JP2010270359A - Extractant and extraction-separating method for rare earth metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extractant for solvent extraction, which has a high capability of selectively separating a desirable rare-earth metal from a system in which a plural kinds of rare earth metals are mixed. <P>SOLUTION: It is possible to effectively and selectively extract the rare earth metal by conducting the solvent extraction which combines 4-isopropyltropolone with 1, 10-phenanthroline. The solvent to be used for the extraction is preferably toluene. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides an extractant that can be used for the separation of rare earth metals and a method for extracting and separating rare earth metals using the extractant.

  In the periodic table of elements, 15 elements from La with atomic number 57 to Lu with atomic number 71 are called lanthanoids (Ln). Permanent magnets, lasers, phosphors, hydrogen storage alloys, ultraviolet absorption lenses, optical fibers, magnetic recording disks, etc. It is a useful element used in From low atomic numbers La to Eu are called light lanthanides, and from large atomic numbers Gd to Lu are called heavy lanthanoids. Since lanthanoid elements have similar chemical properties, separation between Ln is difficult [Non-patent Document 1].

  Solvent extraction is a separation method that utilizes the distribution of solutes between two types of solvents that are almost immiscible with each other, and can be separated and purified from trace amounts to large amounts of substances with simple operations. Widely applied to nuclear fuel reprocessing etc. [Non-Patent Document 2].

Extraction of Ln with β-diketones such as thenoyltrifluoroacetone and 4-isopropyltropolone (Hipt) has been performed for a long time [Non-patent Documents 3-5]. In recent years, extraction of polynuclear complexes including addition (self-addition) of reagents such as Ln ₂ (ipt) ₆ Hipt, which is not found in the β-diketone system in the Hipt system has been reported [Non-patent Documents 6 and 7]. Furthermore, under the condition where multiple rare earths exist, co-extraction in which multinuclear complexes of heterogeneous Ln such as LaLu (ipt) ₆ and LaLu (ipt) ₆ Hipt occur, and it becomes clear that separation is hindered. [Non-Patent Document 8]. The mutual resolution of Ln (III) by a certain extraction system is predicted from the experimental results of each element alone. However, when the mutual separation is actually performed from a system in which a plurality of rare earth metals are present, a result different from the prediction may be obtained due to the influence of co-extraction.

  On the other hand, the cooperative effect is a phenomenon in which when two different types of extraction reagents are used in combination, extraction is dramatically improved compared to when each is used alone. This phenomenon was first discovered in 1954 by extraction of Ln (III) from a nitric acid solution with tenoyltrifluoroacetone and tributyl phosphate [Non-Patent Document 9]. In general, when Ln (III) is extracted using an acidic bidentate ligand (HA), the charge of a complex in which three molecules of HA are bound to Ln (III) having a coordination number of 8 to 9 is neutralized. However, since it has 2 to 3 molecules of coordinated water, its hydrophobicity is low and its extractability is low. On the other hand, in the cooperative extraction of Ln (III) when acidic bidentate ligand (HA) and neutral ligand (B) are used as extraction reagents, water molecules are neutral ligands (B ) Substituted ligand complexes are highly hydrophobic and have excellent extractability.

  There are few examples of cooperative effect extraction systems in which neutral ligands are added to Ln (III) extraction systems using Hipt, but divalent transition metals to chloroform using Hipt and trioctylphosphine oxide (TOPO). Extraction is known, and extraction of a mononuclear complex in the presence of TOPO [Non-Patent Document 10] is known. However, the deterioration of separation has been reported in Ln (III) cooperative effect extraction [Non-Patent Document 11] using TOPO. On the other hand, in the cooperative effect extraction of Ln (III) using 1,10-phenanthroline (phen) [Non-patent Documents 12 and 13], an improvement in separation has been reported.

  Various patent applications have been filed for extractants for separating rare earth metals from an aqueous phase by solvent extraction (for example, Patent Documents 1 and 2). However, conventional extractants have not been satisfactory with respect to the mutual separation performance of rare earth metals.

Japanese Unexamined Patent Publication No. 2007-327085 JP-A-7-34151

Ginya Adachi, Chemistry of rare earths, Chemical coterie (1999) Hisamura Imura, separate volume The latest separation, purification, and detection methods: from principles to applications T. Sekine, D. Dyrssen, J. Inorg. Nucl. Chem., (1967) 29, 1489-1498 J. Alstad, J.H. Augusuton, L. Farbu, J. Inorg. Nucl. Chem., (1974) 36, 899-903 Satoshi Oga, Kazuaki Yamaoka, Kazuyuki Itano, Kyoko Hasegawa, Analytical Chemistry, (2004) 53, 1199-1206 J. Noro, Anal. Sci., (1998) 14, 1099-1105 J. Noro, Anal. Sci, (1999) 15, 1265-1268 Hisamura Imura, Michie Ebisawa, Akira Ohashi, Kozaburo Ohashi, Junji Noro, Tomoki Ishigaki, Rare Earth, (2006) 48, 180-181 Hideo Akaiwa, Extraction and Separation Analysis, Kodansha (1972) T. Sekine, I. Ninomiya, M. Tebakari, J. Noro, Bull. Chem. Soc. Jpn., (1997) 70 1385-1392 T. Shigematsu, M. Tabushi, M. Matui, T. Honjyo, Bull. Chem. Soc. Jpn., (1967) 40, 2807-2812 S. Nakamura, N. Suzuki, Polyhedron, (1986) 5, 1805-1813 S. Nakamura, N. Suzuki, Bull. Chem. Soc. Jpn., (1993) 66, 98-102

  The present invention provides an extraction agent for solvent extraction having a high ability to selectively separate a target rare earth metal from a system in which plural kinds of rare earth metals are mixed, and a method for extracting and separating rare earth metals using the extraction agent The purpose is to do.

The present inventors used 4-isopropyl tropolone (hereinafter sometimes referred to as “Hipt”. An anion generated by proton dissociation from 4-isopropyl tropolone may also be referred to as “ipt”) as an extractant. In the solvent extraction system of the lanthanoid ion Ln (III) to be used, in the extraction system combined with the neutral ligand 1,10-phenanthroline (hereinafter sometimes referred to as “phen”), the mononuclear complex Ln (ipt ) It has been found that ₃ phen is generated as an extraction species, the extraction efficiency is high due to the cooperative effect, and the selective separation ability between rare earth metals is high, and the present invention has been completed.

The present invention includes the following embodiments.
(1) A rare earth metal extractant characterized by being a combination of 4-isopropyltropolone and 1,10-phenanthroline.
(2) An aqueous phase containing a rare earth metal in water and an organic phase containing the extractant of (1) in an organic solvent are contacted under pH conditions at which the target rare earth metal is extracted, An extraction process for extracting the target rare earth metal;
A method for extracting and separating rare earth metals, comprising a recovery step for recovering rare earth metals from the organic phase after the extraction step.
(3) The extraction and separation method according to (2), wherein the organic solvent is toluene.

  According to the present invention, a rare earth metal can be efficiently extracted from an aqueous phase. Further, by appropriately setting the pH conditions in the aqueous phase, it is possible to selectively separate the target rare earth metal from the aqueous phase in which a plurality of types of rare earth metals are mixed.

An outline of the extraction operation in the embodiment will be described. The extraction result of La (III) by Hipt-phen-toluene system is shown. The extraction result of Eu (III) by Hipt-phen-toluene system is shown. The extraction result of Lu (III) by Hipt-phen-toluene system is shown. The logD vs log [Hipt] _org plot (La (III)) in the Hipt-phen-toluene system is shown. The logD vs log [Hipt] _org plot (Eu (III)) in the Hipt-phen-toluene system is shown. The logD vs log [Hipt] _org plot (Lu (III)) in the Hipt-phen-toluene system is shown. The distribution ratio of phen between toluene and water phase is shown. The logD-log [phen] _org plot (La (III)) in the Hipt-phen-toluene system is shown. The logD-log [phen] _org plot (Eu (III)) in the Hipt-phen-toluene system is shown. The logD-log [phen] _org plot (Lu (III)) in the Hipt-phen-toluene system is shown. By changing Hipt concentration (5.0 x 10 ^-3 M or 1.0 x 10 ^-2 M) and phen concentration (2.0 x 10 ^-5 M or 1.0 x 10 ^-4 M), Eu (III ) Is extracted. The extraction result of Ln (III) by Hipt alone-toluene system is shown. The extraction result of Ln (III) by Hipt-phen-toluene system is shown. The extraction result of light Ln (III) by Hipt-phen-toluene system is shown. The extraction result of heavy Ln (III) by Hipt-phen-toluene system is shown. The measured value and calculated value of LogD vs pH plot are shown. The separation factor of other Ln (III) with respect to Eu (III) in the Hipt-phen-toluene system is shown. The separation factor of other Ln (III) with respect to La (III) in the Hipt-phen-toluene system is shown. The separation factor between Ln (III) atoms with adjacent atomic numbers by the Hipt-phen-toluene system.

1. Elements to be extracted and separated The metal extracted by the extractant of the present invention is a rare earth metal composed of scandium (Sc), yttrium (Y) and 15 lanthanoids (Ln), preferably a lanthanoid.
The extractant of the present invention has a high extractability of lanthanoids and a high extraction / separation ability between lanthanoids. For this reason, in addition to being able to separate lanthanoid-containing rare earth metals from other metal elements, it is also possible to selectively separate specific rare earth metals by adjusting the pH of the aqueous phase. .

2. Extractant In the present invention, an acidic bidentate ligand 4-isopropyltropolone (Hipt) and a neutral ligand 1,10-phenanthroline (phen) are used in combination as an extractant. Hipt is also called hinokitiol.

The concentration of Hipt and phen in the organic phase is not particularly limited. Typically, Hipt is 1 × 10 ^{−3 to} 1 × 10 ⁻² M, and phen is 1 × 10 ^{−3 to} 1 × 10 ⁻² M.
The ratio between Hipt and phen is not particularly limited, but the molar concentration ratio is preferably in the range of 10: 1 to 1:10.

  The amount of extractant used for the rare earth metal is not particularly limited, but the molar concentration of Hipt and phen in the organic phase is preferably the molar concentration of the rare earth metal ion to be extracted in the aqueous phase. 10 times or more, more preferably 100 times or more.

3. Extraction separation method The extraction separation method of the present invention is:
An aqueous phase containing a rare earth metal in water and an organic phase containing the extractant in an organic solvent are brought into contact with each other under a pH condition where the target rare earth metal is extracted, and the target rare earth metal is placed in the organic phase. An extraction process to extract;
And a recovery step of recovering the rare earth metal from the organic phase after the extraction step.

The aqueous phase preferably contains a rare earth metal in the form of a trivalent cation.
The ratio between the aqueous phase and the organic phase is not particularly limited. For example, an aqueous phase and an organic phase can be used in a volume ratio of 10: 1 to 1:10.

  The pH condition can be appropriately set according to the rare earth metal to be extracted. For example, as suggested from FIG. 14, when extraction is performed near neutral conditions with a pH value of about 6.50 to 7.00, it is possible to efficiently extract all rare earth metals, but mixing of a plurality of rare earth metals It is not suitable for selectively extracting specific metals from the system. On the other hand, when extraction is performed within a pH value range of 4.0 to 6.00, selective extraction between rare earth metals becomes possible (see FIGS. 14 to 16 and FIGS. 18 to 20).

  The organic solvent is not particularly limited as long as it can dissolve the extractant of the present invention, but is preferably a nonpolar solvent, and particularly preferably toluene, benzene, xylene, chlorobenzene, or dichlorobenzene.

  The contact between the aqueous phase and the organic phase is performed by sufficiently stirring or shaking the mixture of both. The contact time is preferably 30 to 60 minutes. The contact temperature is preferably 20-30 ° C.

After the rare earth metal is extracted into the organic phase, the organic phase and the aqueous phase are separated by ordinary means.
As a method for recovering the rare earth metal from the organic phase, the organic phase and another aqueous phase are brought into contact with each other under a pH condition that is more acidic than the pH condition in the extraction step, and the rare earth metal is added to the other aqueous phase. There is a method of back extraction. A dilute solution such as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid can be used as the aqueous phase for back extraction.

1. Example 1: Cooperative extraction with a neutral ligand (phen) from a system containing a single species of lanthanoid (III)
1.1. Purpose In this example, the effect of 1,10-phenanthroline (phen), a neutral ligand, was clarified in the Hipt-toluene system from which a polynuclear complex of Ln (III) was extracted.

1.2. Experiment
1.2.1. Reagents
Hipt (Hanai Chemical, 98%), Arsenazo III (Dojin Chemical, for research), Toluene (Nacalai Tesque, reagent grade), and phen (ALDRICH, 99%) were used without any particular purification. Water purified by an ultrapure water purifier (MILLIPORE Elix3 / milli-Q gradient A10) was used. Acetic acid (Kanto Chemical Co., Ltd.) and 2-morpholinoethanesulfonic acid (MES) (Dojindo Chemical Co., Ltd.) were used as pH buffering agents, and sodium hydroxide (Sigma Aldrich Co., Ltd.) was used for pH adjustment.

Ln (III) standard solution is a high-purity oxide (La ₂ O ₃ ; Yttrium Japan, 99.9%, Eu ₂ O ₃ ; Yttrium Japan, 99.9%, Lu ₂ O ₃ ; Yttrium Japan, 99.9 %) Was heated at 800 ° C. for 3 hours using an electric furnace and then weighed. After heating and dissolving in concentrated nitric acid, it was evaporated to dryness. Add perchloric acid to the residue, repeat evaporation and drying three times, then make up with perchloric acid and water, and add 1.0 x 10 ^-2 M Ln (III) in 1.0 x 10 ^-1 M perchloric acid solution. Prepared.

1.2.2. A shaker (TAITEC RECIPRO SHAKER SR1) was used to shake the apparatus solution, and a centrifuge (TOMY LC 100) was used to separate the aqueous and organic phases. The pH was measured using a pH meter (HORIBA F52) equipped with a glass electrode (HORIBA 9678-10D). For calibration of pH meter, oxalate standard solution (Sigma Aldrich, pH 1.68), phthalate standard solution (Sigma Aldrich, pH 4.01), neutral phosphate standard solution (Sigma Aldrich, pH 6.86), borate A standard solution (Sigma Aldrich, pH 9.18) was used. For the determination of Ln (III), an ultraviolet-visible spectrophotometer (Shimadzu UV-160) and an inductively coupled plasma mass spectrometer (ICP-MS) (Seiko Instruments SPQ 8000) were used.

1.2.3. Extraction operation Figure 1 shows an overview of the extraction operation. Each operation will be described in detail below.
Contains 2.0 x 10 ^-5 M Ln (III), pH buffer (1.0 x 10 ^-2 M MES or 1.0 x 10 ^-3 M acetic acid), ionic strength to 1.0 x 10 ^-1 M with NaCl or NaClO ₄ The adjusted aqueous phase and an equal volume organic phase containing Hipt and phen were shaken for 1 hour and then centrifuged at 2000 rpm for 5 minutes. The pH of the aqueous phase was measured immediately after centrifugation. The activity coefficient at an ionic strength of 1.0 × 10 ⁻¹ M is 0.83, and the relationship between pH and hydrogen ion concentration [H ⁺ ] is expressed by the following equation.

The organic phase after extraction (4 mL) was separated and shaken with 1.0 × 10 ⁻¹ M HClO ₄ (4 mL) for 1 hour, and Ln was back extracted. Ln (III) partition ratio (D), extraction rate (%) between water phase and organic phase was determined by spectrophotometry using arsenazo III or ICP-MS E) and recovery rate (% R) were determined. The definitions of D,% E and% R are as follows. The subscript org indicates the organic phase, the non-subscript indicates the aqueous phase, and ini indicates the initial concentration.

1.2.4. Quantitative determination of Ln (III) using Arsenazo III The aqueous phase after forward extraction and back extraction was separated, and Arsenazo III concentration 0.01% (w / w), perchloric acid concentration 5.0 x 10 ^-2 M Then, the absorbance at 655 nm was measured using the reagent blank as a control.

1.2.5. Determination of Ln (III) using ICP-MS
Table 1 shows the ICP-MS device settings. The aqueous phase after normal extraction and reverse extraction was fractionated and diluted 20-fold to 200-fold so that the nitric acid concentration became 1.0 × 10 ⁻¹ M to obtain a sample solution. The same measurement procedure as the sample was performed on the blank solution to which the Ln was not added to the Ln solution for the calibration curve. By adding the aqueous phase, the measurement sample and the matrix were matched.

1.2.6. Distribution experiment of phen
Toluene (5 mL) containing 1.0 × 10 ⁻³ M phen and aqueous phase (5 mL) were shaken for 1 hour and then centrifuged at 2000 rpm for 5 minutes. After separating the aqueous phase (2.5 mL) and adding 0.5 mL of 1.0 MH ₂ SO ₄ and 2 mL of water, the toluene was removed by shaking with 1 mL of heptane for 1 hour, and the measurement sample for the phen concentration of the aqueous phase did. The toluene phase (4 mL) was separated, shaken with 1.0 × 10 ⁻¹ MH ₂ SO ₄ (4 mL) for 1 hour, and then centrifuged at 2000 rpm for 5 minutes (back extraction). After separating the aqueous phase (3 mL) after back extraction, toluene was removed in the same procedure to obtain a measurement sample for the phen concentration of the organic phase. The aqueous phase obtained as a measurement sample was diluted with 1.0 × 10 ⁻¹ MH ₂ SO ₄ and then the absorbance at 272 nm was measured to quantify phen in both phases.

1.3. Results and discussion
1.3.1. Extraction of Ln (III) cooperative effects by Hipt and phen
The cooperative effect extraction of Ln (III) using Hipt and phen was performed. The results are shown in FIGS. Hipt only extract D with La (III) by the coexistence of phen as compared with the case of using as a reagent 10 about ^twice, 10 ^three times back and forth Eu (III), 10 ⁴ times back and forth Lu (III) An increase in the extraction of selenium was observed, and a cooperative effect appeared.

In the following, Hipt is expressed as HA, ipt as A, and phen as B. In the case of lanthanoid (III), when the element is not limited to a specific element, Ln or hydrated ion is expressed as Ln ³⁺ .
The extraction of the n-nuclear mixed ligand complex Ln _n A _3n HA _m B _p is represented by the formula (1-1), and the extraction constants K _{ex, s, nmp} are represented by the formula (1-2).

When the main extracted species is Ln _n A _3n HA _m B _p , the distribution ratio D is expressed by equation (1-3).

Here, β _k is a complex formation constant in the aqueous phase and is defined as follows.

  The total concentration of Ln in the aqueous phase can be written as

  Equation (1-3) can be transformed as follows using equations (1-2) and (1-5).

  Taking the logarithm of equation (1-6) yields equation (1-7).

The slope of the logD vs pH plot for the cooperative effect system shown in FIGS. 2-4 was 2.6 to 3.8. From this, the coefficient 3n of −log [H ⁺ ] in the expression (1-7) is 3, that is, n is 1. The slope 3.8 seen in Lu (III) is due to the change in [phen] _org due to phen protonation, as described below. Therefore, it is estimated that any Ln is extracted as a mononuclear complex (n = 1). The extracted species are discussed in more detail in the following sections.

1.3.2. Number of Hipt bonds
From equation (1-7), it can be seen that the slope of logD vs log [Hipt] _org plot at constant pH and [phen] _org indicates the number of bonds in Hipt and the number of metals in the extracted species. The Hipt concentration in the organic phase was determined using the following equation.

Here, K _{d, HA} is a distribution constant, defined by the following equation, and K _{d, Hipt} = 10 ^2.41 [1].

K _{a, HA} is an acid dissociation constant, and is defined by the following formula: ^Ka _{, Hipt} = 10 ^−7.04 [2].

5, 6 and 7 show logD vs log [Hipt] _org plots of La (III), Eu (III) and Lu (III) at a constant pH. Since the slope is 2.9 to 3.0, it is considered that n = 1, m = 0, that is, the extracted species has a central metal number of 1 and a Hipt coordination number of 3.

1.3.3. Number of phen bonds
From the equation (1-7), it can be seen that the slope of the logD vs log [phen] _org plot at constant pH and [Hipt] _org indicates the number of phen bonds to the Ln-ipt complex. (1-7) [B] in Formula _org is represented by (1-8) equation, K _{d, B} and K _a in the _{formula, B} is defined as follows. K _{a, phen} = 10 ^-4.98 [6].

In order to obtain K _{d, phen} , the distribution ratio D _phen of phen in the water-toluene system was obtained and analyzed. D _phen is expressed by equation (1-9) and can be transformed from equation (1-18) and equation (1-19) to equation (1-10). can get.

A logD _phen vs pH plot is shown in FIG. K _a, K _d, performs least square fitting based on (1-11) below for _phen using _phen = 10 ^-4.98 [6], to obtain K _d, the _phen = 10 ^{0.60 ± 0.003.}

9, 10, and 11 show logD-log [phen] _org plots of La (III), Eu (III), and Lu (III). Since the slope is from 0.91 to 0.95, it is considered that one molecule of phen is bound to the extracted species.

These results indicate that the extracted species of Ln (III) in the Hipt-phen cooperative effect system is Ln (ipt) ₃ phen. Therefore, the extraction reaction is expressed by equation (1-12), and the extraction constant is defined by equation (1-13).

K _{ex, s, 101 (La)} = 10 ^{-5.43 ± 0.07 for} _La , K _{ex, s, 101 (Eu)} = 10 ^{-0.84 ± 0.06 for} _Eu , K _{ex, s, 101 (Lu)} = 10 ^{1.57 for} _Lu ^{± 0.03} is obtained.

The separation coefficient α obtained from the ratio of the extraction constants K _{ex, s, 101} was 10 ^4.59 between La and Eu, 10 ^2.41 between Eu and Lu, and 10 ^7.00 between La and Lu. Table 2 shows the extraction constants and separation factors obtained.

  The obtained results were compared with a cooperative effect extraction system using β-diketones such as thenoyltrifluoroacetone (Htta), pivaloyltrifluoroacetylacetone (Hpta) and acetylacetone (Hacac) and phen. The Hipt-phen system showed very high performance for the separation of La-Lu.

  Subsequently, the logD vs pH plot shown above was considered. The distribution ratio D is expressed by the equation (1-14) considering the formation of the ipt complex in the aqueous phase, and the equation (1-15) is obtained when the logarithm is taken.

  Furthermore, considering the phen protonation in the aqueous phase, it can be transformed into (1-16) using (1-8).

When [H ⁺ ] is sufficiently large, that is, the extraction conditions are sufficiently acidic, equation (1-16) can be approximated to equation (1-17).

Therefore, the HipD-phen system logD vs pH plot has a slope of 4 in the acidic region. Lu (III) slope 3.8 shown in FIG. 4 is due to this effect. To evaluate the obtained constants, Eu (III) was changed by changing the Hipt concentration from 5.0 x 10 ^-3 M to 1.0 x 10 ^-2 M and the phen concentration from 2.0 x 10 ^-5 M to 1.0 x 10 ^-4 M. Extracted. The results are shown in FIG. The experimental value and the calculated value based on equation (1-15) are in good agreement. The hydrogen ion concentration obtained from the measured pH was used for the calculation. From the above, it was confirmed that the extracted species was Eu (ipt) ₃ phen within the range of this extraction condition.

1.4. Conclusion By the coexistence of the neutral ligand phen, the extracted species of Ln (III) in the Hipt-toluene system could be changed from a polynuclear complex to a mononuclear complex. The Hipt-phen system showed excellent performance in the separation of Ln (III), and the separation factor between La and Lu reached 10 ^7.00 .

2. Example 2: Extraction separation from mixed system of multiple lanthanoids (III)
2.1. In Example 1, it was confirmed that a mononuclear complex Ln (ipt) ₃ phen was obtained as an extraction species in a system in which phen was added to the extraction of Ln (III) using Hipt.
In this example, extraction and separation are further performed from a solution in which 14 types of Ln (III) except Pm are mixed, and the actual resolution obtained is compared with the result of Example 1.

2.2. In addition to the reagents used in Experimental Example 1, 14 standard solutions of Ln (III) other than Pm were used. The standard solution was prepared in the same manner as described above. Extraction operation and quantitative operation were performed in the same manner as in Example 1.
For ¹⁴² Nd, ¹⁵² Sm, ¹⁵⁸ Gd, and ¹⁶⁴ Dy used for the determination of Ln (III) by ICP-MS, there are isotopes of ¹⁴² Ce, ¹⁵² Gd, ¹⁵⁸ Dy, and ¹⁶⁴ Er, respectively. Was corrected. The following corrections were made with the coefficient rate (cps) obtained as the measured value being c _{n, d} , the coefficient rate of the isotope being measured being c _{n, x and} the isotopic abundance of the isotope being interfering being an _{n, i} .

It can be assumed that the sensitivities between isotopes for a particular element are almost equal, and c _{m, i} is obtained for the measured solution, so this correction gives c _{n, x} from the measured value, and this value is The measured elements were quantified.

2.3. Results and discussion
2.3.1. Simultaneous extraction of 14 Ln (III) species
Ln (III) was extracted from the solution containing 1.0 x 10 ^-6 M of each of 14 types of Ln (III) excluding Pm using the Hipt single system and the Hipt-phen system. The results are shown in FIGS. Regarding the results of FIG. 14, FIG. 15 shows a plot of light lanthanoids from La to Eu, and FIG. 16 shows a plot of heavy lanthanoids from Gd to Lu. It can be seen that the shape of the distribution curve is similar between light lanthanoids (La-Eu) and heavy lanthanoids (Gd-Lu).

Results of extraction of La (III), Eu (III), and Lu (III) shown in FIG. 14 and calculated values using the extraction constants K _{ex, s, 101} obtained in Example 1 and the literature value β ₁ A comparison with FIG.
Since the calculated values and experimental results for La (III) and Eu (III) showed good agreement, the extracted species is Ln (ipt) ₃ phen even in the system where multiple Ln (III) coexists, and the polynuclear complex The co-extraction due to the generation of The same extraction can be considered for extraction of light Ln whose distribution curve shows a similar shape.
On the other hand, the calculated values and experimental results of Lu (III) are greatly different, and the influence of the formation of a heterogeneous Ln polynuclear complex, which is inferior in extractability compared with the phen addition complex, is presumed.

2.3.2. Separation coefficient in Hipt system and Hipt-phen system The actual separation coefficient α was calculated from the ratio of the distribution ratio D using the results shown in FIGS. FIG. 18 shows other Ln (III) separation coefficients for Eu (III). In light Ln (La-Eu), the Hipt-phen system showed a larger separation factor than the Hipt-only system in the separation of the actual Ln (III) mixture, regardless of the pH. On the other hand, for the heavy Ln, the separation performance of the Hipt-phen system greatly changed with the change of pH. Heavy Ln (Gd-Lu) separation behavior is similar between the Hipt-phen system and the Hipt single system, and the extraction of heavy Ln from the mismatch between the calculated and experimental values for Lu (III) described in the previous section It is considered that the co-extraction due to the formation of polynuclear complex between heavy Ln greatly affects.

FIG. 19 shows the separation coefficient α of other Ln (III) with respect to La (III) in the Hipt-phen system. At pH 4.97, the separation factor α of Eu (III), Ho (III), Tm (III), Yb (III), and Lu (III) exceeds 10 ^4.00 . Under these extraction conditions, these Ln (III) It can be quantitatively separated from La (III) by one batch extraction. The separation factor α obtained for La (III) and Eu (III) was ^10.4.65 , which was in good agreement with the separation factor 10 ^4.59 (Table 2) obtained from the ratio of the extraction constants in Example 1.

On the other hand, the separation factor obtained for La (III) and Lu (III) was ^10.49 , which is very different from the separation factor 10 ^7.00 (Table 2) obtained from the ratio of extraction constants. As described above, this is due to the change of the extracted species due to the formation of a polynuclear complex between heavy Ln.

2.3.3. Separation between Ln (III) s with adjacent atomic numbers From the results in FIGS. 13 and 14, the separation coefficient α between Ln (III) with adjacent atomic numbers was obtained. The results are shown in FIG. The Hipt-phen cooperative effect system shows extremely high separation performance approaching α = 10 ^2.00 for La-Ce (57-58), Eu-Gd (63-64), Er-Tm (68-69) It was.

Usually, the extractability in chelate extraction of Ln (III) increases in proportion to the charge density of Ln (III), and therefore increases in order of atomic number. However, in the Hipt-phen system, Eu-Gd (63-64) and Ho-Er (68-69) showed a peculiar behavior in which the order of extractability was significantly reversed from that of atomic numbers. The reversal between Eu and Gd is particularly large. In the Hipt-phen system, the extracted species of Eu (III) is Eu (ipt) ₃ phen, whereas the extracted species of Gd is considered to contain a polynuclear complex. For this reason, it is considered that the separation of similar chemical species exhibited a unique behavior that is not normally obtained.

2.4. Conclusion
The Hipt-phen system shows excellent performance in mutual separation of Ln, and the combination of La (III) and Eu (III), Ho (III), Tm (III), Yb (III), Lu (III) A quantitative separation of> 10 ^4.00 was achieved. In addition, since the behavior of La (III) and Eu (III) was in good agreement with the prediction from the experimental results of the metal alone, the extracted species was La (ipt) ₃ phen even under the condition where multiple Ln (III) were mixed. And Eu (ipt) ₃ phen. Further, a combination of Ln (III) having adjacent atomic numbers, such as La-Ce, Eu-Gd, Er-Tm, etc., which is generally difficult to separate, shows a good value of about ^102.00 .

3. List of references
[1] J. Noro, Anal. Sci., (1998) 14, 1099-1105
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Claims (3)

  A rare earth metal extractant characterized by being a combination of 4-isopropyltropolone and 1,10-phenanthroline. An aqueous phase containing a rare earth metal in water and an organic phase containing the extractant of claim 1 in an organic solvent are brought into contact under pH conditions at which the target rare earth metal is extracted. An extraction process for extracting the rare earth metal;
A method for extracting and separating rare earth metals, comprising a recovery step for recovering rare earth metals from the organic phase after the extraction step.   The extraction separation method of Claim 2 whose organic solvent is toluene.

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