Niobium-tantalum extraction

Another solvent extraction scheme uses the mixed anhydrous chlorides from a chlorination process as the feed (28). The chlorides, which are mostly of niobium, tantalum, and iron, are dissolved in an organic phase and are extracted with 12 Ai hydrochloric acid. The best separation occurs from a mixture of MIBK and diisobutyl ketone (DIBK). The tantalum transfers to the hydrochloric acid leaving the niobium and iron, the DIBK enhancing the separation factor in the organic phase. Niobium and iron are stripped with hot 14—20 wt % H2SO4 which is boiled to precipitate niobic acid, leaving the iron in solution. 

The spectrum of the niobium-containing extract was concluded to be related to the presence of NbFg and NbF5OR" ions [462]. Investigation of the IR absorption spectra confirms the presence of TaFe and NbF6 complex ions in the tantalum and niobium extracts, respectively. 

The second method is based on selective extraction that consists of extraction into two different organic solutions. In the first step, tantalum is extracted into an organic phase. In the second step of the procedure, niobium is extracted into a separate portion of the extractant. Fig. 126 presents a flow chart of the process based on the selective extraction scheme. 

The raffinate from the selective extraction process contains mostly niobium. The tantalum extract is treated by steam stripping to obtain a tantalum strip solution. The method results in the effective separation and relatively high concentration of tantalum and niobium in the respective strip solutions. 

Another way of applying the selective extraction method directly on the initial solution is to produce a solution of low acidity. This can be achieved by using the hydrofluoride method for fluorination and decomposition of raw material. As was discussed in Paragraph 8.2.2, the raw material is fluorinated by molten ammonium hydrofluoride yielding soluble complex fluorides of ammonium and tantalum or niobium. The cake obtained following fluorination is dissolved in water, leading to a solution of low initial acidity that is related for the most part to the partial hydrolysis of complex fluoride compounds. The acidity of the solution is first adjusted to ensure selective tantalum extraction. In the second step, the acidity of the raffinate is increased to provide the necessary conditions for niobium extraction. 

A.G. Babkin, B.G. Miorov, A.I. Nikolaev, Extraction of niobium tantalum and other elements from fluoride solutions, Nauka, Leningrad, 1988 (in Russian). 

C. K. Gupta, Extractive Metallurgy of Niobium, Tantalum and Vanadium, Int. Metals Reviews, Vol. 29,... 

Solvent extraction is often applied to separate two chemically similar metals such as nickel/ cobalt, adjacent rare earths, niobium/tantalum, zirconium/hafnium, etc. For the purpose of elaboration, the example of the separation of two chemically similar elements such as zirconium and hafnium from their nitrate solution, using TBP as an extractant is considered. The solvent extraction process in this case is chemically constant (K) is given by ... 

At this point, it may be worthwhile referring to a specific example that is relevant to the information provided in the previous section, and the extraction of niobium/tantalum can be considered for this purpose. 

There are several processes for extracting and refining niobium from its ores. (Payton, P.H. 1981. Niobium and Niobium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3 . ed., Vol, 15, pp. 820-827. New York Wiley Interscience). The process of choice depends on nature of the ore and end use intended for the metal. Some common steps in these recovery processes involve ore preconcentration, breaking or opening the ore, obtaining pure niobium compounds, reduction of niobium compounds to niobium metal, purification or refining metal and fabrication. If niobium is extracted from a niobium-tantalum ore, the most important step is separation of niobium from tantalum, both of which are chemically very similar. 

Hofmann (1988) showed that crust formation by extraction of partial melt from the mantle could well explain much of the trace-element chemistry of crust-mantle differentiation. However, a few elements, notably niobium, tantalum, and lead, do not fit into the simple pattern of enrichment and depletion due to simple partial melting (Hofmann et al., 1986). The fundamentally different behavior of these elements in the MORB-OIB environment on the one hand, and in the subduction environment on the other, requires the second,... 

PAN has been applied in the determination of Mn in beryllium [79], platinum and gold [80], cadmium [81], steel [82], and in niobium, tantalum, molybdenum, and tungsten [28]. In this case the macro-amounts of Nb, Ta, Mo, and W were separated by extraction as the cupferronates. The azo dyes were used in determining Mn in food [35], and in plants and chemical reagents [36]. 

A continuous nitrate/fluoride process has been proposed to take advantage of the ready solubility of columbite ore in a mixture of nitric and hydrofluoric acids, and thus allow the feed solution to be prepared in a cheap and simple manner. The feed contains 45 g/1. of niobium, about 25 g/1. of tantalum and is 8N in hydrofluoric acid and 3N in nitric acid. It is extracted in six stages with three volumes of solvent, together with an additional stage for acid equilibration . A half volume aqueous strip solution is also 8N in hydrofluoric acid and 3N in nitric acid. About 99 per cent of the niobium is extracted into the solvent and is then backwashed in a second extractor with three volumes of 0-5N hydrofluoric acid. The solvent finally passes to a single-stage backwash extractor for removal of tantalum by sodium carbonate solution. 

The aim of this book is to describe processes which are applicable to the extraction and purification of rare metals and to illustrate by fairly detailed examples from the metals uranium, thorium, zirconium, hafnium, titanium, niobium, tantalum, beryllium and vanadium. The techniques are not necessarily limited to this range of metals, and it is indeed the author s hope that this work may stimulate thought on their application over a wider field. 

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