Removal of Mercury from Flue Gas by Adsorption on Mechanochemically Modified Coconut-Shell Activated Carbon Enriched with CCl 4

Industrial waste coconut-shell activated carbon enriched with CCl4 (SACCl) was employed for the removal of elemental mercury (Hg0) from flue gas via mechanochemical modification. The results demonstrated that the mechanochemically modified SACCl (denoted as SACCl-M20, with a ball-milling duration of 20 min) exhibited excellent Hg0 adsorption performance, with the Hg0 breakthrough rate remaining nearly 0 even after 1 h of continuous adsorption. In the presence of 600 ppm of SO2, the Hg0 removal efficiency of SACCl-M20 decreased from 99.3% to 93.8%. However, this inhibitory effect was attenuated with the introduction of 6% O2, with the efficiency recovering to 97.6%. A slight further improvement in the removal efficiency to 98.2% was achieved by the additional introduction of NO. Thermogravimetric analysis confirmed no release of substances from SACCl-M20 below 150 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed that chloride ions (Cl–) were generated on the SACCl surface via mechanochemical modification, which promoted the oxidation and adsorption of mercury. The main mercury adsorption products on the SACCl-M20 surface were identified as HgCl2 and Hg2Cl2, which could be converted into HgS via mechanochemical ball milling with Na2S. The gas-phase mercury adsorption process on both pristine and mechanochemically treated SACCl surfaces was governed by external diffusion and chemisorption. Mechanochemical modification enhanced the chemisorption of mercury on the SACCl surface but reduced the mass transfer rate of external diffusion.