Performance evaluation of chitosan-based flocculants with good pH resistance and high heavy metals removal capacity

Dual-function chitosan-based flocculants with chelation and flocculation capacity, carboxylated chitosan-graft-polyacrylamide (PCA), carboxylated chitosan-graft-polyacrylamide-co-sodium xanthate (PCAXC), and carboxylated chitosan-graft-poly(acrylamide-2-acrylamido-2-methylpropane sulfonic acid) (PCAAF), are designed and prepared by UV initiation method. The physicochemical characteristics of PCA, PCAXC, and PCAAF were characterized by fourier transform infrared spectroscopy, 1 H nuclear magnetic resonance, and X-ray diffraction pattern to confirm the successful syntheses. Then PCA, PCAXC, and PCAAF are applied to chelate and flocculate Cu, Cr, and Ni from water. Effects of pH, flocculants dosage, reaction time, and stirring speed were investigated systematically to detect the relationship between flocculants structural and chelation-flocculation capacity. The maximum removal rate of Cu and Cr obtained by PCAXC at are 85.1% and 76.1%, respectively, while The maximum removal rate of Ni obtained by PCAAF at is more than 75.7%%. In addition, the relationship between the initial concentration of simulated heavy metal wastewater and the flocculants dosage and the competitive chelation-flocculation properties in the mixed heavy metal solution are also detected in detail. The mechanism can be assigned to the effective interaction between function groups of the flocculants and heavy metal irons by chelation, charge neutralization, and adsorption bridging mechanism.