JP2006063370A - Method for recovering rare earth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering rare earths where the intrusion of impurities is prevented, and large quantities of rare earths are recovered at a low cost. <P>SOLUTION: The method for recovering rare earths comprises: a first stage where rare earth magnet scrap produced from either or both of the production process of a rare earth magnet and the city is fed to sulfuric acid, and rare earths in the rare earth magnet scrap are dissolved in the sulfuric acid; a second stage where components which do not dissolve in the sulfuric acid are removed so as to obtain a rare earth-containing solution; a third stage where an ammonia aqueous solution is added to the solution; a fourth stage where the ammonium salt of rare earth-sulfuric acid produced by the addition of the ammonia aqueous solution is crystallized; and a fifth stage where the crystals of the ammonium salt of rare earth-sulfuric acid produced in the fourth stage are recovered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for recovering rare earth from rare earth magnet scraps such as sludge and tangible scrap generated in the manufacturing process of rare earth magnets and waste rare earth magnets generated in the city.

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, in Patent Document 1, an alloy scrap containing rare earth is melted while being charged into a heating part of a melting furnace, and the alloy solid containing rare earth metal is recovered by gradually lowering the solidified alloy from the lower part and recovering the alloy. A method is disclosed.

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 instead of dilute nitric acid solution.
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 for separating and recovering rare earth metal ions 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 required, 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.

The method for recovering a rare earth according to the present invention in accordance with the above object is to supply the rare earth magnet scrap generated from one or both of the rare earth magnet manufacturing process and the market to sulfuric acid, and the rare earth in the rare earth magnet scrap is converted to the sulfuric acid. A first step of dissolving in
Removing a component that does not dissolve in sulfuric acid to obtain a solution containing the rare earth;
A third step of adding an aqueous ammonia solution to the solution;
A fourth step of crystallizing the rare earth ammonium sulfate salt produced by the addition of the aqueous ammonia solution;
And a fifth step of recovering the rare earth ammonium sulfate crystals produced in the fourth step.

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 a rare earth magnet is supplied to sulfuric acid, it reacts as shown in formula (1) and the rare earth and iron are dissolved.
RE-Fe + nH ₂ SO ₄ → RE ³⁺ + Fex ⁺ + nSO ₄ ²⁻ + nH ₂ ↑ (1)

In addition, impurities contained in the rare earth magnet (for example, one or both of carbon and silicon mixed from the cutting device or the polishing device during cutting or polishing of the rare earth magnet, or rare earth magnet to prevent oxidation of the rare earth magnet) Since the paint applied to the magnet is deposited as an insoluble component, it is separated from sulfuric acid (dissolved solution) in which the rare earth is dissolved by filtration or the like.

Next, as shown in the formula (2), an aqueous ammonia solution is added to the solution and crystallized to deposit rare earth as rare earth ammonium sulfate (NH ₄ RE (SO ₄ ) ₂ ). It can isolate | separate and can isolate | separate with the iron and nickel which are melt | dissolving in a solution (when plating, it is the same below).
RE ³⁺ + Fex ⁺ + nSO ₄ ²⁻ + NH ₄ OH
→ NH ₄ RE (SO ₄ ) ₂ + Fe ^{x +} + (n−2) SO ₄ ²⁻ (2)

In the rare earth recovery method according to the present invention, the rare earth magnet waste is supplied to sulfuric acid to dissolve the rare earth, so that impurities can be easily removed. Further, since an aqueous ammonia solution is added to the solution and crystallized to precipitate a rare earth ammonium sulfate salt, iron and nickel in the rare earth magnet can be removed. In addition, since sulfuric acid is used for melt | dissolution of rare earths, it is not necessary to take corrosion countermeasures, for example to reaction vessels made from stainless steel.

Further, when a predetermined amount of sulfuric acid is used with respect to the amount of rare earth magnet scrap, the recovery rate and purity of the rare earth can be increased. Furthermore, when the pH is maintained at 1 or less in the first step, more rare earth can be dissolved in the sulfuric acid, and when the pH is maintained at 2 or less in the third step, the rare earth is Iron in the magnet scrap is hardly formed as a precipitate (crystal), and precipitation of iron and iron compounds can be prevented, so that the purity of the rare earth to be recovered can be increased.

When rare earth magnet scraps are collected for each rare earth magnet scrap separated by manufacturer, rare earths of other compositions are not mixed in the collected rare earth, and the performance of the rare earth magnet regenerated from this rare earth is reduced. 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 the rare earth magnet scrap, for example, sludge and tangible scrap generated by cutting and polishing in a manufacturing process of a neodymium-iron-boron rare earth magnet were used. Here, in the present embodiment, rare earth magnet scraps manufactured from the same manufacturer and obtained from rare earth magnets having the same composition are 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 with 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, 30 mass% neodymium, terbium 1 0.5 mass% and dysprosium 2.5 mass%). The tangible scrap may be a rare earth magnet scrap separated from a hard disk or the like discarded in the city.

(First step)
For example, the rare earth magnet scrap was supplied to sulfuric acid having a concentration of 1.5 mol / L or more and 3.0 mol / L or less, and dissolved as shown in the formula (1).
Here, if the concentration of sulfuric acid is less than 1.5 mol / L, the rare earth in the rare earth magnet scrap remains undissolved, and if it exceeds 3.0 mol / L, the rare earth sulfate precipitates when the rare earth dissolves in sulfuric acid. To do.

In addition, sulfuric acid is used in an amount of, 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 sulfuric acid used is less than 6 L with respect to 1 kg of rare earth magnet scrap, rare earth sulfate precipitates when the rare earth dissolves in sulfuric acid, and when it exceeds 16 L, crystallization is performed in the fourth step described later. The amount of crystallization decreases.

Furthermore, when sulfuric acid having a concentration of 1.5 mol / L or more and 3.0 mol / L or less is used in an amount of 6 L or more and 16 L or less with respect to 1 kg of rare earth magnet scrap, H ₂ SO _{4 in} sulfuric acid is 1 It is preferable that the content is not less than 4 kg and not more than 2.4 kg. When the amount of H ₂ SO ₄ is less than 1.4 kg, the rare earth in the rare earth magnet scraps remains undissolved, and when it exceeds 2.4 kg, sulfuric acid is wasted and the rare earth sulfate is liable to precipitate.

Here, when the rare earth magnet scrap is supplied to the sulfuric acid, the pH of the sulfuric acid in which the rare earth or the like is dissolved rises. Therefore, sulfuric acid for adjustment is further added to set the upper limit of the pH of the solution, preferably 0 to the lower limit. Keep it at about 5. When the pH of the solution exceeds 1, in the following steps, the amount of ammonia water added to the solution decreases, and the amount of crystallization of the rare earth ammonium sulfate salt produced decreases, that is, the amount of rare earth recovered is reduced. Decrease.

(Second step)
When the rare earth magnet scrap is supplied to sulfuric acid and the rare earth and iron in the rare earth magnet scrap are dissolved, the component does not dissolve in sulfuric acid (hereinafter referred to as insoluble component), for example, one or both of carbon and silicon Remains undissolved. This insoluble component is removed by filtration to obtain a solution in which rare earth and iron are dissolved. The insoluble component may be removed by centrifugation. The concentration of the rare earth in the solution can be calculated from the weight of the rare earth in the rare earth magnet scrap measured in advance, and is preferably 12 g / L or more and 60 g / L or less. Here, if the concentration of the rare earth in the solution is less than 12 g / L, the amount of crystallization in the following steps decreases, and if it exceeds 60 g / L, the rare earth sulfate (RE ₂ (SO _{2 4} ) ₃ ) precipitates.

(Third step)
Ammonia water (ammonia aqueous solution) is added to the resulting solution to prepare a crystallization solution. Here, since the crystallization liquid becomes alkaline when ammonia water is added, another adjustment sulfuric acid is added to set the upper limit of the pH to 2, preferably 1, and to keep the lower limit at about 0.5. When the pH of the crystallization solution exceeds 2, iron and iron compounds are precipitated, and the purity of the rare earth recovered as the rare earth ammonium sulfate is lowered. Moreover, it is preferable that the ammonia water added to a solution is added more than 0 and 2 L or less per 1 kg of rare earths in rare earth magnet scraps. If it is added in excess of 2 L, iron and iron compounds precipitate, so the purity of the collected rare earth decreases.

(4th process)
Since the crystallization liquid is about 50 to 60 ° C., it is cooled to a low temperature, for example, 10 to 30 ° C., and crystallized while stirring. As shown in the formula (2), a rare earth ammonium sulfate salt is precipitated by crystallization.
The crystallization time is preferably 12 hours or more and 18 hours or less. If the crystallization time is less than 12 hours, the amount of crystallization is small, and if it exceeds 18 hours, an iron sulfate ammonium salt is produced and the purity of the rare earth ammonium sulfate salt is lowered. To do.

(5th process)
Crystals (precipitates) of rare earth ammonium sulfate formed by crystallization are collected by filtration. During filtration, the crystallized solution in which iron was dissolved was removed by washing with water. This can prevent iron from being mixed into the rare earth ammonium sulfate. Further, nickel contained in the plating applied to the rare earth magnet in order to prevent oxidation of the rare earth magnet can be removed because it is dissolved in the crystallization solution.

Furthermore, the rare earth ammonium sulfate salt obtained in the fifth step can be baked at 1380 ° C. or more to obtain a rare earth oxide, and a rare earth metal can be obtained by electrolysis of the rare earth oxide by molten salt electrolysis. In addition, since iron does not precipitate as an iron sulfate ammonium salt, it is not necessary to reduce iron by molten salt electrolysis, and electric power can be significantly reduced.

Further, the rare earth remaining in the filtrate obtained by removing the rare earth ammonium sulfate obtained in the fifth step can be recovered as rare earth oxalate or rare earth carbonate by adding oxalic acid or sodium carbonate to the filtrate. Furthermore, iron remaining in the filtrate from which the rare earth has been removed can be recovered as iron hydroxide by oxidation with calcium hydroxide, sodium hydroxide, or the like. This iron hydroxide can be used as a cement raw material.

Applying the method for recovering rare earth according to one embodiment of the present invention, it is generated by cutting, polishing, etc. in a process of manufacturing a rare earth magnet of the neodymium-iron-boron system having the same composition manufactured by the same manufacturer. Rare earth was recovered from rare earth magnet scraps consisting of sludge and tangible scraps. The rare earth magnet scrap used contained 65% by mass of iron, 30% by mass of neodymium, 1.5% by mass of terbium, and 2.5% by mass of dysprosium, as measured by ICP.

First, 100 kg of this rare earth magnet scrap (including 34 kg of rare earth) was supplied to 1000 L of 2 mol / L sulfuric acid to dissolve the rare earth and iron. Incidentally, the amount of sulfuric acid is 10L relative rare earth magnets scraps 1 kg, with respect to rare earth magnets scraps 1 kg, H ₂ SO ₄ in sulfuric acid is used 1.96 kg. Here, when the rare earth magnet scrap is supplied to the sulfuric acid, the pH of the sulfuric acid in which the rare earth is dissolved rises, so sulfuric acid is added to keep the pH of the solution at 1 or less.

Next, insoluble components are removed by filtration. Here, the dissolution liquid decreased to about 900 L due to evaporation and filtration during the dissolution reaction of the rare earth magnet. Since this dissolved solution contains 34 kg of rare earth, the concentration of rare earth in the dissolved solution is approximately 37.8 g / L.
Further, 60 L of ammonia water is added to the solution so that the pH of the solution does not exceed 2 while adding sulfuric acid, that is, 0.6 L of ammonia water per 1 kg of rare earth magnet scrap.

Since the dissolved solution to which ammonia water is added, that is, the crystallization solution is approximately 50 to 60 ° C., the crystallization solution is cooled to a low temperature, for example, 10 to 30 ° C., and crystallization is performed with stirring. Crystallization was performed for 12 hours or more and 18 hours or less.
Further, the crystallized solution containing the crystallized rare earth ammonium sulfate salt is filtered, washed with water to remove the crystallized solution in which iron is dissolved, and 70 kg of rare earth ammonium sulfate tetrahydrate (NH ₄ RE (SO ₄ ) ₂ · 4H ₂ O) was obtained. In this rare earth ammonium sulfate, 80%, 45%, and 25% of neodymium, terbium, and dysprosium contained in the rare earth magnet scrap could be recovered, respectively.

This rare earth ammonium sulfate salt was baked at 1380 ° C. or more 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 uses what was obtained from rare earth magnet scraps having the same composition, rare earths of other compositions are not mixed, and the performance of rare earth magnets manufactured using this rare earth magnet does not deteriorate. .

Note that oxalic acid was added to the filtrate from which the rare earth ammonium sulfate salt had been removed to recover the rare earth oxalate salt. As a result, 10%, 50%, and 45% were recovered from neodymium, terbium, and dysprosium contained in the rare earth magnet scrap, respectively, and 90%, 95%, and 70% were recovered together with the rare earth ammonium sulfate salt. . Further, iron remaining in the filtrate was oxidized with calcium hydroxide and recovered as iron hydroxide.

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.

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

Claims (8)

A first step of supplying rare earth magnet scrap generated from either or both of the rare earth magnet manufacturing process and the city to sulfuric acid, and dissolving the rare earth in the rare earth magnet scrap in the sulfuric acid;
Removing a component that does not dissolve in sulfuric acid to obtain a solution containing the rare earth;
A third step of adding an aqueous ammonia solution to the solution;
A fourth step of crystallizing the rare earth ammonium sulfate salt produced by the addition of the aqueous ammonia solution;
And a fifth step of recovering crystals of the rare earth ammonium sulfate salt produced in the fourth step. 2. The rare earth recovery method according to claim 1, wherein the sulfuric acid used in the first step has a concentration of 1.5 mol / L or more and 3.0 mol / L or less. 3. The rare earth recovery method according to claim 2, wherein the sulfuric acid is used in an amount of 6 L to 16 L with respect to 1 kg of the rare earth magnet scrap. 4. The rare earth recovery method according to claim 3, wherein the sulfuric acid contains 1.4 kg or more and 2.4 kg or less of H ₂ SO ₄ with respect to 1 kg of the rare earth magnet scrap. Rare earth recovery method. The method for recovering a rare earth according to any one of claims 1 to 4, wherein the solution contains a rare earth in a range of 12 g / L to 60 g / L. The rare earth recovery method according to any one of claims 1 to 5, wherein the first step is further performed while adding sulfuric acid for adjustment to keep the pH at 1 or less. Collection method. The rare earth recovery method according to any one of claims 1 to 6, wherein the third step is performed while further adding another sulfuric acid for adjustment and keeping the pH at 2 or less. Rare earth recovery method. The rare earth recovery method according to any one of claims 1 to 7, wherein the rare earth is recovered for each rare earth magnet scrap obtained by separating the rare earth magnet scrap for each manufacturer.

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