KR102746499B1 - A manufacturing method of geopolymer using radioactive concrete waste - Google Patents

Abstract

The present invention relates to a method for producing a geopolymer, comprising: (a) a step of introducing metakaolinite and an alkaline activator into a first reaction tank to produce a fourth mixture; and (b) a method for producing a geopolymer, wherein silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), and calcium hydroxide (Ca(OH) ₂ ) extracted from concrete waste are introduced into a second reaction tank to produce the alkaline activator.

Description

{A manufacturing method of geopolymer using radioactive concrete waste}

The present invention relates to a method for manufacturing a geopolymer using concrete waste, and further to a method for solidifying radioactive waste using concrete waste. The invention relates to a method for manufacturing a geopolymer and a method for solidifying radioactive waste thereby capable of increasing the usability of concrete waste by extracting useful components contained in concrete waste related to construction waste, particularly concrete waste generated by the dismantling of radioactive facilities such as nuclear power plants, and using the extracted useful components to manufacture a geopolymer or to solidify radioactive waste.

Up to now, the development of technology related to construction waste has been started in the early 1990s and has been significantly activated since the early 2000s, but most of it has been focused on the field of utilizing concrete waste as recycled aggregate. In other words, aggregates classified through primary crushing and separation for recycling concrete waste are being recycled as recycled aggregates.

In addition, with regard to radioactive concrete waste generated during the decommissioning of nuclear power plants, since the disposal area for radioactive waste is limited in our country, there is an urgent need for technology to appropriately decontaminate radioactive waste generated during the operation and decommissioning of nuclear power plants and to reduce the amount and volume of radioactive waste ultimately disposed of. Accordingly, research is being conducted in various fields around the world to reduce the amount and volume of radioactive concrete waste generated after the decommissioning of nuclear power plants.

It is known that the amount of waste generated from one nuclear power plant during decommissioning is equivalent to 80,000 200-liter drums. The amount of radioactive concrete waste is expected to be large, as it is estimated that more than 70 to 80% of the waste generated from decommissioning nuclear power plants is radioactive concrete waste. Most of the radioactive concrete waste generated during decommissioning is classified as extremely low-level.

Under these circumstances, reducing the amount of concrete waste actually disposed of by recycling concrete waste, and furthermore radioactive concrete waste, is expected to have positive effects in terms of not only reducing disposal costs but also increasing the safety of disposal and utilizing resources.

Meanwhile, the form of fixing radioactive waste with cement is widely used because the process is easy and simple and it is economical. However, the form of fixing radioactive waste with cement has high porosity, weak adhesive strength, low chemical durability, and weak resistance to acid and alkali. Therefore, research on geopolymer, an alternative form, is being conducted.

Geopolymer is an inorganic binder based on alkaline silicate that is cured by an alkaline activator.

Accordingly, in a situation where cement is being replaced by geopolymer in the method of solidifying radioactive waste, there is an urgent need to research methods of manufacturing geopolymers by recycling concrete waste, especially radioactive concrete waste, or solidifying radioactive waste in order to reduce the amount of concrete waste actually disposed of.

(Patent Document 1) KR 10-1940033 B

In order to solve the problems of the above-described prior art, the present invention proposes a method for manufacturing geopolymer by recycling concrete waste including radioactive concrete waste, and further a method for solidifying radioactive waste by the method for manufacturing geopolymer.

In order to solve the problems of the above-described prior art, the method for producing a geopolymer according to the present invention comprises the step of (a) introducing metakaolinite and an alkaline activator into a first reaction tank to produce a fourth mixture,

Silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), and calcium hydroxide (Ca(OH) ₂ ) extracted from concrete waste can be introduced into the second reactor to produce the alkaline activator.

Preferably, (a-1) a step of mixing the concrete waste and hydrochloric acid (HCl) to produce a first mixture; and (a-2) a step of separating the first mixture into solid and liquid to produce a first filtrate and a first solid.

After the above step (a-2), the above step (a) is performed.

The first solid component contains silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ), and the first solid component can be introduced into the second reaction tank to produce the alkaline activator.

Preferably, (a-3) after step (a-2), the step of mixing the first filtrate and sodium hydroxide (NaOH) to generate a second mixture; (a-4) the step of separating the second mixture into solid and liquid to generate a second filtrate and a second solid; (a-5) the step of mixing the second filtrate and sodium hydroxide (NaOH) to generate a third mixture; and (a-6) the step of separating the third mixture into solid and liquid to generate a third filtrate and a third solid.

After the above step (a-6), the above step (a) is performed, and the third solid component contains calcium hydroxide (Ca(OH) ₂ ).

The above third solid component can be injected into the second reactor to produce the alkaline activator.

Preferably, the third liquid may be injected into the second reaction tank to produce the alkaline activator.

Preferably, for 100 wt% of the fourth mixture, the wt% of metakaolinite introduced into the first reaction tank is 25 to 35, the wt% of the first solid introduced into the second reaction tank is 20 to 30, the wt% of the third filtrate introduced into the second reaction tank is 25 to 35, and the wt% of the third solid introduced into the second reaction tank is 0.1 to 2.

The above concrete waste is radioactive concrete waste.

(b) The method may further include a step of hardening the fourth mixture to produce a geopolymer.

By means of the above-described problem-solving means, it is possible to extract useful components used in the manufacture of geopolymer from concrete waste including radioactive concrete waste, and furthermore, the useful components extracted from the concrete waste can be used to solidify the radioactive waste, thereby increasing the recyclability of the concrete waste and minimizing the amount of concrete waste actually disposed of, thereby reducing disposal costs as well as increasing the safety of disposal and the utilization of resources.

Figure 1 is a drawing schematically illustrating a process of extracting a raw material for an alkaline activator from concrete waste according to the present invention.
Figures 2 to 5 are diagrams illustrating data for tests performed according to the present invention.

Hereinafter, a preferred embodiment according to the present invention will be described with reference to the attached drawings. In this process, the thickness of lines and the size of components illustrated in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are terms defined in consideration of functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions of these terms should be made based on the contents throughout this specification.

1. Manufacturing of zeolite polymers

In general, metakaolinite and an alkaline activator are used to manufacture geopolymers according to conventional techniques, and the alkaline activator is manufactured using sodium hydroxide (NaOH), silicon oxide (SiO ₂ ), calcium hydroxide (Ca(OH) ₂ ), and water (H ₂ O).

In the method for manufacturing a geopolymer according to the present invention, silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) and calcium hydroxide (Ca(OH) ₂ ) extracted from concrete waste can be used to manufacture an alkaline activator. That is, silicon oxide (SiO ₂ ) and calcium hydroxide (Ca(OH) ₂ ) used in manufacturing a geopolymer according to the prior art can be replaced with silicon oxide (SiO ₂ ) and calcium hydroxide (Ca(OH) ₂ ) extracted from concrete waste.

Furthermore, in the method for producing a geopolymer according to the present invention, water (H ₂ O) used in producing a geopolymer according to the prior art can be replaced with alkaline waste liquid generated during the process of extracting silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), and calcium hydroxide (Ca(OH) ₂ ) from concrete waste.

Silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) and calcium hydroxide (Ca(OH) ₂ ) used in manufacturing the geopolymer according to the present invention can be extracted from concrete waste, and more preferably from radioactive concrete waste.

As mentioned above, aggregates classified through primary crushing and separation are recycled as recycled aggregates in order to recycle concrete waste. However, it is known that waste fine powders such as cement paste and fine aggregate powder generated in the process of producing recycled aggregates can also be recycled as they can undergo a rehydration reaction through secondary or higher crushing and calcination chemical treatment.

This study aims to recover useful resources from fine powder of concrete waste and recycle them as raw materials for geopolymer. If geopolymer is manufactured by utilizing useful resources from concrete waste, especially radioactive concrete waste, and furthermore, if radioactive waste is solidified according to the method for manufacturing the geopolymer, the volume of radioactive waste to be treated at a radioactive waste disposal site can be minimized and at the same time, radioactive waste can be safely disposed of. In other words, if radioactive concrete waste to be disposed of at a radioactive waste disposal site is used to manufacture geopolymer, and furthermore, if it is used to manufacture a solidified body for radioactive waste, the amount of radioactive concrete waste to be disposed of at a radioactive waste disposal site can be significantly reduced, and if radioactive concrete waste is used as a raw material for a solidified body for radioactive waste and maintains a certain compressive strength, radioactive waste can be disposed of more safely.

Radioactive concrete waste may be concrete waste generated during the decommissioning of a nuclear power plant.

i) Extraction of alkaline activator according to the present invention

Referring to FIG. 1, a process for extracting a raw material for an alkaline activator from concrete waste according to the present invention is described.

In the first step, concrete waste and hydrochloric acid (HCl) can be mixed and stirred to produce a first mixture. At this time, the solid-liquid ratio can be 1:8 to 1:12. Thereafter, the first mixture can be separated into solid and liquid in a pressure reducing filter to produce a first filtrate and a first solid.

Here, the main components of the first solid are silicon oxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ), and silicon oxide (SiO ₂ ) used as an alkaline activator can be replaced with the first solid.

In the next step, sodium hydroxide (NaOH) may be added to the first filtrate to generate a second mixture. The pH of the first filtrate may be adjusted to 9 to 11. Thereafter, the second mixture may be separated into solid and liquid in a pressure reducing filter to generate a second filtrate and a second solid.

In the next step, sodium hydroxide (NaOH) may be added to the second filtrate to generate a third mixture. The pH of the second filtrate may be adjusted to 12 to 14. Thereafter, the third mixture may be separated into solid and liquid in a pressure reducing filter to generate a third filtrate and a third solid.

The third solid may include calcium hydroxide (Ca(OH) ₂ ). Therefore, calcium hydroxide (Ca(OH) ₂ ) used as an alkaline activator may be replaced with the third solid.

Furthermore, the third filtrate is an alkaline waste liquid, and water ( _H2O ) used as an alkaline activator can be replaced with the third filtrate.

Table 1 shows the XRF analysis results of the first to third solid components. The first solid component appears to contain a high weight ratio of silicon oxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ), and the third solid component appears to contain a high weight ratio of calcium oxide (CaO).

[Table 1]

Figure 2 shows the results of analyzing the particle shape of calcium hydroxide (Ca(OH) ₂ ) included in the third solid component. Calcium hydroxide (Ca(OH) ₂ ) included in the third solid component shows a similar specific shape compared to reagents sold on the market.

ii) Experiment on manufacturing geopolymer according to conventional technology

Geopolymer was manufactured by mixing an alkaline activator and metakaolinite according to conventional technology. The mixing ratio (weight %) of raw materials and the molar ratio of each component of the mixture were as follows. A test was conducted on the compressive strength of the geopolymer manufactured accordingly.

The mixing ratio (weight%) of raw materials for manufacturing geopolymer according to conventional technology is as shown in Table 2 below.

Metakaolinite Alkaline activator total Sodium hydroxide (NaOH) Calcium hydroxide (Ca(OH) ₂ ) Silicon oxide (SiO ₂ ) Water ( _H2O ) 37.48% 12.78% 0.99% 19.44% 29.31% 100%

The molar ratio of each component of a mixture in which raw materials are mixed to manufacture a geopolymer according to conventional technology is as follows.

Na ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 1: 1: 4: 11

First, water ( _H2O ), sodium hydroxide (NaOH), calcium hydroxide (Ca(OH) ₂ ), and silicon oxide ( _SiO2 ) were weighed and mixed, and then stirred in a stirrer for one day to prepare an alkaline activator.

Afterwards, the manufactured alkaline activator and metakaolinite were mixed and stirred, and then the geopolymer slurry was poured into a mold to improve the compressive strength and cured in a constant temperature and humidity chamber at 70℃ for one day. Afterwards, the compressive strength was measured after 6 days at room temperature.

The compressive strength of geopolymers manufactured according to conventional techniques is shown in Table 3 below.

Geopolymer sample manufactured according to prior art Compressive strength (MPa) 1-1 14.664 1-2 15.404 1-3 12.167 average 14.078

iii) Manufacturing of geopolymer according to the present invention

According to the present invention, to manufacture a geopolymer, an alkaline activator manufactured through the above-described process can be mixed with metakaolinite.

For 100 wt% of a mixture in which an alkaline activator and metakaolinite are mixed, the wt% of metakaolinite may be 25 to 35, the wt% of the first solid may be 20 to 30, the wt% of the third filtrate may be 25 to 35, the wt% of the third solid may be 0.1 to 2, and the wt% of sodium hydroxide (NaOH) may be 8 to 18.

The molar ratio of each component of a mixture containing an alkaline activator and metakaolinite may be as follows.

Na ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 0.5 to 1.5: 0.5 to 1.5: 2.5 to 4: 11

In the manufacturing process, the third liquid, sodium hydroxide (NaOH), the first solid, and the third solid are first weighed and mixed, and then stirred in a stirrer for one day to manufacture an alkaline activator.

Afterwards, the manufactured alkaline activator and metakaolinite are mixed and stirred, and then the geopolymer slurry is poured into a mold to improve the compressive strength and cured in a constant temperature and humidity chamber at 50 to 90°C for one day.

An experimental example of manufacturing a geopolymer according to the present invention is described.

According to the present invention, a geopolymer was manufactured by mixing an alkaline activator and metakaolinite. The mixing ratio (weight %) of the raw materials and the molar ratio of each component of the mixture were as follows. A test was conducted on the compressive strength of the geopolymer manufactured accordingly.

The mixing ratio (weight%) of raw materials for manufacturing geopolymer according to the present invention is as shown in Table 3 below.

Metakaolinite Alkaline activator
total Sodium hydroxide (NaOH) Third solid component First solid content Third balance 29.85% 13.07% 0.99% 26.85% 29.24% 100%

The molar ratio of each component of the mixture in which the raw materials are mixed in the above-described weight % to manufacture the geopolymer according to the present invention is as follows.

Na ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 1: 1: 3.2: 11

The third filtrate, sodium hydroxide (NaOH), the first solid, and the third solid were weighed and mixed in the weight % described above, and stirred in a stirrer for one day to prepare an alkaline activator.

Afterwards, the manufactured alkaline activator and metakaolinite were mixed and stirred, and then the geopolymer slurry was poured into a mold to improve the compressive strength and cured in a constant temperature and humidity chamber at 70℃ for one day. Afterwards, the compressive strength was measured after 6 days at room temperature.

The compressive strength of the geopolymer manufactured according to the experimental example of manufacturing the geopolymer according to the present invention is as shown in Table 5 below.

Geopolymer sample manufactured according to the present invention Compressive strength (MPa) 2-1 15.283 2-2 15.183 2-3 18.360 average 16.275

Figure 3 shows the results of FT-IR spectra analysis of geopolymers manufactured according to the above-described conventional technology and the present invention.

In Fig. 3, the peaks at 3,240 cm ^-1 and 1,640 cm ^-1 are peaks related to water molecules. In the case of the geopolymer according to the present invention, mixing was easier than that of the geopolymer according to the prior art when metakaolinite and an alkaline activator were mixed, and the solid-liquid ratio was the same at approximately 7:3.

544 cm ^-1 is the peak of the Si-O-Al band, and 956 cm -1 was also identified as the peak of Si-OT (T: Si or Al).

Accordingly, if useful resources are extracted from concrete waste and used in the manufacture of geopolymer, the volume reduction of the generated concrete waste can be drastically reduced. Furthermore, when a radioactive waste solidified body is manufactured using the above-described geopolymer manufacturing method, the compressive strength of the solidified body according to the radioactive waste delivery regulations can be maintained at a standard value (3.4 MPa) or higher.

2. Production of radioactive waste solidification material

A method for solidifying radioactive waste into a solidified body according to the method for manufacturing the above-described geopolymer is described.

Radioactive waste as a target of solidification can of course be waste containing radioactive nuclides, such as waste resin, concentrated waste liquid, corrosive sludge, soil sludge, concrete waste, metal, and soil.

The description of the alkaline activator used in manufacturing the radioactive waste solidification body according to the above-described geopolymer manufacturing method follows the description of the alkaline activator used in manufacturing the geopolymer according to the present invention described above.

To manufacture a radioactive waste solidification body according to the present invention, radioactive waste, the above-described alkaline activator, and metakaolinite can be mixed.

For 100 wt% of a mixture of radioactive waste, an alkaline activator, and metakaolinite, the wt% of the radioactive waste may be 5 to 25, the wt% of the metakaolinite may be 20 to 30, the wt% of the first solid may be 17 to 27, the wt% of the third filtrate may be 20 to 30, the wt% of the third solid may be 0.1 to 2, and the wt% of sodium hydroxide (NaOH) may be 5 to 15.

The molar ratios of the components of a mixture of radioactive waste, alkaline activator, and metakaolinite are as follows.

Na ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 0.5 to 1.5: 0.5 to 1.5: 2.5 to 4: 11

In the manufacturing process, the third liquid, sodium hydroxide (NaOH), the first solid, and the third solid are first weighed and mixed, and then stirred in a stirrer for one day to manufacture an alkaline activator.

Afterwards, the manufactured alkaline activator, radioactive waste, and metakaolinite are mixed and stirred, and then the geopolymer slurry is poured into a mold to improve the compressive strength and cured in a constant temperature and humidity chamber at 50 to 90°C for one day.

An experimental example of manufacturing a radioactive waste solidification body according to the present invention is described.

According to the present invention, a radioactive waste solidification body was manufactured by mixing simulated corrosive sludge and metakaolinite with an alkaline activator, and a test was conducted on the compressive strength of the solidification body manufactured in this manner.

The radioactive waste used was a simulated corrosive sludge manufactured based on the expected waste characteristics data provided by Korea Hydro & Nuclear Power during the expected decommissioning of a nuclear power plant. The composition ratio of the simulated corrosive sludge is as shown in Table 6.

[Table 6]

XRF characteristic analysis of the manufactured simulated corrosive sludge is shown in Table 7.

[Table 7]

The mixing ratio (weight %) of raw materials for manufacturing a radioactive waste solidification body according to the present invention is as shown in Table 7 below.

[Table 8]

The molar ratio of each component of the mixture in which the raw materials are mixed to manufacture a radioactive waste solidification body according to the present invention is as follows.

Na ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 1: 1: 3.2: 11

The third filtrate, sodium hydroxide (NaOH), the first solid, and the third solid were weighed and mixed in the weight % described above, and stirred in a stirrer for one day to prepare an alkaline activator.

Afterwards, the manufactured alkaline activator, corrosive sludge and metakaolinite were mixed and stirred, and the slurry was poured into a mold to improve the compressive strength and hardened in a constant temperature and humidity chamber at 70℃ for one day. Afterwards, the compressive strength was measured after 6 days at room temperature.

The compressive strength of the radioactive waste solidification body manufactured according to the experimental example of manufacturing the radioactive waste solidification body according to the present invention is as shown in Table 9 below.

[Table 9]

An evaluation test (free water generation test, thermal cycle test, leaching test) was conducted on the solidified radioactive waste body manufactured according to the present invention for the solidified body acceptance criteria.

In the case of the free water test, the prepared 100-mesh filter paper was used to place the radioactive waste solidification body on top and check whether free water was generated for 5 minutes. As shown in Fig. 4, even after 5 minutes, there was still no change in the diameter, height, and weight, confirming that free water was not generated.

In the case of the thermal cycling test, one cycle was considered as maintaining 22℃-->60℃-->-40℃ for 1 hour each according to the test method of ASTM B553, and the compressive strength was measured after 30 cycles, and the compressive strength is as shown in Table 10 below. Figure 5 is a graph showing the weight change before and after thermal cycling.

[Table 10]

In the case of the leaching test, the radioactive waste solidification body was manufactured at the above-mentioned weight % using corrosive sludge manufactured so that the concentration of each of cobalt (Co), cesium (Cs), and strontium (Sr) was 30 mg/g according to the ANSI 16.1 test method, and the leaching index was obtained by soaking it in distilled water for 90 days. If the leaching index is 6 or higher, the solidification body acceptance standard is satisfied, and the leaching index of the radioactive waste solidification body according to the present invention satisfying the solidification body acceptance standard is as shown in Table 11.

[Table 11]

Above, although this specification has been described with reference to the embodiments illustrated in the drawings so that those skilled in the art can easily understand and reproduce the present invention, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible from the embodiments of the present invention. Therefore, the protection scope of the present invention should be determined by the patent claims.

Claims (5)

(a) a step in which metakaolinite and an alkaline activator are introduced into a first reaction tank to produce a fourth mixture;
A method for producing a geopolymer, wherein silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) and calcium hydroxide (Ca(OH) ₂ ) extracted from concrete waste are introduced into a second reactor to produce the alkaline activator.
In paragraph 1,
(a-1) a step in which the concrete waste and hydrochloric acid (HCl) are mixed to produce a first mixture; and
(a-2) further comprising a step in which the first mixture is subjected to solid-liquid separation to produce a first filtrate and a first solid,
After the above step (a-2), the above step (a) is performed.
The first solid component contains silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ).
A method for producing a geopolymer, wherein the first solid component is injected into the second reaction tank to produce the alkaline activator.
In the second paragraph,
(a-3) After the step (a-2), a step in which the first filtrate and sodium hydroxide (NaOH) are mixed to generate a second mixture;
(a-4) A step in which the second mixture is separated into solid and liquid to generate a second filtrate and a second solid;
(a-5) a step in which the second filtrate and sodium hydroxide (NaOH) are mixed to produce a third mixture; and
(a-6) further comprising a step in which the third mixture is separated into solid and liquid to produce a third filtrate and a third solid.
After the above step (a-6), the above step (a) is performed.
The third solid component contains calcium hydroxide (Ca(OH) ₂ ),
A method for producing a geopolymer, wherein the third solid component is injected into the second reaction tank to produce the alkaline activator.
In the third paragraph,
A method for producing a geopolymer, wherein the third residue is injected into the second reaction tank to produce the alkaline activator.
In paragraph 4,
For 100 wt% of the fourth mixture, the wt% of metakaolinite introduced into the first reaction tank is 25 to 35, the wt% of the first solid introduced into the second reaction tank is 20 to 30, the wt% of the third filtrate introduced into the second reaction tank is 25 to 35, and the wt% of the third solid introduced into the second reaction tank is 0.1 to 2.
The above concrete waste is radioactive concrete waste.
(b) A method for producing a geopolymer, further comprising a step of hardening the fourth mixture to produce a geopolymer.