|Main article: Extraction of Niobium |
For complex and poor niobium ores being used, methods of their enrichment in the processing assume greater importance. Physical methods including magnetic and gravity separation techniques have received attention in the processing of tantalum and niobium. The concentrations of Nb2O5 in enriched ore concentrates are: in pyrochlore ores it is no less than 37%, in loparite - 8% and columbite ores contain 30-60% Nb2O5. Most of them are processed converting niobium oxide units into ferro-niobium through the metallothermically reduced with aluminium or sodium powder or by reduction in an electric arc furnace.
Niobium metal processing is quite complex and consists of three steps:
1. Breaking-up of the concentrate;
2. Niobium and Tantalum separation and processing and
3. Reducing and refining.
Niobium metal is produced by the aluminothermic method or using caustic or carbonate fusions of reduction of the oxide. First method includes carbide processing from the mixture of Nb2O5 and cinder at 1800°C in hydrogen atmosphere; then the mixture of pentoxide and carbide is recovered at 1800-1900°C in vacuum until niobium metal. The other methods for niobium extraction from FeNb involve caustic or carbonate fusions, which when leached or washed, give niobium oxide which is fairly pure and may be further purified by chlorination or other means presently known to the art. Ultimately, the oxide must be metallothermically reduced as previously described, or carbothermically reduced to niobium metal. Niobium powders can be produced by the reduction of potassium niobium heptafluoride (K2NbF7) with sodium, or by the reduction of niobium oxide with magnesium. Powder is sintered at 2300°C. Niobium metal ingots are refined via electron beam refining or vacuum arc fusing. Purities exceeding 99.99% can be achieved.
|Sols of niobium have been prepared by sparking electrodes of the metal immersed in isobutyl alcohol by means of an induction coil, or by reducing solutions of niobium salts with hydrazine, formic acid or formaldehyde in the presence of gelatose.|