Effect of hydroxyl on formation of viscoelastic scum during solvent extraction of sulfuric acid with trioctylamine

In the paper, Fourier transform infrared spectroscopy (FTIR) is employed to investigate the formation of viscoelastic scum during solvent extraction of sulfuric acid with trioctylamine (TOA) as extractant. The spectra are deconvolved and peak-fitted to study the change of wave-number and the peak area of O–H stretching vibration. Results suggest that the water plays an important role in viscoelastic scum formation. The water, sulfuric acid and TOA can combined as SO…HOH…N or HOH…OS or NH…OS. With the increase of the molar ratio of sulfuric acid to TOA, the combination of the water, sulfuric acid and TOA would transform to SO…HOH…OS or N+…HOH, which may be form macro-molecules in the extraction system.

► Water is considered in viscoelastic molecule formation of sulfuric acid and amine.
► Water can be bridge of H2SO4 and TOA leading to the viscoelastic molecules.
► It changes from SO…HOH…N, HOH…OS to NH…OS with H2SO4 addition.
► The possible molecular structures are proposed.