment: After the surface of the scandium rod melts, a suspended molten zone appears, and the emission current increases sharply. The electron gun is started and automatically moves upward in a direction parallel to the scandium rod. The moving speed of the electron gun melting is 2 mm / min. As the melting area of the material rod expands, the liquid area fluctuates. The filament current is reduced. During the process of adjusting the filament current, the emission current is controlled within the range of 0.15A~0.25A. Finally, the filament current is adjusted to 25.0A and the emission current is stabilized at 0.22A. The melting power is controlled to 1.76kW, so that the suspended molten zone of the metal scandium can stably exist between the unmelted solid of the material rod without collapsing. The molten zone moves with the rising movement of the electron gun. Under the action of the cooling water of the upper and lower fixed fixtures, the material rod is cooled to a solid state. The average cooling rate during and after the melting process is 15℃ / min, achieving stable electron beam regional melting and purification of the rare earth metal scandium rod.

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

[0094] (6) The smelting area of the metal scandium showed an inward contraction state, and a large amount of metal enrichment appeared on the inside of the observation windows and the furnace door on both sides. The smelting and purification were carried out for a total of 7 times. After the smelting was completed, the effective smelting length was 302 mm. The amount of impurity enrichment areas at both ends was removed, accounting for 13.71% of the total length of the rare earth scandium rod. High-purity rare earth scandium was obtained, and its purity was tested to be >99.996%.

[0095] Example 2

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

[0097] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The diameter of the electron gun tungsten filament is 1.2mm. There is a 3mm distance between the electron gun filament and the edge of the electron gun. Contact is prohibited. An alumina ceramic tube is placed in the middle of the parallel electron gun filament to isolate it. The size is φ1.5mm×φ3mm×30mm. The filament is prohibited from getting close to it. The upper and lower clamping devices of 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 fixture. According to the length of the metal yttrium rod, the upper fixing fixture is controlled to move to a position 10mm beyond the top of the material rod. The upper fixing fixture is controlled to slowly descend at a speed of 7mm / min. The material rod is slowly and steadily inserted into the upper and lower clamps. The position of the yttrium rod is fixed and the clamps are tightened. Use transparent high-temperature resistant tape to stick on 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: The vacuum electron beam zone melting furnace is equipped with a mechanical pump and a molecular pump to simultaneously operate the vacuum. When the absolute pressure in the vacuum electron beam zone melting furnace is 8.3×10 -4 Pa, rotate the metal yttrium rod counterclockwise at a speed of 5r / min, increase the filament current to 80A and bake the filament for 20 minutes.

[0099] (4) Initial smelting: When the vacuum degree of the furnace chamber reaches 7.7×10 -4 Pa, start the acceleration voltage and adjust the value to 20.0kV, adjust the filament current to 80A, and control the emission current to increase to 0.2A. Initially, bright light appears on the surface of the rare earth yttrium rod. As the emission current and power increase, a suspended melt zone with a width of 2mm appears on the rod.

[0100] (5) Stable smelting and cooling treatment: 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 automatically moves upward in a direction parallel to the scandium rod. The moving speed of the electron gun is 5 mm / min. As the melting area of the material rod expands, the liquid area fluctuates. The filament current is reduced. During the process of adjusting the filament current, the emission current is controlled within the range of 0.37A~0.5A. Finally, the filament current is adjusted to 50.0A and the emission current is stabilized at 0.45A. The smelting power is controlled to 9kW, so that the metal yttrium suspended molten zone can stably exist between the unmelted solid of the material rod without collapsing. The molten area moves as the electron gun moves upward. Under the action of the cooling water of the upper and lower fixed fixtures, the material rod is cooled to a solid state. The average cooling rate during and after the smelting process is 10℃ / min, achieving stable electron beam regional smelting and purification of rare earth metal yttrium rods.

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

[0102] (6) The yttrium metal smelting area showed an inward contraction state, and a large amount of metal enrichment appeared on the inside of the observation windows and the furnace door on both sides. The smelting and purification were carried out 10 times in total. After the smelting was completed, 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, respectively. High-purity rare earth yttrium was obtained, and its purity was tested to be >99.996%.

[0103] Example 3

[0104] (1) Providing rare earth metals: The raw material terbium metal is cast in an induction melting furnace to obtain rare earth metal terbium ingots, which are then processed by wire cutting and turning machines into terbium rods with a diameter of φ6 mm and a length of 500 mm; the purity of the rods is 99.96%.

[0105] (2) Fixing the metal rod: An electron gun is installed in the vacuum electron beam zone melting furnace. The diameter of the electron gun tungsten filament is 0.6mm. There is an 8mm distance between the electron gun filament and the edge of the electron gun. Contact is prohibited. Boron nitride insulation is placed in the middle of the parallel electron gun filaments. The size is 6mm×12mm×1.5mm. Close contact is prohibited. The upper and lower clamping devices of the material rod are divided into upper and lower ends. The rare earth metal terbium rod is placed in the material rod fixing device of the electron beam zone melting furnace. The rare earth metal terbium rod is inserted into the lower fixing fixture. According to the length of the metal terbium rod, the upper fixing fixture is controlled to move to a position 5mm beyond the top of the material rod. The upper fixing fixture is controlled to slowly descend at a descending speed of 5mm / min. The material rod is slowly and steadily inserted into the upper and lower clamps. The position of the terbium rod is fixed and the clamps are tightened. Use transparent high-temperature resistant tape to stick on the observation window and the inside of the furnace door to prevent rare earth metal volatilization and condensation on the observation window glass and the furnace door.

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

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

[0108] (5) Stable smelting and cooling treatment: After the surface of the terbium rod melts, a suspended molten zone appears, and the emission current increases sharply. The electron gun is started and automatically moves upward in a direction parallel to the scandium rod. The moving speed of the electron gun is 7 mm / min. As the melting area of the material rod expands, the liquid area fluctuates. The filament current is reduced. During the process of adjusting the filament current, the emission current is controlled within the range of 0.26A~0.35A. Finally, the filament current is adjusted to 35.0A and the emission current is stabilized at 0.32A. The smelting power is controlled to 0.96kW, so that the suspended molten zone of the metal terbium can stably exist between the unmelted solid of the material rod without collapsing. The molten zone moves with the rising movement of the electron gun. Under the action of the cooling water of the upper and lower fixed fixtures, the material rod is cooled to a solid state. The average cooling rate during and after the smelting process is 20℃ / min, achieving stable electron beam regional smelting and purification of the rare earth metal terbium rod.

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

[0110] (6) The terbium metal smelting area showed an inward contraction state, and a large amount of metal enrichment appeared on the inside of the observation windows and the furnace door on both sides. The smelting and purification were carried out 5 times in total. After the smelting was completed, the effective smelting length was 460 mm. The amount of impurity enrichment areas at both ends was cut off, which was 8% of the total length of the rare earth terbium rod. High-purity rare earth terbium was obtained, and the detection purity was >99.995%.

[0111] Example 4

[0112] The method is basically the same as that of Example 2, except that the moving speed of the electron gun is different; specifically, the moving speed of the electron gun in Example 4 is 25 mm / min, and the remaining steps and parameters are the same as those of Example 2.

[0113] In Example 4, after the smelting of the metal yttrium rod is completed, the smelting length is 225 mm, and the amount of impurity-enriched areas removed at both ends is 25% of the total length of the rare earth yttrium rod. Due to the excessively fast movement speed of the molten zone, the impurities in the rare earth metal yttrium molten zone are rapidly solidified before effective separation is achieved, resulting in a relatively poor purification effect on the yttrium rod, and the detected purity is >99.98%.

[0114] Figure 2 Figures 2 and 4 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 relatively smooth after being purified by stable electron beam zone melting, while the spiral pattern of the metal yttrium rod in Example 4 is coarse. This may be due to the fast moving cooling speed and the ineffective melting of the molten metal.

[0115] Example 5

[0116] It is basically the same as Example 2, except that the moving speed of the electron gun is different; specifically, the moving speed of the electron gun in Example 5 is 15 mm / min, and the other steps and parameters are consistent with Example 2.

[0117] In Example 5, when the metal yttrium rod is stably smelted, as the melting area of the material rod expands, the liquid area fluctuates, the filament current is reduced, and the emission current is controlled in the range of 0.31A to 0.45A during the adjustment of the filament current; finally, the filament current is adjusted to 50.0A, and the emission current is stabilized at 0.41A, and the smelting power is controlled to 8.2kW, so that the metal terbium suspension molten zone can be stably present between the unmelted solid of the material rod without collapse, and the molten area moves as the electron gun rises and moves. The metal terbium smelting area shows an inward contraction state, and a large amount of metal enrichment appears on the inside of the observation windows and the furnace door on both sides. A total of smelting and purification are performed 10 times. After the smelting is completed, the effective smelting length is 241mm, and the amount of impurity-enriched areas removed at both ends is 19.66% of the total length of the rare earth yttrium rod, respectively, to obtain high-purity rare earth yttrium with a detection purity of>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 smelting area of the metal terbium rod is an asymmetric suspended melting zone, and the plane state shows a local inward melting contraction-local solidification state, and the melt in the melting zone has a tendency to collapse downward; after the smelting is completed, the effective smelting length is 400 mm, and the amount of impurity-enriched areas removed at both ends is 20% of the total length of the rare earth terbium rod. The metal rod rotates slowly, and the rod plane attracts the electron beam unevenly. Only part of the metal in the melting zone is melted into a melt, and the smelting is insufficient. The detected 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, a suspended molten zone appears on the surface of the metal terbium rod after melting. As the smelting area of the material rod expands, the liquid area fluctuates, the filament current is reduced, the suspended molten zone of the metal terbium becomes larger, the molten metal splashes, and the emission current fluctuates within the range of 0.32~0.47A. The smelting area of the metal terbium shows an inward contraction state, and the melt molten zone fluctuates between the unmelted solid of the material rod and moves with the upward movement of the electron gun. After the smelting is completed, the effective smelting length is 370mm, and the amount of impurity-enriched areas removed at both ends is 26% of the total length of the rare earth terbium rod. The detected purity is>99.991%.

[0124] Comparative Example 1

[0125] The method is basically the same as Example 1, except that the filament current is not reduced after the smelting area appears. Specifically, the steps of Comparative Example 1 are as follows:

[0126] (1) The raw material scandium metal is cast in an induction melting furnace to obtain a rare earth metal scandium ingot, which is then processed by wire cutting and turning into a scandium rod with a diameter of φ16 mm and a length of 350 mm; its 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. There is a distance of 5 mm between the electron gun filament and the edge of the electron gun. Contact is prohibited. A boron nitride insulating piece is placed in the middle of the parallel electron gun filament to isolate it. The size is 5 mm × 10 mm × 1 mm. Close contact is prohibited.

[0128] (3) The upper and lower clamping devices for the material rod are divided into upper and lower ends. Place the rare earth metal scandium rod in the material rod fixing device of the electron beam zone furnace, insert the rare earth metal scandium rod into the lower fixing fixture, and control the upper fixing fixture to move to a position 15mm beyond the top of the material rod according to the length of the metal scandium rod. Control the upper fixing fixture to slowly descend at a speed of 10mm / min, so that the material rod is slowly and steadily inserted into the upper and lower clamps, fix the position of the scandium rod and tighten the clamps. Use transparent high-temperature resistant tape to stick on 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.

[0129] (4) A mechanical pump and a molecular pump are installed outside the vacuum electron beam zone melting furnace to simultaneously operate the vacuum. When the absolute pressure inside the vacuum electron beam zone melting furnace is 7.8×10 -4 Pa, rotate the metal scandium rod clockwise at a speed of 10 r / min, increase the filament current to 70 A and bake the filament for 25 minutes. -4Pa, start the acceleration voltage and adjust the value to 8.0kV, adjust the filament current to 45.0A, and control the emission current to increase to 0.1A. Initially, bright light appears on the surface of the rare earth scandium rod. As the emission current and power increase, a suspended melt zone with a width of 3mm appears on the rod.

[0130] (5) After the surface of the rare earth metal scandium rod melts, a suspended molten zone appears, and the emission current increases sharply. 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, resulting in abnormal high-voltage power supply, making it impossible to effectively perform electron beam zone melting on the metal scandium.

[0131] Comparative Example 2

[0132] It is basically the same as Example 1, except that the time interval between the end of initial smelting and the start of stable smelting is different; specifically, in Comparative Example 2, the interval between the end of initial smelting and the start of stable smelting is 30s.

[0133] In Comparative Example 2, during the process of adjusting and reducing the filament current of the metal scandium rod, the degree of melt fluctuation increased, the degree of contraction of the metal scandium suspended molten zone increased, the melt at the top of the molten zone gathered towards the lower end, and part of the melt flowed downward along the wall of the rod. During the process of adjusting the filament current, the emission current was controlled within the range of 0.23A~0.66A, and the filament current was finally adjusted to 25.0A, and the emission current was stabilized at 0.25A. The smelting power was controlled to 2.0 kW, and the metal scandium suspended molten zone could stably exist between the unmelted solids of the rod without collapse. The degree of inward contraction of the metal scandium smelting area increased. After the smelting was completed, the effective smelting length was 273 mm, and the amount of impurity-enriched zones removed at both ends was 22% of the total length of the rare earth scandium rod, respectively. High-purity rare earth scandium was obtained, and its purity was detected to be >99.993%.

[0134] Impurity content test: GDMS detection analysis was used to test the main impurity elements and their contents in the rare earth metal rods after purification in the above examples and comparative examples. The results are shown in Table 1.

[0135] Table 1

[0136]

[0137] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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 above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for purifying rare earth metals, characterized in that: The steps include: The rare earth metal is subjected to a smelting-cooling treatment to prepare a high-purity rare earth metal rod; the smelting-cooling treatment includes vacuum electron beam zone melting and cooling treatment performed sequentially; removing the impurity-rich region of the high-purity rare earth metal rod; The vacuum electron beam zone melting comprises the following steps: performing initial melting of the rare earth metal, and performing stable melting after a molten zone appears on the surface of the rare earth metal; the interval between the start time of the stable melting and the end time of the initial melting is 5s to 15s; The filament current of the initial smelting is 45A-80A, and the filament current of the stable smelting is 25A-50A.

2. The method for purifying rare earth metals according to claim 1, characterized in that: During the vacuum electron beam zone melting, the moving speed of the electron gun is 1 mm / min to 15 mm / min.

3. The method for purifying rare earth metals according to claim 1, wherein: During the vacuum electron beam zone melting, the rare earth metal has a rotation speed of 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 of the initial smelting is 0.1A~0.4A; (2) The emission current for stable smelting 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 acceleration voltage of the vacuum electron beam zone melting is 3kV~20kV; (2) The vacuum degree of the vacuum electron beam zone melting is less than or equal to 1×10 -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 zone melting, the diameter of the filament 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 comprises the following steps: performing vacuum electron beam zone melting on the rare earth metal using a preheated electron gun; Optionally, the step of preheating the electron gun includes: -4 Pa~1×10 -3 Under the vacuum condition of 1.5 Pa, adjust the filament current of the electron gun to 60A~80A and preheat 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 treatment is 10°C / min to 20°C / min.

9. 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 rare earth metal includes one or more of scandium, yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, holmium, erbium and lutetium; (2) The rare earth metal is in the shape of a rod.

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

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