Geopolymer, geopolymer solidified body, method for producing geopolymer, and method for treating radioactive waste

Abstract

To provide: a geopolymer capable of improving all of compressive strength, fluidity, and fluidity retention time; a geopolymer solidified body; a method for producing the geopolymer; and a method for treating a radioactive waste.SOLUTION: A geopolymer comprises: an alkaline solution; fine powder of mortar, obtained from contaminated concrete; a fly ash; a blast furnace slag; and an admixture. The admixture is at least one of a mixture of lignin sulfonate and polyalkylene glycol derivative, and an oxycarboxylic acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a geopolymer, a solidified geopolymer, a method for producing a geopolymer, and a method for treating radioactive waste. [Background technology]

[0002] At nuclear power plants, radioactive carbon ( 14 C) generated and generated 14 C is radioactive carbon dioxide ( 14 It exists as 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. 14 CO2-contaminated concrete will be disposed of as radioactive waste.

[0003] Radioactive waste discharged from nuclear power plants is solidified in drums before disposal. Currently, cement-based materials are used to solidify radioactive waste, but geopolymers can also be used. Geopolymers have higher compressive strength and radionuclide adsorption capacity than cement, making them a more suitable material for solidifying radioactive waste.

[0004] Solidified radioactive waste forms include homogeneous solidified forms made from powdered waste and packed solidified forms made from bulky waste. When using geopolymers to solidify radioactive waste, the higher the compressive strength of the waste form, the better. Furthermore, the higher the fluidity of the geopolymer, the better it will be for filling the gaps in the packed solidified form.

[0005] A geopolymer composition that can be used to produce a hardened body that can suppress the leaching of heavy metals is known to contain an active filler, aggregate, water, an activator, and a dispersant, and the active filler contains a total of 85 mass% or more of coal ash and granulated blast furnace slag that has not been treated to comply with the standard for fly ash for concrete specified in JIS A6201 (see, for example, Patent Document 1).

[0006] Furthermore, additives for geopolymers are known that can ensure the strength development of the hardened body and also provide a hardened body that can suppress drying shrinkage (see, for example, Patent Document 2).

[0007] In addition, a method for producing a hardened geopolymer body that can sufficiently extend the fluidity retention time of a geopolymer composition is known (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2023-49893 [Patent Document 2] Japanese Patent Application Publication No. 2017-202963 [Patent Document 3] Japanese Patent Publication No. 2020-26357 Summary of the Invention [Problem to be solved by the invention]

[0009] Generally, increasing the concentration of the alkaline solution used improves the compressive strength of geopolymers, but reduces the fluidity and fluidity retention time. On the other hand, decreasing the concentration of the alkaline solution used improves the fluidity and fluidity retention time of geopolymers, but reduces the compressive strength. Furthermore, when the amount of alkaline solution used is reduced, the compressive strength of the geopolymer increases, but the fluidity and fluidity retention time decrease. On the other hand, when the amount of alkaline solution used is increased, the fluidity and fluidity retention time of the geopolymer increase, but the compressive strength decreases.

[0010] As such, the concentration and amount of alkaline solution tend to be in conflict with the strength and fluidity / fluidity retention time of the geopolymer. Therefore, even if the concentration and amount of alkaline solution are considered, it is difficult to improve all of the compressive strength, fluidity, and fluidity retention time.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a geopolymer, a solidified geopolymer, a method for producing a geopolymer, and a method for treating radioactive waste that can improve all of compressive strength, fluidity, and fluidity retention time. [Means for solving the problem]

[0012] The present invention has the following aspects. [1] A method for treating a concrete contaminated with mortar, comprising: an alkaline solution; fine powder of mortar obtained from contaminated concrete; fly ash; blast furnace slag; and an admixture; The admixture is a geopolymer that is at least one of a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, and an oxycarboxylic acid. [2] The geopolymer according to [1], wherein the content of the admixture is 60% by mass or more and 95% by mass or less. [3] A solidified geopolymer consisting of a hardened geopolymer according to [1] or [2]. [4] 14 A crushing process to crush the contaminated concrete contaminated with CO2; a dissolving step of dissolving an admixture in an alkaline solution; a heating step of heating the crushed contaminated concrete; The contamination was generated by heating the contaminated concrete. 14 CO2 gas is captured using an alkaline solution containing an admixture, 14a capturing step of obtaining an alkaline 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 step of kneading an alkaline solution containing CO2 gas, the fine powder, fly ash, and blast furnace slag, The method for producing a geopolymer, wherein the admixture is at least one of a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, and an oxycarboxylic acid. [5] The method for producing a geopolymer according to [4], wherein the amount of the admixture added is 0.5% by mass or more and 4% by mass or less relative to the total mass of the alkaline solution and the admixture. [6] [4] or [5], and obtaining a geopolymer by the method for producing a geopolymer; A method for treating radioactive waste, comprising a solidification step of solidifying the geopolymer. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a geopolymer that can improve all of compressive strength, fluidity, and fluidity retention time, a solidified geopolymer, a method for producing a geopolymer, and a method for treating radioactive waste. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows the results of measuring the compressive strength of geopolymers of Examples 1 and 2 and Comparative Example 1. [Figure 2] FIG. 1 shows the results of compressive strength measurements of geopolymers of Examples 3 and 4 and Comparative Example 2. [Figure 3] FIG. 1 shows the evaluation results of the fluidity of geopolymers of Examples 1 and 2 and Comparative Example 1. [Figure 4] FIG. 1 shows the evaluation results of the fluidity of the compressive strength of geopolymers of Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Embodiments of the geopolymer, the solidified geopolymer, the method for producing the 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.

[0016] [Geopolymer] The geopolymer according to one embodiment of the present invention comprises an alkaline solution, fine powder of mortar obtained from contaminated concrete, fly ash, blast furnace slag, and admixtures.

[0017] Examples of the alkaline solution include an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide. The concentration of the alkaline solution is preferably 1 mol / L or more and 5 mol / L or less, more preferably 2 mol / L or more and 5 mol / L or less, and even more preferably 3 mol / L or more and 5 mol / L or less. The alkaline solution is particularly preferably a sodium hydroxide aqueous solution having a concentration of 1 mol / L or more. When 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 CO2 gas containing CO2 can be captured.

[0018] The total mass of the geopolymer, i.e., 14 The content of the alkaline solution relative to the total mass of the alkaline solution containing CO2 gas, the fine powder of mortar obtained from contaminated concrete, the fly ash, and the blast furnace slag is preferably 30% by mass or more and 60% by mass or less, more preferably 35% by mass or more and 55% by mass or less, and even more preferably 40% by mass or more and 50% by mass or less. 14The geopolymer can be solidified by mixing an alkaline solution containing CO2 gas, finely ground mortar obtained from contaminated concrete, fly ash, and blast furnace slag. If the alkaline solution content is below the upper limit, the geopolymer will solidify.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] The compatibilizer is either a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, or an oxycarboxylic acid, or both a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, and an oxycarboxylic acid.

[0023] Examples of lignin sulfonic acids include those obtained by sulfonating lignin purified from wood vinegar, those purified from waste liquid discharged in a pulp manufacturing process, etc. Among these, those purified from waste liquid discharged in a pulp manufacturing process are preferred from the viewpoint of waste recycling. Examples of polyalkylene glycol derivatives include those obtained by polymerizing alkylene oxides and those refined from petroleum, etc. Among these, those obtained by polymerizing alkylene oxides are preferred from the viewpoint of containing fewer impurities that reduce the effect.

[0024] The compounding ratio of lignosulfonic acid to polyalkylene glycol derivative, i.e., the ratio of lignosulfonic acid to polyalkylene glycol derivative (lignosulfonic acid / polyalkylene glycol derivative), is preferably 1.5 to 3, more preferably 2 to 3, and even more preferably 2.5 to 3. If the compounding ratio is above the lower limit, the porosity decreases and the strength improves. If the compounding ratio is below the upper limit, the geopolymer solidifies.

[0025] Examples of hydroxycarboxylic acids include sodium gluconate, hydroxybutyric acid, etc. Among these, sodium gluconate is preferred from the viewpoint of chemical stability.

[0026] The content of the admixture relative to the total mass of the geopolymer is preferably 0.1% by mass to 5% by mass, more preferably 0.2% by mass to 4% by mass, and even more preferably 0.3% by mass to 3% by mass. If the content of the admixture is above the lower limit, the geopolymer does not become too hard when mixed and solidifies. If the content of the admixture is below the upper limit, the geopolymer does not become too soft when mixed and solidifies.

[0027] According to the geopolymer of this embodiment, since the admixture contains either a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, or an oxycarboxylic acid, it is possible to provide a geopolymer that can improve all of the compressive strength, fluidity, and fluidity retention time.

[0028] [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 dissolving process for dissolving an admixture in an alkaline solution, a heating process for heating the crushed contaminated concrete, and a process for heating the contaminated concrete. 14 CO2 gas is captured using an alkaline solution containing an admixture, 14 A collection step of converting the CO2 gas into an alkaline solution, a separation step of separating the heated contaminated concrete into coarse aggregate and mortar fine powder, and 14 The method includes a kneading step of kneading an alkaline solution containing CO2 gas, the fine powder, fly ash, and blast furnace slag.

[0029] 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. 14CO2 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.

[0030] 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. 14 CO2 gas can be generated.

[0031] "Mixing process" In the mixing step, the admixture is dissolved in an alkaline solution. The alkaline solution and admixture are similar to the geopolymers of the above-described embodiments. The amount of the admixture added relative to the total mass of the alkaline solution and the admixture is 0.3 mass% or more and 6 mass% or less, preferably 0.4 mass% or more and 5 mass% or less, and more preferably 0.5 mass% or more and 4 mass% or less.

[0032] "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 14Heat 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.

[0033] By heating the contaminated concrete, 14 CO2 gas is produced.

[0034] "Collection process" In the collection process, the contaminated concrete was heated during the heating process. 14 CO2 gas is captured using an alkaline solution containing an admixture, 14 It is an alkaline solution containing CO2 gas.

[0035] "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. 14 It 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.

[0036] The grinding process can be carried out in accordance with the method described in JP 2017-227493 A, for example.

[0037] The particle size of the fine powder of mortar obtained by the grinding treatment 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.

[0038] The coarse aggregate obtained in the separation process becomes non-radioactive waste. The non-radioactive waste coarse aggregate is reused.

[0039] "Mixing process" In the kneading process, 14 An alkaline solution containing CO2 gas (including admixtures) is mixed with fine mortar powder, fly ash, and blast furnace slag to obtain a geopolymer. The method for kneading the alkaline solution, fine powder, fly ash, and blast furnace slag is not particularly limited, but it is preferable to, for example, charge the raw materials into a container such as a mortar and knead them using a stirring device such as a twin-screw mixer. From the viewpoint of safety, it is preferable to charge the fine powder, which is radioactive waste, after kneading it with the other raw materials (alkaline solution, fly ash, and blast furnace slag) to form a paste.

[0040] 14 The compounding ratio of the alkaline 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 0.6 to 1.7 by mass, more preferably 0.65 to 1.5, and even more preferably 0.7 to 1. 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 mixture can be kneaded to produce a waste product.

[0041] The blending ratio of the C1 component to the A1 component (C1 component / A1 component) is preferably 0.1 to 1, more preferably 0.3 to 0.7, and even more preferably 0.4 to 0.5, by mass. 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.

[0042] 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.

[0043] According to the method for producing a geopolymer of this embodiment, either a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, or an oxycarboxylic acid is used as an admixture, so that a geopolymer can be provided that can improve all of compressive strength, fluidity, and fluidity retention time.

[0044] [Solidified geopolymer] A geopolymer solidified product according to one embodiment of the present invention is a hardened geopolymer of the above-described embodiment. That is, the geopolymer solidified product according to this embodiment includes alkali carbonate, fine powder of mortar obtained from contaminated concrete, fly ash, blast furnace slag, and an admixture. The admixture does not chemically react with other components. The solidified geopolymer of this embodiment can be obtained by the radioactive waste treatment method of the embodiment described below.

[0045] 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.

[0046] The blending ratio of B2 component to A2 component + C2 component (B2 component / (A2 component + C2 component)) is preferably 0.6 to 1.7 by mass, more preferably 0.65 to 1.5, and even more preferably 0.7 to 1. 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.

[0047] The blending ratio of the C2 component to the A2 component (C2 component / A2 component) is preferably 0.1 to 1, more preferably 0.3 to 0.7, and even more preferably 0.4 to 0.5, by mass. 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.

[0048] 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.

[0049] The solidified geopolymer of this embodiment is made of the hardened geopolymer of the above-described embodiment, so it can provide a solidified geopolymer with excellent compressive strength. 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.

[0050] [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 geopolymer manufacturing method according to the above-described embodiment, and a solidification step of solidifying the geopolymer.

[0051] "Solidification process" In the solidification step, the geopolymer obtained by the geopolymer manufacturing method of the above embodiment is solidified.

[0052] 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.

[0053] The solidified geopolymer will be sent to a final disposal site and disposed of as radioactive waste.

[0054] According to the radioactive waste treatment method of this embodiment, the geopolymer obtained by the geopolymer manufacturing method of the above-mentioned embodiment is solidified, so that a solidified geopolymer with excellent compressive strength is produced, and the solidified geopolymer can be safely and appropriately disposed of as radioactive waste in a final disposal site. [Example]

[0055] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0056] [Example 1] "Geopolymer production" Using a twin-shaft mixer, fly ash, blast furnace slag, 1 mol / L sodium hydroxide solution, sand, and admixtures were mixed to obtain a geopolymer. The mass ratio of fly ash, blast furnace slag, sodium hydroxide solution, and sand was 7:3:5:30. The admixture used was a mixture of lignin sulfonic acid, obtained by purifying waste liquid discharged during the pulp manufacturing process, and alkylene oxide, a polyalkylene glycol derivative with a molecular weight of 20,000 to 200,000, mixed in a mass ratio of 5:2. The content of the admixture relative to the total mass of the geopolymer was set to 0.035% by mass.

[0057] [Example 2] "Geopolymer production" The geopolymer was obtained in the same manner as in Example 1, except that sodium gluconate, an oxycarboxylic acid, was used as the admixture and the content of the admixture relative to the total mass of the geopolymer was 0.1 mass%.

[0058] [Comparative Example 1] "Geopolymer production" A geopolymer was obtained in the same manner as in Example 1, except that no admixture was used.

[0059] [Example 3] "Geopolymer production" A geopolymer was obtained in the same manner as in Example 1, except that a 5 mol / L aqueous solution of sodium hydroxide was used.

[0060] [Example 4] "Geopolymer production" A geopolymer was obtained in the same manner as in Example 2, except that a 5 mol / L aqueous sodium hydroxide solution was used.

[0061] Comparative Example 2 "Geopolymer production" A geopolymer was obtained in the same manner as in Comparative Example 1, except that a 5 mol / L aqueous sodium hydroxide solution was used.

[0062] [evaluation] The geopolymers of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated as follows.

[0063] "Compression strength measurement" The compressive strength of the geopolymers of Examples 1 to 4 and Comparative Examples 1 and 2 was measured. The compressive strength of the geopolymer was measured in accordance with JIS A 1108:2018 "Testing method for compressive strength of concrete," and the compressive strength was measured after 91 days. The results are shown in Figures 1 and 2. From the results shown in Figures 1 and 2, it was found that the geopolymers of Examples 1 to 4 exhibited higher compressive strength than the geopolymers of Comparative Examples 1 and 2. Furthermore, it was found that Example 2, which used an oxycarboxylic acid as an admixture, had a higher compressive strength than Example 1, which used a mixture of lignosulfonic acid and a polyalkylene glycol derivative as an admixture. Similarly, it was found that Example 4, which used an oxycarboxylic acid as an admixture, had a higher compressive strength than Example 3, which used a mixture of lignosulfonic acid and a polyalkylene glycol derivative as an admixture.

[0064] "Liquidity Assessment" The geopolymers of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated for fluidity. The fluidity of the geopolymer was evaluated in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement," measuring the flow rate at 15 strokes. The results are shown in Figures 3 and 4. The results shown in Figures 3 and 4 indicate that the geopolymers of Examples 1 to 4 exhibited higher fluidity than the geopolymers of Comparative Examples 1 and 2 immediately after mixing, one hour after mixing, and two hours after mixing. Furthermore, Example 2, which used an oxycarboxylic acid as an admixture, was found to have higher fluidity than Example 1, which used a mixture of lignosulfonic acid and a polyalkylene glycol derivative as an admixture. Similarly, Example 4, which used an oxycarboxylic acid as an admixture, was found to have higher fluidity than Example 3, which used a mixture of lignosulfonic acid and a polyalkylene glycol derivative as an admixture.

[0065] In Examples 1 and 2 and Comparative Example 1, which used a 1 mol / L aqueous sodium hydroxide solution, regardless of the presence or absence of an admixture, the fluidity decreased with time up to two hours after mixing. However, this decrease in fluidity was not significant enough to be a problem. In Comparative Example 2, which used a 5 mol / L aqueous sodium hydroxide solution, solidification progressed to the point where fluidity could no longer be measured one hour after mixing. In Examples 3 and 4, which used a 5 mol / L aqueous sodium hydroxide solution, fluidity was maintained for up to two hours after mixing. It was found that there was no significant difference in the improvement in fluidity retention time between Example 3, which used a mixture of lignosulfonic acid and a polyalkylene glycol derivative as an admixture, and Example 4, which used an oxycarboxylic acid as an admixture.

Claims

1. The method includes: an alkaline solution; fine powder of mortar obtained from contaminated concrete; fly ash; blast furnace slag; and an admixture; The admixture is a geopolymer that is at least one of a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, and an oxycarboxylic acid.

2. The geopolymer according to claim 1, wherein the content of the admixture is 0.3% by mass or more and 3% by mass or less.

3. A solidified geopolymer comprising a hardened geopolymer according to claim 1 or 2.

4. １４ CO ２ a crushing step of crushing the contaminated concrete; a dissolving step of dissolving an admixture in an alkaline solution; a heating step of heating the crushed contaminated concrete; The contamination was generated by heating the contaminated concrete. １４ CO ２ The gas is captured with an alkaline solution containing an admixture; １４ CO ２ a capturing step of obtaining an alkaline solution containing the gas; 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 an alkaline solution containing a gas, the fine powder, fly ash, and blast furnace slag, The method for producing a geopolymer, wherein the admixture is at least one of a mixture of lignin sulfonic acid and a polyalkylene glycol derivative, and an oxycarboxylic acid.

5. The method for producing a geopolymer according to claim 4, wherein the amount of the admixture added is 0.3% by mass or more and 6% by mass or less with respect to the total mass of the alkaline solution and the admixture.

6. Obtaining a geopolymer by the geopolymer manufacturing method according to claim 4 or 5; A method for treating radioactive waste, comprising a solidification step of solidifying the geopolymer.

Images