preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminum by solvent extraction using ehehpa

The preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminumwas investigated by solvent extraction with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA) and tri-n-butyl phosphate (TBP) as the phase modifier. The extraction and stripping conditions of vanadium (IV) and its separation from iron and aluminum were optimized. Under the optimal extraction conditions, the extraction of vanadium (IV) and iron were 68% and 53%, respectively, while only 2% aluminum was extracted in a single contact, suggesting good separation of vanadium (IV) from aluminum. Sulfuric acid solution was used for the stripping. Nearly 100% vanadium (IV) and 95% aluminum were stripped, while only 10% iron was stripped under the optimal stripping conditions in a single contact, suggesting good separation of vanadium (IV) from iron. After five stages of extraction and stripping, highly pure vanadyl sulfate containing 76.5 g/L V (IV) with the impurities of 12 mg/L Fe and 10 mg/L Al was obtained, which is suitable for the electrolyte of a vanadium redox flow battery. Organic solution was well regenerated after stripping by oxalic acid solution to remove the remaining iron. The mechanism of vanadium (IV) extraction using EHEHPA was also discussed based on the Fourier transform infrared spectroscopy (FT-IR) analysis.