JP6183844B2 - Fractional precipitation of lanthanoid ions using coordination polymerisation - Google Patents

Description

  The present invention relates to a fractional precipitation method of lanthanoid ions utilizing coordination polymerization, and more particularly to a fractional precipitation method of neodymium ions and dysprosium ions.

  In recent years, the supply structure of lanthanoids has become fragile, and the importance of recycling lanthanoids from used products has been advocated as a measure to ensure a stable supply. Separation is particularly important in the recycling process. When lanthanoids are targeted for separation, there are two types of separation. One is separation of lanthanoids from base metals such as iron, and the other is mutual separation of lanthanoids. Since the lanthanides are very similar in nature to each other, the latter separation is particularly difficult.

For example, neodymium magnets mainly composed of neodymium (Nd), iron (Fe), and boron (B) are considered to be the most powerful permanent magnets, and are used for drive motors for hybrid vehicles, compressor motors for air conditioners, etc. It is known that the addition of a small amount of dysprosium (Dy) improves the coercive force.
In recycling lanthanoids from such magnets, it is necessary to first remove a large amount of iron. For example, Naganawa et al. Have developed extraction reagents effective for removing iron (Non-patent Documents 1 and 2). . Shirayama et al. Are studying separation of iron and lanthanoids by a dry method (Non-patent Document 3).

Next, separation of neodymium and dysprosium, which is a mutual separation of lanthanoids, is performed.
Conventionally, a solvent extraction method has been studied as a method for separating neodymium (Nd) and dysprosium (Dy) (Non-Patent Document 4).
This solvent extraction method is a method in which ions to be separated dissolved in an aqueous solution are selectively extracted into an organic solvent and then back-extracted again into an aqueous solution phase. This technique has been applied to many metal ion separation systems, and there are many types of extraction reagents used industrially.
However, it is effective when the target substance has a high concentration, but is not suitable for a low concentration system. In addition, it is the extraction reagent in the organic solvent that is responsible for the selectivity, so the extraction reagent can be selected according to the target, but if the properties of the metal ions, such as mutual separation of lanthanides, are similar, In this case, large-scale equipment, a large amount of organic solvent and energy are required.

One of the metal ion separation methods is an “ion exchange method”.
This method is a method in which a target substance is separated by selectively desorbing after adsorbing metal ions to a porous polymer. In ordinary ion exchange resins and the like, there is no great difference in the interaction between the exchanger itself and the lanthanoid ions, and separation is performed by using a complexing agent having selectivity for the lanthanoid ions in the desorption process. In addition, with a chelate resin in which a highly selective chelating agent is bound to a specific metal ion, the separation process is simplified, but an organic solvent is required for the synthesis of the chelate resin, and the synthesis process is complicated. is there.

As another separation method, an “impregnation resin method” can also be mentioned.
In this method, a solvent extraction reagent is used by being immersed in a porous polymer. The metal ion separation mechanism is the same as the solvent extraction method described above, but is excellent in that no organic solvent is used. However, since only the liquid is infiltrated, deterioration due to the liquid starting to dissolve from the polymer is a problem.

Furthermore, as another separation method, “precipitation separation method” may be mentioned.
Aisin Seiki has announced technology to extract neodymium, dysprosium, etc. from used magnets using inosinic acid contained in skipjack soup (Non-Patent Documents 5 and 6), which is cheaper and safer than conventional methods. It can be said that it is a feature. In this method, 90 grams of Lee Roh chloride neodymium solution 40 grams per liter to the thin acid mixing the 95% of neodymium per liter can be recovered as a precipitate, it passes certain prospect stable procurement of dysprosium It is described.
However, data on the mutual separation of neodymium and dysprosium is not shown.

Further, Non-Patent Document 7, neodymium (Nd), praseodymium (Pr), and erbium (Er) is 62% of d i (2-ethylhexyl) phosphoric acid (HA) and 37% m ono- (2- Etylhexyl) phosphoric acid (H ₂ A ') mixture in acetone solution produces only precipitate with HA, while lanthanum (La) precipitates only with H ₂ A' by complexation Is heading. And as a result of trying to separate these from a mixed solution of lanthanum (La) and neodymium (Nd) using this, for example, in a system in which lanthanum and neodymium were mixed at 1: 1, neodymium 19.8%, lanthanum was It is supposed to be 0.7% precipitated. The results of separation of praseodymium (Pr) and erbium (Er) are not described, but are reported to be worse than the neodymium-lanthanum system.

H. Naganawa, S. Nishihama, K. Yoshizuka, Sov. Extr. Res. Dev. Jpn, 2007, 14, 151. K. Shimojo, H. Naganawa, J. Noro, F. Kubot, M. Goto, Anal. Sci., 2007, 23, 1427. S. Shirayama, T.H.Okabe, Proceeding of Annual Meeting of MMIJ, 2008, Mar. 27-29, 69-70. M. Tanaka, Y. Sato, Y. Huang, H. Narita, K. Koyama, Proceedings of the 10th International Symposium on East Asian Resources Recycling Technology, Nov.2-6, 2009, 200-203. Keiko Shimbun, July 8 Abstracts of the presentation of the Society of Resources and Materials 2013 (Spring Conference), page 81 M. Milanova, D. Todorovsky, M. Arnaudov, N. Minkova, Separation Science and Technology, 1995, 30 (5) 5, 821-8320. Yuiko Tasaki-Handa, Hiroaki Sato, Masaki Torimura, Mikiya Tanaka, Akihiro Wakisaka, Solvent Extraction Research and Development Japan, accepted. Yuiko Tasaki-Handa, Kenta Ooi, Mikiya Tanaka, Akihiro Wakisaka, Analytical Sciences, 2013, 29 (7), 685-687.

As described above, Non-Patent Document 6, there is no description about separation of lanthanoid ion, Non-patent Document 7, d i (2-ethylhexyl ) an effective extraction reagent lanthanoid element PHOSPHORIC acid Although a method for separating lanthanoid ions using (liquid) is described, there is no description about neodymium (Nd) ions and dysprosium (Dy) ions.

  The present invention has been made in view of the current situation, and provides a method for selectively separating lanthanoid ions, particularly neodymium ions and dysprosium ions, which are extremely difficult to separate, at low cost. It is the purpose.

As a result of intensive studies to achieve the above object, the present inventors have found that di-2-ethylhexyl phosphate ester ( d ) known as a solvent extraction reagent having high selectivity to lanthanoid ions (Ln ³⁺ ) ( d i (2-ethylhexyl) phosphoric acid, hereinafter sometimes referred to as “Hdehp ”.) (Liquid) (A in FIG. 1) forms a coordination polymer (solid) with a metal ion (FIG. 1 ) . It was found that the above-mentioned object can be achieved by using C) . That is, Hdehp in normal solvent extraction system 1: those forming the 6 complex, to form a coordination high content child reacts with lanthanide ions (Ln ³⁺⁾ in an alcohol / water mixed solvent It has been found that the reaction rate varies depending on the type of ions and the composition ratio of the mixed solvent.

The present invention has been completed based on this finding, and the following inventions are provided.
[1] A method for fractionally precipitating dysprosium ions from a solution containing neodymium ions and dysprosium ions,
Using di-2-ethylhexyl phosphate as a coordination polymer forming agent, characterized in that dysprosium ions are selectively polymerized and fractionally precipitated in a mixture of water and a water-soluble organic solvent. Fractional precipitation method.
[2] The fractional precipitation method according to [1], wherein an acid is further mixed with the mixed solution to increase the hydrogen ion concentration of the mixed solution.
[3] The fractional precipitation method according to [1] or [2], wherein the water-soluble organic solvent is selected from ethanol, methanol, and acetone.

  According to the present invention, neodymium ions and dysprosium ions can be separated without requiring a multistage process using an organic solvent like solvent extraction. In addition, the method of the present invention solidifies the conventionally used extraction reagent itself, and unlike the impregnating resin that supports the liquid extraction reagent, the solvent required for the preparation is water alone or water and alcohol. Only a hydrophilic organic solvent is used, and the preparation method is very low cost and simple. It can also be applied to lanthanoid ions that are very difficult to separate.

Illustration of Hdehp coordination polymerization Diagram showing the ethanol / water composition dependence of the precipitation rate from a single component solution of Nd and Dy Diagram showing precipitation rate at Dy: Nd: Nadehp = 1: 1: 3 Diagram showing Dy / Nd ratio in coordination polymer in Dy: Nd: Nadehp = 1: 1: 3 mixed solution

The present invention is a fractional precipitation method utilizing the fact that di-2-ethylhexyl phosphate (liquid), which is an effective extraction reagent for separating lanthanoid ions, forms a coordination polymer (solid) with metal ions. Thus, di-2-ethylhexyl phosphate is used as a coordination polymer forming agent, and dysprosium ions are selectively distributed in a mixture of water containing a neodymium ion and dysprosium ion and a water-soluble organic solvent. It is characterized in that it is polymerized and fractionally precipitated.

First, Hdehp coordination polymerization will be described with reference to FIG.
Di-2-ethylhexyl phosphate ester ( Hdehp, A in FIG. 1 ) is described by Peppard et al. (DF Peppard, GW Mason, JL Maier, and WJ Driscoll, J. Inorg. Nucl.Chem.1957,4,334-343.) Was proposed as a solvent extraction reagent having high selectivity for lanthanoid ions. It is said to form dimers in nonpolar solvents. In a normal solvent extraction system, a trivalent metal ion and three dimers form a 1: 6 complex (B in FIG. 1). Further, it is known that when the concentrations of metal ions and Hdehp are high, the metal ions (M = Ln, Fe, Al, etc.) and Hdehp form a gel in the organic phase. The composition of the gel is M: Hdehp = 1: 3, and it is considered to be a complex in which one Hdehp molecule crosslinks two metal ions into a polymer type (T. Harada and M. Smuts, J. Inorg Nucl. Chem., 1970, 32, 649-662) (hereinafter sometimes referred to as [ M (dehp) ₃ ] ) .

In recent years, polymer-type complexes formed by crosslinking organic ions with metal ligands are called coordination polymers or Metal Organic Framework (MOF), and are a group of materials that have attracted attention.
The inventors have found that M and Hdehp are coordinated with ethanol or a mixed solvent of ethanol-water to form [M (dehp) ₃ ] and precipitate (Non-Patent Documents 8 and 9 above). ).

  The present invention relates to a fractional precipitation method using coordination polymerization of metal ions and Hdehp, wherein Hdehp is a dysprosium ion in a mixture of water and a water-soluble organic solvent containing neodymium ions and dysprosium ions. This is because it has been found that neodymium ions and dysprosium ions can be separated by selectively forming a coordination polymer and precipitating the coordination polymer.

In the present invention, the solvent used by mixing with water is not particularly limited as long as it is a water-soluble organic solvent mixed with water. For example, lower alcohol such as ethanol, methanol, propanol, or acetone is used. Can do.
The concentration of the water-soluble organic solvent in the mixed solution is not particularly limited, but is preferably 70 to 90% by volume.
The concentration of di-2-ethylhexyl phosphate (Hdehp) in the mixed solution of water and water-soluble organic solvent is preferably 50 to 500 mM.

  Moreover, in the liquid mixture containing neodymium ions and dysprosium ions, it is desirable that the concentration of Hdehp is mixed so as to be three times the concentration of dysprosium ions to be separately precipitated.

In the present invention, as a method for selectively converting dysprosium ions into a coordination polymer in a mixed solution of water and a water-soluble organic solvent, a coordination polymer is used in a mixed solution in which neodymium ions and dysprosium ions are present. The mixing method is not particularly limited as long as it contains Hdehp which is an agent.
That is, for example, as a solution containing neodymium ions and dysprosium ions, an aqueous solution in which neodymium and dysprosium are dissolved, a solution in which neodymium and dysprosium are dissolved in a water-soluble organic solvent, or a mixture of water and a water-soluble organic solvent A solution in which neodymium and dysprosium are dissolved is used. Then, Hdehp was mixed with any solution containing these neodymium ions and dysprosium ions, or Hdehp was dissolved in a mixed solution of water and a water-soluble organic solvent in any of the above solutions. The solution is mixed and, if necessary, water and / or a water-soluble organic solvent is mixed.
The mixed solution thus obtained is allowed to stand, for example, overnight at room temperature to form a coordination polymer, and then the coordination polymer precipitated in the mixed solution is separated by washing and filtration.

Furthermore, in the present invention, separation efficiency can be increased by mixing an acid with the mixed solution and increasing the hydrogen ion concentration of the mixed solution.
A preferred hydrogen ion concentration is 0.3M.
The acid to be mixed is not particularly limited as long as it is soluble in water. For example, nitric acid or hydrochloric acid is preferably used.

Hereinafter, the precipitation separation method of the present invention using Hdehp forming a metal ion and a coordination polymer (solid) ([M (dehp) ₃ ]) will be described using examples. Is not limited to these examples.

[Preparation of 0.30M Nadehp 80 / 20vol% ethanol / water solution]
Hdehp was changed to Na type using an aqueous NaOH solution so that the pH did not change before and after the reaction.
Hdehp 9.66g, 14.5M NaOH aqueous solution 2.0mL and water 18mL were dissolved in ethanol to make 100mL, and 0.30M Nadehp 80 / 20vol% ethanol / water solution was prepared.

[Preparation of 0.20 M LnCl ₃ ethanol solution]
An ethanol solution of lanthanoid (Ln) was prepared as follows.
Each of NdCl ₃ hexahydrate, DyCl ₃ hexahydrate, and FeCl ₃ hexahydrate was dissolved in ethanol to prepare a 0.20 M solution. Since precipitation may occur only in the case of FeCl ₃ , 2 MH NO ₃ aqueous solution was added at a volume ratio of 1/500.

Example 1
In this example, the molar concentration of the prepared Ln ethanol solution was measured.
0.025 mL was taken from each of the obtained NdCl ₃ ethanol solution, DyCl ₃ ethanol solution, and FeCl ₃ ethanol solution, weighed, and after evaporating the ethanol, it was made up to 100 mL and each solution molar concentration was adjusted to ICP. -Determined by emission spectroscopy (ICP-OES).
The results are summarized in Table 1.

(Example 2)
In this example, the dependence of coordination polymerization on the ethanol / water composition was examined using a single component solution of Nd and Dy.
First, four types of solutions shown in Table 2-1 were mixed, and each weight was recorded.
In addition, Ln and Nadehp are mixed at an equivalence ratio (1: 3) of coordination polymerization, and the final ethanol concentration is 96% (1-1 and 1-4), 81% (1-2 and 1). -5) and 66% (1-3 and 1-6).

Thereafter, the solution was allowed to stand overnight, and the precipitated coordination polymer was washed and filtered, and the weight was measured.
From the weight of the solution mixed with the molar concentration determined in Example 1 and the weight of the precipitate, the precipitation rates of Nd and Dy were determined.
The results are summarized in Table 2-2 and FIG.

It can be seen that almost all Dy and Nd were precipitated by coordination polymerisation.
In many cases, the precipitation rate exceeds 100%, and there is a possibility that Nadehp that has not been polymerized due to insufficient washing during filtration remains.

(Example 3)
In this example, the dependency of acid concentration on coordination polymerization in a mixed solution of Dy: Nd: Nadehp = 1: 1: 3 was examined.
First, as shown in Table 3-1, four kinds of solutions were mixed, and each weight was recorded.
The ethanol concentration was 81%, and the acid concentration of the aqueous solution to be mixed was changed using water or an HNO ₃ aqueous solution. The mixing ratio of Ln and Nadehp was Dy: Nd: Nadehp = 1: 1: 3.

Thereafter, the solution was allowed to stand overnight, and the precipitated coordination polymer was washed and filtered, and the weight was measured.
About 15 mg of the obtained coordination polymer was put in 60% HNO ₃ and decomposed by heating on a hot plate at 160 ° C. for 5 days. Dy, Nd and P in the decomposition solution were quantified by ICP-OES. The molar amounts of Dy, Nd, and P / g of coordination polymer and P / (Dy + Nd) are summarized in Table 3-2.

  P / (Dy + Nd) was about 3.0, and it was confirmed that the polymer was precipitated as a coordination polymer.

The respective precipitation rates of Dy and Nd were determined from the weight of the solution mixed with the molar concentration determined in Example 1, the weight of the precipitated coordination polymer, and the molar concentration in the coordination polymer shown in Table 3-2.
The results are summarized in Table 3-3 and Fig. 3-1.

From the table, it can be seen that in the mixed solution of Dy and Nd, Dy selectively becomes a coordination polymer regardless of the acid concentration.
Moreover, from FIG. 3-2, it turns out that the separation efficiency of Dy and Nd is so good that the acid concentration in a solution is high.

Dy / Nd in the coordination polymer is plotted in FIG. 3-2 with the added HNO ₃ concentration as the H ⁺ concentration.
It can be seen that the higher the acid concentration, the higher the Dy / Nd ratio and the better the separation.

Further, the concentration of Dy and Nd remaining in the solution was calculated from the precipitation weight and the molar amount, and the selectivity coefficient K _c defined below was obtained. K _c is an index of separation of two chemical species (Dy and Nd), and the larger the value, the higher the resolution.

For comparison, the extraction coefficient K _ex in the solvent extraction system

結果を表３−４にまとめる。

The results are summarized in Table 3-4.

As shown in the table, in the separation of Dy and Nd using coordination polymerisation, when the acid concentration is 10 ^-5 M, the selectivity coefficient is comparable to that of the solvent extraction system, and when the acid concentration is high, it is selected over the solvent extraction. The coefficient increases.

Example 4
In this example, coordination polymerization in a Dy: Nd: Nadehp = 1: 5: 3 mixed solution was studied.
Four types of solutions were mixed as shown in Table 4-1 so that Dy: Nd: Nadehp = 1: 5: 3 (Nd was excessive), and each weight was recorded.

After standing overnight, the precipitate was washed and filtered, and the weight was measured.
The coordination polymer was decomposed with HNO ₃ by the same procedure as in Example 3, and the molar amount of Dy, Nd, P per gram of coordination polymer and P / (Dy + Nd), Dy / Nd in the coordination polymer. The selection coefficient was obtained. The results are summarized in Table 4-2.

  As shown in the table, it can be seen that even when Nd is present in excess, Dy selectively becomes a coordination polymer.

(Example 5)
In this example, coordination polymerization in a mixed solution of Nd + Dy with Dy: Nd: Nadehp = 1: 5: 6 was studied.
Four kinds of solutions were mixed as shown in Table 5-1, so that Nadhep was excessive as compared with Example 4. Each weight was recorded.

After standing overnight, the precipitate was washed and filtered, and the weight was measured.
The coordination polymer was decomposed with HNO ₃ by the same procedure as in Example 3, and the molar amount of Dy, Nd, P per gram of coordination polymer and P / (Nd + Dy), Dy / Nd in the coordination polymer. Asked. The results are summarized in Table 5-2.
As a result of the measurement, the precipitation rate was 100% or more, and the selection coefficient could not be calculated.

  As a result, it was found that even if Nadehp and Nd exist excessively, Dy selectively becomes a coordination polymer.

(Example 6)
In this embodiment, the Nd + Dy solution is changed to an aqueous solution, and nitric acid is changed to hydrochloric acid.
Five types of solutions were mixed as shown in Table 6-1. The final ethanol concentration is 81%.

  The precipitation rate of Nd and Dy in the coordination polymer was determined in the same procedure as in Example 3. The results are shown in the table below.

(Example 7)
In this example, Nd and Dy were separated using methanol or acetone instead of ethanol in the above example.
In [Preparation of 0.30M Nadehp 80 / 20vol% ethanol / water solution] described in [0025] above, ethanol is replaced with methanol or acetone to prepare a Nadehp solution, and five kinds of solutions are mixed as shown in Table 7-1. did. The final methanol or acetone concentration is 81%.

  The precipitation rate of Nd and Dy in the coordination polymer was determined in the same procedure as in Example 3. The results are shown in the table below.

(Example 8)
In this example, coordination polymerization in a mixed solution of Dy and Fe was studied.
As shown in Table 8-1, four kinds of solutions were mixed and each weight was recorded. The Dy: Fe: Nadehp of each system is shown in the table.

After standing overnight, the precipitate was washed and filtered, and the weight was measured.
The coordination polymer was decomposed with HNO ₃ in the same procedure as in Example 3, and the molar amount of Dy, Fe, and P per 1 g of coordination polymer and P / (Dy + Fe), Dy / Fe in the coordination polymer. The selection coefficient was obtained.
The results are summarized in Table 8-2.

  As can be seen from the table, both Dy and Fe are likely to be coordinatively polymerized to the same extent, and the separation of both is not good.

Claims (3)

A method for fractionally precipitating dysprosium ions from a solution containing neodymium ions and dysprosium ions,
Using di-2-ethylhexyl phosphate as a coordination polymer forming agent, characterized in that dysprosium ions are selectively polymerized and fractionally precipitated in a mixture of water and a water-soluble organic solvent. Fractional precipitation method.   The fractional precipitation method according to claim 1, wherein an acid is further mixed with the mixed solution to increase a hydrogen ion concentration of the mixed solution. The fractional precipitation method according to claim 1 or 2, wherein the water-soluble organic solvent is selected from ethanol, methanol, and acetone.

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