Fabrication of Novel Nanosulfur-Modified Activated Carbon Adsorbent for Elemental Mercury Removal from Flue Gas

Mercury is a toxic heavy metal, with substantial risks to human health. In China, coal-fired power plants are the largest anthropogenic source of mercury emissions. Despite the high mercury removal performance of commercial chlorine- or bromine-modified activated carbon (AC), concerns have arisen regarding the leaching potential of mercury and halogen species in the product. This work proposed the synthesis of unique nanosulfur-modified AC as a mercury removal adsorbent, assisted with nonthermal plasma technology. Nanosulfur particles were successfully produced and characterized (morphology and size distribution) using high-resolution transmission electron microscopy. The H2S decomposition reaction acceleration mechanism in the plasma area under different H2S concentrations and the influence of the equivalent reduced field were assessed. Fixed-bed mercury adsorption experiments showed the superior performance of the nanosulfur-modified AC adsorbent, achieving a removal efficiency of 88.9%. The effects of adsorption temperature and simulated flue gas components on the nanosulfur-modified AC's performance were investigated. The optimal adsorption temperature was found to be 140 °C, suggesting that it is more suitable for coal-fired power plants without a low-temperature electrostatic precipitator system. Additionally, the simulated flue gas showed promotional effects on the adsorbent performance, resulting in an efficiency increase of 20.2%. In order to reveal the adsorbent mercury removal mechanism, the sulfur species and concentration of both fresh and spent adsorbents were determined through X-ray photoelectron spectroscopy. In summary, this research proposed a novel fabrication method and deepened our understanding of the mercury–sulfur reaction mechanism.