The Conversion from Magnesium Hydroxychloride to Anhydrous Magnesium Chloride by Solid-State Reaction
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INTRODUCTION
MAGNESIUM and its alloys, as the lightest structural materials, have been widely used in transportation industries, military industries, and electronic industries.[1–5] Currently, there are two methods for the industrial production of magnesium, including the electrochemical method and the thermal reduction method.[6] The electrochemical method is more promising because it consumes less energy and causes lower pollution. Nevertheless, the preparation of anhydrous MgCl2 contributes 50 pct of the overall costs in electrolytic magnesium production, which has limited its large-scale application.[7] The key for the preparation of anhydrous magnesium chloride is to control the content of magnesium hydroxychloride in the dehydration product.[8,9] Magnesium hydroxychloride is a harmful impurity in the process of electrolytic magnesium production, which will decrease current efficiency and disturb electrolytic process. To reduce the content of magnesium hydroxychloride in the dehydration product and obtain high-purity anhydrous magnesium chloride, many researchers suppressed the formation of magnesium hydroxychloride in ZHIMIN ZHANG, TIZHUANG WANG and YAN YAN, Assistant Professors, are with the State Key Laboratory of MultiPhase Complex Systems, Institution of Process Engineering, Chinese Academy of Science, Haidian District, Beijing 100190, P.R. China. SHIWEI CHEN, Ph.D. Student, is with the State Key Laboratory of Multi-Phase Complex Systems, Institution of Process Engineering, Chinese Academy of Science, and also with the Graduate University of Chinese Academy of Science, Beijing 100049, P.R. China. XUCHEN LU, Professor, is with the State Key Laboratory of Multi-Phase Complex Systems, Institution of Process Engineering, Chinese Academy of Science, and also with the United Research Center for Resource and Materials, Wuhai 016000, P.R. China. Contact e-mails: [email protected]; [email protected] Manuscript submitted February 14, 2015. Article published online November 5, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
the heating process of magnesium chloride hexahydrate. For example, Braithwaite et al.[10] suppressed the formation of magnesium hydroxychloride by dehydrating magnesium chloride hexahydrate in hydrogen chloride atmosphere. However, the consumption and the reuse of a large quantity of corrosive hydrogen chloride gas are obvious disadvantages. Allain et al.[11,12] dissolved magnesium chloride hexahydrate into a certain kind of organic solvent, and then ammonium gas was introduced to it to form magnesium chloride hexammoniate. The formation of magnesium hydroxychloride was effectively suppressed by heating magnesium chloride hexammoniate. However, the considerable consumption of organic solvent has limited the large-scale industrial applications. Therefore, using corrosive gas or organic solvent to suppress the formation of magnesium hydroxychloride is complicated and costly. In this paper, we converted magnesium hydroxychloride to anhydrous magnesium chloride by its solid-state reaction with ammoni
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