what is the valency of vanadium,niobium and tantalum
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This chapter discusses the history, abundance, distribution, and extraction of vanadium, niobium, and tantalum. Vanadium has been estimated to comprise about 136 ppm of the earth's crustal rocks. Its major commercial source is the titanoferrous magnetites of South Africa and China. Niobium and tantalum usually occur together and their most widespread mineral is known as columbite or tantalite, depending on which metal is preponderant. Vanadium is usually produced along with other metals. Therefore, the availability of vanadium and the economics of its production are intimately connected with the particular coproduct involved. The extraction procedure for vanadium involves roasting of the crushed ore or vanadium residue with sodium chloride or sodium carbonate at 850°C. This produces sodium vanadate that is leached out with water. The chapter discusses the physical properties, chemical reactivity, and group trends of vanadium, niobium, and tantalum. All three elements, vanadium, niobium, and tantalum, are shiny and silvery metals with typical metallic bcc structures. When pure, they are comparatively soft and ductile, but impurities usually have a hardening and embrittling effect.