CN114420337A

CN114420337A - Preparation method of glass-doped geopolymer solidified radionuclide solidified body

Info

Publication number: CN114420337A
Application number: CN202111519751.0A
Authority: CN
Inventors: 彭寿; 柳琪; 孙扬善; 房树清; 张冲; 冯良; 张正义; 曹天启; 曹欣; 王田禾
Original assignee: CNBM Bengbu Design and Research Institute for Glass Industry Co Ltd
Current assignee: CNBM Bengbu Design and Research Institute for Glass Industry Co Ltd
Priority date: 2021-12-13
Filing date: 2021-12-13
Publication date: 2022-04-29

Abstract

The invention provides a preparation method of a glass-doped geopolymer solidified radionuclide solidified body, which comprises the following steps: (1) dissolving sodium hydroxide and target nuclide in silica sol, stirring, and preparing an alkali activator; (2) mixing metakaolin and phosphate glass with the alkali activator to obtain a mixture, and curing the mixture in an oven to obtain a geopolymer precursor; (3) crushing, grinding and sieving the geopolymer precursor to obtain powder; (4) adding the powder into a die for compression molding to obtain a geopolymer solidified body green body; (5) and sintering the green geopolymer solidified body to obtain the geopolymer ceramic solidified body. The preparation method of the invention is adopted to solidify the radioactive nuclear waste material, and has the characteristics of low leaching rate, high mechanical strength, low energy consumption, environmental protection, no toxicity, simple process, easy engineering application and the like.

Description

Preparation method of glass-doped geopolymer solidified radionuclide solidified body

Technical Field

The invention relates to the technical field of nuclear waste treatment, in particular to a preparation method of a glass-doped geopolymer solidified radionuclide solidified body.

Background

With the widespread use of nuclear energy as a new clean energy source, the technology of curing and treating nuclear waste has become a current popular research. The most common treatment techniques for curing the conventional radioactive nuclear waste mainly include cement curing, glass curing and the like, i.e., the nuclear waste is mixed into a base material such as cement or glass to form a cured body and then is deeply buried. Among them, cement has poor setting effect, poor long-term thermal stability and high leaching rate. Under the conditions of high temperature and humidity, glass phase can be corroded and crystallized, the leaching rate is high, the content is low, and the long-term sealing effect is poor after a solidified body is deeply buried.

The ceramic solidification is to perform isomorphous replacement on the nuclide and atoms positioned at the lattice site, so that the nuclide is fixed at the lattice position and is not easy to fall off, and the ceramic solidification has better chemical stability and geological stability. However, the following disadvantages also exist: the temperature required for preparing the ceramic is high, the requirement on equipment is high, the selectivity of the crystal to elements is strong, the influence of nuclides on the ceramic structure is large, and the process for synthesizing the multiphase composite ceramic is complex.

The geopolymer curing is a new curing method, has good curing performance, stronger impermeability and better impact resistance, but has relatively low compactness, and the pores in the geopolymer influence the mechanical strength of the geopolymer and the curing effect of the radioactive nuclide.

Disclosure of Invention

The invention aims to provide a preparation method of a glass-doped geopolymer solidified radionuclide solidified body, so as to improve the mechanical strength of geopolymer and the solidifying effect of radionuclide. The specific technical scheme is as follows:

the invention provides a preparation method of a glass-doped geopolymer solidified radionuclide solidified body, which comprises the following steps:

dissolving sodium hydroxide and target nuclide in silica sol, stirring, and preparing an alkali activator;

mixing metakaolin, phosphate glass powder and the alkali activator to obtain a mixture, and curing the mixture in an oven to obtain a geopolymer precursor cured body;

crushing, grinding and sieving the geopolymer precursor solidified body to obtain powder;

adding the powder into a die for compression molding to obtain a geopolymer solidified body green body;

and sintering the green geopolymer solidified body to obtain the geopolymer ceramic solidified body.

In some embodiments of the invention, the target nuclide is the radionuclide cesium.

In some embodiments of the invention, the molar ratio of the sodium hydroxide to the target species is from 2:8 to 4: 6.

In some embodiments of the invention, the silica sol has a solute mass fraction of 20% to 40%.

In the inventionIn some embodiments, the phosphate glass powder is iron phosphate glass, and the ratio of each component is as follows: p₂O₅ 50mol％～70mol％、Fe₂O₃ 20mol％～30mol％、B₂O₃ 10mol％～20mol％、Na₂O 0mol％～5mol％、K₂O 0mol％～5mol％。

In some embodiments of the present invention, the phosphate glass frit is doped in an amount of 5 wt% to 20 wt% based on the total mass of the metakaolin and the phosphate glass frit.

In some embodiments of the invention, the mass ratio of sodium hydroxide to metakaolin is 0.05 to 0.2.

In some embodiments of the invention, the sintering is performed in an air environment, the sintering temperature is 800-1000 ℃, and the sintering time is 2-4 h.

In some embodiments of the present invention, the leaching resistance of the cured geopolymer ceramic body prepared by the method is analyzed to determine that the normalized leaching rate of cesium element is 3.21X 10^-4g/(m²·d)～1.33×10^-3g/(m²·d)。

The invention has the beneficial effects that: the invention provides a preparation method of a glass-doped geopolymer solidified radionuclide solidified body, which comprises the steps of taking phosphate glass powder with a low melting point as a high-temperature binder to dope geopolymer solidified radioactive element cesium, and then carrying out high-temperature ceramic treatment to form a pollucite ceramic phase. Compared with the common technology for solidifying radioactive nuclide, the nuclear solidification method provided by the invention has the characteristics of low leaching rate, high mechanical strength, low energy consumption, environmental protection, no toxicity, simple process, easy engineering application and the like.

Of course, not all of the advantages described above need to be achieved at the same time in the practice of any one product or method of the invention.

Drawings

In order to more clearly illustrate the technical solutions of the present invention and the prior art, the following briefly introduces embodiments and drawings required in the prior art, and obviously, the drawings in the following description are only some embodiments of the present invention, and other embodiments can be obtained by those skilled in the art according to the drawings.

FIG. 1 is an XRD spectrum of a ceramic solidified body of a phosphate glass-doped polymer-solidified radionuclide prepared in example 1;

FIG. 2 is an SEM photograph (I) and an EDS spectrum (II) of a ceramic solidified body of a phosphate glass-doped polymer-solidified radionuclide prepared in example 1;

FIG. 3 is an XRD spectrum of a ceramic solidified body of a phosphate glass-doped geopolymer-solidified radionuclide prepared in example 2;

FIG. 4 is an SEM photograph (I) and an EDS spectrum (II) of a ceramic solidified body of a phosphate glass-doped polymer-solidified radionuclide prepared in example 2;

FIG. 5 is an XRD spectrum of a ceramic solidified body of a phosphate glass-doped geopolymer-solidified radionuclide prepared in example 3;

FIG. 6 is an SEM photograph (I) and an EDS spectrum (II) of a ceramic solidified body of a phosphate glass-doped polymer-solidified radionuclide prepared in example 3;

FIG. 7 is an XRD spectrum of a ceramic solidified body of a phosphate glass-doped geopolymer-solidified radionuclide prepared in example 4;

FIG. 8 is an SEM photograph (I) and an EDS spectrum (II) of a ceramic solidified body of a phosphate glass-doped polymer-solidified radionuclide prepared in example 4.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other technical solutions obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention.

mixing metakaolin, phosphate glass powder and the alkali activator to obtain a mixture, and curing the mixture in an oven to obtain a geopolymer precursor;

crushing, grinding and sieving the geopolymer precursor to obtain powder;

In some embodiments of the invention, the target nuclide is the radionuclide cesium. The compound for providing the target nuclide is not limited in the present invention as long as the object of the present invention can be achieved, and the radionuclide cesium may be cesium hydroxide monohydrate, for example.

In some embodiments of the invention, the molar ratio of sodium hydroxide to target nuclide is 2:8 to 4:6, preferably 3: 7.

In some embodiments of the invention, the solute mass fraction of the silica sol is between 20% and 40% and the silica sol is added in an amount of between 30% and 40% based on the total mass of the mixture.

In some embodiments of the present invention, the phosphate glass powder is iron phosphate glass, and the ratio of each component is: p₂O₅50mol％～70mol％、Fe₂O₃ 20mol％～30mol％、B₂O₃ 10mol％～20mol％、Na₂O 0mol％～5mol％、K₂O0 mol% to 5 mol%, preferably P₂O₅ 60mol％、Fe₂O₃ 30mol％、B₂O₃ 10mol％。

In some embodiments of the present invention, the phosphate glass frit is doped in an amount of 5 wt% to 20 wt%, preferably 5 wt% to 15 wt%, based on the total mass of the metakaolin and the phosphate glass frit.

In some embodiments of the present invention, the mass ratio of sodium hydroxide to metakaolin is 0.05 to 0.2, preferably 0.1 to 0.13.

In the invention, the sintering is carried out in an air environment, the sintering temperature is 800-1000 ℃, and the sintering time is 2-4 h. The sintering equipment is not limited in the present invention as long as the object of the present invention can be achieved, and sintering may be performed using a muffle furnace, for example.

In the present invention, the container for containing the alkali activator must be a container resistant to alkali corrosion, and the container used is only required to achieve the object of the present invention, and for example, a polytetrafluoroethylene beaker may be used.

In the present invention, stirring is required during the preparation of the alkali activator, and the stirring manner, temperature and time are not limited in the present invention as long as the object of the present invention can be achieved, and for example, magnetic stirring at room temperature can be employed for 3 to 5 days.

In the present invention, after the metakaolin and the phosphate glass are mixed in the alkali activator, a treatment process for uniformly dispersing the metakaolin and the phosphate glass and discharging bubbles generated in the mixing process is required, and the process is not limited in the present invention as long as the purpose of the present invention can be achieved, and illustratively, the metakaolin and the phosphate glass are sufficiently ultrasonically stirred for 1 to 2 hours and placed in a vacuum drier for 30 to 60 minutes to remove bubbles.

In the present invention, the curing temperature and time of the geopolymer precursor cured product are not limited as long as the object of the present invention can be achieved, and illustratively, the curing temperature is 60 ℃ to 70 ℃ and the curing time is 7 days or more.

In the present invention, press molding means that powders are put into a mold, and the powders are pressed by a press machine so as to approach each other in the mold and firmly bonded by an internal friction force to form a green body having a predetermined shape. The press for compression molding of the present invention is not particularly limited and may be one known in the art as long as the object of the present invention is achieved. In the present invention, the molding pressure is required to be sufficient to mold the powder and to have a certain strength, and the pressure value is in the range of 30MPa to 100MPa, and exemplarily, the pressure value is 30 MPa.

In the invention, the binder removal is needed during sintering, the binder removal mode is not limited in the invention as long as the purpose of the invention can be realized, and illustratively, the green geopolymer solidified body is heated to 400-600 ℃ from room temperature, and the temperature is kept for 1-3 h for binder removal.

According to the invention, phosphate glass is used as a high-temperature binder doped geopolymer, the solidified body is further densified in a compression molding mode, and the mechanical strength, the radiation resistance and the leaching resistance of the ceramic solidified body are improved after high-temperature ceramic treatment.

According to the invention, the phosphate glass powder with a low melting point is used as a high-temperature binder to dope the geopolymer with the radioactive element cesium, and then the high-temperature ceramic treatment is carried out to form the pollucite ceramic phase.

In some embodiments of the present invention, the leaching resistance of the cured geopolymer ceramic body is analyzed to determine a normalized leaching rate of cesium at 3.21X 10^-4g/(m²·d)～1.33×10^-3g/(m²D) in between.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. Various tests and evaluations were carried out according to the following methods.

The test method and the test equipment comprise:

the crystalline phase of the cured geopolymer ceramic was analyzed by X-ray diffraction (XRD).

The cross-sectional morphology of the polymer ceramic solidified body is observed by a Scanning Electron Microscope (SEM), and the a position in the SEM picture is analyzed by an EDS (scanning electron microscope energy spectrometer).

The flexural strength of the cured geopolymer body was measured in MPa by means of a universal tester (AGS-X) according to the three-point method of the national Standard GB/T232-88 (Metal bending test method).

The leach resistance of the cured polymer ceramic bodies is measured by the Product Consistency Test (PCT) according to the American Society for Testing and Materials (ASTM) standards, and the normalized leach rate of cesium is measured in g/(m)²·d)。

Example 1

Weighing 30g of silica sol in a polytetrafluoroethylene beaker, weighing 2.4g of sodium hydroxide and 23.5g of cesium hydroxide monohydrate according to the molar ratio of sodium ions to cesium ions of 3:7, dissolving in the silica sol, and stirring for 3 days by using magnetic force to obtain the alkali activator. 24g of metakaolin is weighed and added into the alkali activator, and the mixture is added while stirring to obtain a mixed solution. Weighing 1.26g of iron phosphate glass powder according to the mass fraction of 5 wt% relative to the total mass of the metakaolin and the phosphate glass powder, adding the iron phosphate glass powder into the mixed solution, and shaking for 1 hour in an ultrasonic cleaning instrument to remove bubbles. Then, the mixture was transferred to a vacuum drier, and after evacuation, it was left for 30min to further remove air bubbles. And (3) putting the mixed solution subjected to bubble removal into an oven for curing at the temperature of 60 ℃ for 7 days to obtain the geopolymer precursor curing body. The geopolymer precursor cured body was pulverized, ground and sieved to obtain powder, and the powder was compressed in a 30mm mold under a pressure of 30MPa to obtain a green geopolymer cured body. And sintering the green geopolymer solidified body in a muffle furnace in an air atmosphere, heating to 500 ℃ at the heating rate of 2 ℃/min, preserving heat for 1h to remove glue, heating to 900 ℃ at the heating rate of 5 ℃/min to calcine for 2h, and naturally cooling to room temperature to obtain the geopolymer ceramic solidified body.

XRD and SEM analyses of the obtained geopolymer ceramic solidified body are shown in FIG. 1 and FIG. 2, respectively. As can be seen from FIG. 1, the cured geopolymer ceramic prepared in example 1 has X-ray characteristic peaks consistent with those of a standard PDF card (PDF #88-0055), and thus it was confirmed that a pollucite structure was formed after high-temperature ceramization. As can be seen from the SEM photograph shown in FIG. 2 (I), the cured geopolymer ceramic forms a dense and uniform structure after high-temperature ceramization. The EDS spectrum shown in (II) of FIG. 2 shows that the atomic ratio of cesium to aluminum to silicon is 1:1:2, which corresponds to the stoichiometric ratio of pollucite, and further proves that the pollucite crystal phase is generated by the high-temperature treatment and the ceramization treatment, and the obtained geopolymer ceramic solidified body has higher bending strength and lower leaching rate.

Example 2

The procedure of example 1 was repeated, except that 2.67g of iron-phosphate glass powder was weighed out in a mass fraction of 10 wt% relative to the total mass of metakaolin and phosphate glass powder.

XRD and SEM analyses of the obtained geopolymer ceramic solidified body are shown in FIG. 3 and FIG. 4, respectively. As can be seen from FIG. 3, the cured geopolymer ceramic prepared in example 2 has X-ray characteristic peaks consistent with those of a standard PDF card (PDF #88-0055), which proves that a pollucite structure is formed after high-temperature ceramization. As can be seen from the SEM photograph shown in FIG. 4 (I), the cured geopolymer ceramic forms a dense and uniform structure after high-temperature ceramization. The EDS spectrum shown in FIG. 4 (II) shows that the atomic ratio of cesium to aluminum to silicon is 1:1:2, which is in accordance with the stoichiometric ratio of pollucite, and further proves that the pollucite crystal phase is generated by the high-temperature treatment and the ceramization treatment, and the obtained geopolymer ceramic solidified body has high strength and low leaching rate.

Example 3

The procedure of example 1 was repeated, except that 4.24g of iron-phosphate glass powder was weighed in a mass fraction of 15 wt% relative to the total mass of metakaolin and phosphate glass powder.

XRD and SEM analyses of the obtained geopolymer ceramic solidified body are shown in FIGS. 5 and 6, respectively. As can be seen from FIG. 5, the cured geopolymer ceramic prepared in example 3 has X-ray characteristic peaks consistent with those of a standard PDF card (PDF #88-0055), demonstrating that a pollucite structure is formed after high-temperature ceramming. As can be seen from the SEM photograph shown in FIG. 6 (I), the cured geopolymer ceramic forms a dense and uniform structure after high-temperature ceramization. The EDS spectrum shown in (II) of FIG. 6 shows that the atomic ratio of cesium to aluminum to silicon is 1:2:4, deviating from polluciteStone stoichiometry, after 15 wt.% glass frit addition, the glass phase is too high for the glass phase to react with SiO during the pyrolysis process₂、Al₂O₃When the oxides react, the crystal phase part structure of the pollucite is damaged, so that the leaching rate is improved and the bending strength is reduced.

Example 4

The procedure of example 1 was repeated, except that 6g of iron phosphate glass powder was weighed out in a mass fraction of 20 wt% relative to the total mass of metakaolin and phosphate glass powder.

XRD and SEM analyses of the obtained geopolymer ceramic solidified body are shown in FIGS. 7 and 8, respectively. As can be seen from FIG. 7, the cured geopolymer ceramic prepared in example 4 has X-ray characteristic peaks consistent with those of a standard PDF card (PDF #88-0055), which proves that a pollucite structure is formed after high-temperature ceramization. As can be seen from the SEM photograph shown in FIG. 8 (I), the cured geopolymer ceramic forms a dense and uniform structure after high-temperature ceramization. The EDS spectrum shown in FIG. 8 (II) shows that the atomic ratio of cesium to aluminum to silicon is 1:2:3, deviating from the pollucite stoichiometric ratio, due to the fact that NaOH is converted to Na at high temperature during the high temperature process with more glass phase after the addition of 20 wt% glass frit₂O, and SiO₂、Al₂O₃And the oxides react to further destroy the crystal phase part structure of the pollucite, so that the content of glass powder is increased, the leaching rate is improved, and the bending strength is reduced.

Comparative example 1

The procedure of example 1 was repeated except that the phosphate glass frit was not added.

Flexural strength and leaching rate tests were performed on the cured geopolymer ceramics prepared in examples 1 to 4 and comparative example 1, and the test results are shown in Table 1:

TABLE 1

Note: the "/" in table 1 indicates no corresponding bending strength data. The sample prepared in comparative example 1, which does not have phosphate glass powder as a high temperature binder, releases gas during sintering, and the cured geopolymer body cracks and bulges after high temperature treatment, thereby failing to perform the flexural strength test.

As can be seen from the data in the above table, the phosphate glass frit-doped geopolymer ceramic solidified body can improve the flexural strength and the leaching resistance of the geopolymer solidified body. The bending strength and the standardized leaching rate of the geopolymer ceramic solidified body change along with the change of the content of the doped phosphate glass powder, the content of the phosphate glass powder is low, the pollucite nucleation is influenced, the crystal phase precipitation is more, and the mechanical strength and the nuclide solidification effect are improved little. A proper amount of phosphate glass powder forms a glass liquid phase at high temperature, which is beneficial to improving the mechanical strength of the geopolymer and the solidification effect of nuclide. As the content of the phosphate glass powder is further increased, the molten glass is not favorable for the formation of a crystal phase, and the structure of the crystal phase is destroyed, resulting in the reduction of mechanical strength and the solidification effect of nuclides.

It can be seen from examples 1 to 4 that the doping amount of the phosphate glass frit in the prepared cured geopolymer ceramic body is within the range of the present invention, which can improve the mechanical strength of the cured geopolymer ceramic body and the curing effect on the radionuclide.

The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a glass-doped polymer-cured radionuclide cured body, comprising the steps of:

2. The production method according to claim 1, wherein the target nuclide is cesium radionuclide.

3. The preparation method according to claim 1, wherein the molar ratio of the sodium hydroxide to the target nuclide is 2:8 to 4: 6.

4. The production method according to claim 1, wherein the solute mass fraction of the silica sol is 20% to 40%.

5. The preparation method according to claim 1, wherein the phosphate glass powder is iron phosphate glass, and the ratio of each component is as follows: p₂O₅ 50mol％～70mol％、Fe₂O₃ 20mol％～30mol％、B₂O₃10mol％～20mol％、Na₂O 0mol％～5mol％、K₂O 0mol％～5mol％。

6. The preparation method according to claim 1, wherein the phosphate glass frit is doped in an amount of 5 to 20 wt% based on the total mass of the metakaolin and the phosphate glass frit.

7. The preparation method according to claim 1, wherein the mass ratio of the sodium hydroxide to the metakaolin is 0.05 to 0.2.

8. The preparation method according to claim 1, wherein the sintering is performed in an air environment, the sintering temperature is 800 ℃ to 1000 ℃, and the sintering time is 2h to 4 h.

9. According to claim 1The production method according to any one of claims to 8, wherein the analysis of the leaching resistance of the cured geopolymer ceramic body produced by the method shows that the normalized leaching rate of cesium is 3.21X 10^-4g/(m²·d)～1.33×10^-3g/(m²·d)。