Cupric ion stabilized iron sulfide as an efficient trap with hydrophobicity for elemental mercury sequestration from flue gas

Abstract

Iron sulfides (FeSx) characterized by the nonstoichiometric coordination between iron and sulfur are promising sorbents for elemental mercury (Hg0) adsorption from industrial flue gas. However, the unstable nature of FeSx tending to self-combust under ambient conditions impedes its scalable synthesis. To overcome this critical challenge, this work developed a cupric ion incorporation method to stabilize FeSx. When the compositional ratios of cupric ion and FeSx both equaled 50%, the composite sorbent as synthesized (50Cu-FeSx) exhibited ultra-high Hg0 adsorption capacity and uptake rate that reached 433.2 mg g−1 and 847.4 μg g−1 min−1, outperforming those benchmark metal sulfides as reported in previous studies for practical uses. In this sample, the copper ion well-incorporated into the lattice of amorphous FeSx was an indispensable fundamental that contributed to its outstanding performance and hydrophobic ability. The stabilized FeSx thus enriched its surface with abundant under-coordinated sulfur due to the nonstoichiometric coordination environment, which acted as the primary active sites for the conversion of Hg0 because only under-coordinated sulfur could accept electrons Hg0 donated. The main product after 50Cu-FeSx adsorbed Hg0 was HgS, an extremely stable mercury form in nature. From these perspectives, it is proper to declare that this work not only proposed an efficient sorbent holding great potential for Hg0 removal from high-humidity industrial flue gas but also provided a novel method for the rational design of FeSx-based materials with extensive applicability in the future.