WO2017006973A1

WO2017006973A1 - Method for recovering tritium from tritium absorber, and method for reusing as absorber

Info

Publication number: WO2017006973A1
Application number: PCT/JP2016/070057
Authority: WO
Inventors: 古屋仲　秀樹
Original assignee: 株式会社フォワードサイエンスラボラトリ
Priority date: 2015-07-06
Filing date: 2016-07-06
Publication date: 2017-01-12
Also published as: JP6666612B2; JPWO2017006973A1

Abstract

The purpose of the present invention is to recover tritium at low cost from a tritium-containing manganese oxide and reuse said manganese oxide. Tritium is recovered by evaporation from a tritium-containing manganese oxide, and lithium ions are added to stabilize and reuse said manganese oxide.

Description

Method for recovering tritium from tritium absorbent and method for reusing it as absorbent

The present invention relates to a method for recovering tritium from a tritium absorbent material and a method for reusing it as an absorbent material.

Tritium (T) is dissolved in light water (H ₂ O) as an isotope isomer of water molecules (T ₂ O, HTO). Tritium (T) is an isotope of hydrogen (H), and is a radioactive element that emits β rays (electron beams) and has a half-life of 12.3 years. Further, tritium ions (T ⁺⁾ in order to similar chemical properties and hydrogen ions (H ^+), the nature remain in the body by ion exchange with hydrogen ions (H ⁺⁾ which constitutes the DNA in the body of an organism Have For this reason, it can be a causative substance of internal exposure and is harmful.

Although the natural abundance ratio of tritium is extremely small (one in every 1 × 10 ¹⁸ hydrogen atoms), it is artificially generated in nuclear-related facilities such as fission-type nuclear power generation facilities and fusion experimental facilities. . For this reason, in Japan, the wastewater concentration limit for tritium is set at 60,000 Bq / L (60 Bq / L) per liter of sample water in a notification that specifies dose limits based on the regulations of regulations on the installation and operation of practical power reactors. mL).

Usually, in order to separate tritium from water, the difference in boiling point between water molecules (H ₂ O) and isotope isomer molecules (HTO, DTO, T ₂ O) at high temperatures and high performance platinum catalyst A high-cost and complicated system that uses the difference in reactivity with hydrogen gas (H ₂ ) is required. For example, Vasaru, G. Tritium Isotope Separation 1993, CRC Press, Chap. 4-5, Villani, S. Isotope Separation 1976, Am. Nuclear Soc., Chap. 9, Gould, RF Separation of Hydrogen Isotopes 1978, Am. Nuclear Soc., Chap. 9, etc.

Recently, when the present inventors applied manganese oxide powder having a spinel crystal structure containing hydrogen ions to tritium-containing water, tritium ion exchanged with hydrogen ions (H ⁺ ) contained in the manganese oxide from water, It was revealed that tritium ions (T ⁺ ) were collected in the solid phase of the same manganese oxide. Hideki Koyanaka and Hideo Miyatake, Extracting Tritium from Water Using a Protonic Manganese Oxide Spinel ", Separation Science and Technology, 50, 14, 2142-2146, (2015), WO2015 / 037734. Further, the manganese oxide powder was processed into an electrode. The hydrogen ion conductive film is disposed on one surface of the electrode and the hydrogen ion conductive film is brought into contact with the dilute acid aqueous solution, so that hydrogen ions (H ⁺ ) are continuously supplied from the dilute acid aqueous solution to the electrode. A reaction system was proposed, Hideki Furuya, Yasuto Igarashi, Separation and Recovery of Tritium in Water Using Manganese Oxide Electrode Membrane, 83rd Annual Meeting of the Electrochemical Society, Lecture Number 3Q29, Osaka University (2016). Tritium contained at a low substance concentration of several nanograms per liter of water can be continuously collected from the water at room temperature into the solid phase of manganese oxide by the method using the reaction system.

However, the problem of safely and efficiently recovering tritium collected from manganese oxide having a spinel crystal structure from the manganese oxide without leaking it into the environment has not been solved. It was not easy to reuse as a material.

In the method of recovering tritium from the manganese oxide by heating the manganese oxide that has collected tritium in an airtight container by an existing heat treatment method, not only tritium ions but also ions from the manganese oxide crystal. Exchangeable hydrogen ions will also evaporate. As a result, the hydrogen ions necessary for the ion exchange reaction at the interface between the manganese oxide and water are insufficient in the crystal, so that the performance as a tritium absorbent material is greatly reduced. The phenomenon in which the shortage of hydrogen ions in the crystal deteriorates the performance of the tritium absorber is described in the following documents. H. Koyanaka, and H. Miyatake, Extracting tritium from water using a protonic manganese oxide spinel ", Separation Science and Technology, 50, 14, 2142-2146, (2015), WO2015 / 037734. Is high, the spinel crystal structure of the manganese oxide undergoes a phase transformation to another crystal structure, so that the function as the tritium absorbent is lost and the tritium cannot be reused as the absorbent. The technique of recovering tritium contained in the collected manganese oxide by heat treatment is not the best recovery technique economically.

In order to efficiently separate and recover tritium collected by manganese oxide having a spinel crystal structure from the solid phase of the manganese oxide into the gas phase in the reaction vessel, tritium-containing water is used. The hydrogen ion concentration (pH) is preferably acidic. On the other hand, in order to collect tritium from the tritium-containing water in the solid phase of the manganese oxide using the same manganese oxide, the pH of the tritium-containing water is preferably neutral to weakly alkaline. Hideki Koyanaka and Hideo Miyatake, Extracting Tritium from Water Using a Protonic Manganese Oxide Spinel ", Separation Science and Technology, 50, 14, 2142-2146, (2015). Therefore, when reusing manganese oxide as a tritium absorber. However, it is necessary to adjust the pH of the tritium-containing water from acidic to neutral or weakly alkaline, but the manganese oxide after releasing the collected tritium is the same in a neutral to alkaline aqueous solution. Since manganese ions (Mn ²⁺ ) are eluted from manganese to form manganese hydroxide and oxide in water, sludge is generated as a precipitate in the water to be treated. Not only does the sludge adhere to the surface, the effect of collecting tritium is reduced, but the dissolution of manganese oxide after the release of tritium Therefore, the development of a method for preventing the dissolution of the manganese oxide after the release of tritium and the generation of the sludge makes the tritium separation technology from water according to the present invention practical. This is an important issue.

The present invention has been made in view of the circumstances as described above, and a method for recovering tritium capable of efficiently recovering tritium from manganese oxide having a spinel crystal structure in which tritium is collected, and tritium. An object is to provide an improvement in reusability as an absorbent material.

In order to solve the above-described problems, a method for recovering tritium according to the present invention includes a method in which tritium is collected from the manganese oxide in which tritium is collected in a gas phase in the reaction vessel and water containing tritium in the reaction system vessel. Tritium is released in a small amount of water (H ₂ O) by releasing it as an isotope isomer (HTO) or isotope isomer (HT) of hydrogen gas, and sucking a gas containing tritium from the same gas phase with a pump or the like. To provide a method of introduction and recovery. At that time, when the form of tritium released is HT, the tritium-containing water (HTO) is brought into contact with oxygen (O or O ₂ ) or copper oxide (CuO) heated to 250 to 500 ° C. And recovered in a small amount of water (H ₂ O). The tritium recovery method of the present invention is characterized by accelerating the release of tritium by irradiating the manganese oxide collecting tritium with ultraviolet light. Further, the method for recovering tritium according to the present invention includes applying tritium to a conductive gel by applying a voltage in a state where the manganese oxide that has collected tritium is in contact with a conductive gel containing lithium ions (Li ⁺ ). And a method of recovering in the electrolyte. At that time, in applying the voltage, manganese oxide having a spinel crystal structure containing tritium in contact with a conductive gel containing lithium ions is used as a positive electrode, a carbon rod is used as a negative electrode, and both electrodes are an aqueous solution containing an electrolyte. It is characterized by being arranged inside. Furthermore, in the method for reusing a tritium absorbent material of the present invention, an appropriate amount of lithium ions (Li ⁺ ) is added to the aqueous solution in contact with the manganese oxide, and the pH of the aqueous solution in contact with the manganese oxide is adjusted from neutral to alkaline. Thus, a method for reusing a tritium absorbent that can stabilize the crystal structure of manganese oxide after releasing tritium and suppress elution of manganese ions and generation of sludge by the pH adjustment is provided.

The method for recovering tritium according to the present invention comprises oxidizing an oxide having a spinel crystal structure that collects tritium by irradiating manganese oxide having a spinel crystal structure that collects tritium with various ultraviolet light such as an LED and a discharge lamp. The release of tritium from manganese may be promoted.

In the method for recovering tritium according to the present invention, manganese oxide having a spinel crystal structure in which tritium has been collected is brought into contact with water having an acidic pH to release HTO gas or HT gas from the manganese oxide in which the tritium has been collected. May be promoted. At that time, a small amount of HTO or HT released using various gas cleaning bottles (for example, Walter type, Ichinose type, dresser type, Muenke type, etc.) or a gas dissolution tower using a fine bubble foaming method. You may collect | recover in the medium which has absorptivity with respect to HTO or HT, such as water and various porous bodies.

In the method for recovering tritium according to the present invention, an electrode obtained by fixing manganese oxide powder having a spinel crystal structure to the surface of a conductive material such as metal or carbon with a conductive paint is brought into contact with tritium-containing water to obtain tritium. After the collection, the tritium collected in the manganese oxide may be eluted in the aqueous solution containing the conductive gel or the electrolyte by the above-described voltage application method to collect the tritium.

は In the method for reusing a tritium absorbent material of the present invention, manganese oxide after collecting tritium by the recovery method may be reused as a tritium absorbent material. In the tritium recovery method of the present invention, the lithium ion-containing manganese oxide obtained by substituting tritium with lithium ions by the above recovery method from manganese oxide that has collected tritium is brought into contact with a dilute acid containing hydrogen ions. Then, the lithium ion contained in the spinel crystal structure of the manganese oxide may be regenerated as a tritium absorbent by substituting hydrogen ions.

Further, the method for reusing the tritium absorbent material of the present invention is to stabilize the crystal structure of manganese oxide and adjust the pH of the aqueous solution by adding lithium hydroxide (LiOH) to tritium-containing water in contact with the manganese oxide. May be implemented. Alternatively, a water-soluble lithium salt such as lithium chloride (LiCl) may be added to water containing tritium in contact with the manganese oxide, and the pH of the aqueous solution may be adjusted by adding sodium hydroxide (NaOH) or the like. Further, a water-soluble lithium salt such as lithium chloride (LiCl) may be added to an aqueous solution of dilute hydrochloric acid or dilute nitric acid in contact with the manganese oxide to stabilize the crystal structure of the manganese oxide.

According to the present invention, tritium collected in manganese oxide can be efficiently recovered, and manganese oxide can be reused.

(A) The schematic diagram which showed embodiment for collecting tritium, and (b) The figure which showed the implementation result. (A) The schematic diagram which showed embodiment for detecting tritium, and (b) The figure which showed the implementation result. (A) The schematic diagram which showed embodiment for collect | recovering tritium, and (b) The figure which showed the implementation result. (A) The schematic diagram which showed embodiment for collect | recovering tritium, (b), (c) The figure which showed the implementation result. It is the schematic diagram which showed embodiment for collect | recovering tritium. (A), (b), (c), (d) It is the figure which showed the implementation result for collect | recovering tritium. It is the schematic diagram which showed embodiment for collect | recovering tritium in a gel. (A) The measurement result of the valence of manganese which comprises a tritium absorber, (b) The measurement result of a crystal structure.

The tritium absorbent material of the present invention is composed of hydrogen ion-containing manganese oxide having a spinel crystal structure.

For example, J. C. Hunter, Preparation of a new crystal structure of manganese dioxide: lambda-MnO ₂ ", Journal of Solid State Chemistry 39 (1981) 142-147 And the conditions for optimizing the hydrogenation are H. Koyanaka, O. Matsubaya, Y. Koyanaka, and N. Hatta, Quantitative correlation between Li absorption and H content in Manganese Oxide Spinel λ-MnO ₂ ", Journal of Electroanalytical Chemistry, 559, 77-81 (2003). The hydrogen or lithium-containing manganese oxide having a spinel crystal structure used as a tritium absorber in the present invention can be synthesized by the following method.

Lithium ion-containing manganese oxide having a spinel crystal structure is mixed using chemicals such as manganese carbonate such as manganese carbonate and manganese carbonate hydrate, lithium hydroxide such as lithium hydroxide, etc. as raw materials. It can be obtained through steps of baking and purification. Further, chemicals such as manganese-containing hydroxide and lithium-containing carbonate may be used as a raw material. Furthermore, the hydrogen ion-containing manganese oxide having a spinel crystal structure can be obtained through an acid treatment step in addition to the steps described above.

In the mixing step, for example, the above raw materials are mixed at room temperature. At this time, the mixture is mixed until it becomes black. As a result, crystal nuclei of lithium ion-containing manganese oxide having a spinel crystal structure are generated. In the firing step, the nuclei generated in the mixing step are grown. For example, the mixture is heated in the atmosphere at a temperature of 200 ° C. to 1000 ° C., preferably 300 ° C. to 500 ° C., more preferably 350 ° C. to 450 ° C. for about 1 hour to 10 hours. In the purification step, the fired product obtained in the firing step is suspended in weakly alkaline pure water, and then allowed to stand for a certain time to collect the precipitate. This precipitate is lithium ion-containing manganese oxide having a spinel crystal structure. When storing lithium ion-containing manganese oxide having a spinel crystal structure, the precipitate recovered by filtration or the like may be stored in a cool and dark place in a wet state. In addition, when synthesizing hydrogen oxide-containing manganese oxide through an acid treatment step, lithium ion-containing manganese oxide having a spinel crystal structure is suspended and stirred in an acidic solution such as dilute hydrochloric acid aqueous solution, and then solid-liquid separation is performed. Thus, a hydrogen ion-containing manganese oxide powder is obtained. The hydrogen ion-containing manganese oxide powder having a spinel crystal structure is stored in a cool and dark place in a wet state. The powder should not be dried. The reason for this is that when the reaction in which hydrogen ions in the crystal structure evaporate from the crystal as water progresses due to the drying treatment, the crystal structure changes to the crystal structure of lambda-type manganese dioxide that does not contain ion-exchangeable hydrogen ions, As a result, H. 材 Koyanaka, and H. Miyatake, Extracting tritium from water using a protonic manganese oxide spinel ", Separation Science and Technology, 50, 14, 2142 -Reported on 2146, Jun (2015).

The hydrogen ion-containing manganese oxide having a spinel crystal structure obtained from the above series of steps constitutes a tritium absorber. Of course, the tritium absorbent material is also composed of hydrogen ion-containing manganese oxide having a spinel crystal structure synthesized by a method other than that described above.

The hydrogen ion-containing manganese oxide having a spinel crystal structure preferably has a primary particle diameter in the range of 20 to 70 nm from the viewpoint of tritium absorption ability. In order to obtain a particle size within such a range, the firing temperature may be set in the range of 350 ° C. to 450 ° C. in the above-described firing step.

When the hydrogen ion-containing manganese oxide having a spinel crystal structure is actually applied to tritium-containing water, it is possible to continuously collect tritium by forming a tritium absorption electrode film. The tritium-absorbing electrode film can constitute the electrode film as a structure comprising the above-described lithium ion-containing manganese oxide powder having a spinel crystal structure, a resin binder, and a hydrogen ion conductive film. Specifically, the electrode film has manganese oxide powder fixed on the surface of a conductive material such as a metal or carbon material with a conductive paint, and a hydrogen ion conductive material such as Nafion (registered trademark). It can comprise by arranging on the single side | surface of an electrode film. More specifically, the tritium absorption electrode film is formed by applying lithium ion-containing manganese oxide powder having a spinel crystal structure to a platinum mesh surface by applying and drying with a conductive paint containing a carbon filler, and then fixing the hydrogen. It is obtained by applying and drying an ion conductive material on one side of the electrode film and fixing it. By bringing the electrode film into contact with a dilute acid, lithium ions can be eluted from the lithium ion-containing manganese oxide having a spinel crystal structure in the electrode film to be changed to hydrogen ion-containing manganese oxide. By configuring the electrode film, it is possible to obtain an effect that it is easy to apply a voltage when the tritium collected in the electrode film is recovered from the electrode film. Of course, the powdery absorbent material that collects tritium without forming an electrode may be packed in a metal container or the like, and a voltage applied.

Next, a method for recovering and reusing tritium from the absorbent that has collected tritium according to the present embodiment will be described.

In the tritium recovery method of the present embodiment, in the reaction vessel, the same electrode film containing manganese oxide that has collected tritium from weakly acidic to alkaline tritium-containing water is brought into contact with an acidic aqueous solution to bring the tritium into the reaction vessel. It is characterized by being discharged as water (HTO) gas containing tritium in the gas phase or hydrogen (HT) gas. At this time, HT is oxidized by oxygen in the gas phase in the reaction vessel and converted to HTO. Oxygen in the same gas phase is supplied from an oxidative decomposition reaction (OT ⁻ → T ⁺ + 2e ⁻ + (1/2) O ₂ ) of hydroxide ions (OT ⁻ ) contained in tritium-containing water. Alternatively, it is supplied by oxygen contained in the gas in the reaction vessel. The phenomenon in which manganese dioxide (MnO ₂ ) generates oxygen derived from hydroxide ions (OH ⁻ ) has been reported in the following documents, for example. Hideki Furuya, Ken Takeuchi, Alexander I. Kolesnikov, Generation of electrons, protons and oxygen based on the oxidative decomposition of water molecules by high-purity ramsdelite-type manganese dioxide, and charge / discharge cycle accompanied by precipitation of precious metal fine particles Proceedings of the 80th Annual Conference 1A32, p. 16, (2013).
As described above, the HTO gas released from the electrode film collecting tritium into the gas phase in the reaction vessel can be easily sucked and removed from the gas phase in the reaction vessel with a vacuum pump or the like. For this reason, tritium can be recovered by introducing a gas containing the HTO gas removed by suction into a small amount of water (H ₂ O).

Further, in the tritium recovery method of this embodiment, the HT gas released from the electrode film that collects the tritium is introduced into a heat resistant glass tube and heated to 250 ° C. to 500 ° C. The tritium can be collected by oxidizing HT to convert it to HTO by introducing it into a small amount of water (H ₂ O) as described above.

Further, the tritium recovery method of the present embodiment accelerates the release of tritium from the electrode film into water by irradiating the electrode film collecting the tritium with ultraviolet light, and in a small amount of water (H ₂ O). In addition, tritium can be recovered.

Further, in the tritium recovery method of this embodiment, a voltage is applied to the electrode film that collects the tritium in contact with a gel containing lithium ions, so that lithium ions contained in the gel are converted to manganese oxide. By inserting it into the spinel crystal structure, tritium contained in the manganese oxide is eluted into the gel and an aqueous electrolyte solution electrically connected to the gel. In addition, manganese oxide having a spinel crystal structure into which lithium ions are inserted can be obtained by the same recovery method. If lithium ions are replaced with hydrogen ions by acid treatment with dilute acid again, a hydrogen ion-containing manganese oxide maintaining a spinel crystal structure can be obtained, so that it can be easily reused as a tritium absorbent. .

The method for reusing a tritium absorbent material of the present embodiment is characterized in that after releasing tritium from the electrode film collecting tritium as HTO or HT, lithium ions are added to an aqueous solution in contact with the electrode film. This is a method of reusing tritium absorbent. As described above, the spinel-type manganese oxide after the release of tritium has an unstable crystal structure in neutral to alkaline water, and manganese ions are eluted from the manganese oxide. Therefore, in the present invention, in order to stabilize the crystal structure of the manganese oxide after the release of tritium and suppress elution of manganese ions even in a neutral to alkaline aqueous solution, the electrode film contains lithium ions (Li ⁺ ). A water-soluble chemical containing lithium such as lithium chloride so that the lithium concentration in the aqueous solution in contact with the electrode film is several tens mg / L or less per gram of manganese oxide contained (LiCl), lithium hydroxide (LiOH) and the like were added. When the same manganese oxide after the release of tritium is reused as a tritium absorbent, the dissolution of manganese is suppressed even if the pH of the tritium-containing water is adjusted from neutral to alkaline, and sludge is generated. Can be significantly reduced. As a result, it was possible to reuse the absorbent material while repeatedly collecting and releasing tritium from the absorbent material.

In view of the above, the method of recovering tritium from an electrode film composed of manganese oxide powder having a spinel crystal structure or collecting the tritium according to the present invention provides simple tritium recovery at room temperature. In addition, it provides an economical technology that can reuse the manganese oxide after tritium recovery as a tritium absorber.

Next, an embodiment in which tritium is recovered from manganese oxide having a spinel crystal structure in which tritium is collected according to the present invention will be described in detail.

<Method of synthesizing tritium absorbent material>
A tritium absorbent material composed of hydrogen ion-containing manganese oxide having a spinel crystal structure was synthesized according to the following procedure.
<Mixing with raw materials> Reagent manganese carbonate hydrate (MnCO ₃ · nH ₂ O) and lithium hydroxide hydrate (LiOH · H ₂ O) powder are mixed at a weight ratio of 2 to 1 and blackened at room temperature. Mix well until
<Firing> The mixed powder was heated in the atmosphere at 390 ° C. for 6 hours using an electric furnace, and then cooled to room temperature.

<Purification> The powder after natural cooling was suspended in an appropriate amount of ion-exchanged pure water in a container such as a beaker, and ultrasonic waves were irradiated through the wall surface of the container such as a beaker to loosen the powder. Unreacted manganese carbonate remained turbid in the supernatant of ion-exchanged pure water because of its low specific gravity, and lithium ion-containing manganese oxide having a high specific gravity and a spinel crystal structure precipitated at the bottom of the container. After standing for a certain period of time, the supernatant manganese carbonate was removed using an aspirator or the like, and a lithium ion-containing manganese oxide powder having a precipitated spinel crystal structure was recovered. At this time, the pH of ion-exchanged pure water in which the powder was suspended was maintained from a weak alkali to an alkali side.

<Storage> The lithium ion-containing manganese oxide powder having a spinel crystal structure recovered by filtration or the like was stored in a cool and dark place. When a drying treatment was necessary, the film was dried at room temperature under reduced pressure (about minus 50 cmHg). Or it dried at the temperature of 100 degrees C or less under atmospheric pressure.

By the above operation, a tritium absorbent material composed of lithium ion-containing manganese oxide having a spinel crystal structure with a primary particle size of 20 to 70 nm was obtained.

<Manufacturing method of tritium absorbing electrode film>
The lithium-containing manganese oxide powder obtained by the above synthesis method is fixed to the surface of a platinum mesh or stainless steel mesh using a commercially available conductive paint, and heated and dried at 150 ° C. in the atmosphere using a dryer. A membrane was created. Thereafter, a Nafion (registered trademark) dispersion is applied to one side of the electrode film, dried at 60 ° C. in the atmosphere, and then heated at 120 ° C. in the atmosphere to form a hydrogen ion conductive film on the surface of the electrode film. The tritium absorbing electrode film was manufactured by fixing.

<Test Method for Detecting Water (HTO) Gas and Hydrogen (HT) Gas Containing Tritium>
The fact that tritium-containing water (HTO) gas and hydrogen gas (HT) are generated from the experimental system of this example indicates that a hydrogen isotope concentration analysis test apparatus (HPTGM / PC-1, HPTGM / PHA, HPTGM / GC-1, and TPTGM / PCDT-S). The analytical test apparatus is composed of a cathode (voltage: 0 V) of an aluminum tube (diameter 8 cm, length 50 cm) to which a voltage is applied and a gold wire plated tungsten wire (diameter 20) at the center of the aluminum tube. A proportional counter composed of (μm) anode (voltage: +1750 V) is used as a detector. This detector analyzes the waveform of the output voltage obtained by introducing the sample gas together with the carrier gas at a pressure of 900 KPa, and generates a wave height (a signal derived from tritium and a background signal derived from external radiation such as cosmic rays). By distinguishing from the difference in energy and rise time, it is possible to detect tritium at a very low concentration (detection limit: 1 Bq / L) contained in the gas. In general, in gas chromatograph mass spectrometry (GC-MASS), which is one of the most excellent techniques for analyzing trace components contained in a gas, HT, which is an object to be measured in this experiment, contains helium ( ⁴ Since the mass number is 4 equal to He) and the mass concentration is very low, it is very difficult to analyze.

<Test method for collecting tritium from tritium-containing water using an electrode film having a hydrogen ion conducting film on one side>
The tritium-absorbing electrode film was acid-treated and then contacted with tritium-containing water to collect tritium with the electrode film.
In this test, a commercially available standard reagent for tritium water was diluted with distilled water at room temperature to prepare tritium-containing water. A liquid scintillation counter (Liquid Scintillation Analyzer TRI-CARB 2100TR PACKARD (USA)) was used to measure the radioactivity concentration of tritium. 10 mL of a surfactant containing a fluorescent agent that emits light with β rays as a scintillator was added to 1.0 mL of a tritium-containing water sample, and the radioactivity concentration derived from tritium from the 1.0 mL sample was measured. As a blank sample, scintillator was similarly added to 1.0 mL of distilled water used in the experiment, and the radioactivity concentration derived from tritium was measured to detect 0.41 Bq / mL. For this reason, the liquid scintillation counter used in this test confirmed that the lower limit of detection of the tritium radioactivity concentration was 0.41 Bq / mL. Reagents 0.1M and 0.5M aqueous sodium hydroxide were used to adjust the pH of the tritium-containing water. Further, a pH meter and a pH test paper were used for checking the pH and water temperature.

<Test method for recovering tritium in gel and electrolyte>
Tritium collected by the tritium absorbing electrode film was collected in a gel containing lithium ions and water containing an electrolyte as follows.

First, the upper half of the electrode film in which tritium was collected was inserted into a gel containing lithium ions filled in a metal mold. The lower part of the electrode film inserted into the gel was brought into contact with an aqueous electrolyte solution containing lithium ions.
For example, the gel is prepared by adding a reagent lithium chloride powder and a reagent agar powder to distilled water and heating the mixture. After sufficiently dissolving the agar powder, the gel is poured into a stainless steel mold and allowed to stand at room temperature to solidify the agar. Created. Moreover, the lower half part of the electrode film | membrane which collected tritium was made to contact the distilled water which added electrolyte. Examples of the electrolyte that can be used include hydroxides and chlorides such as lithium, sodium, and potassium, or dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid. Further, an electrode such as a carbon rod is arranged, and an electrode film containing tritium inserted in the gel in the metal mold placed in the conductive aqueous solution is used as a positive electrode, and the electrode film is arranged in the conductive aqueous solution. A carbon rod was used as the negative electrode.

Using a constant voltage power supply, apply a voltage of about 4-5V to the positive and negative electrodes that make up the circuit. At that time, the positive electrode of the constant voltage power source was connected to the metal mold of the gel with a copper wire, and the negative electrode was connected to the carbon rod. After applying a voltage for a certain period of time, the gel was heated and dissolved in a metal sealed container, and a 1.0 mL sample was taken from the solution. In addition, 1.0 mL of sample water is filtered and collected from the electrolyte aqueous solution, and the tritium concentration contained in each sample is measured using a liquid scintillation counter, so that the gel and the electrolyte are collected from the electrode film collecting tritium. The amount of tritium eluted and collected was examined.

<Test method for reusing spinel-type manganese oxide after tritium release as a tritium absorber>
In the test method in which tritium is collected from tritium-containing water using the electrode film having the hydrogen ion conductive film disposed on one side, the concentrations of 0.1M and 0.5M water are used to adjust the pH of the tritium-containing water. An aqueous sodium oxide solution was used. Lithium ions were added to tritium-containing water by using lithium hydroxide monohydrate (LiOH.H ₂ O) having a concentration of 1M instead of sodium hydroxide for pH adjustment. Further, lithium chloride (LiCl) was added to tritium-containing water, and the above sodium hydroxide was used for pH adjustment. In any case, the above-mentioned chemical containing lithium was added so that the amount of lithium in the tritium-containing water did not exceed about 30 mg per gram of the tritium absorbent powder. Moreover, the addition amount was set so that the lithium concentration in the tritium-containing water did not exceed 50 mg / L. If the amount of lithium added is too large, the hydrogen-containing manganese oxide will dissolve, so the amount of lithium added should be limited to the above-mentioned appropriate amount. By adding an appropriate amount of lithium, the crystal structure of spinel-type manganese oxide after tritium release is stabilized. As a result, when the tritium absorbent material is reused, elution of manganese ions can be suppressed and the generation of sludge can be suppressed when the tritium absorbent is brought into contact with neutral to alkaline tritium-containing water. A similar effect can be expected by dissolving lithium in a dilute acid aqueous solution for supplying hydrogen ions to the tritium electrode film.

<Test to measure the valence of manganese constituting the tritium absorber>
An attempt was made to measure the valence of manganese constituting the hydrogen ion-containing manganese oxide used as the tritium absorber by X-ray absorption spectroscopy (XANES). The crystal structure was examined by X-ray diffraction analysis (XRD).

As general knowledge, regarding the valence of manganese (Mn) constituting the hydrogen ion-containing manganese oxide, the valence of manganese constituting the lithium ion-containing manganese oxide (LiMn ₂ O ₄ ) is +3.5. Therefore, it is considered that HMn ₂ O ₄ obtained by replacing lithium ions with hydrogen ions by acid treatment maintains +3.5 valence in order to maintain charge neutrality. However, in recent research reports, the spinel-type hydrogen ion-containing manganese oxide obtained by acid treatment of spinel-type lithium-containing manganese oxide baked at a relatively low temperature of 390 ° C. as in the present invention is as follows. It has been pointed out that the spinel crystal structure lithium manganese oxide obtained by firing at a high temperature such as 500 to 1000 ° C. has a remarkably higher degree of freedom regarding the movement of hydrogen ions inside the crystal. H. Koyanaka, O. Matsubaya, Y. Koyanaka, and N. Hatta, Quantitative correlation between Li absorption and H content in Manganese Oxide Spinel λ-MnO ₂ ", Journal of Electroanalytical Chemistry 559 (2003) 77-81, and H. Koyanaka, Y. Ueda, K. Takeuchi, and AI Kolesnikov, Effect of crystal structure of manganese dioxide on response for electrolyte of a hydrogen sensor operative at room temperature ", Sensors & Actuators: B, Vol. 183, pp. 641-647 , (2013). According to these documents, the main reason for the high degree of freedom of movement of hydrogen ions inside the crystal is that hydrogen ions are trapped in specific oxygen atom pairs by weak covalent bonds in the crystal. ing. However, it has not been clarified in what state the electrons for electrically neutralizing the positive charge (+1) of the hydrogen ion to maintain the charge neutrality are retained in the crystal. Therefore, in this test, a tritium absorbent was prepared using a sample prepared by stirring hydrogen ion-containing manganese oxide (about 1 g) functioning as a tritium absorbent in 100 mL of ultrapure water (H ₂ O) for 2 days. The valence of Mn constituting was examined by X-ray absorption spectroscopy. This analysis method was described in detail in Example 5 below. As a result, the hydrogen ion-containing manganese oxide that functions as the tritium absorbent material had the same spinel crystal structure as the previous knowledge (WO2015 / 037734). It was newly revealed that most manganese valences are +4. The result shows that the composition formula of the present tritium absorbent is (H ⁺ , e ⁻ ) _x Mn ₂ O ₄ , and hydrogen ions (H ⁺ ) having a high degree of freedom of movement (conductivity) in the crystal. By being influenced, it is suggested that the electron (e ⁻ ) is not involved in the d orbital of manganese. This new finding is that the tritium absorber collects tritium in water in the solid phase of the absorber and releases it into the gas phase as water molecule (HTO) gas containing tritium from the solid phase. It was suggested that it progressed like this.

Chemical formula (1) shows a reaction in which the present absorbent (H ⁺ , e ⁻ ) _x Mn ₂ O ₄ is obtained by acid treatment of lithium ion-containing manganese oxide. The chemical formula (2) is based on the ion exchange reaction of H ⁺ and T ⁺ accompanied by an oxidative decomposition reaction with respect to OT ^{− in} tritium-containing water. Reactions trapped in the structure are shown. Chemical formula (3) shows a reaction in which the present absorbent releases tritium as hydrogen gas (HT) from the spinel crystal structure in acidic water. Chemical formula (4) shows an apparent reaction in which the formulas (2) and (3) are integrated, and tritium present in water as OT ⁻ is HTO gas and the reaction vessel is exposed from the position where the present absorbent is exposed to the gas phase. It shows the reaction released by evaporation to the gas phase inside. In the above chemical formulas (1) to (4), the symbol x represents the molar ratio of hydrogen ions or lithium ions contained in the absorbent to other components, and y represents the molar ratio of tritium absorbed in the absorbent to other components and The molar ratio of water (HTO) gas containing tritium generated and hydrogen gas (HT) is shown. In the chemical formulas (3) and (4), empty adsorption sites generated in the crystal with the release of tritium ions (T ⁺ ) indicated by “□” are expressed. In the chemical formulas (3) and (4), the adsorption sites indicated by “□” indicate that, in the actual manganese oxide, the distance between atoms existing in the spinel crystal structure is 2.57 to 2. Equivalent to an oxygen tetrahedral site composed of 60Å oxygen pairs (H. Koyanaka, Y. Ueda, K. Takeuchi, AI Kolesnikov, Effect of crystal structure of manganese dioxide on response for electrolyte of a hydrogen sensor operative at room temperature ", Sens. Act. B 2013, 183, 641-647).
In addition, when this absorbent material is applied as the electrode film, hydrogen ions (H ⁺ ) are replenished from the dilute aqueous acid solution through the hydrogen ion conductive film to the empty adsorbing site. It is considered that the present absorbent (H ⁺ , e ⁻ ) _x Mn ₂ O _{4 on} the left side of is reconstructed, and as a result, the tritium absorption reaction is sustained. Furthermore, this absorbent material can selectively absorb and separate tritium from water. First, the diffusion rate of tritium ions (T ⁺ ) having a large mass inside the spinel-type manganese oxide crystals Since it is lower than the diffusion rate of (H ⁺ ), there is a high probability that it will remain in the crystal as a result, and secondly, based on chemical formulas (2), (3), and (4) As the transfer of tritium from water to the gas phase proceeds, the self-dissociation reaction of HTO (HTO → H ⁺ + OT ⁻ ) does not contain tritium in order to compensate for the lack of OT ⁻ in tritium-containing water. It can be considered that it proceeds faster than the self-dissociation reaction (H ₂ O → H ⁺ + OH ⁻ ) of light water molecules (H ₂ O).

Further, (H ⁺ , e ⁻ ) _xy (□, e ⁻ ) _y Mn ₂ O ₄ shown on the right side of the chemical formula (3) indicates spinel-type manganese oxide after the release of tritium ions (T ⁺ ). In addition, since the crystal structure is unstable as described above, manganese ions are dissolved when the pH is simply adjusted to neutral to alkaline for reuse. Therefore, in order to stabilize the unstable crystal structure as described above, it is necessary to prevent elution of manganese ions by adding lithium ions. Here, if the amount and concentration of lithium added are too high, it is not preferable for absorption of tritium. The addition of lithium of about 1 to 30 mg per gram of the tritium absorbent material of the present invention, and the lithium concentration in the aqueous solution in contact with the tritium absorbent material is about 1 to 50 mg / L from the water using the present manganese oxide. This is preferable for the collection and recovery of tritium.

That is, by applying the tritium-absorbing electrode film of the present invention to weakly acidic to alkaline (for example, pH 6-9) tritium-containing water in the reaction vessel, tritium in water is continuously collected, and tritium-containing water is further collected. When the pH is acidic (for example, pH 3 or lower), the release of tritium becomes active. Through these chemical reactions, it has become possible to move and separate tritium from the reaction system to the outside by suctioning the tritium that has moved to the gas phase in the reaction vessel with a vacuum pump or the like. Moreover, the reusability of this tritium absorbent material can be improved by adding lithium ions to the aqueous solution in contact with the tritium absorbent electrode film. As described above, the technique of the present invention has made it possible to recover low-concentration tritium in water significantly more easily and at a lower cost than conventional techniques.

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

In accordance with the following procedure, a tritium absorbent material composed of lithium ion-containing manganese oxide having a spinel crystal structure and hydrogen ion-containing manganese oxide having a spinel crystal structure was synthesized.
<Mixing with raw materials> Powders of Wako Pure Chemical Industries, Ltd. reagent manganese carbonate hydrate (MnCO ₃ · nH ₂ O) and lithium hydroxide hydrate (LiOH · H ₂ O) were mixed at a weight ratio of 2: 1. Mix well until it turns black at room temperature.
<Firing> The powder mixture was heated in the atmosphere at 390 ° C. for 6 hours using an electric furnace (YAMATO FO-410), and then naturally cooled to room temperature.

<Purification> The naturally cooled powder, for example, 20 g, was suspended in 1 L of ion-exchanged pure water in a glass beaker, and ultrasonic waves were irradiated through the wall of the beaker for 10 minutes to loosen the powder. Since unreacted manganese carbonate has a low specific gravity, it remained turbid in the supernatant of ion-exchanged pure water, and lithium ion-containing manganese oxide having a high specific gravity and a spinel crystal structure precipitated at the bottom of the container. After standing for 30 minutes, supernatant manganese carbonate was removed using an aspirator, and lithium ion-containing manganese oxide powder having a precipitated spinel crystal structure was collected by filtration. At this time, the pH of ion-exchanged pure water in which the lithium ion-containing manganese oxide powder having a spinel crystal structure was suspended was maintained from weak alkali to alkaline. By this purification treatment, manganese carbonate remaining as an unreacted substance in the firing step was removed.

<Storage> The lithium ion-containing manganese oxide powder having a spinel crystal structure recovered by filtration was dried at room temperature in a vacuum desiccator under a pressure of minus 600 hPa.

By the above operation, a tritium absorbent material composed of lithium ion-containing manganese oxide having a spinel crystal structure with a primary particle size of 20 to 70 nm and hydrogen ion-containing manganese oxide having a spinel crystal structure was obtained.

<Production of tritium absorbing electrode film>
Using 0.24 g of lithium ion-containing manganese oxide powder obtained by the above synthesis method, using a conductive paint (Fujikura Kasei DOTITE XC-12) as a binder, a stainless mesh (SUS304, 100 mesh, 6 cm × 1.5 cm × 0. 16 cm) is fixed to the surface (5.0 cm × 1.5 cm × 0.16 cm) with a film thickness of 0.3 mm and dried by heating at 150 ° C. for 3 hours in the air using a dryer (WFO-401 manufactured by EYELA). Thus, the electrode film formed into a porous shape by carbonizing the binder was obtained. Next, a dispersion of Nafion (registered trademark) with a concentration of 20% (manufactured by Wako Pure Chemical Industries, Ltd.) was uniformly applied to one side (5 cm × 1.5 cm) of the electrode film and dried at 60 ° C. for 2 hours in the atmosphere. Finally, Nafion (registered trademark) was fixed to the surface of the electrode film as a hydrogen ion conductive film by heating in the atmosphere at 120 ° C. for 1 hour.

<Formulation of tritium-containing water>
When preparing tritium-containing water, dilute 14 μL of tritium standard reagent (PerkinElmer ³ H, water) with 140 mL of distilled water (manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature, and add tritium-containing water with a radioactive concentration of 3105 Bq / mL. Prepared. Therefore, it is calculated that the radioactivity derived from tritium of 434700 Bq is generated as a total amount from 140 mL of tritium-containing water for the experiment.

<Method of Tritium Collection Test Using Electrode Film Containing Hydrogen Ion-Containing Manganese Oxide with Spinel Crystal Structure and One-side Covered Nafion (Registered Trademark) Film>
In this example, the reaction system shown in FIG. That is, the unit including the tritium absorbing electrode film was brought into contact with tritium-containing water (140 mL) placed in a transparent acrylic container. In manufacturing the unit, the electrode film is closely attached to the acrylic container constituting the unit, and the Nafion (registered trademark) film of the electrode film is coated from a small amount of dilute aqueous acid solution injected into the acrylic container. The reaction surface was arranged so that hydrogen ions (H ⁺ ) were donated. Considering the practical application of this technology, it is economically preferable to treat a large amount of tritium-containing water using a small amount of dilute aqueous acid solution because the waste liquid volume of the dilute acid generated after the treatment can be minimized. Specifically, in this example, dilute nitric acid (7 M) with a concentration of 0.5 M to donate hydrogen ions (H ⁺ ) to the electrode film constituting the tritium absorption electrode film unit shown in FIG. 0.0 mL) was used.
Further, in order to infiltrate the reaction surface of the electrode film with tritium-containing water and dilute acid aqueous solution, the acrylic plate and the silicone rubber film waterproof seal constituting the unit, and the acrylic container have a circular hole (area 12.2 mm). 6 mm ² ) are provided in two places, so that the total area of the holes is 25.2 mm ² . Furthermore, 1 cm from the upper end of the electrode film to which the manganese oxide was fixed was disposed so as to protrude from the water surface of the tritium-containing water and contact the gas phase.

Next, the specific experimental procedure will be described. First, 7.0 mL of dilute nitric acid having a concentration of 0.5 M was injected from a small hole on the upper surface of the acrylic container of the unit shown in FIG. 1A, and the unit was filled in a cubic acrylic container with a concentration of 0. It was immersed in 140 mL of 5M dilute nitric acid for 1 hour. By the acid treatment of this unit, lithium was eluted from the lithium ion-containing manganese oxide contained in the electrode film into dilute nitric acid, and the composition was changed to hydrogen ion-containing manganese oxide. Thereafter, dilute nitric acid was removed from the unit and the cubic acrylic container, and the inner surfaces of these containers were sufficiently rinsed with distilled water to wash away the dilute nitric acid. Thereafter, 7.0 mL of dilute nitric acid with a concentration of 0.5 M was newly injected from the small hole at the top of the unit, and this was added to 140 mL of tritium-containing water with a radioactive concentration of 3105 Bq / mL placed in a cubic acrylic container. Soaked. Further, a copper wire was connected to the upper end of the electrode film and grounded to the ground. Thereafter, while gently stirring the tritium-containing water with a stirrer coated with Teflon (registered trademark) and a magnetic stirrer, an appropriate amount of a 0.5 M sodium hydroxide aqueous solution was added dropwise to add tritium-containing water. The pH was adjusted to 9.5. Using the same equipment and method as in Example 1, 1.2 mL of a sample was taken from tritium-containing water every certain time, and the radioactivity concentration of tritium in 1.0 mL sampled from each sample was determined as in Example 1. Measurements were made with a liquid scintillation counter in the same manner.

The experimental results are shown in FIG. The figure shows the change with time of the radioactivity concentration of tritium in tritium-containing water. From the figure, it can be seen that the tritium radioactivity concentration of tritium-containing water continuously decreases. During the experiment, since the pH of the tritium-containing water gradually decreased, the pH of the tritium-containing water was maintained at 3.0 or more and 9.7 or less by dropping a 0.1M or 0.5M aqueous sodium hydroxide solution at an appropriate time. During the experiment, the position of the electrode membrane unit immersed in the tritium-containing water was finely adjusted at the time of sample collection, so that the water surface of the tritium-containing water filled in the cubic acrylic container and the rarely injected into the electrode membrane unit were A difference in water level between the nitric acid and the water surface was prevented. This is to prevent a static pressure load from being applied to the electrode film due to the same water level difference. The radioactivity concentration of tritium in the tritium-containing water in this experiment varied from the initial concentration (3105 Bq / mL) to the final concentration (2777 Bq / mL). For this reason, the result which showed that the 0.24 g absorber contained in the electrode film absorbed and separated about 45920 Bq of tritium from 140 mL of the same tritium-containing water was obtained. The radioactivity concentration of tritium in 7 mL of dilute nitric acid installed in the electrode membrane unit at the end of the experiment was 113 Bq / mL. For this reason, tritium eluted in dilute nitric acid corresponded to 791 Bq.
As a result of the above, good tritium absorption can be obtained even if the volume of the dilute acid aqueous solution for donating hydrogen ions to the absorbent is 1/20 of the tritium-containing water to be treated. It was proved that tritium re-elution did not occur even when the electrode film was made of a relatively inexpensive metal such as stainless steel, and continuous tritium absorption was obtained.

<Example 2>
<Detection test of tritium evaporating from an electrode film containing a hydrogen ion-containing manganese oxide having a spinel crystal structure and coated with a Nafion (registered trademark) film on one side>
The fact that tritium-containing water (HTO) and hydrogen gas (HT) are generated from the electrode film that collects tritium indicates that hydrogen isotopic concentration analysis test equipment in gas (HPTGM / PC-1, HPTGM) manufactured by IsoShield. / PHA, HPTGM / GC-1, TPTGM / PCDT-S). The experimental system in this example is shown in FIG. Experiments were conducted according to the same method as in Example 1 with respect to the method for synthesizing the tritium absorbent material, the method for preparing the electrode film, the method for arranging the electrode film, and the method for measuring the tritium concentration.

This experimental system is shown in FIG. The unit in which the tritium absorbing electrode film was arranged was immersed in 140 mL of tritium-containing test water having an initial tritium concentration of 5450 Bq / mL filled in a transparent acrylic resin container (5.8 × 5.8 × 5.8 cm ³ ). . Furthermore, the unit in which the electrode film was arranged was arranged in another transparent acrylic resin sealed container (7.8 × 7.8 × 7.8 cm ³ ). Next, as a sample gas obtained by mixing the gas phase gas in the sealed container with the carrier gas (mixed gas of 10% methane and 90% argon) of the same analytical test apparatus at a flow rate of 300 mL / min, manufactured by Pyrex (registered trademark) The glass tube (length 50 cm, outer diameter 9 mm, inner diameter 8 mm) was contacted with a molecular sieve (3A1 / 16, manufactured by Wako Pure Chemical Industries, Ltd. 134-06095) filled over a length of 12 cm for dehydration. Next, the dehydrated sample gas was introduced into the proportional counter of the analytical test apparatus. In this experiment, an integrated output signal obtained by continuously introducing the gas of the sample to be measured into the analytical test apparatus for 50000 seconds was analyzed. As a result, a waveform having a rise time specific to the gas containing tritium (HTO or HT) was detected (FIG. 2B).

In this experiment, the reaction system shown in FIG. In the reaction system, the tritium absorbing electrode membrane is brought into contact with tritium-containing water in a sealed container, the gas in the head space inside the reaction container is passed through a molecular sieve and dehydrated, and then the copper oxide heated to 400 ° C. ( CuO) and 0.1 g were contacted to oxidize HT gas contained in the gas to HTO and attempt to recover it in distilled water in a gas washing bottle.

<Production of tritium absorbing electrode film>
The surface of a stainless mesh (SUS304, 100 mesh, 4 cm × 3 cm) was obtained from the lithium-containing manganese oxide powder (0.8 g) obtained by the above synthesis method using a commercially available conductive paint (DOTITE XC-12 manufactured by Fujikura Kasei). × 0.16 cm), and heated and dried at 150 ° C. for 3 hours in the air using a dryer, thereby carbonizing the binder to obtain a porous electrode film. Then, the process which apply | coated 20% Nafion (trademark) dispersion (Wako Pure Chemical Industries) to one side (4 cm x 3 cm) of the electrode film, and dried at 60 degreeC in air | atmosphere for 1 hour was repeated twice. Subsequently, the tritium absorption electrode film was manufactured by heating at 120 ° C. in the atmosphere for 1 hour to fix the film as a hydrogen ion conductive film on the surface of the electrode film. This electrode film was placed in the acrylic resin container shown in FIG. 3 (a), and 200 mL of dilute nitric acid having a concentration of 0.5 M was injected into both the tritium-containing water tank side and the dilute nitric acid tank, and held for 1 hour. . During the holding, the dilute nitric acid on the tritium-containing water tank side was stirred for 1 hour by a magnetic stirrer using a stirring bar coated with Teflon (registered trademark). By contact with the dilute nitric acid, the composition of the lithium ion-containing manganese oxide contained in the electrode film is changed to hydrogen ion-containing manganese oxide by eluting lithium ions into the dilute nitric acid. Next, after removing 0.5 M dilute nitric acid aqueous solution from both tanks, the dilute nitric acid was removed by sufficiently rinsing with distilled water.

<Experiment for recovering tritium transpiration from the tritium absorbing electrode film>
FIG. 3A shows a reaction vessel of this experimental system. The reaction vessel is a reaction vessel made of an acrylic resin partitioned by a tritium absorption electrode film containing hydrogen ion-containing manganese oxide manufactured by the above method. Furthermore, 1 cm from the upper end of the electrode film to which the manganese oxide was fixed was disposed so as to protrude from the water surface of the tritium-containing water and contact the gas phase. On the side of the tritium-containing water tank, 200 mL of tritium-containing water (initial tritium radioactivity concentration: 99253 Bq / mL, adjusted to an initial pH of 9.29 by adding a 0.1 M sodium hydroxide aqueous solution) was placed, and the dilute nitric acid water tank Distributed 200 mL of dilute nitric acid with a concentration of 0.5M. At that time, the water temperature of the tritium-containing water was 20.0 ° C. The electrode film was grounded through a copper wire. The tritium-containing water was stirred with a magnetic stirrer using a stir bar coated with Teflon (registered trademark). The pH of the tritium-containing water was maintained at pH 6.8 to 9.0 by adding a 0.1 M aqueous sodium hydroxide solution.

The gas in the head space inside the reaction vessel shown in FIG. 3 (a) is pumped by a pump (JPO W600, discharge pressure: 0.16 kg / cm ² ), and has a length of 40 cm, an outer diameter of 9 mm, and an inner diameter of 7 mm. Contact was made with copper oxide (0.1 g, CuO: 99.9%, powder, Wako Pure Chemical Industries, Ltd. 038-13191) placed in a glass tube. At that time, the outer wall of the quartz glass tube was heated and held at 400 ° C. using a heater (Daika Electric Type CL, 100 V, 60 W) with a temperature controller (ASONE TC-3000). By this heating, the temperature of the copper oxide disposed in the quartz glass tube was maintained at 350 to 400 ° C. The position of the copper oxide powder in the quartz glass tube is fixed using glass wool (TOSO Grade: fine 2 to 6 μm, coarse 4 to 9 μm). Further, in the quartz glass tube, water penetrates into the front stage of the copper oxide. In order to prevent this, molecular sieve 3A1 / 16 (Wako Pure Chemical Industries 134-06095) was fixed with glass wool.

Also, using 40 microliters of distilled water (H ₂ O) arranged in advance in a Walter type gas cleaning bottle located at the end of the experimental system shown in FIG. Samples of 1.0 mL were collected. To each sample, 10 mL of a surfactant (Perkin Elmer Ultimate-Gold) containing a fluorescent agent that emits β-rays as a scintillator was added, and the radioactivity concentration derived from tritium from about 1.0 mL of each sample was measured. As a blank sample, 1.0 mL of distilled water used in the experiment was pretreated in the same manner to measure the radioactivity concentration derived from tritium, and 1.1 Bq / mL was detected. For this reason, in this measurement method, it confirmed that 1.1 Bq / mL was the detection lower limit of the radioactivity derived from the tritium added for experiment. With the above procedure, the time change of the amount of tritium recovered in the water in the Walter gas cleaning bottle was examined.

FIG. 3 (b) shows the change in the amount of tritium recovered in the water in the Walter type gas cleaning bottle. In the figure, a result was obtained in which the amount of tritium recovered during 25 hours increased linearly. This increase is caused by the movement of tritium absorbed in the tritium-absorbing electrode film from the tritium-containing water into the gas phase as a gas containing tritium (HTO or HT), and HT and copper oxide in the reaction system of FIG. This is considered to be the result of reaction, conversion to water HTO, and accumulation in the water of the Walter gas scrubber. In this experiment, in order to keep the temperature of the copper oxide at 250 ° C. or higher, the outer wall temperature of the peripheral glass tube where the copper oxide powder is located in the quartz glass tube was kept at 350 to 400 ° C. However, when the temperature was set at 270 ° C., no increase in the radioactivity of tritium in water in the Walter gas scrubber was observed. This is presumably because the temperature in the tube was not sufficiently raised to 250 ° C., which is the minimum temperature required for the oxidation reaction of hydrogen gas using copper oxide.

Furthermore, the gas in the headspace of the experimental system of this example was introduced into a hydrogen isotope concentration analysis test apparatus in gas manufactured by IsoShield using a mixed gas of 10% methane and 90% argon (flow rate 300 mL / min) as a carrier gas. It was confirmed that tritium was contained in the gas in the head space. In this analysis, the gas in the head space inside the reaction vessel is mixed with a mixed gas of 10% methane and 90% argon (flow rate 300 mL / min), which is the carrier gas of the apparatus, and a glass tube made of Pyrex (registered trademark). After dehydrating by contacting with a molecular sieve (3A1 / 16, Wako Pure Chemical Industries 134-06095) loaded over a length of 12 cm in a tube (length 50 cm, outer diameter 9 mm, inner diameter 8 mm), it was introduced into the detector of the same apparatus. Finally, as a result of analyzing the integrated data for 50,000 seconds by the same apparatus, a waveform peculiar to the gas containing tritium (HTO or HT) was detected. Therefore, it was proved that the tritium absorbed from the water was transferred to the gas phase in the tritium absorbing electrode film.

<Experiment for promoting the release of tritium from a tritium absorbing electrode film by irradiation with ultraviolet light>
In this example, a sample of test water (150 mL) was prepared by irradiating the tritium-absorbing electrode film with ultraviolet light from the outside of the reaction vessel using the acrylic resin reaction vessel shown in FIG. The change in the tritium concentration was investigated. To collect a sample of tritium test water, a small hole (diameter 5 mm) is provided in the acrylic plate at the top of the reaction vessel, and a silicon tube can be inserted into the tritium-containing test water from the small hole to collect the sample of the test water. I did it. The small holes were sealed with aluminum tape except during sample collection. As UV light source, UV-LED (wavelength: 375 nm, three-lamp specification, with lens, PW-UV343H-02) manufactured by Nichia Chemical Co., Ltd., contact surface of tritium-absorbing electrode film with test water containing tritium For one hour through the acrylic wall of the reaction vessel. Each 1.3 mL to 1.0 mL of each sample of test water collected at the time before and after irradiation with ultraviolet light is filtered using a disposable filter (DISMIC AS-25) manufactured by Advantech, and emitted as β-rays as a scintillator. 10 mL of a surfactant containing a fluorescent agent (Perkin Elmer Ultimate-Gold) was added, and the radioactivity concentration derived from tritium from about 1.0 mL of the sample was measured.
As a result, the tritium radioactivity concentration in the tritium-containing test water (150 mL) was 3737 Bq / mL before irradiation with the same ultraviolet light, and after the irradiation was continued for 1 hour, the tritium radioactivity concentration in the tritium-containing test water was It increased to 3752 Bq / mL. Furthermore, it was found that the radioactivity concentration of tritium was reduced to 3672 Bq / mL in a sample collected 40 minutes after the irradiation was stopped. This variation in tritium radioactivity concentration caused by ultraviolet light irradiation is suggested to be based on the phenomenon that tritium is eluted from the electrode film into water by ultraviolet light irradiation. That is, the irradiation of the tritium-absorbing electrode film with ultraviolet light has the effect of promoting the release of tritium from the electrode film, and the tritium released in the test water containing tritium is re-dissolved in the test water containing tritium. The concentration is thought to have increased. Further, it is considered that the radioactivity concentration of tritium decreased as a result of reducing the amount of tritium released from the electrode film by stopping the irradiation of ultraviolet light and restarting the absorption of tritium by the electrode film.

An electrode film containing hydrogen ion-containing manganese oxide with one side coated with a Nafion (registered trademark) film was prepared in the same manner as in Example 3. In this example, the reaction system shown in FIG. 4A was configured, and tritium-containing water was brought into contact with the electrode film coated with a Nafion (registered trademark) film on one side. Next, tritium is evaporated to the gas phase inside the reaction vessel from the surface where the electrode film is in contact with the gas phase inside the reaction vessel, and sucked through a silicon tube into distilled water disposed in the gas washing bottle 1 by a pump. It was collected. The reaction vessel and the pump were connected with a silicon tube. Further, the gas exhausted from the gas cleaning bottle 1 is brought into contact with 0.1 g of copper monoxide (CuO) heated to 400 ° C. with a heater in the same manner as in the third embodiment, and led to the gas cleaning bottle 2 in the subsequent stage. Then, it was returned from the upper part of the same reaction vessel and circulated again. In addition, by providing an intake port at the top of the reaction water tank in which dilute nitric acid is arranged, the inside of the reaction vessel is prevented from becoming negative pressure due to pressure loss caused by circulation of the headspace gas inside the reaction vessel, Experiments were performed under atmospheric pressure.

In the experiment, as shown in FIG. 4A, a transparent acrylic water tank was divided into two tanks by the electrode film containing the lithium ion-containing manganese oxide powder. In order to prevent water leakage, each seam of the acrylic tank was coated with a silicon sealer (Chemedine Bascoke) and dried for 2 days. Further, in the reaction vessel of FIG. 4 (a), the head space of the water tank containing tritium-containing water and the water tank containing the dilute nitric acid aqueous solution is shared by both tanks, and external air is sucked into the reaction system. The pressure applied to the electrode membrane partitioning both water tanks was considered to be equal. In manufacturing the electrode film of this example, lithium ion-containing manganese oxide having a spinel crystal structure was synthesized according to the method described in Example 1 above. In the production of the tritium absorbing electrode film in this example, 0.83 g of lithium ion-containing manganese oxide powder was formed on the surface (4 cm × 3 cm × 0.16 cm) of a stainless mesh (SUS304, 100 mesh, 6 cm × 3 cm × 0.16 cm). Was heated and fixed in the same manner using the conductive paint. Next, after uniformly applying a Nafion (registered trademark) dispersion (made by Wako Pure Chemical Industries, Ltd.) having a concentration of 20% on one surface of the electrode film, drying in the atmosphere at 60 ° C. for 2 hours was repeated twice. In addition, Nafion (registered trademark) was fixed to one surface of the electrode film as a hydrogen ion conductive film by heating in the atmosphere at 120 ° C. for 1 hour. The film thickness of the obtained electrode film was about 1.3 mm. In addition, in order to infiltrate the reaction surface of the electrode membrane with tritium-containing water and dilute nitric acid aqueous solution, the acrylic plate and the silicone rubber membrane waterproof seal constituting the unit, and the acrylic container have a circular hole (area of 4 mm in diameter). 12.6 mm ² ) are provided at five locations, so that the total area of the contact holes is 63.0 mm ² . Furthermore, 1 cm from the upper end of the electrode film to which the manganese oxide was fixed was disposed so as to protrude from the water surface of the tritium-containing water and contact the gas phase.

Next, the electrode film was acid-treated in a water tank in the reaction vessel shown in FIG. In this acid treatment, 200 mL of dilute nitric acid having a concentration of 0.5 M is filled in both water tanks in the reaction vessel, and left for 1 hour to dilute lithium from the lithium ion-containing manganese oxide contained in the electrode film. By eluting into nitric acid, the composition was changed to hydrogen ion-containing manganese oxide. Thereafter, the dilute nitric acid was removed from both the water tanks, and the dilute nitric acid was washed away from the inner surfaces of both the water tanks by leaving it to stand for 1 hour in a state where each of the water tanks was filled with 200 mL of distilled water.

When preparing tritium-containing water, dilute tritium standard reagent (PerkinElmer ³ H, water) with 200 mL of room-temperature distilled water (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain tritium-containing water with a radioactivity concentration of 4408.7 Bq / mL. Was formulated. Next, the tritium-containing water (200 mL) is placed in the right-side water tank in FIG. 4A, and a 0.5 M dilute nitric acid aqueous solution (200 mL) (manufactured by Wako Pure Chemical Industries, Ltd.) is placed in the left-side water tank. Arranged. The reaction surface covered with Nafion (registered trademark) of the electrode film is a surface in contact with dilute nitric acid, and the reaction surface of the electrode film in which the hydrogen ion-containing manganese oxide absorbent having a spinel crystal structure is exposed is a surface in contact with tritium-containing water. Arranged to be. In the experiment, the tritium-containing water and the dilute nitric acid aqueous solution filled in each of these two tanks, and the time-dependent change in the radioactivity concentration of tritium in distilled water (50 mL) arranged in advance in two gas washing bottles are shown in Example 1. The liquid scintillation counter was used in the same manner as in 2 and 3. During this experiment, the pH and temperature of tritium-containing water were monitored using a pH meter (HORIBA pH meter, F-55 glass electrode type 6378-10D) and pH test paper. The electrode film was grounded to the earth using a copper wire. In this experiment, as shown in FIG. 4 (a), the gas in the head space inside the reaction vessel was converted into a quartz glass tube (outer diameter 9 mm, inner diameter 6 mm) using a small pump (EP-01 manufactured by ADVANTEC). Into the gas cleaning bottle 1 (Walter type: total volume 100 mL), it was introduced into 50 mL of distilled water (manufactured by Wako Pure Chemical Industries, Ltd.) arranged in advance. Further, the exhaust from the gas cleaning bottle 1 was brought into contact with 0.1 g of copper oxide (CuO) (038-13191 manufactured by Wako Pure Chemical Industries, Ltd.) heated and held at 400 ° C. in a quartz glass tube. In order to maintain the temperature of the copper oxide at 400 ° C., the copper oxide powder is fixed in a quartz glass tube with glass wool (TOSO Grade: 2 to 6 μm, coarse 4 to 9 μm), and the outer wall of the glass tube is heated to a temperature. Heated with a heater (Osaka Denki Type CL, 100V, 60W) with a controller (ASONE TC-3000). Thereafter, the gas that passed through the CuO was introduced into 50 mL of distilled water (manufactured by Wako Pure Chemical Industries, Ltd.) arranged in advance in a subsequent gas cleaning bottle 2 (Walter type: total volume 100 mL). In addition, in order to reduce the pulsation of the gas by a pump, the buffer chamber was provided in piping of this experimental system.

In this example, the tritium-containing water at room temperature (15.7 to 21.6 ° C.) was stirred at a concentration of 0 while stirring the tritium-containing water with a stirrer coated with Teflon (registered trademark) and a magnetic stirrer. The experiment was continued until it was adjusted to an initial pH of 9.36 by adding an appropriate amount of 1 M or 0.5 M sodium hydroxide aqueous solution, and then decreased to pH 4 or less spontaneously. Next, an aqueous sodium hydroxide solution was added to the tritium-containing water again to increase the pH to 8.10, and then the experiment was continued until it naturally decreased to pH 5 or lower again. In order to investigate the change in radioactivity concentration in each aqueous solution in the reaction system, samples were collected from tritium-containing water, dilute nitric acid aqueous solution, and distilled water from

gas wash bottles

1 and 2 by 2.0 mL each. did. For the filtration and collection, a disposable filter (DISMIC GS-25AS020AN manufactured by ADVANTEC) and a disposable syringe (SS-02SZP manufactured by Terumo) were used. 1.0 mL of each sample collected by filtration was collected with a precision micropipette, and the radioactivity concentration of tritium in each sample was measured by the above-described method using a liquid scintillation counter.

The experimental results are shown in FIGS. 4 (b) and (c). First, FIG.4 (b) shows the time-dependent change of the tritium radioactivity density | concentration in tritium containing water. The vertical axis represents the tritium radioactivity concentration of the sample water, and the horizontal axis represents the reaction time. In this experiment, a sample (S1 in the figure) was taken when the pH of the tritium-containing water dropped to 3.8 after about 6 hours from the first pH adjustment for the tritium-containing water. After collecting the sample, an aqueous sodium hydroxide solution was added again to raise the pH to 8.1. At that time, tritium-containing water colored light brown by the same pH adjustment. This coloring is considered to be based on the manganese elution from the electrode film forming manganese hydroxide. Next, a sample (S2 in the figure) was taken when the pH dropped to 5.0 after 46.5 hours. Finally, a sample (S3 in the figure) was taken when the pH dropped to 4.68 after about 50 hours from the start of the experiment. From FIG. 4 (b), the tritium radioactivity concentration of the tritium-containing water shows a tendency to continuously decrease from the initial 4408.7 Bq / mL to about 6 hours and then to slightly increase until 46.5 hours. You can see that. Furthermore, when 50 hours passed and the pH decreased to 4.68, the radioactivity concentration of tritium decreased to 4044.0 Bq / mL. From the difference between the same concentration and the initial concentration, the amount of tritium contained in the tritium-containing water was reduced by about 71116.5 Bq after 50 hours. FIG. 4C shows the change in tritium radioactivity concentration in 50 mL of distilled water disposed in the gas cleaning bottle 1 in the previous stage. From the figure, it was found that approximately 15885 Bq of tritium was recovered in the same distilled water after 50 hours. This is about 5 times more recovered than 3235 Bq recovered after 74 hours in 50 mL of distilled water placed in a similar gas washing bottle after contact with the molecular sieve in Example 3. In addition, when 50 hours passed in this example, the distilled water in the gas cleaning bottle 1 almost maintained the volume obtained by subtracting the volume collected as a sample from the initial volume of 50 mL. Furthermore, the distilled water at the time when 50 hours passed in the gas cleaning bottle 1 was analyzed by atomic absorption method, and the concentrations of manganese (Mn), lithium (Li), and sodium (Na) contained in the distilled water were measured. As a result, it was confirmed that the Mn and Li concentrations were 0.01 mg / L below the detection limit, and the Na concentration was 0.48 mg / L. In this experiment, considering that the total amount of 0.1M NaOH added to the tritium-containing water up to the point of 50 hours is about 0.28 g, the tritium-containing water is temporarily distilled in the gas cleaning bottle 1. If it has just moved to water as a liquid, higher concentrations of Na and Mn should be detected in the distilled water. Therefore, this analysis result suggests that tritium has moved to the distilled water of the gas cleaning bottle 1 as HTO or HT gas. Moreover, the tritium moved into 200 mL of dilute nitric acid when 50 hours passed was about 5881.3 Bq. In addition, 839.5 Bq of tritium was recovered in 50 mL of distilled water disposed in the gas cleaning bottle 2 at the subsequent stage. Since these are less than the amount of tritium recovered in the distilled water of the preceding gas washing bottle 1 (15885 Bq), the tritium extracted from the tritium-containing water is mainly contained in the distilled water of the gas washing bottle 1. You can see that it was recovered.
As a result, the total amount of tritium confirmed to move to the distilled water and dilute nitric acid in the two gas washing bottles after 50 hours was 22605.8 Bq. On the other hand, since the total decrease amount of tritium calculated from the decrease value of the tritium concentration of the tritium-containing water shown in FIG. 4B is 71116.5 Bq, it is about 31.8% of the total decrease amount. Thus, 22605.8 Bq of tritium corresponding to the above could be recovered. About the remaining 68.2% of tritium, water droplets adhere to the inner wall surface of the reaction vessel during the experiment. Therefore, it is considered that these water droplets are not collected and reach the gas washing bottle 1. It is done.

An electrode film containing hydrogen ion-containing manganese oxide with one side coated with a Nafion (registered trademark) film was prepared in the same manner as in Examples 1, 2, 3, and 4. In this example, the reaction system shown in FIG. 5 was configured, and tritium-containing water was brought into contact with the electrode film coated with a Nafion (registered trademark) film on one side. Next, tritium is evaporated from the surface of the reaction vessel where the electrode film is in contact with the gas phase into the gas phase inside the reaction vessel, and a tube made of Teflon (registered trademark) is applied to ultrapure water disposed in a gas cleaning bottle by a pump. It was pumped through and collected. The reaction vessel and the pump were connected with a silicon tube.

In this experiment, as shown in FIG. 5, a transparent acrylic water tank was divided into two tanks by an electrode film containing lithium ion-containing manganese oxide powder coated with a Nafion (registered trademark) film on one side. In order to prevent water leakage, each seam of the acrylic tank was coated with a silicon sealer (Chemedine Bascoke) and dried for 2 days. In addition, in the reaction vessel of FIG. 5, the head space of the water tank in which tritium-containing water is arranged and the water tank in which dilute hydrochloric acid is arranged are shared by both tanks, and both water tanks are supplied when external air is supplied to the reaction system. Consideration was made so that the pressure applied to the electrode film partitioning was equal. In producing the electrode film of this example, lithium ion-containing manganese oxide powder having a spinel crystal structure was synthesized according to the method described in Example 1. In the production of the tritium absorbing electrode film in this example, lithium ion-containing manganese oxide powder 0 was applied to the surface (3.5 cm × 3 cm × 0.16 cm) of a platinum mesh (100 mesh, 5.5 cm × 3 cm × 0.16 cm). .92 g was heated and fixed in the same manner using the conductive paint. Next, after uniformly applying a Nafion (registered trademark) dispersion (made by Wako Pure Chemical Industries, Ltd.) having a concentration of 20% on one surface of the electrode film, drying in the atmosphere at 60 ° C. for 2 hours was repeated twice. In addition, Nafion (registered trademark) was fixed to one surface of the electrode film as a hydrogen ion conductive film by heating in the atmosphere at 120 ° C. for 1 hour. The film thickness of the obtained electrode film was about 1.3 mm. In addition, in order to infiltrate the reaction surface of the electrode membrane with tritium-containing water and dilute hydrochloric acid aqueous solution, the acrylic plate and the silicone rubber membrane waterproof seal constituting the electrode membrane unit, and the acrylic container have a circular hole ( The total contact area was 12.56 mm ² by providing four areas (area 3.14 mm ² ). Furthermore, 1.5 cm from the upper end of the electrode film to which the manganese oxide was fixed was disposed so as to protrude from the water surface of the tritium-containing water and to come into contact with the gas phase.

Next, the electrode film was acid-treated in the reaction vessel shown in FIG. In this acid treatment, 200 mL of dilute hydrochloric acid aqueous solution having a concentration of 0.5 M is filled in both water tanks of the reaction vessel, and left for 1 hour, so that lithium is contained from the lithium ion-containing manganese oxide contained in the electrode film. The composition was changed to manganese ion-containing manganese oxide. Then, the dilute hydrochloric acid aqueous solution was removed from both water tanks, and the dilute hydrochloric acid was washed off from the inner surfaces of both water tanks by leaving the both water tanks filled with 200 mL of ultrapure water for 1 hour.

In preparing the tritium-containing water, a tritium standard reagent (PerkinElmer ³ H, water) was diluted with 150 mL of ultrapure water at room temperature to prepare tritium-containing water having a radioactivity concentration of 4054.2 Bq / mL. Next, 150 mL of the tritium-containing water was placed in the right-side water tank in FIG. 5, and 150 mL of a dilute hydrochloric acid aqueous solution having a concentration of 0.5 M (manufactured by Wako Pure Chemical Industries, Ltd.) was placed in the left-side water tank. The reaction surface of the electrode film coated with Nafion (registered trademark) is the surface in contact with dilute hydrochloric acid, and the reaction surface of the electrode film with exposed hydrogen ion-containing manganese oxide absorbent having a spinel crystal structure is the surface in contact with tritium-containing water. Arranged. In the experiment, tritium-containing water and dilute hydrochloric acid aqueous solution filled in each of these two tanks, and time-dependent changes in the radioactivity concentration of tritium in 50 mL of ultrapure water previously arranged in a gas washing bottle were measured in Examples 1, 2, 3, and In the same manner as in No. 4, a liquid scintillation counter was used. During this experiment, the pH and temperature of tritium-containing water were monitored using a pH meter (HORIBA pH meter, F-55 glass electrode type 6378-10D) and pH test paper. The electrode film was grounded to the earth using a copper wire. In this experiment, as shown in FIG. 5, the gas in the head space inside the reaction vessel was pumped using a small pump (EP-01 manufactured by ADVANTEC), and a Teflon (registered trademark) tube (outer diameter 3 mm, inner diameter 2 mm). And introduced into 50 mL of ultrapure water (manufactured by Wako Pure Chemical Industries, Ltd.) arranged in advance in a gas washing bottle (Walter type: total volume 100 mL).

In this example, tritium-containing water at room temperature (24.0 to 28.2 ° C.) was stirred at a concentration of 0 while stirring the tritium-containing water with a stirrer coated with Teflon (registered trademark) and a magnetic stirrer. After adjusting to an initial pH of 9.26 by adding an appropriate amount of 1 M or 0.5 M sodium hydroxide aqueous solution, the experiment was continued until it naturally decreased to pH 2.7 or lower. Next, an aqueous sodium hydroxide solution was added again to the tritium-containing water to raise the pH to 7, and then the experiment was continued until it naturally decreased to pH 2.7 or lower again. The experiment was continued for 89 hours while such readjustment of pH with respect to tritium-containing water was repeated 5 times. In order to examine changes in the radioactivity concentration in each aqueous solution in the reaction system, 2.0 mL of each sample was collected by filtration from tritium-containing water, dilute hydrochloric acid aqueous solution, and ultrapure water in a gas washing bottle. The timing of collecting each sample was the time when the pH of the tritium-containing water dropped to 2.7 or lower. For the filtration and collection, a disposable filter (DISMIC GS-25AS020AN manufactured by ADVANTEC) and a disposable syringe (SS-02SZP manufactured by Terumo) were used. 1.0 mL of each sample collected by filtration was collected with a precision micropipette, and the radioactivity concentration of tritium in each sample was measured by the above-described method using a liquid scintillation counter. In addition, in order to confirm the detection lower limit value of the tritium radioactivity concentration by the liquid scintillation counter used in this example, the tritium concentration in the sample of the ultrapure water and 0.5M dilute hydrochloric acid aqueous solution used in this example is the same. The measurement results were 1.72 Bq / mL and 1.43 Bq / mL, respectively.

The experimental results are shown in FIGS. 6 (a), (b), (c), and (d). All data plotted in each figure has been corrected to account for the amount of tritium that decreases with sampling. In addition, when 89 hours passed in this example, the ultrapure water in the gas cleaning bottle almost maintained the capacity obtained by subtracting the capacity collected as a sample from the initial capacity of 50 mL. First, FIG. 6 (a) shows the change with time of tritium radioactivity concentration in tritium-containing water. The vertical axis represents the tritium radioactivity concentration of the sample water, and the horizontal axis represents the reaction time. From the result of FIG. 6 (a), the tritium concentration of the tritium-containing water decreased by 858.67Bq / mL from the initial value of 4054.2Bq / mL to 3195.53Bq / mL after 89 hours. It was found that the tritium concentration corresponding to 21.2% decreased. In this experiment, the pH adjustment of tritium-containing water was repeated as described above. However, every time the pH was adjusted to neutral by the addition of an aqueous sodium hydroxide solution, the tritium-containing water colored light brown. The sediment sludge accumulated. This coloring and sludge generation are thought to be caused by the manganese elution from the electrode film forming manganese hydroxide and being oxidized by oxygen in the air supplied to the reaction system to produce manganese oxide. . FIG.6 (b) shows the change of the tritium radioactivity density | concentration in the ultrapure water of a gas washing bottle, and dilute hydrochloric acid. FIG. 6C shows the mass balance regarding the amount of tritium removed from the tritium-containing water, the total amount of tritium accumulated in the ultrapure water and dilute hydrochloric acid in the gas washing bottle, and the amount of tritium accumulated in the dilute hydrochloric acid. The change with time is shown. From the result of FIG. 6C, it can be seen that 45.2% of the tritium removed from the tritium-containing water is transferred to the ultrapure water and the diluted hydrochloric acid in the gas washing bottle. Moreover, it shows that 86% which is the majority of the total amount of tritium accumulated in the ultrapure water in the gas cleaning bottle and the diluted hydrochloric acid is recovered in the ultrapure water in the gas cleaning bottle. FIG. 6 (d) shows the change with time of the amount of tritium collected per unit time collected in the ultrapure water of the gas washing bottle with respect to the pH change of the tritium-containing water. FIG. 6 (d) shows that the recovery rate is significantly improved when the pH of the tritium-containing water is 3 or less. Compared with the results of Example 4 above, in the results of FIG. 4 (b), when the sample was taken from the tritium-containing water, the pH was not lower than 3 and therefore the time when tritium absorption and transpiration occurred simultaneously was long. It is considered that the tritium concentration did not decrease uniformly as shown in FIG. Therefore, it is considered that a uniform reduction in the tritium concentration shown in FIG. 6A can be obtained by collecting the sample after the pH of the tritium-containing water is lowered to 3 or less. Further, it has been reported that this tritium absorbent does not absorb tritium in acidic water having a pH of 3 or less. Hideki Koyanaka and Hideo Miyatake, Extracting Tritium from Water Using a Protonic Manganese Oxide Spinel ", Separation Science and Technology, 50, 14, 2142-2146, (2015). It can be said that tritium is absorbed in the aqueous solution of ˜7) and tritium is released in the acidic aqueous solution, which is an experimental result supporting the reactions of the chemical formulas (2) and (3).

In Example 5 described above, after the tritium-containing water was lowered to pH 3 or lower, the pH was readjusted to pH 7 again by the addition of an aqueous sodium hydroxide solution, whereby the reuse of the tritium absorbent was repeated. However, during the readjustment of the same pH in Example 5, sludge based on manganese elution was generated. In order to solve this problem, an aqueous lithium hydroxide solution was added in place of the aqueous sodium hydroxide solution in Example 5 as a reagent used for readjustment of the same pH. The reaction vessel and the electrode film were the same as in Example 5, and the experiment was performed in the same procedure. Specifically, the addition amount of the lithium hydroxide aqueous solution to the tritium-containing water is such that 0.1 g of 1M LiOH.H ₂ O is added to about 150 mL of tritium-containing water, and the pH of the tritium-containing water is increased. Was adjusted to 8.0 to 8.5. As an effect of this, in Example 5, the amount of sludge generated per readjustment of pH could be reduced to 0.016 g, which is about 1/20 or less of the dry weight. Moreover, coloring of tritium-containing water due to elution of manganese ions could be suppressed.
The preferable effects as described above are that the addition of the lithium hydroxide aqueous solution to the tritium-containing water raises the pH of the tritium-containing water from acidic to neutral or more, and the unstable manganese oxide after the release of tritium. This is presumably based on the effect of lithium ions entering the crystal structure and stabilizing the crystal structure. A similar effect was confirmed when lithium chloride (LiCl) was added to tritium-containing water and the pH was readjusted with an aqueous sodium hydroxide solution. Therefore, if the lithium reagent to be added is water-soluble, the dissolution of manganese and the presence of anions in the lithium-containing complex, such as hydroxides and chlorides, compared to when lithium ions are not added, Generation of sludge can be suppressed.
An appropriate amount of lithium added to the tritium-containing water is preferably about 1 to 30 mg per 1 g of the manganese oxide powder having the spinel crystal structure. The lithium concentration is preferably in the range of about 1 to 50 mg / L. This is because the addition of a large amount or high concentration of lithium ions exceeding the appropriate amount promotes dissolution of the manganese oxide. Therefore, the addition of the above lithium ion that achieves an appropriate amount and an appropriate concentration for the tritium-containing water of the present invention suppresses the generation of sludge when the present technology is put to practical use, and extends the life of the tritium absorbent. This is a useful finding.

Moreover, as a technique for recovering tritium once evaporated from the liquid phase of tritium-containing water into the gas phase as HTO or HT due to the effect of the tritium absorbing electrode film, a small amount is used by using a pump as shown in this example. However, the present invention is not limited to the method of recovering in water, and existing substances such as porous bodies having a high absorption capacity for normal hydrogen and water can be used in place of distilled water and ultrapure water in this embodiment.

As described above, by applying the tritium-absorbing electrode film of the present invention to tritium-containing water, tritium dissolved in water at a nanogram / L order and an extremely low mass concentration that could not be achieved by conventional techniques, It was possible to separate and recover from water easily and inexpensively at room temperature.

<Example 6>
<Experiment to collect tritium in gel and electrolyte from electrode film collecting tritium>
Using the experimental system shown in FIG. 7, an attempt was made to recover tritium in water containing a gel and an electrolyte from an electrode film that collected tritium.

The tritium recovery method of the present invention will be described with reference to FIG. In preparing the conductive gel in the figure, first, 10 g of lithium chloride powder (Wako Pure Chemical Industries, special grade reagent 127-01165, 99% or more) and reagent agar powder (special grade of Wako Pure Chemical Industries, Ltd.) are placed in a glass beaker. 018-15811) 1.7 g was added to distilled water (50 mL) and heated with a heater to dissolve the agar powder. Next, the aqueous solution of agar containing lithium ions obtained by heating is poured into a stainless steel (SUS304) mold (inner diameter 30 mm, height 20 mm, thickness 0.7 mm) and left at room temperature. By solidifying, a conductive gel containing lithium ions that were solidified in close contact with the stainless steel mold was created.

The tritium-containing manganese oxide containing tritium was inserted into the conductive gel containing lithium ions by 15 mm of the electrode film in which tritium was collected in 10 minutes in the tritium collection experiment of Example 1 in 10 minutes. Placed in contact with. Next, the copper wire connected to the stainless steel mold part in the electrode film inserted into the gel in the stainless steel mold was connected to a constant voltage power source, and the electrode film was used as a positive electrode. Further, a copper wire connected to a carbon rod (diameter 5 mm, length 5 cm) was connected to a constant voltage power source to make the carbon rod a negative electrode. These positive electrode and negative electrode were placed in a glass beaker, and placed in 120 ml of distilled water to which 0.5 ml of 1M lithium hydroxide aqueous solution was added as an electrolyte to add conductivity. Next, while stirring 120 mL of distilled water to which the electrolyte has been added with a Teflon (registered trademark) stirrer and a magnetic stirrer, a voltage of 4 to 5 V is applied to the positive and negative electrodes for 10 minutes using a constant voltage power source. did. When 10 minutes had elapsed after the voltage application, 1.2 mL of a sample of distilled water with the same conductivity was collected by filtration. Further, the gel was sealed in a stainless steel can, and the stainless steel can was heated to liquefy the gel from which tritium was eluted, and a sample was collected. For sample collection, DISVIC GS-25AS020AN made by ADVANTEC and disposable syringe SS-02SZP made by Terumo were used. 1.0 mL was collected from the collected sample with a precision micropipette, and the radioactivity concentration of tritium in 1.0 mL of the sample was measured by the above-described method using a liquid scintillation counter.

As a result of this experiment, the tritium concentration in 120 mL of distilled water added with conductivity by the addition of the electrolyte was measured to be 6.86 Bq / mL. This value was converted to the radioactivity of tritium eluted in 120 ml of distilled water to which the same conductivity was added, to obtain 823.2 Bq. The tritium absorbed from the tritium-containing water by the electrode used for the tritium recovery experiment in this example was 2353.0 Bq. Therefore, according to the tritium recovery method of the present invention, about 35% of the absorbed tritium is recovered in distilled water to which an electrolyte is added according to the calculation formula: (823.2 / 2353.0) × 100 = 34.99. The result was obtained.

<Comparison experiment: Tritium recovery experiment without using a gel containing lithium ions>
The tritium recovery experiment was performed using the above-mentioned gel by carrying out the tritium recovery experiment without using the gel containing lithium ions solidified in the stainless steel mold shown in FIG. Compared with the effect. In the experiment, the electrode film containing tritium was directly connected to a constant voltage power source using a copper wire without going through the gel in FIG. The same electrode was used as the positive electrode, and a voltage of 4 to 5 V was applied between the negative electrode and the carbon rod of the negative electrode for 10 minutes as in the case of using gel. As a result, 1.2% of the total amount of tritium contained in the electrode film was recovered in the distilled water. Therefore, it was found that by using a gel containing lithium ions according to the technique of the present invention, a recovery rate of tritium that is 30 times higher than that in the case of not using it can be obtained.

The valence of manganese constituting the hydrogen ion-containing manganese oxide having the spinel type crystal structure which is the present tritium absorbent was analyzed by X-ray absorption spectroscopy (XANES). For this analysis, an Rigaku X-ray absorption spectrometer (R-XAS LOOPER) was used. As a sample for the same analysis, 1 g of the lithium ion-containing manganese oxide was suspended in 100 mL of dilute hydrochloric acid having a concentration of 0.5 M, and stirred for 24 hours with a stirrer coated with Teflon (registered trademark) and a magnetic stirrer. Thus, in accordance with the chemical formula (1), a hydrogen ion-containing manganese oxide in which lithium ions were replaced with hydrogen ions was obtained. Two types of samples were prepared by suspending the hydrogen ion-containing manganese oxide in 100 mL of distilled water adjusted to pH 3 and pH 6 and stirring for 2 days while maintaining each pH. For the pH adjustment, a concentration of 0.1M sodium hydroxide and 0.1M dilute hydrochloric acid were used. Further, a manganese metal powder, a manganese valence powder, a Mn ₂ O ₃ powder, a LiMn ₂ O ₄ powder, and a MnO ₂ powder having a known valence of manganese were prepared. These were obtained from Wako Pure Chemical Industries as commercially available reagents, and were similarly measured as reference samples corresponding to manganese valences of 0, 3, 3, and 4, respectively.

FIG. 8A shows the measurement result of each sample. As is clear from the figure, regarding the hydrogen ion-containing manganese oxide functioning as the present tritium absorbent, both the sample held in the pH 3 aqueous solution and the sample held in the pH 6 aqueous solution were measured as a reference. The absorption edge shape was almost the same as that of manganese (MnO ₂ ). From the results, it has been clarified that the valence of most manganese contained in the hydrogen ion-containing manganese oxide is plus 4.
Moreover, in FIG.8 (b), the X-ray-diffraction (XRD) pattern of this hydrogen ion containing manganese oxide and the lithium ion containing manganese oxide before acid treatment was shown. Both measurement results showed diffraction patterns peculiar to the crystal structure of spinel manganese oxide. In the figure, the diffraction pattern of hydrogen ion-containing manganese oxide shown in the upper part is slightly shifted to the higher angle side than the diffraction pattern of lithium ion-containing manganese oxide shown in the lower part. This is a result consistent with many research reports on manganese oxide having a conventional spinel crystal structure. Since the size of hydrogen ions is smaller than the size of lithium ions, The effect is slightly contracted. For example, J. C. Hunter, Preparation of a new crystal structure of manganese dioxide: lambda-MnO ₂ ", Journal of Solid State Chemistry, 39, 142-147, (1981). When heated for about 24 hours to evaporate hydrogen ions from the spinel crystal structure into the atmosphere, the manganese oxide becomes lambda-type manganese dioxide, but the manganese dioxide is ion-exchangeable. Since the hydrogen ions are lost from the crystal, the hydrogen ion-containing manganese oxide of the present invention does not exhibit any absorbability for lithium ions or tritium ions, for example, Hideki Koyanaka and Hideo Miyatake, Extracting Tritium from Water. Using a Protonic Manganese Oxide Spinel ", Separation Science and Technology, 50, 14, 2142-2146, (2015), and H. Koyanaka, O. Matsubaya, Y. Koyanaka, and N. Hatta, Quantitative correlat ion between Li absorption and H content in Manganese Oxide Spinel λ-MnO ₂ ", Journal of Electroanalytical Chemistry, 559, 77-81 (2003). When lithium ion-containing manganese oxide obtained by firing at a low temperature is subjected to acid treatment, a theoretical composition ratio in which most lithium ions in the crystal are replaced with hydrogen ions: H _x Mn ₂ O ₄ (x = 1 Therefore, it is also described that a manganese ion containing near hydrogen ions can be obtained, so that the valence of manganese constituting the present tritium absorbent containing a large amount of hydrogen ions in the spinel crystal structure is not a plus 3.5 valence, Is positive tetravalent because the composition formula is described as H _x Mn ₂ O ₄ , minus eight valence by four oxygen ions is changed to plus one valence by one hydrogen ion and two manganese ions Charge neutrality is not established when compensation is made with plus 8 valences. Therefore, it is reasonable to describe the composition of the hydrogen ion-containing manganese oxide constituting the present tritium absorbent as (H ⁺ , e ⁻ ) Mn ₂ O _{4 in} which charge neutrality is established. As a report example supporting the same composition, hydrogen ions (H ⁺ ) are bonded to a special oxygen atom pair constituting the crystal by a weak covalent bond (which can be said to be a strong hydrogen bond) inside the crystal of spinel manganese oxide. It is pointed out in the following literature that hydrogen ion conductivity is exhibited according to the concentration gradient of hydrogen ions inside. H. Koyanaka, Y. Ueda, K. Takeuchi, AI Kolesnikov, Effect of crystal structure of manganese dioxide on response for electrolyte of a hydrogen sensor operative at room temperature ", Sens. Act. B 2013, 183, 641-647. Since the tritium ion (T ⁺ ) trapped in the spinel crystal by such a weak covalent bond can be easily removed from the binding by oxygen in the same crystal as the hydrogen ion (H ⁺ ), the tritium of the present invention. In accordance with the chemical formulas (2) to (4), the absorber converts tritium (OT ⁻ ) in water to an isotope isomer (HTO) of water, and the HTO gas is converted from the solid phase to the gas phase of the absorber. It is thought that it is possible to evaporate as.

Claims

A method for recovering tritium, comprising recovering a gas (HTO or HT) containing tritium that evaporates from an absorbent containing tritium.
2. The method for collecting tritium according to claim 1, wherein the pH of the tritium-containing water is 3 or less in order to promote the transpiration of the gas containing tritium.
3. The method for recovering tritium according to claim 1 or 2, wherein a part of the electrode film on which the absorbent material is fixed is exposed to the gas phase in order to promote the transpiration of the gas containing tritium. .
2. The recovery method according to claim 1, wherein the oxidizing agent for converting hydrogen (HT) containing tritium generated from the absorbent containing tritium into water (HTO) by contacting with the oxidizing agent is oxygen (O). Alternatively, a method for recovering tritium, which is copper (II) oxide (CuO) heated to 250 ° C. to 500 ° C.
2. The method for collecting tritium according to claim 1, wherein the tritium-containing absorbing material is accelerated by irradiating the absorbing material containing tritium with ultraviolet light.
The tritium containing the tritium is collected in the conductive gel and the aqueous solution by bringing the absorbent into contact with the conductive gel and the aqueous electrolyte solution and applying a voltage. Recovery method.
The method for recovering tritium according to claim 7, wherein the conductive gel is a gel containing lithium ions.
The method for recovering tritium according to any one of claims 1 to 6, wherein the absorbent is manganese oxide having a spinel crystal structure.
9. The absorbent according to claim 1, wherein the absorbent is manganese oxide characterized by converting tritium hydroxide (OT − ) into tritium-containing water (HTO) or hydrogen (HT). A method for recovering tritium from an absorbent containing tritium according to any one of the above.
10. The tritium according to claim 1, wherein the absorbent contains hydrogen ions (H + ), and manganese has a valence of manganese of +4. To recover tritium from absorbent material.
A method for reusing a tritium absorbent, wherein the absorbent obtained by collecting tritium by the method according to any one of claims 1 to 10 is reused as a tritium absorbent.
After collecting tritium from an absorbent that is manganese oxide having a spinel crystal structure, lithium ions (Li + ) are added to the aqueous solution to be contacted when reused as the tritium absorbent, and the dissolution of manganese is suppressed. To recycle tritium absorbent.