Ceramic solidified body for synergistically solidifying radioactive iodine and cesium as well as preparation method and application of ceramic solidified body

Abstract

The invention belongs to the technical field of radioactive waste treatment, and discloses a ceramic solidified body for synergistically solidifying radioactive iodine and cesium as well as a preparation method and application of the ceramic solidified body. The chemical formula of the ceramic solidified body is (Cs2xBa2-2x) (AgyNa1-y) IO6, x is equal to 0.1-0.9, y is equal to 0.1-0.9, and the ceramic solidified body is prepared by mixing silver iodide, barium hydroxide, sodium periodate and cesium carbonate, carrying out dry pressing molding under 20-60 MPa to obtain a rough blank, sintering at 500-700 DEG C, carrying out cold sintering at 200-300 DEG C, and finally annealing at 500-600 DEG C. The curing amount of iodine in the ceramic cured body is 2.4-20 wt%, the curing amount of cesium is 4-46 wt%, and the ceramic cured body has excellent chemical stability and is suitable for curing radioactive iodine and cesium and long-term geological treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of radioactive waste treatment, and more specifically, relates to a ceramic solidified body (Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6) and its preparation method and application. Background Art

[0002] The exploitation of a large amount of fossil energy has caused serious damage to the surface environment, and in the process of utilization, various types of waste that seriously pollute the human living environment are constantly generated. Nuclear energy, as a clean energy that can be used by people for a long time, occupies a very important position in replacing fossil energy and has become an indispensable alternative energy source. However, a large amount of fission products will be produced during nuclear testing and the nuclear fuel cycle. These radioactive wastes are extremely harmful to the environment and organisms. How to properly deal with these radioactive wastes is very important for the future sustainable development of nuclear energy. Radioactive cesium and iodine are both fission products produced during the operation of nuclear reactors. The former has a high yield and a longer half-life ( 135 Cs is about 2.3×10 6 The latter has high toxicity and long half-life (about 1.574×10 7 The two radionuclides are highly volatile, easy to diffuse, easily absorbed by the human body and enriched in the human thyroid gland, thus causing thyroid radiation damage and causing serious harm to human health. At present, the reasonable disposal measures for the two radionuclides are to solidify them and then carry out geological disposal.

[0003] The current mainstream method for disposing of radioactive cesium is mineral solidification, which mainly produces a thermodynamically stable multiphase mineral solid solution through phase reaction, so that the radioactive nuclides in the waste can directly enter the lattice position of the mineral phase and are thus encapsulated in the crystal structure of the mineral phase. The solidified body is mainly alkali manganese ore, apatite, etc., but there are problems such as poor stability of the solidified body during geological treatment, large loss of nuclides during the solid solution process, and low solidification efficiency.

[0004] The adsorption method has been widely used in the treatment of radioactive iodine due to its advantages such as high efficiency and low cost. Silver-impregnated activated carbon and silver-exchanged zeolite are currently the most widely used iodine adsorbent materials in industry. After adsorption, iodine exists in the form of silver iodide. However, the melting point of silver iodide is 558°C. It will decompose under high temperature conditions and cause secondary pollution. It is not enough to cope with complex geological environments. Further solidification treatment is required to form a solidified body with strong stability. The further treatment of AgI that adsorbs radioactive iodine is mainly to solidify it with a glass matrix, such as borosilicate glass, phosphate glass, etc. However, there is volatilization of iodine during the high-temperature dissolution process, and iodine is easily released from the glass during geological disposal. Therefore, it is necessary to seek a solidified body with better stability to minimize the threat to human health and environmental safety.

[0005] In the literature Cs3Bi2I9-hydroxyapatite composite waste forms for cesium andiodine immobilization., the authors proposed using Cs3Bi2I9 for the synergistic immobilization of radioactive iodine and cesium. However, the experimental results showed that the chemical stability of the non-oxide immobilized body was not good, and the normalized leaching rate at room temperature was about 10 g / (m 2 d), indicating that it is difficult to effectively fix these two nuclides. Ba2NaIO6, a double perovskite structure, has a thermal decomposition temperature of 1050°C and excellent chemical stability. Using it to fix cesium and iodine simultaneously can not only reduce the cost and process of solidifying the nuclides separately, but also cope with complex and harsh geological environments. It is promising to use it to simultaneously treat radioactive cesium and iodine. Summary of the invention

[0006] In order to solve the above-mentioned shortcomings and disadvantages of the prior art, the object of the present invention is to provide a synergistic solidification of iodine and cesium (Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6 ceramic solid body. First, Ag in AgI is dissolved into the position of sodium in Ba2NaIO6, while the radioactive iodine (I) adsorbed in AgI is supplemented into the position of iodine in the matrix, and cesium is dissolved into the position of barium in Ba2NaIO6 to form (Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6 compound, and finally effectively solidify the radioactive iodine and cesium, and the solidified body has low nuclide leaching rate, stable chemical properties, and can be used for long-term storage, thereby solving the problem of solidification of radioactive iodine and cesium in the treatment of nuclear waste, and has good practical significance and application background.

[0007] Another object of the present invention is to provide a method for preparing a ceramic solidified body by synergistically solidifying iodine and cesium, wherein silver iodide, barium hydroxide, sodium periodate and cesium carbonate are mixed, and AgI is firstly used to release heat during heating to increase the reaction activity, and then the target product (Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6 synthesis, and then the solidified body is cold sintered to reduce the volatilization and transfer of nuclides to obtain a dense (Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6 ceramic solidified body, to achieve the solidification of two nuclides.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A ceramic solidified body for synergistically solidifying radioactive iodine and cesium, wherein the chemical formula of the ceramic solidified body is (Cs 2x Ba 2-x )(Ag y Na 1-y )IO6, where x=0.1~0.9, y=0.1~0.9.

[0010] Preferably, the ceramic solidified body is prepared by mixing silver iodide, barium hydroxide, sodium periodate and cesium carbonate, dry pressing at 20-60 MPa to obtain a rough blank, sintering at 500-700°C, cold sintering at 200-300°C, and annealing at 500-600°C.

[0011] More preferably, the particle sizes of the silver iodide, barium hydroxide, sodium periodate and cesium carbonate are all 10 nm to 100 μm.

[0012] Preferably, the solidified iodine content in the ceramic solidified body is 2.4-20wt%, and the solidified cesium content is 4-46wt%.

[0013] The method for preparing the ceramic solidified body of synergistically solidified radioactive iodine and cesium comprises the following steps:

[0014] S1. Silver iodide, barium hydroxide, sodium periodate and cesium carbonate are mixed to obtain a mixed powder, and the mixed powder is dry-pressed at 20 to 60 MPa to obtain a rough blank;

[0015] S2. The rough blank is heated to 500-700°C and sintered for 5-10 hours, cooled to room temperature to obtain a ceramic powder, and the ceramic powder is added to ethanol to obtain a paste mixture;

[0016] S3. Pour the paste mixture into a mold, apply a pressure of 600-800 MPa, heat it to 200-300°C for cold sintering, then cool it to room temperature, dry it at 100-150°C, heat it to 500-600°C for annealing, and cool it naturally to obtain a ceramic solidified body of synergistically solidified radioactive iodine and cesium.

[0017] Preferably, the mixing in steps S1 and S2 is performed by mortar grinding, planetary ball milling or roller ball milling.

[0018] Preferably, the mass ratio of the ceramic powder to ethanol in step S2 is (1-5):1.

[0019] Preferably, the heating and cooling rates in steps S2 and S3 are both 5-10° C. / min.

[0020] Preferably, in step S3, the cold sintering time is 60 to 120 minutes, the drying time is 20 to 30 hours, and the annealing time is 5 to 10 hours.

[0021] The ceramic solidified body for synergistically solidifying radioactive cesium and iodine is used in the field of processing high-level radioactive waste.

[0022] The chemical equation in the reaction process of the present invention is as follows:

[0023] (2-2x)Ba(OH)2+xCs2CO3+yAgI+(1-y)NaIO4+(x / 2+2y)O2=(Cs 2x Ba 2-2x )(Ag y Na 1-y )IO6+(2-2x)H2O+xCO2.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention can fix both radioactive iodine and cesium in the perovskite matrix, realize the synergistic solidification of the two nuclides in the ceramic solid body, significantly improve the solidification efficiency, and the ceramic solid body has good thermal stability and stable chemical properties, which can meet the requirements of long-term storage.

[0026] 2. The present invention adopts a cold sintering method, which greatly reduces the volatilization loss of nuclides compared with the traditional sintering method, has higher curing efficiency and lower cost.

[0027] 3. The present invention adopts reaction sintering, utilizing the heat released by silver iodide during the heating process to increase the reaction activity and make the reaction easier to proceed. DETAILED DESCRIPTION

[0028] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0029] Example 1

[0030] 1. Grind and mix 0.843 g of silver iodide, 6.912 g of sodium periodate, 1.170 g of cesium carbonate and 11.075 g of barium hydroxide for 1 hour, and pass through a 200-mesh sieve to obtain a mixed powder with a particle size of 10 nm to 100 μm;

[0031] 2. Dry-press the mixed powder under a pressure of 20 MPa to obtain a rough blank; place the rough blank in a muffle furnace and heat it to 600°C at 5°C / min, sinter it for 5 hours, then cool it to room temperature, grind it into powder with a mortar and pass it through a 200-mesh sieve, add 25 mL of ethanol and mix it to obtain a paste mixture;

[0032] 3. Pour the paste mixture into a stainless steel mold, apply a uniaxial pressure of 600 MPa using a tablet press, and heat it to 200 °C at 5 °C / min for cold sintering. After sintering for 2 hours, cool it to room temperature, demould it, dry it at 100 °C for 20 hours, and finally heat it to 500 °C at 10 °C / min for annealing for 5 hours, and cool it naturally to obtain a densified (Cs 0.2 Ba 1.8 )(Ag 0.1 Na 0.9 )IO6 ceramic solid body.

[0033] The solidified contents of iodine and cesium in the ceramic solidified body are 2.4wt% and 5.03wt% respectively. The density of the solidified body is about 92%, and the normalized leaching rate of Cs and I is about 10 -4 ~10 -3 g / (m2*d), has good chemical durability, meets the requirements of long-term geological disposal, and can be used for long-term storage.

[0034] Example 2

[0035] The difference from Example 1 is that in step 1, the masses of silver iodide, sodium periodate, cesium carbonate, and barium hydroxide are 7.544 g, 0.764 g, 10.469 g, and 1.223 g, respectively, and their molar ratios are 0.9:0.1:0.9:0.2. In step 2, the sintering temperature is 700°C, and in step 3, the annealing temperature is 600°C, and the annealing time is 5 h, to obtain (Cs 1.8 Ba 0.2 )(Ag 0.9 Na 0.1 )IO6 ceramic solid body.

[0036] The iodine and cesium contents of the ceramic solidified body are 19.39 wt % and 40.62 wt % respectively, and the density of the solidified body is about 93%.

[0037] Example 3

[0038] The difference from Example 1 is that in step 1, the masses of silver iodide, sodium periodate, cesium carbonate, and barium hydroxide are 0.864 g, 7.084 g, 10.791 g, and 1.261 g, respectively, and their molar ratios are 0.1:0.9:0.9:0.2. In step 2, the sintering temperature is 700°C, and in step 3, the annealing temperature is 600°C, and the annealing time is 10 h, to obtain (Cs 1.8 Ba 0.2 )(Ag 0.1 Na 0.9 )IO6 ceramic solid body.

[0039] The iodine and cesium contents of the ceramic solidified body are 2.44 wt % and 45.91 wt % respectively, and the density of the solidified body is about 94 %.

[0040] Example 4

[0041] The difference from Example 1 is that in step 1, the masses of silver iodide, sodium periodate, cesium carbonate, and barium hydroxide are 7.366 g, 0.746 g, 1.136 g, and 10.752 g, respectively, and their molar ratios are 0.9:0.1:0.1:1.8. In step 2, the sintering temperature is 500°C, and in step 3, the annealing temperature is 600°C, and the annealing time is 5 h, to obtain (Cs 0.2 Ba 1.8 )(Ag 0.9 Na 0.1 )IO6 ceramic solid body.

[0042] The solidified contents of iodine and cesium in the ceramic solidified body are 19.16 wt % and 4.46 wt % respectively, and the density of the solidified body is about 92%.

[0043] Example 5

[0044] The difference from Example 1 is that in step 1, the masses of silver iodide, sodium periodate, cesium carbonate, and barium hydroxide are 4.203 g, 3.829 g, 5.833 g, and 6.135 g, respectively, and the molar ratio is 0.5:0.5:0.5:1. In step 2, the sintering temperature is 700°C, in step 3, the pressure is 700 MPa, the annealing temperature is 600°C, and the annealing time is 10 h, and (Cs 1.0 Ba 1.0 )(Ag 0.5 Na 0.5 )IO6 ceramic solid body.

[0045] The iodine and cesium contents of the ceramic solidified body are 11.36 wt % and 23.79 wt % respectively, and the density of the solidified body is about 95%.

[0046] The iodine solidification content of the ceramic solidified body of the present invention is 2.4-20wt%, the cesium solidification content is 4-46wt%, the density of the ceramic solidified body is above 92%, the ceramic solidified body has stable chemical properties and low cost, and is suitable for the solidification of radioactive iodine and cesium and long-term geological disposal.

[0047] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A ceramic solidified body for synergistically solidifying radioactive iodine and cesium, characterized in that: The chemical formula of the ceramic solid body is (Cs 2x Ba 2-x )(Ag y Na 1-y )IO6, where x=0.1~0.9, y=0.1~0.

9.

2. The ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 1, characterized in that: The ceramic solidified body is prepared by mixing silver iodide, barium hydroxide, sodium periodate and cesium carbonate, dry pressing at 20-60 MPa to obtain a rough blank, sintering at 500-700°C, cold sintering at 200-300°C, and annealing at 500-600°C.

3. The ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 2, characterized in that: The particle sizes of the silver iodide, barium hydroxide, sodium periodate and cesium carbonate are all 10nm-100μm.

4. The ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 1, characterized in that: The solidified iodine content in the ceramic solidified body is 2.4-20wt%, and the solidified cesium content is 4-46wt%.

5. The method for preparing a ceramic solidified body of synergistically solidified radioactive iodine and cesium according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Silver iodide, barium hydroxide, sodium periodate and cesium carbonate are mixed to obtain a mixed powder, and the mixed powder is dry-pressed at 20 to 60 MPa to obtain a rough blank; S2. The rough blank is heated to 500-700°C and sintered for 5-10 hours, cooled to room temperature to obtain a ceramic powder, and the ceramic powder is added to ethanol to obtain a paste mixture; S3. Pour the paste mixture into a mold, apply a pressure of 600-800 MPa, heat it to 200-300°C for cold sintering, then cool it to room temperature, dry it at 100-150°C, heat it to 500-600°C for annealing, and cool it naturally to obtain a ceramic solidified body of synergistically solidified radioactive iodine and cesium.

6. The method for preparing a ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 5, characterized in that: The mixing in steps S1 and S2 is performed by mortar grinding, planetary ball milling or roller ball milling.

7. The method for preparing a ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 5, characterized in that: The mass ratio of the ceramic powder to ethanol in step S2 is (1-5):

1.

8. The method for preparing a ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 5, characterized in that: The heating and cooling rates in steps S2 and S3 are both 5-10°C / min.

9. The method for preparing a ceramic solidified body of synergistically solidified radioactive iodine and cesium according to claim 5, characterized in that: In step S3, the cold sintering time is 60 to 120 minutes, the drying time is 20 to 30 hours, and the annealing time is 5 to 10 hours.

10. Use of the ceramic solidified body of synergistically solidified radioactive cesium and iodine according to any one of claims 1 to 4 in the field of treating high-level radioactive waste.