Study On Active Magnesia And Magnesium Oxychloride Cements From Bischofite

A huge amount of magnesium resource in the western salt lakes is not utilized effec-tively due to the limitation of the technicals and economic conditions. An important way to make full use of the magnesium resource in western salt lakes is to develop magnesium prod-ucts such as magnesium oxychloride cement,et.al,which is very importmant to economy and society.Active magnesium oxide was an important inorganic chemical product. Active magne-sium oxide was prepared by calcining bischofite directly. The process was simple and low cost. The activity of magnesium oxide was determined with citric acid method. The effects of calcination temperature and time on activity of MgO were studied. The optimal conditions and the influences of magnesium oxychloride cement's strength on activity of MgO were studied. Experiments were carried out to research the relationship between the activity and the morphology of MgO by XRD and SEM. The results showed that the grain diameter of MgO increased, while the lattice constant and the activity of MgO decreased with the in-crease of temperature. The CAA value was lowest when bischofite was calcined at 550℃for 1h, and the value was 50.5s. MgO, with low degree of crystallinity, small grain size, small average particle size and rough surface, had high activity.Water was widely applied in the absorption of tail gas. The main component of tail gas was hydrogen chloride, which was one of the most important environmental contaminant in active magnesium oxide production.The single-stage absorption was designed, And the ef-fects of temperature of absorption solvent,temperature of intake air, liquid spray amount and weight concentration of cyclic spray liquid on the gas absorption were systematically studied. Finally, the optimal conditions were confirmed.MgO whiskers can be widely applied as reinforced materials due to their predominat characteristics, such as low surface energy, good mechanical strength and high elastic mod-ulus.MgO whiskers were synthesized by high-temperature flux method, using MgCl2·6H2O as raw material and KC1 as flux, and the influence of magnesium oxychloride cement's strength on MgO whiskers as additive was studied. The samples were characterized by XRD,SEM.And the optimum condition was obtained,Magnesia whiskers with a diameter of 1-50μm and a length of 120-700μm were synthesized.MgO whiskers are grown through VLS mechanism.The effects of activity of MgO,variant MgO whisker blend,mixing temperature,different amount of fly ash,the molar ratio of MgO/MgOHCl/H2O on the strength, water resistance of magnesium oxychloride cement were studied. Then the ptimal conditions were confirmed, The strength of magnesium oxychloride cement, after 28 days aging in air, when MgO/MgOHCl/H2O molar ratio was 4:1:8 and the strength was 90MPa, was the largest. The hardening mechanism, the hydration mechanism and the thermal decomposition mechanism of magnesium oxychloride cement were studied via TG-DSC,XRD and SEM.