JPH0574040B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for treating a decomposition liquid obtained by oxidizing and decomposing radioactive sulfur-containing organic waste generated in facilities handling radioactive materials such as nuclear power generation facilities, and a method for treating the decomposition liquid. This invention relates to a method for volume reduction and solidification of radioactive sulfur-containing organic waste.

[Technical background of the invention and its problems] A variety of radioactive solid wastes are generated in facilities that handle radioactive materials such as nuclear power plants, but at present, the final disposal method for most of them has not yet been established and is in a state of flux. Therefore, used ion exchange resins and filter sludge, which are the main components of solid waste, are mainly stored in tanks, etc., and reducing the amount of radioactive waste generated is a priority in storage management. It is considered an urgent and important issue.

Among such solid wastes, radioactive organic wastes such as used radioactive ion exchange resins are generated in large quantities, so reducing the volume of this waste greatly contributes to reducing the amount of wastes generated.

By the way, radioactive organic waste is a polymeric compound, and it is possible to decompose it chemically to reduce its volume. Therefore, conventional methods such as dry incineration, wet incineration, thermal decomposition, chemical decomposition, etc. have been used to reduce the volume. Volume reduction methods are being considered.

Among these methods, the dry incineration method is a method in which waste is incinerated as is in an incinerator, and many methods are being studied and developed. However, when radioactive organic waste is incinerated in an incinerator, it is necessary to control the amount of heat, so pre-treatment such as drying and waste supply methods must be devised, making operations and equipment complicated. There is. Furthermore, since the incinerator itself does not have a function to suppress the scattering of incinerated ash, the scattering of radioactive incinerated ash from the incinerator is extremely large (DF: decontamination factor is approximately 1). Since harmful gases such as SOx and NOx are generated as radioactive gases as incineration gas, post-processing called waste gas treatment is necessary, including measures against radioactivity, and these gases are highly corrosive and may cause damage to equipment materials. There are problems such as difficulty in selecting Furthermore, in this method,
Because radioactive organic waste is processed in a high-temperature environment, there is a problem unique to the handling of radioactivity, which is so-called nuclide migration, in which radioactive components migrate into the generated incineration gas.

Wet incineration is a method of burning radioactive organic waste by pumping oxygen or air into an aqueous solution or an aqueous copper sulfate solution at high temperatures and pressures of 20 to 100 atmospheres and 200 to 300 degrees Celsius. In addition to the drawback that the conditions are severe, the volume reduction rate is also several steps inferior to the dry incineration method described above.

Furthermore, the pyrolysis method is a method of thermally decomposing radioactive organic waste by cutting off the supply of oxygen, and because it thermally decomposes radioactive organic waste at high temperatures in an inert gas atmosphere, it generates more dust than the dry incineration method. It has the advantage that the amount of However, this method requires an extra step of burning the cracked gas, and, like the dry incineration method, there is the problem of radionuclide migration.

On the other hand, the chemical decomposition method oxidizes and decomposes the resin through a chemical reaction with a drug, and the following methods are known.

A method of carbonizing radioactive organic materials with hot concentrated sulfuric acid (130-300℃) and then oxidizing and decomposing them with nitric acid or hydrogen peroxide.

A method of oxidative decomposition of organic waste by contacting it with hydrogen peroxide in a solution containing mainly iron ions, chromate ions, or dichromate ions.

However, these methods have the disadvantage that, for example, the selection of equipment materials is very strict in order to handle strong acids and oxidizing agents at high temperatures. Because sulfate is generated as secondary waste due to the neutralization of sulfate ions derived from sulfur-containing organic waste such as mixed ion exchange resin, the concentration of waste liquid is high and the volume reduction effect of solidification treatment is ineffective. The problem is that it is enough.

[Objective of the Invention] The present invention has been made in response to such conventional circumstances, and it is possible to reduce the concentration of waste liquid by removing even inorganic ions under easy-to-implement and easy-to-implement conditions.
Another object of the present invention is to provide a method for treating a radioactive sulfur-containing organic waste decomposition solution and a method for volume reduction and solidification that achieve a high volume reduction rate when solidified.

[Summary of the Invention] That is, the present invention comprises an oxidative decomposition step in which radioactive sulfur-containing organic waste is oxidized and decomposed in a liquid using hydrogen peroxide or an oxygen-containing gas as an oxidizing agent to generate a decomposed liquid containing sulfate ions; Radioactive sulfur-containing organic waste characterized by comprising a sulfate ion removal step of heating and concentrating this decomposed liquid in the presence of a reducing agent or a metal that has a greater ionization tendency than hydrogen, and decomposing and removing sulfate ions into sulfur dioxide. A method for treating a decomposed liquid, and an oxidative decomposition step in which radioactive sulfur-containing organic waste is oxidized and decomposed in a liquid using hydrogen peroxide or an oxygen-containing gas as an oxidizing agent to produce a decomposed liquid containing sulfate ions, and this decomposed liquid A sulfate ion removal process involves heating and concentrating sulfate in the presence of a reducing agent or a metal that has a greater ionization tendency than hydrogen, decomposing sulfate ions into sulfur dioxide, and then adjusting the pH of the decomposed liquid after this sulfate ion removal process and evaporating it. This is a method for volume reduction and solidification of radioactive sulfur-containing organic waste decomposition liquid, which is characterized by comprising a drying step of drying, and a solidification step of mixing the dried residue after the drying treatment with a solidifying material and solidifying it.

The drawings are process diagrams for explaining the present invention.
In the method of the present invention, for example, as shown in the figure, sulfur-containing organic waste, such as a sulfur-containing ion exchange resin 1, is first oxidized and decomposed by any chemical decomposition method to form an oxidized decomposition liquid 2.

This oxidative decomposition can be carried out by the method of contacting hydrogen peroxide in the presence of the metal salt mentioned above, or by the method of contacting hydrogen peroxide at a temperature of 200 to
This is carried out by pressurizing an oxygen-containing gas into an aqueous solution containing waste or an aqueous copper sulfate solution containing waste at 300°C and a pressure of 20 to 100 atmospheres.

As the metal salt, one or more selected from ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, and copper sulfate are used.
The concentration of these metal salts is determined as the metal content in the reaction solution.
A level of 500 to 10,000 ppm is suitable. The concentration of the hydrogen peroxide solution in the aqueous solution of the reaction system is preferably about 1 to 40% in terms of H ₂ O ₂ . Although the reaction proceeds at room temperature, it is desirable to heat the reaction to proceed. The reaction temperature is 50℃ or higher, especially 90~
A range of 100℃ is suitable.

Typical examples of sulfur-containing organic wastes that are the subject of the present invention include cations or cations commonly used in the treatment of radioactive waste liquid at nuclear power plants;
Anionic mixed ion exchange resin, such as copolymerized styrene and divinylbenzenesulfonic acid,
There are powdered or granular synthetic resins that have sulfonic or amino groups inside them.

In the above oxidative decomposition reaction, carbon components and hydrogen components in the ion exchange resin are oxidized to mainly generate carbon dioxide gas and water vapor, and a transparent liquid product is obtained as an oxidative decomposition liquid. Since this oxidative decomposition reaction is carried out at a lower temperature than in the dry incineration method, the transfer of radioactivity to the generated carbon dioxide gas and water vapor is extremely small, and it can be treated using conventional waste gas treatment techniques. Note that this oxidative decomposition liquid 2 contains, for example, sulfate ions generated when a sulfur-containing ion exchange resin having a sulfon group or the like is oxidized and decomposed, metal ions due to metal salts, sulfate ions, and the like.

This oxidized decomposition liquid 2 is then reductively decomposed, but it is desirable to remove existing metal ions by electrolytic refining prior to this reduction. In this electrolytic refining method, for example, an electrolytic refining tank with Pt as an anode and Cu or Fe as a cathode is used, and the metal ions present in the oxidized decomposition solution 2 are precipitated on the anode by the reaction shown by the following formula. .

Fe ²⁺ +2e ^- −−→Fe Fe ³⁺ +3e ^- −−→Fe Cu ²⁺ +2e ^- −−→Cu Through this reaction, almost 100% of the metal ions in the oxidized decomposition solution are precipitated in the negative and recovered. can do.

The remaining electrolytic residue solution from which metal ions have been precipitated in this way is then heated and concentrated while being brought into contact with a reducing agent such as charcoal or sulfur, or a metal such as Cu, which has a lower ionization tendency than hydrogen. The sulfate radicals are reduced to sulfur dioxide and removed to obtain a reduced decomposition residue solution 3.

When a reducing agent such as charcoal or sulfur is used, the sulfate ion is almost completely converted to sulfur dioxide, and when a metal such as Cu is used, theoretically 50% of it is decomposed.

In other words, in the former case, the sulfate ion becomes sulfur dioxide through the following reaction, 2H ₂ SO ₄ +C −-→ 2SO ₂ ↑+CO ₂ ↑+2H ₂ O↑ In the latter case, when the liquid temperature becomes 130°C or higher, The sulfuric acid and copper in the oxidized decomposition liquid react as follows, and copper sulfate is produced in an equimolar amount to sulfur dioxide.

Cu＋2H ₂ SO ₄ −−→ CuSO ₄ +SO ₂ ↑＋2H ₂ O↑ In other words, in the reaction with Cu, 1 mol of copper sulfate is produced from 1 mol of metallic copper, and at the same time 1 mol of sulfate ion is released from the oxidative decomposition solution 2 as sulfur dioxide. It will be removed. Therefore, even when metallic copper is used, 50% of sulfate ions can be removed.

Regarding the sulfur dioxide generated in this desulfurization reaction, the transfer to radioactive gas is extremely small, similar to the carbon dioxide gas and water vapor that accompany the oxidative decomposition reaction of the resin mentioned above, and it can be treated using conventional waste gas treatment technology. be.

Note that the reduced residue liquid 3 remaining from the desulfurization reaction using metals can be reused to decompose the radioactive ion exchange resin, so if this reaction liquid is used, new metal salts will be generated for oxidative decomposition. There is no need to use sulfate, and the sulfate radicals can be almost completely decomposed and removed. Furthermore, if the radioactivity concentration in the reaction solution exceeds the allowable amount, the metal may be precipitated again if necessary, or the solution may be treated as waste solution 4 in a conventional waste solution treatment system. Alternatively, after neutralization and drying treatment, the obtained powdered dry residue 5 is mixed with, for example, a polyester resin and solidified to form a solidified body 6. According to this method, the generated solidified body The amount of ion exchange resin is 1/10 that of conventional ion exchange resin solidified into cement.
0, it can be 1/20 of the case where the plastic hardens after drying.

[Embodiments of the invention] Examples of the present invention will be described below.

Example 1 In a four-necked flask equipped with a condenser and a stirrer, a dry powdered mixed ion exchange resin (trade name: Powdex) and 5,000 parts of water per 100 parts of this ion exchange resin were added and thoroughly mixed. then
Hydrogen peroxide solution in an amount such that the concentration as H ₂ O ₂ is 10% and the concentration as Fe ₂ (SO ₄ ) ₃ is 0.01 mol /
Add an amount of ferric sulfate and heat to 100℃,
Mixing and stirring was continued at this temperature for 1 hour. As the reaction progresses, gas is generated, and the solution initially becomes dark and turbid, but eventually becomes a clear liquid. The gas generated here was condensed in a condenser, the condensed liquid was returned to the reaction residue liquid in the reactor, and the gas was directly led to the next gas treatment step.

Next, the reaction residue liquid was electrolyzed in an electrolytic refining tank with a Pt anode and Fe as a cathode, and the Fe content in the liquid was reduced to approximately 100% at the electrodes.
% precipitated. Next, a logical amount of charcoal powder was added to the electrolysis residue solution and concentrated by heating. At approximately 130°C, sulfur dioxide and carbon dioxide gas were generated from the liquid due to the reaction between sulfate ions and charcoal, and at 180°C, almost 100% of the sulfate ions were decomposed. This liquid residue is treated with a conventional waste liquid treatment system after adjusting the pH.
It can be disposed of, and when the liquid material after pH adjustment is evaporated and dried and solidified into plastic using polyester resin, it is only oxidized and decomposed, and the cost is about 1/1 compared to when it is neutralized, evaporated and solidified into plastic. We were able to reduce the volume to 5.

Example 2 Into the four-necked flask used in Example 1, a dry powdered mixed ion exchange resin (trade name: Powdex) and 1500 parts per 100 parts of this ion exchange resin with a concentration of about 6000 ppm as metallic copper were added. A copper sulfate aqueous solution was added and heated to a temperature of 80 to 100°C.
Next, while stirring with a stirrer, a hydrogen peroxide solution with a concentration of 60% was added to the dry ion exchange resin at a constant flow rate.
Add 30ml per 1g to oxidize the ion exchange resin,
Decomposed into gaseous products and liquid residue. The remainder of the decomposed solution was electrolyzed in an electrolytic refining tank with a Pt anode and a Cu cathode, so that almost 100% of the Cu content in the solution was deposited on the Cu electrode. Thereafter, the electrolytic residue solution was heated and concentrated while being brought into contact with the precipitated metallic copper. At approximately 130°C, sulfur dioxide was observed to be generated from the liquid due to decomposition of sulfate ions, and at 150°C, 50% of the theoretical amount of sulfate ions were decomposed. After adjusting the pH, this liquid residue can be treated with a conventional waste liquid treatment system and disposed of.Also, when the liquid after adjusting the pH is evaporated and dried and solidified into plastic using polyester resin, it is only oxidized and decomposed. The volume could be reduced to about 1/2 compared to the case of plastic solidification treatment by evaporation drying.

In addition, the copper sulfate-containing residual solution obtained by decomposing this sulfate ion was used in combination with an aqueous hydrogen peroxide solution to perform the same waste ion exchange resin decomposition treatment again, but in this case, a metal salt aqueous solution and a hydrogen peroxide solution were also used. It was confirmed that the method had the same ability to decompose sulfur-containing organic waste.

[Effects of the Invention] As is clear from the above explanation, according to the method of the present invention, a higher volume reduction property can be obtained compared to the conventional method. Furthermore, since there is almost no transfer of radioactivity to the generated gas, it can be dealt with by normal waste gas treatment.

Furthermore, since sulfate ions originating from sulfur-containing organic waste are decomposed, the amount of secondary waste is extremely reduced.

[Brief explanation of the drawing]

The drawings are process diagrams schematically showing the steps of the present invention. 1... Waste ion exchange resin, 2... Oxidized decomposition liquid,
3... Reduction residue liquid, 4... Waste liquid, 5... Dry residue, 6... Solidified body.

Claims (1)

[Scope of Claims] 1. An oxidative decomposition step in which radioactive sulfur-containing organic waste is oxidized and decomposed in a liquid using hydrogen peroxide or an oxygen-containing gas as an oxidizing agent to produce a decomposed liquid containing sulfate ions, and this decomposed liquid A radioactive sulfur-containing organic waste decomposition solution comprising a sulfate ion removal step in which sulfate ions are heated and concentrated in the presence of a reducing agent or a metal having a greater ionization tendency than hydrogen, and sulfate ions are decomposed into sulfur dioxide and removed. processing method. 2. The method for treating a radioactive sulfur-containing organic waste decomposition liquid according to claim 1, wherein the oxidative decomposition step involves oxidatively decomposing the radioactive sulfur-containing organic waste by contacting it with hydrogen peroxide in an aqueous metal salt solution. 3. The oxidative decomposition step is the step of oxidatively decomposing the radioactive sulfur-containing organic waste by injecting oxygen-containing gas under heat and pressure into the liquid containing the radioactive sulfur-containing organic waste. A method for treating radioactive sulfur-containing organic waste decomposition liquid. 4 The oxidative decomposition process is performed at a temperature of 200 to 300℃ and a pressure of 20 to 300℃.
4. The method for treating a radioactive sulfur-containing organic waste decomposition solution according to claim 3, wherein the radioactive sulfur-containing organic waste is oxidized and decomposed by injecting oxygen-containing gas under pressure at 100 atmospheres. 5. The metal salt is a radioactive compound as set forth in claim 2, consisting of one or more selected from ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, and copper sulfate. A method for treating sulfur organic waste decomposition liquid. 6. The method for treating a radioactive sulfur-containing organic waste decomposition solution according to claim 2, wherein the concentration of the metal salt in the aqueous solution is 500 to 10,000 ppm in terms of metal ions. 7. The method for treating a radioactive sulfur-containing organic waste decomposition solution according to claim 2, wherein the concentration of hydrogen peroxide in the aqueous solution is 1 to 40% in terms of H ₂ O ₂ . 8. The method for treating a radioactive sulfur-containing organic waste decomposition liquid according to claim 2, wherein the oxidative decomposition step is carried out at a temperature of 80 to 100°C. 9 An oxidative decomposition step in which radioactive sulfur-containing organic waste is oxidized and decomposed in a liquid using hydrogen peroxide or an oxygen-containing gas as an oxidizing agent to produce a decomposed liquid containing sulfate ions, and this decomposed liquid is treated with a reducing agent or hydrogen. A sulfate ion removal step in which sulfate ions are decomposed into sulfur dioxide and removed by heating and condensing in the presence of metals with a high ionization tendency, and a drying step in which the decomposition liquid after this sulfate ion removal step is subjected to pH adjustment and evaporation drying. ,
A method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition solution, comprising a solidification step of mixing the dry residue after the drying treatment with a solidification material and solidifying it. 10. The oxidative decomposition step is the step of oxidizing and decomposing the radioactive sulfur-containing organic waste by injecting a gas containing oxygen under heat and pressure into the liquid containing the radioactive sulfur-containing organic waste. Volume reduction and solidification method of radioactive sulfur-containing organic waste decomposition liquid. 11 The oxidative decomposition process is performed at a temperature of 200 to 300℃ and a pressure of 20℃.
11. The method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition liquid according to claim 10, wherein the radioactive sulfur-containing organic waste is oxidized and decomposed by injecting oxygen-containing gas under pressure at ~100 atmospheres. 12. The method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition solution according to claim 9, in which the oxidative decomposition step comprises oxidatively decomposing the radioactive sulfur-containing organic waste by contacting it with hydrogen peroxide in an aqueous metal salt solution. . 13 The metal salt is selected from ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate and copper sulfate.
Claim 12 consisting of a species or two or more species
A method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition solution as described in . 14 The concentration of the metal salt in the aqueous solution is 500 to 10,000 ppm in terms of metal ions.
2. The method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition solution according to item 2. 15. The method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition solution according to claim ₁₂ , wherein the concentration of hydrogen peroxide in the aqueous solution is 1 to 40% in terms of _H2O2 . 16. The method for volume reduction and solidification of a radioactive sulfur-containing organic waste decomposition liquid according to claim 12, wherein the oxidative decomposition step is carried out at a temperature of 80 to 100°C.