Study On The High Purity Electro-fused Magnesia Produced By Salt Lake Brine MgO

Taking Saline Lake brine light-burned Magnesium Oxide as raw material, this paper focus on the optimization of high-purity fused magnesia preparation process, the factors of influence on the fused magnesia density and ignition loss, reducing the content of harmful impurity and improving the purity of fused magnesia, also the ratio of Ca/Si. To explore the effect of TiO2 additive on fused magnesia melting crystallization mechanism is another task. All of those talked about above would be helpful for improving the quality of magnesia and make significantly practical and theoretical value for the preparation process. The subject of the using high-purity Magnesium Oxide extracted from Saline Lake is aim at producing fused magnesia with highly economic value. It would promote the extension of Salt Lake of circular economy industrial chain, and make the best of Salt Lake resources.This thesis focuses on the effect of factors on the densification and ignition loss of fused magnesia. Volume density of fused magnesia located at molten pool center is the highest, followed by the middle and external zone, while the porosity is the opposite trend. The highest volume density is 3.57/cm3, and the porosity of samples are maintained at 0.5% below, the minimum could be 0.17%. Due to the purity, the influence of secondary crystalline phase, impurities and other factors, the densification of fused magnesia must be influenced. The lowest of ignition loss reaches 0.0850%, while the maximum of volume density is as high as 1.6370%. The uneven and inadequate of heating environment result in the external magnesite probably being in less burning state. In addition, the high residue value of impurity leads to the formation of low melting-point silicate minerals.Also, we analyze the purity and impurities distribution of electro-fused magnesia. After electro-fused preparation process, the highest magnesium oxide content reached 99.874%. The purity of MgO lying at middle section mostly is high enough as 98%, however, the content of magnesium oxide melting on surface is relatively lower. On the whole, the purity of magnesium oxide melting at pool bottom of middle section is higher than other zones. The content of CaO, SiO2, Al2O3, Fe2O3 definitively determine the purity of fused magnesia. Although trace impurity elements, such as Ti, Na and K are relatively high, the cumulative content of all trace impurity elements are below 0.1%. The ratio of Ca/Si sampling from the molten pool center is close to 2, while the ratio of outer layer decreased greatly because of the high residue of SiO2. The complex minerals, like 3CaO·SiO2,2CaO·SiO2 and 8CaO·5SiO2, are generated at the boundary of amorphous periclase phase which is not tight closely. The samples of middle section contain CaO·SiO2,2CaO·SiO2. Periclase phase particles become larger with small pieces on surface. The samples located at center zone almost have no secondary phase, the characteristic peaks of Magnesium Oxide are greatly high and sharp. Periclase crystal plane distance of samples from inside to outside is gradually becoming larger, also the lattice distortion of 0.0066% is gradually increased to 0.0562%.In addition, effect of TiO2 on melting and crystallization mechanism of electro-fused magnesia is also studied. Results indicated that fused magnesia with purity of 99.472wt%, bulk density of 3.569g/cm3 and apparent porosity of 0.595% could be obtained with addition of TiO2 less than 0.25wt%. The molten pool at the center of the highest purity of MgO, the addition of TiO2 is helpful to improve the purity of fused magnesia. TiO2 has solid solution into magnesium oxide lattice, accelerate the impurity and purification. It can promote impurities diffusion, MgO crystallization and structural densification. However, excess TiO2 (>0.35wt%) over the solid solubility limit reacted with MgO to form magnesium titanate(Mg2TiO4), meanwhile the magnesia crystal was irregular and micro-structure changed. So, the additive of TiO2 for fused magnesia preparation has a positive impact.