Comparison of structures and properties of lignosulfonate in different pulping waste liquors

To better utilize lignosulfonates obtained from different pulping waste liquors, the structures and properties of acidic magnesium lignosulfonate, alkaline sodium lignosulfonate, and commercial sodium lignosulfonate were investigated by ultraviolet spectroscopy, Fourier- transform infrared spectroscopy, ion chromatography, and thermogravimetric analysis. The results showed that alkaline sodium lignosulfonate contained the highest lignin content and acidic magnesium lignosulfonate contained the lowest lignin content. Fourier- transform infrared spectroscopy revealed that the characteristic absorption peak of the three kinds of lignosulfonate was at 1210 cm(-1) to 1170 cm(-1), and that there was no significant difference between the groups. The sulfonic group of acidic magnesium lignosulfonate and alkaline sodium lignosulfonate may be located at different positions in lignin. Moreover, the acidic magnesium lignosulfonate contained fewer impurities than commercial sodium lignosulfonate and alkaline sodium lignosulfonate.