Production of Flocculant from Thermomechanical Pulping Lignin via Nitric Acid Treatment

There is a growing need to utilize lignin (i.e., wasted material) from the pulping industry in the production of value-added products and to develop cost-effective and environmentally friendly processes for removing dyes from wastewater effluents. In this context, lignin can be modified to gain anionic charges, which can successfully remove cationic dyes from wastewater. In this study, lignin was extracted from thermomechanical pulp (softwood) via periodate treatment, and then the extracted lignin was oxidized using 30 wt % nitric acid concentration at 80 degrees C for 1.5 h, which resulted in oxidized lignin with the charge density and solubility of 3.02 mequiv/g and 97% (at a 1 wt % lignin concentration), respectively. The oxidized lignin was used for removing ethyl violet and basic blue cationic dyes from simulated wastewater effluents. It was observed that the dye removals were in the ranges of 70-80 wt % for ethyl violet and of 80-95 wt % for basic blue, while the COD removals were in the ranges of 60-70% for ethyl violet and 70-85% for basic blue when the concentrations of dyes varied between 50 and 400 mg/L. The dye removal was pH dependent, and the removal of basic blue decreased from 84 wt % (in the absence of salt) to 77% in the presence of 3 g/L NaCl, whereas salt had a marginal effect on the removal of ethyl violet from the solution.