JPS6153413B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recycling small pieces, granular scraps, grinding powder, and other powdery scraps generated during the manufacturing process of rare earth cobalt magnets (hereinafter referred to as rare earth magnets). The demand for rare earth magnets has been increasing rapidly in recent years, and because of their characteristics, they are effective in making equipment smaller and improving their performance, so these magnets are often required to be extremely small in size. However, it is extremely difficult to manufacture such extremely small rare earth magnets from scratch, so generally a large shape is finished into the desired small shape by machining or grinding. The amount of scrap generated, such as scrap and grinding powder, can amount to several tens of percent of the initial weight. Therefore, recycling these generated scraps is extremely beneficial in terms of resource conservation. As mentioned above, the scrap alloys generated in the manufacturing process of rare earth magnets are mainly flaky, spherical, and ground scrap, but the rare earth metal, which is one of the main components in rare earth magnets, has a high affinity with oxygen and carbon. It has a very strong affinity for oxygen, especially Mg, Al, which is effective as a deoxidizing agent in steelmaking.
Stronger than Si. Therefore, during the manufacturing process of rare earth magnets, the rare earth elements are considerably oxidized or carbonized. In addition, the scrap of rare earth magnets contains impurities such as fine fragments of grinding wheels and jigs, and adhesives, and especially in the case of grinding powder, the average particle size is 1 to 2 μm.
Since the magnet powder is in the form of fine particles, the oxidation of the rare earth metal in the magnet powder is significant and it also contains a considerable amount of carbon. Therefore, it is impossible to collect scraps of rare earth magnets and use them again as raw material powder for rare earth magnets, and recycling treatment such as reducing the oxygen and carbon content is required. Examples of recycling methods include melting scrap with acid, separating and refining rare earth metals and other metals such as cobalt through chemical treatment, and reducing them to their respective metals; Possible methods include melting at a high temperature and reacting with a slag-forming agent to remove oxides and carbides as slag to obtain metal lumps; the former allows recovery of other metals such as high-purity rare earth metals and cobalt. However, the disadvantage is that the processing process is complicated and the processing cost is high. In addition, when using the latter melting method, as mentioned above, if the scrap contains microscopic oxides and carbides and adsorbs a large amount of gas components, the slag will remain even if held at high temperatures in an argon atmosphere or vacuum. It has the drawback that it is difficult to separate and recover as pure metal lumps, and although the effects of gas can be reduced by melting at high temperature in a flowing gas such as argon, there is a lot of scattering due to evaporation of expensive rare earth metals. It is hard to say that this is a practical method. From the above-mentioned viewpoint, an invention has already been proposed by the same applicant as the present application (Japanese Patent Laid-Open No. 56-38438) regarding a method for recycling rare earth magnet scrap. In connection with the above invention, the present invention seeks to provide an improved method for recycling powdered rare earth magnet scrap alloys such as small pieces, granules, and ground powder, and provides detailed information on the method for recycling these scrap alloys. We have made improvements, especially regarding the amount of calcium added to the scraps.
We also improved the method for removing calcium oxide and calcium carbide compounds from the reduction reaction product, and developed a method for recycling scrap alloy with even better quality. That is, the present invention relates to rare earth magnet scrap alloys made of cobalt, cobalt-copper alloys, cobalt-iron-copper alloys, cobalt-iron-nickel-copper alloys, etc. containing rare earth metals, and oxygen and carbon contained in the scraps. Metallic calcium or calcium hydride in an amount of 2 to 4 times the stoichiometric amount of calcium to be combined with the mixture and heated to a temperature of 900 to 1200°C in an inert gas atmosphere,
The gist of the present invention is to provide a scrap regeneration method for rare earth magnets, which is characterized in that after the completion of the reduction reaction, the reduction product is directly disintegrated in water, and then the reaction products of calcium oxide and calcium carbide compounds are promptly removed. Rare earth magnet scrap to which the method of the present invention can be applied is small pieces outside the product that occur during the manufacturing process of rare earth magnets, especially when machining materials after heat treatment, or magnetic property defects or chips during final product inspection. These include defective products with cracks, etc., and grinding powder that comes out of the polishing machine along with cooling water during mechanical grinding. First, in the case of scrap in the form of small pieces, it is coarsely ground in an inert atmosphere such as argon gas to form a powder. In the case of scrap such as grinding powder, it is passed through a magnetic separator to remove non-magnetic contaminants and water is separated, and then heated in an argon stream or in a vacuum to form a sufficiently dry powder. Metallic calcium or calcium hydride, which is a deoxidizing and decarburizing agent, is added to the powder produced as described above. Calcium hydride is brittle and can be easily made into powder, so it has the advantage of being able to mix well with scrap powder for deoxidation and decarburization, but on the other hand, it is more expensive than calcium metal, and there is a risk of decomposition and explosion in humid air. Moreover, if there is residual moisture in the scrap powder, it will react with it and generate heat, making it difficult to handle. Metallic calcium is ductile and cannot be pulverized, so a granular form is used. In this case, it is thought that it is difficult to obtain contact between particles necessary for reducing granular metallic calcium to rare earth metal salts, but according to the research of the present inventor, granular calcium of -4 mesh (4.77 mm) or less It has been found that sufficient reduction can be achieved by using In addition, metallic calcium is also less expensive than calcium hydride, so it is generally recommended to use granular metallic calcium in this method. Regardless of whether granular calcium hydride or granular metallic calcium is used, the amount of addition is determined by the amount of oxide RE ₂ O 3 and carbide in the scrap powder in chemical reaction equations (1), (2), ( ₃ ) and (4) below. The amount required is 2 to 4 times the stoichiometric amount required to reduce the amount, preferably 2.5 to 3.5 times. RE ₂ O ₃ +3CaH ₂ →2RE+3CaO+3H ₂ ………(1) RE ₂ O ₃ +3Ca→2RE+3CaO ………(2) 3C+CaO→CaC ₂ +CO ………(3) 2C+Ca→CaC ₂ ………(4) Above The reason for this limitation is that metallic calcium or calcium hydride is less than 2 times the stoichiometric amount of calcium required.
If the amount is less than twice that, the effect of reducing the amount of oxygen and carbon is poor, and when the reduction reaction product is placed in water and allowed to disintegrate naturally, almost no disintegration occurs, making it impossible to powderize the resulting calcium oxide and Calcium carbide cannot be removed. Moreover, when the amount exceeds 4 times, a large amount of calcium oxide and calcium carbide compounds as reduction reaction products will be produced, and it will take a long time to remove them. Moreover, the mixed metallic calcium remains unreacted, complicating subsequent treatment steps. Scrap powder mixed with metallic calcium or calcium hydride is charged into a reduction furnace in order to convert oxygen and carbon in the scrap into calcium oxide and calcium carbide through a reduction reaction. Here, in order to increase the capacity per furnace and at the same time raise the oxidation efficiency, it is possible to solidify it by press molding etc. and make it into a compacted body, but considering the treatment process of the reduced product after the completion of the reduction reaction, it is difficult to do so in water. This impairs the disintegrability of magnet powder and increases the processing time, which is undesirable from the standpoint of improving the quality of recycled magnet powder. Therefore, it is preferable to place scrap powder mixed with metallic calcium or calcium hydride in a heat-resistant metal container, and then charge it into a reduction furnace without compression molding. The reduction furnace may be a horizontal tube furnace or a vertical furnace, and after replacing the air in the reduction furnace with argon gas, the furnace is heated at an argon flow rate of about 1 to 5/min. At this time, in the case of pulverized powder such as small pieces of scrap, it is heated to reach 900 to 1100°C in 3 to 6 hours, and maintained at approximately that temperature for 1 hour or more. Further, in the case of ground powder, it is heated to reach 1100 to 1200°C in 3 to 6 hours, and maintained at approximately that temperature for 1 hour or more. After that, the furnace is cooled and the reduced product is taken out. If the temperature is much lower than the above-mentioned temperature range, the reduction reaction will proceed slowly, and if the temperature is much higher than that, the heat resistance of the apparatus must be taken into consideration, which is economically disadvantageous. By the above operation, the oxide (RE ₂ O ₃ ) in the scrap is reduced according to the above formulas (1) and (2), and the carbon impurities are converted to calcium carbide according to the above formulas (3) and (4). The removed reduced product is cooled down in the furnace and then put into water.
This causes the reactions of the following formulas (5) and (6), and the reduced product spontaneously disintegrates. CaO＋H ₂ O→Ca(OH) ₂ ………(5) CaC ₂ +2H ₂ O→Ca(OH) ₂ +C ₂ H ₂ ………(6) Acetylene (C ₂ H ₂ ) in the above formula is insoluble in water and is released into the air. Calcium hydroxide (Ca
(OH) ₂ ) has a low solubility in water, and can be separated from the magnet powder by stirring and pulverization based on the difference in specific gravity, so decantation is repeated to separate and remove calcium hydroxide. The reason why the process of pulverizing the reduced product and then putting it into water is not performed in the present invention is because the following advantages are considered. First, by directly putting the reduced product into water, the reduced product is gradually naturally disintegrated into powder using a chemical reaction, so the pulverization step can be omitted. Moreover, the ring element after the completion of the reduction reaction has become particularly reactive with oxygen, so even if the pulverization process involves rapid crushing even in an inert atmosphere, it cannot be regenerated once by the reduction treatment. This causes a large amount of the rare earth magnet powder to oxidize again, and sometimes causes it to ignite and burn. Therefore, adoption of the above-mentioned method of the present invention is because the pulverization step can be omitted and the pulverization is performed by a chemical reaction that progresses gradually, which helps improve the quality of recycled rare earth magnet powder. After carbon and calcium hydroxide in the form of acetylene gas are removed by repeated decantation, an organic acid such as acetic acid is added to the liquid and stirred to dissolve and remove a small amount of remaining calcium hydroxide. After washing with water, dehydrate and dry. The dried reduced magnet powder has a particle size of 30 μm or less and can be reused as a raw material for rare earth magnets. Next, the effects of the method of the present invention will be described with reference to Examples. Example 1 Small piece-like scraps of SmCo ₅ magnets (composition of 36wt% Sm and 64wt% Co) were collected as scrap alloy of rare earth magnets, and coarsely ground in a ball mill.
As a result of making a powder of 35mesh (500μm) or less and measuring the amount of oxygen and carbon in the powder, each
They were 7.320ppm and 1.420ppm. 13.1 gr of metallic calcium was mixed with 200 gr of this powder and placed in a 50 x 50 mm molbdenum pack.
This was placed in a horizontal tube furnace, and after replacing the air in the furnace with argon gas, it was heated to 1000° C. over 3 hours in argon at a flow rate of 1/min, and maintained as such for 2 hours. Thereafter, the resulting reduced product was directly poured into water, and after being naturally disintegrated into small pieces, the reduced product was made into a slurry using a stirrer. Carbon was removed by generation and release of acetylene gas, and calcium hydroxide was removed by repeated decantation, then dilute acetic acid was added to remove residual calcium hydroxide, washed with water, and then dried. The composition of this recycled magnet powder is 34.0wt%Sm, 66.0wt%Co
Also, the amount of oxygen is 1.800ppm and the amount of carbon is 250ppm.
The average particle size of the recycled powder was 25 μm. The above recycled magnet powder is replaced with new 37wt%Sm, 63wt%Co
It was mixed in a ratio of 10 to 30% with the rare earth magnet raw material powder of the composition, and an Sm-Co rare earth permanent magnet was manufactured from this according to a conventional method. Table 1 shows the results of examining their compositions and magnetic properties.

[Table] As shown in the table above, recycled raw material powder can be sufficiently used by mixing it with new raw material powder, and for comparison, the same scrap was used in the invention previously described (Japanese Patent Application Laid-Open No. 56-38438). The amount of oxygen in the magnet powder regenerated based on the regeneration method of No. 1) was 2.500 ppm, and the amount of carbon was 500 ppm, and it was found that the regeneration method according to the present invention yields better regenerated magnet powder. . Example 2 Small piece-like scraps _of Sm (Co _0.7 Fe _0.2 Cu _0.1 ) ₇ -based magnet were collected and ground into _a powder of 35 mesh or less by ball milling, and the amount _of oxygen and carbon in the powder was measured. The results were 3.500ppm and 850ppm, respectively. 6.5 gr of calcium hydride was mixed with 200 gr of this powder and subjected to reduction treatment in the same manner as in Example 1. The amount of oxygen in this final dried recycled magnet powder is 1.100 ppm, the amount of carbon is 230 ppm, and the average particle size of the recycled powder is 27 μm.
It was hot. Example 3 Small piece-like scraps of Sm _0.5 Pr _0.5 Co _{5 -} based magnets were collected and ground into a powder of 35 mesh or less by ball milling, and the amount of oxygen and _carbon in the powder was measured.
They were 6.250ppm and 730ppm, respectively. 10.5 gr of metallic calcium was mixed with 200 gr of this powder and subjected to reduction treatment in the same manner as in Example 1. After drying, the amount of oxygen in this recycled magnet powder is 2.000ppm, and the amount of carbon is
At 200 ppm, the average particle size of the recycled powder was 18 μm. Example 4 SmCo ₅ as a scrap alloy for rare earth magnets
Grinding powder of the system magnet was collected, magnetically separated and dried, and the oxygen content in the powder was measured to be 28.300 ppm, and the carbon content was also measured to be 5.400 ppm. After adding 1.47 kg of granular metallic calcium to 5 kg of this grinding powder and mixing it using a mixer, this was charged into a horizontal tubular furnace, and the air in the furnace was replaced with argon. Spent 3 hours inside
It was heated to 1150°C and kept there for 1.5 hours. After that, the furnace-cooled reduced product was directly poured into water and allowed to disintegrate naturally. After repeating decantation to remove calcium hydroxide, dilute acetic acid was added to remove residual calcium hydroxide, washed with water, and then dried. The amount of oxygen in this recycled magnet powder was 1.600 ppm, the amount of carbon was 290 ppm, and the particle size of the recycled powder was 15 μm. Example 5 As a scrap alloy for rare earth magnets
As a result of collecting _the ground powder of Sm _{0.5 Pr 0.5} Co ₅ magnet and measuring the amount of oxygen and carbon in the powder, each
They were 21.250ppm and 5.640ppm. Example 4
Recycled magnet powder was made in the same manner as above. However, in this case, 1.24 kg of calcium hydride was mixed instead of granular metallic calcium. The amount of oxygen in this recycled magnet powder was 1.510 ppm, the amount of carbon was 370 ppm, and the particle size of the recycled magnet powder was 9 μm. As described above, the present invention uses metallic calcium or calcium hydride to reduce the oxides in the scrap alloy of rare earth magnets to be regenerated into calcium oxide, and at the same time converts the carbon in the mixture into calcium carbide to convert these calcium Because it removes compounds easily and effectively,
According to the method of the present invention, expensive scrap alloy of rare earth magnets can be recovered with a high yield at a relatively low processing cost, and moreover, it can be easily reused, making it an extremely effective invention in terms of resource conservation. .

Claims (1)

[Claims] 1 Scrap alloy of rare earth cobalt magnet,
Mix metal calcium or calcium hydride in an amount of 2 to 4 times the stoichiometric amount of calcium to be combined with the oxygen and carbon contained in the scrap, and heat to 900 to 1200°C in an inert gas atmosphere. Scrap regeneration of a rare earth cobalt magnet, characterized in that the reduction product in which the oxygen contained is converted into calcium oxide and the carbon is converted into a calcium carbide compound is disintegrated in water as it is, and subsequently the calcium oxide and calcium carbide compound are removed. Method.