One-pot preparation of lignin-based cationic flocculant and its application in dye wastewater

Abstract

Lignin shows good potential as a flocculant material, but more complex reaction processes are often required to obtain products with high flocculation performance. In this work, kraft lignin, acrylamide, and 3-chloro-2-hydroxypropyltrimethylammonium chloride were used as materials to prepare lignin-based flocculants (CPKL) using a one-pot method. The flocculation performance was significantly improved by the optimization of the synthesis conditions. Congo Red, an anionic azo dye, was used as a simulated contaminant to test the flocculation performance. Influencing factors such as flocculant dose, pH, and initial dye concentration were evaluated. The jar test results showed that CPKL has the advantages of a wide flocculation window, strong pH adaptability and the ability to maintain a high decolorization rate at different dye concentrations. Charge neutralization was the main flocculation mechanism, and adsorption bridging showed significant effects only at higher dye concentrations. In addition, lignin-based flocculants (CPKL-s) were prepared by gradient acid fractionation of kraft lignin (APKL-s), and their flocculation performance were further investigated. Among them, the product (CPKL-4) obtained by modifying the grade precipitated at pH 4 (APKL-4) exhibited good flocculation performance with a low dose and high decolorization rate. This method is environmentally friendly, technically feasible and has attractive application prospects in water treatment.