Laboratory Adsorption Studies on Ni(II) and Zn(II) Solutions by Sugarcane-Bagasse Ash

Abstract

Large volumes of sugarcane-bagasse ash are produced as residues from the sucro-alcohol industry and have some practical applications. The use of this ash as an adsorbent for the removal of Ni(II) and Zn(II) is studied in the present paper. Effects of pH, adsorbent concentration and equilibrium time have been studied in order to establish the best conditions for the removal of metal ions. The kinetic parameters, i.e. the constant rate, equilibrium sorption capacity and related coefficients of each kinetic model (pseudo-first order, pseudo-second order and Elovich), have been evaluated by means of nonlinear regression fit: the pseudo-second order best describes the kinetics of the process. The experimental data obtained from the equilibrium study were analysed using nonlinear Freundlich, Langmuir, Temkin and Toth models: the Langmuir and Toth isotherms best represent the sorption of the metal ions. The highest experimental sorption capacities obtained as regards the removal of Ni(II) and Zn(II) from the sugarcane-bagasse ash were 0.0298 and 0.0416 mmol g−1, respectively. The adsorption mechanism through the formation of covalent bonds and hydrogen bonds demonstrates the affinity between the adsorbent and the adsorbates. The studies were conducted separately, using independent solutions of each metal.