JP2981892B1 - Lithium isotope separating agent - Google Patents

Abstract

The present invention provides a novel isotope separating agent which has good separation performance of lithium isotopes ⁶ Li and ⁷ Li and is stable in an aqueous solution. SOLUTION: A sodium superionic conductor type compound or an acid-treated product thereof is used as a lithium isotope separating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a novel lithium isotope separating agent, and more particularly, to a sodium superion containing sodium, zirconium, silicon and phosphorus as a main component and exhibiting excellent separation performance for lithium isotopes. The present invention relates to a lithium isotope separating agent composed of a conductive oxide.

[0002]

2. Description of the Related Art Lithium is used in ceramics, grease,
It is used as a raw material for air-conditioning refrigerants, pharmaceuticals, batteries and the like, and is an important substance expected to be used as an aluminum alloy material in the future. By the way, lithium is mainly used as a mixture of lithium isotopes having an atomic weight of 6 and 7, but is used as a single isotope in the field of nuclear power. For example, lithium having an atomic weight of 6 is used as a raw material for a fusion reactor. Further, lithium having an atomic weight of 7 is used as a neutron scavenger in nuclear power generation. Therefore, there is a need for a technique for mutually separating lithium isotopes from a lithium-containing solution.

Heretofore, as a method for separating lithium isotopes, for example, an amalgam method, a molten salt method, a distillation method, and an adsorption method have been known. 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. I cannot help getting higher. 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.

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 ordinary 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 and zeolite are known. However, strongly acidic ion exchange resins require ⁶ L
Since the separation coefficient between i and ⁷ Li is as low as 1.002, there are drawbacks such as the use of a large amount of resin and the necessity of precise separation treatment in order to completely separate lithium isotopes. On the other hand, zeolite has a drawback that, although the separation coefficient is relatively high, 1.004 to 1.006, it is unstable in an aqueous solution.

[0005] On the other hand, a method for separating lithium isotopes using an organic cryptand resin has also been reported. However, this method has disadvantages that the production cost of the resin is increased and the separation efficiency is not sufficient.

Meanwhile, in the separation of lithium isotopes by the chemical exchange method, a separating agent having high separation efficiency and being stable in an aqueous solution is required. However, if such a separating agent can be developed, it is efficient and economical. A simple lithium isotope separation process can be constructed.

On the other hand, a sodium superionic conductor (Na
Superionic Conductor, NA
It is known that a type compound (abbreviated as SICON) has network-like pores large enough to allow sodium ions to move, and exhibits extremely high ionic conductivity because sodium ions can easily move. In such a NASICON-type compound, sodium ions therein can easily exchange ions with other cations while maintaining the network structure. As a typical NASICON-type compound, an oxide containing sodium, zirconium, phosphorus, and silicon as main components has been found.

[0008]

DISCLOSURE OF THE INVENTION The present invention overcomes the disadvantages of the conventional lithium isotope separation method, has a good separation performance between lithium isotopes ⁶ Li and ⁷ Li, and is excellent in aqueous solution. The purpose of the present invention is to provide a novel stable isotope separating agent.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a novel lithium isotope separating agent which has excellent lithium isotope separation performance and is stable even in an aqueous solution. The present inventors have found that a compound and an acid-treated product thereof can be suitable for the above purpose, and have completed the present invention based on this finding.

That is, the present invention provides a lithium isotope separating agent comprising a NASICON type compound or an acid-treated product thereof.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a NASICON-type compound or an acid-treated product thereof is used as a lithium isotope separating agent. The NASICON-type compound can be prepared by a known method, for example, “Solid State Ionic”.
s ", 9 & 10, pages 895-902 (1983
Year).

According to this method, first, α-type zirconium phosphate and sodium silicate are mixed with water, and a hydrothermal synthesis reaction is performed at a temperature of about 300 ° C. to obtain a NASICON precursor containing sodium, zirconium, phosphorus and silicon. Prepare the body. In order to obtain a good NASICON-type compound, it is preferable that the elements contained in the precursor are well mixed with each other. Next, this precursor is heat-treated to produce a NASICON-type compound. At this time, the heating temperature depends on the condition of the raw material and the like.
A suitable temperature is about 000 to 1300 ° C.

The NASICON-type compound thus obtained has network-like pores large enough to allow sodium ions to move, so that sodium ions can easily move, and exhibits extremely high ion conductivity. The sodium ions easily exchange with other cations while maintaining the network structure.

In the present invention, the NASICON-type compound may be used as it is as a lithium isotope separating agent, or may be immersed in a hydrochloric acid solution.
A product obtained by treating with an acid and replacing a part or all of sodium ions in the NASICON type compound with protons (H ⁺ ) may be used.

In order to separate a lithium isotope using a lithium isotope separating agent composed of the above-mentioned NASICON type compound or an acid-treated product, for example, the separating agent is added to a solution containing the lithium isotope, and the lithium isotope is added. May be repeatedly performed. By repeating such an operation, of the ⁶ Li and ⁷ Li naturally occurring stable, with ⁶ Li moves in stepwise solid phase (separating agent), the proportion of ⁷ Li in the solution phase And the mutual separation is completed.

As a mode of use of the separating agent of the present invention, there is generally used a method in which the separating agent is formed into granules, packed in a column, and a column for chromatography is prepared for separation. That is, a lithium adsorption band is formed by flowing a fixed amount of a solution containing a lithium isotope through a column filled with a separating agent, and then the eluent is kept flowing from the top of the column to move the lithium adsorption band. , Isotope separation. At this time, the eluent
Usually, a neutral or acidic aqueous solution is used. According to this method, ⁶ Li that strongly adsorbs to the separating agent can be concentrated to the rear end side, and ⁷ Li that weakly adsorbs to the front end side can be concentrated. Such an isotope separation treatment by adsorption-elution can also be performed using a fibrous or membrane-like separating agent.

[0017]

Industrial Applicability The lithium isotope separating agent of the present invention is excellent in the separation performance of lithium isotopes ⁶ Li and ⁷ Li and is stable even in contact with an aqueous solution. In addition, ⁶ Li and ⁷ Li can be efficiently and economically separated from a solution containing a lithium isotope.

[0018]

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 α-type zirconium phosphate [Zr (HPO ₄ ) ₂ .H ₂ O]
And sodium orthosilicate (Na ₄ SiO ₄ ) and water were sealed in a sealed container and subjected to a hydrothermal synthesis reaction at 300 ° C. for 20 hours to prepare a NASICON precursor containing sodium, zirconium, phosphorus and silicon as main components. Next, a NASICON-type compound was produced by subjecting this precursor to heat treatment at 1000 to 1300 ° C. for 5 days. next,
In a 8 ml mixed solution containing 0.07 mol / l of lithium hydroxide and 0.03 mol / l of lithium chloride, the NASICON-type compound 0.1 obtained as described above was added.
40 g were immersed and shaken at 25 ° C. for 7 days. The lithium adsorption after shaking was 9.1 mg / g, and 64% of the lithium in the solution was adsorbed. The measured undiluted and ⁷ Li / ⁶ Li isotopic molar ratio in the supernatant after adsorption by thermal ionization mass spectrometer, it was respectively 12.52 and 12.64. The separation coefficient S is calculated by the equation

(Equation 1) (Where α is the isotope ratio in the solution after the adsorption experiment, α ₀ is the isotope ratio in the stock solution, C is the lithium concentration of the solution after the adsorption experiment, and C ₀ is the lithium concentration of the stock solution). However, it was 1.015. From this, it is clear that the lithium isotope separating agent of the present invention has higher isotope separating performance than ion exchange resins and zeolites.

Example 2 1 g of the NASICON type compound obtained in Example 1 was
The solution was added to 500 ml of hydrochloric acid containing 1 mol / liter and acid-treated for 1 day. As a result, 90
% Were replaced by protons. Next, the acid-treated product was collected by filtration and dried to obtain an acid-treated NASICON-type compound. Next, 0.15 g of the acid-treated NASICON-type compound obtained as described above was immersed in 8 ml of a mixed solution containing 0.07 mol / l of lithium hydroxide and 0.03 mol / l of lithium chloride. And shaken at 25 ° C. for 7 days. Lithium adsorption after shaking is 23.1m
g / g, and 63% of the lithium in the solution was adsorbed.
The measured undiluted and ⁷ Li / ⁶ Li isotopic molar ratio in the supernatant after adsorption by thermal ionization mass spectrometer,
12.53 and 12.72, respectively. When the separation coefficient S was calculated in the same manner as in Example 1, 1.024
Met. From this, it is clear that the lithium isotope separating agent of the present invention has higher isotope separating performance than ion exchange resins and zeolites.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hirofumi Kano 2217-14 Hayashi-cho, Takamatsu-shi, Kagawa Prefecture Within the Institute of Industrial Science and Technology, Shikoku Institute of Industrial Technology (72) Inventor Akinari Sonoda 22217-14 Hayashi-cho, Takamatsu-shi, Kagawa Industrial Technology (56) References JP-A-59-145022 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 59/26 C01B 33/12

Claims (1)

(57) [Claims] 1. A lithium isotope separating agent comprising a sodium superionic conductor type compound or an acid-treated product thereof.