A nitriding process for the recovery of niobium from ferroniobium

Abstract

A three-step process based on nitriding-leaching-pyrovacuum decomposition has been developed for the recovery of niobium metal relatively free of iron from ferroniobium. The process essentially involves nitriding of ferroniobium powder with ammonia at 950 °C to 1000 °C. Nitrided ferroalloy was then treated with a 9:1 mixture of 30 pct HNO3 and HC1 to leach out iron nitrides. The residue was then pyrovacuum treated at 1825 °C under a dynamic vacuum of 0.02 m torr to finally yield metal containing about 0.2 pct iron starting from ferroniobium containing about 35 pct iron. The treated material has been further purified by electron-beam melt refining. The refined metal showed a hardness in the range of 80 to 84 VHN under a load of 100 g. The metal on analysis was found to contain 200 ppm of oxygen, less than 100 ppm of nitrogen, and about 100 ppm of carbon. The process appears to be quite attractive because it does not involve the treatment of ferroniobium with halogens or halides at elevated temperatures.