Columbite-tantalite

Gr. Tantalos, mythological character, father of Niobe) Discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rowe in 1844, and Marignac, in 1866, showed that niobic and tantalic acids were two different acids. The early investigators only isolated the impure metal. The first relatively pure ductile tantalum was produced by von Bolton in 1903. Tantalum occurs principally in the mineral columbite-tantalite. 

The purpose of the decomposition of raw materials is to convert tantalum and niobium compounds into a soluble form and prepare the solution for use in subsequent procedures. Fig. 116 presents the process flow chart. The most typical and frequently used raw materials are columbite-tantalite concentrates with the general formula (Fe, Mn)(Nb, Ta Cfo. 

Hydrofluoric acid, at relatively high concentrations and at elevated temperatures, dissolves columbite-tantalite concentrates at a reasonable rate. The dissolution process is based on the fluorination of tantalum, niobium and other metal oxides and their conversion into soluble complex fluoride acids yielding complex fluoride ions. 

The digestion of columbite, tantalite and other raw materials containing tantalum and niobium using both hydrofluoric acid and a mixture of hydrofluoric and sulfuric acids is widely applied in the industiy. The main advantage of the method is its simplicity. The method has, nevertheless, several disadvantages that should be noted, as follows. 

Columbite - tantalite chlorination, 5-6 composition, 4 decomposition by H2S04, 6, 259-263 HF, 6,256-263... 

Beryl Beryl Columbite-tantalite Triplite Triphyllite Be, Nb-Ta Ural Mts., Russia Mayers Ranch, Colorado Dan Patch, South Dakota... 

Columbite-tantalite minerals, 17 134-135 Columbium, 17 132. See also Niobium (Nb) Columnar phase, of liquid crystalline materials, 15 96... 

Occurrence. The most important minerals are pirochlore (NaCaNb206F) and those of the columbite-tantalite series (Fe/Mn)(Nb/Ta)206 with various metallic ratios. 

Tantalum is never found in nature in free elemental form. The most important mineral is columbite-tantalite (Ee,Mn) (Nb,Ta)206. Tantalum also is found in minor quantities in minerals pyrochlore, samarskite, euexenite, and fergusonite. The abundance of tantalum in the earth s crust is estimated as 2 mg/kg. 

Tantalum pentoxide is obtained as an intermediate in extracting tantalum from the columbite-tantalite series of minerals. Also, the oxide can be made by heating Ta metal in oxygen or air at elevated temperatures. 

The elements themselves require little comment. Niobium is 10 to 12 times more abundant in the earth s crust than tantalum. The main commercial sources of both are the columbite-tantalite series of minerals, which have the general composition (Fe/Mn)(Nb/Ta)206, with the ratios Fe/Mn and Nb/Ta continuously variable. Niobium is also obtained from pyrochlore, a mixed calcium-sodium niobate. Separation and production of the metals is complex. Both metals are bright, high melting (Nb, 2468°C Ta, 2996°C), and very resistant to acids. They can be dissolved with vigor in an HN03—HF mixture, and very slowly in fused alkalis. 

Carlson and Nielsen (C3) described the pilot and full-scale plant separation of an ore containing more than 30% combined columbium and tantalum oxide using a sulfuric-hydrofluoric acid leach and methyl isobutyl ketone (MIBK) as solvent in pulsed columns. The —200 mesh columbite-tantalite ore was digested with 70% HF until the combined (Ca + Ta)20s in the leach liquid reached 3 Ib/gal at which time it was diluted to 15N free acid and clarified by filtration. This solution was contacted countercurrently in the pulsed column where Ta and Cb were extracted by MIBK. Columbium was stripped from the organic with demineralized water which diluted the free acid in the solvent, making possible the transfer of all the Cb the Ta-loaded solvent was then stripped with demineralized water causing the transfer of Ta to the aqueous phase. The oxides were then precipitated with 28% ammonium hydroxide solution. Conversion to the respective oxides was by calcination of the precipitates. 

Vanadium, vanadinite, carnotite, KV(S04)2 12H20, VOg, VO+ +, V0O5, NH4VO3. Niobium (columbium), tantalum columbite, tantalite TaC. 

Fig. 243. Extraction of niobium and tantalum from columbite (tantalite).

Tantalum ranks about number 50 among elements found in Earth s crust. It is slighdy more common than tungsten, but less common than arsenic. Its abundance is probably about 1.7 parts per million in the earth. The element is most commonly found in the minerals columbite, tantalite, and microlite. It always occurs with niobium. 

Members of the columbite-tantalite family of minerals also often contain significant U along with rare earths, Fe, Ca and Th. The B site is either Nb or Ta. Like the pyrochlores, these minerals are associated with rare-earth pegmatites and are also known from placer deposits. Most of the compounds probably formed initially with U —most probably as a coupled substitution Ca -t-U for a trivalent ion. Oxidation occurs easily, however, and most specimens contain significant amounts of U. Those minerals which contain radioactive elements are usually metamict and require heating to develop crystallinity. 

Apart from zircon, other common accessory minerals that can be used for U/Th-Pb dating are monazite, rutile, titanite, apatite and allanite results on rarer minerals such as columbite-tantalite, perovskite, baddeleyite and the uranium ore minerals uraninite and davidite have also been reported. 

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