The effect of diluent on the extraction: Amide extracting chromium (VI) as an example

As an essential separation and purification method, solvent extraction was widely used in many fields. In previous studies, extractants had received much attention, while the role of diluents had often been ignored. However, the diluent had a very complex effect on the extraction process. In the study, the influence of diluent on the extraction of chromium with amide as an extractant was discussed in detail. In order to increase the universality of the study, the common organic solvents, including alkanes, aromatic hydrocarbons, and halohydrocarbons, were selected as diluents. The extraction performance, formation of extracted complex, and thermodynamics under different diluents were determined. In addition, FT-IR and UV–Vis spectral analyses have been carried out to investigate the influence of diluent on the spectrum. The results showed that the diluent had an obvious influence on the spectrum of the amide group before extraction, and the influence was weakened after extraction. Based on the analysis of molecular electrostatic potential, the effect of diluent on the reaction site of amide extractant was investigated. Further, the molecular polarity index was used to calculate polarity parameters and deepen the understanding of the effect of diluent on the extraction process. The study provided a theoretical basis for other extraction systems to select appropriate diluents.