Studies On The Preparation Of Anhydrous MgCl₂ Used In Manufacture Of Metal Magnesium From Bischofite Abundant In Salt Lakes By Ammoniation Processes

The dissertation investigates several aspects of a recently developed technique of preparation of anhydrous MgCl₂ for electrolysis manufacturing of metal magnesium, named ammonium method, which by preparing the complex of MgCl₂ with ammonium and then thermally decomposing the complex formed produces anhydrous MgCl₂, from the mineral bischofite-hydrated MgCl₂ which is affluent in brine. Three kinds of the technique are chosen to apply in this work, i.e. using ethylene glycol, methanol, and water as solvent for obtaining the MgCl₂-ammonium complex respectively. The thermal behavior of the complexes is studied for the understanding of the decomposition process in preparing anhydrous magnesium chloride. Substitutes for ammonium in formation of complex in the technique are looked for in organic amine compounds, i.e., triethanolamine and hexamethylenetetramine reacting with MgCb are studied in various solvents. The preparation of highly pure MgCl₂ solution and potassium chloride are tested from carnallite by organic solvents. The content of the investigations in the dissertation and the results are as follows:1. The processes for preparation of MgCl₂ ammoniates in ethlylene glycol, methanol and water solution are investigated by the method suggested by Sheehan et al.. The results shows that the formation of complex of MgCl₂ and ammonium in anhydrous solution of ethylene glycol can be accomplished at lower temperature than reported in the patents, and reaction temperature of ammonization and viscosity affect the formation of the complex, i.e., the lower the reaction temperature is, the higher purity of the complex is obtained, and high viscous anhydrous MgCl₂-ethylene glycol solution used in the complex reaction introduces MgCl₂ diglycollate diammoniate. In methanol solution, unlike the conclusion reported in the Patents, without the removal of water introduced by hydrated MgCb, magnesium chloride ammoniate is obtained with some impurity from the hydrolysis of MgCl₂ even at lower temperature than reported. The complex cannot form in water solution by Sheehan's method unlessliquid NH3 is used to maintain the concentration of ammonium in the range of 35⁶5 percent of the weight of the water solution at low temperature.2. The thermal decomposition reaction of MgC^ hexammoniate and MgC^ diglycollate diammoniate is studied by DTA/TQ with X-ray powder diffraction technique and chemical analysis for identification of the thermal decomposition products in the course. The results indicates that MgCb hexammoniate decomposes by three steps, MgCl2.4NH3, MgCl2.2NH3 and MgC^, into anhydrous magnesium chloride below 450° C, higher temperature makes anhydrous magnesium chloride oxidized by oxygen. MgCl2.2C2H4(OH)2.2NH3 in the produced complex MgCl2.6NH3( lowers the quality of anhydrous MgC^ product by thermal decomposition into C ' and MgO. The process of thermal decomposition of the complex is proceeded in tubular furnace and fluidic bed, indicating that MgCl2.6NH3 can successfully decompose into anhydrous magnesium chloride in inert gas, such as N2 or Ar, at the temperature of 600° C in the former and 400° C with the latter.3. The reactions of MgCk with triethanolamine and hexamethylenetetramine are investigated respectively in water and methanol for examining the ability of the organic amines to substitute ammonium as ligands for forming MgCk complex. The work results in the triethanolamine hydrochloric salt obtained from aqueous solution and methanol solution through reaction of hydrated magnesium chloride and triethanolamine because of the stronger basicity of the organic amine. Hexamethylenetetramine reacts with MgC^ producing a supramolecular compound, di(hexamethylenetetramine) decahydrated magnesium chloride (MgCl2.10H2O.2C6Hi2N4) in water and not in methanol solution. The single crystal structure of the two products are analyzed showing that N(C2H4OH)3.HC1 has a layered structure with hydrogen bonding between layers, and MgCl2.10H2O.2C6Hi2N4 forms netlike structure with hydrogen bonding between molecules. The analysis of the thermal behavior of the two products indicates that NiX^HiQH^.HCl only take place phase transformation without thermal decomposition, and MgCl2.10H2O.2C6Hi2N4 may take a complicated thermal decomposition course into MgCk.xL (x=0.59, L= C6HI2N4).4. Using ethylene glycol and methanol as solvent for preparation of highly pure MgCl2 solution and pure potassium chloride from camallite is studied. The results are that ethylene glycol cannot be used to do so, because that camallite, even dried one, dissolves in the solvent, and even if the system of camallite dissolved in ethylene glycol is dehydrated by vacuum fractionation to aiihydrous solution, a considerable amount of potassium chloride dissolves in the solution. With methanol as solvent, MgCb and KCl in camallite can be substantially separated to highly pure MgCh solution and pure KCl by using dried camallite with less than 4 water molecules.