A radioactive waste resin pyrolysis catalyst composition and a method of pyrolysis treatment of radioactive waste resin

Abstract

This invention discloses a pyrolysis catalyst composition for radioactive waste resin and a pyrolysis treatment method for radioactive waste resin, belonging to the technical field of radioactive waste resin treatment. The pyrolysis catalyst composition for radioactive waste resin provided by this invention comprises 8-12 wt% hydrated copper salt, 52-55 wt% kaolin, 25-30 wt% sodium hydroxide, and 9-12 wt% sodium chloride. The above-mentioned pyrolysis catalyst composition for radioactive waste resin is mixed evenly with radioactive waste resin and then fed into a pyrolysis reaction unit. The mixture is heated to 200-300°C under an oxygen-containing atmosphere to carry out a pyrolysis reaction, thereby obtaining the pyrolysis-treated waste resin residue. This invention can achieve the fixation of radionuclides at relatively low temperatures, and the pyrolysis catalyst composition for radioactive waste resin and the pyrolysis treatment method for radioactive waste resin provided by this invention have low costs.

Description

Technical Field

[0001] This invention relates to the field of radioactive waste resin treatment technology, and in particular to a radioactive waste resin pyrolysis catalyst composition and a method for pyrolysis treatment of radioactive waste resin. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the advancement of research and production of radioactive isotopes, the amount of radioactive waste resin generated is also increasing. The temporary storage of large quantities of radioactive waste resin in waste bins poses significant safety hazards to the environment and personnel: waste resin contains different types of radionuclides with varying specific activities; long-term storage will cause it to pulverize and harden, damaging its structure and potentially releasing radioactivity; and the formation of caking at the bottom of the container makes recycling difficult. Furthermore, waste resin is a diffuse substance that has not yet reached a final stable state and requires further safe treatment before final disposal.

[0004] There are two main approaches to treating radioactive waste resin: The first approach involves preserving the resin's organic structure, such as solidification methods (cement solidification, asphalt solidification, and plastic solidification) and high-integral-capacity (HIC) methods. However, these methods have low containment capacity, increasing the overall waste volume and contradicting the goal of minimizing treatment. The second approach involves breaking down the resin structure to reduce volume and convert waste resin into inorganic products through organic degradation, suitable for long-term storage and disposal. Examples include incineration, wet oxidation (acid boiling, Fenton oxidation, and supercritical water oxidation), and pyrolysis. However, incineration releases radioactive nuclides, and wet oxidation is highly corrosive to equipment and produces radioactive waste liquid, requiring stabilization treatment before disposal. Pyrolysis involves thermally decomposing the sample at high temperatures under anaerobic conditions. It offers advantages such as high volume reduction and inorganic product formation. Compared to incineration, pyrolysis has the advantage of lower temperatures, effectively preventing the volatilization of some radioactive nuclides and significantly reducing the difficulty of tail gas purification. Therefore, pyrolysis can be used as a pretreatment method for radioactive waste resin, and then plasma or cement curing methods can be used to further treat the waste resin.

[0005] Aluminosilicate minerals have strong curing properties for radionuclides. Sodalite, an aluminosilicate mineral with an SOD-type crystal structure, has shown that sodalite obtained through non-in-situ curing has poor curing ability for radionuclides. The temperature for synthesizing sodalite through in-situ curing is usually high (usually above 400℃), which accelerates the release of radionuclides. However, if sodalite is generated at a lower temperature, it is not conducive to the pyrolysis process of radioactive waste resin, thus reducing the volume reduction ratio of the waste resin.

[0006] Therefore, how to simultaneously achieve in-situ formation of sodalite and high-volume-reduction-ratio pyrolysis of radioactive waste resin at a lower temperature, so as to effectively fix radionuclides while effectively reducing the disposal pressure of radioactive waste resin, is an urgent problem to be solved. Summary of the Invention

[0007] In view of this, the present invention provides a radioactive waste resin pyrolysis catalyst composition and a method for pyrolysis treatment of radioactive waste resin. The present invention can achieve effective fixation of radionuclides at a relatively low temperature (200-300℃), while having a high pyrolysis volume reduction ratio and low cost, and has broad application prospects.

[0008] In a first aspect, the present invention provides a radioactive waste resin pyrolysis catalyst composition comprising 8-12 wt% hydrated copper salt, 52-55 wt% kaolin, 25-30 wt% sodium hydroxide and 9-12 wt% sodium chloride.

[0009] Preferably, the copper salt is selected from copper sulfate pentahydrate, copper nitrate dihydrate, or copper chloride dihydrate.

[0010] Secondly, the present invention provides a method for pyrolysis treatment of radioactive waste resin, comprising the following steps:

[0011] The radioactive waste resin pyrolysis catalyst composition is mixed evenly with the radioactive waste resin and then fed into the pyrolysis reaction unit. The mixture is heated to 200-300°C in an oxygen-containing atmosphere to carry out the pyrolysis reaction, thereby obtaining the waste resin residue after pyrolysis treatment.

[0012] Preferably, the mass ratio of the radioactive waste resin pyrolysis catalyst composition to the radioactive waste resin is (1-2):(8-9).

[0013] Preferably, the flow rate of the oxygen-containing atmosphere is 500–900 mL / min.

[0014] Preferably, the oxygen-containing atmosphere is a mixture of oxygen and an inert gas.

[0015] Furthermore, the volume fraction of oxygen is 8% to 30%.

[0016] Furthermore, the inert gas is selected from one or more of nitrogen and rare gases.

[0017] Preferably, the pyrolysis reaction takes 1.5 to 3 hours.

[0018] Preferably, the type of resin used in the radioactive waste resin is selected from one or more of cation exchange resins or anion exchange resins.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0020] In the radioactive waste resin pyrolysis catalyst composition provided by this invention, the Cu in the hydrated copper salt 2+ During the resin pyrolysis reaction, it can react with sulfonic acid groups to form metal sulfides, which are then oxidized in an oxygen-containing atmosphere to generate copper oxide. Due to the defective structure and electronic effect of copper oxide, it can catalyze the pyrolysis of waste resin and reduce the consumption of O2 in the reaction atmosphere, while achieving a high volume reduction ratio. In addition, under the synergistic effect of the alkali activator sodium hydroxide, the structure directing agent sodium chloride, and the hydrated copper salt, kaolin can be converted into sodalite at a lower temperature, thereby achieving the fixation of radionuclides at a lower temperature (200-300℃). Furthermore, the radioactive waste resin pyrolysis catalyst composition and the pyrolysis treatment method for radioactive waste resin provided by this invention have low cost and broad application prospects. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] The present invention provides a radioactive waste resin pyrolysis catalyst composition comprising 8-12 wt% hydrated copper salt, 52-55 wt% kaolin, 25-30 wt% sodium hydroxide and 9-12 wt% sodium chloride.

[0023] In the above-mentioned radioactive waste resin pyrolysis catalyst composition of the present invention, the Cu in the hydrated copper salt 2+During the resin pyrolysis reaction, it can react with sulfonic acid groups to form metal sulfides, which are then oxidized in an oxygen-containing atmosphere to generate copper oxide. Due to the defect structure and electronic effects of copper oxide, it can catalyze the pyrolysis of waste resin and reduce the consumption of O2 in the reaction atmosphere, while achieving a high volume reduction ratio. The crystal water of hydrated copper salt is removed during pyrolysis, and gaseous water molecules can promote the formation of sodalite. Under the synergistic effect of the alkali activator sodium hydroxide, the structure directing agent sodium chloride, and the hydrated copper salt, kaolin can be converted into sodalite at a relatively low temperature. Sodalite belongs to the cubic crystal system and is formed by the stacking of β-cage structures. It is a special microporous structure with a strong ability to solidify radionuclides. Therefore, this invention can achieve the fixation of radionuclides at a relatively low temperature (200-300℃).

[0024] In this invention, the copper salt is selected from copper sulfate pentahydrate, copper nitrate dihydrate, or copper chloride dihydrate; preferably copper sulfate pentahydrate.

[0025] The present invention also provides a method for pyrolysis treatment of radioactive waste resin, comprising the following steps:

[0026] The radioactive waste resin pyrolysis catalyst composition is mixed evenly with the radioactive waste resin and then fed into the pyrolysis reaction unit. The mixture is heated to 200-300°C in an oxygen-containing atmosphere to carry out the pyrolysis reaction, thereby obtaining the waste resin residue after pyrolysis treatment.

[0027] This invention first involves uniformly mixing the radioactive waste resin pyrolysis catalyst composition with the radioactive waste resin. This step allows the radioactive waste resin to pre-adsorb the radioactive waste resin pyrolysis catalyst composition, thereby facilitating the subsequent pyrolysis reaction. This invention does not impose any special limitations on the mixing method; commonly used mixing methods in the art are acceptable.

[0028] The pyrolysis reaction of this invention can be completed at 200-300℃, effectively preventing the volatilization of radioactive nuclides. The sodalite generated in situ during the pyrolysis process effectively immobilizes the radioactive nuclides. Furthermore, the catalytic effect of hydrated copper salts improves the pyrolysis efficiency of waste resin, resulting in a higher volume reduction ratio at lower temperatures and reducing the volume of solid residue.

[0029] This invention does not impose special limitations on the steps before and after the pyrolysis reaction. For example, before the pyrolysis reaction, it includes steps such as introducing inert gas to remove air from the pyrolysis reaction unit and raising the temperature to the pyrolysis reaction temperature; after the pyrolysis reaction, it includes a waste gas treatment step. Those skilled in the art can make adjustments according to actual process requirements.

[0030] In this invention, the mass ratio of the radioactive waste resin pyrolysis catalyst composition to the radioactive waste resin is (1-2):(8-9). A suitable mass ratio can achieve a better catalytic pyrolysis effect.

[0031] In this invention, the flow rate of the oxygen-containing atmosphere is 500–900 mL / min, more preferably 700–900 mL / min. The oxygen in the oxygen-containing atmosphere acts as a reactant gas, causing oxidative decomposition of the waste resin and simultaneously converting copper salts into copper oxide to promote pyrolysis.

[0032] In this invention, the oxygen-containing atmosphere is a mixture of oxygen and an inert gas, wherein the volume fraction of oxygen is 8-30%, more preferably 8-20%; and the inert gas is selected from one or more of nitrogen and rare gases, more preferably nitrogen.

[0033] In this invention, the pyrolysis reaction time is 1.5 to 3 hours. If the pyrolysis reaction time is too long, it will not significantly improve the volume reduction ratio, but will instead increase energy consumption.

[0034] In this invention, the radioactive waste resin is selected from one or more of cation exchange resins and anion exchange resins. The final product of cation exchange resin treatment is mainly sulfur dioxide, carbon dioxide, and water vapor; the product of anion exchange resin is mainly trimethylamine, carbon dioxide, and ethyl formate. When the two resins are mixed, they interact, and the mechanism of this interaction is unclear, making treatment more difficult. However, the pyrolysis treatment method of this invention can effectively treat the mixed waste resin.

[0035] The technical solution of the present invention will be further described below with reference to specific embodiments. In the following embodiments, the radioactive waste resin is a mixed resin of anion exchange resin and cation exchange resin, wherein the mass ratio of anion exchange resin to cation exchange resin is 1:5; the radioactive waste resin contains radioactive elements such as thorium (Th), cesium (Cs), and actinium (Ac).

[0036] Example 1

[0037] This embodiment provides a method for the pyrolysis treatment of radioactive waste resin.

[0038] In this embodiment, the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 9.1 wt% copper sulfate pentahydrate, 53.5 wt% kaolin, 26.7 wt% sodium hydroxide and 10.7 wt% sodium chloride.

[0039] Step 1: Connect the conveying unit, pyrolysis reaction unit, and waste gas treatment unit;

[0040] Step 2: Heat the tube furnace to 220°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continuously introduce nitrogen into the tube furnace at a flow rate of 800 mL / min to purge the air from the furnace.

[0041] Step 3: Mix the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin at a mass ratio of 1:9, and then transfer the mixture to the tube furnace through the conveying unit while introducing an oxygen-containing atmosphere (90% N2 and 10% O2) at a flow rate of 800 mL / min.

[0042] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using a heat source provided by a tubular furnace at a reaction temperature of 220℃ for 2 hours.

[0043] Step 5: The waste gas generated in Step 4 is discharged after being washed and filtered by the waste gas treatment unit to recover the radioactive nuclides it carries.

[0044] Example 2

[0045] This embodiment provides a method for the pyrolysis treatment of radioactive waste resin.

[0046] In this embodiment, the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 10.5 wt% copper sulfate pentahydrate, 52.6 wt% kaolin, 26.3 wt% sodium hydroxide and 10.5 wt% sodium chloride.

[0047] Step 1: Connect the conveying unit, pyrolysis reaction unit, and waste gas treatment unit;

[0048] Step 2: Heat the tube furnace to 220°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continuously introduce nitrogen into the tube furnace at a flow rate of 800 mL / min to purge the air from the furnace.

[0049] Step 3: Mix the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin at a mass ratio of 1:9, and then transfer the mixture to the tube furnace through the conveying unit while introducing an oxygen-containing atmosphere (90% N2 and 10% O2) at a flow rate of 800 mL / min.

[0050] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using a heat source provided by a tubular furnace at a reaction temperature of 220℃ for 2 hours.

[0051] Step 5: The waste gas generated in Step 4 is discharged after being washed and filtered by the waste gas treatment unit to recover the radioactive nuclides it carries.

[0052] Example 3

[0053] This embodiment provides a method for the pyrolysis treatment of radioactive waste resin.

[0054] In this embodiment, the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 9.1 wt% copper sulfate pentahydrate, 53.5 wt% kaolin, 26.7 wt% sodium hydroxide and 10.7 wt% sodium chloride.

[0055] Step 1: Connect the conveying unit, pyrolysis reaction unit, and waste gas treatment unit;

[0056] Step 2: Heat the tube furnace to 300°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continuously introduce nitrogen into the tube furnace at a flow rate of 800 mL / min to purge the air from the furnace.

[0057] Step 3: Mix the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin at a mass ratio of 1:9, and then transfer the mixture to the tube furnace through the conveying unit while introducing an oxygen-containing atmosphere (90% N2 and 10% O2) at a flow rate of 800 mL / min.

[0058] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using a heat source provided by a tubular furnace at a reaction temperature of 300℃ for 1.5 hours.

[0059] Step 5: The waste gas generated in Step 4 is discharged after being washed and filtered by the waste gas treatment unit to recover the radioactive nuclides it carries.

[0060] Example 4

[0061] This embodiment provides a method for the pyrolysis treatment of radioactive waste resin.

[0062] In this embodiment, the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 9.1 wt% copper sulfate pentahydrate, 53.5 wt% kaolin, 26.7 wt% sodium hydroxide and 10.7 wt% sodium chloride.

[0063] Step 1: Connect the conveying unit, pyrolysis reaction unit, and waste gas treatment unit;

[0064] Step 2: Heat the tube furnace to 250°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continuously introduce nitrogen into the tube furnace at a flow rate of 800 mL / min to purge the air from the furnace.

[0065] Step 3: Mix the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin at a mass ratio of 2:8, and then transfer the mixture to the tube furnace through the conveying unit while introducing an oxygen-containing atmosphere (90% N2 and 10% O2) at a flow rate of 800 mL / min.

[0066] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using a heat source provided by a tubular furnace at a reaction temperature of 250℃ for 2 hours.

[0067] Step 5: The waste gas generated in Step 4 is discharged after being washed and filtered by the waste gas treatment unit to recover the radioactive nuclides it carries.

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 1 is that the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 9.1 wt% nickel sulfate hexahydrate, 53.5 wt% kaolin, 26.7 wt% sodium hydroxide and 10.7 wt% sodium chloride.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is that the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 9.1 wt% ferric(III) sulfate hydrate, 53.5 wt% kaolin, 26.7 wt% sodium hydroxide and 10.7 wt% sodium chloride.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that the radioactive waste resin pyrolysis catalyst composition is obtained by mixing 58.8 wt% kaolin, 29.4 wt% sodium hydroxide and 11.8 wt% sodium chloride.

[0074] Comparative Example 4

[0075] The difference between this comparative example and Example 1 is that the radioactive waste resin pyrolysis catalyst composition was obtained by mixing 14.5 wt% copper sulfate pentahydrate and 85.5 wt% sodalite powder.

[0076] The volume reduction ratios of Examples 1-4 and Comparative Examples 1-4 ( The volume before and after volume reduction was measured by compression in the container, and the radioactive solidification rate in the exhaust gas (with the cesium content as a reference) was determined, as shown in Table 1.

[0077] Table 1. Volume reduction ratio and radioactive curing rate data for Examples 1-4 and Comparative Examples 1-4

[0078] Serial Number Reduction ratio Curing rate Serial Number Reduction ratio Curing rate Example 1 2.01 84％ Comparative Example 1 1.20 82％ Example 2 1.88 82％ Comparative Example 2 1.40 83％ Example 3 2.20 85％ Comparative Example 3 0.50 82％ Example 4 2.08 82％ Comparative Example 4 1.95 2％

[0079] Comparing Examples 1-4 and Comparative Examples 1-4, it can be seen that Example 3 has the largest volume reduction ratio of 2.20. Factors affecting the volume reduction ratio include pyrolysis temperature, the type and proportion of catalyst metal salts, etc., with temperature having a relatively small impact on the volume reduction ratio, while the type and proportion of metal salts have a significant impact. The cesium solidification rate in Examples 1-4 and Comparative Examples 1-3 shows little change, all reaching over 80%. The solidification rate in Example 4 is only 2%, which also indicates that the non-in-situ synthesized sodalite has a very small solidification effect on nuclides.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for pyrolysis treatment of radioactive waste resin, characterized in that, Includes the following steps: After the radioactive waste resin pyrolysis catalyst composition is mixed evenly with the radioactive waste resin, it is fed into the pyrolysis reaction unit and heated to 200~300℃ in an oxygen-containing atmosphere to carry out the pyrolysis reaction, thus obtaining the waste resin residue after pyrolysis treatment. The radioactive waste resin pyrolysis catalyst composition comprises 8-12 wt% hydrated copper salt, 52-55 wt% kaolin, 25-30 wt% sodium hydroxide and 9-12 wt% sodium chloride; The copper salt is selected from copper sulfate pentahydrate; The mass ratio of the radioactive waste resin pyrolysis catalyst composition to the radioactive waste resin is (1~2):(8~9).

2. The pyrolysis treatment method as described in claim 1, characterized in that, The flow rate of the oxygen-containing atmosphere is 500~900 mL / min.

3. The pyrolysis treatment method as described in claim 1, characterized in that, The oxygen-containing atmosphere is a mixture of oxygen and an inert atmosphere.

4. The pyrolysis treatment method as described in claim 3, characterized in that, The volume fraction of oxygen is 8-30%.

5. The pyrolysis treatment method as described in claim 3, characterized in that, The inert atmosphere is selected from one or more of nitrogen and rare gases.

6. The pyrolysis treatment method as described in claim 1, characterized in that, The pyrolysis reaction takes 1.5 to 3 hours.

7. The pyrolysis treatment method as described in claim 1, characterized in that, The type of resin used in the radioactive waste resin is selected from one or more of cation exchange resins or anion exchange resins.