Mechanochemical activation of natural metal sulfide minerals for Vapor-Phase mercury immobilization

Abstract

Man-made metal sulfides (MSs) have been proven to be effective traps for permanent elemental mercury (Hg0) immobilization from anthropogenic sources. However, the fabrication of MSs generally involves complex steps and adopts hazardous precursors, hence compromising its cost-effectiveness and environmental-friendliness. The earth-abundant natural MS minerals might be optimal alternatives to the synthetic MSs, while most of them suffer from limited Hg0 adsorption capacity. Herein, a mild mechanochemical approach under a solid state with the aid of cupric chloride (CuCl2) was developed to modify pyrrhotite (Fe7S8) from calcination of natural pyrite for Hg0 capture from flue gas. After the CuCl2 aided mechanical milling, the Hg0 adsorption capacity and uptake rate of the CuCl2 modified pyrrhotite (CuCl2@Fe7S8) reached as high as 283.3 mg g−1 and 188.75 μg g−1min−1, approximately 400 folds higher than that of raw pyrrhotite. The characterization and density functional theory calculation results reveal that the superior performance of CuCl2@Fe7S8 was primarily attributed to the mechanochemical approach which not only introduced hetero-ligands (i.e., Cl) to the adsorbent to combine with Hg0 but also generated extremely active copper sulfide for binding Hg0. The excellent resistance to temperature fluctuation and flue gas interference and its magnetic separation recyclability warrant the application of CuCl2@Fe7S8 in real-world conditions. Integrated Hg0 removal technologies based on the performance-enhanced recyclable CuCl2@Fe7S8 were also proposed for potential applications in different industrial scenarios including coal combustion flue gas.