Heavy metal removal from aqueous solutions by chitosan-based magnetic composite flocculants.

In this study, three magnetic flocculants with different chelating groups, namely, carboxymethyl chitosan-modified Fe3O4 flocculant (MC), acrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCM), and 2-acrylamide-2-methylpropanesulfonic acid copolyacrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCAA) were prepared, synthesized, and characterized by photopolymerization technology. They were applied to the flocculation removal of Cr(III), Co(II), and Pb(II). The effect of flocculation condition on the removal performance of Cr(III), Co(II), and Pb(II) was studied. Characterization results show that the three magnetic carboxymethyl chitosan-based flocculants have been successfully prepared with good magnetic induction properties. Flocculation results show that the removal rates of MC, MCM, and MCAA on Cr(III) are 51.79%, 82.33%, and 91.42%, respectively, under the conditions of 80 mg/L flocculant, pH value of 6, reaction time of 1.5 hr, G value of 200 s-1, and precipitation magnetic field strength of 120 mT. The removal rates of Co(II) by MC, MCM, and MCAA are 54.33%, 84.99%, and 90.49%, respectively. The removal rates of Pb(II) by MC, MCM, and MCAA are 61.54%, 91.32%, and 95.74%, respectively. MCAA shows good flocculation performance in composite heavy metal-simulated wastewater. The magnetic carboxymethyl chitosan-based flocculant shows excellent flocculation performance in removing soluble heavy metals. This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove heavy metals in wastewater.

Magnetic flocculants synthesized by Fe3O4 coated with cationic polyacrylamide for high turbid water flocculation.

A novel magnetic flocculant (CPAMF) was synthesized by using Fe3O4 coated with cationic polyacrylamide (CPAM) for flocculation of high turbid water. The surface morphology and chemical structures of CPAMF were confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) was employed to verify the crystal structure of CPAMF. The magnetic property of CPAMF was compared with Fe3O4 in this study. The flocculation performance by using flocculants CPAMF was evaluated in high turbid water treatment. The maximum transmittance 92.4% of kaolin suspension was achieved at corresponding optimal flocculation conditions. The result indicated that CPAMF was efficient in high turbid water flocculation. Analysis of FTIR, XRD of flocs, and zeta potential (ZP) of supernatant were accomplished for flocculation mechanism investigation. Because of low recovery factor in reflocculation under the effect of shear force on flocs, the bridging effect was found to be dominant in both acidic and alkaline conditions. Sedimentation experiments under the role of permanent magnet indicated that nano-Fe3O4 could effectively improve the settling property of CPAM. Graphical abstract ᅟ.

Rapid and efficient removal of heavy metal and cationic dye by carboxylate-rich magnetic chitosan flocculants: Role of ionic groups.

A multifunctional carboxylate-rich magnetic chitosan flocculant (Mag@PIA-g-CS) was prepared through surface graft copolymerization on magnetite particles. The effect of monomer molar ratio, initiator and pre-neutralized degree on polymerization rate was determined. Various analytical methods were applied to characterize Mag@PIA-g-CS, exhibiting the successful grafting of polymers, good magnetic feature and core-shell structure. The kinetic process of Ni(II) and malachite green (MG) flocculation by Mag@PIA-g-CS reached equilibrium within <60min with the optimal uptake rate of 98.3% and 87.4%, and exhibited satisfactory removal effect in wide pH range (4.0-8.0 for Ni(II), 5.0-10.0 for MG). Mag@PIA-g-CS exhibited superior flocculation performance over chitosan magnetic flocculant (Mag@CS). The pH-dependent behavior, rapid responsiveness and sensitivity to ionic strength in batch flocculation tests indicated the distinct effect of ionic groups. Moreover, sweeping action of linear molecular chains facilitated further flocculation. Mag@PIA-g-CS showed high stability in extreme environments, and can be easily regenerated and separated.