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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.