Adsorption phenomenon and kinetic mechanisms of Hg0 and HgCl2 by innovative composite sulfurized activated carbons

This study investigated the adsorption phenomenon and kinetic mechanisms of Hg(0 )and HgCl2 onto innovative composite sulfurized powdered activated carbons (PACs). The physiochemical properties of PACs were analyzed by energy dispersive spectrometer (EDS), specific surface area analyzer (SSAA), X-ray diffraction spectroscopy (XRD), and Fourier-transform infrared spectroscopy (FTIR). A two-stage adsorption phenomenon was observed and further fitted by Fick's diffusion model, linear driving force approximate model (LDFA model), pseudo second order kinetic model (PSOKM), and Elovich model, respectively, to explore the kinetic mechanisms by two stages. Additionally, the resistances of external film diffusion and interior diffusion of the adsorption were explored as well. Finally, the isothermal equilibriums of the adsorption of Hg(0 )and HgCl2 were simulated by Langmuir and Temkin models, respectively. This study revealed that the adsorption of Hg-0 or HgCl2 on the composite sulfurized PACs was attributed to chemisorption and favorable at elevated temperatures. The fitting level of single kinetic model was not high enough because the kinetic mechanisms for the two-stage adsorption process were different. Additionally, the kinetic mechanism for the adsorption in the same stage varied with different PACs due to the variation of the physiochemical properties of PACs. Finally, the results of both kinetic and thermodynamic simulations showed that the chemisorption of Hg-0 or HgCl2 onto the composite sulfurized PACs can be simulated by Langmuir adsorption model.