Preparation of an enhanced chitosan modified flocculant with both chelation adsorption and flocculation effects for efficient treatment of Pb2+ heavy metal wastewater

In this study, chitosan (CS), acrylamide (AM) and itaconic acid (IA) were selected as raw monomers to prepare a novel flocculant CS-g-P(AM-IA) for heavy metals’ removal. CS-g-P(AM-IA) are rich with carboxylic acid ionic groups through ultrasonic-free radical initiated polymerization. The CS-g-P(AM-IA) has both chelation coordination and flocculation effect, which is used for removing heavy metal Pb 2+ efficiently. The effects of one-factor experimental preparation conditions such as initiator concentration, total monomer concentration, total mono-chitosan mass ratio and ultrasound time on the intrinsic viscosity of CS-g-P(AM-IA) were investigated. Thus, the optimization of ultrasonically initiated CS graft polymerization mechanisms and preparation conditions will be further understood and explored. The results of Fourier-transform infrared spectroscopy, thermo-gravimetry/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) indicated that CS was successfully grafted by AM and IA. In addition, TG/DSC and SEM analyses showed that CS-g-P(AM-IA) had better thermal stability and rougher surface topography, respectively. The chelating–flocculation experimental results showed that the removal rate of Pb 2+ reached 84.5% and 64.3% by CS-g-P(AM-IA) and CS at pH = 5.0, flocculation time of 25 min, flocculant dosage of 3.0 mg/L, respectively. The Pb 2+ removal effect by CS-g-P(AM-IA) was obviously superior than that of CS. The ionic strength and coexisting positive ions have an adverse effect on the adsorption performance for the flocculants, and the effect of Ca 2+ was obvious. Pb 2+ ions were mainly immobilized by CS-g-P(AM-IA) through chelation and flocculation by its IA carboxyl groups. And then it was generated large and dense heavy metal flocs (d 50 = 275.9 μm, D f = 1.91) by adsorption bridge, net trapping and sweeping to enhance the separation and removal performance of Pb 2+ ions.