Advances in magnetically recyclable remediators for elemental mercury degradation in coal combustion flue gas

Abstract

The coal-energy conversion process is recognized as one of the largest single known sources for elemental mercury (Hg⁰) emission worldwide. With the implementation of the Minamata Convention, the rational design of proper remediators for Hg⁰ degradation and recovery from coal combustion flue gas (CCFG) is of great urgency. To achieve these goals, magnetic materials hold unique potentials as magnetic remediators not only exhibiting high Hg⁰ degradation efficiencies, but also achieving remediator recycling by the use of an external magnetic field. With these promises, magnetic Hg⁰ remediators have been evolving in the last ten years and undergoing a revolutionary phase. In this review, the magnetic remediators used for Hg⁰ degradation from CCFG are categorized into two groups, i.e., raw magnetic materials (RMMs) and functionalized magnetic materials (FMMs), among which the FMMs are obtained by (1) adding favorable supports, (2) loading active components, (3) incorporating active ligands, (4) sulfuring/selenizing, and/or (5) activating by external energetic field based on the RMMs. Among these magnetic remediators, RMMs generally exhibited limited Hg⁰ degradation performances. Therefore, the functions of modification methods are summarized to elaborate on their intrinsic roles. Moreover, the influential factors and involved mechanisms accounting for Hg⁰ degradation over different magnetic remediators are reviewed as fundamentals to guide the rational design process. Finally, research gaps are proposed from both macrocosmic and microcosmic visions to shed light on further research directions.