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

Man-made metal sulfides (MSs) have been proven to be effective traps for permanent elemental mercury (Hg-0) 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 Hg-0 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 Hg-0 capture from flue gas. After the CuCl2 aided mechanical milling, the Hg-0 adsorption capacity and uptake rate of the CuCl2 modified pyrrhotite (CuCl2@Fe7S8) reached as high as 283.3 mg g(-1) and 188.75 mu g g(-1) min(-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 Hg-0 but also generated extremely active copper sulfide for binding Hg-0. 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 Hg-0 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.