A Review of Niobium-Tantalum Separation in Hydrometallurgy
Niobium and tantalum are chemically similar and are associated with each other in nature which makes it very difficult to separate. For many years, the separation of tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, this method has been supplanted by solvent extraction from fluoride-containing solutions by the use of solvent extractants such as Octanol, bis(2-ethylhexyl)phosphoric acid (DEHPA), Alamine 336, methyl isobutyl ketone (MIBK), tri-nbutyl phosphate (TBP) or cyclohexanone. A detailed review of the various processes involved in the breakdown treatment of niobium and tantalum primary sources, extraction and separation and newer processes of extraction as well as the various technique involved were discussed. Keyword: Niobium, Tantalum, Columbite, Tantalite, Solvent extractant and Solvent extraction.
Liquid–liquid extraction of niobium and tantalum from aqueous sulphate/fluoride solutions by a tertiary amine
Abstract Niobium–tantalum ore containing euxenite, samarsakite and fergusonite was leached using sulphuric acid. Niobium and tantalum were extracted from the leach liquor with the tertiary amine, Alamine 336, using kerosene and xylene as diluents and n -decanol as a modifier. The effect of contact time, sulphate and fluoride concentrations in the aqueous phase, extractant concentration and aqueous to organic phase ratio were investigated. Both elements were extracted to different extents, with tantalum extraction slightly greater. The separation factor was greater for kerosene diluent. Selective stripping was performed using either 50 g/L potassium hydroxide or 25 g/L ammonium carbonate solutions for niobium and tantalum. Tantalum was stripped first and Ta(OH) 5 was precipitated during stripping. The separation of niobium from tantalum was achieved at this point. Niobium was then precipitated by adding ammonia.
Solvent extraction separation of tantalum from niobium on macro scale using di(2-ethylhexyl) phosphoric acid as extractant
A solvent extraction procedure for the separation of niobium and tantalum has been developed. The method consists of extracting tantalum from its aqueous mixture with niobium, with the help of di(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane. The aqueous feed consists of niobium and tantalum in an aqueous medium containing hydrochloric and oxalic acids. The concentrations of niobium and tantalum were raised to 1 mg/ml in the aqueous solution. The extraction efficiency of tantalum under these conditions was found to be ∼85%. Effects of chloride and oxalate ions as well as those of the concentration of HDEHP on the extraction efficiency were studied and discussed in detail.