WO2016072529A1

WO2016072529A1 - Method for collecting rare earth metals using mixing and extracting agent

Info

Publication number: WO2016072529A1
Application number: PCT/KR2014/010492
Authority: WO
Inventors: 이만승
Original assignee: 목포대학교 산학협력단
Priority date: 2014-11-04
Filing date: 2014-11-04
Publication date: 2016-05-12

Abstract

The present invention relates to a method for collecting rare earth metals, the method being capable of extracting praseodymium (Pr) and neodymium (Nd) from a hydrochloric acid solution containing the elements at excellent efficiency, and further improving separability of praseodymium and neodymium, of which separability is degraded due to similar chemical features therebetween.

Description

Recovery method of rare earth metal using mixed extractant

The present invention relates to a method of recovering a rare earth metal from a hydrochloric acid solution leaching rare earth metal elements. More specifically, the rare earth elements can be efficiently extracted from a hydrochloric acid solution containing praseodymium (Pr) and neodymium (Nd). The present invention relates to a method of recovering rare earth metals which can improve the separation selectivity of praseodymium and neodymium, which can be difficult to separate from each other due to similar chemical properties.

Rare earth elements are materials that are widely used in a variety of key industries such as the metal industry, ceramic technology, electronics and catalysts. Recently, as the demand for high purity rare earth elements increases, there is an increasing interest in the efficient extraction of rare earth elements from the rare earth element leachate and the separation between these elements.

Among these rare earth elements, praseodymium (Pr) and neodymium (Nd) have a similar ionic radius and similar chemical properties, so it is very difficult to separate the extracted Pr and Nd.

As a method of recovering the rare earth element, various methods such as fractional crystallization, fractional precipitation, selective redox, ion exchange chromatography, solvent extraction, and extraction chromatography can be used. Among them, solvent extraction is a competitive method. Known.

Recently, in the solvent extraction of rare earth elements, a method of using a mixed extractant that mixes various kinds of extractants has received a lot of attention, which suggests that the use of the mixed extractant improves the extraction rate of the rare earth elements and the separation selectivity between the extracted materials. This is because there is a possibility to improve.

In the extraction and separation of rare earth elements, various mixed extraction systems have been proposed, wherein mixing of the extractant is known, for example, mixing of acidic extractants, mixing of neutral extractants and mixing between acidic and neutral extractants.

For example, it is known that addition of di-2-ethylhexyl phosphoric acid (D2EHPA) to cyanex 301 (bis-2,4,4 trimethylpentyl dithiophosphinic acid) can improve the extraction rate and stripping of samarium (Sm). have.

In addition, when lanthanum (La) and neodymium (Nd) leached with nitric acid are mixed with cyanex 301 (bis-2,4,4 trimethylpentyl dithiophosphinic acid) and cyanex 923 (trialkylphosphine oxide), lanthanum (La) and It is also known that neodymium (Nd) can be extracted with good efficiency.

In addition, when using a mixed extract of cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) and CA100 (sec-octylphenoxy acetic acid), scandium (Sc), yttrium (Y), and lanthanum leached in hydrochloric acid Rare earth elements such as (La), gadolimium (Gd), and ytterbium (Yb) can be efficiently extracted.

In addition, the extraction of Pr and Nd involves the extraction of organic phosphates such as di-2-ethylhexyl phosphoric acid (D2EHPA), 2-ethyl hexyl phosphonic acid (PC88A), and Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid). It is known that an agent can be used. When Pr and Nd are extracted using these extractants, the extraction efficiency is higher in the order of D2EHPA, PC88A, and Cyanex 272, and the selectivity of the extracted Pr and Nd is inversely cyanex 272, PC88A. It is known that D2EHPA is the highest.

However, the extractants have low separation efficiency when the extraction efficiency is good, and the extraction efficiency is too low when the separation efficiency is good, and the efficiency is low for industrial application.

In addition, there is no known mixed extraction system that can perform extraction and separation of Pr and Nd contained in the hydrochloric acid solution well.

The following patent document discloses a method of extracting rare earth elements from manganese nodules, but discloses that the solvent extraction method can be used to recover the rare earth elements contained in sulfuric acid solution, but Pr and Nd contained in hydrochloric acid solution. It does not disclose a solvent extraction system for extracting with good efficiency.

An object of the present invention is to provide a rare earth metal recovery method that can extract Pr and Nd contained in a hydrochloric acid solution with high efficiency.

Another object of the present invention is to provide a rare earth metal recovery method that can not only extract Pr and Nd contained in the hydrochloric acid solution at a high extraction rate, but also increase the separation of Pr and Nd.

In order to solve the above problems, the present invention, by contacting a hydrochloric acid solution containing Pr and Nd ions, a mixed extractant containing a cation exchange extractant and an amine extractant to extract the Pr and Nd ions, the cation exchange The extractant provides a rare earth element recovery method, which is di-2,4,4-trimethyl pentyl phosphinic acid.

In addition, in order to solve the other problem, the present invention, by contacting a hydrochloric acid solution containing Pr and Nd ions, a mixed extractant containing a cation exchange extractant, an amine extractant and a neutral extractant to contact Pr and Nd ions And cation exchange extractant is di-2,4,4-trimethyl pentyl phosphinic acid, and the neutral extractant is tributyl phosphate.

According to one embodiment of the present invention, the extraction efficiency of Pr and Nd contained in an aqueous hydrochloric acid solution can be improved.

According to another embodiment of the present invention, the extraction efficiency and separability of Pr and Nd contained in the hydrochloric acid aqueous solution can be further improved.

Figure 1 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Example 1 of the present invention.

Figure 2 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Example 2 of the present invention.

Figure 3 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Comparative Example 5 of the present invention.

Figure 4 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Comparative Example 6 of the present invention.

Figure 5 shows the results of the extraction test using the extractant according to Example 3 of the present invention.

Figure 6 shows the change in the synergistic enhancement factor with increasing TBP mole fraction.

Hereinafter, the configuration and operation of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

The rare earth element recovery method according to the present invention is characterized in that Pr and Nd ions are extracted by bringing a hydrochloric acid solution containing Pr and Nd ions into contact with a mixed extractant including a cation exchange extractant and an amine extractant. .

In addition, the rare earth element recovery method according to the present invention may include a neutral extractant in addition to the cation exchange extractant and the amine extractant.

The cation exchange extractant is preferably bis (2,4,4-trimethylpentyl) phosphonic acid (bis (2,4,4-trimethylpentyl) phosphinic acid, hereinafter referred to as 'Cyanex 272').

In addition, as the amine extractant, tri-octyl / dodecylamine (hereinafter referred to as 'Alamine 336') or trioctylamine (hereinafter referred to as 'TOA') is preferable.

Cyanex 272 is an extractant that has not been used because of its selective separability for rare earth elements such as Pr and Nd but its low extraction efficiency. When the amine extractant such as Alamine 336 or TOA is mixed with the Cyanex 272, the hydrogen ion generated during the extraction process of Cyanex 272 is extracted by the amine extractant such as Alamine 336 or TOA with an organic solvent, and thus the extraction rate of Cyanex 272 Is higher. At this time, even if the amine-based extractant is mixed, the good selective separability of Cyanex 272 does not significantly decrease, so the mixed extractant of Cyanex 272 and the amine-based extractant can achieve both good extraction rate and separability.

Preferred examples of the amine extractant include Alamine 336 or TOA, and any amine extractant that can be mixed with Cyanex 272 to act as Alamine 336 or TOA is included in the scope of the present invention.

In addition, among the Alamine 336 and TOA, when Alamine 336 is mixed, the extraction rate of Pr and Nd is further improved, Alamine 336 is most preferred as the amine extractant.

In addition, when a tributyl phosphate (Tri-butyl-phosphate, hereinafter referred to as 'TBP'), which is a neutral extractant, is mixed with a mixed extractant of Cyanex 272 and an amine extractant to form a ternary system, a rare earth element, particularly Pr In addition to improving the extraction rate with respect to Nd, it is more preferable to obtain better separation property than the good separation property that Cyanex 272 has.

As for the mixing ratio of the Cyanex 272 and the amine extractant, it is preferable that the mole fraction X _{cyanex 272} of _{Cyanex 272} is maintained at 0.4 to 0.6 in the organic solvent represented by the following formula (1).

[Equation 1]

X _{cyanex 272} = n _{cyanex 272} / n _T

Where n _{cyanex 272} is cyanex 272 moles and n _T is the total moles of extractant)

This is because the extraction efficiency of Pr and Nd decreases when X _{cyanex 272} is less than 0.4 or more than 0.6, and the more preferable mole fraction X _{cyanex 272} of _{Cyanex 272} is 0.5.

In addition, when the TBP is included, the mole fraction X _TBP of the _TBP is preferably maintained at 0.1 to 0.7 in the organic solvent represented by the following Equation 2 in the mixed extractant.

[Equation 2]

X _{cyanex 272} = n _TBP / n _T

Where n _TBP is the number of moles of TBP and n _T is the total moles of extractant

In addition, the concentration of the mixed extractant in the organic solvent for extracting the Pr and Nd is preferably in the range of 0.5 ~ 1.5M, the extraction rate is lower when less than 0.5M, the viscosity of the organic phase increases when the stirring is more than 1.5M Because it is difficult.

Hereinafter, the present invention will be described in detail based on the preferred embodiments of the present invention, but is not limited to the following preferred embodiments of the present invention, and various ones can be assumed by those skilled in the art. It should be understood to include variations.

Example 1

As an aqueous hydrochloric acid solution containing Pr and Nd for the extraction test, a synthetic solution obtained by dissolving Pr and Nd chloride (purity 99.9%) purchased from Alfa Aesar in hydrochloric acid was used. Hydrochloric acid (HCl) and sodium hydroxide (NaOH) were added to the synthetic solution to adjust the initial pH to about 5. The concentration of Pr in the synthetic solution thus prepared was 0.008M and the concentration of Nd was fixed at 0.023M. This synthetic solution was used in the same manner as in Example 1 as well as Examples 2 and 3 and Comparative Examples 1 to 6.

In Example 1 of the present invention, a mixed extractant of Cyanex 272 (manufactured by cytec industries) and Alamine 336 (manufactured by BASF) was used as a mixed extractant for extracting the Pr and Nd. Each extractant was used as purchased without further purification, and the mixed extractant may include kerosene as a diluent if necessary. The total concentration of extractant in the mixture was fixed at 1M.

In the extraction test, 20 ml of an aqueous solution phase and an organic solvent phase were prepared, respectively, and then put into a mixing vessel, and stirred for 30 minutes using a Burrell wrist action shaker to convert Pr and Nd ions into an organic solvent phase. To be extracted.

The metal ion concentration in the aqueous solution before and after the extraction process was measured using ICP-OES, and the metal content contained in the organic solvent was obtained through mass balance.

The compositions thus measured are used to calculate the distribution ratio D obtained by the following equation.

[Equation 3]

Distribution ratio (D) = organic solvent metal concentration / aqueous metal concentration

In addition, the extraction rate (E%) was calculated | required through the following formula | equation 4.

[Equation 4]

E% = D × 100 / [D + (V _aq / V _org )]

Where D is the partition coefficient, V _aq is the volume of the aqueous phase, and V _org is the volume of the organic solvent phase)

In addition, the separation coefficient (SF) was obtained through Equation 5 below.

[Equation 5]

Separation coefficient (SF) = D _Nd / D _Pr

Where D _Nd is the distribution ratio of Nd and D _Pr is the distribution ratio of Pr)

Example 2

The extraction test of Example 2 of the present invention was performed in the same manner as in Example 1, except that a binary mixture of Cyanex 272 (manufactured by cytec industries) and TOA (manufactured by BASF) was used. At this time, the concentration of the whole mixture was maintained at 1.0M.

Example 3

The extraction test of Example 3 of the present invention was carried out in the same manner as in Example 1, except that the ternary mixture of Cyanex 272 (manufactured by cytec industries), Alamine 336, and TBP was used as the organic solvent extractant. At this time, the concentration of the entire mixture was maintained at 1.5M, the concentration ratio of Cyanex 272 and Alamine 336 was to maintain 1: 1.

Comparative Example 1

The extraction test of Comparative Example 1 was performed in the same manner as in Example 1, except that only Cyanex 272 included in the mixed extractant of Examples 1 to 3 was used as an organic solvent extractant, and compared with Examples 1 to 3. It is for. At this time, the concentration of the extractant was tested in the range of 0.1M up to 1.0M.

Comparative Example 2

The extraction test of Comparative Example 2 was performed in the same manner as in Example 1, except that only Alamine 336 included in the mixed extractant of Examples 1 and 3 was used as an organic solvent extractant, and compared with Examples 1 and 3 It is for. At this time, the concentration of the extractant was tested in the range of 0.1M up to 1.0M.

Comparative Example 3

The extraction test of Comparative Example 3 was performed in the same manner as in Example 1, except that only TOA contained in the mixed extractant of Example 2 was used as the organic solvent extractant, and is for comparison with Example 2. At this time, the concentration of the extractant was tested in the range of 0.1M up to 1.0M.

[Comparative Example 4]

The extraction test of Comparative Example 4 was carried out in the same manner as in Example 1, except that only the TBP contained in the mixed extractant of Example 3 as an organic solvent extractant, it is for comparison with Example 3. At this time, the concentration of the extractant was tested in the range of 0.1M up to 1.0M.

[Comparative Example 5]

The extraction test of Comparative Example 5 was performed in the same manner as in Example 1, except that Cyanex 272 (manufactured by cytec industries) and tri-2-ethylhexylamine (tri-2) were used as amine extractants. -ethylhexyl amine (hereinafter referred to as 'TEHA') was used for comparison with the binary mixed extractant of Examples 1 and 2 in which Alamine 336 and TOA were mixed. At this time, the total concentration of the mixed extractant was 1.0M.

Comparative Example 6

The extraction test of Comparative Example 6 was performed in the same manner as in Example 1, except that Cyanex 272 (manufactured by cytec industries) and TBP was used as an organic solvent extractant, which was a three-way system of Example 3 including TBP. For comparison with mixed extractant. At this time, the total concentration of the mixed extractant was 1.0M.

Extractive Efficiency

(1) single extractant

First, the extraction rate of the extraction test using a single component extractant was investigated. Table 1 below shows the change in extraction rate according to the concentration of Cyanex 272 in the organic solvent when the extraction test using only Cyanex 272 according to Comparative Example 1.

Table 1

Cyanex 272 (M)	E%, Pr	E%, Nd	SF _{Nd / Pr}
0.1	2.2	4.1	1.86
0.3	5.7	8.5	1.55
0.5	6.5	9.6	1.51
0.7	11.6	17.0	1.56
0.9	12.3	18.3	1.57
1.0	15.2	21.5	1.53

As shown in Table 1, as the Cyanex 272 concentration increased to 1M, the extraction rates of Pr and Nd increased, and the maximum extraction rates of Pr and Nd were 15.2% and 21.5%. Among them, Nd tended to be extracted better than Pr due to the difference in acidity of metal ions in aqueous hydrochloric acid solution.

On the other hand, in the case of the separation coefficient of Cyanex 272, the maximum separation coefficient of 1.86 was obtained at 0.1M of Cyanex 272, and thereafter it was degraded to maintain a substantially constant value of 1.51 to 1.56.

Moreover, according to Comparative Examples 2-4, the extraction test of Pr and Nd by Alamine 336, TOA, and TBP single extractant showed that the extraction rate by these was low enough that it cannot be extracted substantially.

(2) binary mixed extractant

The extraction rate of the extraction test using the binary mixed extractant was investigated.

1 shows the results of extracting Pr and Nd from the kerosene using the mixed extractant according to Example 1 of the present invention. As shown in FIG. 1, the extraction _rates of Pr and Nd increased with X _{cyanex 272} , reached maximum at X _{cyanex 272} 0.5, and decreased with increasing fraction of Cyanex 272, then dropped to the same extraction rate as Comparative Example 1. .

That is, according to Example 1 of the present invention, when X _{cyanex 272} was maintained between 0.25 and 0.6, the extraction rate was improved by 2 to 3 times as compared with the case of using Cyanex 272 alone.

This synergistic effect is that in the extraction of metal ions by Cyanex 272, the increase in the concentration of hydrogen in aqueous solution by the hydrogen ions released from Cyanex 272 lowers the extraction rate of Cyanex 272, since the mixed-added Alamine 336 reduces the hydrogen concentration. In addition, Cyanex 272 has been shown to increase the extraction efficiency.

Figure 2 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Example 2 of the present invention in kerosene. As shown in FIG. 2, when using a mixture of Cynex 272 and TOA, an extraction behavior similar to that of Example 1 was observed. Maximum extraction _rates of Nd and Pr were obtained when X _{Cyanex 272} was 0.5 in the mixture.

In addition, when X _{cyanex 272} was maintained between 0.25 and 0.6, the extraction rate was improved by about 1.5 times to 2.5 compared to when using Cyanex 272 alone. That is, for Example 2, the improvement in extraction rate is rather low compared to Example 1, which appears to be due to the relatively poor hydrogen extractability of TOA.

Figure 3 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Comparative Example 5 of the present invention in kerosene. As shown in FIG. 3, in comparison with Examples 1 and 2, the mixture of Cyanex 272 and TEHA showed almost similar extraction rate as that of Cyanex 272 alone.

That is, in the case of Comparative Example 5, no synergistic effect by TEHA mixing was seen, which seems to be due to the very low hydrogen extractability of TEHA.

From these results, it can be seen that synergistic effect can not be obtained by simply adding an amine extractant to Cyanex 272, and only when an extractant such as Alamine 336 or TOA is mixed.

Figure 4 shows the results of the extraction of Pr and Nd using an organic solvent diluted with a mixed extractant according to Comparative Example 6 of the present invention. As shown in FIG. 4, when TBP is mixed with Cyanex 272, the extraction rate of Pr and Nd tends to decrease as the concentration of TBP increases.

In other words, when TBP also becomes a binary mixture with Cyanex 272, it does not have a synergistic effect on the extraction rate, but rather a negative effect that TBP reduces the effective concentration of Cyanex 272.

(3) ternary mixed extractant

Figure 5 shows the results of the extraction test using the extractant according to Example 3 of the present invention. Figure 5 also shows the data of binary extractant (Cyanex 272 + Alamine 336) for comparison.

As shown in FIG. 5, when TBP was added to the mixture of Cyanex 272 and alamine 336, the extraction rate of Pr and Nd was improved, and the improvement effect was increased as the TBP concentration was increased.

The synergy effect of the three-way system was calculated by Equation 6 below.

[Equation 6]

Synergy Enhancement Factor (R) = D _{Ternary System} / D _{Binary System}

Figure 6 shows the change in the synergistic enhancement factor with increasing TBP mole fraction. As shown in FIG. 6, the synergy enhancing factor of TBP increases continuously with increasing TBP mole fraction. The maximum value of the synergy enhancing factor was when the mole fraction of TBP (X _TBP ) was 0.7, showing 17.0 and 14.6 for Pr and Nb, respectively.

That is, in the ternary mixed extractant according to Example 3 of the present invention, the extraction synergy increases with increasing mole fraction of TBP.

If the molar fraction (X _TBP ) of _TBP exceeds 0.7, a separation problem occurs between the organic phase and the aqueous phase after equilibration, so that the mole fraction of TBP that can be added is 0.7. Therefore, in the ternary mixed extractant, the mole fraction of TBP is preferably maintained at 0.1 to 0.7, more preferably 0.3 to 0.7.

Separation Selectivity

(1) single extractant and binary mixed extractant

Table 2 below shows the results of calculating the separation coefficient when 0.5M of Cyanex 272 alone and 0.5M of Alamine 336, TOA, and TEHA were added to Cyanex 272, respectively.

TABLE 2

Extractant	SF _{Nd / Pr}	Remarks
0.5M Cyanex 272	1.51	Comparative Example 1
0.5M Cyanex 272 + 0.5M Alamine 336	1.29	Example 1
0.5M Cyanex 272 + 0.5M TOA	1.29	Example 2
0.5M Cyanex 272 + 0.5M TEHA	1.48	Comparative Example 5

As shown in Table 2, in Examples 1 and 2 of the present invention, while the extraction rate is significantly improved compared to Comparative Example 1, the separability tended to decrease somewhat. In Comparative Example 5, there was little improvement in the extraction rate, but showed a tendency to be slightly lower in the separability.

(2) ternary mixed extractant

Table 3 below shows the extraction rate and the separation coefficient when the Cyanex 272 single extractant, the Cyanex 272 + Alamine 336 binary mixed extractant, and the Cyanex 272 + Alamine 336 + TBP ternary mixed extractant were used.

TABLE 3

Extractant	% E _Pr	% E _Nd	SF _{Nd / Pr}	Remarks
0.5M Cyanex 272	6.5	9.58	1.51	Comparative Example 1
0.5M Cyanex 272 + 0.5M Alamine 336	49.9	56.4	1.29	Example 1
0.5M Cyanex 272 + 0.5M Alamine 336 + 0.5M TBP	72.4	80.7	1.59	Example 3

As shown in Table 3, in the case of binary mixed extractant, the extraction rate is significantly improved compared to the single Cyanex 272, but the separation coefficient of Nd and Pr is 1.29, which is somewhat lower than that of Cyanex 272.

In contrast, the ternary mixed extractant according to Example 3 of the present invention significantly improved the extraction rate of Pr and Nd as well as maintaining the separation coefficient higher than that of the single Cyanex 272, compared to the binary mixed extractant. do.

That is, the ternary mixed extractant is characterized by significantly increasing the extraction rate of Pr and Nd without degrading the separability.

Stripping

Removal of Pr and Nd extracted using the mixed extractant according to Example 1 was carried out using hydrochloric and sulfuric acid solutions.

The extraction solution used for stripping was contacted by stirring an organic solvent mixed with Cyanex 272 0.35M and Alamine 336 0.35M for 30 minutes in an aqueous hydrochloric acid solution containing an initial pH of 5.02 containing Pr and Nd ions. The extracted organic solvent was prepared.

Through this process, the concentration of Pr extracted in the organic solvent was 2.3 × 10 ⁻³ M and the concentration of Nd was 7.2 × 10 ⁻³ M.

Table 4 below shows the stripping ratio according to the concentration of stripping agent from the organic solvent extracted using the binary mixed extractant.

Table 4

Concentration (m)	Stripper
	HCl		H ₂ SO ₄
	% Stripping
	Pr	Nd	Pr	Nd
0.1	0	4.5	91.6	93.4
0.5	89.2	91.8	98.6	100
1.0	97.6	98.2	100	100
2.0	100	100	100	100
4.0	100	100	100	100

As shown in Table 4, the removal rates of Pr and Nd increased as the concentration of the acid used increased, indicating that almost complete stripping is possible when the sulfuric acid is 0.5M or more and hydrochloric acid is 1M or more.

That is, it can be seen that Pr and Nd extracted using the mixed extractant according to the embodiment of the present invention can be easily removed with a relatively low concentration of acid.

Table 5 below shows the stripping ratio according to the concentration of stripping agent from the organic solvent extracted using the ternary mixed extractant.

Table 5

Concentration (m)	Stripper
	HCl		H ₂ SO ₄
	% Stripping
	Pr	Nd	Pr	Nd
0.01	1.27	3.27	15.4	7.6
0.05	1.28	3.31	84.7	88.1
0.1	1.97	3.95	99.5	100
0.3	18.6	21.1	100	100
0.5	100	100	100	100
1.0	100	100	100	100
2.0	100	100	100	100

As shown in Table 5, the removal of Pr and Nd from the organic solvent extracted in the tertiary mixed extractant according to Example 3 of the present invention can be completely removed using a lower concentration of the stripper than the binary system Removal is also easier.

Claims

Pr and Nd ions are extracted by contacting an aqueous hydrochloric acid solution containing Pr and Nd ions with a mixed extractant including a cation exchange extractant and an amine extractant,

Wherein said cation exchange extractant is di-2,4,4-trimethyl pentyl phosphinic acid.
Pr and Nd ions are extracted by contacting an aqueous hydrochloric acid solution containing Pr and Nd ions with a mixed extractant including a cation exchange extractant and an amine extractant and a neutral extractant,

The cation exchange extractant is di-2,4,4-trimethyl pentyl phosphinic acid,

And the neutral extractant is tributyl phosphate.
The method according to claim 1 or 2,

The amine extractant, tri-octyl / dodecylamine (tri-octyl / dodecylamine) or trioctylamine (trioctylamine), rare earth element recovery method.
The method according to claim 1 or 2,

The concentration of the mixed extractant is 0.5M ~ 1.5M, rare earth element recovery method.
The method according to claim 1 or 2,

A mixing ratio of the cation exchange extractant and the amine extractant contained in the mixed extractant is 4: 6 to 6: 4 in molar ratio, rare earth element recovery method.
The method according to claim 1 or 2,

The combined amount of the cation exchange extractant and the amine extractant contained in the mixed extractant is 0.5 M or more, rare earth element recovery method.
The method of claim 2,

Rare earth element recovery method of the mixed extractant, the molar fraction of the tributyl phosphate is 0.1 ~ 0.7.
The method according to claim 1 or 2,

The extracted Pr and Nd is stripped with nitric acid or sulfuric acid,

The rare earth element recovery method, wherein the concentration of nitric acid or sulfuric acid is 0.5M or more.