Neodymium, gadolinium and erbium doped composite ceramic solidified body and preparation method thereof

Abstract

The invention discloses a neodymium, gadolinium and erbium doped composite ceramic solidified body and a preparation method thereof, and belongs to the field of non-metallic materials. The ceramic solidified body is of a two-phase structure, and the two phases are pyrochlore and monazite; the composite ceramic solidified body comprises GdPO4, Er2Ti2O7 and NdErTi2O7, and the leaching rate of the composite ceramic solidified body is 10 <-7 > g.m <-2 >. D <-1 >. The preparation method of the solidified body comprises the following steps: by taking Zn2TiO4, CaHPO4, SiO2 and B2O3 as solidified body matrixes, adding lanthanide oxides Nd2O3, Gd2O3 and Er2O3, mixing, uniformly grinding, carrying out high-temperature solid-phase reaction on the obtained mixed powder, and naturally cooling to room temperature after the reaction is finished, so as to obtain the monazite phase and pyrochlore phase ceramic solidified body. The ternary multiphase ceramic solidified body has good mechanical performance and leaching resistance, the leaching rate of lanthanide series elements is in the order of magnitude of 10 <-7 > g.m <-2 >. D <-1 >, and the ternary multiphase ceramic solidified body has an excellent solidification effect and has reference significance for deep geological storage of high-level waste.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of non-metallic materials, and particularly relates to a neodymium, gadolinium and erbium doped complex phase ceramic solidified body and a preparation method thereof. BACKGROUND

[0002] In recent years, nuclear energy, as one of green, clean and efficient energy sources, has attracted extensive attention in the world. However, a large amount of radioactive waste is also produced, which has caused great threat to the living environment of human beings. Therefore, safe treatment and disposal of radioactive waste has become an important challenge for long-term and healthy development of nuclear power industry.

[0003] High-level waste mainly contains four types of substances: actinides, minor actinides, activation products and fission products. A large amount of lanthanide elements are produced in the waste salt after electrolytic refining reduction. Therefore, it is very valuable to study a solidified body capable of efficiently solidifying lanthanide elements. Ceramic solidification technology has attracted more and more attention due to its excellent physical and chemical properties. Ceramic materials usually have high chemical stability and good mechanical properties. These characteristics enable the ceramic solidified body to better contain radioactive nuclides and reduce the release of radioactive nuclides to the environment during long-term geological disposal.

[0004] Monazite and pyrochlore are two minerals with special crystal structures. Monazite has a rare earth phosphate structure, and pyrochlore belongs to a fluorite derivative structure. They have high containment capacity for radioactive nuclides. Monazite and pyrochlore can form complex phase ceramics within a certain chemical composition range. The complex phase ceramics have higher density, better chemical stability and stronger leaching resistance, thereby providing a more effective material for the solidification of lanthanide radioactive waste.

[0005] In existing researches on ZIT (zinc titanate) composite materials for solidifying lanthanide elements, most of them involve the solidification of binary lanthanide oxides. However, the composition of high-level waste produced in actual production process is extremely complex and diverse. Therefore, ternary lanthanide oxides (Nd2O3, Gd2O3, Er2O3) are doped in ZIT composite materials to further explore the solidification of ceramic solidification on multiple elements. SUMMARY

[0006] The application aims to solve the problem of solidifying ternary lanthanide oxides (Nd2O3, Gd2O3, Er2O3) in ZIT composite materials, and provides a preparation method of a neodymium, gadolinium and erbium doped complex phase ceramic solidified body.

[0007] The application provides a neodymium, gadolinium and erbium doped complex phase ceramic solidification body, the solidification body is a two-phase structure, the two phases are pyrochlore and monazite; the complex phase ceramic solidification body comprises GdPO4, Er2Ti2O7 and NdErTi2O7; the leaching rate of the complex phase ceramic solidification body is 10 -7 g·m -2 ·d -1 .

[0008] The application also provides a preparation method of the neodymium, gadolinium and erbium doped complex phase ceramic solidification body, Zn2TiO4, CaHPO4, SiO2 and B2O3 are used as a solidification body matrix, lanthanide oxides Nd2O3, Gd2O3 and Er2O3 are added, mixed and uniformly ground, and the obtained mixed powder is subjected to high-temperature solid phase reaction, and is naturally cooled to room temperature after the reaction is completed, so that a monazite phase and a pyrochlore phase ceramic solidification body are obtained.

[0009] Further, the preparation method of the Zn2TiO4 is that ZnO and TiO2 with a molar ratio of 1-1.5:1 are sintered at 800-1100 DEG C for 2-6 h in a NaCl-KCl system, and are cooled to room temperature and washed and dried.

[0010] Further, the mass ratio of the Zn2TiO4:CaHPO4:SiO2:B2O3 is 24:7:7:2.

[0011] Further, the mass of the lanthanide oxides accounts for 10wt%-40wt% of the total mass of the mixed powder.

[0012] Further, the mass ratio of the added lanthanide oxides Nd2O3, Gd2O3 and Er2O3 is 1:4:5, 2:3:5, 1:3:6, 2:2:6, 1:2:7, 1:1:8, 1:5:4, 2:4:4 or 3:3:4.

[0013] Further, the high-temperature solid phase reaction is a stage reaction, specifically, in an air atmosphere, the first stage temperature is 700 DEG C, preheating is carried out for 2 h, the second stage temperature is 1200 DEG C, sintering is carried out for 4 h, the third stage temperature is 700 DEG C, and heat preservation is carried out for 2 h, and the reaction is naturally cooled to room temperature after being completed.

[0014] The application also provides application of the neodymium, gadolinium and erbium doped complex phase ceramic solidification body in the field of high-level radioactive waste treatment.

[0015] The application has the following beneficial effects:

[0016] This invention utilizes ZIT composite materials to cure ternary lanthanide oxides. Current research on ZIT composite materials is limited to mono- and binary structures; there are no reports on ternary lanthanide oxides. Compared to ceramic cured bodies containing only a single monazite phase, the ternary ceramic cured body prepared in this invention has both monazite and pyrochlore phases, forming a synergistic effect that results in a more robust curing effect for lanthanide elements. This solves the problem of treating multi-component lanthanide oxides with ZIT composite materials. Furthermore, this ternary multiphase ceramic cured body exhibits good mechanical properties and leaching resistance, with a lanthanide leaching rate of less than 10%. -7 g·m -2 ·d -1 Order of magnitude, meeting international standard leaching levels (≤10). -6 g·m -2 ·d -1 The results indicate that ZIT composite materials have excellent curing effects on ternary lanthanide oxides, which is of reference value for the deep geological storage of high-level radioactive waste. Attached Figure Description

[0017] Fig. 1 XRD patterns of solidified multiphase ceramic bodies with a package size of 10-40 wt.% Nd2O3:Gd2O3:Er2O3 = 1:3:6 prepared in Examples 1-4;

[0018] Fig. 2 XRD patterns of solidified multiphase ceramic bodies with a package size of 10-40 wt.% Nd2O3:Gd2O3:Er2O3 = 3:3:4 prepared in Examples 1-4;

[0019] Fig. 3 Vickers hardness results of multiphase ceramic solidified bodies with different addition ratios of Nd2O3, Gd2O3 and Er2O3 with a capacity of 10-40 wt.% prepared in Examples 1-4;

[0020] Fig. 4 The leaching rates of Nd, Gd and Er elements after immersion for 28 days in ternary multiphase ceramic solidified bodies with a capacity of 10-40 wt.% Nd2O3:Gd2O3:Er2O3 = 3:3:4 prepared in Examples 1-4;

[0021] Fig. 5 The SEM-EDS surface scan of the ternary multiphase ceramic solidified body with a package size of 30 wt.% Nd2O3:Gd2O3:Er2O3 = 3:3:4 prepared in Example 3 is shown. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0026] A method for preparing a neodymium-, gadolinium-, and erbium-doped multiphase ceramic solidified body is disclosed. The method involves using Zn2TiO4, CaHPO4, SiO2, and B2O3 as the solidified body matrix, and lanthanide oxides Nd2O3, Gd2O3, and Er2O3 as simulated radioactive waste raw materials. After mixing and grinding the mixture evenly, the resulting mixed powder is subjected to a high-temperature solid-phase reaction. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain a monazite-phase and pyrochlore-phase ceramic solidified body.

[0027] In the above method, Zn2TiO4 is prepared by using a molar ratio of ZnO to TiO2 of 1 to 1.5:1, sintering in a NaCl-KCl system at 800 to 1100°C for 2 to 6 hours, cooling to room temperature, cleaning, and drying.

[0028] In the above method, Zn2TiO4:CaHPO4:SiO2:B2O3 = 24:7:7:2.

[0029] In the above method, the total mass fraction of the three lanthanide oxides added is 10–40 wt.%.

[0030] In the above method, the three lanthanide oxides are Nd₂O₃, Gd₂O₃, and Er₂O₃, which are used to simulate radioactive lanthanide oxides.

[0031] In the above method, the addition ratios of the three lanthanide oxides, Nd2O3, Gd2O3, and Er2O3, are 1:4:5, 2:3:5, 1:3:6, 2:2:6, 1:2:7, 1:1:8, 1:5:4, 2:4:4, and 3:3:4.

[0032] The phosphates and titanates of lanthanides were prepared using the above method.

[0033] In the above method, the raw material powder is mixed according to the formula, ground evenly, and then carried out under the process conditions of air atmosphere, first stage preheating at 700℃ for 2h, second stage sintering at 1200℃ for 4h, and third stage holding at 700℃ for 2h. After the reaction is completed, it is naturally cooled to room temperature and mechanically crushed to obtain the product.

[0034] Example 1

[0035] A method for preparing a neodymium-, gadolinium-, erbium-doped multiphase ceramic solidified body, comprising:

[0036] Step 1: Add 10 wt.% of ternary lanthanide oxide to the mass ratio of Zn2TiO4:CaHPO4:SiO2:B2O3 = 24:7:7:2. As the lanthanide oxide is added, the other components are reduced in the above ratio, and the total weight is kept at 10g.

[0037] Step 2: Weigh out 54g of Zn2TiO4, 15.75g of CaHPO4, 15.75g of SiO2, and 4.5g of B2O3; weigh out 9 mass ratios of Nd2O3, Er2O3, and Gd2O3, weighing out the following amounts: 1g, 4g, 5g; 2g, 3g, 5g; 1g, 3g, 6g; 2g, 2g, 6g; 1g, 2g, 7g; 1g, 1g, 8g; 1g, 5g, 4g; 2g, 4g, 4g; 3g, 3g, 4g.

[0038] Step 3: Weigh the raw materials, mix them evenly, and put them into a 50mL corundum crucible. Preheat the crucible to 700℃ for 2 hours in an air atmosphere, then grind it for 2 hours and mix it evenly. Sinter it at 1200℃ for 4 hours, hold it at 700℃ for 2 hours, and then take out the solidified body and cool it to room temperature.

[0039] The crystal structure of the product was characterized, and the XRD results are as follows: Figs. 1-2 As shown in the figure, the main components of the cured body obtained in this embodiment are lanthanide phosphates and lanthanide titanates;

[0040] The leaching rates of Nd, Gd, and Er in the product were tested, and the results were... Fig. 4 As shown, after 28 days, the leaching rate of Nd in the solidified multiphase ceramic with a capacity of 30 wt.% was 2.23 × 10⁻⁶. -7 g·m -2 ·d -1 The leaching rate of Gd was 2.5 × 10⁻⁶. -7 g·m -2 ·d -1 The leaching rate of Er was 1.59 × 10⁻⁶. -7 g·m -2 ·d-1 .

[0041] Example 2

[0042] The difference from Example 1 is that 20 wt.% of ternary lanthanide oxides were added. Nd2O3, Er2O3 and Gd2O3 were weighed in 9 different mass ratios: 2g, 8g, 10g; 4g, 6g, 10g; 2g, 6g, 12g; 4g, 4g, 12g; 2g, 4g, 14g; 2g, 2g, 16g; 2g, 10g, 8g; 4g, 8g, 8g; 6g, 6g, 8g. The remaining process steps and parameter settings were the same as in Example 1, resulting in a ternary multiphase ceramic solidified body.

[0043] Example 3

[0044] The difference from Example 1 is that 30 wt.% of ternary lanthanide oxides were added. Nd2O3, Er2O3 and Gd2O3 were weighed in 9 different mass ratios: 3g, 12g, 15g; 6g, 9g, 15g; 3g, 9g, 18g; 6g, 6g, 18g; 3g, 6g, 21g; 3g, 3g, 24g; 3g, 15g, 12g; 6g, 12g, 12g; 9g, 9g, 12g. The remaining process steps and parameter settings were the same as in Example 1, resulting in a ternary multiphase ceramic solidified body.

[0045] Example 4

[0046] The difference from Example 1 is that 40 wt.% of ternary lanthanide oxides were added. Nd2O3, Er2O3 and Gd2O3 were weighed in 9 different mass ratios: 4g, 16g, 20g; 8g, 12g, 20g; 4g, 12g, 24g; 8g, 8g, 24g; 4g, 8g, 28g; 4g, 4g, 32g; 4g, 20g, 16g; 8g, 16g, 16g; 12g, 12g, 16g. The remaining process steps and parameter settings were the same as in Example 1, resulting in a ternary multiphase ceramic solidified body.

[0047] Depend on Figs. 1-2 It can be seen that, with different proportions of lanthanides, the composition of the solidified multiphase ceramic with the same inclusion capacity is roughly the same, mainly including GdPO4, Er2Ti2O7, and NdErTi2O7. For different lanthanide inclusion capacities, the solidified multiphase ceramic with the same proportion consists of pyrochlore titanate and monazite phosphate.

[0048] from Fig. 3The results showed that the Vickers hardness of the cured bodies with different proportions ranged from 800 HV to 2400 HV, with an overall trend of first increasing and then decreasing, indicating relatively high overall hardness. The performance was relatively good when the proportions of lanthanides were different and the inclusion capacity was 30 wt.%, with the hardness of the cured body within a reasonable range, and the change in proportion had little effect on the hardness of the cured body.

[0049] Fig. 4 The leaching rates of Nd, Gd, and Er elements were measured after immersion in a ternary multiphase ceramic solidified body with a capacity of 10–40 wt.% Nd₂O₃:Gd₂O₃:Er₂O₃ = 3:3:4 for 28 days. The leaching rates of the three lanthanides remained relatively stable at around 10%. -7 g·m -2 ·d -1 The magnitude indicates that the solidified body has good chemical stability.

[0050] Fig. 5 This is a SEM-EDS surface scan of a ternary multiphase ceramic solidified body with a matrix of 30 wt.% Nd₂O₃:Gd₂O₃:Er₂O₃ = 3:3:4. It can be observed that O element is widely distributed throughout the sample. Based on the consistent distribution areas of Nd, Gd, Er, and Ti elements in the image, combined with XRD analysis, the substance is identified as a pyrochlore phase titanate. Furthermore, the distribution of P element is basically the same as that of Gd and Er elements; combined with XRD phase analysis, this substance is identified as a monazite phase Gd. 0.5 Er 0.5 PO4; This shows that the elemental surface scan distribution map is consistent with the phase analysis by XRD.

[0051] In summary, the mixed lanthanide oxides of Nd₂O₃, Gd₂O₃, and Er₂O₃ exhibit the best chemical stability and mechanical properties, along with a uniform elemental distribution, at a coverage capacity of 30 wt.%. At this coverage capacity, the solidified multiphase ceramic body with the same proportion still consists of pyrochlore titanate and monazite phosphate. By day 28, the leaching rates of Nd, Gd, and Er elements remained essentially stable at 10%. -7 g·m -2 ·d -1 The solidified multiphase ceramic exhibits good resistance to leaching.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A neodymium-, gadolinium-, erbium-doped multiphase ceramic solidified body, characterized in that, The solidified body has a two-phase structure, wherein the two phases are pyrochlore and monazite; the multiphase ceramic solidified body includes GdPO4, Er2Ti2O7, and NdErTi2O7; the leaching rate of the multiphase ceramic solidified body is 10%. -7 g·m -2 ·d -1 .

2. A method for preparing a neodymium-, gadolinium-, and erbium-doped multiphase ceramic solidified body as described in claim 1, characterized in that, Using Zn2TiO4, CaHPO4, SiO2, and B2O3 as the solidified matrix, lanthanide oxides Nd2O3, Gd2O3, and Er2O3 were added, mixed, and ground evenly. The resulting mixed powder was subjected to a high-temperature solid-state reaction, and after the reaction was completed, it was naturally cooled to room temperature to obtain monazite and pyrochlore phase ceramic solidified bodies.

3. The method for preparing a neodymium-, gadolinium-, and erbium-doped multiphase ceramic solidified body according to claim 1, characterized in that, The preparation method of Zn2TiO4 is as follows: ZnO and TiO2 with a molar ratio of 1 to 1.5:1 are sintered in a NaCl-KCl system at 800 to 1100°C for 2 to 6 hours, cooled to room temperature, washed and dried.

4. The method for preparing a neodymium-, gadolinium-, and erbium-doped multiphase ceramic solidified body according to claim 1, characterized in that, The mass ratio of Zn2TiO4:CaHPO4:SiO2:B2O3 is 24:7:7:

2.

5. The method for preparing a neodymium-, gadolinium-, erbium-doped multiphase ceramic solidified body according to claim 1, characterized in that, The lanthanide oxides account for 10 wt% to 40 wt% of the total mass of the mixed powder.

6. The method for preparing a neodymium-, gadolinium-, erbium-doped multiphase ceramic solidified body according to claim 1, characterized in that, The mass ratio of the added lanthanide oxides Nd2O3, Gd2O3, and Er2O3 is 1:4:5, 2:3:5, 1:3:6, 2:2:6, 1:2:7, 1:1:8, 1:5:4, 2:4:4, and 3:3:

4.

7. The method for preparing a neodymium-, gadolinium-, erbium-doped multiphase ceramic solidified body according to claim 1, characterized in that, The high-temperature solid-state reaction is a staged reaction, specifically: in an air atmosphere, the first stage temperature is 700℃ for 2 hours of preheating, the second stage temperature is 1200℃ for 4 hours of sintering, the third stage temperature is 700℃ for 2 hours of holding, and after the reaction is completed, it is naturally cooled to room temperature.

8. The application of a neodymium-, gadolinium-, and erbium-doped multiphase ceramic solidified body as described in any one of claims 1 to 7 in the field of treating high-level radioactive waste.

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