KR102303795B1 - Method for converting rare earth metal - Google Patents

Abstract

Provided is a method for converting rare-earth metals in which rare-earth elements contained in a rare-earth alloy can be extracted using a molten salt including Mg halide and alkali halide.
The rare-earth metal conversion method according to the present invention comprises the steps of a) immersing a rare-earth alloy in a molten salt containing Mg halide and two kinds of alkali halides, b) the rare-earth alloy and Mg halide are reacted to selectively extract the rare-earth element. c) separating a solid component and a liquid component contained in the reaction product, d) separating the rare earth halide from the separated liquid component, and e) recovering the rare earth metal from the rare earth halide characterized.

Description

METHOD FOR CONVERTING RARE EARTH METAL

The present invention relates to a rare-earth metal conversion method capable of extracting rare-earth elements contained in a rare-earth alloy by using a molten salt containing Mg halide and alkali halide, wherein the reaction proceeds at a low temperature to suppress the formation of by-products and achieve high purity It relates to a rare-earth metal conversion method capable of separating rare-earth elements of

Rare-earth permanent magnets are widely used in electric, automobile, bio, and environmental industries due to their excellent magnetic properties. Since the first generation of Sm-Co magnets, the first-generation rare-earth magnets, were first developed, their demand has steadily increased by more than 20% every year. Research began, and as a result, a new Nd-Fe-B magnet with improved magnetic properties was newly developed.

The production of Nd-Fe-B permanent magnets has been expanded for electronic and information equipment applications due to the spread of computers around the world. In the case of Korea, the demand for Nd-Fe-B magnets is expected to increase continuously, but most of the materials and raw materials are imported. In particular, neodymium (Nd), dysprosium (Dy), praseodymium (Pr), Similarly, rare earth elements, which are the core composition of Nd-Fe-B magnets, are a new approach that can be left for resource-poor countries and potential needs of the next generation because of the problem of supply and demand instability as well as the lack of natural resources themselves. I need a way.

Therefore, it can be said that it is important to develop technologies for recycling rare earth elements in Korea along with exploration and development of resources outside of China for stable securing of rare earth elements. On the other hand, it is also possible to consider the development of a circulation technology in which the resources once mined are continuously circulated without consumption. In the case of recycling technology, it is highly evaluated that it can minimize environmental pollution in the process of commercialization or disposal of products after use, and at the same time increase the resource and energy efficiency of obtaining materials compared to the extraction of natural resources.

Due to the supply and demand of rare earth resources and their importance, research on recycling Nd-Fe-B permanent magnets has been in progress since the past, and since the 1960s, interest in rare earths has increased, and various processes for recycling technology have been developed. Existing technologies for recycling rare earths in Korea are mainly research and development of recycling technologies for rare earths using wet methods. The rare earth separation and purification technology through the wet process has the advantage of recovering high-purity rare earths. is more active than Among them, a technology for a dry rare earth element recycling method of a new concept that can selectively extract only the rare earth elements contained in the magnet scrap using liquid magnesium has been reported. Accordingly, there is a need for a rare-earth metal conversion method that is simple, suppresses by-products of the entire reaction, and can separate high-purity rare-earth elements.

1. Korean Patent Publication No. 10-1341511 2. Korean Patent Publication No. 10-2019-0129557

An object of the present invention is to provide a rare-earth metal conversion method capable of extracting rare-earth elements contained in a rare-earth alloy using a molten salt including Mg halide and alkali halide.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

A rare-earth metal conversion method according to the technical idea of the present invention for achieving the above technical object includes the steps of: a) immersing a rare-earth alloy in a molten salt containing Mg halide and two kinds of alkali halides; b) the rare-earth alloy and Mg halide reacts to selectively extract rare earth elements, c) separating a solid component and a liquid component contained in the reaction product, d) separating the rare earth halide from the separated liquid component, and e) from the rare earth halide and recovering the rare earth metal.

In some embodiments of the present invention, the rare earth alloy may include Nd.

In some embodiments of the present invention, the rare earth alloy may be Nd-Fe-B.

In some embodiments of the present invention, the Mg halide may be MgCl ₂ or MgF ₂ .

In some embodiments of the present invention, the alkali halide may be a compound of a metal selected from Li, Na, and K and a halogen selected from Cl and F, or a mixture of the halogen compound.

In some embodiments of the present invention, the _{molten salt may be a ternary molten salt including MgCl 2} and two chloride-based halides selected from LiCl, NaCl, and KCl.

In some embodiments of the present invention, the molten salt is MgCl _2x LiCl _y KCl _z , 0<x≤33mol%, 10≤y<65mol%, 35≤z≤65mol%, x+y+z=100 can be

In some embodiments of the present invention, the molten salt is MgCl _2x LiCl _y KCl _z , 15≤x≤25mol%, 25≤y≤35mol%, 45≤z≤55mol%, x+y+z=100 can be

In some embodiments of the present invention, the molten salt is MgCl _2x NaCl _y KCl _z , 35≤x≤50mol%, 15≤y≤35mol%, 20≤z≤50mol%, x+y+z=100 can be

In some embodiments of the present invention, the molten salt is MgCl _2x NaCl _y KCl _z , 40≤x≤50mol%, 22.5≤y≤32.5mol%, 22.5≤z≤32.5mol%, x+y+z =100.

In some embodiments of the present invention, the molten salt is MgCl _2x NaCl _y LiCl _z , 26≤x≤45mol%, 36≤y≤55mol%, 5≤z≤37.5mol%, x+y+z= It can be 100.

In some embodiments of the present invention, the molten salt is MgCl _2x NaCl _y LiCl _z , 35≤x≤45mol%, 45≤y≤55mol%, 5≤z≤15mol%, x+y+z=100 can be

In some embodiments of the present invention, the molten salt may be a ternary molten salt including two types of fluoride-based halides selected from _{MgF 2 and LiF NaF and KF.}

In some embodiments of the present invention, the molten salt is MgF _2x LiF _y KF _z , 0<x≤5mol%, 22.5≤y≤72.5mol%, 26≤z≤73mol%, x+y+z= It can be 100.

In some embodiments of the present invention, the molten salt is MgF _2x LiF _y KF _z , 0<x≤5mol%, 42.5≤y≤52.5mol%, 45≤z≤55mol%, x+y+z= It can be 100.

In some embodiments of the present invention, the molten salt is MgF _2x NaF _y KF _z , 0<x≤15mol%, 12.5≤y≤45mol%, 40≤z≤77.5mol%, x+y+z= It can be 100.

In some embodiments of the present invention, the molten salt is MgF _2x NaF _y KF _z , 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100 can be

In some embodiments of the present invention, the molten salt is MgF _2x NaF _y LiF _z , 0<x≤15mol%, 25≤y≤52.5mol%, 37.5≤z≤68mol%, x+y+z= It can be 100.

In some embodiments of the present invention, the molten salt is MgF _2x NaF _y LiF _z , 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100 can be

In the rare-earth metal conversion method according to the present invention, the rare-earth element contained in the rare-earth alloy may be extracted using a molten salt including Mg halide and alkali halide.

In addition, in the rare earth metal conversion method according to the present invention, the reaction proceeds at a low temperature using a ternary molten salt, thereby suppressing the formation of by-products of the entire reaction and separating high-purity rare earth elements.

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a schematic diagram schematically showing a rare earth metal conversion method according to an embodiment of the present invention.
2 is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperature and standard Gibbs free energy of Nd, Dy, Pr, Mg, Ca, Al, Li, K and Na chlorides.
3 is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperatures of Nd, Dy, Pr, Mg, Ca, Al, Li, K and Na fluorides and the standard Gibbs free energy.
4 is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperature of Nd, Dy and Mg chlorides and the standard Gibbs free energy.
5 is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperatures of Nd, Dy and Mg fluorides and the standard Gibbs free energy.
6 is a graph showing the content of _{Nd, NdCl 2} and NdCl _{3 according to temperature.}
7 is a graph showing _{Nd and NdF 3 contents according to temperature.
8 is a state diagram of a MgCl 2} -LiCl-KCl ternary system according to an embodiment of the present invention.
_{9 is a state diagram of the MgCl 2} -NaCl-KCl ternary system according to an embodiment of the present invention.
_{10 is a state diagram of the MgCl 2} -NaCl-LiCl ternary system according to an embodiment of the present invention.
_{11 is a state diagram of a MgF 2} -LiF-KF ternary system according to an embodiment of the present invention.
_{12 is a state diagram of a MgF 2} -NaF-KF ternary system according to an embodiment of the present invention.
_{13 is a state diagram of a MgF 2} -NaF-LiF ternary system according to an embodiment of the present invention.
14 is a graph showing the extraction rate of Nd halide according to the chloride-based and fluoride-based compositions according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey/completely the technical spirit of the present invention to those skilled in the art. As used herein, the term “and/or” includes any one and any combination of one or more of those listed items. The same symbols refer to the same elements from beginning to end. Furthermore, various elements and regions in the drawings are schematically drawn. Therefore, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

1 is a schematic diagram schematically showing a rare earth metal conversion method according to an embodiment of the present invention. A rare-earth metal conversion method according to the technical spirit of the present invention comprises the steps of: a) immersing the rare-earth alloy in a molten salt, b) extracting the rare-earth element, c) separating the solid component and the liquid component, d) preparing the rare-earth halide separating and e) recovering the rare earth metal.

The step a) dipping the rare-earth alloy in the molten salt is a step of immersing the rare-earth alloy in a molten salt containing an Mg halide and two kinds of alkali halides. The rare earth alloy may include Nd and Dy. In particular, it may be a waste magnet containing Fe, and in particular, it may be a Nd-Fe-B permanent magnet. The Mg halide may be MgCl ₂ or MgF ₂ .

In particular, the alkali halide may be a compound of a metal selected from Li, Na, and K and a halogen selected from Cl and F, or a mixture of the halogen compound. The alkali halide can be added to exhibit lower melting point and viscosity as well as volatility compared to pure Mg halide molten salt. In addition, it is possible to provide high conductivity advantageous for electrolysis in the step e) recovering the rare earth metal.

The immersion step includes charging a rare earth alloy (NdFeB scrap) and two kinds of Mg halide and alkali halide into a crucible, and heating the crucible to melt the two kinds of Mg halide and alkali halide.

The step b) extracting the rare earth element is a step in which the rare earth element is selectively extracted by reacting the rare earth alloy with the Mg halide. The rare earth element is extracted as a liquid component, and the remaining alloy remains as a solid component. The reaction product comprises a liquid rare earth halide, a liquid Mg and a solid Fe-B residue. wherein the rare earth alloy is a Nd-Fe-B permanent magnet and the Mg halide is MgCl ₂ In this case, the reaction equation is as follows.

1) Nd-Fe-B(s) + MgCl ₂ (l) → NdCl ₃ (l) + Mg(l) + Fe-B(s)

The halide molten salt preferably has high reactivity with the rare-earth element in the rare-earth alloy and does not react with Fe, so that the rare-earth element can be extracted from scrap including Fe. Also, there is no chemical reaction between the reaction products because there is no solubility between the reaction products.

Considering only the reaction of Nd and MgCl _{2 in} the above reaction equation, it is as follows, and 1.5 mol of Mg is required for 1 mol of Nd.

2) 2Nd(s) + 3MgCl ₂ (l) → 2NdCl ₃ (l) + 3Mg(l)

The step c) separating the solid component and the liquid component is a step of separating the solid component and the liquid component included in the reaction product. In the rare-earth alloy, the Mg halide reacts with the rare-earth element to extract the liquid, and the remaining alloy remains as a solid component. The liquid molten chloride and the rest of the solid alloy can be separated easily and on a large scale through solid-phase separation. In addition, the solid alloy remaining after the rare earth elements are extracted can be used as an alternative raw material in the cement industry or the steel industry, so that waste liquid and solid matter are not generated.

The step d) separating the rare earth halide is a step of separating the rare earth halide from the separated liquid component. The liquid component is Mg, Nd halide, and an alkali halide as a molten salt component. Since Mg is less reactive than Nd halide, it exists in the form of liquid Mg metal and floats on the liquid Nd halide, so that Mg can be separated. Mg with low specific gravity and halide with high specific gravity can be separated using specific gravity difference (gravity separation, etc.). The separated Mg may be used as a raw material for a smelting process.

The step e) recovering the rare earth metal is a step of recovering the rare earth metal from the rare earth halide. Molten salt electrolytic refining, which is a dry method, is available.

Figure 2 is a T-ΔG ° graph (Ellingham diagram) showing the relationship between the temperature and standard Gibbs free energy of Nd, Dy, Pr, Mg, Ca, Al, Li, K and Na chloride, Figure 3 is Nd, Dy, This is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperatures of Pr, Mg, Ca, Al, Li, K and Na fluorides and the standard Gibbs free energy.

When comparing the G° between halides, it can be seen that the RE halide is the most stable (eg, RE or Alk. metal > Alk. Halide > RE halide), and thermodynamically, chloride and fluoride exchange reactions (eg, RE + Mg halide → RE halide) + Mg) is possible. In addition, in the chloride system, an unexpected chemical reaction may occur due to disproportionation. On the other hand, since fluoride does not disproportionate, it can perform a more stable halide reaction than chloride.

4 is a T-ΔG° graph (Ellingham diagram) showing the relationship between the temperatures of Nd, Dy and Mg chlorides and the standard Gibbs free energy, and FIG. 5 is a relationship between the temperatures of Nd, Dy and Mg fluorides and the standard Gibbs free energy. It is a T-ΔG° graph (Ellingham diagram) showing.

Comparing the Gㅀ comparison, it can be seen that G°(Nd + Cl ₂ → NdCl ₂ ) < G°(3/2Dy + Cl ₂ → 3/2DyCl ₃ ) < G°(Mg + Cl ₂ → MgCl ₂ ) . Thus, thermodynamically, chloride and fluoride exchange reactions (eg RE + Mg halide → RE halide + Mg) are possible.

In chloride-based salts, an exchange reaction is possible because G°(Nd + Cl ₂ → NdCl ₂ ) < G°(Mg + Cl ₂ → MgCl _{2 ) over the entire temperature.} G°(3/2Dy + Cl ₂ → 3/2DyCl ₃ ) and G°(Mg + Cl ₂ → MgCl ₂ ) are reversed at about 600-700 °C, and at temperatures above about 600-700 °C, Dy and Mg chloride doesn't react Therefore, in the chloride-based salt, the reaction temperature can be reacted at 600° C. or less.

In fluoride-based salts, G°(2/3Dy + F ₂ → 2/3DyF ₃ ) < G° (2/3Nd + F ₂ → 2/3NdF ₃ ) < G°(Mg + F ₂ → MgF over temperature) ₂ ), so if Dy is included in the waste magnet, Nd and Dy can be recovered together without being separated. The difference between G°(2/3Dy + F ₂ → 2/3DyF ₃ ), G°(2/3Nd + F ₂ → 2/3NdF ₃ ), G°(Mg + F ₂ → MgF ₂ ) is evident above 600℃ Therefore, the reaction temperature in the fluoride-based salt may exceed 600 °C.

6 is a _{graph showing Nd, NdCl 2} and NdCl ₃ contents according to temperature, and FIG. 7 is a graph showing Nd and NdF ₃ contents according to temperature. 6 , according to the stoichiometric ratio, it can be expressed by the following chemical reaction formula. In addition, it can be confirmed that all of them show a forward reaction at ΔG°f (0~1000℃), 1/1.5Nd and Cl ₂ meet to form 1/1.5NdCl ₃ , and Nd and Cl ₂ (g) meet to form _{NdCl 2} have.

1/1.5Nd + Cl ₂ (g) = 1/1.5NdCl ₃ and Nd + Cl ₂ (g) = NdCl ₂

7 , it can be expressed by the following chemical reaction formula according to the stoichiometric ratio. In addition, it can be confirmed that all of them show a forward reaction at ΔG°f (0~1000°C), and that Nd and F ₂ (g) meet _{to form NdF 3 .}

1/1.5 Nd + F ₂ (g) = 1/1.5 NdF ₃

As described above, in the chloride-based reaction, when Nd and Cl(g) react, NdCl ₂ and NdCl ₃ phases may be generated, and during electrolysis after the ion exchange reaction, a disproportionation phenomenon occurs instead of being reduced only to Nd metal. . On the other hand, since fluoride does not cause disproportionation, a more stable halide reaction can be performed compared to chloride.

8 to 13 are diagrams showing the state diagram of the ternary molten salt according to the present invention using the thermodynamic program FactSage. It is advantageous to suppress the formation of by-products of the overall reaction and to proceed at a low temperature possible for the reaction in consideration of the subsequent electrolysis process. Thermodynamic calculations were performed to identify lower melting points and larger liquid regions of _{MgCl 2} including halogenation systems (Cl- and F-sys). Therefore, the range of the composition showing the liquid phase was confirmed in FIGS. 8 to 13 to derive the ternary low-melting-point molten salt composition including the Mg halide.

The molten salt _{may be a ternary molten salt including MgCl 2} and two chloride-based halides selected from LiCl, NaCl, and KCl.

_{8 is a state diagram of a MgCl 2} -LiCl-KCl ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 400° C., and _{the maximum content of MgCl 2} is 33 mol%. MgCl ₂ -LiCl-KCl The range of moles in the liquid phase of the ternary system is MgCl ₂ : 0-33 mol%, LiCl: 10-65 mol%, KCl: 35-65 mol%.

Therefore, the molten salt may be MgCl _2x LiCl _y KCl _z , 0<x≤33mol%, 10≤y<65mol%, 35≤z≤65mol%, x+y+z=100. In particular, the molten salt may be MgCl _2x LiCl _y KCl _z , 15≤x≤25mol%, 25≤y≤35mol%, 45≤z≤55mol%, x+y+z=100.

_{9 is a state diagram of the MgCl 2} -NaCl-KCl ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 400° C., and _{the maximum content of MgCl 2} is 50 mol%. MgCl ₂ -KCl-NaCl The range of moles in the liquid phase of the ternary system is MgCl ₂ : 35-50 mol%, KCl: 15-35 mol%, NaCl: 20-50 mol%.

Therefore, the molten salt may be MgCl _2x NaCl _y KCl _z , 35≤x≤50mol%, 15≤y≤35mol%, 20≤z≤50mol%, x+y+z=100. In particular, the molten salt may be MgCl _2x NaCl _y KCl _z , and 40≤x≤50mol%, 22.5≤y≤32.5mol%, 22.5≤z≤32.5mol%, x+y+z=100.

_{10 is a state diagram of the MgCl 2} -NaCl-LiCl ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 450° C., and _{the maximum content of MgCl 2} is 45 mol%. MgCl ₂ -NaCl-LiCl The range of moles in the liquid phase of the ternary system is MgCl ₂ : 26 to 45 mol%, NaCl: 36 to 55 mol%, LiCl: It can be confirmed that 5 to 37.5 mol%.

Therefore, the molten salt may be MgCl _2x NaCl _y LiCl _z , and 26≤x≤45mol%, 36≤y≤55mol%, 5≤z≤37.5mol%, x+y+z=100. In particular, the molten salt may be MgCl _2x NaCl _y LiCl _z , 35≤x≤45mol%, 45≤y≤55mol%, 5≤z≤15mol%, x+y+z=100.

The molten salt may be a ternary molten salt including two fluoride-based halides selected from _{MgF 2 and LiF NaF and KF.}

_{11 is a state diagram of a MgF 2} -LiF-KF ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 500° C., and _{the maximum content of MgF 2} is 5 mol%. MgF ₂ -LiF-KF The range of moles in the liquid phase of the ternary system is MgF ₂ : 0-5 mol%, LiF: 22.5-72.5 mol%, KF: 26-73 mol%.

Accordingly, the molten salt may be MgF _2x LiF _y KF _z , and 0<x≤5mol%, 22.5≤y≤72.5mol%, 26≤z≤73mol%, x+y+z=100. In particular, the molten salt may be MgF _2x LiF _y KF _z , and 0<x≤5mol%, 42.5≤y≤52.5mol%, 45≤z≤55mol%, x+y+z=100.

_{12 is a state diagram of a MgF 2} -NaF-KF ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 700° C., and _{the maximum content of MgF 2} is 15 mol%. It can be seen that the range of moles in the liquid phase of the _{MgF 2 -NaF-KF ternary system is MgF 2} : 0-15 mol%, NaF: 12.5-45 mol%, KF: 40-77.5 mol%.

Therefore, the molten salt may be MgF _2x NaF _y KF _z , and 0<x≤15mol%, 12.5≤y≤45mol%, 40≤z≤77.5mol%, x+y+z=100. In particular, the molten salt may be MgF _2x NaF _y KF _z , and 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100.

_{13 is a state diagram of a MgF 2} -NaF-LiF ternary system according to an embodiment of the present invention. The minimum temperature for complete dissolution is 650° C., and _{the maximum content of MgF 2} is 15 mol%. It can be seen that the range of moles in the liquid phase of the _{MgF 2 -NaF-LiF ternary system is MgF 2} : 0-15 mol%, NaF: 25-52.5 mol%, LiF: 37.5-68 mol%.

Accordingly, the molten salt may be MgF _2x NaF _y LiF _z , and 0<x≤15mol%, 25≤y≤52.5mol%, 37.5≤z≤68mol%, x+y+z=100. In particular, the molten salt may be MgF _2x NaF _y LiF _z , and 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100.

In the method of the present invention, the rare earth element contained in the rare earth alloy can be extracted using a molten salt containing Mg halide and an alkali halide. It can suppress the formation of by-products and separate high-purity rare earth elements.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention in any sense.

Content not described here will be omitted because it can be technically inferred sufficiently by a person skilled in the art.

Rare Earth Metal Conversion

The rare earth metal conversion according to the present invention is as shown in FIG. 1, a) immersing the rare earth alloy in a molten salt, b) extracting the rare earth element, c) separating the solid component and the liquid component, d) preparing the rare earth halide Separation and e) recovery of the rare earth metal were carried out.

NdFeB scrap granules were immersed in the molten salt of the compositions C1 to C3 and F1 to F3 in Table 1 below. The composition of the NdFeB scrap was Nd: 33wt%, Fe: 66wt%, B: 1wt%, and NdFeB scrap having a size of 1000 to 2000 μm was used.

division Experimental example Molten salt composition (mol%) Mg:Nd=4:1 (weight ratio) MgCl2 LiCl NaCl KCl NdFeB scrap chloride C1 20 30 - 50 2.38g C2 45 - 27.5 27.5 5.355g C3 40 10 50 - 4.76g division Experimental example Molten salt composition (mol%) Mg:Nd=4:1 (weight ratio) MgF2 LiF NaF KF NdFeB scrap fluoride F1 2.5 47.5 - 50 0.13g F2 10 - 40 50 0.514g F3 10 50 40 - 0.514g

It was heated to a temperature of 500° C. for chloride and 800° C. for fluoride. It was heated in an Ar gas atmosphere at a rate of 5° C./min, and maintained for 12 hours to react. The heating temperature was set based on the thermodynamic data of the molten salt. Theoretically, 1.5 mol of Mg is required to reduce 1 mol of Nd (by weight, 1 g of Mg is required to reduce 4 g of Nd), but in the experiment, a sufficient amount of Mg is added did. That is, Mg was added as Mg:Nd=4:1 instead of Mg:Nd=1:4. The residual scrap was taken out and separated from the molten chloride.

ICP component analysis

Table 2 below shows the ICP-OES component analysis results for the residual magnet powder (Fe-B on the bottom) for each experimental condition after the ion exchange reaction experiment, and Tables 3 and 14 are chloride-based and fluoride-based fluoride according to an embodiment of the present invention. This is the result of calculating the Nd halide extraction rate according to the system composition. The Nd halide extraction rate was calculated by the following formula.

Nd halide extraction rate = (1 - (Nd content of residual magnet powder) / (Nd content of raw material Nd-Fe-B)) * 100

Since it is preferable that the residual magnet powder does not contain Nd, the lower the Nd content, the better the result. It was confirmed that the fluoride system having a lower residual Nd content was superior to the chloride system. 6 and 7, disproportionation occurs in the chloride-based salt, and it is determined that the Nd content is higher in the chloride-based salt than in the fluoride-based salt.

Element NdFeB magnet C1 (ppm) C2 (ppm) C3 (ppm) F1 (ppm) F2 (ppm) F3 (ppm) Fe 611000 619800 603400 555700 587900 552800 672700 Li 6.41 154.8 0.8 22.79 21390 11070 2233 Mg 10.24 88650 24970 41360 16050 13100 7603 K 248.4 3387 361.9 241.7 57740 20090 0 B 9968 3992 7738 7392 403.1 204.6 0 Na 0 1477 218.1 431.6 37330 41480 45880 Nd 198800 43680 26870 30620 1925 2781 2696

Experimental example C1 C2 C3 F1 F2 F3 Nd halide extraction rate from residual magnetic powder 78.02 86.48 84.59 99.03 98.6 98.64

As shown in Table 3 and FIG. 14, in the chloride system, the extraction rate of Nd halide was 75% or more, the Nd halide extraction rate of C1 to C3 was 78 to 86.5%, and in particular, C2 showed the best result as 85% or more. In the fluoride system, it can be seen that the extraction rate of Nd halide is 95% or more, and the extraction rate of Nd halide in F1 to F3 is 98 to 99%, and in particular, it can be confirmed that F1 is 99% or more.

As described above, in the rare-earth metal conversion method according to the present invention, the rare-earth element contained in the rare-earth alloy can be extracted using a molten salt containing Mg halide and an alkali halide, and in particular, a ternary molten salt having a low reaction rate is used. It was confirmed that the process was carried out at a temperature to suppress the formation of by-products of the overall reaction and to have the characteristics of separating high-purity rare-earth elements.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

Claims (19)

a) immersing the rare earth alloy in a molten salt comprising an Mg halide and two alkali halides;
b) selectively extracting the rare earth element by reacting the rare earth alloy with the Mg halide;
c) separating a solid component and a liquid component contained in the reaction product;
d) separating the rare earth halide from the separated liquid component; and
e) recovering the rare earth metal from the rare earth halide;
as,
The molten salt is a ternary molten salt provided as any one of two kinds of chloride-based halides selected from _{MgCl 2} and LiCl, NaCl, and KCl or two kinds of fluoride-based halides selected from _{MgF 2 and LiF NaF, KF,}
The molten salt containing the chloride-based halide is MgCl _2x LiCl _y KCl _z (where x,y,z are 15≤x≤25mol%, 25≤y≤35mol%, 45≤z≤55mol%, x+y+ z=100) or MgCl _2x NaCl _y KCl _z (where x,y,z are 40≤x≤50mol%, 22.5≤y≤32.5mol%, 22.5≤z≤32.5mol%, x+y+z=100) or MgCl _2x NaCl _y LiCl _z (where x,y,z is 35≤x≤45mol%, 45≤y≤55mol%, 5≤z≤15mol%, x+y+z=100) above b) The reaction of the step proceeds at 600° C. or less, and the Nd halide extraction rate is 75% or more,
The molten salt containing the fluoride-based halide is MgF _2x LiF _y KF _z (where x, y, z are 0<x≤5mol%, 42.5≤y≤52.5mol%, 45≤z≤55mol%, x+y +z=100) or MgF _2x NaF _y KF _z (where x,y,z are 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100) or When MgF _2x NaF _y LiF _z (where x,y,z is 5≤x≤15mol%, 35≤y≤45mol%, 45≤z≤55mol%, x+y+z=100), step b) above Rare earth metal conversion method, characterized in that the reaction proceeds at 800° C. or less, and the Nd halide extraction rate is 95% or more
According to claim 1,
The rare earth metal conversion method, characterized in that the rare earth alloy comprises Nd
According to claim 1,
The rare earth alloy is a rare earth metal conversion method, characterized in that Nd-Fe-B

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