JPS5849631B2 - How to scrapp and recycle rare earth magnets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recycling grinding powder and other scraps such as powder, granules, and small pieces generated in the manufacturing process of 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 devices smaller and improving their performance, so these magnets are often required to be extremely small in size.

However, since it is extremely difficult to manufacture such extremely small rare earth magnets from scratch, they are generally finished from a large shape into the desired small shape by polishing, but the amount of polishing powder generated during this process is may 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 generated in the manufacturing process of rare earth magnets is mainly polishing powder, but this polishing powder contains impurities such as fine fragments of grinding wheels and jigs, and adhesive waste.
Moreover, since the magnet powder is fine particles with an average particle size of 1 to 2 μm, a considerable portion of the rare earth metal in the magnet powder is oxidized.

Therefore, it cannot be recovered and used as raw material for rare earth magnets, and must be recycled.

Examples of recycling methods include melting scrap using acid, separating and refining cobalt and rare earth metals through chemical treatment, and reducing them to their respective metals; or scrap melting at high temperatures using high-frequency melting, arc melting, plasma melting, etc. Methods such as melting and reacting with a slag-forming agent and removing oxides as slag to obtain metal lumps are considered.The former method can recover highly pure cobalt and rare earth metals, but the processing process is complicated and the processing cost is high. The disadvantage is that it is expensive.

In addition, in the latter melting method, if the scrap polishing powder is oxidized into minute particles and adsorbs a large amount of gas components, the slag cannot be separated even if it is held at high temperature in an argon atmosphere or vacuum. It has the disadvantage that it is difficult to recover as a pure metal lump, and although the effect of gas can be reduced by melting it at high temperature in a flowing atmosphere of argon, etc., there is a lot of scattering due to evaporation of expensive rare earth metals, making it a practical method. It's hard to say.

The present invention aims to eliminate the above-mentioned drawbacks and problems and provide a method for easily, relatively inexpensively and efficiently recycling rare earth magnet scraps. After that, 1.5 to 2.5 times the stoichiometrically required amount of calcium to be combined with the oxygen and carbon contained in the scrap is added in the form of metallic calcium or calcium hydride, and the scrap is compressed and heated under argon. Reductive decarburization is performed in flowing air, and the oxygen contained is converted into calcium oxide, calcium oxide,
The gist of the present invention is a method of converting the contained carbon into a calcium carbide compound, and regenerating it into rare earth magnet raw material powder by removing it by cooling and crushing the shaped body and washing with water.

The method of the present invention can be applied to the recycling of various types of scrap such as powder, granules, and small pieces of rare earth magnets generated in the rare earth magnet manufacturing process, and will be described in detail below using polishing powder of rare earth magnets as an example.

Such polishing powder comes out of the polishing machine together with cooling water during polishing.

This is passed through a magnetic separator to remove non-magnetic contaminants.

After separating the moisture from the magnetically selected polishing powder, it is heated in a nitrogen or argon stream, or in a vacuum, and thoroughly dried.

Metallic calcium or calcium hydride as a reducing agent is added to this.

Calcium hydride is brittle and can be easily made into powder, so it has the advantage of being able to mix well with polishing powder as a reducing agent, 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 polishing 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 the contact between particles necessary for reducing the rare earth metal salt with granular metallic calcium, but according to the research of the present inventor, -4 mesh (4.77
It has been found that sufficient reduction can be achieved if granular calcium with a diameter of 1 mm) or less is used.

In addition, metallic calcium is also less expensive than calcium hydride, so it is generally recommended to use granular metallic calcium in this method.

Even if powdered calcium hydride or granular metallic calcium is used, the amount added is determined by the chemical reaction formula (1) below.
In (1)', (2), the stoichiometric amount necessary to reduce the oxides and carbides in the polishing powder is 1.5
~2.5 times is required.

The reason for the above limitation is 1.
When the amount is less than 5 times, the effect of reducing oxygen and carbon is poor, and when granular metallic calcium of -4 mesh or less is used as a reducing agent, the granular metallic calcium and the rare earth magnet scrap alloy which is the reductant are This is because, if <<<< is not uniformly mixed, the reductant, that is, the scrap alloy, will undergo a heterogeneous chemical reaction during the subsequent reductive decarburization reaction between oxygen and carbon, which is undesirable.

On the other hand, if it exceeds 2.5 times, metallic calcium will remain in the calcium reactant, complicating the treatment process.

Polishing powder mixed with metallic calcium or calcium hydride is hardened by a press or the like and charged into a reduction furnace as a molded body in order to increase the capacity per furnace and at the same time to improve the reduction efficiency.

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 argon flow rate is set to 1 to 5.
The furnace is heated to about t/min.

Heat to reach 1100°C in 3 to 6 hours and hold in warm honey for over 1 hour.

After that, it is cooled in the furnace and the reduced product is taken out.

The optimal heating temperature is 1100° C.; if it is too low, the reduction reaction will proceed slowly, and if it is too high, the heat resistance of the device must be taken into consideration, which is economically disadvantageous.

By the above operation, samarium 35wt%, Kobalu'6
Oxide in the abrasive grains of 5W1% Kumikai (RE 2 03
) is reduced by the following formula (1), (lY/I), and carbon impurities in the polishing powder are converted to calcium carbide according to the following formula (2).

RE203+3CaH2→2RE+3CaO+3H2=
−・−・(1)RE O +3Ca →2RE+3C
aO -... (1)'23 3C+CaO -+CaC+CO =...
(2) 2 The extracted reduced product is crushed and then put into water.

This causes the reactions of the following formulas (3) and (4).

Cao-l-H20-+Ca(OH) 2 songs...(3)C
aC2+2H20-+Ca(OH)2+C2H2.
．． ．． ．． ．． ．． (4) Acetylene (C2H2) of the above formula is insoluble in water and 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 due to the difference in specific gravity, so decantation is repeated to separate and remove calcium hydroxide. Finally, an organic acid such as acetic acid is added to the solution and stirred to dissolve and remove a small amount of remaining calcium hydroxide.

After further washing with water, dehydrate and dry.

The dried magnet reduced powder can now 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.

Polishing powder was collected as scrap of rare earth magnets, dried after magnetic separation, and the amount of oxygen in the powder was measured.The results were 3 4, 60.
0 ppm 1The result of measuring the amount of carbon is 6.0
0 0 I)pm.

Granular metallic calcium 901 was added to 5 kg of this polishing powder, mixed using a mixer, and then a pressure of 0.5 toH was applied to obtain 5 shaped bodies of 70φ×about 90L.

This was charged into a horizontal tube furnace, and after replacing the air in the furnace with argon, it was heated in argon at a flow rate of 11/min.
Heated to 100°C over time and held for 1.5 hours.

After that, the furnace was cooled and the reduced product was taken out from the furnace at 70°C.
After crushing, it was poured into water.

After repeating decantation to remove calcium hydroxide, dilute acetic acid was added to remove residual calcium hydroxide, followed by washing with water and drying.

The composition of this recycled magnet powder is 33.8 wt% samarium, 66.2 wt% cobalt, and the amount of oxygen is 2.60 wt%.
The ppm% carbon content was 350 ppm.

The above-mentioned recycled magnet powder was mixed in a ratio of 10 to 30% with new rare earth magnet raw material grains having a composition of 37 wt% samarium and 63 wt% cobalt, and a samarium cobalt rare earth permanent magnet was manufactured from the powder according to a conventional method.

The results of investigating their composition and magnetic properties are shown in the first
Shown in the table.

As shown in the table above, the recycled raw materials could be used in combination with the new raw materials.

As mentioned above, the method of the present invention uses metallic calcium or calcium hydride to reduce the oxides in the generated scrap of the rare earth permanent magnets to be recycled, and at the same time converts the carbon contaminants into calcium carbide, thereby reducing the calcium reaction. Since materials are removed by washing with water, expensive rare earth metals can be recovered and recycled with a high yield at a relatively low processing cost, so it is extremely effective in terms of resource conservation.

Claims (1)

[Claims] 1.8 to 2.0% of the stoichiometrically required amount of calcium is added to the scrap alloy of 18 earth magnets after dehydration and drying if the wet one is combined with the oxygen and carbon contained in the scrap.
5 times the amount in the form of metallic calcium or calcium hydride, compressed or shaped, and subjected to reductive decarburization in an argon stream, converting the contained oxygen into calcium oxide and carbon into a calcium carbide compound, and reducing the compressed form. A method for recycling scrap of rare earth magnets, which comprises cooling and pulverizing the core-shaped bodies, and then washing the calcium oxide and calcium carbide compounds with water to remove the calcium oxide and calcium carbide compounds.