The Comprehensive Study On Calcined Product Of Magnesite

China is one of the most abundant countries in magnesite resources which are distributing concentrately and exploited easily in the world.However,with the rapid development of national economy,high-grade magnesite resources are increasingly reduced after decades of mining and low-grade magnesites are abandoned for the unreasonable use,leading to a serious waste of magnesite resources.In this study,according to the characteristics of high calcia and low silica magnesite in Sichuan area,the bulk magnesites were directly calcined and the calcined products were crushed,sieved and classified,and different grades and types were obtained.Then different processing technics were employed to produce different properties of magnesium products,achieving the effective use of low grade magnesite resources.The main research contents and conclusions are as follows:?1?The effects of calcination conditions and sieving particle size on the heat-dress purification efficiency of magnesite were investigated.The results show that the best calcination condition of bulk magnesite?MgCO₃?with particle size 30⁸0mm is 800?×3h.Under the calcination conditions,MgCO₃ was completely decomposed to form MgO and CaCO₃ was basically undecomposed which was beneficial to the later purification.Then the calcined products were crushed,sieved,the purity of caustic burned magnesia powder was improved at the range of 2⁰.154 mm.At a certain range of particle size,heat-dress purification can increase the main component MgO contents and decrease the contents of impurity oxides.?2?The main starting materials were caustic burned magnesia powder with sieving particle size less than 0.154 mm which was obtained by the heat-dress purification of low grade magnesite and industrial ? alumina fine powder.The effect of Ti O2 addition on densification behavior of magnesium aluminate spinel synthesized was discussed.The results show that the replacement solid solution of TiO₂ addition and formed magnesium aluminate spinel is the significant mechanism to promote the densification of magnesium aluminate spinel synthesized by solid-state sintering.TiO₂ addition is in favor of the densification process of magnesium aluminate spinel synthesized by solid-state sintering,significantly improving the sintering properties and microstructure of magnesium aluminate spinel effectively.?3?The fused magnesia was produced by caustic burned magnesia powder with sieving particle size 2⁰.154 mm.The melting,crystallization,diffusion and distribution of impurities with the caustic burned magnesia powder during the fusion process were studied.The results show that impurities were diffusion and migrated to the central region and the outmost layer of the melting lumps during the high temperature melting and cooling solidification process of fused magnesia.The areas where fused magnesia was in high purity and crystal was well-developed were under the projection of electrodes but departure from the central region of melting lumps.The areas where the impurities content were highest were at the central region of melting lumps.The impurity minerals mainly existed in the form of silicate mineral phase which was embedded in the matrix of periclase phase.?4?The magnesium oxychloride cement?MOC?was prepared by caustic burned magnesia powder with sieving particle size greater than 2mm.The effect of raw materials ratio on properties of MOC was studied.The results show that with the increase of n?MgO?/n?MgC_l2?molar ratio,the compressive strength and flexural strength of MOC block increased and then decreased,and when n=7,they all reached the maximum.The compressive strength of briquettes immersed in water after 7d were obviously decreased.While with the increase of n?MgO?/n?MgC_l2?molar ratio,the water resistance of briquettes were improved.