JP2016133501A - Radioactive ruthenium removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a removal method for radioactive ruthenium, which is difficult to remove because it has a complex chemical form in aqueous solution.SOLUTION: Contaminated water containing radioactive ruthenium is controlled in salt concentration from sodium chloride and solution temperature and then is brought into contact with an exchanger and/or a chelate exchanger.SELECTED DRAWING: None

Description

Detailed Description of the Invention

  The present invention relates to a method for removing radioactive ruthenium leaked due to an accident at the Fukushima Daiichi nuclear power plant.

  In the accident at the Fukushima Daiichi Nuclear Power Station following the Great East Japan Earthquake on March 11, 2011, various radioactive materials such as radioactive iodine and radioactive cesium were released into the environment from the nuclear reactor. Among these, radioactive cesium is an excellent adsorbent material on which a ferrocyanate metal salt insolubilized material is supported, and is often used. For example, cobalt ferrocyanide and nickel ferrocyanide can selectively remove cesium in seawater and fresh water. Iodine was released in large quantities from the nuclear power plant into the atmosphere at the time of the accident, but since the half-life is as short as 8 days, it is not a big problem now that more than 3 years have passed.

  However, the radioactive ruthenium produced by the decay of nuclear fuel has a continuous release as the fuel breaks, so it must be removed reliably. For removal of radioactive ruthenium, conventional techniques such as coagulation sedimentation, ion exchange, chelate resin, special adsorbent, zeolite, and removal techniques developed for radioactive cesium, radioactive strontium and radioactive iodine are adopted. ing.

  The current equipment is a big problem because radioactive ruthenium cannot be removed sufficiently. In particular, ruthenium has a valence of 0 to 8 and is said to exist in a cation, anion, non-ionic state, etc. in an aqueous solution, depending on the pH, and further in an adsorbed state on colloids and particles. Sometimes it is difficult to remove. In connection with the complicated chemical form of ruthenium in aqueous solution, there are few methods that can adsorb and remove radioactive ruthenium with a sufficiently high removal rate even with various conventional removal techniques (Patent Documents 1 and 2). .

  A method of removing a platinum group such as ruthenium by a solvent extraction method or a method of impregnating a substrate for separation with an extraction reagent has been proposed (Patent Document 3). However, it is difficult to connect the solvent extraction method to a series of removal equipment. Moreover, even if the separation base material is impregnated, there is a problem of leakage. Solvent extraction technology can be used for the treatment of controlled effluents that accompany nuclear fuel reprocessing, etc., but is not suitable for the treatment of radioactive effluents released into the environment.

  The inventors have been engaged in radiation graft polymerization for many years, and for ruthenium adsorbents, an adsorbent material in which an extraction reagent (Patent Document 4) or a low-molecular polyamine compound typified by a nucleobase (Patent Document 5) is introduced into a fiber substrate is used. Proposed.

  However, there is a method of manufacturing an adsorbing material using a large amount of expensive chemicals, but the removal rate and the adsorption capacity may be unstable, which is not always satisfactory and satisfactory. Therefore, even if these adsorbents are used, more stable treatment is desired.

  Patent Document 6 proposes a method of removing radioactive substances such as iodic acid by adding an oxidizing agent, a reducing agent and a pH adjuster to the liquid to be treated, but it does not mention removal of radioactive ruthenium, Even with the proposed method, effective removal of radioactive ruthenium is difficult.

  Therefore, it is desired to optimize the adjustment conditions of the liquid to be treated that can stably exhibit the removal performance even in the existing adsorbent material that has been considered to be able to selectively remove ruthenium, and also in the new material.

JP 61-45998 JP-A-6-265695 JP2012-25994 Japanese Patent Application No. 2014-216670 Japanese Patent Application No. 2014-216669 JP2013-170959A

  Using various existing radioactive ruthenium adsorbents, especially adsorption fibers for removing radioactive ruthenium manufactured using radiation graft polymerization method, optimize the physicochemical conditions of the liquid to be treated to obtain stable radioactive ruthenium removal performance It is an object of the present invention to make it.

  Inventors made various adsorbents as prototypes and evaluated the removal performance against ruthenium, paying attention to the fact that the removal performance is greatly improved when the liquid to be treated is set to a specific condition. Reached.

  The present invention is a method for physicochemical adjustment of a liquid to be treated for removing radioactive ruthenium having the following characteristics. Then, an adsorbent effective for treating the liquid to be treated is proposed.

(1) A method for removing radioactive ruthenium in which contaminated water containing radioactive ruthenium is heated in the presence of chloride ions and / or heated and then brought into contact with the ion exchanger and / or chelate exchanger.

(2) The method for removing radioactive ruthenium according to (1), wherein the contaminated water is heated from 35 ° C. to 70 ° C.

(3) The chloride ion concentration is 1000 mg / L or more, and when it is 1000 mg / L or less, chloride is added so as to be 1000 mg / L or more. (1) or (2) Removal of radioactive ruthenium

(4) The ion exchanger and / or chelate exchanger comprises an anion exchanger having a quaternary ammonium group, a tertiary or lower weakly basic anion exchanger, a tertiary or lower amino group and / or a quaternary ammonium group. (1) The method for removing radioactive ruthenium according to (2) and / or (3), which is an adsorbent having a functional group selected from a polyamine compound-introduced product having a plurality and a C-containing trialkylamine-introduced product

(5) The ion exchanger and / or chelate exchanger are those in which a functional group is introduced into a fiber base material by a radiation graft polymerization method (1), (2), (3) or (4) Removal of radioactive ruthenium

(6) The fiber base material is selected from the group consisting of single fibers, hollow fibers, composite fibers, twisted yarns that are aggregates of fibers, woven fabrics or nonwoven fabrics, and processed products thereof. Removal method

  While searching for a radioactive ruthenium removal material, the present inventors prepared synthetic raw water with varying salt concentrations, such as sodium chloride, and conducted ruthenium removal experiments at various temperatures. It has been discovered that the removal rate is increased by increasing the concentration, and the removal performance is further improved by increasing the temperature of the raw water, and the present invention has been achieved.

As the chloride ion concentration increases, complex ionization of ruthenium to RuCl ₄ ^— or the like is promoted, and it is easy to remove with an anion exchanger. Here, when the liquid is further heated, the removal performance is improved. The reason for this is not clear, but there is an idea that a multinuclear complex of ruthenium is formed.

  When the chloride ion concentration is 1000 mg / L or more, and the temperature is 35 ° C. or more, improvement in ruthenium removal performance is observed.

  Under such physicochemical conditions, ruthenium, which was difficult to remove under normal conditions, can be easily removed with an ion exchanger or a chelate exchanger.

  Here, as an ion exchanger and a chelate exchanger, there are an anion exchanger having a quaternary ammonium group, a tertiary or lower weak base anion exchanger, and an ordinary strong base anion exchange resin or weak base anion exchange. Resin can be used. Further, an adsorbent material introduced with a polyamine compound having a plurality of tertiary or lower amino groups or quaternary ammonium groups, or an adsorbent material having a functional group selected from a trialkylamine introduction product having 2 or more C atoms is preferably used. it can.

  As ion exchangers and chelate exchangers, commercially available bead-shaped ion exchange resins and chelate resins can be used. However, since the method of use is limited to a packed tower type, a fiber that can cope with various polluted environments is preferable. . As a method for producing such a material, a radiation graft polymerization method is optimal.

  In the radiation graft polymerization method, a fiber base material selected from single fibers, hollow fibers, composite fibers, twisted yarns that are aggregates of fibers, woven or non-woven fabrics, and processed products thereof can be used freely. As in the Fukushima Daiichi NPS power plant, it is particularly preferable to use fiber filters with many options for use, such as wind filters, braids, and cut fibers, when contaminated water is placed in various environments. .

  Ruthenium in aqueous solution is very complex in chemical form such as ionic or nonionic such as cation or anion, complex ion, colloidal deposits or adsorbed on particles, but for radioactive ruthenium adsorbents By the prepared stock solution preparation method of the present invention, the chemical form of ruthenium is changed to a form that can be easily removed, so that the removal is possible. By adopting the radiation graft polymerization method, fibers that can be easily molded can be used as a base material, and various forms of radioactive ruthenium can be removed from liquids at various contaminated sites. It became easier.

Ruthenium salt mold Synthetic pathway of radioactive ruthenium removal material with nucleobase Wind filter

  When the concentration of the salt in which ruthenium coexists increases, particularly when the concentration of chloride ion increases, the complex ionization of ruthenium proceeds as shown in FIG. Therefore, what is necessary is just to add the inorganic salt represented by sodium chloride so that it may become such a salt type. As the concentration to be added, the chloride ion concentration is preferably 1000 mg / L or more, more preferably 2000 mg / L or more.

  As the ruthenium is heated, the removal rate becomes higher. For example, when the temperature of the liquid is 40 ° C. or higher, the ruthenium removal rate increases. It is said that when the chloride ion concentration is high and heated, it becomes a binuclear complex and the removal performance is improved.

  The functional group of the adsorbent capable of removing ruthenium is preferably an ion exchange group or a chelate group. Examples of the ion exchange group include an anion exchanger having a quaternary ammonium group and a tertiary or lower weak base anion exchanger, and a normal strong base anion exchange resin and a weak base anion exchange resin can be used. Adsorption having a functional group selected from a low-molecular-weight polyamine compound-introducing adsorbent material in which a polyamine compound having a tertiary or lower amino group or a plurality of quaternary ammonium groups is introduced or a trialkylamine-introducing material having 2 or more C atoms A material can be suitably used. Polyethyleneimine introduced products can also be used.

  The low molecular weight polyamine compound can be selected from compounds having a plurality of amines such as nucleobase selected from adenine, guanine, and cytosine, or hexamethylenetetramine, triethylenediamine, and diazabicycloundecene. Among the nucleobases, adenine and guanine can be preferably used.

As a trialkylamine that can be used as a trialkylamine introduction product having a C number of 2 or more, a radioactive ruthenium removing material in which at least an amine compound represented by the following general formula is introduced into the graft side chain of the polymer substrate is suitable.
(R1, R2, and R3 are all hydrocarbons having 2 or more carbon atoms, and are composed of chain or alicyclic hydrocarbons)

  The alkylamine is a tertiary amine composed of a trialkylamine, wherein each alkyl group of R1, R2, and R3 has 2 or more carbon atoms, and is introduced into the graft side chain by a quaternary ammoniumation reaction. Typically, a tri-n-octylamine introduction product and the like are preferable.

  As ion exchangers and chelate exchangers, commercially available bead-shaped ion exchange resins and chelate resins can be used. However, since the method of use is limited to a packed tower type, a fiber that can cope with various polluted environments is preferable. . As a method for producing such a material, a radiation graft polymerization method is optimal.

  The radiation graft polymerization method is a method of irradiating a substrate with ionizing radiation such as γ-rays or electron beams and utilizing a radical generated on the surface of the substrate or inside the substrate (hereinafter referred to as “monomer”). Is a method of growing a graft chain from a substrate. Although the length of the graft side chain depends on the graft ratio, it usually ranges from several to several hundreds of ethylene units.

  Depending on the energy of the radiation, radicals are generated not only on the fiber surface but also inside. Therefore, the graft chain grows both on the fiber surface and inside the fiber. Since this graft chain is not fixed at one end, it has high mobility. Therefore, when a functional group such as an ion exchange group or a chelate group is introduced, the adsorbed ions easily enter between the graft chains and are captured.

Graft chains introduced with highly hydrophilic quaternary ammonium groups are repelled by the same kind of charges, and a space where anions easily enter between the graft chains is formed. In radioactive ruthenium, a complex anion such as RuCl ₄ ^— is adsorbed and held by a quaternary ammonium group into which a low-molecular polyamine compound, tri-n-alkylamine is introduced. The synthesis route of the low-molecular polyamine compound-introduced fiber used in the present invention is shown in FIG. In FIG. 2, adenine and guanine are used as nucleobases.

  As the ionizing radiation used in the radiation graft polymerization method, alpha rays, beta rays, gamma rays, electron rays, ultraviolet rays, and the like can be used. Industrially available gamma rays and electron rays are suitable for the present invention.

  There are a pre-irradiation graft polymerization method and a simultaneous irradiation graft polymerization method depending on the timing at which the substrate is irradiated with radiation. The former performs graft polymerization by irradiating a substrate with radiation and then contacting with a monomer. The latter is a method of performing radiation irradiation in the state where a substrate and a monomer exist at the same time, and any method can be adopted.

  In addition, a liquid phase graft polymerization method in which the graft polymerization is performed in a monomer liquid, a gas phase graft polymerization method in which the monomer is vaporized, an impregnation gas phase grafting in which an amount of the monomer to be grafted is added and then reacted in an inert gas. Any graft polymerization method such as a polymerization method can be used.

  Examples of the base fiber of the radioactive material adsorbent used in the present invention include synthetic fibers, cellulosic fibers such as cotton, animal fibers, mineral fibers, regenerated fibers, or mixed fibers thereof. Synthetic fibers include polyester, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, fluorine, and the like. Cellulose fibers include natural cellulose fibers such as cotton and hemp, viscose rayon, copper ammonia rayon, regenerated cellulose fibers such as polynosic, purified cellulose fibers such as tencel, and semisynthetic fibers such as acetate and diacetate. It is. Animal fibers include animal hair fibers such as wool, silk and the like. The recycled fiber includes chitin / chitosan fiber, collagen fiber and the like. It is also possible to use blends of these fiber materials.

  When manufacturing by the radiation graft polymerization method, since the fiber is selected as the base material shape, it can be molded into various shapes according to the contaminated environment. For example, at the contaminated site of the Fukushima Daiichi Nuclear Power Station, the installation space is small and the amount of radioactive waste generated is small (or volume can be reduced) due to the increase in storage locations for contaminated water tanks and radioactive waste. A radionuclide removal method that is easy and has low exposure to workers is suitable.

  As examples of the molding process, it can be molded into various filters such as a wind filter (FIG. 3) in which twisted yarn is wound around a perforated core, and a pleated filter in which a nonwoven fabric is folded into a pleated shape and wound around a perforated core. Since these can be used by being housed in an existing filter housing as a filter, a filtration function can also be imparted in the same manner as a normal particulate filtration filter. Because it is compact and easy to handle, it is safer to dispose of the entire housing from the viewpoint of containment of trapped radioactive material. Of course, only the filter body may be replaced depending on the degree of contamination.

  Moreover, the adsorption method which processes to a cut fiber and circulates a powder fiber as a slurry is also possible. Further, it can be used in an adsorption tower system in which a fixed bed is formed by filling an adsorption tower containing a conventional adsorbent. The mall shape is composed of braids and can be used to moor in the flow of contaminated water. To be effective in harbors and lakes

<Manufacture of adsorbents>
(1) Production of adenine-introduced fiber

1 kg of twisted yarn of 6-nylon fiber having a diameter of about 40 μm was put in a polyethylene bag, and the nitrogen substitution operation of evacuation and introduction of nitrogen gas was repeated three times. This bag was put in a foamed polystyrene box together with 5 kg of dry ice and irradiated with gamma rays of 50 kGy under cooling. The irradiated nylon fiber was taken out and placed in a glass ampoule for graft polymerization. It was immersed in a 10% methanol solution of glycidyl methacrylate previously deoxygenated by bubbling with nitrogen gas, and graft polymerization was carried out at 40 ° C. for 8 hours to obtain a graft rate of 136%. This fiber was immersed in a solution of adenine / isopropyl alcohol / water = 10/40/50, pH 13 and reacted at 80 ° C. for 8 hours. The amount of adenine introduced calculated from the weight increase rate was 1.6 mmol / g.
(2) Guanine-introduced fiber

The grafted product of glycidyl methacrylate obtained in (1) was immersed in a solution of guanine / isopropyl alcohol / water = 10/40/50, and reacted at 80 ° C. for 8 hours. The guanine introduction rate calculated from the weight increase rate was 0.8 mmol / g.
(3) Triethylenediamine (TEDA) introduced fiber

The grafted product of glycidyl methacrylate obtained in (1) was immersed in a solution of triethylenediamine / water = 10/90 adjusted to pH 9 with hydrochloric acid, and reacted at 80 ° C. for 3 hours. The triethylenediamine introduction rate calculated from the weight increase rate was 1.62 mmol / g.
(4) Production of trioctylamine (TOA) introduced fiber

The grafted product of (1) glycidyl methacrylate was immersed in 1M hydrochloric acid and heated for 2 hours for hydrochloroxylation. Further, it was immersed in a solution of trioctylamine / dimethyl sulfoxide / water = 10/40/50 and reacted at 70 ° C. for 12 hours to obtain 0.7 mmol / g of trioctylamine-introduced fiber from the weight increase rate.
(Batch type adsorption test-Effect of chloride ion concentration)

Sodium chloride was dissolved in pure water and adjusted so that the chloride ion concentration was 100, 500, 1000, 3500, and 18000 mg / L. 1 ml of a ruthenium stock solution adjusted to a ruthenium concentration of 1000 mg-Ru / l was added to 100 ml of this chloride ion concentration adjusting solution to prepare a test solution having a ruthenium concentration of 10 mg-Ru / L. A 200 ml plastic bottle was used as a test container. The pH of the test solution was adjusted to 2. 1 g of the fiber produced in (1) and (2) was added to the test solution, and the adsorption test was performed by shaking at 25 ° C. for 1 day. The results of measuring the ruthenium concentration of the supernatant after 1 day are shown in Table 1.
From the results in Table 1, it was found that the removal rate of ruthenium increased from a chloride ion concentration of 1000 mg / L.
(Batch type adsorption test-Effect of liquid temperature)

Prepare 8 plastic bottles containing 100 mL of test solution with a chloride ion concentration of 1000 mg / L and ruthenium concentration of 10 mg-Ru / L. I put it in. Next, 1 g of the fibers of (1) and (3) were added to two plastic bottles, respectively, and shaken for 1 day to adsorb ruthenium. Then, it was as Table 2 when the ruthenium density | concentration of the supernatant liquid was measured. A similar test was conducted for a chloride ion concentration of 3500 mg / L. The results are shown in Table 3.
From Tables 2 and 3, it can be seen that the higher the temperature of the test solution and the higher the chloride ion concentration, the higher the ruthenium removal effect.
(Measurement result of distribution coefficient)

1 g of adenine-introduced fiber was added to 100 mL of a test solution having a chloride ion concentration of 3500 mg / L and a ruthenium concentration of 10 mg / L. The plastic bottle was shaken in a constant temperature water bath at 8, 25, 40 and 60 ° C. for 1 week to perform an adsorption test. By measuring the ruthenium concentration in the supernatant after the adsorption test, the partition coefficient defined by the following equation was measured. The results are shown in Table 4.
Partition coefficient = ruthenium concentration in fiber / ruthenium concentration in liquid phase
A high adsorption performance with a distribution coefficient of 20000 at a chloride ion concentration of 3500 mg / L and a liquid temperature of 60 ° C. is obtained. It was.

  The present invention has shown that high radioactive ruthenium removal performance can be obtained even with a conventional ruthenium adsorbent by maintaining the chloride ion concentration in contaminated water at 1000 mg / L or higher and the liquid temperature at 35 ° C. or higher. . Radioactive ruthenium, which has been difficult to remove by simple operations such as adding sodium chloride and heating, can be removed with high efficiency, so it can be used as a countermeasure against contaminated water at the Fukushima Daiichi Nuclear Power Station. Further reduction is possible.

1 Perforated core 2 Adsorbed fiber produced by radiation graft polymerization

Claims (6)

  Method for removing radioactive ruthenium by heating contaminated water containing radioactive ruthenium and / or adding salts containing chloride ions and then contacting the ion exchanger and / or chelate exchanger   2. The method for removing radioactive ruthenium according to claim 1, wherein the contaminated water is heated from 35 ° C. to 70 ° C.   The method for removing radioactive ruthenium according to claim 1 or 2, wherein the salt containing chloride ions is added so that the chloride ion concentration after the addition is 1000 mg / L or more.   The ion exchanger and / or chelate exchanger comprises an anion exchanger having a quaternary ammonium group, a tertiary or lower weakly basic anion exchanger, a tertiary or lower amino group and / or a quaternary ammonium group. The method for removing radioactive ruthenium according to claim 1, 2 or 3, wherein the adsorbent has a functional group selected from a polyamine compound introduced product having a C number of 2 or more and a trialkylamine introduced product.   5. The method for removing radioactive ruthenium according to claim 1, wherein the ion exchanger and / or chelate exchanger is a fiber base material having a functional group introduced by a radiation graft polymerization method.   The method for removing radioactive ruthenium according to claim 6, wherein the fiber base material is selected from a single fiber, a hollow fiber, a composite fiber, a twisted yarn which is an aggregate of fibers, a woven fabric or a non-woven fabric, and a processed product thereof.