A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ.

Abstract

This invention provides a method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salts in situ, belonging to the field of radioactive waste salt solidification treatment technology in the dry reprocessing of spent fuel. The invention involves mixing 4A zeolite powder, radioactive waste salts, alkali metal chloride salts, and a dispersant at a specific liquid-to-solid ratio, followed by heating and drying to obtain a solidification precursor. The precursor is then ground, sieved, and sintered at temperatures not exceeding 900°C to obtain a solidified sodalite body. The method provided by this invention features low energy consumption, simple operation, low 4A zeolite usage, high radioactive waste salt coating rate, and high radioactive element fixation. The synthesized solidified sodalite body exhibits strong thermal stability and high mechanical hardness, with a normalized leaching rate of less than 5 x 10⁻⁶ after soaking in water at 90°C for 28 days. ‑ 4 g / (cm 2 ·d) The sodalite solidified body of the present invention can be geologically stored for a long time, effectively reducing the risk of migration, diffusion and leakage of radioactive materials.

Description

Technical Field

[0001] This invention relates to the field of radioactive waste salt solidification treatment technology in the dry reprocessing of spent fuel, specifically to a method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ. Background Technology

[0002] Nuclear energy has been widely adopted worldwide due to its high energy density, low carbon footprint, and low electricity cost. However, with the rapid development of the nuclear energy industry, efficient and safe spent fuel waste salt treatment technology is one of the keys to achieving the recycling of fast reactor spent fuel and the complete disposal of waste salt. Traditional spent fuel waste salt treatment methods, such as wet processing, suffer from problems such as complex operation, high cost, low processing efficiency, and potential secondary pollution. Currently, dry reprocessing technology is a promising approach for spent fuel waste salt treatment. Dry reprocessing technology mainly involves molten salt electrolytic refining and reduction treatment, aiming to extract valuable materials from used nuclear fuel, while also generating a certain amount of radioactive waste. LiCl-Li2O waste salt, as a byproduct of the electrolytic reduction process, mainly includes fragmented elements (including Cs, Sr, Ba, Ce, etc.) and chlorine, which have extremely high water solubility and radioactivity, strong migration and transformation capabilities in the environment, and are difficult to capture and fix. Improper disposal can cause environmental harm. Therefore, the proper treatment of radioactive waste remains a challenge.

[0003] Among numerous post-processing technologies, solidification and stabilization is an effective strategy. The resulting solidified body not only prevents the migration of radionuclides but also establishes a natural barrier to block radioactivity. Stabilization materials must possess properties such as chemical resistance, heat resistance, radiation resistance, hydrolysis resistance, and low radionuclide leaching rates. Traditional immobilization materials, such as cement and asphalt, have poor thermal and radiation stability, limiting their application to low-level liquid waste. Furthermore, vitrification and asphalt immobilization technologies are energy-intensive, have low solubility for chloride-form fission elements, and require sintering temperatures exceeding 1000 °C, easily leading to the volatilization and escape of target nuclides. Therefore, developing stabilization materials that can effectively capture radioactive fragments and chloride from radioactive liquid waste, molten salt, and solid waste salt and immobilize them within inorganic material structures is crucial for reducing energy consumption, simplifying radioactive waste treatment processes, and ensuring safe disposal.

[0004] Artificial rock solidification technology uses environmentally friendly and inexpensive materials to synthesize artificial rocks through optimized proportions. It can embed fragmented elements and chlorine elements from waste salt into the crystal lattice of mineral phases or adsorb them inside and outside the framework structure, thereby achieving targeted capture and isomorphic substitution solidification of different fragmented elements. This transforms waste salt into a harmless solid form with strong thermal stability, radiation resistance, chemical stability, and geological stability, thereby improving the stability of radionuclides in the solidified artificial rock and effectively reducing the risk of migration and diffusion of radioactive materials.

[0005] Natural minerals such as sodalite and perovskite are used for long-term fixation of radionuclides, exhibiting excellent chemical and mechanical stability and low nuclide leaching rates. Sodalite, in particular, can simultaneously embed fragments and chlorine elements within its crystal lattice, demonstrating good long-term safety under deep geological treatment conditions. Considering factors such as solidification process, cost, mechanical strength, chemical stability, and normalized leaching rate, sodalite is considered a preferred mineral-based material for solidifying fragments and chlorine elements.

[0006] Sodalite (Na8Al6Si6O) 24 Cl2 is a chloride-containing sodium aluminum silicate mineral, belonging to the feldspar-like minerals. Its crystal structure belongs to the P-43n cubic space group, with the basic structural unit being the β-cage. AlO4 and SiO4 tetrahedra are linked together by sharing oxygen atoms, forming four-membered and six-membered rings. These four-membered and six-membered rings are further joined together by sharing edges to form an aluminosilicate framework structure with a diameter of 6.5 Å, becoming the β-cage. The six-membered ring of the β-cage is approximately 2.6 Å in size, allowing some ions to pass through and providing an effective diffusion path for ions within the cage. Through the sharing of four-membered rings, the β-cages are stacked in a simple cubic array, with four Na atoms forming a single ring. + Located within the β cage, it combines with the anion at the center of the cage to form a tetrahedron, Na + Located on the central axis of the six-membered ring, Cl - Located at site 2a in the center of the β cage. Its unique porous structure and ion exchange capacity can fix metal ions inside the cage structure, inhibiting their diffusion and achieving the purpose of nuclide solidification.

[0007] In summary, this invention provides a sodalite solidified body and its solidification method that features low energy consumption during synthesis, simple process operation, small amount of solidified substrate, high radioactive waste salt coating rate, high fixation of radioactive element chlorides, and geological storage stability, thereby greatly reducing the environmental hazards of radioactive elements in radioactive waste salt. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, this invention provides a method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ. By using a small amount of 4A zeolite, more radioactive waste salt can be converted into a stable and harmless solid form, which is beneficial for long-term geological storage and effectively reduces the risk of migration, diffusion, and leakage of radioactive materials.

[0009] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0010] A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ includes the following steps:

[0011] (1) Solid raw materials, including 4A zeolite powder, radioactive waste salt, and alkali metal chloride salt, are mixed with a dispersant at a certain liquid-solid ratio, and then heated and dried to obtain a solidified precursor; wherein the mass ratio of 4A zeolite to alkali metal chloride is (3~5):1; and the mass percentage of radioactive waste salt in the total weight of solid raw materials is 15%~45%;

[0012] (2) Grind, sieve and sinter the solidified precursor to obtain sodalite solidified body.

[0013] The mechanism of this invention for synthesizing sodalite and simultaneously solidifying radioactive waste salt in situ involves controlling the content of sodalite and nepheline in the solidified sodalite body by adjusting the proportion of 4A zeolite powder and alkali metal chloride salt in the solid raw materials and controlling the sintering temperature. Combined with processes such as lattice solidification, adsorption, chemical coordination, and ion exchange, this allows more fragmented elements and chlorides in the radioactive waste salt to be embedded in the artificial rock framework and lattice, or adsorbed inside and outside the structure. This achieves targeted capture of a large number of different elements and isomorphic substitution through lattice solidification, thereby converting all radioactive waste salt into a stable and harmless solid form, which is beneficial for long-term geological storage and effectively reduces the risk of migration, diffusion, and leakage of radioactive elements in the waste salt. Calculations show that the fixation amount of radioactive chlorides in the solidified sodalite body of this invention is as high as 5.061%~15.183%.

[0014] Furthermore, the radioactive waste salt includes radioactive waste salt from the electrolytic reducing salt LiCl-Li2O system or the electrolytic refining salt LiCl-KCl system.

[0015] This invention uses an appropriate proportion of alkali metal chloride salts to reduce the amount of 4A zeolite. Furthermore, 4A zeolite powder, radioactive waste salt, and alkali metal chloride salt are mixed with a solidified precursor at a specific temperature. By controlling the sintering temperature and adjusting the proportion of 4A zeolite powder, radioactive waste salt, and alkali metal chloride salt, the sintered sodalite solidified body is controlled to be a sodalite-nepheline mixture.

[0016] The radioactive waste salts involved in this invention include radioactive waste salts in the LiCl-Li2O system or the electrolytically refined LiCl-KCl system. The residues contain elements such as Cl and Li required for the synthesis of sodalite. Li can replace Na sites and enter the crystal structure of sodalite; on the other hand, alkaline earth metals such as Sr can occupy the basic structure of sodalite AlSiO4. Therefore, the method provided by this invention has its own advantages in solidifying chloride waste salt systems. This invention utilizes the characteristic that alkali metal chloride salts generally have good water solubility or dispersibility. Radioactive waste salts in the LiCl-Li2O system or the electrolytically refined LiCl-KCl system are mixed with alkali metal chloride salts and 4A zeolite in water to prepare a waste salt solidification precursor solution. The water is then evaporated to obtain the solidified precursor for synthesizing sodalite. Sodalite is then synthesized through a high-temperature synthesis and sintering process. This invention uses radioactive waste salts, 4A zeolite (Na... 12 (AlSiO4) 12 The reaction formula for synthesizing sodalite solidified body from raw materials including alkali metal chloride salts (XCl) is shown below:

[0017] Na 12 (AlSiO 4 ) 12 + (4-nx)XCl + nMCl → 2Na (8-nx) M n Al 6 Si 6 O 24 Cl 2

[0018] This invention analyzes the composition and characteristics of radioactive waste salt residue, using 4A zeolite, alkali metal chloride salt, and radioactive waste salt as raw materials. It utilizes the uniform dispersion characteristics of a dispersant in an open system and at specific temperatures to formulate a solidification precursor, and then synthesizes a sodalite solidified body in situ at high temperature. The invention investigates the effects of conditional parameters (temperature, time, coating rate, pressure) on the synthesis of the sodalite solidified body and the solidification of radioactive waste salt during the solidification process. Furthermore, it evaluates the effects and mechanisms of action of the sodalite solidified body on radioactive elements using material characterization methods and normalized leaching rate experiments. This provides theoretical support for the synthesis of novel sodalite solidification materials and a basis for simulating the solidification of radioactive waste salt. It contributes to establishing sodalite solidification technology and its safe application procedures in waste salt treatment and disposal, and provides technical guidance for the practical application of this technology in the field of industrial radioactive waste salt solidification.

[0019] Furthermore, in step (1), the particle size of the 4A zeolite powder is within 1 nm.

[0020] Further, in step (1), the alkali metal chloride salt is one or more of lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl).

[0021] Further, in step (1), the dispersant is one or more of water, ethanol, and acetone.

[0022] Further, in step (1), the liquid-to-solid ratio of the solid raw material to the dispersant is (4~6):1.

[0023] Furthermore, in step (1), the temperature of the heat treatment is 60~100 ℃ and the time is 6~12 h.

[0024] Furthermore, in step (1), the drying temperature is 100 °C and the time is 15~30 h.

[0025] Furthermore, in step (2), the sintering temperature is 600~900 ℃ and the time is 2~12 h.

[0026] Furthermore, in step (2), the pressure applied during sintering when the solidified precursor powder is placed in a mold and pressed into a block ranges from 30 to 70 MPa.

[0027] Further, in step (2), the sintering is carried out in an inert gas atmosphere and is divided into the following three steps: the first step is to heat up at a rate of 5 ℃ / min until the target temperature of 600~900 ℃ is reached; the second step is to hold at 600~900 ℃ for 2~12 h; the third step is to cool down at a rate of 5 ℃ / min until the sodalite solidified body is obtained after cooling down to room temperature.

[0028] Furthermore, the specific steps of the method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ are as follows:

[0029] (1) 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder;

[0030] (2) Preparation of solidified precursor: Mix 4A zeolite powder, radioactive waste salt, alkali metal chloride salt and dispersant at a liquid-solid ratio of (4~6):1, and heat in a 75 ℃ water bath with magnetic stirring at 200 r / min for 8 h. Dry the resulting slurry in a 100 ℃ oven for 15~30 h to obtain the solidified precursor.

[0031] (3) High-temperature sintering: The solidified precursor is ground in an agate mortar for 30 min and then passed through a 0.1 mm sieve. The powder is then sintered at a temperature of 600~900 ℃ for 2~12 h to obtain a solidified sodalite body.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] 1. This invention addresses the problem that existing LiCl-Li2O or electrolytically refined LiCl-KCl systems for solidifying radioactive waste salts cannot efficiently and stably solidify radioactive elements (due to the easy migration and difficulty in capturing fragments and chlorine). It provides an economical, environmentally friendly, low-energy-consumption, simple, safe, reliable, and chemically stable method for solidifying sodalite waste salts that meets the requirements for long-term stable disposal of radioactive waste. This invention uses a small amount of sodalite solidification substrate (and a small amount of 4A zeolite), while achieving a high radioactive waste salt coating rate, enabling long-term stable storage. The method provided by this invention has considerable economic and ecological benefits and is applicable to the adsorption and immobilization of radioactive waste in aqueous solutions, molten salts, and solid waste salts.

[0034] 2. Compared with existing glass or ceramic curing technologies, the method provided by this invention uses readily available raw materials, is economical and environmentally friendly, has a simple operation process, and causes no secondary pollution. Furthermore, it exhibits good compatibility with the dissolution of fracturing elements and chlorine, with a waste salt inclusion rate as high as 45%. The synthesized sodalite cured body has strong thermal stability and high mechanical hardness, and its normalized leaching rate after soaking in water at 90 ℃ for 28 days is less than 5 x 10⁻⁶. -4 g / (cm 2 ·d) It can be stored stably for a long time. Attached Figure Description

[0035] Figure 1 SEM and EDS images of 4A zeolite;

[0036] Figure 2 The XRD phase analysis results of 4A zeolite and its solidified precursor are shown in the figure.

[0037] Figure 3 The XRD phase analysis results are shown for the sodalite solidified bodies synthesized at different sintering temperatures in Example 1.

[0038] Figure 4 The image shows the XRD phase analysis results of the sodalite solidified bodies synthesized using different sintering times in Example 2.

[0039] Figure 5 The image shows the XRD phase analysis results of the sodalite solidified bodies synthesized using radioactive waste salts with different mass percentages in Example 3.

[0040] Figure 6 The image shows the XRD phase analysis results of the sodalite solidified body synthesized using radioactive waste salts of different mass percentages in Example 3 after being soaked in water at 90 °C for 28 days.

[0041] Figure 7 Fourier transform infrared spectra of zeolite 4A, the solidified precursor, and the synthesized sodalite solidified body in Example 3;

[0042] Figure 8 The specific surface area and pore size analysis results of zeolite 4A and the synthesized sodalite solidified body in Example 3 are shown below.

[0043] Figure 9 The results are TG and DSC values ​​for the cured precursor and the synthesized sodalite cured body in Example 3.

[0044] Figure 10 This is a schematic diagram of the two-step high-temperature short-time sintering method in Example 4;

[0045] Figure 11 The density and porosity test results of the sodalite solidified body synthesized in Example 4 are shown below.

[0046] Figure 12 The hardness test results are for the sodalite solidified body synthesized in Example 4. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] This invention provides a method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ, comprising the following steps:

[0049] (1) Solid raw materials, including 4A zeolite powder, radioactive waste salt, and alkali metal chloride salt, are mixed with a dispersant at a certain liquid-solid ratio, and then heated and dried to obtain a solidified precursor; wherein the mass ratio of 4A zeolite to alkali metal chloride is (3~5):1; and the mass percentage of radioactive waste salt in the total weight of solid raw materials is 15%~45%;

[0050] (2) Grind, sieve and sinter the solidified precursor to obtain sodalite solidified body.

[0051] In some examples, the radioactive waste salt includes radioactive waste salt from the electrolytic reducing salt LiCl-Li2O system or the electrolytic refining salt LiCl-KCl system.

[0052] In some examples, the liquid-to-solid ratio of the solid raw material to the dispersant is (4~6):1.

[0053] In some examples, the alkali metal chloride salt is one or more of LiCl, NaCl, and KCl.

[0054] In some examples, the dispersant is one or more of water, ethanol, and acetone.

[0055] In some examples, the heat treatment is performed at a temperature of 60-100 °C for a duration of 6-12 h.

[0056] In some examples, the sintering temperature is 600~900 °C and the time is 2~12 h.

[0057] In some examples, the pressure applied during sintering, where the cured precursor powder is placed in a mold and pressed into a block, ranges from 30 to 70 MPa.

[0058] In the following specific embodiments, the 4A zeolite has a purity of 99% and was purchased from Sinopharm; the alkali metal chloride salt is sodium chloride with a purity of 99% and was purchased from Sinopharm; the radioactive waste salt is simulated LiCl-Li2O system radioactive waste salt, comprising the following components by mass percentage: 32.76% LiCl, 33.50% Li2O, 12.56% CsCl, 11.13% BaCl2, 6.36% SrCl2, and 3.69% CeCl3; details are shown in Table 1; wherein, the LiCl has a purity of 99% and was purchased from Sinopharm; the Li2O has a purity of 99% and was purchased from Sinopharm; the BaCl2 has a purity of 99% and was purchased from Sinopharm; the CsCl has a purity of 99% and was purchased from Aladdin; the SrCl2 has a purity of 99% and was purchased from Maclean; and the CeCl3 has a purity of 99% and was purchased from Sinopharm.

[0059] Table 1: Composition of simulated radioactive waste salt

[0060]

[0061] In the following specific embodiments, the sintered product was subjected to phase identification by X-ray diffraction (XRD) using Cu Ka radiation (λ=1.5418 Å), operated at 60 kV and 55 mA, with scanning parameters of 10. o -70 o The step size is 0.002.

[0062] In the following specific embodiments, the microstructure and morphology of 4A zeolite were observed using a scanning electron microscope (SEM, Zeiss SIGMA) equipped with an energy dispersive spectroscopy (EDS, Oxford X-max 55).

[0063] In the following specific embodiments, Fourier transform infrared spectroscopy (FTIR) was used to test the functional groups of 4A zeolite, the solidified precursor, and the synthesized sodalite. 4A zeolite, the solidified precursor, and the synthesized sodalite were respectively compressed with KBr into pellets, and the spectral range was 400–4000 cm⁻¹. -1 Within the detection range, the resolution is better than 0.4 cm. -1 Beam accuracy better than 0.01 cm -1 .

[0064] In the following specific embodiments, the concentrations of ions (Cs, Ba, Sr, Ce) in the leaching solution of the sintered product were determined by inductively coupled plasma mass spectrometry (ICP-MS, PQ-MS).

[0065] In the following specific embodiments, the specific surface area and pore size of the sodalite solidified body were tested using a fully automated specific surface area and porosity analyzer (BET, Micromeritics ASAP 2460). Before the test, the sodalite solidified body was degassed at 300 °C for 4 h.

[0066] In the following specific embodiment, the thermal stability of the sample was determined using a simultaneous thermal analyzer (HITACHI STA200) under an Ar atmosphere, with the temperature increased from room temperature to 900 °C at a rate of 5 °C / min.

[0067] Example 1

[0068] A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ includes the following steps:

[0069] S1. 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder. Figure 1 The SEM / EDS images show the structure and elemental distribution of 4A zeolite. As can be seen from the figure, the Al:Si ratio in 4A zeolite is close to 1:1.

[0070] S2. 15% (by mass) of radioactive waste salt, 4A zeolite powder, sodium chloride, and water are mixed evenly at a liquid-to-solid ratio of 5:1, wherein the mass ratio of 4A zeolite powder to sodium chloride is 4:1. The mixture is then heated in a 75 ℃ water bath at 200 r / min for 8 h with magnetic stirring. After the water has evaporated, the slurry is dried in a 100 ℃ oven with forced air for 24 h to obtain the solidified precursor. Figure 2XRD phase analysis results showed that the main phases of the cured precursor were sodium chloride salt and type A zeolite aluminosilicate, indicating that the cured precursor was basically consistent with the raw material and no new phases were generated.

[0071] S3. After grinding the cured precursor in an agate mortar for 30 min, the powder was passed through a 0.1 mm sieve. The cured precursor powder was then sintered in a muffle furnace under Ar atmosphere and normal pressure at sintering temperatures of 600, 650, 700, 750, 800, 850 and 900 °C for 2 h, with heating and cooling rates of 5 °C / min, to obtain the cured sodalite.

[0072] Figure 3 XRD phase analysis results show that the sodalite solidified body obtained at sintering temperature below 800 ℃ is mainly composed of aluminosilicate, while the sodalite solidified body obtained at sintering temperature of 800 ℃ and above is mainly composed of sodalite phase.

[0073] Example 2

[0074] A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ includes the following steps:

[0075] S1. 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder.

[0076] S2. 15% (by mass) of radioactive waste salt, 4A zeolite powder, sodium chloride, and water are mixed evenly at a liquid-to-solid ratio of 5:1, wherein the mass ratio of 4A zeolite powder to sodium chloride is 4:1. The mixture is then heated in a 75 ℃ water bath at 200 r / min for 8 h with magnetic stirring. After the water has evaporated, the slurry is dried in a 100 ℃ oven with forced air for 24 h to obtain the solidified precursor.

[0077] S3. After grinding the cured precursor in an agate mortar for 30 min, the powder was passed through a 0.1 mm sieve and sintered in a muffle furnace at 800 °C for 1, 2, 4, 6, 8, and 10 h under Ar atmosphere and normal pressure, respectively, with a heating and cooling rate of 5 °C / min, to obtain the cured sodalite body.

[0078] Figure 4 XRD phase analysis results showed that the sodalite solidified body obtained by sintering time of 2 and 4 h was a sodalite phase; the sodalite solidified body obtained by sintering time of 8 and 10 h was a mixed phase of sodalite and nepheline phases.

[0079] Example 3

[0080] A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ includes the following steps:

[0081] S1. 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder.

[0082] S2. Radioactive waste salts at mass percentages of 15%, 25%, 35%, and 45% were mixed with 4A zeolite powder, sodium chloride, and water at a liquid-to-solid ratio of 5:1, wherein the mass ratio of 4A zeolite powder to sodium chloride was 4:1. The mixture was then heated in a 75 ℃ water bath with magnetic stirring at 200 r / min for 8 h. After the water had evaporated, the slurry was dried in a 100 ℃ oven with forced air for 24 h to obtain the solidified precursor.

[0083] S3. After grinding the cured precursor in an agate mortar for 30 min, it was passed through a 0.1 mm sieve. The cured precursor powder was sintered at 800 °C for 2 h in an Ar atmosphere and at normal pressure in a muffle furnace, with a heating and cooling rate of 5 °C / min, to obtain the sodalite cured body.

[0084] The amount of radioactive element chloride solidified in the sodalite solidified body synthesized in this embodiment is shown in Table 2.

[0085] Table 2: Amount of radioactive elements solidified in the sodalite solidified body synthesized in Example 3

[0086]

[0087] Figure 5 The XRD phase analysis results of sodalite solidified bodies prepared using radioactive waste salt with different mass percentages are shown. The results show that when the mass percentage of radioactive waste salt is 15%, the sodalite solidified body is mainly composed of sodalite phase; when the mass percentage of radioactive waste salt is 25%, 35%, and 45%, the sodalite solidified body is a mixture of sodalite and nepheline. Figure 6 The XRD phase analysis results of sodalite solidified bodies prepared using radioactive waste salts with different mass percentages after soaking in a 90 °C water bath for 28 days show that the phases of the sodalite solidified bodies after soaking are consistent with those before soaking, and no new phases are generated, indicating that the sodalite solidified bodies of the present invention have high structural stability in a hydrothermal environment.

[0088] Infrared characterization analysis was performed on the sodalite solidified bodies synthesized in Example 3 with radioactive waste salt at mass percentages of 15% and 25%. The results are as follows: Figure 7 As shown. Figure 7 The peaks are typical of sodalite Al-O-Si in wavenumber synthesis. Figure 8The specific surface area and pore size analysis of the sodalite solidified body synthesized from 4A zeolite and radioactive waste salt at a mass percentage of 15% show that the sodalite solidified body synthesized in this invention is a mesoporous material. The figure shows that the adsorption-desorption curve of the sodalite solidified body is closed and crosses negative values, indicating that the specific surface area of ​​the synthesized sodalite solidified body is relatively small and dense. Furthermore, the decrease in surface area from 4A zeolite to sodalite solidified body is due to the fact that the sodalite solidified body synthesized in this invention is denser and that metal ions fill and occupy its pores during the synthesis process.

[0089] Table 3 shows the calculated cell parameters of sodalite solidified bodies synthesized with radioactive waste salt at mass percentages of 15% and 25%. The shrinkage of the cell parameters further proves that Li + Replaced Na + It enters the crystal lattice structure of the sodalite solidified body.

[0090] Table 3: Calculation results of cell parameters of sodalite solidified body

[0091]

[0092] The normalized leaching rate of the sodalite solidified body obtained in Example 3 was evaluated as follows: The sodalite solidified body was ground in an agate mortar for 30 min, passed through a 100-200 mesh sieve, 1 g of powder was placed in a reaction vessel, 10 mL of deionized water was added and soaked at a constant temperature of 90 °C. On the 28th day, the leaching solution was taken and the ion concentration in the leaching solution was measured by inductively coupled plasma mass spectrometry (ICP-MS) to calculate the normalized leaching rate.

[0093] Normalized leaching rate is calculated using the following formula:

[0094]

[0095] Among them, NL i Normalized leaching rate, unit: gm -2 d -1 C i The mass concentration of element i in the leachate, in g / m³. -3 V represents the volume of the leachate, in cubic meters (m³). 3 ;f i The mass fraction of element i in the solidified body; SA is the total surface area of ​​the particles, in m². 2 t represents the soaking time, measured in days (d).

[0096] After soaking the solidified sodalite powder in water at 90 °C for 28 days, the normalized leaching rates of the four fragmented elements Cs, Sr, Ba, and Ce were all less than 5 x 10⁻⁶. -4 g / (cm 2·d) This result indicates that the sodalite solidified body synthesized using the method of this invention is a mixture of sodalite and nepheline phases, which can efficiently solidify fragmented elements in radioactive waste salts, thus facilitating long-term geological storage. Furthermore, the inventors discovered that after immersing the sodalite solidified body synthesized in Example 2 with a sintering time of 8 h in water at 90 °C for 28 days, the normalized leaching rate of the four fragmented elements Cs, Sr, Ba, and Ce was at least 7.5 x 10⁻⁶. -4 g / (cm 2 ·d).

[0097] Thermal stability evaluation of sodalite solidified body:

[0098] Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC, downward peak indicates positive) were performed on the sodalite solidified body synthesized from 15% (by mass) of radioactive waste salt in Example 3. The results are as follows: Figure 9 As shown. Figure 9 The results show that the precursor undergoes weight loss due to water content below 200℃, while the temperature range of 200–800℃ corresponds to the phase transformation process of the raw material-synthesized sodalite solidified body. An endothermic peak occurs between 750 and 800℃, corresponding to the endothermic process of the synthesized sodalite solidified body. The synthesized sodalite solidified body remains stable below 700℃, but begins to lose weight above 800℃, corresponding to the volatilization of LiCl within the sodalite solidified body, indicating that the sodalite solidified body possesses excellent thermal stability. Furthermore, the inventors discovered that sodalite solidified bodies synthesized using mass percentages of 25%, 35%, and 45% also exhibit excellent thermal stability below 800℃.

[0099] Example 4

[0100] A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ includes the following steps:

[0101] S1. 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder.

[0102] S2. 25% by mass of radioactive waste salt, 4A zeolite powder, sodium chloride, and water are mixed evenly at a liquid-to-solid ratio of 5:1, wherein the mass ratio of 4A zeolite powder to sodium chloride is 4:1. The mixture is then heated in a 75 ℃ water bath at 200 r / min for 8 h with magnetic stirring. After the water has evaporated, the slurry is dried in a 100 ℃ oven for 24 h with forced air to obtain the solidified precursor.

[0103] S3. After grinding the cured precursor in an agate mortar for 30 min, pass it through a 0.1 mm sieve. Then, using SPS (SPS 3.20MK-II, Japan) in an Ar atmosphere at 30, 40, 50, 60, and 70 MPa respectively, perform a two-step high-temperature short-time sintering process (e.g., Figure 10 (As shown) The sodalite solidified body was synthesized. During sintering, due to the poor conductivity of the solidified precursor powder, in this embodiment, 2 g of solidified precursor powder was wrapped in carbon paper (thickness of 0.1 mm) and placed in a mold (inner diameter 15 mm, outer diameter 45 mm, height 45 mm) with graphite as the main component. The upper and lower ends of the mold were filled with graphite rods (inner diameter 15 mm, height 25 mm). After sintering, in order to remove the carbon on the surface of the sintered sodalite solidified body, it was polished with 100-3000 grit sandpaper. The cylindrical sodalite solidified body (diameter 15 mm, height 4 mm) was polished to a certain depth to ensure that the carbon on its surface was removed.

[0104] The mechanical properties of the sodalite solidified body synthesized in Example 4 were evaluated:

[0105] 1. Hardness: The surface hardness of the sodalite solidified body was tested by applying a force of 0.3 kg within 10 s using a Vickers hardness tester (MHVD-1000 AP).

[0106] 2. Density: The density and porosity of the solidified sodalite were determined using the Archimedes method.

[0107] (1) After drying the cylindrical sodalite solidified body at 70 ℃ for 24 h, the dry weight of the sodalite solidified body at room temperature was measured on an analytical balance. W 1 The accuracy is 0.001 g;

[0108] (2) The dried sodalite solidified body was placed in boiling water for 2 hours, cooled to room temperature, and the floating weight of the saturated sodalite solidified body was measured in water. W 2 );

[0109] (3) Wipe away the moisture on the surface of the sodalite solidified body with a multi-layered gauze filled with water, and measure the wet weight of the saturated sodalite solidified body in air. W 3 );

[0110] (4) Calculate the actual density of the solidified sodalite body according to the following formula ( d ), densification ( D ) and porosity ( P ).

[0111]

[0112] in, d This represents the actual density of the solidified sodalite body; W 1 The dry weight of the solidified sodalite at room temperature; W 2 The floating weight of the saturated sodalite solidified body; W 3 The weight of the saturated sodalite solidified body in air; WDT The density of water at room temperature is taken as 0.9982 g / cm³. 3 (20 ℃).

[0113]

[0114] in, D The degree of densification of the solidified sodalite body; d This represents the actual density of the solidified sodalite body; d 0 The theoretical density of sodalite is taken as 2.25 g / cm³. 3 .

[0115]

[0116] in, P The porosity of the solidified sodalite body W 1 The dry weight of the solidified sodalite at room temperature; W 2 The floating weight of the saturated sodalite solidified body; W 3 This represents the weight of the saturated sodalite solidified body in air.

[0117] The mechanical property evaluation results of the sodalite solidified body synthesized in this embodiment are as follows: Figure 11 , 12 As shown in the figure, the density of the sodalite solidified body synthesized in this embodiment is over 94%, which is lower than the theoretical density, and the hardness can reach up to 416 HV. Furthermore, the inventors' research has found that using radioactive waste salt at mass percentages of 35% and 45% to synthesize sodalite solidified bodies according to the steps of this embodiment also results in a density of over 94% and a hardness exceeding 350 HV.

[0118] In summary, this invention obtains a solidified sodalite body by grinding, sieving, and sintering a solidified precursor obtained through heat treatment of 4A zeolite powder, radioactive waste salt, alkali metal chloride salt, and a dispersant. This method uses a small amount of 4A zeolite, while achieving a high radioactive waste salt coating rate of 45% and a high fixation rate of radioactive element chlorides of 15.183%. Furthermore, the process is simple. The synthesized sodalite solidified body exhibits strong thermal stability and high mechanical hardness; the normalized leaching rate after soaking in water at 90 °C for 28 days is less than 5 x 10⁻⁶. -4 g / (cm 2 ·d) This solidified sodalite can be geologically stored for a long time, effectively reducing the risk of migration, diffusion and leakage of radioactive materials.

[0119] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ, characterized in that, Includes the following steps: (1) Solid raw materials, including 4A zeolite powder, radioactive waste salt, and alkali metal chloride salt, are mixed evenly with a dispersant, and then subjected to heat treatment and drying to obtain a solidified precursor; wherein, the mass ratio of 4A zeolite to alkali metal chloride is (3~5):1; the mass percentage of radioactive waste salt in the total weight of solid raw materials is 15%~45%; the temperature of the heat treatment is 60~100 ℃ and the time is 6~12 h; (2) Grind, sieve and sinter the solidified precursor to obtain sodalite solidified body; the sintering temperature is 600~900℃ and the time is 2~12 h.

2. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The radioactive waste salt includes radioactive waste salt from the electrolytic reducing salt LiCl-Li2O system or the electrolytic refined salt LiCl-KCl system.

3. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The liquid-solid ratio of the solid raw material to the dispersant is (4~6):

1.

4. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The alkali metal chloride salt is one or more of lithium chloride, sodium chloride, and potassium chloride.

5. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The dispersant is one or more of water, ethanol, and acetone.

6. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The particle size of the 4A zeolite powder is less than 1 nm.

7. The method for synthesizing sodalite from 4A zeolite and simultaneously solidifying radioactive waste salt in situ according to claim 1, characterized in that, The specific steps are as follows: (1) 4A zeolite was ball-milled at 200 r / min for 4 h with a ball-to-material ratio of 10:1 and passed through a 0.1 nm sieve to obtain powder; (2) Mix 4A zeolite powder, radioactive waste salt, alkali metal chloride salt and dispersant at a liquid-solid ratio of (4~6):1, heat in a water bath at 60~100 ℃ for 6~12 h, and dry the resulting slurry in an oven for 15~30 h to obtain a solidified precursor; (3) Grind the solidified precursor in an agate mortar for 30 min and then pass it through a 0.1 mm sieve. Sinter the solidified precursor powder at a temperature of 600~900 ℃ for 2~12 h to obtain the solidified sodalite.

8. The sodalite solidified body synthesized by the method according to any one of claims 1 to 7.

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