Recycling method for rare earth sintered magnets

Abstract

To provide a recycling method of a rare earth magnet, which enables recycling of a rare earth magnet by peeling a nickel plating provided on a surface of the rare earth magnet without degrading characteristics of the rare earth magnet, and thereby, can improve a product yield of the rare earth magnet.SOLUTION: Provided is a recycling method of a rare earth magnet, comprising immersing a rare earth magnet, which has on its surface a coating film containing nickel, in a peeling liquid comprising a derivative of nitrobenzene, ethylene diamine, and ammonia.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recycling rare earth magnets, and more particularly to a method for recycling rare earth magnets in which a plating film formed on the surface of a neodymium magnet is removed and the neodymium magnet is reused. [Background technology]

[0002] Rare earth magnets are essential functional materials for energy conservation and high performance, and their range of applications is expanding to a wide range of fields, from general home appliances such as air conditioners to automotive applications such as HEVs and EVs. With the global trend of promoting EVs and the growing demand for ultra-large capacity HDDs for data centers due to the spread of cloud services and video distribution, production volume is expected to increase further in the future.

[0003] A typical rare earth magnet is manufactured by pulverizing a raw alloy adjusted to a specific composition in an inert gas atmosphere, compacting the powder to a certain size while applying a magnetic field, and sintering it in a vacuum or inert gas atmosphere. The manufactured rare earth magnet is processed into the product shape by machining or grinding, and then surface treatment such as plating or painting is performed to become a product. Each process generates losses such as defective products and sludge, but recycling to reduce these losses is positioned as an important process from the viewpoints of effective use of scarce resources, reduction of waste generation, and further reduction of the price of rare earth magnets.

[0004] Among the above processes, in the surface treatment process, the surface of the rare earth magnet is treated to give it corrosion resistance, and Ni plating is generally used in many cases because it has good corrosion resistance and is easy to mass-produce. However, there is a limit to how much the yield can be improved in the surface treatment process of applying Ni plating, and it is inevitable that a certain amount of defective plated products will be generated. As mentioned above, rare earth magnets contain rare earth elements, which are valuable resources, so the reuse of defective plated products is being considered.

[0005] For example, Patent Document 1 describes a technology for removing the Ni coating film of a rare earth alloy by electrolytic oxidation as a method for safely, easily, and inexpensively removing the Ni coating film when reusing Ni-coated waste materials generated in the manufacturing process of Ni-coated rare earth alloys. It reports that electrolytic oxidation is the opposite reaction to electroplating, is easy to control, and can be carried out safely and inexpensively.

[0006] In addition, Patent Document 2 states that, in the case of plating failures that occur during plating, because neodymium magnets are expensive, the plating film is peeled off and re-plated, and that the plating film corrodes the base material of the workpiece, such as neodymium magnets. It has been reported that a non-cyanide based copper and Ni immersion stripper can be provided that is capable of stripping copper and Ni metals or alloys without any chemical reaction. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 5-33074 [Patent Document 2] Japanese Patent Application Publication No. 7-138772 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the technology described in Patent Document 1 aims to remove the Ni plating film as a preliminary step to extracting rare earth elements from rare earth alloys, and makes no mention of the magnetic properties after the Ni plating is removed, which are important when recycling rare earth magnets.

[0009] Furthermore, the technology described in Patent Document 2 leaves room for improvement in terms of the peeling temperature (room temperature to 90°C, particularly 70°C to 80°C). When rare earth magnets are exposed to high temperatures in a basic solution, the base material is not eroded and dissolved, but the characteristics may deteriorate when heating is performed during assembly of the rare earth magnets.

[0010] Furthermore, the technology described in Patent Document 2 is reported to have a plating stripping rate of usually 2 to 10 μm / hr at a treatment temperature of 70 to 80° C., but this stripping rate cannot be said to be sufficient from the viewpoint of improving the efficiency of the recycling process.

[0011] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for recycling rare earth magnets, which selectively dissolves only the Ni plating on the magnet surface without causing any damage to the rare earth magnet base material, which has low corrosion resistance, thereby enabling the rare earth magnets to be recovered as they are and re-plated, etc. [Means for solving the problem]

[0012] As a result of intensive research aimed at solving the above problems, the inventors discovered that magnets can be recycled without losing their magnetic properties by treating them with a liquid containing a nitrobenzene derivative and ethylenediamine, which led to the creation of the present invention.

[0013] That is, the present invention provides the following method for recycling rare earth magnets. 1. A method for recycling rare earth magnets, comprising immersing a rare earth magnet having a Ni-containing coating on its surface in a solution containing a nitrobenzene derivative, ethylenediamine and ammonia. 2. The method for recycling rare earth magnets as described in 1, wherein the nitrobenzene derivative is at least one type of sodium nitrobenzenesulfonate selected from the group consisting of sodium o-nitrobenzenesulfonate, sodium m-nitrobenzenesulfonate, and sodium p-nitrobenzenesulfonate. 3. The method for recycling rare earth magnets according to 1 or 2, wherein the rare earth magnets having a coating containing Ni on their surface are defective products generated during the manufacturing process of rare earth magnets. 4. A method for recycling rare earth magnets as described in any one of 1 to 3, characterized in that while the rare earth magnet having the Ni-containing coating on its surface is immersed in the stripping solution, ultrasonic waves having a frequency of 20 to 100 kHz are applied to the stripping solution. 5. The method for recycling a rare earth magnet according to any one of 1 to 4, wherein the rare earth magnet having the Ni-containing coating on its surface is immersed in the stripping solution at a temperature of 20 to 70°C. 6. The method for recycling a rare earth magnet according to any one of 1 to 5, wherein the pH of the stripping solution is 10.0 to 13.5. 7. The method for recycling rare earth magnets according to any one of 1 to 6, wherein the change in magnetic flux density and coercivity of the rare earth magnet before and after immersion in the stripping solution is 1.0% or less. Effect of the Invention

[0014] According to the present invention, the Ni plating applied to the surface of a rare earth magnet can be removed without compromising the properties of the rare earth magnet, allowing the rare earth magnet to be recycled, thereby improving the product yield of rare earth magnets. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The rare earth magnets to which the rare earth magnet recycling method of the present invention can be applied are those having a coating containing Ni on the surface, and are particularly suitable for Nd sintered magnets that have been subjected to Ni plating (particularly electrolytic Ni plating). Among rare earth magnets, defective products generated during the manufacturing process of rare earth magnets, particularly defective products having defects in the Ni coating, can be suitable for recycling. Here, a defective product mainly refers to a product that has defects (blisters, scratches, no plating, stains, etc.) in the Ni plating film, but has no problems in practical use in the magnet base, and such defective products can be used as good products by applying surface treatment again after peeling off the coating.

[0016] In addition, as a method for recycling rare earth magnets, in addition to the above-mentioned method of reusing them as good products by peeling off the coating and then performing surface treatment again, there is also a method of dissolving each element contained in the rare earth magnet in acid and then returning it to its raw material by a method such as solvent extraction. In such a method, if Ni remains in the solution in which each element contained in the rare earth magnet is dissolved, there is a problem that the extraction efficiency of other elements that are more expensive than Ni is reduced. The Ni-containing coating stripping solution used in the recycling method of the present invention can effectively separate the Ni-containing coating from the rare earth magnet, so it can be used not only for Ni-plated products that have large chips or cracks in the magnet base material that hinder practical use, but also as a pre-treatment for recycling to recover expensive elements from rare earth magnets contained in discarded HDDs collected from the market.

[0017] The stripping solution used in the rare earth magnet recycling method of the present invention for stripping the Ni-containing coating from the rare earth magnet contains an oxidizing agent that dissolves the Ni coating and a Ni-containing solvent that dissolves the Ni coating. 2+ It contains a chelating agent that stabilizes ions. As the oxidizing agent, a derivative of nitrobenzene is used, and preferably at least one type of sodium nitrobenzene sulfonate selected from the group consisting of sodium o-nitrobenzene sulfonate, sodium m-nitrobenzene sulfonate, and sodium p-nitrobenzene sulfonate is used. As the chelating agent, ethylenediamine is used from the viewpoint of the stability of the complex. In addition, ammonia water is added for the purpose of pH adjustment, which makes it easy to achieve the appropriate pH for the peeling reaction. Therefore, the stripping solution used in the rare earth magnet recycling method of the present invention for stripping the Ni-containing coating from the rare earth magnet can be said to be a solution containing a derivative of nitrobenzene and ethylenediamine, the pH of which is adjusted with ammonia. In this way, the rare earth magnet recycling method of the present invention does not use a cyanide compound such as sodium cyanide as a complexing agent, so there is no risk of pollution caused by cyanide wastewater.

[0018] The rare earth magnet recycling method of the present invention can be carried out, for example, by immersing the rare earth magnet having a Ni-containing coating on its surface, which is the object of treatment, in the stripping solution contained in a stripping tank. There are no particular limitations on the method of immersion, and it is sufficient to appropriately adjust the amount of stripping solution and the amount of rare earth magnet to be treated so that the rare earth magnet to be treated is sufficiently in contact with the stripping solution. This method can be applied as either a batch process or a continuous process.

[0019] The amount of the nitrobenzene derivative contained in the stripping solution is preferably 20 to 50 g / L, more preferably 30 to 40 g / L. The saturated solubility of the nitrobenzene derivative, particularly nitrobenzenesulfonate, in water is about 200 g / L, and if the amount used is within the above range, precipitation can be prevented as long as the solvent volatilization amount is realistic (up to 75 vol% is acceptable).

[0020] The amount of ethylenediamine contained in the stripping solution is preferably 50 to 150 g / L, more preferably 80 to 120 g / L. After dissolution, Ni is expressed as [Ni(en) 3 ] 2+ Since it exists in the form of nitrobenzene, stoichiometrically, three times the amount of the nitrobenzene derivative is required. If the amount used is within the above range, it will be about 10 times, so the complex can exist in a very stable manner. It is preferable to place a lid on the stripping tank to prevent a decrease in concentration due to volatilization.

[0021] The pH of the stripping solution is preferably 10.0 to 13.5, more preferably 10.5 to 12.0. For pH adjustment, 25% ammonia water can be used, and the amount used is preferably 10 to 80 g / L. Here, the pH immediately after the stripping solution is adjusted is about 11.0, and the pH increases as Ni dissolution proceeds. When the pH exceeds 12.0, the stripping speed starts to slow down little by little, and the pH when the stripping ability is finally lost is about 13.5. 1 L of the stripping solution can dissolve 10 to 20 g of Ni, and it is economical to use the stripping solution once adjusted until it loses its ability before replacing it. In addition, if the pH during adjustment falls below 10.0, the stripping speed drops significantly. The pH value here is a value measured at 15 to 25°C, and a commercially available device can be used as a measuring device. The concentration of ammonia in the ammonia water used for pH adjustment is not limited to 25 mass%, and can be changed as appropriate. When the ammonia concentration in the ammonia water used for pH adjustment is other than 25% by mass, the amount of ammonia water used is, for example, an amount equivalent to the amount of ammonia used when 25% ammonia water is used in the above-mentioned amount of use. That is, when the ammonia concentration in the ammonia water used for pH adjustment is other than 25% by mass, the amount of ammonia water used is preferably 10 to 80 g / L in terms of 25% ammonia water.

[0022] Furthermore, the immersion temperature of the rare earth magnet in the stripping solution is preferably 20 to 70°C, more preferably 45 to 55°C. Within this range, the decrease in the stripping speed of the coating due to the low liquid temperature of the stripping solution can be suppressed, and the magnetic properties of the rare earth magnet after assembly after stripping can be maintained at a good level. In addition, the pH of the stripping solution may exceed 13 at most, and the higher the liquid temperature, the greater the risk of thermal demagnetization of the sintered Nd magnet. For this reason, it is desirable for the stripping tank containing the stripping solution to have a temperature control mechanism for preventing excessive temperature rise in heating equipment such as a heater.

[0023] The stripping tank that contains the stripping solution preferably has a barrel rotation or rocking mechanism to prevent any part from being left behind. By having such a mechanism, the coating can be stripped efficiently. Although not particularly limited, since rare earth magnets are prone to chipping after the coating has been removed, the rotation speed, particularly when a barrel rotation mechanism is introduced, is preferably 10 rpm or less, and chemically resistant spheres (e.g., Al 2 O 3 Or Zr 2 O 3 Putting about twice the volume of the rare earth magnet to be peeled off into the magnet is very effective in preventing chipping and cracking.

[0024] From the viewpoint of improving the stripping speed during stripping, it is preferable to apply ultrasonic waves with a frequency of 20 to 100 kHz to the stripping solution while the rare earth magnet is immersed in the stripping solution. This not only improves the stripping speed of the coating, but also greatly improves adhesion between the rare earth magnets and the remaining peeling caused by the contact with the stripping cage. In this case, since it becomes difficult to control the liquid temperature due to the application of ultrasonic waves, it is preferable that the capacity of the stripping tank containing the stripping solution is 50 L or more. When the coating is stripped under such conditions, the stripping solution immediately after preparation can strip the Ni-containing coating at a speed of 5 to 20 μm / hr, which makes it possible to strip very efficiently compared to conventional technology.

[0025] In the rare earth magnet recycling method of the present invention, the solution containing a nitrobenzene derivative, ethylenediamine, and ammonia peels off the Ni-containing coating, but hardly corrodes the rare earth magnet base material, so there is almost no change in the magnetic properties of the rare earth magnet before and after the Ni-containing coating is peeled off, and as a result, it is possible to perform Ni plating again without performing a separate process after peeling off the coating, and the recycling efficiency is extremely high. The change in residual magnetic flux density and coercive force before and after peeling off the coating is preferably 1.0% or less, more preferably 0.5%, taking into account variations between individuals and lots. EXAMPLES

[0026] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0027] [Example 1] A 70L stripping solution containing 40g / L of sodium m-nitrobenzenesulfonate, 100g / L of ethylenediamine, and 40g / L of 25wt% ammonia water was prepared and placed in a stripping tank. A 7mm long, 7mm wide, and 1.5mm thick Nd sintered magnet was immersed in the stripping solution for 96 hours under the conditions shown in Table 1, and the presence or absence of weight loss before and after immersion was confirmed. After that, the immersed Nd sintered magnet was magnetized and heat-treated in an oven at 120°C for 1 hour, and then magnetized again to measure the magnetic properties with a pulse tracer (manufactured by Toei Kogyo Co., Ltd.). The results are shown in Table 1.

[0028] [Example 2] The test was carried out in the same manner as in Example 1, except that 15 g / L of Ni was dissolved and the pH was 13.

[0029] [Example 3] A stripping solution (70 L) having a composition of 20 g / L sodium m-nitrobenzenesulfonate, 100 g / L ethylenediamine, and 40 g / L 25 wt% aqueous ammonia was prepared and placed in the stripping tank. Except for this, the test was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0030] [Comparative Example 1] The test was carried out in the same manner as in Example 1, except that 80 g / L of ethylenediamine and 20 g / L of ethylenediaminetetraacetic acid were used as the chelating agent. The results are shown in Table 1.

[0031] [Comparative Example 2] The test was carried out in the same manner as in Example 3, except that ammonium chloride and oxalic acid were used instead of 25 wt % ammonia water to adjust the pH of the stripping solution to 11. The results are shown in Table 1.

[0032] [Table 1] *1 A solution was used that was just about to lose its peeling ability. All other values ​​were measured immediately after adjustment. *2 The demagnetization curve was measured and compared at the intersection with the Pc (permeance) = 0 line. *3 Demagnetization curves were measured and the coercive force values ​​at 90% magnetic flux density were compared.

[0033] As shown in Table 1, when the stripping solutions of Examples 1 to 3 were used, the base material of the sintered Nd magnet was not corroded at all before and after immersion, and the magnetic properties did not deteriorate at all. In contrast, when the stripping solutions of Comparative Examples 1 and 2 were used, it was found that the base material of the sintered Nd magnet was corroded and the magnetic properties were significantly deteriorated simply by immersion. This is thought to be because the components such as oxalate ions and chloride ions used to adjust the pH of the stripping solution corrode the base material of the sintered Nd magnet.

[0034] As described above, a 3.0 mm thick Nd sintered magnet for HDD, which was electrolytically plated with Ni to a thickness of at least 10 μm, was immersed in the stripping solution of Examples 1 and 3, which does not attack the base material of the Nd sintered magnet, and treated under conditions of a stripping solution temperature of 50°C and application of ultrasonic waves at 26 kHz until the plating film was completely peeled off, and the weight loss was recorded. After peeling was confirmed, a new Nd sintered magnet of the same shape was placed in, and this operation was repeated until any remaining plating film remained, and the cumulative weight loss was recorded as the Ni peeling ability. The magnet after peeling was plated again, and reliability tests (corrosion resistance, adhesion) were conducted. The results are shown in Table 2.

[0035] [Table 2] *1 No rust in a pressure cooker test (exposed to 120℃, 2atm saturated steam for 48 hours). *2 Tensile test result: 100kg / cm 2 The end.

[0036] The composition of the stripping solution and Table 2 suggest that the stripping ability depends on the amount of oxidizing agent (nitrobenzene derivative) contained in the stripping solution. In addition, the Nd sintered magnets that had their plating film stripped using the stripping solutions of Examples 1 and 3 and were then re-plated had good corrosion resistance and adhesion.

[0037] As described above, the stripping solutions of Examples 1 to 3 do not attack the base material of the Nd sintered magnet, so they do not deteriorate the magnetic properties, and also do not cause problems with the plating properties when re-plated after the plating film is stripped. Thus, it has been shown that the stripping solution of the present invention can strip the Ni plating applied to the surface of a Nd sintered magnet without compromising the magnetic properties of the magnet, and can re-plate the magnet, allowing the magnet to be recycled, thereby improving the product yield.

Claims

1. A rare earth magnet having a Ni-containing coating on its surface is immersed in a stripping solution containing a nitrobenzene derivative, ethylenediamine, and ammonia; The stripping tank containing the stripping solution has a barrel rotation mechanism, and a barrel in the barrel rotation mechanism includes the rare earth magnet and a chemically resistant sphere; A method for recycling rare earth magnets, wherein the rotation speed of the barrel rotation mechanism is 10 rpm or less.

2. The method for recycling rare earth magnets according to claim 1, characterized in that the derivative of nitrobenzene is at least one type of sodium nitrobenzenesulfonate selected from the group consisting of sodium o-nitrobenzenesulfonate, sodium m-nitrobenzenesulfonate, and sodium p-nitrobenzenesulfonate.

3. 3. The method for recycling rare earth magnets according to claim 1, wherein the rare earth magnets having a coating containing Ni on their surface are defective products generated during the manufacturing process of rare earth magnets.

4. The method for recycling rare earth magnets according to any one of claims 1 to 3, characterized in that while the rare earth magnet having the Ni-containing coating on its surface is immersed in the stripping solution, ultrasonic waves having a frequency of 20 to 100 kHz are applied to the stripping solution.

5. 5. The method for recycling rare earth magnets according to claim 1, wherein the rare earth magnet having the Ni-containing coating on its surface is immersed in the stripping solution at a temperature of 20 to 70° C.

6. 6. The method for recycling rare earth magnets according to claim 1, wherein the pH of the stripping solution is 10.0 to 13.

5.

7. 7. The method for recycling rare earth magnets according to claim 1, wherein the change in magnetic flux density and coercive force of the rare earth magnet before and after immersion in the stripping solution is 1.0% or less.

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