Preparation of macroporous bead adsorbents based on poly(vinyl alcohol)/chitosan and their adsorption properties for heavy metals from aqueous solution

A novel macroporous bead adsorbents based on poly(vinyl alcohol)/chitosan (PVA/CS beads) were prepared, characterized and were used for the adsorption of heavy metal ions from aqueous solution. The resulting PVA/CS beads were perfectly spherical in shape and exhibited good mechanical strength and chemical stability. PVA/CS beads with macroreticular structure had been proved with easy separation and excellent adsorption for heavy metal ions. PVA/CS beads adsorbed heavy metal ions in the following order: Cu2+ > Pb2+ > Cd2+ > Zn2+. The equilibrium data of Cu2+, Pb2+ and Cd2+ conformed to the Freundlich isotherm, while those of Zn2+ were best described by Langmuir isotherm. The presence of NaNO3 (0-0.137 mol/L) had little effect on Cu2+ adsorption, but the adsorption of Pb2+, Zn2+ and Cd2+ decreased significantly in the same conditions. The competitive adsorption showed that PVA/CS beads had higher adsorption selectivity for Cu2+ with the coexistence of Pb2+, Zn2+ or Cd2+. The adsorption kinetics of Cu2+, Pb2+, Zn2+ and Cd2+ were found to follow the pseudo-second-order kinetic model. Various thermodynamic parameters were calculated and the results showed that the adsorption of all metal ions onto PVA/CS beads was feasible and endothermic in nature. The results from the sequential adsorption-desorption cycles showed that PVA/CS bead adsorbents held good desorption and reusability, which would be a potential application in the fixed-bed continuous-flow column for the removal of heavy metals. (C) 2011 Elsevier B.V. All rights reserved.