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The method for extracting and separating Ta and Na by using the solvent extraction system, hydrofluoric acidsulfuric acid-tributyl phoshate (TBP), was investigated. The extractability of fluotantalates and fluoniobiates from HF-H2SO4 solution into TBP was found to be functions of HF acidity, H2S04 acidity, TBP concentration, oxide concentration, organic solvent ratio, and extraction frequency. The results obtained can be summarized as follows: (1) The Ta percentage extraction and the Ta distribution ratio increased with the increase of H2SO4 acidity at a const HF acidity, but decreased with the increasing HF acidity at a constant H2SO4 acidity. They diminished with the decrease of TBP concentration. The Nb percentage extraction and the Nb distribution ratio augmented with increasing HF acidity, H2SO4 acidity, and TBP concentration. (2) In general, the separation coefficient was superior in lcw Hl acidity-low H2SO4 acidity, being inferior at high HF acidity-high H2SO4 acidity. 6) The HF-H2SO4-TBP system has larger extractability of Ta and Nb, particulary Nb, and is higher in purity the organic extract than the HF-112SO4-hexone system which is being used as the industrial extraction system for liquid-liquid extraction of Ta and Nb.

The mechanism of extraction of Ta by TBP in the Ta-hydrofluoric acid-TBP (tributyl phosphate) system is investigated in this report. The results obtained can be summarized as follows: (1) Ta present at a low concentration of HF seemed to be essentially HTaF6 at a high concentration of HF, H2ZTaF7, and at a much higher concentration of HF, H3TaF8 seemed dominant. (2) One molecule of Ta compounds at various concentrations of HF combined with three molecules of TBP organic solvent, and was extracted by TBP in the form of a Ta compound-3 TBP complex. (3) when the polymerization of Ta in the aqueous phase was higher than that in the organic phase, the distribution coefficient of Ta and the percentage extraction of Ta became lower. At a higher concentration of HF the polymerization number of Ta in the aqueous phase was constant and larger than that in the organic phase, independent of the concentration of Ta in the aqueous phase, but at a lower concentration of HF the ratio of the polymerization number in the aqueous phase to that in the organic phase was larger at a higher concentration of Ta, but was smaller at a lower concentration of Ta. (4) The process of Ta-HF-TBP extraction was an exthothermic reaction, and the heat of extraction was 2.41kcal/mol at 6.36N HF concentration and 16g/L Ta concentration. (5) The rate-controlling step in the extraction of Ta in the Ta-HF-TBP extraction system was considered to be the formation reaction of a Ta compound-3TBP complex. (6) In this extraction system, the concentration of Ta in. the aqueous phase showed little change by the distance from the interface, but the change in the TBP phase was remarkable. (7) The activation energy for diffusion of Ta species in a 1.28N HF solution was 3.495kcal/mol, and that of a Ta compound-3TBP complex in the TBP phase was 5.836kcal/mol.

In this report the liquid-liquid solvent extraction and the separation of Ta and Nb have been studied, using tributyl phosphate (TBP) as an organic solvent and hydrofluoric acid solution as an aqueous solution. The extractability of a fluoride complex of Ta and Nb from HF solution into TBP was found to be a function of HF acidity, TBP concentration , oxide concetration, volume ratio of organic solvent to aqueous solution, and number of extraction operation . The results obtained can be summarized as follows: (1) The Ta percentage extractions and the Ta distribution ratio decreased with an increase in HF acidity at a constant TBP concentration, but decreased with a decrease in TBP concentration at a constant HF acidity. The percentage extractions of Nb and Nb distribution ratio rose with a rise in HF acidity and TBP concentration. (2) The separation factor augmented with diminishing HF acidity, especially under 3 N HF. (3) Both percentage extractions of Ta and Nb decreased inversely with the rising oxide concentration in aqueous solution. (4) The increase in the volume ratio and frequency of extraction increased both percentage extractions of Ta and Nb. (5) The organic extract ertracted with TBP included little impurity. (6) The HF-TBP system had larger extractability of Ta and Nb , particularly in low HF acidity, better separation factor and higher purity of the organic extract than the HF-hexone system.

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