Preparation of Active MgO and High Purity Sintered Magnesia from Microcrystalline Magnesite

In order to widen the application of microcrystalline magnesite,the thermal decomposition behavior of the microcrystalline magnesite in Sichuan and Tibet area was firstly studied by thermogravimetric analysis. Then the effects of the calcination temperature,calcination time and particle size on the preparation of active Mg O from microcrystalline magnesite were studied by orthogonal experimental design. At last,high purity sintered magnesia was prepared by two-step calcination,meanwhile the effects of the light burning temperature,particle size of the light-burned Mg O powder,molding pressure and the hydration rate of light-burned Mg O powder on the properties of high purity sintered magnesia were studied.The results show that:（ 1） the calcination temperature has the greatest influence on the activity of light-burned MgO,followed by the holding time and the particle size;the optimal process of light burning for preparing active MgO is the microcrystalline magnesite with particle size of 1-0. 5 mm heat-treating at 700 ℃ for 2 h; under these conditions,the microcrystalline magnesite decomposes completely; the average grain size of the obtained product is about 21. 4 nm,and its activity of CAA is20. 16 s;（ 2） the effect of the light burning temperature on the density of high purity sintered magnesia is not obvious; the fineness of the light burning Mg O powder and molding pressure help to increase the density of sintered magnesia; the lower the hydration rate of the lightburned Mg O, the higher the density of the sintered magnesia; the high-purity sintered magnesite withw（ MgO） ≥98% and bulk density≥3. 40 g/cm;can be prepared by the two-step calcination; the grains are fine with size of 30-200 μm and the impurity at grain boundaries is little.

Preparation of Light-burned MgO by Microcrystalline Magnesite and Its Application Prospect Analysis

In order to widen the application of microcrystalline magnesite, the microcrystalline magnesite in Sichuan and Tibet area was used as the raw material to prepare light-burned MgO at 700,800,900, 1 000, 1 100 and I 200 ~C for 3 h, respectively. Then the physical and chemical properties of the light-burned MgO were detec- ted, and its application prospect was analyzed. The re- sults show that： （1） microcrystalline magnesite com- pletely decomposes forming light-burned MgO calcined at the temperature range of 700 - 1 200 ~C ; the MgO con- tent of the light-burned MgO is higher than 96. 51% ; the chemical activity is 88 - 130 s and the grain size is 40 - 200 nm ; it has the advantages of high purity, high activity and fine grain; （2） the light-burned MgO pre- pared with microcrystalline magnesite can be widely used in many industries; it can be used in refractories indus- try to prepare high-purity sintered magnesia and large crystal fused magnesia, or as an additive for refractory products, etc. ; it can also be used in magnesium chemi- cal industry to prepare electrical grade magnesia, sili- con-steel magnesia, environmental friendly flame retard- ant magnesium hydroxide, magnesium sulfate fertilizer, pharmaceutical grade magnesia, food grade magnesia, etc.

Crystallization Behavior of High Purity Fused Magnesia

The chemical composition and microstructure of Tibetan microcrystalline magnesite were studied by means of XRF,XRD and FESEM. It is found that the microcrystalline magnesite has uniformly distributed grains,mostly in the range of 2-4 μm,and the MgO content is47. 80%. In fused magnesia,the druses are colorless transparent periclase megacrysts without impurity,while the crust sand is white,with a high MgO content up to97%-99%. The periclase crystals are big,appearing as faced and step-growth morphology. Massive secondary long columnar periclase is crystallized.