JPH0254920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating waste, which is a combustible hybrid solid mixture containing radioactive materials.

Currently, mixed solid waste containing radioactive materials generated from nuclear power plants and facilities that handle radioactive materials is stored untreated in containers such as drums, or is stored in containers such as cellulose filters. materials, waste ion exchange resin, etc.
Although they are stored in tanks mixed with waste liquid, it is inevitable that the amount of storage will increase in the future, and storage in tanks mixed with waste liquid is a safety concern. There are many problems, and there is an urgent need to develop practical treatment methods to solve these problems.

Conventional methods for treating hybrid mixed solid waste include compression, incineration, and acid decomposition methods, which are currently under development or in the stage of practical application. , waste gas treatment equipment is required, and radioactive secondary waste is generated accordingly, which negates the volume reduction effect of the incineration method and poses problems such as corrosion of the structural materials of the incineration treatment facility.

A similar technique to this invention is the wet oxidation method (Zimpro method) used in the pollution prevention industry to treat highly concentrated organic waste liquids, but this tends to stop oxidation when the organic acid is present. In order to improve this drawback and improve the degree of oxidation, it is known to add a catalyst such as copper ions. However, the conventional method involves continuously feeding an organic acid contained in a large amount of water into an oxidation reactor, which has the disadvantage of generating a large amount of waste water. In addition, in the special public service 57-56796,
Radioactive waste ion exchange resin, filter sludge, rubber, or vinyl chloride resin at a temperature of 200
A method is described in which oxidative decomposition is performed with a gas containing oxygen at ~300°C and a pressure of 20 to 100 atmospheres, and the decomposition residue is solidified. In this method, whether continuous or batch, waste ion exchange resin, filter sludge, vinyl chloride resin, or rubber is supplied in the form of a slurry, and the necessary water supply is
The water separated in the evaporation and concentration process of decomposition residue is used, but this results in an increase in energy consumption for evaporation and condensation. system is required, operation becomes complicated, and it is not preferable from the viewpoint of reducing radiation exposure. Furthermore, continuous supply of slurry complicates the equipment and poses problems in terms of operational safety. Also, with this method, rubber and other materials are cut to the extent that they do not block the pipes.
The size of the cut greatly affects not only the slurry transportation but also the oxidative decomposition reaction time, which poses an economical problem in terms of reactor design. In addition, when waste cathine exchange resin, vinyl chloride resin, etc. are subjected to oxidative decomposition, the pH of the reaction solution becomes 4 or less, which may put the reactor in a state where corrosion is likely to occur.

This invention is mainly applicable to middle and high level (50mrem/hr)
This method provides a method for safely, energy-saving, and efficient oxidation and volume reduction treatment by cutting or crushing combustible miscellaneous solids containing radioactive materials of The aqueous solution is used repeatedly and the miscellaneous solids are added to it in a state in which almost no moisture is entrained, and the organic components of the miscellaneous solids are almost completely oxidized to water and carbon dioxide in a semi-batch or batch process. The points are distinctive.

In the incineration method, in addition to the problem of corrosion of the equipment materials used to separate and remove acidic substances such as SOx, NOx, Cl ₂ , HCl, etc. generated by the combustion of high-temperature materials and miscellaneous solids from the waste gas, In the case of incineration of combustible miscellaneous solid waste (approximately 50 mrem/hr or more), a considerable amount of radioactive secondary waste is generated due to the infiltration of radioactive materials into the furnace materials and the radioactive materials mixed into the high-temperature waste gas along with the incineration ash. Many problems remain unresolved, including the occurrence of

According to this invention, the organic component in the miscellaneous solid is
Since water and carbon dioxide are completely oxidized, the volume reduction ratio is large, and the sulfur (S) in the miscellaneous solids is
The constituent elements of acidic gases such as nitrogen (N) and chlorine (Cl) are: S remains in solution as SO ₄ ^-2 , and N remains in solution as NH ₄ ⁺ or becomes NH ₃ , which is easy to process. , Cl ^- remains in the solution, so there are almost no SOx, NOx, Cl ₂ , HCl, etc. in the waste gas. Further, the radioactive substances contained in the miscellaneous solids exist in the solution and are hardly contained in the exhaust gas. Therefore, in the exhaust gas treatment process, it is sufficient to install a simple device that prevents only the leakage of trace amounts of radioactive materials due to entrainment of some droplets.

Additionally, depending on the type and amount of substances contained in the miscellaneous solid waste, if the pH of the solution after the oxidation reaction is as low as 1 to 3, there is a problem of corrosion occurring in _the material of the reactor. Ca(OH) ₂ , NaOH, ZnO,
When reacting by adding a basic substance such as, there is no effect on oxidative decomposition until the pH after the reaction is 8, and it is easy to select materials with corrosion in mind.

The method of the present invention will be explained in detail below.

Medium to high level combustible miscellaneous solid wastes to be decomposed by the method of this invention include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride,
Neoprene, waste ion exchange resin, polyamide, polyester, acrylic resin, filter aid, rag,
Targets include gloves (cotton blend), materials with polymer structures such as wood, packing tape, paper, and rubber, and/or flammable materials made of polymers such as machine oil and grease. The combustible materials are radioactive miscellaneous solid waste in solid form or in the form of water from nuclear power plants and other nuclear facilities.
Each type can be discharged individually or as a mixture, but any of them can be oxidized and decomposed by the method of the present invention.

Although these combustible miscellaneous solids maintain the shape suitable for their respective uses, they are difficult to handle in that state and require a long time to react, so the miscellaneous solid waste is preferably 20 mm or less. Cutting or crushing into pieces of 5 mm or less and oxidizing them is extremely advantageous in terms of reaction rate. The method of this invention is characterized by the use of metal ions as catalysts.

Metal ions include Cu ⁺ , Cu ⁺² , Co ⁺² ,
Fe ⁺² , Fe ⁺³ , Pd ⁺² , Ce ⁺² , Ni ⁺² , Cr ⁺³ , Mn ⁺² ,
Use one type of Pb ⁺² or a combination of two or more types.

Among these, Cu ⁺² , Pd ⁺² , Fe ⁺² and Fe ⁺³ are preferably used alone or in combination of two or more.

Furthermore, even if a trace amount of other metal ions is present in the reaction solution, there is no adverse effect and oxidative decomposition is possible. The concentration of metal ions is 1 to 2000 ppm, preferably 1 to 2000 ppm.
It is within the range of 1000ppm. Reaction temperature is 100-300
℃, preferably 190 to 250℃.

The partial pressure of oxygen is 3 to 30 Kg/cm ³ G, and pure oxygen and/or air can be used as the oxygen. The decomposition reactor is preferably of an aeration type or a stirring type, or a combination of the two as shown in FIG. An aqueous solution containing metal ions is held in a reactor 8, and combustible miscellaneous solid waste that has been cut and crushed into pieces of a certain size or less is introduced into the reactor, and the reactor is then sealed, heated, and pressurized. While supplying oxygen to a predetermined oxygen partial pressure, exhaust gas is removed from valve 2, the pressure inside the reactor is kept constant, and the reaction is allowed to proceed for 1 to 3 hours each time the miscellaneous solids are charged.

Even if some unreacted organic components remain in the solution, repeat this reaction by heating, pressurizing, and supplying oxygen until the aqueous solution in the reactor is almost saturated with the ash of the miscellaneous solids, Finally, oxidative decomposition is allowed to proceed for several hours without adding the miscellaneous solids to completely oxidize the organic components. Finally, the reaction solution is evaporated and concentrated to dryness to form radioactive waste whose volume has been reduced. In addition, even if an aqueous solution containing metal ions is used repeatedly several dozen times, the activity of the catalyst will not decrease.
Since no formation occurs, it can be used repeatedly until it is saturated with salts, etc. The solution contains Ca(OH) ₂ , CaCO ₃ , NaOH,
It can also be neutralized with a basic substance such as and evaporated to dryness, but the volume reduction ratio will be small.

In this invention, when miscellaneous solid waste is wet oxidized at high temperature and high pressure, the aqueous solution of metal ions can be used repeatedly, so the volume reduction ratio is large, and the exhaust gas contains carbon dioxide. Only gas and water vapor are released; virtually no SOx, NOx, Cl ₂ or HCl are emitted. Therefore, it does not require a complicated waste gas treatment process such as the incineration method, and it is easy to select materials that are resistant to corrosion, resulting in many benefits in terms of safety, volume reduction, energy conservation, and economics. be able to.

In other words, this method provides a method for efficiently reducing the volume of medium-to-high level combustible miscellaneous solid waste stored in facilities, for which there has not been an appropriate volume reduction treatment method in the past, in a safe and energy-saving manner. Furthermore, the wet oxidative decomposition residue obtained from the volume reduction treatment can be solidified, opening the way to a powerful final treatment method for medium-to-high level combustible miscellaneous solid waste.

The method of the present invention will be specifically illustrated by examples below.

Example 1 An autoclave with an internal volume of 500 ml as shown in FIG. - Corresponding to "hybrid mixed solid waste" in line 5) was decomposed, and the first amount of TOC (total organic carbon) of the solution after the reaction was measured.

Next, the mixture and oxygen shown in each decomposition reaction condition were newly sealed, and a second reaction was carried out. Similarly, reactions were repeated 15 times for each experiment and 13 times for each experiment. As shown in Table 1, the residual TOC of the reaction solution after the oxidative decomposition reaction was kept substantially constant, and it became clear that the activity of the catalyst did not deteriorate during use.

Please note a note regarding Table 1.

Note 1: The decomposition substance mixture used in the experiment was cut into pieces that could pass through a 5 mm sieve. 2.5g of the mixture supplied to the autoclave for the first time
The TOC value measured by elemental analysis was 4941 ppm.

Note 2: The TOC value measured by elemental analysis of 1g of the cation/anion exchange resin mixture, which was the substance to be decomposed in the experiment, was 2170 ppm.

Example 2 An autoclave with an internal volume of 500 ml shown in Figure 1 was used, and as shown in Table 2, the decomposition of the substance to be decomposed was carried out under the respective decomposition reaction conditions, and the reaction was completed. After the reaction solution was cooled to room temperature, the internal gas was released.

SOx, NOx, Cl ₂ and HCl in the released gas were measured using a Drager R detector tube, but as shown in Table 2, none of them were detected.

Residual TOC in the reaction solution after opening the autoclave
The amount was measured using a TOC analyzer, and the results shown in Table 2 were obtained for the TOC decomposition rate (Note 3).

Next, I would like to make a note about Table 2.

Note 3 TOC decomposition rate = (Miscellaneous solid TOC amount - Reaction liquid residual TOC amount) / Miscellaneous solid TOC amount x 100 Note 4 In experiments and experiments, miscellaneous solids were oxidized and decomposed by type under each condition shown in the decomposition reaction conditions. was carried out, and the TOC decomposition rate by type was calculated.

The experiment was conducted on miscellaneous solids such as rags, wood, paper,
The mixture in the polyethylene bottle was subjected to oxidative decomposition under the conditions shown in the decomposition reaction conditions, and the TOC decomposition rate of the mixture was calculated.

Note 5: The miscellaneous solids used as the substance to be decomposed in Example 2 were cut to a size that would pass through a 5 mm sieve.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an autoclave equipped with an aeration pipe and a stirrer used in Examples. 1 Gas inlet valve, 2... Gas outlet valve, 3... Liquid sampling valve, 4... Stirrer, 5... Pressure gauge,
6... Safety valve, 7... Electric furnace, 8... Autoclave, 9... Thermometer, 10... Air diffuser pipe.

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Claims (1)

[Claims] 1 Cu ⁺ , Cu ⁺² , Co ⁺² , Fe ⁺² , Fe ⁺³ , Pd ⁺² ,
Combustible waste containing radioactive waste in an aqueous solution dissolving metal ions selected from the group consisting of Ce ⁺² , Ni ⁺² , Cr ⁺³ , Mn ⁺² , and Pb ⁺² of hybrid mixed solid waste was input, and 100
heated to a temperature within the range of ~300℃, pressurized,
Oxygen-containing gas is introduced and the oxygen partial pressure is 3-30Kg/
cm ² range, the waste is oxidized and decomposed, and then the waste to be decomposed and digested is additionally replenished and the oxidative decomposition operation is repeated, and then the additional replenishment of new waste is stopped and the oxidation A radioactive waste treatment method characterized by allowing decomposition to proceed and, after complete oxidative decomposition of organic matter, remaining salt aqueous solution to be concentrated. 2. The method according to claim 1, wherein the metal ions dissolved in the aqueous solution are present in a concentration range of 1 to 2000 ppm as metal ions. 3. The method according to claim 1 or 2, wherein a substance that neutralizes the acid is added to the extent that the pH of the reaction solution after oxidative decomposition does not exceed 8. 4. The method according to claim 1 or 2, wherein the combustible mixed solid waste is crushed or pulverized into pieces of 20 mm or less and treated in the aqueous solution.