Separation of vanadium(V) using N235 by three-phase system in concentrated HCl media

Abstract

The third phase formed in the process of extracting vanadium in a N235/HCl system was usually regarded as a limit to the throughput of the plant. To have a deep insight on this problem, the formation of the third phase in the extraction of vanadium by tertiary amine N235 in the concentrated HCl system was studied. The optimum parameters of three-phase system extraction were determined, and FTIR analysis was carried out to characterize the structure of extracted complexes and analyze the mechanism of formation and elimination of the third phase. The results showed that vanadium extraction efficiency was 86.5% with 20% v/v N235 and a phase ratio (O:A) of 1:2 in 2 min at 25 °C, though an obvious third phase was found within the experimental HCl concentration range. Cl− is the participant in the process of increasing the vanadium extraction efficiency, whereas H+ has an inhibitory effect on vanadium extraction. Meanwhile, the structure of the extracted complex was confirmed as (R3N)m(HCl)m+x·([Formula: see text])·(H2O)n through a solvation mechanism with molecular association, which was further proved by FTIR spectral analysis. Furthermore, the limited solubility of the ion-extracted complexes in the nonpolar solvent kerosene made the third-phase form. The third phase disappeared when phase modifier (about 5% v/v TBP) was added into the organic phase, as the polarity of the organic phase increased.