Metallurgy and recycling of niobium and tantalum

Niobium (also known as columbium in the USA) and tantalum are element numbers 41 and 73 respectively, found in nature in combined form.

Together with vanadium (no. 23), they form the transition elements in column 5 of the Mendeleyev periodic table. Their external electronic configurations are :

• Nb : (Kr) 4d  ⁴ 5s ¹  ;

• Ta : (Xe) 4f  ¹⁴ 5d ³ 6s ² .

Classified as refractory metals due to their high melting temperatures, they were very early on considered for high-temperature applications; tantalum, for example, was chosen at the beginning of the 20th ^e century for lamp filaments.

Tantalum comes from two raw material sources: on the one hand, it accompanies tin ore in cassiterite and is concentrated in slag during tin processing; on the other, it is present in ores called columbo-tantalites.

Long confined to the chemical industry, tantalum only found a specific niche in the 1960s-1970s with capacitors for cutting-edge electronics: cell phones, camcorders, microcomputers.

This application is a tremendous growth driver for tantalum: annual worldwide consumption has almost doubled in 10-15 years (today between 1,600-1,800 t/year, expressed in metal content, for an ore and slag production of 1,400-1,500 t, the difference coming from recycling).

Although niobium is always associated with tantalum in tin slags and columbo-tantalites, it is largely derived from a specific ore, pyrochlore.

Penalized by hitherto scattered resources, it wasn't until the 1960s, with the discovery of vast pyrochlore deposits in Brazil, that niobium really took off. The precipitation of niobium carbide in steels paved the way for High Strength Low Alloy (HSLA) steels. Even more spectacularly, the superconducting performance of niobium-based alloys has made possible both scientific applications, such as particle gas pedals, and practical applications, such as medical imaging.

In 2007, world niobium production was close to 63,000 t/year (expressed in metal content), as was consumption (which was of the same order). Both have doubled in 10 years.

The boom in the global steel industry, with the arrival of China (32% increase in ferroniobium imports between 2005 and 2006) and India, which had no significant...