Sustainable cationic cellulose for highly efficient flocculation of Kaolin suspension

Green bio-flocculants from renewable biomass resources have received the widespread attention for wastewater treatment, which are promising alternatives to petroleum-based synthetic flocculants. In this paper, sustainable cationic cellulose bio-flocculants with various amino group contents were successfully prepared by a feasible chemical crosslinking with polyethyleneimine (PEI). The flocculation performances of diverse PEI-grafting cellulose (CE-PEI) were evaluated to purify turbid Kaolin suspension. Further, the flocculation kinetics and flocculation mechanism were investigated. Benefiting from the high surface positive charges and supramolecular structure, CE-PEI bio-flocculants with amino group contents of 17.5 mmol/g displayed the best turbidity removal efficiency. The residual turbidity of Kaolin suspension decreased from the initial 480–8.6 NTU, a 98.2% reduction with CE-PEI dosage of 0.15 mg/mL, sedimentation time of 30 min at pH 7.0. Flocculation kinetic results indicated that interaction of aggregation and collision between CE-PEI bio-flocculants and Kaolin particles was sufficient for the flocculation process at the optimal CE-PEI dosage. Moreover, charge neutralization was the dominant mechanism for the flocculation of CE-PEI on Kaolin. Thus, this work not only exploits a promising application of cellulose as a bio-flocculant, but also provides a feasible approach to efficiently purify high turbidity wastewater. Graphic abstract