A method for purifying lanthanide metals using microwave-enhanced hydrogen plasma

Abstract

The application provides a method for purifying lanthanide metals by microwave-enhanced hydrogen plasma, comprising the following steps: (1) pretreating lanthanide metal raw materials, drying, sealing in a microwave reactor, and replacing air with inert gas; (2) adjusting microwave power, heating the lanthanide metal raw materials to melting to obtain liquid metal; (3) maintaining the output of microwave power, introducing hydrogen into the microwave reactor, and starting arc discharge to excite and enhance hydrogen plasma under the action of the microwave energy field, and smelting and purifying the liquid metal; (4) after smelting and purifying, cooling to obtain purified lanthanide metal. The microwave-enhanced hydrogen plasma process can improve hydrogen dissociation rate through uniform energy input, effectively maintain the stable generation of hydrogen plasma, and significantly improve the hydrogen radical concentration. At the same time, combined with the microwave heating effect, the removal efficiency of non-metallic impurities can be greatly improved, which has great advantages in industrialized large-scale production of high-quality lanthanide metals.

Description

Technical Field

[0001] This application relates to the field of dry metallurgical purification technology, and in particular to a method for purifying lanthanide metals using microwave-enhanced hydrogen plasma. Background Technology

[0002] Non-metallic impurities such as carbon (C) and nitrogen (N) in lanthanides have a significant negative impact on their performance. These impurities can form hard and brittle intermetallic compounds (such as LaC2 and CeN) with lanthanides, increasing material brittleness and severely impairing its processing properties. The impact of these impurities is particularly pronounced in functional materials applications: in permanent magnets such as neodymium iron boron (NdFeB), C and N impurities disrupt the continuity of magnetic domains, significantly reducing the material's coercivity and maximum energy product; in optical crystals and semiconductor devices, they introduce deep-level defects, severely affecting the material's photoelectric conversion efficiency and carrier mobility. Furthermore, these impurities accelerate the oxidation and corrosion process, shortening the material's lifespan. Therefore, in cutting-edge applications such as high-performance permanent magnets, the content of non-metallic impurities such as C and N must be strictly controlled at the ppm or even ppb level through purification processes to ensure excellent material performance and long-term service stability.

[0003] Plasma metallurgy is a novel metallurgical method that has emerged in recent years. Its applications have expanded from early surface modification and welding to core metallurgical processes such as metal purification. Hydrogen plasma, as a type of plasma, is a special state formed by the ionization of hydrogen atoms or molecules under high temperature or strong electromagnetic field, primarily composed of free electrons and ions (H+). + The plasma consists of cerium atoms and molecules, along with some unionized hydrogen atoms and molecules. This plasma possesses high energy characteristics and contains a large number of active hydrogen radicals and excited-state particles, thus exhibiting extremely strong chemical reactivity and capable of efficiently participating in various chemical reaction processes. Hydrogen plasma melting has excellent potential for removing non-metallic impurities from lanthanide metals. It can chemically react with non-metallic impurities such as carbon (C) and nitrogen (N) to generate volatile hydrocarbons and nitrogen-hydrogen compounds. This purification mechanism based on active hydrogen has significant advantages: on the one hand, the reaction products have high vapor pressure at high temperatures, allowing for efficient removal through vacuum extraction; on the other hand, the process avoids introducing new impurity elements, maintaining the purity of the metal matrix. Experiments have shown that after 30 minutes of hydrogen plasma melting, the carbon content in cerium metal decreased from 113 ppm to 48 ppm, demonstrating its excellent carbon removal capability. However, the current hydrogen plasma melting process generally suffers from problems such as unstable plasma arcs and limited hydrogen plasma concentration, affecting its purification efficiency. Summary of the Invention

[0004] In view of this, this application aims to overcome the deficiencies in the prior art and propose a method for purifying lanthanide metals using microwave-enhanced hydrogen plasma.

[0005] To achieve the above objectives, the technical solution of this application is implemented as follows: A method for purifying lanthanide metals using microwave hydrogen plasma includes the following steps: (1) The lanthanide metal raw materials are pretreated, dried and then placed in a microwave reactor and sealed, and the air is replaced with inert gas; (2) Adjust the microwave power to heat the lanthanide metal raw material until it melts, and obtain liquid metal; (3) Maintain the output of the microwave power, introduce hydrogen gas into the microwave reactor, and start the arc discharge to excite and enhance the hydrogen plasma under the action of the microwave energy field, so as to melt and purify the liquid metal; (4) After the smelting and purification are completed, the purified lanthanide metals are obtained by cooling.

[0006] Furthermore, the pretreatment process in step (1) includes: soaking the lanthanide metal raw material in an acid solution to remove surface oxides, rinsing and drying.

[0007] Furthermore, the acid solution is a hydrochloric acid solution with a concentration of 1% to 10%.

[0008] Furthermore, the inert gas in step (1) is argon, the number of times the air is replaced is 2 to 5, and the oxygen content in the reactor after replacement is ≤10 ppm.

[0009] Furthermore, the microwave power in step (2) is 1 kW to 15 kW, and the target heating temperature is 1000 ℃ to 1300 ℃.

[0010] Furthermore, the concentration of hydrogen gas introduced in step (3) is 10%~30%.

[0011] Furthermore, the melting and purification time in step (3) is 10 min to 120 min.

[0012] Furthermore, in step (4), the microwave power is reduced to 1 kW to 2 kW, and the cooling rate is 10 ℃ / min to 20 ℃ / min.

[0013] This application also provides a purified lanthanide metal prepared by any of the methods described herein.

[0014] Furthermore, the impurities removed during purification are carbon and / or nitrogen, and the purified lanthanide metals have a carbon content ≤40 ppm and a nitrogen content ≤10 ppm.

[0015] This application utilizes a microwave-enhanced hydrogen plasma melting process to purify lanthanide metals. The purification process achieves higher impurity removal efficiency through the synergistic effect of the microwave energy field and hydrogen plasma. First, a 2.45 GHz microwave source is used to rapidly heat the lanthanide metal raw material, forming a homogeneous melt. Simultaneously, hydrogen gas is introduced, and high-temperature hydrogen plasma is generated through arc excitation. The microwave-assisted effect enhances the hydrogen dissociation rate. These highly reactive hydrogen free radicals react with non-metallic impurities such as nitrogen and carbon in the melt, producing volatile products such as nitrogen-hydrogen compounds and hydrocarbons, which are then discharged. By dynamically adjusting key parameters such as microwave power, hydrogen concentration, and melting time, the content of non-metallic impurities such as C and N is strictly controlled at the ppm or even ppb level, and no harmful gases are emitted throughout the process, meeting the requirements of green metallurgy.

[0016] Compared with the prior art, this application has the following advantages: (1) The microwave-enhanced hydrogen plasma melting process has the function of material preheating, which breaks through the heat conduction barrier of traditional heating methods and can heat lanthanide metals quickly and uniformly. This not only improves energy efficiency, but also creates an ideal high-temperature environment for subsequent purification reactions.

[0017] (2) Compared with conventional DC arc or radio frequency plasma, microwave-enhanced plasma technology effectively increases the hydrogen dissociation rate by 10% to 30% and the arc stabilization time by more than 8 minutes, up from 5 minutes. By using microwaves, a specific energy form, to efficiently and accurately excite and maintain hydrogen, the active hydrogen in the furnace cavity is significantly increased.

[0018] (3) Thanks to the assistance of microwave energy and the improvement of hydrogen dissociation rate, the carbon impurity content in cerium metal was further reduced from 48 ppm to 29 ppm under the same smelting process parameters. Microwave enhancement technology can significantly improve the removal rate of waste metal impurities in lanthanide metals, resulting in a lower content of waste metal impurities in the final material. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 The content of cerium metal C impurities after microwave-enhanced hydrogen plasma melting as described in the embodiments of this application; Figure 2 This is a SEM image of cerium metal after microwave-enhanced hydrogen plasma melting as described in the embodiments of this application; Figure 3 This is a TEM image of cerium metal after microwave-enhanced hydrogen plasma melting as described in the embodiments of this application. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It is evident that the described embodiments are merely a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0021] Furthermore, the technical solutions of the various embodiments of this application can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this application.

[0022] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application, as well as the prior art known to those skilled in the art and the descriptions in this application, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of this application.

[0023] This application utilizes microwave-enhanced hydrogen plasma melting to remove C and N impurities from lanthanide metals. Microwave-enhanced hydrogen plasma refers to continuously applying a microwave energy field to the reaction region while simultaneously exciting hydrogen plasma through arc discharge, thereby enhancing plasma activity.

[0024] A novel microwave-enhanced hydrogen plasma process ensures uniform energy input, effectively improves the hydrogen dissociation rate, ensures stable generation of hydrogen plasma, and maintains its highly active plasma state. The microwave-enhanced hydrogen plasma melting and impurity removal mechanism: The microwave enhancement effect and hydrogen plasma melting constitute a highly efficient synergistic purification system. First, the heating effect of microwaves breaks through the heat conduction barrier of traditional heating methods, enabling rapid and uniform heating of lanthanide metals. This not only improves energy efficiency but also creates an ideal high-temperature environment for subsequent deep reactions. Next, the chemical reduction effect of hydrogen plasma becomes the core of purification. Under the excitation of microwave energy, the hydrogen dissociation rate increases, and hydrogen is efficiently ionized into a plasma state with a higher concentration of active hydrogen particles and hydrogen ions, whose reactivity far exceeds that of molecular hydrogen. These active particles react violently with impurities such as carbon and nitrogen in the lanthanide metals, generating hydrocarbons and nitrogen-hydrogen compounds, respectively. Since these products are insoluble in the molten metal, they escape rapidly as bubbles, thus being completely removed from the system. This synergistic effect of physical high temperature and chemical reduction constitutes a powerful impurity removal mechanism.

[0025] Compared to conventional DC arc or radio frequency plasma, microwave plasma exhibits significant advantages in energy efficiency, hydrogen dissociation rate, stability, and reactivity. Thanks to efficient energy coupling, microwave plasma can generate a higher density of reactive particles (such as electrons, ions, and free radicals). This means that within a unit volume, there are more particles with sufficient energy to initiate chemical reactions. Therefore, microwave-enhanced hydrogen plasma technology holds promise for improving the removal efficiency of non-metallic impurities, while shortening purification time, reducing energy costs, and paving the way for the development of green metallurgy.

[0026] Compared to traditional plasma metallurgical techniques, this application provides a method for purifying lanthanide metals using microwave-enhanced hydrogen plasma. The microwave-enhanced hydrogen plasma process, through uniform energy input, increases the hydrogen dissociation rate, effectively maintains the stable generation of hydrogen plasma, and significantly increases the concentration of hydrogen free radicals. Simultaneously, combined with the microwave heating effect, it can greatly improve the removal rate of non-metallic impurities, offering significant advantages for the large-scale industrial production of high-quality lanthanide metals.

[0027] The present application will be described in detail below with reference to the embodiments.

[0028] Example 1 Using crude cerium blocks as raw material, C and N impurities in cerium metal are removed by microwave-enhanced hydrogen plasma melting. The impurity removal process specifically includes the following steps: (1) Soak the crude cerium metal block in 5% hydrochloric acid solution to remove surface oxides, then rinse with deionized water and dry for later use; (2) Place the cerium material in the crucible of the microwave reactor, seal the reactor, and purge the air with argon gas to replace the air. Repeat this process 3 times to ensure that the oxygen content in the reactor is <10 ppm. (3) Adjust the microwave power to 10 kW and heat it rapidly to 1000 ℃ to form liquid cerium; (4) Introduce 20% hydrogen gas, turn on the electric arc, stimulate the plasma, form high-temperature hydrogen free radicals, and melt for 30 min; (5) Turn off the electric arc, reduce the microwave power to 1 kW, control the cooling rate to 20 ℃ / min, wait for the temperature to drop to 100℃, turn off the microwave source, and let the melt stand until it is completely cooled.

[0029] (6) Sampling and analysis of cerium metal C and N content. For example... Figure 1 As shown in Table 1, after 30 min of microwave hydrogen plasma melting, the carbon content in cerium metal was only 29 ppm, which is significantly lower than that of cerium metal raw materials and cerium metal melted by hydrogen plasma, demonstrating the significant effect of microwave assistance in further reducing the carbon impurity content in cerium metal. Figure 2 As shown, the SEM images and EDS results indicate that the cerium metal has high purity and no other impurity elements. Figure 3 High-resolution images show the presence of only cerium lattice, with no lattice fringes from other phases. Furthermore, its nitrogen content is only 5.2 ppm. These results demonstrate that, under the same smelting process parameters, microwave enhancement technology can significantly improve the removal rate of carbon impurities in cerium metal, ultimately resulting in a material with a lower carbon impurity content, thus illustrating the effectiveness and reliability of the microwave enhancement process.

[0030] Table 1. Content of N impurities and other key impurities in cerium metal after microwave-enhanced hydrogen plasma melting.

[0031] Example 2 Using neodymium metal particles as raw material, carbon impurities in neodymium metal are removed by microwave-enhanced hydrogen plasma melting. The impurity removal process specifically includes the following steps: (1) Soak the neodymium metal particles in a 10% hydrochloric acid solution to remove surface hydrides, then rinse with deionized water and dry for later use; (2) Place the dried neodymium metal particles in the crucible of the microwave reactor. Seal the reaction chamber, purge the air with argon gas, and circulate the gas three times to ensure that the oxygen content in the reactor is <10 ppm; (3) Adjust the microwave power to 12 kW and heat it rapidly to 1200 ℃; (4) Maintain microwave power at 12 kW continuous output, introduce 25% hydrogen gas to excite plasma, form high-temperature hydrogen free radicals, and melt for 60 min; (5) Turn off the plasma, reduce the microwave power to 2 kW, control the cooling rate to 10 ℃ / min, wait for the temperature to drop to 100 ℃, turn off the microwave source, and let the melt stand until it is completely cooled.

[0032] (6) The carbon content in the neodymium metal ingot was sampled and analyzed, and the carbon content was only 35 ppm.

[0033] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for purifying lanthanide metals using microwave-enhanced hydrogen plasma, characterized in that, Includes the following steps: (1) The lanthanide metal raw materials are pretreated, dried and then placed in a microwave reactor and sealed, and the air is replaced with inert gas; (2) Adjust the microwave power to heat the lanthanide metal raw material until it melts, and obtain liquid metal; (3) Maintain the output of the microwave power, introduce hydrogen gas into the microwave reactor, and start the arc discharge to excite and enhance the hydrogen plasma under the action of the microwave energy field, so as to melt and purify the liquid metal; (4) After the smelting and purification are completed, the purified lanthanide metals are obtained by cooling.

2. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, The pretreatment process in step (1) includes: soaking the lanthanide metal raw material in an acid solution to remove surface oxides, rinsing and drying.

3. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 2, characterized in that, The acid solution is a hydrochloric acid solution with a concentration of 1% to 10%.

4. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, The inert gas in step (1) is argon, and the air is replaced 2 to 5 times. After replacement, the oxygen content in the reactor is ≤10 ppm.

5. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, In step (2), the microwave power is 1 kW to 15 kW, and the target heating temperature is 1000 ℃ to 1300 ℃.

6. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, In step (3), the concentration of hydrogen gas introduced is 10% to 30%.

7. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, In step (3), the melting and purification time is 10 min to 120 min.

8. The method for purifying lanthanide metals using microwave-enhanced hydrogen plasma according to claim 1, characterized in that, In step (4), the microwave power is reduced to 1 kW to 2 kW, the cooling rate is 10 ℃ / min to 20 ℃ / min, and the temperature after cooling is ≤100 ℃.

9. A purified lanthanide metal, characterized in that, Prepared by the method according to any one of claims 1 to 8.

10. The purified lanthanide metal according to claim 9, characterized in that, The impurities removed during purification are carbon and / or nitrogen, and the purified lanthanide metals contain ≤40 ppm carbon and ≤10 ppm nitrogen.

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