METHOD FOR RECOVERING RARE EARTH METALS USING ORGANIC ACIDS

Abstract

A method for recovering rare earth metals uses organic acids. The method for recovering the rare earth metals using the organic acids is eco-friendly without using inorganic acids and has an effect of high selectivity for rare earth metals. In addition, impurities generated during the process may be removed only by adjusting the pH of the solvent, thereby significantly reducing the process time compared to conventional methods.

Claims

1. A method for recovering rare earth metals using organic acids, the method comprising: crushing rare earth magnet scrap and pulverizing the crushed rare earth magnet scrap to prepare rare earth magnet fine powder; heat-treating the rare earth magnet fine powder to obtain rare earth magnetic oxide fine powder; leaching the rare earth magnetic oxide fine powder with an organic acid to obtain an organic acid leachate; centrifuging the organic acid leachate to obtain a sludge removal solution; adding an alkaline aqueous solution to the sludge removal solution to obtain a purified solution; and adding oxalic acid to the purified solution to obtain an oxalate-rare earth metal complex.

2. The method of claim 1, wherein crushing the rare earth magnet scrap is performed by a jaw crusher and a cone crusher, and pulverizing the crushed rare earth magnet scrap is performed by a pulverizer, a vibration mill, or a ball mill.

3. The method of claim 1, wherein the rare earth magnet fine powder has an average particle size in a range of 10 m to 100 m.

4. The method of claim 1, wherein heat-treating the rare earth magnet fine powder to obtain the rare earth magnetic oxide fine powder comprises: first heat-treating the rare earth magnet fine powder at a first temperature; and second heat-treating the rare earth magnet fine powder at a second temperature higher than the first temperature.

5. The method of claim 1, wherein heat-treating the rare earth magnet fine powder is performed under a condition where a ratio (P.sub.H2O/P.sub.H2) of a partial pressure of H.sub.2O (P.sub.H2O) to a partial pressure of H.sub.2 (P.sub.H2) is in a range of 0.05 to 0.20.

6. The method of claim 1, wherein leaching the rare earth magnetic oxide fine powder with the organic acid is performed using a deep eutectic solvent.

7. The method of claim 6, wherein leaching the rare earth magnetic oxide fine powder with the organic acid is performed at a pulp density in a range of 1 to 4%, and the pulp density in the range of 1 to 4% is represented by 1 to 4 g of a weight of the rare earth magnetic oxide fine powder per 100 ml of a volume of the deep eutectic solvent.

8. The method of claim 6, wherein the deep eutectic solvent comprises hydrogen bond donors and hydrogen bond acceptors, wherein the hydrogen bond donor includes a carboxyl group-containing compound, and the hydrogen bond acceptor includes at least one of quaternary ammonium halide, quaternary phosphonium halide, tertiary ammonium halide, primary ammonium halide, or any combination thereof.

9. The method of claim 8, wherein the deep eutectic solvent contains the hydrogen bond donors and the hydrogen bond acceptors in a molar ratio in a range of 1:0.40 to 1:0.70.

10. The method of claim 1, wherein leaching the rare earth magnetic oxide fine powder with the organic acid is performed at a temperature in a range of 40 C. to 70 C.

11. The method of claim 1, wherein leaching the rare earth magnetic oxide fine powder with the organic acid is performed for a range of 5 hours to 20 hours.

12. The method of claim 1, wherein in adding the alkaline aqueous solution to the sludge removal solution to obtain the purified solution, the alkaline aqueous solution is added until a pH of the sludge removal solution becomes a range of 3 to 4.

13. The method of claim 1, wherein in adding the oxalic acid to the purified solution to obtain the oxalate-rare earth metal complex, the oxalic acid is added in an amount in a range of 1.5 to 2.0 equivalents per 1 equivalent of the rare earth metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other aspects, features, and advantages of the present disclosure should become more apparent from the detailed description in conjunction with the accompanying drawings, in which:

[0025] FIG. 1 is a flowchart of a method for recovering rare earth metals using organic acids according to one embodiment of the present disclosure.

[0026] The drawing described herein is for illustration purposes only and is not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0027] The present disclosure is described in more detail. However, the following embodiments or examples are only a reference for explaining the present disclosure in detail, and the present disclosure is not limited thereto, and may be implemented in various forms.

[0028] Further, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by those having ordinary skill in the art to which the present disclosure pertains.

[0029] The terminology used in the description in the present disclosure is merely to effectively describe specific embodiments or examples and is not intended to limit the present disclosure.

[0030] In addition, as used in the specification and the appended claims, the singular forms may be intended to comprise plural forms, unless clearly dictated in the contexts otherwise.

[0031] In addition, units used in this specification without special mention are based on weight, and for example, units of % or ratio mean wt % or weight ratio, and wt % means wt % of any one component in the entire composition, unless otherwise defined.

[0032] Further, unless explicitly described to the contrary, when any part comprises any component, it should be understood to further comprise another component rather than excluding another component.

[0033] In addition, the numerical ranges used in the present disclosure may comprise lower and upper limits and all values within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of upper and lower limits of numerical ranges defined in different shapes. Unless otherwise specifically defined in the specification of the present disclosure, values out of the numerical range that may arise due to experimental error or rounding of values are also comprised in the defined numerical range.

[0034] In the present disclosure, each of phrases such as A or B, at least one of A and B, at least one of A or B, A, B or C, at least one of A, B and C, at least one of A, B or C and at least one of A, B, or C, or a combination thereof may include any one or all possible combinations of the items listed together in the corresponding one of the phrases.

[0035] The present disclosure provides a method for recovering rare earth metals using organic acids. The method includes crushing rare earth magnet scrap and pulverizing the crushed rare earth magnet scrap to prepare rare earth magnet fine powder; heat-treating the rare earth magnet fine powder to obtain rare earth magnetic oxide fine powder; leaching the rare earth magnetic oxide fine powder with an organic acid to obtain an organic acid leachate; centrifuging the organic acid leachate to obtain a sludge removal solution; adding an alkaline aqueous solution to the sludge removal solution to obtain a purified solution; and adding oxalic acid to the purified solution to obtain an oxalate-rare earth metal complex. The method for recovering rare earth metals according to an embodiment of the present disclosure may selectively recover rare earth metals contained in rare earth magnets without using inorganic acids by organically combining processes such as heat treatment for sequentially forming iron oxide and rare earth metal oxide, and organic acid leaching using deep eutectic solvents containing organic acids having low melting points and high dissolution. The present disclosure is described in more detail below.

[0036] First, there is a step (S100) of crushing and pulverizing rare earth magnet scrap to prepare rare earth magnet fine powder. Through this step, oxidation and organic acid leaching by heat treatment of rare earth magnet scrap to be described below may be performed with high efficiency, thereby shortening the process time and recovering rare earth metals with high selectivity.

[0037] The rare earth magnet scrap is a general term that includes all magnet chips generated during the manufacturing process of NdFeB-based magnets, processing sludge, waste magnets recovered from used parts such as used waste motors, or the like. Therefore, it should be noted that the rare earth magnet scrap used in herein may include other rare earth magnets widely used in industrial sites or daily life in addition to the waste magnets obtained from the waste motors.

[0038] In one embodiment of the present disclosure, the crushing of the rare earth magnet scrap may be performed by a jaw crusher and a cone crusher, and the pulverizing of the crushed rare earth magnet scrap may be performed by a pulverizer, a vibration mill, or a ball mill.

[0039] In one embodiment of the present disclosure, the rare earth magnet fine powder may have an average particle size of 10 m to 100 m, specifically 20 m to 50 m, and more specifically 25 m to 35 m. If the range is satisfied, oxidation and organic acid leaching by heat treatment are easily performed even inside the powder, thereby recovering rare earth metals with high selectivity.

[0040] Next, there is a step (S200) of heat-treating the rare earth magnet fine powder to obtain rare earth magnetic oxide fine powder. Through this step, all kinds of inorganic materials included in the rare earth magnet scrap may be leached and dissolved to prevent the selectivity of the rare earth metal from being reduced.

[0041] In one embodiment of the present disclosure, the heat-treating of the rare earth magnet fine powder (also referred to as a heat treatment) to obtain the rare earth magnetic oxide fine powder may include first heat-treating the rare earth magnet fine powder at a first temperature; and second heat-treating the rare earth magnet fine powder at a second temperature higher than the first temperature. By performing the heat treatment twice at different temperatures, a single-phase oxide, not an iron-rare earth metal composite oxide, is formed to easily leach the rare earth metal selectively.

[0042] In one embodiment e of the present disclosure, the first temperature may be 800 C. to 1200 C., specifically 900 C. to 1000 C., and the second temperature may be 500 C. to 700 C., specifically 600 C. to 650 C. When the ranges are satisfied, the formation of the iron-rare earth metal composite oxide may be minimized.

[0043] In one embodiment of the present disclosure, the heat treatment may be performed under a condition where a ratio (P.sub.H2O/P.sub.H2) of the partial pressure of H.sub.2O (P.sub.H2O) to the partial pressure of H.sub.2 (P.sub.H2) is 0.05 to 0.20, specifically 0.08 to 0.12, but is not limited thereto as long as the purpose of the present disclosure may be achieved.

[0044] Next, there is a step (S300) of leaching the rare earth magnetic oxide fine powder with an organic acid (also referred to as organic acid leaching) to obtain an organic acid leachate. Specifically, this step is a step of selectively leaching rare earth metals from the rare earth magnetic oxide fine powder without using inorganic acids by utilizing the characteristic that rare earth metals exhibiting high ionicity and polarity are selectively ionized by the deep eutectic solvent, due to hydrogen bonds formed by hydrogen bond donors and hydrogen bond acceptors included in the deep eutectic solvent.

[0045] In one embodiment of the present disclosure, the organic acid leaching may be performed using the deep eutectic solvent.

[0046] In one embodiment of the present disclosure, the deep eutectic solvent may include hydrogen bond donors and hydrogen bond acceptors.

[0047] In one embodiment of the present disclosure, the hydrogen bond donor may include a carboxyl group-containing compound. For example, the hydrogen bond donor may be a carboxyl group-containing compound. Examples of the carboxyl group-containing compound may include fatty acids, such as formic acid, acetic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, eicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, and triacontanoic acid; polyhydric carboxylic acid compounds, such as oxalic acid, malonic acid, succinic acid, adipic acid, itaconic acid, suberic acid, and 1,2,3-propanetricarboxylic acid;

[0048] aromatic carboxylic acid compounds such as benzoic acid; aromatic compounds having a carboxyl group-containing substituent, such as phenylacetic acid, 3-phenylpropionic acid, and trans-cinnamic acid; and carboxyl group-containing compounds having a hydroxyl group, such as levulinic acid, lactic acid, tartaric acid, ascorbic acid, citric acid, 4-hydroxybenzoic acid, p-coumaric acid, caffeic acid, and gallic acid.

[0049] In one embodiment of the present disclosure, the hydrogen bond acceptor may include at least one of quaternary ammonium halide, quaternary phosphonium halide, tertiary ammonium halide, primary ammonium halide, or any combination thereof. For example, the hydrogen bond acceptor may be at least one of quaternary ammonium halide, quaternary phosphonium halide, tertiary ammonium halide, or primary ammonium halide.

[0050] Examples of the quaternary ammonium halide may include choline chloride, tetrabutylammonium chloride, tetramethylammonium chloride, methyltrioctylammonium chloride, tetraoctylammonium chloride, acetylcholine chloride, chlorocholine chloride, tetraethylammonium bromide, N-(2-hydroxyethyl)-N,N-dimethylbenzenemethanaminium chloride, fluorocholine bromide, tetrabutylammonium bromide, and the like.

[0051] Examples of the quaternary phosphonium halide may include methyltriphenylphosphonium bromide, benzyltriphenylphosphonium chloride, and the like.

[0052] Examples of the tertiary ammonium halide may include 2-(diethylamino) ethanol hydrochloride.

[0053] Examples of the primary ammonium halide may include ethylamine hydrochloride, guanidine hydrochloride, and the like.

[0054] In one embodiment of the present disclosure, the deep eutectic solvent may contain the hydrogen bond donors and the hydrogen bond acceptors in a molar ratio of 1:0.40 to 1:0.70, specifically 1:0.45 to 1:0.60. When the range is satisfied, the formation of hydrogen bonds is facilitated, so that selective ionization of the rare earth metals may occur more easily. As a specific example, the deep eutectic solvent may contain 1 mole of lactic acid as the hydrogen bond donor and 0.5 mole of guanidine hydrochloride as the hydrogen bond acceptor.

[0055] In one embodiment of the present disclosure, the organic acid leaching may be performed at 40 C. to 70 C., specifically 60 C. to 70 C. If the range is satisfied, the recovery rate of the rare earth metals may be further improved.

[0056] In one embodiment of the present disclosure, the organic acid leaching may be performed for 5 hours to 20 hours, specifically 10 hours to 13 hours. If the range is satisfied, the recovery rate and selectivity of the rare earth metals may be improved.

[0057] In one embodiment of the present disclosure, the organic acid leaching may be performed at a pulp density of 1 to 4%, specifically 1 to 2%. The pulp density may be represented by the weight (g) of the rare earth magnetic oxide fine powder/100 ml volume of the deep eutectic solvent. If the range is satisfied, the recovery rate of the rare earth metals may be further improved.

[0058] Next, there is a step (S400) of centrifuging the organic acid leachate to obtain a sludge removal solution. Through this step, after performing the organic acid leaching, sludge including iron oxide and a small amount of residual rare earth magnetic oxide fine powder that has not been leached may be removed.

[0059] In one embodiment of the present disclosure, the centrifugation may be performed at a speed of 5,000 to 20,000 rpm, specifically 8,000 to 15,000 rpm.

[0060] Next, there is a step (S500) of adding an alkaline aqueous solution to the sludge removal solution to obtain a purified solution. Specifically, the step is a step of adjusting the pH through the alkaline aqueous solution to transform an iron component included in the sludge removal solution into a hydroxide form and precipitating and removing impurities transformed into the hydroxide form. In one embodiment of the present disclosure, the impurities may include an iron component. The iron component transformed into the hydroxide form may be removed by a method commonly used in the art, and for example, may be removed through filtration.

[0061] In one embodiment of the present disclosure, the alkaline aqueous solution may include at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, or any combination thereof.

[0062] In one embodiment of the present disclosure, the alkaline aqueous solution may be added until the pH of the sludge removal solution becomes 3 to 4, specifically, 3.3 to 3.8. If the range is satisfied, the selectivity of the rare earth metals may be improved.

[0063] Next, there is a step (S600) of adding oxalic acid to the purified solution to obtain an oxalate-rare earth metal complex.

[0064] In one embodiment of the present disclosure, the oxalic acid may be added in an amount of 1.0 to 1.5 equivalents, specifically, 1.2 to 1.3 equivalents, per 1 equivalent of the rare earth metal.

[0065] In one embodiment of the present disclosure, the method for recovering the rare earth metals using the organic acids may further include filtering and then calcining (S700) the oxalate-rare earth metal complex.

[0066] In one embodiment of the present disclosure, the calcining may be used without limitation if it is a conventionally known method in the industry.

[0067] Examples of the present disclosure and Comparative Examples are described below. However, the following Examples are merely examples of the present disclosure, and the present disclosure is not limited to the following Examples.

Example 1

[0068] NdFeB-based magnets recovered from waste motors were used as raw materials.

[0069] The NdFEB-based magnets recovered from the waste motors were crushed using a jaw crusher, and pulverized sequentially using a roll mill and a vibration mill to have an average particle size of 30 m.

[0070] Then, the pressure was applied so that P.sub.H2O/P.sub.H2 was 0.1, and the rare earth magnet fine powder was first heat-treated at 950 C. for 3 hours, cooled to room temperature, and then second heat-treated at 650 C. for 3 hours to be converted into an oxide.

[0071] Next, a deep eutectic solvent containing guanidine hydrochloride and lactic acid in a molar ratio of 1:2 was prepared. The rare earth magnetic oxide fine powder was added to the deep eutectic solvent so that the pulp density was 2%, and leached by rotary stirring at 60 C. for 10 hours.

[0072] The organic acid leachate was centrifuged at a rotation speed of 10,000 RPM to separate the solvent and sludge, and the sludge was removed, and then the filtrate was analyzed by ICP (inductively coupled plasma), and the results were shown in Table 2 below. The ICP analysis was performed using iCAP 7000 Series ICP-OES from Thermo Scientific for all of Examples and Comparative Examples of the present disclosure.

[0073] A sodium hydroxide aqueous solution was added until the pH of the sludge removal solution became 3.5 to precipitate impurities including iron, and filtered to obtain an oxalate-rare earth metal complex.

[0074] The oxalate-rare earth metal complex was heat-treated at 950 C. for 5 hours to recover the rare earth metals.

Examples 2 to 4

[0075] Rare earth metals were recovered in the same manner as in Example 1, except that the oxide fine powder was leached at a temperature shown in Table 1 below.

Examples 5 to 7

[0076] Rare earth metals were recovered in the same manner as in Example 1, except that the oxide fine powder was leached at a reaction time shown in Table 1 below.

Examples 8 to 10

[0077] Rare earth metals were recovered in the same manner as in Example 1, except that the oxide fine powder was leached at a pulp density shown in Table 1 below.

TABLE-US-00001 TABLE 1 Organic acid leaching Temperature Reaction Pulp ( C.) time (Hr) density (%) Example 1 60 10 2 Example 2 40 10 2 Example 3 50 10 2 Example 4 70 10 2 Example 5 60 5 2 Example 6 60 15 2 Example 7 60 20 2 Example 8 60 10 1 Example 9 60 10 3 Example 10 60 10 4

Comparative Example 1

[0078] NdFeB-based magnets recovered from waste motors were used as raw materials.

[0079] The NdFeB-based magnets recovered from the waste motors were crushed using a jaw crusher, and pulverized sequentially using a roll mill and a vibration mill to an average particle size of 30 m.

[0080] The rare earth magnet fine powder was heat-treated only at 650 C. for 3 hours.

[0081] 10 wt % of the oxide fine powder reacted in a 2.5 M hydrochloric acid solution at 60 C. for 2 hours with rotary stirring. After the reaction was completed, the filtrate was filtered and analyzed by ICP.

Comparative Example 2

[0082] Rare earth metals were recovered in the same manner as in Example 1, except that the rare earth magnet fine powder was heat-treated only at 650 C. for 3 hours to be converted into oxide.

TABLE-US-00002 TABLE 2 Recovery rate Fe Pr Nd Tb Dy TRE Example 1 6.01% 93.88% 94.04% 93.67% 93.85% 93.97% Example 2 4.62% 67.90% 60.22% 62.34% 62.47% 61.86% Example 3 5.67% 79.01% 82.56% 80.87% 79.88% 81.71% Example 4 6.87% 94.15% 96.61% 96.96% 95.51% 96.19% Example 5 3.25% 55.14% 56.37% 52.24% 52.68% 55.68% Example 6 8.95% 94.25% 95.24% 94.02% 94.25% 94.92% Example 7 12.50% 96.04% 95.67% 94.56% 95.03% 95.62% Example 8 6.58% 94.16% 95.68% 94.76% 95.24% 95.30% Example 9 5.67% 88.24% 86.37% 85.42% 86.24% 86.61% Example 10 5.08% 67.55% 62.54% 63.47% 59.64% 63.51% Comparative 62.11% 91.92% 91.23% 83.33% 91.76% 91.34% Example 1 Comparative 84.83% 89.98% 88.85% 91.16% 90.15% 89.33% Example 2 TRE: Total Rare Earth

[0083] As shown in Table 2, it may be seen that Comparative Example 1 using a conventional method for recovering rare earth metals using inorganic acids showed a recovery rate of 62.11% for iron, so that an additional process for removing iron was necessarily required. In addition, it may be seen that Comparative Example 2, in which the heat treatment was performed in a single step, showed a recovery rate of 84.83% for iron, so that the selectivity of the rare earth metals was reduced when a single-phase oxide was formed. Unlike Comparative Examples, Examples 1 to 10 using the method for recovering rare earth metals of the present disclosure showed a recovery rate of iron that was reduced by up to about 26 times compared to that of the Comparative Examples to exhibit significantly high selectivity without using inorganic acids, and recovered rare earth metals.

[0084] Features, structures, effects, and the like described in the above-described examples are comprised in at least one embodiment of the present disclosure, and are not necessarily limited to one example. Furthermore, the features, structures, effects, and the like illustrated in each example or embodiment may be combined or modified even in other examples or embodiments by those of ordinary skill in the art to which the present disclosure pertains. Accordingly, the contents related to these combinations and modifications should be interpreted to cover the scope of the present disclosure.