Rare earth oxide recovery method

Abstract

The present invention provides a means that makes it possible to reduce the amount of flux used in a rare earth oxide recovery method which uses a boron-containing flux. The present invention provides a rare earth oxide recovery method for recovering a rare earth oxide from waste that contains matter containing a rare earth element, said method comprising: a melt preparation step (1) for heating and melting the waste and at least one borate selected from the group consisting of alkali metal borates and alkaline earth metal borates and / or a precursor thereof to prepare a melt containing at least a rare earth oxide, the borate, and an oxide of an easily oxidizable metal; and a separation step (2) for separating, from the melt, a Fe-C phase and a rare earth enriched phase in which the rare earth oxide is concentrated in the borate.

Description

Method for recovering rare earth oxides

[0001] The present invention relates to a method for recovering rare earth oxides, and more particularly to a method for recovering rare earth elements as rare earth oxides from waste containing rare earth element-containing materials.

[0002] Rare earth elements are used in a variety of products, including display phosphors, fluorescent lights, sensors, permanent magnets, and fuel cells, and are essential materials for the manufacture of high-tech devices such as personal computers, smartphones, and electric vehicles. While demand for rare earth elements has increased in recent years with the widespread use of these high-tech devices, rare earth elements are only produced in limited areas, are scarce, and have risen in price. Therefore, there is a need to develop and improve technologies for recovering rare earth elements from rare earth-containing materials in discarded high-tech devices.

[0003] Known methods for recovering rare earth elements from rare earth-containing materials include wet methods, in which the material is dissolved in an acid or solvent and separated into individual rare earth elements by solid-liquid separation or solvent extraction, and dry methods, in which the material is heated and melted with a flux to extract rare earth oxides into the flux. Among these methods, the wet method requires the use of large amounts of chemicals such as acid and solvent, resulting in the generation of a large amount of waste liquid after treatment. Another problem with the wet method is the time required to leach the rare earth elements from the material into the acid or solvent. On the other hand, the dry method has the advantage of easily extracting rare earth elements by simply heating and melting the rare earth-containing material in the presence of a flux, while also minimizing the generation of waste liquid.

[0004] As a flux in the dry method, boron oxide (B ２ O ３ For example, Japanese Patent Application Laid-Open No. 2016-186121 discloses that a melting point depressant, an oxidizing agent, and sodium borate are added to waste products or semi-finished products containing rare earth magnets and steel, and the resulting mixture is melted to produce RE magnets. ｘ O ｙ -B ２ O ３This document discloses a method for recovering rare earth elements from rare earth-containing materials (a method for recovering rare earth elements as oxides), which involves separating the material into two phases: a slag (RE: Nd, Pr, Dy, Tb) and an Fe-C phase, and recovering the separated rare earth elements. According to this document, the use of sodium borate as a flux reduces the viscosity of the slag compared to conventional methods using boron oxide, making it possible to recover rare earth elements more easily and efficiently from rare earth-containing materials.

[0005] However, the recovery method described in the above document has the problem that a large amount of flux (sodium borate) is used, which increases costs (raw material costs, waste disposal costs). Moreover, boron is an environmentally regulated substance, and there has been a demand for reducing the amount of boron used.

[0006] Therefore, an object of the present invention is to provide a means for reducing the amount of flux used in a method for recovering rare earth oxides using a flux containing boron.

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by using an alkali metal or alkaline earth metal borate as a flux in the dry method, and allowing an easily oxidizable metal in the system to coexist in the form of an oxide when extracting a rare earth oxide into the flux, thereby completing the present invention.

[0008] That is, a method for recovering rare earth oxides according to one embodiment of the present invention is a method for recovering rare earth oxides from waste containing rare earth element-containing materials, and includes a melt preparation step (1) of heating and melting the waste and at least one borate selected from the group consisting of borates of alkali metals and borates of alkaline earth metals and / or a precursor thereof to prepare a melt containing at least rare earth oxide, the borate, and an oxide of an easily oxidizable metal; and a separation step (2) of separating from the melt a rare earth-enriched phase in which rare earth oxides are concentrated in the borate, and an Fe—C phase.

[0009] FIG. 1 shows the rare earth element-containing material, Nd ２ O３ , Al as an oxide of an easily oxidizable metal ２ O ３ and SiO ２ , sodium tetraborate (Na ２ B ４ O ７ ) is used as a rare earth element-containing material. ２ O ３ (RE: Nd, Pr, Dy, Tb), Al as oxide of easily oxidizable metal ２ O ３ and SiO ２ , sodium tetraborate (Na ２ B ４ O ７ ) is a pseudo-quaternary phase diagram at 1400°C.

[0010] Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the range "X to Y" means "X or more and Y or less."

[0011] One aspect of the present invention is a method for recovering rare earth oxides from waste containing rare earth elements, the method comprising: a melt preparation step (1) of heating and melting the waste with at least one borate selected from the group consisting of alkali metal borates and alkaline earth metal borates and / or its precursor to prepare a melt containing at least rare earth oxides, the borate, and an oxide of an easily oxidizable metal; and a separation step (2) of separating from the melt a rare earth-enriched phase in which rare earth oxides are concentrated in the borate and an Fe—C phase. This aspect of the present invention allows for a reduction in the amount of flux used in the method for recovering rare earth oxides using a boron-containing flux.

[0012] Hereinafter, each step of the method for recovering rare earth oxides according to this embodiment will be described in detail.

[0013] <Melt Preparation Step (1)> In this step (1), waste containing a rare earth element-containing material and at least one borate selected from the group consisting of alkali metal borates and alkaline earth metal borates and / or a precursor thereof are heated and melted to prepare a melt containing at least a rare earth oxide, the borate, and an oxide of an easily oxidizable metal.

[0014] [Waste] The waste contains a rare earth element-containing material. The waste may be a product or semi-finished product containing a rare earth element-containing material. The rare earth element-containing material is not particularly limited as long as it contains one or more rare earth elements (i.e., scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium).

[0015] The rare earth element-containing material can take various forms, such as a mixture, a compound, a sintered product, an alloy, or a combination thereof. The rare earth element-containing material can also be contained in products that use alloys containing rare earth elements, waste products or semi-finished products, or waste products such as scraps or defective products generated during the manufacturing process.

[0016] Among rare earth element-containing materials, rare earth magnets rich in rare earth elements (including sludge generated during their production) are preferred. Rare earth magnets are not particularly limited as long as they are magnets made of alloys containing one or more rare earth elements. Specific examples of rare earth magnets include neodymium magnets, samarium-cobalt magnets, praseodymium magnets, and samarium-iron-nitrogen magnets, with neodymium magnets being preferred. Neodymium magnets using rare metals such as rare earths (Nd, Pr, Dy, and Tb) are used in drive and power-generating motors for environmentally friendly electric vehicles (EVs) and hybrid electric vehicles (HEVs). Rare earths (rare earth elements) present procurement risks, and with the expected increase in demand for environmentally friendly vehicles in Japan, which is poor in natural resources, recycling rare earths from neodymium magnets is important. Recycling the rare earths in neodymium magnets is advantageous in that it reduces the procurement risk of rare earths. Neodymium magnets are generally defined as a type of rare earth magnet whose main components are neodymium, iron, and boron. However, in this specification, neodymium magnets refer to magnets defined as R-T-B alloys containing R, T, and B (where R must contain at least one element selected from the group consisting of Nd, Pr, Dy, and Tb, T is a transition metal that must contain Fe, and B is boron, some of which can be substituted with carbon or nitrogen).

[0017] The rare earth oxide recovery method of the present invention can be applied to products or semi-finished products containing rare earth magnets, not only when the rare earth magnet is a single component, but also when the rare earth magnet is included as an integral component. Examples include motors and compressors for air conditioning equipment that contain rare earth magnets as integral components. The shape of such products or semi-finished products containing rare earth magnets may be the original shape of the main components of the product or semi-finished product, or they may be disassembled. It is extremely difficult to remove a rare earth magnet incorporated into a motor from a discarded motor. In contrast, the recovery method of this embodiment allows the motor itself to be processed without separating the magnet from the discarded motor. This simplifies the recycling of products or semi-finished products containing rare earth magnets. Furthermore, there is no need to crush the rare earth magnets beforehand. The shapes of waste vary depending on the type of product, and in order to extract rare earth magnets, it is necessary to design rare earth magnet extraction equipment suited to the shape of the waste, as described, for example, in "Recovery of Neodymium Magnets in Home Appliance Recycling" (November 29, 2011, Association for Electric Home Appliances; https: / / www.meti.go.jp / shingikai / sankoshin / sangyo_gijutsu / haikibutsu_recycle / pdf / 016_06_00.pdf). The high cost of this has been one of the factors hindering magnet recycling. According to the recovery method of this embodiment, at least one borate (flux) selected from the group consisting of alkali metal borates and alkaline earth metal borates, and optionally an easily oxidizable metal (e.g., aluminum, silicon) and / or its oxide, a melting point depressant (e.g., carbon), and / or an oxidizer (e.g., iron oxide) are added to the waste, and the mixture is heated and melted to separate and recover the rare earth magnets. This eliminates the need to extract the rare earth magnets from the waste, making this a highly economical method.

[0018] Furthermore, in conventional techniques, when rare earth magnets are processed, they are demagnetized by heating or the like (see, for example, pages 9 to 11 of the above-mentioned "Recovery of Neodymium Magnets in Home Appliance Recycling"). However, with the recovery method according to the present embodiment, it is also possible to use products or semi-finished products that contain rare earth magnets that have not been demagnetized.

[0019] Furthermore, some finished products or semi-finished products have various platings applied to the surface of steel materials such as magnetic steel sheets or magnets in order to improve rust resistance and corrosion resistance. From the perspective of recovering rare earth elements, plating is undesirable because it increases impurities, and in conventional methods, this plating is removed in advance by polishing or the like. However, according to the recovery method of this embodiment, the finished products can be recovered as they are without removing the plating.

[0020] The waste may contain materials other than rare earth element-containing materials. Examples of materials other than rare earth element-containing materials include steel and copper. That is, according to a preferred embodiment of the present invention, the waste further contains at least one of steel and copper.

[0021] Examples of steel materials include steel plates and screws that are integrated with products and contain iron as a primary component, as well as product cases and chassis. The iron content is not particularly limited. The steel material may be magnetic steel, and its composition may include various elements including Ni, Cr, Si, Co, and the like. When a rare earth magnet and steel material are included, the two phases of a rare earth-enriched phase and an Fe—C phase can be separated by appropriately adjusting the carbon content relative to the total iron content. On the other hand, when a steel material is not included, for example, when only the rare earth magnet contains iron, the two phases of a rare earth-enriched phase and an Fe—C phase can be separated by appropriately adjusting the carbon content relative to the iron content in the rare earth magnet.

[0022] Furthermore, in this embodiment, when the waste contains copper, it can be separated into three phases: a rare earth-enriched phase, an Fe—C phase, and a Cu phase. In conventional techniques, aluminum and silicon are mixed into the Fe—C phase, making it difficult to efficiently recover only Cu. However, the recovery method according to this embodiment can improve the recovery efficiency of Cu. This point will be explained in detail in the section on separation step (2) below.

[0023] [Borate and / or Precursor Thereof] In the recovery method according to the present embodiment, at least one borate selected from the group consisting of borates of alkali metals and borates of alkaline earth metals is used as a flux.

[0024] Examples of borates of alkali metals and alkaline earth metals include sodium tetraborate (Na ２ B ４ O ７ ), lithium tetraborate (Li ２ B ４ O ７ ), potassium tetraborate (K ２ B ４ O ７ ), rubidium tetraborate (Rb ２ B ４ O ７ ), cesium tetraborate (Cs ２ B ４ O ７ ), sodium metaborate (NaBO ２ ), lithium metaborate (LiBO ２ ), potassium metaborate (KBO ２ ), rubidium metaborate (RbBO ２ ), cesium metaborate (CsBO ２ ), barium tetraborate (BaB ４ O ７ ), magnesium tetraborate (MgB ４ O ７ ), calcium tetraborate (CaB ４ O ７ ), strontium tetraborate (SrB ４ O ７ ), magnesium borate (MgB ２ O ４ ), calcium borate (CaB ２ O ４ ), strontium borate (SrB ２ O ４ ), barium borate (BaB ２ O ４ Among these, examples of the alkali metal borates include sodium tetraborate (Na ２ B４ O ７ ) can be preferably used. Sodium tetraborate (Na ２ B ４ O ７ ) is the B used as flux in the existing dry method described in the Background Art. ２ O ３ It can be obtained more cheaply than calcium borate and magnesium borate, which are specifically used in other existing dry processes, and can greatly contribute to reducing the recovery cost of rare earth oxides. Borates containing alkaline earth metals such as magnesium and calcium are mainly composed of sodium tetraborate (Na ２ B ４ O ７ ) (alkali metal borates) can also be used in combination. As the alkaline earth metal borates, for example, barium tetraborate (BaB ４ O ７ ), calcium borate (CaB ２ O ４ Among them, barium tetraborate (BaB) is preferred because it can greatly contribute to reducing the cost of recovering rare earth oxides. ４ O ７ ) is more preferred.

[0025] In the recovery method according to the present embodiment, instead of or in addition to borate, a precursor that generates borate when heated and melted can be added. Such a precursor can be boric acid (B ２ O ３ ) and alkali metal oxides (Na ２ O, Li ２ O.K. ２ O ７ , Rb ２ O ７ , Cs ２ O), boric acid (B ２ O ３ ) and alkaline earth metal oxides (BaO, MgO, CaO, SrO), boric acid (B ２ O ３) and alkali metal hydroxides (NaOH, LiOH, KOH, RbOH, CsOH), boric acid (B ２ O ３ ) and alkaline earth metal hydroxides (Ba(OH) ２ , Mg(OH) ２ , Ca(OH) ２ , Sr(OH) ２ ), combination with boric acid (B ２ O ３ ) and alkali metal carbonates (Na ２ CO ３ , Li ２ CO ３ , K. ２ CO ３ , Rb ２ CO ３ , Cs ２ CO ３ ), combination with boric acid (B ２ O ３ ) and alkaline earth metal carbonates (BaCO ３ , MgCO ３ , CaCO ３ , SrCO ３ The amounts of the boron source and the alkali metal source or alkaline earth metal source can be adjusted appropriately depending on the desired composition of the borate.

[0026] The amount of borate or its precursor added may be sufficient so that the rare earth element contained in the rare earth-containing material and the oxide of the easily oxidizable metal form a homogeneous melt (liquid phase region). In other words, the amount of borate added is an amount equal to or greater than the liquidus line in a phase diagram determined by the mass of rare earth oxide in the rare earth-containing material and the content of the easily oxidizable metal oxide. Here, in this specification, "the mass of rare earth oxide in the rare earth-containing material" refers to the mass of rare earth elements (e.g., Nd, Pr, Dy, and Tb) contained in the rare earth-containing material (e.g., rare earth magnet) that are present in the rare earth oxide (Nd ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３The mass of the rare earth oxides is the total mass of the rare earth oxides when they are considered to be oxidized to the metal oxides of the easily oxidizable metals. The content of the oxides of the easily oxidizable metals refers to the content of each type. For example, Al ２ O ３ When only Al is contained, the content of the oxide of the easily oxidizable metal is Al ２ O ３ It refers to the content of Al as an oxide of an easily oxidizable metal. ２ O ３ and SiO ２ When the oxide of the easily oxidizable metal is contained, the content of the oxide of the easily oxidizable metal is Al ２ O ３ and SiO ２ Refers to the content of each of the above.

[0027] Hereinafter, the "amount above the liquidus in the phase diagram determined by the mass of rare earth oxide in the rare earth element-containing material and the content of easily oxidizable metal oxide" will be explained with reference to FIG. 1. ２ O ３ , Al as an oxide of an easily oxidizable metal ２ O ３ and SiO ２ , sodium tetraborate (Na ２ B ４ O ７ ) is a pseudo-quaternary phase diagram at 1400°C. Each side of the regular tetrahedron shown in Figure 1 represents the concentration of the four components. For example, in the regular tetrahedron shown in Figure 1, Nd ２ O ３ and Na ２ B ４ O ７ Consider an edge with vertices A and Nd at any point A on this edge. ２ O ３ : Na ２ B ４ O ７ The composition ratio (mass ratio) of "from point A to the vertex (Na ２ B ４ O ７ ) distance from point A to the vertex (Nd ２ O ３ ) (leverage principle). Here, each side of the equilateral triangle to the left of the regular tetrahedron is Nd ２O ３ , Al ２ O ３ and SiO ２ The concentration of Nd is shown, and a point on the face of the equilateral triangle (for example, point X indicated by an arrow in FIG. 1) indicates the composition of these three components. More specifically, in the regular tetrahedron shown in FIG. ２ O ３ and Al ２ O ３ and SiO ２ Consider an equilateral triangle with vertices Nd at point X on this surface. ２ O ３ :Al ２ O ３ : SiO ２ The composition ratio (mass ratio) of "Al ２ O ３ and SiO ２ The distance of the perpendicular line from the line segment connecting the two points to point X: Nd ２ O ３ and SiO ２ The distance of the perpendicular line from the line segment connecting the two points to point X: Nd ２ O ３ and Al ２ O ３ The composition of the three components corresponds to the distance from the line segment connecting the two points to the perpendicular line to point X. ２ O ３ , Al ２ O ３ and SiO ２ The distance from point X to the vertex (Na ２ B ４ O ７ ) is the composition of the three components shown by point X. ２ B ４ O ７ When the three components and Na were added, ２ B ４ O ７ The concentration of the vertex (Na ２ B ４ O ７ ) as Na ２ B ４ O ７ This means that the concentration of Na increases for the three-component composition shown at point X.２ B ４ O ７ As the concentration of is increased, at a certain concentration, the solid-liquid mixed region changes to a liquid region (a region in which a homogeneous melt is produced). The boundary where the solid-liquid mixed region changes to the liquid region is called the "liquidus line", and on the liquid region, the liquid phase and a part of the solid phase usually exist in equilibrium. In the pseudo-quaternary phase diagram shown in Figure 1, the boundary between the solid-liquid mixed region and the liquid region exists as a surface, and therefore the boundary in such a case may also be called the "liquidus surface". However, in this specification, the term "liquidus line" will be used consistently regardless of whether the boundary is a line or a surface. The content of borate being "amount above the liquidus line" refers to a concentration corresponding to the liquidus line or a concentration in the liquid region. In the case shown in Figure 1, the "amount above the liquidus line" refers to the distance from the intersection (not shown) of the straight line and the liquidus line to the vertex (Na ２ B ４ O ７ ) line segment (however, vertex (Na ２ B ４ O ７ ) except for ２ B ４ O ７ Equivalent to concentration.

[0028] In the above, the "amount above the liquidus in the phase diagram determined by the mass of rare earth oxide in the rare earth element-containing material and the content of easily oxidizable metal oxide" was explained using a pseudo-quaternary phase diagram. However, this "amount above the liquidus" can be determined without creating a phase diagram. That is, by determining the mass of rare earth oxide in the rare earth element-containing material and the content of easily oxidizable metal oxide in advance, the borate concentration corresponding to the liquidus can be experimentally determined by increasing the borate concentration for this composition. This makes it possible to determine the composition that produces a homogeneous melt regardless of the composition of rare earth element and easily oxidizable metal (oxide) contained in the rare earth element-containing material. Therefore, the recovery method according to this embodiment can be applied to wastes having various element compositions.

[0029] [Easily oxidizable metal and / or its oxide] In this step (1), in addition to the waste containing a rare earth element-containing substance and the borate and / or its precursor, an easily oxidizable metal and / or its oxide may be added. In this specification, the term "easily oxidizable metal" refers to an oxidizing agent (e.g., iron oxide (Fe)) described later. ２ O ３ )). Examples of easily oxidizable metals include aluminum (Al), silicon (Si), titanium (Ti), and zirconium (Zr). Among these, the easily oxidizable metal is preferably at least one or both of aluminum (Al) and silicon (Si), and more preferably a combination of aluminum (Al) and silicon (Si). These easily oxidizable metals may also be added in the form of oxides. Examples of easily oxidizable metal oxides include aluminum oxide (Al ２ O ３ : alumina), silicon dioxide (SiO ２ : silica), titanium oxide (TiO ２ : titania), zirconium oxide (ZrO ２ Among them, aluminum oxide (Al ２ O ３ : alumina) and silicon dioxide (SiO ２ It is preferable that the material is at least one of aluminum oxide (Al : silica), and aluminum oxide (Al : silica). ２ O ３ : alumina) and silicon dioxide (SiO ２ It is more preferable to use a rare earth element-containing material in combination with an easily oxidizable metal and / or its oxide. However, if the waste containing the rare earth element-containing material contains a sufficient amount of an easily oxidizable metal and / or its oxide, no separate addition is necessary. Thus, according to a preferred embodiment, the waste contains a rare earth element-containing material and an easily oxidizable metal. According to a more preferred embodiment, the waste contains a rare earth element-containing material, aluminum, and silicon.

[0030] [Melting Point Depressant] Waste may contain a large amount of iron. For example, discarded motors contain a much larger amount of iron, derived from the electromagnetic steel plate portion of the motor, compared to rare earth magnets alone. When waste contains a large amount of iron, the melting point of iron is as high as 1538°C. Therefore, considering the efficiency of phase separation and the reduction of energy required for melting, it is preferable to melt the waste in the presence of a melting point depressant. Carbon is preferably used as the melting point depressant. Carbon has the effect of preventing iron oxidation and preventing iron from migrating to the rare earth-enriched phase, thereby improving separability. Examples of carbon sources include using a carbon crucible in a heating furnace (melting furnace), coating the furnace walls with carbon, and adding Fe—C alloys such as pig iron, coke, graphite, commercially available recarburizers, plastics, organic substances, etc. to the reaction system as additives. Other examples include blowing in a gaseous carbon source such as carbon dioxide or a hydrocarbon gas. Furthermore, as will be described later, when carbon is used as a melting point depressant, high-purity iron such as electrolytic iron added for the purpose of producing an Fe—C alloy is also included in the melting point depressant. Also, when the heating furnace or its furnace wall is used as the carbon supply source (melting point depressant) as described above, the carbon material on the surface of the furnace wall dissolves in the molten waste, etc., and is added as a melting point depressant.

[0031] Furthermore, when a melting point depressant is added to waste electrical steel sheets containing rare earth magnets and then heated and melted, electrolytic iron can be added. While electrolytic iron is not necessarily required when heating and melting electrical steel sheets containing rare earth magnets at high temperatures of 1500°C or higher, when carbon is added as a melting point depressant, the electrolytic iron reacts with the carbon in the melting point depressant to produce an Fe—C alloy. By producing an Fe—C alloy that melts at a temperature of about 1200°C prior to heating and melting the electrical steel sheets, the melting of the electrical steel sheets can be accelerated, and the molten state of the electrical steel sheets can be achieved in a shorter time and at a lower temperature.

[0032] The amount of such melting point depressant added is preferably near the eutectic point composition because this results in the lowest melting temperature. When carbon is used as a melting point depressant, it is preferable to heat and melt the waste in a carbon-saturated state, i.e., when no more carbon dissolves in the melt, from the perspective of melting point depression and oxidation prevention effects. As a general guideline, the amount of melting point depressant added is considered to be in the range of 5% to 10% by mass relative to the iron element content of the waste. This range is only a guideline when the melting point depressant is added to the reaction system as an additive, such as an Fe-C alloy such as pig iron, coke, graphite, commercially available recarburizers, plastics, or organic matter, or when a gaseous carbon source such as carbon dioxide or a hydrocarbon gas is blown in. When a carbon crucible or a carbon-coated furnace wall is used as a carbon source or in combination with the carbon crucible, the melting point depressant is not limited to the above range. However, when using part of such a heating furnace (melting furnace) as a carbon source, it is necessary to periodically repair the furnace wall and replace the crucible, so it is preferable to use another carbon source.

[0033] [Oxidizing Agent] In the recovery method according to the present embodiment, an oxidizing agent for oxidizing the rare earth element can be added in step (1) to convert the rare earth element contained in the rare earth element-containing material into a rare earth oxide form before phase separation. Furthermore, when an easily oxidizable metal (e.g., Al and / or Si) is contained, the metal is converted into an easily oxidizable metal oxide form by the oxidizing agent, followed by phase separation. Preferably, at least 90 mol % of the easily oxidizable metal in the system is converted into an easily oxidizable metal oxide form, more preferably 95 mol % or more, even more preferably 99 mol % or more, and preferably 100 mol %. Increasing the proportion of the oxide form can further reduce the amount of borate used (particularly, the increase in the amount used due to the reduction of the borate, as described below, can be more effectively suppressed). Furthermore, it is possible to more efficiently recover the easily oxidizable metal. The oxidizing agent is added to the heated and melted rare earth element-containing material and the easily oxidizable metal to supply sufficient oxygen for the oxidation of the rare earth element and the easily oxidizable metal. Accelerating the oxidation of the rare earth element and the easily oxidizable metal is preferable from the viewpoint of improving the phase separation property and the recovery rate of the rare earth oxide.

[0034] Examples of the oxidizing agent include oxidizing gases such as air, oxygen, and carbon dioxide, iron oxide, and composite oxides containing iron oxide. Among these, iron oxide is preferred because it not only supplies sufficient oxygen for the oxidation of rare earth elements and easily oxidizable metals, but also reduces impurities in the recovered iron.

[0035] The amount of iron oxide added is preferably such that the molar ratio of the amount of oxygen is 1.5 to 2.0 times the amount of rare earth elements and easily oxidizable metals in the rare earth element-containing material (e.g., rare earth magnet) in the waste. If iron oxide is not added in an inert atmosphere, the added borate may react with the rare earth elements in the magnet and be reduced, potentially reducing its function as a flux. Therefore, if iron oxide is not added, it is preferable to carry out step (1) in the presence of an oxidizing gas such as air, oxygen, or carbon dioxide.

[0036] In this step (1), as described above, waste containing a rare earth element-containing material and a borate and / or its precursor are heated and melted. The heating temperature is preferably 1250°C to 1700°C. At 1250°C or higher, a homogeneous melt (liquid phase region) is easily produced. Furthermore, from the viewpoint of the durability of the refractory material used in the melting furnace used for the heat melting, the heating temperature is preferably 1700°C or lower. Furthermore, from the viewpoint of improving the two-phase separation between the rare earth-enriched phase and the Fe—C phase, the heating temperature is more preferably 1400°C to 1600°C. At 1400°C or higher, the rare earth element-containing material (e.g., a rare earth magnet) is more easily melted. Furthermore, the melting point of pure iron is 1535°C; 1600°C or lower is more preferable because tilting facilitates separation of the rare earth-enriched phase and the Fe—C phase due to the density difference.

[0037] It is preferable to avoid heating to a temperature higher than the above temperature range, as this deteriorates the two-phase separation property. However, heating to a temperature higher than the above temperature range before maintaining the temperature within the range is effective in dissolving rare earth elements mixed in high-melting-point materials such as iron. Therefore, the temperature change during heating and melting may involve heating to the above temperature range suitable for two-phase separation and then cooling. Alternatively, in order to form a homogeneous melt, the material may be heated to a temperature higher than the above temperature range suitable for two-phase separation (e.g., above 1600°C to 1700°C), then the temperature may be lowered and maintained within the above temperature range suitable for two-phase separation, and then cooled.

[0038] From the viewpoint of improving the phase separation property, the heated and melted melt is preferably kept in the above temperature range for 10 minutes or more, more preferably for 60 minutes or more. However, since an effect exceeding the theoretical distribution ratio is not obtained even if the keeping time is too long, from the viewpoint of economic efficiency, the keeping time is preferably 180 minutes or less.

[0039] When the waste further contains copper and is separated into three phases, that is, a rare earth-rich phase, an Fe—C phase, and a Cu phase, the preferred heating temperature range is the same as above.

[0040] It is preferable that this step (1) comprises the following steps (1a) to (1c) in order: step (1a): adding a melting point depressant to the waste containing a rare earth element-containing material, aluminum, and silicon, and then heating and melting the waste to obtain a melt (1a); step (1b): bringing an oxidizing agent into contact with the melt (1a) to obtain a melt (1b); step (1c): adding the borate and / or a precursor thereof to the melt (1b) to obtain a melt (1c).

[0041] According to these steps (1a) to (1c), it is possible to prepare a melt suitable for phase separation by a simpler operation.

[0042] The melt obtained in step (1) contains at least a rare earth oxide, a borate, and an oxide of an easily oxidizable metal. Here, the oxide of the easily oxidizable metal is aluminum oxide and silicon dioxide, and the borate is sodium tetraborate (Na ２ B ４ O ７ ) the composition of these components is preferably within the following ranges. That is, according to a preferred embodiment of the present invention, the ratio of the aluminum oxide content to the sum of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 0 to 31.34 mass%, the content of silicon dioxide is 12.71 to 51.87 mass%, and the content of the borate is 10.0 to 70.1 mass%. According to a more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the above sum is 0 to 31.34 mass%, the content of silicon dioxide is 17.79 to 51.87 mass%, and the content of the borate is 10.0 to 35.0 mass%. According to a further preferred embodiment of the present invention, the ratio of the aluminum oxide content to the above total is 0 to 31.34 mass%, the silicon dioxide content is 18.43 to 51.80 mass%, and the borate content is 10.0 to 34.6 mass%. By adding a rare earth element-containing substance, a borate or its precursor, and an easily oxidizable metal or its oxide so as to achieve this composition, a homogeneous melt can be more easily obtained.

[0043] It is also preferable that the composition be in the following ranges. That is, according to a preferred embodiment of the present invention, the ratio of the aluminum oxide content to the sum of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 4.1 to 10.8 mass%, the content of silicon dioxide is 13.2 to 34.5 mass%, and the content of the borate is 21.5 to 70 mass%. According to a more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the above sum is 4.1 to 10.7 mass%, the content of silicon dioxide is 13.2 to 34.1 mass%, and the content of the borate is 22.5 to 70 mass%. According to a further preferred embodiment of the present invention, the ratio of the aluminum oxide content to the total is 8.4 to 10.7 mass %, the silicon dioxide content is 26.9 to 34.1 mass %, and the borate content is 22.5 to 38.7 mass %. By adding a rare earth element-containing substance, a borate or its precursor, and an easily oxidizable metal or its oxide so as to achieve this composition, a homogeneous melt can be more easily obtained.

[0044] According to a preferred embodiment of the present invention, the ratio of the aluminum oxide content to the sum of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 5.4 to 14.0 mass%, the content of silicon dioxide is 17.4 to 45.0 mass%, and the content of the borate is 22.5 to 70 mass%. According to a more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the sum is 5.4 to 13.5 mass%, the content of silicon dioxide is 17.4 to 43.5 mass%, and the content of the borate is 25.0 to 70 mass%. According to an even more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the sum is 13.2 to 13.5 mass%, the content of silicon dioxide is 42.7 to 43.5 mass%, and the content of the borate is 25.0 to 26.4 mass%. By adding a rare earth element-containing material, a borate or a precursor thereof, and an easily oxidizable metal or an oxide thereof so as to achieve such a composition, a homogeneous melt can be more easily obtained.

[0045] <Separation Step (2)> In this step (2), a rare earth-enriched phase in which rare earth elements are concentrated in borate and an Fe—C phase are separated from the melt obtained in step (1). In the melt state, the Fe—C phase, which has a relatively high density, separates into a lower layer, and the rare earth-enriched phase, which has a relatively low density, separates into an upper layer. Here, the rare earth-enriched phase contains, in addition to the rare earth oxides extracted by the borate, oxides of easily oxidizable metals (for example, Al ２ O ３ and / or SiO ２) may also be included. The recovery method described in the above document states that "the amount of sodium borate added is 0.5 to 10 times the mass of the rare earth magnet." Expressing this amount of sodium borate as a ratio to the "mass of rare earth oxide in the rare earth element-containing material" in this specification, it becomes "the amount of sodium borate added is 60% by mass or more relative to the sum of the amount of sodium borate added and the mass of rare earth oxide in the rare earth element-containing material." According to the recovery method of this embodiment, by allowing an oxide of an easily oxidizable metal to coexist when extracting rare earth oxide in the flux (borate), it is possible to obtain a homogeneous melt even with a smaller amount of flux used than in conventional techniques. In the composition of Reference Example 7 described below, it can be seen that the borate content can be reduced to at least 41% by mass relative to the sum of the mass of borate and the mass of rare earth oxide in the rare earth element-containing material. Furthermore, in the composition of Reference Example 16 described below, the borate content can be reduced to at least 54.7 mass% relative to the sum of the borate and the rare earth oxide mass of the rare earth element-containing material. Furthermore, the inventors' studies have revealed that, depending on the type of waste, a larger amount of borate may be required to obtain a homogeneous melt than the amount predicted from the rare earth oxide mass. This phenomenon is thought to be due to the reduction of borate by the oxidizable metal when the waste contains an oxidizable metal, resulting in a decrease in its function as a flux. According to the recovery method of this embodiment, by converting the oxidizable metal into an oxide form, the decrease in function due to borate reduction can be suppressed, thereby reducing the amount of borate used. Therefore, in these respects, the recovery method of this embodiment has advantageous effects compared to conventional techniques.

[0046] After the rare earth-enriched phase and the Fe—C phase are formed, the phases can be separated and recovered by separating them while they are in a liquid state. According to the recovery method of this embodiment, the rare earth-enriched phase has a low viscosity due to the use of borate as the flux, so that the rare earth-enriched phase can be removed from the upper part of the furnace by tilting, facilitating separation.

[0047] Another method for separating the phases is to discharge them from the bottom of the furnace in order of density. Another method is to cool the melt to solidify it and then cut it along the boundary between the phases with a cutter or the like. When cooling, it is preferable to cool it slowly until it solidifies in order to improve separability, but it is also possible to cool it rapidly to solidify it.

[0048] When the waste contains copper, the melt separates into three phases: a rare-earth-enriched phase, an Fe—C phase, and a Cu phase. That is, according to a preferred embodiment of the present invention, the waste further contains copper, and in the separation step (2), a rare-earth-enriched phase in which rare earth elements are concentrated in borates, an Fe—C phase, and a Cu phase are separated from the melt. When the melt contains copper, the melt is separated into a rare-earth-enriched phase (upper layer), an Fe—C phase (middle layer), and a Cu phase (lower layer) in order of decreasing density. These phases can be extracted by any of the following methods, as in the case of two-phase separation: tilting, discharging from the bottom of the furnace, or solidifying and cutting. When aluminum and silicon are not converted into oxide forms as in the prior art, aluminum and silicon are contained in the Fe—C phase, which can make it difficult to separate the Fe—C phase and the Cu phase. According to the recovery method of this embodiment, by converting the oxidizable metal into an oxide form, the oxide of the oxidizable metal is contained in the rare earth-enriched phase. As a result, the oxidizable metal is hardly contained in the Fe—C phase, and the phase separation between the Fe—C phase and the Cu phase is good, making it possible to recover Cu efficiently. Therefore, in this respect, the recovery method of this embodiment has an advantageous effect compared to the conventional technology.

[0049] The rare earth-enriched phase (rare earth-enriched product) separated in the separation step (2) contains a rare earth oxide, an oxide of an easily oxidizable metal, and a borate. That is, according to another aspect of the present invention, a rare earth-enriched product is provided that contains a rare earth oxide, an oxide of an easily oxidizable metal, and at least one borate selected from the group consisting of alkali metal borates and alkaline earth metal borates. According to the rare earth oxide recovery method of the present invention, when extracting rare earth oxides in the flux (borate), the amount of flux (borate) used can be reduced by allowing the easily oxidizable metal in the system to coexist in the form of an oxide. Therefore, the rare earth-enriched product obtained by the recovery method of the present invention is characterized by containing an oxide of an easily oxidizable metal and having a reduced borate content compared to rare earth-enriched products obtained by conventional recovery methods. By reducing the borate content in the rare earth-enriched product, the boron content in the waste liquid discharged when recovering rare earth oxides from the rare earth-enriched product in steps (3a) to (3c) described below can be reduced. The proportions (by mass) of the rare earth oxides, easily oxidizable metal oxides, and borates contained in the rare earth-enriched product can be substantially the same (within a range of ±10%) as the proportions (by mass) of these components in the melt in the melt preparation step (1). That is, according to a preferred embodiment of the present invention, the proportion of aluminum oxide relative to the sum of the rare earth oxide content, easily oxidizable metal oxide content, and borate content in the rare earth-enriched product is 0 to 31.34 mass%, the proportion of silicon dioxide content is 12.71 to 51.87 mass%, and the proportion of borate content is 10.0 to 70.1 mass%. According to a more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the total is 0 to 31.34 mass%, the silicon dioxide content is 17.79 to 51.87 mass%, and the borate content is 10.0 to 35.0 mass%. According to an even more preferred embodiment of the present invention, the ratio of the aluminum oxide content to the total is 0 to 31.34 mass%, the silicon dioxide content is 18.43 to 51.80 mass%, and the borate content is 10.0 to 34.6 mass%.

[0050] <Steps (3a) to (3c)> The recovery method according to this embodiment may further include steps (3a) to (3c) of recovering rare earth oxides from the rare earth-enriched phase after the separation step (2). That is, according to a preferred embodiment of the present invention, the separation step (2) is followed by the following steps (3a) to (3c), in order: step (3a): leaching the rare earth-enriched phase obtained in step (2) with an acid to obtain a rare earth leachate, step (3b): precipitating the rare earth elements in the rare earth leachate as salts to obtain a precipitate, and step (3c): heating the precipitate to recover the rare earth elements as oxides.

[0051] Examples of acids used in the leaching treatment in step (3a) include oxalic acid, hydrochloric acid, and sulfuric acid. After acid leaching in step (3a) to dissolve the rare earth elements, in step (3b) an alkali (e.g., ammonium hydroxide, ammonium sulfate, or sodium hydroxide) is added to adjust the pH (e.g., to pH 2) to precipitate a precipitate (salt of the rare earth element). At this time, components derived from the borate remain dissolved in the leachate, so the precipitate (salt of the rare earth element) can be recovered by solid-liquid separation. Thereafter, in step (3c), the precipitate (salt of the rare earth element) can be recovered as a rare earth oxide by calcining it at 600°C to 1000°C for 30 to 90 minutes.

[0052] Furthermore, in the recovery method according to the present embodiment, after steps (3a) to (3c), the obtained rare earth oxides can be reduced to simple rare earth elements and recovered by a known method such as a molten salt electrolysis method (molten salt reduction method) or a Ca reduction method (calcium reduction method), which are existing methods for reducing oxides to metals.

[0053] The following embodiments are also included within the scope of the present invention: the recovery method according to claim 1 having the characteristics of claim 2; the recovery method according to claim 1 or 2 having the characteristics of claim 3; the recovery method according to any one of claims 1 to 3 having the characteristics of claim 4; the recovery method according to any one of claims 1 to 4 having the characteristics of claim 5; the recovery method according to any one of claims 1 to 5 having the characteristics of claim 6; the recovery method according to any one of claims 1 to 6 having the characteristics of claim 7; the recovery method according to claim 4 having the characteristics of claim 8; the recovery method according to claim 8 having the characteristics of claim 9; the recovery method according to claim 9 having the characteristics of claim 10; the recovery method according to any one of claims 1 to 10 having the characteristics of claim 11; the recovery method according to any one of claims 1 to 11 having the characteristics of claim 12; the rare earth enriched material according to claim 13 having the characteristics of claim 14.

[0054] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0055] <Confirmation of Liquidus> [Reference Example 1] Nd with a purity of 99.9% by mass ２ O ３ 0.127g and Na ２ B ４ O ７ 0.7 g and Al ２ O ３ 0.041 g and SiO ２ The mixture was used as the sample for this reference example. ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２The ratio was 42.3:13.7:44.0. This sample was inserted into an iron crucible with an inner diameter of 8 mm, a thickness of 1 mm, and a height of 50 mm, and heated in a Kanthal furnace at 1400°C in an air atmosphere for 24 hours. After the predetermined time, the sample was quenched by water cooling. The quenched sample was subjected to structural observation using an optical microscope and a scanning electron microscope (SEM), and phase identification using an X-ray diffractometer (XRD). Based on these results, Nd ２ O ３ Na ２ B ４ O ７ The melting ability of the flux was investigated, and as a result, only a vitrified structure was observed in the rapidly cooled sample, confirming that the sample of this reference example produced a homogeneous melt at high temperatures.

[0056] [Reference Example 10] Nd with a purity of 99.9% by mass ２ O ３ 0.072g and Na ２ B ４ O ７ 0.7 g and Al ２ O ３ 0.054 g and SiO ２ The mixture was used as the sample for this reference example. ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ The ratio was 24.0:18.0:58.0. This sample was inserted into an iron crucible with an inner diameter of 8 mm, a thickness of 1 mm, and a height of 50 mm, and heated in a Kanthal furnace at 1400°C in an air atmosphere for 24 hours. After the predetermined time, the sample was quenched by water cooling. The quenched sample was subjected to structural observation using an optical microscope and a scanning electron microscope (SEM), and phase identification using an X-ray diffractometer (XRD). Based on these results, Nd ２ O ３ Na ２ B ４ O ７The melting ability of the flux was investigated, and as a result, only a vitrified structure was observed in the rapidly cooled sample, confirming that the sample of this reference example produced a homogeneous melt at high temperatures.

[0057] [Reference Examples 2 to 9, 11 to 16, Comparative Reference Examples 1 to 7] Nd with a purity of 99.9% by mass ２ O ３ And Na ２ B ４ O ７ And Al ２ O ３ and SiO ２ The components were weighed and mixed to obtain the composition shown in Table 1 below to prepare the sample for each example. ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd to Nd was almost the same as that in Reference Example 1 (error ±0.1 mass%). ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd to Nd was almost the same as that in Reference Example 10 (error ±0.1 mass%). This sample was inserted into an iron crucible with an inner diameter of 8 mm, a thickness of 1 mm, and a height of 50 mm, and heated in a Kanthal furnace at 1350°C or 1400°C (see Table 1) in an air atmosphere for 24 hours. The sample held for the predetermined time was quenched by water cooling. The quenched sample was subjected to structural observation using an optical microscope and SEM, and phase identification using XRD. Based on these results, Nd ２ O ３ Na ２ B ４ O ７ The melting ability of the flux was investigated, and whether or not only a vitrified structure was observed in the rapidly cooled sample was used to determine whether a homogeneous melt was formed at high temperature or whether a mixture of liquid and solid phases was formed.

[0058] The results are shown in Table 1 below. In Table 1, "L" indicates that a homogeneous melt was produced, and "L+S" indicates that a liquid phase and a solid phase were mixed.

[0059]

[0060] From the results shown in Table 1, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 42.3:13.7:44.0, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 20.0 mass% and not more than 22.5 mass%. ２ B ４ O ７ The proportion of Nd is at least 22.5 mass% or more ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 41 mass % or more. The compositions of Reference Examples 1 to 7 and Comparative Reference Examples 1 to 5 were determined by dividing the composition of the pseudo-quaternary phase diagram shown in FIG. 1 by the point X and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0061] In addition, from the results shown in Table 1, Nd ２ O ３ And Al２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 24.0:18.0:58.0, and when the temperature of the melt is 1400 ° C., Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 20.0 mass% and not more than 22.5 mass%. ２ B ４ O ７ The proportion of Nd is at least 22.5 mass% or more ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 54.7 mass % or more. The compositions of Reference Examples 10 to 16 and Comparative Reference Example 7 were determined by the relationship between point Y and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0062] [Reference Examples 17 to 69, Comparative Reference Examples 8 to 15] Nd with a purity of 99.9% by mass ２ O ３ And Na ２ B ４ O ７ And Al ２ O ３ and SiO ２The above were weighed and mixed to obtain the compositions shown in Tables 2 to 9 below, and used as samples for each example. This sample was inserted into an iron crucible with an inner diameter of 8 mm, a thickness of 1 mm, and a height of 50 mm, and heated and held in a Kanthal furnace at 1400°C in an air atmosphere for 24 hours. After holding for the specified time, the sample was quenched by water cooling. The quenched sample was subjected to structural observation using an optical microscope and SEM, and phase identification using XRD. Based on these results, Nd ２ O ３ Na ２ B ４ O ７ The melting ability of the flux was investigated, and whether or not only a vitrified structure was observed in the rapidly cooled sample was used to determine whether a homogeneous melt was formed at high temperature or whether a mixture of liquid and solid phases was formed.

[0063] The results are shown in the following Tables 2 to 9. In Tables 2 to 9, "L" indicates that a homogeneous melt was produced, and "L+S" indicates that a liquid phase and a solid phase were mixed.

[0064]

[0065] From the results shown in Table 2, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 22.7:18.4:58.9 (error ±0.1), and when the temperature of the melt is 1400 ° C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 20.0 mass% and not more than 22.5 mass%.２ B ４ O ７ The proportion of Nd is at least 22.5 mass% or more ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 56.1 mass %. The compositions of Reference Examples 17 to 24 and Comparative Reference Example 8 were determined by the relationship between point Z and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0066]

[0067] From the results shown in Table 3, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 31.4:43.2:25.4, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is greater than 26.00 mass% and not more than 27.50 mass%. ２ B ４ O ７ The proportion of Nd is at least 27.50 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 54.7 mass % or more. The compositions of Reference Examples 25 to 28 and Comparative Reference Example 9 were determined by the relationship between point V and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0068]

[0069] From the results shown in Table 4, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 20.6:36.6:42.8, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is greater than 17.50 mass% and less than 20.00 mass%. ２ B ４ O ７ The proportion of Nd is at least 20.00 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 54.8 mass % or more. The compositions of Reference Examples 29 to 34 and Comparative Reference Example 10 were determined by dividing the composition by the point W and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0070]

[0071] From the results shown in Table 5, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 50.0:0.0:50.0, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 10.00 mass% and not more than 12.50 mass%. ２ B ４ O ７ The proportion of Nd is at least 12.50 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 22.22 mass % or more. The compositions of Reference Examples 35 to 38 and Comparative Reference Example 11 were determined by the relationship between point Q and the vertex (Na ２ B ４ O ７) corresponds to the composition on the line segment connecting

[0072]

[0073] From the results shown in Table 6, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 37.2:28.8:34.0, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 10.00 mass% and not more than 12.50 mass%. ２ B ４ O ７ The proportion of Nd is at least 12.50 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 27.8 mass % or more. The compositions of Reference Examples 39 to 47 and Comparative Reference Example 12 were determined by the relationship between point R and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0074]

[0075] From the results shown in Table 7, Nd ２ O ３ And Al２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 22.8:26.0:51.2, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is greater than 12.50 mass% and not more than 15.00 mass%. ２ B ４ O ７ The proportion of Nd is at least 15.00 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 43.6 mass %. The compositions of Reference Examples 48 to 52 and Comparative Reference Example 13 were determined by the relationship between point S and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0076]

[0077] From the results shown in Table 8, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２= 46.7:11.1:42.2, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O ３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is more than 10.00 mass% and not more than 12.50 mass%. ２ B ４ O ７ The proportion of Nd is at least 12.50 mass% or more (Nd ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 23.4 mass %. The compositions of Reference Examples 53 to 60 and Comparative Reference Example 14 were determined by the relationship between point T and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0078]

[0079] From the results shown in Table 9, Nd ２ O ３ And Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ = 26.8:15.5:57.6, and when the temperature of the melt is 1400°C, Na ２ B ４ O ７ and Nd ２ O ３ And Al ２ O３ and SiO ２ and the total mass of Na ２ B ４ O ７ It can be seen that the liquidus exists in the range where the ratio of Na is greater than 7.50 mass% and less than 10.00 mass%. ２ B ４ O ７ The proportion of Nd is at least 10.00 mass% or more ２ O ３ and Na ２ B ４ O ７ With respect to the total mass of ２ B ４ O ７ It was confirmed that a homogeneous melt was formed when the mass ratio of Na was at least 29.3 mass % or more. The compositions of Reference Examples 61 to 69 and Comparative Reference Example 15 were determined by dividing the composition of the quaternary phase diagram shown in FIG. 2 by the point U and the vertex (Na ２ B ４ O ７ ) corresponds to the composition on the line segment connecting

[0080] <Recovery of Rare Earth Oxides> [Example 1-1] 15.1 kg of a rotor as waste containing rare earth element-containing material and steel, 2,000 g of pig iron as a melting point depressant, and 920 g of recarburizer were placed in a graphite silicon carbide crucible (Phoenix) manufactured by Nippon Crucible Co., Ltd. (Model: CD 100HP, maximum processing capacity per run: 100 kg), and heated using a high-frequency induction furnace. The rotor contained 1,771 g of a neodymium magnet (Magnet 1) as the rare earth element-containing material, with a composition of 21.0 mass% Nd, 5.0 mass% Pr, 2.5 mass% Dy, 0.4 mass% Tb, 1.0 mass% B, and 70.2 mass% Fe. The rotor also contained 290 g of silicon and 103 g of aluminum. After being heated to 1440°C and melted, the mixture was treated with iron oxide (Fe) as an oxidizer. ２ O ３ ) 1,980 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air.２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0081] After holding for 30 minutes, the rare earth-rich phase RE was poured out of the crucible by tilting. ｘ O ｙ -Na ２ B ４ O ７ The slag (RE: Nd, Pr, Dy, and Tb) and the molten Fe—C phase were taken out and air-cooled. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 10 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al is almost the same as in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 5. ２ O ３ : SiO ２ The borate content was 55.6 mass % based on the total mass of the borate and rare earth oxide.

[0082]

[0083] The results of the component analysis of the recovered Fe-C phase are shown in Table 11 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.03 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0084]

[0085] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 12 below. The amount of rare earth oxides in the powder was 98.5% by mass relative to the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0086]

[0087] [Example 1-2] 15.1 kg of a rotor as waste containing rare earth element-containing material and steel and 811.9 g of recarburizer were placed in a graphite silicon carbide crucible (Phoenix) manufactured by Nippon Crucible Co., Ltd. (Model: CD 100HP, maximum processing capacity per run: 100 kg), and heated using a high-frequency induction furnace. The rotor contained 1,771 g of a neodymium magnet (Magnet 1) as the rare earth element-containing material, with a composition of 21.0 mass% Nd, 5.0 mass% Pr, 2.5 mass% Dy, 0.4 mass% Tb, 0.95 mass% B, and 70.15 mass% Fe. The rotor also contained 290.1 ​​g of silicon and 102.9 g of aluminum. After being heated to 1400°C and melted, the mixture was mixed with iron oxide (Fe) as an oxidizer. ２ O ３ ) 1,810 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0088] After holding for 30 minutes, the rare earth-rich phase RE was poured out of the crucible by tilting. ｘ O ｙ -Na ２ B ４ O ７ The slag (RE: Nd, Pr, Dy, and Tb) and the molten Fe—C phase were taken out and air-cooled. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 13 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al is almost the same as in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 5. ２ O ３ : SiO ２ The ratio of the borate to the rare earth oxide was 42.3:13.8:44. The content of borate was 40.7 mass % based on the total mass of the borate and the rare earth oxide.

[0089]

[0090] The results of the component analysis of the recovered Fe-C phase are shown in Table 14 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0091]

[0092] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 15 below. The amount of rare earth oxides in the powder was 97.9 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0093]

[0094] Example 2: 945.8 g of a rotor and 1,219.5 g of a stator as waste containing rare earth elements, steel, and copper, 93.6 g of a recarburizer as a melting point depressant, and 1,248.2 g of copper to promote phase separation were placed in a graphite crucible (model No. 8, maximum processing capacity per run: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated using a high-frequency induction furnace. The rotor contained 110.7 g of a neodymium magnet (Magnet 1) as the rare earth element-containing material, with a composition of 21.0% by mass of Nd, 5.0% by mass of Pr, 2.5% by mass of Dy, 0.4% by mass of Tb, 0.95% by mass of B, and 70.15% by mass of Fe. The rotor and stator contained a total of 42.0 g of silicon, 14.9 g of aluminum, and 323.8 g of copper. After heating to 1400°C and melting, iron oxide (Fe ２ O ３ 229 g of sodium tetraborate (Na tetraborate) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0095] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ Oｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 16 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 10 to 16 and Comparative Reference Example 7. ２ O ３ : SiO ２ The borate content was 54.7 mass % based on the total mass of the borate and rare earth oxide.

[0096]

[0097] The results of the component analysis of the recovered Fe-C phase are shown in Table 17 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0098]

[0099] The results of the component analysis of the recovered Cu phase are shown in Table 18 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was 0 mass% in total relative to the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0100]

[0101] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 19 below. The amount of rare earth oxides in the powder was 98.8 mass% based on the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0102]

[0103] Example 3: 945.8 g of a rotor containing rare earth element-containing material, steel, and copper, 50.7 g of a recarburizer as a melting point depressant, and 676.7 g of copper for promoting phase separation were placed in a graphite crucible (model number: No. 8, maximum processing capacity per run: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated using a high-frequency induction furnace. The rotor contained 110.7 g of a neodymium magnet (Magnet 1) containing rare earth elements, with a composition of 21.0 mass% Nd, 5.0 mass% Pr, 2.5 mass% Dy, 0.4 mass% Tb, 0.95 mass% B, and 70.15 mass% Fe. The rotor and stator contained a total of 18.1 g of silicon, 6.4 g of aluminum, and 0.0 g of copper. After being heated to 1400°C and melted, the mixture was treated with iron oxide (FeO) as an oxidizer. ２ O ３ ) 113 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0104] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 20 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al is almost the same as in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 5. ２ O ３ : SiO ２ The ratio of the borate to the rare earth oxide was 42.3:13.8:44. The content of borate was 40.7 mass % based on the total mass of the borate and the rare earth oxide.

[0105]

[0106] The results of the component analysis of the recovered Fe-C phase are shown in Table 21 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was 0 mass% in total relative to the total mass of the Fe-C phase. The Fe-C phase contains almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet have migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0107]

[0108] The results of the component analysis of the recovered Cu phase are shown in Table 22 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was 0% by mass, based on the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0109]

[0110] The recovered rare earth-enriched phase (RE ｘ Oｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 23 below. The amount of rare earth oxides in the powder was 99.3 mass% based on the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0111]

[0112] Example 4: 945.8 g of a rotor and 1219.5 g of a stator as waste materials containing rare earth elements, steel, and copper, 99.3 g of a recarburizer as a melting point depressant, and 1324.6 g of copper to promote phase separation were placed in a graphite crucible (model No. 8, maximum processing capacity: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated using a high-frequency induction furnace. The rotor contained 110.7 g of a neodymium magnet (Magnet 1) as the rare earth element-containing material, with a composition of 21.0% by mass of Nd, 5.0% by mass of Pr, 2.5% by mass of Dy, 0.4% by mass of Tb, 0.95% by mass of B, and 70.15% by mass of Fe. The rotor and stator contained a total of 45.2 g of silicon, 16.0 g of aluminum, and 323.8 g of copper. After heating to 1400°C and melting, iron oxide (Fe ２ O ３ 244 g of sodium tetraborate (Na tetraborate) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0113] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 24 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 17 to 24 and Comparative Reference Example 8. ２ O ３ : SiO ２ The borate content was 56.1 mass % based on the total mass of the borate and rare earth oxide.

[0114]

[0115] The results of the component analysis of the recovered Fe-C phase are shown in Table 25 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.02 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0116]

[0117] The results of the component analysis of the recovered Cu phase are shown in Table 26 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was a total of 0.05 mass% relative to the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0118]

[0119] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 27 below. The amount of rare earth oxides in the powder was 98.9 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0120]

[0121] Example 5: 12 kg of a rotor as waste containing rare earth element-containing material and steel and 623.1 g of recarburizer were placed in a graphite silicon carbide crucible (Phoenix) manufactured by Nippon Crucible Co., Ltd. (Model: CD 100HP, maximum processing capacity per run: 100 kg), and heated using a high-frequency induction furnace. The rotor contained 1,645 g of a neodymium magnet (Magnet 2) as the rare earth element-containing material, with a composition of 29.2 mass% Nd, 0.0 mass% Pr, 1.6 mass% Dy, 0.5 mass% Tb, 0.95 mass% B, and 67.75 mass% Fe. The rotor also contained 227.4 g of silicon and 80.7 g of aluminum. After being heated to 1400°C and melted, the mixture was mixed with iron oxide (FeO) as an oxidizer. ２ O ３ ) 1,499 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0122] After holding for 30 minutes, the rare earth-rich phase RE was poured out of the crucible by tilting. ｘ O ｙ -Na ２ B ４ O ７ The slag (RE: Nd, Pr, Dy, and Tb) and the molten Fe—C phase were taken out and air-cooled. The composition of the neodymium magnet (Magnet 2) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 2) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 28 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 25 to 28 and Comparative Reference Example 9. ２ O ３ : SiO ２ The ratio of the borate to the rare earth oxide was 31.4:43.2:25.4. The content of borate was 54.7 mass % based on the total mass of the borate and the rare earth oxide.

[0123]

[0124] The results of the component analysis of the recovered Fe-C phase are shown in Table 29 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.02 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0125]

[0126] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 30 below. The amount of rare earth oxides in the powder was 99.1% by mass relative to the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0127]

[0128] Example 6: 751.6 g of a rotor and 1029.9 g of a stator as waste materials containing rare earth elements, steel, and copper, 78.8 g of a recarburizer as a melting point depressant, and 1051.1 g of copper to promote phase separation were placed in a graphite crucible (model No. 8, maximum processing capacity: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated using a high-frequency induction furnace. The rotor contained 102.8 g of a neodymium magnet (Magnet 2) as a rare earth element-containing material, with a composition of 29.2% by mass of Nd, 0.0% by mass of Pr, 1.6% by mass of Dy, 0.5% by mass of Tb, 0.95% by mass of B, and 67.75% by mass of Fe. The rotor and stator contained a total of 36.4 g of silicon, 12.9 g of aluminum, and 288.1 g of copper. After heating to 1400°C and melting, iron oxide (Fe ２ O ３ 201 g of sodium tetraborate (Na tetraborate) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0129] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ Oｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 2) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 2) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 31 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 29 to 34 and Comparative Reference Example 10. ２ O ３ : SiO ２ The borate content was 54.8 mass % based on the total mass of the borate and rare earth oxide.

[0130]

[0131] The results of the component analysis of the recovered Fe-C phase are shown in Table 32 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0132]

[0133] The results of the component analysis of the recovered Cu phase are shown in Table 33 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was 0 mass% in total relative to the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0134]

[0135] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 34 below. The amount of rare earth oxides in the powder was 98.9 mass% based on the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0136]

[0137] [Example 7] In a graphite crucible (model: No. 8, maximum processing amount per run: 8 kg) manufactured by Nippon Crucible Co., Ltd., 110.7 g of a neodymium magnet (Magnet 1) as a rare earth element-containing material and 807.3 g of electrolytic iron powder as a reagent were placed, simulating the composition of a rotor and a stator as waste containing a rare earth element-containing material and a steel material; all silicon contained in the rotor and the stator was oxidized (SiO ２ The SiO2 of the reagent was ２ 37.3 g of the rare earth element-containing neodymium magnet (Magnet 1) was added, and 47.5 g of a recarburizer acting as a melting point depressant was added, followed by heating in a high-frequency induction furnace. The composition of the rare earth element-containing neodymium magnet (Magnet 1) was 21.0 mass % Nd, 5.0 mass % Pr, 2.5 mass % Dy, 0.4 mass % Tb, 0.95 mass % B, and 70.15 mass % Fe. After the temperature was raised to 1400°C and melted, iron oxide (FeO) was added as an oxidizer. ２ O ３ 25 g of sodium tetraborate (Na ) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements with iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0138] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３, Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 35 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 35 to 38 and Comparative Reference Example 11. ２ O ３ : SiO ２ = 50.0:0.0:50.0 The content of borate was 22.2 mass % based on the total mass of borate and rare earth oxide.

[0139]

[0140] The results of the component analysis of the recovered Fe-C phase are shown in Table 36 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.04 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0141]

[0142] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 37 below. The amount of rare earth oxides in the powder was 99.3 mass% based on the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0143]

[0144] Example 8: 15.067 kg of a rotor as a waste material containing rare earth elements and steel and 812.9 g of recarburizer were placed in a graphite silicon carbide crucible (Phoenix) manufactured by Nippon Crucible Co., Ltd. (Model: CD 100HP, maximum processing capacity per run: 100 kg), and heated using a high-frequency induction furnace. The rotor contained 1,761 g of a neodymium magnet (Magnet 3) as a rare earth element-containing material, with a composition of 26.1% by mass of Nd, 0.0% by mass of Pr, 4.277% by mass of Dy, 0.221% by mass of Tb, 0.89% by mass of B, and 68.485% by mass of Fe. The rotor also contained 267.6 g of silicon and 257.4 g of aluminum. After being heated to 1400°C and melted, the mixture was mixed with iron oxide (FeO) as an oxidizer. ２ O ３ ) 2,185 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. Then, sodium tetraborate (Na ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0145] After holding for 30 minutes, the rare earth-rich phase RE was poured out of the crucible by tilting. ｘ O ｙ -Na ２ B ４ O７ The slag (RE: Nd, Pr, Dy, and Tb) and the molten Fe—C phase were taken out and air-cooled. The composition of the neodymium magnet (Magnet 3) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 3) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 38 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 39 to 47 and Comparative Reference Example 12. ２ O ３ : SiO ２ The borate content was 27.7 mass % based on the total mass of the borate and rare earth oxide.

[0146]

[0147] The results of the component analysis of the recovered Fe-C phase are shown in Table 39 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0148]

[0149] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 40 below. The amount of rare earth oxides in the powder was 99.2 mass% based on the total mass of the powder. The composition of the powder was determined by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0150]

[0151] Example 9: 941.7 g of a rotor and 1203.9 g of a stator as waste materials containing rare earth elements, steel, and copper, 100.4 g of a recarburizer as a melting point depressant, and 1338.8 g of copper to promote phase separation were placed in a graphite crucible (model No. 8, maximum processing capacity: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated in a high-frequency induction furnace. The rotor contained 110.1 g of a neodymium magnet (Magnet 3) as a rare earth element-containing material, with a composition of 26.1% by mass of Nd, 0.0% by mass of Pr, 4.277% by mass of Dy, 0.221% by mass of Tb, 0.89% by mass of B, and 68.485% by mass of Fe. The rotor and stator contained a total of 40.9 g of silicon, 23.6 g of aluminum, and 293.8 g of copper. After heating to 1400°C and melting, iron oxide (Fe ２ O ３ 251 g of sodium tetraborate (Na tetraborate) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0152] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 3) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 3) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 41 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 48 to 52 and Comparative Reference Example 13. ２ O ３ : SiO ２ The ratio of the borate to the total mass of the borate and the rare earth oxide was 43.5 mass %.

[0153]

[0154] The results of the component analysis of the recovered Fe-C phase are shown in Table 42 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0155]

[0156] The results of the component analysis of the recovered Cu phase are shown in Table 43 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was 0% by mass in total, relative to the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0157]

[0158] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 44 below. The amount of rare earth oxides in the powder was 98.4 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0159]

[0160] Example 10: 16.461 kg of a rotor as waste containing rare earth element-containing material and steel and 820.6 g of recarburizer were placed in a graphite silicon carbide crucible (Phoenix) manufactured by Nippon Crucible Co., Ltd. (Model: CD 100HP, maximum processing capacity per run: 100 kg), and heated using a high-frequency induction furnace. The rotor contained 1,908 g of a neodymium magnet (Magnet 4) as the rare earth element-containing material, with a composition of 23.3% by mass of Nd, 0.0% by mass of Pr, 7.808% by mass of Dy, 0.0% by mass of Tb, 0.4% by mass of B, and 68.485% by mass of Fe. The rotor also contained 290.7 g of silicon and 87.1 g of aluminum. After being heated to 1400°C and melted, the mixture was heated with iron oxide (Fe) as an oxidizer. ２ O ３ ) 1,735 g was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0161] After holding for 30 minutes, the rare earth-rich phase RE was poured out of the crucible by tilting. ｘ O ｙ -Na ２ B ４ O ７ The slag (RE: Nd, Pr, Dy, and Tb) and the molten Fe—C phase were taken out and air-cooled. The composition of the neodymium magnet (Magnet 4) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 4) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 45 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 53 to 60 and Comparative Reference Example 14. ２ O ３ : SiO ２ The borate content was 23.4 mass % based on the total mass of the borate and rare earth oxide.

[0162]

[0163] The results of the component analysis of the recovered Fe-C phase are shown in Table 46 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was 0 mass% in total relative to the total mass of the Fe-C phase. The Fe-C phase contains almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet have migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined by ICP-AES.

[0164]

[0165] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 47 below. The amount of rare earth oxides in the powder was 98.9 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0166]

[0167] Example 11: A graphite crucible (model No. 8, maximum processing capacity per run: 8 kg) manufactured by Nippon Crucible Co., Ltd. contained 1028.8 g of a rotor and 1249.5 g of a stator as waste materials containing rare earth elements, steel, and copper, 104.9 g of a recarburizer as a melting point depressant, and 1048.6 g of copper to promote phase separation. The crucible was then heated in a high-frequency induction furnace. The rotor contained 119.3 g of a neodymium magnet (Magnet 4) as a rare earth element-containing material, with a composition of 23.3% by mass of Nd, 0.0% by mass of Pr, 7.808% by mass of Dy, 0.0% by mass of Tb, 0.89% by mass of B, and 67.995% by mass of Fe. The rotor and stator contained a total of 43.1 g of silicon, 13.2 g of aluminum, and 306.3 g of copper. After heating to 1400°C and melting, iron oxide (Fe ２ O ３ 230 g of sodium tetraborate (Na tetraborate) was added as a borate, and the molten metal (melt) was stirred with a carbon rod in the atmosphere to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. ２ B ４ O ７ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0168] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The system slag (RE: Nd, Pr, Dy, and Tb), the Fe—C phase, and the Cu phase were extracted. The composition of the neodymium magnet (Magnet 4) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 4) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 48 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Examples 61 to 69 and Comparative Example 15. ２ O ３ : SiO ２ The borate content was 29.2 mass % based on the total mass of the borate and rare earth oxide.

[0169]

[0170] The results of the component analysis of the recovered Fe-C phase are shown in Table 49 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0171]

[0172] The results of the component analysis of the recovered Cu phase are shown in Table 50 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Cu phase was a total of 0.03 mass% relative to the total mass of the Cu phase. The Cu phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Cu phase was determined using ICP-AES.

[0173]

[0174] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 51 below. The amount of rare earth oxides in the powder was 98.3 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0175]

[0176] Example 12: 945.8 g of a rotor containing rare earth element-containing material and steel and 50.7 g of a recarburizer as a melting point depressant were placed in a graphite crucible (model number: No. 8, maximum processing capacity per run: 8 kg) manufactured by Nippon Crucible Co., Ltd., and heated using a high-frequency induction furnace. The rotor contained 110.7 g of a neodymium magnet (Magnet 1) as a rare earth element-containing material, with a composition of 21.0 mass% Nd, 5.0 mass% Pr, 2.5 mass% Dy, 0.4 mass% Tb, 0.95 mass% B, and 70.15 mass% Fe. The rotor and stator contained a total of 18.1 g of silicon and 6.4 g of aluminum. After being heated to 1400°C and melted, the mixture was treated with iron oxide (FeO) as an oxidizer. ２ O ３ 113 g of boric acid (B) was added, and the molten metal (melt) was further stirred with a carbon rod in the atmosphere, and the rare earth elements, silicon, and aluminum were sufficiently oxidized by the iron oxide and oxygen in the air. ２ O ３ ) 20.3 g and sodium carbonate (Na ２ CO ３ ) was added, and the molten metal (melt) was stirred with a carbon rod.

[0177] After holding for 30 minutes, the mixture was air-cooled, and then the rare earth-rich phase, RE, was removed from the crucible by cutting. ｘ O ｙ -Na ２ B ４ O ７ The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rare earth oxide mass of the rare earth element-containing material in this example (Nd, Pr, Dy, and Tb contained in Magnet 1) was calculated by the following formula: ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ When it is considered to be oxidized to ２ O ３ , Pr ２ O ３ , Dy ２ O ３ and Tb ２ O ３ the total mass of the easily oxidizable metal oxides (SiO ２ and Al ２ O ３ ) and borate (Na ２ B ４ O ７ The amount of rare earth oxide and Al is shown in Table 52 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al is almost the same as in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 5. ２ O ３ : SiO ２ The ratio of the borate to the rare earth oxide was 42.3:13.8:44. The content of borate was 44.1 mass % based on the total mass of the borate and the rare earth oxide.

[0178]

[0179] The results of the component analysis of the recovered Fe-C phase are shown in Table 53 below. The amount of residual RE (RE: Nd, Pr, Dy, and Tb) in the Fe-C phase was a total of 0.01 mass% relative to the total mass of the Fe-C phase. The Fe-C phase contained almost no rare earth elements, and it is believed that the rare earth components in the neodymium magnet had migrated to the slag phase (rare earth-enriched phase). The composition of the Fe-C phase was determined using ICP-AES.

[0180]

[0181] The recovered rare earth-enriched phase (RE ｘ O ｙ -Na ２ B ４ O ７ Ten grams of the slag (based on the slag) was acid-leached with 200 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 100 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 2 by adding aqueous ammonia. The pH-adjusted solution was stirred and held at 40°C for 1 to 2 hours to obtain a precipitate of rare earth oxalates. The rare earth oxalates were separated by filtration and calcined in a muffle furnace at 900°C for 60 minutes to obtain a powder containing rare earth oxides. The analysis results of the powder are shown in Table 54 below. The amount of rare earth oxides in the powder was 98.9 mass% based on the total mass of the powder. The composition of the powder was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0182]

[0183] In this example, a borate precursor (boric acid (B ２ O ３ ) and sodium carbonate (Na ２ CO ３ )) is used as a flux, but borate (sodium tetraborate (Na ２ B ４ O ７ Similar to Examples 1-1, 1-2 and 3 using a rare earth-rich phase (RE ｘ O ｙ -Na ２ B ４ O ７It was confirmed that the composition of the recovered rare earth oxides was the same as that in Examples 1-1, 1-2, and 3. In the melt preparation step, sodium carbonate (Na ２ CO ３ Although carbon dioxide gas was generated by the decomposition of Fe—C, the rare earth-enriched phase and the Fe—C phase could be separated without any problems in the separation process.

[0184] As can be seen from the reference examples, comparative reference examples, and examples shown above, the recovery method according to this embodiment can reduce the amount of flux used in a method for recovering rare earth oxides using a flux containing boron.

[0185] This application is based on Japanese Patent Application No. 2024-071472, filed on April 25, 2024, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for recovering rare earth oxides from waste containing rare earth elements, the method comprising: (1) a melt preparation step of heating and melting the waste and at least one borate selected from the group consisting of borates of alkali metals and borates of alkaline earth metals and / or a precursor thereof to prepare a melt containing at least rare earth oxides, the borate, and an oxide of an easily oxidizable metal; and (2) a separation step of separating from the melt a rare earth-enriched phase in which the rare earth elements are concentrated in the borate, and an Fe—C phase.

2. A method for recovering rare earth oxides according to claim 1, wherein the content of the borate is equal to or greater than the liquidus line in a phase diagram determined by the mass of rare earth oxide in the rare earth element-containing material and the content of the oxide of the easily oxidizable metal.

3. The method for recovering rare earth oxides according to claim 1, wherein the waste further contains copper, and in the separation step (2), a rare earth-enriched phase in which rare earth elements are concentrated in the borate, an Fe-C phase, and a Cu phase are separated from the melt.

4. The method for recovering rare earth oxides according to claim 1, wherein the oxide of the easily oxidizable metal is aluminum oxide and / or silicon dioxide.

5. The method for recovering rare earth oxides according to claim 4, wherein the oxides of easily oxidizable metals are aluminum oxide and silicon dioxide.

6. The borate is sodium tetraborate (Na ２ B ４ O ７ 6. The method for recovering rare earth oxides according to claim 5, wherein the 7. The method for recovering rare earth oxides according to claim 1, wherein the rare earth element-containing material includes a neodymium magnet.

8. A method for recovering rare earth oxides according to claim 4, wherein the ratio of the aluminum oxide content to the sum of the mass of rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 0 to 31.34 mass%, the content of silicon dioxide is 12.71 to 51.87 mass%, and the content of the borate is 10.0 to 70.1 mass%.

9. The method for recovering rare earth oxides according to claim 8, wherein the ratio of the aluminum oxide content to the sum of the mass of rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 0 to 31.34 mass%, the content of silicon dioxide is 17.79 to 51.87 mass%, and the content of the borate is 10.0 to 35.0 mass%.

10. A method for recovering rare earth oxides according to claim 9, wherein the ratio of the aluminum oxide content to the sum of the mass of rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the borate in the rare earth element-containing material is 0 to 31.34 mass%, the silicon dioxide content is 18.43 to 51.80 mass%, and the borate content is 10.0 to 34.6 mass%.

11. A method for recovering rare earth oxides according to claim 1, wherein the melt preparation step (1) comprises the following steps (1a) to (1c) in order: step (1a): adding a melting point depressant to the waste containing rare earth element-containing material, aluminum, and silicon, and then heating and melting the waste to obtain melt (1a); step (1b): bringing an oxidizing agent into contact with the melt (1a) to obtain melt (1b); step (1c): adding the borate and / or a precursor thereof to the melt (1b) to obtain melt (1c).

12. The method for recovering rare earth oxides according to claim 1, comprising the following steps (3a) to (3c) in sequence after the separation step (2): step (3a): leaching the rare earth-enriched phase obtained in step (2) with an acid to obtain a rare earth element leachate; step (3b): precipitating the rare earth elements in the rare earth element leachate as salts to obtain a precipitate; and step (3c): heating the precipitate to recover the rare earth elements as oxides.

13. A rare earth-enriched material comprising a rare earth oxide, an oxide of an easily oxidizable metal, and at least one borate selected from the group consisting of borates of alkali metals and borates of alkaline earth metals.

14. The rare earth-enriched material according to claim 13, wherein the proportion of the aluminum oxide content relative to the total of the rare earth oxide content, the easily oxidizable metal oxide content, and the borate content is 0 to 31.34 mass%, the silicon dioxide content is 12.71 to 51.87 mass%, and the borate content is 10.0 to 70.1 mass%.

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