JP2012251912A - Method for removing and adsorbing iodide ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently removing and adsorbing iodide ions in liquid.SOLUTION: There is provided a method for removing iodide ions including processes of: 1) acting an oxidant to the iodide ions in solution; and 2) removing and adsorbing iodine molecules, and/or polyiodine ions by an adsorbent when the iodide ions existing in the solution by the adsorbent. According to the method, it becomes possible to efficiently remove and adsorb the iodide ions in liquid.

Description

  The present invention relates to a technique for efficiently removing and adsorbing iodide ions in a liquid.

In nuclear power plants, especially reactor cooling and exhaust systems, if nuclear fuel rods are damaged, such as pinholes, ¹²⁹ I and ¹³¹ I fission products are discharged. Of these, ¹²⁹ I has a very long half-life of 10 ⁷ years, but is characterized by low emissions and low energy. On the other hand, ¹³¹ I has a short half-life of 8 days, but has a feature of high emission and high energy. Therefore, the most dangerous fission product nuclide in the reactor drainage / exhaust system is ¹³¹ I, which is the object of measurement and evaluation at nuclear facilities.

In the spent nuclear fuel reprocessing facility, a long period of time has passed before the spent nuclear fuel is carried from the nuclear facility, and the amount of ¹³¹ I having a short half-life is small, but the long half-life is ^129. I is present in large amounts.

The main chemical forms of radioactive iodine discharged from nuclear facilities are said to be iodine (I ₂ ), hydroiodic acid (HI), and methyl iodide (CH ₃ I).

Conventionally, the following method is used as a method for removing radioactive iodine discharged from nuclear facilities.
(1) Using a large amount of impregnated activated carbon impregnated with potassium iodide (KI), the radioactive iodine ¹³¹ I is collected by isotope exchange with non-radioactive iodine;
(2) The iodine-containing gas or liquid is removed by contacting the activated carbon impregnated with triethylenediamine (TEDA) to react the tertiary amino group with methyl iodide;
(3) Iodine-containing gas or liquid is brought into contact with silver zeolite and collected as silver iodide.

Of these, the removal techniques (2) and (3) are applied to the removal of methyl iodide. Moreover, since hydroiodic acid is acidic, it can be removed with an alkali-impregnated activated carbon or a strongly basic anion exchanger. Further, as a method for removing molecular iodine (I ₂ ), there are a method in which KI is absorbed, a method using a polymer material obtained by graft polymerization of polyvinylpyrrolidone, and the like.

However, the method of using the impregnated activated carbon impregnated with potassium iodide or TEDA as described above requires a large amount of activated carbon, which increases the cost, and at the same time, the treatment of the activated carbon after use becomes a problem. In addition, the method using silver zeolite is complicated in the process such as dehydration and heating at 150 ° C. at the same time that silver zeolite is expensive, and the removal rate of radioactive iodine is not satisfactory. .

The bigger problem is that ionic substances such as iodine (I ₂ ) and hydroiodic acid and non-ionic substances such as methyl iodide are completely different in the removal method. Therefore, both techniques must be used in combination, and the removal method becomes complicated.

Japanese Patent Laid-Open No. 9-150066 Japanese Patent Laid-Open No. 62-238337 JP 2001-11320 A Japanese Patent Laid-Open No. 6-227813 JP-A-1-234428

  The present invention has been made in view of such circumstances, and an object thereof is to provide a method for efficiently removing and adsorbing iodide ions in a solution.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors made an oxidant act on iodide ions in a solution to form molecular iodine or polyiodine ions, which are then removed by an adsorbent. As a result, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, one of the features of the present invention is that when the iodide ions present in the solution are removed by the adsorbent, 1) a step of causing an oxidant to act on the iodide ions in the solution, 2) iodine molecules, and / or A method for removing iodide ions, comprising a step of removing and adsorbing polyiodine ions by an adsorbent.

  Another feature of the present invention is a method for removing iodide ions, wherein the adsorption saturated iodine amount of the adsorbent is 100 g / kg or more.

  Another feature of the present invention is a method for removing iodide ions, wherein the adsorbent is an ion exchanger having a polyamine chelating substituent.

  Another feature of the present invention is a method for removing iodide ions, wherein the polyamine-based chelating substituent is a low-molecular polyamine.

  Another feature of the present invention is that the low molecular weight polyamine is ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, triethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenetetramine, pentaethylene. A method for removing iodide ions, comprising at least one compound selected from the group consisting of hexamine and hexamethyleneheptamine.

  Another feature of the present invention is a method for removing iodide ions, wherein the ion exchanger is a chelating fiber.

  Another feature of the present invention is that the chelating fiber is a chelating fiber comprising a base polymer (A) and a blend polymer (B) having a chelating substituent derived from a polyamine compound. This is a method for removing iodide ions.

  Another feature of the present invention is a method for removing iodide ions, wherein the base polymer (A) in the chelating fiber is a polymer obtained by polymerizing a monomer composition containing acrylonitrile. is there.

  Another feature of the present invention is a method for removing iodide ions, wherein a polymer obtained by polymerizing the monomer composition containing acrylonitrile is a modacrylic polymer.

  Another feature of the present invention is a method for removing iodide ions, wherein the oxidizing agent is selected from the group consisting of sodium hypochlorite, chlorine, and hydrogen peroxide.

  Another feature of the present invention is a method for removing iodide ions, wherein the iodide ions contain radioactive iodine.

  According to the method of the present invention, iodide ions in a liquid can be efficiently removed and adsorbed.

It is the figure which showed the total iodine adsorption rate of each adsorbent which concerns on Examples 1-5 of this invention. It is the figure which showed the total iodine adsorption rate of each adsorbent which concerns on Comparative Examples 1-5 of this invention.

  In the present invention, when an iodide ion present in a solution is removed by an adsorbent, 1) a step of causing an oxidizing agent to act on the iodide ion in the solution, and 2) an iodine molecule and / or polyiodine A method for removing and adsorbing iodide ions characterized by a step of removing and adsorbing ions by an adsorbent.

Examples of such a solution containing iodide ions include those containing radioactive iodine such as ¹²⁹ I and ¹³¹ I, and iodine-containing brine that springs out from a natural gas deposit. The iodine may be a radioisotope such as ¹³¹ I, ¹²⁹ I, ¹²³ I, or a stable isotope ¹²⁷ I.

  As the adsorbent used in the present invention, an adsorbent capable of adsorbing iodine molecules and / or polyiodine ions can be used. Examples include normal activated carbon, activated carbon, zeolite, anion exchanger, polyamine type ion exchanger, and the like. As the activated carbon or zeolite, those added with a polyamine compound such as triethylenediamine or silver to further improve the efficiency of collecting iodide ions can be used.

  It is preferable to use an adsorbent having a large iodine saturated adsorption amount. A preferable value is 100 g / kg or more, more preferably 300 g / kg or more, and further preferably 500 g / kg or more. By using an adsorbent having a large iodine saturated adsorption amount, iodide ions can be adsorbed efficiently.

  Among them, polyamine type ion exchangers are excellent in selectivity and can be suitably used because they can efficiently remove and adsorb iodine molecules and / or polyiodine ions from treated water in which other ions are present in large quantities. I can do it.

  Such polyamine type ion exchangers have chelating substituents derived from polyamine compounds. The chelating substituents derived from these polyamine type compounds may be introduced by any method, but in particular, a method using a polymer having a substituent that reacts with a polyamine compound as a precursor of a blend polymer is preferably used. It is done. This is because by introducing a polyamine-based chelating substituent by such a method, a cross-linking structure is simultaneously introduced, and a chelating substituent with little elution can be obtained. Moreover, as a substituent which reacts with the said polyamine type compound, a cyano group, an epoxy group, a carboxyl group etc. are mentioned, for example. In particular, use of an epoxy group is preferable because a chelating substituent can be introduced under mild conditions. Especially, the polymer obtained by superposing | polymerizing the monomer composition containing the said glycidyl methacrylate can be used suitably.

  As the polyamine compound, a low molecular polyamine can be preferably used. Low molecular weight polyamines include, for example, primary diamines such as ethylenediamine, 1,4-diaminobutane and 1,6-diaminohexane; primary-tertiary diamines such as dimethylaminopropylamine and diethylaminopropylamine. An oligomeric diamino marketed as, for example, diethylenetriamine, 1,9-diamino-5-azanonane, 1,13-diamino-7-azatridecane, triethylenetetramine and tetraethylenepentamine, and Polymin® Diprimary-secondary amines such as mixtures of polyethyleneimines; and secondary amines and diamines such as piperidine, piperazine, di-n-butylamine, morpholine; such as ethanolamine, diethanolamine and Diisopropanolamine; for example, polymeric polyamines such as polyethyleneimine and polyallylamine are exemplified, and any of these compounds may be used alone, or two or more compounds may be used in combination. good.

  Among these, ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, triethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenetetramine, pentaethylenehexamine, hexamethyleneheptamine and the like are preferable.

  In addition, as the ion exchanger having a polyamine-based chelating substituent, polyamine-based chelating fibers having a fiber shape can be used. The chelating fiber has a feature that the reaction rate is high because the specific surface area is larger than that of a general bead-shaped ion exchanger and the contact efficiency with treated water is high. For this reason, iodine and / or polyiodine ions generated by the action of the oxidizing agent are efficiently adsorbed and removed and adsorbed at high speed and with high efficiency.

  Further, by utilizing the fiber shape, it can be processed into various shapes such as a nonwoven fabric, a woven fabric, and a knitted fabric, and can be applied to a wide range of uses. As a method for producing such a fiber, a known spinning method can be used. For example, a method according to the purpose such as a melt spinning method, a wet spinning method, or a dry spinning method can be used.

  As a method for producing such a chelating fiber, any method capable of introducing a chelating substituent derived from a polyamine compound may be used. For example, a blending method in which a blend polymer (B) having a chelating substituent derived from a polyamine-based compound is blended into a base polymer (A) as a base material, or radiation grafting or graft polymerization on a base fiber There is a grafting method in which a chelating substituent derived from a polyamine compound is introduced using the method. Among them, the blend method is preferable because a large amount of chelating substituents can be introduced and the adsorption amount of iodide ions is increased.

  As the blend polymer (B) used in this blending method, a blend polymer obtained by introducing a polyamine compound into a polymer having an epoxy group can be suitably used. As the polymer having an epoxy group, a polymer obtained by polymerizing a monomer composition containing glycidyl methacrylate can be suitably used. Glycidyl methacrylate is easily copolymerizable with other vinyl monomers, and has a feature that an epoxy group can be introduced into a polymer structure relatively easily.

  As the chelating fiber of the present invention, a fiber into which a crosslinked structure is introduced can be suitably used. The cross-linked structure may have a cross-linked structure between the base polymer (A) and the blend polymer (B), and the base polymer (A) and / or the blend polymer (B) has a cross-linked structure therein. You may have it or both.

  In particular, when a polyamine is used as a reagent for introducing a chelating substituent, when both the base polymer (A) and the blend polymer (B) contain a substituent that reacts with an amine, the base polymer In addition to the crosslinking in (A) and the blend polymer (B), an ion exchanger having a crosslinked structure introduced between the base polymer (A) and the blend polymer (B) is obtained, which is more preferable. . This is because such an ion exchanger has less elution of the polymer component. Examples of such ion exchangers include, for example, a polymer having a monomer unit containing a cyano group as the base polymer (A) as described above, and an epoxy group or the like as the reactive functional group as the blend polymer (B). The thing with a polymer is mentioned.

  The base polymer (A) used in the present invention is not particularly limited as long as it can be blended with the blend polymer (B). It is essential that the blend polymer (B) contains a chelating substituent, but at the same time, the base polymer (A) may contain a chelating substituent. As the base polymer (A), a polymer obtained by polymerizing a monomer composition containing a monomer having a cyano group can be suitably used. A polymer obtained by polymerizing a monomer composition containing a monomer having a cyano group has moderate reactivity and high chemical resistance, and it is possible to introduce a crosslinked structure. Can do. As the monomer having a cyano group, acrylonitrile can be preferably used. A polymer obtained by polymerizing a monomer composition containing acrylonitrile is not only highly resistant to chemicals, but also has a characteristic that it is not affected by the physical properties of oils, molds, insects, bacteria, etc. .

  Therefore, a modacrylic polymer can be suitably used as the base polymer (A) of the present invention. The modaacrylic polymer contains, as monomer units, 30 to 70 parts by weight of acrylonitrile, 70 to 30 parts by weight of a halogen-containing vinylidene monomer and / or a halogen-containing vinyl monomer, and 0 to 10 parts by weight of a vinyl monomer copolymerizable therewith. It is a polymer obtained by polymerizing 100 parts by weight of the total amount of monomers to be contained. Examples of the monomer copolymerizable with these include acrylic acid and its ester, methacrylic acid and its ester, acrylamide, methacrylamide, vinyl acetate, vinyl sulfonic acid and its salt, methallyl sulfonic acid and its salt, styrene Examples thereof include sulfonic acid and a salt thereof, 2-acrylamido-2-methylsulfonic acid and a salt thereof, and one or more of them are used.

  The chelating fiber produced by the method as described above has a feature that the adsorption amount of iodine is large, and it is possible to adsorb a large amount of iodine with a smaller amount of the adsorbent.

  The oxidizing agent used in the present invention is not particularly limited as long as it can oxidize iodide ions to iodine and / or polyiodine ions. Among them, sodium hypochlorite, chlorine, hydrogen peroxide, etc. are preferably used. Can do.

  The addition amount of the oxidizing agent varies depending on the quality of the treated water and the concentration of iodide ions contained in the treated water, but is more than the amount necessary to oxidize all the iodide ions in the treated water. Usually, sodium hypochlorite (12% NaClO aqueous solution) is in the range of 2 to 12 parts, preferably 5 to 10 parts, per 100 parts of treated water.

  The feature of the present invention is that it is converted into iodine and / or polyiodine ions that are relatively easy to adsorb by acting an oxidant on iodide ions that are difficult to remove and adsorb by ordinary adsorbents. It is to adsorb.

  Furthermore, the feature of the present invention is most remarkably exhibited when a chelating fiber having a polyamine substituent is used as the adsorbent. By using a chelating fiber having an excellent adsorption rate, it is possible to efficiently remove and adsorb iodine and / or polyiodine ions generated by oxidation at high speed.

  Under such a configuration, iodine produced by the reactions shown in (Formula 1) and (Formula 2) and / or polyiodine ions are immediately removed and adsorbed, so that the equilibrium is inclined and the remaining iodine The fluoride ions are sequentially converted into iodine molecules and / or polyiodine ions. Therefore, iodide ions can be removed and adsorbed at high speed and with high efficiency.

2I ⁻ → I ₂ + 2e ⁻ (Formula 1)
nI ₂ + I ⁻ → I _{2n + 1} ⁻ (Formula 2)

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these at all. Prior to the description of the examples, definitions of measurement methods and the like will be described.

<Measurement method of iodine saturation adsorption amount>
0.2 g of the adsorbent was immersed in 20 g of 0.05N iodine standard solution and left to stand for 3 days. Thereafter, 2 mL of the supernatant was collected, and 10 mL of ion-exchanged water and starch solution were added. This solution was titrated with a 0.01N aqueous sodium thiosulfate solution to determine the iodine concentration of the supernatant. From the result, the iodine saturated adsorption amount was determined by the following (Equation 3).

A = (0.05−a) × 253.8 × 20 / 0.2 (Formula 3)
(A: iodine saturation adsorption amount, a: iodine concentration of supernatant after adsorption)
In this patent, the saturated iodine adsorption amount is expressed in g / kg, and 1 g / kg means that 1 kg of adsorbent adsorbs 1 g of iodine in a saturated state.

<Production of chelating fiber>
60 parts by weight of a modacrylic polymer obtained by polymerizing 100 parts by weight of a monomer composition consisting of 56 parts by weight of acrylonitrile, 42 parts by weight of vinyl chloride and 2 parts by weight of sodium parastyrene sulfonate, and 40 parts by weight of polyglycidyl methacrylate are added to acetone. To obtain a spinning stock solution having a stock solution concentration of 30% by weight. This spinning dope was wet-spun by a known method to obtain a modacrylic fiber as a precursor substrate. Next, 5 g of this precursor base material was reacted at 120 ° C. for 6 hours in a reaction solution containing 140 g of water and 60 g of triethylenetetramine to obtain a polyamine-type chelating fiber. The saturated iodine adsorption amount of this chelating fiber was 948 g / kg.

<Other adsorbents>
As the activated carbon, silver impregnated activated carbon (product name: TS) manufactured by Kuraray Chemical Co., Ltd. was used. The iodine saturated adsorption amount was 644 g / kg. As the zeolite, a silver-impregnated zeolite (product name: Zeolum A3) manufactured by Tosoh Corporation was used. The iodine saturated adsorption amount was 0.03 g / kg. As the ion exchange resin, a chelating ion exchanger (product name: MC-850) manufactured by Sumika Chemtex Co., Ltd. was used. The iodine saturated adsorption amount was 500 g / kg. As the inorganic adsorbent, a cerium hydroxide-based adsorbent (product name: READ-F) manufactured by Nihonkaikai was used. The iodine saturated adsorption amount was 0.05 g / kg. The iodine saturated adsorption amount of each adsorbent is shown in Table 1.

(Examples 1-5)
Potassium iodide was dissolved in seawater to prepare an iodide ion standard solution containing 35 ppm iodide ions. 0.15 g of the chelating fiber, activated carbon, zeolite, ion exchange resin, or inorganic adsorbent is added to 15 g of this standard solution, and 0.2 g of 30% hydrogen peroxide is added under hydrochloric acid acidity. added. After stirring at room temperature, the adsorbent was removed by filtration after 5 minutes, 10 minutes, 30 minutes, 60 minutes, and 11 hours, respectively. The remaining amount of iodide ion at each time was quantified by ion chromatography. Moreover, the iodine adsorption amount in each time was quantified by the same titration operation as the quantification of the iodine saturated adsorption amount. From these measurement results, the concentrations of iodide ions and iodine contained in the filtrate at each time were determined, and the total iodine adsorption rate at each time was determined by comparison with the initial concentration. In addition, the total iodine adsorption rate was calculated | required by the following (Formula 4).

Total iodine adsorption rate (%) = [C ₀ − (C _I− + C _I2 × 2)] × 100 / C ₀ (Formula 4)
(C _I- : Iodide ion concentration, C _I2 : Iodine concentration, C ₀ : Initial iodide ion concentration)
The concentrations of iodide ion and iodine in the filtrate at each time are shown in Table 2. In addition, Table 3 shows the total iodine adsorption rate at each time obtained from these values. A graph of Table 3 is shown in FIG.

  As can be seen from the results, the total iodine adsorption rate after 11 hours was 90% or more when any adsorbent was used, and iodide ions could be efficiently removed and adsorbed. In particular, when ion exchange fibers were used as the adsorbent, the total iodine adsorption rate reached 90% or more within 30 minutes, and iodide ions could be removed and adsorbed at high speed and with high efficiency.

(Comparative Examples 1-5)
Potassium iodide was dissolved in seawater to prepare an iodide ion standard solution containing 55 ppm iodide ions. To 15 g of this standard solution, 0.15 g of the chelating fiber, activated carbon, zeolite, ion exchange resin, or inorganic adsorbent was added and stirred at room temperature. As in Examples 1 to 5, after 5 minutes, 10 minutes, 30 minutes, 60 minutes, and 11 hours, the adsorbents were removed by filtration, and the remaining amount of iodide ion concentration and iodine concentration at each time was determined. It was measured. From this result, the total iodine adsorption rate at each time was determined.

  Table 4 shows the iodide ion and iodine concentrations in the filtrate at each time. In addition, Table 5 shows the total iodine adsorption rate at each time obtained from these values. A graph of Table 5 is shown in FIG.

  As can be seen from this result, when adsorption is performed without adding an oxidizing agent, the total iodine adsorption rate is 40% or less even after 11 hours, and iodide ions can be efficiently removed and adsorbed. There wasn't.

  As can be seen from these results, iodide ions can be efficiently removed and adsorbed by adding an oxidizing agent to convert iodide ions to iodine and / or polyiodine ions. In particular, when a chelating fiber is used as the adsorbent, the adsorption speed increases, and adsorption at high speed and high efficiency is possible.

Claims (11)

When removing iodide ions present in the solution with the adsorbent,
1) A step of allowing an oxidant to act on an iodide ion in a solution 2) A step of removing and adsorbing iodine molecules and / or polyiodine ions with an adsorbent.   The method for removing iodide ions according to claim 1, wherein the adsorbent has an iodine saturated adsorption amount of 100 g / kg or more.   The method for removing iodide ions according to claim 1, wherein the adsorbent is an ion exchanger having a polyamine-based chelating substituent.   4. The method for removing iodide ions according to claim 3, wherein the polyamine-based chelating substituent is a low-molecular polyamine.   The low molecular weight polyamine is selected from the group consisting of ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, triethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenetetramine, pentaethylenehexamine, hexamethyleneheptamine. The method of removing iodide ions according to claim 4, wherein the compound is one or more compounds.   The method for removing iodide ions according to any one of claims 3 to 5, wherein the ion exchanger is a chelating fiber.   The chelating fiber according to claim 6, wherein the chelating fiber is a chelating fiber composed of a base polymer (A) and a blend polymer (B) having a chelating substituent derived from a polyamine compound. Removal method.   The method for removing iodide ions according to claim 7, wherein the base polymer (A) in the chelating fiber is a polymer obtained by polymerizing a monomer composition containing acrylonitrile.   The method for removing iodide ions according to claim 8, wherein the polymer obtained by polymerizing the monomer composition containing acrylonitrile is a modacrylic polymer.   10. The method for removing iodide ions according to claim 1, wherein the oxidizing agent is selected from the group consisting of sodium hypochlorite, chlorine and hydrogen peroxide.   The method for removing iodide ions according to claim 1, wherein the iodide ions contain radioactive iodine.

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