REFINING OF CRUDE NIOBIUM BY MOLTEN-SALT ELECTROLYSIS AND ELECTRON-BEAM MELTING

Crude niobium has been purified by a refining process consisting of mo lten salt electrolysis and electron beam melting. The molten salt elec trorefining was carried out galvanostatically using a FLINAK bath (26. 3 mass%LiF-10.5 mass%NaF-47.0 mass%KF-16.2 mass%K2NbF7) at 963 K under Ar atmosphere. After the molten salt electrorefining and the electron beam melting, the contents of metallic impurity components in the pur ified niobium were determined by ICP emission spectrography analysis. Refractory metals such as tantalum, tungsten and molybdenum in crude n iobium could be eliminated by means of molten salt electrorefining. Es pecially, the molten salt electrorefining method using fluoride bath w as remarkably effective for the removal of metallic tantalum in crude niobium. Nonmetallic impurity components such as oxygen and nitrogen c ould be also removed by electron beam melting. Crude niobium of 99.8 m ass% purity was found to be purified to 99.99 mass% by this refining p rocess.