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Manufacturing Principles of Refractory Magnesia in China

Only ordinary sintered magnesia (dead burnt magnesia – DBM92) is directly produced from natural magnesite. Magnesite is charged in the blend with coal as fuel in a shaft kiln, where calcination and sintering take place in one process. Middle-grade sintered magnesia (DBM95) is made of caustic magnesia that is calcined in a reverberatory furnace, by using a process of calcining, first wet-briquetting strongly, secondary briquetting, drying and sintering. Natural gas has to be used as the fuel in both processes, because high grades of magnesite are downgraded to lower purity of magnesia after sintering. High-purity sintered magnesia (DBM97) is produced by briquetting caustic calcined magnesia and sintered in a shaft kiln fired by cracked oil or natural gas and at the temperature over 1900 °C. After calcining floated magnesite in Multiple Hearth Furnace (MHF), the production of DBM98 is made with the maximum bulk density of 3,37 g/cm3. There is no one of industrial production lines available to produce DBM98 with 3,40 g/cm3 or higher from natural macrocrystalline magnesite, because of the technical limitation in the processes of calcining in reverberatory or MHF and sintering in a shaft kiln. There are four routes to produce fused magnesia in China, namely direct fusion of magnesite, fusion of caustic calcined magnesia, fusion of blends of floated magnesite and caustic magnesia and advanced fusion process with high power, energy saving and clean emission. Magnesite beneficiation provides an opportunity for producing high grades of magnesia. Reverse flotation, removing SiO2, is a mostly prevailing and effective process to purify magnesite in China at present.

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