Stabilized oxidation and adsorption of elemental mercury by activated carbon

The catalytic oxidation and adsorption capabilities for elemental mercury (Hg⁰) on activated carbon (AC) were evaluated in a simulated coal-derived gas containing hydrogen sulfide (H₂S) and oxygen (O₂). The Hg⁰ removal efficiency is close to 78% in the atmosphere containing H₂S and O₂ in 180min at 160℃, whereas the retention of mercury without H₂S and O₂ sharply decreases from 69% to 28% in the same duration. Higher adsorption temperature, larger size of sorbent and higher Hg⁰ concentration may deteriorate to the absorption capability. XRD was used to characterize properties of the sorbents. It shows that mercury sulfide (HgS) is formed over the AC after the adsorption. It is suggested that the oxidation reaction of Hg⁰ with H₂S and O₂ may contribute to the efficient capture of Hg⁰ over AC sorbent. HgS formation is beneficial to improve the Hg⁰ removal efficiency and the adsorption capacity of the AC sorbent. Furthermore, it has the advantage to reduce the secondary pollution due to HgS being inert and nontoxic to the environment.