A borosilicate glass, its preparation method and use

Abstract

The application discloses borosilicate glass and a preparation method and application thereof. High radioactive waste liquid produced by nuclear power industry has great environmental risk and must be treated safely and reliably. Borosilicate glass is widely used as base glass for solidifying high radioactive waste liquid in the international society. However, the solubility of molybdenum in the borosilicate base glass is low, which leads to the problem that molybdate yellow phase is easily separated out in the solidified body glass. The application adjusts the composition of the borosilicate glass to obtain the base glass with high molybdenum inclusion rate. Specifically, firstly, B2O3 is gradually replaced by Al2O3 to obtain the optimal composition that can add 8mol% of MoO3 without crystallization. On the basis, Li2O is used to replace Na2O and CaO, and the molar ratio of Na2O to CaO is kept unchanged in the process to obtain the borosilicate glass that can add 11mol% of MoO3 without crystallization. The phenomenon that the high radioactive nuclear waste has low inclusion rate in the glass solidification process is improved.

Description

Technical Field

[0001] This invention belongs to the field of nuclear waste treatment, and mainly relates to a borosilicate glass for solidifying highly radioactive nuclear waste, its preparation method and application. Background Technology

[0002] Energy has always been a key concern for countries worldwide. The use of fossil fuels causes severe air pollution and greenhouse gas emissions. Nuclear energy is a supplement to fossil fuels, but the disposal of spent fuel generates large amounts of highly radioactive waste. This nuclear waste poses significant safety hazards, and an accident could cause catastrophic damage to humanity and the environment. Currently, the most effective method for disposing of this nuclear waste is to solidify it and then carry it through deep geological remediation.

[0003] Using glass as the matrix for solidifying high-level radioactive waste is currently a successfully applied method. Borosilicate glass, due to its good chemical stability, is widely used as the base glass for solidifying high-level radioactive waste; however, it also has limitations. For example, high-level radioactive waste from the nuclear industry has a high molybdenum content, while its solubility in borosilicate glass is low. The highest reported solubility of molybdenum (MoO3) in the literature (hereinafter the same) does not exceed 5 mol% (usually less than 2 mol%). Once the molybdenum content exceeds its solubility in glass, the solidified glass is prone to phase separation and crystallization, especially the precipitation of the molybdate yellow phase (particularly soluble Na2MoO4), thereby reducing the chemical stability of the solidified glass and increasing the leaching rate of nuclear waste elements, posing serious safety hazards. Therefore, borosilicate glass with low molybdenum solubility is difficult to use for solidifying high-level radioactive waste. Adjusting the composition of the base glass is a possible method to improve the solubility of molybdenum in borosilicate glass. Table 1 summarizes the existing literature results, showing that the solubility of molybdenum in borosilicate glass remains low.

[0004] Table 1. Molybdenum solubility data in borosilicate glasses from the literature.

[0005]

[0006] Summary of the Invention

[0007] The purpose of this invention is to solve the problem of yellow phase precipitation in the cured borosilicate glass due to the low solubility of molybdenum. Through innovative compositional design, the solubility of molybdenum in borosilicate glass is further improved. Specifically, the content of Al₂O₃ is increased and the content of B₂O₃ is decreased in the borosilicate glass composition. Furthermore, Li₂O is used to replace [Na₂O + CaO]. Results show that, through the compositional design of the base glass, the borosilicate glass prepared by this invention can contain up to 11 mol% MoO₃, resulting in a cured body without molybdate yellow phase precipitation, demonstrating a significant improvement in molybdenum solubility.

[0008] To achieve the above objectives, a set of borosilicate glass compositions were designed, with specific oxide content (mol%) ranges shown in Table 2. It should be noted that the total amount of B2O3 and Al2O3 in the base glass composition remains constant at 19.78%. Increasing the Al2O3 content results in a corresponding decrease in the B2O3 content. The sum of Li2O, Na2O, and CaO in the base glass composition is 16.79%, with the molar ratio of Na2O to CaO remaining constant at 1.02; alternatively, Na2O and CaO can both be zero, in which case the highest Li2O content in the base glass is 16.79%.

[0009] The preparation of borosilicate glass based on the composition given in Table 2 requires the following steps:

[0010] (1) Based on the molar content of each oxide in the basic glass composition, weigh the raw materials required for glass preparation. The specific raw materials and introduced oxides are as follows: SiO2 is introduced by silica sand; Na2B4O7·10H2O is introduced by Na2O and B2O3. If the B2O3 introduced by borax is insufficient, H3BO3 is used to make up the difference. If the introduced Na2O is insufficient, Na2CO3 is used to make up the difference. Al(OH)3 is introduced by Al2O3; CaCO3 is introduced by CaO; ZnO is introduced by ZnO; Li2CO3 is introduced by Li2O; ZrO2 is introduced by ZrO2.

[0011] (2) Mix the weighed raw materials thoroughly until uniform, and place them in a suitable corundum crucible for melting.

[0012] (3) Place the crucible containing the batching material into the melting furnace, heat it to 1550°C at a rate of 5°C / min, and melt it at this temperature for 2 hours.

[0013] (4) After melting, the molten glass is poured onto the copper plate and allowed to cool freely to room temperature.

[0014] Table 2. Design composition (mol%) of the borosilicate glass of this invention

[0015] Components <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[B2O3]]> <![CDATA[Na2O]]> CaO ZnO <![CDATA[Li2O]]> <![CDATA[ZrO2]]> percentage 60.28 7-10 9.78-12.78 0-5.8 0-5.7 2.45 5.29-16.79 0.7

[0016] When preparing cured glass, 1-11 mol% MoO3 was added externally, directly introduced from the MoO3 raw material, while maintaining the original glass oxide ratio. The raw materials were weighed according to step (1), and the remaining experimental steps were the same as (2)-(4). It should be noted that XRD and Raman spectroscopy were used to determine whether molybdate yellow phase precipitated in the cured glass. The XRD and Raman spectra of the obtained MoO3-containing cured glasses (including samples from Examples 1-4 and Comparative Examples 1-3 within the scope of this invention) are shown below. Figure 1 and Figure 2 As shown. Among them, Figure 1 The XRD curves of the four example samples showed only one peak spanning 15-35° 2θ, proving that no crystals were precipitated in these four examples. However, the XRD curves of the three comparative examples all showed some sharp peaks, with the strongest peak located at 28.775° 2θ. This indicates that the samples precipitated the CaMoO4 (PDF#29-0351) phase. Figure 2 The Raman spectra of the four example samples are at 970 cm⁻¹. -1 There is a broad peak and 322cm -1 The relatively weak peaks indicate that all four samples contain only free [MoO4]. 2- There was no CaMoO4 crystal; while the Raman spectra of all the samples corresponding to Comparative Examples 1-3 were at 322, 389, 790, 845, and 878 cm⁻¹, respectively. -1 The presence of sharp peaks indicates the presence of CaMoO4 crystals in these samples. Based on these two test results, the maximum amount of MoO3 that can be added to the base borosilicate glass when there is no yellow phase precipitation in the cured glass can be determined. For example, when Al2O3 is 7 mol%, the maximum amount of added MoO3 can reach 6 mol%; when Al2O3 is 10 mol%, and the glass contains no sodium oxide or calcium oxide, or the sum of both is less than or equal to 3.5 mol%, the maximum amount of added MoO3 can reach 11 mol%.

[0017] Highly radioactive waste liquids generated by the nuclear energy industry pose significant environmental risks and must be handled safely and responsibly. Vitrification of highly radioactive waste liquids is a practical method internationally, with borosilicate glass being a widely used base glass. However, the low solubility of molybdenum in nuclear waste within borosilicate base glass leads to the precipitation of molybdate yellow phases in the solidified glass. This invention aims to obtain a base glass with high molybdenum inclusion capacity by adjusting the composition of borosilicate glass. Specifically, firstly, Al₂O₃ is gradually replaced with B₂O₃ to obtain an optimal composition that allows for the addition of up to 8 mol% MoO₃ without crystallization. Then, Li₂O is used to replace Na₂O and CaO, while maintaining a constant molar ratio of Na₂O to CaO, resulting in borosilicate glass that can accommodate up to 11 mol% MoO₃ without crystallization. This improves the low inclusion capacity of highly radioactive nuclear waste during vitrification.

[0018] Compared with existing technologies, this invention exhibits higher molybdenum solubility, allowing for the addition of up to 11 mol% MoO3 to borosilicate-based glass. This further enhances the inclusion rate of highly radioactive nuclear waste in borosilicate glass. Furthermore, two scenarios emerged during the development of the glass composition in this patent. First, when the amount of MoO3 added to the glass is below the maximum solubility, neither Na2MoO4 nor CaMoO4 precipitates, resulting in a completely amorphous glass. Second, when the amount of MoO3 added exceeds the maximum solubility, CaMoO4 precipitates but not Na2MoO4. Since CaMoO4 is not water-soluble, it has a smaller impact on the chemical stability of the cured glass compared to water-soluble Na2MoO4. Therefore, the borosilicate glass of this invention has potentially wide-ranging practical value. Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the examples and comparative samples.

[0020] Figure 2 The Raman spectra of the examples and comparative samples are shown. Detailed Implementation

[0021] The present invention will be further illustrated below with specific embodiments. It should be understood that the following description is for illustrative purposes only and does not limit its scope. Table 3 shows the oxide design composition of the base glasses in Examples 1-4 and the base glasses in Comparative Examples 1-3. The preparation of these borosilicate base glasses all includes the following steps:

[0022] (1) Based on the oxide content given in Table 3, weigh out the raw materials required for glass preparation, totaling 30g. The specific raw materials and introduced oxides are as follows: SiO2 is introduced from silica sand; Na2B4O7·10H2O is introduced from Na2O and B2O3. If the B2O3 introduced from borax is insufficient, H3BO3 is used to make up the difference. If the introduced Na2O is insufficient, Na2CO3 is used to make up the difference. Al(OH)3 is introduced from Al2O3; CaCO3 is introduced from CaO; ZnO is introduced from ZnO; Li2CO3 is introduced from Li2O; and ZrO2 is introduced from ZrO2.

[0023] (2) Mix the weighed raw materials thoroughly until uniform, and place them in a suitable corundum crucible for melting.

[0024] (3) Place the crucible containing the batching material into the melting furnace, heat it to 1550°C at a rate of 5°C / min, and melt it at this temperature for 2 hours.

[0025] (4) After melting, the molten glass is poured onto the copper plate and allowed to cool freely to room temperature.

[0026] When preparing the cured glass, 1-11 mol% MoO3 is added to the base glass oxide ratio, which is introduced directly from the MoO3 raw material. Weigh each raw material according to step (1), and the remaining experimental steps are the same as (2)-(4). The cured glass is then tested by XRD and Raman spectroscopy to determine whether molybdate yellow phase precipitates in the cured glass.

[0027] Table 3. Basic glass design composition and added MoO3 (mol%) / cured body of the examples and comparative examples.

[0028]

[0029]

[0030] To determine the maximum amount of MoO3 that can be added to the base glass, based on the design composition in Table 3, different amounts of MoO3 were added. The cured glass containing MoO3 prepared by steps (1)-(4) above was analyzed by XRD and Raman spectroscopy. The results of the base glass being able to contain MoO3 are as follows:

[0031] In Example 1, up to 6 mol% MoO3 can be added to the base glass, and no yellow phase precipitation occurs in the resulting cured glass.

[0032] In Example 2, up to 8 mol% MoO3 can be added to the base glass, and no yellow phase precipitation occurs in the resulting cured glass.

[0033] Compared with Examples 1 and 2, when the Al2O3 content in the base glass was reduced to 5 mol%, and 5 mol% MoO3 was added, a yellow phase was precipitated in the resulting cured glass.

[0034] Compared with Examples 1 and 2, the Al2O3 content in the base glass of Comparative Example 2 was reduced to 3.7 mol%, and 3 mol% MoO3 was added to the base glass. The resulting cured glass already had a yellow phase precipitated.

[0035] In Example 3, up to 11 mol% MoO3 can be added to the base glass, and no yellow phase precipitation occurs in the resulting cured glass.

[0036] In Example 4, up to 11 mol% MoO3 was added to the base glass, and no yellow phase precipitation was observed in the resulting cured glass. In Comparative Example 3, compared to Examples 3 and 4, the Li2O content in the base glass was reduced to 9.29 mol%, and with the addition of 11 mol% MoO3, a yellow phase precipitation was observed in the resulting cured glass.

Claims

1. A borosilicate base glass for solidifying high-level radioactive waste, characterized in that: The oxides and their molar contents in the glass are as follows: SiO2 60.28%, Al2O3 7-10%, B2O3 9.78-12.78%, Na2O 0-5.8%, CaO 0-5.7%, ZnO 2.45%, Li2O 5.29-16.79%, and ZrO2 0.7%. Among them, the total amount of B2O3 and Al2O3 in the glass remains constant at 19.78%. When the Al2O3 content increases, the B2O3 content decreases accordingly. The sum of Li2O, Na2O, and CaO in the glass is 16.79%. The molar ratio of Na2O and CaO in the composition remains constant at 1.02, or both of their contents are 0%. In this case, the Li2O content in the base glass is the highest at 16.79%.

2. A method for preparing the base glass according to claim 1, characterized in that, Includes the following steps: (1) Based on the content of each oxide in the glass composition, weigh the raw materials required for glass preparation. The specific raw materials and introduced oxides are as follows: SiO2 is introduced by silica sand; Na2B4O7·10H2O is introduced by Na2O and B2O3. If the B2O3 introduced by borax is insufficient, H3BO3 is used to make up the difference. If the introduced Na2O is insufficient, Na2CO3 is used to make up the difference. Al(OH)3 is introduced by Al2O3; CaCO3 is introduced by CaO; ZnO is introduced by ZnO; Li2CO3 is introduced by Li2O; ZrO2 is introduced by ZrO. 2； (2) Mix the weighed raw materials thoroughly until homogeneous, and place them in a suitable corundum crucible for melting; (3) Place the crucible containing the batch material into the melting furnace, heat it to 1550°C at a rate of 5°C / min, and melt it at this temperature for 2 hours; (4) After melting, pour the molten glass onto the copper plate and let it cool freely to room temperature.

3. A MoO3-containing borosilicate cured glass, characterized in that: Based on the composition of the base glass described in claim 1, 6-11 mol% of MoO3 is added.

4. A method for preparing the cured glass according to claim 3, characterized in that, Includes the following steps: (1) Based on the content of each oxide in the glass composition, weigh the raw materials required for glass preparation. The specific raw materials and introduced oxides are as follows: SiO2 is introduced by silica sand; Na2B4O7·10H2O is introduced by Na2O and B2O3. If the B2O3 introduced by borax is insufficient, H3BO3 is used to make up the difference. If the introduced Na2O is insufficient, Na2CO3 is used to make up the difference. Al(OH)3 is introduced by Al2O3; CaCO3 is introduced by CaO; ZnO is introduced by ZnO; Li2CO3 is introduced by Li2O; ZrO2 is introduced by ZrO2; and MoO3 is introduced by MoO3. (2) Mix the weighed raw materials thoroughly until homogeneous, and place them in a suitable corundum crucible for melting; (3) Place the crucible containing the batch material into the melting furnace, heat it to 1550°C at a rate of 5°C / min, and melt it at this temperature for 2 hours; (4) After melting, pour the molten glass onto the copper plate and let it cool freely to room temperature.

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