Separation of niobium from ferroniobium by chlorination
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INTRODUCTION
NIOBIUMhas become of major interest recently due to its particular properties for nuclear reactor and superconductor uses. Also, there is a great demand for ferroniobium in the steel industry.~'2 Pyrochlore has become the most important source of niobium because of its abundance and the fact that it contains less tantalum.3-6 But a recent trend of ore producing countries such as Brazil and Canada is that of exporting ferroniobium after separating valuable metals such as rare earth and thorium from the ore. Imported ferroniobium accounts for more than 60 pct of all niobium in Japan. Since ferroniobium is a main source of the world's niobium supply, investigation of the direct process of separating niobium from ferroniobium by chlorine metallurgy is necessary. Mass production of niobium is very urgent because of the increasing demand for niobium. Few papers reported on chlorination of ferroniobium in the 1960s. 7,8 Based on the above consideration, the present work was directed toward exploring the possibility of a new process via chlorine metallurgy. Chlorine metallurgy is one of the most valuable methods, having advantages in many areas, including fine powder chemistry, molten salt chemistry, chemical vapor deposition, and so on. In this paper, extraction of niobium from ferroniobium was tried as one of the newer-method metallurgies for the extraction of rare metals which will be able to utilize ferroalloys such as ferrosilicon and ferrochromium as raw materials. Furthermore, ferroalloys will become the only resources of rare metals which can be imported from their producing country to Japan.
NBC1267, and NbCI2. ~~
However, other lower niobium chlorides such as NbC14 and NbCI3 are reported, 19'2~the thermodynamic values of which are not available, and therefore the domains for NbC14 and NbC13 are omitted from this diagram. Under a pressure of 10 -j~ atmosphere of chlorine gas, selective chlorination producing ferrous chloride and niobium pentachloride is possible. Though the volatility difference between these chlorides becomes large, it is not practical to adopt the very low pressure system from the standpoint of productivity. Table I shows the vapor pressure of pure niobium pentachloride ferric and ferrous chlorides as a function of temperature. 21-25 From these data, it would appear that by condensing the ferric chloride at 600 K and the niobium pentachloride at 400 K, a rough separation of these two components should occur with practically 100 pct recovery in both cases. However, the situation is not so simple, as the solids are miscible. When the ferric chloride is reduced to ferrous chloride selectively by some reductant, it is suggested that a clearer separation of the iron and the niobium will be possible. Morozov and coworkers present phase diagrams of NbC15-FeClj, NbCIs-FeCI~ systems as shown in Figure 2 by dotted and solid lines. =6Our data for the NbC15-FeC13 system are also shown in Figure 2 as small circuits. Both data coincide well in a wide range of composition. The eutectic poin
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