JP6668021B2 - Rare metal recovery method - Google Patents

Description

  Embodiments of the present invention relate to a method for recovering rare metals contained in an alloy.

In recent years, neodymium (Nd), dysprosium (Dy), samarium (Sm), and the like, among rare earth elements, which are a kind of rare metal, have been attracting attention as magnetic material raw materials.
Rare metal is a general term for elements that have a small abundance on earth or metals that are technically and economically difficult to extract and for which securing a stable supply is important in policy.
Rare metals are used in various fields such as electronic materials and magnetic materials.

The rare earth elements described above are generally contained in ores such as bastnaesite and ion-adsorbed ore, and are recovered through mining, beneficiation, and wet / dry processing.
Rare earth-containing ores are found all over the world, but supply risks have been an issue in recent years due to the limited area where economical mining is possible.
Another problem is that radioactive substances such as uranium or thorium are generated as waste when rare earths are recovered from ores.

In order to solve these problems, there has been a movement to recover rare earth elements and other rare metals from rare earth-containing products from magnet-containing waste, thereby stably supplying resources and reducing the amount of waste.
Promising targets for collection include process waste generated during the production of Nd magnets and Nd magnets that have been marketed as products.
These magnets are used in compressors of air conditioners, motors of washing machines, motors of electric vehicles, and the like.
In the future, with the increase in the amount of magnets used, it is expected to be recovered from process waste or magnet-containing waste such as magnets in products.

When recovering these rare-earth elements from magnet-containing waste, usually, first, a rare-earth compound such as a rare-earth oxide is precipitated from the magnet-containing waste by acid dissolution or the like.
Then, the rare earth compound is dissolved again to extract rare earth ions, and the rare earth ions are reduced to recover a single rare earth element.

For example, a method has been proposed in which the rare earth compound is immersed in a molten salt of a halide salt, a halide of the rare earth element is extracted into the molten salt, and then the molten salt containing the halide is vaporized to recover the rare earth halide.
In this recovery method, the amount of used chemicals, the amount of waste, and the number of steps can be reduced as compared with the conventional method.

JP 2012-188695 A JP 2014-051731 A JP-A-2005-120973

  However, the conventional technique using the above-mentioned metal halide has a problem in that toxic halogen gas is generated from the anode during molten salt electrolysis included in the reduction step.

  The present invention has been made in view of such circumstances, and has as its object to provide a rare metal recovery method capable of recovering a rare metal without generating a halogen gas in a reduction step.

The rare metal recovery method according to the present embodiment includes a step of dipping a rare metal-containing alloy in a molten salt, a step of adding iron oxide Fe ₂ O ₃ to the molten salt, and a step of adding a metal oxide. And extracting the rare metal into ions. Tep, is to execute.

  According to the present invention, a rare metal recovery method capable of recovering a rare metal without generating a halogen gas in the reduction step is provided.

(A) is an explanatory diagram of the rare metal recovery method according to the embodiment when extracting a rare metal, and (B) is an explanatory diagram of the rare metal recovery method according to the embodiment when a rare metal is reduced. 4 is a flowchart illustrating a rare metal recovery method according to the embodiment. 9 is a flowchart showing a modified example of the rare metal recovery method according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Embodiment)
FIG. 1A is an explanatory diagram at the time of extracting the rare metal 13 in the recovery method according to the embodiment, and FIG. 1B is an explanatory diagram at the time of reduction of the rare metal 13 in the recovery method according to the embodiment.
As shown in FIG. 1, the rare metal recovery method according to the embodiment (hereinafter, simply referred to as “recovery method”) involves extracting a rare metal 13 contained in a rare metal-containing alloy 11 into a molten salt 12 and then reducing the same to form a solid. A rare metal 13 is obtained.

The rare metal-containing alloy 11 targeted by the recovery method according to the embodiment includes rare earth elements, Li, Be, B, Ti, V, Cr, Mn, Co, Ni, Ga, Ge, Se, Rb, Sr, Zr, and Nb. , Mo, Pd, In, Sb, Te, Cs, Ba, Hf, Ta, W, Re, Pt, Tl and Bi are included as the rare metal 13.
Hereinafter, description will be given on the assumption that the rare metal 13 is Nd recovered from the Nd magnet.
The rare metal-containing alloy 11 may be a precipitate obtained by precipitating a Nd magnet through a wet pretreatment of pulverization, firing and acid dissolution, or may be a used Nd magnet itself.

FIG. 2 is a flowchart illustrating a collection method according to the embodiment.
As shown in FIGS. 1A, 1B and 2, the recovery method according to the embodiment includes a molten salt immersion step (S11), a metal oxide addition step (S12), and a molten salt extraction step (S13). And a reduction step (S14).
The order of the molten salt immersion step (S11) and the metal oxide addition step (S12) may be reversed.

In the molten salt immersion step (S11), the rare metal-containing alloy 11 put in the basket 14 is immersed in the molten salt 12 at about 500 to 900 ° C.
In the metal oxide addition step (S12), a metal oxide 16 is added to the molten salt 12 to dissolve metal ions contained in the metal oxide 16.

Then, in the molten salt extraction step (S13), the Nd ions 17a (17) are eluted from the Nd-containing alloy 11a (11) into the molten salt 12 in the molten salt extraction step (S13) according to the following equation (1). Is extracted.
Dissolution of Nd ions from Nd-containing alloy: Nd + 3M ⁺ → Nd ³ + + M (1)
Here, M represents a metal oxidized in the metal oxide 16.
The metal oxide 16 added in the metal oxide addition step (S12) is a powdery oxide firmly bonded to oxygen, such as Fe ₂ O ₃ , and is not easily dissolved in the molten salt 12.

Therefore, it is preferable that the molten salt 12 contains a fluoride salt such as LiF—CaF ₂ because of its high reactivity with a metal.
By including at least one kind of fluoride salt in the molten salt 12, the metal oxide 16 can be easily dissolved in the molten salt 12 by ionization.
However, another halide salt such as a chloride salt can be used for the molten salt 12 instead of the fluoride salt.

Further, in order for the formula (1) to become a forward reaction and dissolve Nd as ions, it is necessary to select an appropriate metal oxide 16.
That is, it is necessary to select a metal oxide 16 capable of performing a molten salt extraction reaction based on the free energy of oxide formation, the free energy of fluorination, etc. in the formula (1).

For example, the iron ion Fe ³⁺ has a negative free energy in the formula (1) and causes a forward reaction in the above formula (1), and becomes a suitable extractant for the Nd ion 17a.
Therefore, it is desirable to use iron oxide Fe ₂ O ₃ for the added metal oxide 16.
Further, since iron Fe is also contained in the Nd magnet, it is desirable to use Fe ³⁺ as an extractant from the viewpoint that iron Fe does not become an unnecessary impurity even when the precipitated Nd contains iron Fe.

When the metal oxide 16 is iron oxide Fe ₂ O ₃ , the iron oxide Fe ₂ O ₃ dissolves in the molten salt 12 as in the following formula (2) to generate iron ions Fe ³⁺ .
When the metal oxide 16 is iron oxide: Fe ₂ O ₃ → 2Fe ³⁺ + 3O ^2- (2)

The above equation (1) is specifically the following equation (3).
Dissolution of Nd ions from Nd-containing alloy: Nd + Fe3 ⁺ → ^Nd3 ++ Fe (3)
That is, Nd contained as a solid metal in the Nd-containing alloy 11a is dissolved in the iron ions Fe ³⁺ to become Nd ions 17a and is dissolved in the molten salt 12.
That is, by using a fluoride salt as the molten salt 12, the solid metal oxide 16 (iron oxide Fe ₂ O ₃ ) can be dissolved, and the eluted iron ions Fe ³⁺ are contained in the Nd-containing alloy 11a. Nd can be extracted into the molten salt 12.

In the reduction step (S14), the rare metal ions 17 (Nd ions 17a) obtained in the molten salt extraction step (S12) are reduced and recovered as a metal.
The reduction step (S14) is performed, for example, by a method of molten salt electrolysis.

When Nd is collected in the cathode 21 using the molten salt electrolysis, O ²⁻ reacts at the anode 22 because O ^{2 −} ions derived from the metal oxide are present in the molten salt 12.
That is, as represented by the following equations (4) and (5), carbon dioxide CO ₂ is generated at the anode 22.
Cathodic ^{reaction: Nd 3+ + 3e - → Nd} (4)
Anodic _{^{reaction: C + 2O 2- → CO 2}} + 4e - (5)

Conventionally, a metal halide or the like has been used as an extractant for extracting Nd ions 17a into the molten salt 12.
Therefore, a highly toxic halogen gas was generated at the anode 22 in the reduction step (S14) using the molten salt electrolysis.

However, the non-halogen gas 23 of carbon dioxide CO ₂ (or carbon monoxide CO) is generated at the anode 22 instead of the halogen gas by the above-described steps (S11 to S13).
That is, no toxic halogen gas is generated even if the molten salt electrolysis is performed in the reduction step (S14).

Note that the reduction step (S14) is not limited to the above-described method using molten salt electrolysis.
As a method of reducing the Nd ions 17a other than the electrolysis, for example, a method of adding a reducing agent of an active metal such as Ca can be used.
When a reducing agent is added, Nd can be recovered according to the following equation (6).
Reduction reaction: 3Ca + 2Nd ³⁺ → 2Nd + 3Ca ²⁺ (6)

Next, FIG. 3 is a flowchart illustrating a modification of the collection method according to the embodiment.
When the molten salt extraction reaction in the molten salt extraction step (S13) proceeds as shown in equation (3), metallic iron Fe resulting from the iron ion Fe ³⁺ of the extractant precipitates in the molten salt 12 as a metal residue 24.
Therefore, iron Fe is appropriately collected in a basket, and as shown in FIG. 3, the iron Fe is oxidized with air or the like in the oxidation step (S15).
By reusing the iron oxide Fe ₂ O ₃ obtained by oxidation of the iron Fe, which is the metal residue 24, as an extractant again, it is possible to reduce the materials consumed in the recovery operation of the rare metal 13.

  As described above, according to the recovery method according to the embodiment, the rare metal 13 can be recovered without generating a halogen gas in the reduction step (S14).

溶融塩としてLiF-CaF₂、レアメタル含有合金としてNd磁石、金属酸化物としてFe₂O₃、反応温度として850℃の条件にてNd磁石からのNdイオン溶解試験を実施した。
溶融塩中にNd磁石およびFe₂O₃を添加し、溶融塩抽出反応を12時間行った。
この結果、表１に示されるように、12時間後の溶融塩中には、Nd磁石に含まれるNdのうち70%が存在することを確認し、本手法を用いてNd磁石からNdイオンを溶解回収することが可能なことを確認した。 (Example)
Table 1 is a table showing an example of the recovery method according to the embodiment.

An Nd ion dissolution test was performed from a Nd magnet under the conditions of LiF—CaF ₂ as a molten salt, a Nd magnet as a rare metal-containing alloy, Fe ₂ O ₃ as a metal oxide, and a reaction temperature of 850 ° C.
A Nd magnet and Fe ₂ O ₃ were added to the molten salt, and a molten salt extraction reaction was performed for 12 hours.
As a result, as shown in Table 1, it was confirmed that 70% of the Nd contained in the Nd magnet was present in the molten salt after 12 hours, and Nd ions were removed from the Nd magnet using the present method. It was confirmed that dissolution and recovery were possible.

The above-mentioned 12 hours is the time from the start of the experiment to the time when the experiment was confirmed, and does not mean the time required for the molten salt extraction reaction required to recover 70% of Nd.
That is, it is considered that the time required for the molten salt extraction reaction required for recovering 70% of Nd is even shorter.

Although the embodiments and examples have been described above, the embodiments of the present invention are presented as examples, and are not intended to limit the scope of the invention.
This embodiment can be implemented in other various forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention.
This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and equivalents thereof.

  11 (11a): rare metal-containing alloy (Nd-containing alloy), 12: molten salt, 13: rare metal, 14: basket, 16: metal oxide, 17 (17a): rare metal ion (Nd ion), 21: cathode, 22 ... Anode, 23 ... Non-halogen gas, 24 ... Metal residue.

Claims (7)

A molten salt immersion step of immersing the rare metal-containing alloy in the molten salt,
A metal oxide adding step of adding iron oxide Fe ₂ O ₃ to the molten salt;
A step of extracting a rare metal contained in the rare metal-containing alloy into ions and extracting the rare metal into the molten salt. The rare metal recovery method according to claim 1, wherein the molten salt contains at least one kind of fluoride salt. The rare metal-containing alloy includes rare earth elements, Li, Be, B, Ti, V, Cr, Mn, Co, Ni, Ga, Ge, Se, Rb, Sr, Zr, Nb, Mo, Pd, In, Sb, Te, The rare metal recovery method according to claim 1 or 2, wherein the method includes at least one of Cs, Ba, Hf, Ta, W, Re, Pt, Tl, and Bi. The rare metal recovery method according to any one of claims 1 to 3, wherein the metal oxide is generated by oxidizing a metal residue obtained after the metal oxide addition step. The rare metal recovery method according to any one of claims 1 to 4, further comprising a reduction step of reducing the ions obtained in the molten salt extraction step and recovering the ions as a metal. The rare metal recovery method according to claim 5, wherein the reducing step is performed by adding a reducing agent. The rare metal recovery method according to claim 5, wherein the reduction step is performed by electrolysis.

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