The lack of a fundamental understanding of microcosmic reaction mechanisms for elemental mercury (Hg 0 ) accommodation over a mineral selenide significantly impedes evaluations of their performances and potential applications for Hg 0 adsorption from coal combustion flue gas. Hence, in this work, Hg 0 adsorption profiles and conversion pathways were established for heterogeneous Hg 0 conversion over an efficient and cost-effective mineral selenide, i.e., copper selenide (CuSe). Hg 0 was found to be first physiosorbed by Cu-top sites over an intact CuSe(001) surface to form a Hg−Cu amalgam, which was then converted into stably chemisorbed mercury selenide (HgSe) when encountering surface active ligands such as Se monomer. The reaction pathway for Hg 0 adsorption and transformation over CuSe(001) surface was Hg 0 → Hg−Cu → HgSe. This proposed road map for Hg 0 conversion was further proven by experimental results, in which the formation of Hg−Cu amalgam over CuSe surface was observed. The influences of typical coal combustion flue gas such as oxygen (O 2 ), sulfur dioxide (SO 2 ), and water vapor (H 2 O) on Hg 0 capture over the CuSe(001) surface were also investigated. O 2 was found to exhibit negligible influence on Hg 0 removal, while SO 2 and H 2 O had slight detrimental impacts on the physisorption stage of Hg 0 on the Cu-top site. These results were also cross-checked by experimental observations to fully justify the accuracy of the predictions. This work thus gives in-depth microcosmic understandings on Hg 0 removal over CuSe and guides further design of efficient CuSe based sorbent for Hg 0 capture from coal combustion flue gas.
The amorphous molybdenum intercalated magnetite [MoSe3(inter)Fe3O4] was purposefully designed and synthesized as an efficient and recyclable sorbent for immobilizing elemental mercury (Hg0) from industrial flue gases into extremely stable mercury selenide (HgSe).
Transition Metal sulfides (TMSs) are effective sorbents for entrapment of highly polluting thiophiles such as elemental mercury (Hg0). However, the application of these sorbents for mercury removal is stymied by their low accommodation capacities. Among the transition metal sulfides, only CuS has demonstrated industrially relevant accommodation capacity. The rest of the transition metal sulfides have 100-fold lower capacities than CuS. In this work, we overcome these limitations and develop a simple and scalable process to enhance Hg0 accommodation capacities of TMSs. We achieve this by introducing structural motifs in TMSs by in situ etching. We demonstrate that in situ acid etching produces TMSs with defective surface and pore structure. These structural motifs promote Hg0 surface adsorption and diffusion across the entire TMSs architecture. The process is highly versatile and the in situ etched transition metal sulfides show over 100-fold enhancement in their Hg0 accommodation capacities. The generality and the scalability of the process provides a framework to develop TMSs for a broad range of applications.
Atmospheric mercury (Hg) pollution has attracted global attention as a result of its great harm to the ecosystem. By virtue of abundant surface Hg-philic sulfur sites, metal sulfides have been regarded as a promising Hg adsorbent. The Hg adsorption performance of metal sulfides is mainly determined by the distribution of surface active sites; thus, it is crucial to understand the interactions between the Hg atom and different surface sites. In this review, the immobilization mechanism of the Hg atom over metal sulfides was systematically summarized. First, the roles of surface active sites, i.e., metal and sulfur sites, played in Hg 0 adsorption were systematically elaborated, to explain the excellent performance of metal sulfides. Second, the improvement on the Hg 0 adsorption ability of engineered metal sulfides was attributed to the reasonable regulation of surface unsaturation and the introduction of alien active sites. Eventually, the effects of flue gas components on mineral sulfides were illuminated from the perspective of the introduction/consumption of surface active sites. The objective of this review was to interpret the detailed Hg 0 immobilization mechanism and to provide guidance for developing metal-sulfide-based sorbents, and the future prospects and challenges related to the Hg 0 adsorption mechanism by metal sulfides were discussed.
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