Manufacturing method for carbonated quicklime and carbonated quicklime

Abstract

To provide a manufacturing method for carbonated quicklime that fixes carbon dioxide more efficiently at lower temperatures than conventional methods, and that has a better long-term expansion rate and storage stability.SOLUTION: In the manufacturing method for carbonated quicklime, raw materials are heated at a temperature between 850 and 1,300°C to produce a material containing calcium oxide, which is then reacted with a gas containing carbon dioxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbonated quicklime and carbonated quicklime. [Background technology]

[0002] In recent years, in the fields of civil engineering and construction, the demand for highly durable concrete and cement admixtures that enhance durability is expected to increase due to an increase in the number and size of structures using concrete, as well as the need to repair or reinforce aging structures.

[0003] Quicklime-based expansive additives are known as cement admixtures that are used to suppress cracking and improve durability. Patent Document 1 describes an expansive additive that contains an expansive calcined material containing free quicklime, the expansive calcined material having a specific particle size distribution. Patent Document 2 describes an expansive additive whose active ingredient is quicklime in which one or more elements selected from the group consisting of Co, Ni, and Mn are dissolved in a specific molar ratio.

[0004] On the other hand, from an environmental perspective, various mortars and concretes that use cement and admixtures that emit less CO2 during production have been investigated.

[0005] Carbonation technology has also been known to reduce carbon dioxide emissions. This technology primarily involves immobilizing carbon dioxide through a reaction in which calcium hydroxide (Ca(OH)2) contained in cement compositions reacts with carbon dioxide to produce calcium carbonate (CaCO3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-129210 [Patent Document 2] Japanese Patent Application Publication No. 2017-114753 Summary of the Invention [Problem to be solved by the invention]

[0007] However, quicklime-based expanding materials are produced by burning raw materials such as limestone at high temperatures, and therefore emit a large amount of carbon dioxide in total.

[0008] In view of the above, an object of the present invention is to provide a method for producing carbonated quicklime that can efficiently fix carbon dioxide at a lower temperature than conventional methods and that has a good long-term expansion coefficient and storage stability. [Means for solving the problem]

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the problems can be solved by a method in which a material is heated at a lower temperature than conventional methods and then reacted with a carbon dioxide-containing gas, and have arrived at the present invention. That is, the present invention is as follows.

[0010] [1] A method for producing carbonated quicklime, comprising heating a raw material at a temperature of 850 to 1300°C to produce a CaO-containing material, and reacting the CaO-containing material with a carbon dioxide-containing gas. [2] The method for producing carbonated quicklime according to [1] above, wherein the CaO content in the CaO-containing material is 40 mass% or more. [3] The method for producing carbonated quicklime according to [1] or [2] above, wherein the carbon dioxide-containing gas contains carbon dioxide generated when the raw material is heated. [4] The method for producing carbonated quicklime according to any one of the above [1] to [3], wherein the carbon dioxide concentration of the carbon dioxide-containing gas is 5 vol % or more. [5] The method for producing carbonated quicklime according to any one of [1] to [4] above, wherein the temperature of the carbon dioxide-containing gas is 100°C or higher. [6] The method for producing carbonated quicklime according to any one of the above [1] to [5], wherein the particle size of the CaO-containing material is adjusted before the reaction with the carbon dioxide-containing gas. [7] Carbonated quicklime obtained by the method for producing carbonated quicklime according to any one of [1] to [6] above. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for producing carbonated quicklime that can efficiently fix carbon dioxide at a lower temperature than conventional methods and that has a good long-term expansion coefficient and storage stability. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment. In this specification, "%" and "parts" are based on mass unless otherwise specified.

[0013] [Method of producing carbonated quicklime] In the method for producing carbonated quicklime according to this embodiment, raw materials are heated at a temperature of 850 to 1300° C. to produce a CaO-containing material, and the CaO-containing material is reacted with a carbon dioxide-containing gas.

[0014] (raw materials) The raw material according to the present invention is not particularly limited as long as it contains calcium, but preferably contains 40% by mass or more of calcium carbonate, calculated as CaO, more preferably 60% by mass or more, and even more preferably 80% by mass or more. The upper limit is not particularly limited, but may be 100% by mass. In the present invention, the calcium carbonate content in the raw material can be calculated by fluorescent X-ray measurement.

[0015] As the raw material, limestone, slaked lime, marble, chalk, eggshell, coral, seashell, etc. can be used, and these may be used alone or in combination of two or more. In this embodiment, the raw material preferably includes limestone.

[0016] The raw material may contain components such as sulfur, iron, silica, magnesium, and aluminum in addition to calcium.

[0017] (CaO-containing material) The CaO-containing material according to this embodiment is produced by heating the above-mentioned raw materials at a temperature of 850 to 1300° C. If the temperature is lower than 850° C., when the produced carbonated quicklime is used, the long-term expansion rate and storage stability may be reduced, and if the temperature exceeds 1300° C., the long-term expansion rate may be excessive.

[0018] The heating temperature of the raw material is preferably 900 to 1200° C., more preferably 950 to 1100° C., and even more preferably 980 to 1050° C. When the heating temperature of the raw material is within the above range, the long-term expansion coefficient, short-term length change rate, compressive strength, storage stability, and flow are likely to be better.

[0019] The heating time of the raw material is preferably 30 minutes to 3 hours, and more preferably 1 to 2 hours. By keeping the heating time within the above range, the total amount of carbon dioxide emitted during the production of carbonated quicklime can be reduced.

[0020] In this embodiment, the CaO content of the CaO-containing material is preferably 40% by mass or more, preferably 60% by mass or more, and more preferably 80% by mass or more. There is no particular upper limit, but it may be 100% by mass. When the CaO content in the CaO-containing material is within the above range, the long-term expansion coefficient can be made better. In the present invention, the CaO content in the CaO-containing material can be measured by the mass loss determined by differential thermogravimetry analysis (TG-DTA).

[0021] (carbon dioxide-containing gas) The carbon dioxide-containing gas according to this embodiment can be reacted with a CaO-containing material to immobilize the carbon dioxide (CO2) in the gas, thereby producing carbonated quicklime. The carbon dioxide-containing gas can be an exhaust gas emitted from a cement factory, a coal-fired power plant, or the like, and the components other than carbon dioxide can be an inert gas such as air or nitrogen.

[0022] The carbon dioxide-containing gas according to this embodiment preferably contains carbon dioxide generated when the raw materials are heated as described above. When the carbon dioxide-containing gas contains carbon dioxide generated when the raw materials are heated, the total amount of carbon dioxide emitted during the production of carbonated quicklime can be reduced. By producing carbonated quicklime in two stages, namely, a stage of heating the raw materials to produce a CaO-containing material and a stage of reacting the CaO-containing material with the carbon dioxide-containing gas, the carbon dioxide generated by heating the raw materials can be separated and reused for producing the CaO-containing material.

[0023] The carbon dioxide-containing gas according to this embodiment preferably has a carbon dioxide concentration of 5 vol% or more, more preferably 10 vol% or more, and even more preferably 20 vol% or more. It is also preferably 100 vol% or less, more preferably 80 vol% or less, and even more preferably 50 vol% or less. Having a carbon dioxide concentration within the above ranges tends to improve the long-term expansion rate, short-term length change rate, compressive strength, storage stability, and flow.

[0024] The temperature of the carbon dioxide-containing gas according to this embodiment is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 200°C or higher. The temperature is preferably 800°C or lower, more preferably 600°C or lower, and even more preferably 500°C or lower. By keeping the reaction temperature within the above range, carbon dioxide can be immobilized more efficiently.

[0025] The reaction time between the CaO-containing material and the carbon dioxide-containing gas is preferably 1 minute to 2 hours, and more preferably 15 to 30 minutes. By keeping the reaction time within the above range, carbon dioxide can be immobilized more efficiently.

[0026] In the method for producing carbonated quicklime according to this embodiment, it is preferable to adjust the particle size of the CaO-containing material before the reaction with the carbon dioxide-containing gas. By adjusting the particle size of the CaO-containing material before the reaction between the CaO-containing material and the carbon dioxide-containing gas, the reaction between the CaO-containing material and the carbon dioxide-containing gas can be carried out more efficiently, and the long-term expansion coefficient and storage stability can be improved. Furthermore, since there is no need to adjust the particle size again after the reaction step with the carbon dioxide-containing gas, exposure of the interior of the carbonated quicklime can be prevented.

[0027] The fineness of CaO-containing materials is 1000 to 5000 cm in terms of Blaine specific surface area. 2 / g, and 1500 to 4500 cm 2 / g, and 2000 to 4000 cm 2 / g. The fineness of the CaO-containing material can be adjusted by pulverizing and sieving the raw material after heating. When the Blaine specific surface area of the CaO-containing material is within the above range, carbon dioxide can be immobilized more efficiently, and the long-term expansion coefficient and storage stability can be improved. In the present invention, the Blaine specific surface area can be measured in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement."

[0028] (carbonated quicklime) The carbonated quicklime according to this embodiment is obtained by the method for producing carbonated quicklime of the present invention. By using the carbonated quicklime of the present invention in mortar or concrete, it is possible to improve both the initial expansion and the long-term expansion rate.

[0029] The type of cement used in mortar or concrete using carbonated quicklime is not particularly limited, and examples include various Portland cements such as normal, early-strength, ultra-early-strength, low-heat, and medium-heat; various blended cements obtained by mixing these Portland cements with blast furnace slag, fly ash, or silica fume; environmentally friendly cements (ecocements) made from raw materials such as municipal waste incineration ash or sewage sludge incineration ash; commercially available fine particle cements; and white cements. Various cements can also be finely powdered and used. Also, cements prepared by increasing or decreasing the content of components normally used in cement can be used. Furthermore, combinations of two or more of these can also be used.

[0030] The CaO content of carbonated quicklime is preferably 35 to 80% by mass, more preferably 40 to 78% by mass, and even more preferably 50 to 75% by mass. By setting the CaO content of carbonated quicklime within the above range, it is possible to improve not only the initial expansion but also the long-term expansion rate and storage stability. In the present invention, the CaO content of carbonated quicklime can be measured by the mass loss determined by differential thermogravimetry analysis (TG-DTA).

[0031] The carbonation rate of carbonated quicklime is preferably 25 to 65%, more preferably 28 to 60%, and even more preferably 30 to 50%. By setting the carbonation rate of carbonated quicklime within the above range, it is possible to improve not only the initial expansion but also the long-term expansion rate and storage stability. In the present invention, the carbonation rate of carbonated quicklime can be calculated using the following formula (Mathematical Formula 1) by quantifying the mass loss at 500 to 850°C using differential thermogravimetric analysis.

[0032]

number

[0033] The length change rate of mortar using carbonated lime after 7 days is 550-750×10 -6 is preferably 600 to 700 × 10-6 It is more preferable that the length change rate at 28 days is 200 to 300 × 10 -6 It is preferable that the ratio is 220 to 280 × 10 -6 In the present invention, the length change rates at ages of 7 days and 28 days can be measured in accordance with the method specified in Appendix A "Test method for expansive additives using mortar" of JIS A 6202:2017 "Expansive additives for concrete."

[0034] The long-term expansion rate of mortar using carbonated lime at 180 days is 550-750×10 -6 It is preferable that the ratio is 600 to 720 × 10 -6 It is more preferable that the long-term expansion rate at 180 days of age is ×. In the present invention, the long-term expansion rate at 180 days of age can be measured in accordance with the method specified in Appendix A "Test method for expansion properties of expansive additives using mortar" of JIS A 6202:2017 "Expansive additives for concrete", by measuring the length change rate at 7 days of age, placing the test specimen in a water tank at 20±1°C for curing, and removing it from the water tank at 180 days of age to measure the length change rate.

[0035] The compressive strength of mortar using carbonated quicklime after 3 days is 25-45N / mm 2 It is preferable that the strength is 28 to 40 N / mm 2 It is more preferable that the compressive strength at 7 days is 45 to 65 N / mm 2 It is preferable that the strength is 48 to 60 N / mm 2 Furthermore, the compressive strength at 28 days is 55 to 75 N / mm 2 Preferably, the strength is 58 to 70 N / mm 2 In the present invention, the compressive strength at ages of 3 days, 7 days, and 28 days can be measured in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement."

[0036] The flow value of mortar using carbonated quicklime immediately after mixing with water (0 minutes) is preferably 195 to 204 mm, more preferably 200 to 204 mm. Furthermore, the flow 30 minutes after mixing with water is preferably 173 to 189 mm, more preferably 181 to 189 mm. Furthermore, the flow 60 minutes after mixing with water is preferably 159 to 175 mm, more preferably 166 to 175 mm. In the present invention, the flow value after mixing with water can be measured in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement." [Example]

[0037] The present invention will be further explained below based on experimental examples, but the present invention is not limited to these.

[0038] <Experimental Example 1> Raw material 1: massive limestone (density: 2.69~2.71g / cm 3 Size width: 35 to 85 mm, calcium carbonate content (CaO equivalent): 55.8% by mass. Raw material 2: By-product slaked lime (density: 2.18~2.20g / cm 3 Size range: 0.1 to 0.5 mm, calcium carbonate content (CaO equivalent): 23.1% by mass. Raw material 3: Powdered limestone (density: 2.60~2.63g / cm 3 Size width: 0.5 to 2 mm, calcium carbonate content (CaO equivalent): 36.7% by mass. Raw material 4: Granular limestone (density: 2.53~2.58g / cm 3 Size width: 5 to 15 mm, calcium carbonate content (CaO equivalent): 47.3% by mass. These raw materials were heated for 1 hour at the heating temperatures shown in Table 1 below, and pieces of 3 mm or less were selected from the fired material and crushed to obtain powders with a Blaine specific surface area of 1500 to 4000 cm. 2A CaO-containing material having a CaO content of 1 / g was prepared. The CaO content of the obtained CaO-containing material was measured by differential thermogravimetric analysis (NETZSCH: STA2500). The results are also shown in Table 1 below. The prepared CaO-containing material was reacted with a carbon dioxide-containing gas having a carbon dioxide concentration and temperature shown in Table 1 below to produce carbonated quicklime. The mass loss of the obtained carbonated quicklime at 500 to 850°C was quantified by differential thermogravimetric analysis (NETZSCH: STA2500), and the CaO content and carbonation rate were calculated. The results are also shown in Table 1 below. The carbonation rate can be calculated using the above-mentioned formula (Mathematical Formula 1).

[0039] [Table 1]

[0040] <Experimental Example 2> The carbonated quicklime produced in Experimental Example 1 was mixed with cement so that the carbonated quicklime was 6.7% by mass to produce a cement composition. The resulting cement composition was mixed with fine aggregate so that the fine aggregate was 300 parts by mass per 100 parts by mass of cement, and water was added to give a water / cement ratio of 0.5 to produce mortar in a room at 20°C. The resulting mortar was subjected to the following measurements. The measurement results are shown in Table 2 below.

[0041] (Materials used) Cement: Ordinary Portland cement, commercially available, density 3.16 g / cm 3 , Blaine specific surface area 3260cm 2 / g. Fine aggregate: Sand (manufactured by the Cement Association), standard sand for JIS strength tests. Water: Tap water.

[0042] (Measurement method) Length change rate: The length change rate was measured at 7 and 28 days of age in accordance with the method specified in Appendix A of JIS A 6202:2017 "Expansive additives for concrete" "Test method for expansion properties of expansive additives using mortar."

[0043] Long-term expansion rate: In accordance with the method specified in Appendix A "Test method for expansion properties of expansive additives using mortar" of JIS A 6202:2017 "Expansive additives for concrete," the long-term expansion rate was measured by measuring the rate of change in length at 7 days of age, then placing the specimen in a water tank at 20±1°C to cure, and then removing it from the tank at 180 days of age and measuring the rate of change in length.

[0044] Compressive strength: Compressive strength was measured at ages of 3, 7, and 28 days in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement." After demolding, the concrete was cured underwater.

[0045] Immediately after preparation, each carbonated quicklime was placed in a sealed plastic bag and stored for one month at a temperature of 40°C and humidity of 90%. Mortar was prepared using the carbonated quicklime stored for one month as described above, and the length change of the mortar after 7 days was measured according to the method specified in Appendix A of JIS A 6202:2017 "Expansive Additives for Concrete," "Test Method for Expansion of Expansive Additive Mortar." Mortars with a length change of less than ±20% compared to the length change of mortar made with carbonated quicklime immediately after preparation were evaluated as excellent (○), those with a change of ±20-30% were evaluated as good (△), and those with a change of more than ±30% were evaluated as unacceptable (×).

[0046] Flow: Flow values were measured 0 minutes, 30 minutes, and 60 minutes after mixing with water in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement."

[0047] [Table 2]

[0048] <Experimental Example 3> A cement composition was produced and a mortar was prepared in the same manner as in Experimental Example 2, except that the addition rate of carbonated quicklime was changed. The following measurements were carried out on the obtained mortar. The measurement results are shown in Table 3 below.

[0049] [Table 3] [Industrial Applicability]

[0050] The method for producing carbonated quicklime of the present invention can be applied to the production of cement admixtures used for various cements used in the fields of civil engineering and construction.

Claims

1. A method for producing carbonated quicklime, comprising heating a raw material at a temperature of 850 to 1300°C to produce a CaO-containing material, and then reacting the CaO-containing material with a carbon dioxide-containing gas.

2. 2. The method for producing carbonated quicklime according to claim 1, wherein the CaO content in the CaO-containing material is 40 mass% or more.

3. 3. The method for producing carbonated quicklime according to claim 1, wherein the carbon dioxide-containing gas contains carbon dioxide generated when the raw material is heated.

4. 3. The method for producing carbonated quicklime according to claim 1, wherein the carbon dioxide concentration of the carbon dioxide-containing gas is 5 vol% or more.

5. 3. The method for producing carbonated quicklime according to claim 1, wherein the temperature of the carbon dioxide-containing gas is 100°C or higher.

6. 3. The method for producing carbonated quicklime according to claim 1, wherein the particle size of the CaO-containing material is adjusted before the reaction with the carbon dioxide-containing gas.

7. Carbonated quicklime obtained by the method for producing carbonated quicklime according to claim 1 or 2.

Images