JP7228873B2 - Recycling method of rare earth-ferrous magnetic materials - Google Patents

Description

The present invention relates to a method for recycling rare earth-iron magnetic materials.

For effective use of resources, used magnets collected from waste are recycled. Patent Literature 1 proposes a recycling method of removing a binder component from a bonded magnet by heat treatment when used magnets are bonded magnets. This method is also applicable when the bonded magnet contains a rare earth element. Since rare earth elements are scarce compared to other elements, it is desired to actively recycle them in the future.

JP-A-10-55908

The heat treatment proposed in Patent Document 1 aims only at removing the binder component. Therefore, when the ferromagnetic material in the bonded magnet is composed of a magnetic compound containing a rare earth element and an iron element, the above heat treatment cannot sufficiently decompose the magnetic compound.

However, there are cases where the rare earth element is reused in a form that is not combined with the iron element, and where it is desired to combine the rare earth element with the iron element again to recreate the ferromagnetic material. In that case, a process is required to decompose the magnetic compound into at least a rare-earth-containing substance containing a rare-earth element and an iron-containing substance containing an iron element.

However, decomposition of the magnetic compound requires time and effort. That is, although the magnetic compound can be decomposed by heating, it takes a long time to decompose the magnetic compound by heating. Therefore, a technique capable of rapidly decomposing the magnetic compound is desired.

In addition, although the technique of Patent Document 1 targets only bonded magnets for recycling, it is desired to recycle rare earth-iron magnetic materials having the above-mentioned magnetic compounds, without being limited to bonded magnets.

An object of the present invention is to provide a method for recycling a rare earth-iron magnetic material, which can quickly decompose a magnetic compound containing a rare earth element and an iron element into at least a rare earth-containing material and an iron-containing material. be.

The rare earth-iron magnetic material recycling method according to the present invention comprises:
a preparation step of preparing a rare earth-iron magnetic material having a magnetic compound containing a rare earth element and an iron element, the magnetic compound having a Curie temperature lower than the Curie temperature of α-iron;
The rare earth-iron magnetic material is heated to a temperature lower than the Curie temperature of α-iron in a magnetic field of 5 T or higher and in an atmosphere having an oxygen partial pressure of 6 Pa or higher to convert the magnetic compound into a magnetic field heating step of decomposing into at least a rare earth-containing material containing the rare earth element and an iron-containing material containing the iron element;
have

The preparation step may include a pulverization step of pulverizing a used rare earth-iron magnet containing the magnetic compound to produce a pulverized material as the rare earth-iron magnetic material.

The rare earth-iron magnet is a bonded magnet,
The rare earth-iron magnetic material has a binder component that constitutes the bonded magnet,
In the magnetic field heating step, heat applied to the rare earth-iron magnetic material to decompose the magnetic compound may be used to decompose the binder component.

the rare earth element is Sm,
The magnetic compound may consist of Sm ₂ Fe ₁₇ N ₃ .

According to the present invention, the rare earth-iron magnetic material is heated in a magnetic field, and the heating temperature is set to a temperature lower than the Curie temperature of α-iron. is promoted. As a result, the rare earth-iron magnetic material can be quickly decomposed into at least the rare earth-containing material and the iron-containing material as compared with the case where no magnetic field exists.

Flowchart of Recycling Method for Rare Earth-Iron Magnetic Materials According to Embodiment 1 Flowchart of Recycling Method for Rare Earth-Iron Magnetic Materials According to Embodiment 2 Graph showing the results of experiments conducted in a magnetic field and in a zero magnetic field for the decomposition of a Sm--Fe--N magnetic material as a rare earth-iron magnetic material. Graph showing the results of experiments conducted in low vacuum and high vacuum for the decomposition of Sm--Fe--N magnetic materials as rare earth-iron magnetic materials.

[Embodiment 1]
A method for recycling a rare earth-iron magnetic material according to an embodiment will be described along the flowchart shown in FIG.
(a) Recovery Step First, used rare earth-iron magnets are recovered from various industrial product wastes (step S11). Here, the rare earth-iron magnet refers to a magnet in which a ferromagnetic material is composed of a magnetic compound containing a rare earth element and an iron element. Examples of rare earth elements include Sm, Nd, and Dy.

The rare earth-iron magnet may be a bonded magnet obtained by binding magnetic powder made of a magnetic compound with a binder, or may be a sintered magnet obtained by sintering magnetic powder.

However, in the present embodiment, among the rare earth-iron magnets, those in which the Curie temperature of the magnetic compound constituting the ferromagnetic material is lower than the Curie temperature of α-iron are targeted for recycling. Examples of magnetic compounds having a Curie temperature lower than that of α-iron include Sm ₂ Fe ₁₇ N ₃ , Nd ₂ Fe ₁₄ B, and (Nd _0.53 Dy _0.47 ) ₂ Fe ₁₄ B.

Such rare earth-iron magnets are used, for example, in hybrid vehicles, electric vehicles, motors used in home electric appliances, hard disks used in computer storage devices, magnet rollers used in copiers, medical equipment, magnets, etc. It can be collected from a sensor or the like. It is preferable to collect rare earth-iron magnets having the same composition of magnetic compounds containing the rare earth element to be collected.

(b) Pulverization Step Next, the recovered rare earth-iron magnet is pulverized to produce a pulverized material as a rare earth-iron magnetic material (step S12). The particle size of the pulverized product is preferably less than 1 mm, more preferably less than 75 μm, and more preferably less than 45 μm, from the viewpoint of promoting the decomposition reaction in the magnetic field heating step (step S13) described later. preferable.

In this specification, the particle size of less than d means that the particles pass through a sieve with a mesh size of d defined in JIS-Z8801.

As described above, the rare earth-iron magnetic material to be decomposed was prepared. In other words, the recovering step (step S11) and the pulverizing step (step S12) are significant as preparatory steps for preparing the rare earth-iron magnetic material.

(c) Magnetic Field Heating Step Next, the prepared rare earth-iron magnetic material is heated in a magnetic field (step S13). As a result, the magnetic compounds forming the rare earth-iron magnetic material are decomposed.

In this embodiment, the rare earth-iron magnetic material is heated in a magnetic field in an oxygen-containing atmosphere. In an atmosphere in which oxygen is present, decomposition of the rare earth-iron magnetic material can be carried out more quickly than in the absence of oxygen. The partial pressure of oxygen in the atmosphere is preferably 6 Pa or higher. The atmosphere may be air.

A magnetic compound in the rare earth-iron magnetic material is decomposed into at least a rare earth-containing substance containing a rare earth element and an iron-containing substance containing an iron element by heating in a magnetic field.

Specifically, when the magnetic compound is Sm ₂ Fe ₁₇ N ₃ , rare earth-containing substances include Sm and Sm oxides, and iron-containing substances include α-iron and α-iron oxides. . Also, when Sm ₂ Fe ₁₇ N ₃ is decomposed, nitrogen gas is produced as well as rare earth and iron inclusions.

Further, when the magnetic compound is Nd ₂ Fe ₁₄ B, examples of rare earth-containing substances include Nd, Nd borides, and oxides thereof, and iron-containing substances include α-iron, α-iron borides, and Their oxides are exemplified.

When the magnetic compound is (Nd _0.53 Dy _0.47 ) ₂ Fe ₁₄ B, examples of the rare earth-containing material include Nd, Dy, compounds of Nd and Dy, borides thereof, and oxides thereof. Examples of iron-containing materials include α-iron, α-iron borides, and oxides thereof.

The temperature for heating the rare earth-iron magnetic material is lower than 770° C., which is the Curie temperature of α-iron. As a result, the α-iron, which separates from the magnetic compound upon heating, maintains its ferromagnetic properties even during heating. On the other hand, as described above, since the Curie temperature of the magnetic compound is lower than that of α-iron, the magnetization of the magnetic compound is lower than that of α-iron.

Thus, the magnetic field promotes the separation of alpha-iron from the magnetized material such that the alpha-iron is selectively drawn from the magnetic compound. As a result, the decomposition of the rare earth-iron magnetic material can be carried out more quickly than in the absence of a magnetic field.

The temperature for heating the rare earth-iron magnetic material is preferably a temperature equal to or higher than the Curie temperature of the magnetic compound. As a result, the magnetic compound loses its ferromagnetic properties, so that the difference in magnetization between the magnetic compound and the α-iron can be increased. As a result, the separation of α-iron is further promoted, and the rare earth-iron magnetic material can be decomposed more quickly.

Although the magnitude of the magnetic field applied to the rare earth-iron magnetic material is not particularly limited, it is preferably 5 T or more. As the magnetic field applied to the rare earth-iron magnetic material increases, the separation of α-iron from the magnetized material is promoted, so that the rare earth-iron magnetic material can be quickly decomposed.

If the rare earth-iron magnet is a bonded magnet and the rare earth-iron magnetic material has a binder component that constitutes the bonded magnet, the rare earth-iron magnetic material is used to decompose the magnetic compound. The applied heat can also be used to decompose the binder component.

Moreover, since the rare earth-iron magnetic material is heated in a magnetic field in an oxygen-containing atmosphere, the binder component can be oxidized and removed. Thus, in the magnetic field heating step, the binder component can be decomposed in parallel with the decomposition of the magnetic compound.

(d) Magnetic separation step Next, the iron-containing material is separated from at least the rare earth-containing material and the iron-containing material remaining after the rare earth-iron magnetic material is decomposed using a magnetic force (step S14). .

Above room temperature, ferrous inclusions are magnetic, while rare earth inclusions are non-magnetic materials that are not magnetized, or materials that are less magnetized than iron inclusions. Thus, magnetic forces can separate the iron-containing material from at least the rare-earth-containing material and the iron-containing material. As described above, the rare earth-containing material can be obtained in a form separated from the iron-containing material.

It should be noted that the decomposition magnet that generates the magnetic field applied to the rare earth-iron magnetic material in the magnetic field heating step (step S13) described above is the magnetic separation magnet that forms the magnetic field for magnetic separation in the magnetic separation step (step S14). It may also serve as a magnet. As a result, equipment for recycling rare earth-iron magnetic materials can be simplified.

(e) Purification Step Next, the rare earth-containing material obtained as described above is subjected to a purification process to bring the rare earth-containing material closer to a simple substance of the rare earth element (step S15).

For example, when the rare earth element-containing material is an oxide of a rare earth element, a simple substance of the rare earth element can be obtained by subjecting the oxide to reduction treatment as purification treatment. The obtained rare earth element or the rare earth element-containing substance brought close to a simple substance can be reused.

In addition, in the purification step, a purification treatment may be performed to bring the iron-containing material closer to a simple substance of iron. As a result, iron can also be reused.

As described above, according to the present embodiment, the rare earth-iron magnetic material is heated in a magnetic field, and the heating temperature is lower than the Curie temperature of α-iron. separation of alpha-iron from compound is facilitated. As a result, the rare earth-iron magnetic material can be quickly decomposed into at least the rare earth-containing material and the iron-containing material as compared with the case where no magnetic field exists.

[Embodiment 2]
In the above embodiment, the purification step (step S15) is provided after the magnetic separation step (step S14), but the order of these steps may be reversed. A specific example will be described below.

As shown in FIG. 2, in this embodiment, the purification step (step S15) is performed before the magnetic separation step (step S14). Other conditions are the same as in the first embodiment. According to the present embodiment, since the target of magnetic separation is the purified rare earth-containing material and iron-containing material, it is possible to improve the accuracy of magnetic separation.

Although Embodiments 1 and 2 have been described above, the present invention is not limited thereto. For example, the modifications described below are also possible.

In Embodiments 1 and 2 above, the magnetic field heating step is performed in an oxygen-containing atmosphere in order to promote the decomposition of the rare earth-iron magnetic material. It may be carried out in a non-oxidizing atmosphere in which oxidation of the magnetic material is avoided. In that case, the reduction treatment as the purification treatment can be omitted.

In Embodiments 1 and 2 above, before the magnetic field heating step (step S13), that is, between the recovery step (step S11) and the crushing step (step S12), or between the crushing step (step S12) and the magnetic field heating step (Step S13) may be provided with a foreign matter removing step for removing foreign matter other than the magnetic compound. For example, if the used rare earth-iron magnet is a plated magnet covered with plating, the plating may be removed in the foreign matter removal step.

Experimental results of decomposing a Sm--Fe--N system magnetic material as a rare earth-iron system magnetic material will be described below. The Sm--Fe--N system magnetic material contains Sm as a rare earth element and an iron element, and has a magnetic compound represented by Sm ₂ Fe ₁₇ N ₃ .

First, an alloy of Sm and Fe was pulverized into an alloy powder having fine crystal grains, and the alloy powder was nitrided to prepare an Sm--Fe--N system magnetic material. The grain size of the Sm--Fe--N system magnetic material is less than 75 μm.

Then, as Example 1, the Sm--Fe--N system magnetic material was decomposed by heating to 400.degree. Since oxygen exists in a low vacuum, the magnetic compound in the Sm--Fe--N system magnetic material decomposes, for example, according to the following chemical reaction formula (1).
_2Sm2Fe17N3 + _3O2 → _{2Sm2O3 + 34Fe} + _{3N2 (} 1)

That is, the magnetic compound in the Sm--Fe--N magnetic material is decomposed into Sm ₂ O ₃ as a rare earth-containing material, Fe as an iron-containing material, and nitrogen gas. Fe as an iron inclusion can be present in the form of alpha iron. Iron inclusions can also include iron _oxides such as _Fe2O3 .

In addition, in order to confirm the effect of the magnetic field to promote the decomposition reaction represented by the above chemical reaction formula (1), as Comparative Example 1, the Sm--Fe--N magnetic material was placed in a zero magnetic field where no magnetic field was present. decomposed in The experimental conditions of Comparative Example 1 are the same as those of Example 1 except for the magnetic field.

FIG. 3 shows a graph of experimental results of Example 1 and Comparative Example 1. In FIG. The horizontal axis indicates elapsed time [h]. The vertical axis indicates the degree of progress of the decomposition reaction represented by the above chemical reaction formula (1).

The degree of progress of the decomposition reaction was evaluated by the ratio [wt%] of α-iron in the solid residue left after the decomposition reaction to the original Sm—Fe—N magnetic material. A larger value indicates that the Sm--Fe--N system magnetic material is well decomposed because a larger amount of the iron-containing material is produced. Quantitative analysis of the proportion of α-iron in the residue was performed by Rietveld analysis of the X-ray diffraction pattern of the residue.

As shown in FIG. 3, in both Example 1 and Comparative Example 1, the degree of progress of the decomposition reaction tends to increase with the lapse of time. However, in Example 1, the degree of progression of the decomposition reaction is greater than in Comparative Example 1. From this result, it was found that the magnetic field accelerates the decomposition of the magnetic compound. This is probably because the magnetic field facilitated the separation of α-iron from the magnetized material. This point will be specifically described below.

The heating temperature of the Sm--Fe--N system magnetic material is 400.degree. C., which is lower than 770.degree. C., which is the Curie temperature of .alpha.-iron. Therefore, the α-iron that separates from the magnetic compound maintains its ferromagnetic properties even during heating. On the other hand, the Curie _temperature of Sm ₂ Fe ₁₇ N ₃ is 475° C., which is lower than the Curie _temperature of α-iron _. Become.

Thus, the magnetic field promotes the separation of alpha-iron from the magnetized material such that the alpha-iron is selectively drawn from the magnetic compound. Separation of α-iron from the magnetized substance means decomposition of Sm ₂ Fe ₁₇ N ₃ as shown in the above chemical reaction formula (1). Therefore, according to Example 1, it is considered that the Sm--Fe--N based magnetic material was decomposed more quickly than Comparative Example 1 in which no magnetic field was present.

Next, an experiment for examining the influence of the atmosphere surrounding the Sm--Fe--N magnetic material on the progress of the decomposition reaction will be described.

As Example 2, the above Sm--Fe--N magnetic material was decomposed by heating to 450.degree.

Further, as Examples 3 and 4, the above Sm--Fe--N magnetic materials were decomposed in a high vacuum of 1 Pa. The heating temperature of the Sm--Fe--N system magnetic material was set to 450.degree. In both Examples 3 and 4, the magnetic field applied to the Sm--Fe--N system magnetic material was set to 5 T as in Example 2.

FIG. 4 shows graphs of experimental results of Examples 2, 3, and 4. FIG. As in FIG. 3, the horizontal axis indicates the elapsed time [h] and the vertical axis indicates the degree of progress of the decomposition reaction represented by the chemical reaction formula (1). As shown in FIG. 4, the degree of progress of the decomposition reaction is greater in Example 2, in which decomposition was performed in a low vacuum, than in Examples 3 and 4, in which decomposition was performed in a high vacuum.

The partial pressure of oxygen in the atmosphere is higher in low vacuum than in high vacuum. Therefore, it was found from the results of FIG. 4 that the degree of progress of the decomposition reaction is greater when the partial pressure of oxygen in the atmosphere is higher. Specifically, the partial pressure of oxygen in the low vacuum in Example 2 is 6 Pa. Therefore, it can be said that the magnetic compound is preferably decomposed in a magnetic field in an atmosphere with an oxygen partial pressure of 6 Pa or more.

Although the embodiments and examples of the present invention have been described above, the present invention is not limited thereto. The above embodiments and examples are for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention. The scope of the invention is indicated by the claims. Various modifications within the scope of the claims and their equivalents are considered to be within the scope of the present invention.

Claims (4)

a preparation step of preparing a rare earth-iron magnetic material having a magnetic compound containing a rare earth element and an iron element, the magnetic compound having a Curie temperature lower than the Curie temperature of α-iron;
The rare earth-iron magnetic material is heated to a temperature lower than the Curie temperature of α-iron in a magnetic field of 5 T or higher and in an atmosphere having an oxygen partial pressure of 6 Pa or higher to convert the magnetic compound into a magnetic field heating step of decomposing into at least a rare earth-containing material containing the rare earth element and an iron-containing material containing the iron element;
A method for recycling a rare earth-iron magnetic material. The preparation step includes a pulverization step of pulverizing a used rare earth-iron magnet containing the magnetic compound to produce a pulverized product as the rare earth-iron magnetic material,
The method for recycling a rare earth-iron magnetic material according to claim 1 . The rare earth-iron magnet is a bonded magnet,
The rare earth-iron magnetic material has a binder component that constitutes the bonded magnet,
In the magnetic field heating step, the binder component is decomposed using heat applied to the rare earth-iron magnetic material to decompose the magnetic compound,
The method for recycling a rare earth-iron magnetic material according to claim 2 . the rare earth element is Sm,
wherein _the magnetic compound consists _{of Sm2Fe17N3} ;
A method for recycling a rare earth-iron magnetic material according to any one of claims 1 to 3 .

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