What is magnesia? Magnesia carbon brick wholesale

       Magnesite is made from magnesite, magnesite or magnesium hydroxide extracted from seawater and calcined at high temperature. The wholesale of magnesia-carbon bricks is a collective name for the products of magnesite and other magnesia raw materials that have been sintered through high-temperature treatment. High-speed equipment such as shaft kiln and rotary kiln are used for one-time calcination or two-step calcination process. The magnesia made from natural magnesite is called sintered magnesia; magnesite is used as the raw material to be melted by arc furnace melting. After the state is cooled, it is called seawater magnesia, which is made by extracting magnesium oxide from seawater.

       Magnesia is one of the most important raw materials for refractory materials. It is used to manufacture various magnesia bricks, magnesia-aluminum bricks, ramming materials, recharge materials, etc., and contains a lot of impurities, and is used for laying the bottom of steelmaking furnaces.

       High-purity magnesia is selected from natural super magnesite ore flotation and calcined by light-burning, fine-grinding ball and ultra-high temperature oil shaft kiln. It is a high-quality raw material for making refractory bricks.

       Medium-grade magnesia is produced from light-burned magnesia with a MgO content of 97% as raw materials, and is processed by ball pressing and high-temperature shaft kiln calcination. The product has good sintering degree and dense crystals. It is a high-quality raw material for producing mid-grade magnesium refractory products.

       Fused magnesia is made by selecting special grade A natural magnesite or high-purity light-burned magnesium particles in an electric arc furnace. This product has the characteristics of high purity, large crystal grains, compact structure, strong slag resistance, good thermal shock stability, and is an excellent high temperature electrical insulation material. It is also used to make high-grade magnesium bricks, magnesium carbon bricks and amorphous refractory materials. Important raw materials.

       Types and production methods of magnesia

       Magnesia is divided into two varieties: sintered magnesia and fused magnesia, and it is also divided into two varieties: ordinary magnesia and high-quality magnesia; according to the different raw materials, it can be divided into magnesite magnesia, seawater magnesia and salt lake magnesia. According to different purposes, it can be divided into brick making, magnesia for refractory and bottom working layer of smelting furnace, metallurgical magnesia for furnace or lining of furnace.

       There are two methods for producing magnesia: sintering and electrofusion.

       The difference between fused magnesia and sintered magnesia

       Fused magnesia is a raw material obtained by pure natural magnesite or light-burned magnesia, which is melted by the high temperature of an electric arc furnace and then naturally cooled. During the electric melting process, the melting temperature is high and the cooling time is long, and the periclase crystal has sufficient time to develop. Compared with sintered magnesia, fused magnesia has the characteristics of perfect crystallization, coarse grains and dense structure.

       For example, the size of periclase grains in sintered magnesia is 60-200 μm, the size of periclase grains in ordinary fused magnesite is 200-400 μm, and the size of periclase in large-grain fused magnesite can reach 1000-5000 μm. , Even above 10000μm, because of this feature, fused magnesia has better high temperature resistance, erosion resistance and creep resistance than sintered magnesia, so it is widely used in the manufacture of high and medium grade alkaline refractory materials.

       Recycled magnesia

       Recycled magnesia, commonly known as black magnesia, is a recycling technology for the use of waste materials for magnesia. The purpose is to save production costs, recover resources, and make full use of resources.

       Using waste magnesium carbon to recover magnesia (magnesia sand regeneration) is a new idea and technology that saves energy, reduces emissions, and saves costs. It has now been successfully applied in production. The carbon in magnesium carbon bricks is spontaneously combusted through a special process. This process No fuel is needed and the particles break down naturally after combustion. The overall content of recovered magnesite particles is usually above 92%. Magnesia-carbon bricks generally use fused magnesia. Although the content of magnesia particles has only reached the level of mid-range magnesia, other components are not completely impurities. Instead, it contains alumina and some residual carbon in aluminum-magnesium-carbon. As a tundish vibrating material, the presence of alumina can generate spinel at high temperatures, thus significantly improving the performance of the material.

       The recycled magnesia product series are generally divided into: recycled magnesia, recycled magnesia fine powder, recycled magnesia aggregate. On the basis of regenerated magnesia, 0 ~ 3mm, 3 ~ 5mm, 5 ~ 8mm fused magnesia granules are refined, and some are added for the production of unburned products such as magnesium carbon and aluminum magnesium carbon bricks, which have good effects and significant economic benefits.

       Sintered magnesia

       The natural magnesite ore or light-burned magnesia powder is calcined in a rotary kiln or shaft kiln at a temperature range of 1500 ~ 2000 ° C, so that MgO is transformed into almost inert sintered magnesia through crystal growth and compact change. Reburned magnesia. Sintered magnesia is an important raw material in magnesia products.

       The main composition of sintered magnesia is located in the MgO-CaO-Si02 ternary system. The minerals that coexist with MgO in the ternary system change with CaO / Si02 &. For specific changes, see the MgO-CaO-Si02 ternary system.

       Light burned magnesia powder

       Light burned magnesia powder is also called caustic bitter earth and active magnesia, often called light burned magnesia powder, which is a natural magnesite ore. Activated magnesium oxide obtained by calcining magnesium [Mg (OH) 2] from seawater and salt lakes at a temperature of 700 ~ 1100 ° C. Light-burned magnesia is loose in texture, has a high specific surface area, has a large chemical activity, and easily reacts with water at room temperature. The hydrate Mg (OH) 2 hardens in the air.

       Light-burned magnesia powder is an industrial raw material with medium alkalinity and chemical activity. In addition to being used as refractory raw materials and gelling materials, it is also used in the pharmaceutical industry, chemical industry and other fields. In addition, with the development of converter steelmaking slag splashing furnace protection technology, the scope of application of light-burned magnesia has been further expanded.

       The difference between lightly burned magnesia and bitter clay powder

       The lightly burned magnesium oxide shall comply with the requirements of the following table for its chemical composition in accordance with the People's Republic of China material management industry standard WB / T1019-2002.

       The main component of light-burned magnesia is magnesium oxide (MgO). The reactive light-burned magnesia is reacted in the production of magnesite products. Light-burned magnesia is calcined and ground from ore magnesium carbonate at a temperature of 600 ~ 900 ° C. Magnesite powder is the main raw material for gelling magnesite products.

       Magnesite powder: commonly known as bitter soil powder, bitter soil, bitter soil, etc. From the 1970s to the 1980s, MgO was usually called bitter soil powder. In the 1990s, in order to distinguish the quality, people began to refer to those with MgO content above 80% as light burnt powder, and those below 80% or lower were called bitter soil. powder. Magnesite products produced with bitter powder are low-grade products. All products that require durability and high strength using bitter powder in production are inferior products.

       Metallurgical magnesia

       Metallurgical magnesia is often used for sintering and repairing the bottom of metallurgical furnaces. It is divided into two types, one is ordinary metallurgical magnesia, and the other is synthetic metallurgical magnesia (also known as Martin sand).

       Ordinary metallurgical magnesia is obtained by crushing sintered magnesite to a certain particle composition.

       A synthetic metallurgical magnesia is added with a sintering accelerator in advance. Magnesite has a high melting point and is very difficult to sinter. Therefore, ordinary magnesia should be added with a flux of 10% to 25% when it is used. Generally, open hearth slag is added. The mineral composition of open hearth slag is calcium silicate and spinel (MgO • R2O3). When they coexist, the temperature of the liquid phase is very low (less than 1400 ℃), which can be used as a flux for metallurgical magnesia. However, since ordinary metallurgical magnesia is mechanically agitated with magnesite particles and flux during use, it is not easy to be uniform. When it is sprayed into the furnace, particle segregation also occurs, which destroys the uniformity during mixing. It is not easy to sinter in the place with a lot of magnesia, and the porosity is loose. Where there are many fluxes, a large amount of liquid phase will appear, affecting the quality of the furnace bottom. In view of the above, another type of metallurgical magnesia has been developed, namely synthetic metallurgical magnesia, also known as martin sand. Magnesia, dolomite (or limestone), and iron ore are mixed according to a certain proportion, uniformly mixed, then pelletized, calcined, and then crushed to a certain particle composition to obtain metallurgical magnesia. This synthetic metallurgical magnesite already contains flux minerals, and no additional flux is required when used.

       How to measure the performance of magnesia can be measured from the following points.

       (1) Purity of magnesia The higher the purity of magnesia, the better the performance. According to the purity of magnesia, magnesia can be divided into the following categories.

       (2) n (CaO) / n (SiO2) ratio generally requires n (CaO) / n (SiO2) ratio of 1.87. Only within this range, magnesia has a high melting point bonding phase. When the n (CaO) / n (SiO2) ratio is low, the silicate surrounds the magnesium oxide to form a film or shell; when the n (CaO) / n (SiO2) ratio is high, the silicate film forms poorly and becomes isolated. Periclase is bonded directly.

       (3) Bulk density This is an index to judge the sintering degree and density of magnesia. The higher the bulk density, the better the sintering and the better the hydration resistance.

       (4) Size of periclase grains The size of periclase grains mainly depends on the firing temperature and heating time. The periclase grain size increases, and the anti-hydration performance of magnesite increases accordingly.

       Effect of magnesite properties on refractory

       The properties of magnesia are divided into chemical properties and physical properties. The chemical properties of magnesite mainly refer to magnesite is the main component of periclase MgO. Periclase is one of the common minerals in cement clinker. Periclase can be used with the four main minerals C3S, C2S, C3A and C4AF coexist. Therefore, periclase has extremely good erosion resistance to cement clinker.

       Periclase is an equiaxed crystal mineral and can form a complete solid solution with FeO, NiO, and MnO. The Mohs hardness is 6, the relative density is 3.58, the melting point is as high as 2800 ℃, the thermal expansion coefficient of 0 ~ 1000 ° C is 13.5X10-6 / K, and the thermal conductivity of 100 ~ 1000 ℃ is 3.39 ~ 4.19W / (m • K).

       These physical properties make magnesium refractories in cement rotary kiln often show the following phenomena:

       The periclase has a high melting point, so that many magnesia refractory materials have fairly good high temperature resistance;

       Cyanite has good thermal conductivity. When high refractory materials with high MgO are used and the kiln skin cannot be hung, the surface temperature of the kiln body rises. At this time, not only the heat loss is large, but the cylinder is also easy to burn out;

       The high thermal expansion coefficient of periclase makes the thermal shock resistance of the magnesia refractory material insufficient. In use, the magnesia refractory material often peels off.

       Raw materials for producing magnesia

       The main raw material for producing magnesia refractory is magnesite, which refers to sintered magnesite with a certain particle composition. It is broken from sintered magnesite. Sintered magnesite can be obtained by calcining magnesite.

       In addition, sintered magnesite can also be extracted from seawater, salt lake brine, dolomite, serpentine, and brucite. But so far, China's sintered magnesite is still mainly obtained by calcining natural magnesite, and the salt lake magnesium extraction project is still under construction.

       The production of fused magnesia in China is mainly concentrated in Liaoning and Shandong, with magnesite mainly.

       Production principle of seawater magnesia

       The production of seawater magnesia is based on the low solubility of Mg (OH) 2, and it is easy to form a supersaturated solution in seawater to precipitate Mg (OH) 2. The precipitated Mg (OH) 2 can be calcined at high temperature to obtain seawater magnesia. . The reaction equation of this process is as follows:

       At present, the main method of producing magnesium hydroxide is seawater and lime. The methods for obtaining high-quality magnesium hydroxide are: taking out impurities in raw limestone; removing impurities and carbonic acid components in seawater; and improving the precipitation and filterability of magnesium hydroxide.

       The quicklime fired in a Beckenbah shaft kiln is aged into a lime milk in a rotary lime eliminator. However, the quality of this lime milk has a great influence on the quality of the produced magnesium hydroxide. Therefore, the calcium carbonate and coarse particles remaining without thermal decomposition are used to remove such refined lime milk by a centrifugal separator or the like.

       The method of removing CO2 components in seawater is the first method, which is to add lime milk to produce calcium carbonate, and the second method is to add acid to remove carbonic acid gas. The acid method removes CO2 components at a high rate (95%). The alkaline method has the advantage that when seawater passes through the calcium carbonate precipitation tank, it can reduce the impurity components such as SiO2 and Al2O3 at the same time, and the CO2 content can be reduced below 10mg / kg.

       The magnesium hydroxide produced by the seawater-lime method is in the form of a slurry, and the primary particle diameter is small, about 0.1 μm. The problems are the concentration, precipitation, salt removal and filterability in the thickener. For this reason, the problem is solved by the seed crystal circulation of magnesium hydroxide and the addition of a coagulant so that the diameter of the secondary particles is 2 to 3 μm.

       The sintering process of magnesia is not much different from the calcination process of magnesite. According to the quality of magnesia, it can be divided into primary sintering method and secondary sintering method. From the beginning of the development of seawater magnesia industry to 1955, the magnesium hydroxide block was directly put into the firing furnace for sintering. In order to improve the sinterability, magnesium hydroxide agglomerates were added, and mineralization agents and high-temperature firing were studied. In 1955, the magnesium hydroxide block was dried, pressed and then sintered. With the increase of magnesium oxide content, magnesium hydroxide blocks have been lightly burned since 1957, and the obtained magnesium oxide was pressure-molded and sintered to achieve high density. The high-temperature kiln multi-hearth baking furnace and rotary kiln used in light firing; the molding machine uses high pressure molding machines such as ball presses; the firing furnace uses shaft kiln and rotary kiln. Magnesia with a magnesia content of less than 97% is sintered at 1500 ~ 1800 ° C; high-purity magnesia with more than 98% is sintered at 1900 ~ 2100 ° C.

       Generally speaking, 1t of seawater magnesia can be produced for every 300t of seawater.

       Production method of seawater magnesia and impurity control

       The impurities in the seawater magnesia are mainly brought in by the precipitating agent except for the seawater itself. The impurities in seawater magnesia are mainly SiO2, Al2O3, Fe2O3, CaO and B2O5.

       The control of SiO2, Al2O3, and Fe2O3 impurities in seawater magnesia mainly depends on the selection of ore or wind power to remove lime slurry before reacting with seawater. As for the SiO2 and Al2O3 impurities brought in from seawater, the sand particles can be removed by filtration.

       As for B2O5, one is to use its volatility, add some substances to promote the volatilization of B2O5 at high temperature, and the other is to add excess alkali in the Mg (OH) 2 precipitation stage, thereby reducing the adsorption of B2O5 by the precipitate.

       Deboronization of seawater magnesia

       After 1965, there have been many reports about the effects of magnesia's B2O3 content and CaO / SiO2 ratio on the temperature strength of magnesia. It can be known from the report that the higher the B2O3 content, the more significant the reduction in high temperature strength. For seawater magnesia, adjust