Kinetics, equilibrium and mechanism of Cu2+, Ni2+ and Zn2+ ions biosorption using wheat straw

The kinetics of adsorption is described by a pseudo-second order reaction kinetic model, allowing the determination of kinetic parameters for each of the considered metal ions. The ion exchange mechanism was confirmed assuming that the alkali-earth metals (mostly calcium), from wheat straw, are substituted by the considered heavy metal ions and protons. For a single metal ion system, the adsorption equilibrium data can be modeled by the Langmuir adsorption isotherm for all considered ions. The maximum adsorption capacity of 5 mg g−1 was achieved for copper ions, while the adsorption capacity for nickel and zinc ions was 2.5 mg g−1 and 3.25 mg g−1, respectively. The obtained results show that wheat straw can be successfully used as an adsorbent for the adsorption of Cu2+, Zn2+ and Ni2+ ions from weakly acidic effluents.