Novel Method to Prepare Magnesium by Aluminothermic Reduction of Magnesia and Calcium Hydroxide at Normal Atmosphere, 12

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GNESIUM

is widely applied in the automobile, aviation and aerospace, and military fields due to its lightweight, high-specific strength, and high-specific stiffness. Nevertheless, magnesium is mainly prepared by the Pidgeon process, which has the disadvantage of high-energy consumption and serious environmental pollution.[1] Carbothermic reduction is a very promising method to extract magnesium, and many studies on the kinetics and mechanism of carbothermic reduction of magnesia have been carried out.[2–7] Yet, there are still several problems that prevent this method from being applied further in industrial fields.[8] Some researchers try to use the aluminothermic reduction method to obtain magnesium, which has a lower reaction temperature than carbothermic reduction.[9,10] On the one hand, thermodynamic calculation of the aluminothermic reduction reaction that was used to prepare magnesium has been done.[11,12] On the other hand, extracting magnesium from a mixture of calcined magnesite and calcined dolomite applying the vacuum aluminothermic reduction method has been studied, and it was found that three reduction stages were classified during the aluminothermic reduction of magnesia.[13,14] Some researchers try to obtain high-whiteness aluminum hydroxide by making use of the residues that TENG ZHANG and BIN ZHENG, Lecturers, SHUANG-MING DU, Professor, WAN-CHANG SUN, JU-MEI ZHANG, and LI-BIN NIU, Associate Professors, and XIAO-HU HUA, Engineer, are with the School of Material Science and Engineering, Xi’an University of Science and Technology, Yanta District, Xi’an 710054, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 13, 2015. Article published online October 18, 2016. 488—VOLUME 48B, FEBRUARY 2017

were produced by aluminothermic reduction of magnesia.[15] The kinetics of the isothermal and nonisothermal of the reaction were also reported.[16–18] Although these reported results have been acquired, some problems still exist in the aluminothermic reduction processes of magnesia. First, the reduction ratio of magnesia and the utilization ratio of aluminum are lower because of the formation of magnesium aluminate spinel. Second, the reduction temperature is higher than 1473 K (1200 C). High-energy ball milling has a very good reinforcement effect on a solid phase reaction,[19–24] and it could make the reaction temperature lower by increasing the mechanical energy storage of reactants, accelerating the reaction rate extremely by increasing the interfacial area of the sample. It was found that high-energy ball milling could reduce the reaction temperature compared with the reaction that was not subjected to high-energy ball milling.[25] In our previous work, silvery white magnesium crystal was obtained by carbothermic reduction of magnesia reinforced by high-energy ball milling at 1000 Pa, 1273 K (1000 C).[26,27] In this article, the new experimental apparatus was designed to study the aluminothermic reduction reaction of magnesia, which was reinforced by high-energy ball milling at normal