Method for fixing carbon dioxide to modified soil and method for producing modified soil using the same

Abstract

To provide a method for fixing carbon dioxide to modified soil and a method for producing modified soil that can simplify necessary processes and improve work efficiency.SOLUTION: A method for fixing carbon dioxide to modified soil, which fixes carbon dioxide when modifying construction sludge into granular modified soil, includes a mixing granulation step S02 for mixing a modifier with construction sludge to form granules, and a carbon dioxide supply step S03 for supplying carbon dioxide-containing gas in the mixing granulation step, wherein the method fixes carbon dioxide to the modified soil as carbonate by reacting carbon dioxide with calcium in the modifier through supply of the carbon dioxide-containing gas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for fixing carbon dioxide in modified soil obtained by modifying construction sludge with a modifier, and a method for producing modified soil using this method.

Background Art

[0002] As a method for improving soft construction sludge, a method of mixing a paper sludge incineration ash (PS ash) - based modifier is known. As such a modifier, for example, a water-absorbing soil modifier "Wator" (trade name) is sold (Ministry of Land, Infrastructure, Transport and Tourism NETIS (New Technology Information Provision System) registration number TTH - 160010 - VR) (see Non - Patent Document 1). Also, after the modified soil is solidified, there is a method of loosening it into a granular state (loosening granulation) and using it as a civil engineering material (see Non - Patent Document 2). Such a modifier itself has a lower pH compared to cement, but is alkaline, and the modified soil immediately after mixing is also alkaline (pH = 9 - 11). However, due to the modification, the soil becomes granular and is more likely to come into contact with air, reacting with carbon dioxide in the air and proceeding with neutralization to stabilize in the neutral range.

[0003] Patent Document 1 discloses a method for producing neutral recycled soil by a carbon dioxide immobilization technique that can efficiently produce high - quality neutral recycled soil that surely neutralizes alkaline construction sludge and does not remudify. The method includes a modification and solidification step of adding and mixing an alkaline modification and solidification material to construction sludge to produce a modified and solidified treated soil, a loosening and granulation step of producing loosened and granulated soil by loosening the modified and solidified treated soil when it becomes semi - solid to make it finer, and a drying, neutralization, and carbon dioxide fixation step of promoting the drying and neutralization of the loosened and granulated soil using hot compressed air, which is heated compressed air, and carbon dioxide gas, and further fixing the carbon dioxide gas as calcium carbonate in the loosened and granulated soil (paragraph 0016).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Document

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Non-Patent Document 2 is a method of performing loosening granulation after solidification of the improved soil, but it does not perform carbon dioxide fixation. The carbon dioxide (CO2) fixation method of Patent Document 1 requires each process such as mixing and solidifying the modifier into construction sludge, loosening granulation, and CO2 supply and fixation, so the process becomes complicated and the working efficiency decreases.

[0007] In view of the problems of the prior art as described above, an object of the present invention is to provide a method for fixing carbon dioxide to improved soil and a method for manufacturing improved soil that can simplify the processes necessary for fixing carbon dioxide when obtaining the improved soil and improve the working efficiency.

Means for Solving the Problems

[0008] The method for fixing carbon dioxide to improved soil for achieving the above object is a method for fixing carbon dioxide when modifying construction sludge into granular improved soil, including a mixing granulation step of mixing a modifier into the construction sludge to make it granular, and a carbon dioxide supply step of supplying a carbon dioxide-containing gas in the mixing granulation step. By supplying the carbon dioxide-containing gas, carbon dioxide is reacted with calcium in the modifier to be fixed in the modified soil as a carbonate.

[0009] According to this method for fixing carbon dioxide in the modified soil, when the construction sludge is modified into granular modified soil by adding and mixing the modifier and carbon dioxide is fixed, the mixing granulation step and the carbon dioxide supply step are performed simultaneously. Therefore, the steps required for fixing carbon dioxide when obtaining the modified soil can be simplified and the working efficiency can be improved.

[0010] In the method for fixing carbon dioxide in the above-mentioned modified soil, carbon dioxide may be fixed in the modifier by supplying a carbon dioxide-containing gas to the modifier before the mixing (see FIG. 1 to which steps S11 and S12 shown by broken lines are added).

[0011] Also, when carbon dioxide is fixed in the modified soil before the mixing, the supply of the carbon dioxide-containing gas in the mixing granulation step may be omitted (see FIG. 8).

[0012] Also, the construction sludge preferably has a cone index of 200 kN / m 2 as follows.

[0013] Also, as the modifier, it is preferable to use any one of cement, paper sludge incineration ash-based modifier, and blast furnace slag fine powder, or at least any two of them.

[0014] Also, by continuously performing the mixing and the carbon dioxide supply after the granulation, or by continuously performing the carbon dioxide supply after the granulation, the amount of carbon dioxide fixed can be increased.

[0015] Also, the modifier may be one that has fixed carbon dioxide before the mixing.

[0016] Also, the construction sludge may be one containing cement (such as cement solidified treated soil, sludge from high-pressure jetting or deep mixing, etc.).

[0017] In addition, by supplying the heated carbon dioxide-containing gas to evaporate the moisture contained in the construction sludge, more efficient granulation and carbon dioxide fixation become possible.

[0018] In addition, when the granular modified soil dries in the carbon dioxide supply step, the amount of carbon dioxide fixed can be increased by spraying water or repeating wet and dry conditions so as to achieve a predetermined water content ratio.

[0019] Moreover, a carbon-containing material such as biochar may be further added to the construction sludge, and thereby, a carbon storage effect can be expected.

[0020] In addition, dry ice may be added and mixed in the mixing granulation step, and the carbon dioxide-containing gas generated by the vaporization of the dry ice may be supplied in the carbon dioxide supply step.

[0021] A method for producing modified soil for achieving the above object is a method for producing granular modified soil from construction sludge, and when producing the modified soil, carbon dioxide is fixed in the modified soil by the above-described method for fixing carbon dioxide to the modified soil.

[0022] According to this method for producing modified soil, when producing granular modified soil by adding and mixing a modifier to construction sludge and fixing carbon dioxide in the modified soil, the mixing granulation step and the carbon dioxide supply step are performed simultaneously. Therefore, the steps necessary for fixing carbon dioxide when producing modified soil can be simplified, the working efficiency can be improved, and modified soil with fixed carbon dioxide can be efficiently produced.

[0023] In the above method for producing modified soil, by adjusting the time of carbon dioxide supply to control the amount of carbon dioxide fixed, a predetermined strength of the modified soil can be ensured.

Effects of the Invention

[0024] According to the present invention, it is possible to provide a method for fixing carbon dioxide to improved soil and a method for producing improved soil that can simplify necessary processes and improve work efficiency.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0026] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining each step of the carbon dioxide fixation method in the production of modified soil according to the present embodiment.

[0027] As shown in FIG. 1, in the carbon dioxide fixation method in the production of modified soil according to the present embodiment, first, a modifier is added to construction sludge (S01), and the construction sludge and the modifier are mixed to form granules (S02). In this mixing and granulation step S02, a carbon dioxide-containing gas (CO2-containing gas) is supplied (S03). By supplying the CO2-containing gas, calcium (Ca) in the modifier reacts with carbon dioxide (CO2) to fix CO2 as a carbonate such as calcium carbonate (CaCO3) (S04). In this way, a large number of granular modified soils in which CO2 is fixed are produced (S05). Note that granulation by mixing the construction sludge and the modifier can be performed by adjusting the blending conditions by adjusting the water content ratio of the construction sludge and the amount of modifier added and the mixing time.

[0028] Construction sludge is industrial waste earth and sand containing a large amount of water generated in construction work and excavation work, and cannot be piled up in a dump truck, and people cannot walk on it, and the cone index is 200 kN / m 2 Hereinafter (approximately uniaxial compressive strength 50 kN / m 2The following shall apply. For construction sludge, those containing cement (such as cement solidified soil, sludge from high-pressure jet grouting or deep mixing, etc.) may be used.

[0029] As the modifier, any one of cement, paper sludge incineration ash (PS ash)-based modifier, and blast furnace slag fine powder can be used, or at least any two of them may be used in combination.

[0030] According to the carbon dioxide fixation method in the production of the modified soil in FIG. 1, since the mixing granulation step S02 and the carbon dioxide supply step S03 are performed simultaneously, the steps necessary for fixing carbon dioxide when producing granular modified soil can be simplified and the working efficiency can be improved. In this way, the loosening granulation step in Patent Document 1 can be omitted. Also, the curing after mixing the conventional modifier can be omitted. The produced granular modified soil can be used as a dike building material, embankment material, etc. in the same way as ordinary earth and sand.

[0031] In addition, a carbon-containing material such as biochar may be added when adding the modifier in FIG. 1, and thus, a carbon storage effect can be expected. The carbon-containing material preferably has a carbon content of at least 10% by mass.

[0032] Next, embodiments of the mixing granulation step S02 and the CO2 supply step S03 in FIG. 1 will be described with reference to FIGS. 2 to 7. FIG. 2 is a diagram schematically showing an example in which exhaust gas containing CO2 is supplied from the bottom of the storage section during mixing granulation by an excavator. FIG. 3 is a diagram schematically showing an example in which exhaust gas containing CO2 is supplied from the operation section of the excavator during mixing granulation by an excavator. FIG. 4 is a diagram schematically showing an example in which exhaust gas containing CO2 is supplied from the bottom in a mixing granulation yard during mixing granulation by a shallow mixing treatment machine.

[0033] In the example of FIG. 2, when a CO2 supply pipe 12 extending from the CO2 supply device 11 is laid at the bottom of the storage section 14 and construction sludge and a modifier are mixed in the mixing bucket BK of the backhoe BH within the storage section 14, exhaust gas containing CO2, which is heated and discharged from the internal combustion engine that is the power source of the backhoe BH, is supplied to the modified soil 10 during mixing and granulation through the CO2 supply pipe 12 at the bottom of the storage section 14.

[0034] In the example of FIG. 3, a CO2 supply pipe 13 is provided from the CO2 supply device 11 to the mixing bucket BK, which is the mixing operation section at the tip of the arm of the backhoe BH. When construction sludge and a modifier are mixed in the mixing granulation yard 15 with the bucket BK, exhaust gas containing CO2, which is heated and discharged from the internal combustion engine that is the power source of the backhoe BH, is supplied from the bucket BK to the modified soil 10 during mixing and granulation.

[0035] In the example of FIG. 4, a CO2 supply pipe 16 is provided from the CO2 supply device 11 to the mixing granulation yard 15. When construction sludge and a modifier are mixed by the shallow layer mixing processor 20 at the stirring section 20a at its tip in the mixing granulation yard 15, exhaust gas containing CO2, which is heated from the generator or internal combustion engine used for the blower of the CO2 supply device 11 or various plants, is supplied to the modified soil 10 during mixing and granulation through the CO2 supply pipe 16 at the bottom of the mixing granulation yard 15.

[0036] As shown in FIGS. 2 to 4, by supplying exhaust gas containing CO2 in the process of mixing and granulating construction sludge and a modifier with the backhoe BH or the shallow layer mixing processor 20, calcium (Ca) contained in the modifier reacts with CO2 in the exhaust gas and is chemically fixed as calcium carbonate (CaCO3), etc., and CO2 is physically and stably retained in the granular modified soil 10.

[0037] Note that, with both configurations of FIG. 2 and FIG. 3, exhaust gas may be supplied from both the mixing bucket BK and the bottom of the storage section 14. Also, in FIGS. 2 and 4, since exhaust gas containing CO2 heated from the bottom is supplied to the granular modified soil 10, the modified soil 10 is subjected to CO2 fixation treatment and drying treatment.

[0038] FIG. 5 is a diagram schematically showing an example of supplying exhaust gas containing CO2 into a rotary drum during mixing granulation by a mixer truck. In the example of FIG. 5, the exhaust gas containing CO2 discharged from the internal combustion engine, which is the power source of the mixer truck MD, is supplied from the CO2 supply device 31 into the rotary drum 30 through the CO2 supply pipe 32. During the mixing granulation of construction sludge and a modifier, calcium (Ca) contained in the modifier reacts with CO2 contained in the exhaust gas and is chemically fixed as calcium carbonate (CaCO3) or the like, and CO2 is physically and stably retained in the granular modified soil 10. The rotational speed of the rotary drum 30 of the mixer truck MD is preferably 1 to 13 rpm, the drum capacity is preferably 2.5 to 10 m 3 is preferred, and the mixing capacity is preferably 1.2 to 5 m 3 is preferred. Further, FIG. 5 shows a configuration in which exhaust gas is supplied during mixing granulation in the rotary drum 30 of the parked mixer truck MD. However, the CO2 supply device 31 may be mounted on the mixer truck MD, and the exhaust gas may be supplied inside the moving mixer truck MD.

[0039] FIG. 6 is a diagram schematically showing an example of supplying exhaust gas containing CO2 into a treatment tank during mixing granulation by an intermediate layer mixing treatment device. In the example of FIG. 6, the exhaust gas containing CO2 discharged from the internal combustion engine, which is the rotational power of the two-shaft rotating part 44 of the intermediate layer mixing treatment device 40, is supplied from the CO2 supply device 41 through the CO2 supply pipe 42 to the bottom of the treatment tank 43 of the intermediate layer mixing treatment device 40. During the mixing granulation of construction sludge and a modifier by the rotational stirring of the stirring parts 45 and 46 of the rotating part 44 in the treatment tank 43, calcium (Ca) contained in the modifier reacts with CO2 contained in the exhaust gas and is chemically fixed as calcium carbonate (CaCO3) or the like, and CO2 is physically and stably retained in the granular modified soil.

[0040] FIG. 7 is a side view (a) schematically showing an example of supplying exhaust gas containing CO2 into the inside during mixing granulation by a scoop type mixing granulation apparatus, and a view (b) schematically showing mixing granulation inside the apparatus by a stirrer. The scoop type mixing granulation apparatus 50 in FIG. 7 includes a mixing tank 52 that extends in the horizontal direction and mixes construction sludge and a modifier, a stirrer 51 that stirs the construction sludge and the modifier in the mixing tank 52, and a CO2 supply pipe 53 that supplies exhaust gas containing CO2 from an internal combustion engine or the like into the mixing tank 52. The stirrer 51 has an endless belt 51a inclined and stretched between an upper rotating part 51b rotated by a motor (not shown) and a lower sub-rotating part 51c to form a conveyor type conveying part (see, for example, Japanese Patent Laid-Open No. 2011-207657). The stirrer 51 scoops up the construction sludge and the modifier put into the mixing tank 52 at the lower end of the endless belt 51a while moving horizontally in the horizontal direction H, conveys them obliquely upward a, and drops them downward near the rotating part 51b. When the stirrer 51 reaches near the left end of the mixing tank 52, the sub-rotating part 51c is pulled upward to be in a horizontal state, then returns to the original position on the right end side and returns to the original state, and repeats the above-described operation to perform mixing granulation of the mixed material 10. During such mixing granulation, exhaust gas containing CO2 is supplied from the CO2 supply pipe 53 into the mixing tank 52, calcium (Ca) contained in the modifier reacts with CO2 contained in the exhaust gas, and is chemically fixed as calcium carbonate (CaCO3) or the like, and CO2 is physically and stably retained in the granular modified soil.

[0041] In addition, in FIGS. 2, 3, 5 to 7, exhaust gas containing CO2 discharged from a generator, an internal combustion engine, or various plants used for a CO2 supply blower or the like as the CO2-containing gas may be used, or commercially available CO2 gas may be used, but it is not limited thereto. For example, dry ice may be added and mixed in the mixing granulation process of the mixed material, and the CO2-containing gas generated when the dry ice vaporizes may be used. For example, dry ice is put into FIGS. 2 to 7 and mixed with the mixed material. In this case, the supply of the CO2-containing gas by the CO2 supply pipe may not be necessary. Further, in the present embodiment, the CO2 concentration of the exhaust gas including the exhaust gas from the internal combustion engine is assumed to be about 5 to 20%.

[0042] Also, the modifier may fix CO2 before (before mixing). For this purpose, steps S11 and S12 shown by the broken lines in FIG. 1 are added. That is, a CO2-containing gas is supplied to the modifier (S11), CO2 is fixed in the modifier (S12), the modifier in which CO2 is fixed is added to construction sludge (S01), mixed and granulated (S02), a CO2-containing gas is supplied (S03), CO2 is fixed (S04), and a large number of granular modified soils with CO2 fixed are produced (S05). In this case, the CO2 supply step S03 and the CO2 fixation step S04 may be omitted. That is, as shown in FIG. 8, a CO2-containing gas is supplied to the modifier (S11), CO2 is fixed in the modifier (S12), the modifier in which CO2 is fixed is added to construction sludge (S13), mixed and granulated (S14), and a large number of granular modified soils with CO2 fixed are produced (S15).

[0043] When producing modified soil in a production plant, the steps S11 and S12 shown by the broken lines in FIG. 1 and in FIG. 8 can be carried out in a modifier storage silo or before and after it.

[0044] FIG. 9 is a diagram schematically showing a silo configuration for pre-mixing (before mixing) CO2 fixation of a modifier. As shown in FIG. 9, a CO2 supply pipe 62 is provided at the bottom inside a silo 60 which is a cylindrical sealed container, and a CO2-containing gas is supplied from an external CO2 supply device 61 through the CO2 supply pipe 62 to a powdery modifier WA inside the silo 60 to fix CO2 in the modifier WA. Although the modifier WA is in a powdery state, since the silo 60 is sealed, there is no risk of scattering to the outside. In a production plant, while the modifier WA is stored in the silo 60, CO2 is fixed in the modifier WA inside the silo 60, and then the mixing and granulation step S02 in FIG. 1 is carried out as shown in FIGS. 2 to 7. In the silo 60, the modifier WA is only stored, and for example, CO2 may be fixed in the modifier WA in the same manner in a sealed container arranged before or after it.

[0045] Incidentally, the construction sludge may be treated to fix CO2 before (before mixing). For example, in Fig. 2, the construction sludge is put into the storage section 14 (before adding the modifier), and exhaust gas containing CO2 is supplied to the construction sludge through the CO2 supply pipe 12 at the bottom of the storage section 14. Calcium (Ca) contained in the construction sludge reacts with CO2 contained in the exhaust gas and is chemically fixed as calcium carbonate (CaCO3) or the like. After the CO2 in the construction sludge is fixed in the storage section 14, a modifier can be added to the construction sludge, and a mixing and granulation process can be performed. The same can be done as in the case of Fig. 2 in Fig. 4.

[0046] Also, in Figs. 2, 4, 6, and 7, after granulation, mixing and CO2 supply can be continued, or CO2 supply can be continued after mixing and granulation, so that the amount of CO2 fixed can be increased. In addition, after granulation, CO2 supply can be continued as it is without involving the movement of the mixed material or the change of the working area, realizing the improvement of work efficiency and the space saving of the working area. Also, once granulated, a good air permeability state is maintained, so CO2 is easily fixed. Therefore, by simply spreading the granulated mixed material relatively thinly and leaving it, Ca in the mixed material reacts with CO2 in the atmosphere (CO2 concentration: 400 ppm = 0.04%), and CO2 is fixed. Therefore, leaving such a relatively thinly spread granulated mixed material is also a form of continuing CO2 supply after mixing and granulation.

[0047] Also, there is a water content ratio at which the fixation of CO2 proceeds efficiently. When using heated exhaust gas, excess moisture contained in the construction sludge can be evaporated by heat, enabling more efficient granulation and CO2 fixation.

[0048] Also, when the granular modified soil dries during the process of CO2 fixation treatment, the amount of CO2 fixed can be increased by spraying water to achieve a suitable water content ratio or by repeating drying and wetting.

[0049] Also, although the strength of the modified soil decreases as the amount of CO2 fixed increases, by adjusting the CO2 fixation treatment time to an appropriate amount of CO2 fixed, it is possible to ensure a predetermined strength.

[0050] Regarding the CO₂ supply timing, with reference to Fig. 10, (a) the construction sludge before mixing, (b) during the mixing of the construction sludge and the modifier, and (c) after granulation of the mixed material will be described. In the case of the construction sludge in Fig. 9(a), if CO₂ is supplied beforehand (before mixing), even if it contains calcium (Ca), as shown in the schematic diagram of Fig. 10(a), the soil particles are in water, the air permeability is at a low level, the surface area per unit weight of the construction sludge is small, and the CO₂ fixation efficiency is low. In the case of mixing the construction sludge and the modifier in Fig. 10(b), it is before the completion of granulation. As shown in the schematic diagram of Fig. 10(b), the CO₂-containing gas contacts both the modifier and the soil particles, but the air permeability is at a medium level, and the surface area per unit weight of the mixed material is also at a medium level, so the CO₂ fixation efficiency is at a medium level.

[0051] In the case of the construction sludge and the mixed material of the modifier after granulation in Fig. 10(c), as shown in the schematic diagram of Fig. 10(c), the air permeability is high, the surface area per unit weight of the mixed material is also large, and the CO₂-containing gas easily contacts both the modifier and the soil particles, so the CO₂ fixation efficiency is high. Also, when the temperature rises due to heated CO₂-containing gas or the like, the moisture easily evaporates, so the water content ratio can be efficiently adjusted. Among Figs. 10(a) to (c), the CO₂ supply after granulation of the mixed material results in the highest CO₂ fixation efficiency.

[0052] (Experimental Example) Next, the experimental examples of the present invention will be described. Note that the present invention is not limited to these experimental examples.

[0053] Experimental Example 1 This experimental example was about the pre (before mixing) CO₂ fixation in the modifier and construction sludge. CO₂-containing gas was supplied to the PS ash-based modifier and the construction sludge respectively, and the change over time in the CO₂ fixation amount under the condition of 25 °C was confirmed. The construction sludge was blue clay (liquid limit 40.7%, water content ratio 40.7%) with 39 kg / m of blast furnace cement 3The sludge was used as a mock construction sludge. The CO2 fixation process was carried out using gas with a CO2 concentration of 5% in an incubator at 25°C. The amount of CO2 fixation was confirmed by measuring the calcium carbonate (CaCO3) content.

[0054] Figure 11 shows the experimental results of changes in calcium carbonate (CaCO3) content (wt%) depending on the CO2 supply time. Figure 11 shows that the amount of CaCO3 in the PS ash-based modifier increases with the passage of CO2 supply time, while the CO2 fixation rate decreases with the passage of CO2 supply time. It can also be seen that the amount of CaCO3 in the construction sludge is smaller than that in the PS ash-based modifier.

[0055] Experimental Example 2 In this experiment, the CO2 fixation in the improved soil was carried out by adding blast furnace cement at 39 kg / m to blue clay (liquid limit 40.7%, water content 40.7%). 3 The cone index is 200 kN / m 2 The following simulated construction sludge was used, to which 200 kg / m of PS ash-based modifier was added. 3 The modified soil was prepared by adding and mixing. The experimental cases were: Case 0 (comparative example) where no CO2 fixation treatment was performed, Cases 1 to 5 where CO2 fixation treatment was performed in advance in the PS ash-based modifier (corresponding to FIG. 8, no CO2 fixation treatment during mixing and granulation), Cases 6 to 8 where CO2 fixation treatment was performed during mixing and granulation (corresponding to FIG. 1, no CO2 fixation treatment in advance in the PS ash-based modifier), and Cases 9 to 11 where CO2 fixation treatment in advance in the PS ash-based modifier and CO2 fixation treatment during mixing and granulation were performed in combination (corresponding to FIG. 1, including S11 and S12 shown by the dashed lines in FIG. 1). Gas with a CO2 concentration of 5% was used for the CO2 fixation treatment. The calcium carbonate (CaCO3) content was measured as the amount of CO2 fixed. In addition, referring to the soil compaction test method by tamping (JIS A 1210:2020), uniaxial compression tests after compaction were carried out 7 and 28 days after mixing, 3 layers x 25 times, using a ram (φ20 mm, weight 500 g, made of steel) as a rammer. In addition, pH measurements were carried out 28 days after mixing. The test conditions and test results are shown in Table 1.

[0056]

Table 1

[0057] From Table 1, in any of Cases 1 to 5 of the pre-CO2 fixation treatment of the modifier, Cases 6 to 8 of the CO2 fixation treatment during mixing granulation, and Cases 9 to 11 of the combined use of the pre-CO2 fixation treatment of the modifier and the CO2 fixation treatment during mixing granulation, the amount of CaCO3 exceeded that of the comparative example without CO2 fixation treatment (however, the amount of CaCO3 in Case 7 was the same). As shown in Fig. 12, when comparing those with similar CO2 fixation treatment conditions, it was confirmed that the amount of CaCO3 in the modified soil increased by the combined use of the pre-CO2 treatment of the modified soil and the CO2 fixation treatment during mixing granulation.

[0058] Also, in Cases 1 to 5 of the pre-CO2 fixation treatment of the modifier and Cases 6 to 8 of the CO2 fixation treatment during mixing granulation, as the CO2 fixation treatment time increased, the amount of CaCO3 in the modified soil increased in most cases, while the uniaxial compression strength at 28 days of age decreased. From such results, it was confirmed that a predetermined strength could be ensured by adjusting the CO2 fixation treatment time to an appropriate CO2 fixation amount.

[0059] Experimental Example 3 In this experimental example, the material obtained by adding 39 kg / m of blast furnace cement to blue clay (liquid limit 40.7%, water content ratio 40.7%) was used as simulated construction sludge with a cone index of 200 kN / m or less. To this, 200 kg / m of a PS ash-based modifier and 10, 50, 100 kg / m of dry ice were added and mixed for 10 minutes. Then, the calcium carbonate (CaCO3) content was measured as the CO2 fixation amount in the modified soil. The results are shown in Table 2. As shown in Table 2, the CaCO3 content showed a high value in Cases 12 to 14 where dry ice was added and mixed, and it was confirmed that CO2 fixation during mixing using dry ice was possible. When adding and mixing dry ice, a predetermined uniaxial compression strength can be obtained by adjusting the amount of dry ice to be mixed or by adjusting the amount of the modifier to be added according to the added amount of dry ice to be mixed. 3 added was used as simulated construction sludge with a cone index of 200 kN / m 2 or less, and 200 kg / m of a PS ash-based modifier and 10, 50, 100 kg / m of dry ice were added to this and mixed for 10 minutes. Then, the calcium carbonate (CaCO3) content was measured as the CO2 fixation amount in the modified soil. The results are shown in Table 2. As shown in Table 2, the CaCO3 content showed a high value in Cases 12 to 14 where dry ice was added and mixed, and it was confirmed that CO2 fixation during mixing using dry ice was possible. When adding and mixing dry ice, a predetermined uniaxial compression strength can be obtained by adjusting the amount of dry ice to be mixed or by adjusting the amount of the modifier to be added according to the added amount of dry ice to be mixed. 3 and dry ice 10, 50, 100 kg / m 3 and were added and mixed for 10 minutes, and then the calcium carbonate (CaCO3) content was measured as the CO2 fixation amount in the modified soil. The results are shown in Table 2. As shown in Table 2, the CaCO3 content showed a high value in Cases 12 to 14 where dry ice was added and mixed, and it was confirmed that CO2 fixation during mixing using dry ice was possible. When adding and mixing dry ice, a predetermined uniaxial compression strength can be obtained by adjusting the amount of dry ice to be mixed or by adjusting the amount of the modifier to be added according to the added amount of dry ice to be mixed.

[0060]

Table 2

[0061] The embodiments for carrying out the present invention have been described above. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the implementation of the hybrid granulation steps S02 and S14 in FIGS. 1 and 8 is not limited to the methods and apparatuses in FIGS. 2 to 7, and other methods and apparatuses may be used, and various mixers can be used. For example, a kneading granulation apparatus using a swing blade (such as the VZ series kneading granulator Peregaia (registered trademark) sold by Kitakawa Iron Works Co., Ltd.), a granulation mixer with a variable tilt barrel mechanism (such as Tsuvler / Tsubura- (registered trademark) sold by Nikkai Co., Ltd.), a batch granulation mixer having a stirring blade with outer blades and inner blades rotating in opposite directions on concentric two axes (https: / / penta-ocean-int.com / wp-content / uploads / 2014 / 11 / g32-14.pdf), etc. can be used. Further, these apparatuses can be configured to supply a CO2-containing gas inside for performing hybrid granulation.

Industrial Applicability

[0062] According to the method for fixing carbon dioxide to the modified soil and the method for producing the modified soil of the present invention, the necessary steps can be simplified and the working efficiency can be improved. Therefore, carbon dioxide can be efficiently fixed when converting construction sludge into modified soil, which can contribute to enhancing the carbon storage effect, and at the same time, a modified soil that can be used as a practical material can be obtained.

Explanation of Reference Numerals

[0063] 10 Modified soil, mixing material 11 CO2 supply device 12, 13, 16 CO2 supply pipe 14 Storage part 15 Hybrid granulation yard 20 Shallow layer mixing processor 20a Stirring part 30 Rotating drum 31 CO2 supply device 32 CO2 supply pipe 40 Middle layer mixing treatment device 41 CO2 supply device 42 CO2 supply pipe 43 Treatment tank 44 Rotating part 45, 46 Stirring part 50 Scoop type mixing granulation device 51 Stirrer 52 Mixing tank 53 CO2 supply pipe 60 Silo 61 CO2 supply device 62 CO2 supply pipe BH Backhoe BK Mixing bucket MD Mixer truck WA Modifying material

Claims

1. A method for fixing carbon dioxide when modifying construction sludge into granular modified soil, comprising: a mixing and granulation step of mixing a modifier with the construction sludge to form granules; a carbon dioxide supply step of supplying a carbon dioxide-containing gas in the mixing and granulation step, wherein the supply of the carbon dioxide-containing gas causes carbon dioxide to react with calcium in the modifier and be fixed in the modified soil as a carbonate. A method for fixing carbon dioxide in modified soil.

2. The method for fixing carbon dioxide in modified soil according to claim 1, wherein carbon dioxide is fixed in the modifier by supplying a carbon dioxide-containing gas to the modifier before mixing.

3. The method for fixing carbon dioxide in modified soil according to claim 2, wherein the supply of the carbon dioxide-containing gas in the mixing and granulation step is omitted.

4. The construction sludge has a cone index of 200 kN / m ２ The method for carbon dioxide fixation in the modified soil according to claim 1, wherein the following conditions are satisfied.

5. The method for fixing carbon dioxide in modified soil according to claim 1, wherein as the modifier, any one of cement, paper sludge incineration ash-based modifier, and fine powder of blast furnace slag, or at least any two of them are used.

6. The method for fixing carbon dioxide in modified soil according to claim 1, wherein after granulation, the mixing and the carbon dioxide supply are continued.

7. The method for fixing carbon dioxide in modified soil according to claim 1, wherein after granulation, the carbon dioxide supply is continued.

8. The method for fixing carbon dioxide in modified soil according to claim 1, wherein the modifier has fixed carbon dioxide before mixing.

9. The method for fixing carbon dioxide in modified soil according to claim 1, wherein the construction sludge contains cement.

10. The method for fixing carbon dioxide in modified soil according to claim 1, wherein by supplying the heated carbon dioxide-containing gas, moisture contained in the construction sludge is evaporated.

11. The method for fixing carbon dioxide in modified soil according to claim 1, wherein when the granular modified soil dries in the carbon dioxide supply step, watering or repeating wetting and drying is performed so as to obtain a predetermined water content ratio.

12. The method for fixing carbon dioxide in modified soil according to claim 1, wherein a carbon-containing substance is further added to the construction sludge.

13. The method for fixing carbon dioxide in modified soil according to claim 1, wherein dry ice is added and mixed in the mixing and granulation step, and the carbon dioxide-containing gas generated by vaporization of the dry ice is supplied in the carbon dioxide supply step.

14. A method for producing granular modified soil from construction sludge, comprising: A method for producing the modified soil, wherein carbon dioxide is fixed in the modified soil by the method for fixing carbon dioxide in the modified soil according to any one of claims 1 to 13 when producing the modified soil.

15. The method for producing a modified soil according to claim 14, wherein a predetermined strength of the modified soil is ensured by controlling the amount of carbon dioxide fixed by adjusting the time of carbon dioxide supply.

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