Sulfomethylated kraft lignin as a flocculant for cationic dye.

In this work, sulfomethylated softwood kraft lignin (OSKL) was prepared by oxidation with nitric acid and sulfomethylation. The product was then used as an anionic flocculant for removing a cationic dye from a simulated dye solution. The present study showed that the efficiency of OSKL was improved with the increment in the charge density of OSKL. The formation of dye/lignin complexes in solution and the precipitation of formed complexes were evident in this work. Based on charge neutralization, the experimental and theoretical amounts required for removing the dye were determined, and the results were compared. The results showed that the pH of the dye solution affected the chemical oxygen demand (COD) removal from the solution, as well as the hydrodynamic diameters of OSKL in solutions. Under the optimal conditions of 300 mg/L of dye, pH 9 and room temperature, 300 mg/L of OSKL was sufficient for removing 99.1% of dye and 90% of COD from the solution. The analysis also confirmed that inorganic salts decreased the efficiency of OSKL in removing dye and time extension to 2 h improved the dye removal. [ABSTRACT FROM AUTHOR]