The Mechanism of Extraction of Tantalum in the Tantalum-Hydrofluoric Acid-Tributyl Phosphate System

Abstract

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.

Quantification of Hydrofluoric Acid Species by Chemical-Modeling Regression of Near-Infrared Spectra

“…Many industrial processes require careful monitoring and control of hydrofluoric acid levels, due to HF's corrosive nature, complexing ability, and high toxicity. Frequently, these measurements must be made over wide concentration and pH ranges as may be found in etching baths and dissolver solutions. − …”

Extraction of Trace Niobium from Titanium Sulfate Solutions

“…May et al (1961) developed a procedure for extracting Nb from H2SO4-HF solutions using MIBK and indicated no appreciable extraction of Ti. TBP (tributyl phosphate) was reported by Nishimura et al (1964b) to be more efficient than MIBK for extracting Nb from H2SO4-HF solutions. Fletcher et al (1956) indicated that the extraction of Ti by TBP from H2SO4-HF was low.…”