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 Hg0 over spinel compounds are reviewed. The reaction processes and mechanisms of Hg0 adsorption, oxidation, and desorption on the surface of spinel compounds are analyzed deeply. The current methods for improving Hg0 catalytic oxidation performance by spinel-based photocatalytic materials are also introduced. There are two main types of spinel compounds for Hg0 removal: conventional spinel and loaded spinel compounds. Loaded spinel compounds are favorable for the adsorption and oxidation of Hg0 due to more active sites and a larger surface area than ordinary spinel compounds. Both O2 and HCl contribute to Hg0 removal with Hg0 oxidation efficiency being sensitive to both O2 and HCl concentrations. The presence of SO2 has a detrimental effect on the removal of Hg0 due 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 Hg0 catalytic oxidation process, it was discovered that for most catalysts the Hg0 oxidation process is the rate-limiting step for the reaction.