Pre-concentration of Ta(V) by solvent extraction before determination of trace amounts of Ta in Nb and Nb compounds

Abstract

The paper presents the results of a study on the efficiency of the separation of Ta(V) and Nb(V) from fluoride solutions by solvent extraction with methyl isobutyl ketone with a view to applying the extraction process to the purification of Nb from Ta and for the pre-concentration of Ta prior to its determination in Nb and its compounds over a wide range of initial concentrations. With strict control of the hydrofluoric acid concentration and the re-extraction of Ta into an aqueous phase using an ammonium oxalate solution, the mean recovery factors [%] for Ta were 94–108% in the initial weight ratio m_Nb : m_Ta = (ρ_Nb/Ta) range 10–1 000 000 with only a small scatter about the mean value (RSD ≤ 6%), with the exception of (ρ_Nb/Ta) = 1 000 000. The effect of the composition of the re-extraction solution on the excitation conditions of Ta in ICP-OES (ICP-MS) plasma was negligible and small amounts of Nb and other contaminants co-extracted with Ta did not affect its determination.