Method for manufacturing a self-hardening material, and the self-hardening material

Abstract

It suppresses the leaching of heavy metals while also suppressing a decrease in strength. [Solution] A method for producing a self-hardening material, comprising: a first kneading step of kneading fly ash that has been treated with mechanochemicals with a silicon mixture containing an alkaline solution and a silicon material; a standing step of letting the mixture stand for a predetermined time after the first kneading step; and a second kneading step of adding an insolubilizing agent to suppress the elution of heavy metals contained in the fly ash and kneading the mixture after the standing step.

Description

[Technical Field]

[0001] This invention relates to a method for producing a self-hardening material, and to a self-hardening material. [Background technology]

[0002] It is known that a self-hardening material with compressive strength equivalent to concrete can be obtained by activating the surface of fly ash, a type of coal ash, by grinding it in a ball mill, for example (mechanochemical treatment), and then adding and mixing it with a silicon mixture containing potassium hydroxide solution and silicon material.

[0003] Fly ash contains trace amounts of harmful substances (heavy metals) such as arsenic, and the amount leached may exceed environmental standards. For example, Patent Document 1 discloses a technique for suppressing the leaching of heavy metals by adding (mixing) a chemical agent (immobilizer). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-162772 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, adding an immobilizing agent may reduce the strength (compressive strength) compared to when no immobilizing agent was added.

[0006] This invention has been made in view of the above-mentioned problems, and its purpose is to suppress the decrease in strength while suppressing the leaching of heavy metals. [Means for solving the problem]

[0007] The main invention for achieving the above objective is a method for producing a self-hardening material, characterized by comprising: a first kneading step of kneading fly ash that has been treated with mechanochemicals with a silicon mixture containing an alkaline solution and a silicon material; a standing step of letting the mixture stand for a predetermined time after the first kneading step; and a second kneading step of adding an insolubilizing agent to suppress the elution of heavy metals contained in the fly ash and kneading the mixture after the standing step.

[0008] Other features of the present invention will be revealed in the specification and drawings described below. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the elution of heavy metals while suppressing a decrease in strength. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart showing a typical method for manufacturing self-hardening materials (comparative example). [Figure 2] This figure shows an example of the relationship between time from the start of mixing and viscosity in a comparative example. [Figure 3] This is a schematic diagram illustrating the hardening mechanism. [Figure 4] This is a flowchart illustrating the manufacturing method of the self-hardening material of this embodiment. [Figure 5] This figure shows an example of the relationship between time from the start of mixing and viscosity in this embodiment. [Figure 6] This figure compares the viscosity changes of the comparative example and this embodiment. [Figure 7] This figure shows the test results of the example. [Figure 8] Figures 8A to 8E show the evaluation results of the relationship between the amount of immobilizing agent (magnesium oxide) added and the amount of heavy metals leached out. Figure 8A shows the leaching results for "arsenic," Figure 8B for "selenium," Figure 8C for "hexavalent chromium," Figure 8D for "fluorine," and Figure 8E for "boron." [Figure 9]It is a figure showing the evaluation results of the relationship between the added amount of insolubilizing material (magnesium oxide) and compressive strength.

Mode for Carrying Out the Invention

[0011] At least the following matters will be made clear from the description of the specification and drawings described below.

[0012] A method for producing a self-hardening material, comprising: a first kneading step of kneading fly ash subjected to mechanochemical treatment and a silicon mixture containing an alkali solution and a silicon material; a standing step of allowing the mixture to stand for a predetermined time after the first kneading step; and a second kneading step of adding an insolubilizing material for suppressing elution of heavy metals contained in the fly ash and kneading the mixture after the standing step.

[0013] According to such a method for producing a self-hardening material, elution of heavy metals contained in fly ash can be suppressed, and a decrease in strength can be suppressed as compared with the case where an insolubilizing material is mixed before mixing the silicon mixture. Further, it is possible to slow down the hardening rate (improve fluidity) and suppress difficulty in filling into a mold.

[0014] In such a method for producing a self-hardening material, it is preferable that the insolubilizing material contains one or more of polyferric sulfate, gypsum dihydrate, potassium alum, and magnesium oxide.

[0015] According to such a method for producing a self-hardening material, elution of heavy metals can be suppressed.

[0016] In such a method for producing a self-hardening material, it is preferable that the fly ash has been subjected to a treatment for removing unburned carbon before the mechanochemical treatment.

[0017] This method for manufacturing self-hardening materials suppresses the leaching of heavy metals even when using fly ash from which unburned carbon has been removed (decarburized). Furthermore, by removing unburned carbon, the decrease in strength can be suppressed and fluidity can be increased.

[0018] A method for producing such a self-hardening material, wherein the insolubilizing agent is magnesium oxide, and the resulting self-hardening material has a 7-day compressive strength of 50 N / mm². 2 It is desirable that the above be the case.

[0019] This method for manufacturing self-hardening materials allows for the suppression of heavy metal leaching by using magnesium oxide as an immobilizing agent. Furthermore, it enables the acquisition of high compressive strength.

[0020] Furthermore, a self-hardening material is revealed that is characterized by containing fly ash that has been treated to remove unburned carbon and mechanochemically, a silicon mixture containing an alkaline solution and a silicon material, and one or more of ferric polysulfate, gypsum dihydrate, potassium alum, and magnesium oxide.

[0021] With such self-hardening materials, even when fly ash that has undergone treatment to remove unburned carbon and mechanochemical treatment is used, it is possible to suppress the leaching of heavy metals while suppressing a decrease in strength.

[0022] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0023] ===Implementation Method=== The object, features, advantages, and ideas of the present invention will be apparent to those skilled in the art from the description herein, and will be easily reproducible to those skilled in the art from the description herein. The embodiments and specific examples of the invention described below are examples of preferred embodiments of the present invention and are provided for illustrative or explanatory purposes only, and do not limit the present invention thereto. It will be apparent to those skilled in the art that various modifications and modifications can be made based on the description herein, within the intent and scope of the present invention as disclosed herein.

[0024] <<Self-hardening material>> Self-hardening materials are materials that harden when left at a predetermined temperature (for example, 15 to 40°C). The self-hardening material according to this embodiment includes at least fly ash, a silicon mixture, and an immobilizing agent. The self-hardening material according to this embodiment can suppress the amount of heavy metals that leach out due to the inclusion of an immobilizing agent. The immobilizing agent and other components used in this embodiment will be described later.

[0025] [Fly ash] Fly ash is a type of coal ash discharged from coal-fired power plants and other sources. The main components of fly ash are amorphous silicon and aluminum, with some crystalline quartz (SiO2) and mullite (Al6Si2O2O2). 13 ) and others are included.

[0026] Fly ash contains heavy metals derived from its raw material, coal. These heavy metals include, for example, cadmium, lead, arsenic, selenium, mercury, chromium, fluorine, and boron. Note that the term "heavy metals" in this specification includes not only elemental heavy metals but also their compounds and ions. The heavy metal content varies depending on the fly ash. For example, the heavy metal content of fly ash discharged from a thermal power plant using coal mined in one area may differ significantly from that of fly ash discharged from a thermal power plant using coal mined in a different area.

[0027] In this embodiment, the fly ash is treated to remove unburned carbon from coal ash (so-called "raw ash") discharged from coal-fired power plants, etc., and then subjected to mechanochemical treatment.

[0028] Unburned carbon is the residue of carbon components contained in coal ash. Unburned carbon can be removed by well-known methods such as heating, electrostatic separation, and flotation. In this embodiment, the fly ash is obtained by heating coal ash discharged from coal-fired power plants, etc., at 600°C to remove unburned carbon. Hereinafter, this process of removing unburned carbon will also be referred to as decarbonization. In this embodiment, "removing unburned carbon" does not mean completely removing unburned carbon from coal ash, but rather reducing (decreasing) the content of unburned carbon in the coal ash. Therefore, coal ash that has undergone decarbonization may contain a small amount of unburned carbon.

[0029] Mechanochemical treatment (hereinafter also referred to as MC treatment) utilizes mechanochemical phenomena. Specifically, mechanochemical treatment involves applying mechanical energy to a substance through impact, compression, grinding, crushing, mixing, etc., to activate the substance.

[0030] The MC treatment method according to this embodiment is not particularly limited, but examples include grinding using a ball mill such as a planetary ball mill. By grinding fly ash using a ball mill, the surface area of ​​the hollow fly ash is increased through polishing, and the fly ash can be efficiently activated. The material of the ball mill and conditions such as the rotation speed in the grinding process can be appropriately selected by those skilled in the art.

[0031] When the above MC treatment is performed on 50g of fly ash using, for example, a Fritsch P-5 planetary ball mill, the particle size of the fly ash becomes fine (for example, about 1 / 10 of the initial size). Hereafter, fly ash that has undergone such MC treatment may be referred to as "MC ash." Furthermore, fly ash that has undergone both decarburization and MC treatment may be referred to as "decarburized MC ash."

[0032] [Silicon mixture] The silicon mixture is used to bind fly ash particles together. The silicon mixture is used as a slurry. The silicon mixture contains an alkaline solution and silicon material.

[0033] The alkaline solution is a solution containing an alkali such as potassium hydroxide (KOH), sodium hydroxide (NaOH), or calcium hydroxide (Ca(OH)2). The molar concentration of the alkali is preferably 1 to 5 mol / L. For example, a 3 mol / L aqueous solution of KOH can be used as the alkaline solution.

[0034] The silicon material is, for example, a fine silicon powder such as silica fume. As the silicon material, for example, silica fume with a silica concentration of about 40,000 ppm in a 3 mol / L alkaline solution (control value) can be used.

[0035] [Isolating agent] The immobilizing agent is a chemical agent that adsorbs and immobilizes heavy metals and other substances leached from fly ash.

[0036] While thiourea and magnesium oxide had been confirmed to be effective immobilizers for fly ash that had not had unburned carbon removed, subsequent studies revealed that removing unburned carbon could improve the fluidity of the paste and the strength (compressive strength) of the hardened material.

[0037] However, when the above-mentioned immobilizing agent was applied to fly ash from which unburned carbon had been removed, the amount of leached harmful substances (heavy metals) sometimes exceeded environmental standards, depending on the type of harmful substance. This is thought to be because unburned carbon has the function of adsorbing harmful substances, and by removing the unburned carbon, the adsorption effect of the unburned carbon is lost.

[0038] Therefore, in this embodiment, the chemicals used for treating contaminated water and immobilizing contaminated soil were re-examined, and iron (Fe), calcium (Ca), aluminum (Al), and magnesium (Mg) based chemicals that showed an immobilizing effect on decarbonized MC ash were selected.

[0039] Specifically, we selected ferric polysulfate (hereinafter referred to as polyiron) as the iron-based agent, gypsum dihydrate as the calcium-based agent, potassium alum as the aluminum-based agent, and magnesium oxide as the magnesium-based agent.

[0040] [Other additives] Self-hardening materials may contain appropriate additives as long as they do not affect their function. Examples of additives include water-reducing agents. Water-reducing agents are used to adjust the filling properties and curing time of the self-hardening material.

[0041] <<Manufacturing Method for Self-Hardening Materials>> <Comparative Example> Figure 1 is a flow chart showing a typical method for manufacturing a self-hardening material (comparative example). Figure 2 is a diagram showing an example of the relationship between time from the start of mixing and viscosity in the comparative example. In Figure 2, the horizontal axis represents time (time), and the vertical axis represents viscosity. Figure 2 is a diagram that assumes the hardening state (viscosity change) as time progresses. Figure 3 is a schematic diagram illustrating the hardening mechanism.

[0042] First, obtain (prepare) coal ash (fly ash) from a coal-fired power plant or similar source (S11 in Figure 1).

[0043] Next, the fly ash is subjected to a decharging treatment (for example, heating at 600°C for 1 hour) to remove unburned carbon contained in the fly ash (S12 in Figure 1).

[0044] Next, the fly ash from which unburned carbon has been removed (decharred) is subjected to mechanochemical treatment (MC treatment) to activate the surface of the fly ash (S13 in Figure 1). This yields MC ash (in this case, decharred MC ash).

[0045] Next, at time t0' in Figure 2, an immobilizing agent is added to the MC ash (decarbonized MC ash) and mixed (S14 in Figure 1).

[0046] Furthermore, immediately afterward, a liquid silicon slurry (silicon mixture) is added and kneaded (S15 in Figure 1). Note that the insolubilizing agent and the silicon compound may be added simultaneously.

[0047] As a result, at time t1' in Figure 2, the MC ash and the immobilizing agent come into contact with the highly alkaline silicon mixture solution, causing aluminum ions to leach from the MC ash and metal ions to leach from the immobilizing agent.

[0048] At time t2', aluminum ions eluted from the MC ash react with silicon monomers in the silicon slurry (alkaline solution) and combine with the silicon compound as shown on the left side of Figure 3. In the comparative example, metal ions eluted from the insolubilizing agent also react with silicon monomers.

[0049] At time t3', aluminum ions crosslink the silicon complex and polymerize, forming a geopolymer (GP) as shown on the right side of Figure 3 (curing begins). Geopolymers are formed when silicon and aluminum eluted from fly ash or blast furnace granulated slag crosslink the silicon complex with a high-alkali silicon slurry. At this time, metal ions eluted from the insolubilizing agent also crosslink the silicon complex and polymerize.

[0050] Then, at time t5', the material is filled into the mold (S16 in Figure 1). Note that, in order to correspond with the embodiment described later, time t4' is skipped and the time is shown as t5'.

[0051] In the comparative example, in addition to aluminum ions leaching from MC ash, metal ions also leach from the immobilizing agent. When polymerization is promoted by these metal ions from the immobilizing agent (derived from the immobilizing agent), the strength tends to be lower compared to cases where the immobilizing agent is not mixed in (see the examples described later). Furthermore, hardening begins immediately after mixing, and the hardening rate is fast, which may make it difficult to fill the mold.

[0052] <This embodiment> Figure 4 is a flow chart showing the manufacturing method of the self-hardening material according to this embodiment. Figure 5 is a diagram showing an example of the relationship between time from the start of mixing and viscosity in this embodiment. In Figure 5, the horizontal axis represents time (time), and the vertical axis represents viscosity. Figure 5, like Figure 2, is a diagram that assumes the hardening state (viscosity change) as time progresses.

[0053] Steps S01 to S03 in Figure 4 correspond to steps S11 to S13 in the comparative example (Figure 1), respectively, so their explanation is omitted.

[0054] In this embodiment, after the MC treatment (step S03), at time t0 in Figure 5, silicon slurry is added to the MC ash (charred MC ash) and mixed (S04 in Figure 4: first mixing step).

[0055] Then, the mixture is left to stand for a predetermined time (S05 in Figure 4: standing step). The standing time is preferably 5 to 30 minutes. In this embodiment, the standing time (the time until time t4, described later) is, for example, 10 minutes.

[0056] As a result, at time t1 in Figure 5, the MC ash comes into contact with the highly alkaline silicon slurry solution, causing the aluminum ions contained in the MC ash to dissolve.

[0057] Then, at time t2 in Figure 5, aluminum ions bond with silicon monomers in the silicon slurry. Subsequently, at time t3, the aluminum ions crosslink the silicic acid complex, resulting in polymerization (curing begins).

[0058] Next, at time t4, when polymerization has progressed to a certain extent, an insolubilizing agent is added and the mixture is kneaded (S06 in Figure 4: Second kneading step). Then, at time t5 in Figure 5, the material is filled into the mold (S07 in Figure 4).

[0059] As explained above, in this embodiment, the aluminum ions eluted from the MC ash combine with silicon monomers, and the insolubilizing agent is added when the polymerization has progressed to a certain extent.

[0060] By doing so, polymerization is mainly carried out via aluminum ions (derived from MC ash) eluted from the MC ash, thus suppressing the contribution of metal ions from the insolubilizing agent to polymerization. Therefore, it can be estimated that the polymer structure will be more homogeneous compared to the comparative example, and the compressive strength will be increased.

[0061] Figure 6 is a diagram comparing the viscosity changes of the comparative example and this embodiment. As shown in the figure, the comparative example begins to harden earlier. Specifically, the time t3' at which hardening begins in the comparative example is earlier than the time t3 at which the effect of this embodiment begins. Furthermore, in the comparative example, not only are there aluminum ions eluted from the MC ash, but there are also metal ions eluted from the insolubilizing agent, so polymerization proceeds rapidly and the viscosity increases.

[0062] Therefore, for example, even if you try to fill the mold at time t5', the viscosity will have already increased, which may make filling difficult.

[0063] In contrast, in this embodiment, polymerization is slower compared to the comparative example, so the material can be filled into the mold while maintaining fluidity even at time t5, which is later than time t5'. Thus, in this embodiment, the contribution of metal ions derived from the insolubilizing agent to polymerization can be suppressed, and the material can be filled into the mold while maintaining fluidity.

[0064] Furthermore, as mentioned above, in this embodiment, the polymer structure is more homogeneous compared to the comparative example, and therefore the compressive strength can be increased compared to the comparative example.

[0065] = Photo example = Photo <Conditions for preparing hardened paste> [Materials used] • Fly ash (coal ash): Raw ash obtained from thermal power plants is used. In the comparative example, ash A was used, and in the example, ash B was used. • Silicon slurry: A solution of silicon material (silica fume) dissolved in a high-concentration KOH aqueous solution is used. • Immobilizing agent: Polyferrous iron, gypsum dihydrate, potassium alum, magnesium oxide, no additives (example) [Coal ash decoction treatment] Heat at 600°C for 1 hour [MC treatment of coal ash] Ball mill 3 hours [Mixing method] Comparative example: Flowchart in Figure 1 Example: Flowchart in Figure 4 (standing time 10 minutes)

[0066] <Exam Content> • Amount of heavy metals leached The elution amounts of arsenic, selenium, hexavalent chromium, fluorine, and boron were measured based on the elution method specified in JIS K 0058. • Compressive strength The 7-day compressive strength of the hardened specimen was measured according to the uniaxial compression test method of JIS A 1216. • Slurry (fluidity) The decision is based on the workability when filling the test specimen into the mold.

[0067] <Conditions for determining compressive strength and slurry> • Criteria for determining compressive strength: 20 N / mm² 2 Larger values ​​are indicated with "◎", and the range is 5-20 N / mm². 2 In the case of 2-5 N / mm, we mark it as "○". 2 In the case of 2N / mm, we will use "△" and 2 A lower value is marked with "×". • Criteria for determining slurry (fluidity): If the viscosity of the specimen was low and it could be easily filled into the mold (high fluidity), it was marked with "◎", and if it was filled well, it was marked with "〇". In addition, if the viscosity of the specimen was somewhat high but it could be filled into the mold by applying sufficient vibration with a vibrator, it was marked with "△", and if the viscosity of the specimen was high and it was difficult to fill into the mold, it was marked with "×".

[0068] <Test Results> Figure 7 shows the test results of the examples. Here, the amount of immobilizing agent added to the comparative example and the examples was set to 5% (mass%). As mentioned above, no immobilizing agent was added to the reference example. Also, the numbers below each heavy metal (arsenic, selenium, hexavalent chromium, fluorine, boron) in Figure 7 represent the environmental standard value (mg / l) for the amount eluted.

[0069] In each comparative example and example in which an immobilizing agent was added, the elution of each heavy metal was suppressed more effectively than in the reference example (without an immobilizing agent). In particular, the magnesium oxide in Example 4 was within environmental standards except for selenium and boron.

[0070] Furthermore, in Examples 2 and 3, the fluidity was higher and it was easier to fill the mold compared to the comparative example (Example 1 was equivalent to Comparative Example 1).

[0071] Furthermore, in Comparative Examples 1-3, the addition of an immobilizing agent resulted in lower compressive strength compared to the Reference Example (without an immobilizing agent), while in Examples 1-3, the compressive strength was higher compared to the corresponding Comparative Examples (comparative examples with the same immobilizing agent). In particular, the magnesium oxide in Example 4 achieved a compressive strength of 50 N / mm². 2 It exceeds that.

[0072] As described above, by selecting polyferric sulfate, gypsum dihydrate, potassium alum, and magnesium oxide respectively as the insolubilizing materials and producing the self-hardening material according to the flow shown in Fig. 4, it was possible to increase the fresh properties (fluidity) and compressive strength while suppressing the elution amount of heavy metals.

[0073] Figs. 8A to 8E are diagrams showing the evaluation results of the relationship between the addition amount of the insolubilizing material (magnesium oxide in this case) and the elution amount of heavy metals. Fig. 8A shows the elution results of "arsenic", Fig. 8B shows that of "selenium", Fig. 8C shows that of "hexavalent chromium", Fig. 8D shows that of "fluorine", and Fig. 8E shows that of "boron", respectively. In each figure, the horizontal axis represents the addition amount (%) of the insolubilizing material (magnesium oxide), and the vertical axis represents the elution amount (mg / l). In each figure, comparative examples are indicated by "○", and the example (Example 4 in Fig. 7) is indicated by "●".

[0074] Since the types of ash used are different between the comparative examples and the examples, the comparative examples and the example (Example 4) cannot be compared under the same conditions. However, compared with the comparative examples, the insolubilization effect is more likely to be exhibited in the example, and remarkable hardening occurs when 5% of the insolubilizing material is added. Although not shown herein, other insolubilizing materials (polyferric sulfate, gypsum dihydrate, potassium alum) also showed the same tendency.

[0075] Further, Fig. 9 is a diagram showing the evaluation results of the relationship between the addition amount of the insolubilizing material (magnesium oxide in this case) and compressive strength. In Fig. 9, the horizontal axis is the addition amount (%) of the insolubilizing material (magnesium oxide), and the vertical axis is the compressive strength (N / mm 2 ). In Fig. 9, comparative examples are indicated by "○", and the example (Example 4 in Fig. 7) is indicated by "●".

[0076] As shown in Fig. 9, in the comparative examples, the compressive strength is below the standard of 20N / mm 2 at any addition amount, whereas in the example, the compressive strength exceeds the standard in all cases. In particular, as described above, when the addition amount is 5%, the compressive strength exceeds 50N / mm 2 .

[0077] As described above, by adding an immobilizing agent to fly ash that has undergone decarburization and MC treatment using the flow method of this embodiment, it was possible to suppress the leaching of heavy metals and other substances while increasing the fluidity of the test specimen and the compressive strength of the hardened test specimen. In particular, when magnesium oxide was added using the flow method of this embodiment, excellent results were obtained regarding the leaching of heavy metals, fluidity, and compressive strength.

[0078] ===Other=== The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved without departing from its spirit, and it goes without saying that the present invention includes equivalents thereof.

[0079] In the embodiments (examples) described above, one of the following was added as an immobilizing agent: polyferric iron (polyferric sulfate), gypsum dihydrate, potassium alum, and magnesium oxide. However, multiple agents may be added. Other immobilizing agents may also be added.

Claims

1. A first mixing step involves mixing mechanochemically treated fly ash with a silicon mixture containing an alkaline solution and silicon material. After the first mixing step, a settling step is performed in which the mixture is left to stand for a predetermined time. After the standing step, a second mixing step is performed in which an insolubilizing agent is added to suppress the elution of heavy metals contained in the fly ash and the mixture is kneaded. A method for producing a self-hardening material, characterized by having the following:

2. A method for producing a self-hardening material according to claim 1, The aforementioned insolubilizing agent is A compound containing one or more of the following: ferric polysulfate, gypsum dihydrate, potassium alum, and magnesium oxide. A method for producing a self-hardening material characterized by the above.

3. A method for producing a self-hardening material according to claim 2. The fly ash is subjected to a treatment to remove unburned carbon prior to the mechanochemical treatment. A method for producing a self-hardening material characterized by the above.

4. A method for producing a self-hardening material according to claim 1, The aforementioned insolubilizing agent is magnesium oxide. The resulting self-hardening material has a 7-day compressive strength of 50 N / mm². ２ That's all. A method for producing a self-hardening material characterized by the above.

5. Fly ash that has undergone treatment to remove unburned carbon and mechanochemical treatment, A silicon mixture containing an alkaline solution and silicon material, One or more of the following: ferric polysulfate, gypsum dihydrate, potassium alum, and magnesium oxide, A self-hardening material characterized by containing [a specific substance].

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