Cadmium Removal from Synthetic Aqueous Solutions by Adsorption on Peanut Shells: Kinetic and Thermodynamic Studies

Abstract

Peanut shells were used in this study as an adsorbent carrier in the treatment of wastewater containing a trace metal element (TME), namely cadmium, a pollutant with adverse effects on health and the environment. The influences of contact time between adsorbent and adsorbate, initial cadmium concentration, adsorbent mass, reaction medium temperature and solution pH were evaluated. To determine the optimum parameters, pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental results of the contact time study. Similarly, experimental results relating to the influence of concentration and temperature were modeled. Modeling of the data from the adsorbate-adsorbent contact time study showed that the kinetics of the cadmium adsorption reaction are well described by the pseudo-second-order kinetic model. The isotherm of the adsorption mechanism of cadmium ions (Cd2+) by peanut shells is perfectly described by the Freundlich equation. Thermodynamic studies using temperature variation have shown that adsorption is spontaneous and endothermic. This study led to a low entropy during cadmium adsorption. The best adsorption capacity was obtained at low pH = 5, i.e. favorable adsorption in acidic media.