Equilibrium and kinetics studies on adsorption of Zn(II) from aqueous solutions onto a graft copolymer of cross-linked starch/acrylonitrile (CLSAGCP)

A synthetic graft copolymer of cross-linked starch/acrylonitrile was used as an adsorbent for the removal of Zn(II) ions from an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) at different temperatures and fixed pH. The amount adsorbed increased with increasing concentration of Zn(II) ions, and with increasing temperature. The length of time taken to reach equilibrium of the adsorption of Zn(II) ions was the same at all temperatures tested. Kinetics studies showed that the adsorption process obeyed first-order reversible kinetics and the adsorption isotherms followed the Freundlich model. Furthermore, the thermodynamic parameters, i.e. standard free energy (ΔGθ), standard enthalpy (ΔHθ), and standard entropy (ΔSθ), of the adsorption process were calculated, and the results are discussed in detail.