Radioactive waste resin pyrolysis catalyst composition and pyrolysis treatment method of radioactive waste resin

Abstract

The invention discloses a radioactive waste resin pyrolysis catalyst composition and a radioactive waste resin pyrolysis treatment method, and belongs to the technical field of radioactive waste resin treatment. The radioactive waste resin pyrolysis catalyst composition provided by the invention comprises 8-12wt% of hydrated copper salt, 52-55wt% of kaolin, 25-30wt% of sodium hydroxide and 9-12wt% of sodium chloride. The radioactive waste resin pyrolysis catalyst composition and radioactive waste resin are uniformly mixed and then fed into a pyrolysis reaction unit, the temperature is raised to 200-300 DEG C in an oxygen-containing atmosphere for a pyrolysis reaction, and waste resin residues after pyrolysis treatment are obtained. The radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin pyrolysis treatment method can realize fixation of radionuclides at a low temperature, and the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin pyrolysis treatment method provided by the invention are low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive waste resin treatment, and in particular to a radioactive waste resin pyrolysis catalyst composition and a radioactive waste resin pyrolysis treatment method. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] With the advancement of radioactive isotope research and production, more and more radioactive waste resins are generated. The temporary storage of large amounts of radioactive waste resins in waste barrels will bring great safety hazards to the environment and personnel: the waste resins contain different types of radioactive nuclides with large differences in specific activity; long-term storage will cause powdering and hardening, which will damage the structure of the resin, and the radioactivity therein may also escape, causing compaction at the bottom of the container, making it difficult to recover and use; the waste resin is a diffuse substance that has not yet reached its final stable state and requires further safe treatment before final disposal.

[0004] There are two main directions for the treatment of radioactive waste resin: the first direction is not to destroy the organic structure of the resin itself, such as solidification method (cement solidification, asphalt solidification and plastic solidification, etc.) and high integral container method (HIC method), but this type of treatment method has low packaging capacity and will increase the total volume of waste, which runs counter to the original intention of minimizing treatment. The second direction is to destroy the resin structure, and the organic degradation of waste resin with the goal of reducing volume and converting into inorganic products is suitable for long-term storage and disposal; such as incineration, wet oxidation (acid boiling, Fenton oxidation and supercritical water oxidation, etc.) and pyrolysis. However, the incineration process will cause the release of radioactive nuclides, and wet oxidation is highly corrosive to equipment and will produce radioactive waste liquid, which requires stabilization treatment before disposal. Pyrolysis refers to the thermal decomposition of samples by high temperature under anaerobic conditions. It has the advantages of high volume reduction ratio and inorganic product. Compared with the incineration method, pyrolysis has the advantage of low temperature, which can effectively avoid the volatilization of some radioactive nuclides, thereby greatly reducing the difficulty of tail gas purification. Therefore, pyrolysis can be used as a pretreatment method for radioactive waste resin, and the waste resin can be further treated by plasma or cement curing.

[0005] Aluminosilicate minerals have strong solidification properties for radioactive nuclides. Among them, sodalite is an aluminosilicate mineral with a SOD-type crystal structure. Studies have shown that sodalite obtained by non-in-situ solidification has a very poor solidification ability for radioactive nuclides. The temperature of existing in-situ solidification synthetic sodalite is usually high (usually higher than 400°C), and high temperature will accelerate the escape of radioactive nuclides; however, if sodalite is generated at a lower temperature, it is not conducive to the thermal decomposition process of radioactive waste resin, which reduces the volume reduction ratio of the waste resin.

[0006] Therefore, how to simultaneously achieve the in-situ formation of sodalite and the high volume reduction ratio pyrolysis of radioactive waste resin at a relatively low temperature, so as to effectively fix the radioactive nuclides and reduce the disposal pressure of the 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 pyrolysis treatment method for radioactive waste resin. The present invention can achieve effective fixation of radioactive nuclides at a relatively low temperature (200-300°C), while the pyrolysis volume reduction is relatively high and the cost is low, and the application prospect is broad.

[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] In a second aspect, 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 a pyrolysis reaction unit. The temperature is raised to 200-300° C. in an oxygen-containing atmosphere to perform a pyrolysis reaction, thereby obtaining a 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 the oxygen is 8-30%.

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

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

[0018] Preferably, the type of the radioactive waste resin is selected from one or more of cation exchange resins and 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 the present invention, the Cu in the hydrated copper salt is 2+ It can react with sulfonic acid groups to form metal sulfides during the resin cracking reaction, and then be oxidized in an oxygen-containing atmosphere to generate copper oxide. Since copper oxide has a defective structure and electronic effect, it can catalyze the thermal decomposition 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 alkaline 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, thereby achieving the fixation of radioactive nuclides at a relatively low temperature (200-300°C). In addition, the radioactive waste resin thermal decomposition catalyst composition and the thermal decomposition treatment method of radioactive waste resin provided by the present invention have low costs and broad application prospects. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

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

[0023] In the above radioactive waste resin pyrolysis catalyst composition of the present invention, the Cu in the hydrated copper salt is 2+It can react with sulfonic acid groups to form metal sulfide during the resin cracking reaction, and then be oxidized in an oxygen-containing atmosphere to generate copper oxide. Since copper oxide has defective structure and electronic effect, it can catalyze the pyrolysis of waste resin and reduce the consumption of O2 in the reaction atmosphere, and can achieve a high volume reduction ratio. The crystal water of hydrated copper salt will be removed during the pyrolysis process, and the gas phase water molecules can promote the formation of sodalite to a certain extent. Under the synergistic effect of the alkaline activator sodium hydroxide, the structure-directing agent sodium chloride and the hydrated copper salt, kaolin can be transformed into sodalite at a lower temperature. Sodalite belongs to the cubic system and is formed by stacking β cage structures. It is a special microporous structure with strong curing ability for radioactive nuclides. Therefore, the present invention can achieve the fixation of radioactive nuclides at a lower temperature (200-300°C).

[0024] In the present 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 a pyrolysis reaction unit. The temperature is raised to 200-300° C. in an oxygen-containing atmosphere to perform a pyrolysis reaction, thereby obtaining a waste resin residue after pyrolysis treatment.

[0027] The present invention firstly mixes the radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin uniformly. This step can pre-adsorb the radioactive waste resin to the radioactive waste resin pyrolysis catalyst composition, thereby facilitating the subsequent pyrolysis reaction. The present invention does not impose any special restrictions on the mixing method, and the mixing method commonly used in the art can be used.

[0028] The pyrolysis reaction of the present invention can be completed at 200-300°C, which can effectively avoid the volatilization of radioactive nuclides; the sodalite generated in situ during the pyrolysis reaction can effectively fix the radioactive nuclides. In addition, the catalytic effect of the hydrated copper salt can improve the pyrolysis efficiency of the waste resin, so that it has a higher volume reduction ratio at a lower temperature and reduces the volume of the solid residue.

[0029] The present invention does not impose any special restrictions on the steps before and after the pyrolysis reaction. For example, before the pyrolysis reaction, an inert gas is introduced to remove the air in the pyrolysis reaction unit and the temperature is raised to the pyrolysis reaction temperature; after the pyrolysis reaction step, an exhaust gas treatment step is included. Those skilled in the art can adjust according to actual process requirements.

[0030] In the present 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 the present 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 reaction gas, which causes the waste resin to undergo oxidative cracking and can convert copper salts into copper oxide to promote thermal decomposition.

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

[0033] In the present invention, the pyrolysis reaction time is 1.5 to 3 hours. If the pyrolysis reaction time is too long, the volume reduction ratio will not be improved much, but energy consumption will be increased.

[0034] In the present invention, the type of the radioactive waste resin is selected from one or more of a cation exchange resin or an anion exchange resin. The cation resin treatment finally produces mainly sulfur dioxide, carbon dioxide and water vapor; the anion resin mainly produces trimethylamine, carbon dioxide and ethyl formate. When the two resins are mixed, they interact with each other, and the mechanism of action is unclear, so the treatment is more difficult, but the pyrolysis treatment method of the present invention can effectively treat the mixed waste resin.

[0035] The technical solution of the present invention is further described below in conjunction with 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 the anion exchange resin to the 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 pyrolysis treatment of radioactive waste resin.

[0038] In this embodiment, the radioactive waste resin thermal decomposition 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 transport unit, the pyrolysis reaction unit and the exhaust gas treatment unit;

[0040] Step 2: Heat the tubular furnace to 220°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continue to pass nitrogen into the tubular furnace at a flow rate of 800mL / min to exhaust the air in the furnace.

[0041] Step 3: The radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin are mixed in a mass ratio of 1:9, and then the mixture is transferred to a tubular furnace through a conveying unit, and an oxygen-containing atmosphere (90% N2 and 10% O2) is introduced at a flow rate of 800 mL / min;

[0042] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using the heat source provided by the tube furnace, the reaction temperature is 220°C, and the reaction time is 2 hours;

[0043] Step 5: The waste gas generated in step 4 is filtered and discharged after the radioactive nuclides it carries are recovered by the waste gas treatment unit.

[0044] Example 2

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

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

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

[0048] Step 2: Heat the tubular furnace to 220°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continue to pass nitrogen into the tubular furnace at a flow rate of 800mL / min to exhaust the air in the furnace.

[0049] Step 3: The radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin are mixed in a mass ratio of 1:9, and then the mixture is transferred to a tubular furnace through a conveying unit, and an oxygen-containing atmosphere (90% N2 and 10% O2) is introduced at a flow rate of 800 mL / min;

[0050] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using the heat source provided by the tube furnace, the reaction temperature is 220°C, and the reaction time is 2 hours;

[0051] Step 5: The waste gas generated in step 4 is filtered and discharged after the radioactive nuclides it carries are recovered by the waste gas treatment unit.

[0052] Example 3

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

[0054] In this embodiment, the radioactive waste resin thermal decomposition 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 transport unit, the pyrolysis reaction unit and the exhaust gas treatment unit;

[0056] Step 2: Heat the tubular furnace to 300°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continue to pass nitrogen into the tubular furnace at a flow rate of 800mL / min to exhaust the air in the furnace.

[0057] Step 3: The radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin are mixed in a mass ratio of 1:9, and then the mixture is transferred to a tubular furnace through a conveying unit, and an oxygen-containing atmosphere (90% N2 and 10% O2) is introduced at a flow rate of 800 mL / min;

[0058] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using the heat source provided by the tube furnace, the reaction temperature is 300°C, and the reaction time is 1.5h;

[0059] Step 5: The waste gas generated in step 4 is filtered and discharged after the radioactive nuclides it carries are recovered by the waste gas treatment unit.

[0060] Example 4

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

[0062] In this embodiment, the radioactive waste resin thermal decomposition 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 transport unit, the pyrolysis reaction unit and the exhaust gas treatment unit;

[0064] Step 2: Heat the tubular furnace to 250°C at a heating rate of 5°C / min, then open the nitrogen cylinder control valve and continue to pass nitrogen into the tubular furnace at a flow rate of 800mL / min to exhaust the air in the furnace.

[0065] Step 3: The radioactive waste resin pyrolysis catalyst composition and the radioactive waste resin are mixed in a mass ratio of 2:8, and then the mixture is transferred to a tubular furnace through a conveying unit, and an oxygen-containing atmosphere (90% N2 and 10% O2) is introduced at a flow rate of 800 mL / min;

[0066] Step 4: In the pyrolysis reaction unit, the waste resin is pyrolyzed using the heat source provided by the tube furnace, the reaction temperature is 250°C, and the reaction time is 2 hours;

[0067] Step 5: The waste gas generated in step 4 is filtered and discharged after the radioactive nuclides it carries are recovered by the waste gas treatment unit.

[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 % of iron (III) sulfate hydrate, 53.5 wt % of kaolin, 26.7 wt % of sodium hydroxide and 10.7 wt % of 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 % of kaolin, 29.4 wt % of sodium hydroxide and 11.8 wt % of 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 is obtained by mixing 14.5 wt % of copper sulfate pentahydrate and 85.5 wt % of sodalite powder.

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

[0077] Table 1 Volume reduction ratio and radioactive curing rate data of Examples 1 to 4 and Comparative Examples 1 to 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] By comparing Examples 1-4 and Comparative Examples 1-4, it can be seen that the maximum volume reduction ratio of Example 3 is 2.20. The factors affecting the volume reduction ratio include pyrolysis temperature, the type and proportion of the catalyst metal salt, etc. Among them, temperature has a small effect on the volume reduction ratio, and the type and proportion of the metal salt have a large effect. The cesium element solidification rate of Examples 1-4 and Comparative Examples 1-3 did not change much, both reaching more than 80%. The solidification rate of Example 4 is only 2%, which also shows that the non-in-situ synthesized sodalite has little effect on the solidification of nuclides.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A radioactive waste resin pyrolysis catalyst composition, characterized in that: The invention comprises 8-12 wt% of hydrated copper salt, 52-55 wt% of kaolin, 25-30 wt% of sodium hydroxide and 9-12 wt% of sodium chloride.

2. The radioactive waste resin pyrolysis catalyst composition according to claim 1, characterized in that: The copper salt is selected from copper sulfate pentahydrate, copper nitrate dihydrate or copper chloride dihydrate.

3. A method for pyrolysis treatment of radioactive waste resin, characterized in that: The steps include: The radioactive waste resin pyrolysis catalyst composition according to any one of claims 1 to 2 is mixed evenly with the radioactive waste resin and then fed into a pyrolysis reaction unit, and heated to 200 to 300° C. in an oxygen-containing atmosphere for pyrolysis reaction to obtain waste resin residue after pyrolysis treatment.

4. The pyrolysis treatment method according to claim 3, characterized in that: The mass ratio of the radioactive waste resin pyrolysis catalyst composition to the radioactive waste resin is (1-2):(8-9).

5. The pyrolysis treatment method according to claim 3, characterized in that: The flow rate of the oxygen-containing atmosphere is 500-900 mL / min.

6. The pyrolysis treatment method according to claim 3, characterized in that: The oxygen-containing atmosphere is a mixture of oxygen and inert gas.

7. The pyrolysis treatment method according to claim 6, characterized in that: The volume fraction of the oxygen is 8-30%.

8. The pyrolysis treatment method according to claim 6, characterized in that: The inert gas is selected from one or more of nitrogen and rare gases.

9. The pyrolysis treatment method according to claim 3, characterized in that: The pyrolysis reaction time is 1.5 to 3 hours.

10. The pyrolysis treatment method according to claim 3, characterized in that: The type of the radioactive waste resin is selected from one or more of cation exchange resin and anion exchange resin.