Method for removing calcium element in rare earth permanent magnet alloy and application thereof

Abstract

The application provides a method for removing calcium in a rare earth permanent magnet alloy and application thereof. The rare earth permanent magnet alloy contains one or more of calcium oxide, calcium hydride and metallic calcium. The method comprises the following steps: performing a first mixing process on the rare earth permanent magnet alloy and water to obtain a rare earth permanent magnet alloy containing calcium hydroxide; performing a second mixing process on the rare earth permanent magnet alloy containing calcium hydroxide and a resin emulsion to obtain a mixed solution of agglomerated particles containing calcium hydroxide and the rare earth permanent magnet alloy, wherein the resin emulsion comprises a base resin, an anionic surfactant and water, and the base resin is selected from vinyl acetate resin and / or polyacrylate; and separating the rare earth permanent magnet alloy from the mixed solution under the action of a magnetic field. The method can remove calcium in the rare earth permanent magnet alloy, and is particularly suitable for removing calcium in a rare earth permanent magnet alloy prepared by a reduction diffusion method.

Description

Technical Field

[0001] This invention relates to the field of magnetic material preparation technology, and more specifically, to a method for removing calcium from rare earth permanent magnet alloys and its application. Background Technology

[0002] In recent years, research on the preparation of rare earth permanent magnet alloys has mainly focused on melting methods, mechanized alloying methods, rapid quenching methods, and reduction-diffusion methods. Among these, the reduction-diffusion method uses metallic calcium or calcium hydride (CaH2), calcium chloride (CaCl2), etc., along with inexpensive metal oxides or metal chlorides and metal raw materials such as iron. Under a high-temperature argon or nitrogen atmosphere, the strong reducing properties of metallic calcium or calcium hydride allow for a redox reaction with the metal oxides, producing the desired alloy. However, this process also generates calcium-containing compounds and leaves calcium residues. If these impurities are mixed in the alloy, they can significantly affect the product's performance.

[0003] To remove calcium residue from rare-earth permanent magnet alloys, water washing is a common method. In this method, the rare-earth permanent magnet alloy powder obtained by reduction diffusion, along with residual impurities such as CaO, CaH2, and Ca, is added to water. These impurities react with water to form calcium hydroxide (Ca(OH)2), and the reaction releases a large amount of heat, potentially causing oxidation of the alloy, and in severe cases, even ignition. Furthermore, Ca(OH)2 is only slightly soluble in water, and its solubility decreases with increasing temperature. This means that a large amount of Ca(OH)2 remains in solid form in water. Moreover, Ca(OH)2 residues also remain within the rare-earth permanent magnet alloy powder particles, making it difficult to remove Ca(OH)2 using water alone.

[0004] Based on this, it is particularly important to study and develop a method to improve the removal rate of calcium in rare earth permanent magnet alloys prepared by reduction diffusion. Summary of the Invention

[0005] The main objective of this invention is to provide a method for removing calcium from rare earth permanent magnet alloys and its application, so as to solve the problem that it is difficult to remove residual calcium from rare earth permanent magnet alloys prepared by reduction diffusion method in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for removing calcium from a rare earth permanent magnet alloy, wherein the rare earth permanent magnet alloy contains one or more of calcium oxide, calcium hydride, and metallic calcium. The method for removing calcium from the rare earth permanent magnet alloy includes: subjecting the rare earth permanent magnet alloy to water in a first mixing process to obtain a rare earth permanent magnet alloy containing calcium hydroxide; subjecting the rare earth permanent magnet alloy containing calcium hydroxide to a second mixing process with a resin emulsion to obtain a mixture of agglomerated particles containing calcium hydroxide and the rare earth permanent magnet alloy, wherein the resin emulsion includes a matrix resin, an anionic surfactant, and water, and the matrix resin is selected from vinyl acetate resin and / or polyacrylate; and separating the rare earth permanent magnet alloy from the mixture under the action of a magnetic field.

[0007] Furthermore, the weight ratio of rare earth permanent magnet alloy, matrix resin and anionic surfactant is 100:(2-6):(1-1.5).

[0008] Furthermore, the solid content of the vinyl acetate resin is 28-32%; the solid content of the polyacrylic acid resin is 15-18%.

[0009] Furthermore, the temperatures of the first mixing process, the second mixing process, and the separation process are each independently selected from 1 to 5 °C.

[0010] Furthermore, the second mixing process is carried out under ultrasonic conditions, namely: ultrasonic power of 1 to 1.2 W / cm2 and ultrasonic cleaning time of 5 to 120 min.

[0011] Furthermore, the anionic surfactant is selected from one or more of the group consisting of anionic polyacrylamide, sodium alkylbenzene sulfonate, and primary alkyl sulfate.

[0012] Furthermore, the rare earth permanent magnet alloy is in the form of blocks or powder; wherein when the rare earth permanent magnet alloy is in the form of blocks, the particle size of the rare earth permanent magnet alloy is 0.5 to 50 mm, preferably 1 to 5 mm; when the rare earth permanent magnet alloy is in the form of powder, the particle size of the rare earth permanent magnet alloy is 1 to 5000 μm, preferably 1 to 50 μm.

[0013] Furthermore, the magnetic field strength is 0.1–0.3 A / m.

[0014] Furthermore, the rare earth permanent magnet alloy is selected from one or more of the group consisting of samarium iron alloy, samarium cerium iron manganese alloy, neodymium iron nitrogen alloy, cerium iron nitrogen alloy and samarium praseodymium iron alloy.

[0015] To achieve the above objectives, another aspect of the present invention provides the application of the method for removing calcium from the rare earth permanent magnet alloy provided in this application in the field of rare earth permanent magnet alloy preparation.

[0016] By applying the technical solution of the present invention, in the first mixing process, the calcium oxide, calcium hydride or metallic calcium contained in the rare earth permanent magnet alloy will react with water to generate calcium hydroxide, thereby obtaining a rare earth permanent magnet alloy containing calcium hydroxide.

[0017] Anionic surfactants in resin emulsions can impart a negative charge to the surface of the matrix resin particles, enabling the formation of a stable system with an electric double layer structure within the emulsion. During the second mixing process, calcium hydroxide ionizes to release a small amount of calcium ions. These positively charged calcium ions neutralize the negative charge on the resin particles, reducing the charge density and causing a decrease in surface potential and compression of the electric double layer thickness, thereby lowering the potential barrier. As more and more calcium ions are adsorbed, the potential barrier gradually disappears. When the barrier disappears, the surface potential approaches zero. At this point, the matrix resin particles, carrying calcium ions, coat the surface of the calcium hydroxide and agglomerate to form the aforementioned calcium hydroxide aggregates.

[0018] The aggregated calcium hydroxide particles and the water in the system are non-magnetic, while the rare earth permanent magnet alloy is magnetic. Based on the difference in their magnetic properties, the rare earth permanent magnet alloy can be separated from the mixture by the action of a magnetic field, thus achieving the removal of calcium. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] As described in the background section, existing reduction-diffusion methods for preparing rare-earth permanent magnet alloys suffer from the problem of difficulty in removing calcium impurities. To address this technical problem, this application provides a method for removing calcium from rare-earth permanent magnet alloys. The rare-earth permanent magnet alloy contains one or more of calcium oxide, calcium hydride, and metallic calcium. The method includes: a first mixing process of the rare-earth permanent magnet alloy with water to obtain a rare-earth permanent magnet alloy containing calcium hydroxide; a second mixing process of the rare-earth permanent magnet alloy containing calcium hydroxide and a resin emulsion to obtain a mixture of agglomerated particles containing calcium hydroxide and the rare-earth permanent magnet alloy, wherein the resin emulsion comprises a matrix resin, an anionic surfactant, and water, and the matrix resin is selected from vinyl acetate resin and / or polyacrylate; and separation of the rare-earth permanent magnet alloy from the mixture under the action of a magnetic field.

[0021] In the first mixing process, the calcium oxide, calcium hydride or metallic calcium contained in the rare earth permanent magnet alloy will react with water to generate calcium hydroxide, thus obtaining a rare earth permanent magnet alloy containing calcium hydroxide.

[0022] Anionic surfactants can give the surface of the matrix resin particles a negative charge, enabling the formation of a stable double-layer structure in the emulsion. During the second mixing process, calcium hydroxide ionizes to release a small amount of calcium ions. These positively charged calcium ions neutralize the negative charge on the resin particles, reducing the charge density and causing a decrease in surface potential and compression of the double-layer thickness, thus lowering the potential barrier. As more and more calcium ions are adsorbed, the potential barrier gradually disappears. When the barrier disappears, the surface potential approaches zero. At this point, the matrix resin particles, carrying calcium ions, coat the surface of the calcium hydroxide and agglomerate to form the aforementioned calcium hydroxide aggregates.

[0023] The coagulated particles of calcium hydroxide and the water in the system are non-magnetic, while the rare earth permanent magnet alloy is magnetic. Based on the difference in their magnetic properties, the rare earth permanent magnet alloy can be separated from the mixture by the action of a magnetic field, thus achieving the removal of calcium.

[0024] In a preferred embodiment, the weight ratio of rare earth permanent magnet alloy, matrix resin, and anionic surfactant is 100:(2-6):(1-1.5). When the amount of rare earth permanent magnet alloy is too small, although it will not reduce the calcium removal rate, it will significantly increase the process cost; when the amount of rare earth permanent magnet alloy is too large, only a portion of the calcium hydroxide generated after the calcium reacts with water can be neutralized by the anionic surfactant, leading to a decrease in the calcium removal rate. Compared to other ranges, limiting the weight ratio of rare earth permanent magnet alloy, matrix resin, and anionic surfactant to the above range is beneficial to further improve the agglomeration rate of calcium hydroxide particles, thereby improving the calcium removal rate in the rare earth permanent magnet alloy.

[0025] In a preferred embodiment, the solid content of the vinyl acetate resin is 28%–32%, and the solid content of the polyacrylic acid resin is 15%–18%. Compared to other ranges, limiting the solid content of the vinyl acetate resin to the above range is beneficial for the subsequent formation of more structurally stable calcium hydroxide agglomerates, increasing the calcium content in the agglomerates. It also increases the density difference between the agglomerates and the rare earth permanent magnet powder, thereby further improving the separation rate between the agglomerates and the rare earth permanent magnet alloy. Through these two effects, the removal rate of calcium from the rare earth permanent magnet alloy is further improved.

[0026] The cavitation, acceleration, and direct flow effects of ultrasound in liquids can disperse, emulsify, and peel off contaminants, achieving the purpose of cleaning. To ensure that residual calcium-containing compounds and metallic calcium in the rare-earth permanent magnet alloy are well dispersed and peeled off, and to absorb the large amount of heat released when these compounds and metallic calcium react with water, preventing localized overheating and oxidation, in a preferred embodiment, the temperatures of the first mixing process, the second mixing process, and the separation process are independently set to, but not limited to, 1–5°C. Furthermore, this allows for better utilization of the matrix resin's suitable viscosity at low temperatures, enabling better coating of the peeled calcium hydroxide surface and reducing the likelihood of calcium hydroxide agglomeration with the rare-earth permanent magnet alloy, thereby further improving the calcium removal rate.

[0027] To improve the dispersion uniformity of rare earth permanent magnet alloys in water, enhance the bonding force between calcium hydroxide and matrix resin particles, and thus increase the calcium removal rate from the rare earth permanent magnet alloys, in a preferred embodiment, the second mixing process is carried out under ultrasonic conditions, specifically: ultrasonic power of 1–1.2 W / cm². 2 The ultrasonic cleaning time is 5 to 120 minutes.

[0028] Anionic surfactants can dissociate in water into negatively charged hydrophobic surfactant ions and positively charged counterions. During the second mixing process, the anionic surfactant can impart a negative charge to the surface of the matrix resin, forming a stable system with an electric double layer structure. In a preferred embodiment, the anionic surfactant includes, but is not limited to, one or more of anionic polyacrylamide, sodium alkylbenzene sulfonate, and primary alkyl sulfates.

[0029] In a preferred embodiment, the rare earth permanent magnet alloy is in block or powder form. To improve the uniformity of dispersion of the rare earth permanent magnet alloy in water, ensuring sufficient contact and reaction between the calcium-containing compounds and metallic calcium contained therein and the water, the particle size of the rare earth permanent magnet alloy is 0.5–50 mm when it is in block form. To further increase the contact area between the rare earth permanent magnet alloy and water, increase the formation rate of calcium hydroxide, and shorten the reaction time of the first mixing process, the particle size of the rare earth permanent magnet alloy is preferably 1–5 mm.

[0030] To improve the uniformity of rare earth permanent magnet alloy dispersion in water, ensuring sufficient contact and reaction between the calcium-containing compounds and metallic calcium, the particle size of the rare earth permanent magnet alloy in powder form is 1–5000 μm. To further increase the contact area between the rare earth permanent magnet alloy and water, improve the calcium hydroxide formation rate, and shorten the reaction time of the first mixing process, the particle size of the rare earth permanent magnet alloy is preferably 1–50 μm.

[0031] In order to improve the separation effect of the magnetic rare earth permanent magnet alloy with other non-magnetic impurities, and thus improve the removal rate of calcium, in a preferred embodiment, the magnetic field strength is 1 to 1.2 A / m.

[0032] In this application, the rare earth permanent magnet alloy can be a conventional type of rare earth-iron alloy and / or a nitrided rare earth-iron alloy. In a preferred embodiment, the rare earth permanent magnet alloy includes, but is not limited to, one or more of the group consisting of samarium-iron alloy, samarium-cerium-iron-manganese alloy, neodymium-iron-nitrogen alloy, cerium-iron-nitrogen alloy, and samarium-praseodymium-iron alloy.

[0033] The second aspect of this application also provides the application of the method for removing calcium from the rare earth permanent magnet alloy provided in this application in the field of rare earth permanent magnet alloy preparation.

[0034] The method provided in this application can significantly reduce the content of calcium oxide, calcium hydride or metallic calcium in rare earth permanent magnet alloys, thereby reducing the impurity content. Its application in the field of rare earth permanent magnet alloy preparation is beneficial to greatly improve the purity of rare earth permanent magnet alloys.

[0035] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0036] Example 1

[0037] A method for removing calcium from rare earth permanent magnet alloys, the specific steps of which are as follows:

[0038] Take 100g of samarium-iron alloy block prepared by reduction diffusion process and coarsely crush it into small pieces with a D50 of 2mm. Set the temperature of the constant temperature ultrasonic cleaning equipment containing water to 5℃. After the water temperature reaches the set value, add the coarsely crushed samarium-iron alloy into the container containing water for the first mixing process. The stirring time is 2min.

[0039] 10g of vinyl acetate resin emulsion was added to the above container for a second mixing process. The vinyl acetate resin emulsion consisted of ethyl acetate resin, anionic surfactant, and water. The solid content of the ethyl acetate resin was 29%, and the anionic surfactant was anionic polyacrylamide. The weight ratio of samarium iron alloy, vinyl acetate resin, and anionic polyacrylamide was 100:3:1.2. The container containing the samarium iron alloy was placed in a water-based constant-temperature ultrasonic cleaning device, and the ultrasonic power was turned on at 1.1W / cm². 2 The ultrasonic cleaning time is 15 minutes.

[0040] After ultrasonic treatment, a magnet is used to gather the rare earth permanent magnet alloy powder at the bottom of the device using a magnetic field of 0.1 A / m. The separated rare earth permanent magnet alloy powder is collected, and the water is discarded. The collected rare earth permanent magnet alloy powder is then placed in a vacuum drying oven at 40°C to dry, thus completing the removal of calcium.

[0041] A small amount of the rare-earth permanent magnet alloy obtained after the above removal method was taken, and its oxygen and calcium contents were tested. The oxygen content was found to be 1.78%, and the calcium content was 0.40%.

[0042] Example 2

[0043] The difference from Example 1 is as follows: 250g of samarium cerium iron manganese alloy block was taken and coarsely crushed into small pieces with a D50 of 5.7mm; the stirring time was 4min; the amount of vinyl acetate resin emulsion added was 20g; the weight ratio of samarium cerium iron manganese alloy, vinyl acetate resin and anionic polyacrylamide was 100:3:1.2; and the ultrasonic cleaning time was 30min.

[0044] The measured oxygen content was 1.96%, and the calcium content was 0.38%.

[0045] Example 3

[0046] The difference from Example 1 is as follows: 400g of NdFeNi alloy powder with a D50 of 6.4μm was used; the stirring time was 5min; the amount of vinyl acetate resin emulsion added was 25g; the weight ratio of NdFeNi alloy, vinyl acetate resin and anionic polyacrylamide was 100:3:1.2; and the ultrasonic cleaning time was 50min.

[0047] The measured oxygen content was 2.30%, and the calcium content was 0.31%.

[0048] Example 4

[0049] The difference from Example 1 is as follows: 400g of cerium-iron-nitrogen alloy powder with a particle size D50 of 8μm was taken; the stirring time was 8min; the amount of vinyl acetate resin emulsion added was 30g; the weight ratio of cerium-iron-nitrogen alloy, vinyl acetate resin and anionic polyacrylamide was 100:3:1.2; and the ultrasonic cleaning time was 60min.

[0050] The measured oxygen content was 1.64%, and the calcium content was 0.14%.

[0051] Example 5

[0052] The difference from Example 1 is that the weight ratio of samarium iron alloy, vinyl acetate resin and anionic polyacrylamide is 100:2:1.

[0053] The measured oxygen content was 1.76%, and the calcium content was 0.40%.

[0054] Example 6

[0055] The difference from Example 1 is that the weight ratio of samarium iron alloy, vinyl acetate resin and anionic polyacrylamide is 100:6:1.5.

[0056] The measured oxygen content was 1.77%, and the calcium content was 0.39%.

[0057] Example 7

[0058] The difference from Example 1 is that the weight ratio of samarium iron alloy, vinyl acetate resin and anionic polyacrylamide is 100:1:0.5.

[0059] The measured oxygen content was 1.78%, and the calcium content was 0.92%.

[0060] Example 8

[0061] The difference from Example 1 is that the solid content of the vinyl acetate resin is 28%.

[0062] The measured oxygen content was 1.80%, and the calcium content was 0.42%.

[0063] Example 9

[0064] The difference from Example 1 is that the solid content of the vinyl acetate resin is 32%.

[0065] The measured oxygen content was 1.81%, and the calcium content was 0.39%.

[0066] Example 10

[0067] The difference from Example 1 is that the solid content of the vinyl acetate resin is 20%.

[0068] The measured oxygen content was 1.76%, and the calcium content was 0.54%.

[0069] Example 11

[0070] The difference from Example 1 is that the temperature of the first mixing process, the second mixing process, and the separation process is 1°C.

[0071] The measured oxygen content was 1.74%, and the calcium content was 0.38%.

[0072] Example 12

[0073] The difference from Example 1 is that the temperature of the first mixing process, the second mixing process, and the separation process is 25°C.

[0074] The measured oxygen content was 2.1%, and the calcium content was 1.4%.

[0075] Example 13

[0076] The difference from Example 4 is that the temperature of the first mixing process, the second mixing process, and the separation process is 25°C.

[0077] The measured oxygen content was 1.80%, and the calcium content was 1.75%.

[0078] Example 14

[0079] The difference from Example 1 is that the ultrasonic power is 1 W / cm. 2 The ultrasonic cleaning time is 120 minutes.

[0080] The measured oxygen content was 1.77%, and the calcium content was 0.41%.

[0081] Example 15

[0082] The difference from Example 1 is that the ultrasonic power is 1.2 W / cm. 2 The ultrasonic cleaning time is 5 minutes.

[0083] The measured oxygen content was 1.78%, and the calcium content was 0.37%.

[0084] Example 16

[0085] The difference from Example 1 is that the ultrasonic power is 0.5 W / cm. 2 The ultrasonic cleaning time is 120 minutes.

[0086] The measured oxygen content was 1.95%, and the calcium content was 0.60%.

[0087] Example 17

[0088] The difference from Example 1 is that the anionic surfactant is sodium alkylbenzene sulfonate.

[0089] The measured oxygen content was 1.92%, and the calcium content was 0.42%.

[0090] Example 18

[0091] The difference from Example 1 is that the matrix resin includes polyacrylate, anionic polyacrylamide, and water, wherein the solid content of polyacrylate is 16%. The weight ratio of samarium iron alloy, polyacrylic acid resin, and anionic polyacrylamide is 100:3:1.2.

[0092] The measured oxygen content was 1.82%, and the calcium content was 0.43%.

[0093] Example 19

[0094] The difference from Example 18 is that the solid content of the polyacrylate is 15%.

[0095] The measured oxygen content was 1.81%, and the calcium content was 0.42%.

[0096] Example 20

[0097] The difference from Example 18 is that the solid content of the polyacrylate is 18%.

[0098] The measured oxygen content was 1.79%, and the calcium content was 0.43%.

[0099] Example 21

[0100] The difference from Example 18 is that the solid content of the polyacrylate is 10%.

[0101] The measured oxygen content was 1.98%, and the calcium content was 0.69%.

[0102] Example 22

[0103] The difference from Example 18 is that the weight ratio of samarium iron alloy, polyacrylic resin and anionic polyacrylamide is 100:2:1.

[0104] The measured oxygen content was 1.78%, and the calcium content was 0.42%.

[0105] Example 23

[0106] The difference from Example 18 is that the weight ratio of samarium iron alloy, polyacrylic resin and anionic polyacrylamide is 100:6:1.5.

[0107] The measured oxygen content was 1.76%, and the calcium content was 0.41%.

[0108] Example 24

[0109] The difference from Example 18 is that the weight ratio of samarium iron alloy, polyacrylic resin and anionic polyacrylamide is 100:1:0.5.

[0110] The measured oxygen content was 1.95%, and the calcium content was 0.68%.

[0111] Comparative Example 1

[0112] The difference from Example 1 is that only the first mixing and separation process was carried out, the second mixing process was not carried out, and vinyl acetate resin emulsion was not added; in the first mixing process, 100g of samarium praseodymium iron alloy with a D50 of 4.5mm was taken; the water temperature was 25℃ and the stirring time was 10min.

[0113] The measured oxygen content was 3.40%, and the calcium content was 6.24%.

[0114] Comparative Example 2

[0115] The difference from Example 1 is that the vinyl acetate resin emulsion is composed of vinyl acetate resin, a zwitterionic surfactant dodecylbenzenesulfonic acid, and water.

[0116] The measured oxygen content was 2.30%, and the calcium content was 2.15%.

[0117] The test results of all embodiments and comparative examples of this application are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0122] Comparative Examples 1, 5 to 7 and Comparative Examples 18, 22 to 24 show that, compared to other ranges, limiting the weight ratio of rare earth permanent magnet alloy, matrix resin and anionic surfactant within the preferred range of this application is beneficial to improving the agglomeration rate of calcium hydroxide particles, and thus beneficial to improving the removal rate of calcium in rare earth permanent magnet alloy.

[0123] Comparative examples 1, 8 to 10, and 18, 19 to 21, show that limiting the solid content of vinyl acetate resin and polyacrylic acid resin to the preferred range of this application, compared to other ranges, is beneficial for the subsequent formation of more structurally stable calcium hydroxide agglomerated particles, increasing the calcium content in the agglomerated particles. It also increases the density difference between the agglomerated particles and the rare earth permanent magnet powder, thereby further improving the separation rate between the agglomerated particles and the rare earth permanent magnet alloy. Through these two effects, the removal rate of calcium in the rare earth permanent magnet alloy is further improved.

[0124] Comparative studies of Examples 1, 11, and 12, and Examples 4 and 13, show that limiting the temperatures of the first mixing process, the second mixing process, and the separation process to the preferred range of this application is beneficial for effectively dispersing and stripping the residual calcium-containing compounds and metallic calcium in the rare earth permanent magnet alloy. Simultaneously, this helps absorb the large amount of heat released when the calcium-containing compounds and metallic calcium react with water, preventing excessively high local temperatures that could lead to oxidation. Furthermore, it allows for better utilization of the suitable viscosity of the vinyl acetate resin emulsion at low temperatures, enabling the matrix resin to better coat the surface of the stripped calcium hydroxide and reducing the likelihood of agglomeration between calcium hydroxide and the rare earth permanent magnet alloy, thereby further improving the calcium removal rate.

[0125] Comparing Examples 1, 14 to 16, it can be seen that conducting the second mixing process under ultrasonic conditions and limiting the ultrasonic conditions to the preferred range of this application is beneficial to improving the dispersion uniformity of rare earth permanent magnet alloy in water, improving the bonding force between calcium hydroxide and matrix resin particles, and thus improving the removal rate of calcium element in rare earth permanent magnet alloy.

[0126] Comparing Examples 1 and 17 with Comparative Example 2, it can be seen that anionic surfactants can dissociate into negatively charged hydrophobic surfactant ions and positively charged counterions in water. In the second mixing process, using the preferred type of anionic surfactant of this application is beneficial for forming a more stable electric double layer structure on the surface of the matrix resin particles.

[0127] Comparing all embodiments with Comparative Example 1, it can be seen that, using the technical solution of this application, in the first mixing process, the calcium oxide, calcium hydride, or metallic calcium contained in the rare earth permanent magnet alloy reacts with water to generate calcium hydroxide, resulting in a rare earth permanent magnet alloy containing calcium hydroxide. The anionic surfactant in the resin emulsion can make the surface of the matrix resin particles negatively charged, forming a stable system with an electric double layer structure in the emulsion. In the second mixing process, because calcium hydroxide ionizes to release a small amount of calcium ions, the positively charged calcium ions neutralize the negative charge on the resin particles, reducing the charge density, causing a decrease in surface potential and compression of the electric double layer thickness, thereby lowering the potential barrier. As more and more calcium ions are adsorbed, the potential barrier gradually disappears. When the potential barrier disappears, the surface potential approaches zero. At this time, the matrix resin particles carry calcium ions, coat the surface of calcium hydroxide, and agglomerate into the aforementioned calcium hydroxide agglomerate particles. The coagulated particles of calcium hydroxide and the water in the system are non-magnetic, while the rare earth permanent magnet alloy is magnetic. Based on the difference in their magnetic properties, the rare earth permanent magnet alloy can be separated from the mixture by the action of a magnetic field, thus achieving the removal of calcium.

[0128] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for removing calcium from rare earth permanent magnet alloys, characterized in that, The rare earth permanent magnet alloy contains one or more of calcium oxide, calcium hydride, and metallic calcium, and the method for removing calcium from the rare earth permanent magnet alloy includes: The rare earth permanent magnet alloy is mixed with water in a first mixing process to obtain a rare earth permanent magnet alloy containing calcium hydroxide. The rare earth permanent magnet alloy containing calcium hydroxide and the resin emulsion are subjected to a second mixing process to obtain a mixture of calcium hydroxide-containing aggregated particles and the rare earth permanent magnet alloy, wherein the resin emulsion includes a matrix resin, an anionic surfactant and water, and the matrix resin is selected from vinyl acetate resin and / or polyacrylic acid resin. Under the influence of a magnetic field, the rare earth permanent magnet alloy is separated from the mixture.

2. The method for removing calcium from rare earth permanent magnet alloys according to claim 1, characterized in that, The weight ratio of the rare earth permanent magnet alloy, the matrix resin and the anionic surfactant is 100:(2-6):(1-1.5).

3. The method for removing calcium from rare earth permanent magnet alloys according to claim 1 or 2, characterized in that, The solid content of the vinyl acetate resin is 28-32%; the solid content of the polyacrylic acid resin is 15-18%.

4. The method for removing calcium from rare earth permanent magnet alloys according to claim 1, characterized in that, The temperatures of the first mixing process, the second mixing process, and the separation process are each independently selected from 1 to 5°C.

5. The method for removing calcium from rare earth permanent magnet alloys according to claim 4, characterized in that, The second mixing process is carried out under ultrasonic conditions, wherein the ultrasonic power is 1–1.2 W / cm². 2 The ultrasonic cleaning time is 5 to 120 minutes.

6. The method for removing calcium from rare earth permanent magnet alloys according to claim 1 or 2, characterized in that, The anionic surfactant is selected from one or more of the group consisting of anionic polyacrylamide, sodium alkylbenzene sulfonate, and primary alkyl sulfate.

7. The method for removing calcium from rare earth permanent magnet alloys according to claim 6, characterized in that, The rare earth permanent magnet alloy is in block or powder form; wherein when the rare earth permanent magnet alloy is in block form, the particle size of the rare earth permanent magnet alloy is 0.5-50 mm. When the rare earth permanent magnet alloy is in powder form, the particle size of the rare earth permanent magnet alloy is 1 to 5000 μm.

8. The method for removing calcium from rare earth permanent magnet alloys according to claim 7, characterized in that, When the rare earth permanent magnet alloy is in block form, the particle size of the rare earth permanent magnet alloy is 1-5 mm.

9. The method for removing calcium from rare earth permanent magnet alloys according to claim 7, characterized in that, When the rare earth permanent magnet alloy is in powder form, the particle size of the rare earth permanent magnet alloy is 1 to 50 μm.

10. The method for removing calcium from rare earth permanent magnet alloys according to claim 1, characterized in that, The magnetic field strength is 0.1 to 0.3 A / m.

11. The method for removing calcium from rare earth permanent magnet alloys according to claim 6, characterized in that, The rare earth permanent magnet alloy is selected from one or more of the group consisting of samarium iron alloy, samarium cerium iron manganese alloy, neodymium iron nitrogen alloy, cerium iron nitrogen alloy and samarium praseodymium iron alloy.

12. The application of the method for removing calcium from rare earth permanent magnet alloys according to any one of claims 1 to 11 in the field of rare earth permanent magnet alloy preparation.

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