Niobium extraction

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. 

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. 

Alcohols with a C8 - Cn chain length, characterized by low solubility in aqueous media, may have a particular commercial potential as perspective extractants for tantalum and niobium hydrometallurgical processing. Particular emphasis has been placed recently on the investigation of tantalum and niobium extraction using octanol (C8Hi80) in the forms of 1-octanol and 2-octanol [462,466-473]. 

Details of the tantalum and niobium extraction process depend on the type of raw material used, decomposition method, initial solution composition, extractant type, equipment specifications, type of final products and desired purity. Therefore, process parameters are usually defined individually for each specific case. This may be the reason for the existence of the wide variety of publications devoted to the liquid-liquid extraction of tantalum and niobium. Nevertheless, some common features of the process should be emphasized. 

The raffinate obtained following selective extraction of tantalum is used as the initial solution for niobium extraction. The acidity of the initial solution is increased by adding sulfuric acid up to a concentration of at least 6M. It was... 

Table 63 presents the complete process parameters, including tantalum and niobium extraction. Fig. 134 gives the flow chart of the complete process. 

Table 63. Optimal parameters of tantalum and niobium extraction with 2-octanol.

Niobium and tqntalum have similar chemical properties and the normal methods of niobium extraction do not remove the tantalum. Separation of these two elements is necessary, for example, when the niobium is required for nuclear purposes, and several solvent extraction processes are suitable. Hexone i (methyl isobutyl ketone) and tributyl phosphatei are the two principal solvents which are used, although processes have also been developed using methyl dioctylaminei and di-isopropyl ketone.i ... 

This laboratory research was confirmed by large-scale ex riments conducted in an induction furnace with 20 kg charges of Nb-Fe-C alleys. The results of Table 2 indicate that the treatment of liquid alloys by sodium sulphate at 1473 K for 10 minutes provided about 90% niobium extraction into the slag. 

V. Korovin, S. Randarevich, and Y. Shestak, Niobium extraction hy TBP and TVEX-TBP from hydrochloric media based on 31P, 93Nb NMR data, Rus. J. Inorg. Chem., 36, 3167-3171 (1991). 

V. Korovin and Y.Shestak, Niobium extraction by TVEX— polymer resin containing tri-butilphosphate, Reac. Polym., 40, 107-113 (1999). 

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