Theoretical Experimental Study On The Preparation Of High-purity Magnesium And The Separation Of Impurities

As the lightest structural metal,magnesium metal has the advantages of high strength ratio,low density and good ductility.It is widely used in the material industry and is called the 21st century green engineering material.At present,with the rapid development of science and technology,people's demand for high-purity metals is increasing.In the fields of biomedical materials and aerospace materials,magnesium with a purity of 99.99%is required.The most mainstream process for preparing high-purity magnesium is vacuum distillation.However,due to the operation under high vacuum conditions,there is no liquid phase of magnesium,which causes problems such as poor magnesium crystallization effect,low yield,high cost and inability to continuous production.Based on this,this research innovatively proposes a process for preparing high-purity magnesium under the protection of low vacuum argon,and conducts theoretical analysis and experimental research on the evaporation and impurity separation behavior of magnesium,aiming at the efficient preparation and continuous realization of high-purity magnesium Chemical production provides theoretical basis and guidance.This article focuses on the process of preparing high-purity magnesium under low vacuum under argon atmosphere,focusing on systematic research on the removal mechanism of impurities in magnesium,the evaporation and purification experiment of magnesium,the theory and experimental verification of magnesium and zinc separation,and the evaporation and purification experiment of crude magnesium.The main research contents are as follows:(1)Through evaporation kinetics and thermodynamic calculations,the migration and phase transition of impurities in magnesium during the distillation process are analyzed,and the conclusion is drawn:in order to ensure that magnesium produces a liquid phase,the system pressure should be higher than 333Pa;The saturated vapor pressures of nickel,tin,titanium,aluminum and copper are extremely low,and the separation coefficient is much less than 1.The impurities are difficult to volatilize and are basically enriched in the liquid phase;the magnesium raw material used in the experiment meets the Mg99.95B national standard.In the first low vacuum distillation,in order to keep the iron,manganese,silicon,nickel,tin,titanium,aluminum and copper impurities in the liquid magnesium without forming a solid phase precipitation Analyzing the phase diagram of impurities and magnesium,it is concluded that the evaporation of magnesium cannot be higher than 92.73%,95.64%,96.97%and 97.82%at the four temperatures of 923K,973K,1023K and 1073K,respectively.(2)The conclusion is obtained through the experiment of preparing high-purity magnesium by low vacuum distillation under argon protective atmosphere:when the argon protective gas is introduced to make the system pressure 60KPa,increasing the distillation temperature and prolonging the distillation time will increase the volatilization rate of magnesium,showing a tendency to increase first and then stabilize.When the distillation temperature is 973K,the maximum evaporation rate can reach 6.19×10^-4g/(cm²·s),when the distillation temperature rises to 1123K,the maximum evaporation rate can reach 1.47×10^-3 g/(cm²·s),and the evaporation rate is below 973K,1023K and 1123K can reach more than 90%;after magnesium distillation,the condensate is detected by ICP-MS:when the distillation temperature is 973K,1023K and 1073K,the impurity content in the condensed magnesium meets the national 99.99Mg standard.When the distillation temperature is At 973K and 1023K,the removal rate of most impurities in magnesium is higher than 80%,and the purity of magnesium increases from 99.97%to over 99.995%.When the distillation temperature is 1023K,the direct yield of magnesium increases from 62.43%to 99.94%.(3)As the alloy separation coefficient?of Mg-Zn is close to 1,the MIVM model is used to predict the vapor-liquid equilibrium diagram of Mg-Zn and the distillation temperature is predicted.The result shows that the two-phase separation coefficient of Mg-Zn is introduced after the activity is introduced.It is still very close to 1,and it is not easy to separate.(4)When the system pressure is in the range of 40-80KPa,conduct the condensation experiment in the sub-temperature zone,the magnesium vapor is mainly condensed at773K,and the zinc vapor is mainly condensed at 633K;combined with the separation temperature predicted by thermodynamics,start the staged condensation experiment of crude magnesium dezincification.When the system pressure is 40KPa,60KPa and 80KPa,the zinc content in crude magnesium will be reduced from 0.0089%to 0.00167%,0.00171%and 0.00177%at the distillation temperature of 1094K,1130K and 1158K,reaching the grade of Mg9999 in GB/T 3499-2011 High-purity standards;the staged condensation experiment is carried out with the best distillation conditions of crude magnesium.When the system pressure is 80KPa,the crystalline magnesium obtained in the 773K condensation zone has a removal rate of most of the impurities higher than 90%,and the direct recovery rate of magnesium above 98%,the purity of magnesium reaches the standard of 99.98%high-purity magnesium.