Single and competitive adsorption of Cd(II) and Pb(II) ions from aqueous solutions onto industrial chili seeds (Capsicum annuum) waste

In this work, the single and binary adsorption of Cd(II) and Pb(II) onto industrial chili seeds (CS) (Capsicum annuum) from aqueous solutions was investigated as a possible low-cost biosorbent for the removal of toxic heavy metals from aqueous solutions. The dependence of the adsorption capacity of CS on the solution pH and temperature, and the presence of competitive metal were also studied in detail. The adsorption equilibrium experiments of Cd(II) and Pb(II) on CS were conducted in a batch adsorber. The Freundlich and Langmuir isotherm models were fitted to the single adsorption equilibrium data and the latter provided a better fit. Moreover, it was found that the adsorption capacity of CS towards Cd(II) and Pb(II) ions was greatly increased by increasing the solution pH. The effect of the pH was attributed to the electrostatic interaction between the negatively charged CS surface and the Cd2+ and Pb2+ cations in the aqueous solution. The adsorption capacity was slightly increased by raising the temperature because the adsorption of Cd(II) or Pb(II) ions on CS was an endothermic process. The experimental binary adsorption data were satisfactorily interpreted using the modified Langmuir multicomponent isotherm and the competitive adsorption of Cd(II)-Pb(II) on CS revealed that the affinity of Pb(II) for CS was more than 5 times higher than that of Cd(II).