Analysis of Magnesia Carbothermic Reduction Process in Vacuum
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INTRODUCTION
MAGNESIUM is produced by two main processes: electrolysis of molten magnesium chloride and thermal reduction of magnesia.[1] Electrolysis is the predominant route in Western countries, accounting for about 77 pct of total production in these countries, but this process is characterized by high-energy requirements.[2] More than 95 pct of China’s production of magnesium is based on the pidgeon process, which uses the silicothermic reduction of dolomitic ores. Even though the pidgeon process is energy intensive and labor intensive, it is simple and has low capital cost.[3] Carbothermic reduction is an alternative to both the silicothermic and electrolytic processes for the production of magnesium.[4,5] The reaction between MgO and C may provide a new route toward the production of magnesium. But for the carbothermic reduction reaction type, one point of view was that the main reaction is a solid–solid reaction, whereas the other was that the main reaction is a gas– solid reaction.[6–8] Researchers have proposed that in the incipient stage, CO and magnesium vapors are formed
through the reaction MgO(s) + C(s) = Mg(g) + CO(g) at the points of contact between the reactant particles. In addition, the reaction rate increases along with the compacting pressure of MgO with C and increasing C/MgO ratio. As reduction proceeds, the contact area between MgO and C particles decreases as the particle size increases, and the solid–solid reaction is no longer the main reaction process. Then the reaction MgO(s) + CO(g) = Mg(g) + CO2(g) is now the main reaction. The possible rate-determining step is the gas diffusion of gases through the porous compacts.[9,10] The aim of the present work[11,12] was to investigate a definite mechanism of the MgO reduction process. The reactions of the carbothermic reduction process were also proposed. The residue and product were studied by X-ray diffraction (XRD), and the composition of the condensation product was examined by energy-dispersive spectroscopy (EDS).
II.
EXPERIMENTAL DETAILS
A. Raw Material YANG TIAN and BAO-QIANG XU, Associate Professors, CHENG-BO YANG, Master Student, BIN YANG and DA-CHUN LIU, Professors, TAO QU, Lecturer, HONG-XIANG LIU, Ph.D. Student, and YONG-NIAN DAI, Academician, are with the National State Key Laboratory of Complex Nonferrous Metal Resources Clear Utilization, Kunming University of Science and Technology, Kunming 650093, P.R. China; the National Engineering Laboratory for Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, P.R. China; the Key Laboratory of Non-Ferrous Metals Vacuum Metallurgy of Yunnan Province, Kunming 650093, P.R. China; and the College of Metallurgy and Energy engineering, Kunming University of Science and Technology, Kunming 650093, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 30, 2013. Article published online July 4, 2014. 1936—VOLUME 45B, OCTOBER 2014
Analytical-grade magnesia and carbon were used as the raw materials in our experiments.
B. Schematic Diagram of Vacuum
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