Heterogeneous Reaction Mechanisms and Functional Materials for Elemental Mercury Removal from Industrial Flue Gas

Abstract

Gaseous elemental mercury (Hg0) is of increasing concern in industrial flue gases because of its difficult disposal. Currently, catalysis conversion and adsorption to oxidized species (Hg2+) and particle-bonded states (Hgp) are two common Hg0 disposal methods. While no clear boundary exists between these methods, the selection of technologies for practical applications highly depends on the gas temperature, mercury concentration, and gas components over a solid material. This review aims to describe some principles for solid material selection, discusses the heterogeneous reaction mechanisms for gaseous Hg0 conversion, classifies the various types of catalysts and sorbents, and summarizes their potential applications. Gaseous Hg0 undergoes interface physical adsorption, catalytic oxidation, and chemical adsorption processes. Overcoming the surface bonding energies can convert the Hg0 to Hg2+ via the catalytic process. Meanwhile, strong bonding energies can ensure chemical adsorption, resulting in mercury surface solidification. On this basis, the catalysts and sorbents materials, the reaction mechanism, and different types of solid materials were evaluated. We clearly discussed the reaction mechanism over different type of functional materials for Hg0 removal, to provide recommendations for studies to address concerns regarding laboratory-scale to full-scale applications. Moreover, some key parameters and a basic understanding of the practical applications were proposed.

Regulation of the Sulfur Environment in Clusters to Construct a Mn–Sn2S6 Framework for Mercury Bonding

“…However, to date, there are few reported sorbents that can simultaneously remove Hg 0 and Hg 2+ . Commonly, the bonding stability and reaction rate between sulfur with Hg 0 and Hg 2+ highly depend on sulfur forms (S 2– , S 1– , S n 2– , and S 0 ). , Thus, the efficient route to enhance the performance of sulfur-based materials is generally to activate the sulfur sites by adjusting the coordination environment.…”

SO2-Driven In Situ Formation of Superstable Hg3Se2Cl2 for Effective Flue Gas Mercury Removal

“…, Hg 2 SO 4 and HgO). Among them, mercury chalcogenides (HgS and HgSe) exhibited relatively higher thermostability and lower solubility . Notably, compared with HgS and HgSe, Hg 3 Se 2 Cl 2 had higher thermal stability and lower solubility in an acid solution.…”

“…Although chalcogen elements (O, S, or Se) could be used for Hg 0 uptake and stabilization, their field applications were seriously limited by the harsh flue gas conditions such as high temperature, high concentration of SO 2 , and water vapor , because the fluctuation of flue gas temperature may destroy the mercury–chalcogen bond, while SO 2 and H 2 O can occupy the Hg 0 adsorption sites and lead to surface Hg 2+ dissolution and re-emission . Obviously, the ultimate remediation goal is to separate Hg 0 from flue gas and simultaneously convert it to superstable states for safe storage, which has not been achieved as far as we know.…”

Reverse Conversion Treatment of Gaseous Sulfur Trioxide Using Metastable Sulfides from Sulfur-Rich Flue Gas

“…Many experimental and theoretical studies have recently reported that metal sulfides have great tolerance to SO 2 . 23,24 Notably, Liu et al found that SO 3 would compete with Hg 0 for adsorption sites on the CuS surface. 25 Yang et al observed that SO 3 could oxidize HgS to HgSO 4 and was reduced to SO 2 .…”

“…The aim was to develop a material that can efficiently reduce SO 3 at a specific temperature and has a high resistance against coexisting flue gas components, especially high concentrations of SO 2 . Many experimental and theoretical studies have recently reported that metal sulfides have great tolerance to SO 2 . , Notably, Liu et al found that SO 3 would compete with Hg 0 for adsorption sites on the CuS surface . Yang et al observed that SO 3 could oxidize HgS to HgSO 4 and was reduced to SO 2 .…”