The Exploration And Utilization Of Bischofite Resources Of Qinghai Saline Lake

This article mainly aimed at the Qinghai Chaerhan saline Lake bischofite dehydration of ammoniation-alcohol method to conduct the related basic research.In the method, ammonia content is a key parameter in the crystallization reaction system, the purity of production and the granularity inluenced by crystallization condition, high purity anhydrous magnesium chloride influenced directly by calcination conditions. Therefore, this thesis includes three aspects and as follows:1. Solubility of ammonia: The experimental results of 143 points solubility data of ammonia in liquid mixtures of methanol and ethylene glycol are reported, in which, the eleven (gas-free) solvent compositions were considered from 0.0 to 1.0(mass fraction of ethylene glycol), the seven temperatures amounted to 278 K, 288 K, 298 K, 308 K, 318 K, 328 K and 338 K, and the solubility pressures were 101.3 kPa and 70.0 kPa respectively. A thermodynamic model which based on the extended Raoult’s law and the extended Henry’s law, was proposed to describe the ammonia solubility in the mixture solvent under the experiment’s conditions, the calculated solubility show good agreement with the experimental data.2. In the reaction crystallization process, the influence of ammonia content and temperature was studied. The reaction crystallization was influenced by temperature and ammonia content in the solution greatly, if the ammonia content too little, the reaction could not be completely; too much, the need of ammonia wonld increase largely. If temperature is too low, the viscosity of ethylene glycol would increase making it difficult to spread for ammonia, leading the reaction not completely. Too high temperature leads to side reaction react and can not get the hexammoniate magnesium chloride crystal, high content of magnesium chloride in the solution and low recovery. Experiment result shows that the proper operating conditions are as follows: 40 kPa, <305 K; 70 kPa and 101.3 kPa, <323 K.3. The therma decomposition characteristics of MgCl2?6NH3 and preparation of anhydrous magnesium chloride: MgCl2?6NH3 synthesized by bischofite was characterized by chemical analysis and X-ray powder diffraction. The results of TG-DTA show that the thermal decomposition of MgCl2?6NH3 could be divided into four stages. The results of DSC show that the thermal decomposition of MgCl2?6NH3 has four endothermic stages, getting the heat quantity of endothermic for each stage and total process. Comparing TG-DTA and DSC results, it was considered that the second and third peaks in TG-DTA are the two parts of the middle temperature stage and the third and fourth peaks in DSC are the two parts of the high temperature stage. Thus, the thermal decomposition of MgCl2?6NH3 were divided into three stages briefly. The heat quantity and the number of losing ammonia molecule were calculated at each stage.4. The effect of crystal purity, up rates and shielding gas was studied by the temperature-controlling calcination, and getting the appropriate operating conditions of anhydrous magnesium chloride preparation. The proper calcination temperature is from 653.15 K to 693.15 K.