Dissolution of columbite and tantalite in acidic fluoride media
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Ri = koa(H+)l2C(F )1.1 e x p ( - E a / R T ) where an apparent activation energy, E~, ranges from 53.9 kJ mol -~ to 65.5 kJ mol -~.
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INTRODUCTION
B O T H Nb and Ta are metals which have high melting points and are difficult to dissolve with ordinary mineral acids. These metals are important materials in producing alloys, optical glass, condensers, and superconducting magnets. The principal minerals of Nb and Ta are columbite and tantalite, whose chemical formulae are [Nb205(Fe, Mn)O] and [Ta2Os(Fe, Mn)O], respectively. However, these minerals used in industrial processes usually have a chemical formula of [(Nb, Ta)2Os(Fe, Mn)O]. The Nb-rich mineral is called c01umbite, while that of Ta-rich is tantalite. The ores containing these minerals are currently leached in Japan with hydrofluoric acid, followed by solvent extraction, neutralization, precipitation, filtering, drying, and roasting to recover Nb205 and Ta205. Although the leaching of columbite or tantalite is an important step in the hydrometallurgical process of Nb and Ta recovery, only a limited number of studies have been reported. Most minerals containing Nb and Ta are decomposed by hot concentrated hydrofluoric acid. Sometimes concentrated sulfuric or oxalic acids are added to the hydrofluoric acid to achieve better efficiency. I1~ Muir and Lloyd studied the leaching of material~ containing Nb and Ta with hydrofluoric acid [2'31and Baram investigated the kinetics of tantalite dissolution in a mixture of hydrofluoric and sulfuric acids. I41 Sato and Kigoshi examined the leaching of columbite in 20 mol pct NO2-80 mol pct HF solution.IS~ Hoberg and Goette studied the influence of mechanical activation on the kinetics of the columbite leaching process.[6] Mechanochemical activation of columbite concentrates was also studied by Batsuev et al. i71 Majima et al. studied the dissolution of oxides, such as cupric oxide and hematite, in hydrochloric acid, perchloric acid, and sulfuric acid from a kinetic point of view, and elucidated the role of hydrogen ions and anions on the dissolution reactions. Also they determined the changes of HIROSHI MAJIMA, Professor, and YASUHIRO AWAKURA, Lecturer, are with the Department of Metallurgy, Kyoto University, Kyoto, Japan 606. MUNENORI MASHIMA, formerly Graduate Student, Department of Metallurgy, Kyoto University, Japan, is with Mitsubishi Metal Corporation, Osaka Refinery, Osaka, Japan 530. TETSUJI HIRATO is Postdoctoral Fellow, Department of Metallurgy and Materials Science, The University of Toronto, Toronto, ON, Canada, M5S 1A4. Manuscript submitted April 3, 1987. METALLURGICALTRANSACTIONSB
dissolution rates by the addition of various saltsJ 8'9'~~ As a part of oxide dissolution studies, it is interesting to know the leaching mechanism of complex oxide minerals in a weak acid solution. In this study, kinetics of the dissolution of Nb and Ta from columbite and tantalite were studied. In connection with this, Omori et al. examined the solvent extraction of Nb and Ta from hydrochloric acidhydrofluoric acid mixtures, and
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