JPH0697277B2 - Treatment method of radioactive waste ion exchange resin - Google Patents

Description

Detailed Description of the Invention

 Purpose of the invention

[Industrial applications]

The present invention relates to a treatment method for oxidatively decomposing a radioactive waste ion exchange resin under irradiation of infrared rays.

[Prior art]

The low-level radioactive waste liquid generated in the waste treatment equipment of a nuclear power plant is evaporated and concentrated to solidify the concentrated waste liquid, and the evaporated water is condensed and treated with an ion exchange resin for reuse. The used radioactive waste ion exchange resin generated by this condensate treatment needs to be mineralized and volume-reduced while avoiding the diffusion of radionuclides in order to reduce the accumulated amount as much as possible. There are two types of so-called wet method and dry method as such a method for mineralizing and reducing the volume of waste resin. As the wet method, there is a method of decomposing the waste resin by using hydrogen peroxide in the presence of an iron catalyst, as disclosed in, for example, JP-A-57-1446. However, this method consumes a large amount of expensive H ₂ O _{2 and} thus requires a high processing cost, and requires a large amount of energy to process a large amount of waste liquid. On the other hand, as a dry method, the waste resin is heated to 400 to 500 ° C to carbonize the organic matter in the first stage, and the copper oxide catalyst is used in the second stage.
A two-stage process has been proposed in which the decomposition product of the first stage is oxidatively decomposed at 600 to 700 ° C. (JP-A-60-35038). According to this method, the sulfur compound generated by the first-stage decomposition treatment may deactivate the second-stage catalyst, and the second-stage decomposition treatment requires high temperature (heating in an electric furnace). There's a problem. Alternatively, the metal catalyst is adsorbed on the exchange group of the waste resin in the first step, and the exchange group is removed at a low temperature (350 ° C) in an inert atmosphere, and the inorganic substances (SO _x , NO _x, etc.) generated by the removal are removed. )
Is treated with a scrubber, and the residue is heated to 500 to 700 ° C. for oxidative decomposition (JP-A-60-125600). Since this method is a two-step method similar to the above method, the apparatus becomes complicated and large. In addition, an acid decomposition method using sulfuric acid-nitric acid (JP-A-53-88500)
No.), a high pressure wet oxidation method using a copper catalyst (JP-A-51-2873).
No. 9) was proposed, but all of them have difficulties and have not been put to practical use.

[Problems to be Solved by the Invention]

As a result of research to solve the above-mentioned problems of the prior art, the inventors of the present invention have conventionally used energy that gives a high temperature of 600 ° C. or more for the thermal decomposition of the polymer substrate after the ion-exchange groups of the waste resin are eliminated. However, it was discovered that by using infrared rays and utilizing photochemical reaction, it can be oxidatively decomposed in a single step at a relatively low temperature of 500 ° C or less. Further, the inventors of the present invention, by adsorbing a specific metal ion to the ion exchange group of the waste resin and performing the above infrared irradiation, oxidative decomposition occurs at a lower temperature, and heat generation is suppressed, and H ₂ S is suppressed. We also found the fact that An object of the present invention is to provide a method for treating radioactive waste ion-exchange resin by one step oxidative decomposition while avoiding the risk of diffusion of radionuclide, and treating safely and at low cost by utilizing these findings. . Structure of the invention

[Means for solving problems]

The method for treating a radioactive waste ion exchange resin of the present invention is a method of adsorbing one or more ions of a metal selected from Fe, Cu, Co, Ni and Mn to a radioactive waste ion exchange resin to form an ion exchange group. It is characterized in that at least 30% of these metals are replaced with oxygen or air under the irradiation of infrared rays to cause oxidative decomposition at a temperature of 400 to 500 ° C. "Oxygen or air" may be a mixture thereof or oxygen enriched air. But air is sufficient. The waste ion exchange resin is usually sent to the treatment step in a wet state, but it does not matter. The above representative example will be described with reference to the drawings. In FIG. 1, reference numeral 1 is a horizontal reactor for decomposing waste resin, an infrared irradiation device 2 is provided above the inside, and waste resin is transferred in the longitudinal direction. A belt conveyor 3 for use is provided. At the inlet side of the reactor 1, the waste resin stored in the hopper 4 is supplied together with the air from the blower 5 in a fixed amount on the conveyor 3 by the screw 41, and is transferred to the outlet side of the reactor 1 while receiving infrared irradiation. To do. Waste resin is preferably 400-500 ° C by irradiation with infrared rays
To be heated. The treatment time in the reactor varies depending on the treatment temperature and the type of waste resin, that is, cation exchange resin or anion exchange resin, but is 20 to 30, preferably about 25 g dry resin / hr per reactor volume. The transfer speed of the belt conveyor 4 is adjusted so that When air is used as a source of oxygen, the amount is suitably 1 to 4 m ³ / min per 1 kg of waste resin. The treatment time can be shortened by increasing the decomposition treatment temperature, but from the viewpoint of preventing the scattering of radionuclides, it is preferably not longer. The waste resin is completely oxidized and decomposed by the belt conveyor 4 before reaching the outlet side of the reactor. When the waste resin is a Na-type cation exchange resin (typically, a copolymer of styrene and divinylbenzene is used as a polymer substrate and has a sulfonic acid group as an ion exchange group), it is heated to First, the exchange group is released from the polymer substrate. About half of the sulfonic acid group (—SO ₃ Na) is converted into Na ₂ SO ₄ and is recovered in the residue recovery tank 6 at the outlet of the reactor 1. Of the other sulfur compounds, H ₂ S and SO _x , H ₂ S is adsorbed or decomposed in the decomposition tower 7, and is recovered and removed with alkali scrubbing water in a scrubber 8 equipped with a circulating recovery liquid tank 9 together with SO _x. To be done. On the other hand, the polymer substrate is oxidatively decomposed and produced into CO ₂ , H ₂ O, etc., and the produced harmless gas is discharged from the top of the scrubber 8. If the H ₂ S decomposition tower 7 is filled with, for example, ZnO, the reaction of ZnO + H ₂ S → ZnS + H ₂ O (1) ZnS + 3O ₂ → ZnO + 2SO ₂ (2) SO ₂ + O ₂ 2SO ₃ (3) is continuous. Occurs, H ₂ S is decomposed. This catalyst has no risk of deterioration. In addition to ZnO, vanadium oxide, a titanium-molybdenum-based composite oxide catalyst, etc. can also be used. When the waste resin is an anion exchange resin having an exchange group such as a quaternary ammonium salt (NR ₃ OH) instead of the sulfonic acid group, NH ₃ , NO _x, etc. are produced by oxidative decomposition. Since this is also oxidized by the oxide catalyst, HNO ₃
Alternatively, it may be recovered as NaNo ₃ .

[Action]

Below, the fact that the waste resin decomposes at low temperature due to infrared irradiation will be explained based on experimental data. FIG. 2 is a graph showing the results of differential thermal analysis of Na-type cation exchange resin IR-120B (Na) in air and nitrogen atmosphere. In air, the weight loss is about 390-400 ℃
It reached 80%, and the exothermic peak indicating the removal of the exchange group and the generation of white smoke were confirmed. Also, at 400 to 720 ° C, CC, C-
A peak suggesting the cleavage of the H bond was observed, and the weight loss was
Reached 85%. On the other hand, in a nitrogen atmosphere, 270-4
The weight loss at 20 ° C was about 60%, and no clear peak suggesting the elimination of the exchange group was observed. Even at 1000 ° C, the weight loss is as small as 73%. This is probably because oxidative decomposition due to combustion does not occur. FIG. 3 shows the results of differential thermal analysis of the cation exchange resin SK-1B (H). A similar peak pattern is shown in air and in a nitrogen atmosphere, where the exchange group is rapidly released at around 400 ° C., and thereafter C—C and C—H are gradually cleaved. Thus, unlike the Na type, the H type causes an exothermic reaction at the same position as in the air even in a nitrogen atmosphere. In the case of the anion exchange resin IRA-400 (Cl), as shown in FIG. 4, a phenomenon which is markedly different from that of the cation resin is observed. That is, compared with the cation exchange resin, the heat generation is large, the peak pattern in the air and the nitrogen atmosphere does not change so much, the weight loss is fast, and it becomes almost constant at 650 ° C. Separately, in order to clarify the effect of infrared irradiation,
As shown in the figure, an alumina tube 12 was placed between the quartz reaction tube 10 and the infrared electric furnace 11 to fabricate an experimental device for partially blocking direct irradiation of infrared rays. In the figure, 13 is a blower, 14 and 15 are absorption bottles containing 10% -H ₂ O ₂ , 16 is a buffer,
17 is a gas meter. This reaction tube 10 was filled with 20 g of cation exchange resin IR-120B (11.2 g on a dry basis), the decomposition temperature was 400 ° C, and the air flow rate was 20
After the oxidative decomposition treatment under the conditions of Nl / hr and decomposition time of 6 hr, the residue in the No. 2, 4 and 6 portions of the reactor was subjected to differential thermal analysis. The result is shown in FIG. The residue of the part protected by the alumina tube 12 (No.3 to No.6) is black, and the chart is as shown in No.4 and No.6 of FIG. 6, showing that the decomposition has not progressed. Indicated. In addition, the residue of the part irradiated with infrared rays (No. 2) is white,
No further weight loss was observed, indicating complete decomposition. This white residue was readily soluble in water and was identified as Na ₂ SO _{4 by} X-ray diffraction. Na ₂ SO ₃ and NaHS
The presence of O ₃ , NaHSO ₄ · H ₂ O, and Na ₂ S ₂ O ₃ was also examined, but no similar peak pattern was detected. From the above experimental facts, it became clear that the waste resin can be decomposed at a low temperature by irradiating it with infrared rays. ⁶⁰ Co, ¹³⁷ Cs, ⁵⁹ Fe, ⁹⁰ S, which are listed as radionuclides
The oxide or salt thereof, such as r or ⁵⁴ Mn, having a melting point closest to the decomposition temperature used in the treatment method of the present invention is Cs ₂ O (melting point 490 ° C.). Here, as a representative, Na ₂
SO ₄ (melting point 884 ℃) was selected and the transfer of Na into the waste gas was examined, but Na ⁺ was not detected. That is,
As a result of the decomposition treatment, both H ₂ O ₂ absorption bottles 14 and 15
No Na ⁺ was observed (ICP analysis measurement), and it can be fully inferred that the scattering of radionuclides or their associated emissions are virtually negligible. Next, a mode in which a specific metal ion is adsorbed on the exchange group of the radioactive waste ion exchange resin and the oxidative decomposition is performed under the irradiation of infrared rays will be described based on experimental data. Fig. 12 shows that Na-type cation exchange resin IR-120B (Na) was
3 is a graph similar to FIG. 2, showing the results of a thermobalance and a differential thermal analysis of a Cu ion adsorbed as a catalyst for an oxidative decomposition reaction. As can be seen from the change in weight by the thermobalance in the figure, compared to the catalyst with the decomposition initiation temperature (405 ° C), the one with Fe adsorbed (220 ° C), the one with Cu adsorbed (270 ° C), and the range of 130-180 ℃ lower. According to the differential thermal analysis, exothermic peaks are seen around 450 ° C and 570 ° C in the absence of catalyst, whereas those adsorbing Fe have only a peak at 500 ° C, and those adsorbing Cu are very small. small. From this, it can be said that these metals have an effect of reducing heat generation. From the thermobalance measurement of cation exchange resin SKN-1 (H) with various metals adsorbed, it was found that the difference in the effect depending on the kind of the metal adsorbed as the catalyst was in the following order. (Large) Fe-Cu-Co-Ni-Mn-H (Small) When the same Cu is adsorbed, the decomposition start temperature is IR-120B.
It was also found that (Na) is closer to SKN-1 (H) by about 30 ° C. The results of the differential thermal analysis when various metal ions were adsorbed on the SKN-1 resin are as shown in FIGS. 13A and 13B, and when Cu was used, the heat generation was negligible. It can be seen that the faster the decomposition is, the lower the exothermic onset temperature is, even if there is heat generation. The influence of the amount of metal adsorbed as a catalyst is as shown in Fig. 14, and the one in which Na is replaced with Cu or Fe by about 30% or more is not much different from the one in which the thermal decomposition initiation temperature is 100%. Became clear.

[Reference Example 1] In the apparatus shown in FIG. 5, the alumina tube 12 was removed, and various waste resins shown in the table were filled in the reaction tube 10 (11.2 g on a dry basis), and the temperature was set to 500 under infrared irradiation. ° C, air flow rate
The decomposition treatment was performed under the conditions of 60 Nl / hr and reaction time of 6 hr, and the sulfur material balance was determined. The results are shown in FIG. The analysis of the amount of sulfur was carried out as follows by separating the decomposition residue and the gas. (1) The decomposition residue was converted to SO ₂ after high temperature combustion and measured by infrared spectrum. (2) Similarly, the decomposition residue was dissolved in water, and SO ₄ ²⁻ was measured by ion chromatography, and Na ⁺ was measured by ICP. (3) The water-insoluble sulfur in the residue is S in the above (1).
-Required as S in (2) above. (4) The sulfur content in the gas was measured by SO ₄ ^2- ion chromatography for the one absorbed by the H ₂ O ₂ water absorbing solution, and for the unabsorbed one as H ₂ S by the detector tube. According to the result, the amount of H ₂ S produced was larger in the mixture of the cation resin and the anion resin. This is probably because the concentration increases corresponding to the hydrogen content generated from the anion resin. In addition, about 73% of S is released (see Experiment No. 119). Furthermore, when the waste resin decomposes in a wet state, Na ₂ SO ₄ tends to be easily generated, and the amount of H ₂ S produced is reduced.

Reference Example 2 As in Reference Example 1, IR-120B as a waste resin was filled in the reaction tube 10 shown in FIG. 5, and the effects of temperature and time on the decomposition of the waste resin were examined. The relationship between the decomposition temperature and the residual rate of the residue is shown in the graph of FIG. The temperature dependence on decomposition is large, and the residual rate at 500 ° C decreases to about 30%. This value corresponds to Na in the waste resin.
Is calculated to be converted to Na ₂ SO ₄ 28.6
Matches well with%. The relationship between the decomposition temperature and the removal rates of carbon, sulfur and hydrogen is shown in the graph of FIG. It can be seen that the removal of sulfur begins rapidly around 300 ° C. It can be seen that the removal of sulfur, that is, the elimination of the exchange group, proceeds before the cleavage of the C—C bond, and the temperature of 400 to 500 ° C. is required for the cleavage of the benzene ring. The residue after 1 hr of reaction time is black and still contains C
It shows that the cleavage of the C bond has not progressed (50%).
It became white (Na ₂ SO ₄ ) after 6 hours. However, most of the hydrogen was gone in one hour. The relationship between the decomposition time and the -SO ₃ Na residual rate converted to Na ₂ SO ₄ ,
It is shown in the graph of FIG. Decomposition rate is 57% within 1 hour after reaction
Although the remaining rate is 30% as Na ₂ SO ₄ , it reaches almost 100% in 6 hours.

【Example】

Using the apparatus shown in FIG. 5, 10.4 g of IR-120B resin (dry amount basis) having 30% of the exchange capacity of Fe adsorbed was irradiated with infrared rays at a temperature of 400 ° C., an air flow rate of 120 Nl / hr, and a reaction. The decomposition treatment was performed under the condition of time of 3 hours. The temperature is about average in the reaction tube
30 ℃, 50 ℃ higher, which is considered to be exothermic due to oxidation reaction. The results of elemental analysis in this decomposition treatment are as follows. (Unit: g) Based on this result, the weight of the waste resin can be reduced to about 1/4 by oxidizing and decomposing the waste resin. Separately, I investigated the material balance of sulfur. The result is shown in FIG. The analysis method is as described in Example 1. EFFECTS OF THE INVENTION According to the treatment method of the present invention, the radioactive waste ion exchange resin can be oxidatively decomposed in a single stage by irradiation of infrared rays, so that the apparatus is extremely simplified as shown in FIG. Decomposition is carried out at a low temperature of 400 to 500 ° C,
It is safe without scattering of radionuclides, and it is easy to select the material of the reactor, operate and maintain the equipment, and keep the processing cost including equipment cost and operation cost low. In the case of Na-type cation exchange resin, Na ₂ SO ₄ is the main residue due to the decomposition treatment of the waste resin, and in the case of anion exchange resin, there is virtually no residue, and almost all of it becomes CO ₂ , CO, H ₂ O. Since it is oxidatively decomposed, the volume reduction ratio can be increased. Other decomposition products, SO _x and NO _x gas, can be easily treated and can be fixed in the form of sulfate or nitrate without fear of contamination caused by radionuclides. According to a preferred embodiment in which metal ions are adsorbed and used as a catalyst for oxidative decomposition reaction, the reaction proceeds rapidly at a lower temperature. In this case, since no H ₂ S is produced, the treatment of exhaust gas is easy. Waste resin supplied usually contains water (moisture content 50-70
%). The inclusion of water in the resin suppresses the exothermic reaction that occurs during oxidative decomposition. That is, it is considered that the endothermic reaction shown in the following formula occurs. C + H ₂ O → Co + H ₂ −31.4kcal / g.mol C + H ₂ O → CO ₂ + 2H ₂ −21.5kcal / g.mol

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus for carrying out the processing method of the present invention. 2, 3 and 4 are graphs showing the results of differential thermal analysis of various waste resins for explaining the principle of the present invention. FIG. 5 is an explanatory diagram of an experimental device used for completing the present invention. FIG. 6 is a graph showing the result of differential thermal analysis of the decomposition residue of waste resin under infrared irradiation, again for explaining the principle of the present invention. FIG. 7 is a system diagram and data showing the mass balance of sulfur in the ion exchange resin in the reference example of the present invention. 8 to 12 all show data of the reference example of the present invention. FIG. 8 shows the relationship between the decomposition temperature and the residual rate of the residue, and FIG. 9 shows the decomposition temperature and carbon, sulfur. And the removal rate of hydrogen, Figure 10 shows the relationship between the decomposition time and the removal rates of carbon and hydrogen, and Figure 11 shows the decomposition time and -SO ₃ Na.
It is a graph showing the relationship between (Na ₂ SO ₄ equivalent) residual ratio. FIG. 12 is a graph similar to FIG. 2, showing the results of differential thermal analysis of waste resin having metal ions adsorbed thereon, for explaining the principle of the present invention. 13A and 13B are graphs similar to FIG. 6 showing the results of differential thermal analysis when various metal ions were adsorbed on the waste resin. FIG. 14 is a graph showing the influence of the adsorption amount of metal ions of the waste resin on the thermal decomposition start temperature. FIG. 15 is a system diagram similar to FIG. 7, showing the mass balance of sulfur in the ion exchange resin in the example of the present invention. 1 ... Reactor, 2 ... Infrared irradiation device 3 ... Belt conveyor, 4 ... Hopper 5 ... Blower, 6 ... Residue recovery tank 7 ... H ₂ S decomposition tower, 8 ... Scrubber 9 ... Circulation recovery liquid tank

Claims (3)

[Claims] 1. A radioactive waste ion exchange resin containing Fe, Cu, Co, Ni
By adsorbing one or more ions of a metal selected from Mn and Mn and replacing at least 30% of the ion-exchange groups with these metals, by applying oxygen or air under irradiation of infrared rays. A method for treating a radioactive waste ion exchange resin, which comprises oxidative decomposition at a temperature of 400 to 500 ° C. 2. The treatment method according to claim 1, which is carried out by circulating air at a rate of 1 to 4 l / min with respect to 1 g of radioactive waste ion exchange resin (on a dry weight basis). 3. The radioactive waste ion exchange resin is a sulfonic acid type cation exchange resin, and about half of the sulfur contained in the terminal group is recovered as Na ₂ SO ₄ , and the rest is converted to SOx and fixed with alkali. The processing method according to claim 1, including the step of: