Extraction of V(V) and Cr(VI) from aqueous solution using primary amine extractants: extraction mechanism and oxidation of extractants.

The extraction mechanism and the oxidation of extractants are essential to optimize the extraction process. To investigate the two problems for selective extraction of V(V) and Cr(VI), the extraction complexes of V(V) and Cr(VI) formed in the process of extraction with primary amines were obtained by solvent-out crystallization, respectively. The average compositions of the extraction complexes were determined by element analysis, X-ray photoelectron spectroscopy, and inductive couple plasma-optical emission spectrometry. The chemical functional groups of the extraction complexes were confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy. The structures of the extraction complexes of V(V) were speculated with their functional groups and average compositions. The hydrogen bond association mechanism of V(V) extraction was illustrated with the structure of the complexes, and the oxidation reaction of extractants with Cr(VI) was also demonstrated. According to the oxidation reaction of extractants with Cr(VI) and experiment conditions for the initial pH value, the optimized operation condition of the initial pH value ≥5.5 was determined to prevent the oxidation of extractants. The interaction of V(V) and Cr(VI) for the vanadium extraction and extractant oxidation was also investigated. Graphical Abstract: [ABSTRACT FROM AUTHOR]