JP5146658B2 - Recovery method of rare earth elements - Google Patents

Description

  The present invention relates to a method for recovering a rare earth element from a raw material containing a rare earth magnet alloy, such as grinding powder generated during processing of a rare earth magnet, and waste powder generated during pulverization or molding.

  In recent years, rare earth magnets are widely used in various motors and sensors used in HDDs, air conditioners, mobile phones and the like.

  On the other hand, rare earth elements, which are raw materials, are limited in their country of origin and prices are rising due to resource issues. Therefore, there is a strong demand to collect and recycle valuable materials from magnet powder and scraps and defective scrap generated during the production of magnets.

  As a method for recovering rare earth elements, Japanese Patent Application Laid-Open No. 62-83433 (Patent Document 1) discloses a rare earth element salt prepared by heating a rare earth element-iron-containing alloy by air oxidation and then using an acid elution method using a strong acid. A method is disclosed in which it is produced, dissolved in the filtrate, and separated by filtration. This method is advantageous in that iron is an oxide that is hardly soluble in an acid and the amount of acid used is reduced. However, under the oxidation conditions of this method, metal Fe remains and a large amount of hydrogen is generated when dissolving a strong acid, which is a safety problem, the iron content is high in quality, and the elution rate of rare earth elements There is a low problem.

In Japanese Patent Laid-Open No. 01-183415 (Patent Document 2), scraps of rare earth magnets and the like are dissolved in acid (HCl) to separate and remove insoluble residues, and an oxidizing agent (HNO ₃ ) is added to prepare an oxalic acid solution. In addition, it is disclosed that the rare earth element is precipitated as oxalate by adjusting to a predetermined pH. However, this method is dangerous because hydrogen gas is generated when the acid is dissolved, and there is a problem that a large amount of acid is used to dissolve almost the entire amount of scrap.

  In Japanese Patent Application Laid-Open No. 05-287405 (Patent Document 3), a slurry is maintained with an acid at a pH of 3 to 5 in the presence of an oxidizing agent to selectively leach rare earth elements, and the resulting leachate contains alkali carbonate or carbonic acid. A method is disclosed in which a hydrogen alkali is added to separate a rare earth element as a sparingly soluble salt in water. However, this method has problems such as generation of hydrogen gas, increase in the amount of acid used, and mixing of iron into the rare earth carbonate.

In Japanese Patent Application Laid-Open No. 09-217132 (Patent Document 4), while circulating air in a slurry, a dilute nitric acid solution is added to maintain the pH at 5 or higher, and a metal containing rare earth and cobalt is dissolved at 50 ° C. or lower. A method of separating by filtration from an insoluble element compound containing iron, and adding a fluorine compound or oxalic acid to the rare earth-containing nitrate solution to precipitate a rare earth fluoride or rare earth oxalate, and a cobalt-containing nitric acid solution And a method of separating by filtration. However, in this method, there is a risk of using nitric acid, which is expensive and has regulated drainage, and generating toxic NO ₂ gas.

  Japanese Patent Application Laid-Open No. 2007-231379 (Patent Document 5) supplies rare earth magnet scraps to a sulfuric acid solution having a concentration of 1.5 mol / L or more and 3.0 mol / L or less, dissolves rare earths in the scraps, and insoluble components. A method is disclosed in which an ionic substance having a molecular weight smaller than that of rare earth is added and then crystallized to precipitate and collect rare earth sulfate.

However, this method uses a highly dangerous sulfuric acid, and it is necessary to calcinate the sulfate at a high temperature in order to obtain an oxide. There is a problem of generation of harmful SO ₂ gas and mixing of S into the oxide. is there.

JP-A-62-83433 Japanese Patent Laid-Open No. 01-183415 JP 05-287405 A JP 09-217132 A JP 2007-231379 A

  An object of the present invention is to solve the problems of conventional recovery methods and to provide a method for recovering rare earth elements excellent in economy and safety.

As a result of intensive investigations aimed at solving the above problems, the present inventors heated rare earth magnet alloys, particularly rare earth-iron alloy waste powders such as magnet sludge, to oxidize by heating to 800 ° C. or higher, and then into water. This oxide is added to form a slurry, and heated, particularly while maintaining the temperature at 70 ° C. or higher, concentrated hydrochloric acid is preferably 0.20 to 0.70 times the theoretical amount (equivalent) required for dissolving the total amount of oxide for 10 minutes. After adding for 5 hours and keeping at a predetermined temperature, preferably an alkaline solution is added so that the pH is 2.0 to 6.0, and Fe is precipitated as iron hydroxide, and the solution and solid matter are Separating, and if necessary, separating rare earth element-containing solution obtained by solvent separation into light rare earth element and heavy rare earth element or each rare earth element And being able to be collected safely And finding, the present invention has been accomplished.

Accordingly, the present invention provides the following rare earth element recovery method.
Claim 1:
(A) heating a raw material containing a rare earth magnet alloy to 800 ° C. or higher in an oxidizing atmosphere to form an oxide of the alloy component;
(B) a step of mixing the oxide and water to form a slurry, and adding hydrochloric acid while heating;
(C) adding an alkali while heating the resulting solution;
(D) A method for recovering a rare earth element, comprising a step of separating an undissolved and precipitated solid and a solution containing the rare earth element.
Claim 2 :
Step (B) and recovery process of claim 1 Symbol placement heating temperature (C) is 70 ° C. or higher, respectively.
Claim 3 :
The method according to claim 1 or 2 , wherein the pH for alkali adjustment in the step (C) is 2.0 to 6.0.
Claim 4 :
As a step between steps (C) and step (D), oxidizing agent added a solution of divalent of claims 1 to 3 comprising the step of oxidizing the iron ions to trivalent according to any one of Collection method.
Claim 5 :
The recovery method according to claim 4 , wherein the oxidizing agent is sodium hypochlorite.
Claim 6 :
The recovery method according to any one of claims 1 to 5 , wherein the oxide obtained in the step (A) has a mass increase of 0.15% or less when heated in air at 900 ° C for 1 hour.
Claim 7 :
The collection method according to any one of claims 1 to 6 , wherein a mixing ratio (mass ratio) of the oxide and water in the step (B) is water: oxide = 0.5 to 5: 1.
Claim 8 :
The concentration of hydrochloric acid in step (B) is 10 to 35% by mass, the amount of hydrochloric acid added is 0.20 to 0.70 times the theoretical amount (equivalent) required to dissolve the total amount of oxide, and the addition time is 10 The recovery method according to any one of claims 1 to 7 , wherein the recovery time is from min to 5 hours.
Claim 9 :
The recovery method according to any one of claims 1 to 8 , wherein the alkali in the step (C) is a 10 to 50 mass% NaOH solution.
Claim 10 :
The recovery method according to any one of claims 1 to 9 , wherein the solution containing the rare earth element obtained in the step (D) is separated and recovered into a light rare earth element and a heavy rare earth element or each rare earth element by a solvent extraction method.
Claim 11 :
The recovery method according to claim 10 , wherein the extractant used for solvent extraction is 2-ethylhexyl phosphate mono-2-ethylhexyl ester or di-2-ethylhexyl phosphate.
Claim 12 :
The recovery method according to any one of claims 1 to 11 , wherein the raw material containing the rare earth magnet alloy is waste powder of a rare earth magnet.

  According to the present invention, inexpensive hydrochloric acid can be used, the amount of hydrochloric acid can be reduced, the risk of hydrogen gas generation can be reduced, and the recovery rate of rare earth elements can be improved. A method for recovering rare earth elements having excellent properties is provided.

  In the present invention, as a raw material used in the recovery method, a powder containing iron generated in a manufacturing process of a magnet made of a rare earth alloy or the like, particularly a waste powder, is mainly used. Examples of the powder include waste powder sludge generated in a pulverization process, a molding process, a processing process, and the like. In addition, a lump of defective scrap that has been pulverized by coarse pulverization / fine pulverization mechanical pulverization such as a stamp mill, jaw crusher, brown mill, and jet mill can also be used.

  First, in step (A), the raw material containing the rare earth magnet alloy, particularly the waste powder sludge of the rare earth-Fe-B magnet is heated in an oxidizing atmosphere, particularly heated to a temperature of 800 ° C. or higher and oxidized.

  As waste powder sludge, there are grinding powder, cutting powder, polishing powder, etc. that are generated when a magnet is processed, and it is usually processed by a wet method using a liquid such as water if necessary. Sludge containing about mass%). In addition, non-standard waste powder generated at the time of pulverizing the magnet alloy, defective powder at the time of molding, etc. can be used, and these are usually powders having a particle size of 1 mm or less, preferably 0.5 mm or less. Can be used by. If the particle size exceeds 1 mm, it takes a long time to oxidize.

  In the present invention, even if magnet sludge such as rare earth-Fe-N or Sm-Co is mixed, it can be recovered.

  Although these powders are easily ignited, burned and oxidized in a dry state, they are still insufficiently oxidized by being burned, and metal Fe remains on the order of several to 20% (mass%). In order to oxidize this residual metal Fe, it has been found effective to heat in an oxidizing atmosphere at a temperature of 800 ° C. or higher for 15 minutes or longer.

Preferred oxidation conditions are a sludge temperature in air of 800 ° C. or higher and 1200 ° C. or lower, more preferably 850 ° C. or higher and 1100 ° C. or lower. The higher the temperature, the shorter the time, but preferably 30 minutes or longer, More preferably, one hour or more is required. Usually, a holding time of 3 hours or less is preferable. However, an inert gas may be included in the oxidizing atmosphere. When the heating temperature is low, oxidation of metal Fe becomes insufficient, and hydrogen gas is generated and divalent Fe is generated when hydrochloric acid is dissolved. On the other hand, if the temperature is too high, there will be a problem of wasting heating energy and the powder becoming baked. If the time is short, a large amount of unoxidized Fe remains. As a result of identification by X-ray diffraction, the oxide powder thus oxidized was confirmed to contain Fe ₂ O ₃ , RFeO ₃ (R is a rare earth element), and CoFe ₂ O ₄ in the case of an R—Fe—B magnet. B has not been identified, but appears to exist as RBO ₃ .

  As the oxidizer, an ordinary box-type electric furnace, tunnel kiln, rotary kiln or the like can be used. The oxidation may be performed in two or more stages. That is, combustion powder once stabilized after burning (metal Fe remains) can be oxidized again under the above-described temperature and time oxidation conditions.

  The amount of unoxidized metallic Fe can be estimated by measuring the peak intensity of Fe by powder X-ray diffraction or measuring the increase in mass when the powder is heated again. As the oxide powder used in the present invention, the peak of Fe is not observed by X-ray diffraction, and the mass increase when heated at 900 ° C. for 1 hour is 0.15% or less, preferably 0.10% or less. It is desirable to be. Insufficient oxidation increases the generation of hydrogen, and metal Fe elutes as divalent and does not precipitate as iron hydroxide by pH adjustment in the subsequent step (C). In this case, the amount of oxidizing agent used is increased for precipitation, which is not desirable.

Next, in the step (B), while stirring the slurry of water: oxidized powder = 0.5-5: 1 (mass ratio), it is heated to 70 ° C. or higher, preferably 80 ° C. or higher and lower than 100 ° C. Add 0.20 to 0.70 volumes of hydrochloric acid in 10 minutes to 5 hours. Thereafter, the temperature is preferably maintained for 10 minutes to 2 hours. In this step (B), Fe ₂ O ₃ in the oxide powder remains undissolved and the rare earth compound is preferentially dissolved.

  The concentration of hydrochloric acid is not particularly limited, but is preferably 10% by mass or more so as not to prevent the selective elution of rare earth elements. More preferably, it is 30% by mass or more. The upper limit is usually 35% by mass or less.

  The amount of hydrochloric acid added can be 0.20 to 0.70 times the theoretical amount (equivalent) required to dissolve the total amount of oxide, but the elution rate can be prevented from decreasing, and the amount of neutralizing agent used is economical. Is.

  The addition time of hydrochloric acid is preferably 10 minutes or more and 5 hours or less in order to promote selective elution of rare earth elements.

  The holding time is preferably about 10 minutes to 2 hours in order to reduce Fe elution.

  The heating is preferably steam heating, but other heating means such as a throwing heater can also be used.

  If the temperature is too low, the elution of rare earth elements will be insufficient, and the elution of iron oxide will increase, making it impossible to selectively elute rare earth elements.

  Next, in step (C), an alkali is added while maintaining the temperature, and the pH is adjusted to 2.0 to 6.0, preferably 2.0 to 4.0. As the alkali, NaOH, ammonia, KOH or the like can be used, but NaOH is preferable in terms of economy and waste liquid treatment.

  Thereby, the partly eluted Fe present in the solution is precipitated as a hydroxide and removed from the solution as a solid.

  Fe ions remaining in the solution even after pH adjustment are those in which a small amount of unoxidized metallic Fe is eluted and exist as divalent ions. By adding an oxidizing agent to oxidize divalent Fe ions to trivalent ions, the hydroxide easily precipitates, and finally 99% or more of Fe can be precipitated and removed.

  As an oxidizing agent, sodium hypochlorite, perchloric acid, etc. can be oxidized by bubbling air or oxygen into the solution, but sodium hypochlorite is economically and instantly oxidized. Is preferable.

  The amount of the oxidizing agent may be an amount that can oxidize divalent Fe ions to trivalent, and depends on the amount of metal Fe remaining in the oxide. An excess amount of 10 to 20% by mass is preferable to a necessary amount for oxidizing Fe ions to trivalent.

  The concentration of the NaOH solution is not limited. However, when the solution is too thick, it is necessary to control the addition amount more strictly. When the solution is too thin, the volume of the solution increases and it is not economical. The concentration of the NaOH solution is 10 to 50% by mass, preferably 20 to 30% by mass.

  Moreover, 80% by mass or more of Co is dissolved by the recovery method of the present invention, and can be recovered as Co hydroxide by neutralization after recovery of rare earth elements, and B is processed by evaporative concentration recovery or wastewater treatment equipment. Is done.

  Next, in the step (D), the solution in which the solid mainly composed of iron oxide and the rare earth element are eluted is separated by a usual method such as suction filtration using a filter press, a centrifuge, or a Nutsche.

  The obtained solution contains rare earth elements such as Nd, Pr, Dy, and Tb, which are magnet components. In the production of high-performance magnets, two or more types of magnet alloy powders composed of light rare earth and heavy rare earth are mixed, and a heavy rare earth rich phase is precipitated at the grain boundary to improve the characteristics. . Therefore, it is desirable to separate each rare earth element, not as a mixed rare earth.

  Therefore, in order to separate light rare earth elements (Nd, Pr) and heavy rare earth elements (Dy, Tb) or each rare earth element from the above solution, a separation step by a solvent extraction method can be added. In the solvent extraction method, when Fe is mixed, the purification of the rare earth element is adversely affected. Therefore, it is desirable to remove as much as possible in the previous step, and the method of the present invention can reduce Fe to the extent that it is not affected. If necessary, a step of removing Fe can be added before step (D).

  As an extracting agent used for solvent extraction, PC-88A (2-ethylhexyl phosphate mono-2-ethylhexyl ester) or D2EHPA (di-2-ethylhexyl phosphate) is used.

  The separated rare earth element is recovered as an oxalate by adding a precipitant, for example, oxalic acid, and is converted into an oxide by heating to 800 to 1000 ° C. Using this oxide as a starting material, a rare earth metal is produced by a molten salt electrolysis method or a metal thermal reduction method and used again as a magnet material.

  Although the present invention has been described in detail above, the present invention is characterized in that (1) oxidation of metal Fe is performed by heating in step (A), and (2) the slurry heated in step (B) is converted into hydrochloric acid. And selectively eluting rare earth elements, (3) precipitating partly eluted Fe as hydroxide by adjusting the pH in step (C), and (4) solid in step (D). A rare earth element-containing solution obtained by separation is separated into a light rare earth element and a heavy rare earth element or each rare earth element by a solvent extraction method.

  Hereinafter, the effect will be clarified by examples. The scope of the present invention is not limited by this embodiment. In the following examples, “%” means “% by mass” unless otherwise specified.

[Examples 1 to 8, Reference Examples 1 and 2 ]
As magnetic sludge, grinding powder having an average particle diameter of 20 μm generated in the alloy processing step (water content 35%, Nd 16% in dry powder, Pr 0.5%, Dy 3%, Tb 0.1%, Fe 41% , Co 2%, B 1%, other metal elements 1%, residual oxygen and other non-metal elements).
This sludge was dried and combusted and oxidized by a rotary kiln (heating temperature 600 ° C.). During the movement to the heating zone, it was observed that when water was evaporated and then the temperature was raised to about 300 ° C., it burned with flames. The flame temperature was 700-800 ° C. as a result of measurement with a radiation thermometer. Moreover, the flame was generated only at the entrance of the heating zone, and after burning, it turned into red hot powder and moved through the rotary kiln. The residence time in the heating zone was 30 minutes.
As a result of powder X-ray diffraction of the obtained oxide powder, an Fe peak was also confirmed in addition to Fe ₂ O ₃ , FeRO ₃ (R represents the rare earth element), and CoFe ₂ O ₄ . Moreover, as a result of measuring the weight change (oxidation increase) when this oxide powder was heated in air at 900 ° C. for 1 hour in an electric furnace, it showed a mass increase of 9.2% and oxidation was insufficient. understood.
Therefore, 0.5 kg of this sludge was put in a quartz container, and oxidized again in a box-type electric furnace at a temperature of 700 to 1250 ° C. for 15 to 60 minutes.
Under the conditions where the temperature was 800 ° C. and the time was 15 minutes or longer, the Fe peak of powder X-ray diffraction disappeared.
Moreover, the heating mass increase (900 degreeC x 1 hour) of the oxide powder oxidized on these conditions was 0.15% or less.
300 g of each oxidized powder sample was mixed with 300 g of water in a beaker to form a slurry. This was heated to 90 ° C. on a hot plate, and 410 g of 35% concentrated hydrochloric acid (0.40 times the equivalent amount) was added in 15 minutes, and held there for 60 minutes. The pH of this solution was ≦ 1.

A 25% NaOH solution was then added to adjust the pH to 3. After cooling, this was filtered through 5C filter paper with Nutsie to separate the solid and the solution. Further, the solid was washed with 3 L of water, and the solution adhering to the solid was washed out.
The rare earth elements, Fe, and Co in the solution and the cleaning liquid were measured by ICP method (SPS3100 manufactured by SII), and the dissolution rate of the rare earth elements and Co in the solution and the residual ratio in the solution were obtained for Fe. The elution rate and the residual rate were calculated as (mass of each element in the collected solution and cleaning liquid / mass of each element in the used oxide powder) × 100%. How much Nd (Dy, Co) is eluted with respect to the amount of Nd (Dy, Co) in the oxide used, and how much Fe is in solution even if Fe is precipitated as Fe hydroxide % Of what remains inside.
The higher the elution rate of rare earth elements and Co, the better, and the lower the residual rate of Fe, the better.
The results are shown in Table 1. It can be seen that when the heating temperature is less than 800 ° C., the elution rate of rare earth elements slightly increases, but the residual ratio of Fe increases. Moreover, the higher the temperature, the more solidified by sintering, and the elution into hydrochloric acid decreased.

[Examples 9 to 14 ]
The grinding powder sludges of Examples 1 to 7 were heated to 900 ° C. in a box-type electric furnace and held for 30 minutes for oxidation. As a result of X-ray diffraction, no Fe peak was observed, and the mass increase upon reoxidation at 900 ° C. for 1 hour was 0.05%. An elution test was conducted in the same manner as in Examples 1 to 7 except that the oxidized powder of this grinding powder sludge was used and the temperature of the slurry was changed. The results are shown in Table 2.
It can be seen that when the temperature is less than 80 ° C., the elution of rare earth elements is small and the elution of Fe is increased.

[Examples 15 to 20 ]
An elution test was conducted in the same manner as in Example 10 except that the ratio of water and oxidized powder was changed. The results are shown in Table 3. In Example 15 , the slurry viscosity was high, and the stirring could not be performed sufficiently.

[Examples 21 to 27 ]
The elution test was conducted in the same manner as in Example 10 except that the amount of hydrochloric acid was changed. The results are shown in Table 4. When the amount of hydrochloric acid was less than 0.20 times the equivalent, the elution rate of rare earth elements decreased. In order to reduce the amount of hydrochloric acid and the amount of alkali necessary for neutralization, 0.70 times or less is desirable.

[Examples 28 to 34 ]
The dissolution test was conducted in the same manner as in Example 10 except that the pH when the NaOH solution was added was changed. The results are shown in Table 5. If the pH is less than 2, all of iron remains in the solution without being precipitated, and if the pH exceeds 6, the rare earth element hydroxide is precipitated and the elution rate is deteriorated.

[Example 35 ]
In Example 1, in order to further reduce the residual ratio of Fe, after adding a 25% NaOH solution, 20 ml of a 10% sodium hypochlorite solution was added to the solution while maintaining the temperature, and the eluted divalent divalent solution was added. Fe was changed to trivalent. Thereafter, in the same manner as in Example 1, the elution rate of Nd, Dy, and Co and the residual rate of Fe were determined by the ICP method. As a result, the elution rate did not change, the Fe residual rate decreased to <0.1%, and Fe was removed.

[Example 36 ]
Using the solution of Example 10 , rare earth elements were separated by a solvent extraction method. The concentrations of rare earth elements in the solution were Nd: 0.1 mol / L, Pr: 0.02 mol / L, Dy: 0.1 mol / L, Tb: 0.003 mol / L.
PC88A was used as an extractant, and light rare earth elements (Nd, Pr) and heavy rare earth elements (Dy, Tb) were separated by an 8-stage mixer settler. Further, the heavy rare earth element was separated into Dy and Tb using the extractant PC88A.
(Nd, Pr) oxalate, Dy oxalate, and Tb oxalate are precipitated from each solution containing these using oxalic acid, filtered, and oxalate is fired at 950 ° C. to obtain each rare earth oxide. It was. Each purity was 99.9% or more, and Fe was <0.1%. Using these oxides as starting materials, (Nd, Pr) metal was produced by the molten salt electrolysis method, and Dy metal and Tb metal were produced by the Ca reduction method. These metals were sufficiently usable as raw materials for magnet alloys.

Claims (12)

(A) heating a raw material containing a rare earth magnet alloy to 800 ° C. or higher in an oxidizing atmosphere to form an oxide of the alloy component;
(B) a step of mixing the oxide and water to form a slurry, and adding hydrochloric acid while heating;
(C) adding an alkali while heating the resulting solution;
(D) A method for recovering a rare earth element, comprising a step of separating an undissolved and precipitated solid and a solution containing the rare earth element. Step (B) and recovery process of claim 1 Symbol placement heating temperature (C) is 70 ° C. or higher, respectively. The method according to claim 1 or 2 , wherein the pH for alkali adjustment in the step (C) is 2.0 to 6.0. As a step between steps (C) and step (D), oxidizing agent added a solution of divalent of claims 1 to 3 comprising the step of oxidizing the iron ions to trivalent according to any one of Collection method. The recovery method according to claim 4 , wherein the oxidizing agent is sodium hypochlorite. The recovery method according to any one of claims 1 to 5 , wherein the oxide obtained in the step (A) has a mass increase of 0.15% or less when heated in air at 900 ° C for 1 hour. The collection method according to any one of claims 1 to 6 , wherein a mixing ratio (mass ratio) of the oxide and water in the step (B) is water: oxide = 0.5 to 5: 1. The concentration of hydrochloric acid in step (B) is 10 to 35% by mass, the amount of hydrochloric acid added is 0.20 to 0.70 times the theoretical amount (equivalent) required to dissolve the total amount of oxide, and the addition time is 10 The recovery method according to any one of claims 1 to 7 , wherein the recovery time is from min to 5 hours. The recovery method according to any one of claims 1 to 8 , wherein the alkali in the step (C) is a 10 to 50 mass% NaOH solution. The recovery method according to any one of claims 1 to 9 , wherein the solution containing the rare earth element obtained in the step (D) is separated and recovered into a light rare earth element and a heavy rare earth element or each rare earth element by a solvent extraction method. The recovery method according to claim 10 , wherein the extractant used for solvent extraction is 2-ethylhexyl phosphate mono-2-ethylhexyl ester or di-2-ethylhexyl phosphate. The recovery method according to any one of claims 1 to 11 , wherein the raw material containing the rare earth magnet alloy is waste powder of a rare earth magnet.