Niobium - Production

Production

After the separation from the other minerals, the mixed oxides of tantalum Ta₂O₅ and niobium Nb₂O₅ are obtained. The first step in the processing is the reaction of the oxides with hydrofluoric acid:

Ta₂O₅ + 14 HF → 2 H₂ + 5 H₂O

Nb₂O₅ + 10 HF → 2 H₂ + 3 H₂O

The first industrial scale separation, developed by de Marignac, exploits the differing solubilities of the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K₂·H₂O) and dipotassium heptafluorotantalate (K₂) in water. Newer processes use the liquid extraction of the fluorides from aqueous solution by organic solvents like cyclohexanone. The complex niobium and tantalum fluorides are extracted separately from the organic solvent with water and either precipitated by the addition of potassium fluoride to produce a potassium fluoride complex, or precipitated with ammonia as the pentoxide:

H₂ + 2 KF → K₂↓ + 2 HF

Followed by:

2 H₂ + 10 NH₄OH → Nb₂O₅↓ + 10 NH₄F + 7 H₂O

Several methods are used for the reduction to metallic niobium. The electrolysis of a molten mixture of K₂ and sodium chloride is one; the other is the reduction of the fluoride with sodium. With this method niobium with a relatively high purity can be obtained. In large scale production the reduction of Nb₂O₅ with hydrogen or carbon is used. In the process involving the aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium:

3 Nb₂O₅ + Fe₂O₃ + 12 Al → 6 Nb + 2 Fe + 6 Al₂O₃

To enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is aluminium oxide and ferroniobium, an alloy of iron and niobium used in the steel production. The ferroniobium contains between 60 and 70% of niobium. Without addition of iron oxide, aluminothermic process is used for the production of niobium. Further purification is necessary to reach the grade for superconductive alloys. Electron beam melting under vacuum is the method used by the two major distributors of niobium.

The United States Geological Survey estimates that the production increased from 38,700 tonnes in 2005 to 44,500 tonnes in 2006. The worldwide resources are estimated to be 4,400,000 tonnes. During the ten-year period between 1995 and 2005, the production more than doubled, starting from 17,800 tonnes in 1995. Since 2009 production is stable at around 63,000 tonnes per year.