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

Abstract

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: Cu 2+ > Pb 2+ > Cd 2+ > Zn 2+. The equilibrium data of Cu 2+, Pb 2+ and Cd 2+ conformed to the Freundlich isotherm, while those of Zn 2+ were best described by Langmuir isotherm. The presence of NaNO 3 (0–0.137 mol/L) had little effect on Cu 2+ adsorption, but the adsorption of Pb 2+, Zn 2+ and Cd 2+ decreased significantly in the same conditions. The competitive adsorption showed that PVA/CS beads had higher adsorption selectivity for Cu 2+ with the coexistence of Pb 2+, Zn 2+ or Cd 2+. The adsorption kinetics of Cu 2+, Pb 2+, Zn 2+ and Cd 2+ 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.