Geopolymer, solidified product of the same, radioactive waste treatment method

Abstract

To provide a geopolymer capable of suppressing elution of carbonate ions including 14C, and to provide a solidified product of the geopolymer and a radioactive waste treatment method.SOLUTION: A geopolymer is provided, comprising a sodium hydroxide aqueous solution containing 14CO2 gas, fine mortar powder obtained from contaminated concrete, fly ash, and blast furnace slag, where the concentration of the sodium hydroxide aqueous solution is less than 5 mol / L.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a geopolymer containing radioactive waste, a solidified geopolymer, and a method for treating radioactive waste generated in the volume reduction treatment of concrete. [Background technology]

[0002] At nuclear power plants, radioactive carbon ( 14 C) generated and generated 14 C is radioactive carbon dioxide ( 14 CO2). 14 Although CO2 is absorbed by the concrete of the reactor buildings of nuclear power plants, the gaseous substance remains free to move, spreading contamination over a wider area. 14 It is known that CO2 can penetrate concrete to a depth of several tens of centimeters. 14 CO2-contaminated concrete (hereinafter referred to as " 14 The amount of CO2-contaminated concrete (called "CO2-contaminated concrete") will be enormous.

[0003] Becomes radioactive waste 14 In order to reduce the amount of CO2 contaminated concrete, when decommissioning aging nuclear power plants, the contaminated parts are removed and the contaminated parts ( 14 CO2 containing area) and non-contaminated area ( 14 It is divided into two parts:

[0004] Contaminated areas are solidified with cement or geopolymers and disposed of as radioactive waste. Non-contaminated areas are treated as non-radioactive waste. When radioactive waste is disposed of by burial, it is desirable that it is in a state where radioactive materials are unlikely to leach into groundwater, etc.

[0005] 14The use of geopolymers for CO2 fixation is being considered (see, for example, Patent Document 1). Geopolymers are made by mixing industrial waste such as fly ash (coal ash) and blast furnace slag (a by-product generated during steelmaking) with an alkaline aqueous solution such as sodium hydroxide and solidifying it. In general, geopolymers are superior to cement-solidified materials in terms of strength, heat resistance, durability, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-178761 Summary of the Invention [Problem to be solved by the invention]

[0007] The sodium hydroxide solution contained in the geopolymer is generally high concentration (5 mol / L to 8 mol / L). Geopolymers using high concentration sodium hydroxide solution are: 14 The elution of carbonate ions containing C increases. 14 It is necessary to suppress the elution of carbonate ions, including C.

[0008] The present invention has been made in view of the above circumstances, 14 The present invention aims to provide a geopolymer capable of suppressing the elution of carbonate ions containing C, a solidified geopolymer, and a method for treating radioactive waste. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] 14 The method comprises: a sodium hydroxide solution containing CO2 gas; fine powder of mortar obtained from contaminated concrete; fly ash; and blast furnace slag. A geopolymer, wherein the concentration of the aqueous sodium hydroxide solution is less than 5 mol / L. [2] A solidified geopolymer consisting of a hardened geopolymer according to [1]. [3] 14 A crushing process to crush the contaminated concrete contaminated with CO2; a heating step of heating the crushed contaminated concrete; The contamination was generated by heating the contaminated concrete. 14 CO2 gas is captured with a sodium hydroxide solution, 14 a capturing step of forming a sodium hydroxide aqueous solution containing CO2 gas; a separation step of separating the heated contaminated concrete into coarse aggregate and fine mortar powder; The aforementioned 14 A kneading process of kneading a sodium hydroxide aqueous solution containing CO2 gas, the fine powder, fly ash, and blast furnace slag to form a geopolymer; A solidification step of solidifying the geopolymer, A method for treating radioactive waste, wherein the concentration of the aqueous sodium hydroxide solution in the collection step is less than 5 mol / L. [Effects of the Invention]

[0010] According to the present invention, 14 It is possible to provide a geopolymer capable of suppressing the elution of carbonate ions containing C, a solidified geopolymer, and a method for treating radioactive waste. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the relationship between the concentration of an aqueous sodium hydroxide solution and the amount of carbonate ions eluted in an experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiments of the geopolymer, the solidified geopolymer, and the method for treating radioactive waste of the present invention will be described below. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0013] [Geopolymer] The geopolymer according to one embodiment of the present invention comprises: 14 It contains an aqueous sodium hydroxide solution containing CO2 gas, fine powder of mortar obtained from contaminated concrete, fly ash, and blast furnace slag.

[0014] The concentration of the sodium hydroxide aqueous solution is less than 5 mol / L, preferably 0.9 mol / L or more and 3.0 mol / L or less, and more preferably 1 mol / L or more and 1.25 mol / L or less. When the concentration of the sodium hydroxide aqueous solution is less than 5 mol / L, it is possible to suppress the elution of carbonate ions from the solidified geopolymer. It is preferable that the lower limit of the concentration of the sodium hydroxide aqueous solution is 1 mol / L or more. When the lower limit of the concentration of the sodium hydroxide aqueous solution is 1 mol / L or more, 14 For example, 1 mol / L of sodium hydroxide solution at 25°C will absorb 12.3 L of CO2 gas. 14 It is possible to capture CO2 gas containing CO2. Here, the concentration of the sodium hydroxide solution refers to the concentration of the sodium hydroxide solution before it is mixed with the fine powder of mortar obtained from contaminated concrete, fly ash, and blast furnace slag.

[0015] The total mass of the geopolymer, i.e., 14 The content of the sodium hydroxide aqueous solution relative to the total mass of the sodium hydroxide aqueous solution containing CO2 gas, the fine powder of mortar obtained from contaminated concrete, the fly ash, and the blast furnace slag is preferably 25% by mass or more and 40% by mass or less, more preferably 30% by mass or more and 40% by mass or less, and even more preferably 35% by mass or more and 40% by mass or less. When the content of the sodium hydroxide aqueous solution is equal to or more than the lower limit, 14The sodium hydroxide solution containing CO2 gas, fine powder of mortar obtained from contaminated concrete, fly ash, and blast furnace slag can be mixed. When the content of the sodium hydroxide solution is below the upper limit, the geopolymer can be solidified.

[0016] The fine mortar powder was obtained by separating contaminated concrete into coarse aggregate and fine mortar powder. The particle size of the fine powder of the mortar is preferably 0.15 mm to 5 mm, more preferably 0.15 mm to 4 mm, and even more preferably 0.15 mm to 3 mm. When the particle size of the fine powder is above the lower limit, not much energy is required when kneading with the alkaline solution, fly ash, and blast furnace slag, as described below. When the particle size of the fine powder is below the upper limit, the fine powder can be sufficiently mixed with these raw materials when kneading with the alkaline solution, fly ash, and blast furnace slag, as described below.

[0017] Fly ash is a type of ash produced when coal is burned. Examples of fly ash include fly ash types I to IV, whose quality standards are defined in JIS A 6201:2015. In addition, in the present invention, fly ash raw powder that does not meet JIS standards and that has not been subjected to any classification treatment or the like may be used, which is obtained from fly ash generated from a coal-fired power plant. The fly ash can be used alone or in combination of two or more types.

[0018] As the blast furnace slag, either slowly cooled blast furnace slag or granulated blast furnace slag can be used. As an example of blast furnace slag, for example, blast furnace slag powder for concrete (Blaine value 3000 cm) whose quality standard is specified in JIS A 6206:2013 is used. 2 / g class, 4000cm 2 / g class, 6000cm 2 / g class, 8000cm 2 / g class).

[0019] [Geopolymer manufacturing method] A method for producing a geopolymer according to one embodiment of the present invention includes: 14 A crushing process for crushing contaminated concrete contaminated with CO2, a heating process for heating the crushed contaminated concrete, and a process for heating the contaminated concrete. 14 CO2 gas is captured with a sodium hydroxide solution, 14 a capturing step of converting the CO2 gas into a sodium hydroxide aqueous solution; a separating step of separating the heated contaminated concrete into coarse aggregate and mortar fine powder; 14 The method includes a kneading step in which a sodium hydroxide aqueous solution containing CO2 gas, the fine powder, fly ash, and blast furnace slag are kneaded to produce a geopolymer.

[0020] Crushing process In the crushing process, radioactive materials generated in the reactor are 14 Crushing contaminated concrete contaminated with CO2. Contaminated concrete is subject to change depending on the operating conditions of the reactor. 14 CO2 has penetrated deep into the interior, and in some places has penetrated to a depth of several tens of millimeters. In decontamination treatment for such contaminated concrete, the surface layer of the contaminated concrete is removed to a thickness of at least several tens of millimeters, and this removed portion is then treated as radioactive waste. The method for crushing the contaminated concrete is not particularly limited, but examples thereof include grinding and removing the surface layer of the contaminated concrete.

[0021] The particle size of the contaminated concrete after crushing is preferably 10 mm or more and 80 mm or less, more preferably 10 mm or more and 60 mm or less, and even more preferably 10 mm or more and 40 mm or less. If the particle size of the contaminated concrete after crushing is equal to or greater than the lower limit, the contaminated concrete can be efficiently separated into coarse aggregate and fine mortar powder in the separation step described below. If the particle size of the contaminated concrete after crushing is equal to or less than the upper limit, the contaminated concrete can be efficiently separated into fine mortar powder in the heating step described below. 14CO2 gas can be generated.

[0022] "Heating process" In the heating step, the contaminated concrete crushed in the crushing step is heated. The temperature to which the contaminated concrete is heated is preferably 200° C. or higher and 450° C. or lower, more preferably 250° C. or higher and 400° C. or lower, and even more preferably 300° C. or higher and 350° C. or lower. If the temperature to which the contaminated concrete is heated is above the lower limit, a large amount of 14 Heat treatment can be performed without volatilizing CO2. When the temperature to which the contaminated concrete is heated is equal to or lower than the upper limit, the strength of the contaminated concrete decreases due to heating, and the contaminated concrete can be efficiently separated into coarse aggregate and fine mortar powder.

[0023] By heating the contaminated concrete, 14 CO2 gas is produced.

[0024] "Collection process" In the collection process, the contaminated concrete was heated during the heating process. 14 CO2 gas is captured with a sodium hydroxide solution, 14 It is an aqueous sodium hydroxide solution containing CO2 gas.

[0025] "Separation process" In the separation step, the contaminated concrete heated in the heating step is separated into coarse aggregate and fine mortar powder. In order to separate the contaminated concrete into coarse aggregate and fine mortar powder, it is preferable to subject the contaminated concrete to a grinding treatment. 14It is known that CO2 gas penetrates the mortar portion of concrete, so contamination is observed in the mortar portion, but not in the coarse aggregate. In the separation process, contaminated concrete is separated into coarse aggregate and fine mortar powder, with the coarse aggregate becoming non-radioactive waste and the fine mortar powder becoming radioactive waste. For example, by subjecting contaminated concrete to a grinding process, the contaminated concrete can be separated into coarse aggregate and fine mortar powder, reducing the volume of radioactive waste. In particular, by heating the contaminated concrete, 14 After generating CO2 gas, the contaminated concrete can be ground to reduce the volume of fine mortar powder that becomes radioactive waste.

[0026] The grinding process can be carried out in accordance with the method described in JP 2017-227493 A, for example.

[0027] The particle size of the fine powder of mortar obtained by the grinding treatment is preferably 0.15 mm or more and 5 mm or less, more preferably 0.15 mm or more and 4 mm or less, and even more preferably 0.15 mm or more and 3 mm or less. 14 When the particle size of the fine powder is equal to or less than the upper limit, the following can be achieved: 14 When kneading with the sodium hydroxide aqueous solution containing CO2 gas, fly ash, and blast furnace slag, these raw materials can be thoroughly mixed with the fine powder.

[0028] The coarse aggregate obtained in the separation process becomes non-radioactive waste. The non-radioactive waste coarse aggregate is reused.

[0029] "Mixing process" In the kneading process, 14 A geopolymer is obtained by kneading a sodium hydroxide aqueous solution containing CO2 gas with fine mortar powder, fly ash, and blast furnace slag. 14The method for kneading the sodium hydroxide aqueous solution containing CO2 gas, the fine powder, the fly ash, and the blast furnace slag is not particularly limited, but it is preferable to, for example, put the raw materials into a container such as a mortar and knead them using a stirring device such as a twin-screw mixer. Note that, from the viewpoint of safety, the fine powder, which is radioactive waste, should not be mixed with other raw materials ( 14 It is preferable to mix the sodium hydroxide solution containing CO2 gas, fly ash, and blast furnace slag to form a paste and then add it.

[0030] 14 The compounding ratio of the sodium hydroxide aqueous solution containing CO2 gas (hereinafter referred to as "A1 component"), fly ash (hereinafter referred to as "B1 component"), blast furnace slag (hereinafter referred to as "C1 component"), and fine powder (hereinafter referred to as "D1 component") is not particularly limited, but for example, the range shown below is preferable. The blending ratio of B1 component to A1 component + C1 component (B1 component / (A1 component + C1 component)) is preferably 0.0 to 3.0 in mass ratio, more preferably 0.1 to 2.0 in mass ratio, and even more preferably 0.2 to 1.0 in mass ratio. When the blending ratio (B1 component / (A1 component + C1 component)) is equal to or greater than the lower limit, the geopolymer solidifies. When the blending ratio (B1 component / (A1 component + C1 component)) is equal to or less than the upper limit, the geopolymer can be kneaded to produce a waste body.

[0031] The blending ratio of the C1 component to the A1 component (C1 component / A1 component) is preferably 0.0 to 3.0 by mass, more preferably 0.25 to 2.0, and even more preferably 0.5 to 1.0. When the blending ratio (C1 component / A1 component) is within the range between the lower and upper limits, the quality of the fly ash is stable even if the type of fly ash is changed.

[0032] The blending ratio of D1 component to A1 component + B1 component + C1 component (D1 component / (A1 component + B1 component + C1 component)) is preferably 0.5 or more and 2.5 or less, more preferably 1 or more and 2.5 or less, and even more preferably 1.5 or more and 2.5 or less, by mass. When the blending ratio (D1 component / (A1 component + B1 component + C1 component)) is equal to or more than the lower limit, the waste blend is efficient when it is made into waste. When the blending ratio (D1 component / (A1 component + B1 component + C1 component)) is equal to or less than the upper limit, the waste can be produced by kneading.

[0033] According to the geopolymer of this embodiment, the concentration of the sodium hydroxide aqueous solution is set to less than 5 mol / L, which is lower than that of conventional geopolymers, 14 It is possible to suppress the elution of carbonate ions containing C. It is also possible to suppress the elution of carbonate ions that are generated by heating contaminated concrete. 14 The method involves mixing a sodium hydroxide solution containing CO2 gas with fine mortar powder obtained by separating heated contaminated concrete, fly ash, and blast furnace slag to form a geopolymer, which is then solidified into radioactive waste, allowing for efficient and appropriate disposal of radioactive waste.

[0034] [Solidified geopolymer] The solidified geopolymer according to one embodiment of the present invention is a hardened geopolymer according to the above embodiment, which includes alkali carbonate, fine mortar powder obtained from contaminated concrete, fly ash, and blast furnace slag. The solidified geopolymer of this embodiment can be obtained by the radioactive waste treatment method of the embodiment described below.

[0035] In the solidified geopolymer of this embodiment, the compounding ratio of alkali carbonate (hereinafter referred to as "component A2"), fly ash (hereinafter referred to as "component B2"), blast furnace slag (hereinafter referred to as "component C2"), and fine powder (hereinafter referred to as "component D2") is not particularly limited, but for example, the range shown below is preferable. Alkali carbonate is dissolved in the above alkaline solution. 14 It is made up of CO2 gases combined together.

[0036] The blending ratio of B2 component to A2 component + C2 component (B2 component / (A2 component + C2 component)) is preferably 0.0 to 3.0 in mass ratio, more preferably 0.1 to 2.0 in mass ratio, and even more preferably 0.2 to 1.0 in mass ratio. When the blending ratio (B2 component / (A2 component + C2 component)) is equal to or greater than the lower limit, the geopolymer solidifies. When the blending ratio (B2 component / (A2 component + C2 component)) is equal to or less than the upper limit, the mixture can be kneaded to produce a waste product.

[0037] The blending ratio of the C2 component to the A2 component (C2 component / A2 component) is preferably 0.0 to 3.0 by mass, more preferably 0.25 to 2.0, and even more preferably 0.5 to 1.0. When the blending ratio (C2 component / A2 component) is within the range between the lower and upper limits, the quality of the fly ash is stable even if the type of fly ash is changed.

[0038] The blending ratio of D2 component to A2 component + B2 component + C2 component (D2 component / (A2 component + B2 component + C2 component)) is preferably 0.5 or more and 2.5 or less, more preferably 1 or more and 2.5 or less, and even more preferably 1.5 or more and 2.5 or less, by mass. When the blending ratio (D2 component / (A2 component + B2 component + C2 component)) is equal to or greater than the lower limit, the waste blend is efficient when it is made into waste. When the blending ratio (D2 component / (A2 component + B2 component + C2 component)) is equal to or less than the upper limit, the waste can be produced by kneading.

[0039] According to the solidified geopolymer of this embodiment, since it is made of the hardened geopolymer of the above embodiment and the content of alkali carbonate is less than 2.0 mass%, it is more effective than conventional 14 It is possible to suppress the elution of carbonate ions containing C. Furthermore, since all components of the solidified geopolymer of this embodiment are waste, it can be safely and appropriately disposed of as radioactive waste in a final disposal site without using any materials other than waste.

[0040] [Radioactive waste disposal methods] A method for treating radioactive waste according to one embodiment of the present invention includes a step of obtaining a geopolymer by the method for producing a geopolymer according to the above-described embodiment, and a step of solidifying the geopolymer. That is, the method for treating radioactive waste according to one embodiment of the present invention includes the steps of: 14 A crushing process for crushing contaminated concrete contaminated with CO2, a heating process for heating the crushed contaminated concrete, and a process for heating the contaminated concrete. 14 CO2 gas is captured with a sodium hydroxide solution, 14 a capturing step of converting the CO2 gas into a sodium hydroxide aqueous solution; a separating step of separating the heated contaminated concrete into coarse aggregate and mortar fine powder; 14 The method includes a kneading step in which a sodium hydroxide aqueous solution containing CO2 gas, the fine powder, fly ash, and blast furnace slag are kneaded to form a geopolymer, and a solidification step in which the geopolymer is solidified.

[0041] "Solidification process" In the solidification process, the geopolymer obtained in the kneading process is solidified.

[0042] A geopolymer containing an alkaline solution, fine powder, fly ash, and blast furnace slag is poured into a formwork and left to harden for, for example, 1 to 14 days, resulting in a solidified geopolymer.

[0043] The solidified geopolymer will be sent to a final disposal site and disposed of as radioactive waste.

[0044] According to the radioactive waste treatment method of this embodiment, the concentration of the sodium hydroxide aqueous solution is set to less than 5 mol / L, which is lower than that in conventional radioactive waste treatment methods. 14 It is possible to suppress the elution of carbonate ions containing C. It is also possible to suppress the elution of carbonate ions that are generated by heating contaminated concrete. 14The radioactive waste can be efficiently and appropriately treated by mixing a sodium hydroxide solution containing CO2 gas with fine mortar powder obtained by separating heated contaminated concrete, fly ash, and blast furnace slag to form a geopolymer, which is then solidified to produce radioactive waste. In other words, since all of the components used in the radioactive waste of this embodiment are waste, the waste can be effectively utilized to solidify the radioactive waste. [Example]

[0045] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0046] [Experimental Example] "Geopolymer production" A twin-screw mixer was used to knead fly ash, blast furnace slag, and aqueous sodium hydroxide solution to obtain a kneaded mixture. Here, the mass ratio of fly ash, blast furnace slag, and aqueous sodium hydroxide solution was set to 7:3:5. The aqueous sodium hydroxide solutions used had concentrations of 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 5 mol / L. To the above kneaded product, 14 2% by mass of sodium carbonate was added as a CO2 simulant, and geopolymers containing various concentrations of sodium hydroxide aqueous solution were prepared. The resulting geopolymer was subjected to a carbonate ion elution test in accordance with JIS K 0058-1. The results are shown in Figure 1. From the results shown in FIG. 1, it was found that the amount of carbonate ions eluted decreased (the elution of carbonate ions was suppressed) as the concentration of the aqueous sodium hydroxide solution decreased. The results shown in Figure 1 indicate that the geopolymer prepared using 1 mol / L sodium hydroxide solution had approximately one-third the amount of carbonate ions eluted compared to the geopolymer prepared using 5 mol / L sodium hydroxide solution. In this experimental example, 14 As a CO2 simulant 14Although sodium carbonate containing no C was used, 14 A similar trend is observed in CO2-contaminated concrete. Furthermore, since a 1 mol / L sodium hydroxide solution is not considered a toxic or hazardous substance (a sodium hydroxide solution of 1.25 mol / L or more is considered a toxic or hazardous substance), it is possible to produce a geopolymer that suppresses the leaching of carbonate ions without using toxic or hazardous chemicals.

Claims

1. １４ CO ２ The method comprises: a gas-containing aqueous sodium hydroxide solution; fine powder of mortar obtained from contaminated concrete; fly ash; and blast furnace slag. A geopolymer, wherein the concentration of the aqueous sodium hydroxide solution is less than 5 mol / L.

2. A solidified geopolymer comprising the hardened geopolymer of claim 1.

3. １４ CO ２ a crushing step of crushing the contaminated concrete; a heating step of heating the crushed contaminated concrete; The contamination was generated by heating the contaminated concrete. １４ CO ２ The gas is collected with an aqueous sodium hydroxide solution. １４ CO ２ a capturing step of forming a gas-containing aqueous sodium hydroxide solution; a separation step of separating the heated contaminated concrete into coarse aggregate and fine mortar powder; The aforementioned １４ CO ２ A kneading step of kneading a gas-containing sodium hydroxide aqueous solution, the fine powder, fly ash, and blast furnace slag to form a geopolymer; A solidification step of solidifying the geopolymer, A method for treating radioactive waste, wherein the concentration of the aqueous sodium hydroxide solution in the collection step is less than 5 mol / L.

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