Recovery Behavior of Rare Earth from Bayan Obo Complex Iron Ore
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THE Bayan Obo ore deposit in the Inner Mongolia region of North China is one of the best known ironLREE-niobium deposits in the world. It accounts for 35 pct of rare-earth resource of world’s proven reserves and approximately 80 pct of China.[1–3] Currently, it is mined mainly as an iron ore. After grinding to smaller than76 lm of 90 to 95 pct, a feeble magnetic powerful magnetic-flotation process is used for recovering about 70 pct of iron and less than 10 pct of the rare earth. Most of the rare metal minerals remain in the tailings. Because there is only 230 million tons of the complex iron ore left in Main and East Ore Body, and the current designed capacity is 12 million tons per year, the ore will be used up within 20 years.[4–6] Therefore, the comprehensive utilization of Bayan Obo ore has become an urgent task. Besides physical concentration method, the blast furnace process has been used for processing of Bayan Obo run-of-mine ore.[7,8] The ore was directly loaded into blast furnace for ironmaking, and rare-earth elements remained in the slag with fluorine. The slag, containing 14 pct RE2O3, i.e., rare earth oxide, has been used for making rare-earth alloys. Investigations of the composition, slow-cooling crystallization and mineral processing of the slags have been conducted. Several YINGUI DING and GUANG WANG, Ph.D. Candidates, and QINGGUO XUE and JINGSONG WANG, Professors, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 13, 2012. Article published online November 8, 2012. 28—VOLUME 44B, FEBRUARY 2013
mineral and metallurgical processes have been employed to concentrate the rare-earth mineral from the slag, such as gravity separation, magnetic separation combined with gravity separation, and hydrometallurgy.[9–13] Nonetheless, the running condition of blast furnace gets worse with the coke ratio increasing, the productivity dropping, and furnace lining eroded seriously; this process is no longer used. A new process has been proposed by the authors’ laboratory for the rare earth and iron separation based on carbon-bearing pellet reduction and melting technology.[14,15] In this work, a simulation test of rotary hearth furnace was conducted using Bayan Obo complex ore and pulverized coal as raw materials. The Bayan Obo complex iron ore was reduced and melting separated to produce iron nugget and rare-earth-rich slag. Subsequently, the slag was leached by hydrochloric acid to recover rare earth. The main objective of this research is to investigate the behavior of rare earth in the carbothermic reduction and melting separation process, and to develop a reasonable slag treatment model to make full use of the rare-earth-rich slag without slag modification.
II.
EXPERIMENTAL
A. Raw Materials The chemical composition of iron ore is given in Table I. The main useful mineral phases are iron oxides, bastnaesite-(Ce), and fluorite. The reducing and carburizing agent
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