JPH06107450A - Production of magnesia clinker - Google Patents

Abstract

PURPOSE:To inexpensively produce a magnesia clinker containing >=99.0wt.% MgO and <=0.02wt.% B2O3, having 2.2-5.0 CaO/SiO2 mol ratio, >=3.40 g/cm<3> bulk density and >=80mum average particle diameter of periclase crystal and excellent in hot deflective strength and corrosion resistance. CONSTITUTION:At the time of producing the magnesia clinker containing >=99.0wt.% MgO and <=0.02wt.% B2O3 and having >=3.40g/cm<3> bulk density and >=80mum average particle diameter of periclase crystal from a burning raw material, which is a calcined magnesia pellet having >=99.0wt.% MgO, 0.30-0.60wt.% CaO, 0.06-0.12wt.% B2O3 and 2.2-5.0 CaO/SiO2 in ignition residual composition, the calcined magnesia pellet is burnt at >=2100 deg.C in the state that the each of the magnesia pellets is directly in contact with a high temp. combustion gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia clinker used for basic refractories and having high hot strength. Furthermore, the CaO / SiO ₂ molar ratio is 2.2 to
It is in the range of 5.0, the purity of MgO is as high as 99.0% by weight or more, the content of B ₂ O ₃ is as low as 0.02% by weight or less, and the average particle size of periclase crystals is 80 μm or more. The present invention relates to a method for inexpensively producing a clinker.

[0002]

2. Description of the Related Art CaO / SiO of magnesia clinker
_{In the} range where the ₂ molar ratio is larger than 2.0, the hot pile bending strength of the brick made from this becomes maximum, and the CaO / SiO ₂ molar ratio at which the maximum value of the hot pile bending strength of this brick is obtained is It is already known that the high-purity magnesia having a smaller content of SiO _{2 has} a higher molar ratio of 2 → 3 → 4. It is well known that the corrosion resistance of magnesia clinker is superior as the purity of MgO is higher, the particle size of periclase crystals is larger, and the content of B ₂ O ₃ is smaller.

On the other hand, the bulk density of magnesia clinker increases as the B ₂ O ₃ content decreases, and the bulk density of CaO /
The higher the SiO ₂ molar ratio is, the higher the molar ratio is 2.
It is also known that it is difficult for the bulk density to increase in the vicinity. Therefore, the conventional MgO content is 99.0% by weight or more and Ca
In order to produce a large crystal magnesia clinker with a high bulk density and an O / SiO ₂ molar ratio of higher than ₂ , B _{2 is used in} the raw material stage before firing as in Japanese Patent Publication No. 22007/1990.
Although a method of reducing the O ₃ content to 0.05% by weight or less has been carried out, there is a problem that the cost is remarkably increased because a large amount of seawater is treated.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied to solve the above problems, and as a result, in producing a magnesia clinker from pellets of calcined magnesia, a firing method unique to the pellets of calcined magnesia was used. It has been found that by adopting, the hot pile strength and the corrosion resistance are improved.

[0005]

[Means for Solving the Problems] That is, according to the present invention, the chemical composition after thermal loss is 99.0 wt% or more of MgO, CaO
0.30 to 0.60 wt%, B ₂ O ₃ 0.06~0.1
2% by weight and CaO / SiO ₂ molar ratio of 2.2-5.
Mg from calcination magnesia pellet firing raw material in the range of 0
O 99.0 wt% or more, B ₂ O ₃ 0.02 wt% or less,
In producing a magnesia clinker having a bulk density of 3.40 g / cm ³ or more and an average particle size of periclase crystals of 80 μm or more, high temperature combustion gas directly contacts the periphery of each pellet of the calcined magnesia. The method for producing a magnesia clinker is characterized by firing at a high temperature of 2100 ° C. or higher while flowing.

The present invention will be described below. The calcined raw material which is the pellet of calcined magnesia of the present invention can be obtained by combining known methods as follows. When producing magnesium hydroxide by the reaction of seawater or brine and lime, by adding a slight excess of calcium hydroxide to magnesium ions contained in seawater, the B ₂ O ₃ content at the time of ignition loss Of 0.06 to 0.20 wt% magnesium hydroxide can be obtained.

In order to bring CaO to the range of 0.30 to 0.60% by weight of the present invention, almost all of CaO can be obtained by selecting the lime raw material and purifying and washing the magnesium hydroxide produced by the reaction. In the range of low content, for example, the above-mentioned magnesium hydroxide disclosed in Japanese Patent Publication No. 57-31547 is calcined to obtain hydrated CaO.
The composition can be adjusted by mixing a small amount of magnesium hydroxide with the above magnesium hydroxide.

Also, CaO / SiO₂The molar ratio is 2.2
SiO to be in the range of 5.0₂0.10 to 0.30
Addition of wt% is also within the range achieved hitherto. the above
Magnesium hydroxide is calcined in a multi-stage calciner, for example.
And can be pelletized with briquette machine
It Calcinated magnesia pellets thus obtained
The firing raw material has a chemical composition of MgO 99.0 after ignition loss.
Weight% or more, CaO 0.30 to 0.60 weight%, B ₂O
₃0.06-0.12 wt% and CaO / SiO₂Mo
It is necessary that the rule ratio be in the range of 2.2 to 5.0.

The above-mentioned loss on ignition means that 1 g of a sample is weighed in a platinum crucible, ignited at about 1000 ° C. for about 30 minutes, cooled and then weighed, and this operation is repeated until the weight becomes constant. (JIS R 2212
-55), the above-mentioned chemical composition subjected to ignition loss refers to a chemical composition in a weight obtained by subtracting the weight lost by ignition from the weight before calcination.

The shape of the pellets of the calcined magnesia may be spherical, angular, almond-shaped, etc.
The size is preferably such that the minor axis thereof is in the range of 8 to 50 mm in order for the high temperature combustion gas to come into direct contact with the periphery of each pellet. Furthermore, when a soda compound and / or a potassium compound are added, they can be added before calcination in this multi-stage calcination furnace or before briquette after calcination. This soda compound and / or potassium compound is
It combines with B ₂ O ₃ in the firing raw material to lower the evaporation temperature of B ₂ O ₃ . As a result, B ₂ O ₃ in the firing raw material was 0.1
When the content is 2% by weight or more and 0.20% by weight or less, the magnesia clinker of the quality intended in the present invention can be obtained.
Further, when B ₂ O ₃ in the firing raw material is 0.12% by weight or less, compared to the case where soda or potassium compound is not added,
Higher bulk density clinker is obtained. B ₂ O
_{Since 3} has a negative effect on increasing the bulk density of the clinker as described above, it is desirable to remove 3 as early as possible in the sintering process.

Next, it is necessary to perform firing at a high temperature of 2100 ° C. or higher in a state where the respective firing raw materials and the high-temperature combustion gas flow in direct contact with each other around the firing raw materials which are the pellets. This state of firing can be industrially carried out in a state in which a high temperature gas is flowing in the packed bed of the firing raw material, for example, with a shaft kiln or a sintering machine disclosed in JP-A-55-46318. Even in the firing method of directly contacting with the high-temperature combustion gas, since the firing only contacting the surface with the high-temperature gas in the state where the firing material is deposited does not always come into contact with the high-temperature gas, the firing state of sometimes contacting only, For example, in the rotary kiln firing or the tunnel kiln firing, since the high temperature combustion gas cannot directly contact the periphery of the pellet, the effect of the present invention cannot be sufficiently exhibited.

For baking into a bulky clinker
Is B₂O₃The stage where the bulk density is still low in the initial stage of firing
Must be evaporated off on the floor. Early stage of sintering
In the stage, the temperature of the firing raw material is also relatively low, and B₂O₃Steam of
Atmospheric pressure is also low. However, the gas around the firing raw material of the present invention
Evaporated B in a state where it constantly flows while contacting₂O
₃Is always removed with the gas, resulting in
B₂O₃Even if the steam pressure is low
B₂O₃Can be removed by evaporation. However, conventional
In the firing method in which the firing raw material is deposited, the B on the surface is
₂O₃Evaporative removal of B progresses, but B₂O₃Steam of
Becomes saturated and evaporation removal does not proceed to high temperature
Become.

Further, in a state where the high temperature combustion gas is flowing in direct contact with the periphery of each pellet firing material, 21
It is presumed that when the temperature is higher than 00 ° C, it may be due to the direct contact with the combustion gas with high steam partial pressure. However, the growth of periclase crystals is remarkable as compared with the case where the calcined raw material is in a deposited state, and MgO 99.0 wt. %, The average crystal grain size becomes 80 μm or more.

In order to evaporate and remove B ₂ O ₃ before the firing raw material is sintered and the bulk density becomes high, the firing raw material is heated to a temperature at which the vapor pressure of B ₂ O ₃ becomes high in the shortest possible time. It is effective to do. For this purpose, it is preferable that the temperature rising rate is 15 ° C./minute or more. This rate of temperature increase is especially 800
It is important in the range of ℃ to 1600 ℃, and in this temperature range 1
Good results are obtained when kept at 5 ° C / min or higher.

[0015]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. The measurement of each test item in Examples and Comparative Examples was performed by the following measuring method. (1) Chemical composition The sample was heated and dissolved with hydrochloric acid, and then analyzed with a plasma emission spectrophotometer (ICPA). (2) Bulk Density (BD) Proposal by the Japan Society for the Promotion of Science 124th Committee Test Method Subcommittee Apparent porosity (AP) of magnesia clinker,
The apparent specific gravity (AD) and the bulk specific gravity were measured. (3) Average particle size of periclase crystals Gakushin method 3. The size of the periclase in the magnesia clinker was measured and the method described therein was used. (4) Hot bending strength (Kg / cm ² ) The clinker was crushed and classified, and then the clinker in the following particle size range was blended in the following blending ratio.

3.36-2.00 mm 20% by weight 2.00-1.00 mm 20% by weight 1.00-0.25 mm 20% by weight 0.25 mm or less 40% by weight Magnesium sulfate is used as a binder in this composition. Mix and
It was molded into a rectangular parallelepiped shape of 25 × 25 × 150 mm at a molding pressure of 1 ton / cm ² . Next, at 1800 ° C in the LPG-O ₂ furnace
A test piece was obtained by firing for 2 hours.

These were subjected to a hot bending strength measurement (Kg / cm ² ) at 1400 ° C. using a bending strength measuring device integrated with an electric furnace.
Was measured.

[0018]

Example 1 A calcium hydroxide slurry was obtained by adding 6 equivalent% excess of calcium hydroxide slurry to decarboxylated seawater with respect to equivalents of Mg ions. This was washed with fresh water, filtered, dried, and then calcined at 900 ° C. to obtain magnesium oxide powder A having the composition of Table 1 in terms of oxide.

Next, this powder was hydrated and washed in an acidic aqueous solution having a pH of 3 or less to remove the Ca component to obtain a magnesium hydroxide slurry. This was filtered, dried, and then calcined at 900 ° C. to obtain magnesium oxide powder B having the composition of Table 1 in terms of oxide. Next, in the magnesium oxide powder B,
Calcium oxide powder having a purity of 99% by weight or more was added and mixed to adjust the CaO content to 0.55% by weight. This is a briquette machine with a major axis of 40 mm, a minor axis of 24 mm and a thickness of 20.
mm almond shape with a bulk density of 2.0 g / cm
² pellets were obtained.

These pellets were placed in a firing furnace at 2300
Baked at ° C. The temperature raising process at this time is shown in FIG. During firing, the combustion gas flows between the pellets from the bottom upwards, with the individual pellets being placed in a gas stream. Physical properties of clinker obtained by cooling and hot bending strength (K
The g / cm ² ) is shown in Table 2.

[0021]

[Example 2] The same procedure as in Example 1 was carried out except that the washing of magnesium hydroxide in Example 1 was replaced by the use of a solution excluding previously dissolved SiO ₂ instead of using fresh water. . Table 2 shows the physical properties and hot bending strength (Kg / cm ² ) of the clinker obtained by cooling.

[0022]

Comparative Example 1 A calcium hydroxide slurry was obtained by adding the same amount of calcium hydroxide slurry to Mg ions to decarbonated seawater. A cake obtained by washing this with fresh water, filtering and drying it is calcined at 900 ° C., and magnesium oxide powder C having the composition shown in Table 1 in terms of oxides.
Got

This powder was molded with a briquette machine,
Pellets having a bulk density of 2.0 g / cm ² were obtained. Using the same firing furnace as in Example 1, firing was performed in the same temperature rising process. Table 2 shows the physical properties and hot bending strength (Kg / cm ² ) of the clinker obtained by cooling.

[0024]

[Example 3] In Comparative Example 1, the magnesium oxide powder after calcination was replaced with Na ₂ CO ₃ powder of 0.4 in terms of MgO.
The same procedure as in Comparative Example 1 was performed, except that the mixture was added by weight% and mixed and then molded. Table 2 shows the physical properties and hot bending strength (Kg / cm ² ) of the clinker obtained by cooling.

[0025]

Comparative Example 2 The crucible made of magnesia was filled with the pellets used in Example 1 and the lid was closed. Then, the temperature was raised to 2200 ° C. at a heating rate of 4 hours using an LPG-O ₂ furnace, and then 1 Firing was performed at the same temperature for a time. At this time, the temperature rise process is 800 ℃
To 1600 ° C. for 1 hour. Physical properties of clinker obtained by cooling and hot bending strength (Kg /
cm ² ) is shown in Table 2.

[0026]

Comparative Example 3 The pellets used in Example 1 were fired at a maximum temperature of 2100 ° C. using a rotary kiln. At this time, the heating rate of the pellets was 2100 ° C. for 5 hours. Table 2 shows the physical properties and hot bending strength (Kg / cm ² ) of the clinker obtained by cooling.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

According to the manufacturing method of the present invention, MgO9
It has a high purity of 9.0 wt% or more and B ₂ O ₃ 0.02 wt% or less, a CaO / SiO ₂ molar ratio of 2.2 to 5.0, and a bulk density of 3.40 or more. Thus, a magnesia clinker having an average particle size of periclase crystals of 80 μm or more and having high hot bending strength and excellent corrosion resistance can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a temperature rising process during firing in Examples 1, 2, 3 and Comparative Example 1.

Claims (3)

[Claims] 1. A chemical composition whose ignition loss is reduced is MgO99.
0% by weight or more, CaO 0.30 to 0.60% by weight, B ₂
O ₃ 0.06 to 0.12 wt%, and CaO / SiO ₂
MgO 99.0 wt% or more, B ₂ O ₃ from the calcined magnesia pellet firing raw material having a molar ratio of 2.2 to 5.0
In producing a magnesia clinker having a bulk density of 0.02% by weight or less, a bulk density of 3.40 g / cm ³ or more, and an average particle size of periclase crystals of 80 μm or more, the circumference of each pellet of the calcined magnesia is A method for producing a magnesia clinker, which comprises calcination at a high temperature of 2100 ° C. or higher in a state where a high-temperature combustion gas is flowing in direct contact. 2. The method for producing a magnesia clinker according to claim 1, wherein the temperature is raised from room temperature to a high temperature of 1800 ° C. at a rate of 15 ° C./min or more when firing at a high temperature of 2100 ° C. or higher. . 3. A calcined magnesia pellet firing raw material is B
₂ O ₃ 0.06 to 0.20 wt% and 0.05 to 1.50 wt% N in Na ₂ O and / or K ₂ O composition.
The method for producing a magnesia clinker according to claim 1, which contains a soda compound such as a ₂ CO ₃ , NaHCO ₃ , and NaOH and / or a potassium compound such as K ₂ CO ₃ , KHCO ₃ , and KOH.