Study On New Technology And Fundamental Theory Of Anhydrous Magnesium Chloride Prepared From Ammonium Carnallite

As one of the lightest structural materials, magnesium is applied increasingly in various areas. The two main processes of producing magnesium are thermal reduction and electrolysis. The thermal reduction process is an old one with high energy consumption and severe pollution. By comparison, the electrolysis process shows some advantages such as lower energy consumption and lower pollution. It is a very promising technology. The key to electrolysis process is to obtain the suitable raw material of high-puried anhydrous magnesium chloride. There is a great reserve of magnesium chloride in Salt Lake in Qinghai province of China which can provide high grade raw materials for producing magnesium metal. In this thesis, processes of producing high-puried anhydrous magnesium chloride are studied. Ammonium carnallite is synthesized by using bischofite from Salt Lake and filtrate stock of deposit magnesium. Anhydrous magnesium chloride is prepared by organic solvent, reaction of ammonia and gas-solid reaction of ammonium carnallite. The crystallization kinetic equations at low temperature are established with solubility data of ammonium carnallite. The dehydration kinetic parameters of ammonium carnallite are calculated by thermogravimetric analysis. Kinetics of non-isothermal decomposition is studied for ammoniation magnesium chloride and ammoniation ammonium carnallite to eliminate ammonia.The dehydration of MgCl₂·6H₂O is studied by thermal calculation and kinetic analysis. The results show that dehydration is difficult at lower temperature and hydrolysis will take place when MgCl₂·6H₂O is dehydrating at higher temperature. In flowing air condition, when heating temperature is between 110℃ and 200℃, MgCl₂·6H₂O will be changed to MgCl₂·2H₂O without hydrolysis. It must be carried out in a protected atmosphere if it continues to be dehydrated afterwards. Otherwise, hydrolysis would occur when it is being dehydrated.It is studied that the optimum preparative technology of ammonium carnallite with bischfite from Salt Lake and filtrate stock of deposit magnesium by ammonia. When the molar ratio of MgCl₂ : NH4Cl is 1: 1, pH=6.0, reaction temperature is at 85℃, agitating speed is 500r·min^-1 , heating time is 1h, crystallization at 7℃ is 4h, the crystal ratio of ammonium carnallite after filtration and drying is about 60% at first time. The crystal ratio is over 80% for the second time. Solubility of ammonium carnallite is measured from 10℃ to 100℃. Crystallization kinetic equations are established with kinetic parameters...