| Magnesium and its alloys named "21st century green project metal" is the lighted metal material in the application of project for its advantages of abundant reserves, light weight, high strength, good vibration, and environmental compatibility. Therefore, magnesium has a bright future in the 21st century of growing emphasis on energy conservation, environmental protection and sustainable development.The properties, applications and preparation methods of primary magnesium and its alloys are overviewed in this paper. China is rich in deposits of magnesium ore resources and magnesium brine water resources, one of about 3.145 billion tons magnesite, a first in the world, Dolomite about 4 billion tons, Salt Lake brine magnesium in the magnesium salt reserves of 4. 816 billion tons. The world's annual production of magnesium, more than 80 percent is produced by moltensalt electrolysis, production of silicothermic reduction of oxides is less than 20%. But because China has the advantages in dolomite resources and labor cost, production of magnesium in China by Pidgeon process has dominated, more than 90 per cent is produced by Pidgeon process. There are grave defects both in moltensalt electrolysis and silicothermic reduction of oxides. The former process is complex which needs vast investment, and emits toxic gases like chlorine gas; treatment of wastes is overburden costly; erosion of the equipments and plant buildings is badly, and maintenance cost overwhelming. The flaws in the process of magnesium extraction by silicothermic reduction of oxides are: high cost of major reductant, ferrosilicon (75%) ; the boosted production cost accordingly; short service life of reduction retort, which is made of high Ni-Cr alloy; vacuum inside the retort heated under the normal pressure, small-size of the retort, low forced filling rate, low production capacity thermal efficiency, batch production, low productivity and production.Therefore, the research of vacuum carbon reduction system magnesite magnesium funded under the national "973" preliminary studies - "basis study of light metal Almagate vacuum reductionUse cheap coal instead of expensive ferrosilicon, self-developed heat Vacuum Furnace replacing reduction cans, and the scale of vacuum furnaces can break constraints of jar capacity; improve the thermal efficiency and capacity single equipment. It is possible to reduce production costs and improve working conditions. All the metallurgical processes of this experimental design are made in a closed vacuum system with less pollution.Experimental design is divided into two steps: 1, the decomposition of magnesite and the coke end of material; 2, carbon reduction Preparation of magnesium to produce metal magnesium.Mix magnesite, coal and calcium fluoride uniformly at a certain proportion, agglomerate at 20Pa, keep the temperature of coke end at 600℃for 30 minutes to make the magnesite decompose completely and gain coke material of large intension. Therefore, the experiment gets satisfying effect.Continue to increase the temperature at the end of the process of coke end, and C starts to deoxidize the magnesia to produce magnesium. The higher the reaction temperature is, the more completion of the reaction. Direct collcetion rate of magnesium reaches 58.8% if reaction temperature is 1450℃. If condensation temperature falls between 400—550℃and temperature distribution is isostalic, most condensate takes the shape of fiber, and contamination by C from the decomposition of CO on the wall of the condenser becomes omissible. Eventually be the product of internal magnesium as high as 99. 5 percent purity, the purity of 93 percent of the surface. With the proceeding of the reaction, pressure in the furnace fluctuates. At 600—800℃, because of the decomposition of magnesite and change of coal, pressure in the furnace climbs high the first time. The high pressure value comes the second time when the reaction of C with magnesia initiates. |
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