The preparation of gallic acid-grafted cationic chitosan as effective salt-tolerant flocculants

In this work, gallic acid was successfully grafted onto quaternary aminated chitosan to prepare a high efficiency cationic flocculant. The mechanism of flocculation and different influencing factors were studied in detail. The prepared flocculant only needs 60 mg L−1 to achieve a 98.7% and 94.5% removal rate on methyl blue (MB) and Congo red (CR), respectively. The high removal rate (93.2%) of a CR-MB mixed dye also confirms the universality of flocculation. In addition, kaolin as a simulated suspended solid was removed at a rate of 97% in the experiment at a dosage of 3 mg L−1. A zeta potential test showed that it worked best when the potential of the flocculation system was zero; this was because an electrostatic balance was reached between the flocculant and pollutant. Importantly, the three-functional molecules can provide more possibilities to form hydrogen bonds with water molecules, which is conducive to the stretching of flocculant molecular chains in salt water. The flocculant maintained a high stability in four different salt environments and has a positive industrial application significance. Furthermore, the flocculation experiment of the actual wastewater of the printing and dyeing plant found that the dye wastewater changed obviously from turbidity to clarification, which proved the practical application potential of the flocculant. This work provides a feasible idea for the preparation of bio-based flocculants.