JPS62265164A - Calcia magnesia base clinker and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a calcia-magnesia clinker having high purity, high density and excellent digestibility and suitable as a raw material for basic refractories, and a method for producing the same.

[Conventional technology] In recent years, the steel manufacturing industry has become increasingly geared towards streamlining operations, such as using higher quality steel and continuous casting, leading to the introduction of higher temperatures in converters and ladles, or the introduction of ladle refining methods. There is. Therefore, the refractories used in converters and steel refining furnaces can withstand harsher conditions than the conventionally used magnesia/carbon, magnesia/chromium, high alumina, and zircon refractories. something is desired.

As a basic refractory material, calcia has a melting point of 2580'
It has a high heat resistance and thermal shock resistance.

It also has excellent properties such as absorbing Al2O3 inclusions in steel. Since our country is rich in resources, it is highly anticipated as a durable material for steelmaking furnaces.

Among calcia-based refractories, calcia-magnesia-based refractories have the advantage of possessing the excellent properties of calcia and magnesia without compromising their respective properties. As a use,
It is expected to be used in ladle smelting furnaces and tanditshu. Despite this, the main reason why calcia-magnesia-based refractories are not being used in earnest for the above-mentioned new applications is that calcia has low resistance to water digestion. Magnesia-based clinker also has low digestibility and is difficult to handle, store, or
Due to the difficulty of the brick manufacturing process and the lack of high-density clinker, slag resistance,
and insufficient strength.

Conventionally, as a method to improve digestion resistance, Fe2O3, A
Digestion resistance is improved by incorporating large amounts of impurities such as 12O2, TiO2, and SiO2 into the clinker.

For example, Fe2O3, C in CaO or CaO+MQO
A method of containing 5 to 10% by weight of one or more of r2o3 and TiO2 (Japanese Unexamined Patent Publication No. 131612/1983), containing CaO or CaO and MCl0 as main components, and Fe
2030.4-1.2% by weight, TiO20.1-0.5
Weight%, SiO21.5% or less, Al2031.0
Contains % by weight or less, and contains Fe2O3, TiO2, SiO
2. A method in which the total amount of Al2O3 is 0.5 to 3 layers (
JP-A No. 59-35060). In all of these methods, an impurity that forms a low melting point compound with CaO or MCl0 is added to coat the calcia crystal with the low melting point compound, thereby obtaining high digestion resistance. In addition, the total of MCJO, cao, Fe20) is 99% by weight or more, MgO is 10% by weight or more, Fe2030
．． A high-density magnesia-calcia clinker (Japanese Patent Application Laid-Open No. 112666/1983) in which a part of the iron component is solid-dissolved in the periclase crystal has been reported.

Another method is to add light burnt dolomite or light burnt lime to magnesium hydroxide slurry that has been washed with water to reduce the chlorine ion content to 0.4% by weight or less, and then slaked the resulting raw material, which is then fired. A method (Japanese Patent Publication No. 4B-16322) has been reported to produce magnesia dolomite clinker having a total loading of 99% or more and a high bulk specific gravity. This is an attempt to obtain a certain degree of digestion resistance by increasing the bulk specific gravity.

Although the above-mentioned conventional techniques essentially attempt to improve the digestion resistance of clinker, several methods have also been proposed in which the clinker surface is coated with a substance that does not hydrate. For example, there is a method of heating and carbonating CaO refractory particles by melting method (Japanese Unexamined Patent Application Publication No. 1988-88825), or a method of heating and carbonating CaO refractory particles using a melting method, or using a clinker containing free lime in a carbon dioxide-containing atmosphere at 95%
A method of forming a protective layer of calcium carbonate on the clinker surface by heating to 0°C or higher and then cooling (Japanese Patent Laid-Open No. 60-9
0858 Publication).

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, the method of adding impurities causes the added impurities to form low melting point compounds with CaO, which deteriorates the corrosion resistance and strength at high temperatures. This results in the loss of the excellent properties that it possesses. In addition, with regard to the method of dissolving iron components in periclase crystals, repeated use may cause the iron components to migrate to grain boundaries, deteriorating corrosion resistance and strength, and the purity is low, making it difficult to use. Limited. In general, the digestion resistance of the clinkers obtained by these methods is not as slow as the inventors intended. In addition, the method described in Japanese Patent Publication No. 48-16322, in tests conducted by the present inventors,
Many coarse crystals of calcia exist in the clinker, and even if a clinker with high density is obtained, its resistance to digestion is poor.

The method of forming a calcium carbonate layer on the clinker surface is clearly effective in improving digestion resistance, but
If the physical properties of the original clinker are not satisfactory, the effect will be small. Furthermore, there are many unknown points, such as optimal conditions, and it is difficult to say that it is technically established.

An object of the present invention is to provide a calcia-magnesia clinker that has high purity, high density, and excellent digestion resistance, and a method for producing the same.

[Means for solving the problems] The present invention focuses on obtaining high digestion resistance and high density while maintaining high purity of calcia-magnesia-based clinker, and develops a manufacturing method and physical properties of the resulting clinker. As a result of detailed research on and organization, we found that
It has been found that if the crystal sizes of the constituent calcia crystals and magnesia crystals are smaller than a certain size, a high degree of digestion resistance that has not been previously achieved can be obtained. We also discovered that such a structure can be obtained by classifying the raw materials, magnesium hydroxide and calcium hydroxide, and established a manufacturing method. In general, Calcia, which has the above structure,
magnesia-based clinker in carbon dioxide-containing gas at 55%
It was discovered that digestion resistance was significantly improved by heating to 0 to 750°C to form a layer of calcium carbonate of a certain thickness on the surface, and the appropriate carbonation conditions were found and the present invention was completed. I ended up doing it.

That is, the structure of the present invention is as follows: (1) The composition is expressed in weight percent on a scorching basis,
It is a calcia-magnesia-based clinker that carbonates MCl0' 10-75 on Cl0 98.5jX, has a relative density of 96% or more, and has an average grain size of calcia crystals of 15 μm or less, and its manufacturing method is ( 2) A SUM method for calcia-magnesia-based clinker, in which coarse particles in the calcium hydroxide raw material and magnesium hydroxide raw material are removed to obtain a particle size distribution of 44μ.
These high-purity raw materials, which have 99% or more of double concavities of m or less, and 90% or more of 25 μm or less by weight, are mixed and molded to form a molded product with a density of 1.2 g/cm3 or more, and this molded product is This is a method for producing calcia-magnesia clinker that carbonates firing.

The purity of the calcia-magnesia clinker of the present invention, that is, the content of CaO + MCJO, is 98.5% by weight or more, preferably 98.8% by weight for the purpose of the invention.
, more preferably 99.0% by weight or more. The calcia-magnesia clinker of the present invention contains MqO in an amount of 10% to 75% by weight.

When CaO+MgO is within the composition range defined in the present invention, if MCl0 is less than 10% by weight, the digestion resistance will decrease. When MCl0 exceeds 75 mm, calcia crystals exist only slightly at the grain boundaries of magnesia crystals, and the properties as a calcia-magnesia clinker are lost.

The amount of Fe203 contained in the calcia-magnesia clinker of the present invention is less than 0.2% by weight, preferably less than 0.1% by weight. As mentioned above, Fe2O] forms a low melting point compound with CaO, which lowers the strength at high temperatures, so it is not preferable for the content to be large.

Other impurities, such as A120x, Sio2, B2
The content of O3 is particularly preferably less than 1.0% by weight. In addition, the clinker of the present invention has a characteristic compared to conventional ones in that the content of impurities is extremely small. Note that all of these impurities are Ca
o or MgO, forming a low melting point compound, which is not preferred.

Therefore, the product of the present invention is clearly different from the conventional product even in terms of composition, and its strength at high temperatures and slag corrosion resistance are clearly higher than the conventional product, and it is expected to be used in a variety of applications.

From the purpose of the invention, the relative density of the calcia-magnesia clinker of the present invention is 96% or more, preferably 97%.
The above shall apply. If the relative density is lower than this, the desired digestion resistance, slag penetration resistance, and strength cannot be obtained.

The average particle size of calcia crystals in the calcia-magnesia clinker of the present invention is 15 μm or less, preferably 10 μm or less.

When the average grain size of calcia crystals is larger than 15 μm,
Digestibility is reduced. The unprecedentedly high digestive resistance observed in the product of the present invention is manifested only when the product has the above-mentioned structure.

The size of calcia crystals is correlated with the degree to which magnesia crystals are rounded. In order for the calcia crystals in the clinker to be small, one of the requirements is that the magnesia crystals are small.
It can become one. In this way, a structure in which both calcia crystals and magnesia crystals are small becomes a structure in which both are uniformly dispersed, and in this case, the digestion resistance is greatly improved. Therefore, the average particle size of magnesia crystals in the clinker is preferably 15 μm or less, more preferably 10 μm or less.

General 1'': It is known that ceramics (polycrystals) have higher strength as the crystal size of the constituent crystals is smaller and more uniform. It is expected that the CaO-MgO clinker will have unprecedented strength not only in terms of digestion resistance but also in terms of strength. It is also expected that the erosivity will be considerably improved. 9 Calcia, whose surface is composed of magnesia and calcium carbonate,
The magnesia-based clinker can be obtained by heat-treating the above-mentioned clinker in a carbon disuride-containing gas. Ca
As mentioned above, the method of carbonating the surface of an O-based refractory material to improve its digestion resistance is a well-known technique, but the method of carbonating the calcia/magnesia clinker having a fine and uniform structure according to the present invention 9, the digestion resistance is greatly improved, and a calcia-magnesia clinker having a high digestion resistance that has never been seen before can be obtained. The thickness of the calcium carbonate layer formed by carbonation of calcia on the surface of these clinkers is 0.05 to 4 μm, as observed by electron microscopy. It has been determined by electron microscopy that the surface of the calcia-magnesia clinker on which the calcium carbonate layer is formed is composed of a structure in which magnesia crystals and calcium carbonate crystals are tightly and uniformly bonded. It is also observed that the rough carbon bed calcium layer is a dense aggregate of very fine calcium carbonate crystals with a grain size of 1 μm or less. Because it has such a structure, it exhibits a high degree of digestive resistance that has never been seen before.

Next, the method for producing the calcia-magnesia clinker of the present invention will be explained in detail.

The calcia-magnesia-based tallincar of the present invention is mainly produced by: a) a step of classifying raw diagonal calcium hydroxide and magnesium hydroxide;

b) Mixing step of calcium hydroxide and magnesium hydroxide.

C) Filtration molding process of mixed slurry.

d) Cake or molded body baking step.

It consists of each process.

The raw materials, calcium hydroxide and magnesium hydroxide, are
It can be obtained by conventional industrial methods. That is, calcium hydroxide is obtained by calcining limestone or synthetic calcium carbonate, etc., and slaked quicklime in water. Magnesium hydroxide is obtained by reacting seawater with an alkali such as calcium hydroxide, JQ is obtained by purifying the obtained precipitate.The water-soluble calcium and magnesium hydroxide obtained by these methods have a mass of several tens of μm as they are.
It often contains coarse particles (agglomerated particles) of about 1.0 m in size. These coarse particles not only reduce the sintering strength but also become a factor in generating coarse crystals. Therefore, in order to obtain the calcia-magnesia-based tallincar having high density and fine crystals according to the present invention, it is essential to remove coarse particles contained in these raw materials, and for both raw materials, 99% by weight or more of 44 μm or less In addition, a classification step is required in which 90% or more of the particles are 25 μm or smaller. These classifications include wet sieving,
This can be easily done using liquid Zyclone or the like.

The raw material for final classification is impurity, and calcium hydroxide is Si.
Magnesium hydroxide contains SiO2, B2O3, C1, etc., and these impurities are not only harmful to sintering but also an obstacle to obtaining a fine and uniform structure. For the purpose of the invention, it is necessary to remove these impurities as much as possible. Among these impurities, SiO2, Al2O3, Fe2O3, CaC0,3, etc. are contained in the raw material as coarse particles.

It is often possible to remove them to some extent by classifying them. In this way, the classification step is a necessary step in terms of achieving high purity.

In particular, when the raw material magnesium hydroxide is 1q extracted from seawater, the C1 content must be reduced to 0.2% by weight or less on a dry matter basis by washing. If the CI in magnesium hydroxide exceeds 0.2% by weight on a dry matter basis, it will evaporate during firing and will damage the sintering, making it difficult to obtain the calcia-magnesia-based tallinker of the present invention having a high density and fine structure. I can't. Washing can be performed by washing the magnesium hydroxide slurry with water before the mixing step described below, or by washing with water simultaneously with filtration in the filtration step after mixing with calcium hydroxide.

Calcium hydroxide cI5 and magnesium hydroxide purified as described above are stirred and mixed in water.

The obtained calcium hydroxide/magnesium hydroxide mixed slurry is filtered under pressure, or after filtered and dried, it is molded under pressure to form a cake or molded body with a density of 1.2 g/cm3 or more on a dry basis. do. If the density of the cake or molded body is less than 1.2 Mcm3, baking is performed after that.
The resulting sintered body has a structure with many pores, and high-density talincar cannot be obtained. For Calo pressure filtration, a pressure filtration machine such as a filter press that is usually used industrially can be used. However, with normal filtration methods such as vacuum filtration that does not apply pressure, the density is 1.2g on a dry basis.
It is difficult to produce 1 q of cake of /cm3 or more. In this case, after drying the filtered cake, it is necessary to pressurize it using a molding machine such as a Briquera mill machine to obtain a molded product with a density of 1.2 g/rm3 or more. . When using such a process, uniform and
In order to obtain a molded product with a certain degree of strength, it is desirable to crush the dried material before pressure molding. Pressure filtration,
There is no problem in obtaining the calcia-magnesia clinker of the present invention, regardless of which process is used, including filtration and drying followed by pressure molding. The cake or molded body obtained in this way has a density of 1.2 g/cm or more on a dry basis,
Its composition has C1 of 0.2% by weight or less.

Based on the scorching heat standard, CaO + MQO is 98.5% by weight or more,
Desirably 98.8% by weight or more, and preferably Fe
It is preferable to adjust the content so that 2O3 is less than 0.2% by weight and other impurities are less than 1.0% by weight.

If MgO is less than 10% by weight, the sinterability is significantly reduced, the size of the calcia crystals becomes larger than 15 μm, and the relative density is also reduced.

“If e203 is more than 0.21% by weight, it will promote the growth of calcia crystals, making it impossible to obtain a fine structure.

Next, these cakes or molded bodies are crushed to an appropriate particle size if necessary and then fired at 1600°C or higher,
The calcia-magnesia clinker of the present invention has high purity, high density, and excellent digestion resistance. For firing here, a rotary kiln or the like that is normally used when firing magnesia clinker can be used as is.

Calcia, whose surface consists of magnesia and calcium carbonate
The magnesia-based clinker is produced in a gas containing 5% or more of the clinker produced as described above in terms of CO2 partial pressure.
Obtained by heating to 550-750"C for 0 minutes or more, preferably by heating to 550-750"C for 20 minutes or more in a gas containing 15% or more CO2 partial pressure. Lower than 550"C. temperature, and 750°C
At higher temperatures, the rate of carbonation is slow and it is difficult to obtain a calcium carbonate layer thick enough to provide high digestibility, making it difficult to significantly improve digestibility.

For the carbonation treatment, a rotary furnace such as a rotary kiln, a vertical rotary furnace, etc. can be used.

Next, Examples and Comparative Examples of the present invention will be given and specifically explained. In addition, various measuring methods in the present invention are as follows.

1) Relative density (RD> Relative density was determined by the following formula, assuming that the theoretical density of calcia was 3.389/Cm3 and the theoretical density of magnesia was 3.58 Mcm3.

RD (%) = [BD/ (3,38/(R+1)+
3.58 R/(R+1) ) ] xlOO In the formula, R
are calcia-magnesia clinker MgO and CaO
BD is the weight content ratio (MqO/Ca0) of This is the value of bulk specific gravity of calcia-magnesia clinker measured according to the measurement method of

2) Chemical composition Gakusatsu Law 1 proposed by the 124th Committee of the Japan Society for the Promotion of Science
It was measured according to the chemical analysis method for magnesia clinker. B2O3 was measured by dissolving the sample in hydrochloric acid according to the boron trioxide quantitative method (1) direct method in the analytical method for silicate glass [JIS R3105 (1981)].

C1 uses the Polhardt method, in which the sample is dissolved in nitric acid, a certain amount of silver nitrate is added, and an iron alum solution is used as an indicator.
It was determined by back titration with 43CN solution.

3) Calcia/magnesia crystal diameter Ful1man method (J, of Metals, 447
．． 1953>. That is, a straight line is arbitrarily drawn on a photograph of the polished surface, the line segments cut by the grain boundaries on the calcia and magnesia crystals are averaged, and the average value is multiplied by 1.5 to obtain the calcia and magnesia crystals. It was taken as the magnesia crystal diameter. In calculating the average value, 100 or more line segments were used for each of calcia and magnesia crystals for one sample.

4) Natural weight increase rate As a measure of digestion resistance, clinker classified into 2.0θ to 3.36 mm was left standing in air at a relative humidity of 65% and a temperature of 20"C for 20 days, and the weight increase was measured. , the increase in weight relative to the original weight is expressed as a percentage.

5) Particle size of calcium hydroxide and magnesium hydroxide The water slurry was classified using a sieve, and the portion remaining on the sieve was dried, then weighed and expressed as a percentage by weight based on the total dry matter.

[Example] Preparation of raw material slurry Add 100 Q of quicklime per 1 liter of water at 60°C, hydrate by stirring for 1 hour, classify in water using 0.5 mm rJ6 to remove coarse particles, and remove calcium hydroxide. A slurry (A>) was obtained. Part of it was classified using a liquid cyclone to separate and remove coarse particles to obtain a calcium hydroxide slurry (B). (A)
The particle size distribution of the solid content of ) and (B) was as shown in Table 1.

Table 1 Next, calcium hydroxide slurry (A) was gradually added to the seawater after decarboxylation treatment while stirring until the DH reached 10.8 to produce magnesium hydroxide, which was then sedimented and concentrated. A crude magnesium hydroxide slurry having an MgO content of 40 MM was obtained. After adding 20 times the volume of water to a portion and stirring, it was sedimented and concentrated to obtain 1 q of magnesium hydroxide slurry (A> with an MQO equivalent of 200 (7/m). Next, the remainder of the crude magnesium hydroxide slurry was Classified with a liquid cyclone, part of it is sedimented and concentrated as it is, and the other part is mixed with 20 times the volume of water and stirred, then sedimented and concentrated to form a magnesium hydroxide slurry (B ) and (C) were obtained.

The particle size distribution of the solid content of each magnesium hydroxide slurry was determined as shown in Table 2.

Table 2 Examples 1 to 4 MC10 of calcium hydroxide slurry (B) and magnesium hydroxide slurry (C) was 30.40 based on the fired product.
．． After mixing, the cake was vacuum filtered and 1 q was dried in a box type dryer. A molded body was made using an Amsler molding machine. Table 3 shows the chemical composition of the obtained molded body on a scorching heat basis, the C1 content ω on a dry basis, and the density on a dry basis. This compact was crushed into pieces of 5 mm or less and fired at 1700'C for 1 hour.

Table 4 shows the physical properties of the calcia-magnesia clinker obtained by cooling. Reflection micrographs of the polished surfaces of the clinkers of Examples 1 to 4 obtained are shown in 1-a.
- Shown in Figure 1-d.

Example 5 Calcium hydroxide slurry (B) and magnesium hydroxide slurry (C) were blended so that MgO was 30% by weight in the fired product We, and after mixing, a filter press was used to prepare 30kl; l/Cm' A cake was obtained by pressure filtration. Table 3 shows the chemical composition of the obtained cake on a burning basis, the C1 content on a dry basis, and the density on a dry basis.

Table 4 shows the physical properties of the calcia-magnesia clinker obtained by firing and cooling in the same manner as in Example 1.

Example 6 The calcia-magnesia clinker of Example 2 was converted into CO2
700'C in a gas containing 30% partial pressure.

The treatment was carried out for 20 minutes. FIG. 2 shows an electron micrograph of the surface of the calcia-magnesia clinker obtained by cooling. In addition, these clinkers are 2.00 mm to 3.0 mm.
It was classified into 66 mm, and the relative density was 65%, and the weight increase was measured by standing in air at a temperature of 20'C. The relationship between elapsed days and weight increase rate is plotted in FIG. For comparison, an untreated sample (Example 2) was also plotted. Here, the O mark corresponds to Example 2, and the * mark corresponds to Example 6.

Comparative Example 1 Calcium hydroxide slurry (B) and magnesium hydroxide slurry (C) were mixed with MCJO of 7% by weight based on the fired product.
Firing was performed in the same manner as in Example 5, except that the ingredients were blended so as to be as follows. The chemical composition of the cake on a burning basis, the CI content on a dry matter basis and the density on a dry matter basis are shown in Table 3.

Table 4 shows the physical properties of the calcia-magnesia clinker obtained by cooling.

Comparative Example 2 Calcium hydroxide slurry (B), magnesium hydroxide slurry (C), and a ferric chloride aqueous solution of Sarani reagent were mixed to have MCl0 of 30% by weight and Fe2O3 of 0.30% based on the fired product.
The same procedure as in Example 5 was carried out except that the ingredients were blended and mixed in such a manner as to achieve a weight percentage. The chemical composition of the cake on a burning basis, the 01 content on a dry basis and the density on a dry basis are shown in Table 3. Table 4 shows the physical properties of the calcia-magnesia clinker obtained by cooling.

Comparative Example 3 The same procedure as in Example 1 was carried out, except that the cake obtained by vacuum filtration was dried without pressure molding, and the dried product obtained was directly fired. The chemical composition of the cake on a burning basis, the CI content on a dry matter basis and the density on a dry matter basis are shown in Table 3. Table 4 shows the physical properties of the calcia-magnesia clinker obtained by cooling.

Comparative Example 4 The same procedure as in Example 5 was carried out except that the calcium hydroxide slurry (B) and the magnesium hydroxide slurry (B) were mixed so that the MgO content was 30% by weight based on the fired product. The chemical composition of the cake on a burning basis, the 01 content on a dry basis and the density on a dry basis are shown in Table 3.

Table 4 shows the physical properties of the calcia-magnesia clinker obtained by cooling.

Comparative Example 5 The same procedure as in Example 5 was carried out except that the calcium hydroxide slurry (A) and the magnesium hydroxide slurry (A> were blended so that the MgO content was 30 heavy based on the baked product. The chemical composition and the C1-containing material on a dry basis and the density on a dry basis are shown in Table 3.The physical properties of the calcia-magnesia clinker obtained by cooling are shown in Table 4.

Table 3 Tables 1 and 4 [Effects of the Invention] According to the present invention, 1 q of calcia-magnesia clinker having high purity, high density and excellent digestibility is produced.

This product is expected to be used in a variety of fields, including large-sized materials for steel-making furnaces due to its superior properties.

[Brief explanation of drawings]

Figures 1-8 to 1-d are reflection micrographs of the polished surface of the calcia-magnesia clinker of the present invention, Figure 2 is an electron micrograph of the surface of the clinker of Example 6, and Figure 3 is the book. Digestion resistance (weight increase rate) of the clinker of the invention
This is a graph showing. Patent applicant Shin Nippon Chemical Industry Co., Ltd. agent Patent attorney Hidetake Komatsu Agent Patent attorney Hiroshi Asahi 4= J-a; 11, J 0jJm

Claims (6)

[Claims] (1) The composition is based on scorching heat, expressed in weight %, CaO + M
A calcia-magnesia clinker characterized in that gO is 98.5 or more, MgO is 10 to 75, the relative density is 96% or more, and the average particle size of calcia crystals is 15 μm or less. (2) The calcia-magnesia clinker according to claim (1), wherein the average particle size of magnesia crystals is 15 μm or less. (3) The composition is CaO+M expressed in weight percent on a scorching heat basis.
gO98.8 or more MgO10-75 Less than Fe_2O_30.2 Other impurities Less than 1.0 However, among the above impurities, less than B_2O_30.4, less than SiO_20.4, less than Al_2O_30.15, as described in claim (1) Calcia/magnesia clinker. (4) The calcia-magnesia clinker according to claim (1) or (2), the surface of which is composed of magnesia and calcium carbonate. (5) When the coarse particles in the calcium hydroxide raw material and magnesium hydroxide raw material are removed, the particle size distribution is 44 μm or less.
These high-purity raw materials, in which 90% by weight or more is 25 μm or less by weight, are mixed and molded to have a density of 1.
A method for producing a calcia-magnesia clinker, which comprises forming a compact of 2 g/cm^3 or more and firing the compact. (6) Calcia-magnesia clinker obtained by firing in a gas containing 5% or more of CO_2 partial pressure.
The method for producing a calcia-magnesia-based clinker according to claim (5), wherein CaO on the surface of the clinker is carbonated by heating at 550 to 750° C. for more than a minute.