JP2011001584A - Method for extracting and separating rare earth elements - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for extracting and separating rare earth elements which can satisfactory extract and separate adjacent rare earth elements such as neodymium/praseodymium.SOLUTION: An organic phase with diglycol amide acid as an extract and low-polar alcohol as a solvent and a water phase composed of an aqueous solution comprising two or more of rare earth elements are contacted under an acid condition at the pH of ≤3, and solvent extraction is performed using a countercurrent multistage mixer-settler. A rare earth element solution 1, an organic phase 2 and an alkali aqueous solution 3 are introduced from respective pipings into an extraction part A, and acid aqueous solutions 4, 6 are introduced from the respective pipings into a scrub part B and a back-extraction part C. A water phase 5 comprising the rare earth element(s) not extracted into the organic phase and remaining and an aqueous solution 7 into which the rare earth element(s) extracted into the organic phase is back-extracted are recovered.

Description

  The present invention provides at least two or more rare earth elements, particularly light rare earth elements (La, Ce, Pr, Nd, Sm, Eu), or at least one of the light rare earth elements and other rare earth elements. The present invention relates to a method for extracting and separating at least one of (including Y).

In recent years, rare earth magnets typified by Nd magnets are widely used in various motors and sensors used in hard disks, air conditioners, hybrid vehicles, and the like.
However, the current state of rare earth elements, which are raw materials for rare earth magnets, is almost limited in their producing countries, and it is expected that demand will exceed supply in the near future. Therefore, there is a strong demand for magnet powder, scraps and defective scrap generated during the production of rare earth magnets, as well as for the recycling (recycling) of valuable rare earth elements from products collected from the city, exploration and development of new rare earth deposits. It has been.

Examples of rare earth elements used in rare earth magnets include cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), terbium (Tb), dysprosium (Dy), and the like. Known ion exchange resin methods (solid-liquid extraction methods) and solvent extraction methods (liquid-liquid extraction methods). In industrial refining and separation of rare earth elements, a solvent extraction method is mainly used because large-scale processing can be efficiently performed by a continuous process.
The solvent extraction method is a method in which an aqueous phase composed of an aqueous solution containing a metal element intended for separation is brought into contact with an organic phase composed of an extractant for extracting a specific metal element and an organic solvent for diluting it. In this method, an element is extracted by an extractant and separated.

  Conventionally, TBP (tributyl phosphate), carboxylic acid (versaic acid 10), phosphoric acid ester, phosphonic acid compound, phosphinic acid compound, and the like are used as the extractant. For example, di-2-ethylhexyl-phosphoric acid (D2EHPA) or the like is used as the phosphate ester, and 2-ethylhexyl phosphate mono-2-ethylhexyl ester [2 -Ethylhexyl-phosphoric acid-mono-2-ethylhexyl ester (PC-88A: trade name, manufactured by Daihachi Chemical Industry Co., Ltd.)] and the like, and bis (2,4,4-trimethylpentyl) phosphoric acid as the phosphinic acid compound [Bis (2,4,4-trimethylpentyl) phosphoric acid (Cyanex 272: product name manufactured by American Cyanamid Co., Ltd.] and the like are commercially available and generally used.

  The separation efficiency of the solvent extraction method depends on the performance of the extractant, particularly the separation factor. That is, the larger the separation factor, the higher the separation efficiency of the solvent extraction method, and the simplification of the separation process and the reduction in the size of the separation equipment, resulting in process efficiency and cost reduction. On the other hand, if the separation factor is small, the separation process becomes complicated and the separation equipment becomes large.

  Currently, PC-88A, which is said to have a large separation coefficient for rare earth elements among commercially available extractants, has a small separation coefficient between adjacent elements. For example, it may be the most difficult separation among rare earth elements. The neodymium / praseodymium separation factor referred to is less than 2 and about 1.4. This separation factor is not sufficient for separating neodymium / praseodymium, and in order to separate them with sufficient purity, a large-scale facility is required and a large cost is required. Therefore, when these elements are refined and separated, the development of an extractant and an extraction / separation method having a larger separation factor than before has been awaited.

  Diglycolamide acid is known as an extractant having a large separation factor for lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm), which are rare earth elements, particularly light rare earth elements. (Patent Document 1: Japanese Patent Application Laid-Open No. 2007-327085). By performing solvent extraction using the extractant, the extraction / separation process of rare earth elements, particularly light rare earth elements, can be made more efficient. However, although the extraction / separation method of rare earth elements using it has obtained good results at the experimental level, diglycolamide acid is commercially available and put to practical use with D2EHPA, PC-88A, and Cyanex272. Since various physical properties are different, various conditions to be put into practical use have not been found, and industrialization has not been achieved.

JP 2007-327085 A

  The present invention provides a method for extracting / separating rare earth elements that solves the above-mentioned problems, and can extract rare earth elements, particularly adjacent rare earth elements such as neodymium / praseodymium, better than conventional extraction / separation methods. An object of the present invention is to provide a method for extracting and separating rare earth elements that can be separated.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that an aqueous solution containing diglycolamide acid as an extractant, an organic phase using a low polarity alcohol as a solvent, and a rare earth element to be extracted. A method for extracting and separating rare earth elements that has a good separation performance for adjacent light rare earth elements such as neodymium / praseodymium by solvent extraction of a certain aqueous phase using a countercurrent multistage mixer settler, etc. The present inventors have found that this method is effective in selectively separating a specific rare earth element from a mixture of various rare earth elements, and have made the present invention.

（式中、Ｒ¹及びＲ²は、互いに同一又は異種のアルキル基であり、少なくとも一方は炭素数６以上の直鎖又は分岐鎖状のアルキル基を示す。）
で表されるジグリコールアミド酸を抽出剤とし、下記一般式（２）
Ｃ_nＨ_2n+1ＯＨ （２）
（式中、ｎは５〜８の整数である。）
で表される低極性アルコールを溶媒とする有機相と、２種以上の希土類元素を含む水溶液からなる水相とをｐＨ３以下の酸性条件下で接触させることにより、前記希土類元素のうち抽出すべき希土類元素を前記有機相に抽出し、その後この有機相を酸水溶液にて逆抽出することで前記有機相に抽出した希土類元素を回収すると共に、前記有機相に抽出されずに前記水相中に残留した希土類元素を回収することを特徴とする希土類元素の抽出・分離方法。
請求項２：
抽出及び逆抽出処理を向流多段ミキサーセトラーによって行うことを特徴とする請求項１記載の希土類元素の抽出・分離方法。
請求項３：
有機相と水相とを有機相に用いた式（２）の低極性アルコールの引火点より低い温度で接触させることを特徴とする請求項１又は２記載の希土類元素の抽出・分離方法。
請求項４：
水相に含まれる抽出・分離すべき希土類元素が、Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ及びＥｕから選ばれる軽希土類元素の中の少なくとも２種、又は前記軽希土類元素の中の少なくとも１種とそれ以外のＹを含む希土類元素の中の少なくとも１種とであることを特徴とする請求項１〜３のいずれか１項記載の希土類元素の抽出・分離方法。
請求項５：
水相に含まれる希土類元素が、Ｎｄ及びＰｒであり、Ｎｄを有機相に抽出すると共に、Ｐｒを水相に残留させることによりＮｄとＰｒとを分離するようにしたことを特徴とする請求項１〜３のいずれか１項記載の希土類元素の抽出・分離方法。 That is, the present invention provides the following rare earth element extraction / separation method as a method for solving the above problems.
Claim 1:
The following general formula (1)

(In the formula, R ¹ and R ² are the same or different alkyl groups, and at least one of them represents a linear or branched alkyl group having 6 or more carbon atoms.)
As an extractant, diglycolamide acid represented by the following general formula (2)
C _n H _{2n + 1} OH (2)
(In the formula, n is an integer of 5 to 8.)
It should be extracted from the rare earth elements by contacting an organic phase containing a low polar alcohol represented by the formula (1) and an aqueous phase comprising an aqueous solution containing two or more rare earth elements under acidic conditions of pH 3 or less. A rare earth element is extracted into the organic phase, and then the organic phase is back-extracted with an aqueous acid solution to recover the rare earth element extracted into the organic phase, and not extracted into the organic phase but into the aqueous phase. A method for extracting and separating rare earth elements, which comprises collecting residual rare earth elements.
Claim 2:
2. The method for extracting and separating rare earth elements according to claim 1, wherein the extraction and back-extraction processes are carried out by a countercurrent multistage mixer settler.
Claim 3:
3. The method for extracting and separating rare earth elements according to claim 1 or 2, wherein the organic phase and the aqueous phase are contacted at a temperature lower than the flash point of the low polarity alcohol of the formula (2) using the organic phase.
Claim 4:
The rare earth element to be extracted and separated contained in the aqueous phase is at least two kinds of light rare earth elements selected from La, Ce, Pr, Nd, Sm and Eu, or at least one kind of the light rare earth elements. The method for extracting and separating rare earth elements according to any one of claims 1 to 3, which is at least one of the other rare earth elements containing Y.
Claim 5:
The rare earth element contained in the aqueous phase is Nd and Pr, and Nd is extracted into an organic phase and Pr is left in the aqueous phase to separate Nd and Pr. The method for extracting and separating rare earth elements according to any one of 1 to 3.

  The extraction method using the extractant / extraction solvent of the present invention has a large separation factor, and can extract and separate rare earth elements with high separation efficiency, so that the initial investment is suppressed and the industrial utility value is great.

It is explanatory drawing of a countercurrent multistage mixer setter.

で表されるジグリコールアミド酸を用いる。 In the present invention, as the extractant, the following general formula (1)

The diglycol amide acid represented by these is used.

Here, R ¹ and R ² are the same or different alkyl groups, but at least one of them is a straight or branched chain having 6 or more carbon atoms, preferably 6 to 18, more preferably 7 to 12 carbon atoms. It is an alkyl group. If the number of carbon atoms is less than 6, the lipophilicity is not sufficient, so the stability of the organic phase is lacking, the phase separation with the aqueous phase becomes poor, and the dissolution of the extractant itself in the aqueous phase is ignored. Can no longer function as an extractant. In addition, when the carbon number is excessively large, it does not contribute to the improvement of the extraction performance and separation performance itself, which are basic performances, although the production cost of the extraction agent becomes high. As for R ¹ and R ^2, if the lipophilicity is secured, the other may be less than 6 as long as one is 6 or more carbon atoms. For example, a compound having two octyl groups (—C ₈ H ₁₇ ) introduced therein, N, N-dioctyl-3-oxapentane-1,5-amidic acid: dioctyl diglycolamidic acid [N, N-dioctyl-3-oxapentane-1,5-amidic acid: dioctyl diglycolamidic acid (N, N-dioctyl-3-oxapentane-1,5-amicacid: dioctyldiglycamic acid, hereinafter referred to as DODGAA)].

The normal organic phase consists of an extractant and a nonpolar solvent. As the nonpolar solvent, a solvent that is low in solubility in water, high in solubility in the extractant, light in specific gravity, and further suitable for improving the extraction ability is selected. For example, toluene, xylene, hexane, isododecane, kerosene and the like.
However, since toluene, xylene, hexane, etc. are all highly volatile and the flash point is lower than 20 ° C., they must be handled with care. In addition, isododecane, kerosene, etc., which have a low volatility and a flash point higher than 20 ° C., have a minimum required DODGAA extraction concentration of 0.4 mol for treating a rare earth aqueous solution of about 0.2 mol / L, which is the actual operational condition. When a concentration of / L or higher is used, the phase separation takes time, so the flow rates of the organic phase and the aqueous phase are limited. Therefore, productivity cannot be increased.

Therefore, the organic phase of the present invention is represented by the following general formula (2) as a solvent for the diglycolamide acid
C _n H _{2n + 1} OH (2)
(In the formula, n is an integer of 5 to 8.)
A low-polar alcohol that is a linear or branched liquid represented by the formula: By doing so, an organic phase having an extractant concentration of 0.4 mol / L or more can be obtained, and a treatment of about 0.2 mol / L, which is a rare earth element concentration in the rare earth aqueous solution in actual operation, is possible. When n is less than 5, alcohol is highly polar and hydratable and dissolves in the aqueous phase in solvent extraction, so the organic phase / aqueous phase is not sufficiently separated, and in addition, the extractant in the organic phase Not suitable because the concentration becomes unstable and cannot be controlled. The alcohol used in the present invention may be linear or branched, but if the alcohol has a linear structure and n is 12 or more, it is not suitable because it becomes a solid at room temperature. Further, even if it is liquefied by heating, the polarity with diglycolamide acid does not match, so that its solubility is lowered and the gelation of the liquid occurs, which is not suitable. In the case of an alcohol having a linear structure, 1-pentanol, 1-hexanol, 1-heptanol and 1-octanol with 5 ≦ n ≦ 8 are preferable, and they have low solubility in water and are extracted. It is suitable because of its high solubility in diglycolamide acid, a light specific gravity and high flash point.

The extractant concentration C _{O in} the organic phase of the present invention is preferably 0.1 mol / L ≦ C _O ≦ 1.5 mol / L. In the case of C _O <0.1 mol / L, the extractant concentration is too low, which makes it impossible to process the rare earth element concentration in the rare earth aqueous solution in actual operation. In fact, the rare earth aqueous solution having a concentration of 0.05 mol / L or less Since it cannot be processed, it is not efficient, resulting in an increase in the scale of the separation equipment, which may increase the cost. In the first place, it is difficult to make the extractant concentration C _O > 1.5 mol / L due to the solubility of diglycolamide acid itself in the alcohol, and a solvent such as an entrainer or a surfactant such as sodium dioctylsulfosuccinate. Therefore, conditions for controlling stable operation may become more complicated. Therefore, the extractant concentration C _{O in} the organic phase for efficient extraction / separation is preferably 0.2 mol / L ≦ C _O ≦ 1.0 mol / L.

On the other hand, the rare earth element to be extracted by the extractant is contained in the aqueous phase as an aqueous solution. In this case, the rare earth element can be used in the form of a water-soluble salt such as a chloride (PrCl ₃ , NdCl _3, etc.).

Among the diglycolamide acids of the extractant used in the present invention, DODGAA is particularly excellent in separability in light rare earth elements and separability between light rare earth elements and other rare earth elements. However, separability other than light rare earth elements, that is, heavy rare earth elements, is inferior to D2EHPA, PC-88A, and Cyanex272, which are commercially available and put to practical use. The element is at least two of light rare earth elements (La, Ce, Pr, Nd, Sm, Eu), or at least one of light rare earth elements and other rare earth elements (including Y). It is preferable that it consists of 1 or more types. Examples of other rare earth elements containing Y include Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
In this case, in the present invention, a specific rare earth element can be extracted into the organic phase. For example, in the extraction / separation of Nd and Pr, Nd is preferentially extracted into the organic phase.

The ease of extraction of the rare earth element in the solvent extraction depends on its ionic radius, and among the extracted elements, those having a small ionic radius are extracted into the organic phase. Therefore, for example, when two adjacent light rare earth elements are extracted, the result is as follows.
Element La / Ce Ce extracted in combined organic phase
Ce / Pr Pr
Pr / Nd Nd
Nd / Sm Sm
Sm / Eu Eu

The rare earth element concentration C _A contained in the aqueous phase is preferably 0.01 mol / L ≦ C _A ≦ 0.7 mol / L. In the case of C _A <0.01 mol / L, there is no problem in the extraction ability and separation ability itself in the extraction / separation, but since the rare earth element concentration C _A is dilute, a sufficient amount of the target substance (rare earth element) can be obtained. A large amount of aqueous phase is required to obtain. As a result, the scale of the separation facility is increased, which may increase the cost. When C _A > 0.7 mol / L, it is difficult to obtain a diglycolamide acid concentration in the organic phase that matches the rare earth element concentration to be extracted. Is not sufficient, the organic phase may coagulate and may not be separated and purified by solvent extraction.

Here, in the present invention, the ratio C ₀ / C _A of the extractant concentration C _{O in} the organic phase and the rare earth element concentration C _{A in} the aqueous phase is preferably 2 ≦ C ₀ / C _A ≦ 10. If the ratio C ₀ / C _A <2, the concentration of diglycolamide acid as an extractant is not sufficient with respect to the rare earth element concentration, so that the organic phase may coagulate and separation and purification by solvent extraction may not be possible. Further, if the ratio C ₀ / C _A > 10, it does not contribute to improvement of the basic performance, ie, extraction ability and separation ability itself, but the cost becomes high because the organic phase concentration is too high with respect to the aqueous phase concentration.

  Further, the pH of the extraction layer (organic phase / aqueous phase) during the extraction step is controlled to 3 or less. If the pH exceeds 3, the rare earth element forms a rare earth hydroxide and becomes a precipitate, so that extraction / separation becomes impossible when the organic phase and the aqueous phase are brought into contact with each other. As a result, phase separation failure occurs and a problem occurs in the extraction process. In addition, when the pH is a strong acid, it is not preferable because the amount of a base used when adjusting the equilibrium acid concentration increases, and the pH of the extraction layer (organic phase / aqueous phase) during the extraction step is preferably 1 to 1. 3.

  Furthermore, the temperature of the extraction layer (organic phase / aqueous phase) during the extraction step is controlled below the flash point of the alcohol constituting the organic phase. The higher the temperature, the higher the solubility of the extractant in the organic phase and the better the separation of the organic and aqueous phases, but to prevent fires from the flash point, do not exceed the flash point of the solvent used. Is necessary, and the flash point is preferably controlled at − (5 to 10) ° C.

In the present invention, in order to efficiently contact an organic phase composed of an extractant / diluent and an aqueous solution containing a rare earth element to be separated for efficient extraction / separation, a countercurrent multistage mixer as shown in FIG. It is preferable to use a settler.
In FIG. 1, A is an extraction unit, B is a scrubbing unit, C is a back extraction unit, and the number of stages is set as appropriate. Reference numerals 1 to 8 denote flows that flow into or out of the mixer settler, and are pipes. Introduce a rare earth element solution from 1, an organic phase containing an extractant from 2, an alkaline aqueous solution such as an aqueous sodium hydroxide solution from 3, and an aqueous acid solution such as an aqueous hydrochloric acid solution from 4 and 6. The aqueous phase containing the remaining rare earth element and the aqueous solution obtained by back extracting the rare earth element extracted into the organic phase from 7 are collected. In the extraction part A, the pH of the aqueous phase is adjusted according to the type of rare earth element, and the rare earth element is separated into an organic phase and an aqueous phase. In the scrubbing section B, the organic phase is washed with an acid aqueous solution that selectively extracts only rare earth elements that should remain in the aqueous phase dissolved in a small amount in the organic phase. In the back extraction unit C, the rare earth element extracted in the organic phase is back extracted into the acid aqueous solution. Further, the extractant from which the rare earth element is back-extracted from 8 can be circulated and reused.

  In this case, in the extraction part A, the rare earth element solution 1 and the organic phase 2 containing the extractant are brought into contact with each other, extraction is performed, and a specific rare earth element in the rare earth element solution 1 is extracted into the organic phase 2. The aqueous phase 5 containing the rare earth element remaining without being extracted into 2 is discharged and recovered from the extraction unit A. The aqueous alkaline solution 3 is introduced for the purpose of adjusting the equilibrium acid concentration. The organic phase 2 from which the specific rare earth element has been extracted is introduced into the scrubbing section B, where the pH is adjusted so as to selectively extract only the rare earth element that should remain in the aqueous phase dissolved in a small amount in the organic phase 2. The organic phase 2 is washed with an acid aqueous solution 4 (for example, in the case of extraction / separation of Nd / Pr, Pr is selectively separated by adjusting the pH to 1 to 2). The acid aqueous solution 4 that selectively extracts only the rare earth elements to remain is introduced into the extraction section A, and the washed organic phase 2 is introduced into the back extraction section C, where the rare earth elements in the organic phase 2 are introduced. Is back-extracted with an acid aqueous solution 6 adjusted to a desired pH, and the obtained aqueous solution 7 containing rare earth elements is discharged and recovered. The organic phase 2 (8) from which the rare earth element has been back-extracted is circulated to the extraction section A.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
(Mutual separation of rare earth metals)
A test was conducted to examine the separation performance of the mixed rare earth metal when the solvent extraction according to the present invention was performed.
DODGAA was dissolved in 1-hexanol to prepare a 0.3 mol / L concentration solution to obtain an organic phase.
As a rare earth metal, a mixed solution of praseodymium chloride and neodymium chloride was prepared so that Pr + Nd = 0.1 mol / L at a Pr: Nd = 1: 1 molar ratio. 100 ml of the organic phase and 100 ml of the aqueous phase were placed in a separatory funnel, shaken at room temperature (20 ° C.) for about 20 minutes, extracted, and after reaching equilibrium, the organic and aqueous phases were separated. Furthermore, 100 ml of the organic phase was placed in a separatory funnel together with 100 ml of 5N hydrochloric acid, and shaken at room temperature (20 ° C.) for about 20 minutes, and the rare earth element extracted into the organic phase was back extracted into an aqueous hydrochloric acid solution. The concentration of praseodymium and neodymium in the aqueous hydrochloric acid solution back-extracted with the aqueous phase was measured with an ICP emission spectrometer (ICP-7500: trade name, manufactured by Shimadzu Corporation), and [Nd] org. = 0.028 mol / L, [Nd] aqua = 0.022 mol / L, [Pr] org. = 0.017 mol / L, [Pr] aqua = 0.033 mol / L. From this result, the neodymium / praseodymium separation factor of the DODGAA1-hexanol solution was 2.5.

[Examples 2 to 6]
(Separation of organic phase and aqueous phase)
When the solvent extraction according to the present invention was performed, a test was conducted to examine the time (phase separation state) required for separation of the organic phase / aqueous phase temperature and the organic phase-aqueous phase.
DODGAA was dissolved in 1-hexanol to prepare a 0.3 mol / L concentration solution to obtain an organic phase.
As a rare earth metal, a mixed solution of praseodymium chloride and neodymium chloride was prepared so that Pr + Nd = 0.1 mol / L at a Pr: Nd = 1: 1 molar ratio. 100 ml of the organic phase and 100 ml of the aqueous phase were put in a separatory funnel, shaken at a predetermined temperature for about 20 minutes, extracted, and after reaching equilibrium, the organic phase and the aqueous phase were separated. The results of examining the organic phase / aqueous phase temperature and the time (phase separation state) required for separation of the organic phase and the aqueous phase are shown in Table 1. The closer the organic phase / aqueous phase temperature was to the 1-hexanol flash point (about 63 ° C.), the shorter the time required for separation of the organic phase and the aqueous phase, and good results were obtained.

[Examples 7 to 10, Comparative Examples 1 and 2]
(Separation of various solvents and rare earths, separation of organic and aqueous phases)
When the solvent extraction according to the present invention was performed, a test was conducted to examine the type of solvent, the separation performance between rare earths, and the time (phase separation state) required for the separation between the organic phase and the aqueous phase.
DODGAA was dissolved in various solvents (alcohols) to prepare a 0.3 mol / L concentration solution as an organic phase.
As a rare earth metal, a mixed solution of praseodymium chloride and neodymium chloride was prepared so that Pr + Nd = 0.1 mol / L at a Pr: Nd = 1: 1 molar ratio. 100 ml of the organic phase and 100 ml of the aqueous phase were placed in a separatory funnel, shaken at room temperature (20 ° C.) for about 20 minutes, extracted, and after reaching equilibrium, the organic and aqueous phases were separated. Furthermore, 100 ml of the organic phase was placed in a separatory funnel together with 100 ml of 5N hydrochloric acid, and shaken at room temperature (20 ° C.) for about 20 minutes, and the rare earth element extracted into the organic phase was back extracted into an aqueous hydrochloric acid solution. The separation factor (Nd / Pr) and the state of phase separation measured for the concentration of praseodymium and neodymium in an aqueous hydrochloric acid solution back-extracted from the aqueous phase with an ICP emission spectrometer (ICP-7500: trade name, manufactured by Shimadzu Corporation) are shown. It is shown in 2. The neodymium / praseodymium separation factor using 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol as the solvent for DODGAA was 2.5. Moreover, following formula (2)
C _n H _{2n + 1} OH (2)
Can be separated into an organic phase and an aqueous phase, but n = 9 (nonanol) and n = 10 (decanol) can be separated into an organic phase and an aqueous phase. I could not.

[Example 11]
Hereinafter, an example using the mixer settler extraction device of FIG. 1 will be shown.
A mixed solution of neodymium chloride and praseodymium chloride in which the same 0.3 mol / L DODGAA 1-hexanol solution as in Example 1 is used as an organic phase and neodymium: praseodymium = 1: 1 molar ratio is neodymium + praseodymium = 0.1 mol / L. It was set as the water phase.
In FIG. 1, the organic phase and the aqueous phase are mixed and extracted at room temperature (20 ° C.) using a countercurrent multi-stage mixer settler with 24 stages for A, 24 stages for B, and 8 stages for C. Then, the rare earth elements in the organic phase were back extracted into an aqueous hydrochloric acid solution, and the concentrations of neodymium and praseodymium in the aqueous hydrochloric acid solution back extracted from the aqueous phase were measured with the above-described ICP emission spectrometer. The neodymium concentration in the back-extracted hydrochloric acid aqueous solution is 0.2 mol / L, the praseodymium concentration is 0.0002 mol / L, the praseodymium concentration in the aqueous phase is 0.04 mol / L, and the neodymium concentration is 0.0002 mol / L. The neodymium purity [Nd / (Nd + Pr)] in the back-extracted hydrochloric acid aqueous solution was 99.9%. From this result, the neodymium / praseodymium separation factor of the DODGAA1-hexanol solution was 2.5.
1, the mixed solution of neodymium chloride + praseodymium chloride from 1 at a flow rate of 15 liters / h, and from 2, the 0.3M DODGAA1-hexanol solution of the extractant at a flow rate of 6 liters / h. 3 from 4 mol / L sodium hydroxide aqueous solution was introduced at 0.75 liter / h, from 5 the aqueous phase was recovered at 16.75 liter / h, and from 6 to 4 mol / L hydrochloric acid aqueous solution was flowed at 3 liter / h. The aqueous hydrochloric acid solution containing neodymium back-extracted from 7 was collected at a flow rate of 3 liter / h. The extractant was circulated from 8 and reused.

[Comparative Example 3]
A PC-88A-kerosene solution adjusted to 1 mol / L is used as the organic phase, and a neodymium chloride and praseodymium chloride mixed solution in which neodymium: praseodymium = 1: 1 molar ratio is neodymium + praseodymium = 0.1 mol / L is water. Phased. In FIG. 1, using a countercurrent multistage mixer settler with 72 stages for A, 72 stages for B, and 8 stages for C, in the same manner as in Example 11, neodymium and praseodymium in a hydrochloric acid aqueous solution back-extracted from the aqueous phase. The concentration was measured with the ICP emission spectrometer described above. The neodymium concentration in the back-extracted hydrochloric acid aqueous solution is 0.2 mol / L, the praseodymium concentration is 0.0002 mol / L, the praseodymium concentration in the aqueous phase is 0.04 mol / L, and the neodymium concentration is 0.0002 mol / L. The neodymium purity [Nd / (Nd + Pr)] in the back-extracted hydrochloric acid aqueous solution was 99.9%. From this result, the neodymium / praseodymium separation factor of the PC-88A-kerosine solution was 1.4.
In addition, the PC-88A-kerosene solution of the extractant was introduced at a flow rate of 6 liter / h as in the example.

  As described above, when the extraction agent having a large separation coefficient according to the present invention is used, the number of extraction stages can be reduced to process the same amount with the same purity, and the initial investment can be suppressed.

  In this way, high-concentration DODGAA was dissolved with a low-polarity alcohol, and purification and separation at a low cost became possible by a solvent extraction method using a mixer settler from a rare earth mixed aqueous solution of about 0.02 to 0.5M. This solvent can also be achieved by mixing low-polarity alcohols or mixing low-polarity alcohols and alkane solvents.

DESCRIPTION OF SYMBOLS 1 Rare earth element solution or piping which introduces this 2 Organic phase containing extractant or piping which introduces this 3 Alkaline aqueous solution or piping which introduces this 4 Acid aqueous solution or piping which introduces this 5 Without being extracted to the organic phase Aqueous phase containing residual rare earth element or pipe for collecting this 6 Acid aqueous solution or pipe for introducing this 7 Aqueous solution obtained by back-extracting rare earth element extracted in organic phase or pipe for collecting this 8 Extractant or circulating this Piping A Extracting section B Scrub section C Back extraction section

Claims (5)

The following general formula (1)

(In the formula, R ¹ and R ² are the same or different alkyl groups, and at least one of them represents a linear or branched alkyl group having 6 or more carbon atoms.)
As an extractant, diglycolamide acid represented by the following general formula (2)
C _n H _{2n + 1} OH (2)
(In the formula, n is an integer of 5 to 8.)
It should be extracted from the rare earth elements by contacting an organic phase containing a low polar alcohol represented by the formula (1) and an aqueous phase comprising an aqueous solution containing two or more rare earth elements under acidic conditions of pH 3 or less. A rare earth element is extracted into the organic phase, and then the organic phase is back-extracted with an aqueous acid solution to recover the rare earth element extracted into the organic phase, and not extracted into the organic phase but into the aqueous phase. A method for extracting and separating rare earth elements, which comprises collecting residual rare earth elements.   2. The method for extracting and separating rare earth elements according to claim 1, wherein the extraction and back-extraction processes are carried out by a countercurrent multistage mixer settler.   3. The method for extracting and separating rare earth elements according to claim 1 or 2, wherein the organic phase and the aqueous phase are contacted at a temperature lower than the flash point of the low polarity alcohol of the formula (2) using the organic phase.   The rare earth element to be extracted and separated contained in the aqueous phase is at least two kinds of light rare earth elements selected from La, Ce, Pr, Nd, Sm and Eu, or at least one kind of the light rare earth elements. The method for extracting and separating rare earth elements according to any one of claims 1 to 3, which is at least one of the other rare earth elements containing Y.   The rare earth element contained in the aqueous phase is Nd and Pr, and Nd is extracted into an organic phase and Pr is left in the aqueous phase to separate Nd and Pr. The method for extracting and separating rare earth elements according to any one of 1 to 3.

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