A solidified body of Zr-site solid solution reinforced perovskite ceramic, its preparation method and application

Abstract

The application belongs to the field of high-radioactivity solid nuclear waste solidification treatment, and discloses a Zr-site solid solution strengthened calcium titano-zirconite ceramic solidification body and a preparation method and application thereof. 1‑x Ce x (Zr, Hf, Sn) y Ti 3‑2x‑y Al 2x O7, wherein x=0.05-0.3 and y=1-2. The method is to mix calcium titanate, titanium dioxide, zirconium oxide, cerium oxide, hafnium oxide, tin oxide and aluminum oxide, ball mill, dry, shape, and then sinter at 1300-1500 DEG C to obtain the Zr-site solid solution strengthened calcium titano-zirconite ceramic solidification body. The Zr-site solid solution strengthened calcium titano-zirconite ceramic solidification body has high density, the main phase is calcium titano-zirconite, phase separation is avoided, the chemical property is stable, the nuclide leaching rate is low, is suitable for long-term deep geological storage, and is applied to the field of high-radioactivity waste treatment.

Description

Technical Field

[0001] This invention belongs to the field of high-level radioactive nuclear waste treatment technology, and more specifically, relates to a solidified body of Zr-site solid solution-reinforced perovskite ceramic, its preparation method, and its application. Background Technology

[0002] Highly radioactive waste (HLW) originates from spent nuclear fuel reprocessing and separation operations, and contains radionuclides with long half-lives and high radiotoxicity. Achieving safe and permanent solidification of HLW is crucial for preventing the migration of radionuclides into the biosphere and mitigating long-term environmental and health risks. Solidification of HLW requires materials with excellent radiation resistance and leaching resistance, such as glass, ceramics, and glass-ceramics. Borosilicate glass, due to its compositional flexibility and mature vitrification process, has been widely used as a form of commercial waste solidification. However, its low solid solubility for actinides and high leaching rate limit its application in solidifying highly radioactive actinides. Perovskite (nominal composition CaZrTi2O7), a key component in the SYNROC formulation, has been extensively studied as an advanced ceramic waste form for solidifying actinides and fission products. It possesses high waste carrying capacity, compositional flexibility to accommodate polyvalent cation substitution, and excellent chemical and radiation stability.

[0003] However, the nuclides in the solidified body will continuously fission and generate radiation, causing damage to the solidified body. Furthermore, after deep burial, the corrosive effects of groundwater further complicate matters, necessitating improved leaching resistance and reduced radiation intensity. This invention develops a method that uses the neutron absorber Hf dissolved at Zr sites to reduce the radiation intensity of the solidified body while simultaneously improving its leaching resistance. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the primary objective of this invention is to provide a solidified body of Zr-site solid solution-reinforced perovskite ceramic.

[0005] Another objective of this invention is to provide a method for preparing the solidified body of the Zr-site solid solution-reinforced perovskite ceramic. Since plutonium (Pu) has strong radioactivity, this method uses cerium to simulate plutonium, employs Ce with similar ionic radii and the same valence state for simulation, and dops Hf and Sn in equal molar ratios at the Zr sites. The solidified body of the Zr-site solid solution-reinforced perovskite ceramic is then prepared by solid-state reaction sintering.

[0006] Another object of the present invention is to provide the application of the above-mentioned Zr-site solid solution reinforced perovskite ceramic solidified body.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A solidified form of Zr-site solid solution-reinforced perovskite ceramic with the chemical formula Ca 1-x Cex (Zr,Hf,Sn) y Ti 3-2x-y Al 2x O7, where x = 0.05~0.3, y = 1~2.

[0009] Preferably, the solidified body is prepared by dissolving equimolar amounts of Hf and Sn at Zr sites (i.e., equimolar ratio of Hf, Sn, and Zr), adding a mixed powder of calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide, and aluminum oxide to a solvent and ball milling with zirconium oxide grinding balls, drying, and then dry pressing to obtain a ceramic blank, which is then sintered at 1300~1500℃.

[0010] Preferably, the particle size of the calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide and aluminum oxide is 20 nm to 10 μm.

[0011] Preferably, the solvent is anhydrous ethanol or acetone.

[0012] Preferably, the pressure of the dry pressing is 30~100MPa.

[0013] The method for preparing the solidified body of the Zr-site solid solution reinforced perovskite ceramic includes the following steps:

[0014] S1. A mixture of calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide, and aluminum oxide powder is added to a solvent and zirconium oxide grinding balls for ball milling, dried, and then sieved to obtain the mixed powder.

[0015] S2. The mixed powder is dry-pressed at 30~100MPa to obtain a ceramic blank;

[0016] S3. The ceramic blank is heated to 1300~1500℃ and sintered, then cooled to room temperature to obtain a solidified Zr-site solid solution reinforced perovskite ceramic.

[0017] Preferably, the ball milling speed in step S1 is 200~300 r / min, the ball milling time is 12~24 h, and the sieve aperture is 100~200 mesh.

[0018] Preferably, the heating and cooling rates in step S3 are both 5~10℃ / min, and the sintering time is 10~24h.

[0019] The application of the Zr-site solid solution reinforced perovskite ceramic solidified body in the field of high-level radioactive waste treatment.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention achieves equimolar solid solution of Hf and Sn elements at Zr sites, effectively suppressing the formation of perovskite with high leaching rates.

[0022] 2. The Zr-site solid solution-reinforced perovskite ceramic prepared by this invention has high density (greater than 99%) and low leaching rate of the simulated nuclide Ce (10%). -8 g / (m 2 ·d)), suitable for long-term deep geological storage.

[0023] 3. This invention introduces Hf, a high neutron cross-sectional factor, into the perovskite structure. Since Hf is a neutron absorber, it can effectively reduce the radioactivity intensity of the solidified body. Attached Figure Description

[0024] Figure 1 Ca in Example 4 0.75 Ce 0.25 (Zr,Hf,Sn) 1.8 Ti 0.7 Al 0.5 Microscopic morphology of the polished surface of sample O7.

[0025] Figure 2 Ca in Example 4 0.75 Ce 0.25 (Zr,Hf,Sn) 1.8 Ti 0.7 Al 0.5 SEM image of the polished surface of sample O7. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments 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 this technical field.

[0027] The calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide, and aluminum oxide powders used in the embodiments of the present invention all have a particle size of 20 nm to 10 μm. Example 1

[0028] When x = 0.05 and y = 1.8, the chemical formula is Ca. 0.95 Ce 0.05 (Zr,Hf,Sn) 1.8 Ti 1.1 Al 0.1O7 was used to add anhydrous ethanol and zirconia balls to a mixed powder of calcium titanate (1 μm), titanium dioxide (1 μm), zirconium oxide (1 μm), hafnium oxide (1 μm), tin oxide (1 μm), aluminum oxide (1 μm) and cerium oxide (1 μm). The mixture was ball-milled in a planetary ball mill at 300 r / min for 4 h. After drying, the mixed powder was dry-pressed into ceramic blanks at 30 MPa. The blanks were then placed in a muffle furnace and heated to 1500 °C at a rate of 5 °C / min and held for 12 h. The temperature was then lowered to room temperature at a rate of 5 °C / min to obtain a solidified body of Zr-site solid solution reinforced calcium titanium zirconium ceramic.

[0029] The Zr-site solid solution-reinforced perovskite ceramic solidified body in this embodiment is a pure perovskite phase with a density of 99%. PCT leaching experiments were conducted on it at 42 days, 90°C, and deionized water conditions. The leaching rates of Ca, Ti, and Sn were measured to be 4.8 × 10⁻⁶. -4 g / (m 2 ·d), 5.3×10 -6 g / (m 2 ·d) 1.1×10 -6 g / (m 2 ·d), the leaching rates of Zr and Hf elements are below the detection limit (less than 10). -9 g / (m 2 The leaching rate of the simulated nuclide Ce was 4.2 × 10⁻⁶. -8 g / (m 2 ·d). Example 2

[0030] When x = 0.1 and y = 1.8, the chemical formula is Ca. 0.9 Ce 0.1 (Zr,Hf,Sn) 1.8 Ti 1.0 Al 0.2 O7 was used to add a mixed powder of calcium titanate (1 μm), titanium dioxide (1 μm), zirconium oxide (1 μm), hafnium oxide (1 μm), tin oxide (1 μm), aluminum oxide (1 μm), and cerium oxide (1 μm) to anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300 r / min for 4 h. After drying, the mixed powder was dry-pressed into ceramic blanks at 30 MPa. The blanks were then placed in a muffle furnace and heated to 1500 °C at a rate of 5 °C / min and held for 12 h. The temperature was then lowered to room temperature at a rate of 5 °C / min to obtain a solidified body of Zr-site solid solution reinforced calcium titanium zirconium ceramic.

[0031] In this embodiment, the Zr-site solid solution-reinforced perovskite ceramic solidified body contains 98.15 wt.% perovskite and 1.85 wt.% perovskite, with a density of 99.2%. PCT leaching experiments were conducted on it at 42 days, 90°C, and deionized water, and the leaching rates of Ca, Ti, and Sn were measured to be 4.1 × 10⁻⁶. -5 g / (m 2 ·d) 3.8×10 -6 g / (m 2 ·d), 6.5×10 - 7 g / (m 2 ·d), the leaching rates of Zr and Hf elements are below the detection limit (less than 10). -9 g / (m 2 The leaching rate of the simulated nuclide Ce was 6.2 × 10⁻⁶. -8 g / (m 2 ·d). Example 3

[0032] When x = 0.20 and y = 1.8, the chemical formula is Ca. 0.8 Ce 0.2 (Zr,Hf,Sn) 1.8 Ti 0.8 Al 0.4 O7 was used to add a mixed powder of calcium titanate (1 μm), titanium dioxide (1 μm), zirconium oxide (1 μm), hafnium oxide (1 μm), tin oxide (1 μm), aluminum oxide (1 μm), and cerium oxide (1 μm) to anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300 r / min for 4 h. After drying, the mixed powder was dry-pressed into ceramic blanks at 30 MPa. The blanks were then placed in a muffle furnace and heated to 1500 °C at a rate of 5 °C / min and held for 12 h. The temperature was then lowered to room temperature at a rate of 5 °C / min to obtain a solidified body of Zr-site solid solution reinforced calcium titanium zirconium ceramic.

[0033] In this embodiment, the Zr-site solid solution-reinforced perovskite-zirconium ceramic solidified body contains 99.16 wt.% perovskite and 99.16 wt.% black aluminum calcium stone phase (CaAl). 12 O 19 The content of the substance was 0.84 wt.%, with no perovskite phase and a density of 99.4%. PCT leaching experiments were conducted on it at 42 days, 90℃, and deionized water. The leaching rates of Ca, Ti, and Sn were measured to be 1.2 × 10⁻⁶. -5 g / (m 2 ·d) 1.6×10 -6 g / (m 2 ·d), 6.5×10 -7 g / (m 2·d), the leaching rates of Zr and Hf elements were both below the detection limit (less than 10). -9 g / (m 2 The leaching rate of the simulated nuclide Ce was 1.5 × 10⁻⁶. -8 g / (m 2 ·d). Example 4

[0034] When x = 0.25 and y = 1.8, the chemical formula is Ca. 0.75 Ce 0.25 (Zr,Hf,Sn) 1.8 Ti 0.7 Al 0.5 O7 was used to add a mixed powder of calcium titanate (1 μm), titanium dioxide (1 μm), zirconium oxide (1 μm), hafnium oxide (1 μm), tin oxide (1 μm), aluminum oxide (1 μm), and cerium oxide (1 μm) to anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300 r / min for 4 h. After drying, the mixed powder was dry-pressed into ceramic blanks at 30 MPa. The blanks were then placed in a muffle furnace and heated to 1500 °C at a rate of 5 °C / min and held for 12 h. The temperature was then lowered to room temperature at a rate of 5 °C / min to obtain a solidified body of Zr-site solid solution reinforced calcium titanium zirconium ceramic.

[0035] In this embodiment, the Zr-site solid solution-reinforced perovskite-zirconium ceramic solidified body contains 98.73 wt.% perovskite and 1.27 wt.% black aluminum calcium oxide phase, with no perovskite phase and a density of 98.9%. PCT leaching experiments were conducted on it at 42 days, 90°C, and deionized water conditions, and the leaching rates of Ca, Ti, and Sn were measured to be 3.1 × 10⁻⁶. -5 g / (m 2 ·d) 2.3×10 -6 g / (m 2 ·d) 8.8×10 -7 g / (m 2 ·d), the leaching rates of Zr and Hf elements were both below the detection limit (less than 10). -9 g / (m 2 The leaching rate of the simulated nuclide Ce was 3.6 × 10⁻⁶. -8 g / (m 2 ·d).

[0036] Figure 1 Ca in Example 4 0.75 Ce 0.25 (Zr,Hf,Sn) 1.8 Ti 0.7 Al 0.5 Microstructure of the polished surface of sample O7. Figure 1As can be seen from the data, the main phase of this sample is perovskite, containing a small amount of black aluminum calcium silicate (CaAl). 12 O 19 After refinement, the contents obtained were 98.73 wt.% and 1.27 wt.%, respectively. This indicates that the solidified body of the Zr-site solid solution reinforced perovskite ceramic has high purity. Figure 2 Ca in Example 4 0.75 Ce 0.25 (Zr,Hf,Sn) 1.8 Ti 0.7 Al 0.5 SEM image of the polished surface of O7. From Figure 2 As can be seen from the sample, it is densely sintered and contains a small amount of porosity and a second phase. Besides the labeled black aluminum calcium stone (CaAl... 12 O 19 The peak of ) is the peak of perovskite. This indicates that the solidified body of Zr-site solid solution reinforced perovskite ceramics has high purity and high density. Example 5

[0037] When x = 0.25 and y = 1.6, the chemical formula is Ca. 0.75 Ce 0.25 (Zr,Hf,Sn) 1.6 Ti 0.9 Al 0.5 O7 was used to add a mixed powder of calcium titanate (1 μm), titanium dioxide (1 μm), zirconium oxide (1 μm), hafnium oxide (1 μm), tin oxide (1 μm), aluminum oxide (1 μm), and cerium oxide (1 μm) to anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300 r / min for 4 h. After drying, the mixed powder was dry-pressed into ceramic blanks at 30 MPa. The blanks were then placed in a muffle furnace and heated to 1500 °C at a rate of 5 °C / min and held for 12 h. The temperature was then lowered to room temperature at a rate of 5 °C / min to obtain a solidified body of Zr-site solid solution reinforced calcium titanium zirconium ceramic.

[0038] In this embodiment, the Zr-site solid solution-reinforced perovskite-zirconium ceramic solidified body contains 98.1 wt.% perovskite and 98.1 wt.% black aluminum calcium stone phase (CaAl). 12 O 19 The content of the substance was 1.9 wt.%, with no perovskite phase and a density of 99.2%. PCT leaching experiments were conducted on it at 42 days, 90℃, and deionized water. The leaching rates of Ca, Ti, and Sn were measured to be 7.2 × 10⁻⁶. -5 g / (m 2 ·d) 8.1×10 -6 g / (m2·d), 7.8×10 -7 g / (m 2·d), the leaching rates of Zr and Hf elements were both below the detection limit (less than 10). - 9 g / (m 2 The leaching rate of the simulated nuclide Ce was 8.2 × 10⁻⁶. -8 g / (m 2 ·d).

[0039] The Zr-site solid solution-reinforced perovskite-zirconium ceramic solidified body of the present invention contains more than 98 wt.% perovskite and black aluminum calcium stone phase (CaAl). 12 O 19 The content of the substance was 1.9 wt.%, with no perovskite phase and a density of over 98.9%. PCT leaching experiments were conducted on it under deionized water conditions at 42 days, 90℃, and with the leaching rates of Ca, Ti, and Sn were measured to be 1×10⁻⁶. -5 ~5×10 -4 g / (m 2 ·d), (1.5~8.5)×10 -6 g / (m 2 ·d) 1×10 -6 ~8.8×10 -7 g / (m 2 ·d), the leaching rates of Zr and Hf elements were both below the detection limit (less than 10). -9 g / (m 2 The leaching rate of the simulated nuclide Ce was (1.5~8.2)×10⁻⁶. -8 g / (m 2 ·d).

[0040] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A solidified body of a Zr site solid-solution-strengthened calc zircon ceramic, characterized by, The chemical formula of the solidified body of the Zr-site solid solution strengthening zirconolite ceramic is Ca 1-x Ce x (Zr, Hf, Sn) y Ti 3-2x-y Al 2x O7, wherein x=0.05~0.3, y=1~2; the solidified body is prepared by adding mixed powders of calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide and aluminum oxide into a solvent and zirconium oxide grinding balls for ball milling, drying, dry pressing to form a green body, heating the green body to 1300~1500℃ for sintering for 10~24h, and cooling to room temperature; the heating and cooling rates are both 5~10℃ / min, and the density of the solidified body is greater than 99%.

2. The solidified body of the Zr-site solid-solution-strengthened calc zirite ceramic according to claim 1, characterized by, The particle size of the calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide and aluminum oxide is 20 nm to 10 um.

3. The solidified body of the Zr-site solid-solution-strengthened calc zirite ceramic according to claim 1, characterized by, The solvent is anhydrous ethanol or acetone, and the pressure of the dry pressing is 30-100 MPa.

4. The method for producing a solidified body of Zr-site solid-solution-strengthened schertelite ceramics according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1. The mixed powder of calcium titanate, titanium dioxide, zirconium oxide, hafnium oxide, tin oxide, cerium oxide and aluminum oxide is added into a solvent and zirconium oxide grinding balls for ball milling, dried and sieved to obtain a mixed powder; S2. The mixed powder is dry-pressed at 30-100 MPa to obtain a green body; S3. The green body is heated to 1300-1500℃ for sintering for 10-24 h, and then cooled to room temperature to obtain a solidified body of the Zr-site solid-solution-strengthened calcium titan-zirconite ceramic; the heating and cooling rates are both 5-10℃ / min.

5. The method for producing a solidified body of Zr-site solid-solution-strengthened calcizirconite ceramic according to claim 4, characterized by, In step S1, the rotation speed of the ball milling is 200-300 r / min, the ball milling time is 12-24 h, and the sieve aperture is 100-200 mesh.

6. Application of the solidified body of the Zr-site solid-solution-strengthened calcium titan-zirconite ceramic according to any one of claims 1-3 in the field of high-level waste treatment.

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