JPH0329016B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnesia clinker with increased density. As steel manufacturing technology advances, the physical properties required for refractories are becoming increasingly strict. Regarding magnesia clinker used as a steelmaking furnace material, it is desired to develop a magnesia clinker with high purity, high density, and large periclase crystal grains. One of the reasons behind this seems to be that the demand for magnesia-carbon bricks has recently increased rapidly. Magnesia carbon brick is an unfired brick made by mixing magnesia clinker and graphite and molding it under pressure. have. The reason for this is thought to be that graphite acts as a cushioning material for magnesia clinker or has poor wettability with slag. The wear mechanism of the magnesia-carbon brick is therefore believed to be due to the gradual erosion of the magnesia clinker portion by the slag, rather than the graphite portion being attacked by the slag. It is said that magnesia-carbon bricks using magnesia clinker with high purity, high density, or in addition large periclase grains are actually worn out more slowly by using such magnesia clinker. An object of the present invention is to provide a magnesia clinker having large periclase grains with high density and increased density, and with reduced micropores inside the crystals. Other objects and advantages of the invention will become apparent from the description below. According to the invention, such objects and advantages of the invention are such that, expressed in weight percent, as oxides, MgO 97.0% or more, CaO 1.2-1.8%, SiO ₂ 0.21-0.6%, Fe ₂ O ₃ 0.3-0.8 % Al ₂ O ₃ 0.15% or less, B ₂ O ₃ 0.1% or less, the bulk density is 3.48 g/cm ³ or more, and the particle size is
This is achieved by a magnesia clinker with an increased density, characterized in that periclase grains of 125μ or more account for more than 8%. The magnesia clinker of the invention preferably has periclase grains with an average grain size of at least 90μ. In addition, the magnesia clinker of the present invention preferably has 37% periclase crystal grains with a grain size of 100μ or more.
This accounts for the above. According to the present invention, the magnesia clinker of the present invention is produced by adding a water-soluble iron compound to a decarbonated aqueous solution of seawater, bittern or brine, and then adding dolomite calcined product or lime or their hydrates to produce mainly magnesium hydroxide. It is produced by a production method characterized by producing a precipitate consisting of the following: and then calcining the obtained precipitate. The magnesium-containing aqueous solution used in the above method is a decarbonated aqueous solution of seawater, bittern or brine. Such a decarboxylated aqueous solution can be obtained by adding an alkaline compound such as lime or calcium hydroxide or a strong acid such as sulfuric acid to seawater, bittern or brine according to known methods. It is well known that magnesium hydroxide is precipitated by adding an alkaline compound such as calcium hydroxide to the decarbonated aqueous solution, but in the above method, before adding an alkaline compound such as lime to the decarbonated aqueous solution, It is essential to add a ferrous iron compound. If a water-soluble iron compound is added after adding an alkaline compound such as lime, it is at least very difficult to produce magnesia clinker having the increased density targeted by the present invention. It has been known that an iron compound is added as a sintering promoter to magnesium hydroxide derived from seawater to promote sintering of the magnesium oxide. However, this method replaces Fe ₂ O ₃ formed from iron compounds by calcination with CaO and impurities that inevitably exist in magnesium hydroxide originating from seawater.
Al ₂ O ₃ and calcium ferrite (2CaO・Fe ₂ O ₃ )
and bromerite (4CaO・Al ₂ O ₃・Fe ₂ O ₃ )
This is a method of accelerating the sintering of magnesium oxide by forming a compound that melts at a low temperature (hereinafter referred to as a low-melting compound), and utilizing the fact that the low-melting compound forms a liquid phase during firing. With this method, it is therefore not possible to produce magnesia clinker with high density and high purity, and it is not possible to obtain large periclase crystals. According to the above method in which the water-soluble iron compound is added before adding the alkaline compound such as lime, the density is increased compared to the conventional method in which the water-soluble iron compound is added after adding the alkaline compound such as lime. The reason why magnesia clinker is obtained is not necessarily clear, but according to the above method, when lime, etc. is added to a decarbonated aqueous solution containing a water-soluble iron compound, fine iron hydroxide particles are first formed, and then water is released using these as nuclei. This is thought to be because magnesium oxide is produced, and therefore water-soluble iron compounds have an advantageous effect in producing precipitation of magnesium hydroxide, but on the other hand, there is little opportunity to produce low-melting compounds during calcination. The water-soluble iron compound may be an inorganic or organic acid salt of divalent iron or trivalent iron. Inorganic acid salts, especially mineral acid salts, are preferred iron compounds. Examples of such water-soluble iron compounds include inorganic acid salts such as iron chloride, iron sulfate, iron nitrate, iron phosphate, acetate, iron benzoate, p-toluenesulfonate, and the like. Water-soluble iron compounds have a Fe ₂ O ₃ equivalent value of 0.3 to 0.3 based on magnesia clinker.
It can be used in amounts ranging from 0.8% by weight. If the Fe ₂ O ₃ content is less than 0.3% by weight, the bulk density of the obtained magnesia clinker tends to decrease, and the proportion occupied by Pericles crystal grains having a grain size of 125 μm or more tends to decrease, which is not preferable. In addition, this refractory material made of magnesia clinker is used in places where rapid heating and cooling are repeated at extremely high temperatures, and under such severe usage conditions, Fe solid-solved in the clinker's periclase crystals is removed. As ₂ O ₃ increases in Fe ₂ O ₃ content, dissolution begins to occur, deteriorating the spalling resistance of the refractory material, and leading to an increase in the rate of erosion of slag. Therefore, it contributes to the improvement of bulk density and coarsening of periclase crystals.
There is also an upper limit to the Fe ₂ O ₃ content. Moreover, even if the Fe ₂ O ₃ content exceeds 0.8% by weight, the bulk density does not increase accordingly, nor does the proportion of periclase crystal grains with a grain size of 125 μm or more increase significantly. Under harsh usage conditions, the above-mentioned drawbacks begin to appear. The addition of an alkaline compound such as lime to a decarbonated aqueous solution containing a water-soluble iron compound is carried out so that the pH of the aqueous solution becomes about 10.8 or higher, which produces magnesium hydroxide, but preferably the pH is 11 to 12. It will be done. When the pH of the aqueous solution exceeds 10.8, the alkaline compound will be added in some excess, thereby producing magnesium hydroxide with a lower boron content, thus also resulting in Magnesia clinker with low boron content can be produced.
When the pH is set to 11 to 12, as mentioned above, the alkaline compounds such as lime in this reaction liquid are somewhat excessive, so before separating the formed precipitate mainly consisting of magnesium hydroxide from this reaction liquid. It is preferable to react this reaction solution with a decarbonated aqueous solution of seawater, bittern or brine to dissolve excess alkaline compounds such as lime. In this case, it is possible to obtain a precipitate of magnesium hydroxide which not only contains boron but also has a reduced calcium content. If boron, which is unavoidably introduced into magnesia clinker as an impurity due to the above-mentioned production method, exceeds 0.1% by weight in terms of B ₂ O ₃ , it will have a negative effect on the sinterability of the clinker and In addition, if calcium exceeds 1.8% by weight calculated as CaO, it will lead to a decrease in MgO purity, which will further affect the hot properties of the clinker. This is undesirable due to adverse effects. On the other hand, the substance that forms between the periclase crystals is a dicalcium silicate (2CaO・SiO ₂ ) phase or a tricalcium silicate (3CaO・SiO ₂ ) phase, and in order to form a phase that fills the intercrystals, at least 1.2% by weight of CaO is required. According to the above method, the produced precipitate mainly consisting of magnesium hydroxide is separated, for example, with a thickener, washed with water if necessary, and after pressure molding, it is fired. Firing is usually at a temperature of 1900 to 2100℃ for about 15 minutes to 1
Time will be carried out. Pressure molding is preferably 2 to 3
It is carried out under pressure of tons/cm ² to give a compact with a density of about 1.5 to 1.7 g/cm ³ . According to the above method, before calcination, _{a SiO 2 source} such as water glass is added to the magnesium hydroxide precipitate in an amount of 0.21 to 0.6% by weight in terms of SiO ₂ based on magnesia clinker. , preferably in an amount of 0.5% by weight or less. If the amount of SiO ₂ added is less than 0.21% by weight, the amount of SiO ₂ added as a sintering aid will be insufficient, causing problems in the sinterability of the clinker. On the other hand, when the amount of SiO ₂ added is more than 0.6% by weight, the total content of impurities in the clinker increases and merwinite (MgO・3CaO・2SiO ₂ ) is formed near the semi-calcination temperature.
Low melting compounds such as Therefore, during firing, the low-melting compound forms a liquid phase, which inhibits the growth of periclase crystals. Furthermore, Al ₂ O ₃ , which is a component that inevitably exists as an impurity in magnesium hydroxide derived from seawater, tends to form a low-melting compound with other impurities. Therefore, the Al ₂ O ₃ content is 0.15
It is desirable that the content be as small as possible, no more than % by weight.
By doing so, a magnesia clinker with higher density can be obtained. In order to make the above method easier to understand, preferred embodiments up to the formation of magnesium hydroxide precipitation in the above method will be described as follows. For example, an aqueous solution of iron sulfate is added to a carbonated aqueous solution of seawater, and then lime is added to produce a reaction solution with a pH of 11.2 to 11.8, and CaO is 2 to 4% by weight on a scorching basis, and B ₂ O ₃ is 0.05 to 0.1% by weight. % Fe ₂ O ₃ 0.3 to 0.8% by weight of a precipitate mainly consisting of magnesium hydroxide, and before separating this precipitate from the reaction solution, for example, a decarbonated aqueous solution of seawater is added to the reaction system to adjust the pH.
9.8 to 10.8 to form a precipitate mainly consisting of magnesium hydroxide, including CaO 1.8 to 3.0% by weight, B ₂ O ₃ 0.05 to 0.1% by weight, Fe ₂ O ₃ 0.3 to 0.8% by weight, based on scorching heat, and then washed with water if necessary. As a result, a precipitate mainly consisting of oxides and magnesium hydroxide of 97% by weight or more of MgO, 1.2 to 1.8% by weight of CaO, 0.1% by weight or less of B ₂ O ₃ , and 0.3 to 0.8% by weight of Fe ₂ O ₃ is produced. Thus, according to the above method, the above magnesia clinker of the present invention can be produced. For example, it has a bulk density of 3.48 g/cm ³ or more, and has periclase crystal grains of about 100 μ or more,
A coarse grained magnesia clinker with reduced micropores inside the crystal can be produced. The presence of pores affects the growth of periclase crystals, and when the bulk density is lower than 3.48 g/cm ³ , the presence of pores increases and periclase crystals do not grow sufficiently. In addition, the particle size
Occupancy rate of periclase crystals with a diameter of 125μm or more is 8
%, the obtained magnesia clinker tends to have poor erosion resistance against slag. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited in any way by the Examples. In addition, various physical property values in this specification were measured by the following methods. Chemical composition Measured according to the "JSPS 1: Chemical analysis method of magnesia clinker" determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science (see 1981 Edition Refractory Handbook). In particular, the analysis of B ₂ O ₃ was carried out using the curcumin method (absorption photometry), which was adopted as the Kamishin method under consideration by the same committee. Bulk Density (Bulk Specific Gravity) “JSPS Method 2 Measuring Method of Apparent Porosity, Apparent Specific Gravity and Bulk Specific Gravity of Magnesia Clinker” (1981 Edition Refractory Notebook) determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science (see ),
It was calculated using the following calculation formula. Bulk specific gravity = W ₁ / W ₃ − W ₂ ×S W ₁ : Dry weight of clinker (g) W ₂ : Weight of sample saturated with white kerosene in white kerosene (g) W ₃ : Sample saturated with white kerosene Weight (g) S: Specific gravity of white kerosene at measurement temperature (g/cm ³ ) Average particle size of periclase crystals Considering the particle size distribution of clinker, particles with a particle size of about 5 to 10 mm are randomly taken out. This is ground and polished, and the polished surface is observed using a reflection microscope. Photographs of three representative areas are taken at 50x magnification, enlarged to 3x and printed on photographic paper. The particle sizes of all the periclase particles in the three photographs are measured, and the average value is taken as the average particle size of the periclase crystals. In addition, in order to show the distribution of crystal grain size, the proportion occupied by crystals, the proportion occupied by particles of 100μ or more, and
The proportion of particles larger than 125μ was determined. Examples 1 to 3 Milk of lime was added to seawater to reduce dissolved carbonate ions (80ppm CO ₂ equivalent) in seawater to 10ppm CO ₂ equivalent
It was reduced to This decarbonated water treated seawater11.8
The _Fe2O3 content in the final product _magnesia clinker is approximately 0.3% by weight, 0.45% by _weight .
After adding to weight% or 0.6% by weight,
Add 258ml of lime milk (CaO concentration 12g/100ml) and adjust the pH.
Magnesium hydroxide was produced under conditions with a value of 11.3-11.5. Next, the supernatant layer was separated and the decarboxylated seawater was added to the concentrated magnesium hydroxide slurry.
660 ml was added and the reaction was carried out again under the condition of pH value 10.0 to 10.4. This operation was repeated 20 times. The magnesium hydroxide finally produced in this way is
Rinse with decarbonated tap water and use scorching heat standards.
It was possible to obtain magnesium hydroxide containing an iron compound with an MgO content of 97.5% by weight or more. Table 1 shows the chemical composition of this magnesium hydroxide (numbers are in weight percent).

[Table] Water glass was added to each of the magnesium hydroxides shown in Table 1 in an amount of about 0.4% by weight based on scorching heat, and then dried until the water content reached 8% by weight. The dried product is pressure molded at a pressure of 3t/ ^cm2 ,
It was fired at 2000℃ in an oxygen-propane gas furnace. The chemical composition, bulk density, and average particle size and distribution of periclase crystals of the obtained sintered body are shown in Table 2. Note that FIG. 1 of the accompanying drawings shows a microscopic photograph of the sintered body of Example 3.

[Table] Example 4 The magnesium hydroxide containing the iron compound obtained in Example 3 was dried to a water content of 8% by weight without adding water glass. 3t/3t of the dried material
It was press-molded at a pressure of cm ² and fired at 2000°C in an oxygen/propane gas furnace. Table 3 shows the chemical composition, bulk density, and average particle size and distribution of periclase crystals of the obtained sintered body. Further, FIG. 2 of the accompanying drawings shows a microscopic photograph of the sintered body.

[Table] Comparative Example 1 Seawater decarboxylated using the same method as Examples 1 to 3
Add 258ml of lime milk (CaO concentration 12g/100ml) to 11.8.
and produced magnesium hydroxide under the condition of pH value 11.3-11.6. Next, the supernatant layer was separated, and 660 ml of decarboxylated seawater was added to the concentrated magnesium hydroxide slurry, and the mixture was reacted again under the condition of a pH value of 10.0 to 10.4. This operation was repeated 20 times.
The magnesium hydroxide finally produced in this way was washed with decarboxylated tap water to obtain magnesium hydroxide with an MgO content of 97.5% by weight or more based on scorching heat. Water glass was added to this magnesium hydroxide in an amount of about 0.4% by weight based on scorching heat, and then dried until the moisture content was 8% by weight. the dried food
It was pressure molded at a pressure of 3t/cm ² and fired at 2000°C in an oxygen/propane furnace. Table 4 shows the chemical composition, bulk density, and average particle size and distribution of periclase crystals of the obtained sintered body. FIG. 3 of the accompanying drawings shows a microscopic photograph of the sintered body.

[Table] Comparative Example 2 0.4% by weight and 0.45% by weight of water glass and iron sulfate were added to the magnesium hydroxide obtained in Comparative Example 1, respectively.
After adjusting the addition so that the water content was 8% by weight, the mixture was dried until the water content was 8% by weight. The dried product was pressure molded at a pressure of 3 t/cm ² and fired at 2000°C in an oxygen/propane furnace. Table 5 shows the chemical composition, bulk density, and average particle size and distribution of periclase crystals of the obtained sintered body. FIG. 4 of the accompanying drawings shows a microscopic photograph of the sintered body.

[Table] Comparative Example 3 Seawater decarboxylated using the same method as Examples 1 to 3
11.8 to 0.25 wt% _Fe2O3 content in the final product magnesia clinker with water-soluble _{FeSO3 solution}
After adding milk of lime (CaO concentration 12
g/100ml) was added to produce magnesium hydroxide under the condition of a pH value of 11.3 to 11.5. Next, the supernatant layer was separated and concentrated, and 660 ml of decarboxylated seawater was added to the magnesium hydroxide slurry, and the pH value was determined.
Re-reacted under conditions of 10.0-10.4. This operation was repeated 20 times. The magnesium hydroxide finally produced in this way is washed with decarboxylated industrial water, and the MgO content is 97.5% by weight based on scorching heat.
Magnesium hydroxide containing the above iron compounds could be obtained. Water glass was added to this magnesium hydroxide in an amount of about 0.4% by weight based on scorching heat, and then dried until the moisture content was 8% by weight. the dried food
It was press-molded at a pressure of 3t/cm ³ and fired at 2000°C in an oxygen/propane furnace. Table 6 shows the chemical composition, bulk density, and average particle size and distribution of periclase crystals of the obtained sintered body.

【table】 [Brief explanation of drawings]

Figures 1 and 2 of the accompanying drawings are micrographs showing the crystal grain structure of the magnesia clinker of the present invention. FIGS. 3 and 4 are micrographs showing the crystal grain structure of magnesia clinker produced by a conventional method.

Claims (1)

[Claims] 1. As oxides, MgO 97.0% by weight or more, CaO 1.2 to 1.8% by weight, SiO ₂ 0.21 to 0.6% by weight, Fe ₂ O ₃ 0.3 to 0.8% by weight, Al ₂ O ₃ 0.15% by weight or less, B ₂ O ₃ 0.1% by weight or less, the bulk density is 3.48 g/cm ³ or more, and the particle size is
A magnesia clinker with an increased density characterized by periclase grains of 125μ or more accounting for 8% or more. 2 The average grain size of the periclase crystal grains is at least
The magnesia clinker according to claim 1, which has a diameter of 90μ. 3 37% periclase crystal grains with a grain size of 100μ or more
The magnesia clinker according to claim 1, which covers the above.