Multiform Sulfur Adsorption Centers and Copper-Terminated Active Sites of Nano-CuS for Efficient Elemental Mercury Capture from Coal Combustion Flue Gas

Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer–Emmett–Teller surface area was for the first time applied for the capture of elemental mercury (Hg0) from coal combustion flue gas. The optimal operation temperature of nano-CuS for Hg0 adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible. This assures that the sorbent is free of the adverse influence of nitrogen oxides. Oxygen (O2) and sulfur dioxide exerted a slight influence on Hg0 adsorption over the nano-CuS. Water vapor was shown to moderately suppress Hg0 capture efficiency via competitive adsorption. The simulated adsorption capacities of nano-CuS for Hg0 under pure nitrogen (N2), N2 + 4% O2, and simulated flue gas reached 122.40, 112.06, and 89.43 mgHg0/g nano-CuS, respectively. Compared to those of traditional commercial activated carbons and metal sulfides, the simulated adsorption capacities of Hg0 over the nano-CuS are at least an order of magnitude higher. Moreover, with only 5 mg loaded in a fixed-bed reactor, the Hg0 adsorption rate reached 11.93–13.56 μg/g min over nano-CuS. This extremely speedy rate makes nano-CuS promising for a future sorbent injection technique. The anisotropic growth of nano-CuS was confirmed by X-ray diffraction analysis and provided a fundamental aspect for nano-CuS surface reconstruction and polysulfide formation. Further X-ray photoelectron spectroscopy and Hg0 temperature-programmed desorption tests showed that the active polysulfide, S–S dimers, and copper-terminated sites contributed primarily to the extremely high Hg0 adsorption capacity and rate. With these advantages, nano-CuS appears to be a highly promising alternative to traditional sorbents for Hg0 capture from coal combustion flue gas.