KR20050120312A - Method for recovering of the spent ion exchange materials selective for the cs and sr ion sorption - Google Patents

Abstract

The present invention relates to a method of regenerating an ion exchanger that selectively acts on a specific radionuclide, and specifically, to selectively contaminate soils by oxidizing and reducing the saturated ion exchange resins by chemical adsorption. To dramatically reduce the amount of secondary waste generated by decontamination.

The present invention is to reduce the waste generated by treating the waste contaminated with radioactive decontamination with a selective ion exchanger, to treat a large amount of waste, and to recycle the used ion exchanger can be reused do

Description

METHODS FOR RECOVERING OF THE SPENT ION EXCHANGE MATERIALS SELECTIVE FOR THE Cs AND Sr ION SORPTION}

The present invention relates to a method of regenerating an ion exchanger selectively acting on a specific radionuclide, and specifically, to selectively contaminate soil contaminated with a chemical solution by selectively adsorbing and regenerating a saturated ion exchange resin by oxidation and reduction. A method for dramatically reducing the amount of secondary waste generated by decontamination.

As the industry develops, the seriousness of environmental pollution is increasing day by day. In particular, since nuclear power generation is widely used in various economic aspects such as facility investment cost as energy supply source required for various industries, the efficiency of radioactive waste treatment generated by nuclear power plants and nuclear-related research institutes depends on the radionuclide. There is an urgent need to develop a selective ion exchanger that can be exchanged, and research on this is being actively conducted.

Radioactively contaminated soils can directly damage humans and terrestrial flora and fauna, and secondly, they can contaminate groundwater flowing through the soil and adversely affect the entire environment, such as the marine and atmospheric environments. Is required. The method of treating radioactive contaminated soil is to measure the radioactive contamination level of the soil, and then transfer the radioactive contaminated soil to a radioactive waste disposal site for long-term storage or to treat the radioactive contaminated soil with decontamination agents according to the measured radioactive contamination degree. To remove radionuclides. If the measured levels of radioactive contamination are very low, it is efficient to treat them as decontaminated soils with decontamination agents without the need for long-term storage of radioactive soils at radioactive waste disposal sites.

However, treatment of radioactive soils with decontamination can remove radionuclides from radioactive soils, but the resulting waste fluid contains a large amount of radionuclides and also by using a large amount of decontamination solutions in solution, This is happening and costs a lot. Therefore, in order to solve this problem, a technique for treating waste generated after decontamination of radioactively contaminated soil has been developed.

Background Art A method for regenerating an ion exchange resin by replacing an ion exchange resin saturated with metal ions with an acid or a base using a metal is currently widely used.

Bradbury et al. Reported in 1981 the International Society of Hydrochemistry for Nuclear Reactor Systems "Reduction of Radioactive Waste Volume by Continuous Ion Exchange-Cesium Resin Regeneration". The ion exchange method reported here is a widely used method for obtaining radioactive radionuclides in solid or concentrated form existing within the systems of conventional nuclear power plants. In general, non-radioactive metal ions present in the aqueous solution cause a decrease in the ion exchange capacity for radionuclides, so there is a problem that an unnecessarily large volume of ion exchange resin is required. Therefore, in the method proposed by Bradbury et al., A radionuclide was described as a method of regenerating a resin with an acid or a base after ion exchange in a normal manner and removing a small amount of radioactive cesium generated at this time with a selective ion exchange resin.

Giovanni et al., 1996, described a method for high-purity regeneration of chromium metal adsorbed by carboxylic acid based cation exchange resin. The study relates to a method of regenerating an ion exchange resin using a continuous use of an oxidant and an acidic solution. The first step is to convert trivalent chromium ions present in the resin into hexavalent chromium ions using a hydrogen peroxide solution in an alkaline medium. The aluminum is changed to solubility to elute into the solution, and the aluminum component present in the solution is removed by the precipitation method so that the chromium component is present purely in the solution. And eluting other metal components.

Japanese Patent Application No. 341937 (1991) discloses a technique relating to a method for treating decontamination waste liquid. The patent treats waste generated after Ce4 + ion treatment of radioactive contaminated soil with ion exchange resin, and separates the Ce4 + ion by acid treatment of the ion exchange resin adsorbed with Ce4 + ions, and then treats the neutralizer to use Ce4 + ions again. It is about how to. The process allows for the regeneration of Ce4 + ions but requires separate acid treatment and neutralizer treatment.

In Japanese Patent No. 63224786A, a technique related to a liquid waste concentrator is known. The patent inputs the amount and concentration of liquid waste supplied to the discharge controller during volume reduction and concentration of the liquid waste in the liquid waste concentrator to maintain the proper concentration regardless of the type of liquid waste and to reduce the liquid waste volume. A liquid waste concentrator. In the patent, the amount of waste can be reduced by concentrating the liquid waste, but there is a disadvantage in that the used decontamination agent cannot be separated and used.

Japanese Patent No. 7308590A describes a method for producing and regenerating a granular ion exchanger having high selectivity to cesium and easy solid-liquid separation. This invention is a cesium separation ion characterized by contacting copper ions simultaneously with reduction treatment in the presence of a monovalent cation after oxidation treatment of an insoluble copper salt of hexacyano iron (II) acid supported on a porous anion exchange resin. Method of preparing exchanger and insoluble copper salt of hexacyano iron (II) acid adsorbed on cesium adsorbed in porous anion exchange resin, desorption of cesium and reduction treatment in the presence of monovalent cation The present invention relates to a method for regenerating a cesium separated ion exchanger, which comprises contacting copper ions. This technology is mainly used for the manufacture and regeneration of cesium separation ion exchangers, which are mainly composed of nitrate or sodium acetate from nuclear-related facilities, such as spent nuclear fuel reprocessing facilities, and are particularly suitable for the recovery and recovery of radioactive cesium in the waste liquid. It is done. However, there are disadvantages in that the effect of secondary waste reduction is inadequate and uneconomical.

Japanese Patent No. 239138A2 (2001) manufactures a liquid waste treatment device that has a function of adsorbing ions and a function of removing fine particles, thereby effectively removing ions and particles in one process to greatly reduce the amount of secondary waste. will be. In the present invention, a filtration membrane is used, which effectively removes ions and particles. However, since the fine particles generated in large quantities during soil decontamination must be completely removed using a precipitation, hydrocyclone and a filtration device, the Japanese patent including the filtration process cannot be used.

As described above, in the conventional method of treating radioactive contaminated soil with decontamination agent and treating waste generated therefrom, the amount of waste generated can be reduced. However, the decontamination agent used in the treatment of waste cannot be recycled and reused, which requires excessive disposal costs. Therefore, there is a demand for a method for reducing the amount of waste generated after decontamination of radioactively contaminated soil and at the same time regenerating and using the used ion exchanger.

In order to solve the above problems, the present inventors have regenerated an ion exchanger selectively acting on a specific radionuclide by oxidation and reduction, confirming that there is a reduction effect of secondary waste in the regeneration method of the ion exchanger. The invention has been completed.

The present invention relates to a method of regenerating an ion exchanger that selectively acts on a specific radionuclide by regenerating the ion exchanger by oxidation and reduction.

In order to achieve the above object, the present invention provides a method that is effective in reducing the costs associated with ion exchanger by selectively adsorbing specific radionuclide to regenerate saturated ion exchanger by oxidation and reduction. .

Hereinafter, the present invention will be described in detail.

The present invention,

Oxidizing by adding an oxidizing agent to an ion exchanger saturated with radionuclide ions (first step); and

It provides a method for regenerating the selective ion exchanger consisting of a step (second step) of reducing by adding a reducing agent to the ion exchanger oxidized in the first step.

In the first step, an oxidant is added to an ion exchanger saturated with radionuclides to oxidize ions in the ion exchanger so that radionuclide ions are desorbed from the ion exchanger. The ion exchanger is a selective ion exchanger prepared by adsorbing an anion to an anion exchange resin and adsorbing a transition metal thereto. The ion exchanger is composed mainly of strong basic anion exchange resin, weakly basic anion exchange resin or polyacrylonitrile (PAN). In the present invention, it is prepared by supporting hexacyano iron (II) on the ion exchanger and then adding cobalt (Co) ions or nickel (Ni) ions. The substance to be oxidized and reduced here is not an ion that is selectively adsorbed, but an anion supported on an ion exchanger. The ion exchanger has an anion adsorbed on its inner surface, and an anion exchange resin is used in the present invention.

The oxidizing agent includes hydrogen peroxide (H ₂ O ₂ ), ozone (O ₃ ), hypochlorous acid (NaClO), sodium chlorate (NaClO ₃ ), chlorine dioxide (ClO ₂ ), chlorine (Cl ₂ ) and the like. Hydrogen peroxide is most preferred. In the present invention, an oxidant in the range of 0.1-10.0 M is used based on 100 g of the ion exchanger selective for the specific radionuclide. In the present invention, cesium and strontium are preferable as the radionuclides.

Among radioactive materials, cesium (Cs) has a half-life of about 30 years and strontium (Sr) is an element with a half-life of 28.1 years, and has a half-life compared to other elements such as cobalt (Co) with a half-life of 5.72 years or iodine (I ₂ ) with 8 days. Is much longer, nuclides such as cesium and strontium require special control in the solidification process after radioactive waste treatment. Therefore, the selective separation and solidification of cesium ions or strontium ions contained in the radioactive waste can be expected to have a great effect in terms of stability and energy efficiency for radioactivity.

In the second step, the ion exchanger oxidized in the first step to remove the radionuclide is immersed in a reducing agent and reduced. Examples of the reducing agent include hydrazine (NH ₂ NH ₂ ), formaldehyde (HCHO), sodium formate (HCOONa), and the like. In the present invention, a reducing agent solution in the range of 0.1-10.0 M is used based on 100 g of the ion exchanger selective to the specific radionuclide.

The present invention configured as described above can decontaminate the contaminated soil using a chemical solution by allowing the radioactive ion exchanger selectively adsorbed to the specific radionuclide to remove and reuse the specific radionuclide through the oxidizing and reducing step. It is useful for the treatment of secondary wastes generated by

Hereinafter, the present invention will be described in detail by Examples and Experimental Examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Example 1 Oxidation and Reduction of Cesium Ion

1.oxidation

In the present invention, a selective ion exchanger was prepared by adsorbing hexacyano iron (II) as anion to anion exchange resin and adsorbing Co as a transition metal thereto. Anion exchange resin was used as an ion exchanger.

5 g of an ion exchange resin saturated with cesium ions was treated with 50 ml of hydrogen peroxide solution for 24 hours to oxidize iron (II) ions contained in the ion exchange resin to iron (III) ions.

The results are shown in FIG.

As shown in FIG. 1, as the concentration of hydrogen peroxide water increased, the amount of cesium desorbed from the ion exchange resin also increased. However, cobalt and iron ions were hardly desorbed into the solution regardless of the concentration of hydrogen peroxide.

This Fe (CN) in order to reduce a positive charge because the iron 2 is present in Fe (CN) ₆ ^4- ions by hydrogen peroxide are iron 3 is oxidized to increase the ion positive charge, such as Fe (CN) ₆ ^3- This is because anions are bound to ₆ ^3- or cations must be removed from Fe (CN) ₆ ^3- . In this system, cesium ions must be removed to achieve electrical equilibrium. This relates to electroneutralization conditions, which process is represented by the formula below.

Co ²⁺ -Fe (CN) ₆ ^4- -Cs ⁺ + H ₂ O ₂ → Co ²⁺ -Fe (CN) ₆ ^3- + Cs ⁺ + H ₂ 0 + 1 / 2O ₂

Here, Co ²⁺ -Fe (CN) ₆ ^4- -Cs ⁺ and Co ²⁺ -Fe (CN) ₆ ^3- are in a bonded state with an anion exchange resin.

2. Reduction

It is immersed in the hydrazine solution in the range of 0.1 ~ 10.0M based on 100g of the oxidized ion exchange resin in Example 1.

Co ²⁺ -Fe (CN) ₆ ^3- in the state oxidized by the oxidizing agent is reduced to the original Co ²⁺ -Fe (CN) ₆ ^4- by the hydrazine solution and the nitrogen component of the hydrazine is oxidized to nitrogen gas. Is released. This reaction can be expressed as in the following formula (2).

4Co ²⁺ -Fe (CN) ₆ ^3- + N ₂ H ₅ ⁺ → 4Co ²⁺ -Fe (CN) ₆ ^4- + 5H ⁺ + N ₂

In the above reduction reaction, a small amount of Fe (CN) ₆ ^4- ions elute into the solution, but this does not significantly affect the performance of the ion exchange resin. In addition, cesium ions and strontium ions are selectively adsorbed to the resin by Co ²⁺ -Fe (CN) ₆ ^4- ions regenerated in the ion exchange resin.

Example 2 Oxidation and Reduction of Strontium Ions

The same procedure as in Example 1 was performed except that strontium ions were used instead of cesium as the radionuclide.

The results are shown in FIG.

As shown in FIG. 2, as the concentration of hydrogen peroxide solution increased, the amount of strontium ions desorbed from the ion exchange resin also increased. However, cobalt and iron ions were hardly desorbed into the solution regardless of the concentration of hydrogen peroxide.

This is similar to the case of cesium of Example 1, it is related to the electro-neutralization conditions, the iron divalent ions present in Fe (CN) ₆ ^4- by hydrogen peroxide ^solution , such as Fe (CN) ₆ ^3- iron trivalent ions Because of the increase in positive charge due to oxidation, the Fe (CN) ₆ ^3- anion must be combined or the cation removed from Fe (CN) ₆ ^3- in order to reduce the positive charge. In this system, strontium ions must be removed to achieve electrical equilibrium. This phenomenon is represented by the following formula (3).

Co ²⁺ -Fe (CN) ₆ ^4- -Sr ²⁺ + H ₂ O ₂ → Co ²⁺ -Fe (CN) ₆ ^3- + Sr ²⁺ + H ₂ 0 + 1 / 2O ₂

Experimental Example Comparison of Adsorption Capabilities of Cesium and Strontium Ions on Selective Ion Exchangers

When the ion exchange resin was regenerated by oxidation and reduction according to the present invention, the adsorption capacity of the first and second regenerated selective ion exchange resins and the original selective ion exchange resins against cesium and strontium ions was relatively compared.

The results are shown in FIG.

As shown in the figure, when the adsorption capacity of the initially unselected selective ion exchange resin was 100%, the adsorption capacity for cesium was 99.3% (1) compared to the initial stage during the first regeneration of the selective ion exchanger. Tea regeneration was 98.6% (2). In addition, the adsorption capacity for strontium at the first regeneration of the selective ion exchanger was 99.4% (3) compared to the initial stage, and 98.6% (4) at the second regeneration. The results show that there was almost no difference in the adsorption capacity of the initial selective ion exchange resin and that of the ion exchanger in the first and second regeneration.

Thus, it can be seen that even if the regeneration method by oxidation and reduction of the ion exchanger is repeated several times, the adsorption capacity of the ion exchanger has little effect.

Therefore, it can be seen that the method for regenerating the selective ion exchanger according to the present invention is effective in reducing the required cost of the selective ion exchanger by regenerating using a redox method different from the conventional chemical substitution method.

The present invention is to reduce the waste generated by treating the waste contaminated with radioactive decontamination with a selective ion exchanger, to treat a large amount of waste, and to recycle the used ion exchanger can be reused do.

FIG. 1 is a graph showing changes in concentrations of cesium ions, cobalt ions, and iron ions desorbed into an aqueous solution depending on the concentration of hydrogen peroxide when hydrogen peroxide water is contacted with an ion exchange resin saturated with cesium ions for 24 hours.

FIG. 2 is a graph showing changes in concentrations of cesium ions, cobalt ions, and iron ions desorbed into an aqueous solution according to the concentration of hydrogen peroxide when the hydrogen peroxide solution is in contact with an ion exchange resin saturated with strontium ions for 24 hours.

3 is a graph showing a comparison of adsorption capacity for cesium and strontium ions of the primary regenerated selective ion exchange resin and the original selective ion exchange resin according to the present invention.

Claims (8)

Oxidizing by adding an oxidizing agent to an ion exchanger saturated with radionuclide ions (first step); And Reducing method by adding a reducing agent to the ion exchanger oxidized in the first step (second step) of the regeneration method of the selective ion exchanger. The method of claim 1, wherein the radionuclide is cesium or strontium. The method of claim 1, wherein the ion exchanger is a strong basic anion exchange resin, weakly basic anion exchange resin or polyacrylonitrile (polyacrylonitrile, PAN) regeneration method of the selective ion exchanger. The method of claim 1, wherein the selective ion exchanger is prepared by supporting hexacyano iron (II) on the ion exchanger of claim 3 and then adding cobalt (Co) ions or nickel (Ni) ions. Regeneration method of selective ion exchanger. The oxidizing agent used in the first step is hydrogen peroxide (H ₂ O ₂ ), ozone (O ₃ ), hypochlorous acid (NaClO), sodium chlorate (NaClO ₃ ), chlorine dioxide (ClO ₂ ), chlorine (Cl ₂ ) Regeneration method of the selective ion exchanger, characterized in that one of. 6. The method of claim 5, wherein the oxidant is hydrogen peroxide. The method of claim 1, wherein the reducing agent used in the second step is one of hydrazine (NH ₂ NH ₂ ), formaldehyde (HCHO), sodium formate (HCOONa). 8. The method of claim 7, wherein the reducing agent is hydrazine.