Conversion of Gaseous Hg ⁰ Capture by CuS from Surface Adsorption to the Replacement Reaction through Intermittent Acid Washing

Metal sulfides are promising for capturing gaseous Hg 0, but their adsorption capacities are limited due to Hg 0 adsorption only on superficial unsaturated sulfur (S) coordination. Therefore, enabling saturated S coordination beneath the surface to participate in Hg 0 adsorption is an innovative and effective strategy. In this study, surface adsorption of Hg 0 on CuS was converted into a replacement reaction with a stoichiometric ratio of 1:6 through intermittent acid washing, allowing 2/3 of sulfur in CuS to contribute to Hg 0 adsorption, significantly increasing the capacity theoretically to 348 mg g –1 . The formation of a Cu vacancy due to the dissociation of four-coordinated Cu1 with one dangling bond and the transformation of four-coordinated Cu0 without a dangling bond to Cu1 alternately happened during each acid washing and Hg 0 adsorption, respectively, resulting in a chain reaction of the substitution of Cu in CuS by Hg 0 . Ultimately, 1/4 of four-coordinated Cu 1.5+ in CuS can be isomerous-substituted by Hg and dissociated into the acid washing solution, resulting in the growth of one-dimensional HgS in destroyed CuS crystals. CuS with intermittent acid washing demonstrates significant potential for recovering gaseous Hg 0 from flue gas, with Hg content in spent CuS exceeding 20%, offering a valuable approach for resource recycling.