Occurrence and Preparation
Tantalum occurs in the minerals tantalite and columbite (columbium being an archaic name for niobium), which occur in pegmatites, an igneous rock formation. Mixtures of columbite and tantalite are called coltan. Tantalite was discovered by Anders Gustaf Ekeberg at Ytterby, Sweden, and Kimoto, Finland. The minerals microlite and pyrochlore contain approximately 70% and 10% Ta, respectively.
Tantalum oxide is obtained from the aforementioned ores. The powdered mineral is fused with sodium hydroxide to give a slurry of mixed insoluble "niobic acid" and "tantalic acid", the hydrated oxides. These oxides are extracted with anhydrous hydrofluoric acid and potassium fluoride (or the bifluoride) to yield the salt potassium heptafluorotantalate (K2TaF7). This salt can be purified by a liquid-liquid extraction process, using various ketones as the liquids.
- (FeMn)(NbTa)2O6 + 6 NaOH → Ta2O5·7H2O + Nb2O5·7H2O
- ½ Ta2O5·7H2O + ½ Nb2O5·7H2O + 14 KF → K2TaF7 + K2NbF7 + 2 H2O + 10 KOH
Or,
- ½ Ta2O5 + ½ Nb2O5 + 4 KF + 10 HF → K2TaF7 + K2NbF7 + 5 H2O
Metallic Ta is obtained by the electrolysis of the purified molten K2TaF7. Roasting tantalum in oxygen at temperatures above 1000 °C, gives the pentaoxide:
It can also be produced by hydrolysis of its alkoxide:
-
- 2 Ta(OCH2CH3)5 + 5 H2O → Ta2O5 + 10 CH3CH2OH
Read more about this topic: Tantalum Pentoxide
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