Properties of dolomite and application in refractory industryRelease date：2019-11-12 18:32:40 Page View：202
Dolomite is mainly composed of magnesium and calcium carbonate. The chemical composition was CaMg(CO3)2. Theoretical chemical composition CaO30.4%, MgO21.7%, CO247.9%, the Mg in the composition can be replaced by Fe, Mn, Co, Zn, Ca can be replaced by Pb, Na, when the number of iron or manganese atoms more than magnesium, known as ferric dolomite or manganese dolomite. After heating, MgCO3 in dolomite decomposed at 750℃ and CaCO3 decomposed at 950℃. Dolomite is a trigonal mineral with relative density of 2.8~2.9 and mohs hardness of 3.5~4.
Dolomite is white, gray, flesh color, colorless, green, brown, black, dark pink, transparent to translucent, with glass luster. Aggregates are usually granular; The crystal structure resembles calcite and is often rhombohedral. Mohs hardness: 3 ~ 4; Density 2.86 ~ 3.20g/cm3, when cold dilute hydrochloric acid bubbles; The calcination of dolomite is divided into two stages: MgCO3 starts to decompose in the calcium and magnesium carbonate at 730~740℃ to produce MgO and CO2. When the temperature continues to rise to about 910℃, CaCO3 in dolomite begins to decompose. At this point all the carbon dioxide is removed and a mixture of calcium oxide and magnesium oxide is formed.
Reserves and distribution
Dolomite is a kind of nonmetallic mineral with a wide range of USES. China is rich in dolomite resources, many areas are distributed, has proven reserves of more than 4 billion tons, dolomite resources throughout China's provinces, especially shanxi, ningxia, henan, jilin, qinghai, guizhou and other provinces and regions.
China is rich in dolomite resources, and mostly produced in sinian rocks, such as the northeast liaohe group, Inner Mongolia sanggan group, fujian jinou group. Liaoning east peninsula, hebei east, Inner Mongolia, shanxi, jiangsu, hubei, hunan, guangxi, guizhou and other places.
Application of dolomite
Dolomite is widely used in metallurgy, refractories, building materials, ceramics, glass, chemical industry, agriculture, forestry, environmental protection, energy conservation, and other fields, is a kind of can carry out a number of development and utilization of nonmetallic mineral resources, and with the development of modern science and technology, development and application of dolomite has deep into every field of social development, has become a great economic value of mineral resources.
Dolomite, as one of the important raw materials of basic refractory, is mainly used in steelmaking converter lining, open hearth furnace, electric furnace wall, and then used in refining equipment and cement kiln. Dolomite can be made into dolomite bricks; When dolomite brick is used as furnace lining, the service life of the furnace can be improved obviously by using the method of spraying white marble.
Magnesium smelting industry
Dolomite with particle size of 30 ~ 120mm is an important raw material for magnesium production. The methods of smelting magnesium from dolomite are mainly divided into two categories: electrolytic method and silicon thermal reduction method. The silicothermic reduction method is to mix dolomite calcined with ferrosilicon and fluorite and make balls. The balls are heated in a vacuum furnace at 1100℃ to generate magnesium steam and other substances. After cooling, the steam is recovered and cast into magnesium ingots.
(3) production of magnesium compounds
Dolomite can produce magnesium carbonate, magnesium oxide, magnesium sulfate, magnesium hydroxide and other magnesium compounds. Currently, 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 raw material of inorganic chemical industry. It is mainly used in the production of magnesium salt, magnesium oxide, elemental magnesium, fireproof materials, printing ink, ceramics, daily chemical industry, rubber products as filler and reinforcing agent. It can also be used in shipbuilding, boiler, steelmaking, glass, pigment, medicine and other industries. As a filler, magnesium oxide is widely used in rubber, enamel, wire and cable industry. Magnesium sulfate crystal (MgSO4·7H2O) also known as xieli salt, used in medicine, agriculture, cement, printing and dyeing, food and other aspects.
(4) production of glass
Dolomite and limestone are the third major constituent of glass materials after silica sand and baking soda. Soda powder is the most expensive ingredient in the production of glass bottles and jars. Adding limestone can partially replace soda powder, but it has adverse effects. The introduction of magnesium oxide in dolomite can further reduce the cost. Dolomite in the glass industry can also provide calcium oxide, adding soda - gray - silica system, as a flux. In addition, dolomite can also reduce the aging of glass, prevent the chemical erosion of atmosphere or water, improve the plasticity of stained glass, improve the strength of glass.
5 production of ceramics
Dolomite was used in billets and glazes, MgO and CaCO3 were introduced to replace talc and calcite. The function of MgO is to change the composition of the mixing system so as to reduce the firing temperature of the blank body. Promote the dissolution of quartz and the formation of mullite, increase the amount of quartz, reduce the amount of feldspar, so as to increase the transparency of the body. The addition of dolomite in the glaze is not easy to fumigate than that of calcite, and the crystallization phenomenon rarely occurs.
6 production coating
Dolomite can be used to produce new constitutive pigments. Its chemical composition is stable, with weather resistance, anti - sink, fine powder, easy to disperse, high whiteness, low cost, unique process and many other advantages, for a variety of paint use. The coating can reduce the amount of titanium dioxide, high hardness, good hand feel, good flu, strong adhesion and other characteristics, the application effect is better than heavy calcium carbonate.
Sintering of dolomite
Because the dolomite is composed of 47.72% CO2, after it is decomposed by heat, the dolomite can produce a great loss of weight or contraction, and a series of reactions must occur between the oxides. Therefore, the dolomite must be calcined into sintered dolomite clinker with stable property and volume and dense texture before it can be used to make firebrick.
The product of dolomite under 1000℃ is light burned dolomite, also known as caustic dolomite. The relative density of light burned dolomite is low, only about 1.45, the mechanical strength is very small, the stomatal rate and chemical activity are high, it is easy to absorb moisture, so it cannot be directly used as brick raw materials.
When dolomite is calcined at 1700~1800℃, the crystal size of lime and calcite reaches a larger value, and the volume is stable, has the water-resistance, does not contain or contain a small amount of free CaO, and the volume density reaches 3.0~3.4 g/cm3, it is called dead burned dolomite.