The two elements niobium (columbium) and tantalum occur together, and the stories of their discovery are entangled as well. English chemist Charles Hatchett in 1801 examined a heavy ore that had come from the former Massachusetts colony. Having satisfied himself that it contained a new element, he named that element columbium. One year later, Swedish chemist Anders Gustaf Ekeberg discovered a heavy metal that he called tantalum. But, other chemists in follow-on investigations concluded that the two similar ores, called columbite and tantalite, both contained the same element. This belief persisted for a few decades.
A German chemist in 1846, Heinrich Rose, argued that tantalite contained additional new elements. As tantalum was named after Tantalus of Greek mythology, the new metals were named after his children, niobium and pelopium (from Niobe and Pelops). Finally, in the 1860s, the situation was disentangled by several chemists. There are two metals in the two ores, niobium (formerly columbium) and tantalum. Columbite contains more niobium and tantalite contains more tantalum. The third supposed element was probably a mixture of the other two.
Mining and Production
Niobium and tantalum almost always occur together in various proportions. The largest producers of niobium are Brazil and Canada, with 90% and 8% respectively of the 59,000 tonnes mined in 2014. As for tantalum, Australia was historically the largest supplier. In recent years, that mining has been shut down, however. The largest producers in 2014 of the 787 tonnes mined were Rwanda (32%), DR Congo (23%), and Brazil (12%). Some of this mining is in and near the armed conflict in eastern Congo, which it helps fund.
Various ores of the metals are treated first by leaching with hydrofluoric acid, one of the few solvents that dissolves them. The fluorides of the two metals are still mixed together. They are transferred in solution from the acid to an organic solvent, then separated by their different solubilities. The pure metals can be extracted by electrolysis.
Properties and Uses
Niobium and tantalum are both ductile, hard, and fairly inert metals. Tantalum is twice as dense. They both belong to a small group of metals with very high melting points, along with molybdenum and tungsten. In fact, niobium was used as the filament in incandescent lights before it was replaced with tungsten.
The primary use of niobium is in tiny amounts (0.1%) as a hardener for steel. Niobium is also a component (around 5%) of several superalloys used in jet engines.
Niobium becomes a superconductor at cryogenic temperatures. Consequently, niobium alloyed with tin, germanium, and titanium is formed into wires for the powerful superconducting magnets used in MRI machines and particle accelerators.
Tantalum is primarily used in electronic capacitors. The metal itself is highly conductive, of both electricity and heat. The oxide coating that it forms in air is much less so, and that thin oxide can be exploited as the dielectric of a capacitor. Tantalum capacitors are found in cellphones and other electronics where weight is a major concern.
Tantalum is sufficiently inert that it is used for surgical instruments and implants. Because of its high melting point, it can be a target for vapor deposition of aluminum and similar high-temperature applications. Tantalum is also used in superalloys.