Co2 fixation equipment and co2 fixation method

Abstract

To provide CO2 fixation equipment and a CO2 fixation method, each enabling reduction of cost related to equipment and energy associated with CO2 fixation, and furthermore enabling improvement of the precipitation efficiency of alkaline earth metal carbonates.SOLUTION: One or more decompression tanks and a crystallization tank connected in series are arranged in downstream side of an extraction tank that extracts alkaline earth metals. Alkaline earth metal carbonates are precipitated while performing stepwise decompression in the decompression tanks and the crystallization tank. The alkaline earth metal carbonates precipitated in the decompression tank are supplied to the crystallization tank as seed crystals. CO2 gas generated in the decompression tanks and the crystallization tank is pressurized and supplied to the extraction tank.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a CO 2 immobilization device and a CO 2 immobilization method.

Background Art

[0002] As one of the CO 2 immobilization technologies aimed at reducing the amount of CO 2 gas emissions into the atmosphere, mineral carbonation is known, which involves reacting alkaline earth metals such as Mg and Ca contained in ores, steel slag, waste concrete, construction waste, coal ash, cement slag, industrial waste, etc. with CO 2 gas emitted from, for example, factories and power plants to immobilize the CO 2 gas. Alkaline earth metal carbonates such as magnesium carbonate and calcium carbonate produced by the immobilization of CO 2 gas can be used as industrial raw materials such as fillers for plastics, paper, rubber, paints, etc., additives for building materials, soil conditioners, and cement raw materials.

[0003] Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-501726) describes "a method for fixing or binding CO 2 as a carbonate, comprising the following steps: a step of preparing an aqueous solution of water and coal ash or coal residue; a step of contacting a gas containing CO 2 with the aqueous solution; and a step of reacting the CO 2 with the aqueous solution to produce a carbonate, thereby fixing or binding the CO 2 ". 2

[0004] Patent Document 2 (Japanese Patent Application Laid-Open No. 2021-524806) describes "a) providing an aqueous slurry containing an aqueous liquid and particulate solids containing activated magnesium silicate minerals; b) in the dissolution stage, CO 2A step of contacting the aqueous slurry with a first pressure to provide a slurry containing a gas stream, magnesium dissolved from the mineral, a magnesium ion-enriched carbonated aqueous solution, and a magnesium-depleted solid residue; and c) In the precipitation step, magnesium carbonate is precipitated from the magnesium ions dissolved in step b) by a plurality of successive stepwise pressure reductions to a lower pressure compared to the preceding step; An integrated process for the recovery, isolation and utilization of carbon dioxide, wherein CO 2 is released by each successive stepwise pressure reduction, correspondingly compressed step by step and recycled to the dissolution step, is described.

[0005] Patent Document 3 (International Publication No. 2013 / 131193) discloses a method for isolating carbon dioxide from a carbon dioxide-containing gas, the method comprising contacting the carbon dioxide-containing gas with an aqueous slurry containing an alkaline earth metal-containing material in a carbonation unit for carbonating at least a part of the alkaline earth metal to produce a carbon dioxide-depleted gas and a carbonate-containing slurry containing a precipitable carbonate and substantially free of precipitated alkaline earth metal carbonate; removing the carbonate-containing slurry from the carbonation unit and separating the carbonate-containing slurry into an aqueous phase and a solid phase containing the precipitable carbonate; and feeding the aqueous phase to a precipitation device to precipitate an alkaline earth metal carbonate in the precipitation device to produce a precipitation slurry.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Ions of alkaline earth metals and CO 2 In order to efficiently precipitate alkaline earth metal carbonates from a solution in which ions of alkaline earth metals and CO are dissolved, it is generally known to recover the precipitated alkaline earth metal carbonates and return a part of them to the solution as seed crystals and introduce them. As the precipitation process progresses, the seed crystals grow and their particle size increases. As a result, the surface area per unit mass of the seed crystals decreases, and the precipitation efficiency due to the introduction of the seed crystals decreases. It is also conceivable to pulverize the grown seed crystals into fine particles and then introduce them into the solution, but costs related to equipment and energy for pulverization are incurred.

[0008] Ions of alkaline earth metals and CO 2 By reducing the pressure of the atmosphere in which a solution in which ions of alkaline earth metals and CO are dissolved exists and releasing CO from the solution into the gas phase, the pH of the solution rises and alkaline earth metal carbonates precipitate. When the pressure reduction is carried out in one step to atmospheric pressure, the pressure of the CO gas released from the solution into the gas phase also becomes atmospheric pressure. Therefore, when reusing the CO gas whose pressure has been reduced to atmospheric pressure in the extraction process of alkaline earth metals, it is necessary to increase the pressure to the CO pressure in the extraction process, and energy costs associated with the pressure increase are incurred. This energy cost associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 to the gas phase, the pH of the solution rises and alkaline earth metal carbonates precipitate. When the pressure reduction is carried out in one step to atmospheric pressure, the pressure of the CO gas released from the solution into the gas phase also becomes atmospheric pressure. Therefore, when reusing the CO gas whose pressure has been reduced to atmospheric pressure in the extraction process of alkaline earth metals, it is necessary to increase the pressure to the CO pressure in the extraction process, and energy costs associated with the pressure increase are incurred. This energy cost associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 gas becomes atmospheric pressure. Therefore, when reusing the CO gas whose pressure has been reduced to atmospheric pressure in the extraction process of alkaline earth metals, it is necessary to increase the pressure to the CO pressure in the extraction process, and energy costs associated with the pressure increase are incurred. This energy cost associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 gas in the extraction process of alkaline earth metals, it is necessary to increase the pressure to the CO pressure in the extraction process, and energy costs associated with the pressure increase are incurred. This energy cost associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 pressure, and energy costs associated with the pressure increase are incurred. This energy cost associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 associated with the pressure increase of CO accounts for a proportion that should be considered in CO immobilization, and thus it is strongly desired to reduce it. 2 should be considered in CO immobilization, and thus it is strongly desired to reduce it.

[0009] The present disclosure provides a CO immobilization device and a CO immobilization method that can increase the precipitation efficiency of alkaline earth metal carbonates while reducing the costs related to equipment and energy associated with CO immobilization. 2 immobilization while increasing the precipitation efficiency of alkaline earth metal carbonates, a CO immobilization device and a CO immobilization method. 2 immobilization device and a CO 2 immobilization method. Means for Solving the Problems

[0010] The inventors of the present invention arranged one or more vacuum tanks and a crystallization tank connected in series downstream of an extraction tank for extracting alkaline earth metals, and precipitated alkaline earth metal carbonates while gradually reducing the pressure in the vacuum tanks and the crystallization tank. The alkaline earth metal carbonates precipitated in the vacuum tanks were supplied as seed crystals to the crystallization tank, and the CO 2 gas generated in the vacuum tanks and the crystallization tank was respectively pressurized and supplied to the extraction tank, and found that the precipitation efficiency of alkaline earth metal carbonates can be increased while reducing the costs related to equipment and energy.

[0011] The present disclosure includes the following aspects. [Aspect 1] CO 2 An extraction tank equipped with a CO gas supply port and a slurry discharge port, and a first solid-liquid separator equipped with a liquid-phase discharge port connected to the slurry discharge port of the extraction tank; One or more vacuum tanks, when there are two or more of the one or more vacuum tanks, the one or more vacuum tanks are connected in series with each other, and the uppermost upstream vacuum tank among the one or more vacuum tanks is connected to the liquid-phase discharge port of the first solid-liquid separator; one or more vacuum tanks; A crystallization tank connected to the lowermost downstream vacuum tank among the one or more vacuum tanks; A second solid-liquid separator and a pressure reducing valve on the downstream side of the second solid-liquid separator, arranged between the lowermost downstream vacuum tank among the one or more vacuum tanks and the crystallization tank; When there are two or more of the one or more vacuum tanks, one or more second solid-liquid separators respectively arranged between the one or more vacuum tanks and one or more pressure reducing valves on the downstream side of the one or more second solid-liquid separators; A plurality of CO 2 gas recovery pipes connected to each of the one or more vacuum tanks and the crystallization tank; A plurality of compressors having a primary side and a secondary side and connected in series, configured such that the CO 2 gas supplied to the primary side is pressurized and discharged from the secondary side, and the secondary side of the lowermost downstream compressor among the plurality of compressors is connected to the CO 2 gas supply port; a plurality of compressors. CO containing 2 A fixation device, For each of the primary sides of the plurality of compressors, the CO supplied to the primary sides of the plurality of compressors from the upstream side to the downstream side 2 gas pressure increases, the plurality of CO 2 is connected to one of the gas recovery pipes, A CO in which the solid-phase enrichment side of the second solid-liquid separation device is connected to the crystallization tank 2 Fixation device. [Aspect 2] The second solid-liquid separation device is selected from the group consisting of a cross-flow filter, a pleated filter, an auto-strainer, a cyclone strainer, a filter press, a rotary filter, a leaf filter, a hunderback filter, and a hydrocyclone. The CO according to Aspect 1 2 Fixation device. [Aspect 3] The volume of the crystallization tank is 1 to 15 times the volume of the one or more decompression tanks. The CO according to Aspect 1 or 2 2 Fixation device. [Aspect 4] Further includes a third solid-liquid separation device connected downstream of the crystallization tank and a solid-phase supply device for supplying the solid phase obtained by the third solid-liquid separation device to the crystallization tank. The CO according to any one of Aspects 1 to 3 2 Fixation device. [Aspect 5] In an extraction tank, by mixing a slurry containing alkaline earth metal-containing particles and an aqueous medium with a CO 2 gas, extracting the ions of the alkaline earth metal in the alkaline earth metal-containing particles into the liquid phase, Solid-liquid separating the mixture in which the ions of the alkaline earth metal are extracted into the liquid phase to obtain a liquid phase containing the ions of the alkaline earth metal and a solid phase containing extraction residues, Precipitating alkaline earth metal carbonate from the liquid phase while gradually reducing the pressure in one or more serially connected decompression tanks and in the crystallization tank, and fixing the CO as the alkaline earth metal carbonate 2 thereby. Supplying the alkaline earth metal carbonate precipitated in the one or more vacuum tanks to the crystallization tank as seed crystals, CO generated in the one or more vacuum tanks and in the crystallization tank 2 Pressurizing the gas with a compressor, and The pressurized CO 2 Supplying the gas to the extraction tank, A CO 2 Immobilization method. [Aspect 6] The residence time of the crystallization tank is 1 to 15 times the residence time of each of the one or more vacuum tanks, and the CO described in Aspect 5 2 Immobilization method. [Aspect 7] Supplying 0.1 mass% to 10 mass% of the seed crystals of the liquid amount in the crystallization tank to the crystallization tank, and the CO described in Aspect 5 or 6 2 Immobilization method. [Aspect 8] Mixing in the extraction tank is performed in a pressure atmosphere of 0.5 MPaG to 10 MPaG, and the CO described in any one of Aspects 5 to 7 2 Immobilization method. [Aspect 9] The alkaline earth metal is calcium, and the CO described in any one of Aspects 5 to 8 2 Immobilization method. [Aspect 10] The alkaline earth metal-containing particles include at least one selected from the group consisting of concrete, concrete sludge, and cement, and the CO described in any one of Aspects 5 to 9 2 Immobilization method.

Advantages of the Invention

[0012] The CO of the present disclosure 2 Immobilization device and CO 2 According to the immobilization method, while reducing the costs related to the facilities and energy related to CO immobilization, 2 The precipitation efficiency of the alkaline earth metal carbonate can be increased.

[0013] Note that the above description should not be regarded as disclosing all embodiments of the present invention and all advantages related to the present invention.

Brief Description of Drawings

[0014]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0015] Hereinafter, for the purpose of exemplifying typical embodiments of the present invention, a more detailed description will be given with reference to the drawings, but the present invention is not limited to these embodiments.

[0016] [CO 2 Immobilization Device] A CO 2 immobilization device according to an embodiment includes an extraction tank having a CO 2 gas supply port and a slurry discharge port; a first solid-liquid separation device having a liquid phase discharge port connected to the slurry discharge port of the extraction tank; one or more decompression tanks, when there are two or more of the one or more decompression tanks, the one or more decompression tanks are connected in series with each other, and the uppermost decompression tank among the one or more decompression tanks is connected to the liquid phase discharge port of the first solid-liquid separation device, the one or more decompression tanks; a crystallization tank connected to the lowermost decompression tank among the one or more decompression tanks; a second solid-liquid separation device and a decompression valve on the downstream side of the second solid-liquid separation device disposed between the lowermost decompression tank among the one or more decompression tanks and the crystallization tank; when there are two or more of the one or more decompression tanks, one or more second solid-liquid separation devices respectively disposed between the one or more decompression tanks and one or more decompression valves on the downstream side of the one or more second solid-liquid separation devices; a plurality of CO 2 gas recovery pipes connected to each of the one or more decompression tanks and the crystallization tank; a plurality of compressors having a primary side and a secondary side and connected in series, the CO 2 gas supplied to the primary side is configured to be pressurized and discharged from the secondary side, and the secondary side of the lowermost compressor among the plurality of compressors is CO 2It includes a plurality of compressors connected to a gas supply port. The primary sides of the plurality of compressors are each supplied with CO that is supplied to the primary sides of the plurality of compressors from the upstream side to the downstream side 2 gas so that the pressure of the plurality of CO 2 gases is increased, and is connected to one of the plurality of CO gas recovery pipes. The solid-phase enrichment side of the second solid-liquid separator is connected to a crystallization tank. In the present disclosure, the "second solid-liquid separator" is, unless otherwise specified, a general term for the second solid-liquid separator disposed between the most downstream decompression tank and the crystallization tank, and the second solid-liquid separator disposed between the decompression tanks.

[0017] Figure 1 shows a schematic diagram of a CO 2 immobilization device. The CO 2 immobilization device 1 includes an extraction tank 10, a first solid-liquid separator 20, decompression tanks 30A, 30B, a crystallization tank 40, second solid-liquid separators 50A, 50B, decompression valves 60A, 60B, CO 2 gas recovery pipes 70A, 70B, 70N, and compressors 80A, 80B, 80N.

[0018] The extraction tank 10 is provided with a CO 2 gas supply port 11 and a slurry discharge port 12. The extraction tank 10 may be provided with a stirring device having stirring blades and a motor, and may also be provided with other mechanisms related to stirring, such as a slurry circulation device. In an extraction tank equipped with a slurry circulation device, a part of the slurry is extracted from the extraction tank, and the slurry is stirred by the circulation flow generated when the slurry is circulated through the slurry circulation device. The extraction tank 10 may be provided with a temperature adjustment mechanism, and may be a sealed container provided with a mechanism for pressurizing the internal atmosphere. A pipe for introducing CO 2 gas extending to below the slurry liquid level through the CO 2 gas supply port 11 may be provided. A nozzle may be provided at the tip or in the middle of the pipe, and CO 2 gas may be introduced into the slurry from the nozzle. The extraction tank 10 may be a wet mill, or may be a pressure vessel provided with the slurry circulation device.

[0019] In the extraction tank 10, the slurry containing alkaline earth metal particles and an aqueous medium is mixed with CO 2 gas, and the ions of the alkaline earth metal in the alkaline earth metal-containing particles are extracted into the liquid phase of the slurry.

[0020] The first solid-liquid separation device 20 is connected to the slurry discharge port 12 of the extraction tank 10. The first solid-liquid separation device 20 includes a liquid phase discharge port 22 and a solid phase discharge port 23. Examples of the first solid-liquid separation device 20 include a vacuum separation device, a centrifugal separation device, a multi-disc separation device, a belt press, a screw press, a roller press, a rotary drum screen, a belt screen, a vibrating screen, a thickener, a ceramic filter, a pleated filter, and a multi-plate undulating filter.

[0021] The slurry from which the ions of the alkaline earth metal have been extracted into the liquid phase by the first solid-liquid separation device 20 is separated into a liquid phase containing the ions of the alkaline earth metal and a solid phase containing the extraction residue. The liquid phase is discharged from the liquid phase discharge port 22, and the solid phase is discharged from the solid phase discharge port 23.

[0022] The decompression tanks 30A and 30B are connected in series with each other, and the decompression tank 30A, which is the uppermost decompression tank, is connected to the liquid phase discharge port 22 of the first solid-liquid separation device 20. Examples of the decompression tanks 30A and 30B include a flash drum and a decompression drum. The decompression tanks 30A and 30B may be the same devices as the crystallization tank 40 described later. In FIG. 1, two decompression tanks 30A and 30B connected in series are shown, but the number of decompression tanks may be one, or two or more decompression tanks may be connected in series. When there is one decompression tank, the decompression tank is both the uppermost decompression tank and the lowermost decompression tank. CO 2 Considering the reduction in energy related to the recompression of the CO gas and the increase in capital investment, installation area, and operating costs related to the decompression tank, the number of decompression tanks is preferably 2 or 3, and more preferably 2.

[0023] In the decompression tanks 30A and 30B, the CO dissolved in the liquid phase containing the ions of the alkaline earth metal 2Gas is released into the gas phase, and alkaline earth metal carbonate precipitates from the liquid phase. CO 2 The pressure of the gas phase containing the gas gradually decreases toward the downstream decompression tank. That is, the pressure of the gas phase becomes lower in the order of the decompression tank 30A and the decompression tank 30B. The decompression tanks 30A and 30B are (1) to recover the CO 2 gas released into the gas phase in each decompression tank at as high a pressure as possible and reduce the energy related to the recompression of the CO 2 gas, and (2) are arranged to generate alkaline earth metal carbonate used as seed crystals in the crystallization tank 40. In other words, the decompression tanks 30A and 30B function not only as a supply device for recycled CO 2 gas but also as a seed crystal production device. Since the seed crystals generated in the decompression tanks 30A and 30B can be obtained in the form of fine particles by appropriately setting the operating conditions of the decompression tanks, even when they are put into the crystallization tank 40 without going through additional processes such as grinding, the precipitation efficiency of the alkaline earth metal carbonate can be increased.

[0024] The crystallization tank 40 is connected to the decompression tank 30B, which is the most downstream decompression tank. The crystallization tank may be equipped with a temperature control mechanism, an air bubbling mechanism or a vacuum pump, or a combination of two or more of these.

[0025] In the crystallization tank 40, the CO 2 gas dissolved in the liquid phase containing alkaline earth metal ions is released into the gas phase, and alkaline earth metal carbonate precipitates from the liquid phase.

[0026] As described above, the decompression tanks 30A and 30B are arranged for the purpose of recovering higher-pressure CO 2 gas and generating seed crystals, while the crystallization tank 40 is for the purpose of final CO 2 immobilization by precipitation of alkaline earth metal carbonate. In the decompression tank and the crystallization tank, the precipitation of alkaline earth metal carbonate proceeds more slowly compared to the release of CO 2 gas into the gas phase. Therefore, the volume of the crystallization tank 40 is the same as or larger than the volume of the decompression tanks 30A and 30B in order to 2It is preferable for enhancing the efficiency of immobilization. In one embodiment, the volume of the crystallization tank 40 is 1 to 15 times, 1.1 to 12 times, or 1.5 to 10 times the volume of the decompression tanks 30A and 30B.

[0027] The second solid-liquid separation device 50B is disposed between the crystallization tank 40 and the decompression tank 30B which is the most downstream decompression tank. The second solid-liquid separation device 50A is disposed between the decompression tank 30A and the decompression tank 30B. The decompression valves 60A and 60B are respectively disposed on the downstream sides of the second solid-liquid separation devices 50A and 50B. The second solid-liquid separation devices 50A and 50B each include a liquid phase discharge port 52A, 52B and a solid phase discharge port 53A, 53B. Since the second solid-liquid separation devices 50A and 50B are operated under a pressure equal to or higher than normal atmospheric pressure, it is preferable that they are selected from the group consisting of a cross-flow filter, a pleat filter, an auto-strainer, a cyclone strainer, a filter press, a rotary filter, a leaf filter, a hunderback filter, and a hydrocyclone. Examples of the decompression valves 60A and 60B include an angle valve and a globe valve. By disposing the decompression valves 60A and 60B on the downstream sides of the second solid-liquid separation devices 50A and 50B, wear or damage of the decompression valves 60A and 60B caused by the alkaline earth metal carbonate precipitated in the decompression tanks 30A and 30B can be prevented.

[0028] The slurry containing the alkaline earth metal carbonate precipitated in the decompression tanks 30A and 30B is separated by the second solid-liquid separation devices 50A and 50B into a liquid phase containing alkaline earth metal ions and a solid phase containing alkaline earth metal carbonate. The liquid phase is discharged from the liquid phase discharge ports 52A and 52B, and the solid phase is discharged from the solid phase discharge ports 53A and 53B, respectively. The liquid phase is supplied to the decompression tank 30B through the decompression valve 60A and to the crystallization tank 40 through the decompression valve 60B.

[0029] The solid phase discharge ports 53A and 53B of the second solid-liquid separation devices 50A and 50B are connected to the crystallization tank 40 as the solid phase enrichment side. Thereby, the solid phase containing alkaline earth metal carbonate can be supplied to the crystallization tank 40 and used as seed crystals in the crystallization tank 40.

[0030] CO 2 The gas recovery pipes 70A, 70B, and 70N are respectively connected to the vacuum tanks 30A, 30B, and the crystallization tank 40. High-pressure CO 2 gas is recovered from the vacuum tank 30A, medium-pressure CO 2 gas is recovered from the vacuum tank 30B, and low-pressure CO 2 gas is recovered from the crystallization tank 40, and the CO 2 gas is respectively recovered through the gas recovery pipes 70A, 70B, and 70N.

[0031] The compressors 80N, 80B, and 80A respectively have a primary side 81N, 81B, 81A and a secondary side 82N, 82B, 82A, and are connected in series. The CO 2 gas supplied to the primary sides 81N, 81B, 81A is pressurized by the compressors 80N, 80B, 80A and discharged from the secondary sides 82N, 82B, 82A. The secondary side 82A of the compressor 80A, which is the most downstream compressor, is connected to the CO 2 gas supply port 11 of the extraction tank 10. Examples of the compressors 80N, 80B, 80A include centrifugal, axial flow, and reciprocating compressors. The number of compressors is usually the same as the number of CO 2 gas recovery pipes. In FIG. 1, three compressors 80N, 80B, 80A connected in series corresponding to the CO 2 gas recovery pipes 70N, 70B, and 70A are shown. Generally, a CO 2 gas supply source outside the immobilization device is connected to the primary side 81N of the compressor 80N, which is the most upstream compressor. The CO 2 gas supplied from the gas supply source is pressurized through the compressors 80N, 80B, 80A. 2 The CO 2 gas supplied from the gas supply source is pressurized through the compressors 80N, 80B, 80A.

[0032] The primary sides 81N, 81B, 81A of the compressors 80N, 80B, 80A are respectively connected to one of the CO 2 gas recovery pipes 70N, 70B, 70A so that the pressure of the CO 2 gas supplied to the primary sides 81N, 81B, 81A of the compressors 80N, 80B, 80A increases from upstream to downstream. Specifically, high-pressure CO2 CO for gas recovery 2 The gas recovery pipe 70A is connected to the primary side 81A of the most downstream compressor 80A. Medium-pressure CO 2 CO for gas recovery 2 The gas recovery pipe 70B is connected to the primary side 81B of the intermediate compressor 80B. Low-pressure CO 2 CO for gas recovery 2 The gas recovery pipe 70N is connected to the primary side 81N of the most upstream compressor 80N. CO 2 Low-pressure CO gas supplied from the gas recovery pipe 70N 2 The gas is compressed by the compressor 80N to CO 2 Medium-pressure CO gas supplied from the gas recovery pipe 70B 2 The pressure of the gas is boosted to the pressure of the medium-pressure CO 2 gas and is supplied to the compressor 80B together. The CO supplied to the compressor 80B 2 The gas is compressed by the compressor 80B to CO 2 High-pressure CO gas supplied from the gas recovery pipe 70A 2 The pressure of the gas is boosted to the pressure of the high-pressure CO 2 gas and is supplied to the compressor 80A together. The CO supplied to the compressor 80A 2 The gas is further boosted by the compressor 80A and supplied to the extraction tank 10. CO 2 By arranging and connecting the gas recovery pipes and compressors in this way, CO 2 The energy related to the re-boosting of the gas can be effectively reduced.

[0033] CO 2The immobilization device 1 may further include a third solid-liquid separation device 90 connected downstream of the crystallization tank 40 and a solid-phase supply device 95 that supplies the solid phase obtained by the third solid-liquid separation device 90 to the crystallization tank 40. The third solid-liquid separation device 90 includes a liquid-phase discharge port 92 and a solid-phase discharge port 93. Examples of the third solid-liquid separation device 90 include a vacuum separation device, a centrifugal separation device, a multi-disc separation device, a belt press, a screw press, a roller press, a rotary drum screen, a belt screen, a vibrating screen, a thickener, a ceramic filter, a pleated filter, and a multi-plate ripple filter. The solid-phase discharge port 93 is connected to the solid-phase supply device 95. Examples of the solid-phase supply device 95 include a rotary pump, a volute pump, and a hose pump.

[0034] By the third solid-liquid separation device 90, the alkaline earth metal carbonate precipitated in the crystallization tank 40 is separated from the liquid phase and recovered from the solid-phase discharge port 93. The alkaline earth metal carbonate may be used as a product or can also be supplied to the crystallization tank 40 as seed crystals via the solid-phase supply device 95. The liquid phase separated by the third solid-liquid separation device 90 is discharged from the liquid-phase discharge port 92. As shown by the dotted line in FIG. 1, the liquid phase may be returned to the extraction tank 10. Thereby, the water used for immobilization can be effectively reused. 2 The water used for immobilization can be effectively reused.

[0035] [CO 2 Immobilization method] The CO 2 immobilization method of one embodiment is (1) In the extraction tank, by mixing a slurry containing alkaline earth metal-containing particles and an aqueous medium with CO 2 gas, extracting the ions of the alkaline earth metal in the alkaline earth metal-containing particles into the liquid phase; (2) Separating the mixture in which the ions of the alkaline earth metal have been extracted into the liquid phase by solid-liquid separation to obtain a liquid phase containing the ions of the alkaline earth metal and a solid phase containing the extraction residue; (3) Precipitating alkaline earth metal carbonate from the liquid phase while gradually reducing the pressure in one or more decompression tanks connected in series and in the crystallization tank, and immobilizing CO as alkaline earth metal carbonate 2Fixing, (4) Supplying the alkaline earth metal carbonate precipitated in one or more decompression tanks to the crystallization tank as seed crystals, (5) Compressing the CO 2 gas generated in one or more decompression tanks and in the crystallization tank with a compressor, and (6) Supplying the pressurized CO 2 gas to the extraction tank, is included. The CO 2 fixing method of this embodiment can be preferably implemented using the above-described CO 2 fixing device.

[0036] Fig. 2 shows an outline of the CO 2 fixing method of one embodiment in a flow chart. In the flow chart of the present disclosure, the parts surrounded by squares indicate steps or devices. An aqueous medium is added to the alkaline earth metal-containing particles to obtain a slurry. In the extraction tank, the ions of the alkaline earth metal in the alkaline earth metal-containing particles are extracted into the liquid phase by mixing the slurry and the CO 2 gas. By solid-liquid separation, a liquid phase containing ions of the alkaline earth metal and a solid phase containing extraction residue are obtained. The alkaline earth metal carbonate is precipitated from the liquid phase while gradually reducing the pressure in one or more decompression tanks connected in series and in the crystallization tank, and CO 2 is fixed as the alkaline earth metal carbonate. The alkaline earth metal carbonate precipitated in the decompression tank is supplied to the crystallization tank as seed crystals. The CO 2 gas generated in the decompression tank and in the crystallization tank is pressurized with a compressor. In Fig. 2, the CO 2 gas generated in the decompression tank and in the crystallization tank is gradually pressurized corresponding to the stepwise pressure reduction in the stepwise pressure reduction and precipitation process. That is, the low-pressure CO 2 gas generated in the crystallization tank is pressurized through three compressors, and the medium-pressure CO 2 gas generated in the second decompression tank from the top is pressurized through two compressors, and the high-pressure CO 2 gas generated in the top decompression tank is pressurized through one compressor. The pressurized CO 2 gas is supplied to the extraction tank. CO 2It is immobilized as an alkaline earth metal carbonate precipitated in the crystallization tank. The alkaline earth metal carbonate can also be purified as needed and used as a product.

[0037] (1) Extraction step By mixing a slurry containing alkaline earth metal-containing particles and an aqueous medium with CO 2 gas, the ions of the alkaline earth metal in the alkaline earth metal-containing particles are extracted into the liquid phase.

[0038] The alkaline earth metal-containing particles are not particularly limited as long as they contain an alkaline earth metal. In the present disclosure, "alkaline earth metal" means a Group 2 element of the periodic table. The alkaline earth metal is preferably at least one selected from the group consisting of Mg, Ca, Sr, and Ba, more preferably at least one selected from the group consisting of Mg and Ca, still more preferably containing Ca, and particularly preferably Ca.

[0039] Examples of the alkaline earth metal-containing particles include Mg-containing ores, Mg-containing slags, Ca-containing slags, coal ash, clinker kiln dust, concrete, concrete sludge, and cement particles.

[0040] In one embodiment, the alkaline earth metal-containing particles include at least one selected from the group consisting of concrete, concrete sludge, and cement. In a series of processes related to concrete production, the CO 2 gas discharged from the rotary kiln used for the production of clinker, which is a cement raw material, accounts for a considerable proportion. By using alkaline earth metal-containing particles including at least one selected from the group consisting of concrete, concrete sludge, and cement, the closed-loop recycling of concrete can be further promoted.

[0041] The alkaline earth metal-containing particles may be formed by pretreating an alkaline earth metal-containing raw material. The alkaline earth metal-containing raw material may be the materials described with respect to the alkaline earth metal-containing particles, for example, Mg-containing ore, Mg-containing slag, Ca-containing slag, coal ash, clinker kiln dust, concrete (including waste concrete), concrete sludge, or cement.

[0042] Examples of the pretreatment include pulverization and heat treatment. In the pretreatment of concrete, pulverization is generally performed.

[0043] Pulverization can be carried out using a known pulverization device. By pulverization, the average particle size of the alkaline earth metal-containing particles can be reduced to increase the surface area per unit mass, or the active surface of the alkaline earth metal-containing particles can be exposed. Thereby, the extraction efficiency of the alkaline earth metal can be enhanced. Pulverization can be performed under conditions such that the alkaline earth metal-containing particles have a suitable average particle size described later. If necessary, the alkaline earth metal-containing particles may be classified using a sieve or the like after pulverization.

[0044] Heat treatment can be carried out using a known heat treatment device. The heat treatment temperature can be, for example, 500°C to 800°C, and the heat treatment time can be 1 minute to 2 hours. It is preferable that the alkaline earth metal-containing particles are heat-treated. By heat-treating the alkaline earth metal-containing raw material, the crystal water in the alkaline earth metal-containing raw material is removed, and the alkaline earth metal in the alkaline earth metal-containing particles is activated into a form in which it is easily eluted into the liquid phase, thereby enhancing the extraction efficiency of the alkaline earth metal. Since heat is more easily transmitted to the inside of the particles as the particle size is smaller and the efficiency of the heat treatment is increased, it is preferable that the heat treatment is performed after the above-mentioned pulverization.

[0045] In the present disclosure, devices used for pretreatment such as a pulverization device, a heat treatment device, and a classification device are collectively referred to as a pretreatment device.

[0046] The average particle size of the alkaline earth metal-containing particles can be appropriately determined according to the volume of the extraction tank, stirring ability, etc., and is not particularly limited. The average particle size of the alkaline earth metal-containing particles can be, for example, in the range of 10 μm to 500 μm, 20 μm to 450 μm, or 100 μm to 400 μm. By setting the average particle size of the alkaline earth metal-containing particles to 10 μm or more, 2 solid-liquid separation in the CO fixation can be facilitated. By setting the average particle size of the alkaline earth metal-containing particles to 500 μm or less, the extraction efficiency of the alkaline earth metal can be increased without excessively increasing the power consumption required for stirring in the extraction process. In the present disclosure, the average particle size of the alkaline earth metal-containing particles is defined as the 50% cumulative volume average diameter D 50 by the laser diffraction scattering method.

[0047] The aqueous medium has the ability to dissolve CO 2 and is generally water. The aqueous medium may contain water-soluble organic solvents such as alcohols, esters, and ethers, in addition to water, as necessary. Salts such as sodium chloride, potassium chloride, ammonium chloride, sodium sulfate, magnesium sulfate, ammonium hydrogen sulfate, and sodium bicarbonate may be dissolved in the aqueous medium. The water content in the aqueous medium is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more.

[0048] The slurry can be prepared by adding and mixing alkaline earth metal-containing particles in an aqueous medium. In one embodiment, the slurry supplied as a raw material contains 0.5 mass% to 50 mass% of alkaline earth metal-containing particles. The lower the content of alkaline earth metal-containing particles in the slurry, the higher the ratio of the liquid phase to the solid phase (alkaline earth metal-containing particles), so the extraction efficiency of the alkaline earth metal increases, but large equipment is required for extraction. On the other hand, the higher the content of alkaline earth metal-containing particles in the slurry, the smaller the equipment required for extraction, but the extraction efficiency of the alkaline earth metal decreases. By setting the content of alkaline earth metal-containing particles in the raw material slurry to 0.5 mass% or more, an increase in equipment cost related to the extraction of alkaline earth metal can be suppressed. By setting the content of alkaline earth metal-containing particles in the raw material slurry to 50 mass% or less, the extraction efficiency of the alkaline earth metal can be increased. In one embodiment, the slurry does not contain an acid added from the outside other than CO 2 gas.

[0049] CO 2 Examples of the source of the CO 2 gas include at least one selected from the group consisting of a coal power plant, an oil power plant, a natural gas power plant, a biomass power plant, a coal boiler, a smelting facility, a neutralization facility, and a roasting facility. Since the coal power plant has a particularly large amount of CO 2 gas emissions, by using the CO 2 immobilization method of the present disclosure, the CO 2 gas emissions can be effectively reduced.

[0050] CO 2 gas supply rate can be optimized in consideration of design factors such as the saturation solubility of CO 2 , the extraction efficiency, the power required for supply, the volume of the extraction tank, and the stirring ability. The CO 2 gas supply rate is preferably determined such that the dissolved amount of CO 2 in the liquid phase of the slurry saturates at the temperature and pressure during stirring. The CO 2 gas supply rate is the CO 2 outside the CO 2 immobilization device from the CO2 The supply rate of the gas and the recycled CO supplied from the decompression tank and the crystallization tank 2 is the total of the supply rates of the gases.

[0051] The slurry and CO 2 gas are mixed in the extraction tank, whereby the ions of the alkaline earth metal in the alkaline earth metal-containing particles are extracted into the liquid phase. By the mixing, CO 2 dissolves in the liquid phase of the slurry and the pH of the liquid phase decreases. Thereby, the dissolution and ionization of the alkaline earth metal in the alkaline earth metal-containing particles into the liquid phase are promoted. The mixing can be carried out in the above-described extraction tank 10.

[0052] In one embodiment, the mixing is carried out at a temperature equal to or higher than the freezing point of the aqueous medium and equal to or lower than 50°C, preferably 0°C to 30°C. When a substance soluble in the slurry, such as sodium chloride, is contained, the freezing point of the aqueous medium may decrease below 0°C. By carrying out the mixing at a temperature equal to or higher than the freezing point of the aqueous medium, the mixing can be carried out uniformly, and an excessive increase in power consumption associated with the mixing can be prevented. By carrying out the mixing at a temperature equal to or lower than 50°C, the concentration of CO dissolved in the aqueous medium 2 can be set within a desired range. In one embodiment, the mixing is carried out at ambient temperature without heating.

[0053] In one embodiment, the mixing is carried out in a pressure atmosphere of 0.5 MPaG (gauge pressure) to 12 MPaG, preferably 0.5 MPaG to 5 MPaG, more preferably 0.5 MPaG to 2 MPaG. Generally, the higher the CO 2 pressure, the more CO dissolves in the liquid phase of the slurry, so the extraction efficiency of the alkaline earth metal increases. On the other hand, by setting the pressure to a low-pressure condition, the power consumption related to the extraction of the ions of the alkaline earth metal can be effectively reduced. 2 The stirring time of the slurry can be appropriately set according to the extraction efficiency and is not particularly limited, but can be, for example, 10 minutes to 2 hours.

[0054]

[0055] ​The ions of alkaline earth metals extracted into the liquid phase may exist in the form of alkaline earth metal hydroxides, alkaline earth metal silicates or alkaline earth metal silicate double salts. As the alkaline earth metal hydroxide, Mg(OH) formed by hydration of MgO or CaO 2 and Ca(OH) 2 can be mentioned. As the alkaline earth metal silicate, Mg 2 SiO 4 (magnesium silicate) and Ca 2 SiO 4 can be mentioned. As the alkaline earth metal silicate double salt, for example, silicates of alkaline earth metals and alkali metals, Mn, Fe, Co, Ni, Cu, Zn, or Al, or two or more of these can be mentioned. A typical alkaline earth metal silicate double salt is (Mg,Fe)SiO 4 (magnesioferrite).

[0056] (2) Solid-liquid separation step The mixture in which the ions of alkaline earth metals are extracted into the liquid phase is subjected to solid-liquid separation to produce a liquid phase containing the ions of alkaline earth metals and a solid phase containing the extraction residue. The solid-liquid separation can be performed by the aforementioned first solid-liquid separation device 20. The extraction residue may be discarded or may be further processed to produce valuable products.

[0057] (3) Stepwise decompression and precipitation step By gradually reducing the pressure in one or more decompression tanks connected in series and in the crystallization tank, alkaline earth metal carbonates precipitate from the liquid phase obtained in the solid-liquid separation step. As a result, CO 2 is immobilized as the alkaline earth metal carbonate. The solubility of the alkaline earth metal carbonate decreases as the temperature rises. Therefore, the precipitation of the alkaline earth metal carbonate can be promoted by raising the temperature of the liquid phase. The precipitation of the alkaline earth metal carbonate can also be promoted by bubbling air through the liquid phase. The stepwise decompression and precipitation can be performed in the aforementioned decompression tanks 30A, 30B and in the crystallization tank 40.

[0058] The pressure in the vacuum tank decreases from upstream to downstream, and the pressure in the crystallization tank is the lowest. The pressure in the uppermost upstream vacuum tank can be, for example, 0.2 MPaG (gauge pressure) to 10 MPaG. The pressure in the crystallization tank can be, for example, -0.1013 MPaG to 2 MPaG. The pressure difference between adjacent vacuum tanks or between the vacuum tank adjacent to the crystallization tank and the crystallization tank can be, for example, more than 0 MPa and 6 MPa or less.

[0059] Stepwise depressurization is preferably carried out by two or three vacuum tanks and a crystallization tank, and more preferably carried out by two vacuum tanks and a crystallization tank.

[0060] The temperature of the liquid phase can be, for example, 10°C to 80°C. By increasing the temperature of the liquid phase from upstream to downstream of the vacuum tank and making it the highest in the crystallization tank, the precipitation efficiency can be increased.

[0061] The residence times of the vacuum tank and the crystallization tank can each be, for example, 1 minute to 10 hours. In the vacuum tank and the crystallization tank, CO 2 The precipitation of alkaline earth metal carbonate proceeds slowly compared to the release of CO gas into the gas phase. Therefore, for the purpose of recovering higher-pressure CO 2 gas and generating seed crystals, the residence time of each vacuum tank is the same as or shorter than the residence time of the crystallization tank for the purpose of final CO 2 immobilization due to the precipitation of alkaline earth metal carbonate. This can increase the efficiency of CO 2 immobilization. In one embodiment, the residence time of the crystallization tank is 1 to 15 times, 1.1 to 12 times, or 1.5 to 10 times the residence time of each vacuum tank.

[0062] For example, in the CO 2 immobilization device shown in FIG. 1, the pressure, temperature, and residence time of the vacuum tanks 30A, 30B, and the crystallization tank 40 can be set as follows. Vacuum tank 30A: Pressure 0.2 MPaG to 0.4 MPaG; Temperature 10°C to 30°C; Residence time 1 minute to 2 hours Vacuum tank 30B: Pressure 0 MPaG to 0.2 MPaG; Temperature 10°C to 30°C; Residence time 1 minute to 2 hours Crystallization tank 40: Pressure -0.1013 MPaG to 0.1 MPaG; Temperature 10°C to 30°C; Residence time 10 minutes to 2 hours

[0063] It is preferable not to introduce seed crystals into the vacuum tank. As a result, alkaline earth metal carbonate can be precipitated in the form of fine particles in the vacuum tank, and without the need for additional processes such as pulverization, it can be made into a suitable size as seed crystals for use in the crystallization tank.

[0064] (4) Seed crystal supply step The alkaline earth metal carbonate precipitated in one or more vacuum tanks is supplied as seed crystals to the crystallization tank. The alkaline earth metal carbonate precipitated in the vacuum tank can be separated from the liquid phase by the aforementioned second solid-liquid separation devices 50A and 50B. It is preferable to use the entire amount of the alkaline earth metal carbonate precipitated in the vacuum tank as seed crystals for the crystallization tank.

[0065] It is preferable to supply 0.1 mass% to 10 mass% of the seed crystals based on the liquid volume in the crystallization tank to the crystallization tank. Thereby, the precipitation efficiency of the alkaline earth metal carbonate in the crystallization tank can be increased.

[0066] (5) Pressure increase step The CO 2 gas generated in one or more vacuum tanks and in the crystallization tank is pressurized by a compressor. The CO 2 gas is supplied to compressors 80A, 80B, and 80N respectively through the aforementioned CO 2 gas recovery pipes 70A, 70B, and 70N and can be pressurized by these compressors. The CO 2 gas generated in the vacuum tank and in the crystallization tank is pressurized step by step corresponding to the stepwise pressure reduction in the stepwise pressure reduction-precipitation step. That is, the lower-pressure CO 2 gas is pressurized through more compressors, and the higher-pressure CO 2 gas is pressurized through fewer compressors. Thereby, the energy related to the recompression of the CO 2 gas can be effectively reduced.

[0067] For example, the CO shown in FIG. 1 2 In the immobilization device, the pressures on the primary and secondary sides of compressors 80A, 80B, and 80N can be set and operated as follows. Compressor 80A: Primary side 0.2 MPaG to 0.4 MPaG; Secondary side 0.5 MPaG to 2 MPaG Compressor 80B: Primary side 0 MPaG to 0.2 MPaG; Secondary side 0.2 MPaG to 0.4 MPaG Compressor 80N: Primary side -0.1013 MPaG to 0.1 MPaG; Secondary side 0 MPaG to 0.2 MPaG

[0068] (6) CO 2 Gas supply process The pressurized CO 2 gas is supplied to the extraction tank and reused. The CO supplied from the decompression tank and the crystallization tank 2 gas volume does not reach the aforementioned desired CO 2 gas supply rate, then CO 2 from outside the immobilization device 2 CO from the gas supply source 2 gas can be used for supplementation.

[0069] The device and method of the present disclosure can be suitably used for CO 2 immobilization and the accompanying production of alkaline earth metal carbonates.

[0070] It is obvious to those skilled in the art that the above embodiments and examples can be variously modified without departing from the basic principles of the present invention. Also, it is obvious to those skilled in the art that various improvements and modifications of the present invention can be implemented without departing from the spirit and scope of the present invention.

Industrial Applicability

[0071] The device and method of the present disclosure can be advantageously used for CO 2 immobilization and the accompanying production of alkaline earth metal carbonates.

Explanation of Reference Numerals

[0072] 1 CO 2 Immobilization device 10 Extraction tank 11 CO 2 Gas supply port 12 Slurry discharge port 20 First solid-liquid separation device 22 Liquid phase discharge port 23 Solid phase discharge port 30A, 30B Vacuum tank 40 Crystallization tank 50A, 50B Second solid-liquid separation device 52A, 52B Liquid phase discharge port 53A, 53B Solid phase discharge port 60A, 60B Vacuum valve 70A, 70B, 70N CO 2 Gas recovery pipe 80A, 80B, 80N Compressor 81A, 81B, 81N Primary side 82A, 82B, 82N Secondary side 90 Third solid-liquid separation device 92 Liquid phase discharge port 93 Solid phase discharge port 95 Solid phase supply device

Claims

Claim 1 CO ２ An extraction tank equipped with a gas supply port and a slurry discharge port, and A first solid-liquid separator having a liquid-phase discharge port connected to the slurry discharge port of the extraction tank; One or more decompression tanks. When there are two or more of the one or more decompression tanks, the one or more decompression tanks are connected in series with each other, and the uppermost-stream decompression tank among the one or more decompression tanks is connected to the liquid-phase discharge port of the first solid-liquid separator; one or more decompression tanks; A crystallization tank connected to the lowermost-stream decompression tank among the one or more decompression tanks; A second solid-liquid separator and a decompression valve on the downstream side of the second solid-liquid separator, arranged between the lowermost-stream decompression tank among the one or more decompression tanks and the crystallization tank; When there are two or more of the one or more decompression tanks, one or more second solid-liquid separators respectively arranged between the one or more decompression tanks and one or more decompression valves on the downstream side of the one or more second solid-liquid separators; A plurality of CO gas recovery pipes respectively connected to each of the one or more vacuum tanks and the crystallization tank ２ and, A plurality of compressors having a primary side and a secondary side and connected in series, wherein CO supplied to the primary side ２ gas is configured to be pressurized and discharged from the secondary side, and the secondary side of the lowermost compressor among the plurality of compressors is the CO ２ gas supply port, and a plurality of compressors CO containing ２ An immobilization device comprising The primary sides of the plurality of compressors are each connected to one of the plurality of CO gas recovery pipes such that the pressure of the CO gas supplied to the primary sides of the plurality of compressors increases from the upstream side toward the downstream side. ２ gas recovery pipes so that the pressure of the CO ２ gas increases from the upstream side toward the downstream side, and is connected to one of the plurality of CO A CO immobilization device in which the solid-phase enrichment side of the second solid-liquid separation device is connected to the crystallization tank. ２ Immobilization device. Claim 2 The second solid-liquid separation device according to claim 1, which is selected from the group consisting of a cross-flow filter, a pleated filter, an auto-strainer, a cyclone strainer, a filter press, a rotary filter, a leaf filter, a hunderback filter, and a hydrocyclone, for the CO ２ immobilization device. Claim 3 The volume of the crystallization tank is 1 to 15 times the volume of the one or more decompression tanks, and the CO according to claim 1 or 2 ２ Immobilization device. Claim 4 The CO according to claim 1 or 2, further comprising a third solid-liquid separation device connected downstream of the crystallization tank, and a solid-phase supply device for supplying the solid phase obtained by the third solid-liquid separation device to the crystallization tank ２ immobilization device. Claim 5 In an extraction tank, by mixing a slurry containing alkaline earth metal-containing particles and an aqueous medium with CO ２ gas, ions of the alkaline earth metal in the alkaline earth metal-containing particles are extracted into the liquid phase. Solid-liquid separating the mixture in which the ions of the alkaline earth metal are extracted into the liquid phase to obtain a liquid phase containing the ions of the alkaline earth metal and a solid phase containing extraction residues; Precipitating alkaline earth metal carbonates from the liquid phase while gradually reducing the pressure in one or more decompression tanks connected in series and in a crystallization tank, and fixing CO ２ thereby as the alkaline earth metal carbonate. Supplying the alkaline earth metal carbonate precipitated in the one or more decompression tanks to the crystallization tank as seed crystals; CO generated in the one or more vacuum tanks and in the crystallization tank ２ boosting the pressure of the gas with a compressor, and The boosted CO ２ Supplying the gas to the extraction tank, CO containing ２ Immobilization method Claim 6 The residence time of the crystallization tank is 1 to 15 times the residence time of each of the one or more vacuum tanks, and the CO according to claim 5 ２ Immobilization method. Claim 7 The method for immobilization according to claim 5 or 6, comprising supplying the seed crystals in an amount of 0.1% by mass to 10% by mass of the liquid volume in the crystallization tank to the crystallization tank. ２ Method for immobilization. Claim 8 The mixing in the extraction tank is carried out in a pressure atmosphere of 0.5 MPaG to 10 MPaG, and the CO immobilization method according to claim 5 or 6. ２ Immobilization method. Claim 9 The CO immobilization method according to claim 5 or 6, wherein the alkaline earth metal is calcium. ２ method. Claim 10 The CO immobilization method according to claim 5 or 6, wherein the alkaline earth metal-containing particles contain at least one selected from the group consisting of concrete, concrete sludge, and cement. ２ immobilization method.

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