Review and Perspectives of Mercury Removal by Spinel Compounds

Several preparation methods for current spinel compounds are briefly introduced. The effects of temperature and flue gas components on the removal of Hg0over spinel compounds are reviewed. The reaction processes and mechanisms of Hg0adsorption, oxidation, and desorption on the surface of spinel compounds are analyzed deeply. The current methods for improving Hg0catalytic oxidation performance by spinel-based photocatalytic materials are also introduced. There are two main types of spinel compounds for Hg0removal: conventional spinel and loaded spinel compounds. Loaded spinel compounds are favorable for the adsorption and oxidation of Hg0due to more active sites and a larger surface area than ordinary spinel compounds. Both O2and HCl contribute to Hg0removal with Hg0oxidation efficiency being sensitive to both O2and HCl concentrations. The presence of SO2has a detrimental effect on the removal of Hg0due to the competition for the active adsorption sites on the surface of catalysts and adsorbents. The impact of temperature is bidirectional, and an optimum temperature exists. Based on the analysis of three stages (adsorption, oxidation, and desorption) included in the Hg0catalytic oxidation process, it was discovered that for most catalysts the Hg0oxidation process is the rate-limiting step for the reaction.