Extraction of tantalum and niobium from tin slags by chlorination and carbochlorination
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I.
INTRODUCTION
NIOBIUM and tantalum are important elements used in many high-technology applications such as electronic, energy, superconductors, and aerospace.[1,2] Industrialized countries consume the majority of the world production (≥95 pct) of these refractory metals and produce less than 5 pct.[3] These elements are not abundant in the earth’s crust. The average content of Nb and Ta in the earth’s crust (Clarke*)[4] are 20 and 2.3 ppm, respectively. This may ex*Average content of a specific element in the earth’s crust.
plain the high price of their concentrate (about 30 US$/Ib.[5]) Their main bearing minerals are pyrochlore, microlite, tantalite, columbite, and columbo-tantalite. These minerals are often associated to cassiterite. The mineral processing of these ores leads to a cassiterite (SnO2) concentrate containing up to 2 pct of Nb and Ta oxides as mixed grains or inclu-
I. GABALLAH, Senior Researcher, Laboratoire Environnement et Mine´ralurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing and Environmental Engineering Team, INPL-ENSG, rue du Doyen M. Roubault, BP 40, 54501 Vandoeuvre Cedex, France. E. ALLAIN, formerly Research Associate with the Mineral Processing and Environmental Engineering Team, is Postdoctoral Research Associate with INASMET, Camino de Portuexte 12, 20009 San Sebastian, Spain. M. DJONA, formerly Research Associate with the Mineral Processing and Environmental Engineering Team, is Postdoctoral Research Associate with the Universite´ du Que´bec, Institut National de la Recherche Scientifique, INRS-Ge´oressources, Complexe Scientique, 2700 rue Einstein, CP 7500, Sainte Foy, G1V 4C7 Canada. Manuscript submitted October 31, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS B
sions.[6] During the pyrometallurgical extraction of tin from cassiterite, oxides of Ta, Nb, Ti, Zr, rare earth elements, Si, Fe, Al, and Ca are concentrated in the slag. Conventional methods used for the extraction of niobium and tantalum compounds from tin slags consist of full dissolution with HF, HF 1 H2SO4,[7] or smelting in electric furnaces.[8] Currently, these processes are limited either by economic or by environmental considerations.[9] Due to the currently low metal market and new environmental regulations, more efficient, flexible and environmentally friendly processes are required for the extraction of these metals from ores, industrial byproducts, or wastes. The recovery of tantalum and niobium from tin slag was carried out in our laboratory using a two-step process of leaching[10] followed by the chlorination or the carbochlorination of the resulting concentrates. This article focuses on the kinetics of chlorination and carbochlorination of these tantalum- and niobium-bearing concentrates with Cl2-N2 and Cl2-CO-N2 gas mixtures. Two concentrates differentiated by their tantalum and niobium oxide contents were used in this study. They were designated as low-grade concentrate (LGC) and high-grade concentrate (HGC). II.
LITERATURE REVIEW
Almost all the publica
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