Study on Viscosity of the La 2 O 3 -SiO 2 -Al 2 O 3 Slag System
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INTRODUCTION
RARE-EARTH hydrogen storage alloys, NdFeB permanent magnets, and SmCo permanent magnets are new rare-earth materials that have been used extensively. Waste from these material production processes and end-of-life rare-earth materials serve as a secondary source of rare earth and other valuable metal elements.[1,2] Hydro- and pyrometallurgical methods can be used to recycle metals or elements. Hydrometallurgy has generally been applied for NdFeB waste treatment in ways such as the double sulfate method and preferential or complete dissolution by hydrochloric acid.[3–5] Despite its higher rare-earth recovery, the hydrometallurgical approach has some shortcomings, such as the inability to recover other valuable elements simultaneously and remaining excess acid that contributes to environmental pollution. Despite the pyrometallurgical approach being shorter and more environmentally friendly, with more value-added products, it needs to be studied further. Pyrometallurgical processes have been applied to extract alloys from Ni-metal hydride battery electrode materials, such as from Ni-Fe alloying[6–8] and hydrogen storage alloy regeneration.[9,10] Currently, pyrometallurgy focuses on rare-earth recovery and comprehensive valuable element recovery. The molten slag method has become a specific area of research focus.
YONG-CHUN DENG, Lecturer, is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China, and also with the School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Inner Mongolia, Baotou 014010, China. SHENG-LI WU, Professor, is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing. YIN-JU JIANG, Professor, and SU-QI JIA, Master Student, are with the School of Materials and Metallurgy, Inner Mongolia University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted December 25, 2015 Article published online June 9, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
A glass slag method was used to extract rare-earth elements from rare-earth hydrogen storage alloys and NdFeB[11,12] by Saito et al. The intermetallic compound and boron oxide were mixed together. High-activity rare-earth elements were transferred into the glass slag as oxides by high-temperature melting and the resultant alloy contained inert elements and boron. Rare-earth oxide was separated from glass slag hydrometallurgically. Using hydrogen storage alloys as an example, the following chemical reactions occurs 2LaNi5 + B2 O3 = La2 O3 + 4Ni + 2Ni3 B:
½1
In a waste Ni-metal hydride battery recycling program,[13,14] which was financed by the German government, Ni-Co alloys and rare-earth slag could be recovered from waste Ni-metal hydride batteries by melting separation. Rare earth could be extracted from rare-earth slag to recycle Ni-metal hydride battery electrode materials. The program has not yielded any breakthroughs, mainly because of problems expe
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