Gregory Carson Engineering – Engineering services for high-value industrial and strategic minerals

Tantalum and niobium are transition metals with very similar chemical and physical properties. Both show outstanding chemical inertness and thermal refractoriness (melting points at 3020°C and 2469°C respectively).

The major part of niobium produced is used in the production of high strength low alloy (HSLA) steels (main uses in structural, piping and automotive applications) and superalloys used in the aerospace industry while the remainder is sold as niobium carbides (e.g. cutting tools) and chemicals.

There is a variety of widespread emerging applications for tantalum including mobile electronic devices such as laptops and smartphones. The electronic industry is the main consumer of tantalum using up to half of world production, while the other half goes into tantalum metal products, ingots and carbides.

Both, tantalum and niobium exhibit exceptionally high specific performance in capacitors and resistors thereby enabling further miniaturization in electronics. Other hi-tech uses for Ta include use as a sputtering target and in prosthetics while Nb finds applications in superconductors.

In nature tantalum and niobium usually occur together as a result of their chemical similarity, tantalum being present in subordinate proportions. They do not occur in metallic form but are present in a variety of oxidic minerals with columbite-tantalite, pyrochlore, wodginite and loparite being the most important ore minerals.

Major deposits hosted in carbonatite complexes are found in Brazil (Araxá and Catalão) and Canada (Saint-Honoré). Alkaline to peralkaline rocks such as the Illimaussaq complex in Greenland also host significant niobium occurrences. Historically pegmatites located in Canada (Bernic Lake) and Australia (Greenbushes and Wodgina) have been important sources of tantalum. Tantalum is also recovered from placer deposits as a by-product of tin.

Brazil accounts for more than 90% of the global niobium production with Canada and Africa accounting for the rest. CBMM in Brazil holds a near market monopoly for niobium.

Main producers of tantalum are located in Africa (>60%), where it is mined largely in artisanal mining operations in the politically unstable DRC and Brazil (20%), followed by less significant producers in Australia, Canada and Malaysia.

Tantalum and niobium are traded in a variety of forms including carbides, metal powders and other chemicals.

NB-TA-MINERALS RESOURCES

In nature tantalum and niobium are rare since they are depleted in the continental crust (Nb < 10 ppm; Ta < 1 ppm). Usually they occur together as a result of their chemical similarity. Main ore minerals are oxides with columbite-tantalite, pyrochlore, wodginite and loparite being the principal pay minerals.

Three main types of niobium/tantalum deposits are distinguished: carbonatite complexes, alkaline to peralkaline rocks and pegmatites.

All three deposit types have in common that they are hosted in rocks that preferentially accommodate incompatible elements such as niobium, rare earth elements etc. which do not occur in common rock forming minerals.

Carbonatite complexes are host to the world’s most significant niobium deposits. It is either mined in the lateritic caps of such carbonatite complexes in which pyrochlore has been strongly concentrated by tropical weathering as in Araxá and Catalão deposits in Brazil or it is mined from mineralized lenses as is the case in Saint-Honoré in Canada. Brazil accounts for more than 90% of the global niobium production with Canada and Africa accounting for the rest.

Alkaline to peralkaline rocks can also host significant niobium occurrences as in the Kvanefjeld project in the Illimaussaq complex in Greenland. Typically deposits in this kind of geological setting are enriched in zirconium, rare earth elements and niobium with only minor amounts of tantalum.

Historically rare element pegmatites located in Canada (Bernic Lake) and Australia (Greenbushes and Wodgina) have been important sources of tantalum. Nowadays most of the tantalum produced comes from artisanal mining in central Africa. Tantalum is also recovered from placer deposits as a by-product of tin mining.

Main producers of tantalum are located in Africa (>60%) and Brazil (20%), followed by less significant producers in Australia, Canada and Malaysia.

NB-TA-EXTRACTION

After physical concentration niobium and tantalum have to be extracted from the mineral concentrate. Though some niobium-rich ores, such as pyrochlore can be decomposed in sulfuric acid decomposition is commonly carried out in hydrofluoric acid. Due to the highly refractory nature of most niobium and tantalum ore minerals other mineral acids fail in decomposition.

Since hydrofluoric acid is a rather expensive chemical, its use has to be minimized. This can be achieved by a chemical treatment with alternative, less expensive chemicals prior to dissolution in HF. The most appropriate treatment is chosen depending on the nature of impurities present in the ore.

For elements such as silicon or tin (which frequently accompany niobium and tantalum) caustic fusion in NaOH can be chosen. In this step soluble silicates and stannates are formed which can be leached with water.

Other impurities such as iron or rare earth elements can be leached by acids such as HCl or H₂SO₄.

If necessary both acid and caustic treatment can be combined.

After removal of the majority of nuisance elements the residue is dissolved in HF. The resulting liquor is now extracted with organic solvents to transfer niobium and tantalum to the organic phase. Commonly Methyl-Isobutylketone (MIBK) is applied for that purpose, but several other solvents can be used alternatively.

Niobium can then be selectively recovered from the organic phase by stripping with diluted acid. When all niobium has been removed from the organic phase, tantalum is recovered by stripping with water.

Tantalum values in solution are converted into potassium tantalum fluoride (K₂TaF₇) or tantalum oxide (Ta₂O₅).

Niobium is recovered as niobium oxide (Nb₂O₅) by neutralising the niobium fluoride complex with ammonia to form the hydroxide, followed by calcination to the oxide.