Rare earth oxide recovery method

Abstract

The present disclosure provides a rare earth oxide recovery method in which a boron-free flux is used. The present disclosure relates to a rare earth oxide recovery method for recovering a rare earth oxide from waste that includes a rare-earth-element-containing material. The recovery method has: a melt preparation step (1) for melting, by heating, the aforementioned waste and at least one oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides to prepare a melt containing at least a rare earth oxide, the aforementioned oxide, and an oxide of an easily oxidizable metal; and a separation step (2) for separating, from the melt, a rare-earth-enriched phase in which the rare earth oxide is concentrated in the oxide, and an Fe-C phase.

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 (a fluxing agent) 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 that it takes a long time to leach the rare earth elements from the material into the acid or solvent. On the other hand, the dry method has the advantage that rare earth elements can be easily extracted by simply heating and melting the rare earth-containing material in the presence of a flux, and the generation of waste liquid is minimized.

[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, boron and its compounds are subject to regulation as harmful substances that may cause damage to human health, and there has been a demand to reduce their use.

[0006] Therefore, an object of the present invention is to provide a method for recovering rare earth oxides using a boron-free flux.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by using an oxide of an alkali metal or alkaline earth metal 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 oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides to prepare a melt containing at least the rare earth oxide, the oxide, 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 the rare earth oxide is concentrated in the oxide, and an Fe—C phase.

[0009] FIG. 1 shows the rare earth element-containing material, Nd ２ O ３ , Al as an oxide of an easily oxidizable metal ２ O ３ and SiO ２1 is a pseudo-quaternary phase diagram at 1450° C. when calcium oxide (CaO) is used as the oxide.

[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 and at least one oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides to prepare a melt containing at least the rare earth oxide, the oxide, 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 the rare earth oxide is concentrated in the oxide, and an Fe—C phase. This aspect provides a method for recovering rare earth oxides using a boron-free 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 oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides are heated and melted to prepare a melt containing at least the rare earth oxide, the oxide, 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 usually 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 oxide (flux) selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, 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 waste is then 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] [Alkali Metal Oxide and / or Alkaline Earth Metal Oxide] In the recovery method according to the present embodiment, at least one oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides (hereinafter also simply referred to as "oxide (AMO / AEMO)") is used as a flux.

[0024] Examples of alkali metal oxides and alkaline earth metal oxides include sodium oxide (Na ２ O), lithium oxide (Li ２ O), potassium oxide (K ２ O), rubidium oxide (Rb ２ O), cesium oxide (Cs ２ O), barium oxide (BaO), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), etc. Among them, sodium oxide (Na ２ Of these, barium oxide (BaO), barium oxide (BaO), and calcium oxide (CaO) are preferred, with calcium oxide (CaO) being more preferred.

[0025] The amount of oxide (AMO / AEMO) added (when two or more oxides are used, this refers to the total amount) may be an amount sufficient for the rare earth element contained in the rare earth element-containing material and the oxide of the easily oxidizable metal to form a homogeneous melt (liquid phase region). In other words, the amount of oxide (AMO / AEMO) 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 element-containing material and the content of the oxide of the easily oxidizable metal. Here, in this specification, "mass of rare earth oxide in rare earth element-containing material" refers to the amount of rare earth element (e.g., Nd, Pr, Dy, Tb) contained in the rare earth element-containing material (e.g., rare earth magnet) that is present in the rare earth oxide (e.g., Nd ２ O ３ , Pr ２ O ３ , Dy ２ O ３ , 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.

[0026] 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 This is a pseudo-quaternary phase diagram at 1450°C when calcium oxide (CaO) is used as the oxide (AMO / AEMO). 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 Consider an edge with vertices Nd and CaO. ２ O ３ : The composition ratio (mass ratio) of CaO is "the distance from point A to the vertex (CaO)": "the distance from point A to the vertex (Nd ２ O ３ ) distance (leverage principle). Here, each side of the equilateral triangle to the left of the regular tetrahedron is Nd ２ O ３ , Al ２ O ３ and SiO ２ The concentration of Nd is shown, and one point (for example, point W) shown on the face of the equilateral triangle indicates the composition of these three components. ２O ３ and Al ２ O ３ and SiO ２ Consider an equilateral triangle with vertices Nd at point W 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 W: Nd ２ O ３ and SiO ２ The distance of the perpendicular line from the line segment connecting the two points to point W: 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 the point W. ２ O ３ , Al ２ O ３ and SiO ２The line drawn from point W to the vertex (CaO) represents the concentrations of the three components and CaO when CaO is added to the three-component composition indicated by point W. The closer to the vertex (CaO), the higher the CaO concentration. As the CaO concentration increases relative to the three-component composition indicated by point W, the solid-liquid mixed region transitions to the liquid region (the region where a homogeneous melt is formed) at a certain concentration. The boundary between the solid-liquid mixed region and the liquid region is called the "liquidus." On the liquidus, the liquid phase and a portion of the solid phase typically 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 this boundary is sometimes referred to as the "liquidus surface." However, in this specification, the term "liquidus" is used consistently regardless of whether the boundary is a line or a surface. The content of the oxides (AMO / AEMO) being "amount above the liquidus" means that the content is a concentration corresponding to the liquidus or a concentration in the liquidus region. In the case shown in Figure 1, the "amount above the liquidus" corresponds to the CaO concentration represented by the line segment (excluding the vertex (CaO)) connecting the intersection (not shown) of the straight line and the liquidus line to the vertex (CaO).

[0027] In the above, the "amount above the liquidus in a phase diagram determined by the rare earth oxide mass of a 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, if the rare earth oxide mass of a rare earth element-containing material and the content of easily oxidizable metal oxide that may be present in the system are determined in advance, the oxide (AMO / AEMO) concentration corresponding to the liquidus can be experimentally determined by increasing the oxide (AMO / AEMO) concentration for this composition. This makes it possible to determine the composition that produces a homogeneous melt regardless of the composition of rare earth elements and easily oxidizable metals (oxides) 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.

[0028] [Easily oxidizable metal and / or its oxide] In this step (1), in addition to the above-mentioned waste containing rare earth elements and oxides (AMO / AEMO), 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, from the viewpoint of improving phase separation, the easily oxidizable metal is preferably at least one or both of aluminum (Al) and / or silicon (Si), and more preferably, aluminum (Al) and silicon (Si) are used in combination. Furthermore, these easily oxidizable metals may be added in the form of oxides. Examples of oxides of easily oxidizable metals include aluminum oxide (Al) and silicon (Si). ２ O ３ : alumina), silicon dioxide (SiO ２ : silica), titanium oxide (TiO ２ : titania), zirconium oxide (ZrO ２ Among them, aluminum oxide (Al: zirconia) is preferred from the viewpoint of improving the phase separation property. ２ O ３ : alumina) and / or 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.

[0029] [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.

[0030] 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.

[0031] 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.

[0032] [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 easily oxidizable metal in the oxide form can further reduce the amount of oxide (AMO / AEMO) used (particularly, the increase in the amount of oxide (AMO / AEMO) used due to the reduction of the oxide (AMO / AEMO) described below can be more effectively suppressed). Furthermore, the recovery of the easily oxidizable metal can be more efficiently performed. 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.

[0033] 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.

[0034] 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 under an inert atmosphere, the added oxides (AMO / AEMO) may react with the rare earth elements in the magnet and be reduced, potentially reducing their 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.

[0035] In the recovery method according to this embodiment, since boron and its compounds are subject to regulation as hazardous substances as described above, it is preferable to minimize their use. In other words, step (1) preferably does not include the addition of boron-containing substances other than the waste. Furthermore, the boron (B) content in the melt is preferably low. In other words, the boron (B) content in the melt is preferably 4.3 mass% or less, relative to the total mass of rare earth elements. This allows for a reduction in the boron content in the waste liquid discharged when recovering rare earth oxides from the rare earth-enriched phase in steps (3a) to (3c), described below. Note that if boron is contained in the waste, the melt will contain boron derived from the waste. In such cases, the boron (B) content in the melt may be 2.4 mass% or more and 4.3 mass% or less, relative to the total mass of rare earth elements.

[0036] In this step (1), as described above, waste containing a rare earth element-containing material and oxides (AMO / AEMO) 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 generated. 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 a heating temperature of 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; since tilting facilitates separation of the rare earth-enriched phase and the Fe—C phase due to the density difference, the heating temperature is more preferably 1600°C or lower.

[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 oxides (AMO / AEMO) 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, an oxide (AMO / AEMO), and an oxide of an easily oxidizable metal. When the oxide of the easily oxidizable metal is aluminum oxide and silicon dioxide and the oxide (AMO / AEMO) is calcium oxide (CaO), the composition of these components preferably falls within the following ranges: the ratio of the content of aluminum oxide to the sum of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the oxide (AMO / AEMO) in the rare earth element-containing material is 15.7 to 17.5 mass%, the content of silicon dioxide is 50.0 to 55.9 mass%, and the content of the oxide (AMO / AEMO) is 5.0 to 15.0 mass%; and the ratio of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the oxide (AMO / AEMO) in the rare earth element-containing material is 15.7 to 17.5 mass%. The ratio of the content of aluminum oxide to the sum of the content of the rare earth oxide of the rare earth element-containing material, the content of the oxide of the easily oxidizable metal, and the content of the oxide (AMO / AEMO) is 27.5 to 29.3 mass%, the content of silicon dioxide is 32.1 to 34.2 mass%, and the content of the oxide (AMO / AEMO) is 20.0 to 25.0 mass%; the ratio of the content of aluminum oxide to the sum of the mass of the rare earth oxide of the rare earth element-containing material, the content of the oxide of the easily oxidizable metal, and the content of the oxide (AMO / AEMO) is 10.9 the ratio of the aluminum oxide content to the total of the mass of rare earth oxides in the rare earth element-containing material, the content of easily oxidizable metal oxides, and the content of oxides (AMO / AEMO) is 11.6 to 12.9 mass%, and the ratio of the silicon dioxide content is 49.5 to 54.9 mass%. and the content ratio of the oxides (AMO / AEMO) is 10.0 to 18.9 mass%; the content ratio of the aluminum oxide to the sum of the mass of the rare earth oxide, the content of the easily oxidizable metal oxide, and the content of the oxides (AMO / AEMO) of the rare earth element-containing material is 17.0 to 22.5 mass%, the content ratio of the silicon dioxide is 35.9 to 47.6 mass%, and the content ratio of the oxides (AMO / AEMO) is 10.0 to 32.1 mass%.By adding rare earth elements, oxides (AMO / AEMO), and easily oxidizable metals or their oxides to achieve such a composition, a homogeneous melt can be more easily obtained.

[0043] <Separation Step (2)> In this step (2), a rare earth-enriched phase in which rare earth elements are concentrated in the oxides (AMO / AEMO) 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 oxides (AMO / AEMO), oxides of easily oxidizable metals (for example, Al ２ O ３ and / or SiO ２ According to the recovery method of this embodiment, when rare earth oxides are extracted in the oxides (AMO / AEMO) as a flux, by making the oxides of easily oxidizable metals coexist, it is possible to avoid the use of boron oxide (B ２ O ３ It is possible to obtain a homogeneous melt without using boron compounds such as borates or boron compounds.

[0044] After the rare earth-enriched phase and the Fe—C phase are formed, they can be separated and recovered by separating the phases 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 oxides (AMO / AEMO) as a flux, so that the rare earth-enriched phase can be removed from the upper part of the furnace by tilting, facilitating separation.

[0045] 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.

[0046] 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 oxides (AMO / AEMO), an Fe—C phase, and a Cu phase are separated from the melt. When the melt contains copper, the melt separates into a rare-earth-enriched phase (upper layer), an Fe—C phase (middle layer), and a Cu phase (lower layer) in descending order of density. As in the case of two-phase separation, these phases can be extracted by any of the following methods: tilting, discharging from the bottom of the furnace, or solidifying and cutting. When easily oxidizable metals (aluminum, silicon) are not converted to oxide forms as in conventional techniques, the easily oxidizable metals 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.

[0047] The rare earth-enriched phase (rare earth-enriched product) separated in the separation step (2) contains rare earth oxides, oxides of easily oxidizable metals, and oxides (AMO / AEMO). 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 oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides. Furthermore, according to the present invention, since the rare earth-enriched phase (rare earth-enriched product) is obtained using a boron-free flux, the rare earth-enriched product has a low boron content. This allows for a reduction in the boron content in the waste liquid discharged when recovering oxides of rare earth elements from the rare earth-enriched product in steps (3a) to (3c) described below. According to one embodiment of the present invention, the boron content in the rare earth-enriched product is preferably 4.3 mass% or less, and may be 2.4 mass% to 4.3 mass% based on the total mass of rare earth elements.

[0048] <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.

[0049] Examples of acids used in the leaching treatment in step (3a) include oxalic acid, hydrochloric acid, and sulfuric acid. After dissolving the rare earth elements by acid leaching in step (3a), an alkali (e.g., ammonium hydroxide, ammonium sulfate, or sodium hydroxide) is added in step (3b) to adjust the pH (e.g., pH 1.5 to 2) to precipitate a precipitate (salt of the rare earth elements). Since components derived from the oxides (AMO / AEMO) remain dissolved in the leachate, the precipitate (salt of the rare earth elements) can be recovered by solid-liquid separation. Subsequently, in step (3c), the precipitate (salt of the rare earth elements) can be recovered as a rare earth oxide by calcining it at 600°C to 1000°C for 30 to 90 minutes.

[0050] 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 rare earth oxides to metals.

[0051] 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 any one of claims 1 to 7 having the characteristics of claim 8; the recovery method according to any one of claims 1 to 8 having the characteristics of claim 9; the recovery method according to claim 6 having the characteristics of claim 10; the recovery method according to claim 6 having the characteristics of claim 11; the recovery method according to claim 6 having the characteristics of claim 12; the recovery method according to claim 6 having the characteristics of claim 13; the recovery method according to claim 6 having the characteristics of claim 14; the recovery method according to any one of claims 1 to 14 having the characteristics of claim 15; the recovery method according to claim 15 having the characteristics of claim 16; the recovery method according to any one of claims 1 to 16 having the characteristics of claim 17; the rare earth enriched material according to claim 18 having the characteristics of claim 19.

[0052] 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.

[0053] <Confirmation of Liquidus> [Reference Example 1] Nd with a purity of 99.9% by mass ２ O ３ 0.155g, CaO 0.250g, and Al ２ O ３ 0.274 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 20.6:36.6:42.8. 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 1450°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 The dissolving ability of CaO flux for the molten metal was investigated. As a result, in the rapidly cooled sample, only a vitrified structure was observed, which confirmed that the sample of this reference example produced a homogeneous melt at high temperatures.

[0054] [Reference Examples 2 to 4, Comparative Reference Examples 1 to 4] Nd with a purity of 99.9% by mass ２ O ３ and CaO and Al ２ O ３ and SiO ２ The mixture (1 g in total) was weighed and mixed to obtain the composition shown in Table 1 below, and used as a 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%). 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 or 1450°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 ３The dissolving ability of CaO flux for CaO was investigated. Then, depending on whether or not only a vitrified structure was observed in the rapidly cooled sample, it was determined whether a homogeneous melt was formed at high temperature or whether a mixture of liquid and solid phases was formed. The results are shown in Table 1 below. In the table below, "L" indicates a sample that formed a homogeneous melt, and "L+S" indicates a sample that formed a mixture of liquid and solid phases.

[0055]

[0056] 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 = 20.6:36.6:42.8, and when the temperature of the melt is 1450°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is more than 15.0 mass% and not more than 20.0 mass% with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 20.0 mass% or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of Fe and CaO was at least 54.8 mass%.

[0057] In addition, 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 = 20.6:36.6:42.8, and when the temperature of the melt is 1400°C, Nd ２ O３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is greater than 22.5 mass % and less than or equal to 23.5 mass % relative to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 23.5 mass % or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of CaO and CaO was at least 59.8 mass %. The compositions in Reference Examples 1 to 4 and Comparative Reference Examples 1 to 4 correspond to the compositions on the line segment connecting point W and the vertex (CaO) in the pseudo-quaternary phase diagram shown in FIG.

[0058] [Reference Example 5] Nd with a purity of 99.9% by mass ２ O ３ 0.204 g, CaO 0.100 g, and Al ２ O ３ 0.166 g and SiO ２ The mixture of 0.530 g and 0.530 g (total of 1 g) was used as the sample of 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 22.7:18.4:58.9. 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 1450°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 The dissolving ability of CaO flux for the molten metal was investigated. As a result, in the rapidly cooled sample, only a vitrified structure was observed, which confirmed that the sample of this reference example produced a homogeneous melt at high temperatures.

[0059] [Reference Examples 6 to 8, Comparative Reference Examples 5 to 7] Nd with a purity of 99.9% by mass ２ O ３ and CaO and Al ２ O ３ and SiO ２ The mixture (1 g in total) was weighed and mixed to obtain the composition shown in Table 2 below, and used as a 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 5 (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 1400°C or 1450°C (see Table 2) 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 The dissolving ability of CaO flux for the CaO melt was investigated. Then, depending on whether or not only a vitrified structure was observed in the rapidly cooled sample, it was determined whether a homogeneous melt was formed at high temperature or whether a mixture of liquid and solid phases was formed. The results are shown in Table 2 below.

[0060]

[0061] 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, and when the temperature of the melt is 1450°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２It can be seen that the liquidus exists in the range where the ratio of CaO is greater than 0.0 mass % and not more than 5.0 mass % with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 5.0 mass % or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of Fe and CaO was at least 18.8 mass %.

[0062] In addition, 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, and when the temperature of the melt is 1400°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is more than 5.0 mass% and not more than 10.0 mass% with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 10.0 mass% or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of CaO and CaO was at least 32.9 mass %. The compositions in Reference Examples 5 to 8 and Comparative Reference Examples 5 to 7 correspond to the compositions on the line segment connecting point Z and the vertex (CaO) in the pseudo-quaternary phase diagram shown in FIG.

[0063] [Reference Example 9] Nd with a purity of 99.9% by mass ２ O ３ 0.250 g, CaO 0.177 g, and Al ２ O ３ 0.109 g and SiO ２ The mixture was used as the sample for this reference example. ２ O ３And, Al ２ O ３ and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ The ratio was 30.4:13.2:56.4. This sample was placed in 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 1450°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 The dissolving ability of CaO flux for the molten metal was investigated. As a result, in the rapidly cooled sample, only a vitrified structure was observed, which confirmed that the sample of this reference example produced a homogeneous melt at high temperatures.

[0064] [Reference Example 10, Comparative Reference Examples 8 to 9] Nd with a purity of 99.9% by mass ２ O ３ and CaO and Al ２ O ３ and SiO ２ These were weighed and mixed (total 1 g) to obtain the composition shown in Table 3 below, and used as 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 9 (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 1450°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 SEM, and phase identification using XRD. Based on these results, Nd ２ O ３The dissolving ability of CaO flux for CaO was investigated. Then, depending on whether or not only a vitrified structure was observed in the rapidly cooled sample, it was determined whether a homogeneous melt was generated at a high temperature or whether a mixture of a liquid phase and a solid phase was formed.

[0065]

[0066] 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 = 30.4:13.2:56.4, and when the temperature of the melt is 1450°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is more than 10.0 mass% and not more than 14.0 mass% with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 14.0 mass% or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of CaO and CaO was at least 34.9 mass%. The compositions in Reference Examples 9 and 10 and Comparative Reference Examples 8 and 9 correspond to the compositions on the line segment connecting point G and the vertex (CaO) in the pseudo-quaternary phase diagram shown in FIG.

[0067] [Reference Example 11] Nd with a purity of 99.9% by mass ２ O ３ 0.200 g, CaO 0.189 g, and Al ２ O ３ 0.116 g and SiO ２ The mixture was used as the sample for this reference example. ２ O ３ And, Al ２ O ３and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ The ratio was 24.7:14.3:61.0. 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 1450°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 The dissolving ability of CaO flux for the molten metal was investigated. As a result, in the rapidly cooled sample, only a vitrified structure was observed, which confirmed that the sample of this reference example produced a homogeneous melt at high temperatures.

[0068] [Reference Example 12, Comparative Reference Example 10] Nd with a purity of 99.9% by mass ２ O ３ and CaO and Al ２ O ３ and SiO ２ The components were weighed and mixed (total 1 g) to obtain the composition shown in Table 4 below, and the resulting mixture was used as a 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 11 (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 1450°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 SEM, and phase identification using XRD. Based on these results, Nd ２ O ３The dissolving ability of CaO flux for CaO was investigated. Then, depending on whether or not only a vitrified structure was observed in the rapidly cooled sample, it was determined whether a homogeneous melt was generated at a high temperature or whether a mixture of a liquid phase and a solid phase was formed.

[0069]

[0070] 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 = 24.7:14.3:61.0, and when the temperature of the melt is 1450°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is greater than 0.0 mass % and less than or equal to 10.0 mass % with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 10.0 mass % or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of CaO and CaO was at least 31.1 mass %. The compositions in Reference Examples 11 and 12 and Comparative Reference Example 10 correspond to the compositions on the line segment connecting point F and the vertex (CaO) in the pseudo-quaternary phase diagram shown in FIG.

[0071] [Reference Example 13] Nd with a purity of 99.9% by mass ２ O ３ 0.150 g, CaO 0.321 g, and Al ２ O ３ 0.170 g and SiO ２ The mixture was used as the sample for this reference example. ２ O ３ And, Al ２ O ３and SiO ２ The mass ratio of Nd ２ O ３ :Al ２ O ３ : SiO ２ The ratio was 22.1:25.0:52.9. 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 1450°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 The dissolving ability of CaO flux for the molten metal was investigated. As a result, in the rapidly cooled sample, only a vitrified structure was observed, which confirmed that the sample of this reference example produced a homogeneous melt at high temperatures.

[0072] [Reference Example 14, Comparative Reference Example 11] Nd with a purity of 99.9% by mass ２ O ３ and CaO and Al ２ O ３ and SiO ２ The components were weighed and mixed (total 1 g) to obtain the composition shown in Table 5 below, and the resulting mixture was used as a 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 13 (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 1450°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 SEM, and phase identification using XRD. Based on these results, Nd ２ O ３The dissolving ability of CaO flux for CaO was investigated. Then, depending on whether or not only a vitrified structure was observed in the rapidly cooled sample, it was determined whether a homogeneous melt was generated at a high temperature or whether a mixture of a liquid phase and a solid phase was formed.

[0073]

[0074] 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 = 22.1:25.0:52.9, and when the temperature of the melt is 1450°C, Nd ２ O ３ and CaO and Al ２ O ３ and SiO ２ It can be seen that the liquidus exists in the range where the ratio of CaO is greater than 0.0 mass % and less than or equal to 10.0 mass % with respect to the total mass of Nd. Therefore, at this composition and this temperature, it is considered that the ratio of CaO is at least 10.0 mass % or more (Nd ２ O ３ It was confirmed that a homogeneous melt was produced when the mass ratio of CaO to the total mass of CaO and CaO was at least 33.4 mass %. The compositions in Reference Examples 13 and 14 and Comparative Reference Example 11 correspond to the compositions on the line segment connecting point H and the vertex (CaO) in the pseudo-quaternary phase diagram shown in FIG.

[0075] <Recovery of Rare Earth Oxides> [Example 1] 945.8 g of a rotor and 1,219.5 g of a stator as waste containing rare earth element-containing material and steel, and 99.3 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 the rare earth element-containing material. The composition of the neodymium magnet (Magnet 1) was 21.0% by mass Nd, 5.0% by mass Pr, 2.5% by mass Dy, 0.4% by mass Tb, 0.95% by mass B, and 70.15% by mass Fe. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rotor and the stator contained a total of 45.2 g of silicon and 16.0 g of aluminum. After the temperature was raised to 1400° C. and the mixture was melted, iron oxide (Fe ２ O ３ 244 g of calcium oxide (CaO) was added, and the molten metal (melt) was stirred with a carbon rod under atmospheric pressure to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. 18.3 g of calcium oxide (CaO) was then added as an alkaline earth metal oxide, and the molten metal (melt) was stirred with a carbon rod.

[0076] 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 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 as follows: 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 ３the total mass of the easily oxidizable metal oxide (SiO ２ and Al ２ O ３ The amounts of rare earth metal oxides (CaO) and alkaline earth metal oxides (CaO) are shown in Table 6 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 5 to 8 and Comparative Reference Examples 5 to 7. ２ O ３ : SiO ２ The ratio of the alkaline earth metal oxides to the total mass of the alkaline earth metal oxides and the rare earth oxides was 22.7:18.4:58.9. The content of the alkaline earth metal oxides was 32.9 mass % based on the total mass of the alkaline earth metal oxides and the rare earth oxides.

[0077]

[0078] The results of the component analysis of the recovered Fe-C phase are shown in Table 7 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.

[0079]

[0080] The recovered rare earth-enriched phase (RE ｘ O ｙ 0.5 g of the slag (CaO-based slag) was acid-leached with 20 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 10 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 1.8 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 8 below. The amount of rare earth oxides in the powder was 98.6 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).

[0081]

[0082] 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, 99.3 g of a recarburizer as a melting point depressant, and 392 g of copper to promote 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) 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 calcium oxide (CaO) was added, and the molten metal (melt) was stirred with a carbon rod under atmospheric pressure to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. 18.3 g of calcium oxide (CaO) was then added as an alkaline earth metal oxide, and the molten metal (melt) was stirred with a carbon rod.

[0083] 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 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 as follows: 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 Tb２ O ３ the total mass of the easily oxidizable metal oxide (SiO ２ and Al ２ O ３ The amounts of rare earth metal oxides (CaO) and alkaline earth metal oxides (CaO) are shown in Table 9 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al is almost the same as in Reference Examples 5 to 8 and Comparative Reference Examples 5 to 7. ２ O ３ : SiO ２ The ratio of the alkaline earth metal oxides to the total mass of the alkaline earth metal oxides and the rare earth oxides was 22.7:18.4:58.9. The content of the alkaline earth metal oxides was 32.9 mass % based on the total mass of the alkaline earth metal oxides and the rare earth oxides.

[0084]

[0085] The results of the component analysis of the recovered Fe-C phase are shown in Table 10 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.

[0086]

[0087] The results of the component analysis of the recovered Cu phase are shown in Table 11 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.

[0088]

[0089] The recovered rare earth-enriched phase (RE ｘ O ｙ0.5 g of the slag (CaO-based slag) was acid-leached with 20 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 10 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 1.8 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 98.0 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).

[0090]

[0091] Example 3: 945.8 g of a rotor containing rare earth element-containing material and steel, 53.6 g of a recarburizer as a melting point depressant, and 30.4 g of silicon dioxide and 4.1 g of aluminum oxide as reagents 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. The composition of the neodymium magnet (Magnet 1) was 21.0% by mass Nd, 5.0% by mass Pr, 2.5% by mass Dy, 0.4% by mass Tb, 0.95% by mass B, and 70.15% by mass Fe. The composition of the neodymium magnet (Magnet 1) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rotor contained a total of 18.1 g of silicon and 6.4 g of aluminum. The total amount of silicon contained in the rotor and the reagent was 32.3 g, and the total amount of aluminum was 8.6 g. After the rotor was heated to 1450°C and melted, iron oxide (Fe ２ O ３ 192 g of calcium oxide (CaO) was added, and the molten metal (melt) was stirred with a carbon rod under atmospheric pressure to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. 26.4 g of calcium oxide (CaO) was then added as an alkaline earth metal oxide, and the molten metal (melt) was stirred with a carbon rod.

[0092] 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 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 as follows: 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 oxide (SiO ２ and Al ２ O ３ The amounts of the rare earth oxides and the alkaline earth metal oxide (CaO) are shown in Table 13 below. ２ O ３ and SiO ２ The mass ratio of rare earth oxide to Al was almost the same as in Reference Examples 9 and 10 and Comparative Reference Examples 8 and 9. ２ O ３ : SiO ２ The ratio of the alkaline earth metal oxides to the total mass of the alkaline earth metal oxides and the rare earth oxides was 30.4:13.3:56.4. The content of the alkaline earth metal oxides was 41.4 mass % based on the total mass of the alkaline earth metal oxides and the rare earth oxides.

[0093]

[0094] 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 0.02 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.

[0095]

[0096] The recovered rare earth-enriched phase (RE ｘ O ｙ 0.5 g of the slag (CaO-based slag) was acid-leached with 20 ml of 6 mol / L hydrochloric acid and filtered to obtain a filtrate. 10 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 1.8 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 98.7 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).

[0097]

[0098] Example 4: 751.6 g of a rotor and 1029.9 g of a stator as waste containing rare earth elements and steel, 77.8 g of a recarburizer as a melting point depressant, and 42.2 g of aluminum oxide as a reagent were placed in a graphite crucible (model number: 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 the rare earth element-containing material. The composition of the neodymium magnet (Magnet 2) was 29.2% by mass Nd, 0.0% by mass Pr, 1.6% by mass Dy, 0.5% by mass Tb, 0.95% by mass B, and 67.75% by mass Fe. The composition of the neodymium magnet (Magnet 2) was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The rotor and the stator contained a total of 36.4 g of silicon and 12.9 g of aluminum. The total amount of silicon contained in the rotor and the reagent was 36.4 g, and the total amount of aluminum was 35.2 g. After the rotor and the reagent were heated to 1400°C and melted, iron oxide (Fe ２ O ３200.5 g of calcium oxide (CaO) was added, and the molten metal (melt) was stirred with a carbon rod under atmospheric pressure to fully oxidize the rare earth elements, silicon, and aluminum with the iron oxide and oxygen in the air. 60.6 g of calcium oxide (CaO) was then added as an alkaline earth metal oxide, and the molten metal (melt) was stirred with a carbon rod.

[0099] 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 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 as follows: 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 oxide (SiO ２ and Al ２ O ３ The amounts of rare earth metal oxides (CaO) and alkaline earth metal oxides (CaO) are shown in Table 16 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 4 and Comparative Reference Examples 1 to 4. ２ O ３ : SiO ２ The ratio of the alkaline earth metal oxides to the total mass of the alkaline earth metal oxides and the rare earth oxides was 20.6:36.6:42.8. The content of the alkaline earth metal oxides was 61.8 mass % based on the total mass of the alkaline earth metal oxides and the rare earth oxides.

[0100]

[0101] 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 0.17 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.

[0102]

[0103] The recovered rare earth-enriched phase (RE ｘ O ｙ One gram of the slag (CaO-based slag) was acid-leached with 20 ml of 6 mol / L hydrochloric acid, followed by filtration to obtain a filtrate. 20 ml of 1 mol / L oxalic acid solution was added to the filtrate, and the pH was adjusted to 1.9 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 18 below. The amount of rare earth oxides in the powder was 99.1 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).

[0104]

[0105] As can be seen from the above-described Reference Examples, Comparative Reference Examples, and Examples, the recovery method according to the present embodiment makes it possible to recover rare earth oxides using a boron-free flux.

[0106] This application is based on Japanese Patent Application No. 2024-014088, filed on February 1, 2024, the disclosure of which is hereby incorporated 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 oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides to prepare a melt containing at least the rare earth oxide, the oxide, 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 oxide, and an Fe—C phase.

2. A method for recovering rare earth oxides according to claim 1, wherein the content of the oxide 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 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 oxides, 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 the easily oxidizable metals are aluminum oxide and silicon dioxide.

6. The method for recovering rare earth oxides according to claim 5, wherein the oxide is calcium oxide (CaO).

7. The method for recovering rare earth oxides according to claim 1, wherein the rare earth element-containing material includes a neodymium magnet.

8. The method for recovering rare earth oxides according to claim 1, wherein the melt preparation step (1) does not include adding any boron-containing substance other than the waste material.

9. The method for recovering rare earth oxides according to claim 1, wherein the boron content in the melt is 4.3 mass % or less based on the total mass of rare earth elements.

10. A method for recovering rare earth oxides according to claim 6, wherein the ratio of the aluminum oxide content to the sum of the rare earth oxide mass, the easily oxidizable metal oxide content, and the oxide content of the rare earth element-containing material is 15.7 to 17.5 mass%, the silicon dioxide content is 50.0 to 55.9 mass%, and the oxide content is 5.0 to 15.0 mass%.

11. The method for recovering rare earth oxides according to claim 6, wherein the ratio of the aluminum oxide content to the sum of the rare earth oxide mass, the easily oxidizable metal oxide content, and the oxide content of the rare earth element-containing material is 27.5 to 29.3 mass%, the silicon dioxide content is 32.1 to 34.2 mass%, and the oxide content is 20.0 to 25.0 mass%.

12. The method for recovering rare earth oxides according to claim 6, 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 oxide in the rare earth element-containing material is 10.9 to 11.4 mass%, the silicon dioxide content is 46.4 to 48.5 mass%, and the oxide content is 14.0 to 17.7 mass%.

13. The method for recovering rare earth oxides according to claim 6, wherein the ratio of the aluminum oxide content to the sum of the rare earth oxide mass, the easily oxidizable metal oxide content, and the oxide content of the rare earth element-containing material is 11.6 to 12.9 mass%, the silicon dioxide content is 49.5 to 54.9 mass%, and the oxide content is 10.0 to 18.9 mass%.

14. A method for recovering rare earth oxides according to claim 6, wherein the ratio of the aluminum oxide content to the sum of the rare earth oxide mass, the easily oxidizable metal oxide content, and the oxide content of the rare earth element-containing material is 17.0 to 22.5 mass%, the silicon dioxide content is 35.9 to 47.6 mass%, and the oxide content is 10.0 to 32.1 mass%.

15. 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 oxide to the melt (1b) to obtain melt (1c).

16. The method for recovering rare earth oxides according to claim 15, wherein the melting point depressant lowers the melting point of iron and contains carbon, and the oxidizing agent oxidizes rare earth elements and contains at least one selected from air, oxygen, carbon dioxide, iron oxide, and composite oxides containing iron oxide.

17. 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.

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

19. The rare earth-enriched material according to claim 18, wherein the boron content is 4.3 mass % or less, based on the total mass of the rare earth elements.

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