Excellent salt- and temperature-resistant chitosan-based flocculants for treating and recycling of saline textile effluents

To overcome the limitations of salinity and temperature inherent in traditional flocculation methods, a novel chitosan-based flocculant (CT-IPGE) with great salt tolerance and high temperature resistance was synthesized via grafting glycidyl isopropyl ether (IPGE) onto chitosan. With an increasing salt concentration from 0 to 100 g/L, the flocculation experiments demonstrated sustained dye removal efficiency exceeding 90 %, significantly surpassing pristine CT with 18 % dye removal efficiency. This performance was attributed to the H-bond hydration effect of IPGE segments, which counteracted the salt-induced polyelectrolyte effect and enabled an extended polymer conformation. Additionally, the hydrophilic-hydrophobic transition caused by increased IPGE hydrophobic group substitution reduced the solubility of flocculation precipitations, further enhancing dye removal. Excitingly, as the solution temperature increased from 20 to 90 °C, CT-IPGE consistently maintained a dye removal efficiency of over 93 %, achieved through synergistic mechanisms including charge neutralization, adsorption and bridging. Furthermore, after flocculation and sedimentation, the high-salinity dye wastewater demonstrated excellent reusability in subsequent dye baths without compromising color reproduction quality. The work provided a new methodology for excellent salt- and temperature-resistant chitosan-based flocculants, overcoming longstanding salinity/temperature barriers in textile wastewater management and promoting practical solutions practices in the textile industry.