Mercury adsorption in the gas phase by regenerable Au-loaded activated carbon foams: a kinetic and reaction mechanism study

Mercury has been the focus of environmental concern and scientific research for decades due to the risks associated with its use, release and emission. An international agreement established in 2017 during the UN Minamata Convention highlighted the need for innovative approaches and technology to tackle these problems. The use of regenerable sorbents for mercury removal in the gas phase is a possible solution that can avoid the generation of new mercury-contaminated waste. However, to make significant progress in this field, it is necessary to develop efficient, economic and environmentally friendly sorbents, for which, a good understanding of the mechanism of adsorption in this type of process is needed. In this study, several kinetic models were applied to determine the rate-controlling step in the adsorption process of elemental mercury by regenerable sorbents based on gold. Three diffusional models (Weber and Morris, Bangham and pseudo-first order models) and two adsorptive models (pseudo-second order and Elovich models) were tested. The results of this study show that external diffusion from the gaseous phase to the sorbent particles is the rate-limiting step. The complexity of the process is also reflected in the results obtained, which indicate that pore diffusion plays a significant role over most of the mass transfer zone, while adsorption itself becomes determinant only when the saturation of the sorbent is near. External diffusion is the rate-controlling step in the adsorption of gas phase Hg 0 with Au-loaded activated carbon foams (pseudo-first order kinetic model).