Method for producing calcium carbonate powder

Abstract

To provide a method for producing calcium carbonate powder capable of efficiently producing a large amount of calcium carbonate powder in a small area / space-saving using atmospheric carbon dioxide based on salt field effect on high-porosity, large-surface-area concrete aggregate by sprinkling and drying a calcium hydroxide solution.SOLUTION: A method 1 for producing calcium carbonate powder of the present invention comprises: a sprinkling step s2 of sprinkling a calcium hydroxide solution 3 on the surface of a concrete aggregate 2; a curing step s3 of drying and curing the concrete aggregate 2 thereby depositing calcium carbonate crystals 4 on the surface of the concrete aggregate 2; and a separation and recovery step s4 for separating the calcium carbonate crystals 4 from the concrete aggregate s2 and recovering the same as the calcium carbonate powder 1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing calcium carbonate powder, and more particularly to a method for producing calcium carbonate powder which can efficiently produce a large amount of calcium carbonate powder in a small area / space by using carbon dioxide in the atmosphere through the "salt field effect" in which a calcium hydroxide solution is sprinkled on concrete aggregate having high porosity and a large surface area and then dried. [Background technology]

[0002] White powdered calcium carbonate (CaCO3) is used as an admixture for concrete and synthetic resins. Patent Document 1 discloses a method for producing calcium carbonate powder by using a concrete sludge treatment apparatus including a sludge separation apparatus that separates concrete sludge water into a sludge cake and a sludge liquid, a precipitation reaction apparatus that precipitates calcium carbonate from the sludge liquid, and a calcium carbonate separation apparatus that separates the calcium carbonate from the precipitation liquid, supplying calcium carbonate seed crystals and carbon dioxide into the precipitation reaction apparatus, and dispersing the contents with a dispersion means. In the actual manufacturing process, for example, concrete sludge water is diluted in a dissolution tank, the sludge liquid is squeezed out using a filter press, the sludge liquid filled in a crystallization tank is stirred by passing boiler exhaust gas through it to precipitate calcium carbonate, and the calcium carbonate is recovered from the sludge liquid and dried to produce calcium carbonate powder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-279552 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional technology, calcium carbonate is dispersed in the sludge liquid and precipitated, so it is difficult to recover calcium carbonate as a powder from the sludge liquid. In detail, the sludge liquid containing calcium carbonate is dehydrated again by a filter press to separate calcium carbonate as a solid content, and the calcium carbonate is dried and powdered by a heating and drying equipment, which requires many manufacturing steps and is inefficient. In addition, special manufacturing equipment such as a high-pressure filter press, a crystallization tank with an agitator, and a heating and drying facility are required, which increases the costs of introducing the equipment and maintaining and managing it.

[0005] An object of the present invention is to provide a method for producing calcium carbonate powder that solves the above-mentioned problems of the conventional technology. [Means for solving the problem]

[0006] The method for producing calcium carbonate powder of the present invention is characterized by comprising a sprinkling step of sprinkling a calcium hydroxide solution onto the surface of concrete aggregate, a curing step of dry curing the concrete aggregate to precipitate calcium carbonate crystals on the surface of the concrete aggregate, and a separation and recovery step of separating the calcium carbonate crystals from the concrete aggregate and recovering them as calcium carbonate powder.

[0007] In the method for producing calcium carbonate powder of the present invention, the calcium hydroxide solution may be a supernatant of sludge water discharged after washing a concrete production facility.

[0008] In the method for producing calcium carbonate powder of the present invention, the concrete aggregate may be a granulated recycled aggregate derived from residual concrete.

[0009] The method for producing calcium carbonate powder of the present invention includes a granulation step, prior to the water sprinkling step, of mixing a granulation admixture with the residual concrete and stirring the mixture to produce granulated recycled aggregate, and the granulation admixture may contain a water-absorbent polymer and a quick-setting promoter.

[0010] In the method for producing calcium carbonate powder of the present invention, in the curing step, the concrete aggregate may be cured in an environment having a higher CO2 concentration than that in the atmosphere. Effect of the Invention

[0011] The method for producing calcium carbonate powder of the present invention has at least one of the following effects. <1> By sprinkling calcium hydroxide solution onto concrete aggregate, which has a large surface area, allowing it to absorb a large amount of calcium hydroxide solution, and then drying and curing it, a large amount of calcium carbonate powder can be efficiently produced in a small area / space. <2> During the calcium carbonate crystal precipitation process, large amounts of carbon dioxide (CO2) from the atmosphere can be adsorbed and fixed (CCUS: Carbon dioxide Capture, Utilization and Storage). <3> At the same time as producing calcium carbonate powder, the water absorption and density of concrete aggregate can be modified. [Brief description of the drawings]

[0012] [Figure 1] Illustrative diagram of calcium carbonate powder manufacturing method [Diagram 2] Illustration of the granulation process [Diagram 3] Illustration of the watering process [Figure 4] Illustration of the curing process [Diagram 5] Carbon content measurement test table [Figure 6A] Coarse aggregate density and water absorption test table (before testing) [Figure 6B] Coarse aggregate density and water absorption test table (after test) [Figure 7A] Fine aggregate density and water absorption test table (before testing) [Figure 7B] Fine aggregate density and water absorption test table (after testing) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the method for producing calcium carbonate powder of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0014] <1> Manufacturing method of calcium carbonate powder (Figure 1) The method for producing calcium carbonate powder of the present invention is a method capable of efficiently producing calcium carbonate powder 1 by using a material derived from a concrete production facility C. Here, "production" means separating and recovering the chemically precipitated calcium carbonate powder 1. The method for producing calcium carbonate powder includes at least a water sprinkling step S2, a curing step S3, and a separation and recovery step S4. In this example, the method further includes a granulation step S1 before the water sprinkling step S2. The method for producing calcium carbonate powder of the present invention has a feature in that it can efficiently produce a large amount of calcium carbonate powder (CaCO3) in a small area / space by using carbon dioxide (CO2) in the atmosphere through the so-called "salt field effect" in which a calcium hydroxide solution (Ca(OH)2) is sprinkled on a concrete aggregate 2 having high porosity and a large surface area and then dried.

[0015] <1.1> Uses of calcium carbonate powder The calcium carbonate powder 1 has the following uses, for example. (1) Concrete admixture: improves the fluidity of concrete, prevents bleeding, and increases strength (2) Synthetic resin additives: Strengthening plastic products (3) Flue gas desulfurization material: Removes sulfur oxides from exhaust gas (4) White pigments: Improves the whiteness of paper and paint However, the uses of the calcium carbonate powder 1 are not limited to those mentioned above, and the powder can be used in any applications for which its physical properties are suitable.

[0016] <1.2> Use of concrete manufacturing plants This embodiment is characterized in that the process for producing the calcium carbonate powder 1 can be completed within the concrete production plant by utilizing by-products generated within the concrete production plant. Because the amount of ready-mix concrete used at a construction site is an estimated calculation, there will inevitably be "remaining concrete" that remains in the agitator truck after unloading, and "returned concrete" that is returned to the concrete manufacturing plant without being unloaded from the agitator truck (hereinafter, "remaining concrete" is used to include "returned concrete"). In addition to the residual concrete, "washing wastewater" containing mortar is generated by cleaning the inside of the drum of the agitator truck after transporting ready-mix concrete. The washing wastewater is separated and recovered into coarse aggregate and fine aggregate using a sieve or the like, and discharged as a suspension liquid, sludge water D. The sludge water D is separated and recovered into sludge solids D1 and supernatant water 31 by settling in a settling tank or high-pressure dehydration in a dehydrator.

[0017] <1.3> Concrete aggregate The concrete aggregate 2 is a base material for precipitating calcium carbonate crystals 4. In this embodiment, granulated recycled aggregate 21 derived from residual concrete is used as the concrete aggregate 2. A method for producing the granulated recycled aggregate 21 will be described later. The granulated recycled aggregate 21 has a structure in which the surface of the raw aggregate in the remaining concrete is coated with fine mortar paste, and therefore has high porosity and high water absorption, so that it can adsorb a large amount of calcium hydroxide solution 3 in a small space. The concrete aggregate 2 is not limited to the granulated recycled aggregate 21, but is preferably an aggregate having a particle size distribution with high porosity.

[0018] <1.4> Calcium hydroxide solution The calcium hydroxide solution 3 is a solution to be sprayed onto the concrete aggregate 2 . In this embodiment, as the calcium hydroxide solution 3, supernatant water 31 obtained by separating sludge solids D1 from sludge water D extracted from washing wastewater of a concrete manufacturing facility C is used. The supernatant water 31 contains a large amount of calcium hydroxide that has dissolved from the cement adhering to the concrete manufacturing equipment C.

[0019] <2> Granulation process (Figure 2) The granulation step S1 is a step of granulating the residual concrete to produce the granulated recycled aggregate 21. Specifically, the granulation step S1 is performed, for example, in the following procedure. With remaining concrete remaining in the drum of the agitator vehicle, granulated admixture B is poured into the drum and the drum is rotated to mix / agitate the granulated admixture B into the remaining concrete. In this example, the granulated admixture B contains a water-absorbing polymer B1 and a quick-setting accelerator B2. Such a granulated admixture B is available, for example, under the trade name "Re-Con Zero Evo (trademark)" from MAPEI (Italy). As the drum rotates, the mortar paste is layered on the surface of the aggregate in the remaining concrete, forming granulated recycled aggregate 21. After the drum has been rotated for a predetermined time, the discharge port is opened and the granulated recycled aggregate 21 is discharged from the chute. The discharged granulated recycled aggregate 21 is dried and cured for a predetermined time. In addition, the granulation step S1 may be performed by utilizing thermal energy from air temperature or the like, instead of using the granulation admixture B. In addition, when an aggregate other than the granulated recycled aggregate 21 is used as the concrete aggregate 2, this step is not necessary.

[0020] <3> Watering process (Fig. 3) The water sprinkling step S2 is a step of sprinkling supernatant water 31 onto the granulated recycled aggregate 21. Specifically, the water sprinkling step S2 is performed, for example, in the following procedure. Granulated recycled aggregate 21 is laid out on the production yard. The grain size of the granulated recycled aggregate 21 does not matter, but since fine aggregate has a larger surface area per mass than coarse aggregate, a mixture containing a large amount of fine aggregate is preferable. Supernatant water 31 is sprinkled on the surface of the granulated recycled aggregate 21. By sprinkling water, the supernatant water 31 penetrates into the micropores on the surface of the granulated recycled aggregate 21, and the granulated recycled aggregate 21 absorbs a large amount of the supernatant water 31. Although there is no particular limit to the method of sprinkling water, it is preferable to sprinkle water evenly so that the surface of the granulated recycled aggregate 21 is thoroughly wetted.

[0021] <4> Curing process (Fig. 4) The curing step S3 is a step of curing the granulated recycled aggregate 21 sprayed with the supernatant water 31. Specifically, the curing step S3 is performed, for example, in the following procedure. The granulated recycled aggregate 21 is dry cured. The dry curing may be performed at room temperature or in a high temperature environment. During dry curing, calcium (Ca) in the supernatant water 31 reacts with carbon dioxide (CO2) in the air to become carbonated, and calcium carbonate crystals 4 (CaCO3) precipitate on the surface and in the pores of the granulated recycled aggregate 21, causing the aggregate to turn white. The water sprinkling step S2 and the curing step S3 may be repeated multiple times until a predetermined amount of calcium carbonate crystals 4 is precipitated. In the present invention, calcium carbonate attached to the granulated recycled aggregate 21 is distinguished as calcium carbonate crystals 4, and calcium carbonate separated from the granulated recycled aggregate 21 is referred to as calcium carbonate powder 1.

[0022] <5> Separation and recovery process The separation and recovery step S4 is a step of separating and recovering calcium carbonate from the granulated recycled aggregate 21. Specifically, the separation and recovery step S4 is performed, for example, in the following procedure. Granulated recycled aggregate 21 on the production yard is placed into a horizontal vibrating sieve for classifying aggregate and vibration is applied to sieve off calcium carbonate crystals 4 adhering to the surface of the granulated recycled aggregate 21. Subsequently, the calcium carbonate crystals 4 (calcium carbonate powder 1) that have fallen below the vibrating sieve are collected by a dust collector. However, the separation and recovery step S4 is not limited to the above procedure. For example, the granulated recycled aggregate 21 may be fed into a trommel to separate and recover the calcium carbonate powder 1. The calcium carbonate powder 1 naturally peeled off from the granulated recycled aggregate 21 in the curing step S3 can be recovered directly from the production yard without being subjected to the separation and recovery step S4.

[0023] <6> Carbon dioxide adsorption (Figure 5) One feature of the method for producing calcium carbonate powder of the present invention is that the curing step S3 allows calcium carbonate crystals 4 to precipitate and simultaneously adsorb carbon dioxide (CO2) in the air. In this example, the carbon content was measured for a sample of the granulated recycled aggregate 21 immediately after granulation and a sample that had been subjected to the watering step S2 and the curing step S3 and was aged 19 days. Granulated recycled aggregate: 18-18-25 ·Super clear water sprinkling: Total 21.5L [Before implementation] (Sample 1) Carbon content: 0.233wt% (Sample 2) Carbon content: 0.233wt% [After implementation: 19 days old] (Sample 1) Carbon content: 0.956wt% (Sample 2) Carbon content: 0.948wt% [Amount of carbon adsorbed] (Sample 1) Carbon content: 0.723wt% (Sample 2) Carbon content: 0.715wt% [CO2 equivalent per ton (x 3.67)] (Sample 1) 1,000kg x 0.723wt% x 3.67 = 26.5kg (Sample 2) 1,000kg x 0.715wt% x 3.67 = 26.2kg In this example, a large amount of carbon dioxide, approximately 26 kg (2.6%), was adsorbed per ton of granulated recycled aggregate.

[0024] <7> Modification of concrete aggregate (Figures 6A to 7B) The method for producing calcium carbonate powder according to the present invention has one feature in that the watering step S2 and the curing step S3 can improve the quality of the concrete aggregate 2 (granulated recycled aggregate 21) while precipitating calcium carbonate crystals 4. In this example, the granulated recycled aggregate 21 was subjected to the water sprinkling step S2 and the curing step S3, and the water absorption rate and density were measured before and after these steps. [1] Coarse aggregate: 25mm gravel [Before implementation] (Figure 6A) Surface dry density: 2.35g / cm 3 Water absorption rate: 8.91% [After implementation] (Figure 6B) Surface dry density: 2.37g / cm 3 Water absorption rate: 7.19% [Improvement value] Surface dry density: 0.02g / cm 3 Water absorption rate: 1.72 points [2] Fine aggregate: sand [Before implementation] (Figure 7A) Surface dry density: 2.03g / cm 3 Water absorption rate: 22.81% [After implementation] (Figure 7B) Surface dry density: 2.19g / cm 3 Water absorption rate: 15.96% [Improvement value] Surface dry density: 0.16g / cm 3 Water absorption rate: 6.85 points Granulated recycled aggregate is made by coating the surface of aggregate in residual concrete with mortar paste, so it generally has a lower density and a higher water absorption rate than regular recycled aggregate, which can affect the strength and weather resistance of the concrete produced. In this example, the watering step S2 and the curing step S3 were able to increase the density of the granulated recycled aggregate 21 and reduce the water absorption rate, thereby improving the quality of the aggregate. This is thought to be because calcium carbonate crystals 4 are precipitated in the micropores of the granulated recycled aggregate 21, blocking the micropores and increasing the density, while preventing water from penetrating into the micropores, thereby reducing the water absorption rate. EXAMPLES

[0025] [Example of curing in a high CO2 environment] In this embodiment, in the curing step S3, the granulated recycled aggregate 21 is cured in a high CO2 environment. Here, the "high CO2 environment" refers to an environment in which the CO2 concentration is higher than that in the atmosphere. In detail, a curing tank is installed in a production yard of the calcium carbonate powder 1, and supernatant water 31 is sprayed onto the granulated recycled aggregate 21 in the curing tank. Next, the curing tank is sealed, and high-concentration CO2 gas is filled into the curing tank, and the granulated recycled aggregate 21 is dry-cured in a high-CO2 environment. High-concentration CO2 gas can be recovered, for example, from a boiler in a cement factory, a blast furnace in a steelworks, etc. In addition, the exhaust heat generated in the boiler or the blast furnace may be reused as thermal energy for promoting the drying of the granulated recycled aggregate 21. In the case of this example, a large amount of CO2 is adsorbed to the calcium carbonate powder 1, and the amount of precipitated calcium carbonate crystals 4 is increased, so that the recovery efficiency of the calcium carbonate powder 1 can be further improved. [Explanation of symbols]

[0026] 1. Calcium carbonate powder 2. Concrete aggregate 21 Granulated recycled aggregate 3. Calcium hydroxide solution 31 Clear water 4. Calcium carbonate crystals A Remaining concrete B Granulated admixture B1 Water-absorbent polymer B2 Rapid setting promoter C Concrete manufacturing equipment D Sludge water D1 Sludge solids S1 Granulation process S2 Watering process S3 curing process S4 Separation and recovery process

Claims

1. A water spraying step of spraying a calcium hydroxide solution onto a surface of the concrete aggregate; a curing step of dry curing the concrete aggregate to cause calcium carbonate crystals to precipitate on the surface of the concrete aggregate; and a separation and recovery step of separating the calcium carbonate crystals from the concrete aggregate and recovering them as calcium carbonate powder. A method for producing calcium carbonate powder.

2. The calcium hydroxide solution is a supernatant of sludge water discharged from a concrete manufacturing facility after cleaning the facility. A method for producing the calcium carbonate powder according to claim 1.

3. The concrete aggregate is a granulated recycled aggregate derived from residual concrete. The method for producing calcium carbonate powder according to claim 1 or 2.

4. A granulation step is provided in which a granulation admixture is mixed with the remaining concrete and stirred to generate granulated recycled aggregate prior to the water sprinkling step. The granulated admixture comprises a water-absorbing polymer and a quick-setting promoter. The method for producing the calcium carbonate powder according to claim 3.

5. In the curing step, the concrete aggregate is immersed in CO from the atmosphere. ２ It is characterized by being cured in a high concentration environment. A method for producing the calcium carbonate powder according to claim 1.

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