Short-term laboratory adsorption of zinc and cadmium ions from aqueous solutions to ground canna indica roots

Abstract

The current work presents the competitive removal of zinc (Zn) and cadmium (Cd) ions by adsorption using the roots of the Canna indica plant in order to study the metal-plant interactions at the microscopic scale that occur in constructed wetlands and phytoremediation processes. The sorption process was described in association with the data generated from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Kinetic variables and constants were calculated, optimized, and analyzed. The pseudo-second-order kinetic model provided the best fit to the experimental data and the sorption equilibrium was achieved in nearly 300 min. The equilibrium isotherms of zinc and cadmium were described using the nonlinear models of Langmuir, Freundlich, Sips, and their multi-component equivalents. The dimensionless separation factor (R L) showed that the adsorption system in this study is favorable. The Langmuir monolayer adsorption capacities were 71.20 and 298.6 μg g−1 for Zn2+ and Cd2+ respectively. The parameters of the metal adsorption isotherm fitted better to the extended Freundlich isotherm. This study reveals the association between surface properties and the biosorption capacity of heavy metals by plant roots on the one hand and the implication of the ion exchange mechanism through chemisorption on the uptake of Zn2+ and Cd2+ ions from aqueous solution by this adsorbent on the other hand.