| There are about 4 million tons of ascharite minerals, which contain higher ingredient of MgO and lower SiO2 comparing with the nomal minerals, in Kuandian, Liaoning province. The current utilizing method of this resource is to produce borax by carbon dioxide-soda process. However, the high content of MgO makes the ground paste sticky and thick which leads to the waste of resources and pollution of environment In order to solve this problem, according to the characteristic of higher MgO and lower SiO2 of the mineral crystal structure, firstly, in the process of calcinations, the high activity of magnesiat was measured. Then the vacuum-thermal reduction method was utilized with the reductants of ferrosilicon alloy, silicon-aluminum alloy and calcium carbide. As a result, the magnesium is produced from the dissociate MgO and the B2O3 is enriched in residual materials.In the theory analysis part, the initial reaction temperature is obtained by thermo-calculation. As a result, the initial reduction reaction temperatures are 1453K,1782K, 1034K respectively under the condition of vacuum and adding calcium oxide, with silicon-aluminum alloy, ferrosilicon alloy and calcium carbide as reluctants.In the process of roasting, the decomposition circumstances were analyzed by calcinations and the thermogravimetry method under different temperatures. The ignition loss rate was measured at selected temperature for various holding time, and then the activity of the calcined magnesia was measured with the citric acid method. Consequently, it obtains that the suitable calcinations temperature range is 1173-1223K and holding time is 0.5-1.0h. The optimum calcinations temperature is 1223K and holding time is 0.5h.In the reduction experiment, when ferrosilicon alloy is the reluctant, the orthogonal experiment shows the optimum reduction condition is the temperature of 1453K, the time of 2h, the briquette pressure of 35 Mpa and the excess reductant of +5%, which leads reduction rate to 48.16%. However, as to the factor of lower reduction rate and higher ferrum content in the residual materials, ferrosilicon alloy is not suitable to be applied in this experiment; When increasing excess reductant and calcium oxide quantity, which is over 30%, the reduction rate can be made at the summit,71%, with the silicon-aluminum alloy as reluctant; when calcium carbide is the reductant, the optimum condition is the temperature of 1453K, the time of 2h, the briquette pressure of 35 Mpa and the excess reductant of 10%, which leads reduction rate to 64.5%.When compares residual materials with the raw mineral, there is almost no change in the gross quantity of boron oxide. But it indicates that after more reductants and calcium oxide are added, the content of boron is brought down. Against the problem, the residual materials were grinded and dealed with water, making the CaO into Ca(OH)2 and the separate C floating upon the surface, the residual CaC2 into ethyne. Therefore, the content of B2O3 is increased, and the proportion of magnesium and boron changes from former MgO:B2O3= 2.5:1 to present round MgO:B2O3=1:1.2. That may approach to the standard of producing alkali-free fiberglass and make the residual materirials more available and profitable.Among the three reductants, ferrosilicon alloy does not suit to this experiment; silicon-aluminum alloy has higher reduction rate, but lower content of boron, further reserach shoud be done; Calcium carbide is the best reductant, according to the analysis.In a word, as to the ascharite minerals of chemistry composition and mine structure that is composed of camsellite, dolomite and magnesite, this experiment utilizes the vacuum-thermal reduction to separate boron and magnesium, producing metal magnesium and residual materials containing higher boron which is suitable to manufacture alkali-free fiberglass. It is undoubtedly a new way to take full advantage of resources, which can enhance the economic effect of ascharite minerals, reduce environmental pollution and realize clean production.
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