Abstract
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.
Highlights
Vanadium has found a variety of applications in alloys, catalysts, advanced materials, batteries, etc. [1,2,3]
Vanadium and some impurities were extracted by EHEHPA and stripped by sulfuric acid, generating a loaded strip solution, which was used as the feed solution for the present study
The results showed that the extraction of vanadium (IV) was 67%, similar to that obtained using fresh organic solution, proving that the extractant could be well regenerated
Summary
Vanadium has found a variety of applications in alloys, catalysts, advanced materials, batteries, etc. [1,2,3]. Vanadium has found a variety of applications in alloys, catalysts, advanced materials, batteries, etc. The application in vanadium redox flow battery (VRFB) is important due to itsadvantages over similar technologies, such as high energy efficiency, short response time, low self-discharge, and a long lifetime [4]. Vanadium based electrolytes in sulfuric acid solutions are a crucial component of VRFB systems, and, their preparation has attracted much attention. V2 O5 and vanadium-bearing solutions are conventionally used as the raw materials for the preparation of vanadyl sulfate electrolytes. V2 O5 was dissolved in dilute sulfuric acid and subsequently reduced with a reducing agent to obtain highly concentrated vanadyl sulfate electrolytes by Zhong et al [6]. The detailed dissolution properties of V2 O5 using concentrated sulfuric acid were investigated by Mao et al [7]
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