Study On Preparation Of High Purity Magnesia By Thermal Decomposition Of Magnesium Chloride

Brine contains varieties of valuable extract substances, among them, magnesium chlo-ride is one of high-content and value-added products. Magnesium chloride not only has great value of developing but also can be used to produce other magnesium series products which have extensive applications. One of them is high purity magnesia. At present, there are a lot of methods to produce high purity magnesia; magnesium chloride pyrolysis is one of the most popular methods in recent years. For the reason that it needs no additives, lower production cost, no pollution and easy to prepare, it becomes the best choice for many companies willing to put into mass production.In this study, uses the process of thermal decomposition to produce high purity mag-nesium oxide from high quality magnesium chloride, which was made from bromine ex-traction waste brine. There are three parts to explore the parameters of producing high pu-rity magnesium oxide. Studied the influence of one single factor, such as calcination time, calcinations temperature on the purity, activity of magnesium oxide and decomposition rate of magnesium chloride, also investigated the relationship between activity of magnesium oxide and its microstructure. Study showed that, with the increase of magnesium chloride calcination temperature and calcination time, the purity of magnesium oxide, decomposi-tion rate of magnesium chloride and grain size has an increasing trend, while magnesium oxide activity decreases gradually. From the relationship between magnesium oxide activity and the grain size, calcination temperature and time influence the crystallinity of magnesi-um oxide.With the increase of temperature and time, magnesium oxide crystals tend to be more complete, the activation center reduces.In the purification stage of impurities, examined the single factor, washing temperature and washing time, stirring speed and solid-liquid ratio on the chloride ion removal rate and purity of magnesium oxide, got the optimal parameters by orthogonal experiment:washing temperature was80℃, washing time was40min, stirring speed was830r/min, solid-liquid ratio was0.05g/ml.In the second calcination stage, studied the effect of calcination tem-perature and calcination time on the purity and activity of magnesium, concluded the opti-mizing parameters:calcination temperature was650℃and calcination time was one hour. Finally, concluded the optimal parameters in preparation of high purity magnesia. The pu-rity of the final product was more than99%. In this paper, also studied the mechanism and dynamics of thermal decomposition of magnesium chloride by TG-DTG analysis method, choose Doyle method to calculate, the results is Ei=68.26KJ/mol, A)=7.59×105s-1; E2=123.99KJ/mol, A2=1.38×1012s-1; E3=138.70KJ/mol, A3=6.70×1012s-1; E4=176.06KJ/mol, A4=3.41×1015s-1.This study invested the reaction mechanism and kinetic parameters of magnesium chloride, which provide theoretical basis for producing high purity magnesium oxide by thermal decomposition of magnesium chloride. Based on the study and optimization of thermal decomposition parameters, it provided feasibility parameters for the basis of indus-trial production.