US-12616936-B2 - Lithium isotope concentration device, multi-stage lithium isotope concentration device, and lithium isotope concentration method

US12616936B2US 12616936 B2US12616936 B2US 12616936B2US-12616936-B2

Abstract

A lithium isotope concentration device includes a treatment tank partitioned in a supply tank and a recovery tank by an electrolyte membrane having a lithium-ion conductivity. The electrolyte membrane is cooled by a cooling device via an Li-containing aqueous solution in the supply tank to have a low temperature at which the Li isotope separation coefficient is larger. A power supply device, connected between electrodes provided on opposite surfaces of the electrolyte membrane, applies a positive voltage to an electrode on a supply tank side.

Inventors

Kazuya Sasaki
Kiyoto SHINMURA

Assignees

HIROSAKI UNIVERSITY

Dates

Publication Date: 20260505
Application Date: 20210706
Priority Date: 20200707

Claims (7)

1 . A lithium isotope concentration device which includes a treatment tank partitioned into a first tank and a second tank and which recovers, from an aqueous solution being held in the first tank and containing 6 Li and 7 Li in a state of lithium ions, a lithium ion-containing aqueous solution having a higher isotope ratio of 6 Li than that of the aqueous solution into the second tank, the lithium isotope concentration device comprising: a lithium-ion conductivity electrolyte membrane partitioning the treatment tank; electrodes having porous structures, the electrodes being provided in contact respectively with opposite surfaces of the lithium-ion conductivity electrolyte membrane; a power supply device configured to apply a voltage between the electrodes; and a cooling device configured to cool the lithium-ion conductivity electrolyte membrane at a temperature of 20° C. or lower, wherein the lithium-ion conductivity electrolyte membrane is made of a material comprising lithium lanthanum titanium oxide (La 2/3−x Li 3x TiO 3 ), wherein the power supply device is configured to apply a voltage, and wherein the voltage applied is between 0.5 V and 1.5 V.
2 . The lithium isotope concentration device according to claim 1 , wherein the voltage applied by the power supply device is applied intermittently.
3 . The lithium isotope concentration device according to claim 1 , wherein the power supply device is configured to alternately apply positive and negative voltages.
4 . The lithium isotope concentration device according to claim 1 , wherein the cooling device is configured to cool the aqueous solution held in at least one of the first tank and the second tank.
5 . A multi-stage lithium isotope concentration device comprising: two or more of the lithium isotope concentration devices according to claim 1 , which are coupled such that treatment tanks are integrated, wherein the lithium-ion conductivity electrolyte membranes of the respective lithium isotope concentration devices are arranged away from each other in such a manner as to partition the integrated treatment tanks into three tanks or more, the second tank of one of neighboring two of the lithium isotope concentration devices serves as the first tank of the other, and the cooling device cools the aqueous solution held in at least one tank of the partitioned treatment tanks.
6 . A lithium isotope concentration method for in a treatment tank partitioned into a first tank and a second tank by a lithium-ion conductivity electrolyte membrane, recovering, from an aqueous solution being held in the first tank and containing 6 Li and 7 Li in a state of lithium ions, a lithium ion-containing aqueous solution having a higher isotope ratio of 6 Li than that of the aqueous solution into the second tank, the lithium isotope concentration method comprising: applying a voltage of between 0.5 V and 1.5 V between electrodes having porous structures, the electrodes being provided in contact respectively with opposite surfaces of the lithium-ion conductivity electrolyte membrane, with an electrode on a first tank side being set as positive while cooling the lithium-ion conductivity electrolyte membrane to a temperature of 20° C. or lower, wherein the lithium-ion conductivity electrolyte membrane is made of a material comprising lithium lanthanum titanium oxide (La 2/3−x Li 3x TiO 3 ).
7 . The lithium isotope concentration method according to claim 6 , wherein a coagulation point of each of the aqueous solutions held in the first tank and the second tank is lower than 0° C., and the voltage is applied while the lithium-ion conductivity electrolyte membrane is cooled to a temperature of higher than the coagulation point and lower than 0° C.

Description

TECHNICAL FIELD The present invention relates to a lithium isotope concentration device, a multi-stage lithium isotope concentration device, and a lithium isotope concentration method for separating a lithium isotope. BACKGROUND ART Lithium (Li) has two stable isotopes, 7Li and 6Li, and the natural abundances of these are 92.41 mol % and 7.59 mol %. The properties of 7Li having a mass number of 7 and 6Li having a mass number of 6 are largely different, and for example, 7Li is used for adjustment of pH (concentration of hydrogen ions) of coolants of nuclear reactors. On the other hand, 6Li is used for production of tritiated hydrogen (tritium), which is a fuel of fusion reactors. For this reason, techniques for concentrating or separating one of 7Li and 6Li into a state where the content of the other is lower have been developed. The amalgam method, the molten salt method, and the distillation method as well as the adsorption method and the electrodialysis method (for example, Patent Literature 1), which are also methods for selectively recovering lithium ions Li+ from seawater, are known. In comparison with the amalgam method, which uses a large amount of mercury, and the molten salt method and the distillation method, which heat lithium compounds and the like at high temperatures, the adsorption method and the electrodialysis method are relatively excellent from the viewpoints of environmental loads and the like. Meanwhile, these methods utilize the fact that a large amount of 6Li+, which has a smaller mass and thus has a higher moving speed, is recovered. Meanwhile, these methods have small isotope separation coefficients, and thus have low productivity as concentration methods. In view of this, regarding the concentration of lithium isotopes by the electrodialysis method, the present inventors found that the isotope separation coefficient is large only for a short period of time immediately after the start of operation, and invented a method for enhancing the efficiency by intermittently applying a voltage (Patent Literature 2, Non-Patent Literature 1). CITATION LIST Patent Literature Patent Literature 1: JP5429658Patent Literature 2: JP2019-141808 Non-Patent Literature Non-Patent Literature 1: Shunsuke Honda, Kiyoto Shin-mura, Kazuya Sasaki, “Lithium isotope enrichment by electrochemical pumping using solid lithium electrolytes”, Journal of the Ceramic Society of Japan, Volume 126, Issue 5, pp 331-335, May 2018 SUMMARY OF INVENTION Technical Problem The methods described in Patent Literature 2 and the like still have room for further improvement in order to increase the isotope separation coefficient. The present invention has been made in view of the above-described problems, and an object thereof is to provide a lithium isotope concentration device, a multi-stage lithium isotope concentration device, and a lithium isotope concentration method which are safe and have high efficiency. Solution to Problem As a result of earnestly studying the concentration of lithium isotopes by the electrodialysis method, the present inventors found that 7Li+ and 6Li+ have different degrees of temperature dependency and voltage dependency of mobility, and conceived of setting the temperature and the applied voltage within appropriate ranges. Specifically, a lithium isotope concentration device according to the present invention includes a treatment tank partitioned into a first tank and a second tank and recovers, from an aqueous solution being held in the first tank and containing 6Li and 7Li in a state of lithium ions, a lithium ion-containing aqueous solution having a higher isotope ratio of 6Li than that of the aqueous solution into the second tank. The device includes: a lithium-ion conductivity electrolyte membrane partitioning the treatment tank; electrodes having porous structures, the electrodes being provided in contact respectively with opposite surfaces of the lithium-ion conductivity electrolyte membrane; a power supply device configured to apply a voltage between the electrodes; and a cooling device configured to cool the lithium-ion conductivity electrolyte membrane. In addition, a multi-stage lithium isotope concentration device according to the present invention includes: two or more of the lithium isotope concentration devices which are coupled such that the treatment tanks are integrated. The lithium-ion conductivity electrolyte membranes of the respective lithium isotope concentration devices are arranged away from each other in such a manner as to partition the integrated treatment tanks into three tanks or more. The second tank of one of neighboring two of the lithium isotope concentration devices also serves as the first tank of the other. The cooling device cools the aqueous solution held in at least one tank of the partitioned treatment tanks. With such configurations, lithium ions move in the lithium-ion conductivity electrolyte membrane at a low temperature at which the difference in mobility