JP3020146B2 - Lithium isotope separating agent and method for separating lithium isotope using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lithium isotope separating agent having good separation performance between lithium isotopes ⁶ Li and ⁷ Li, and a method for separating lithium isotopes using the same. Things.

[0002]

2. Description of the Related Art In recent years, lithium has been used as a raw material for ceramics, grease, refrigerants for air conditioning, pharmaceuticals, batteries, and the like. In addition, lithium is an important substance expected to be used as an aluminum alloy material in the future. is there.

[0003] Ordinary lithium is a mixture of lithium isotopes of atomic weights 6 and 7, but lithium separated into single atomic weights each is useful in the field of nuclear power, for example, lithium of atomic weight 6 is a fusion reactor. On the other hand, lithium having an atomic weight of 7 has attracted attention as a neutron scavenger in nuclear power generation. Therefore, there is a strong demand for establishing a technique for mutually separating lithium isotopes from a lithium-containing solution.

Conventionally, as a method for separating lithium isotopes, for example, an amalgam method, a molten salt method, a distillation method, and an adsorption method are known. However, the amalgam method is a method in which isotopes are separated by electrolyzing lithium as mercury amalgam. However, since mercury is used, there is a major problem in environmental health. The molten salt method is a method in which a lithium compound is heated to a molten state, and electrophoresis is performed to separate isotopes.However, high energy is required for heating, and the separation cost is high because the apparatus is complicated. It has the disadvantage that it is inevitable to be expensive. On the other hand, the distillation method is a method of separating isotopes by evaporating lithium metal or a lithium compound.However, since the raw materials are expensive and need to be heated to a high temperature, the disadvantage that the separation cost is still high. is there.

[0005] In contrast to these methods, the adsorption method is a method of separating isotopes by utilizing an adsorption reaction from a solution to a solid phase such as an ion exchange reaction, which can be operated at room temperature and has a simple apparatus. Therefore, it is a suitable separation method,
In order to perform isotope separation, an adsorbent having high separation performance must be used. As a lithium isotope separating agent, conventionally, a strongly acidic ion exchange resin, zeolite, and the like are known. However, strongly acidic ion exchange resins are
For separation factor of ⁶ Li and ⁷ Li is low and 1.002, in order to perform the complete separation of lithium isotopes, a large amount of a resin, and problems such as the separation process is necessary to accurately perform Zeolite, on the other hand, has a separation factor of 1.
Although relatively high as 004 to 1.006, it has the disadvantage of being unstable in aqueous solution.

On the other hand, a method for separating lithium isotopes using an organic cryptand resin has also been reported, but has a disadvantage that the production cost of the resin is high and the separation efficiency is not sufficient.

By the way, if a separating agent having a high separation efficiency and being stable in an aqueous solution is present, an efficient and economical lithium isotope separation process can be constructed by a chemical conversion method. No possible separating agent has been found.

[0008]

Under these circumstances, the present invention provides a novel lithium isotope which is excellent in the separation performance of lithium isotopes ⁶ Li and ⁷ Li and is stable even in contact with an aqueous solution. An object of the present invention is to provide a lithium isotope separating agent and a method for efficiently separating lithium isotopes using the same.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies on a separating agent capable of efficiently separating lithium isotopes. As a result, monensin or a derivative thereof has high separation efficiency with respect to lithium isotopes. By showing, and by using this as an extractant or liquid membrane transport agent,
The present inventors have found that lithium isotope ions in an aqueous solution can be efficiently separated, and have completed the present invention based on this finding.

That is, the present invention provides a compound represented by the general formula

Embedded image (Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom or a hydrocarbon group) represented by the formula: Monensin or a derivative thereof, ⁶ Li and ⁷ Li
Is adjusted to alkalinity, and then contacted with a water-immiscible organic solvent containing monensin or a derivative thereof represented by the general formula (I), and a part of the lithium ions is dissolved in the organic solution. To
⁷ L of lithium ion remaining in aqueous solution to ⁶ Li
a method for separating a lithium isotope, characterized by increasing the content of i, and a method for separating a lithium isotope from a water-immiscible organic solvent containing monensin or a derivative thereof represented by the general formula (I). ⁷ Li for ⁶ Li by continuously migrate lithium ions of the lithium ion-containing aqueous solution adjusted to an aqueous solution was adjusted to acidic
The present invention provides a method for separating lithium isotopes, characterized by obtaining an aqueous solution containing lithium ions having a low content ratio of lithium.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, monensin represented by the general formula (I) or a derivative thereof is used as a lithium isotope separating agent. In the general formula (I), R ¹ , R ² , R ³ and R ⁴ are a hydrogen atom or a hydrocarbon group. As the hydrocarbon group, a linear, branched or cyclic alkyl group, for example, Methyl group, ethyl group,
aryl groups such as n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, hexyl group and cyclohexyl group; alkaryl groups such as phenyl group and naphthyl group; and tolyl And aralkyl groups such as a benzyl group and a phenethyl group.

In the general formula (I), monensin, in which R ^{1 to} R ⁴ are all hydrogen atoms, is a kind of cyclic polyether antibiotic produced by actinomycetes, and has several ether groups. It has a carboxyl group and a hydroxyl group and is known as an ionophore of an alkali metal ion. This ionophore has a lipophilic binding site as an outer wall when it is alkaline, adopts a macrocyclic conformation that afferently takes in metal ions, and takes in metal ions. In addition, it takes a chain structure under acidity and releases metal ions. In particular, it is known to selectively take in sodium ions.

A monensin derivative in which a hydrogen atom of a carboxyl group or a hydroxyl group of the monensin is substituted by a group represented by R ^{1 to} R ⁴ , that is, an alkyl group, an aryl group, an alkaryl group or an aralkyl group, is also used. Metal ions can be incorporated.

[0014] The monensin and its derivatives, lithium selective adsorptivity is not very strong, the energy to be different between ⁷ Li ions and ⁶ Li ions and the dehydration during lithium is adsorbed, adsorption energy is ⁶ Li-ion By taking advantage of the difference between Li and ⁷ Li ions, lithium isotope ions can be separated.

In order to separate a lithium isotope using a lithium isotope separating agent comprising monensin or a derivative thereof, the separating agent is dissolved in an organic solvent immiscible with water, and then the solution is alkalized. The prepared lithium ion-containing aqueous solution may be contacted to extract lithium ions into the organic solution, or may be further back-extracted with an acidic aqueous solution. By repeating such operation, mutual separation of isotopes proceeds. Of ⁶ Li ions and ⁷ Li-ion Li isotopic ion, ⁶ Li ions strongly adsorbed by the separating agent is gradual transition in the reverse extract (acidic aqueous solution), whereas ⁷ Li ions in the original solution Is gradually increased, and Li isotope ions are separated from each other.

In order to perform such an extraction-back extraction process in a large number and in multiple stages, a countercurrent distribution extractor is generally preferably used. That is, an organic solvent solution containing monensin or a derivative thereof flows downward from the upper portion, while an aqueous solution containing lithium ions flows downward from the lower portion,
By contacting them continuously, lithium isotope ions can be efficiently separated.

[0017] Separation of lithium isotope ions can also be performed efficiently by membrane separation using a liquid membrane.
That is, if an organic solvent solution containing monensin or a derivative thereof is used as a liquid film and a cell composed of a lithium ion-containing aqueous solution phase (alkaline) / liquid film phase / aqueous phase (acidic) is constructed, lithium ions are converted into the liquid film phase. From the aqueous solution phase containing lithium ions to the aqueous phase side. At this time, the ⁶ Li ions strongly adsorbed to the separating agent easily move to the aqueous phase side, and thus the ⁶ Li ions are concentrated in the aqueous phase. By stacking the liquid membranes in multiple stages, the concentration of ⁶ Li ions proceeds, and lithium isotope ions are separated from each other.

The organic solvent used for preparing the organic solvent solution containing monensin or a derivative thereof used in the above-mentioned lithium isotope separation method has good solubility in monensin and its derivatives, and has good solubility in water. Any substance that is substantially immiscible with, for example, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, hydrocarbons such as benzene and toluene, and water-immiscible alcohols such as hexyl alcohol and octyl alcohol And the like. As described above, monensin or a derivative thereof adsorbs lithium ions in an alkaline aqueous solution and desorbs the lithium ions in an acidic aqueous solution. Therefore, the original aqueous solution is adjusted to, for example, an alkaline pH of 7 to 12, and the recovery aqueous solution is prepared. For example, it is necessary to adjust the pH to an acidic value of 1 to 6.

[0019]

Industrial Applicability The lithium isotope separating agent of the present invention comprises monensin or a derivative thereof, and has excellent separation performance of lithium isotopes ⁶ Li and ⁷ Li,
By using this separating agent as an extracting agent or a transport agent for a liquid membrane, the lithium isotope ion can be efficiently separated.

[0020]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Monensin (102 mg) was dissolved in dichloromethane (20 ml) to prepare a monensin (7 mmol / liter) solution. This solution was shaken vertically for 30 minutes together with 20 ml of an aqueous solution (pH 12) having a concentration of lithium hydroxide of 14 mmol / l. After shaking, the mixture was allowed to stand and separated into an aqueous phase and an organic phase. The aqueous phase had a lithium ion concentration of 8 mmol / L, which means that 43% of the lithium ions in the aqueous solution were solvent-extracted into the organic phase. ⁷ Li ion / ^{6 in} the aqueous phase after the undiluted solution and the solvent extraction experiment
The Li ion isotope molar ratio was measured by a surface ionization type mass spectrometer to be 12.56 and 12.75, respectively. The separation coefficient S is calculated by the equation

(Equation 1) [However, α is a molar ratio of ⁷ Li ion / ⁶ Li ion isotope in the aqueous phase after the solvent extraction experiment, α ₀ is a molar ratio of ⁷ Li ion / ⁶ Li ion isotope in the stock solution, and C is the molar ratio of the solvent extraction experiment. Lithium ion concentration in the aqueous phase of (mmol / l),
C ₀ is the lithium ion concentration (mmol / liter) in the stock solution], and was 1.033. From this, it is understood that the separating agent of the present invention comprising monensin has higher isotope separation performance as compared with ion exchange resins and zeolites.

Example 2 After dissolving monensin in anhydrous benzene, it was reacted with methyl iodide for 5 days to obtain monensin methyl ester [In the above formula (I), R ¹ is a methyl group, R ² , R ³ and R ⁴ is a hydrogen atom].
0.0003 mol of this monensin methyl ester was dissolved in 30 ml of dichloromethane to prepare a solution. Using this solution as a liquid film, 15 ml of an aqueous solution of lithium iodide 2 mol / l (tris buffer pH 8) was set as a raw liquid phase on one side of the liquid film, and 0.01 mol as a permeate liquid phase on the other side. A 15 mL / liter hydrochloric acid solution was set to form a membrane permeable cell. After performing a permeation experiment for two days, the lithium ion concentration in the hydrochloric acid solution was measured by an atomic absorption method to determine the amount of permeated lithium ions.
Mmol. The measured ⁷ Li-ion / ⁶ Li-ion isotope mole ratio of stock solution phase and permeate phase were respectively 12.35 and 12.00. From this, it is clear that the separating agent of the present invention comprising a monensin derivative can selectively transport and separate lithium isotopes in a liquid membrane transport system.

Continued on the front page (72) Inventor Akinari Sonoda 2217-14 Hayashi-cho, Takamatsu-shi, Kagawa Prefecture Within the Institute of Industrial Technology Shikoku Institute of Industrial Technology (72) Inventor Takahiro Hirotsu 22217-14 Hayashi-cho, Takamatsu-shi, Kagawa Prefecture (56) References JP-A-59-145022 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 59/24-59/30

Claims (3)

(57) [Claims] 1. A compound of the general formula (Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom or a hydrocarbon group) represented by the formula: Monensin or a derivative thereof, which is a lithium isotope separating agent. 2. After adjusting a lithium ion aqueous solution containing isotopes of ⁶ Li and ⁷ Li to be alkaline, the lithium ion is converted to a general formula: (Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom or a hydrocarbon group) by contacting with a water-immiscible organic solvent containing monensin or a derivative thereof to form a lithium ion is shifted partially to the organic solution, the method of separating lithium isotopes, characterized in that to increase the content ratio of ⁷ Li for ⁶ Li of lithium ions remaining in the aqueous solution. 3. A compound of the general formula (Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom or a hydrocarbon group) through a liquid film comprising a water-immiscible organic solvent containing monensin or a derivative thereof. lithium, characterized in that the content of ⁷ Li for ⁶ Li by continuously migrate lithium ions in the lithium ion-containing aqueous solution adjusted to an alkaline aqueous solution was adjusted to acidic obtain an acidic aqueous solution containing a low lithium ion Isotope separation method.