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TANTALUM Tantalum was discovered in 1802 and named after the Greek mythological hero Tantalus. In 1844, it was reported that two similar elements, tantalum and niobium, were obtained from columbite (Fe,Mn)(Nb,Tah0 6 . In 1866, these two elements were separated. Tantalum is a gray, body-centered cubic metallic element, with atomic number 73 and atomic weight 180.948. It has two natural isotopes 180 and 181, the latter being the more abundant. The electronic configuration of tantalum is [Xe]4f 14 3d 3 6s 2 , with common valence of 5 +.Its ionic radius for coordination number 6 is 0.72 A and electronegativity, 1.5. Tantalum has similar chemical properties to those of niobium. Its boiling point is 5425°C. It is a refractory metal, with a high melting point of 2996°C, and is resistant to corrosion. Tantalum is mainly used in electronics and optics (50%) and in cemented carbides or as an alloying additive in superalloys (30~40%). Ta-dominant minerals (e.g. tantalite-columbite, wodginite, microlite, tapiolite, simpsonite and alumotantalite) are mainly found in the highly fractionated rare element granitic pegrnatites. The most important economic sources of tantalum are alkali granites, greisenized granites, rare element granitic pegmatites and tantalum-bearing cassiterite (Sn0 2 ) deposits. Pollard (1989) indicates the most important characteristics of granitehost tantalum deposits. Tantalum mineralization of most economic interest occurs among the complex pegmatites of syodumene and petalite and the albite-spodumene pegrnatites (Cerny, 1989a). Geochemical methods to distinguish between tantalum-bearing and barren pegmatites are presented by Morteani and Gaupp (1989) and Cerny (1989b ). Ta enrichment over Nb in granitic pegmatites depends more on the degree of pre-enriclnnent in parental leucogranite than on fractionation during crystallization of the pegmatite itself, but the latter is important (Moller, 1989). From the most primitive to the highly fractionated rare element granitic pegmatites there is an increase in the Ta/Nb ratio of the (Nb,Ta) mineral species (Cerny et al., 1985). A systematic increase of Ta at the expense of Nb is evidenced by the increase in the Ta/(Ta + Nb) ratios of micas and Ta~Nb mineral species from
the outer wall zone to the core of Li-enriched rare element granitic pegmatites (Spilde and Shearer, 1992). TheTa enrichment trend is continued in most of the alteration products that replace these yre-existing mineral species in highly fractionated pegmatites (Cerny et al., 1985). A.M.R. Neiva
Bibliography
* Additional bibliographic references may be found in this work. *Cerny, P. ( 1989a) Characteristics of pegmatite deposits of tantalum, in Lanthanides, Tantalum and Niobium (eds P. Moiler, P. Cerny and F. Saupe). Berlin: Springer-Verlag, pp. 195~239. Cerny, P. ( 1989b) Exploration strategy and methods for pegmatite deposits of tantalum, in Lanthanides, Tantalum and Niobium (eds P. Moiler, P. Cerny and F. Saupe). Berlin: Springer-Verlag, pp. 274~302. Cerny, P., Meintzer, R. and Anderson, A.J.
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