Kinetic study of liquid-phase adsorptive removal of heavy metal ions by almond tree (Terminalia catappa l.) leaves waste

Abstract

The kinetic sorption of five metal ions - Al³⁺ ,Cr⁶⁺ ,Zn²⁺ , Ag + and Mn²⁺ - from aqueous solution onto almond tree leaves (ATL) waste in single component system has been studied. The experimental data was analyzed in terms of intraparticle diffusion and rate of adsorption, thus comparing transport mechanism and chemical sorption processes. The sorption rates based on the pseudo-second order rate constants for the five metal ions are 0.018 (Al³⁺ ), 0.016 (Cr⁶⁺), 0.023 (Zn²⁺ ), 0.021 (Ag⁺ ) and 0.022 (Mn²⁺ ) g/mg.min. The adsorption rates are rapid and within 180 min of agitation more than 85 percent of these metal ions has been removed from solution by the ATL waste biomass. The kinetic data suggest that the overall adsorption process is endothermic, and that the rate-limiting step is a surface diffusion controlled process. The results from this study have revealed that the ATL waste, which is hitherto an environmental nuisance, has the ability to adsorb metal ions from solution and the data are relevant for optimal design of wastewater treatment plants. The low cost and easy availability of ATL waste make potential industrial application a strong possibility.