lo American plc (through its subsidiary Mineração Catalão), also hosted within a carbonatite intrusion . Altogether these two Brazilian mines produce around 75% of world supply. The third largest producer of niobium is the carbonatite-hosted Niobec Mine, Saint-Honoré near Chicoutimi, Quebec owned by Iamgold Corporation Ltd , which produces around 7% of world supply.though unexploited resources are located in Nigeria, Democratic Republic of Congo, Malawi, Australia and in Russia.
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:
O5 + 14HF? 2H2 [TaF7] + 5H2O, andO5 + 10HF? 2H2 [NbOF5] + 3H2O
first industrial scale separation, developed by de Marignac, used the difference in solubility between the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K2 [NbOF5] В· H2O) and dipotassium heptafluorotantalate (K2 [TaF7] ) 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:
[NbOF5] + 2KF? K2 [NbOF5]? + 2HF, then
H2 [NbOF5] + 10NH4OH? Nb2O5? + 10NH4F + 7H2O
methods are used for the reduction to metallic niobium. The electrolysis of a molten mixture of K2 [NbOF5] 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 aluminum:
Nb2O5 + Fe2O3 + 12Al? 6Nb + 2Fe + 6Al2O3
enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is aluminum 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.United States Geological Survey estimates that the production increase...
