JPS5944700A - Method of decomposing radioactive ion-exchange resin waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is useful in various industrial fields, but particularly relates to an improved resin decomposition treatment method for volume reduction treatment of waste ion exchange resin generated from nuclear facilities.

As volume reduction treatment technologies for waste ion exchange resin containing radioactive materials, incineration methods, acid digestion methods, wet oxidation methods using oxygen or air, and oxidation methods using hydrogen peroxide are in the development stage, but none of these technologies are definitive. It has not become.

Among these methods, the decomposition method using hydrogen peroxide includes a method of adding sulfuric acid (JP-A-53-88-00) and a method of decomposing in the presence of iron ions (JP-A-57-1446, etc.). However, the latter method of decomposition in the presence of iron ions has the advantage of milder treatment conditions than other treatment methods.

However, a method of decomposing waste ion exchange resin using hydrogen peroxide as an oxidizing agent in the presence of iron ions decomposes the cation exchange resin almost completely, but the anion exchange resin can only be dissolved or Even if large amounts of hydrogen peroxide and iron ions are used, the maximum decomposition rate is about 90%.

This invention improves this disadvantage, and uses not only cation resins but also anion exchange resins, and even mixed resins of cation exchange resins and 7 anion exchange resins. This is a method of almost completely decomposing ion exchange resins such as (mostly) with hydrogen peroxide. That is, it has become possible to improve the decomposition rate of ion exchange resins such as 7-ion resins and anion-cation mixed resins. This makes it possible to improve the radioactive waste volume reduction ratio when disposing of radioactive waste ion exchange resin, and when solidifying the decomposition residue.
It is also possible to reduce the negative influence of organic residues in the decomposition residue on the solidified body filling rate and the dehydration operation of the decomposition residue. Furthermore, almost complete decomposition has become possible even in the reaction region of near-neutral and basic solutions. In the conventional method, the reaction system becomes strongly acidic with a pH of 1 to 3 due to the catalyst itself or resin decomposition products (carboxylic acid due to the decomposition of the organic skeleton of the resin and sulfuric acid generated from the sulfone group of the cation exchange resin), and the reaction system becomes sludge. are also exposed to harsh conditions, resulting in material corrosion problems. The iron catalyst has the disadvantage of being deactivated when an alkali is added to bring the reaction system to near neutrality. When using the catalyst of the invention, ie copper or a mixture of copper and iron, it is sufficiently active even in the near-neutral and basic reaction regime.The process of the invention will now be described in detail.

The ion exchange resins targeted by this invention are cationic resins alone, anionic resins alone, and mixtures of cationic resins and 7-ionic resins.

These ion exchange resins are mainly based on styrene and dihinylbenzene copolymers with anion exchange groups or cation exchange groups introduced into them, but are not limited to these, and can also have other structures. can also be decomposed according to the present invention. The anion exchange resin can be decomposed in a state in which radioactive anions are ion-exchanged or adsorbed in the C/, SO, and OH types as well as the OH type. Cation exchange resins are H type and Na type.

It is possible to decompose other metal ions and radionuclides in an ion-exchanged or adsorbed state.

Regarding copper ions in the reaction region between pH 3 and 110, there are anion exchange resins (G and cation exchange resins). Copper salts such as copper sulfate and copper nitrate exhibit considerably high activity in the decomposition of each cation exchange resin alone. However, when copper alone is applied as a catalyst to a mixture of anion exchange resin and cation exchange resin, the activity is slightly low, and the decomposition rate is difficult to improve. Reaction mixture to pH 3
It has been found that by disassociating between 1 and 11, a nearly complete decomposition rate can be obtained.

Even in the case of treatment with cations or anions alone, it is very important to be able to decompose the reaction system with a copper catalyst in the pH range of 3 to 11, also from the viewpoint of preventing sludge corrosion in the reactor.

Inorganic and organic salts of copper such as copper sulfate, steel nitrate, copper chloride, copper acetate, etc. can be used as sources of copper catalysts. The amount of copper ions is usually O,] ~ 2 mmol per 1 g of resin to be treated, and the concentration in the solution is 0001 ~ 002 mol/
Liters are preferred. In order to maintain the pH of the reaction system between 3 and 11, a basic substance is added.

Basic substances include Na, Ca, and Ba.

M g + Z n + Cu and Periodic Table 1 and ■
Group metal oxides, hydroxides, carbonates and ammonium hydroxides are suitable. These basic substances may be added in their entirety before the start of the reaction, or may be added intermittently or continuously as the reaction progresses while measuring the pH of the reaction system.

By combining copper ions and iron ions, a high decomposition rate of not only cation exchange resins but also anion exchange resins can be obtained, which cannot be obtained with each metal ion alone. Also, when a copper-iron catalyst is applied to a mixture of an anion exchange resin and a cation exchange resin, a high decomposition rate can be obtained. In this case, inorganic and organic salts such as copper sulfate, copper nitrate, copper chloride, and copper acetate can be used as sources of copper ions serving as catalysts.

Various salts such as iron sulfate, iron nitrate, and iron chloride can be used as sources of iron ions used as catalysts.

In this reaction system, the combined amount of copper and iron and the ratio of copper and iron have a significant influence on the activity. One amount of copper and iron is usually 0.05 to 2.0 per gram of resin.
mmol, the concentration in the solution is 0.0005 to 002 mol/liter, and the proportion of iron in the steel is preferably up to 95 mol percent, depending on the type of resin, the amount of treatment, and whether the cation or 7-ion resin is treated alone. , mixing treatment, or treatment at the optimum value taking into consideration reaction conditions, etc.

FIG. 1 is an example showing the influence of the composition of a copper-iron catalyst on the decomposition of an anionic resin. C u S in Figure 1
A suitable molar ratio of 04 F et (S On)s ranges from 9515 to 5/95. Another advantage of the copper-iron catalyst is that it exhibits high activity even in near-neutral reaction systems. This is a very desirable feature from the viewpoint of preventing corrosion of the reactor material.

FIG. 2 shows an example in which an anion resin was decomposed by adding ZnO to a copper-iron catalyst. Cu5O*-F ex (S
In the 0J)s catalyst system, the addition of ZnO as a basic substance significantly reduced the decomposition rate as Few(SO4)s increased, that is, the Fe ion content of the reaction system increased.

When adding a basic substance and performing decomposition treatment near neutrality, add the basic substance intermittently or continuously, or
Alternatively, the objective can be achieved by adding the entire required amount of the basic substance in advance at the start of the reaction. In this case, the basic substances include Na, Ca, Ba, Mg, Zn, Cu, oxides and hydroxides of metals of Groups 1 and 2 of the periodic table, as in the case of copper ion alone.

Carbonates as well as ammonium hydroxide are suitable. Next, the decomposition reaction operation method and reaction conditions will be described.

There is no particular restriction on the concentration of hydrogen peroxide added to the reaction system as a decomposing agent. Commercially available products with concentrations of 35% and 50% can be used directly or after being diluted appropriately.

The required amount of hydrogen peroxide varies depending on the type of resin and catalyst and the reaction conditions, but in order to achieve almost complete decomposition of the resin, it is usually 5 to 20 g per 1 g of resin in terms of OO% H2O2. is necessary.

The reaction is carried out with the ion exchange resin suspended in water.

The amount of resin in water is not particularly limited, but is usually in the range of 5 to 30%.

Hydrogen peroxide may be added in its entirety to the solid-liquid mixture of resin, catalyst, and water at the start of the reaction, or may be added intermittently at appropriate intervals. In some cases, the resin can be added sequentially to the catalyst and H2O2 mixture.

The reaction temperature is preferably in the range from room temperature to the temperature at which the reaction mixture is boiling (about 100°C).

The reaction pressure is usually normal pressure, but operation under increased pressure or reduced pressure is also possible.

Since the reaction is exothermic, it is preferred to use a reactor equipped with a condenser.

In addition, it is preferable to stir the reaction mixture.As described above, by using the catalyst system of the present invention, the decomposition of not only cation exchange resins but also anion exchange resins and mixtures of cation exchange resins and 7 anion exchange resins can be prevented. It can be done almost completely. As a result, the amount of decomposition residue is
This makes it possible to reduce the volume of radioactive waste and improve the solidification process.

Furthermore, when performing decomposition treatment by setting the decomposition rate of the resin to a certain value, it is possible to achieve the objective with a smaller amount of hydrogen peroxide, resulting in a reduction in treatment costs.

Furthermore, according to the copper or copper-iron catalyst of the present invention, it is possible to operate the reaction system in a near-neutral or basic region, providing mild conditions for corrosion prevention, making it possible to economically select materials for the reaction equipment. This makes operation and maintenance easier.

In addition, adding a basic substance to the decomposition reaction system of radioactive waste ion-exchange resin is a good way to prevent acidic substances such as sulfur, nitrogen, chlorine, etc., and basic substances generated in the reaction solution during the decomposition of waste ion-exchange resin. Since salt is produced in the reaction, it is possible to suppress the mixing of acidic substances into the exhaust gas generated from the decomposition reaction system. This eliminates the need for an acidic substance removal step during exhaust gas treatment, making the exhaust gas treatment easier. Second, there is no generation of waste liquid that occurs with the removal of acidic substances from exhaust gas, so it is also possible to reduce the amount of radioactive waste generated.

This invention can be applied not only to waste ion exchange resins but also to the decomposition treatment of radioactive organic solid wastes generated from nuclear power plants.

Examples of the present invention are shown below as Table 1.

Table 1-44 Reaction additive Distilled water, ml 50 22 ・Reaction time 1 minute Approx. 120 120 ・Reaction temperature 1°C Approx. 100 Approx. 100 Note) Example 1
~6 and Comparative Example 2 Resin decomposition rate calculation formula: Resin decomposition rate =
((TOC of ion exchange resin - TOC of decomposition reaction layer)/TOC of ion exchange resin) x 100 TOC: total organic carbon amount Example I Example 2 - Reaction additive distilled water, ml 22 22 - Reaction time 1 minute 120 ] 20
・Reaction temperature 1℃ Approx. 100 Approx. 1009 p of reaction solution 5.9->4.1
], 9.Resin decomposition rate, ratio 99.95
99.9 Example 3 Example 4 - Reaction additive ion exchange resin Same as Example 2 Same as Example 1 Distilled water, ml 22 22 Catalyst, mmol Same as Example 2 Cupric sulfate 05 (
zinc oxide), I 4
Millimoles/reaction time 9 minutes 120 1
20・Reaction temperature 1℃ Approx. 100 Approx. 100
-pH of reaction solution 6.9 → 6.3 11.0 → 8
3. Resin decomposition rate, φ 99.1 96.
7 Example 5 Example 6 - Reactive additive ion exchange resin Same as Example 2 Same as Example 2 Distilled water, mA 22 22 Catalyst, mmol Cupric sulfate 10 Cupric sulfate 10
(Zinc oxide) 1,9 ・Reaction time 2 minutes 120 120 ・Reaction temperature 2℃ Approx. 100 Approx.

[Brief explanation of drawings]

Figure 1 shows an example showing the influence of the composition of a copper-iron catalyst on the decomposition of an anion resin, and Figure 2 shows an example of the influence of the composition of a copper-iron catalyst on the decomposition of an anion resin.
FIG. 2 is a diagram showing an example in which an anion resin is decomposed by adding O. Applicant Toyo Engineering Co., Ltd. Agent Dai
洲明mine→Fex(SD+”)a し tJrlf7(mobX)CuSO4-NJ717 amount (mo1%) ÷--2nd
7fi

Claims (1)

[Claims] ]) A method for decomposing an ion exchange resin, which comprises using copper ions as a catalyst when decomposing waste ion exchange resin containing radioactive substances using hydrogen peroxide as an oxidizing agent. 2) The method for decomposing an ion exchange resin according to claim 1, wherein iron ions are allowed to coexist with copper ions as a catalyst. 3) The method for decomposing an ion exchange resin according to claim 1, wherein the pH of the decomposition reaction system for waste ion exchange resin containing radioactive substances is adjusted to 3-11, and copper ions are used as a catalyst.