A process for recycling neodymium iron boron magnets

Abstract

The present invention belongs to the technical field of recycling and reusing waste rare earth permanent magnets, and in particular, relates to a process for recycling and reusing NdFeB magnets, comprising the following steps: coating removal, ultrasonic water washing, water washing, drying, and surface treatment; the coating removal includes primary treatment and / or secondary treatment. The NdFeB magnet recycling and reusing process provided by the present invention can reduce material loss and reduce costs; the alkaline nickel removal agent and metal cleaning agent are used, which are environmentally friendly and have good coating removal effects, and are suitable for nickel, copper, zinc, nickel-phosphorus alloys, zinc-nickel alloys and their combined coatings, and almost do not corrode the NdFeB substrate; the magnet obtained by the present invention after high-temperature heat treatment has high moisture and heat resistance, small irreversible loss and excellent cleanliness performance; the obtained electroplated product has excellent bonding strength, high corrosion resistance and good adhesive affinity; the product appearance after treatment is uniform and there is no corrosion phenomenon.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling and reusing waste rare earth permanent magnets, and in particular relates to a process for recycling and reusing neodymium iron boron magnets. Background Art

[0002] Based on the advantages of NdFeB magnets, they are widely used in motors, wind power, hybrid vehicles, smart consumer electronics and other industries. NdFeB magnets are composed of Nd2Fe14B main phase and intergranular Nd-rich phase, but the electrochemical phase difference between the phases of this multiphase structure is large, which is easy to cause electrochemical corrosion. Neodymium is one of the elements with high chemical activity and is very prone to corrosion. Therefore, surface treatment must be performed before application to prevent corrosion. The surface anti-corrosion processes of NdFeB magnets include phosphating, electroplating, electrophoresis, spraying and physical vapor deposition.

[0003] The coatings obtained by electrodeposition on the surface of conventional NdFeB magnets on the market are generally single-layer nickel, double-layer nickel, nickel-copper-nickel (-chemical nickel), nickel-copper-nickel-nickel (-chemical nickel), copper-nickel (-chemical nickel), zinc-zinc-nickel alloy-copper-nickel (-chemical nickel), etc. If equipment failure, bumps, pollution and other abnormalities occur during the production process, product abnormalities will occur. In addition, the magnets after the motor is disassembled are oily, damaged or rusty and cannot be circulated and used normally. However, direct scrapping has caused a waste of rare earth materials that are scarce and expensive on a global scale. Therefore, it is of great significance to recycle and reuse waste magnets. Summary of the invention

[0004] In view of the above shortcomings of the prior art, the object of the present invention is to provide a process for recycling and reusing NdFeB magnets.

[0005] To achieve the above objectives, the technical solutions adopted are:

[0006] One of the purposes of the present invention is to provide a process for recycling and reusing NdFeB magnets, comprising the following steps: (S2) coating removal, (S3) ultrasonic water washing, (S4) water washing, (S5) drying, and (S7) surface treatment. The step (S2) coating removal includes primary treatment and / or secondary treatment.

[0007] Furthermore, before (S2) removing the coating, (S1) pre-treatment is also included.

[0008] Furthermore, between (S5) drying and (S7) surface treatment, (S6) remelting is also included.

[0009] Furthermore, the pre-treatment in step (S1) includes at least one of demagnetization, ultrasonic degreasing, primary water washing, ultrasonic rust removal, and secondary water washing.

[0010] Furthermore, the demagnetization is carried out in a high temperature box, the demagnetization temperature is 390±5°C, and the time is greater than 10min. The ultrasonic degreasing is treated with a degreasing liquid, which is composed of sodium carbonate, sodium metasilicate, sodium phosphate, a surfactant, sodium polyphosphate and water, the degreasing temperature is 60±5°C, the time is 1-10min, and the ultrasonic frequency is 25-28kHz. The primary water washing is used to remove the degreasing liquid remaining on the surface of the product. The ultrasonic rust removal process is carried out in an ultrasonic tank, and the rust removal liquid is an acid, such as hydrochloric acid and nitric acid, with a concentration of 10-50mL / L, a time of 0.5-20min, and an ultrasonic frequency of 25-28kHz. The secondary water washing is used to remove the rust removal liquid and impurities remaining on the surface of the product and clean the surface of the product.

[0011] Furthermore, the primary treatment includes the following steps: immersing and moving the NdFeB magnet with an environmentally friendly alkaline nickel removal agent; the treatment temperature of the primary treatment is 40-90°C, and the treatment time is 0.5-30min; the secondary treatment includes the following steps: immersing and moving the NdFeB magnet with an environmentally friendly metal cleaning agent, and the treatment temperature of the secondary treatment is 60-95°C, and the treatment time is 0.2-5h.

[0012] Among them, there is no special restriction on the immersion method, as long as it is ensured that the adjusted product and the environmentally friendly alkaline nickel-removing agent or the environmentally friendly metal cleaning agent can achieve sufficient contact; the movement method is also not particularly limited, the purpose is to prevent the product from sticking to the wall or adhering to the wall and affecting the contact between the product and the environmentally friendly alkaline nickel-removing agent or the environmentally friendly metal cleaning agent, for example, it can be drum rotation, polishing machine rotation, vibration machine, ultrasonic vibration, hanger movement, etc.; to prevent product sticking, the product to be treated and the glass beads can also be immersed and moved together.

[0013] Furthermore, water washing is also included between the primary treatment and the secondary treatment, for example, the product after the primary treatment is washed with water to clean the surface residue, and then the secondary treatment is performed.

[0014] Furthermore, in terms of mass percentage, the environmentally friendly alkaline nickel removal agent includes 10-30% of a corrosion inhibitor, 0.5-10% of a promoter, 1-15% of a complexing agent, 0.1-1.5% of a surfactant and the remainder of water. To ensure the efficiency of the (S2) coating removal process, a pH adjuster is used to adjust the pH value of the environmentally friendly alkaline nickel removal agent to >11, and the environmentally friendly alkaline nickel removal agent stock solution is replenished according to the surface area of ​​the treated product to maintain the ability to remove the coating; wherein the corrosion inhibitor is at least one of monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, and 2-aminoethanol, preferably 2-aminoethanol; the promoter is sodium hydroxide, potassium hydroxide, and sodium carbonate, preferably sodium hydroxide; the complexing agent is sodium citrate, sodium thiosulfate, and citric acid, preferably sodium thiosulfate; the surfactant is sodium dodecyl sulfate; and the pH adjuster is an alkaline agent, preferably sodium hydroxide.

[0015] Furthermore, in terms of mass percentage, the environmentally friendly metal cleaning agent includes 10-25% corrosion inhibitor, 15-30% oxidant, 5-10% complexing agent, 0.5-3% promoter, 0.5-3% surfactant and the balance water. To ensure the efficiency of the (S2) coating removal process, a pH adjuster is used to adjust the pH value of the environmentally friendly metal cleaning agent to >10, and the environmentally friendly metal cleaning agent stock solution is replenished according to the surface area of ​​the treated product to maintain the ability to remove the coating. Among them, the corrosion inhibitor is one or more of hexamethylenetetramine, ethylenediamine, thiourea, etc., preferably a combination of ethylenediamine and thiourea; the oxidant is an organic acid oxidant, preferably oxalic acid; the complexing agent is one or two of citric acid and sodium citrate; the promoter is a hydroxide, preferably sodium hydroxide; the surfactant is sodium alkylbenzene sulfonate; the pH adjuster is an alkaline agent, preferably sodium hydroxide.

[0016] The step (S3) is to perform ultrasonic water washing on the magnet after the step (S2), and the number of ultrasonic water washing can be one, two or more times, preferably two times.

[0017] The step (S4) is to wash the magnet with water to remove the residual cleaning liquid and impurities on the surface of the magnet. The washing may be performed once, twice or more times, preferably once.

[0018] The step (S5) is to dry the magnet after the step (S4). The drying method is not limited, for example, hot air drying can be used until there is no water stain on the surface of the product. The hydrogen content of the product after the coating is removed is less than 10ppm.

[0019] Furthermore, the step (S6) is to remelt and reprocess the dried product, specifically: remelting to obtain flake alloy, powder making, pressing, heat treatment, machining, diffusion, polishing, ultrasonic water washing, water washing and drying to obtain the product to be surface treated.

[0020] The step (S7) is to perform surface treatment on the magnet after the step (S5) or (S6), wherein the surface treatment is at least one of electrodeposition, thin film coating, paint coating, and high temperature heat treatment. The thin film may be a phosphating film, a passivation film, an oxide film, etc.

[0021] Furthermore, the high-temperature heat treatment includes the following steps: placing the NdFeB magnet into a tubular furnace, followed by vacuum treatment, the vacuum degree is <10Pa, oxygen is introduced to wash the furnace, the temperature in the furnace is maintained at 300-450°C, and then the furnace atmosphere is maintained, oxygen is introduced for 10 minutes every 40 minutes, the pressure divider valve is at 0.25-0.45Mpa, and the process is continued for 0.5-4h, and then the NdFeB magnet is cooled, and the cooling process is first furnace cooling and then air cooling.

[0022] Furthermore, before the NdFeB magnet enters the tube furnace, the following steps are also included: polishing, ultrasonic degreasing, water washing, ultrasonic water washing, and drying.

[0023] Furthermore, before the NdFeB magnet with the coating removed enters the tube furnace, the following steps are also included: product cutting, polishing, ultrasonic degreasing, water washing, ultrasonic water washing, and drying.

[0024] The product is recut to be processed into the target size, parallelism and verticality according to the requirements of the drawing; the polishing is to put the product into a polishing machine for grinding, the polishing machine is one of a vibration polishing machine, a centrifugal polishing machine and a flow polishing machine, the grinding medium is water or an antiseptic liquid, preferably, the abrasive is silicon carbide, the polishing machine frequency is 15-50Hz, and the time is 10-180min; the ultrasonic degreasing can use a degreasing liquid to treat the surface of the recut NdFeB magnet, immerse the NdFeB magnet in the degreasing liquid, remove the surface of the NdFeB magnet and Grease in the pores, preferably, the degreasing liquid is a bubble-free and phosphorus-free room temperature degreasing liquid, the degreasing treatment time is 60-200s, the degreasing treatment temperature is room temperature-50°C, and the ultrasonic frequency is 25-28KHz; the water washing is used to remove the degreasing liquid remaining on the surface of the product; the ultrasonic water washing is used to remove impurities such as magnetic powder remaining on the surface of the product to ensure the cleanliness of the product; the drying refers to drying the product after ultrasonic water washing, and the drying method can be hot air drying, for example, hot air can be used to blow dry until there is no water stain on the surface of the product visually.

[0025] The beneficial effects of the above-mentioned high-temperature heat treatment are: the surface oxygen content of the product after the high-temperature heat treatment is 20-30%; the product after the high-temperature heat treatment has high cleanliness; the product after the high-temperature heat treatment has high moisture and heat resistance, and the moisture and heat resistance performance can reach more than 3.5h; the product after the high-temperature heat treatment has high pencil hardness, and the pencil hardness can reach more than 6H; the product after the high-temperature heat treatment has low irreversible loss, and the irreversible loss is less than 1%.

[0026] Furthermore, the electrodeposition includes the following steps: heating treatment, electrodeposition pre-treatment, electrogalvanizing, and post-treatment.

[0027] Furthermore, the electroplating process comprises the following steps: product cutting, heating treatment, electroplating pre-treatment, electrogalvanizing, and post-treatment.

[0028] Among them, the product is cut to the target size, parallelism and verticality according to the requirements of the drawing. The heating treatment is carried out in an oven at a temperature of 350-400°C and a time of 0.5-4h. The electroplating pretreatment includes ultrasonic degreasing, water washing, pickling, and ultrasonic water washing; the pickling can use dilute nitric acid to treat the degreased magnet surface to remove rust and oxide scale on the magnet surface; for example, the volume concentration of the dilute nitric acid is 1-10%, preferably 1-6%; for example, the pickling treatment temperature is room temperature, and the pickling treatment time is 10-300s, preferably 30-200s; the ultrasonic water washing is used to remove impurities such as acid, magnetic powder, boric ash, etc. remaining on the product surface to ensure the cleanliness of the product, and then ensure the bonding strength between the subsequent substrate and the coating. The electrogalvanizing adopts sulfate zinc plating solution, which includes zinc sulfate, boric acid, potassium sulfate, potassium oxalate, and additives; preferably, the zinc sulfate concentration is 300-420 g / L, the potassium sulfate concentration is 15-35 g / L, the potassium oxalate concentration is 0.5-3 g / L, the boric acid concentration is 25-45 g / L, and the additive concentration is 4-40 mL / L; for example, the plating solution temperature of the electrogalvanizing process is 25-35° C., the pH is 4.0-5.0, and the specific gravity of the plating solution is 25-35; the number of electrogalvanizing can be one or two times; the additive is not particularly limited, and commercially available sulfate zinc plating system additives can be used, but the additive needs to have the functions of improving cathode polarization, refining crystals, enhancing brightness and leveling.

[0029] Furthermore, the post-processing includes light extraction, and the light extraction is to process the NdFeB magnet with a light extraction liquid.

[0030] Furthermore, the post-processing includes light extraction, primary passivation, secondary passivation, and aging.

[0031] Furthermore, the post-processing includes light extraction, water washing, primary passivation, water washing, secondary passivation, water washing, aging, and drying.

[0032] Wherein, the light emitting adopts a light emitting liquid to treat the product, and the light emitting liquid includes nitric acid, trivalent chromium salt, rare earth compound, and water; preferably, the nitric acid concentration is 1-20mL / L; the trivalent chromium salt is at least one of chromium sulfate and chromium nitrate, preferably chromium sulfate, and the concentration is 1-5g / L; the rare earth compound is at least one of lanthanum oxide, cerium nitrate, and cerium sulfate, preferably cerium sulfate, and the concentration is 0.1-5g / L, and the rest is water. The present invention adds trivalent chromium salt and rare earth compound to the nitric acid solution, the purpose is to make the zinc coating layer form a passivation film as soon as possible, so as to prevent the zinc layer from being oxidized and affecting the continuity and consistency of the passivation film formed in the subsequent passivation process, thereby affecting the salt spray effect.

[0033] For example, the light emission process is carried out at room temperature, and the treatment time is 15-60s. The washed product is passivated, wherein the passivation is one or two passivations, preferably two passivations. If two passivation treatments are carried out, the product needs to be washed between the two passivation treatments; the first passivation process is treated with trivalent chromium passivation solution, and the passivation solution includes 20-40g / L chromium sulfate, 3-20g / L cerium sulfate, 1-10g / L zinc chloride, 25-35g / L sodium nitrate, and 0.1-1.5g / L sodium phosphite; the first passivation process is carried out at room temperature, the pH value of the passivation solution is 2.0-3.0, and the passivation time is 15-35s; the solution used for the second passivation is the same as the first passivation, the passivation process is carried out at room temperature, the pH value of the passivation solution is 2.0-3.0, and the passivation time is 3-10s. The washing is to wash the residue of the previous step, and the number of washings can be one, two or more times. The aging is used to enhance the performance of the passivation film, and the aging solution temperature is 55-70°C. The drying process includes pre-dehydration and deep dehydration. Pre-dehydration can be carried out by using a hair dryer or a spin dryer until there are no water drops on the surface of the product. Deep dehydration is to place the product in a vertical oven or drying tunnel for treatment to remove surface crystal water to enhance the corrosion resistance of the product. The temperature is 60-110°C and the dehydration time is 20-60 minutes.

[0034] The dried product has good bonding strength, high corrosion resistance and good adhesive properties, wherein the shear force is greater than 43MPa, the SST is greater than 144h, the wet heat is greater than 192h, and the dyne is greater than 40.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The method for recycling and reusing waste NdFeB products containing metal coatings provided by the present invention can reduce material loss and reduce costs;

[0037] The alkaline nickel removal agent and metal cleaning agent used in the present invention are environmentally friendly, have good removal effect on the coating, are suitable for nickel, copper, zinc, nickel-phosphorus alloy, zinc-nickel alloy and their combined coatings, and hardly corrode the NdFeB substrate;

[0038] The magnet obtained after high-temperature heat treatment by the recycling and reuse method of the present invention has a uniform appearance and no corrosion, has high moisture and heat resistance, small irreversible loss and excellent cleanliness; the obtained electroplated product has excellent bonding strength, high corrosion resistance and good adhesive affinity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a cross-sectional view of the product after treatment in Example 1 (S2);

[0040] Figure 2 is a cross-sectional view of the product after treatment in Example 2 (S2);

[0041] Figure 3 This is the appearance diagram of Example 1 after high temperature heat treatment;

[0042] Figure 4 This is a cross-sectional view of the product after electrogalvanizing in Example 3. DETAILED DESCRIPTION

[0043] The present invention is described below in conjunction with examples, which are only used to explain the present invention and are not used to limit the scope of the present invention.

[0044] Example 1

[0045] The product to be processed is a waste NdFeB product with two layers of metal coatings, a nickel coating and a nickel-phosphorus alloy coating, wrapped around the substrate in sequence. The processing process is as follows:

[0046] (S2) Plating removal:

[0047] Primary treatment: put the product to be treated and glass beads into the drum together, immerse the drum containing the product to be treated and glass beads into the environmentally friendly alkaline nickel removal agent, the drum speed is 3-15r / min, the temperature of the environmentally friendly alkaline nickel removal agent is 85℃, and the immersion time is 5min. Among them, the environmentally friendly alkaline nickel removal agent includes 20% 2-aminoethanol, 8% sodium hydroxide, 10% sodium thiosulfate, 0.2% sodium dodecyl sulfate and the balance water in terms of mass percentage. During the treatment process, sodium hydroxide aqueous solution is used to keep the pH of the environmentally friendly alkaline nickel removal agent at 11.5;

[0048] (S3) Ultrasonic water washing: the ultrasonic frequency is 25kHz, the washing water is pure water at room temperature, and the washing time is 1 min;

[0049] (S4) Water washing: using room temperature pure water to wash the product;

[0050] (S5) Drying: The washed product is dried using a drying machine, wherein the drying machine frequency is 15 Hz, the time is 20 min, and the temperature is 70°C;

[0051] (S7) Surface treatment, the specific steps are as follows:

[0052] 1) Polishing: Place the product in a vibration polishing machine for polishing. The polishing machine frequency is 30Hz and the time is 1h.

[0053] 2) Ultrasonic degreasing: the processing time is 100s, the degreasing processing temperature is room temperature, and the ultrasonic frequency is 25kHz;

[0054] 3) Washing: Put the degreased product into tap water at room temperature for washing;

[0055] 4) Ultrasonic water washing: immerse the above products in pure water at room temperature with an ultrasonic frequency of 25kHz;

[0056] 5) Drying: The washed products are dried in a drying machine with a frequency of 15 Hz, a time of 20 minutes and a temperature of 70°C;

[0057] 6) High temperature heat treatment: Use tubular atmosphere furnace SLG1400-60, put the product into the tubular furnace, and then evacuate it, the vacuum degree is less than 10Pa, and oxygen is introduced to wash the furnace. The temperature in the furnace is maintained at 350℃, and then the atmosphere in the furnace is maintained. Oxygen is introduced for 10 minutes every 40 minutes, and the pressure divider valve is at 0.25-0.45Mpa. Continue for 1 hour, and then cool the product. The cooling process is first cooled with the furnace and then air cooled.

[0058] Example 2

[0059] The product to be processed is a waste NdFeB product with four layers of metal coatings, namely nickel coating, copper coating, nickel coating and nickel-phosphorus alloy coating, wrapped around the substrate in sequence. The processing process is as follows:

[0060] (S2) Plating removal:

[0061] The primary treatment is carried out according to Example 1. After the primary treatment, the drum containing the product and the glass beads is washed with water, and then the drum containing the product to be treated and the glass beads is immersed in an environmentally friendly metal cleaning agent for secondary treatment. The drum speed is 3-15r / min, the temperature of the environmentally friendly metal cleaning agent is 70°C, the pH is 11, and the immersion time is 30min. Wherein, the environmentally friendly metal cleaning agent includes 15% ethylenediamine, 8% thiourea, 16% oxalic acid, 7% sodium citrate, 2.5% sodium hydroxide, 0.5% sodium dodecylbenzene sulfonate and the balance water in terms of mass percentage;

[0062] (S3) Ultrasonic water washing: the same as step (S3) in Example 1;

[0063] (S4) washing with water: the same as step (S4) in Example 1;

[0064] (S5) Drying: the same as step (S5) in Example 1;

[0065] (S7) Surface treatment: the same as step (S7) in Example 1.

[0066] Example 3

[0067] Step (S2) to step (S5): the same as step (S2) to step (S5) of Example 1;

[0068] (S7) Surface treatment, the specific steps are as follows:

[0069] 1) Heating treatment: The heating treatment process is carried out in an oven at a temperature of 380° C. for 2 h;

[0070] 2) Ultrasonic degreasing: the processing time is 100s, the degreasing processing temperature is room temperature, and the ultrasonic frequency is 25kHz;

[0071] 3) Washing: Put the degreased product into tap water at room temperature for washing;

[0072] 4) Pickling: Use 2% nitric acid solution to pickle the product for 40 seconds;

[0073] 5) Ultrasonic water washing: Use flowing pure water to clean the product, the ultrasonic frequency is 25kHz, until it is clean;

[0074] 6) Electrogalvanizing: the plating solution includes 350 g / L zinc sulfate, 25 g / L potassium sulfate, 1 g / L potassium oxalate, 35 g / L boric acid, 15 mL / L JC-552 type additive, the zinc plating solution temperature is 30°C, pH=4.3, the plating solution specific gravity is 28, the current is 40 A, and the electroplating time is 45 min;

[0075] 7) Light extraction: Light extraction is performed using a light extraction liquid, which includes nitric acid, chromium sulfate, cerium sulfate, and water; the concentration of the nitric acid is 5 mL / L, the concentration of the chromium sulfate is 1.5 g / L, the concentration of the cerium sulfate is 0.8 g / L, and the balance is water. The processing time is 20 s;

[0076] 8) Washing: Wash the surface of the product with water for 15 seconds;

[0077] 9) Primary passivation: The product is passivated with trivalent chromium passivation solution, which includes 28g / L chromium sulfate, 5.5g / L cerium sulfate, 5.5g / L zinc chloride, 27g / L sodium nitrate, and 0.5g / L sodium phosphite. The temperature is room temperature. A 10% sodium hydroxide solution or a 6% nitric acid solution is used to adjust the pH value to 2.3. The passivation time is 20s.

[0078] 10) Washing;

[0079] 11) Use the same trivalent chromium passivation solution as the primary passivation to perform secondary passivation on the product at room temperature, pH=2.3, and passivation time of 5s;

[0080] 12) Washing;

[0081] 13) Aging: solution temperature 60°C, time 15s;

[0082] 14) Drying: Pre-dehydration uses a hair dryer to dry the water stains on the surface of the product, and then deep dehydration is performed, with the temperature being 70°C and the dehydration time being 30 minutes.

[0083] Example 4

[0084] Step (S2) to step (S5): the same as step (S2) to step (S5) of Example 3;

[0085] (S7) Surface treatment, the specific steps are as follows:

[0086] Step 1) to step 10): the same as step 1) to step 10) of embodiment 3;

[0087] 11) Aging: solution temperature 60°C, time 15s;

[0088] 12) Drying: Pre-dehydration uses a hair dryer to dry the water stains on the surface of the product, and then deep dehydration is performed, with the temperature being 70°C and the dehydration time being 30 minutes.

[0089] Comparative Example 1

[0090] The only difference from Example 3 is that in the surface treatment step (S7),

[0091] 7) Light extraction: Light extraction is performed using a light extraction liquid, the light extraction liquid includes nitric acid and water; the concentration of the nitric acid is 5 mL / L, the balance is water, and the processing time is 20 s.

[0092] Comparative Example 2

[0093] The only difference from Example 1 is that in step (S7) of surface treatment,

[0094] 6) High temperature heat treatment: Use tubular atmosphere furnace SLG1400-60, place the product in the tubular furnace, and heat it in a natural air atmosphere. The temperature in the furnace is maintained at 350°C for 1 hour, and then the product is cooled. The cooling process is first cooled with the furnace and then air cooled.

[0095] Comparative Example 3

[0096] The only difference from Example 3 is that the light emitting liquid does not include cerium sulfate.

[0097] The NdFeB magnets obtained in the embodiment and the comparative example were tested for bonding strength, corrosion resistance, and moisture and heat resistance. The test results are shown in Tables 1-3.

[0098] Table 1. Performance of NdFeB magnets obtained by (S2) treatment in Example 1 and Example 2

[0099]

[0100] The weight loss test equipment is EHS-211MESPEC, and the test conditions are: 130℃, 95%RH, 2.6Bar. From Table 1, it can be seen that the product after the coating removal treatment is not corroded. Figure 1 , Figure 2 It can be seen that the surface grains and grain boundaries of the magnet are uniform and intact without being damaged.

[0101] Table 2. Performance test of anticorrosion magnets prepared in Examples and Comparative Examples

[0102]

[0103] The test conditions of the double 85 damp heat test are: place the magnet in a closed environment at 85°C and 85%RH, and observe the rust of the product every 0.5h. The damp heat time in Table 2 is the time when the film coating begins to rust.

[0104] The method of irreversible test is: test the magnetic flux of the magnet at room temperature, then absorb one side of the magnet onto a 3mm iron plate and place it in a 180℃ high temperature box for 2 hours, take out the magnet and cool it to room temperature, test the magnetic flux of the magnet again after high temperature, and calculate the magnetic flux loss rate before and after high temperature.

[0105] The cleanliness test is carried out with cleanliness tape. The two large surfaces of the product are adhered to the cleanliness tape, which is then pressed and flattened several times with a scraper. The product is then removed and the cleanliness tape is observed to see if there is any magnetic powder or dust residue. The test is made based on the residue. Level 0 means no residue, and the higher the level, the more residue there is.

[0106] The oxygen content was obtained by electron microscope.

[0107] As can be seen from Table 2, the performance of the product obtained by Example 1 is comparable to that of the product obtained by Example 2; the irreversible loss of the product obtained by Comparative Example 2 is greater than that of Example 1 or Example 2, and the moisture and heat resistance is not as good as that of Example 1 or Example 2; Figure 3 It can be seen that the product obtained in Example 1 has uniform appearance and good cleanliness.

[0108] Table 3. Performance test of anticorrosion magnets prepared in Examples and Comparative Examples

[0109]

[0110] The test conditions of the SST salt spray test are: 35°C, NaCl aqueous solution concentration of 50±5g / L, pH between 6.5-7.2, and the salt spray is deposited on the anti-corrosion magnet in the form of spray, and the rust of the coating is observed. The salt spray time in Table 3 is the time when the coating begins to rust.

[0111] The dyne experiment is tested using different types of dyne pens, from high to low.

[0112] It can be seen from Table 3 that the corrosion resistance of secondary passivation after galvanizing is better than that of primary passivation, because the secondary passivation process can repair the discontinuity or unevenness of the passivation film in the primary passivation process and obtain a denser passivation film. It can also be seen from Table 3 that the corrosion resistance of the products treated with a mixed solution of nitric acid, chromium sulfate and cerium sulfate is better than that of the products treated with a mixed solution of nitric acid and chromium sulfate and the products treated with a simple nitric acid polishing solution, because chromium sulfate is added to the nitric acid solution to form a passivation film on the galvanized layer as soon as possible, and chromium sulfate and cerium sulfate are added to the nitric acid solution at the same time to make the formed passivation film denser and more consistent, so as to prevent the oxidation of the zinc layer from affecting the continuity and consistency of the passivation film formed in the subsequent passivation process, thereby affecting the salt spray effect. Figure 4 It can be seen that the coating presents uniform and fine columnar crystals, and is well integrated with the grains and grain boundaries of the substrate. The coatings obtained by Examples 3 and 4 have excellent bonding strength.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for recycling and reusing NdFeB magnets, characterized in that: The following steps are involved: Plating removal, ultrasonic washing, water washing, drying, surface treatment; The coating removal includes primary treatment and secondary treatment; The primary treatment comprises the following steps: using an environmentally friendly alkaline nickel removal agent to soak and move the NdFeB magnet; the treatment temperature of the primary treatment is 40-90°C, and the treatment time is 0.5-30min; the secondary treatment comprises the following steps: using an environmentally friendly metal cleaning agent to soak and move the NdFeB magnet; the treatment temperature of the secondary treatment is 60-95°C, and the treatment time is 0.2-5h; The pH value of the environmentally friendly alkaline nickel removal agent is greater than 11. In terms of mass percentage, the environmentally friendly alkaline nickel removal agent includes 10-30% of a corrosion inhibitor, 0.5-10% of an accelerator, 1-15% of a complexing agent, 0.1-1.5% of a surfactant and the balance of water; The pH value of the environmentally friendly metal cleaning agent is greater than 10. In terms of mass percentage, the environmentally friendly metal cleaning agent includes 10-25% corrosion inhibitor, 15-30% oxidant, 5-10% complexing agent, 0.5-3% promoter, 0.5-3% surfactant and the balance water; the corrosion inhibitor is one or more of hexamethylenetetramine, ethylenediamine, thiourea, etc.; the oxidant is an organic acid oxidant; the complexing agent is one or two of citric acid and sodium citrate; the promoter is a hydroxide; and the surfactant is sodium alkylbenzene sulfonate; The surface treatment is at least one of electrodeposition, thin film coating, paint film coating, and high temperature heat treatment; the electrodeposition includes the following steps: heating treatment, electrodeposition pre-treatment, electrogalvanizing, and post-treatment; The post-processing includes light extraction, primary passivation, secondary passivation, and aging; The light extraction is to treat the NdFeB magnet with a light extraction liquid, wherein the light extraction liquid includes nitric acid, trivalent chromium salt, rare earth compound and water; The trivalent chromium salt is at least one of chromium sulfate and chromium nitrate, and the rare earth compound is at least one of lanthanum oxide, cerium nitrate and cerium sulfate.

2. The NdFeB magnet recycling process according to claim 1, characterized in that: Before the coating is removed, pre-treatment is also included.

3. The NdFeB magnet recycling and reuse process according to claim 1, characterized in that: Between drying and surface treatment, remelting is also included.

4. The NdFeB magnet recycling and reuse process according to claim 1, characterized in that: The high-temperature heat treatment comprises the following steps: placing the NdFeB magnet into a tubular furnace, and then performing a vacuum treatment, wherein the vacuum degree is less than 10Pa, introducing oxygen to wash the furnace, and maintaining the temperature in the furnace at 300-450°C, and then starting to maintain the atmosphere in the furnace, introducing oxygen for 10 minutes every 40 minutes, with the pressure divider valve at 0.25-0.45Mpa, for a period of 0.5-4h, and then cooling the NdFeB magnet, wherein the cooling process is first furnace cooling and then air cooling.

5. The NdFeB magnet recycling and reuse process according to claim 4, characterized in that: Before the NdFeB magnet enters the tube furnace, the following steps are also included: polishing, ultrasonic degreasing, water washing, ultrasonic water washing, and drying.

6. The NdFeB magnet recycling and reuse process according to claim 1, characterized in that: The light extraction is to treat the NdFeB magnet with a light extraction liquid, wherein the light extraction liquid includes 1-20 mL / L nitric acid, 1-5 g / L trivalent chromium salt, 0.1-5 g / L rare earth compound, and the rest is water.

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