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

摘要

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 NaN03 (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.