Chemical Refining Of Tantalum

Tantalum ores generally contain significant amounts of niobium, so both are refined and sold. The entire hydrometallurgical process begins with a drenching, where the ore is immersed in hydrofluoric and sulfuric acids to produce water-soluble hydrofluorides. This separates the tantalum from various non-metallic impurities.

Ta2O5 + 14 HF → 2 H2[TaF7] + 5 H2O
Nb2O5 + 10 HF → 2 H2[NbOF5] + 3 H2O
Tantalum and niobium hydrofluoride can be extracted from aqueous solution by solvent extraction; suitable organic solvents include cyclohexanone and methyl isobutyl ketone. This step removes water-soluble fluoride from various metal impurities (e.g., iron, manganese, titanium, zirconium). Tantalum can be separated from niobium by adjusting the pH. Niobium requires a higher acidity to dissolve in organic solvents, so it can be easily removed in a less acidic environment. The remaining pure tantalum hydrofluoride solution, when neutralized with ammonia, forms tantalum hydroxide (Ta(OH)5), which when calcined produces tantalum pentoxide (Ta2O5).

H2[TaF7] + 5 H2O + 7 NH3 → Ta(OH)5 + 7 NH4F
2 Ta(OH)5 → Ta2O5 + 5 H2O
Tantalum hydrofluoride can also react with potassium fluoride to form potassium heptafluorotantalate (K2[TaF7])

H2[TaF7] + 2 KF → K2[TaF7] + 2 HF
It reacts with sodium in a molten salt at around 800 °C in a reduction reaction to make tantalum metal.

K2[TaF7] + 5 Na → Ta + 5 NaF + 2 KF
An earlier method of isolation added potassium fluoride to a mixed solution of hydrofluoride in a process called the Demarinya process.

H2[TaF7] + 2 KF → K2[TaF7] + 2 HF
H2[NbOF5] + 2 KF → K2[NbOF5] + 2 HF
The K2[TaF7] and K2[NbOF5] thus produced have different water solubilities, so they can be separated using the separation crystallization method.