Influence of Oxygen on Hg⁰ Adsorption on Non-Impregnated Activated Carbons

Both physisorptive and chemisorptive mechanisms play a role in the adsorption of mercury. The present publication investigates the influence of oxygen on the adsorption of Hg⁰ by breakthrough curve measurements and temperature-programmed desorption (TPD) experiments. The presence of O₂ in the gas phase promotes chemisorption. Because of slow adsorption mechanisms, no equilibrium capacities of mercury chemisorption can be determined. For further investigations, coupled adsorption and desorption experiments with concentration swing adsorption and TPD experiments are performed. The results of TPD experiments are simulated and quantitatively evaluated by means of an extended transport model. From the number of desorption peaks, we obtain the number of different adsorption and desorption mechanisms. A detailed simulation of the peaks yields the reaction order, the frequency factor, and the activation energy of the desorption steps. The kinetic reaction parameters allow a mechanistic interpretation of the adsorption and desorption processes. Here, we suppose the formation of a complex between the carbon surface, mercury, and oxygen.