A study of Zinc ions adsorption by native and chemically modified leaves of earleaf acacia (Acacia auriculiformis)

Abstract

Isotherms of Zn2+ ions adsorption by native and 3% H2SO4 solution-treated leaves of Acacia auriculiformis were plotted. The resulting adsorption isotherms were processed using the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. It was found that the isotherms of these Zn2+ ions adsorption with native leaves of earleaf acacia are most accurately described by the Temkin model and with modified leaves by the Langmuir model. It was found that the modification of acacia leaves with a 3% H2SO4 solution contributes to an increase in the maximum sorption capacity for Zn2+ ions from 9.5 mg/g to 30.5 mg/g. It was found that the kinetics of Zn2+ ions adsorption by native and modified Acacia auriculiformis leaves is most accurately described by a pseudo-second order model. The calculated values of the Biot's coefficient are in the range of 1 < Bi < 20, which indicates mixed diffusion in all cases. Thermodynamic parameters of the process of Zn2+ ions adsorption by native and acid-modified Acacia auriculiformis leaves were determined. The calculated adsorption (E) and Gibbs (∆G0) energies, as well as enthalpy and entropy indicate spontaneous, self-induced endothermic physical adsorption process in both cases.