KR100276976B1 - Manufacturing method of electrolytic dolomite - Google Patents

Abstract

The present invention relates to a method for producing electrolytic dolomite which is strong in fire resistance and corrosion resistance, can reduce manufacturing costs, and is used as basic refractory materials such as electric acro for steelmaking and refining furnaces, and pulverizing natural dolomite and molding into pellets. In the method for producing electrolytic dolomite by a-king melting in the electric a-chrom, the natural dolomite heat treatment at 800-1300 ℃ to discharge the gas, such as CO ₂ and decarbonation step of generating fine crystallites by pyrolysis; And adding and kneading an inorganic additive for transforming free CaO into a stable phase and a seed crystal material for promoting crystal growth in an electrolytic melt to the decarboxylated dolomite powder, and the decarbonated dolomite powder and inorganic materials. the additive and the seed crystal material is mixed-composition as 1000kg / cm ² or more and the pressure Φ3-4cm Φ7-8cm-form of pellets A method of producing a jeonyung dolomite comprising the steps of: forming a high pressure.

Description

Manufacturing method of electrolytic dolomite

The present invention relates to a method for producing electrolytic dolomite used as basic refractory materials, such as electric arc for steelmaking, refining furnaces, and more particularly, to a method for producing electrolytic dolomite which is strong in fire resistance and corrosion resistance and can reduce manufacturing costs. It is about.

As a steel refractories, refractory or sintered magnesia-based refractory materials having a high melting point are mainly used. However, the magnesia-based refractory material has a disadvantage in that the hot expansion property is large and thus the volume change rate is high due to temperature change, so that cracks and tissues collapse.

In order to prevent such cracking, magnesia-chromium refractory materials in which chromium oxide and the like are mixed have been proposed. However, in recent years, the danger of chromium has emerged as a social problem, in particular, hexavalent chromium is already used in advanced countries as a highly toxic pollutant.

In addition, in order to compensate for the high coefficient of thermal expansion of magnesia, it is possible to prepare a refractory by putting an impression graphite. However, such graphite additive magnesia has a problem that it is difficult to produce low carbon steel when the graphite oxidation problem and the graphite addition amount is large.

Dolomite refractory is a basic refractory material made of high lime (dolomite), which is suitable for the manufacture of clean steel because it has high fire resistance, high load softening point, and excellent removal effect of sulfur (S) and non-metallic inclusions in molten steel. will be.

Dolomite clinker is produced by calcining the dolomite ore. By heating, MgCO ₃ is first decomposed at about 800 ° C. and CaCO ₃ is decomposed at about 950 ° C. to form a mixture of CaO and MgO.

(MgCa) (CO ₃ ) ₂ → CaCO ₃ + MgO + CO ₂

CaCO ₃ → CaO + CO ₂

In Reaction Scheme 1, calcium oxide (CaO) reacts with moisture in the air to produce high heat, and is digested with calcium hydroxide with CaO + H ₂ O → Ca (OH) ₂ .

In order to prevent digestion, a dolomite clinker having a CaO component reacted with SiO ₂ , Fe ₂ O ₃ , TiO ₂ , or the like has been proposed. However, since the dolomite clinker is sintered, there is a disadvantage in that long-term preservation is impossible, and further, most of the impurities contained generate low-melting point materials, which lowers corrosion resistance.

On the other hand, the organic coating material is applied to the dolomite particle surface to reduce the impurity content and enhance the corrosion resistance, but since the treatment material does not reach the inside of the clinker, since free CaO and moisture react to cause digestion, There is a problem.

Therefore, the present invention was invented to solve the above problems, to prepare an electrolytic dolomite that develops crystals at high temperature with a-king melting, heat-treating the natural dolomite prior to electrolytic decarbonation step, decarbonated Adding a seed additive which promotes crystal growth in the dolomite electrolysate and an inorganic additive which lowers the melting temperature while changing free CaO of dolomite into a stabilized phase, and the decarbonated dolomite powder and inorganic additives and By formulating the seed crystal material and forming the molten dolomite, including high pressure molding the pellet, the melting temperature of the dolomite during the melting is lowered while the fire resistance and erosion resistance are significantly improved compared to the conventional sintering and molten dolomite. Electrolysis dolomye to reduce manufacturing costs The purpose is to provide a method for the production of tart.

1-X-ray diffraction diagram of the electrolytic dolomite in accordance with Examples and Comparative Examples of the present invention

Figure 2-reflecting micrograph of the electrolytic dolomite in accordance with the Examples and Comparative Examples of the present invention

Figure 3-Cross section photograph of the erosion test of the electrolytic dolomite according to the Examples and Comparative Examples

The method for producing the electrolytic dolomite of the present invention for achieving the above object, in the method for preparing the electrolytic dolomite by grinding the natural dolomite, molding into a pellet form and a-king melting in the electric acro- Decarbonation step of discharging gas such as CO ₂ by heat treatment at 1300 ° C. to generate fine crystallites by pyrolysis, and inorganic additives and electrolysis to change free CaO into stable phase in the decarboxylated dolomite powder Adding and kneading the seed crystal material for promoting crystal growth in water, and mixing the decarboxylated dolomite powder, the inorganic additive, and the seed crystal material at a pressure of 1000 kg / cm ² or more at a diameter of Φ 3-4 cm and Φ 7-8 cm. It characterized in that it comprises the step of high-pressure molding on a pellet.

The decarbonation step of the present invention, in contrast to the conventional method for producing molten dolomite, which melts the dolomite ore directly, separates the carbonate component from the CaCO ₃ and MgCO ₃ components by heat treatment before melting the natural dolomite. When the dolomite ore is directly melted, gas such as CO ₂ is prevented from remaining in the form of bubbles in the melt, and fine crystallites can be generated by thermal decomposition. Here, the heating temperature range is 800-1300 ℃, natural dolomite of the starting material is preferably high magnesia dolomite.

The calcined product obtained in the decarbonation step was pulverized to a particle size of 53-88 μm, and then the free calO of the powder component was changed to a stable phase to prevent digestion caused by moisture, thereby preventing spinel having a high melting point. Mineral additives that form a protective layer on the movable surface of the molten dolomite to improve corrosion resistance to molten steel, and promote the growth of crystallites in the molten material during the melting step, thereby developing crystallite size. In the reaction with molten steel, a seed crystal material is added and kneaded to lower the activity of the grain boundary to improve corrosion resistance.

Inorganic additives used in the present invention is an oxide, such as Cr, Fe, Hf, Th, Zr small amount, the additive is the decarboxylation of the harmful free calcia (free CaO) in a powder stable CaCr ₂ O _4, Ca _By changing to ₂ Fe ₂ O ₅ , CaHfO ₃ , CaThO ₃ , CaZrO ₃ phases, they adhere to the surface of CaO or exist at grain boundaries between crystals, which greatly improves fire resistance and can also lead to improved corrosion resistance.

For example, when 3-7% of Fe ₂ O ₃ is added as the Fe oxide in the inorganic additive of the present invention, the CaO-MgO-Fe ₂ O ₃ three-component reaction mechanism is a standard product free energy change of thermodynamics (ΔG _f °). If you have a review based on the 1700.K near steelmaking temperature CaO (c) of the ΔG ° _f = -108.917Kcal and so ΔG ° _f = -91.346Kcal of MgO (c), as shown in Scheme 2 below, Ca ₂ Fe ₂ O ₅ is generated and exists on the surface of CaO and the grain boundary of CaO.

2 (CaOMgO) + Fe ₂ O ₃ → Ca ₂ Fe ₂ O ₅ + 2MgO

The Ca ₂ Fe ₂ O ₅ is stable only when the oxygen partial pressure is high, and decomposition reaction occurs as shown in Scheme 3 when the reducing atmosphere or the oxygen partial pressure is reduced.

2Ca ₂ Fe ₂ O ₅ → 4CaO + 4FeO + O ₂

In this case, when MgO is present around Ca ₂ Fe ₂ O ₅ , the reaction of Scheme 4 occurs.

2Ca ₂ Fe ₂ O ₅ + 4MgO → 4CaO + 4 (Mg, Fe) O + 3O ₂

Ca ₂ Fe ₂ O ₅ that existed on the surface or grain boundary of the CaO particles is decomposed into CaO, as shown in Scheme 4, outflowed into molten steel, and unstable (Mg, Fe) O is produced. As the oxygen partial pressure increases during cooling, Fe ²⁺ ions are oxidized to Fe ³⁺ ions to form a stable spinel material of MgFe ₂ O ₄ . That is, the high melting point MgFe ₂ O ₄ spinel continues to form on the movable surface of the molten dolomite to form a protective layer, thereby providing corrosion resistance to molten steel.

Ca ₂ Fe ₂ O ₅ generated in the CaO-MgO-Fe ₂ O ₃ three-component process reaction can be confirmed through the X-ray diffraction diagram of FIG. 1 according to the embodiment described below, MgFe ₂ O ₄ is molten steel After reaction with, it was confirmed from the operation surface of the electrolytic dolomite sample.

In addition, the addition of the oxides such as Cr, Fe, Hf, Th, Zr as described above can reduce the melting point of the dolomite slightly to reduce the amount of power due to the melting. When melting the pelletized dolomite molded product like glass in a typical electric arc, a heating temperature of about 2400-2800 ° C. or more is required, whereas oxides such as Cr, Fe, Hf, Th, and Zr of the present invention When added, the effect is lowered by about 200 ° C. than the conventional melting temperature, thereby reducing the manufacturing cost.

As the seed crystal material added to the decarbonated dolomite powder together with the inorganic additive, a small amount of electrolytic dolomite particles having a size of 20-50 μm is used. When the crystallites are grown to 200 μm or more in the dolomite electrolytic melt, the number of crystal grain boundaries decreases, thereby lowering the activity in the reaction with molten steel, thereby providing corrosion resistance. It was confirmed by the reflection microscope observation of FIG. 2 according to the embodiment of the present invention that the crystallites in the electrolytic dolomite were formed in the size of 200-400 μm by the addition of the seed crystal material.

The composition in which the decarboxylated dolomite powder, the inorganic additive, and the seed crystal material are blended as described above is formed into two types of pellets of Φ 3-4 cm and Φ 7-8 cm at a high pressure of 1000 kg / cm ² or higher. Through such high pressure molding, not only the melting operation is easy, but also the density of the product after the melting can be achieved.

Hereinafter, the manufacturing method of the present invention will be described in detail with reference to Examples.

(Example)

High magnesia dolomite ore is decarbonated by heating to 100 ± 1100 ° C. in a muffle kiln.

The decarbonated calcined product is ground into particles of 53-88 μm with a Raymond mill.

4.5% by weight of Cr ₂ O ₃ , Fe ₂ O ₃ , HfO ₂ , ThO ₂ , ZrO ₂ and 2.0% by weight of 10 ± 30 μm of electrolytic dolomite particles are added and kneaded in a fan mixer while adding a small amount of an aqueous solution. . Here, the addition ratio of the iron oxide and the electrolytic dolomite is a ratio with respect to 100% by weight of the chemical composition shown in Table 1.

After kneading, if a suitable molding viscosity is produced, it is formed under high pressure with pellets of Φ 3-4 cm and Φ 7-8 cm at a pressure of 1000 kg / cm ² or more, and dried in a drying furnace at 100-300 ° C.

The pellets are placed in an electric arc with a capacity of 4 tons and melted and cooled to a temperature of 100 ± 2500 ° C. under conditions of a current of 5500-7000 A and a voltage of 75-100 V. It takes 8-12 hours to obtain the electrolytic dolomite coagulum.

The chemical composition, volume specific gravity, apparent porosity, crystallite size, hydration index, and erosion index of the electrolytic dolomite were measured by the following method, and the results are shown in Table 1.

Samples were taken according to Korean Industrial Standard KS A 3101-81, and chemical composition analysis was performed according to KS L 3120 and KS L 3316-88.

The apparent specific gravity and porosity were measured according to KS L 3114-77, but white kerosene (specific gravity 0.8) was used instead of water in the catcher measurement method.

The particle size was measured according to KS L 3523-78, and the hydration rate (digestibility) was measured according to KS L 3524-81.

The microstructure (crystal and crystallite size) of the electrolytic dolomite shown in FIG. 2 was observed by a reflection microscope and a scanning electron microscope. That is, the coagulation sample was taken to a certain size, cut into two parts in the diagonal direction, and the resin was impregnated into the cut surface. The average area of three places where the surface was polished was selected and measured. Electron microscopic observation was performed after resin impregnation and polishing on the sample surface and gold coating or carbon coating.

The erosion index in the erosion test of the electrolytic dolomite shown in Figure 3 when the erosion degree of the conventional electrolytic dolomite (Comparative Example 1) is 100, the index is expressed as a percentage.

(Comparative Example 1)

Natural dolomite was not subjected to decarbonation treatment and inorganic additives (oxides of Cr, Fe, Fh, Th, and Zr) and electrolytic dolomite particles were added. It was.

(Comparative Example 2)

After the decarbonated calcined product of the above example was pulverized, the preparation was carried out in the same manner as in the example of the pellet without the addition of the mineral additive and the electrolytic dolomite particles, followed by electrolytic treatment, and the results are shown in Table 1.

Comparative example Example One 2 Chemical composition (%) SiO ₂ 1.03 0.99 0.98 Al ₂ O ₃ 0.49 0.46 0.45 Fe ₂ O ₃ 0.87 0.83 0.82 CaO 34.42 34.51 34.50 MgO 62.59 62.40 62.42 MnO 0.18 0.15 0.16 Additives (oxides of Cr, Fe, Hf, Th, Zr) - - 4.5 Electrolytic Dolomite Particles - - 2.0 Physical properties Volume specific gravity 3.0 3.1 3.4 Apparent porosity (%) 5.8 4.2 2.0 Determinant (μm) 10-40 20-80 200-400 Hydration Index 100 80 50 Erosion Index 100 80 60

As shown in Table 1, compared to Comparative Examples 1 and 2, the electrolytic dolomite according to the embodiment of the present invention showed that the crystallization was greatly developed so that the volume specific gravity was increased and the apparent porosity was decreased while the fire resistance and corrosion resistance were improved by about 2 times. You can check it.

As described above, according to the present invention, in the production of electrolytic dolomite in which the dolomite ore is melted by arc-melting to develop crystals at high temperature, the gas generated during melting by heat-treating the natural dolomite in advance prior to the melting is performed. To prevent bubbles from remaining in the melt in the melt and to generate fine crystals by pyrolysis to induce dense tissue, and to stabilize the free-calcium (free CaO) in the decarboxylated dolomite component in the water environment. Production cost by reducing the melting temperature and lowering the melting temperature.In addition, crystal additives in the dolomite electrolytic material and inorganic additives which have high melting point spinel are formed on the moving surface of the molten dolomite to form a protective layer and have corrosion resistance to molten steel. To promote low activity in reaction with molten steel Adding a seed crystal material which has a resistance to chewing, and mixing the decarboxylated dolomite powder, an inorganic additive, and a seed crystal material, and molding the pellets at high pressure for easy melting and inducing densification of the melt. By manufacturing the molten dolomite including a, the microstructure is compact and greatly improved the fire resistance and erosion resistance can be provided a method of manufacturing the molten dolomite which can reduce the manufacturing cost by reducing the melting temperature of the dolomite during melting have.

Claims (3)

In a method for producing electrolytic dolomite by grinding natural dolomite, molding into pellets and arc-melting in electric arc A decarbonation step of heat-treating natural dolomite at 800-1300 ° C. to discharge gas such as CO ₂ to prevent remaining of bubbles in the melt and to generate fine crystallites by thermal decomposition; Adding and kneading an inorganic additive that changes free CaO into a stable phase and a seed crystal material that promotes crystal growth in the molten metal to the decarboxylated dolomite powder, High pressure molding the composition comprising the decarboxylated dolomite powder, the inorganic additive, and the seed crystal material into a pellet of Φ 3-4 cm and Φ 7-8 cm at a pressure of 1000 kg / cm ² or higher. Manufacturing method. 2. The method of claim 1, wherein the inorganic additive is an oxide of Cr, Fe, Hf, Th, Zr. The method of claim 1, wherein the seed crystal material is 20-50μm sized electrolytic dolomite particles, characterized in that for producing the electrolytic dolomite.