Rare earth extraction and separation from mixed bastnaesite-monazite concentrate by stepwise carbochlorination-chemical
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ements have found a wide range of applications in modern technology. The worlds largest rare earth deposit is located at Baiyunebo[1] (or translated as Bayan Obo[2] or Baiyun Obo[3]) in China where bastnaesite and monazite co-occur intimately as associated minerals in a fluorite-containing iron ore. At present, the mixed bastnaesite-monazite concentrate is industrially treated using a hightemperature sulfuric acid process at about 800 ⬚C, followed by solvent extraction. But, the sulfuric acid process leads to a large amount of HF-containing waste gas and a slagto-concentrate weight ratio up to 0.66, annually yielding tens of thousands of tons of slag containing 0.2 wt pct of thorium, which has to be stored as radioactive waste,[4] and the solvent extraction process is energy and time consuming. Therefore, the development of environmentally conscious and energy saving processes is highly desirable for rare earth extraction and separation from the mixed concentrate. A carbochlorination process at 1000 ⬚C to 1200 ⬚C with carbon as reductant and chlorine gas as chlorination agent (Goldschmidt process[5]) has been applied industrially for bastnaesite concentrate. An important advantage with this dry process is its economy and efficiency as compared with ZHI-CHANG WANG, Professor, PENG-XIANG LEI, Graduate Student, and MING-YU CHI, Assistant Professor, are with the Department of Chemistry, Northeastern University, Shenyang 110004, P.R. China. [email protected] LI-QING ZHANG, formerly Graduate Student, Department of Chemistry, Northeastern University, is currently Associate Professor, Shenyang Institute of Chemical Technology, Shenyang 110021, P.R. China. Manuscript submitted December 20, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
wet extraction processes. But, it has not been applied industrially for the mixed bastnaesite-monazite concentrate mainly due to the high fluorine content in the rare earth chloride product and the thorium radioactive contamination both for rare earth chloride product and for non–rare earth volatile by-product. As one of the notable successes on rare earth metallurgy, Adachi and co-workers have recently developed a chemical vapor transport (CVT) process for the concentrates of monazite,[6] xenotime,[6] and bastnaesite[7] and for waste materials such as used polish[8] mediated by rare earth vapor complexes at 1000 ⬚C using carbon as reductant, chlorine gas as chlorination agent, and AlCl3 or alkali chloride as complex former. This method permits the rare earth extraction and separation to be achieved in one process. Due to the remaining contamination problem, however, they concluded that the direct use of the concentrates as raw materials would not always be appropriate and that a two-step process of the direct chlorination followed by the CVT reaction would be advantageous.[6] We[9,10] have reported the higher separation factors of neighboring rare earth elements La:Ce, Pr:Ce, and Pr:Nd from their oxide mixtures than from their chloride mixtures due to selective carbochlorination of the oxi
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