JPH1123793A - Method for treating ion exchange resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover metal ions without adding any causative agents of secondary wastes by removing ion exchange groups from used ion exchange resin, separating the water containing removed metal ions and the residue of the ion exchange resin, keeping the water containing the metal ions and the ion exchange groups at high temperature and pressure to react it and recovering the metal ions in the form of hydroxides or oxides. SOLUTION: In a process 1 for removing ion exchange groups, the water is kept at a temperature of 20 deg.C or lower and under the pressure equal to or higher than the saturated vapor pressure of water to desorb and remove ion exchange groups from an ion exchange resin. In the first solid-liquid separation process 2, a solid phase containing the residue of the resin is separated from a liquid phase. In a process 3 for recovering metal ions, the liquid phase containing sulfuric acid and metal ions is kept at supercritical temperature and pressure for a certain time to cause a reaction. After precipitating the metal ions in a solution in the form of hydroxides or oxides, a solid phase is separated from a liquid phase in the second solid liquid separation process 4. Metal oxides and sulfuric acid are recovered in the solid phase and in the liquid phase respectively. The residue is incinerated in an incineration process 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for decomposing a used ion exchange resin.

[0002]

2. Description of the Related Art In recent years, in response to heightened awareness of the global environment, disposal of substances that are difficult to decompose, such as ion exchange resins, has become a major problem.

[0003] Conventionally, ion-exchange resins can be decomposed by a chemical oxidation method in which ozone or hydrogen peroxide is added to water containing used ion-exchange resin and reacted at a temperature of 100 ° C or less under normal pressure. Exchange resin and water, catalyst and oxygen at high temperature and pressure below the critical point of water (200 ~ 300 ℃, 1.5
To 10 MPa), or an incineration method in which an ion-exchange resin is incinerated with other combustibles and a combustion aid using, for example, a microwave.

[0004]

However, among these decomposition methods, in the chemical oxidation method, a catalyst is used.
Since divalent iron ions are used, not only must iron ions be recovered after decomposition, but also the decomposition reaction is slow. In addition, after decomposition of the ion exchange resin, since metal ions captured by the resin remain in the decomposition solution, it was necessary to add a substance that causes secondary waste to recover the metal ions. .

[0005] In addition, the wet oxidation method not only requires a catalyst but also has a problem that the decomposition reaction of the ion exchange resin is slow and a lower carboxylic acid such as acetic acid remains.

Further, in the incineration method, although the volume reduction rate is large,
Since the ion exchange group is decomposed to generate toxic substances such as sulfur dioxide, there is a problem that exhaust gas treatment is required.

Further, when these methods are applied to the disposal of ion exchange resins generated in nuclear facilities, incineration produces oxides such as technetium which easily migrate into the gas phase together with the generation of sulfur dioxide and the like. Need to be collected. Oxide such as technetium is recovered when it comes into contact with an alkaline solution, but it has been difficult to stably treat this solution.

[0008] In the chemical oxidation method and the wet oxidation method, since the radioactive substance captured by the ion exchange resin remains in the aqueous solution after decomposition, treatment of the radioactive substance poses a problem.
Most of the radioactive substances precipitate as hydroxides when the pH of the solution is neutralized. However, it is necessary to add new chemicals to the solution, and a large amount of secondary waste is generated. was there.

The present invention has been made in order to solve these problems. Metal ions generated by decomposition of an ion exchange resin can be efficiently used without requiring addition of a substance causing secondary waste. It is an object of the present invention to provide a method for treating an ion exchange resin which can be separated and recovered in a specific manner.

[0010]

According to a method for treating an ion exchange resin of the present invention, a used ion exchange resin mixed with water is maintained at a temperature of 200 ° C. or less at a pressure higher than the saturated vapor pressure of water. An ion exchange group removing step of removing an ion exchange group capturing a metal ion from the ion exchange resin, water containing the metal ion removed in the ion exchange group removing step, and a residue of the ion exchange resin. A solid-liquid separation step of separating, an incineration step of burning the residue of the ion exchange resin separated in the solid-liquid separation step, and water containing the metal ions and ion exchange groups separated in the solid-liquid separation step. A metal ion recovery step of causing the metal ions to react under a high temperature and pressure exceeding the critical point of water and recovering the metal ions as hydroxides or oxides.

In the present invention, the used ion exchange resin (for example, a cation exchange resin having a sulfone group as an ion exchange group) is decomposed in the ion exchange group removing step.
After the ion exchange group capturing the metal ions is removed, water containing the ion exchange group and the residue of the ion exchange resin are
After being separated in the solid-liquid separation step, the separated solution is kept at a high temperature and pressure exceeding a critical point of water for a certain time in the metal ion recovery step.

At a high temperature and pressure exceeding 374.2 ° C. and 22.12 MPa, which are the critical temperature and pressure of water, the metal ions react as shown in equation (1) to form hydroxides and precipitate. If the temperature is sufficiently high, the produced hydroxide is dehydrated as shown in the equation (2) to produce an oxide.

M (SO ₄ ) _{x / 2} + xΗ ₂ O → M (OΗ) _x + x / 2Η ₂ SO ₄ (1) M (OΗ) _x → MO _{x / 2} + x / 2Η ₂ O (2) The ion-exchange resin capturing the metal ions undergoes an ion-exchange group removal step, a solid-liquid separation step, and a metal ion recovery step, so that the metal ions captured by the ion-exchange resin are converted into metal oxides (including hydroxides). ), The ion exchange group is recovered as sulfuric acid or the like. Also,
The residue of the ion-exchange resin from which the ion-exchange groups have been eliminated / removed is incinerated in the incineration step.

As described above, in the present invention, metal ions can be easily recovered as hydroxides or oxides without generating secondary waste. In addition, in the present invention, for example, sulfone groups, which are ion exchange groups of the cation exchange resin, are separated and incinerated in advance, so that even if the residue of the ion exchange resin is incinerated, no sulfur dioxide is generated. Therefore, there is no need to treat the exhaust gas, and the construction cost and running cost of the treatment equipment can be significantly reduced.

In the metal ion recovery step of the present invention,
When water (solution) containing metal ions is reacted under high temperature and pressure exceeding the critical point of water, a metal oxide can be easily formed by adding an oxidizing agent such as oxygen. , And this hydroxide can be recovered.

When the ion-exchange group is eliminated from the ion-exchange resin in the ion-exchange group removal step, a water-soluble organic substance may be generated at the same time, but this water-soluble organic substance is hardly decomposed like acetic acid. If it is a substance, it is mixed into sulfuric acid in the metal ion recovery step. At this time, by adding an oxidizing agent such as oxygen in excess, the above-mentioned organic matter can be easily decomposed.

Here, in addition to oxygen, hydrogen peroxide and ozone can be used as the oxidizing agent. In particular, when decomposing organic substances in addition to oxidizing metal ions, it is effective to use hydrogen peroxide or ozone.

For example, hydrogen peroxide is decomposed as shown in the following formula (3) to generate OΗ radicals, which act on organic substances to oxidize and decompose water-soluble organic substances.

{ ₂ O ₂ → ₂ O} (3) Also, ozone has the oxidizing power of ozone itself represented by the equation (4),
Organic substances are decomposed by the OΗ radical generated by the reaction represented by the formulas (5) and (6).

O ₃ + 2Η ⁺ + 2e ⁻ → O ₂ + Η ₂ O 2.07 vs. NHE (4) O ₃ + Η ₂ O → 2ΗO _2. (5) O ₃ + ΗO _2. → OΗ. + 2O ₂ (6) When hydrogen peroxide or ozone is used in addition to oxygen as an oxidizing agent, OΗ radicals are generated,
Η Radicals effectively decompose water-soluble organic substances.

Further, when an oxidizing agent such as hydrogen peroxide or ozone is added in the metal ion recovery step,
Irradiation with ultraviolet rays or radiation can decompose water-soluble organic substances more efficiently.

That is, ozone is irradiated by ultraviolet rays.
It reacts as shown in the following equation (7) to generate hydrogen peroxide. Hydrogen peroxide reacts by irradiation of ultraviolet rays as shown in equation (8) to generate OΗ radicals.

O ₃ + { ₂ O + hν → { ₂ O ₂ + O ₂ (7)} ₂ O ₂ + hν → 2O} (8) Further, when water is irradiated with radiation, the water reacts as shown in equation (9) and reacts with OΗ. Generates radicals.

Η ₂ O → Η + OΗ (9) For example, when treating waste containing a radioactive substance, since the radioactive substance is contained in the used ion exchange resin, radiation is not irradiated from the outside. In addition, a radiation field can be easily created.

As described above, in the metal ion recovery step, by irradiating ultraviolet rays and / or radiation in the presence of an oxidizing agent, OΗ radicals are efficiently generated, and the water-soluble organic matter is more efficiently decomposed. be able to.

In the metal ion recovery step of the present invention, when a reaction containing a metal ion is carried out at a high temperature and a high pressure exceeding the critical point of water, the reaction is partially carried out at a temperature below the critical point of water. By performing the reaction under pressure and pressure, metal ions can be effectively converted into hydroxides. That is, under subcritical conditions below the critical point, the ionic product of water becomes larger than normal temperature and normal pressure, and the hydrolysis reaction easily occurs. Product formation is caused significantly. Further, since the temperature and pressure conditions under which this reaction occurs vary depending on the type of metal, by treating the solution under controlled conditions, metal ions can be separated from each other and collected.

Further, in the present invention, before the step of removing the ion-exchange groups, a pre-treatment step of drying the used ion-exchange resin and further pulverizing it by a ball mill or the like to form a powder is provided. Can be easily transported to the reactor. That is, the ion exchange resin has a particle size of about 500 to 1000 μm and a specific gravity of 1.2 to 1.4 m.
g / ml and heavier than water, it is difficult to transport, but if the particle size is reduced to about 1/10 by crushing, transportation becomes easier, and the resin is continuously supplied to the reactor. Can be processed.

In the present invention, the liquid phase separated from the metal hydroxide-containing solid phase in the metal ion recovery step is neutralized by adding an alkali, and the obtained liquid is concentrated and dried. It can also be done. Formula (10) shows a reaction in which sodium sulfate is generated by adding sodium hydroxide as a neutralizing agent to a sulfuric acid solution constituting a liquid phase.

{ ₂ SO ₄ + 2NaOH → Na ₂ SO ₄ +2} ₂ O (10) Since the residue of the ion exchange resin is incinerated in the incineration step and converted into water and carbon dioxide, according to the present invention, It becomes possible to collect and dispose the exchange resin as stable metal oxides and sulfates. For example, when decomposing an ion exchange resin containing a radioactive substance generated in a nuclear power plant or the like, the radioactive substance can be recovered and disposed as a metal oxide, and sulfuric acid containing no radioactive substance can be recovered and disposed as a sulfate. Therefore, it is possible to reduce the volume of waste containing radioactive substances.

Further, in the present invention, the sulfuric acid in the liquid phase separated from the solid phase containing the metal hydroxide in the metal ion collecting step is concentrated and recovered by dialysis, and the remaining sulfuric acid is neutralized. From which it can be concentrated and dried, thus allowing some of the sulfuric acid to be recycled and the remaining sulfuric acid to be recovered as sulfate. And the residue of the ion exchange resin is
Since it is converted into water and carbon dioxide through the incineration process, the products from the ion exchange resin are only sulfuric acid, metal oxides and sulfates. Therefore, according to this method, concentrated sulfuric acid can be recovered and reused from the ion exchange resin, and the remainder can be recovered and disposed of as metal oxides and sulfates. For example, radioactive materials generated in nuclear power plants and the like can be used. In the case of decomposing an ion-exchange resin containing, it is possible to reduce the volume of waste containing radioactive substances.

Further, in the metal ion recovery step of the present invention, after reacting water containing metal ions at a high temperature and pressure exceeding the critical point of water, an oxide such as technetium which has been transferred as a gas into the gas phase. Can be recovered in water by contact with water. The technetium compounds which are volatile and move into the gas phase are technetium heptaoxide of VII valence and pertechnetate. Ditechnetium heptaoxide reacts with water to form pertechnetate as shown in the following formula (11).
As shown in the formula (12), it is dissolved in water to form an acid.

Tc ₂ O ₇ + Η ₂ O → 2ΗTcO ₄ (11) ΗTcO ₄ → Η ⁺ + TcO ₄ ⁻ (12) Therefore, the technetium component is removed from the gas phase by bringing the steam containing pertechnetate into contact with water. Can be recovered. Also, since technetium compounds are acids,
Technetium can be easily recovered by contact with an alkaline solution.

In the conventional incineration method, a large amount of waste liquid is generated because technetium transferred into the gas phase is brought into contact with water together with carbon dioxide and sulfur dioxide, so that a large amount of waste liquid is generated. Since the residue of the ion-exchange resin is separated, no carbon dioxide is mixed into technetium which moves into the gas phase, and no sulfur dioxide is generated.
Therefore, the amount of waste liquid can be greatly reduced. Since the waste liquid containing the radioactive substance is concentrated and then disposed of in the formation as a solid such as cement, the present invention makes it possible to reduce the volume of radioactive waste.

Further, in the present invention, a volatile technetium oxide such as ditechnetium heptaoxide or pertechnetate, which has migrated into the gas phase, is reduced with hydrogen or the like, so that a low technetium oxide such as technetium dioxide is reduced. Volatile oxides and metallic technetium can be recovered, thus greatly reducing waste volume.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram showing one embodiment of the method for treating an ion exchange resin of the present invention.

In the examples, a strongly acidic cation exchange resin into which a sulfone group was introduced was used as the ion exchange resin, and this resin was subjected to a decomposition treatment. This cation exchange resin is obtained by introducing sulfone groups as ion exchange groups into a copolymer of styrene and divinylbenzene. When heated to a temperature of about 180 ° C, the ion exchange groups are desorbed from the resin. , And becomes a copolymer of styrene and divinylbenzene.

In an embodiment, such a cation exchange resin is mixed with water in the ion exchange group removing step 1.
After being held at a temperature of 200 ° C. or less under a pressure equal to or higher than the saturated vapor pressure of water for a certain period of time, the ion-exchange groups capturing the metal ions are desorbed and removed from the ion-exchange resin. In the separation step 2, the solid phase and the liquid phase containing the residue of the ion exchange resin are separated. The liquid phase contains sulfuric acid from the ion exchange group and metal ions trapped by the ion exchange group. Next, the liquid phase (solution containing sulfuric acid and metal ions) thus obtained is reacted in a metal ion recovery step 3 by maintaining the liquid phase at a supercritical temperature and pressure exceeding a critical point of water for a certain period of time, thereby causing a solution. After the metal ions therein are precipitated as hydroxides and oxides, the solid phase and the liquid phase are separated in the second solid-liquid separation step 4, and the metal oxides (including hydroxides) are contained in the solid phase. And sulfuric acid are recovered in the liquid phase. Further, the ion-exchange group is removed in the ion-exchange group removal step 1, and the ion-exchange resin residue separated and recovered in the solid phase in the first solid-liquid separation step 2 is incinerated in the incineration step 5 to remove carbon dioxide and carbon dioxide. It becomes steam and is processed.

In the embodiment constructed as described above,
Metal ions can be easily recovered as hydroxides and oxides, and do not generate secondary waste. Also,
After previously separating the sulfone group, which is an ion exchange group,
Since the ion exchange resin is incinerated, the incineration process 5
Does not generate sulfur dioxide. Therefore, there is no need for exhaust gas treatment, and construction costs and running costs of the treatment equipment can be significantly reduced.

Next, specific examples of the present invention will be described.

EXAMPLE Iron ions were trapped on a strongly acidic cation exchange resin having a sulfone group as an ion exchange group.
100 times volume of water was added and kept at 200 ° C. for 2 hours. Next, the resulting solution was treated at 400 ° C. and a high pressure of 30 MPa for 30 minutes, and then a solid phase containing a residue of the ion exchange resin and a liquid phase containing an ion exchange group capturing iron ions were separated. And the proportion of iron in the solid and liquid phases was examined.

As a comparative example, a cation exchange resin in which iron ions were captured in the same manner as in the example was decomposed by a chemical oxidation method in which hydrogen peroxide was added to decompose, and then the solid phase and the liquid phase were separated. Separation was performed, and the proportion of iron in the solid and liquid phases was examined. Table 1 shows the measurement results.

[0043]

[Table 1] From Table 1, according to the conventional chemical oxidation method, all of the iron ions captured by the ion-exchange groups remain in the decomposition solution. However, in Examples, since the iron ions precipitate as oxides and the like, It can be seen that almost no residue remains. Therefore, according to the embodiment, metal ions (iron ions) can be easily collected in a solid phase.

[0044]

As is apparent from the above description, according to the method for treating an ion exchange resin of the present invention, the following effects can be obtained.

(1) After desorbing and removing metal ions from the ion exchange resin together with the ion exchange groups, the metal ions are recovered as metal oxides and the like, so that there is no need to add a chemical and secondary waste is generated. do not do.

(2) Since ion-exchange groups are previously removed from the ion-exchange resin, even if the residue of the ion-exchange resin is incinerated, there is no generation of sulfur dioxide and the like, and the load on an exhaust gas treatment device such as a scrubber is reduced. be able to.

(3) To remove the ion exchange group in advance,
Radioactive substances trapped in ion-exchange resin used in nuclear power plants can be confined in water, and resin residues can be made non-radioactive, reducing the cost of processing equipment. it can.

(4) By pulverizing the ion-exchange base resin in advance, continuous supply to the apparatus becomes possible, and the throughput per unit time can be increased.

[Brief description of the drawings]

FIG. 1 is a process diagram showing one embodiment of a method for treating an ion exchange resin according to the present invention.

[Explanation of symbols]

 1 ... Ion exchange group removal step 2 ... First solid-liquid separation step 3 ... Metal ion recovery step 4 ... Second solid-liquid separation step 5 ... Incineration step

Claims (11)

[Claims] 1. A used ion exchange resin mixed with water is maintained at a temperature not higher than 200 ° C. at a pressure not lower than a saturated vapor pressure of water, and an ion exchange group capturing metal ions from the ion exchange resin is used. An ion exchange group removing step of removing; a water-containing metal ion removed in the ion exchange group removing step; and a solid-liquid separation step of separating the ion-exchange resin residue; and a solid-liquid separation step. An incineration step of incinerating the residue of the ion-exchange resin thus obtained; and reacting the water containing the metal ions and the ion-exchange groups separated in the solid-liquid separation step, while maintaining the water under a high temperature and pressure exceeding a critical point of water. And recovering the metal ions as hydroxides or oxides. 2. The ion exchange according to claim 1, wherein in the metal ion recovery step, an oxidizing agent is added when the water containing the metal ions is kept at a high temperature and a high pressure exceeding a critical point of the water. Resin treatment method. 3. The method for treating an ion exchange resin according to claim 2, wherein the oxidizing agent is oxygen. 4. The method according to claim 2, wherein the oxidizing agent is hydrogen peroxide or ozone. 5. The method according to claim 5, wherein the oxidizing agent is added to the water containing the metal ions in the step of recovering the metal ions, and the reaction is performed under a high temperature and a high pressure exceeding a critical point of the water. The method for treating an ion exchange resin according to any one of claims 2 to 4. 6. In the metal ion recovery step, when the water containing the metal ions is reacted at a high temperature and a pressure higher than the critical point of water and reacted, a part of the reaction is performed at a temperature and pressure lower than the critical point of water. The method for treating an ion exchange resin according to any one of claims 1 to 5, wherein the treatment is performed under the following conditions. 7. The method according to claim 1, wherein a pretreatment step of drying and pulverizing the used ion exchange resin is provided before the ion exchange group removing step.
The method for treating an ion-exchange resin according to the above item. 8. In the metal ion recovery step, after reacting water containing the metal ions at a high temperature and pressure exceeding a critical point of water, the obtained liquid is neutralized and then concentrated. The method for treating an ion exchange resin according to claim 1, wherein the ion exchange resin is dried. 9. In the metal ion recovery step, after reacting water containing the metal ion at a high temperature and pressure exceeding the critical point of water, the remaining acid and alkali are recovered by dialysis, and then obtained. The method for treating an ion-exchange resin according to any one of claims 1 to 8, wherein the obtained liquid is neutralized, concentrated and dried. 10. In the metal ion recovery step, after reacting water containing the metal ions at a high temperature and a high pressure exceeding a critical point of water, and reacting the volatile oxides transferred into the gas phase, The method for treating an ion-exchange resin according to claim 1, wherein the ion-exchange resin is recovered by contacting with water. 11. In the metal ion recovery step, after reacting water containing the metal ions at a high temperature and a high pressure exceeding a critical point of water, the volatile oxides transferred into the gas phase are reduced. 2. The method according to claim 1, wherein the low-volatility oxide or metal is recovered by reducing with an agent.
The method for treating an ion-exchange resin according to any one of claims 0 to 10.