Processing of Ores of Titanium, Zirconium, Hafnium, Niobium, Tantalum, Molybdenum, Rhenium, and Tungsten: International Trends and the Indian Scene

Abstract

The current international status and Indian scene on the resource position and processing practice of the strategically important transition metals—titanium, zirconium, hafnium, niobium, tantalum, molybdenum, rhenium, and tungsten—are briefly reviewed. With the exception of molybdenum these metals are strongly lithophilic, forming stable oxide and silicate minerals that are resistant to weathering processes. Their minerals, therefore, become concentrated in residual and placer deposits, especially in the case of titanium, zirconium, hafnium, niobium, and tantalum. Gravity beneficiation methods are commonly employed for the pre-concentration of these minerals followed by a combination of magnetic, high-tension, and flotation techniques to obtain marketable concentrates. Beneficiation of wolframite and scheelite, the main tungsten minerals, normally needs complex multi-stage operations, involving classification followed by gravity, magnetic, high-tension, and flotation techniques. Where marketable grade concentrates cannot be produced, chemical methods are employed to upgrade the economic level concentrates produced by physical methods. Molybdenite, MOS2, is the chief source of molybdenum and is universally recovered by froth flotation. Though molybdic porphyry ores are readily amenable to benefication, recovering molybdenite from copper porphyry ores (an important source of molybdenum) is complex, requiring multi-stage selective depression of copper minerals. Hafnium and rhenium occur only as diadochic substitutions in zirconium and molybdenum minerals, respectively, and can be recovered only by chemical methods. India is endowed with adequate deposits of titanium and zirconium but is in a none too happy position with respect to niobium and tantalum. There are practically no worthwhile working deposits of tungsten and molybdenum. However, several low-grade deposits of tungsten have been recently reported, and sustained research efforts are being made to develop suitable beneficiation technology for the exploitation of these deposits. © 1990, Walter de Gruyter. All rights reserved.