JP2007231378A - Method for collecting rare earth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively collecting a large amount of rare earths while preventing the contamination due to impurities. <P>SOLUTION: The collecting method comprises: the first step of supplying a scrap of a rare earth magnet produced in a process of manufacturing a magnet, to a sulfuric acid solution having a concentration of higher than 3.0 mol/L but 6.5 mol/L or lower, dissolving at least the rare earth in the scrap of the rare earth magnet into the sulfuric acid solution, and precipitating the dissolved rare earth as a rare earth sulfate; the second step of separating precipitates containing the precipitated rare earth sulfate, from the solution; and the third step of redissolving the precipitates to remove an undissolved component in the precipitates to obtain a rare earth solution containing the dissolved rare earth sulfate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for recovering rare earth from sludge generated in a rare earth magnet manufacturing process and fine powder rare earth magnet scrap.

Conventionally, in the process of manufacturing a rare earth magnet, a large amount of sludge and tangible waste containing rare earth (rare earth elements) are generated by cutting and polishing. In addition, products using rare earth magnets (such as hard disk motors) are discarded in the city. These rare earth magnet scraps contain about 30% by mass of rare earth, and a method for collecting the rare earth has been developed.
For example, Patent Document 1 discloses a method in which an alloy scrap containing rare earth is melted while being put into a heating part of a melting furnace, and the alloy solidified from the lower part is gradually lowered to recover the alloy.

Patent Document 2 discloses a method in which a rare earth in a rare earth magnet is dissolved in a dilute nitric acid solution, a fluorine compound or oxalic acid is added to the solution, the rare earth is precipitated as a salt, and separated from iron in the solution. Is disclosed. Patent Document 3 discloses a method of dissolving rare earth with hydrochloric acid.
Furthermore, in Patent Document 4, an aqueous solution containing two or more types of rare earths and a non-aqueous organic solvent containing an extraction reagent are mixed to move the rare earths to the organic solvent, and then the rare earths in the organic solvent are reversed. A method obtained by extraction is disclosed.

JP-A-11-241127 JP-A-9-217132 JP-A-5-287405 Japanese Patent Laid-Open No. 11-100522

However, in the invention of Patent Document 1, carbon and silicon and paint applied to prevent oxidation of the rare earth magnet are simultaneously collected as a residue from a grinding machine or the like used when cutting and polishing the rare earth magnet. There has been a problem that the purity of the collected rare earth is lowered, and the performance of the rare earth magnet using the rare earth is lowered. In addition, in the inventions of Patent Documents 2 and 3, since rare earth is dissolved using nitric acid or hydrochloric acid, there is a problem that countermeasures against corrosion of the reaction vessel are necessary, and the amount of nitric acid or hydrochloric acid per liquid amount There was also a problem that the amount of rare earth dissolved was small and not practical. Furthermore, in the invention of Patent Document 4, there is a problem that complicated operations such as solvent extraction and back extraction and processing of an organic solvent are required.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a rare earth recovery method that prevents contamination of impurities and recovers a large amount of rare earths at low cost.

In the rare earth recovery method according to the present invention that meets the above-mentioned object, the concentration of rare earth magnet waste generated in the manufacturing process of the rare earth magnet exceeds 3.0 mol / L and is 6.5 mol / L or less (preferably 5.0 mol / L). The following is a first step in which at least a rare earth in the rare earth magnet scrap is dissolved in the sulfuric acid solution, and the dissolved rare earth is precipitated as a rare earth sulfate. When,
A second step of separating the precipitate containing the precipitated rare earth sulfate from the solution;
A third step of obtaining a rare earth solution in which the rare earth sulfate is dissolved by dissolving the precipitate again to remove insoluble components in the precipitate.
L represents liters (the same applies hereinafter).

Here, the rare earth magnet (RE-Fe) includes, for example, a neodymium (Nd) -iron-boron (B) system or a samarium (Sm) -cobalt (Co) system, and includes neodymium, samarium, dysprosium (Dy), One or more rare earths (rare earth elements) such as terbium (Tb), praseodymium (Pr), and cerium (Ce) are included. When the rare earth magnet is supplied to the sulfuric acid solution, it reacts as shown in formula (1), and the rare earth and iron are dissolved.
RE-Fe + nH ₂ SO ₄ → RE ³⁺ + Fe ²⁺ + nSO ₄ ²⁻ + nH ₂ ↑ (1)

Furthermore, in a high-concentration sulfuric acid solution, a rare earth sulfate is precipitated by reacting as shown in equation (2).
RE ³⁺ + Fe ²⁺ + nSO ₄ ²⁻ → RE ₂ (SO ₄ ) ₃ ↓ + Fe ²⁺ + (n−3) SO ₄ ^2-
... (2)
Here, when the concentration of the sulfuric acid solution is 3.0 mol / L or less, the amount of sulfuric acid is small, and the dissolved rare earth hardly becomes a sulfate, and when it exceeds 6.5 mol / L, the water content in the sulfuric acid solution is small. Thus, iron ions (Fe ²⁺ ) may be precipitated as iron sulfate.
Moreover, as an insoluble component isolate | separated at a 3rd process, there exists impurities, such as carbon and silicon which are mixed from a cutting device or a grinding | polishing apparatus at the time of cutting or grinding | polishing of a rare earth magnet, for example.

In the rare earth recovery method according to the present invention, in the first step, the amount of water in the sulfuric acid solution is 6 L or more and 16 L or less with respect to 1 kg of the rare earth magnet scrap.
Here, when the amount of water in the sulfuric acid solution is less than 6 L with respect to 1 kg of rare earth magnet scrap, iron sulfate precipitates when the rare earth is dissolved in the sulfuric acid solution, and when it exceeds 16 L, precipitation of rare earth sulfate The amount decreases.
In the rare earth recovery method according to the present invention, the sulfuric acid solution used in the first step contains 2.4 kg or more and 5.0 kg or less of H ₂ SO ₄ with respect to 1 kg of the rare earth magnet scrap. Yes.
Here, if the amount of H ₂ SO ₄ is less than 2.4 kg, the rare earth sulfate is difficult to precipitate, and if it exceeds 5.0 kg, the precipitated crystals become a slurry and the stirring of the sulfuric acid solution is suppressed. Undissolved material increases.

In the rare earth recovery method according to the present invention, in the first step, it is preferable that the oxidation-reduction potential of the sulfuric acid solution in which the rare earth is dissolved is −50 mV or more.
When the oxidation-reduction potential of the sulfuric acid solution in which the rare earth is dissolved is less than −50 mV, the sulfuric acid solution is foamed, and the rare earth is taken into the foam, thereby reducing the recovery rate of the rare earth. The redox potential is preferably +600 mV or less.
In the rare earth recovery method according to the present invention, the oxidation-reduction potential may be adjusted by adding one or both of an oxide and an oxidizing liquid, and in particular, the oxide is an oxidation of tangible waste of a rare earth magnet. It is preferable that it is a thing.
Examples of the oxide include potassium permanganate, and examples of the oxidizing liquid include hydrogen peroxide as a peroxide. In addition, examples of tangible scraps of rare earth magnets include defective products during the production of rare earth magnets. Moreover, the rare earth magnet scraps and tangible scraps generated in the manufacturing process of the same manufacturer can be used so that the recovered rare earths have the same composition. In addition, a metal rare earth can also be used as tangible waste.

In the rare earth recovery method according to the present invention, after the rare earth in the rare earth solution obtained in the third step is crystallized as a hydroxide, carbonate, or oxalate, the crystal is separated to obtain a rare earth salt. May be obtained.
In the rare earth recovery method according to the present invention, in the second step, after the remaining solution that recovered the precipitate containing the rare earth sulfate is crystallized, iron in the solution is precipitated and removed. The solution from which the iron has been removed is preferably used when the rare earth in the rare earth magnet scrap is dissolved in the first step.
In the rare earth recovery method according to the present invention, it is preferable to use the rare earth magnet waste sorted by manufacturer.

In the rare earth recovery method according to any one of claims 1 to 9, the rare earth magnet scrap generated in the rare earth magnet manufacturing process is supplied to a sulfuric acid solution having a concentration of more than 3.0 mol / L and not more than 6.5 mol / L. Therefore, the rare earth in the rare earth magnet scrap dissolved in the sulfuric acid solution reacts with sulfuric acid to obtain a precipitate containing rare earth sulfate, and further dissolves the precipitate to remove insoluble components in the precipitate. Thus, a rare earth solution substantially free of impurities can be obtained.

Particularly, in the rare earth recovery method according to claim 2, in the first step, the amount of water in the sulfuric acid solution is 6L or more and 16L or less with respect to 1kg of the rare earth magnet waste, so that it is dissolved in the sulfuric acid solution. The rare earth is precipitated as rare earth sulfate, and the dissolved iron ions are not precipitated as iron sulfate.
In the rare earth recovery method according to claim 3, the sulfuric acid solution used in the first step contains 2.4 kg or more and 5.0 kg or less of H ₂ SO ₄ with respect to 1 kg of rare earth magnet scrap. Therefore, rare earth sulfate is easy to deposit.

In the rare earth recovery method according to the fourth aspect, since the oxidation-reduction potential of the sulfuric acid solution in which the rare earth is dissolved in the first step is set to -50 mV or more, foaming of the sulfuric acid solution can be prevented.
In the rare earth recovery method according to the fifth aspect, since the oxidation-reduction potential is adjusted by adding one or both of the oxide and the oxidizing liquid, the oxidation-reduction potential can be easily adjusted.
In the rare earth recovery method according to the sixth aspect, since the oxide is a tangible scrap oxide of a rare earth magnet, the composition of the rare earth in the obtained rare earth solution can be made substantially the same.

In the rare earth recovery method according to claim 7, since the rare earth in the rare earth solution obtained in the third step is crystallized as a hydroxide, carbonate or oxalate, and then the crystals are separated. A rare earth salt can be obtained.
In the rare earth recovery method according to claim 8, in the second step, the remaining solution from which the precipitate containing the rare earth sulfate is recovered is crystallized, and iron in the solution is precipitated and removed. In the first step, when the rare earth magnet is dissolved, the amount of the sulfuric acid solution for dissolving the rare earth can be reduced, and in the second step, the rare earth sulfate crystals (precipitation) are used. The rare earth remaining in the remaining solution from which the product is recovered can be recovered.
In the rare earth recovery method according to claim 9, since rare earth magnet wastes sorted by manufacturer are used, rare earths of other compositions are not mixed in the collected rare earth, and the rare earth regenerated from this rare earth is used. The performance degradation of the magnet can be prevented.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is a flowchart of a rare earth recovery method according to an embodiment of the present invention.

With reference to FIG. 1, a rare earth recovery method according to an embodiment of the present invention will be described.
As rare earth magnet scraps for collecting rare earth, for example, sludge generated by cutting, polishing, etc. in the manufacturing process of a neodymium-iron-boron rare earth magnet having the same composition in the same manufacturer was used. As a result, rare earths of other compositions are not mixed in the rare earth magnets regenerated from the collected rare earths, and the performance of the rare earth magnets can be prevented from deteriorating. In addition, as a result of analyzing the rare earth in the rare earth magnet scrap in advance by using an ICP (inductively coupled plasma) apparatus, an atomic absorption apparatus or the like, the rare earth magnet scrap contains about 30 mass% rare earth (for example, 19.3 mass% neodymium, Praseodymium 7.1% by mass and dysprosium 2.8% by mass).

(First step)
For example, the rare earth magnet scrap is supplied to a sulfuric acid solution having a concentration of more than 3.0 mol / L and not more than 6.5 mol / L, and is dissolved by the reaction shown in the formula (1). Here, the amount of water in the sulfuric acid solution is, for example, 6 L or more and 16 L or less with respect to 1 kg of rare earth magnet scrap. When the amount of water in the sulfuric acid solution is less than 6 L with respect to 1 kg of rare earth magnet scrap, iron sulfate precipitates when the rare earth dissolves in the sulfuric acid solution, and when it exceeds 16 L, the precipitation amount of the rare earth sulfate is increased. Decrease. Further, when the amount of water in the sulfuric acid solution having a concentration exceeding 3.0 mol / L and not more than 6.5 mol / L is 6 L or more and 16 L or less with respect to 1 kg of rare earth magnet scrap, It is preferable that H ₂ SO ₄ is contained in an amount of 2.4 kg or more and 5.0 kg or less. If the amount of H ₂ SO ₄ is less than 2.4 kg, the rare earth sulfate is difficult to precipitate, and if it exceeds 5.0 kg, the precipitated crystals become a slurry, and the stirring of the sulfuric acid solution is suppressed and undissolved matter Will increase.

Here, when the oxidation-reduction potential of the sulfuric acid solution in which the rare earth is dissolved is less than −50 mV, for example, the oxide of the tangible scrap of the rare earth magnet generated during the production of the rare earth magnet is supplied, and the oxidation reduction of the sulfuric acid solution is performed. Increase the potential to -50 mV or higher. At this time, the pH of the sulfuric acid solution in which rare earth or the like is dissolved rises, but since the sulfuric acid concentration in the sulfuric acid solution is high, the pH is maintained at 5 or lower, so that iron ions in the sulfuric acid solution precipitate as iron sulfate. Can be prevented. In addition, when the oxidation-reduction potential of the sulfuric acid solution in which the rare earth is dissolved is −50 mV or more, it is not necessary to add an oxide.
Here, since the concentration of sulfuric acid in the sulfuric acid solution is high, the dissolved rare earth and sulfuric acid react as shown in the above formula (2), and the rare earth sulfate octahydrate (RE ₂ (SO ₄ ) ₃ · 8H precipitation of ₂ O) is produced. In this case, for example, a component (insoluble component) that does not dissolve in sulfuric acid such as carbon or silicon also dissolves and remains as a precipitate, resulting in a precipitate containing a rare earth sulfate and an insoluble component.

(Second step)
The precipitate containing the precipitated rare earth sulfate is separated from the solution by filtration. Separation of the precipitate may be performed by centrifugation. In order to recover the rare earth remaining in the remaining dissolved solution in the first step, the iron contained in the dissolved solution from which the precipitate was separated was precipitated as iron sulfate by crystallization, and then separated. When the rare earth is recovered from the next rare earth magnet scrap, it can be used instead of the sulfuric acid solution or mixed with a new sulfuric acid solution. As a result, the amount of sulfuric acid used in the first step can be reduced, and the rare earth recovery rate can be improved. In addition, nickel contained in the plating paint applied to the rare earth magnet to prevent oxidation of the rare earth magnet can be removed because it is dissolved in the solution. The recovered iron sulfate can be used as a sewage treatment agent.

(Third step)
For example, after washing the precipitate with water, the rare earth sulfate in the precipitate is dissolved in water and insoluble components are precipitated, and the precipitate is removed by filtration or the like to obtain a rare earth solution in which the rare earth sulfate is dissolved. .

Oxalic acid is added to the rare earth solution obtained in the third step to crystallize the rare earth as an oxalate, and then the rare earth oxalate crystals are separated by filtration or the like to obtain a rare earth salt. Sodium hydroxide may be added to the rare earth solution to form a hydroxide, or sodium carbonate may be added to form a carbonate. Furthermore, after the rare earth oxalate obtained is baked at 700 ° C. or higher to form a rare earth oxide, a rare earth metal oxide can be obtained by molten salt electrolysis of the rare earth oxide. In addition, since iron does not precipitate as iron sulfate (iron sulfate), it is not necessary to reduce iron by molten salt electrolysis, and electric power can be significantly reduced.

Examples carried out by applying the rare earth recovery method of the present invention will be described. First, rare earth magnet scraps having sludge and fine powder generated by cutting and polishing in the manufacturing process of a neodymium-iron-boron rare earth magnet having the same composition manufactured by the same manufacturer were collected. When the collected rare earth magnet scraps were measured by ICP, they contained 68.9% by mass of iron, 19.3% by mass of neodymium, 7.1% by mass of praseodymium, and 2.8% by mass of dysprosium.

First, 230 kg of this rare earth magnet scrap (including 60 kg of rare earth) was supplied to 3000 L of a 4 mol / L sulfuric acid solution to dissolve the rare earth and iron. The sulfuric acid solution was prepared by dissolving 1200 kg of 98 wt% sulfuric acid in 2500 L of water. H ₂ SO ₄ (pure sulfuric acid) in the sulfuric acid solution is 1182 kg. Further, the oxidation-reduction potential of the sulfuric acid solution was about -200 mV. Next, 61 kg (including 16.2 kg of rare earth) of rare earth magnet tangible oxide generated during the production of the rare earth magnet is supplied to the sulfuric acid solution in which the rare earth is dissolved, and the oxidation-reduction potential of the sulfuric acid solution is set to -50 mV or more. Raised. The dissolved rare earth reacts with sulfuric acid and precipitates as rare earth sulfate.

Next, the precipitate containing rare earth sulfate and insoluble components is filtered to remove the solution. The deposit was obtained as 96 kg containing 1.8 kg of insoluble components, and contained 0 kg of iron, 20.1 kg of neodymium, 7.5 kg of praseodymium, and 3.3 kg of dysprosium.
The solution (2775 L) from which the precipitates were separated contained 104.4 kg of iron, 9.3 kg of neodymium, 3.3 kg of praseodymium, and 1.2 kg of dysprosium. Here, iron contained in the solution was crystallized and recovered as iron sulfate. The remaining solution from which the iron has been recovered is mixed with a fresh sulfuric acid solution instead of the sulfuric acid solution when the rare earth is dissolved from the next rare earth magnet scrap, and the rare earth remaining in the dissolved solution is recovered. As a result, the amount of sulfuric acid used in the first step can be reduced, and the recovery rate of rare earth is improved, so that the recovery rate is substantially 100%.

The precipitate is washed with water and then dissolved in water to dissolve the rare earth sulfate in the precipitate and to precipitate insoluble components. The precipitate is removed by filtration or the like, and the rare earth sulfate dissolved in the rare earth sulfate is dissolved. A solution was obtained. Further, oxalic acid was added to the rare earth solution to crystallize the rare earth as an oxalate, and then the rare earth oxalate crystals were separated by filtration to obtain 63 kg of rare earth oxalate decahydrate (RE). ₂ ((COO) ₂ ) ₃ · 10H ₂ O was obtained. The rare earth oxalate contained 96%, 83%, and 100% of neodymium, praseodymium, and dysprosium contained in the rare earth magnet scrap and tangible scrap, respectively.

This rare earth oxalate was baked at 700 ° C. or higher to obtain a rare earth oxide, and a rare earth metal was obtained by electrolysis of the rare earth oxide by molten salt electrolysis. Since this metal rare earth was obtained from rare earth magnet scraps having the same composition, rare earths of other compositions were not mixed, and the performance of the rare earth magnet manufactured using this rare earth magnet was not deteriorated.

The present invention is not limited to the above-described embodiment, and can be changed without changing the gist of the present invention. For example, a part or all of the above-described embodiment and modification examples are combined. Thus, the rare earth recovery method of the present invention is also included in the scope of the present invention.
For example, in the rare earth recovery method of the above embodiment, neodymium-iron-boron type was used as the rare earth magnet scrap, but samarium-cobalt type may be used. Moreover, although the oxidation-reduction potential was adjusted with the tangible scrap oxide of the rare earth magnet, the oxidation-reduction potential may be adjusted by adding one or both of the oxide and the oxidizing liquid.

It is a flowchart of the collection | recovery method of the rare earths concerning one embodiment of this invention.

Claims (9)

The rare earth magnet scrap generated in the manufacturing process of the rare earth magnet is supplied to a sulfuric acid solution having a concentration exceeding 3.0 mol / L and not more than 6.5 mol / L, and at least the rare earth in the rare earth magnet scrap is dissolved in the sulfuric acid solution. A first step of precipitating the dissolved rare earth as a rare earth sulfate;
A second step of separating the precipitate containing the precipitated rare earth sulfate from the solution;
And a third step of obtaining a rare earth solution in which the rare earth sulfate is dissolved by dissolving the precipitate again to remove insoluble components in the precipitate. 2. The rare earth recovery method according to claim 1, wherein in the first step, the amount of water in the sulfuric acid solution is 6L or more and 16L or less with respect to 1 kg of the rare earth magnet scrap. Recovery method. 3. The rare earth recovery method according to claim 2, wherein the sulfuric acid solution used in the first step contains 2.4 kg or more and 5.0 kg or less of H ₂ SO ₄ with respect to 1 kg of the rare earth magnet scrap. A method for collecting rare earths. The rare earth recovery method according to any one of claims 1 to 3, wherein, in the first step, an oxidation-reduction potential of a sulfuric acid solution in which the rare earth is dissolved is set to -50 mV or more. Method. 5. The rare earth recovery method according to claim 4, wherein the oxidation-reduction potential is adjusted by adding one or both of an oxide and an oxidizing liquid. 6. The rare earth recovery method according to claim 5, wherein the oxide is an oxide of a tangible scrap of a rare earth magnet. The method for recovering a rare earth according to any one of claims 1 to 6, wherein the rare earth in the rare earth solution obtained in the third step is crystallized as a hydroxide, carbonate, or oxalate, A method for recovering a rare earth, wherein the rare earth salt is obtained by separating the crystals. The rare earth recovery method according to any one of claims 1 to 7, wherein in the second step, the remaining solution obtained by recovering the precipitate containing the rare earth sulfate is crystallized in the solution. A method for recovering rare earths, comprising depositing and removing the iron, and then using the solution from which the iron has been removed at the time of dissolving the rare earth in the rare earth magnet scrap in the first step. The method for recovering rare earth according to any one of claims 1 to 8, wherein the rare earth magnet scrap is separated for each manufacturer.

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