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Properties of dolomite and its application in refractory industry

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Properties of dolomite and its application in refractory industry

Date of release:2019-06-09 Author: Click:

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The main component is calcium magnesium carbonate; the chemical composition is CaMg (CO3) 2; the theoretical chemical composition is CaO 30.4%, MgO 2 1.7%, CO 247.9%. The Mg in the composition can be replaced by Fe, Mn, Co and Zn, and Ca can be replaced by Pb and Na. When the number of iron or manganese atoms exceeds that of magnesium, it is called iron dolomite or manganese dolomite. After heating, MgCO3 in dolomite decomposes at about 750 C and CaCO3 decomposes at about 950 C. Dolomite is a trigonal mineral with relative density of 2.8-2.9 and Mohs hardness of 3.5-4. Dry material


Physical property


Dolomite is mostly white, gray, flesh-colored, colorless, green, brown, black, dark pink, etc., transparent to translucent, with glass luster. Aggregates are usually granular; crystalline structures are similar to calcite and often rhombohedral. Mohr hardness: 3-4; density 2.86-3.20 g/cm 3, foaming in cold dilute hydrochloric acid; calcination of dolomite can be divided into two stages: MgCO 3 begins to decompose in calcium-magnesium carbonate at 730-740 C to produce MgO and CO2. The decomposition of CaCO3 in dolomite does not begin until the temperature continues to rise to about 910 C. Carbon dioxide is removed and a mixture of calcium oxide and magnesium oxide is formed.


Reserves and Distribution


Dolomite is a kind of non-metallic mineral with a very wide range of uses. It is an important calcium and magnesium resource on the earth and has a very rich reserves. Dolomite resources are abundant in China, and are distributed in many areas. The proven reserves are over 4 billion tons. Dolomite resources are found in all provinces and regions of China, especially in Shanxi, Ningxia, Henan, Jilin, Qinghai, Guizhou and other provinces and regions.


Place of Origin


Dolomite resources are abundant in China, and most of them occur in Sinian strata, such as Liaohe Group in Northeast China, Sanggan Group in Inner Mongolia and Jinou Group in Fujian Province. Liaoning East Peninsula, Jidong, Inner Mongolia, Shanxi, Jiangsu, Hubei, Hunan, Guangxi, Guizhou and other places.


Application of Dolomite


Dolomite is widely used in metallurgy, refractory materials, building materials, ceramics, glass, chemical industry, agriculture, forestry, environmental protection and energy saving and other fields. It is a non-metallic mineral resource that can be exploited and utilized in many ways. With the development of modern science and technology, the development and application of dolomite has penetrated into all fields of social development. Domain has become a mineral resource of great economic value.


(1) Refractories


Dolomite, as one of the important raw materials of alkaline refractories, is mainly used for converter lining, open hearth, electric furnace wall, and secondly for thermal equipment such as furnace refining equipment and cement kiln. Dolomite can be used to make dolomite bricks. When dolomite bricks are used as furnace lining, the service life of the furnace can be significantly improved by spraying dolomite with gunning material.


(2) Magnesium smelting industry


Dolomite with a particle size of 30-120 mm is an important raw material for magnesium production. The methods of dolomite smelting magnesium are mainly divided into two categories: electrolysis and silicothermic reduction. The process of electrolysis is complex and difficult to obtain economic benefits, so it is not suitable for small magnesia plants to adopt this method; silicothermic reduction is to make dolomite calcined and mixed with ferrosilicon and fluorite into spheres, which are heated in a vacuum furnace at 1100 C to produce magnesium vapor by reduction. Magnesium and other substances are then recovered and cast into magnesium ingots by cooling the magnesium vapor.


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(3) Production of magnesium compounds


Dolomite can produce magnesium compounds such as magnesium carbonate, magnesium oxide, magnesium sulfate and magnesium hydroxide. At present, there are three main types of magnesium carbonate produced: light magnesium carbonate, light spherical magnesium carbonate and light transparent magnesium carbonate. Light magnesium carbonate is the basic material of inorganic chemical industry. It is mainly used in the manufacture of magnesium salts, magnesium oxide, elemental magnesium, fire-proof materials, printing ink, ceramics, daily chemical products, rubber products, fillers and reinforcing agents. It can also be used in shipbuilding, boiler, steel-making, glass, pigments, pharmaceuticals and other industries. Magnesium oxide as filler is widely used in rubber, enamel, wire and cable industries. Magnesium sulfate crystals (MgSO4. 7H2O), also known as cathartic salts, are used in medicine, agriculture, cement, printing and dyeing, food and other fields.


(4) Production of glass


Dolomite and limestone are the third major components of glass raw materials besides silica sand and soda powder. In the production of bottle glass, soda powder is the most expensive component. Limestone can partly replace soda powder, but it will have adverse effects. The introduction of magnesium oxide in dolomite can further reduce costs. Dolomite in the glass industry can also provide calcium oxide, adding soda-lime-silica system, play the role of flux. In addition, dolomite can also reduce glass aging, prevent chemical erosion caused by atmosphere or water, improve the plasticity of stained glass and increase glass strength.


Production of ceramics


Dolomite is used in billet and glaze, MgO and CaCO3 are introduced to replace talc and calcite. The function of MgO is to change the composition of mixing system to reduce the sintering temperature of green body, to promote the dissolution of quartz and the formation of mullite, to increase the amount of quartz, to reduce the amount of feldspar, and thus to increase the transparency of green body. The glaze with dolomite in glaze is not easy to smoke than that with calcite, and crystallization rarely occurs.


Production of Coatings


Dolomite can be used as a new type of physical pigments. Its chemical composition is stable. It has many advantages, such as weatherability, anti-sinking, fine powder, easy dispersion, high whiteness, low cost, unique process and so on. It can be used in various paints. The coatings produced have the characteristics of reducing the amount of titanium dioxide, high hardness, good handle, good flu and strong adhesion. The application effect is better than that of heavy calcium carbonate.


Sintering of Dolomite


Because dolomite contains 47.72% CO2, it can cause great weight loss or shrinkage after thermal decomposition, and a series of reactions between oxides occur, so it must be calcined into sintered dolomite clinker with stable properties, volume and compact texture before it can be used to make refractory bricks.


The product of dolomite raw material reaction below 1000 C is lightly burned dolomite, also known as caustic dolomite. Light-fired dolomite has low relative density, about 1.45, low mechanical strength, high porosity and chemical activity, and is easy to absorb water and deliquescence, so it can not be directly used as raw material for brick making.


When dolomite is calcined at 1700-1800 C, the crystal size of lime and periclase reaches a larger value, and the volume is stable. It has hydration resistance, does not contain or contains a small amount of free CaO, and its bulk density reaches 3.0-3.4 g/cm3, it is called dead-burnt dolomite.


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