Selenide Functionalized Natural Mineral Sulfides as Efficient Sorbents for Elemental Mercury Capture from Coal Combustion Flue Gas

Abstract

Directly using earth-abundant natural mineral sulfides (MSs) for elemental mercury (Hg0) removal from coal combustion flue gas remains a challenge because extremely low surface areas of natural MSs largely suppressed their capabilities in Hg0 immobilization. In this work, a new mindset was proposed for the activation of natural MSs by introducing surface selenide (Se2−) ligands to achieve an efficient and rapid Hg0 uptake from coal combustion flue gas. The Se2− loaded pyrrhotite (xSe-FeS) exhibited four folds higher Hg0 uptake rate compared to bare pyrrhotite. The immobilized mercury over the xSe-FeS surface was primarily converted into mercury sulfide (HgS), a mercury species known for its extreme stability when environmentally exposed. The superiority of xSe-FeS was ascribed to that Hg0 bound more weakly with active selenide sites than sulfide sites, and the lower binding energy decreased the diffusion barrier of mercury and improve the reaction rate. The same mindset was proven to be also applicable in tailoring other natural MSs into efficient Hg0 sorbents. From these advantageous perspectives, this work provides a highly promising way for efficiently utilizing naturally enriched MSs as economically feasible and scientifically sound sorbents for Hg0 removal from coal combustion flue gas.