Mercury Capture Performance and Kinetics of CCl₄-Adsorbed Activated Carbon Pretreated by the Mechanochemical Method

In the present work, CCl₄-adsorbed activated carbon pretreated by the mechanochemical method (CCl₄-AC) was produced for gas-phase mercury capture. The physicochemical properties of the CCl₄-AC sorbent were analyzed via N₂ adsorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The mercury capture performance of the CCl₄-AC sorbent under different flue gas components was investigated in a fixed-bed experimental device. The programmed temperature desorption of mercury was used to determine the mercury capture product of the spent CCl₄-AC. Finally, the mass transfer factor model proposed by Fulazzaky was used to analyze mercury capture on the CCl₄-AC for clarifying its characteristics. The results showed that the prepared CCl₄-AC can be used as a mercury sorbent because of its high mercury capture performance. Mercury capture by the CCl₄-AC was interfered by SO₂ and promoted by O₂ and H₂O. Hg-temperature programmed desorption (Hg-TPD) analysis indicated that the main mercury capture products of the CCl₄-AC were HgCl₂ and HgO. Because of the presence of SO₂ in flue gas, there was a little Hg₂SO₄ formation on the sorbent. XPS analysis showed that the functional group of C-Cl played the dominant role in Hg⁰ capture, and part of the C-Cl groups were converted into Cl^- after mercury capture. The mercury desorption energy of the spent CCl₄-AC was 50.49 kJ/mol and stronger compared with that of raw activated carbon. Mass transfer analysis displayed that surface adsorption was the main form at the beginning of mercury adsorption, and the external mass transfer was the mercury adsorption rate-controlling step. Then, mercury adsorption entered the second stage; internal diffusion adsorption stage with internal mass transfer became the adsorption rate control step.