Tantalite

The element is found in niobite (or columbite), niobite-tantalite, parochlore, and euxenite. Large deposits of niobium have been found associated with carbonatites (carbon-silicate rocks), as a constituent of parochlore. Extensive ore reserves are found in Canada, Brazil, Nigeria, Zaire, and in Russia. 

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. 

Tantal, n. tantalum, -erz, n. tantalum ore, specif, tantalite. tantalig, a. tantalous, tantalisch, a. of tantalum, tantalic. Tantal-lampe, /. tantalum lamp, -ozyd, n. 

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 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. 

Majima, Awakura, Mashima and Hirato [451] investigated in detail the kinetics of the dissolution process of columbite and tantalite in aqueous solutions of HF, HF - HC1, NH4F - HC1 and NH4F - H2S04, in the 60-80°C temperature range. 

Results of the measurements were analyzed in the form of the initial dissolution rate (R ), which is the first derivative of the dissolution fraction of a said element, in this case, niobium or tantalum. The dissolution fraction is defined as the molar ratio between the amount of metal dissolved and its total concentration in the said sample, in this case, columbite or tantalite. Table 60 presents some relevant values of the initial dissolution rate taken from [451]. 

Table 60. Initial dissolution rates (RJ of niobium and tantalum dissolved from columbite or tantalite in different solutions, at 80% . (Compositions of solutions are given in mol/l)(qfter Majima et al. [415]).

Based on an analysis of the initial dissolution rate in different solutions at different temperatures, several very useful conclusions and recommendations were made. It was found that the apparent activation energies for the dissolution of niobium and tantalum in 10 mol/1 HF solution are 56.5 and 65.5 kJ/mol, respectively for columbite, and 42.7 and 61.1, respectively, in the case of tantalite. It was also concluded that the mechanism of dissolution is the same for both columbite and tantalite. In addition, the initial dissolution rate of niobiuth (RNb) from columbite is controlled primarily by the activities of the... 

Akimov and Chernyak [452] investigated and reported on the mechanism of the interaction between columbite and tantalite and sulfuric acid. The said interaction is presented as comprising two steps. The first step is related to the formation of iron and manganese sulfates and of tantalum and niobium hydroxides ... 

The results of a thermodynamic analysis of the interactions in Equations (127) and (128), as presented in [452], show that a coherent shell of tantalum and niobium hydroxides is formed on the surface of the columbite or tantalite during the interaction with sulfuric acid. The formation of the shell drives the process towards a forced thermodynamic equilibrium between the initial components and the products of the interaction, making any further interaction thermodynamically disadvantageous. It was also shown that, from a thermodynamic standpoint, the formation of a pseudomorphic structure on the surface of columbite or tantalite components is preferable to the formation of tantalum and niobium oxysulfates. Hence, the formation of the pseudomorphic phases catalyzes the interaction described by Equation (127) while halting that described by Equation (128). 

This approach explains the experimental fact that the complete decomposition of columbite or tantalite by sulfuric acid yields hydroxides of tantalum and niobium according to the first step of Equation (127). 

Analysis of the volumetric effects indicates that as a result of such mechanical activation, iron and manganese are concentrated in the extended part of the crystal, while tantalum and niobium are predominantly collected in the compressed part of the distorted crystal structure. It is interesting to note that this effect is more pronounced in the case of tantalite than it is for columbite, due to the higher rigidity of the former. Akimov and Chernyak [452] concluded that the effect of redistribution of the ions might cause the selective predominant dissolution of iron and manganese during the interaction with sulfuric acid and other acids. 

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. 

Another method of raw material decomposition is based on the fluorination of the raw material by the hydrofluoride method. No published data exists on hydrofluoride decomposition of columbite or tantalite concentrates. The interaction can, nevertheless, be discussed based on available information on the decomposition of lithium tantalate, LiTaC>3, and lithium niobate, LiNb03, using the hydrofluoride method [113,118,122]. 

An initial solution was prepared by the hydrofluoride method, i.e. melting of a mixture of ammonium hydrofluoride and tantalite, followed by the digestion of soluble components with water and separation of the solution by filtration. The prepared initial solution contained no free HF or any other acid, and had a pH 3. In order to obtain an optimal acidity level, sulfuric acid was added to the solution. Concentrations of Ta2Os (50-60 g/1) and Nb205 ( 30 g/1) were kept approximately constant during the preparation of the solutions. Extraction was performed using a polypropylene beaker and a magnetic stirrer. 

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... 

Complex Spodumene Beryl Tantalite Lepidolite Ambylgonite Topaz Li, Rb, Cs, Be, Ta, Sn, Ga Manono, Zaire Hugo, South Dakota Tanco, Manitoba Londonberry, Australia Marlagalla, India... 

Albite-spodumene Spodumene Tantalite Beryl Cassiterite Li, Sn, Ta, Be Kings Mt., N. Carolina Volta Grande, Brazil... 

Albite Tantalite Cassiterite Beryl Ta, Sn Tin Dyke, Manitoba Hengshan, China Bastar, India... 

Complex oxides Chromite niobite-tantalite pyrochlore ilmenite wolframite scheelite... 

Ta/Nb minerals often occur as impurities in ilmenite, rutile, cassiterite, wolframite and perovskite, most of which contain REE. Because tantalite and columbite have similar chemical properties, they often replace each other, and are usually found as isomorph mixtures. Tantalum and niobium can also be found as separate minerals. Tantalite and microlite are primary sources of tantalum. 

Ores of magnetic origin. Tantalum/columbite granites are of economic interest when the columbite content of the ore ranges from 0.001% to 0.01% and the tantalite up to 0.2%. These deposits are most common in Nigeria (Africa). Because they are a low-grade ore, they do not represent significant economic value. 

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