EP1346373B1 - Method for reducing the volume of radioactively charged ion exchangers to be stored - Google Patents

Abstract

The invention relates to a method for reducing the volume of radioactively charged ion exchangers to be stored. The inventive method enables radioactively charged ion exchangers, which are especially used in the nuclear domain as adsorber materials, to be disposed of. The radioactive metals and/or radionuclides are eluted from the ion exchangers, the eluate is decontaminated by means of biosorbents, the biosorbents are burned with the combined, radioactive metals and/or radionuclides, and the solid residue of combustion is enclosed in glass powder, cement or bitumen.

Description

The invention relates to a method for reducing the volume of stored, radioactively charged ion exchangers. The inventive method can be radioactively contaminated ion exchangers, which are used in particular in the nuclear area as Adsorbermaterialien dispose of the radioactive metals and / or radionuclides are eluted from the ion exchangers, the eluate is decontaminated with Biosorbentiea, the biosorbents with the bound radioactive metals and or radionuclides are burned and the solid combustion residues are trapped in glass powder, cement or bitumen. The process of the invention has significance for the disposal and disposal of radioactive constituents from ion exchangers used in industrial plants, such as e.g. in nuclear power plants and in radioactive metal and / or radionuclide scientific and hospital facilities.

As with all decontamination methods for dissolved, toxic metals from the environment, even ion exchangers with radioactive metals and radionuclides can not be eliminated. These materials can only be disposed of by transferring them to safe, environmentally sealed, intermediate and / or repositories. The demand for safe intermediate and final storage facilities is increasing due to the increase in radioactive material Nuclear power plants, scientific institutions and hospitals. However, this need can not be met for a variety of reasons. Reducing the amount of radioactive material that can be stored is therefore immensely important.

For example, to transfer the ion exchangers loaded with radionuclides, they are enclosed in glass or cement according to certain technologies, e.g. according to US Pat. No. 4,483,789. In this case, however, the volume of radioactive material to be disposed of in intermediate or final storage facilities is increased even more. Moreover, the inclusion of synthetic organic ion exchangers, whose matrix is in many cases a copolymer of polystyrene, is expensive in glass or cement and technologically difficult. As a result, large quantities of radioactive nuclide-laden ion exchangers, which are waiting for suitable and inexpensive disposal, are stored temporarily in the nuclear power plants and storage facilities for radioactive waste.

The object of the present invention was therefore to provide a cost-effective, easy to carry out and effective method for the volume-reducing disposal of radioactively charged ion exchangers to be stored, which are e.g. To provide in huge quantities in the decontamination of water from nuclear power plants to provide, especially those based on polystyrene.

According to the invention the object is achieved by eluting radioactively loaded ion exchangers and the eluates are brought into contact with the radioactive metals and / or radionuclides with biosorbents, which are bound in the solutions contained radioactive metals and / or radionuclides to the biosorbents, the loaded Biosorbents are separated from solutions liberated to the tolerable limits of radioactive metals and / or radionuclides, which are subjected to a combustion process involving the bound radioactive metals and / or radionuclides, which reduced to a very small volume, solid burn residues of the loaded biosorbents in be enclosed in a material such as glass, cement or bitumen and so volume-reduced and stable storable a radioactive waste disposal or disposal are fed.

Above all, the invention relates to organic-synthetic ion exchangers, in particular polystyrene-based ion exchangers, more particularly to spherical resin ion exchangers.

The elution of the radioactive metals and / or radionuclides from the ion exchangers is carried out under suitable and technically known conditions, as a rule and therefore preferably under acidic pH conditions at pH values of less than 7, preferably between 1 and 3. The elution is of course also with aqueous solutions of complexing agents, eg EDTA (ethylenediaminetetraacetic acid) or NTE (nitrilotriacetic acid) possible.

As biosorbents for the purposes of the present invention, all insoluble materials of biological origin can be used, which are capable of biosorbing radioactive metals and / or radionuclides. The biosorbing process which can be carried out with biosorbents is a relatively new and very economical possibility for removing toxic metals from the environment (Biotechnol Prog., 1995, 11, 235-250 and Appl. Microbiol. Biotechnol., 1997, 48, 577-587), since biosorbents different origin and structure can bind toxic metals with sometimes very high binding rates. Biosorbents are in cheap and easily accessible in most cases. Biosorbents are known materials that can be obtained, inter alia, from the biomass of mosses, algae, fungi or bacteria. They are sometimes even large-scale in large-scale fermentations - often even as waste. Above all, however, from very cheap and easily accessible, renewable biological (cellulose- and lignocellulose-containing) raw materials and residues of agriculture, forestry, paper, food and fish industry biosorbents can be obtained with good metal-binding properties, such as wood residues, sawdust , Straw, corn spindles, beet pulp, pulp, bran and crab shells. Although these biosorbents in their natural occurrence often already have a good binding behavior towards toxic metals, they are often further chemically modified to increase their binding capacity even further. All previously mentioned modified and unmodified biosorbents, but also from biological material isolated and purified and optionally also chemically and / or biologically modified Biomakromolelcüle such as celluloses, starch, xylans, agarose, dextranes, lignins, humic acids, chitin, chitosan and co- Macromolecules of the abovementioned biomacromolecules are understood as bioadsorbers in connection with their use in this patent.

In an advantageous embodiment of the invention, biosorbents according to DE 197 184 52 A1 are used.

Before the radioactively charged eluates of ion exchangers of any origin are brought into contact with the listed biosorbents, the biosorbents must be brought to a pH suitable for the binding of the radioactive metals and / or radionuclides. The pH range at which a connection of radioactive metals and / or radionuclides to Biosorbentien is at pH values between 2.0 to 14, especially between 4.0 and 8.0. The contacting of the radioactively loaded liquid sample with the biosorbent is carried out in two ways, either by the batch process or by the column method.

In the batch process, the radioactive metals and radionuclide-binding biosorbents are added to the reactor in a radioactively loaded eluate and the resulting suspension is different times at temperatures of 5 ° C to 50 ° C, preferably at a temperature of 15 ° C to 30 ° C stirred. The stirring times are from 5 minutes to 10 hours, preferably from 1 hour to 3 hours.

In the column method, the biosorbents are filled in a column suitable for chromatography in a suitable amount for the application, through which the radioactive metals and / or radionuclides containing eluate is passed. Flow through the filled chromatography column binds the radioactive metals and / or radionuclides to the biosorbents. Again, the operating temperatures apply as in the batch process.

The conditions for binding are selected in the specific application case within the given and above-mentioned general binding conditions so that the prescribed release values for radioactive effluents (eluate residue) in the receiving waters, which must be less than or 25 Bq / l. Influencing factors for this are, for example, the amount of radioactive metals and / or radionuclides to be bound, the amount of biosorbents, the pH of the eluate solutions to be purified, the working temperatures and stirring or throughput times.

After the binding process, the biosorbents are separated from the purified radioactive eluate solutions, advantageously by filtration through suitable barrier layers or by suitable membrane modules, optionally after addition of combustible and thereby no soot-producing filter aids. In some cases, where the properties of the loaded biosorbents do not permit filtration, the separation may also be by centrifugation. Residues of this process step then remain the biosorbents loaded according to the invention and still to be disposed of, as well as the eluate solutions which can be released from the effluents and freed of radioactivity, and ion exchangers which can be used again.

The biosorbents loaded with radioactive metals and / or radionuclides are subsequently burned. Although the combustion process has already been tried for radioactively loaded polystyrene-based organic ion exchangers, it has hitherto not been technically possible due to the difficulties described. However, biosorbents loaded with radioactive metals and / or radionuclides are very well suited for their disposal by incineration and a concomitant dramatic reduction in the volume of radioactive waste because they burn only to form gaseous products, water and a very low inorganic material ashes. During the combustion of these biosorbents, no soot is formed, which has hitherto made the use of combustion technology in the disposal of radioactive material on the basis of polystyrene so difficult or completely prevented.

The combustion of biosorbents loaded with radioactive metals and / or radionuclides takes place in such a way that that the biosorbents loaded with radioactive metals and / or radionuclides are registered in a customary, nuclear-approved incineration plant. So far, these incinerators have been used to incinerate waste generated, for example, during operation and dismantling of nuclear installations, such as protective suits or combustible building materials from nuclear power plants, which must be disposed of.

This combustion plant with a throughput of about 50 kg / hour consists of a combustion furnace, a post-combustion chamber and downstream equipment for particle separation and flue gas scrubbing. A built-in suction filter keeps the entire incinerator to the feed system under vacuum, so that before they are cleaned to remove radioactive particles and gases, no exhaust gases leave the incinerator and can reach the environment untreated. After their purification and analytical control, the exhaust gases are fed through a chimney to the environment. The feeding of the incinerator is automatic and discontinuous depending on the temperature and pressure conditions in the incinerators and the concentrations of added oxygen and combustion of resulting carbon monoxide or carbon dioxide in the flue gases. The ashes obtained after the combustion are automatically discharged from the plant and, according to the invention, fed to a further preparation by inclusion in glass powder, cement or bitumen. Biosorbents are burned in the oven at <1100 ° C. In the afterburner chamber (NBk), after the last combustion air supply for a residence time of the combustion gases of 2 seconds, the minimum temperature shall be 850 ° C and the minimum oxygen content 6%.

The small residual residue after incineration is ashes consisting of inorganic material which give only a negligible fraction of the volume of radioactive biosorbents and still much less of the liquid radioactive eluate solutions used to load the biosorbents. According to the method described so far for the reduction of radioactively contaminated waste, a previously unachieved volume reduction effect on radioactively contaminated waste occurs. The volumes decrease in the disposal of the radioactively loaded polystyrene-based ion exchangers and, depending on the type of burned bioadsorber and the amount of bound radioactive metals and / or radionuclides, to 0.05 to 5% of the initial volume of the decontaminated ion exchanger Polystyrene base, wherein the ion exchanger itself is operational again.

The inclusion products according to the invention produced for the intermediate or final disposal according to the method of the invention are easy to handle during transport and storage, as they can be shaped and packed according to their type of storage during the manufacturing process. So they can be stored in the intermediate or final storage, saving space. The previously low storage capacities for radioactive waste can thus be used much more effectively. The achieved according to the invention volume reduction effect of the radioactive waste produced contributes significantly to a more economical intermediate or final disposal of radioactive waste.

The biosorbents used according to the invention are obtained from renewable raw materials. They are cheap and easily accessible. Upon their incineration, significantly lower levels of radioactive waste pollute the storage capacities than in the current state of the art. As main combustion residue only as much carbon dioxide is formed, as was consumed for the biological synthesis of biosorbents from the atmosphere. The combustion process is advantageously CO ₂ neutral. Combustion does not require the addition of additional combustion promoting materials. The combustion of biosorbents loaded with radioactive metals and / or with radionuclides only requires low temperatures, so that the risk of contamination of the environment with radioactive material via the combustion products is technically minimized or eliminated altogether by simpler means.

The remaining as ash in inorganic form, radioactive residues occupy only a small volume, are dry and can be easily processed into mixtures with glass powder, cement or bitumen. There are no problems of segregation of individual components of the materials used for inclusion, especially when mixing bitumen with aqueous radioactively contaminated wastewater concentrates. On high-quality and expensive special components, such as can be used in US Patent 5 707 922 and also required for the conversion into stable storage products special cements can be omitted in the process of the invention.

For the reduction of the volume of ion exchangers, there has hitherto been no technically relevant solution. For cost reasons, they were therefore often in unchanged form and packaged in their unaltered volume in barrels of intermediate or final storage supplied.

By the method according to the invention arise from large volumes small amounts of solid, well interchangeable and / or storable, radioactive waste with very good storage properties. A particular advantage of the method set forth in the description of the invention is that polystyrene-based ion exchangers loaded with radioactive material can be inexpensively decontaminated and disposed of while eliminating the previous disadvantages of their disposal technologies.

embodiments example 1

All work is done behind a screen. 50 ml polystyrene-based ion exchangers loaded with radionuclides (from the cycle cleaning of a nuclear power plant) are filled into a chromatography column (diameter: 25 mm, height: 500 mm) with ceramic frit, which is behind a shield made of lead bricks. The activity of the loaded ion exchanger is 4.0 × 10 ¹⁰ Bq / l, with the major part of the activity attributable to the two cobalt isotopes Co-58 and Co-60.

The filled column is then eluted with 0.1 molar hydrochloric acid, with a flow rate of about 20 ml / min is set. After a flow of about 5000 ml, the elution is complete, the residual activity of the ion exchanger is then at about 2.0 x 10 ¹ Bq / l. With this residual activity, it can be sent to normal waste recycling or reuse.

The recovered eluate containing the radioactivity becomes adjusted to pH 7.0 by adding 5 molar sodium hydroxide solution. 200 ml of pre-swollen bioadsorber (prepared according to DE 197 18 452 A1) are now filled into a second chromatography column with identical dimensions as above. Thereafter, the neutralized eluate is also run at a flow rate of about 20 ml / min over this second column, which is also behind a shield made of lead bricks. The eluate obtained in this case still has a radioactive residual activity of about 5.0 x 10 ° Bq / l and is fed to the normal wastewater. The column with the loaded bio-adsorber remains on site for 24 hours to dry thoroughly. The loaded Bioadsorber is removed from the column, filtered off over a ceramic frit, sucked dry and fed to the combustion. This is done in the described and nuclear approved incinerator. The residues of the waste gas purification are again bound to Bioadsorbern, which can be burned again. As a residue of the combustion incurred inorganic ash, which now occupies only a volume of 1.5 ml, is disposed of according to the prior art, ie either glazed or cemented.

Example 2

An identical test setup as described in Example 1 is created. For the elution of the ion exchanger but instead of hydrochloric acid 0.1 molar sulfuric acid is used. The neutralization of the eluate is now carried out with solid calcium hydroxide (about 70 g). The suspension is allowed to stand overnight and then filtered from precipitated calcium sulfate. This has bound about 90% of the initial activity and is concreted or glazed together with the resulting ashes of the Bioadsorbers. The bond of the water in the Eluates remaining residual activity is analogous to the above, except in this case the binding to 40 ml of an ion exchanger of phosphorylated cellulose.

Claims (8)

1. A method for the volume-reducing disposal of radioactively polluted ion exchangers to be stored,
   characterized in that
   the radioactive metals and/or radionuclides are eluted from the ion exchangers, the eluate is decontaminated with biosorbents, the biosorbents including the bound radioactive metals and/or radionuclides are subjected to combustion, and the solid combustion residues are entrapped in glass powder, cement or bitumen.
2. The method according to claim 1,
   characterized in that
   the ion exchangers are ion exchangers based on polystyrene.
3. The method according to claim 1 or 2,
   characterized in that
   elution of the radioactive metals and/or radionuclides from the ion exchangers is effected using aqueous solutions under acidic pH conditions at pH values <7, preferably at pH values between 1 and 3.
4. The method according to claim 1 or 2,
   characterized in that
   elution of the radioactive metals and/or radionuclides from the ion exchangers is effected using complexing agents dissolved in aqueous solutions.
5. The method according to any of claims 1 to 4,
   characterized in that
   water-insoluble, renewable biological raw materials are employed as biosorbents, particularly cellulose- and lignocellulose-containing raw materials and residuals from agriculture, forestry, and from the paper, food and fish industries, or components thereof.
6. The method according to claim 5,
   characterized in that
   biomacromolecules are employed as biosorbents, preferably celluloses, starch, xylans, agarose, dextrans, lignins, humic acids, chitin, chitosan, or co-macromolecules of the above-mentioned biomacromolecules.
7. The method according to claim 5 or 6,
   characterized in that
   said biosorbents have undergone chemical and/or biological modification.
8. The method according to any of claims 5 to 7,
   characterized in that
   decontamination of the ion exchanger eluates is effected using said biosorbents in a column or batch process at temperatures of from 5°C to 50°C, preferably from 15°C to 30°C, at a pH value of from 2 to 14, preferably from 4 to 8.