MERCURY ADSORPTION ON SULFURIC ACID-IMPREGNATED CARBONACEOUS SURFACE: THEORETICAL STUDY
Abstract
Density functional theory calculations are performed to provide a molecular-level understanding of the mechanism of mercury adsorption on sulfuric acid-impregnated carbonaceous surface. The carbonaceous surface is modeled by a nine-fused benzene ring in which its edge carbon atoms on the upper side are unsaturated to simulate the active sites for reaction. SO4 clusters with and without charge are examined to act as the representative species to model the sulfuric acid absorbed on the carbonaceous surface. All of the possible approaches of SO4 clusters with and without charge on the carbonaceous surface are conduced to study their effects on mercury adsorption. The results suggest that sulfuric acid effect on the mercury adsorption capacity of the carbonaceous surface is very complicated, and it depends on a combination of concentration and charge of SO4 cluster. SO4 cluster presents a positive effect on mercury adsorption on the carbonaceous surface, but higher concentration of SO4 cluster decreases the adsorption capacity of the carbonaceous surface for mercury removal because there is considerable competition for active sites between Hg and SO4 cluster. Since all of the possible approaches of mercury on the carbonaceous surface with 
cluster, excluding one that mercury is adsorbed at bridge active site, can lead to the decrease in the adsorption energies of mercury on the carbonaceous surface, 
cluster presents a negative effect on the capacity of the carbonaceous surface for mercury adsorption regardless of the concentration of 
cluster. The results also indicate that SO2 cluster and surface oxygen complex can be formed from SO4 cluster with or without charge if mercury is adsorbed at bridge active site, which facilitates the mercury removal for the carbonaceous surface.
