Researching On The Dynamics And Parameters’ Optimization Of Smelting Magnesium By Silicon-thermo-reduction

In China, Baishan, Jilin province has abundant dolomite resources, which, as weall know, is a kind of important raw materials in smelting magnesium bysilicon-thermo-reduction. In recent years, Baishan has built two industrial parks andmany magnesium smelting companies while developing magnesium industry withgreat effort. The trend of development is anticipated and the technology breakthroughis discussed in the future according to investigates and surveys on current situation ofmagnesium resources and industry in Bishan.Experiments are carried out using optical microscope, X-ray diffraction,scanning electron microscope and infrared spectroscopy to identify the quality of themagnesium smelting dolomite from Tian’an Magnesium Industry Co., Ltd inHunjiang area, Baishan. The results show that these dolomite stones, which areexcellent in quality, have high purity with magnesium oxide in an amount about13.04%by weight and a very small amount of silicon dioxide as impurity. In addition,the atomic ratio of magnesium and calcium is1:1. Therefore, the dolomite fromBaishan is relatively an ideal raw material for smelting magnesium.It can be proved that silicon can be used as reducing agent in reducingmagnesium oxide and calcined dolomite. The temperature, at which reductionreaction starts, can also be calculated. Without CaO in reactants, the temperature inreducing MgO is2349.71K. The temperature drops to2106.11K when SiO2and MgOare slagged to be2MgO·SiO2. With CaO in reactants, the temperature in reducingMgO·CaO is1768.07K when SiO2and CaO are slagged to be2CaO·SiO2. It showsthat slag formation benefits the reaction temperature reducing. Because calcineddolomite contains CaO, there is no need to add CaO, which makes the productiontechnology easier.The reduction reaction of silicothermic process for producing magnesium is analyzed by macrokinetics. There are all kinds of factors influencing the reaction rate,such as contact area between two solid phases, diffusion rate of substances, heattransfer form environment to reactants, heat transfer between products, briquettingpressure of reactants and diffusion rate of magnesium vapor. The condensation rate ofmagnesium vapor has nothing to do with the reduction reaction rate.The energy consumption in the reduction reaction of silicothermic process forproducing magnesium is calculated using thermodynamics methods and technologicalparameters from Tian’an Magnesium Industry Co., Ltd. The results show that there isa potential of energy saving of16.12%in the reduction reaction.The quality of crystallized primary magnesium from Tian’an MagnesiumIndustry Co., Ltd is identified using optical microscope and X-ray diffraction. Itshows that the crystallization is fine and close and in the shape of dendrites. Thecrystallized primary magnesium has high purity and a very small amount of SiO2andAl2O3as impurity, which illustrates that the production process and technologicalparameters are well controlled.The technological parameters influencing the reaction rate and magnesiumoutput rate in the reduction reaction of silicothermic process for producingmagnesium are optimized to increase reaction efficiency and reduce production costs,including reduction temperature, reduction time and briquetting pressure. Thereduction temperature should be controlled from1448K to1473K. The reductiontime should be controlled from7hours to9hours and the briquetting pressure canrange between150kg/cm2and160kg/cm~2.