A nitriding process for the recovery of niobium from ferroniobium
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I.
INTRODUCTION
N I O B I U M for industrial applications is mainly derived from its naturally occurring mineral pyrochlore and, to a small extent, from the mineral columbite-tantalite. Over 85 pet of world production of niobium comes from Brazil. Brazil exports most of its niobium as ferroniobium, niobium oxide, niobium alloys, and niobium metal but not as a primary mineral concentrate, t~ At present, the Niobec mine of Canada is the only source that supplies the pyrochlore concentrate. For producing niobium and its allied products, ferroniobium can be regarded as a relatively cheap niobium source that is available abundantly in the commercial market. At present, ferroniobium is processed by the chlorination route to produce other usable products of niobium. Albrecht and Rockenbauer, in their recent publication, t2j have described a process that has been adopted at Herman C. Starck, Germany. In the process, ferroniobium is chlorinated by charging it along with NaC1 in a molten bath of NaFeCI4. The composition of the salt is controlled by the addition of chlorine. The volatilized fractions are then separated first by distillation to separate fractions with vastly different boiling points and then by fractional distillation to separate chlorides that have small differences in boiling temperatures. The pure chlorides are then converted to oxide by means of special steam hydrolysis and finally reduced to metal. Sugai and Watanabe t3j have described a process that is adopted at Toho Titanium, Japan. In this process, ferroniobium is chlorinated with chlorine to produce a mixture of chlorides. The chloride mixture is vaporized at about 350 ~ in a hydrogen atmosphere to convert ferric chloride to nonvolatile ferrous chloride and thereby effect separation of niobium pentachloride. NbC15 is then magnesiothermically reduced in a Kroll type of reactor. The reduced sponge is then subjected to vacuum distillation to produce pure niobium. A.K. SURI, Head, Chemical Metallurgy Division, KULWANT SINGH, Scientific Officer, Metallurgy Division, and C.K. GUPTA, Associate Director, Materials Group, are with the Bhabha Atomic Research Centre, Trombay, Bombay 400 085, India. Manuscript submitted May 30, 1991. METALLURGICAL TRANSACTIONS B
Sato and Nanjo t4t have described a process for separation of niobium from ferroniobium by chlorination. It has been shown that preliminary separation of niobium chloride from ferric chloride could be accomplished by selective condensation with temperature gradient techniques. Subsequently, ferric chloride is selectively reduced to ferrous chloride by iron powder. Niobium pentachloride and ferrous chloride are then separated by differences in their volatility. Besides these, a number of processes have been developed that utilize the difference in volatility of chlorides, particularly of niobium and tantalum, either as such I5} or in the presence of other additives. The additives that have been used include CaO" CaF2, t61 molten NaA1C14, tT} alkali metal chlorides in the presence of hydrogen, ts~ the r
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