JP5867929B2 - Method for producing γ-2CaO · SiO 2 - Google Patents

Description

The present invention mainly relates to a method for producing γ-2CaO · SiO _{2 that} can be used as a cement admixture.

More attention has been given to the durability of cement and concrete than ever before. In order to significantly improve the durability of cement and concrete, the present inventors have proposed γ-2CaO · SiO ₂ as a cement admixture (Concrete Engineering Annual Papers, vol. 26, No. 1, 2004). By using γ-2CaO · SiO ₂ as a cement admixture, it has a great effect on neutralization and suppression of salt damage, which causes early deterioration of concrete structures. For this reason, great expectations are placed on the use of γ-2CaO · SiO ₂ .

In order to utilize γ-2CaO · SiO ₂ , it is necessary to establish an industrial production method. However, as for the synthesis method of γ-2CaO · SiO ₂ , although there is knowledge at the research level, the actual manufacturing method has not been studied so much. In addition, there is nothing about a method for producing γ-2CaO · SiO ₂ continuously in large quantities.

So far, as a method for producing γ-2CaO · SiO ₂ , 0.5 to 5 parts by weight of graphite powder or amorphous carbon powder is added to 100 parts by weight of a mixture of calcareous raw material and siliceous raw material. There has been proposed a method of firing in a rotary kiln with an oxygen concentration of the kiln bottom of 3% or less (Patent Document 1). However, since carbon is added to the raw material in this method, there is a problem in that carbon remains in the product after baking or calcium carbide is by-produced by the reaction between the calcareous raw material and carbon when the baking temperature is high. If carbon remains, when used as a cement admixture, the carbon adsorbs a water reducing agent or a high performance water reducing agent, which adversely affects fluidity. When calcium carbide is produced as a by-product, flammable acetylene gas is generated when it comes into contact with water, which may make handling difficult in terms of safety.

Further, in the method of Patent Document 1, even gamma-2CaO · a measure of SiO ₂ generated da gamma-2CaO of · SiO ₂ purity is determined from Sting phenomena were those not so high. Specifically, a 40 μm passage rate was measured as an index representing the degree of dusting, but the maximum was about 80%. Thus, the method of Patent Document 1 is not sufficient as an industrial production process of γ-2CaO · SiO _2.

Recently, regarding a method for producing γ-2CaO · SiO ₂ , there has been a strong demand for the development of a rational method capable of obtaining a product with higher purity, industrial productivity, and stable quality.

Japanese Unexamined Patent Publication No. Sho 61-256913

The present invention provides a rational method for producing a product of higher quality, industrially high productivity, and stable quality with respect to a method for producing γ-2CaO · SiO ₂ .

As a result of various investigations, the present inventors have selected a specific raw material, granulated one having a specific particle size, and fired with a rotary kiln using a specific brick or specific mortar as a firing zone, γ-2CaO · SiO ₂ has been found to be generated.

The gist of the present invention is as follows.
(1) CaO and SiO ₂ as main components, CaO / SiO ₂ molar ratio is 1.8 to 2.2, and the total content of Al ₂ O ₃ and Fe ₂ O ₃ after heating to 1000 ° C. Is less than 5% by mass, granulated raw material having a particle size of 90% by mass or more with a 150 μm passage rate, and the granulated raw material is magnesia-spinel brick, Al ₂ O ₃ content is 85% by mass or more of alumina. At least one or more bricks or mortar selected from the group consisting of quality bricks, silicon carbide bricks, magnesia-spinel mortar, and alumina mortar with an Al ₂ O ₃ content of 85% by mass or more are used for the inner surface of the firing zone was in a rotary kiln and calcined at burn point temperature 1350-1,600 ° C., 40 [mu] m pass of 85% or more in a γ-2CaO · SiO ₂ of the manufacturing method.
(2) The manufacturing method as described in said (1) in which the said rotary kiln uses a magnesia-spinel brick for the brick of a baking zone.
(3) The rotary kiln process according to the above (1) to the brick in Al ₂ O ₃ content ratio of the burned zone using 85 wt% or more alumina bricks.
(4) The manufacturing method as described in said (1) in which the said rotary kiln uses a silicon carbide brick for the brick of a baking zone.
(5) The manufacturing method as described in said (1) in which the said rotary kiln uses the brick which apply | coated the magnesia spinel mortar to the brick of a baking zone.
(6) The rotary kiln is, the production method according to (1) using a brick firing zone Al ₂ O ₃ content was applied 85 wt% or more alumina mortar bricks.
(7) The process according to any one of the molar ratio of CaO / SiO ₂ of the raw material is 1.85～2.2.15 above (1) to (6).
Raw material after (8) 1000 ° C. heating method according to any one of the above containing _Fe 2 _{O 3} less than 2% by weight (1) to (7).
(9) The manufacturing method in any one of said (1)-(8) in which a raw material has a particle size of 90 mass% or more by 100 micrometer passage rate.
(10) The production method according to any one of (1) to (9), wherein granulation is performed using water having a water / raw material mass ratio of (0.1 to 0.3) / 1.
(11) The production method according to any one of (1) to (10), wherein firing is performed at a baking temperature of 1400 to 1500 ° C.
(12) The manufacturing method according to any one of (1) and (5) to (10) above, wherein the mortar on the brick surface of the firing zone of the rotary kiln has a thickness of 5 to 10 mm.
(13) the granulated material, while continuously supplied to the firing zone of the rotary kiln, producing how according to any of the above taking out the calcined product continuously from the rotary kiln (1) to (12).

According to the method for producing γ-2CaO · SiO ₂ of the present invention, it is possible to rationally produce γ-2CaO · SiO ₂ having high purity, industrially high productivity and stable quality. Become.

Unless otherwise specified, parts and% in the present invention are shown on a mass basis.
Γ-2CaO · SiO _{2 referred} to in the present invention is a kind of dicalcium silicate (2CaO · SiO ₂ ) among compounds mainly composed of CaO and SiO ₂ . Dicalcium silicate includes α type, α prime type, γ type, and γ type. The present invention relates to γ-type dicalcium silicate.

In the present invention, a CaO raw material and a SiO ₂ raw material are used as main components. The main component preferably means that the total content of CaO and SiO ₂ in the raw material is preferably 70% or more, more preferably 90% or more, and the content of other components is as small as possible. .
As the CaO raw material, calcium carbonate, calcium hydroxide, or calcium oxide can be used. As the SiO ₂ raw material, siliceous fine powder, clay, silica fume, fly ash, amorphous silica, and other siliceous substances by-produced from each industry can be selected.
In the present invention, it is preferable to limit the presence of impurities. Specifically, the total of Al ₂ O ₃ and Fe ₂ O ₃ mixed from the CaO raw material and the SiO ₂ raw material needs to be less than 5% in the raw material after heating at 1000 ° C. The total of Al ₂ O ₃ and Fe ₂ O ₃ is more preferably less than 4%, and most preferably less than 3%. In particular, the content of Fe ₂ O ₃ is preferably less than 2%, more preferably less than 1.5%, and most preferably less than 1% in the raw material after heating at 1000 ° C. . If the total of Al ₂ O ₃ and Fe ₂ O ₃ is not less than 5% by mass with respect to the raw material after heating at 1000 ° C., β-2CaO · SiO ₂ is easily formed, and the purity of γ-2CaO · SiO ₂ is Deteriorate. In particular, since the influence of Fe ₂ O ₃ is great, in addition to the total of Al ₂ O ₃ and Fe ₂ O ₃ being less than 5% by mass with respect to the raw material after heating at 1000 ° C., Fe ₂ O ₃ The content is preferably less than 2% by mass with respect to the raw material heated at 1000 ° C. When the content of Fe ₂ O ₃ is less than 1.5% by mass or less with respect to the raw material after heating at 1000 ° C., the quality stability is remarkably improved.

The mixing ratio of the CaO raw material and the SiO ₂ raw material needs to be adjusted so that the CaO / SiO ₂ molar ratio of the raw material is 1.8 to 2.2. When the CaO / SiO ₂ molar ratio of the raw material is less than 1.8, α-type wollastonite or lankinite is by-produced, and the content of γ-2CaO · SiO ₂ is lowered. When CaO / SiO ₂ molar ratio of the raw material is more than 2.2, no 3CaO · SiO ₂ and free lime by-again γ-2CaO · SiO ₂ content ratio is low. CaO / SiO ₂ molar ratio of the starting materials is preferably 1.85 to 2.15.

The particle size of the CaO raw material and the SiO ₂ raw material needs to be adjusted so that the 150 μm passage rate is 90% or more, that is, the 150 μm sieve is 90%, and the 100 μm passage rate is 90% or more, that is, a 100 μm sieve. It is more preferable to prepare so that the bottom is 90%. If the particle size of the raw material is not fine within the above range, the purity of γ-2CaO · SiO ₂ will be deteriorated. Specifically, free lime and insoluble residue tend to increase.

In the present invention, it is preferable to granulate the raw material obtained by compounding in order to facilitate the production of γ-2CaO · SiO _2. Granulation is an operation of forming the prepared raw material into a dumpling shape. The granulation is performed so that the particle size is preferably 1 to 50 mm, preferably 10 to 30 mm. Examples of the granulation method include a method of granulating a raw material and water into a disc-shaped rotary drum, a method of using a so-called pelletizer in which the raw material is placed in a mold and press-molded. The amount of water used for granulation is preferably (0.1 to 0.3) / 1, more preferably (0.15 to 0.25) / 1 in terms of the mass ratio of (water / raw material). . If the usage-amount of water is less than 0.1 / 1, the granulated raw material will be easy to collapse, and a baking reaction may not fully advance at the time of baking with a rotary kiln. On the other hand, if the amount of water used exceeds 0.3 / 1, the granulated raw material becomes watery, and it tends to collapse, and the firing reaction may not sufficiently proceed during firing in the rotary kiln. Since the raw material contains a large amount of water, a large amount of firing energy is required to evaporate the raw material, which is uneconomical and undesirably increases the environmental load.

In the present invention, the granulated raw material is fired in a rotary kiln. The temperature needs to be fired at a baking temperature of 1350 to 1600 ° C, more preferably 1400 to 1550 ° C, and particularly preferably 1400 to 1500 ° C. When the baking temperature is lower than 1350 ° C., the purity of γ-2CaO · SiO ₂ is deteriorated. Specifically, free lime and insoluble residue tend to increase. On the other hand, if the burning point temperature exceeds 1600 ° C., it may melt and the coating may adhere to the kiln, making operation difficult, resulting in large energy consumption and being uneconomical. In addition, the burning point temperature said by this invention means the highest temperature in a kiln. Usually, the highest temperature in the kiln is near the front of the flame (flame shape) extending from the burner.

The material of bricks and mortar used for the inner surface of the rotary kiln firing zone is important. In the present invention, at least one brick or mortar selected from the group consisting of the following (1) to (5) is used.
(1) Magnesia-spinel brick (2) Alumina brick with Al ₂ O ₃ content of 85% or more, preferably 96% or more among alumina bricks specified in JIS R 2305 (3) JIS R 2011 It is difficult to stably produce γ-2CaO · SiO ₂ with bricks other than the silicon carbide bricks (1) to (3) defined in, and β-2CaO · SiO ₂ may be mixed.
(4) Magnesia-spinel mortar (5) Alumina mortar with an Al ₂ O ₃ content of 85% or more, preferably 96% or more

In the present invention, when the mortar is used for the firing zone, it is difficult to stably produce γ-2CaO · SiO ₂ with a mortar other than the above (4) or (5), and β-2CaO · SiO ₂ is May be mixed.
These mortars are preferably used by being applied to the surface of a brick in a rotary kiln firing zone. Although the use conditions of the mortar apply | coated to a brick are not specifically limited, It is preferable that the thickness of a mortar is 5-10 mm. Water is preferably (0.15 to 0.2) / 1 with respect to the mortar component.
Moreover, it is preferable that both the above bricks and mortar are for a cement rotary kiln and are chromium-free.

In the present invention, the firing atmosphere in the rotary kiln is preferably in a mixed gas of oxygen / nitrogen having an oxygen concentration of 10 to 21% by volume, in the atmosphere, or in a combustion gas containing 10 to 21% by volume of oxygen, More preferably in volume%. The firing time is preferably 1 to 5 hours, more preferably 2 to 4 hours. The rotational speed of the rotary kiln is preferably 400 to 800 rpm, more preferably 500 to 700 rpm.
The production method of γ-2CaO · SiO ₂ of the present invention is preferably a batch production method by batch firing or a continuous production method by continuous firing, and a continuous production method is more preferred from the viewpoint of productivity. Here, the continuous production method means a production method in which the fired product is continuously taken out from the rotary kiln while continuously supplying the granulated raw material to the firing zone of the rotary kiln.
In the continuous production method, from the viewpoint of productivity, the residence time of the granulated raw material in the maximum temperature zone of the rotary kiln is preferably 30 to 180 minutes, and more preferably 50 to 150 minutes.

  In the present invention, a cooling operation is performed after firing, but the cooling conditions are not particularly limited, and a special rapid cooling operation may be omitted. Specifically, it may be a method according to the general cooling conditions of Portland cement clinker, and after firing with a rotary kiln, it may be cooled through a cooler or the like in an atmospheric environment.

According to the method for producing γ-2CaO · SiO ₂ of the present invention, it is possible to obtain γ-2CaO · SiO ₂ having a 40 μm passage rate after dusting of 85% or more, that is, high purity. Further, according to the γ-2CaO · SiO ₂ of the manufacturing method of the present invention, 40 [mu] m pass rate after dusting 90% or more, more can be obtained more than 95%.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention more concretely, this invention should not be limited and limited to the following Examples.
"Experiment 1"
The following CaO raw material, SiO ₂ raw material, Al ₂ O ₃ component, and Fe ₂ O ₃ component are blended, and as shown in Table 1, the CaO / SiO ₂ molar ratio is 2.0, and Al ₂ after heating at 1000 ° C. O ₃ content and _Fe 2 _{O 3} content was prepare a raw material of a variety of different formulations. These raw materials were granulated with a granulator (Mitsubishi Heavy Industries, Eyeplate Granulator MG-180; Eyeplate Diameter 1800 mm, Depth 450 mm), and the particle size was 10 on the condition that the mass ratio of water / raw material was 0.2 / 1. It granulated so that it might become -40mm, and it baked at 1450 degreeC with the rotary kiln which changed the material of the baking belt inner surface as shown in Table 1. The results of evaluating the sample after firing are also shown in Table 1.

<Rotary kiln>
The rotary kiln used in the experimental example has a cylindrical shape with an inner diameter of 1 m and a length of 20 m. The material of the refractory material on the inner surface of the rotary kiln firing zone was a brick (thickness 50 mm) described in the following (1) to (5) or a brick surface coated with mortar.
Firing zone material (1): Magnesia-spinel brick (commercially available)
Firing zone material (2): Alumina brick with 90% Al ₂ O ₃ content (commercially available)
Firing zone material (3): Silicon carbide brick (commercially available)
Firing zone material (4): magnesia-spinel mortar on the surface of silica-alumina brick with Al ₂ O ₃ content of 60% and SiO ₂ content of 40%, water / mortar component mass ratio of 0.17 / 1 and applied with a thickness of 7 mm.
Firing zone material (5): Alumina mortar having an Al ₂ O ₃ content of 90% by mass on the surface of a silica-alumina brick having an Al ₂ O ₃ content of 60% and an SiO ₂ content of 40%. / Mortar component mass ratio of 0.17 / 1, with a thickness of 7 mm.

<Materials used>
CaO raw material: Limestone fine powder. CaO is 55.4%, MgO is 0.37%, Al ₂ O ₃ is 0.05%, Fe ₂ O ₃ is 0.02%, and SiO ₂ is 0.10%. C) was 43.57%, carbon content was not detected. The 150 μm passage rate is 97.0%, and the 100 μm passage rate is 91.9%.
SiO ₂ raw material: silica fine powder. CaO 0.02%, MgO 0.04%, Al ₂ O ₃ 2.71%, Fe ₂ O ₃ 0.27%, SiO ₂ 95.83%, and TiO ₂ 0.23% No carbon content is detected. The ignition loss (1000 ° C.) is 0.51%, the 150 μm pass rate is 95.1%, and the 100 μm pass rate is 90.3%.
Al ₂ O ₃ component: Alumina for industrial use. The purity is 99% or more.
Fe ₂ O ₃ component: ferric oxide for industrial use. The purity is 99% or more.
Water: tap water

<Measurement method>
Compound identification: The compound was identified by powder X-ray diffraction.
Quantification of chemical components: Al ₂ O ₃ components, Fe ₂ O ₃ components, free lime, and insoluble residue were analyzed according to JIS R 5202.
Degree of dusting: evaluated by 40 μm passage rate.

From Table 1, the total of Al ₂ O ₃ and Fe ₂ O ₃ mixed from CaO raw material and SiO ₂ raw material must be less than 5% by mass (mass%) with respect to the raw material after heating at 1000 ° C. I understand. The total of Al ₂ O ₃ and Fe ₂ O ₃ is more preferably 4% by mass or less, and most preferably 3% by mass or less. In particular, the content of Fe ₂ O ₃ is preferably 2% by mass or less, more preferably 1.5% by mass or less, and 1% by mass or less with respect to the raw material heated at 1000 ° C. Is most preferred. If the total of Al ₂ O ₃ and Fe ₂ O ₃ is not less than 5% by mass with respect to the raw material heated at 1000 ° C, β-2CaO · SiO ₂ is likely to be formed, and the purity of γ-2CaO · SiO ₂ is Deteriorate. Also, magnesia-spinel brick, alumina brick with Al ₂ O ₃ content of 90%, silicon carbide brick, magnesia-spinel mortar, and alumina mortar with Al ₂ O ₃ content of 90% by mass are used for the firing zone. Thus, high-purity γ-2CaO · SiO ₂ can be stably produced.

"Experimental example 2"
The CaO / SiO ₂ molar ratio of the raw material is set to 2.0, the Fe ₂ O ₃ content is fixed to 0.3%, the Al ₂ O ₃ content is fixed to 1.7%, and bricks and mortar in the fired zone are fixed. It carried out similarly to Example 1 except having changed into following (5)-(12). The results are shown in Table 2.

<Materials used>
Firing zone material (5): Al ₂ O ₃ content 95% alumina brick (commercially available)
Firing zone material (6): Alumina brick with 85% Al ₂ O ₃ content (commercially available)
Firing zone material (7): Alumina mortar with 95% Al ₂ O ₃ content (Myoyo Corporation M) on the surface of silica-alumina brick with 60% Al ₂ O ₃ content and 40% SiO ₂ content. -AW) coated with a water / mortar component mass ratio of 0.17 / 1 and a thickness of 7 mm Material of the calcined zone (8): Silica with an Al ₂ O ₃ content of 60% and an SiO ₂ content of 40% Aluminum bricks coated with alumina mortar with 85% Al ₂ O ₃ content (MA, manufactured by Yotai Co., Ltd.) with a water / mortar component mass ratio of 0.17 / 1 and a thickness of 7 mm. Material (9): Silica-alumina brick with a Al ₂ O ₃ content of 45% and a SiO ₂ content of 55% (commercially available)
Firing zone material (10): Magnesia brick with 85% MgO content (commercially available)
Firing zone material (11): Silica-aluminum brick with an Al ₂ O ₃ content of 60% and an SiO ₂ content of 40% on the surface of silica with an Al ₂ O ₃ content of 80% and an SiO ₂ content of 20% -Aluminous mortar (Myo-Mawag, manufactured by Yotai Co., Ltd.) coated with a water / mortar component mass ratio of 0.17 / 1 and a thickness of 7 mm. Material of calcined zone (12): Al ₂ O ₃ content 60%, SiO _2. A magnesia mortar with an MgO content of 95% applied to the surface of a silica-alumina brick with a content of 40% at a water / mortar component mass ratio of 0.17 / 1 and a thickness of 7 mm.

It can be seen from Table 2 that high-purity γ-2CaO · SiO ₂ can be stably produced by using alumina brick or alumina mortar having an Al ₂ O ₃ content of 85% by mass or more in the fired zone. When bricks or mortars other than the present invention are used, it is difficult to stably produce γ-2CaO · SiO ₂ , and β-2CaO · SiO ₂ is generated.

"Experiment 3"
As shown in Table 3, the CaO / SiO ₂ molar ratio of the raw material is fixed at 2.0, the Fe ₂ O ₃ content is fixed at 0.3%, the Al ₂ O ₃ content is fixed at 1.7%. The procedure was the same as in Example 1 except for the change. The results are shown in Table 3.

From Table 3, it is necessary to prepare the particle sizes of the CaO raw material and the SiO ₂ raw material so that the 150 μm pass rate is 90% or more, and it is more preferable that the 100 μm pass rate is 90% or more. Recognize. If the particle size of the raw material is not fine within the above range, the purity of γ-2CaO · SiO ₂ is deteriorated, and free lime and insoluble residue increase.

"Experimental example 4"
The same procedure as in Experimental Example 3 was performed except that the CaO / SiO ₂ molar ratio of the CaO raw material and the SiO ₂ raw material was changed as shown in Table 4. The results are shown in Table 4.

From Table 4, it can be seen that the mixing ratio of the CaO raw material and the SiO ₂ raw material needs to be adjusted so that the CaO / SiO ₂ molar ratio of the raw material is 1.8 to 2.2. If the CaO / SiO ₂ molar ratio of the raw material is outside this range, the purity of γ-2CaO · SiO ₂ may be deteriorated.

“Experimental Example 5”
The experiment was performed in the same manner as in Experimental Example 3 except that the burning temperature was changed as shown in Table 5. The results are shown in Table 5.

From Table 5, it is necessary to fire at 1350 to 1600 ° C. at the baking temperature, and 1400 to 1550 ° C. is more preferable. When the baking temperature is lower than 1350 ° C., the purity of γ-2CaO · SiO ₂ is deteriorated. On the other hand, if the baking temperature exceeds 1600 ° C, it will melt and the coating will adhere to the kiln, making it difficult to operate, and β-2CaO · SiO ₂ will be mixed.

"Experimental example 6"
The experiment was performed in the same manner as in Experimental Example 3 except that the mass ratio of (water / raw material) during granulation was changed as shown in Table 6. The results are shown in Table 6.

  From Table 6, it can be seen that the amount of water used for granulation is preferably 10 to 30% by mass and more preferably 15 to 25% by mass in terms of the water / raw material ratio. When the amount of water used is less than 10% by mass, the granulated raw material is liable to collapse and the firing reaction does not proceed sufficiently during firing in the rotary kiln. On the other hand, if the amount of water used exceeds 30% by mass, the granulated raw material becomes watery, and is easily broken, and the firing reaction does not proceed sufficiently during firing in the rotary kiln.

The method for producing γ-2CaO · SiO ₂ of the present invention can be widely used because it has high purity, is industrially highly productive, and provides a product with stable quality.
Japanese Patent Application No. 2011-010964 filed on January 21, 2011, Japanese Patent Application No. 2011-130285 filed on June 10, 2011, Japanese Patent Application filed on June 10, 2011 Application No. 2011-130361, Japanese Patent Application No. 2011-172226 filed on Aug. 5, 2011, and Japanese Patent Application No. 2011-200265 filed on Sep. 14, 2011, claims , And the entire contents of the abstract are hereby incorporated by reference as disclosure of the specification of the present invention.

Claims (13)

CaO / SiO ₂ as the main components, CaO / SiO ₂ molar ratio is 1.8 to 2.2, and the total content of Al ₂ O ₃ and Fe ₂ O ₃ is less than 5% by mass after heating at 1000 ° C. Then, a raw material having a particle size of 90% by mass or more with a passage rate of 150 μm is granulated, and the granulated raw material is made of magnesia-spinel brick, alumina brick with an Al ₂ O ₃ content of 85% by mass or more, silicon carbide In a rotary kiln using at least one brick or mortar selected from the group consisting of brick, magnesia-spinel mortar, and alumina mortar having an Al ₂ O ₃ content of 85% by mass or more on the inner surface of the firing zone, A method for producing γ-2CaO · SiO ₂ baked at a point temperature of 1350 to 1600 ° C. and having a 40 μm passage rate of 85% or more.   The said rotary kiln is a manufacturing method of Claim 1 which uses a magnesia-spinel brick for the brick of a baking zone. The manufacturing method according to claim 1, wherein the rotary kiln uses an alumina brick having an Al ₂ O ₃ content of 85 mass% or more for the brick in the fired zone.   The said rotary kiln is a manufacturing method of Claim 1 which uses a silicon carbide brick for the brick of a baking zone.   The said rotary kiln uses the brick which apply | coated the magnesia spinel mortar to the brick of a baking zone, The manufacturing method of Claim 1 used. The manufacturing method according to claim 1, wherein the rotary kiln uses a brick obtained by applying an alumina mortar having an Al ₂ O ₃ content of 85% by mass or more to a brick in a fired zone. The manufacturing method according to any one of claims 1 to 6, wherein the raw material CaO / SiO ₂ molar ratio is 1.85 to 2.15. 1000 ° C. After heating the raw material, the production method according to claim 1 containing 2% by weight of less than _Fe 2 _{O 3.}   The manufacturing method in any one of Claims 1-8 in which a raw material has a particle size of 90 mass% or more by 100 micrometer passage rate.   The manufacturing method in any one of Claims 1-9 granulated using water whose mass ratio of water / raw material is (0.1-0.3) / 1.   The manufacturing method according to any one of claims 1 to 10, wherein the baking is performed at a baking temperature of 1400 to 1500 ° C.   The manufacturing method according to claim 1, wherein the mortar on the brick surface of the firing zone of the rotary kiln has a thickness of 5 to 10 mm. The granulated material, while continuously supplied to the firing zone of the rotary kiln, producing how according to any one of claims 1 to 12 to take out the baked product to the rotary kiln continuously.