Structural analysis of NH⋯O in viscoelastic scum formation during solvent extraction of sulfuric acid with trioctylamine

In the paper, Fourier transform infrared spectroscopy combined with Gaussian function linear fitting is used to analyze the structure of the viscoelastic scum formed during solvent extraction of sulfuric acid with trioctylamine (TOA). The results show that when the molar ratio of sulfuric acid to TOA is low in the system, it would form N⋯HO through TOA coupling with sulfuric acid or TOA coupling with water. The N⋯H stretching vibration is around 3400 cm−1. With the increase of molar ratio of sulfuric acid to TOA, three peaks, near 2660 cm−1, 2610 cm−1, and 2535 cm−1, appear in the infrared spectrum and they are assigned to NH+ combining with water, NH+ combining with OS, NH+ combining with water and OS in the extraction system. The wave-number of CN stretching vibration increases with the increase of molar ratio of sulfuric acid to TOA.

► There are two kinds of reactions in the TOA extraction of sulfuric acid system.
► There are three peaks during 2750–2450 cm−1 and assigned to three kinds of NH+.
► They may be NH+ combining with water, sulfuric acid and water.
► The possible molecular structures are proposed.