JP2003051418A - Method for recycling rare-earth magnet scrap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method for obtaining recycled ingots of quality equal to virgin ingots by making scrap of R-Fe-B-based rare-earth magnet scrap containing carbon and turning into low-carbon and low-oxygen. SOLUTION: Powdery scrap is heat treated in an atmosphere, containing oxygen at a temperature of 700-1,200 deg.C for 1-10 hours for reducing carbon through oxidation and decarburization. Then metallic calcium as a reducing agent is added to the scrap, and the scrap is heated in an inert gas by direct reduction. The scrap is turned low in oxygen through deoxidation, in this way, and is fused and solidified for forming recycled ingots.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rare earth magnet, particularly
R-Fe-B rare earth magnets represented by Nd-Fe-B system (R
Is a rare earth metal whose main component is at least one of Nd, Pr, Dy, Ho, and Tb), and is used for recycling scraps of rare earth magnets generated from manufacturing processes and used equipment as rare earth magnet raw materials. , A method for recycling rare earth magnet scrap.

[0002]

2. Description of the Related Art Rare earth magnets, especially Rd such as Nd-Fe-B series which have excellent magnetic properties and mechanical properties and workability.
The —Fe—B rare earth magnets are widely used in various electronic products, personal computers, mobile phones, mobile terminals, and electronic parts such as automobiles. Rare earth magnets are generally roughly classified into sintered magnets and bonded magnets in which magnet powder is bonded with a binder such as rubber or plastic. Sintered magnets containing no binder have a better magnetic property. Sintered magnets are mainly used for the above-mentioned various applications because of the characteristics obtained.

The production amount of sintered R-Fe-B rare earth magnets is about 10,000 tons in the world, of which about 5,500 tons in Japan, and is increasing year by year at a rapid rate of about 20%. It is going all the way. Of these, about 2,400 tons of scrap (solid scrap and powder scrap) are generated during the domestic manufacturing process, and about 30% of them are expensive rare earth elements (in this specification, unless otherwise specified, “%” is used). Means "mass%"), but most of them are currently disposed of as industrial waste. Furthermore, most rare earth element veins are unevenly distributed in China, and the reserves are small, so
Depending on the world situation, there may be a situation where the price rises. Therefore, from this perspective, establishing an effective recycling method for rare earth magnet scrap is
It is important for resource saving and price stabilization.

From the viewpoint of environmental protection, there is also an increasing trend to collect valuable resources from used electronic equipment and reuse them. Therefore, it is expected that the demand for reuse of rare earth magnet scrap recovered from used equipment will increase further in the future, and from this point as well, it is necessary to establish a recycling technology for rare earth magnet scrap.

The general manufacturing process of a sintered rare earth magnet is as follows: smelting of raw material alloy ingot → crushing → press molding in a magnetic field → firing (crystallization and sintering) → processing → rust prevention (surface treatment by plating etc.) is there. Since the powder metallurgy method is used for molding, a processing step for improving dimensional accuracy is essential. The processing details include cutting from a medium-sized sintered product (using an outer peripheral blade, wire saw, etc.) and processing of a sintered product with excess thickness formed (boring,
For example, grinder etc.), deburring (barrel etc.) are used.

[0006] A large amount of powder scrap is generated in such processing steps. In addition to processing steps, molding, firing,
Defective products occur in each rust prevention process. It is said that the yield loss at the time of manufacturing reaches as much as 30 to 50% of the total production amount in these days when the ratio of small parts has been increasing.

[0007] Such a large amount of defective products and grinding dust are generated.
It is important to recover defective products in the production of sintered rare earth magnets, because not only the production cost will rise, but also the rare earth element with a small reserve will be depleted in the future and the price will rise.

The rare earth magnet scrap generated in the processing step is very fine and has a high ignitability in a dry state. Therefore, it is generally treated as a slurry mixed with water. The powder scrap obtained by drying this slurry generally contains about 1-2% carbon. This amount of carbon is
Carbon content in raw material alloy of R-Fe-B rare earth magnet (0.06%
It is extremely higher than that of (below) and causes deterioration of magnetic properties as described later, so it cannot be used as a magnet raw material unless decarburized. In addition, defective scraps in the forming, firing, and rust-prevention processes also contain about 0.07 to 0.1% of carbon, and the carbon content is at least about 10 times higher than that of the above raw material alloy. Is desirable.

The carbon content of the powder scrap generated in the processing step is particularly high because of the abrasive particles (carbides such as diamond and tungsten carbide) generated by the abrasion of the grinding member used for the processing and the binder of the abrasive particles. External resin-containing contaminants such as certain resin powder, carbon powder from a graphite plate used as an auxiliary plate for grinding, etc. are mixed in the scrap,
This is because the water-soluble cutting oil (W / O emulsion) used for processing is mixed.

Further, the carbon content of scraps generated in other steps is generally higher than that of the raw material powder, mainly due to crushing. The pulverization of the melted rare earth alloy is usually carried out by hydrogenation pulverization (pulverization utilizing embrittlement of the rare earth alloy due to hydrogen absorption) and then mechanical pulverization. Since zinc stearate is added as a grinding aid during the mechanical grinding, the ground rare earth alloy has a higher carbon content than the raw material alloy. A part of this carbon content is burned out and removed in the firing step, but the scrap generated in the forming step and the processing step before firing contains the carbon content derived from the grinding aid as it is. On the other hand, the scrap generated in the calcination process and rust prevention process has undergone calcination, so it has a low carbon content, but when it is powdered for reprocessing, the same hydrogen as above is used. It is necessary to carry out crushing and mechanical crushing, and since a crushing aid is used at this time, the carbon content also becomes high.

In order to improve the performance of the rare earth magnet,
It is necessary to reduce the amount of carbon in the raw material as much as possible. Carbon mixed in the manufacturing process exists as R carbide in the sintered magnet. It is also necessary to remove carbon from R carbide.

Another problem of rare earth magnet powder scraps generated in the processing step is that the average particle size measured by the aeration type particle size measuring method is 1 to 2 μm, and the powder is very fine. Particle size of powder suitable for press molding is 3 to 5 μm
Therefore, even if this fine powder can be decarburized, the decarburized powder is too fine to be directly used for press molding. Further, since this fine powder scrap has a large surface area, it is being oxidized, and the amount of oxygen is the amount of oxygen (.0.) In the raw material alloy of the R-Fe-B rare earth magnet.
(1% or less) is much higher.

As a method of regenerating such powder scraps of rare earth magnets, it is possible to melt them in an inert atmosphere to form a raw material alloy and make them into ingots. Even if the powder scrap is fine as described above, if it is made into an ingot, it can be pulverized to a powder having an optimum particle size. But,
The powder scrap, especially the fine powder scrap generated in the processing step, has extremely bad solubility because its surface is excessively oxidized to have a high melting point. In addition, a large amount of slag is generated due to the oxide at the time of melting, and the yield of metal content is reduced. Furthermore, even if it can be melted, the molten alloy contains a large amount of carbon as described above, and even if a rare earth magnet is manufactured from the above by the manufacturing process, the product will have a greatly deteriorated magnetic property.

The cause of the deterioration of magnetic properties due to this large amount of carbon is considered as follows. Nd-Fe-B type R-Fe-
The B-based rare earth magnet is a ferromagnetic main phase (R ₂ Fe ₁₄ B),
It is composed of two non-magnetic grain boundary phases (R oxide, R carbide, R carbonate, etc.). If the carbon content of the material alloy is too high (0.07% or more), the carbon cannot be completely removed only by burnout during firing, and a large amount of R carbide phase or R carbonate will be generated in the grain boundary phase. It is not possible to obtain sufficient coercive force (Hc), resulting in a product with deteriorated magnetic properties.

Therefore, in the recycling of powder scraps of rare earth magnets, low carbonization is an extremely important point.
It is also necessary to reduce the oxygen content of powder scrap. This is because if the amount of oxygen is too high, the magnetic properties are deteriorated, and as described above, the melting work of scrap for ingot formation is hindered and the yield is deteriorated. The present invention is
The challenge is to establish a recycling technology that can reduce carbon (decarburization) and oxygen (deoxidation) of powder scrap of rare earth magnets.

[0016]

For efficient deoxidation of rare earth oxide powder, rare earth oxide powder and other metal powders are blended so as to have a required alloy composition, and alkaline earth metal such as metal calcium is added. A reducing agent and an alkali metal chloride or alkaline earth metal chloride are mixed and heated to cause a diffusion reaction, and the resulting reaction product is purified by a wet treatment to directly produce an alloy powder of interest (directly Reduction method) is known (Japanese Patent Laid-Open Nos. 62-7831 and 63-33506).
No. 63-114927, JP-A Nos. 1-127643, 1-1381.
(See each bulletin No. 19). According to this method, a low-oxygen raw material powder for rare earth magnets can be obtained without undergoing melting and pulverization.

On the other hand, for decarburizing powder scraps of rare earth magnets, there is a method in which not only deoxidation but also decarburization are simultaneously performed by direct reduction using calcium metal or calcium hydroxide as a reducing agent. No. 58-1367
No. 28 is proposed. However, this method cannot sufficiently decarburize. Because these publications describe that carbon in rare earth magnet scrap is reacted with metallic calcium or calcium hydroxide to produce calcium carbide, and the mixed reaction product is washed with pure water and dried to remove calcium carbide. However, from the viewpoint of thermodynamics, R carbide is more stable than calcium carbide, and it is difficult to generate calcium carbide from R carbide to remove carbon. In addition, when this method is applied to a rare earth magnet powder scrap having a high carbon content, cost increase due to an increase in the amount of metallic calcium or calcium hydroxide added,
Furthermore, there are problems such as damage to the furnace body due to active calcium and an increase in the cleaning cost of the mixed reaction product, which is not practical.

Therefore, it is possible to efficiently decarburize powder scraps of rare earth magnets having a high carbon content, particularly powder scraps of fine rare earth magnets whose surfaces are oxidized and which are generated in large amounts, and which are powders of rare earth magnets. At present, the practical recycling method of scrap has not been established yet.

[0019]

As a result of exploring a decarburizing method for scrap of a rare earth magnet having a high carbon content, the present inventors have found that the R carbide existing in the grain boundary phase in the rare earth magnet is 10
We found that oxygen was decarburized (oxidative decarburization) when heat-treated in an oxygen-existing atmosphere at a high temperature of about 00 ° C.

For example, the oxidative decarburization of the R carbide having the composition represented by RC ₂ occurs by the reaction of one of the following formulas (1) and (2), and the rare earth oxide represented by R ₂ O ₃ is formed. To do.

2RC ₂ + 3.5O ₂ (g) → R ₂ O ₃ + 4CO (g) (1) ΔG = −440 kcal (1000 ° C.) 2RC ₂ + 5.5O ₂ (g) → R ₂ O ₃ + CO ₂ (g) (2) ΔG = −610 kcal (1000 ° C.) The present inventors utilize this oxidative decarburization reaction to decarburize scrap, and decarburize the scrap into a known direct It has been found that a deoxidation method using a reduction method can be used to construct a practical recycling method for rare earth magnet scrap.

In the firing step of the sintered R-Fe-B rare earth magnet, the powder compacted by molding is a liquid of R-rich phase (R carbide, R oxide, R carbonate, etc.) at the grain boundary. Sintering and densification by phase conversion. When powdered like this,
Even if firing is performed in an oxygen-existing atmosphere, decarburization of R carbide hardly occurs.

On the other hand, as in the present invention, when the powder is heat-treated in an oxygen-existing atmosphere without being compacted, the particles are gently bonded by the liquid-rich R-rich phase, and the R-rich phase is formed in the bonding portion. It was discovered that the segregated segregated particles have a size of several hundreds of microns and are easily disintegrated. Therefore, if heat treatment is performed in an atmosphere with oxygen, that is, in an oxygen-existing atmosphere,
It is presumed that only the R-rich phase in the bond part is preferentially oxidized, and the oxidative decarburization shown in Formula (1) and Formula (2) proceeds effectively.

When the heat treatment conditions for efficiently carrying out the oxidative decarburization of this scrap were examined, it was found that at least in an atmosphere containing oxygen.
For scraps such as sinter scraps with a low oxygen content, a certain amount of oxygen is required for decarburization, so it is more efficient to carry out under atmospheric pressure.
In the case of grinding dust, since it contains a large amount of oxygen, the maximum degree of vacuum that can be achieved in an industrial heat treatment furnace is about
It has been found that 0.01 Pa may be sufficient, and conversely, if the oxygen concentration in the heat treatment atmosphere is too high, the oxidation becomes excessive and some of the iron in the main phase is oxidized to form iron oxide.

When iron oxide is produced, it can be reduced by heating it in a hydrogen atmosphere. However, it is more cost effective to avoid generation of iron oxide due to oxidative decarburization. It was found that when the vacuum degree of the heat treatment atmosphere is 677 Pa or less, that is, the oxygen partial pressure is 140 Pa or less, the generation of iron oxide during oxidative decarburization can be suppressed to the extent that the above-mentioned adverse effects are not exerted.

The agglomerated particles (decarburized product) produced by this heat treatment that are easy to disintegrate show good recoverability (easy sedimentation) at the time of washing after reduction in the direct reduction method which is a subsequent step. By doing so, we have also found that it has an operational advantage.
Further, regarding the reducibility, it was also found that, for example, a reducing agent such as molten metal calcium penetrates into the inside of the porous agglomerated particles, whereby deoxidation at the same level as the primary particle level can be obtained.

The present invention completed based on the above findings heat-treats rare earth magnet powder scrap containing carbon and containing no binder in an atmosphere in the presence of oxygen at a temperature of 700 to 1200 ° C. for 1 to 10 hours. And a step of oxidatively decarburizing the rare earth magnet scrap.

In the method for recycling rare earth magnet scrap according to the present invention, the atmosphere in the presence of oxygen has an oxygen partial pressure of 14
It is exemplified that it is an oxygen-containing atmosphere or an air atmosphere that is 0 Pa or less.

Preferably, the rare earth magnet is R-Fe-B.
It is made of a system alloy (R is a rare earth metal whose main component is at least one of Nd, Pr, Dy, Ho, and Tb). The oxygen-containing atmosphere is preferably a reduced pressure atmospheric atmosphere of 667 Pa or less.

In a preferred embodiment, in the method of the present invention, following the heat treatment step, the decarburized product obtained in this step is deoxidized by a direct reduction method in which a reducing agent is added and heated in an inert gas. The method further includes the step of acidifying and the step of dissolving and solidifying the deoxidized product to prepare an ingot. As a result, it is possible to obtain an ingot of a raw material alloy for a rare earth magnet, which has been carbon-reduced and oxygen-reduced to the same level as a new ingot (virgin ingot).

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The scrap which is the object of the recycling method of the present invention is a rare earth magnet powder containing carbon and containing no binder. As described above, this carbon is mixed in during the crushing process and the molding process. Therefore,
All scraps generated after the crushing step in the above-mentioned sintered rare earth magnet manufacturing process and used rare earth magnets recovered from electronic devices and the like are targeted. Further, also in the case of manufacturing a bonded magnet, the powder scrap generated in the manufacturing process before molding using the binder is a target of the recycling method of the present invention. Further, even in the case of an amorphous quenched rare earth magnet obtained by quenching a melted raw material alloy, scrap containing carbon and containing no binder can be regenerated by the present invention.

Scrap containing a binder, such as bonded magnet scrap, generally has a carbon content of, for example, 5%.
Since it is very high before and after, and most of the carbon is a combustible organic substance, it is more efficient to burn the scrap in advance and remove the binder by decomposition (burnout) than to regenerate by the method of the present invention. Can be decarburized. However, since decarburization is not sufficient by firing alone, the scrap of the bonded magnet in which the binder is decomposed by firing can be further decarburized and regenerated by the method of the present invention.

If the scrap is not in powder form, it is ground to powder by suitable grinding means before applying the method of the invention. For example, among the scraps generated in the process of manufacturing the sintered rare earth magnet described above, scraps that have been compacted but not sintered, such as defective moldings and molding scraps generated in the molding process, are mechanically crushed. Can be crushed alone. Scraps that have been sintered, such as defective firing products generated in the firing process and defective plating products generated in the rust prevention process, are first pulverized by hydrogenation and then mechanically pulverized into powder. These mechanical grindings are usually carried out with the addition of small amounts of grinding aids such as zinc stearate.

The particle size of the powder scrap is not particularly limited, but when the scrap is crushed as described above, it is preferable that the average particle size is 2 to 10 μm, more preferably 2.5 to 5 μm. The method of the present invention can recycle powder scraps which are generated in a large amount in the processing step, have a very high carbon content of 1 to 2%, and have an extremely fine average particle size of 1 to 2 μm, and which have advanced oxidation. . But,
When crushing scrap, if such a fine powder is used, oxidation will proceed, the amount of reducing agent consumed in the subsequent process will increase, and the powder will become ignitable and difficult to handle.
Not preferable.

Slurry powder scraps, such as powder scraps generated in the processing step, are filtered before heat treatment.
The powder is taken out by centrifugation or the like. You may heat-process this powder while it is wet. In that case, the water evaporates and dries before reaching the heat treatment temperature and pressure. The wet powder may be dried before being inserted into the heat treatment furnace, but in the case of fine powder scrap, the drying poses a risk of ignition, so care must be taken in the drying temperature and handling.

The present invention was completed with scraps of R—Fe—B rare earth magnets in mind, but the alloy composition is not limited to this. For example, scraps of rare-earth cobalt-based magnets such as Sm—Co-based magnets and rare-earth iron-nitrogen intrusion type magnets can also be regenerated by the method of the present invention. However, since the R-Fe-B system, especially the Nd-Fe-B system rare earth magnet has a large amount of production and therefore a large amount of scrap, the rare earth magnet is a main processing target. Hereinafter, the rare earth magnet will be mainly described.

According to the present invention, carbon-containing rare earth magnet powder scrap is subjected to oxidative decarburization by heat treatment in an oxygen-containing atmosphere to produce decarburized agglomerated particles. Thereby, oxidative decarburization of scrap can be efficiently performed.

Further, for a scrap having a small oxygen content such as a sintered body scrap, since a certain amount of oxygen is required for decarburization, it is better to perform the heat treatment at atmospheric pressure for oxidative decarburization. This can be done efficiently, but in the case of grinding dust, it contains a large amount of oxygen, so even if it is not under atmospheric pressure, the maximum degree of vacuum that can be achieved in an industrial heat treatment furnace is about 0.01 Pa. An atmosphere containing oxygen to some extent may be used. On the contrary, if the oxygen concentration in the heat treatment atmosphere is too high, the oxidation becomes excessive and a part of the iron in the main phase is oxidized to produce iron oxide.

Further, the oxidative decarburization of the scrap can also be efficiently performed by heat treating the rare earth magnet powder scrap containing carbon in an oxygen-containing atmosphere having an oxygen partial pressure of 140 Pa or less. You can It is economical to obtain an oxygen partial pressure of 140 Pa or less by depressurizing the atmosphere, but it can also be obtained with a mixed gas (pressure is not particularly limited) in which an inert gas such as argon is mixed with oxygen or air. . When decompressing the atmosphere, 14
The oxygen partial pressure of 0 Pa or less corresponds to the case where the pressure is 667 Pa or less.

Oxygen decarburization occurs sufficiently under the heat treatment conditions other than the oxygen partial pressure or the pressure of the reduced pressure atmospheric atmosphere (that is, when the carbon content is the same level as the newly prepared alloy raw material <R-Fe-B alloy). It is reduced to 0.06% or less>), and aggregate particles that can be easily disintegrated are generated. The heat treatment temperature is preferably not so high as to cause welding of the low-melting-point grain boundary phase during the heat treatment.

The preferable heat treatment conditions are a temperature of 700 ° C. or higher and 1200 ° C. or lower, a time of 1 to 10 hours, and especially R-Fe.
In the case of a -B rare earth magnet, this heat treatment condition is suitable. When the heat treatment temperature is lower than 700 ° C, the formula (1) and the formula
The oxidative decarburization reaction shown in (2) becomes insufficient, carbon cannot be sufficiently removed, and the R-rich phase at the grain boundary is less likely to be liquefied, and aggregate particles that are easily disintegrated are less likely to be generated. If agglomerated particles are not formed, the heat-treated product becomes an active dry powder from which water and the like have been completely removed, so there is a problem in handling such as ignition due to reaction with the atmosphere when taken out from the furnace. Occurs. When the heat treatment temperature is such that oxidative decarburization occurs sufficiently, aggregate particles are generated by the heat treatment. When the heat treatment temperature is higher than 1200 ° C, the decarburizing property is good, but the R-rich phase with a low melting point drips, for example, on the bottom surface of the stainless steel container, and the entire powder is welded to the container, making recovery difficult. Becomes

If the heat treatment time is shorter than 1 hour, the decarburization reaction of the R-rich grain boundary phase does not proceed sufficiently even if the heat treatment temperature is increased to 1200 ° C. On the other hand, if the heat treatment time is longer than 10 hours, the decarburizing property is good, but the furnace operation cost is high, and even if the heat treatment temperature is lowered to 700 ° C, the welding of particles progresses and the crushing occurs. Since coarse sintered particles that cannot be formed are formed, deoxidation inside the coarse sintered particles becomes insufficient and deoxidation decreases in the direct reduction method in the subsequent step.

By subjecting the powder scrap to the heat treatment as described above, a carbon-reduced agglomerated particle is obtained. Since carbon reduction occurs by oxidative decarburization, the oxygen content of the agglomerated particles obtained by the heat treatment is higher than the oxygen content of the scrap before the heat treatment. Therefore, it is preferable to deoxidize the aggregated particles obtained by the heat treatment by a suitable method to reduce oxygen.

This deoxidation can be carried out by any method, but in the preferred embodiment of the present invention, it is carried out by the known direct reduction method described above, that is, the method of adding a reducing agent and heating in an inert gas. Deoxidize. This direct reduction method can be performed as follows, for example.

Powder scrap (in the case of the present invention, agglomerated particles oxidized and decarburized by the above heat treatment) together with a reducing agent is put into a suitable container made of stainless steel or the like, and the mixture is placed under an argon atmosphere at atmospheric pressure. Then, it is carried out by heating to a temperature at which the reducing agent melts to cause a reduction reaction. In order to lower the melting temperature of the reducing agent, it is preferable to add an appropriate flux to the container. It is preferable that the reducing agent and the flux be thoroughly mixed with the powder scrap in advance.

As the reducing agent, it is preferable to use granular metallic calcium capable of reducing the R-Fe-B type rare earth oxide. In order to prevent a decrease in deoxidation due to evaporation during melting and heating, the amount of Ca added should be approximately 1.0 to 2.0 times the chemical equivalent required for the complete reduction of oxides in scrap.

When the reducing agent is metallic calcium, the flux is generally chlorides of alkali metals such as lithium, sodium and potassium, chlorides of alkaline earth metals such as magnesium and calcium, etc. Uses anhydrous calcium chloride that does not volatilize when heated. The amount of flux added is preferably 3 to 20% with respect to the powder scrap.

When the reducing agent is metallic calcium, the heating temperature required for the reduction reaction is 800 ° C. or higher, and the heating time is usually about 1 to 3 hours. The cooling conditions are not particularly limited, and may be furnace cooling, for example. If the heating temperature exceeds 1200 ° C, the vapor pressure of calcium metal will exceed 131 hPa and the loss of calcium will increase.
The temperature is preferably 00 ° C or lower.

In the present invention, the powder scrap to be reduced is agglomerated particles, but since it is not densely sintered, molten metal calcium easily penetrates into the agglomerated particles. That is, the reduction reaction proceeds as easily as in the case of non-aggregated primary particles.

After the reduction reaction, the cooled reaction mixture is taken out of the reaction vessel, preferably roughly crushed, and then washed with pure water having a specific resistance of 50 MΩ · cm / 25 ° C., for example. The unreacted deoxidizer (eg, calcium metal) and by-products (eg, calcium oxide) in the reaction mixture dissolve or suspend in water, causing the reaction mixture to collapse, resulting in a reduced powder slurry. .

When pure water is used for cleaning, anions (Cl ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ^2−, etc.) which are harmful to the rare earth magnet are reduced, and the reduced powder is oxidized and hardly soluble. The formation of calcium salts is prevented. Since the upper layer of the slurry is a suspension of hydroxide such as calcium hydroxide, the washing is repeated by decantation (removal of the supernatant) -water injection-decantation-water injection. In this case, as a method for confirming that the unreacted deoxidizing agent and by-products have been sufficiently removed, the pH of the solution may be measured and the pH may be 10 or less. The reduced powder thus obtained is replaced with ethanol and vacuum dried at room temperature. In the present invention, since the powder is agglomerated particles and easily settles, it can be easily separated from the liquid by decantation, and the workability of washing is good.

The powder scrap (reduced powder) deoxidized by the direct reduction method can be easily redissolved into an ingot. The melting can be performed by high frequency melting, arc melting, plasma melting or the like. As a preliminary treatment for dissolution, dehydration solidification treatment by a filter press or the like may be performed. By carrying out the re-dissolution, there is a possibility that a trace amount remains in the reduced powder, for example, metallic calcium,
Impurities such as calcium oxide and anhydrous calcium chloride are slagged or evaporated, so that a high-quality regenerated ingot equivalent to a virgin ingot can be obtained.

This recycled ingot has the carbon content and the oxygen content reduced to the same level as the virgin ingot, and when a rare earth magnet is produced by using this as a raw material alloy, the magnetic characteristics are deteriorated by the excess carbon and oxygen. A rare earth magnet can be obtained. The rare earth magnet manufactured from this recycled ingot may be of a sintered type, a bond type, or a quenching type (remelting and quenching).

[0054]

EXAMPLE The following example illustrates a method of recycling scraps generated in various manufacturing processes of sintered rare earth magnets. In the following Examples and Comparative Examples,% means mass% unless otherwise specified. The measurement methods of the samples used are summarized below: Metal composition value and rare earth content: ICP (plasma emission spectroscopy), Moisture content: Atmospheric heating moisture content measuring device, Carbon content, Oxygen content: LECO (Infrared absorption) Method), average particle size: aeration type particle size meter.

[Example 1] This example illustrates a reclaiming process of slurry powder scraps generated in the processing step of Nd-Fe-B magnets. The metal composition value and water content of this slurry were as follows: Metal composition of scrap: 19.5% Nd-4.9% Pr-2.4% Dy-
1.0% B-The balance Fe moisture content: 38%.

3.0 kg of this slurry was heated in an air drying furnace to 80
After drying at ℃ for 24 hours, 1.86 kg of dried powder scrap (A) was obtained. Carbon content of this powder scrap (A),
Table 1 shows the measured values of oxygen content and rare earth content (Nd + Pr + Dy) and the average particle size. Since it is processing scrap in which carbon-containing contaminants are mixed from the outside, the carbon content was high, exceeding 1%. Also, since the average particle size was as fine as 1.1 μm, the oxygen content was also very high at 5.60%.

1.8 kg of this powder scrap (A) was placed in a stainless steel container and heat-treated in a reduced pressure atmosphere to oxidize and decarburize. The heat treatment condition is a heating rate of 5 ° C /
Min, maximum temperature 1000 ℃, pressure 0.05 Pa (oxygen partial pressure 0.01 Pa),
The heating (heat treatment) time was set to 5 hours, and after the heat treatment, furnace cooling was performed in an argon atmosphere to obtain decarburized powder (hereinafter referred to as heat treated powder). The heat-treated powder was agglomerated particles that were easily crushed, and had an average particle size of 280 μm and was coarse. Table 2 shows the carbon content, oxygen content, rare earth content, and average particle size of the heat-treated powder. The rare earth metal content remained almost unchanged, the oxygen content increased above 8.00%, and the carbon content decreased significantly below 0.06%.

About 1.8 kg of this heat-treated powder was used for deoxidation by the direct reduction method as follows. Particle size 2 to deoxidizer
7 mm of 99% pure granular metallic calcium was used, and the addition amount was 1.5 times the deoxidation equivalent. The flux used was anhydrous calcium chloride having a purity of 95%, and was added in an amount of 5% with respect to the heat-treated powder.

After thoroughly mixing the heat-treated powder, the reducing agent and the flux, the mixture was placed in a stainless steel reaction vessel, heated to 900 ° C. in a high-purity argon gas stream over 3 hours, and kept for 1 hour. After that, the mixture was cooled to room temperature and the reduction reaction mixture was taken out.

The reaction mixture was roughly crushed to a diameter of about 5 mm with a jaw crusher, then cooled with a chiller to 15 ° C. or lower, and immersed in 10 liters of pure water having a specific resistance of 50 MΩ · cm / 25 ° C. for about 1 hour to react. An initial disintegration of the mixture was performed. The solution (washing liquid) becomes pH 10 or less by repeating the water injection-stirring-decantation process such as decantation, pouring pure water into the slurry clouded with calcium oxide, stirring for 5 minutes, and decantation again. Was washed up to. The reduced powder in the washed slurry is separated by an aspirator, replaced with ethanol, and vacuum dried at room temperature for 24 hours.
I went on time.

The carbon content, oxygen content, and rare earth content of the thus obtained reduced powder are also shown in Table 2. The reduced powder was found to be a good regenerated alloy powder. This reduced powder 1.
0 kg was melted and solidified under vacuum in a high-frequency melting furnace using a magnifying crucible to produce a recycled ingot. Table 2 also shows the carbon content, oxygen content, and rare earth content of the recycled ingot. It was of good quality with the same amount of impurities as the virgin ingot.

[Embodiment 2] This embodiment illustrates a recycling process of scraps, which are defective in powder compacting, which occurred in the press molding process. The composition and shape of this poorly compacted product were as follows: Composition of poorly compacted product: 23.3% Nd-7.1% Pr-1.00% Dy
-1.1% B-Remaining Fe Shape of powder compacting defective product: Solid cylindrical product with diameter of about 30 mm and height of about 10 mm.

3.0 kg of this defective powder compacting product was pulverized by a pulsarizer and then a jet mill in an argon atmosphere to obtain a powder scrap (B). Table 1 shows the measured values of carbon content, oxygen content and rare earth content of this powder scrap (B) and the average particle size. It can be seen that both the amount of carbon and the amount of oxygen are smaller than the powder scrap (A) generated in the processing process. In particular, the amount of oxygen is very low.

Using this powder scrap, heat treatment was carried out in the same manner as in Example 1 under a reduced pressure atmosphere to oxidize and decarburize. Table 2 shows the properties of the heat-treated powder thus obtained. As in Example 1, a decrease in carbon content was observed. Oxygen content increased about 10 times due to oxidative decarburization.

Then, using this heat-treated powder, deoxidation by the direct reduction method was carried out in the same manner as in Example 1 to obtain a reduced powder. As shown in Table 2, a good regenerated alloy powder was obtained. I knew it was.

Further, using this reduced powder, Example 1
A reclaimed ingot was produced in exactly the same manner as described above, and as shown in Table 2, it was a good quality ingot having an impurity level equivalent to that of the virgin ingot.

[Example 3] This example was generated in the firing process.
An example of a recycling process of scrap made of defective products will be described.
The composition and shape of the defective sintering product used in this example were as follows: Composition of defective sintering product: 22.9% Nd-7.0% Pr-1.00% Dy-1.1
% B-remaining Fe Shape of defective sintered product: solid cylindrical product with diameter of about 30 mm and height of about 10 mm.

3.0 kg of this defective sintered product was placed in a stainless steel closed container, and hydrogen was sealed at room temperature under a pressure of 0.3 MPa.
It was left for a minute and hydrogenated and ground. Then, under reduced pressure at 600 ° C
After heating for 10 hours for dehydrogenation, pulverization was performed in a jet mill in an argon atmosphere to obtain powder scrap (C). Table 1 shows the measured values of carbon content, oxygen content and rare earth content of this powder scrap (C) and the average particle size.

Using this powder scrap (C), heat treatment was carried out in a reduced pressure atmosphere atmosphere in the same manner as in Example 1 to oxidize and decarburize. Table 2 shows the properties of the heat-treated powder thus obtained.
As in Example 1, a decrease in carbon content was observed and the oxygen content was significantly increased.

Then, using this heat-treated powder, deoxidation was carried out by the direct reduction method in exactly the same manner as in Example 1. The obtained reduced powder was a good regenerated alloy powder as shown in Table 2.

Further, using this reduced powder, Example 1
A reclaimed ingot was produced in exactly the same manner as described above, and as shown in Table 2, it was a good ingot having an impurity level equivalent to that of the virgin ingot.

[Embodiment 4] This embodiment illustrates a recycling process of scraps made of defective plating products, which occurred in the rust-prevention process by Cu plating and Ni plating. The defective plating product used in this example had exactly the same composition and shape as the defective sintering product used in Example 3 before plating.

After completely removing copper plating and Ni plating by shot blasting, 3.0 kg of this defective plating product was placed in a closed container made of stainless steel, hydrogen was filled at 0.3 MPa at room temperature, and allowed to stand for 20 minutes for hydrogenation. Crushed. Then, under reduced pressure
After heating at 600 ° C. for 10 hours to carry out dehydrogenation, it was ground in a jet mill in an argon atmosphere to obtain powder scrap (D). Table 1 shows the measured values of carbon content, oxygen content and rare earth content of this powder scrap (D) and the average particle size.

Using this powder scrap (D), heat treatment was performed in the same manner as in Example 1 in a reduced pressure atmosphere to oxidize and decarburize. Table 2 shows the properties of the heat-treated powder thus obtained.
As in Example 1, a decrease in carbon content was observed. The amount of oxygen increased significantly.

Then, using this heat-treated powder, deoxidation was carried out by the direct reduction method in exactly the same manner as in Example 1. The obtained reduced powder was a good regenerated alloy powder as shown in Table 2.

Further, using this reduced powder, Example 1
A reclaimed ingot was produced in exactly the same manner as described above, and as shown in Table 2, it was a good ingot having an impurity level equivalent to that of the virgin ingot.

[Prior Art Examples 1 to 4] Each of the powder scraps (A) to (D) used in Examples 1 to 4 was subjected to a direct reduction method without oxidative decarburization by heat treatment in a reduced pressure atmosphere. To obtain a reduced powder. As shown in Table 2, the obtained reduced powder had low oxygen content, but no reduction in carbon content was observed.

Then, when a recycled ingot was prepared by melting in exactly the same manner as in Example 1, as shown in Table 2, the carbon content remained high, and the quality was unsuitable as a raw material alloy for rare earth magnets. I knew it was.

[Comparative Example 1] The maximum temperature of the powder scraps (A) to (D) used in Examples 1 to 4 was 550 ° C.
Alternatively, heat treatment was performed in a reduced pressure atmosphere atmosphere under the same conditions as in Example 1 except that the temperature was changed to 1250 ° C.

Table 2 shows the carbon content, oxygen content, and rare earth content of the heat-treated powder obtained. When the maximum temperature was 550 ° C, the oxygen content increased slightly in all the powders, but no change in the carbon content was observed and decarburization did not occur. Maximum temperature
At 1250 ° C, all the powders were heavily welded to the bottom of the container, and the heat-treated powder could not be collected.

Subsequently, only in the case of the maximum temperature of 550 ° C., the recovered heat-treated powder was deoxidized by the direct reduction method in the same manner as in Example 1 to obtain a reduced powder, as shown in Table 2. Moreover, the amount of carbon remained high. Furthermore, when a regenerated ingot was manufactured in exactly the same manner as in Example 1, it was found that the carbon content remained high as shown in Table 2 and the quality was unsuitable as a raw material alloy for rare earth magnets.

[Comparative Example 2] Similar to Example 1 except that the heating time was changed to 0.5 hours or 11 hours for each of the powder scraps (A) to (D) used in Examples 1 to 4. Under the conditions described above, heat treatment was performed in a reduced pressure atmosphere.

Table 2 shows the carbon content, oxygen content, and rare earth content of the heat-treated powder obtained. When the heating time was 0.5 hours, the amount of carbon did not change at all in all the powders, and particle coarsening due to aggregation was not observed. When the heating time is 11 hours, the amount of carbon is significantly reduced, but the heat-treated powder is completely welded to each other and becomes coarse particles that cannot be crushed. Was given.

Subsequently, using these heat-treated powders, direct reduction was carried out in the same manner as in Example 1 to obtain reduced powders.
Table 2 shows the carbon content, oxygen content, and rare earth content of these reduced powders. When the heating time was 0.5 hours, the carbon content remained high in all the powders, and when the heating time was 11 hours, the particles became coarse and fused in all the powders, resulting in a decrease in deoxidation and a high oxygen content. there were.

Regarding the production of regenerated ingots from these reduced powders, as shown in Comparative Examples 1 and 2, it was expected that problems would occur in terms of cost and quality.
It was not ingot.

[0086]

[Table 1]

[0087]

[Table 2]

[Example 5] Grinding powder generated in the manufacturing process
The treatment shown in Table 3 was performed using [A of Table 1] as a starting material. The metal component of the grinding dust powder used was 19.5% Nd-
It was 4.9% Pr-2.4% Dy-1.0% B-bal.Fe.

Some of the powder slurry was used as it was.
(No dust removal step in Table 3) or some only washed with water (dust removal step in Table 3), or washed with water-after that to remove coarse dust using a 1 mm sieve
(Dust removal step in Table 3) After air drying at 80 ° C. for 24 hours, oxidative decarburization and hydrogen reduction were performed.

Since some of the powders after oxidative decarburization and hydrogen reduction were slightly sintered, they were all crushed to 1 mm or less, the particle size was adjusted, and Ca reduction treatment was performed.

In the Ca reduction treatment, granular metal Ca (purity 99%) of 2 to 7 mm was added 1.5 times the chemical equivalent calculated from the amount of oxygen contained, and 95% anhydrous calcium chloride was added 5% as a flux. After kneading these mixtures, they were treated in an Ar gas atmosphere at 900 ° C. for 3 hours and cooled to room temperature. The obtained reaction product was coarsely pulverized to 5 mm or less, sufficiently decanted with pure water to remove calcium hydroxide and calcium chloride, and then dried to obtain a Ca-reduced powder.

The Ca-reduced powder thus obtained was compacted into a raw material for melting. Using this melting raw material, it was melted at 1550 ° C. in an Ar gas atmosphere and then poured into a mold at 1500 ° C. to obtain a recycled ingot. Table 3 shows the process conditions and the analysis results.

The atmosphere O _{2 under} the oxidizing heat treatment conditions shown in Table 3 was used.
"21%" in indicates that it is an atmospheric atmosphere, and "0.
"1 to 10%" indicates the amount of oxygen in the Ar carrier gas atmosphere.
Further, in the atmosphere H _{2 under} the hydrogen heat treatment conditions of Table 3, “101k
“Pa” and “67 Pa to 13 kPa” indicate the pressure of pure hydrogen gas.

[0094]

[Table 3]

From Table 3, it can be seen that a low carbon product having a carbon content of 600 ppm or less can be obtained in an oxidizing atmosphere of 700 ° C. or higher. Furthermore, as shown in Table 3, the oxygen concentration before Ca reduction was lowered by including the hydrogen reduction step together with the oxidation heat treatment step. As a result, it was found that the amount of Ca used for Ca reduction was reduced, the powder deposition during Ca reduction was reduced, and the water washing time during decantation was shortened, which was desirable for the entire process.

[Example 6] Powder dust (E) generated in the manufacturing process
, Green compact waste (B), sintered waste (C), defective plating (D)
Using the used product (F) recovered from the market as a starting material, the treatment shown in Table 4 was performed.

Table 1 shows the measured carbon content, oxygen content and rare earth content (Nd + Pr + Dy) of the scraps used and the average particle size.

[0098]

[Table 4]

Although the metal components of the used scraps varied a little, 19-20% Nd-4-6% Pr-2-4% Dy-0.
It was 8 to 1.0% B-bal.Fe. C and O were as shown in Table 5, respectively.

[0100] The powder dust is left as it is, the green compact dust is lightly crushed into powder, and the sintered dust is crushed in the air to 1 mm.
The following powder was used. For the defective plating product, the surface plating layer was removed by shot blasting and then treated in the same manner as the sintered body layer to obtain a powder of 1 mm or less. Used products (VCM magnets for HDDs) collected from the market are demagnetized and separated from the equipment by heat treatment at 500 ° C in the air, and after removing only the magnets, they are the same as defective plating products. Processing 1
The powder was less than mm.

The various powdery raw materials were subjected to oxidative decarburization and hydrogen reduction under the conditions shown in Table 4. Since some of the powders after oxidative decarburization and hydrogen reduction were slightly sintered, they were all crushed to 1 mm or less, the particle size was adjusted, and Ca reduction treatment was performed. Ca reduction treatment is 2-7 mm granular metallic Ca (purity 99%)
Was added 1.5 times the chemical equivalent calculated from the amount of oxygen contained, and 95% anhydrous calcium chloride was added as a flux at 5%. After kneading these mixtures, in an Ar gas atmosphere,
The mixture was treated at 0 ° C for 3 hours and cooled to room temperature. The obtained reaction product was roughly pulverized to 5 mm or less, sufficiently decanted with pure water to remove calcium hydroxide and calcium chloride, and then dried to obtain a powder.

The Ca-reduced powder thus obtained was compacted into a raw material for melting. This raw material was melted at 1550 ° C. in an Ar gas atmosphere, and then poured into a mold at 1500 ° C. to obtain a recycled ingot.

Table 4 shows the process conditions and the analysis results thereof. As shown in Table 4, it can be seen that a low carbon product having a carbon content of 600 ppm or less can be obtained in the oxidizing atmosphere of 700 ° C. or higher.

Further, it can be seen from Table 4 that the oxygen concentration before Ca reduction is lowered by including the hydrogen reduction step. As a result, it was found that the amount of Ca used for Ca reduction was reduced, the deposition of powder during Ca reduction was reduced, and the washing time during decantation was shortened, which was desirable for the entire process.

[0105]

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to efficiently reduce carbon of scrap of rare earth magnet, which has been difficult to reduce carbon in the past, and at the same time, the scrap is fine powder which is difficult to handle. In some cases, a coarse powder that can be easily handled thereafter can be obtained. The obtained low carbonized coarse powder can then be efficiently deoxidized by a direct reduction method, and from this deoxidized product, a high quality recycled ingot similar to a virgin ingot can be obtained. You can Therefore, the method for recycling rare earth magnet scrap of the present invention is extremely effective for effective utilization of precious rare earth metal and resource saving.

Further, according to the method of the present invention, it is possible to reduce the carbon content by heat-treating a rare earth magnet scrap having a high carbon content and a high carbon content in an oxidizing atmosphere. Reduction of oxides of organic elements and direct reduction of rare earth element-containing oxides with Ca
It can be regenerated as a low carbon and low oxygen rare earth magnet alloy powder.

Furthermore, these regenerated powders enable the production of high-quality regenerated ingots using the existing high-frequency melting furnace, and are extremely effective for effective utilization of rare earth metal elements.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01F 41/00 H01F 1/04 H (72) Inventor Akihiko Saguchi 1-8 Fuso-cho Amagasaki-shi Hyogo Sumitomo (72) Inventor Katsutoshi Ono, Yoshida Honmachi, Sakyo-ku, Kyoto Prefecture Kyoto University Faculty of Engineering, Graduate School of Engineering, Energy Sciences (72) Inventor Ryosuke Suzuki Yoshidahonmachi, Sakyo-ku, Kyoto Prefecture Kyoto Prefecture Kyoto University F-term in the Graduate School of Energy Science, Faculty of Engineering (reference) 4K018 BA18 BC01 BC09 BC18 BD02 KA43 5E040 AA04 CA01 CA20 5E062 CD04

Claims (5)

[Claims] 1. A powder scrap of a rare earth magnet containing carbon and containing no binder, in an atmosphere in the presence of oxygen.
A method for recycling rare earth magnet scrap, comprising a step of heat-treating at a temperature of 00 to 1200 ° C for 1 to 10 hours for oxidative decarburization. 2. The atmosphere in the presence of oxygen has an oxygen partial pressure of
The method for recycling rare earth magnet scrap according to claim 1, wherein the atmosphere is an oxygen-containing atmosphere of 140 Pa or less or an air atmosphere. 3. The rare earth magnet is an R—Fe—B based alloy.
(R is a rare earth metal whose main component is at least one of Nd, Pr, Dy, Ho, and Tb). 4. The method for recycling rare earth magnet scrap according to claim 2, wherein the oxygen-containing atmosphere is a reduced pressure atmosphere atmosphere of 667 Pa or less. 5. A step of deoxidizing the decarburized product obtained by the heat treatment step by a direct reduction method of adding a reducing agent and heating in an inert gas, and dissolving and coagulating the deoxidized product. The method for reclaiming rare earth magnet scrap according to any one of claims 1 to 4, further comprising a step of producing an ingot.