Tantalum minerals

Deposits of niobium-tantalum ores are found in Australia, Brazil, Canada, China, Malaysia, Namibia, Nigeria, Russia, Rwanda, Spain, Thailand, Zaire, and Zimbabwe. A more detailed analysis of worldwide tantalum mineral raw material supply can be found in Linden s comprehensive overview [22,23]. 

Tantalum metal dust, exposure to, 24 334 Tantalum minerals, chemical compositions of, 24 315t. See also Tantalum ores Tantalum-Niobium International Study Center (TIC), 24 331 Tantalum nitrides, 24 335 Tantalum ores, 24 316. See also Tantalum minerals... 

It should be noted that the ytterbium listed above was a mixture discovered in the mineral erbia by de Marignac in 1878 and not the neoytterbium/aldebaranium element renamed ytterbium that was foimd in the mineral ytterbia. The columbium was a mixture found in the mineral samarskite and was not the present day columbium/niobium. The ionium listed above was a mixture of terbium and gadolinium that was found in the mineral yttria and does not refer to °Th. Finally, the neptunium refers to material fovmd in niobium/tantalum minerals and does not refer to the 1940 discovery of the trans-uranium element produced via a neutron capture reaction on a uranium sample. 

Arsenazo HI was applied in the determination of thorium in biological materials [103,104], natural waters [34,105,106], fertilizers [107], glass [108], silicate minerals [2,10,27,55,109], niobium and tantalum minerals [110], uranium minerals [3,18], manganese ores [19], lanthanide compounds [26,44], zirconium minerals [111], titanium concentrates [111], ilmenite and rutile [112]. Thorium was determined in waters with the use of the FIA technique [106]. 

Cunningham LD (1998) Columbium (niobium) and tantalum. Minerals Yearbook, Metals and Minerals 1999. Vol. 1, pp. 21.1-21.13. US Department of Interior, U S Geological Survey, US Government Printing Office, Washington DC. 

Reserves Large resources of yttrium in monazite and xenotime are available worldwide in ancient and recent placer deposits, carbonatites, uranium ores, and weathered clay deposits (ion-adsorption ore). Additional large subeccaiomic resources of yttrium occur in apatite-magnetite rocks, deposits of niobium-tantalum minerals, nonplacer monazite-bearing deposits, sedimentary phosphate deposits, and uranium ores. The world s resources of yttrium are probably very large [39]. 

Niobium and Tantalum Minerals 557 Table 22.1 Similarities in the history of vanadium and niobium discoveries... 

Table 23.1 World production in 2001 of tantalum mineral concentrates (contained tantalum)...

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. 

Occurrence. Niobium and tantalum usually occur together. Niobium never occurs as the metal, ie, ia the free state. Sometimes it occurs as a hydroxide, siUcate, or borate most often it is combiaed with oxygen and another metal, forming a niobate or tantalate ia which the niobium and tantalum isomorphously replace one another with Htde change ia physical properties except density. Ore concentrations of niobium usually occur as carbonatites and are associated with tantalum ia pegmatites and alluvial deposits. Principal niobium-beariag minerals can be divided iato two groups, the titano- and tantalo-niobates. 

Tantalum [7440-25-7] atomic number 73, is the heaviest element in Group 5 (VA) of the Periodic Table. This tough, ductile, silvery gray metal has an atomic weight of 180.948 amu. The element was discovered by A. K. Ekeberg in 1802 in minerals taken from Kimito, Finland, and Ytterby, Sweden (1). 

The cooled reaction mass is extracted from the retort, cmshed and leached first with dilute mineral acid, and then with water to separate the tantalum powder from the salts. After drying and classification, the primary powder is ready for processing to sheet, rod, wire, or capacitor-grade powder. 

The corrosion behavior of tantalum is weU-documented (46). Technically, the excellent corrosion resistance of the metal reflects the chemical properties of the thermal oxide always present on the surface of the metal. This very adherent oxide layer makes tantalum one of the most corrosion-resistant metals to many chemicals at temperatures below 150°C. Tantalum is not attacked by most mineral acids, including aqua regia, perchloric acid, nitric acid, and concentrated sulfuric acid below 175°C. Tantalum is inert to most organic compounds organic acids, alcohols, ketones, esters, and phenols do not attack tantalum. 

Columbium (Niobium) and Tantalum in 1994 U.S. Bureau of Mines, Mineral Industry Survey, 1995. 

In the same year that del Rio found his erythronium, C. Hatchett examined a mineral which had been sent to England from Massachusetts and had lain in the British Museum since 1753. From it he isolated the oxide of a new element which he named columbium, and the mineral columbite, in honour of its country of origin. Meanwhile in Sweden A. G. Ekeberg was studying some Finnish minerals and in 1802 claimed to have identified a new element which he named tantalum because of the difficulty he had had in dissolving the mineral in acids. It was subsequently thought that the two elements were one and the same, and this view persisted until at least 1844 when H. Rose examined a columbite sample and showed that two distinct elements were involved. 

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

Lupton, D. and Aldinger, F., Possible Substitutes for Tantalum in Chemical Plant Handling Mineral Acids, in Trends in Refractory Metals, Hard Metals, and Special Materials and Their Technology, Proceedings of the 10th Plansee Seminar, Reutte, Austria 101-130 (1981)... 

Niobium and tantalum are rare elements. The content of niobium and of tantalum in the Earth s crust is lxl0"3 and 2x1 O 4 wt. %, respectively [21]. Niobium and tantalum are encountered in nature together, mostly in the form of oxides that are derived from orthoniobic (orthotantalic), metaniobic (metatantalic) and pyroniobic (pyrotantalic) acids. The main minerals are listed in Table 2, which reveals that the most important source of tantalum and niobium is tantalite-columbite, (Fe,Mn)(Nb,Ta)206. 

Table 2. Composition of main tantalum-niobium-containing minerals [21,24]...

Two main methods exist for the production of tantalum and niobium from the mineral raw material. The first method is based on the chlorination of raw material, followed by separation and purification by distillation of tantalum and niobium in the form of pentachlorides, TaCl5 and NbCl5 [24, 29]. Boiling points of tantalum and niobium pentachlorides (236°C and 248°C, respectively) are relatively low and are far enough apart to enable separation by distillation. 

The processing of tantalum and niobium begins with the fluorination of the raw material, which always consists of complex oxide compounds containing tantalum and niobium. The main types of tantalum- and niobium-containing minerals are discussed in Chapter 1, and typical compositions of such minerals are presented in Table 2. 

Another point is related to the high acidity level of the final solution, which leads to certain limitations in the subsequent technological steps. Specifically, the high acidity of the initial solution eliminates any possibility for selective extraction, i.e. sequential separation of tantalum and then of niobium. Due to the high concentration of acids, only collective extraction (of tantalum and niobium together) can be performed, at least at the first step. In addition, extraction from a highly acidic solution might cause additional contamination of the final products with antimony and other related impurities. In order to reduce the level of contaminants in the initial solution, some special additives are applied prior to the liquid-liquid extraction. For instance, some mineral acids and base metals are added to the solution at certain temperatures to cause the precipitation of antimony [455 - 457]. 

It is recommended that the concentration of sulfuric acid in the initial solution be kept at 2-4 mol per liter for the extraction of tantalum, whereas for the extraction of niobium, the concentration of sulfuric acid must be increased to a minimum of 6 mol per liter [458,481]. In some cases, the presence, in the initial solution, of titanium in the form of fluorotitanic acid ensures the successful and selective extraction and purification of tantalum and niobium with no addition of any other mineral acid [482]. 

T.B. Tripp, Tantalum - Proceeding of a Symposium held at the 125th TMS Annual Meeting and Exhibition, Anaheim, Calif. (February 5-8, 1996) Ed. E.S. Chen, Minerals, Metals Materials Society, Warrendale, Pa, (1996) 23. 

Ta and Nb containing minerals, 4 Ta and Nb oxides dissolution, 258 Tantalum fluoride properties, 25 Tantalum extraction, 285-288... 

The examination and analysis of minerals have provided x-ray emission spectrography with a challenge and an opportunity. This situation has arisen because of a great growth of interest in uranium and thorium minerals in the rare-earth oxides and in metals such as tantalum and niobium, or hafnium and zirconium. On the whole, x-ray emission spectrography has met the challenge successfully, and the investigations that prove this also demonstrate the versatility and the value of the method.70"72... 

For papers on the analysis and examination of tantalum and niobium minerals by x-ray emission, see the following references listed in Appendix VI 17, 65, 82, 89. 

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