Tantalum partitioning

Separation of tantalum from niobium in hydrofluoric acid is carried out by solvent extraction due to solubility difference, using a suitable organic solvent such as methyl isobutyl ketone. At low acidity tantalum partitions from water into immiscible organic solvent leaving behind niobium in the aqueous HF extract. Tantalum is thus separated from this aqueous HF solution. The acidity of the aqueous HF solution is now increased and the solution again extracted with fresh methyl isobuty ketone to recover niobium, which partitions into the organic solvent, leaving any impurity that may remain dissolved in the HF solution. 

The organic extract containing tantalum is treated with pure water upon which tantalum partitions into the aqueous phase as a water-soluble salt. 

A good correlation between niobium and tantalum partition coefficients leads to... 

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. 

Principal experimental data on spinel-melt partitioning are those of Nielsen et al. (1994) for scandium, nickel, vanadium, zirconium, hafnium, niobium, tantalum, uranium, and thorium and Horn et al. (1994) for scandium, vanadium, gallium, zinc, cobalt, zirconium, hafnium, niobium, and tantalum. These are supplemented by data for hydrous melts by Nielsen and Beard (2000). 

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