A kinetic and thermodynamic study of cyanide adsorption in activated carbon

Abstract

During last decades, cyanide adsorption has been studied in plain and in modified activated carbon, although the adsorption mechanism is not clarified. In this context, the investigation of adsorption energetics is of fundamental importance and can substantially contribute to understand the mechanism. In addition, determination of activation energies and adsorption and desorption constants are required in the modeling of adsorption and in the design and operation of adsorption equipment. For this purpose, the adsorption equilibrium and kinetics of cyanide adsorption in a commercial activated carbon were experimentally determined at various temperatures. By applying equilibrium and kinetics equations based on the Langmuir model, the respective constants were calculated i.e. equilibrium constant and adsorption and desorption kinetic constants. Calculation modality is not applied in literature yet. Further, by applying the classical Arrhenius methodology the pre-exponential factors and activation energies of adsorption and desorption were calculated. This procedure differs from that usually applied in the literature. It was found that CN− is most probably hydrated and loosely adsorbed at room temperature. By increasing the temperature, hydration shield is destroyed and CN− is adsorbed in a higher energy configuration.