KR102306749B1 - Solidifying method of carbonate mineral comprising radioactive carbon - Google Patents

Abstract

The present invention relates to a method for solidifying a carbonate mineral containing radioactive carbon, and more particularly, Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ Providing a low-melting-point glass containing; providing a glass mixture in which a carbonate mineral containing radiocarbon and the low-melting-point glass are mixed; and heating the glass mixture.

Description

Solidifying method of carbonate mineral comprising radioactive carbon

The present invention relates to a method for solidifying a carbonate mineral containing radiocarbon, and more particularly, to a method for solidifying a carbonate mineral containing radioactive carbon obtained by mineralization of carbon dioxide containing radioactive carbon.

The spent activated carbon generated in the air purification system of nuclear facilities contains organic and/or inorganic ³ H and ¹⁴ C in excess of the allowable concentration for its own disposal, and since a significant amount is currently stored inside the nuclear facility, it is classified as radioactive waste. If it is treated, it is expected that a significant amount of treatment cost for permanent disposal will be incurred.

In order to solve this problem, ^{many studies have been conducted to remove 3} H and ¹⁴ C in the spent activated carbon below the allowable concentration for self-disposal by using a thermochemical method. ^{On the other hand, 14} C, which is removed from the spent activated carbon through a thermochemical method, ^{is emitted in a gaseous form such as 14} CO ₂ , so a technology to capture it in a stable form is required. By developing a highly efficient ¹⁴ CO ₂ mineralization technology, it was confirmed that the CO ₂ carbonation rate was three times higher _{than the conventional CO 2 mineralization.}

However, since the carbonated mineral in powder form finally produced through this mineralization technology ^{contains 14} CO ₂ , it is necessary to additionally develop a technology for solidifying it in a stable form. _{In particular, since carbonated minerals are separated into oxides and CO 2} at a temperature of 650° C. or higher, a technology capable of solidifying them at a lower temperature should be developed.

Japan Special 2016-508228

Accordingly, one aspect of the present invention is to provide a method for stably solidifying a carbonate mineral containing radiocarbon.

In one aspect of the present invention, the present invention Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ To provide a low-melting glass comprising; providing a glass mixture in which a carbonate mineral containing radiocarbon and the low-melting-point glass are mixed; and heating the glass mixture.

_{Carbonate minerals, such as those obtained from CO 2} gas containing radiocarbon ( ¹⁴ C), may emit harmful substances by decomposition or dissociation at a temperature of 600° C. or higher, but according to the solidification method of the present invention, a lower sintering temperature condition It is possible to produce a high-density homogeneous solidified body with a high waste loading rate of about 30% to 40% in the present invention, so that radioactive waste can be effectively solidified without generating harmful substances. In addition, the solidification method of the present invention is considered to have high utility as a method for solidifying radioactive waste for final disposal because the process is simple and the process time is relatively short.

1 shows an image observed with the naked eye of the low-melting-point glass powder used in the Examples of the present invention.
Figure 2 shows the XRD analysis result of the low-melting-point glass powder to confirm that the low-melting-point glass powder used in Examples of the present invention is a homogeneously mixed powder.
Figure 3 shows the result of heating the low melting point glass powder used in Examples of the present invention to 450 ℃.
Figure 4 shows an image observed with the naked eye of the solidified product solidified by mixing _{CaCO 3} containing a low-melting-point glass powder and radioactive carbon in an embodiment of the present invention.
5 shows the results of XRD analysis of the solidified body to confirm the structural characteristics of the materials constituting the solidified body obtained in the embodiment of the present invention.
6 shows the result of analyzing the solidified material of the present invention through SEM-mapping to confirm whether the solidified material is a homogeneously mixed material.
7 is a graph showing the result of confirming the weight loss according to the loading amount by controlling the mixing amount of the glass powder and the carbonate mineral powder.
8 is a graph showing the results of confirming the effect of the temperature change in the step of heating the glass mixture.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

^{According to the 14} CO ₂ mineralization technology to stably capture radioactive carbon emitted in gaseous form such as 14 CO ₂ , carbonate minerals containing radioactive carbon are obtained, and for final disposal, the technology of solidifying it in a more stable form is required. necessary. In particular, such a solidification technique should be performed below the dissociation temperature of the carbonate mineral.

According to the present invention, there is provided a method for solidifying a carbonate mineral containing radiocarbon, which has a high loading rate and can be performed below the dissociation temperature of the carbonate mineral.

More specifically, the method for solidifying a carbonate mineral containing radiocarbon of the present invention comprises the steps of: providing a low-melting-point glass comprising _{Bi 2} O ₃ , B ₂ O ₃ , ZnO and SiO _{2 ;} providing a glass mixture in which a carbonate mineral containing radiocarbon and the low-melting-point glass are mixed; and heating the glass mixture.

The carbonate mineral containing radiocarbon may include at least one selected from the group consisting of _{calcium carbonate (CaCO 3} ), strontium carbonate (SrCO ₃ ) and barium carbonate (BaCO _{3 ), preferably calcium carbonate (} CaCO ₃ ). In particular, although calcium carbonate has a low dissociation temperature of about 600° C., according to the present invention, solidification can be stably obtained at a temperature lower than this.

In the present invention the radioactive carbon is a preferable example of 14C for example, not limited thereto, 9C (p), 10C ( β +), 11C (β +, EC), 14C (β -), 15C (β ^- ), 16C(n), etc.

On the other hand, the melting point of the low-melting glass may be 440 to 460 ℃, preferably 450 ℃. When the melting point of the glass is out of the above range, when the glass and the mixture of the carbonate mineral containing radioactive carbon are mixed and solidified, the adjustment of the solidification temperature and the mixing ratio of the low melting point glass and the mixture for producing a homogeneous solidified body may vary.

The carbonate mineral containing radioactive carbon may be included in an amount of 20 to 40 wt%, preferably 30 to 40 wt%, based on the total weight of the mixture. If the carbonate mineral containing radioactive carbon is less than 20% by weight based on the total weight of the mixture, the amount of waste to be treated is small, which may be undesirable in terms of process economy, and the loading rate is preferably as high as possible, but exceeding 40% by weight In this case, carbonate mineral powder that does not solidify beyond a level that the solidification medium can cope with occurs, and the weight loss rate tends to increase rapidly.

Furthermore, so that the solidified body obtained by the solidification method may be in the form of a homogeneous crystal, the carbonate mineral containing the radiocarbon and the low-melting-point glass may be provided in powder form, respectively, and the average particle of the low-melting-point glass powder The size (particle diameter) and the average particle size (particle diameter) of the carbonate mineral powder containing radioactive carbon are preferably at a similar level, for example, the average particle size of the low melting point glass powder is that of the carbonate mineral powder containing radioactive carbon. It may be 0.8 to 1.2 times the average particle size.

On the other hand, the pulverization step for the pulverization of the carbonate mineral and the low-melting-point glass containing the radiocarbon may be carried out individually or by mixing each component, and thus may be performed without limitation together or separately with the step of mixing these components. .

On the other hand, the step of heating the mixture may be performed at 450 to 550 °C, preferably at 450 to 500 °C. When the step of heating the mixture is performed at a temperature of less than 450 ° C., the solidification of the solidified body is not sufficiently performed, and a problem that the surface density of the solidified body may be lowered occurs, and a problem that the solidified body is easily broken may occur. And, when it is carried out at a temperature exceeding 550° C., the weight loss may be rapidly increased by the progress of the decomposition reaction in which _{CaCO 3} is dissociated into CaO and CO _{2 .}

The low-melting-point glass of the present invention includes Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ , in detail, the low-melting-point glass is Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO _{2 A} mixture of powder to do; melting the mixed powder; cooling the molten material; and drying and pulverizing the cooled material.

At this time, the _{step of mixing the Bi 2} O ₃ , B ₂ O ₃ , ZnO and SiO ₂ powder is mixing each powder in a certain ratio, and based on the total number of moles of the powder, Bi ₂ O ₃ 32 to 38 mol% , B ₂ O ₃ 25 to 30 mol%, ZnO 29 to 35 mol%, and SiO ₂ 5 to 7 mol% may be mixed. When the glass powder is prepared using the powder mixed in the above molar ratio, the glass powder having a melting point of 440 to 460°C can be prepared. At this time, for homogeneous mixing of each powder, an appropriate type of powder stirring device can be used depending on the mixing amount. ), and at this time, it is preferable to perform mixing for 10 minutes or more, but is not limited thereto.

As described above _{, it is preferable to heat-treat the powder in which the Bi 2} O ₃ , B ₂ O ₃ , ZnO and SiO ₂ powder is mixed at a temperature of 880 to 950° C. for 1 to 2 hours, but the mixed powder can be melted. If it is a temperature, it is not limited thereto. In addition, during heat treatment, the temperature is raised to about 5 to 10 ° C per minute, and the inside of the heat treatment container is not affected by the atmosphere during heat treatment. It is free to heat treatment with However, when an inert gas such as argon or nitrogen is used, the cost of using gas and airtightness are considered together, and disadvantages may occur in terms of device manufacturing cost and material cost, so it is judged that heat treatment in this condition is not preferable.

Furthermore, it is necessary to rapidly cool the melt of powder produced by the heat treatment as described above in order to have a low-melting-point glass structure, and for this, water cooling of the melt is most effective. For this purpose, the melt can be rapidly cooled by rapidly pouring it into distilled water.

The cooling water of the glass structure obtained through the above cooling process can be crushed using various crushing devices according to the amount of crushing to make the powder into a powder form. It may be carried out so that the average particle size is 180 to 220 mesh. If the average particle size of the low-melting-point glass powder is remarkably small, scattering may occur and handling may not be easy. This may cause a problem in that the rigidity and homogeneity of the manufactured solidified body are lowered and the surface density of the solidified body is significantly reduced.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to help the understanding of the present invention, and the scope of the present invention is not limited thereto.

Example

One. low melting point Glass powder production

Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ powders are mixed so as to be 35 mol%, 27 mol%, 32 mol%, and 6 mol%, respectively, based on the total number of moles of powder, and heated to 900° C. to melt Then, the molten powder was water-cooled through distilled water. Furthermore, the water-cooled powder was dried and then pulverized to a particle size of 200 mesh to prepare a low-melting-point glass powder.

A photograph taken of the prepared low-melting-point glass powder is shown in FIG. 1 , and XRD analysis was performed to confirm that the low-melting-point glass powder was homogeneously mixed, and the results are shown in FIG. 2 . As can be seen in FIG. 2 , it was confirmed that the low melting point glass powder was a state in which Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ powder were homogeneously mixed.

On the other hand, the low-melting-point glass powder was heated to check the melting point of the low-melting-point glass powder, and as a result, it was confirmed that the low-melting-point glass powder was melted at a level of 450° C. as shown in FIG. 3 .

2. Solidification of carbonate minerals

¹⁴ CaCO ₃ to simulate the sample having a thermal and chemical properties, such as CO ₂ gas mineralized product comprising CO ₂ The reagent (assay>99%) powder was pulverized to have a particle size of about 200 mesh. The low-melting-point glass powder and carbonate mineral powder obtained in step 1. were charged into a powder mixer so that 60 wt% of the glass powder and 40 wt% of the carbonate mineral powder were homogeneously mixed based on the total weight of the two components. 5 g of the mixture thus obtained was placed in a cylindrical sintering vessel and compressed, and the sintering vessel was charged into a heating furnace and heated at a temperature of about 500° C. for 1 hour, and then cooled to room temperature. The sintered solid was recovered from the sintering vessel cooled to room temperature. At this time, an image of the recovered solid body is shown in FIG. 4 .

Meanwhile, the result of confirming the weight loss in the solidification process according to the loading amount by controlling the mixing amount of the glass powder and the carbonate mineral powder is shown in a graph in FIG. 7 . As can be seen in FIG. 7 , it can be confirmed that when the loading amount of calcium carbonate exceeds 40% by weight, the weight loss rapidly increases. At this time, the weight loss was calculated using Equation (1).

- Weight before solidification (A)

- Weight after solidification (B)

- Weight loss = (A-B)/A ⅹ100 Equation (1)

In addition, the result of confirming the effect of the temperature change of the step of heating the glass mixture is shown as a graph in FIG. 8 . As can be seen in FIG. 8 , when the temperature exceeds 550° C., it can be confirmed that the residual amount of _{CO 2 is rapidly reduced.} At this time, the CO ₂ residual amount is the the total weight loss to a value calculated using the weight loss of the CaCO ₃ dissociates into CaO and CO ₂ CO ₂ is assumed (conservative), to be caused by the discharged calculated values, CO ₂ The emission level was directly calculated using Equation (2).

_{- Calculation of CO 2} content based on the loading rate (A)

- calculating the weight loss of the CO ₂ emission (B)

- CO ₂ residual amount (%) = (AB)/A × 100 Equation (2)

3. solid analysis

(1) Measurement of surface density of solidified body

The surface density of the solidified body was measured using Archimedes' principle. As a result, the surface density of the solidified body was measured at a level of 3.38 kg/L, and it was confirmed that the solidification method of the present invention could provide a solidified body of excellent density.

(2) Measurement of homogeneity of solidified material

In order to analyze the structural characteristics of the materials constituting the solidified body, XRD analysis was performed by pulverizing the solidified body. A result, also has been confirmed that co-exist in a crystalline form with the main component of the CaCO ₃ and glass medium, as shown in 5, you proceed to solidify in a manner suggested by the present invention is almost no loss weight CO ₂ mineralized product CaCO _{3, it} was found that CO ₂ did not leak to the outside by maintaining the shape as it is.

Furthermore, the distribution of main components in the solidified material prepared through SEM-mapping in FIG. 6 was shown, _{and it was confirmed that the CO 2} mineralization product CaCO ₃ and the solidification medium were homogeneously distributed without phase separation.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope without departing from the technical spirit of the present invention described in the claims. It will be apparent to those of ordinary skill in the art.

Claims (10)

Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ based on the total number of moles of Bi ₂ O ₃ 32 to 38 mol%, B ₂ O ₃ 25 to 30 mol%, ZnO 29 to 35 mol% and SiO ₂ 5 providing a low-melting-point glass comprising in an amount of to 7 mol%;
providing a glass mixture in which a carbonate mineral containing radiocarbon and the low-melting-point glass are mixed; and
heating the glass mixture
A method of solidifying a carbonate mineral comprising a radioactive carbon.
According to claim 1, wherein the carbonate mineral containing radioactive carbon includes at least one selected from the group consisting of _{calcium carbonate (CaCO 3} ), strontium carbonate (SrCO ₃ ) and barium carbonate (BaCO _{3 ), radioactive carbon} A method for solidifying a carbonate mineral comprising
The method of claim 1, wherein the melting point of the low-melting glass is 440 to 460°C.
The method of claim 1 , wherein in the glass mixture, the carbonate mineral is included in an amount of 30 to 40% by weight based on the total weight of the glass mixture.
The method of claim 1 , wherein the carbonate mineral and the low-melting glass are each provided as a powder.
The method for solidifying a carbonate mineral containing radiocarbon according to claim 5, wherein the particle diameter of the low-melting-point glass powder is 0.8 to 1.2 times the average particle diameter of the carbonate mineral powder.
The method of claim 1, wherein the heating of the glass mixture is performed at 450 to 550°C.
According to claim 1, wherein the low-melting glass Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ mixing the powder; melting the mixed powder; cooling the molten material; and radioactive carbon, obtained comprising the step of drying the cooled material;
Bi ₂ O ₃ , B2O ₃ , ZnO and SiO ₂ Mixing the powder is based on the total number of moles of the powder, Bi ₂ O ₃ 32 to 38 mol%, B ₂ O ₃ 25 to 30 mol%, ZnO 29 to A method of solidifying a carbonate mineral performed by mixing 35 mol% and _{5 to 7 mol% of SiO 2 .}
delete The method for solidifying a carbonate mineral containing radiocarbon according to claim 8, further comprising pulverizing the low-melting-point glass to have an average particle diameter of 180 to 220 mesh.

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