Tantalum and Niobium Minerals

For niobium production very big quantities of pyrochlore are extracted in Brazil and Canada. The world production of mineral concentrates (pyrochlore) was 25 600 tonnes in 2001 (counted as niobium) of which 22 000 tonnes (86%) were produced in Brazil and 3180 tonnes (12%) in Canada [22.1]. 

Mineral Chemicai formula Crystalline Density Nb Oj form g/cm % TajOj % 

According to Dana s System of Mineralogy, 7. Ed., Vol. 1, 7th ed. Table arranged by S. V. Solver, Mining and Metallurgical School, Filipstad, Sweden. 

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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. 

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

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. 

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

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. 

The ore used in this example contained a mixture of pyrochlore and columbite as the major niobium minerals. The tantalum is mainly associated with columbite. The major gangue minerals present in this ore were soda and potassium feldspars with small amounts of mica and quartz. Beneficiation of this ore using cationic flotation, normally employed for flotation of niobium, was not applicable for this particular ore, since most of the mica and feldspar floated with the niobium and tantalum. The effect of amine on Ta/Nb flotation is illustrated in Figure 23.9. The selectivity between Ta/Nb and gangue minerals using a cationic collector was very poor. 

Niobium is the 33rd most abundant element in the Earths crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in several mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, NaljNbjOg (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nbl Og] are also products from tin mines in Malaysia and Nigeria. Niobium... 

However, the story does not end there. It was not until 1844 when Heinrich Rose (1795-1864) rediscovered the element by producing two similar acids from the mineral niobic acid and pelopic acid. Rose did not reahze he had discovered the old columbium, so he gave this new element the name niobium. Twenty years later, Jean Charles Galissard de Marignac (1817—1894) proved that niobium and tantalum were two distinct elements. Later, the Swedish scientist Christian Wilhelm Blomstrand (1826—1899) isolated and identified the metal niobium from its similar twin, tantalum. 

Euxenite (Loranskite). (Y, Ca, Ce, U, Th)-(Nb, Ta, Ti)20. A rare-earth mineral, occurring in Norway, Madagascar, Canada Pennsylvania. It is brownish-black, brilliant to vitreous sp gr 5.0—5.9 and hardness 5— 6. Used as a source of uranium, niobium and tantalum... 

Schilling, Zeitsch. angeu Chem., 1905, 18, 883. All analyses of minerals containing tantalum previously published are here collected by Schilling. The densities, percentages of niobium and tantalum present, the localities in whioh the minerals occur, and the references to the literature, are tabulated,... 

The detection of niobium and tantaluA ideg nfli almost entirely on the reactions given by niobic acid and tanxanc acid. All the common niobium and tantalum compounds are hydrolysed on bdng boiled in acid solutions, and yield precipitates of the respective adds. Natural minerals are previously fused with potassium hydrogen sulphate, and the aqueous extract of the melt usually precipitates the mixed acids... 

Addition of ammonium hydroxide or ammonium sulphide to solutions of niobic acid and tantalic acid in mineral acids reprecipitates the niobic and tantalic acids, which may, however, retain some of the ammonia. This test does not distinguish between niobium and tantalum, and it does not proceed in the presence of tartaric acid. 

The most readily available pure compounds of niobium and tantalum are the pentoxides9 Nb205 and Ta205. As expected, these are more acidic than Zr02 and Hf02, dissolving readily in concentrated alkali but inappreciably in the common mineral acids (except for concentrated HF). 

Another effect of lanthanide contraction is that the third row of the d-block elements have only marginally larger atomic radii than the second transition series. For example, zirconium and hafnium, niobium and tantalum, or tungsten and molybdenum have similar ionic radii and chemical properties (Zr + 80 pm, Hf + 81 pm Nb + 70 pm, Ta + 73 pm Mo + 62 pm, W + 65 pm). These elements are also found in the same natural minerals and are difficult to separate. 

The prominent niobium and lead spikes of continental materials are not matched by any of the OIBs and MORBs reviewed here. They are, however, common features of subduction-related volcanic rocks found on island arcs and continental margins. It is therefore likely that the distinctive geochemical features of the continental crust are produced during subduction, where volatiles can play a major role in the element transfer from mantle to crust. The net effect of these processes is to transfer large amounts of lead (in addition to mobile elements like potassium and rubidium) into the crust. At the same time, niobium and tantalum are retained in the mantle, either because of their low solubility in hydrothermal solutions, or because they are partitioned into residual mineral phases such as Ti-minerals or certain amphiboles. These processes are the subject of much ongoing research, but are beyond the scope of this chapter. 

Niobium and tantalum (both rare, 3x 10 %) are extracted (Fig. 243) from a mineral which is a mixed niobate and tantalate of iron and manganese, (Fe,Mn) (Nb,Ta,Og)2. When it contains more niobium than tantalum it is known as columbite, otherwise as tantalite. 

Ewing RC (1975) The crystal chemistry of complex niobium and tantalum oxides IV. The metamict state Discussion. Am Mineral 60 728-733... 

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