| As a light and loose white powder insoluble in water, light magnesia of high purity has high apparent specific volume and has been widely applied in ceramics, refractory products, various adhesives, paint filler, rubber accelerators and activators, medicine, glass, plastic, as well as food industry. China has rich salt lake resources, and magnesium resources in Qinghai Qarhan Salt Lake and Xinjiang Lop Nur salt lake are in urgent need of development; meanwhile, the development of salt lake magnesium resources in preparation of magnesia on one hand can promote the comprehensive utilization of salt lake, on the other hand, it can help solve our current depletion of solid magnesium ore and declining quality of magnesium products; besides, it can greatly ease the harm caused by excessive magnesium due to the development of the potassium salt industry. Hence, the development of salt lake magnesium resources in preparation of magnesia brings about great social and economic benefits to the society.The magnesium precipitation-carbonation-calcination three-step new process involves brine in Xinjiang Lop Nur salt lake subtype sulfate salt lake as the raw material, the precursor of magnesium hydroxide by ammonia preparation, and light magnesia of high purity after carbonation and calcination. The experiments show that ammonium bicarbonate carbonation of magnesium hydroxide can effectively reduce the amount of S and B in magnesia, and improve the apparent specific volume and purity of magnesia. The purity of magnesia produced under the optimal conditions exceeds99%, the apparent specific volume reaches10mL/g, and the main indicators reach HG1-324-77grade indicators.With the bischofite in Qinghai Qarhan Salt Lake as the raw material, and lime as the precipitant, the precursor of magnesium hydroxide is prepared. Light magnesia with high purity is produced through calcination carbonation, and the new process is established. According to the principle of thermodynamic equilibrium, the CaCl2-Ca(OH)2-H2O system in273.15K conditions has been researched, which is involved in the lime preparation by calcium chloride mother liquor circulation in the magnesium hydroxide preparation, this thesis draws out the thermodynamic equilibrium log c-pH diagram of Ca(OH)2-H2O system in273.15K conditions, and figures out the impact of pH and concentration of CaCl2on the concentration of Ca(OH)2. Through applying the Debye-Huckel limit law, the thesis calculates the relations of concentrations between CaCl2and Ca(OH)2, and finds that the experimental values match the calculated values. When the calcium chloride concentration is bigger than2.5720mol/1, the CaClOH phase precipitates, and the calcium chloride mother liquor is not available to allocate lime, the calcium chloride mother liquor can be recycled to prepare lime by132times. The experiments show that the two-way-the base solution combination is the best. The increasement of the mass percent concentration and volume of calcium chloride solution contribute to the reduction of reaction system super saturation. Lime method is superior to the traditional milk of lime method, since the contents of impurities in magnesium hydroxide are far less than that of traditional milk of lime method, and purity can reach more than99%after washing. Continuous experimental preparation of magnesium hydroxide has good deposition property as well as stable products quality. Prepared by calcinating after carbonization, magnesia has its apparent specific volume improved efficiently. With high purity, the magnesia has complete crystal forms, and product quality has reached the grade index of HG1-324-77. |
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